The University of Manchester

BIOREFINERY ENGINEERING COURSE WORKCHEN 40091-64281

2010-2011

PRODUCTION OF POLYHYDROXYBUTYRATE (PHB) FROM WHEAT BASED FEEDSTOCK

By:Afnan AlnajeebiRoshan Menon

Sudhanshu MohantyArunachalam Subbiah

Contents: 1. Introduction………………………………………………………………………………………………….022. Polyhydroxybutyrate………………..……………………………………………………………………….02

a. Physical Properties………………..……………………………………………..............................02b. Biological Properties………………..……………………………………………………………...02c. PHB Applications………………..……………………………………………...............................04

3. Microorganism: Ralstonia Eutropha………………………………………………………………………...04a. Morphology of Ralstonia Eutropha……………………………………………..............................04b. Characteristics of Ralstonia Eutropha……………………………………..……………………….04c. Biosynthesis of PHB……………………………………………………………………………….04

4. PHB Production Process…………………………………………………………………………………….05a. Part 1: Production of Feedstock from Wheat………………………………………………………05b. Part 2: Production and Recovery of PHB……………………………………….............................06c. Process Flow Diagram for the PHB Production Process………………………..............................07d. Production Plant Layout Scheme…………...……………………………………………………...08

5. Geographical Location………..……….…………………………………………………………………….096. Economic Analysis…………………………………..…………………...………………………………….10

a. Total Operating and Capital Costs…………………………………………………………………10b. Price of PHB…………………………………………………………………….............................12c. PHB Production Area Requirement……………………………………………..............................12

7. Environmental Impact of PHB Production………………………..………………………………………...128. Conclusion……….…………………………………………………………………….................................149. References…………………………………..……………………………………………………………….15

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1. Introduction

Plastics have become an integral part of society, as they can be moulded into almost anything and have desirable mechanical properties like being lightweight, durable and cheap to purchase. The benefit of current plastics does not erase the harmful environmental effects caused by the production and disposal. The global production of current plastics has to match the consumption, which has been rising by approximately 7 million tonnes per year.

This report is based on the production of the plastic polyhydroxybutyrate or more commonly referred to as PHB. This plastic is biodegradable and can be broken down into smaller, simpler parts by living organisms, thus it essentially has minimal harmful effects on the environment. The process incorporates a fermentation reaction of a natural feedstock, rich in glucose and free-amino nitrogen, with the bacterium Ralstonia eutropha. Instead of purchasing the natural feedstock, the proposed process recommends the harvesting and processing of wheat to generate the feedstock for the production of PHB. With the dwindling world fossil fuel supply, it is essential for industry to start shifting their attention away from a petroleum based production to a natural feedstock based production. Research and development has been done on various suitable natural feedstock that could act as a direct substitute for the current fossil fuel based economy. Wheat has been established as a suitable natural feedstock because it contains essential nutrients that, when coupled with a microorganisms, can allow for microbial growth. The proposed production is based in the Harbin province in Heilongjian in the northeastern part of the People’s Republic of China. The economics of the production process have been evaluated and the PHB price has been set to $15.12 per kg. Environmental concerns have been taken into considerations and explained. The scope of this report is to propose a production plant that uses wheat based feedstock for the production of 4750 tonnes/year of PHB.

2. Polyhydroxybutyrate

PHB, a type of polyhydroxyalkanoate (PHA), is a biodegradable plastic material produced by hydrogen-oxidizing bacterium such as Ralstonia eutropha in the presence of Carbon and Nitrogen sources. PHB in cells serves as a reserve of carbon and energy; this is analogous to fat in animals. Production of decomposing plastics is done in biorefinery industries which use renewable resources. It has large industrial applications; especially since production of petroleum plastics have had a major concern on the environment.

a. Physical Properties

The molecular mass of PHB can vary from 50,000 to 1,000,000 Da. This is a substantial increase from the early range of 20,000 to 30,000 Da. Experimentation and comparison with conventional, non-degradable, plastics has shown that PHB with high molecular masses have similar mechanical and physical properties. Table 2.1 below compares the melting temperature Tm, the glass transition temperature Tg (temperature of transformation of amorphous fraction from glassy phase to rubbery phase), crystallinity and extension at break. It can be observed that P(3HB-co-4HB) has physical properties close to that of polypropylene.

