Determination of Biodiesel Oxidation and Thermal Stabilitybiodiesel.org/reports/19970212_gen-230.pdf · DETERMINATION OF BIODIESEL OXIDATION AND THERMAL STABILITY ... Formation, 2

NATIONAL BIODIESEL BOARD

DETERMINATION OF BIODIESEL OXIDATION AND THERMAL STABILITY

FINAL REPORT

PREPARED BY:

SYSTEM LAB SERVICES a division of Williams Pipe Line Company

February 12,1997

Table of Contents

I.

II.

III.

IV.

V.

VI.

VII.

Page

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Project Scope . . . . e . . . . . . . . . . . . . . . . . . . . 1

Review of Past Research . . . . . . . . m . . . . . . . . . . . 2 Mechanisms of Sediment Formation, 2. Predictive Test Methods, 3.

Project Design . . . . . . . . . . . . . . . . . . . . . . . . . 4

Description of Analytical Procedures . . . . . . 0 . . . . . . . . 5

Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Base Fuels, 6. Blended Fuels, 8.

Data Evaluation and Interpretation . . . . . . . . . . . . . . . . 9 Long Term Test Results, 9. Accelerated Methods, 16.

VIII. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . .

IX. Items for Subsequent Research ..................

X. Bibliography ...........................

APPENDIXES

A. Oxidation Stability . . . . . . . . . . . . . . . . . . . . . . . . 24

21

22

23

i

I. Background

Fuel instability, both oxidative and thermal, can give rise to sediment and gum formation and fuel darkening. These product characteristics can cause filter plugging, injector fouling, depositions in the engine combustion chamber, and malfunctions in various components of the fuel system. In past engine tests with biodiesel fuel, instability appeared to contribute to malfunctions of fuel system and engine components.’ This experience, coupled with other field and laboratory tests, created a need to further evaluate biodiesel stability.

II. Project Scope

This project was developed to evaluate stability of biodiesel and biodiesel blends via test methods used by the petroleum industry. Additionally, selected diesel fuel stability additives and another antioxidant were evaluated for their efficacy in controlling chemical reactions associated with fuel instability in biodiesel and biodiesel blends. This project did not attempt to further investigate the chemical mechanisms associated with biodiesel instability. The test methods used and evaluated were selected from the numerous methods published and used by the petroleum industry. The additives selected for this project are commonly used across a wide range of diesel fuels produced from a variety of crude oils using various refining processes.

February 12, 1997 Prepared By: System Lab Services Page 1

III. Review of Past Research

A. Mechanisms of Sediment Formation Since World War II, diesel fuel stability has been the focus of a great deal of research. Prior to WWII, diesel fuel demand could be met with middle distillate production from straight run crude processing. The rapid rise in demand for fuel oils was met by introducing streams from cracking processes into the middle distillate fuels.(*s3) It is the components of these cracked stocks which have mainly been attributed as being the culprits for storage instability. Therefore, researchers evaluating diesel fuel stability have extensively used cracked stocks, such as light catalytic cycle oil (LCCO), in their research.

Fuel stability is usually defined in terms of color, soluble gum and insoluble sediment values. Each can be an important stability characteristics. Color is primarily a marketing concern, but it should be noted that color normally is a predecessor of sediment. Fuels which form color do not necessarily develop gum and sediment. However, rarely does a fuel develop gum and sediment without a concurrent degradation in color. Sediment and gum are the predominant stability concern. Formation of sediment or gum can result in operational problems with plugging and fouling in end use equipment, as well as in intermediate handling and filtration equipment.

There is an abundance of literature on fuel instability. A review of 320 papers, articles and books on fuel stability theory presented a summary of theories on ageing mechanisms and predictive tests.* This summary reveals there is no universal agreement as to the mechanisms associated with fuel instability. Some hold that the major reactions involved in fuel sedimentation are acid/base reactions, others polymerization and still others oxidation at points of unsaturation.

Though the theories regarding the mechanisms of sediment formation in fuel oils are diverse, they generally involve chemical species which are virtually nonexistent in distilled biodiesel. These species include indoles, pyrroles, aromatic thiols, heterocyclic aromatics and carbozoles. (*m4s5) The absence of these species in biodiesel suggests that the reactions of instability in petro-based and bio-based diesel fuels differ markedly.

Sulfur reduction in the production of low sulfur diesel fuel is commonly achieved through hydrotreating. Data from analyses of hydrotreated fuel reveal that hydrotreating can both increase levels of hydrocarbons susceptible to peroxidation and lower the level of peroxidation inhibitors naturally present in diesel fuel.” Peroxidation susceptibility resulting from hydotreating has been well known for many years, with susceptibility increasing by as much as 1,000 fold in hydrotreated jet fuel.7 The major concern regarding hydroperoxide formation in jet fuels is chemical attack of elastomers in fuel systems.


Oxidation of biodiesel is results in the formation of hydroperoxides. The formation of the hydroperoxide follows a well known peroxidation chain mechanism. As in petrodiesel, a major concern of users and sellers of biodiesel is chemical attack of fuel system components.

