Economic Exploitation of Rice Straw

8/12/2019 Economic Exploitation of Rice Straw

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Acknowledgement

First of all and above all great thanks to ALLAH blessings on me cannot be

counted.

I am greatly and deeply indebted to Prof. Dr. Raafat M. Issa and Prof. Dr.

Morsy M. Abou-Sekkina, Professors of Physical and Inorganic Chemistry,

Department of Chemistry, Faculty of Science, Tanta University, for suggesting the

subject of the present thesis, their kind supervision, unlimited help, appreciable

encouragement and continuous scientific discussions during carrying out the work

and reviewing entirely the thesis from the initial to the final stages.

I would like also to express my sincere gratitude to Prof. Dr. Alam El-deenMohamed Bastawisy Professor of Chemical Engineering, Faculty of Engineering,

Tanta University for his constructive supervision, great help, valuable instruction,

fruitful criticism, continuous support to continue this work.

My great and sincerest thanks to Dr. Abdalla Mohamed Khedr, Assistant

Professor of Analytical Chemistry, Chemistry Department, Faculty of Science, Tanta

University for his kindly instructions during the experimental work, valuable and

scientific discussions during carrying out this work and reviewing critically the

thesis.

The author

Wael Abd-Allah El-Helece


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Dedication

To my family with my deep and sincere appreciation for their great efforts

during my life and my studies

To my wife, daughters, sun and my brother with my great thanks for hishelp


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CONTENTS

CONTENTS page

LIST OF TABLES 9

LIST OF FIGURES... 12

KEY OF SAMPLES 16

ABBREVIATIONS... 17

AIM OF THE WORK... 18

CHAPTER I

INTRODUCTION ...... 19

1. Annual plants.... 19

2. Rice straw.... 26

2.1. On -farm non-burn alternatives .... 28

2.1.1. Straw decomposition... 28

2.1.2. Chopping and incorporating straw into soil.... 28

2.1.3. Rolling..... 29

2.2. Baling and transportation / disposal... 29

2.3. Off-farm non-burn alternatives.. 30

2.3.1. Energy conversion... 30

2.3.1.1. Anaerobic digestion. 30

2.3.1.2. Direct combustion.... 31


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2.3.1.3. Ethanol production... 31

2.4. Pulp products.. 33

2.4.1. Paper / cardboard.... 33

2.4.2. Fiberboard... 33

2.5. Construction products.... 34

2.5.1. Wood replacement materials... 34

2.5.2. Bricks and cement boards... 34

2.5.3. Panel construction... 35

2.5.4. Straw bale structure construction.... 35

2.6. Composting.... 35

2.7. Mushroom production.... 36

2.8. Erosion control... 36

2.9. Livestock feed.... 37

2.10. Additional available resources..... 37

2.11. Chemical composition of wood and straw... 40

3. Pulping processes .... 42

3.1. Mechanical pulping .. 46

3.2. Chemical pulping .. 46

3.2.1. Soda process .. 46

3.2.2. Kraft process .. 47

3.2.3. Sulfite process ... 48


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3.2.4. IRSP (impregnation rapid steam pulping process) process. 48

a- Impregnation .... 48

b- Rapid steam pulping .... 49

4. Bleaching... 50

4.1. Chlorination (C). 51

4.2. Alkaline extraction (E)... 51

4.3. Hypochlorite bleaching (H)... 51

4.4. Chlorine dioxide bleaching (D). 51

4.5. Oxygen bleaching (O).... 52

4.6. Ozone bleaching (Z)... 52

4.7. Peroxide bleaching (P)... 52

5. Cellulose derivatives. 53

6. Mercerization.... 54

7. Black liquor usage.... 55

CHAPTER II

EXPERIMENTAL..... 57

1- Raw material used... 57

2. Equipments 57

3. Analysis of raw material... 57

3.1 Moisture content..... 58

3.2 Water soluble matter... 58


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3.3 Determination of ash and silica in rice straw and pulp.. 58

3.4 Alpha cellulose estimation ..... 59

4. Cooking in sodium hydroxide solutions (pulping)... 59

Cooking conditions... 60

4.1 Effect of sodium hydroxide concentration .... 60

4.2 Effect of time at optimum alkalinity... 60

4.3 Effect of weight / volume ratio..... 60

4.4 Effect of cooking temperature on the pulp yield ... 61

4.5. Effect of the nature of rice straw on the pulp yield.. 61

5. Bleaching.... 61

6. Permanganate number. 62

7. Determination of the contents of black liquor.... 63

7.1. Isolation of alkali lignin..... 63

7.2. Separation of silica from sodium silicate solution obtained.. 64

8. Xanthation....... 64

CHAPTER III

RESULTS AND DISCUSSION.... 65

1. Analysis of raw materials..... 65

1.1. Moisture content... 65

1.2. Water soluble matters... 65

1.3. Ash content... 66


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2. Effect of cooking conditions .... 67

2.1. Effect of sodium hydroxide concentration ...... 67

2.2. Effect of time at optimum alkalinity...... 68

2.3. Effect of weight / volume ratio (w/v).... 69

2.4. Effect of cooking temperature on the pulp yield .. 70

2.5. Effect of the nature of rice straw on the pulp yield..... 71

2.6. Alpha cellulose estimation... 72

3. Infrared spectrophotometric study of cellulose obtained from high yield

soda rice straw pulps

73

3.1. Infrared spectrophotometric determination of lignin in soda yield ricestraw pulp ...

80

3.2. TGA study of cellulose samples ... 94

3.3. Differential thermal analysis (DTA) of cellulose sample.. 98

3.4. Kappa number .. 99

4. Bleaching ..... 102

5. Determination of the content of black liquor ... 106

5.1. Extraction of lignin and other organic matters ... 106

5.2. Studying the alkali lignin contained in black liquor . 110

5.3. Infrared spectrophotometric determination of lignin in samples

separated from black liquor remained.

113

5.4. TGA Study of lignin sample. 118

5.5. Differential thermal analysis (DTA) of lignin sample .. 119


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6. Relationship between bleaching and brightness of the produced pulpaccording to kappa number ......................................................

120

7. Silica precipitated from sodium silicate solution obtained.. 121

7.1. TGA studies on silicate samples... 125

7.2. Differential thermal analysis (DTA) of silicate sample ... 126

8. Xanthation .. 127

8.1. IR spectral analysis for xanthated cellulose samples prepared... 127

8.2. TGA studies for xanthated cellulose samples.. 129

8.3. Differential thermal analysis (DTA) of xanthated cellulose samples. 130

9. SEM microscopic investigations ... 131

9.1. Super molecular structure of cellulose samples .. 132

9.2. Super molecular structure of bleached cellulose samples . 135

9.3. Super molecular structure of xanthated cellulose sample . 136

CHAPTER IV

SUMMARY ........................................................................................ 139

CHAPTER V

REFERENCES ... 142

ARABIC SUMMARY ...... 153


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List of tables

Table

no.

Title Pageno.

1 Chemical composition of natural fibers 21

2 Average annual yields of some raw materials 24

3 Worldwide availability of annual plant fiber 25

4 The technological, economic, and commercial

feasibility of each non-burn alternative

27

5 Average chemical composition of rice straw 39

6 Pulping processes for annual plants 44

7 Pulping processes and yields 45

8 The approximate composition of dry rice straw 66

9 Rice straw composition according to Houston 67

10 The effect of NaOH concentration on the yield of the

pulp

68

11 The effect of time of pulping 69

12 The effect of weight / volume ratio 70

13 The effect of cooking temperature on the pulp yield 70

14 The effect of rice straw nature on the pulp yield 71

15 -cellulose content of rice straw 72

16 -cellulose content of pre-treated rice straw (pulp) 73

17 Assignments of bands in the IR spectrum of rice straw

pulp

75


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18 a The lignin content of the pulp of rice straw samples 1,

2, 3 and 4 related to the relative intensity according to

Saad et. al. method

83

18 b The lignin content of the pulp of rice straw samples 1,

2, 3 and 4 related to the relative intensity according tothe background correction method

84

18 c The lignin content of the pulp of rice straw samples 1,


the base line technique method85

18 d The lignin content of the pulp of rice straw samples 1,


the Pislot method

86

19 a The lignin content of the pulp of rice straw samples 5,


Saad et. al. method

87

19 b The lignin content of the pulp of rice straw samples 5,


the background correction method

88

19 c The lignin content of the pulp of rice straw samples 5,


the base line technique method

89

19 d The lignin content of the pulp of rice straw samples 5,


the Pislot method

90

20 a The relation between sodium hydroxide solution andthe lignin content determined from the methods from

IR charts when pulping for 1 hr

92

20 b The relation between sodium hydroxide solution and the

lignin content determined from different methods from

93


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IR charts when pulping for 2 hrs

21 TGA analysis for cellulose samples 96

22 The kappa number for samples 1, 2, 3 and 4 100

23 The kappa number for samples 5, 6, 7 and 8 101

24 IR analysis of RSA samples 108

25 IR analysis of lignin from rice straw samples 111

26 a Lignin content of samples 15, 16, 17 and 18 related to

the relative intensity according to Saad et al. method

113

26 b Lignin content of samples 15, 16, 17 and 18 related to

the relative intensity according to the background

correction method

114

26 c Lignin content of samples 15, 16, 17 and 18 related to

the relative intensity according to the base line

technique method

115

26 d Lignin content of samples 15, 16, 17 and 18 related to

the relative intensity according to the pislot method

116

27 Lignin content of samples 15, 16, 17 and 18 related tothe relative intensity determined by different methodsfrom IR charts

117

28 The relation between conditions of preparation ofsamples and the brightness (opacity) according toKappa number

120

29 IR analysis of samples 19, 20 and 21 and calciumsilicate hydrate

121


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LIST OF FIGURES

Fig.no.