Plastic Crystallinity (%) Extension at break (%)PHB 177 2 70 5P(3HB-co-4HV) 145 -1 56 50P(3HB-co-4HB) 150 -7 45 444Polypropylene 176 -10 60 400

Tm (°C) Tg (°C)

Table 2.1: Propeties of PHAs and polypropylene (Xu, Yunji. 2007)

b. Biological Properties

The main biological property of PHB is its biodegradability. The plastic can be broken down into carbon dioxide and water by numerous microorganisms present in nature. Current production techniques employ the use of agricultural based feedstock which provides the required carbon and nitrogen source. The feedstock itself derives carbon dioxide and water and is converted to PHB. This continuous cycle of production and degradation has labelled PHB as being a renewable resource.

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c. PHB Applications

PHB when blended with materials, such as starch, have been used in various applications such as films, containers, coated paper and board, compost bags, disposable food service-ware, moulded products and personal hygiene articles such as diapers...etc. PHB finds various applications in medicine as it can be digested by the human body and as it is produced by microorganisms from natural raw materials rather than chemical synthesis. Materials made from PHB, due to their biodegradability, have been expected to replace traditional petroleum based polymers. PHB have been widely used as a drug carrier and have found its application in drug delivery.

3. Microorganism: Ralstonia Eutropha

a. Morphology of Ralstonia Eutropha

Ralstonia eutrophus is a gram-negative and nonpathogenic bacterium. R. Eutropha in general can be found in both soil and water. Their scientific classification is as follows:

Kingdom: Bacteria Phylum: Proteobacteria Class: Beta Proteobacteria Order: Burkholderiales Family: Ralstoniaceae Genus: Ralstonia

b. Characteristics of Ralstonia Eutropha

Ralstonia Eutropha can grow on a variety of substrates like sugars, organic acids and alcohols as its carbon source and in the presence of several heavy-metals (Zinc, Cadmium, Cobalt, Lead, Mercury, Nickel and Chromium). They are facultative aerobes which can live in both aerobic and anaerobic environments. Its optimal temperature is 30°C. Ralstonia eutropha produces the homopolymer poly(β-hydroxybutyrate) (PHB) and it accumulates as granules in its cytoplasm, when it is provided with propionate in the feedstock. Ralstonia eutrophus is used for the production of a biodegradable thermoplastic (Biopoly) on an industrial scale. R. eutropha strain H16’s has the capability to store large percent of poly[R-(–)-3-hydroxybutyrate] and other polyesters.

c. Biosynthesis of PHB

The biosynthesis mechanism is depicted in Figure 3.1 below. The PHB biosynthetic pathway contains three enzymes. The first enzyme is Acetyl CoA acetyl transferase(1) which catalyzes the reversible condensation reaction to produce acetoacetyl-CoA from two acetyl-CoA molecules.

+

.

Figure 3.1: Biosynthesis pathway for the production of PHB

Secondly, acetoacetyl-CoA reductase (2) reduces Acetoacetyl-CoA to (R)-3-Hydroxybutyryl-CoA. Finally, PHB is formed by the polymerization of (R)-3-Hydroxybutyryl-CoA, in the presence of poly-β-hydroxybutyrate polymerase(3).

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(1) (2)

(3)2 Acetyl-CoA

Acetoacetyl-CoA (R)-3-Hydroxybutyryl-CoA

Poly-3-hydroxybutyrate (PHB)

4. PHB Production Process

The PHB production process is based heavily on the fermentation stage. This is regarded as the rate limiting stage of the whole process, as the culture time is approximately 50 hours. The overall process can be split into two main parts: 1) feedstock production and 2) PHB production. The feedstock production has been adapted from a novel wheat biorefining process for continuous production of fermentation feedstock by Arifeen, N. et al., developed at the Satake Centre for Grain Process Engineering. The complete process flow diagram (PFD) is presented in Figure 4.1 at the end of this section with a simplified production plant in Figure 4.2

a. Part 1: Production of Feedstock from Wheat

The current wheat biorefining process used in industry firstly uses dry-milling to convert wheat to whole wheat flour. Hydrolysis is then applied to the starch that is present in whole wheat flour to produce glucose with the aid of commercial enzymes such as α-amylase, β-amylase as well as some others. The wheat biorefining process proposed by Arifeen N. et al. has certain changes that benefit the process economics and minimize waste disposal. The key differences between the current process and the proposed process are as follows:

The production of two byproducts: bran-rich pearling and gluten. These byproducts can be sold to the market and consequently will help process economics.