A study of high and low sulfur middle distillates demonstrated that as the severity of fuel storage conditions increased, the low sulfur diesel fuel became increasingly more susceptible to hydroperoxide formation relative to the high sulfur fuel.5 In the relatively mild storage conditions of ASTM D4625 (43 “C for up to 12 weeks) the low sulfur fuels developed hydroperoxide levels which were only moderately greater than the high sulfur counterparts. However, the low sulfur fuels developed one half the amount of total insolubles as the high sulfur fuels. From these data there is no indication that, for petrodiesel fuels, formation of insolubles is associated with hydroperoxide formation.

B. Predictive Test Methods Short term tests which predict fuel storage stability are desirable so that quality control procedures can be established for this important fuel characteristic. MacDonald and Jones’ delineated 26 test methods for evaluating fuel stability. In a Department of Energy study, a literature search was conducted to provide a list of stability test techniques and interpretations which could be used in a correlative distillate fuel stability test program. A large number of test techniques (approximately 116) were reviewed. All these efforts have not resulted in a method which satisfies the needs of all producers, distributors and users. The methods developed to date can generally be placed into one of two categories: methods which are conducted at 43 “C for extended periods and those employing elevated temperatures, pressures or both.

The 43 “C tests are generally regarded as being predictive of storage characteristics. As such, ASTM D4625 was accepted as a standardized stability test. D4625, along with other long term tests, are unacceptable for process and quality control because their use may result in supply disruption and product outages. Therefore, these tests, with their test durations of up to 24 weeks, limit their use to research applications. However, the 43 “C test procedures are used as the benchmark against which the short term tests are correlated.

The shorter test methods, which rely on elevated temperatures and/or pressures, attempt to accelerate the chemical reactions which normally occur under ambient conditions. These attempts are generally held to not provide reliably predictive test results.(“,“) In some instances reactions occur under the severe conditions which do not take place during ambient storage. In other cases, the accelerated methods result in extended induction periods before the onset of sedimentation’. It is quite possible that a good correlation of a short term test to actual storage characteristics could be established for an individual refiner using a consistent crude slate and processing scheme.


IV. Project Design

The experimental portion of this project was designed to evaluate test methods used for determining fuel stability and additives developed to control instability. A long-term storage test and two accelerated methods were used. The long term test was a modified ASTM D4625. The two accelerated methods were Du Pont F21 and an oxygen overpressure method employing analysis using ASTM D381.

The long term test is universally recognized as being a good predictor of fuel stability characteristics associated with field storage. In this research, the modified D4625 method was used as the standard for validation of the two short term tests.

The Du Pont F21 test was selected because it is by far the most prevalently used test method for predicting the storage characteristics of diesel fuel.” The method measures both color degradation and sediment formation. Though the color degradation is not necessarily indicative of sediment formation, it is generally regarded as an indicator of oxidation or decomposition. The color was determined using ASTM D1500 before and after the oxidation period. The sediment was measured by filtering the sample and then comparing the filter pad to a set of standard filter pads.

The oxygen overpressure method has been used by many refiners in the Midwest for over 40 years. It is similar to other accelerated techniques, such as ASTM D873. In contrast to many of the other analytical methods, this method directly measures oxygen uptake. (Most of the other methods measure only the negative effect of oxidation or decomposition, namely the formation of plugging or fouling sediments. If the fuel were to oxidize or decompose without the formation of gum or sediment, the test method would not detect this oxidative instability.) This in turn allows for a comparison of the ability of additives to hinder or retard fuel oxidation. This method also measures the total insolubles formed during the oxidation process.

Oxygen overpressure methods have been shown to have a weak correlation to the long term test across a broad spectrum of diesel fuels. This is due to the test conditions stressing the fuel to the point where reactions may occur which may not occur under the less severe ambient storage conditions. This researcher feels that due to the oxygen overpressure test conditions there is a greater likelihood that the test method will result in false positive results, relative to fuel instability, than false negatives. Given this and the aforementioned tendency for this test design to promote hydroperoxide formation, which may not naturally occur, it is felt that this method will exaggerate the degree to which the peroxidation reaction of biodiesel will occur. This exaggeration should assist in the evaluation of the relative efficacies of stability additives.


V. Description of Analytical Procedures

The ASTM D4625 test method requires a known volume of fuel to be stored in an over at 110 “F for a period of time ranging from 4 to 12 weeks. After long term storage, the fuel is filtered and the amount of sediment captured on the filter pad is gravimetrically determined. Any insoluble matter which developed during the storage period and adhered to the storage vessel is dissolved with trisolvent. The trisolvent is evaporated using the D381 test procedure and the adherent insolubles are measured gravimetrically. The modification of the method includes a reduction in sample size from 400 mL to 50 ml, enabling a greater number of samples to be analyzed simultaneously.

The Du Pont test methodI involves heating a 50 mL sample to 300 “F for 90 minutes and then cooling, measuring the sample color and filtering. The filter pad containing the sediment resulting from the accelerated aging process is then compared to a set of standard pads.