TitlePageno.

1 The steam explosion effect of a fibril 50

2 Important cellulose derivatives 54

3 IR. absorption spectra of samples 1, 2, 3 and 4 78


5 The relation between the lignin content of the pulp of rice

straw samples 1, 2, 3 and 4 to the relative intensity

according to Saad et. al. method

83



according to the background correction method

84



according to base line technique method

85

8 The relation between The lignin content of the pulp of rice


according to Pislot method

86



according to Saad et. al. method

87



according to the background correction method

88



89


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according to the base line technique method



according to the Pislot method

90

13 The relation between sodium hydroxide solution and the

lignin content determined from different methods from IR

charts when pulping for 1 hr

92

14 The relation between sodium hydroxide solution and the

lignin content determined from different methods from IR

charts when pulping for 2 hrs

93

15 TGA thermograph of sample 3 94




19 DTA thermograph of sample 8 98

20 The relation between sodium hydroxide solution

concentration and Kappa number (boiling for 1hr)

100

21 The relation between sodium hydroxide solution

concentration and Kappa number (boiling for 2 hrs)

101

22 Oxidation of residual lignin during bleaching sequences 103

23 IR. absorption spectra of samples 9, 10 and 11 105


25 A typical IR spectrum for lignin extracted 110


27 The relation between the lignin content of samples 15, 16, 113


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17 and 18 to the relative intensity according to Saad et al.

method

28 The relation between the lignin content of samples 15, 16,

17 and 18 related to the relative intensity according to the

background correction method

114


17 and 18 related to the relative intensity according to the

base line technique method

115


17 and 18 to the relative intensity according to the pislot

method

116

31 The relation between lignin content of samples 15, 16, 17

and 18 to the relative intensity determined by different

methods from IR charts

117

32 TGA thermograph of lignin sample 15 118

33 DTA thermograph of lignin sample 15 119

34 The relation between conditions of treatment and the

brightness of the produced pulp according to Kappa number

120


36 XRD patterns of samples 19, 20 and 21 124


38 DTA thermograph of sample 21 126





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42 DTA thermograph of 24 131

43 SEM of rice straw sample 132

44 SEM of sample no.1 133

45 SEM of sample no. 4 133






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ABBREVIATIONS

AGU Anhydrous glucose unit

APMP Alkaline peroxide mechanical pulping

AQ Anthraquinone

ASAM Alkaline sulfite anthraquinone methanol

ASTM American society for testing and materials

ATR Attenuated total reflection

CMC Carboxymethyl cellulose

CTMP Chemi-thermomechanical process

DMAc Dimethylacetamide

DMSO Dimethylsulfoxide

DP Degree of polymerization

DS Degree of substitution

ECF Elementary chorine free

FAO Food and agriculture organization

IR Infra-red spectroscopy

HPLC High performance liquid chromatography

IDE Impregnation de-polymerization extractionIRSP Impregnation rapid steam pulping

ISO International standards organization

MC Methylcellulose

NMR Nuclear magnetic resonance

SEC Size exclusion chromatography

SEM Scanning electron microscopy

TAPPI Technical association of the pulp and paper industry (USA)

TCF Totally chlorine free

THF Tetrahydrofuran

TGA Thermo gravimetric analysis

XRD X-ray diffraction


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AIM OF THE WORK

The objective of this dissertation is to study rice straw as an alternative source

for the production of cellulose pulp and some other useful materials such as xanthated

cellulose. The conditions of preparation (pulping, bleaching and xanthation) and

factors affecting the main properties of the produced cellulose pulp and xanthated

cellulose (the effect of alkali concentration, time of pulping and weight / volume ratio

when boiling) are intended. The resulting intermediate products as well as the final

products, were characterized and compared at each experimental step.

The IR absorption spectral analysis were undertaken according to differentmethods (Saad et. al., base line technique, back ground and Pirlot methods)

Experiments were done according to the following six steps;

1. Characterization of rice straw from El-Delta region, Egypt.

2. Mechano-Chemical pulping and bisulphate pulping methods.

3. Bleaching with bisulphate and H2O2.

4. Improving accessibility and reactivity of bleached pulps.

5. Xanthation of both unbleached and bleached pulps.

6. Characterization of synthesized xanthates.


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INTRODUCTION

1. Annual plants

Crop residues and other agricultural by-products once categorized as wastes have

become major components of livestock feed in many countries. The rapid increase in

their use is due to several factors, such as increasing demand for food, greater

pressure for agricultural land use, raising cost of better-quality feed, pollution

problems due to waste disposal, and the realization of the wasting of enormous

quantities of potential sources of carbohydrates [1, 2].

Agricultural by-products have many uses, rice straw is used in paper industry,

small quantity of straw used for the feeding and bedding of cattle and buffaloes, most

of the straw produced in Egypt is either ploughed in the land or burned directly on the

field. Cereal straws are often used for thatching houses in Asian countries. Straw is

also a good packing material. Many farmers use straw and stubble as a mulch.

The chemical compositions of annual fibers vary greatly, not only according to

their species, plantation location, and growth environment but also to their harvest

times. Studies have reported many varieties in fiber sources, fiber ages, anddetermination methods. Data on the chemical composition of several common plant

fibers are shown in table 1 [3]. Generally, about 40 to 50 % of the weight of annual

plants is cellulose (which is the main component of these plants), except for cotton,

which has much higher cellulose content. About 10 to 30 % of the weight of annual

plants is lignin and 20 to 30 % is hemicellulose. The ash content varies greatly.

Annual plants have much higher ash content than woods [4].The chemical compositions in table 1 show that all annual plants have similar

chemical properties, such as lower lignin contents, higher pentosan or hemicellulose

contents and higher ash contents than woods.


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Annual plants and agricultural residues, received more attention in recent years

for produce of pulp, paper, paperboard, and cellulose derivatives. In fact, non-wood

materials had been used to produce cellulosic products since the invention of

papermaking by a Chinese, Cai Lun [5].

Wood is not available in sufficient quantities in many countries, alternative new

non-wood raw materials need to be investigated and exploited for the potential

substitution of wood. Therefore, the cellulose industry included the investigation of

such new resources as overproduced crops, agricultural waste, unconventional plants

and common wild plants to decide whether it is feasible to use them to produce paper,

paperboard and cellulose derivatives, such as tailor-designed methylcellulose as an

additive for cement, food and drug [6, 7].

Annual plants are considered as potential resources because of overproduction of

agricultural crops [8, 9], their higher yield of cellulose than wood [10, 11], lower

lignin contents and consumption of less pulping chemicals and energy [12]. Cellulose

can be obtained from annual plants by a mild pulping process, which consumes less

energy and chemicals in a shorter cooking time [13]. The investment on producing

processes reduces at the same time. Annual plants can be planted, cultivated, and

harvested every year.


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Table 1. Chemical composition of natural fibers

Fiber source Cellulose (%) -Cellulose (%) Lignin (%) Pentosans (%) Ash (%) Silica (%)

Leaf fibers

Abaca 56-63 7-9 15-17 1-3


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These special characters were the dominant direct importance for their

development. However, the annual plants have some specific problems as raw

materials of cellulosic products. Harvesting is limited to only a few weeks of a year.

Annual plants are planted and scattered in many small fields that thus cause the

difficulty of transportation and collection. A sufficient store capacity is needed to set

up to ensure an all-year supply. Most annual plants are attacked easily by

microorganisms. To minimize degradation, these plants should be stored as dry as

possible.

Transportation of wood is more expensive and difficult than annual plant, under

the consideration of the economical objective, the environment influence, the

sufficient supply, and the higher yield of cellulose, annual plants are now gradually

substituting woods as alternative resources of cellulosic products [14].