There is a lower energy requirement and capital investment due to introduction of simultaneous gelatinization, liquefaction, and saccharifaction at temperatures slightly lower than 70°C.

The proposed process incorporates combined flour hydrolysis and fungal autolysis, which could lead to reduced capital investment.

Wheat is harvested from the fields surrounding the production plant, transported and kept in a storage tank at a temperature of 25°C and 1 bar pressure, before feedstock production. The process begins with the extraction of the wheat from the storage tank, the wheat is then milled in a hammer mill and three product streams are generated: whole wheat flour, fermentation feedstock and pearling. For simplification reasons, the pearling has not been considered in the economic analysis. The flour is sent to the kneader which, with the addition of water, produces gluten and the product stream. The gluten is kept in a storage tank at a temperature of 25°C and 1 bar pressure for sale to the market. The product stream contains starch which is separated out of the solution using a centrifuge. While this is happening, the fermentation feedstock passes through a paddle-mixer and is heated to a temperature of 30°C by a shell and tube heat exchanger. The heated stream enters a continuous bioreactor where the pH is maintained at 4.5 with the equivalent addition of acid. The bioreactor output stream is separated into a filtrate and solids stream using vacuum filtration. The filtrate stream meets the centrifuged stream (from the kneader) in the gelatinization and dextrinization stage. Gelatinization breaks down starch’s intermolecular bonds when heated to approximately 68°C and in the presence of water. Dextrinization is the process of converting starch into dextrins by the use of heat. Dextrins are known to be various soluble polysaccharides. The resulting stream from the gelatinization and dextrinization unit is directed to the combined flour hydrolysis and fungal autolysis tank. In order for the successful conversion to a carbon and nitrogen rich feedstock the unit temperature is kept at 55°C. The wet solids stream separated with vacuum filtration from the bioreactor exit stream is directed to the combined unit as the basis for the fungal autolysis. However, the two input streams are not added at the same time. This is because they both enter at different temperatures. For flour hydrolysis, a temperature of 68°C is optimum for accelerated gelatinization and dextrinization of starch. The problem lies in the production of FAN during the fungal autolysis phase. Koutinas et al reported that the concentration of FAN is reduced significantly when exposed to temperatures above 55°C. Thus, fungal autolysis and flour hydrolysis cannot begin together. In order to remedy this problem, it is proposed to split the combined process into two stages. The first stage involves allowing the gelatinization and dextrinization product to cool to 55°C in the combined unit and then add the wet filtrate stream (from the bioreactor) to the flour suspension. This temperature is maintained by using a heating jacket on the combined unit. After the continuous combined flour hydrolysis and fungal autolysis the product stream is sent through a vacuum filter that separates the stream into solids (which is used as a recycle stream) and the microbial feedstock. The feedstock stream has a volumetric flow rate of 8 m3/h and contains glucose and FAN concentrations of 238 kg/m3 and 0.78 kg/m3 respectively.

b. Part 2: Production and Recovery of PHB

The feedstock produced in section 1 enters the process with a mass flow rate of 2.36 tonnes/h (it is more convenient to use tonnes/hr as the quantities are larger in this section of the overall process). The stream is heat sterilized to remove any forms of life such as fungi, bacteria, viruses etc. contained in the fluid. The core of the

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PHB production process is the fermentation stage. In order to achieve acceptable levels of PHB, a fed-batch culture is used. Air, first compressed then filtered (to remove particulates), and feedstock are continuously added to the microorganism which has been inoculated to a suitable quantity. Three fermentors are used for the PHB generation stage. The fermentors have a residence time of 50 hours in a pressure for 1 bar with the temperature maintained at 30°C. This has been determined to be the optimum temperature for microbial growth.