The oxygen overpressure procedure entails exposing 50 mL of sample to a pure oxygen environment at 212 “F for a period of 16 hours. The amount of oxygen uptake is measured during the reaction period by recording the pressure inside the reaction chamber. As oxygen is consumed the pressure inside the chamber declines. After the 16 hour reaction period, the color of the sample is determined using ASTM D1500 and total insolubles is determined using ASTM D381, with steam jet evaporation.


VI. Results

A. Base Fuels The base fuels used in this project were obtained from bulk storage facilities. They were tested for compliance with National Biodiesel Board (NBB) specifications. The specifications and the results of the analyses of these products are presented in Tables 1 and 2.

Property 1. Flash Point 2. Water & Sediment 3. Carbon Residue,

100% sample 4. Sulfated Ash 5. Kinematic

Viscosity, 40°C 6. Sulfur 7. Cetane 8. Cloud Point 9. Copper Strip

Corrosion 10. Acid Number 11. Free Glycerin 12. Total Glycerin

TABLE 1

NATIONAL BIODIESEL BOARD BIODIESEL SPECIFICATION

for Pure (100%) Biodiesel 12-04-95

ASTM Method Limits Units 93 100.0 min. “C 1796 0.0560 max vol % 4530 0.050 max wt %

874 0.020 max wt % 445 1.9 - 6.0 mm2/sec

2622 0.05 max wt % 613 40 min. 2500 By Customer “C 130 No. 3b max

664 0.80 max mg KOH/gm GC 0.020 max wt % GC 0.240 max wt %

Proiect Result >I 77°C 0.00% 0.03%

0.000% 4.022CST

0.000% 49.0 +O”C lb

0.72 0.000 w-t % 0.029 w-t %

Project Specific Tests: 1. Specific Gravity 2. Vapor Pressure 3. Pour Point 4. CHN

Carbon Content Hydrogen Content Nitrogen Content

5. Gross Heat of Comb. 6. Net Heat of Comb. 7. LTFT

1298 5191 97 5291

240 240 1539

0.8838 0.55 psi -4°C

77.57 w-t % 12.11 wt% 0.16 wt % 17,980 Btullb 17,023 BtuAb Fail at -3°C


TABLE 2

NATIONAL BIODIESEL BOARD SPECIFICATION ON DIESEL FUELS

Propertv ASTM Method 1. Cetane Number 613 2. Distillation 86

IBP 10% pt 50% pt 90% pt EP

3. API Gravity 287 4. Sulfur 2622 5. Aromatics 1319 6. Flash 93 7. Viscosity 445

Limits 42-47

340-400 400-460 470-540 560-630 61 O-690 33-36 0.025-0.05 28-40 130 min. 2.0-3.2

Units

“F “F “F “F “F 0

W-t% vol % “F cst

Proiect Result 43.2

345°F 412°F 498°F 608°F 659 35.3 0.0317% 32.8% 150°F 2.537 cSt

Project Specific Tests: 1. Sediment 1796 2. Cetane Number 613 3. Ash 482 4. Corrosion 130 5. Cloud Point 2500 6. Carbon Residue 524 7. Conductivity 2624 8. Corrosion NACE 9. Corrosion 130 IO. Stability Du Pont F21 11. Potential Color WPL 12. Potential Gum WPL

0.00% 43.2 0.000 mass% IA 2°F 0.14% 102 pS/m A IA 8 rating L3.0 10.2 mg/lOO mL


B. Blended Fuels Biodiesel was blended into petrodiesel fuel in the following percentages: 0, 2, 20, 40, 60 and 100% on a volume/volume basis. These blended fuels were used as the base stocks into which the selected additives were introduced.

Appendix A contains the data for the three test methods used in this project. As mentioned previously, the ASTM D4625 test method is generally accepted as a good predictor of storage characteristics of diesel fuel. The fuel color is a qualitative measure of fuel stability. It is not used to determine the ability to store a fuel for long periods without sediment formation. “Filterable Insolubles” measures the sediment which has developed during the test period. This insolubles measurement is viewed by many as the most important criterion for evaluating fuel storage stability. Sediment can cause filter plugging problems and injector fouling. “Adherent Insolubles” measures the sediments which form and adhere to the walls of the storage containers. These insolubles can cause malfunctions of various fuel system components, including valves in fuel pumps.

The color and pad ratings in the Du Pont F21 procedure provides the means of evaluating the relative tendency for a fuel to develop harmful sediments. The test procedure relies on the sediment resulting from the fuel instability being captured on the filtration medium (pad). There is also a measurement of fuel color for a qualitative assessment of the progression of fuel degradation reactions. This reliance results in a test method which can be easily performed by people other than laboratory personnel. The drawbacks of this method are that monitoring the color is not beneficial if the instability reactions do not result in the formation of chromophores and the filtration step will not provide quantitatively significant results if the sediment formed is of lesser porosity than the filter pad. Whatman #I filter paper is commonly used in this test and was used in this research. The porosity of Whatman #I filter paper is approximately 10 to 11 microns, and the particle size of degradation products are often less than 10 microns’“.