Currently, about 55 % of the feedstock for the production of pulps is virgin

wood, 9 % is non-woody sources, and 16 % is recycled paper [15]. The main woods

for cellulosic products are from rapid growth species such as eucalyptus and pine.

Agricultural crops (especially straw and bagasse) and natural plants can be alternative

sources to forest woods if they can be found in sufficient supply, the most important

annual plants for the pulp industry are agricultural residues (bagasse and cereal straw)

and naturally cultivated bamboo and reeds. Other important annual plants, such as

miscanthus, flax, kenaf, sisal, jute, hemp, and cotton, are valuable raw materials for

the production of special pulps, special papers, and cellulose derivatives [16].

Annual plants have several advantages over wood resources. Firstly, they grow

to maturity much more quickly than wood species. Hemp can be harvested within

three to four months. Other annual plants such as straw, flax, abaca etc. can be

harvested yearly. This brings quicker profits for the farmers and obtains a higher

cellulose yield. Secondly, crop residual fibers such as bagasse, straw, flax, jute, and

wild plants can be used, so profits are higher profit thanks to these low-value


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lignocellulosic sources. Thirdly, annual plant sources are usually chipped to smaller

sizes (about 4 cm in length) than wood chips in the pulp digester. Annual plant stalks

have more porous fiber structures and weaker inter-fiber lignin deposits. This

requires less cooking energy and less time. Bagasse and straw, for example, cooked

within 10 to 15 minutes, save a lot of energy in a short time. Finally, fewer cooking

and bleaching chemicals are used for annual plants than for wood chips.

Annual plants generally have lower lignin contents, higher pentosan contents,

higher hemicellulose contents, and higher ash contents (especially silica) than woods,

while the cellulose contents are almost equivalent. So far these plants have only been

used in the manufacture of textiles and paper products that constantly compete with

synthetic and wood fibers. The feasibility of using annual plant fibers in other

applications has not been widely researched or developed [17]. The most widely

available annual plants are the straw of cereals, the stems of corn and sugar cane,

which are listed in tables 2 and 3.


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Table 2.Average annual yields of some raw materials [18]

Plant Fiber yield

(Tones /year/ha)

Pulp yield

(Tones/year/ha)

Scandinavian softwood 1.5 0.7

Fast growing softwood 8.6 4

Temperate softwood 3.4 1.7

Fast growing hardwood 15 7.4

Wheat straw 4 1.9

Rice straw 3 1.2

Bagasse 9 4.2

Bamboo 4 1.6

Kenaf 15 6.5

Hemp 15 6.7

Miscanthus 12 5.7

Canary grass 8 4.0


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Table 3. Worldwide availability of annual plant fibers

Fiber type Potential availability for pulping (MillionBDMT)*

Agricultural residues

Wheat straw 600.0Other cereal straws 290.0

-Barley straw 195.0

-Oat straw 55.0

-Rye straw 40.0

-Rice straw 360.0

Grass seed straw 3.0

Seed flax straw 2.0

Corn stalks 750.0

Sorghum stalks 252.0

Cotton fibers 89.0

-Cotton staple fiber 18.3

-Cotton linters (first & second 2.7

-Cotton stalks 68.0

Sugar cane bagasse 102.2

Non woody crop fibersStem fibers 13.9

-Jute, kenaf, hemp, etc.

Leaf fibers 0.6

-Sisal, henequen, maguey, abaca

Natural growing plants

Reeds (Estimate) 30.0

Bamboo (Estimate) 30.0

Papyrus (Estimate) 5.0

Esparto grass (Estimate) 0.5

Sabai grass 0.2

*: Fibers available for delivery to pulp mills. Bone Dry Metric Ton (BDMT).


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2. Rice strawRice straw, unlike other crop residues, is difficult to dispose off and has limited

economical alternative uses. Traditionally, burning was the preferred method of

ridding the field of the waste straw. However, recent clean-air legislation phase out

rice straw burning. Farmers now are faced with the challenge of finding new ways to

eliminate the straw in time to plant the subsequent year's crop.

As burning is phased out, alternative disposal methods for straw residues must

be found. Although limited burning is still possible, other alternative methods of in-

field disposal being used more frequently include various combinations of chopping,

rolling discing and alternate flooding and draining [19, 20].

Other alternative uses for rice straw have been investigated by growers and

industry members and through rice industry organizations such as the California Rice

Industry Association (CRIA). Some alternative uses that have been looked at include

straw bale construction, industrial building materials, packing materials, animal feed

and bedding, erosion control and a variety of there uses. The CRIA has produced a

booklet entitled "Rice Straw Information" that provides more complete information

on rice straw, its uses and surrounding issues [21-25].

Disadvantages of rice straw burning are primarily related to air quality

I- Generation of air pollutants, including; particulates, carbon monoxide (CO),

hydrocarbons, nitrogen oxides (NOx) and sulfur dioxide (SO2).

II- Production of poly-nuclear aromatic hydrocarbons in both gas and particulate

forms, many of which are carcinogenic.

III- Release of airborne silica fibers (small particles of straw ash with possible

carcinogenic health effects).

The amount of pollutants emitted by rice straw burning depends on the moisture

content of the straw, the manner in which the field is burned (heading fire, backing


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fire, strip-light fire), and the emission factor (the pollution emitted per weight unit of

the fuel being burned). The farmer is responsible for monitoring the moisture content

of the straw and proceeding with the burn only if the straw passes the so- called

"crackle" test (indicating low moisture and emission factor) in the field. It is also up

to the farmer to select the method of burning that best suits the environmental

circumstances on the day that the burn is scheduled.

Two central questions for the rice industry are: what are the alternatives to

burning, and how will they affect the competitiveness of California rice according to

the CRIA, it costs the average rice farmer approximately $ 2 per acre to burn rice

straw, and between $ 25 and $ 70 per acre to either plow it under or remove it [26].

Table 4. The technological, economic, and commercial feasibility of each non-burn

alternative

On-farm non-burn alternatives Off-farm non-burn alternatives

Crop rotationStraw decompositionBaling

Energy conversionPulp products manufacturingConstruction products manufacturing

Straw bale structureConstructionCompostingMushroom productionErosion controlLivestock feed

The pressing need for economic alternatives to burning has spurred substantial

public and private investment in research into solutions, as well as implementation ofpilot-scale, and even large-scale programs. The California Rice Research Board has

invested over 15 million $ of its income from rice farmer's contributions since 1969

to fund research projects concerned with the use of rice straw [27].


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2.1. On-farm non-burn alternatives

Straw decomposition is a management practice developed as an alternative to

burning. It is implemented by either of the following methods; chopping the straw

and incorporating it into the soil by tillage and rolling the standing straw into the soil

using a mechanical crimping/rolling device.

A variety of field implements can be used to chop straw. Harvester-mounted

choppers shred the straw into long pieces; flail choppers pulled behind a tractor

produce a range of sizes of shredded pieces. Self-propelled forage choppers leave the

straw in pieces less than 2 inches long. Smaller pieces are easier to incorporate with

field tillage equipment. The use of choppers on rice straw is effective, but the high

silica content of the straw causes a great deal of wear on chopper blades relative to

other crops.

Straw incorporation is usually accomplished by chisel or disk tillage. The

number and type of field operations required to achieve a good straw/soil mixture

depends on soil type. Clayey rice growing soils are difficult to till, making

incorporation more difficult.

Even though micro-organisms are abundant in rice soils, certain other

environmental conditions are required to accomplish the decomposition process [28].

Temperature, moisture, and available oxygen are all essential factors affecting

decomposition. Straw breakdown occurs between 40 and 86 oF and is more rapid at

the upper end of this temperature range. Soil moisture also influences the rate of

straw decomposition. Straw can decay with or without air, but the pathways and

byproducts produced under each condition are quite different. For straw to

decompose most rapidly, an optimal mixture of air and water in soil pores is helpful.


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For the clay soils on which rice is grown, this moisture content is about 30 %, with an

air content of about 20 %, both by volume. Decomposition rates decrease as soil

moisture levels become extremely dry or wet.

Rice straw rolling is a decomposition method that was developed to reduce

straw incorporation costs while leaving unharvested rice grain accessible to foraging

wildlife. The roller design was developed with funding from the Dow Chemical

Company, Dow Elanco, and the National Fish and Wildlife Foundation [29]. Rollers

take a variety of forms (e.g., rolling cages, fluted drums). Each design flattens most

straw to the soil, while pressing some slightly into the soil.

A typical protocol involves draining the field and harvesting the grain,

reflooding to a depth of 2 to 6 inches, and then using the roller to crush straw and

stubble into the soil. The stirring action creates a good mixture of soil, water, and

straw, bringing the crop residue into contact with the soil micro-organisms that begin

the decomposition process. This approach has the demonstrated advantage to

waterfowl of preserving residual rice seed as a carbohydrate source and of creating

winter habitat that fosters the growth and development of dietetically important

invertebrate species [30].