The process flow sheet for the recovery process is shown in tonnes per run, as a certain amount is made every 50 hours instead of every hour. The recovery of the PHB is conducted during the 50 hours residence time. The recovery process begins with the culture broth being moved from the fermentors to the holding tank to cool down and then sent through a disk-stack centrifuge where the aqueous waste is centrifuged out and sent to the waste treatment site. The solids obtained from the centrifugation go through a surfactant-hypochlorite digestion process. A blending tank is used to thoroughly mix 1% (w/v) surfactant solution with the harvested cells (solids) for 1 hour at 25°C. The resulting PHB solution is mixed with hypochlorite solution. The mixer shown in Figure 4.1 is not actually a piece of industrial equipment. Instead, the hypochlorite digestion is done in a flow-through manner. The aqueous solution is then centrifuged and the aqueous solution containing non-PHA cellular materials (NPCM) are removed and sent to the waste treatment site. The PHB rich stream is then washed with water in a continuous manner in a blending tank. In order to remove the water, the resulting stream is centrifuged and the aqueous waste is removed. The pellet or PHB rich stream is sent to a storage tank where it is kept at 1 bar pressure and 25°C. The surfactant-hypochlorite digestion process allows for 95% recovery of PHB from the culture broth and requires 12 hours.

Finally, the stored PHB is sent to the packaging and shipping section of the production plant where it is packaged and distributed. The complete process takes 62 hours. According to the production time, 141 runs can be conducted during the 8760 hours of operating time per year. The proposed production process yields 4750 tonnes of PHB per year after recovery. This yield requires 23,000 tonnes per year of wheat as the raw material.

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c. Process Flow Diagram for PHB Production

Figure 4.1: Process Flow Diagram for the production of feedstock from wheat and the production of PHB. Includes flow rates, temperatures and pressures of each stream.

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d. Production Plant Layout Scheme

Figure 4.2: Simplified Production Plant layout.

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Truck

5. Geographical Location

In order to construct a production plant, a suitable location had to be chosen which would favour the needs such as crop growth, climatic conditions….etc. The Harbin province in Heilongjiang, China was suitable to meet the needs for setting up a production plant.

Heilongjiang is a province located in the northeastern part of China. The agriculture of Heilongjiang, heavily defined by its cold climate, is based upon crops such as soyabean, maize and wheat. Various commercial crops are also grown such as beets, flax and sunflowers. A humid continental climate predominates in the province, though areas in the far north are subarctic. Winters are long and bitter, with an average of −31 to −15 °C (-24 to 5 °F) in January, and summers are short and warm to very warm with an average of 18 to 23 °C (64 to 73 °F) in July. The annual average rainfall is 400 to 700 millimetres (16 to 28 in), concentrated heavily in summer. Clear weather is prevalent throughout the year.

As one of the country’s most important commodity grain production bases, Heilongjiang occupies first place in terms of both volume of commodity grains and storage. The province’s total grain output was around 37.8 million tons during the year of 2006. The pillar industries in Heilongjiang include equipment manufacturing, petrochemicals, energy and food processing. The pillar industries’ total output is listed in Table 5.1

Table 5.1: The pillar industries in Heilongjiang and their industrial output value.

Harbin is a sub-provincial city and the capital of Heilongjiang province in Northeast China. It lies on the southern bank of the Songhua river, is the tenth largest city in China with an area of 56579 km2 and it includes 8 districts and 12 counties with a population of 9.87 million serving as a key political, economic, scientific cultural and communications hub in the northeast part of China.

Harbin is located in southern part of Heilongjiang, its latitude ranges from 44°04-46°40 and the longitude ranges from125°42-130°10. The production plant is located 35.3 km outside the city of Harbin and the area, as shown in Figure 5.1 below. The entire production plant (including wheat fields) is approximately 80 km2 as marked on the Figure 5.2 below.

Figure 5.1: City – A, Production Plant – B Figure 5.2: Production Plant marked in green.