As in the other test methods, the color measurements in the Oxygen Overpressure method serve as a qualitative tool. The Induction Period data serve as a measure of the total sediments, both adherent and filterable, which result as a consequence of the reactions which occurred during the induction period. One consideration associated with this procedure is that significant amounts of sediments and gum may form during the evaporation step of the gum test”. The Induction Period data represents the time, in minutes, of the induction period. The induction period is a time of slow oxidation which precedes a more rapid oxidation process. In this research the break point was measured in the same manner as it is in the ASTM D525 test procedure “the point...that is preceded by a pressure drop of exactly 14 kPa (2 psi) within 15 min and succeeded by a drop of not less than 14 kPa (2 psi) in 15 min.”


VII. Data Evaluation and interpretation

A. Long term test results The ASTM D1500 color scale provides for measurement of fuel color at half unit increments, i.e. 0.0, 0.5, 1 .O, 1.5, 2.0, etc. Fuels failing between the half unit gradations are noted as being less than the color of the next greater scale value, e.g. L1.5. For the purposes of graphical presentations those fuels with color ratings of “less than” were assigned a numeric value half way between the values of the two closest absolute scale values. For example, a fuel with a rating of Ll .O was assigned a value of .75, which is half way between 0.5 and 1.0.

Chart 1 presents the color values of the blends of #l and #2 diesel fuels which did not contain stability additives. The base #2 diesel fuel had a color of Ll .O. The increase in color during the test period for the straight #2 diesel fuel and the blend containing 2% biodiesel suggests the fuel mildly degraded during the test. The graph reveals that as the percentage of biodiesel increases, color development decreases. When the biodiesel concentration was 60%, there was no color increase in the test sample, Obviously, in the #2 diesel fuel blends the biodiesel had a positive effect on color stability.

Chart 1

I Long Term Test

3.00 - Color Generation During Storage

8 2.50 --______-_______________________________--------

I j 20% 40% 60% 80% 100%

% Biodiesel

~--B-- #1 Fuel Oil -+#2 Fuel Oil


The base #I diesel fuel had a pretest color of LO.5 The absence of a color increase suggests this fuel was very stable. All of the values for the #I diesel/biodiesel fuels were either LO.5 or 0.5. The difference between these values is not considered to be significant. As with the #2 diesel fuel blends, the presence of biodiesel did not have an adverse affect on the fuel color.

The effects of stability additives on fuel color of #I an #2 diesel fuel blends are presented in Charts 2 and 3. All the results, except one, are LO.5 or 0.5. There is no significant difference between these results. The fuel was inherently stable, so additive effectiveness was not demonstrated.

Chart 2

LongTemTests-Cob-m #lFudoil

?/4%-rem & FCA 1/4%TB-D&HTd

February 12, 1997 Prepared By: System Lab Services

31A 14723

Page 10

Chart 3

Long Term Tests - Color #2 Fuel Oil

Generation

40% 60%

% Biodiesel

80% 100%

Q8FOA 31A & HiTech 4733

Charts 4 and 5 present total insolubles as a function of biodiesel concentration. The curved line was developed from empirical data generated during the course of the project. The straight line, denoted as “calculated”, was defined by the insoluble content of the two pure components. It represents the total insolubles which would result from bio/petro diesel combination if there were no bio/petrodiesel interactions. The fact that the amount of insolubles generated from the combinations of fuels was greater than what can be attributed to their separate contributions, clearly demonstrates that there is an interactive effect. The interactive effect produces more insolubles than what would be predicted using a interpolative approach. The magnitude of the interactive effect for any ratio of fuels is represented by the vertical distance between the two lines at that ratio.

The relatively consistent shapes of the graphs is revealing. The distance between the actual and predicted lines increase as the percentage of biodiesel increases until a maximum is reached, at which point the distance declines. Based on these data, along with knowledge of the chemical compositions of the two components, biodiesel appears to serve as an oxidizer or degradation contributor for petrodiesel. This effect increases as the amount of biodiesel increases until the increase impinges on the amount of petrodiesel available for oxidation.


Chart 4

Long Term Tests Total insolubles vs. Biodiesel Concentration

#1 Fuel Oil

30.0

f 25.0 8 Z $20.0

J LL = 15.0 s c

= +10.0 c

5.0

0.0 ’

0% 204i 40% X Biodiesal M)% 80% 100%

Chart 5

Long Term Tests Total Insolubles vs. Biodiese Concentration

15.0

13.0

~ 11.0 E

x 5 9.0 E i

2 7.0

2 : ! D 5.0

= 5 8 3.0

1.0


The cause for this interactive effect being significantly greater in #Idiesel fuel than #2 diesel fuel is unknown.

The impact additives had on the formation of total insolubles is presented in Charts 6 and 7. The data reflected in these graphs were evaluated from two perspectives. First, comparisons of blends containing an additive to blends which did not contain an additive were made. Then the relative efficacy of the different additives were compared.