Baling can involve several operations, the most important of which is cutting the

straw below the water line, which is the principal infection point for stem rot. Baling

and removing rice straw from the field can be as effective as burning in controlling

stem rot if the straw is cut below the waterline and completely removed from the

field. The usefulness of baling is restricted by the limited markets available for rice

straw, rice straw products and the high cost of bale transport. Purchase, removal, and


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transport of straw bales from the field currently range from $ 4 to $ 6 per bale,

depending on the transporter and destination. Alternative uses for rice straw, such as

bio-energy production and building materials, are currently being evaluated for

feasibility [31].

2.3. Off-farm non-burn alternatives

This is an attractive alternative because rice straw has relatively high energy

content (up to 8,000 Btu per pound). Bio-energy production plants often cannot

afford to transport feedstock more than 15 to 20 miles, which precludes this option

for the majority of rice producers. Potential methods of energy conversion include:

a- Anaerobic digestion to produce methane gas

b- Direct combustion to produce electric power

c- Ethanol production

This is a fermentation process in which organic waste is converted to methane

and carbon dioxide gases in three stages:

1. Pretreatment to break down complex organic compounds into soluble

components.

2. Oxidation to produce low-molecular-weight organic acids.

3. Fermentation to produce methane gas.

The economic feasibility of agriculturally produced methane is highly dependent

on the demand for methane and on the cost of competitive materials, e.g., natural gas.

Taking into account high transportation costs, anaerobic digestion can only compete

with natural gas in remote and isolated areas where it is feasible to generate methane

on-farm [32].


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Direct combustion alternatives include burning rice straw in biomass power

plants for power generation, and the use of rice straw in logs or pellets for home

heating.

At power plants, the alkalinity of rice straw (associated with the potassium and

chloride content) creates costly, and seemingly insurmountable, slugging problems in

furnaces. When rice straw is burnt, a large volume of ash is generated because of

the high silica content of the straw. The high silica content also compromises the

straw's energy conversion efficiency. Ash disposal is a significant logistical and

permitting challenge. The large volumes produced, as well as the potential presence

of crystalline silica, can cause its classification as a hazardous waste, potentially

making ash disposal time-consuming and costly.

The process for converting rice straw to ethanol includes the following steps:

a- Pulverizing the straw.

b- Blending to produce a liquid slurry mix.

c- Hydrolyzing cellulose molecules in the slurry mixture to produce simple

sugars.

d- Fermenting the sugar-rich liquid.

f- Distilling fermentation products to ethanol.

Two methods of hydrolysis are available, acid and enzymatic. They differ in the

means by which the cellulose is broken down into fermentable sugars. Acid

hydrolysis occurs in a single step in which the cellulose is exposed to a strong acid to

produce the sugar liquor. Enzymatic hydrolysis is a two-step process in which the

straw is pretreated to separate the cellulose and hemicellulose components. A dilute


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acid breaks down the hemicellulose to simple sugars, and then enzymes produced

from genetically engineered fungi or bacteria break down cellulose. The two-step

process is potentially more efficient because it can produce higher overall yield of

ethanol from a given amount of rice straw.

The Sutter ethanol partners project proposes to construct a cogeneration facility

north of Sacramento, California. The facility will burn natural gas to produce steam

for power generation. Residual steam will be used to break down rice straw into sugar

components that will then be converted to ethanol and other byproducts. The facility

would convert 132,000 tons of rice straw into 10 million gallons of ethanol annually.

If successful, the plant will consume up to 15 percent of the Valley's rice straw while

producing clean- burning ethanol to power internal combustion engines and for other

uses. The Sutter project would eliminate the need to burn rice straw on 50,000 acres

near Sacramento while making cleaner-burning fuel available for automobiles [33].

The City of Gridley (California USA) plans to construct an experimental plant to

convert rice straw into ethanol and power. The facility would dispose of

approximately 20 percent of California's rice straw, harvested annually from 80,000

acres of nearby rice fields. The facility would produce about 20 million gallons of

ethanol annually, which would in turn be used to generate surplus power in an

amount equal to half of Gridley's annual demand. The project is part of a feasibility

study funded by Congress since 1994. It is being conducted at the University of

California, Davis, and at the U. S. Department of Energy pilot plant in Golden,

Colorado, that went into operation in mid-1995. The CRIA is currently preparing to

deliver 85 tons of straw to the National Renewable Energy Labs in Golden, Colorado,

for this study. Construction of the Gridley facility is planned to begin in 1998,

pending favorable feasibility study results [34, 35].


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The pulping process changes raw, cellulose-rich materials (e.g., rice straw) to a

form that can be used in the production of paper, fiberboard, and many molded

products. Rice straw contains the highest level of silica. High-silica content makes

handling difficult because it is abrasive and rigid. Also, disposal of residual high-

silica black liquor sludge is difficult. These factors result in increased manufacturing

costs and economic disincentives for the use of rice straw when other less demanding

materials are available [36].

In the early 1980s, the Rice Research Board and Louisiana Pacific joined in a

study on the technological and economic feasibility of producing corrugated paper

from rice straw. The study indicated that the market was inadequate to support a

production facility on the West Coast. A plant producing corrugated paper from rice

straw was established in California, but the plant was closed in 1989 [37].

Manufacturing fiberboard from rice straw requires the use of chemical binders

which are different from the binders used in the manufacture of fiberboard from

wood chips. These binders represent a fairly new technology which is still under

development. Difficulties encountered during experimental production of medium-

density fiberboard from a 50/50 mixture of rice straw and hardwood chips are

reported in the "Economic Uses for Rice Straw" from the Report to California Rice

Farmers, 1969-84.


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2.5. Construction products

Construction of products, for which rice straw is a raw material candidate,

include, wood replacement materials, bricks and cement boards, panels, and straw

bale structure.

Agronomic systems is the name of a process for manufacturing a wood

replacement material using 70 percent biomass and 30 percent recycled plastic. The

material, marketed under the name Bio Comp, is waterproof, resistant to rot and

insects, withstands the sun, and can be shaped and nailed. This biological composite

uses a patented steam process to explosively break apart the biomass, releasing the

starch, sugars, resin, and other raw materials of the fiber. The process works on any

long-cell biomass, including wheat, rye, corn, rice, and barley straws.

Fiber reinforced composite building materials have been used for centuries in

the form of adobe bricks and other products. When straw is combined with cement,

the alkalinity of cement can have adverse effects on the long-term durability of the

fibers. Although alkalinity can be controlled with additives, the resulting product is

heavy and difficult to handle, cut, and fasten.

When rice straw is combined with clay, the resulting product insulates well, but

is not waterproof. If the straw/clay mixture is kiln fired, the composite end-product

loses biomass during the firing process, resulting in a lighter weight product and

further improves insulation properties.


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Manufacture of straw panels or boards, was pioneered in Sweden in the 1930s

and first commercialized in Germany in the 1940s. A number of areas of the world

including Belgium, Australia, China, and the Philippines produce and use straw

panels in construction today.

2.5.4. Straw bale structure construction

Straw bale construction was first used in the Midwestern U.S. in the 1800s and

its use is currently being revived. A 1,600- square-foot house requires approximately

500 bales. At 80 pounds per bale, this corresponds to about 20 tons or the rice straw

from 6 acres. The bale wall structure is typically sealed with plaster or stucco and

will have walls approximately 18 to 24 inches thick with an insulation R value

around 50. The National Research Council of Canada demonstrated the plastered

surface will withstand 1850F for 2 hours before cracking. The straw is sufficiently

dense that it does not readily support combustion.

2.6. Composting

Commercial compost companies use a mixture of several agricultural materials

to produce a desired end product. Candidate materials include straw, manure, fruit

and vegetable waste, leaves, grass clippings, and any other widely available

biodegradable materials. The mix of ingredients is piled into long windrows

(typically 5 feet high, 10 feet wide, and several hundred feet long). Compost turning

equipment mixes and aerates the piles.

The carbon to nitrogen (C: N) ratio of a compost mix is critical. The goal of the

composter is to acquire and mix the ingredients to a 30 C: 1 N ratio and then compost

them down to a finished product of significantly smaller mass and a C: N ratio of

approximately 10:1. Commercial compost-makers use straw in their production mix


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and storage) have not been well established and appear to be the major constraint in

establishing a solid niche for rice straw in erosion-control or fire-rehabilitation

markets.