Approximately 80 km2

Harbin features a monsoon-influenced, humid continental climate with hot, humid summers and very cold winters. Its winters are dry and bitterly cold, with a 24-hour average in January of only −18.4 °C (−1.1 °F). Yet the city sees little precipitation during the winter and is often sunny. Summers can be hot, with a July mean temperature of 23.0 °C (73.4 °F). Summer is also when most of the year's rainfall occurs. Spring and autumn constitute brief transition periods with variable wind directions. The variation in temperature is shown in Table 5.2 below.

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Table 5.2: The temperature ranges during each month in Harbin province.

The ideal temperature for the production of wheat ranges from 23°C to -1°C. Therefore, the yield of wheat would be high from April to the month of October and the yield would be considerably low in the months of January, February, March, November and December.

The soil in Harbin, called “black earth” is one of the most nutrient rich in all of China, making it valuable for cultivating food and textile-related crops; Harbin is China’s base for the production of grain and an ideal location for setting up agricultural businesses. Harbin also has industries such as light industry, textile, medicine, foodstuff, metallurgy and chemicals which help to form a fairly comprehensive industrial system. China is the world’s number one producer of wheat and rice, and is second in maize after the U.S. Its total grain output at 435 million tonnes.

6. Economic Analysis

a. Total operating and capital costs

The total operating costs associated with the PHB production has been determined to be $71,812, 411.25 per year. The capital costs required is $106,956,506.36. This implies a total initial investment of $178,798,917.62. The economic analysis, to determine the costs, was split into two sections: direct fixed capital – costs associated with the construction of the plant, annual operating costs – costs associated with the production of PHB from wheat, including labour and other items. Tables 6.1 and 6.2 below shows the cost of the equipment used in the feedstock and PHB production respectively.

Equipment (Quantity) Description Cost ($)Storage Tank (2) Volume = 240 m3 (ea) 336,934.00Hammer Mill Mass Flow rate = 30135 kg/h 206,597.00Kneader Volumetric Flow rate = 21.36 m3/h 2,317,841.00Paddle-Mixer Power: 47 kW 213,124.00Heat Exchanger (2) Heat Transfer Area = 20 m2 496,140.00Gelatinizer Volume = 36.16 m3 214,322.00Hydrolyzis Tank (2) Volume = 115 m3 (ea) 2,726,450.00Rotary Dryer Peripheral Area = 137 m3 259,118.00Centrifuge Flow rate = 2278 kg/h 286,957.00Vacuum Filter (2) Filter Area = 18 m2 25,250.00  Filter Area = 48 m2 67,333.00Bioreactor Volume = 200 m3 1,185,413.00Total   8,335,479.00

Table 6.1: Equipment costs for feedstock production from wheat.

Equipment (Quantity) Description Cost ($)Heat Sterilizer Diameter = 0.1m 319,000.00Compressor Pressure Change = 5 bar 771,909.00Air Filter (2) Throughput =0.70 m3 354,408.00Fermentor (3) Volume = 200 m3 (ea) 13,762,268.00Holding Tank Volume = 60 m3 111,287.40Blending Tank (2) Volume = 42.48 91,397.00  Volume = 40.56 87,266.00Disk-Stack Centrifuge (3) Power = 5.5 kW 26,141.00

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  Power = 6.7 kW 31,844.00  Power = 13.5 kW 64,165.00Storage Tank (1) Volume = 40.8 m3 63,813.00Total   15,683,498.40

Table 6.2: Equipment costs for PHB production.