Chart 6

LmgTmTests-TaMlnsolubies #PlFWlOil

40.0 114% lE#2 & FM 31A 30.0 114% TH-Q & HTti 4733

20.0

10.0

0.0


Chart 7

hgTetmTests=Totallnsdubles #ZFudOil

The differences in the amounts of total insolubles in the base #I fuel oil, the 2/98% biodiesel/petrodiesel blends and the 20180% biodiesel/petrodiesel blends are viewed as not being significant. Where there are significant differences in the total insoluble concentrations, the 40, 60 and 100% biodiesel blends, the blends containing FOA 31A generally contained more total insolubles than the blends which contained a different additive. In the blends containing 40 and 60% biodiesel, the sample which did not contain an additive, the blank, had the greatest amounts of total insolubles. This is what is expected in that the additive is supposed to hinder the formation of sediment. Interestingly, in the blends of 100% biodiesel, the blank did not form as much sediment as the sample


containing the petroleum industry additives. However, the difference in the total insoluble level for the blank and the sample containing HiTech 4733 was not significant. The FOA 31A actually appears to promote sediment formation in biodiesel. In the 40, 60 and 100% biodiesel blends the sample containing a combination of HiTech 4733 and TBHQ had the lowest level of sediment. The TBHQ in the TBHQ/FOA 31A blends appeared to combat the tendency of FOA 31A to promote sediment formation. This is evidenced by the lower level of sediment in these blends relative to the sediment levels in the FOA 31A blends. This can be explained by the recognition that FOA 31A was designed to hinder/prevent the chemical reactions which result in sediment formation in petroleum based diesel fuels. It is evident that the reactions which lead to sediment formation in diesel fuels are not the same reactions which lead to sediment formation in biodiesel.13

In summary there is a complex matrix of influences occurring with these samples. As seen by the data in the charts of total insolubles in different ratios of petro and biodiesel, Charts 6 and 7 above, the biodiesel is promoting sediment formation in petrodiesel. At the same time, the petroleum industry additives are hindering the formation of sediment in the diesel fraction. Additionally, one of the additives appears to be contributing to the formation of sediment in the biodiesel fraction. These influences and interactions appear to be reasonably certain. This does lead to variations in the ranking of additive efficacy as the level of biodiesel changes.

The data reflected in Chart 6 reveal that as the concentration of biodiesel increases, so does the relative efficacy of the TBHQ and TBHQ/HiTech 4733 combinations. In each of the 40, 60 and 100% biodiesel blends one of these two samples contained the lowest level of total insolubles.

In the samples containing a predominance of petrodiesel (0, 2 & 20% biodiesel) there is no significant difference in the amount of sediment formed. (The high sediment concentration in the sample containing FOA 31A in straight #2 fuel oil appears to be an anomaly. This conclusion is supported by the lack of sediment in the samples containing FOA 31A in the series of 2% and 20% blends.)

The data from this set of samples suggests that FOA 31A promotes sediment formation in biodiesel. Again, this additive was designed to prevent sediment formation in petrodiesel fuels where other chemical mechanisms are at work.


B. Accelerated methods The two accelerated methods, Du Pont F21 and Oxygen Overpressure, were evaluated for suitability for measuring instability of biodiesel and biodiesel blends by comparison tothe modified D4625, long term test method. The same samples were tested by these two methods as were tested in the long term test.

1. Du Pont F21 In this test method, the oxidation of the biodiesel blends did not result in color development. The data are presented in Appendix A. The test is predicated on capturing the color containing components of the oxidation process on a filter pad upon filtration. Since color development of biodiesel does not accompany oxidation, the Du Pont test would consistently generate low ratings regardless of the amount of sediment on the pad.

The lack of color development can pose problems for users of biodiesel. Historically, the users of petroleum diesel fuel have relied on color development as an indication of the progression of oxidation. Though the correlation between color and sediment was not extremely high, it was sufficiently high to serve as a means of field monitoring. The Du Pont F21 test was a refinement of the this principle for field monitoring by providing a standard rating scale. This scale and rating scheme allows comparisons across samples. The lack of color development in biodiesel and biodiesel blends does not allow the end user to monitor the progression of oxidation, with the possible subsequent formation of sediment, via this historical means.

The violation of the basis for measuring oxidation in the Du Pont F21 method rendered the evaluation of the test results using this test method against the results of the long term test pointless. Thus, a correlation between the two methods was not established.

2. Oxygen Overpressure Three data points were established for each sample: color after oxidation, oxygen consumed and total gum. The oxygen consumption was measured by determining the induction period and the total gum was measured by both the soluble and insoluble gum and sediment. The data are presented in Appendix A.

As discussed earlier in this report, the oxidation of biodiesel in this research did not result in a darkening of the fuel. Therefore, the color upon ageing did not result in data which can be used for measuring the degree of oxidation.


Charts 8 and 9 show the induction periods of the fuel blends containing #I diesel fuel. All of the blends containing 100% petrodiesel and the Z/98% biodiesellpetrodiesel blends had induction periods in excess of 960 minutes. The 20/80, 40/60, 60/40 and 100/O% petrodiesel/biodieseI blends revealed differences in the induction periods as a result of composition and additives.

Chart 8


Chart 9

1000 -

900 -

I

600 700

#2 Fuel 011

0% Blcdlesel 2% Slodiesel

-

.

.

.