2.9. Livestock feed

Rice straw is poorly digested by cattle. Cattle use 42 to 48 percent of ingested

rice straw as compared to 65 to 70 percent utilization of alfalfa hay [39]. Part of the

reason for this may be that rice straw is high in fiber, low in protein, and does not

supply enough nitrogen for the efficient metabolism and growth of rumen microbes

necessary to carry out the initial breakdown of the straw. Also, silica has no nutritive

value and may interfere with the digestion process. It can be used, however, by adult

or pregnant animals because their requirements for energy and protein are small

compared to their capacity to consume feed. Diets composed of 75 to 85 percent rice

straw were adequate to support pregnant cows and result in calves with a birth weight

comparable to those kept under conventional management practices on dry range or

on irrigated pasture for an equivalent period of time.

2.10. Additional available resources

a- Energy

Centre of Biomass Technology:This is a Danish biomass information network

comprising four technological institutes dedicated to generating power from biomass.

CBT collects and disseminates technical and economic know-how and experiences

associated with the establishment and operation of straw and wood chip-fired

combustion plants.


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b- Construction

Straw bale construction has been used for more than 100 years in America.

Recently, many new efficient homes have been built with straw bales.

Rice straw, the major agricultural by-product of Egypt, is high in lignin and

silica. Both of these components play an important role in reducing the digestibility

of straw. The crude protein content of rice straw is generally between 3 and 5 per cent

of the dry matter. Any crop residue with less than 8 per cent crude protein is

considered inadequate as a livestock feed because it is unlikely that such residues,

without supplementation, could sustain nitrogen balance in an animal. A further

deficiency in most fibrous material, especially in rice straw, is the low content of

calcium, phosphorus, and trace elements

table 5 [40].

The composition of residues varies with variety, location, and the cultural

practices employed in growing the crop from which they are obtained. If the full

potential of agricultural residues available in vast quantities throughout Asia is to be

realized, it is necessary that some types of treatment before feeding them to livestock

should be considered.


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Table 5. Average chemical composition of rice straw

Component Percentage (%)

Digestible energy 1.9 (kcal/kg)

Crude protein 4.5

Crude fiber 35.0

Ether extract 1.5

Lignin 4,5

Cellulose (%) 34.0

Nitrogen-free extract 42.0

Total digestible nutrients 43.0

Ash 16.5

Silica 14.0

Calcium 0.19

Phosphorus 0.10

Potassium 1.2

Magnesium 0.11

Sulphur 0.10

Cobalt 0.05 (mg/kg)

Copper 5.0 (mg/kg)

Manganese 4.0 (mg/kg)

A number of physical, biological, and chemical methods of treatment have been

described. Their aim was to increase digestibility and voluntary consumption, thereby

increasing the intake of digestible energy (DE). The treated material is often enriched

with nitrogen and mineral supplements in order to make it more completenutritionally. Some of these methods will be described, the emphasis being placed on

chemical methods of treatment.

Fibrous raw materials for pulp and paper production are generally divided into

three main categories, wood fibers which constitute about


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75 % of all fibrous raw materials supply of paper mills, reclaimed waste paper about

20 % and remaining 5 % are non wood fibers [41]. Rice straw could be very

important as a source for paper production especially in Egypt. Cereal straw, in

particular wheat straw, is a major source of pulp for paper production in china and

other Asian countries [42].

The high silica content of rice straw (9-14 %) however prohibits the economic

use of rice straw for this purpose. The silica will cause problems in the recovery of

chemicals used in the pulping process. For rice straw, there is currently no

commercially available solution for this problem. Other problems with the use of rice

straw for pulp are the higher water retention capacity of straw, the lower yield per ton

of raw material compared to wood, straw yields 45 % of pulp whereas wood yields

55 %, and the low bulk density of straw [43].

2.11. Chemical composition of wood and straw

The main components of wood and straw are cellulose, lignin, hemicelluloses

and soluble substances (extractives). The major polysaccharides component of wood

is cellulose, which has high molecular weight and is a highly crystalline material. The

term hemicelluloses refers to a mixture of low molecular weight polysaccharide

which is closely associated in plant tissues with cellulose. Lignin comprises 20-35 %

of wood substance and consists of the total non-carbohydrate fraction of extractive

free wood. Lignin compounds are essentially substituted phenyl propane three

dimensional polymers which are held together by ether or carbon bonds.

Some international applied solutions

1- The NACO (North American papermaking Cooperation) International system,

devised in Foggia, Italy in 1982, claims that its recovery system can handle high

levels of silica. The Arisa group in Australia intends to build a second NACO


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process for straw, but plans haven't materialized yet. It is not clear why other

paper manufacturers don't seem interested in this process [44].

2- Al Wong of Arbokem proposes to run a pulp mill in such a way that the effluent

can be used as a liquid fertilizer. According to Mr. Wong [45], growers would be

interested in exchanging their straw for his fertilizer. The concept has been setup

in a pilot plant in Alberta but hasn't matured yet. Some trials were carried out

with a blend of California rice straws and Oregon Rye Grass with mixed results.

3- Granit SA of Switzerland claims a new technology to solve the recovery problem.

They're working on a pilot plant in Thonon, France, to prove the concept, which

seems very promising. This technology is not mature either, and needs a couple

of more years to develop [46].

4- Weyerhaeuser spent a great deal of time and money in the 90's figuring out a

decent straw supply system, and figuring out the staketech steam explosion

system. Weyco built a complete pilot plant in Springfield, Oregon and made it

work. Nevertheless Weyco decided not to pursue straw pulping, and as of yet it is

unclear what the exact reason for discontinuation was. The project reports are not

public, but if you contact Bill Fuller at the Weyco research facility in Tacoma one

may be able to find more knowledge [47].

5- A pulp and paper manufacturing group called ABC pulp and paper in India claims

two patents and a pilot process proof of treating silica rich black liquor effluent

from a straw pulping process. The process is defunct and has not been proved on

industrial scale [48].

6- The Finnish company Conox claims similar results.

7- Universal Pulping of Eugene, Oregon claims a low-temperature, low pressure, low

emission process particularly suitable for non-wood pulping. The process,

patented by Eric Prior, was evaluated by the pulping labs at NCSU, WSU and the

University of Washington with very promising results. Although promising, the


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technology is not "off-the-shelf" yet, it has to be scaled up and debugged first. UP

is working on a pilot project to establish the technology [49].

Only the NACO process in Italy has been demonstrated on an industrial scale

for a significant period of time. All other technologies are in the R&D stage and do

not have a guaranteed performance [50].

The ultimate solution

Government support for straw utilization in papermaking is the most likely

way to get straw pulping accepted in Egypt.

Straw competes with wood as a raw fiber material. Only when we run low on

wood fiber will straw become an economically viable alternative. It is impossible to

anticipate a rise in pulping wood fiber cost in the near future to the extent where an

investment in straw based pulping can be justified. Fiber supply experts talk about a

variety of market effects:

a- Will paper use continue to increase?

b- Will the new Economy and the electronic office slow down the use of paper?

c- Will the recycling rate increase?

d- Will tree farms be able to supply sufficient fiber?

e- Will fiber imports from tropical countries and overseas tree farms continue?

f- Will consumer awareness shape the demand for paper that uses particular types of

fiber?

3. Pulping processes

There are many pulping processes, see table 7, these include mechanical pulping,

semi-mechanical pulping, chemical pulping, and bio-pulping. The pulping processes

suitable for annual plants are listed in table 6 the most common commercial method

for annual plant pulping is the soda method [51]. There are also several new


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physiochemical methods table 6 with good potential for producing high quality pulp

from annual plants. The kraft and neutral sulfite processes are less used. The acid

sulfite process is not used because it produces brittle pulps with high ash contents and

inadequate strengths. For higher yield pulping, the chemi-refiner mechanical pulping

process is used. Mechanical pulps are suitable for newspaper but not for cellulose

derivatives, which need celluloses of high purity to ensure high quality [52]. The

pulping processes concentrate not only on optimizing pulp quality but also on

improving pulp yields, reducing energy consumption, reducing chemical

consumption (and improving the recovery processes of the chemicals), reducing

pollution and developing sulfur-free pulping processes and chlorine-free bleaching

sequences .