The direct fixed capital incorporates the equipment prices from both the production processes with other costs associated with the constructing of the production plant. These costs are shown, as well as how they have been calculated, in Table 6.3 below:

Item Details Cost ($)Total Plant Direct Cost (TPDC)    Equipment Purchase Cost (PC) 24,018,977.40Installation    Process Piping (0.40 x PC) 9,607,590.96Instrumentation (0.45 x PC) 10,808,539.83Insulation (0.10 x PC) 2,401,897.74Electrical (0.15 x PC) 3,602,846.61Buildings (0.45 x PC) 10,808,539.83Auxiliary Facilities (0.40 x PC) 9,607,590.96TPDC   70,855,983.33Total Plant Indirect Cost (TPIC)  Engineering (0.30 x PC) 7,205,693.22Construction (0.40 x PC) 9,607,590.96TPIC   16,813,284.18Other Costs (OTC)  Contractor's Fee (0.07 x (TPDC + TPIC) 6,136,848.73Contingency (0.15 x (TPDC + TPIC) 13,150,390.13OTC   19,287,238.85Direct Fixed Capital (DFC) (TPDC + TPIC + OTC) 106,956,506.36

Table 6.3: Total capital costs associated with the purchase of equipment and construction of the production plant.

The annual operating cost requires more analysis than the direct fixed capital. The operating costs include raw materials, utilities, labour, manufacturing expenses and waste treatment/disposal. Table 6.4 below lists all the items involved in the total operating costs.

Item Details Cost ($)Annual Operating Cost (AOC)  Depreciation   10,695,650.64Maintenance Material   1,069,565.06Insurance (0.01 x DFC) 1,069,565.06Local Taxes (0.02 x DFC) 2,139,130.13Factory Expenses (0.05 x DFC) 5,347,825.32AOC   20,321,736.21     Labor Dependant Items (LDI)  a) Opearting Labor (OLC) 1,506,000.00b) Maintenance Labor (0.10*TPDC) 2,401,897.74c) Fringe benefits [0.45 x (a + b)] 1,953,948.87d) Supervision [0.25 x (a + b)] 2,778,397.74e) Operating Supplies (0.15 x a) 225,900.00f) Laboratory (0.20 x a) 301,200.00LDI   9,167,344.35

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     Adminstration and Overhead Expenses [0.7 x (a+b+c)] 4,103,292.63     Raw Materials    a) Land/Wheat Procurement (RW) 3,822,295.50     Utilites (UTI)  a) Process Water 200 m^3/h, $0.14/m^3 1,800,000.00b) Process Steam 11000 kg/h, $0.015/kg 1,397,647.00c) Cooling Water 500 m^3/h, $0.028/m^3 112,833.00d) Electricity cost 2200 kW, $0.0228/MJ 1,569,282.00e) Surfactant (Triton-X100) 3.54 tonnes/run, $31.4/L 7,986,240.00f) Hypochlorite Solution 3.20 tonnes/run, $4.68/L 2,157,120.00UTI   18,845,417.50     Total Production Costs (TPC) AOC + LDI + RW + UTI 48,334,498.06     General Manufacturing Expenses (GME)  Administration Costs (0.25 x OLC + 0.02 x DFC) 2,515,630.13Distribution and Selling Costs (0.20 x TPC) 9,666,899.61Research and Development (R&D) (0.10 x TPC) 4,833,449.81GME   17,015,979.54Waste Treatment/Disposal   7,181,241.13Revenue From Gluten Market Price: $1400/tonne -4,169,760.00Total Annual Operating Costs (TAOC) 71,812,411.25

Table 6.4: All costs involved in the total annual operating costs

b. Price of PHB

The production plant generates 4750 tonnes of PHB with an operating cost of $71,812,411.25 per year. This equates to a PHB price of $15.12 per kg to break-even. This is lower than the current market price of $16.0 per kg. The proposed price is lower because wheat is being cultivated and the feedstock is produced instead of being bought from outside sources.

c. PHB Production Area Requirement

The amount of wheat required to achieve this yearly PHB is 23,000 tonnes. The Harbin province in Heilongjiang, China has an approximate wheat yield of 3.8 tonnes per hectare. The area required to achieve the wheat requirement is 60.5 km2, coupled with 2.0 km2 allocated for the production plant. The total area available for wheat harvesting and the production plant is 1963 km2, which is depicted as a circle with a 25 km radius. All of the allotted area is not used, only 3% of the area is used. This leaves approximately 1900 km2 of unused area. If all the area is utilized, this would result in harvesting 745,180 tonnes per year of wheat and consequently producing 153,896 tonnes per year of PHB. However, this scaling up would require very large production plants and equipment which is currently unavailable; hence it is not feasible at this moment.