I

. . . . _ . . . . . . . . . . . . . . . . . . . . . . .

.............

................ . . . . . . . . . . . .

. . . . . . . . . ..IM3%.aiodies.el

............................... ...........

....... ... ...

..... .... ... ...

....... ... ... .

... .....

I :- t

,. . . . . ‘aI

__ . . . I

60% Sdiesel

Of the 20/80% blends, the sample which did not contain an additive and the sample containing FOA 31A had induction periods of less than 960 minutes. The FOA 31A had a slightly longer induction period than the sample which did not contain an additive. The sample containing Hitech 4733 and those which contained TBHQ all demonstrated satisfactory stability, having induction periods greater than 960 minutes. These data indicate that TBHQ and Hitech 4733 retard oxidation and FOA 31A has minimal influence on oxygen uptake.

February 12, 1997 Prepared By, System Lab Services Page 18

All of the samples in the 40160 biodiesel/petrodieseI blends had induction periods of less than 960 minutes. The samples which did not contain TBHQ had induction periods which were significantly less than those containing TBHQ: 255 minutes for FOA 31A, 260 minutes for the sample which did not contain an additive and 345 minutes for the Hitech 4733 sample versus 695 minutes for TBHQ/FOA 31A, 775 minutes for TBHQ and 855 minutes for the TBHQ/Hitech 4733 sample. In this sample set, the Hitech 4733 performed better than the sample with FOA 31A or the sample without additive. The TBHQ/Hitech 4733 sample had the longest induction period, indicating a complimentary relationship for this additive combination.

All of the samples in the 60/40 biodiesel/petrodieseI series had short induction periods, except the sample with TBHQ/ FOA 31A combination, which had an induction period at least twice as long as any other sample. An explanation for this data point is not presented because it can not be reconciled with the other data points in the Oxygen Overpressure or the D4625 tests. The induction periods for the remaining five samples ranged from 105 minutes to 215 minutes.

The effect of TBHQ was even more pronounced in the 100% biodiesel samples. All of the samples containing TBHQ had induction periods greater than three times the induction periods of the samples not containing TBHQ. There was not a significant difference in the induction periods of the samples which did not contain TBHQ. Additionally, there were no significant differences in the induction periods of the samples which did contain TBHQ.

The data from the samples containing #2 diesel fuel blends exhibit the same tendencies as observed in the #I diesel fuel set: as the percentage of biodiesel increased, the stability of the fuel declined. The samples containing TBHQ were more stable than those without this additive. For the sample series containing 20/80% and 40/60% biodiesel/petrodieseI, samples containing Hitech 4733 were generally oxidized to a lesser extent than the samples not containing an additive or those containing FOA 31A. In the samples not containing TBHQ in the other series of samples, a relative ranking was not possible. The combination of TBHQ and Hitech 4733 appeared to be the most effective at reducing oxygen uptake.

As was the case with the #I diesel fuel blends, the straight #2 diesel fuel and the 2/98% biodiesel/petrodieseI blends all had induction periods greater than 960 minutes.


In the series containing 20% biodiesel, the samples containing TBHQ had induction periods greater than 960 minutes, demonstrating the superior performance of this additive. The samples which did not contain TBHQ had induction periods of less than 960 minutes. The sample containing Hitech 4733 had a significantly longer induction period than the samples not containing an additive or containing FOA 31A.

The samples in the series containing 40/60% biodiesel/petrodiesel all had induction periods greater than 960 minutes, except the sample containing the Hitech 4733/TBHQ combination. The samples which did not contain TBHQ had shorter induction periods than those containing TBHQ. The samples containing Hitech 4733 performed better than the samples not containing an additive and those which contained FOA 31A. These data indicate that the TBHQ and Hitech 4733 are complimentary.

The trends exhibited in the 20/80% and 40/60% blends are also present in the 60/40% biodiesel/petrodieseI blends. The samples containing TBHQ have induction periods at least twice as long as those which do not. The data points comprising these two subgroups, those containing and not containing TBHQ, were not significantly different, which did not allow a relative ranking.

The graph of the 100% biodiesel induction periods for the #2 diesel fuel samples is virtually identical to that of the #I diesel fuel samples. The induction periods of the TBHQ samples are over three times as greater as the induction periods of the samples which did not contain TBHQ. There was not a significant difference in the induction periods of the samples which did not contain TBHQ. Similarly, there was no significant difference in the induction periods for the samples which did contain TBHQ.

Appendix A presents the total gum content of the blends of #I and #2 diesel fuels with biodiesel which formed during the oxygen overpressure period. The normal range of gum content in this test is from 1 to 50 mg/mL of sample. The biodiesel did not evaporate during the drying phase, resulting in exceedingly high gum content results. The gum contents were as high as 13,000 mg/mL. It is apparent that biodiesel is outside the scope of products successfully evaluated by this test method.


VIII. Conclusions

Biodiesel oxidizes by different chemical mechanisms than the mechanisms associated with diesel fuel instability. This makes the application of much of the research relative to diesel fuel stability inappropriate. This research goes beyond the research which identified chemical mechanisms. It includes research involving the development of accelerated methods for the determination of storage stability. Additionally, it includes the identification of compounds and combinations of compounds (additives) which inhibit the formation of the sediments and other insolubles.