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Table 6.Pulping processes for annual plants

Pulping process Chemical treatment Mechanical treatment Frequency

Chemical pulping

Soda (+AQ NaOH (+AQ) None Commonly used

Kraft (+AQ) Na2S + Na2OH (+AQ) None Commonly used

Sulfite NaHSO3 and/or SO2/Na2CO3 None Commonly used

Phosphate Na3PO4 None Potentially used

Milox Formic acid None Potentially used

Impregnation- NaOH, sodium carbonates None Potentially used

Depolymerization- ethanol- water blend

Extraction (IDE)

Alcell Ethanol-water blend None Potentially used

Processes other than chemical pulping

Thermo-mechanical Steam None Potentially used

Biopulping White rot fungi Disc refiner Potentially used

Ceriporiopsis subvermispora Disc refiner Potentially used

Alkaline peroxide NaOH, H2O2 Disk refiner Potentially used

mechanical pulping (APMP)

Chemi-thermomechanical Steam + NaHSO3 + Disc refiner Potentially used

(CTMP) NaOH

Cold caustic soda mechanical NaOH Disc refiner Potentially used

IRSP NaOH (+AQ) + Steam None Potentially used


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Table 7. Pulping processes and yields*

Pulping process Chemical treatmentMechanicaltreatment

Plant**Yield

%

Mechanical pulpingStone groundwood None Grindstone S 9399Steamedgroundwood Steam Grndstone S 8090Refiner mechanical None Disc refiner A, S 9398Thermomechanical Steam

Disc refiner(Pressure)

A, S 9198Asplund Steam Disc refiner A, S 8090Biopulping

White rot fungi Ceriporiopsis

subvermisporaDiscrefinerDisc refiner

A, H, SA, H, S

Chemi -mechanical and Chemi-thermomechanical pulpingChemigroundwood

Neutral sulfite or Na2S +NaOH

GrindstoneH, SH, S

H, S

80928090

8590Chemi refinermechanical pulp

NaOHorNaHSO3or Alkalinesulfite orAcidic sulfite

Disk refiner A, H, S 8090

Chemithermomechanicalpulp

Steam+Na2SO3+NaOHDisc refiner(pressure)

A, H, S 6597

Semi-mechanical pulpingNeutral sulfite Na2SO3+Na2CO3or NaHCO3 Disk refiner A, H 6590Cold soda NaOH Disk refiner A, H 6590Alkaline sulfite Na2CO3, Na2S, NaOH Disk refiner A, H, S 65-90Sulfate Na

2S + NaOH Disk refiner A, H 6590

Soda NaOH Disk refiner A, H 6590Green liquor Na2CO3 + Na2S Disk refiner A, H 6590Non-sulfur Na2CO3+ NaOH Disk refiner A, H 6590

Chemical ProcessesKraft (High yield) Na2S + NaOH Disk refiner A, H, S 5565Sulfite (High yield)

Acidic sulfite (Ca, Na, Mg)Or Bisulfite (Na, Mg)

Disk refiner A, H 5570

Kraft (+AQ) Na2S+NaOH (+AQ) Mild to none A, H, S 4555Kraft (Polysulfide) (Na2S+NaOH)x None A, H, S 4560Soda NaOH None A, H 4055Soda- AQ NaOH + AQ Mild to none A, H 4555Soda- oxygen NaOH, O2 Disk refiner A, H 4560

Acidic sulfiteAcidic sulfite (Ca, Na, Mg,

NH3)Mild to none A, S 4555

Bisulfite Bisulfite (Na, Mg, NH3) Mild to none A, H, S 4560Neutral sulfite Neutral sulfite Mild to none A, H, S 4560

**: A: annual plants; H: hardwood; S: softwood.


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3.1. Mechanical pulping

Mechanical pulps are obtained by disintegrating and physically separating the

fibers. These pulps have very intense yellow color and are often used for newspapers

or paperboards. Because of the large quantity of residue lignin in the pulps, the color

of these pulps easily turns yellow, but this can be overcome by subsequent chemical

bleaching. Softwood is the most common raw material of mechanical pulps, which

are relatively white. Annual plants are the easiest materials to use with mechanical

pulping because of their porous stalks. Mechanical pulping does not use chemicals to

eliminate lignin and hemicellulose, so yield is often high (90-98 %) as shown in table

7.

3.2. Chemical pulping

With chemical pulping, delignification is carried out with the help of acidic or

alkaline reagents in reactors. The lignin and hemicellulose are partially eliminated so

yields are between 40 and 60 %. On the other hand, the fibers are whiter and better

separated. Chemical pulping is divided into sulfite pulping and alkaline pulping

depending on the pH and nature of the pulping reagents. Sulfite pulping is a stronger

process because the separation of cellulose is better and their pulps can be used to

produce chemicals and papers of particularly good quality.

3.2.1. Soda process

This is the oldest and simplest pulping process. The soda process is a

common way to produce annual pulp. With this process, the cooking chemical is

mainly sodium hydroxide. Soda process leaves more insoluble carbohydrates in the

pulp and obtains a better yield than the kraft method. The strength and lignin content

of pulps produced with the soda and kraft processes are similar. Easily bleachable

short fibers that are abundant in pentosan are produced. This process often uses easily


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pulped species such as cereal straws, flax, abaca etc. Stevens et al. [53], proposed a

soda pulping process in which a catalyst, anthraquinone (AQ), is added. This catalyst

has two fundamental effects: the alkaline delignification process is accelerated and

the carbohydrates are stabilized. Soda-AQ pulping improves the yields under the

same operation conditions as conventional soda pulping. The use of this catalyst

(AQ) is only limited to 0.1 % of the dry biomass. Since annual plants are impregnated

easily, and have a low reactive lignin content table 6, the amount of pulping

chemicals needed for annual plants is lower than for woods. With soda pulping, 10

15 % NaOH, which depends on the raw material, is normally used at a pulping

temperature of 160170 C. Yields range from 40 to 55 % and are influenced greatly

by the species and quality of the raw material.

3.2.2. Kraft process

Kraft pulping is the most important pulping method. At present, more than half

of the worldwide production of pulps is manufactured using this method [54]. Yields

vary between 40 and 60 %. Kraft pulping requires shorter cooking times and is not

very selective. The pulping chemicals used are mainly NaOH and Na2S [55, 56]. The

raw material is treated with a highly alkaline solution of NaOH, which is known to

cleave lignin but also eliminates some of the hemicellulose. The undesirable

breakdown of hemicellulose is largely avoided by adding Na2S to the solution, which

avoids a very high concentration of NaOH in the pulping liquor. Kraft pulping

usually operates in batch reactors with a temperature between 160 and 180 C and a

cooking time between 4 and 6 hours. Continuous kraft pulping operates at a

temperature between 190 and 200 C and a cooking time between 15 and 30 min [57].


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3.2.3. Sulfite process

The main pulping chemicals are NaHSO3and/or Na2SO3[58, 59]. The reactors

for this process can be continuous or batch and operate at temperatures between 125

and 180 C depending on the final product (paper, cardboard, etc.). This process has a

yield of between 40 and 60 %. In the pulping process, sulphonates form and are

hydrated and the swelling of fibers helps delignification. The strongly ionized

sulphonic acids increase the acidity of the pulping medium, which results in

condensation reactions between phenolic moieties in lignin. This forms insoluble

resin-like polymers. These side reactions include degradation of the hemicelluloses

and celluloses. However, these carbohydrates are less degraded, which causes a

higher degree of polymerization and therefore a lower resistance of the pulps than in

the kraft process. Sulphite pulps are easier to bleach and are used to produce paper

with specific properties, such as toilet and tissue paper, which must be soft,

absorbent, and strong.

3.2.4. IRSP (impregnation rapid steam pulping process) process

Montan et al. [60], developed the IRSP process using wheat straw, which is

also tested by other annual plants and woods such as pine, miscanthus, sugar cane,

cardoon, and eucalyptus [61]. This process differs from the steam explosion pulping

in the nature of the impregnation, which generally uses concentrated NaOH solutions,

moderate pressures, and short impregnation times of 12 hours. This process consists

of two steps:

a- Impregnation

The aim of impregnation is to obtain a uniform distribution of pulping

chemicals in chips. Uniform distribution leads to more uniform pulp, better quality,

fewer rejects, and shorter cooking times [62]. The reactive pulping chemicals are


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mass-transferred into the stalk voids by penetration (which is governed by the

pressure gradient) and by diffusion (which is controlled by the concentration gradient

of the penetrating chemicals) [63].

NaOH and anthraquinone (AQ) are used as pulping chemicals under mild

pressure. Chemicals penetrate and diffuse into the capillaries and stalk voids. The

stalk fibers swell until maximum absorption is reached. Water, NaOH, AQ, and

alkaline soluble chemicals transfer between the fiber and the bulk solution until an

equilibrium stage is reached. Delignification, the softening of fibers and defibration

occur during the swelling and penetration stages. Some lignin that reacts with NaOH

degrades and dissolves in the alkaline solution. The initial white color of the alkaline

solution becomes darker and blacker [64].

b- Rapid steam pulping

Explosion pulping was invented by Mason [65]. Vit and Kokta [66] developed

the process to produce pulps that are suitable for papermaking, using techniques such

as the chemical impregnation of chips, short-duration saturated steam cooking and

sudden pressure release. Steam explosion pulping can be divided into two stages:

rapid steam cooking and steam explosion. In the rapid steam cooking stage, typical

cooking time is several minutes and typical cooking temperature is above 180oC. The

short cooking time prevents side reactions, it improves the selectivity and the yield of

pulps. Water has a plasticizing action on the glass transition temperature of lignin and

hemicellulose, and their softening temperature is reduced to about 100 oC. Steam

cooking at temperatures above their glass transition temperature leads to an additional

permanent fiber softening because of internal structural changes. The increasing

numbers of voids helps and improves the effect of the subsequent steam explosion

pulping.