7. Environmental Impact of PHB Production

PHB has very nominal effects over the environment compared to the polyolefins (Polypropylene(PP),Polyethylene(PE)). The Bio-degradability and its production from renewable resources are the two main advantages of PHB that makes it superior over the conventional polyolefins which are produced from non-renewable resources and non-biodegradable too. Though there are many bio-polymers present only PHB exhibits properties that are very similar to synthetic polymers. It has also been found that greenhouse gas emission from PHB production was much lower. Many experiments were carried out on PHB production process and the most important was the life cycle assessment(LCA) to give its impact on all categories and finally the results were compared with those of PP& PE. The 1000kg of all the three polymers were produced and then LCA was carried out and the results were compared. Steam production and electricity requirement are

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the main harmful effects on the environment. In peculiar steam production subjugates abiotic depletion, global warming, photochemical oxidation and acidification. Electrical requirements subjugate ozone layer depletion, human toxicity, fresh water ecotoxicity, marine ecotoxicity and terrestrial ecotoxicity. The impact on PHB production on various environmental sectors are shown in Figure 6.1 below.

Figure 6.1: Percentage Contribution of PHB towards the environmental impacts

It has been found that PHB was benevolent in all the impacts of LCA than PP. The 1000kg production of PP discharges CO2 80% greater than that of the PHB which production is also the same 1000kg. In the case of ozone layer depletion PP discharges 50 times greater more than PHB. It means that PP is discharging much more greater than PHB in all the categories(since ozone layer depletion is combined of almost all impacts). In the case of terrestrial ecotoxicity, PP production discharges 10 times more than PHB production. The main reason behind this is the greater requirement of CRUDE OIL for PP production whereas PHB requires only a little. Its evident from the scores of LCA that abiotic depletion, human toxicity, photochemical oxidation, fresh water aquatic ecotoxicity are double that of PHB production. Acidification & eutrophication are 100 & 12% greater than PHB respectively.

PE is classified in to two types based up on their densities. The types are high density polyethylene(HDPE) and low density polyethylene(LDPE). Both of the above mentioned PE has the same order of significance for all the impacts expect for the photochemical oxidation. During photochemical oxidation HDPE emanates ethane so it is less favourably selected in this process. But both HDPE & LDPE production has lower impacts in all categories than PP production except for the human toxicity & photochemical oxidation. Eutrophication is the only process in which PHB has 500% more impact than PE. Acidification and marine aquatic ecotoxicity levels are balanced in both PHB & PE production. This comparison is shown in Figure 6.2.

Figure 6.2: Comparison of environmental impacts between PHB, PP and two types of PEs.

PE production shows increased impacts in the rest of the following categories:Impacts Fold increase than PHB

Abiotic depletion 1.7 folds13

Fresh water toxicity 1.6-1.9 folds Terrestrial toxicity 3-4 folds Human toxicity 3 folds Photochemical oxidation(HDPE) 22 folds Ozone layer depletion 4-10 folds

8. Conclusion

A production process has been proposed for the production of polyhydroxybutyrate (PHB). The process includes the growing and harvesting of wheat. Wheat is the sole raw material as it can provide a feedstock rich in carbon and nitrogen, which is essential for microbial growth. The proposed process uses Ralstonia Eutropha as the microorganism of choice. The optimal location for the growing and harvesting is Harbin province in Heilongjian, China. This location was selected because of China is the leading producer of wheat and the “black earth” soil that is present in Harbin is the most nutrient rich soil in China. A production capacity of 4750 tonnes per year of PHB has been established with the proposed production process. This will require approximately 80 km2 of land, which includes the production plant and the wheat fields. Economic analysis on the production processes has yielded a direct capital cost of $71,812, 411.25 per year. The capital costs required is $106,956,506.36. This is a total initial investment of $178,798,917.62. Using the total annual operating costs and the production capacity, the price of PHB has been set to $15.12 per kg. This price is slightly lower than the current market price of $16.0 per kg. Finally, environmental data has shown that PHB production has lower detrimental effects on the environment when compared to polypropylene and polyethylene.

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