The long term, 43 “C test, produced test data which were in line with past experiences with petroleum based diesel fuel. The amount of sediments which developed during the test were greater than what would have been predicted from the behavior of the individual components. An antagonistic synergy influenced the results.

The Du Pont F21 test method is not applicable to biodiesel or biodiesel blends. This leaves field personnel without a method which can be used easily to monitor the stability of a fuel. Without a tool the number of instances of fuel with advanced oxidation will be greater than if a QC test method was available.

Induction periods provide a means by which the relative efficacies of additives can be established. The induction period determinations do not directly measure the results of fuel oxidation which are the concern of the end user; namely sediments. Therefore, the degree to which oxidation results in a problem is not established.


IX. Items for Subsequent Research

The amount of total insolubles which were generated in the long term test in the blended samples is a source of concern. The apparent antagonistic synergy which was observed may restrict satisfactory handling and storage practices. The data generated in this project are not sufficient for determining that this negative interaction will be universal across all petrodiesel/biodieseI blends. Therefore, substantiating data needs to be generated before storage practice decisions are made.

A reliable, quick test to determine biodiesel stability is highly desirable. Since the Du Pont F21 test method is not suitable for this purpose, an investigation into possible alternatives may be warranted. The chemical make-up, and the number of compounds associated with instability in petroleum based diesel fuels, is such that it is impractical to monitor fuel stability from a species identification perspective. Speciation of biodiesel oxidation products may be possible because there are fewer fuel components which result in fewer possible primary instability mechanisms. This suggests that the progression of fuel oxidation could be monitored through a simple wet chemical or instrumental analyses. Confirmation of this thesis requires additional research.


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2.

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43.

Bibliography

Or-tech International. 1995. Operation of Cummins N14 Diesel on Biodiesel: Performance, Emissions, and Durability. Final Report tot he National Biodiesel Board. Ortech report No. 95El I-8004524. December 20.

Derst, P. “Mechanisms for ageing of Middle Distillates manufactured from Crude Oils” Presented October, 1994, 5th International Conference on Stability and Handling of LiquidFuels, Rotterdam, the Netherlands.

Taylor, W.F.;Frankenfield, J.W. “Chemistry Mechanisms of Distillate Fuel Stability”; Proceedings of 2nd International Conference on Stability and Handling of Liquid Fuels, san antonio, Texas, July, 1986.

Hiley, R.W.;Pedley, J.F. “Storage Stability of petroleum-Derived Diesel Fuel 2. The Effect of Sulphonic Acids on the Stability of Diesel Fuels and a Diesel Fuel Extract”:Fuel 1988, 67, pp 469-473.

Waynick, J.A.; Taskila, S.M., “A Comparison of Low and High Sulfur Middle Distillate Fuels in the United States”, Presented October, 1994, 5th International Conference on Stability and Handling of LiquidFuels, Rotterdam, the Netherlands

Vardi, J.;Kraus, B.J. “Peroxide Formation in Low Sulfur Automotive Diesel Fuels,” SAE Paper No. 920826,1992.

Watkins, J.M., et al. “Hydroperoxide Formation and Reactivity in jet Fuels,” Energy and Fuels 1989, 3, pp 231-236.

Lundberg, W.O., A&oxidation and Antioxidants. Interscience (John Wiley and Sonds), 1961.

MacDonald, J.W.; Jones, R.T., 1959, ASTM-STP 244, 5-l 4.

Stavinoha, L.L.; Henry, C.P. ASTM Special Tech. Pub. 751, 1980.

Stavinoha, L.L.; Westbrook, S.R. Accelerated Stability Test Techniques for Middle Distillate Fuels. Report No. DOE/BCI10043-12, USA, 1980.

Waynick, J.A., Research Scientist with Amoco Oil Company, Personal communication, February, 1996.

Waynrck, J.A., Research Scientist with Amoco Oil Company, Personal communication, February, 1997.


APPENDIX A

February 12, 1997 Prepared By: System Lab Set-vices Page 24

Oxidation Stability DuPont F2l Oxygen Overpressure D 4625 (modified)

Insolubles

Lab # Fuel Blend Additive Used Before After Before After 16 hr Potential Induction Color Color Pad Pad Color Gum Period