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Fig. 1. The steam explosion effect of a fibril

During steam cooking, interior capillaries and fibril voids are gradually filled

with high-pressure liquid. When the cooking pressure is suddenly released, the high-

pressure liquid evaporates, which subjects the fibers to high impact forces. The fibers

are lacerated figure 1.

There are some other techniques as Pulping with organic solvents,

ASAM (alkaline sulfite-anthraquinone-methanol) process, Organocell

process, Alcell process, Acetocell process, Milox process and The IDE

(impregnationdepolymerizationextraction) process are collected in table 7.

4. Bleaching

Pulp bleaching is carried out in a sequence of several stages to eliminate as

much residual lignin as possible. Usually lignins are physically dissolved in alkaline

solution or chemically modified to form soluble chemicals in aqueous/alkaline

solutions [67, 68].

This process often uses two types of reagents (oxidants and alkali) though

reductants are sometimes used [69]. The oxidants are used to degrade and whiten the

lignins. The alkali is also used to dissolve the lignin. The alkali extraction can be used

to eliminate hemicellulose if the objective is to obtain dissolving pulps. The

following bleaching stages are often used in the contemporary bleaching industry

[70].


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4.1. Chlorination (C)

Chlorine is a common, effective, selective bleaching agent that reacts quickly

with lignin to form water-soluble degraded chemicals, which can be extracted with

alkaline solution. Chlorination is carried out at about 300oC and usually lasts for 30

min for sulfite pulp and up to 60 min for kraft pulp at a consistency of about 3 %.

Shortly after this chlorination bleaching, the next bleaching process is alkaline

extraction.

4.2. Alkaline extraction (E)

Alkali solution can dissolve some degraded lignins, degraded hemicelluloses

and some depolymerized celluloses of low molecular weights. Alkaline extraction is

often carried out using 11.5 % NaOH (based on o.d. pulp) for sulfite pulps and 3 %

for kraft pulps, which often lasts for 6090 min at 4060 C at a consistency of about

10 %. If dissolving pulps of high as 90 C and the alkali charge as high as 5 % NaOH

based on o.d. (oven dried) pulp.

4.3. Hypochlorite bleaching (H)

The oxidation reagents attack the free phenolic hydroxyl groups or the phenolic

ethers of the phenyl propane side chain of lignins. Usually, 12 % hypochlorite

based on o.d. pulp is used at 3050 C at a consistency of 10 % and the bleaching

lasts for 24 h.

4.4. Chlorine dioxide bleaching (D)

Chlorine dioxide is an extremely effective and selective bleaching

agent. The chlorine dioxide attacks phenolic OH groups of lignins. Phenoxy

radicals formed in this way undergo further reactions either to provide


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quinoid structures or to form muconic acid derivatives after a ring cleavage.

Chlorine bleaching uses 0.5 and 1.5 % active chlorine based on o.d. pulp,

which is carried out at 7080 C for 34 h at a consistency of 10-12 %.

4.5. Oxygen bleaching (O)

The bleaching agent is gaseous oxygen. The process must be carried out under

mild pressure for a sufficient amount of oxygen to be available in the bleaching

liquor. As a biradical, oxygen can remove an electron from the phenolate ions, which

are present in the alkaline medium. The formed phenoxy radical undergoes further

degradation reactions. Hydroperoxides are produced, which are further degraded by

intermolecular nucleophilic attack of the peroxide anions. The oxygen bleaching, in

which 24 % alkali and 12.5 % oxygen are used, lasts 3090 min.

4.6. Ozone bleaching (Z)

The most important reaction of ozone with lignin is the cleavage of the bonds

between the lignin units. Ozone can attack both the aryl and the alkyl moieties. The

attack on the aromatic rings leads to ring cleavage. Double bonds in the aliphatic side

chain, where carbonyl and peroxide structures are formed, are also attacked.

4.7. Peroxide bleaching (P)

The bleaching of mechanical pulp destroys the chromophoric groups by

cleaving conjugated double bonds. At 7080 C, the highly nucleophilic per

hydroxyl ion formed can further degrade quinoid lignin structures, which are

produced by the electrophilic bleaching chemicals. The peroxide bleaching

uses 12 % based on o. d. pulp at a consistency of 10 % at 7080 C.

Traditionally, the bleaching reagents are chosen for their economy and

selectivities as well as their capacity for bleaching efficiency and quality. Currently,


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due to the strict environmental restrictions on the emission of organic chlorides and

dioxins in effluents, the bleaching sequences increasingly use Elementary Chlorine

Free (ECF) or Totally Chlorine Free (TCF) processes [71]. TCF bleaching is the

current trend for contemporary delignification. TCF bleaching produces no

organochlorines, which are hazardous substances such as dioxin, an endocrine

disrupter, and human carcinogen.

5.Cellulose derivativesCellulose cannot dissolve in water. Introducing hydrophilic groups along the

chain of cellulose cleaves hydrogen bonds and renders its derivatives soluble in

conventional solvents, widening its applications to, for example, functional celluloseethers and esters [72-76].

Commercial cellulose derivatives are either ethers or esters that are soluble in

water or organic solvents. The three free hydroxyl groups in the AGUs react with

various functional substitution groups. The resultant substituents therefore disturb the

inter- and intra-molecular hydrogen bonds in cellulose, reduce the hydrophilic

character of the numerous hydroxyl groups, and increase the hydrophobicity.Introducing ester and ether groups separates the cellulose chains so completely that

the fiber structure is either altered or destroyed. The solubility of a cellulose

derivative in a solvent or in water depends on the type of substituents, the degree of

substitution and the molecular weight. These cellulose derivatives are grouped

according to the processes and chemical substituents. The most important commercial

cellulose derivatives are shown in figure 2 [77-82].


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Fig. 2. Important cellulose derivatives

6. Mercerization

In modern mercerization processes, 3070 % NaOH solution is sprayed onto

dry cellulose powder in fast-turning, dry-mixing aggregates. The cellulose powder

can also be impregnated with an inert organic solvent, which is used to produce

carboxymethyl cellulose (CMC). The cellulose can be mercerized in an organic

solvent in normal stirred vessels, which use powder NaOH after the slurry of

cellulose is formed.

The alkali cellulose for subsequent etherification must contain at least 0.8 mol

of NaOH per mole of anhydroglucose, which is a basic requirement to produce

Cellulose derivatives

esters ethers

Soluble in organic

solvents

Soluble in waterinorganic organic

Cellulose

nitrate

xanthate

Acetate

propionate

Acetate

ro ionate

Acetate

buthirate

Ethyl cellulose

Benz cellulose

Methyl cellulose

Carboxymethyl

cellulose

Hydroxymethylcellulose


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uniformly substituted ethers. Cellulose ethers of lower viscosities are usually adjusted

in the alkalization step, which is referred to as the ageing process. In the ageing

process, carefully designed conditions must be adjusted according to the products

final application. The optimum parameters which often control the process are ageing

time, temperature, NaOH concentration and the presence of catalytic amounts of iron,

cobalt, or manganese salts, which catalyze the oxidative de-polymerization.

7. Black liquor usage

Lignins are probably the most complex and the least well characterized group

of substances in nature. It comprises 20-35 % of wood substance; lignin forms the

adhesive reinforcing component and binds together the cellulosic fiber structure.

Lignin is obtained during pulping of lignocellulosic material. Lignin is essentially a

substituted phenyl propane unit held together by ether and carbon bonds.

Characteristics of lignin are highly affected by the pulping process and kind of

lignocellulosic material. So, during pulping process, lignin is demethylated and

degrades which causes the increase in phenolic hydroxyl groups [83]. The lignin oforganosolv pulping process has many physical and chemical properties which

distinguish it from produced lignin from kraft and sulfite process [84]. Increasing

temperature, time and pH of the pulping process increase hydroxyl groups in the

separated lignin [85].

Spectroscopic methods e.g. ultra-violet (UV), infrared (IR) and

(H NMR) can be used to give information about the structure of lignin[86, 87]. It was found that the methoxyl contents as well as oxidation level of soda

lignin is higher than that in case of kraft lignin [88]. Also, phenolic and carbonyl

groups of organosolv are higher than that in case of kraft lignin, while as hydroxyl

and methoxyl groups in kraft lignin are higher than organosolv lignin [89]. Alecell


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lignin has a lower molecular weight and lower methoxyl groups than kraft and soda

lignin, it might be sensitive to highly depolymerizing bleaching methods e.g.

hypochlorite bleaching [90, 91].


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EXPERIMENTAL

1. Raw material used

The raw material used in this work was Egyptian rice straw. It was directly

collected from different regions from the Nile delta.

2. Equipments

IR absorption spectra were recorded as KBr discs within the 4000-200 cm-1

range on a Perkin Elmer 1430 infrared spectrophotometer. The thermogravimetricanalysis (TGA) was carried out on a Shimadzu TG 50 thermogravimetric analyzer

from room temperature up to 1000oC using 10

oC/min heating rate under nitrogen as

atmosphere. The differential thermal analysis (DTA) was performed on 990 Du-Pont

differential thermal analyzer of 1200 C cell using Al2O3 as a reference. X-ray

powder diffraction diagrams were measured on Debye-Scherrer PW 1050 (Cux-K;

Ni-filter) from Philips. The surface of rice straw and pulp from rice straw samplesimaged with the (SEM) scanning electron microscopy type, JEOL JEM-850 operating

at 35 kV employed in the Central laboratory, National Research Centre, Cairo, Egypt.

Samples were investigated as it is without any change in their physical form.

3. Analysis of raw material

Many methods for the analysis of the plant materials and pulp have been

developed and tested for their reliability. The standard methods mostly in current

usage nowadays are the American Tappi standard, the German (Deutsche Einheiten)


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methods, and the Swedish methods. In this work the Tappi standards [92] were used

in most of the chemical analysis of the raw material and pulp.

3.1. Moisture content

An amount of air dry sample (w) was dried in an oven at 105 oC till constant

weight (w1) and the moisture content was calculated using equation (1).

100w

)w-(wcontentMoisture 1 = (1)

3.2. Water soluble matter

An amount of air dry sample was washed in distilled water in different ratios

with boiling for different time periods to determine the water soluble matters in the

samples used.

3.3. Determination of ash and silica in rice straw and pulp

The contents of ash and silica were determined by the Chinese standard

methods for non-wood raw materials [93]. The test specimen was transferred to a

crucible, carbonized gently over a Bunsen burner, then ignited in a muffle furnace at

575 +25 C, and the residue was weighed as ash. Because of the high silica content

of rice straw, a solution in ethanol of magnesium acetate, which contained 4.054 g of

Mg(AcO)2.4H2O in one liter of 95 % aqueous ethanol, was added to the test

specimen that originated from rice straw to prevent incomplete carbonization caused

by fusion of ash and silica. The ash obtained as described above was treated with


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concentrated HCl. The acid-insoluble residue was filtered, washed with hot water

until no chlorides were detectable, ignited, and finally weighed as silicon dioxide.

3.4. -cellulose estimation [94]

The term alpha cellulose is meant to describe the part of cellulose which does

not dissolve in 17.5 % NaOH (w/w). About 3 grams of rice straw were placed in the

porcelain beaker with 250 ml capacity, then 25 ml of sodium hydroxide (17.5 % w/w)

were added and left to swell for 4 minutes. The pulp was pressed with a glass rod for

3 minutes. After pressing, another 25 ml of sodium hydroxide were added and the

contents were mixed thoroughly till one gets a homogeneous past. The beaker was

then covered and left for 35 minutes at 25 oC. Then 100 ml of distilled water were

added and quickly filtered under suction using a sintered glass funnel (1G2 of 5 cm

diameter and 4.5 cm length). After washing with distilled water till neutrality 100 ml

of 10 % acetic acid were added drop wise for washing followed by distilled water.

The alpha cellulose was estimated gravimetrically after drying in an air oven at 105-

106 oC then weighing, the produced alpha cellulose was also ignited to calculate the

ash in the -cellulose samples.

4. Cooking in sodium hydroxide solutions (pulping)

The raw material, rice straw was cut into small pieces of 2-3 cm length before

pulping. Pulping was carried out in a porcelain beaker heated on electrical hot plate

under atmospheric pressure. All cooks were made with oven dried raw material from

rice straw samples. After pulping, the pulp was defibrated then filtered and washed


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with water till neutrality. The pulp was screened and analyzed chemically as in case

of the raw material.

Cooking conditions

In these tests, samples from rice straw were treated with NaOH solutions of

different concentrations for different time periods at different temperatures.

4.1. Effect of sodium hydroxide concentration

Sodium hydroxide acts as a solublizing agent for both silica and lignin found in

raw materials. 10 gm samples were boiled with 100 ml NaOH solution of certain

concentrations (4 %, 6 %, 8 %, 10 % and 12 %) for 2 hours.

4.2. Effect of time at optimum alkalinity

10 g samples were leached with 100 ml of 10 % NaOH solutions and were boiled

for different time periods (1, 2, 3 and 4 hours).

4.3. Effect of weight / volume ratio

10 g samples from rice straw were treated with 10 % NaOH solutions whileboiling for 2 hrs. in different weight per volume ratios 1/5, 1/10, 1/20 and 1/50 (w/v).


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4.3. Effect of cooking temperature on the yield of pulp

10 g samples from rice straw were treated with 100 ml 10 % NaOH solutions for

2 hrs. at different temperatures (40, 60, 80 and 100 oC).

4.4. Effect of the nature of rice straw on the pulp yield

10 g samples from rice straw were treated with 100 ml of 10 % NaOH solutions

for 2 hrs. at boiling point, length of samples used were the whole plant (80-120 cm

length), 20 cm, 10 cm, 5 cm and mechanically devided plant (less than 1cm).

5. Bleaching

The pulps produced by NaOH pulping are pale to intense yellow in color and

requires bleaching to reach acceptable brightness. Chlorine (C) and sodiumhypochlorite (H) with intermediate caustic extraction (E) and hydrogen peroxide (P)

with CEHEP and HEP sequences were used to evaluate bleaching capability of rice

straw pulps.

There are many sequences for bleaching rice straw pulp as examples; S-O-D1-

E/P-D2-P and O-D1-E/P-D2-P where:

S (saponification): 412 % NaOH on pulp, 5 % consistency, 60 C and 2hrs.

O-stage: 410 % NaOH on pulp, 12 % consistency, O2 pressure of 5kg/cm

2, 100 C and 1 hr.


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D-stage: 0.6 % (D1) or 0.4 % (D2) ClO2on pulp, 12 % consistency, 70 Cand 3 h.

E/P-stage: 2 % NaOH on pulp, 0.5 % H2O2on pulp, 12 % consistency, 70C and 2 h.

P-stage: 0.5 % H2O2 on pulp, 1.5 % NaOH on pulp, 12 % consistency, 70C and 2 h.

The brightness of bleached pulp depends on the bleaching sequences and

conditions. This is used on the industrial range and stated here to show that it is a

very expensive and complicated condition. So in this study the pulp were treated

with sodium bisulphate solution (4 % and 8 %), and with sodium hydroxide

solution (4 %) then with hydrogen peroxide solution (4 %) and the resulting

samples were subjected to IR spectrophotometric analysis to compare these results

with that obtained from previous work [95].

6. Permanganate number [96]

It is a method of expressing bleachability of pulp. It is determined by the

number of mls of 0.1 N KMnO4 consumed by one gram of moisture free pulp under

certain specific conditions of time, temperature and acidity.

Required volume of 0.1 N KMnO4(20 40 ml depending upon the rawness of

the pulp) were paced in one beaker, an equal amount of 4N H2SO4 is placed into

another beaker and enough water combined with H2SO4, so that, in the final reactionmixture of the permanganate solution will be 1/300 N. When the reagent is ready, the

pulp specimen is added to the reaction beaker, followed by addition of sulfuric acid

and then by addition of permanganate. After exactly 5 minutes at 25 oC an excess of

KI is added to stop the reaction. The residual KMnO4 in the mixture released an


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equivalent weight of iodine from the iodide salt solution. The liberated iodine is then

titrated against stander sodium thiosulphate solution [95]. The volume of

permanganate consumed by the pulp is then calculated. The permanganate number is

obtained by dividing the number of mls of 0.1 N KMnO4consumed by the moisture

free weight of the test specimen.

W

V-25numbertePermengana = (2)

where V is the number of milliliters of 0.1 N Na2S2O3consumed in the titration,

W is the weight of moisture free pulp and 25 is the number of mls of 0.1 N KMnO4.

7. Determination of the contents of black liquor

The recovery of the contents of the black liquors of rice straw is very difficult

because of the high viscosity of the liquor, the low caloric value and, in particular,

the high silica content, which is much higher in straw, especially rice straw, than inwood. As a result, such black liquors are discharged without any treatment and cause

serious water pollution. Novel and non-polluting pulping

Documents

Economic Exploitation of Rice Straw