Color Filterable Adherent Total

13595 #lF.O. None LO 5 LO.5 1 1 LO.5 0.0 960 LO.5 0.4 1.4 1.75

13596 #lF.O HITech 4733 LO.5 LO.5 1 1 LO 5 3.2 960 0.5 0.5 1.6 2.55

13597 #l F.O. FOA 3lA LO.5 LO.5 1 1 LO 5 2.8 960 LO.5 0.8 40 4.15

13598 #IF.0 l/4% TBHQ LO.5 LO 5 1 1 05 45 2 960 05 0.7 38 4 55

13599 MF.0. l/4% TBHQ & HrTech 4733 LO 5 LO5 1 1 05 28.6 960 0.5 02 2.6 2.8

13600 #iF.O. 114% TBHQ & FOA 31A LO.5 LO.5 1 1 0.5 82.0 960 0.5 0.9 2.4 33

13601 #lF.O. w/2% Bio None LO.5 LO.5 1 1 LO.5 02 960 LO5 07 2.8 2.75

13602 #IF.0 w/2% BIO HrTech 4733 05 05 1 1 05 04 960 0.5 0.6 26 3.1

13603 #lF.O. w/2% 910 FOA 31A LO.5 LO.5 1 1 LO 5 1.2 960 LO 5 08 18 2.7

13604 HF.0 w/2% Bio 114% TBHQ LO.5 LO 5 1 1 L1.0 126.6 960 LO.5 07 1.6 2.65

13605 #IF.0 w/2% Bio l/4% TBHQ & HiTech 4733 LO.5 LO 5 1 1 Ll 0 107.6 960 0.5 1.1 1.4 2 45 -

13606 #lF.O. ~12% Bio 114% TBHQ (L FOA 31A LO.5 LO.5 1 1 LO.5 141.8 960 LO.5 09 1.8 25

13607 #IF 0 w/20% 810 None LO.5 LO.5 1 1 LO.5 2614.2 765 05 2.4 38 6

13608 #IF.0 w/20% Bio HITech 4733 05 0.5 1 1 Ll .o 59.0 960 1 .o 3.3 26 5.4

13609 #lF.O. w/20% Bio FOA 3tA LO.5 LO 5 1 1 0.5 2076.0 795 LO.5 1.1 2.2 3.7

13610 #lF.O. w/20% Bio 114% TBHQ LO.5 LO.5 1 1 Ll .o 90.8 960 0.5 1.6 5.4 7 05

13611 #I F.O. w/20% Bio 114% TBHQ 8 HiTech 4733 LO.5 LO 5 1 1 Ll .o 90.4 960 0.5 1.5 3.4 4.95

13612 #IF.0 w/20% Bio 114% TBHQ (L FOA 31A LO.5 LO.5 I 1 Ll.O 96.2 960 0.5 2.6 2.2 4.85

13613 #IF 0. w/40% Bio None 0.5 05 1 2 1 .o 5969 8 260 LO.5 18.6 126 33 25

13614 #lF.O. ~140% BIO HrTech 4733 Ll.0 05 1 2 Ll 0 6200 4 345 LO 5 17.2 4.6 22 6

13615 #lF.O. w140°b Bio FOA31A 0.5 LO.5 1 2 1.0 5989.6 255 LO5 22.9 7.6 27.85

13616 #lF.O.w/40% Bio 114% TBHQ 0.5 05 1 2 L1.0 4820.8 775 0.5 2.7 26 5.65

13617 #lF.O. w14OU Bio 114% TBHQ L HiTech 4733 0.5 0.5 1 2 Ll 0 2180.7 a55 0.5 22 1.4 2.7

13618 #lF.O. w/40% Bio 114% TBHQ (L FOA 31A 0.5 05 1 2 Ll .o 5559.4 695 0.5 3.3 1.4 5.25 I

Oxidation Stability DuPont F21 Oxygen Overpressure 0 4625 (modified)

insolubles

Additive Used Before After Before After 16 hr Potential Induction

Lab # Fuel Blend Color Color Pad Pad Color Gum Period

Color Filterable Adherent Total

13619 #I F.O. w/60% Bio None 0.5 0.5 1 2 L1.0 8131 4 125 LO.5 18.1 1.6 25.1

13620 #lF.O. w/60% Bio HrTech 4733 L1.0 0.5 1 2 1 .o 9037.4 215 LO.5 12.2 50 152

13621 #lF 0. w/60% Bio FOA 31A 0.5 0.5 1 2 1 .o 10068 8 105 LO.5 144 4.8 13.65

13622 #lF.O. w/60% Eio 114% TBHQ 0.5 0.5 1 2 10 7402 6 130 LO.5 7.0 3.2 13.75

13623 #lF.O. w/60% Bio 114Y TBHQ 8 HrTech 4733 0.5 05 1 1 L1.0 7239 0 145 0.5 2.5 1.2 4.25

13624 #IF 0. w/60% Bio 114% TBHQ & FOP. 31A 0.5 05 1 1 Ll 0 5945 0 515 05 5.5 1.8 5.5

13625 #2F.O. None 05 15 3 4 2.0 12.8 960 2.0 2.2 1.8 4

13626 #ZF.O. HiTech 4733 L1.5 1.5 2 3 2.5 8.4 960 2.0 2.8 1.6 3.45

13627 #2F.O. FOA 31A 1.5 15 2 3 L2.5 5.4 960 2.0 0.7 106 6.7

13628 #2F.O. 114% TBHQ 20 L2.5 1 4 3.0 60.4 960 2.5 1.6 34 4.55

13629 #2F.O. 114% TBHQ & HiTech 4733 2.0 2.5 1 4 3.0 74.6 960 2.5 2.1 2.0 4.15

13630 #2F.O. 114% TBHQ a FOA 31A L2.5 2.5 2 3 3.0 758 960 2.5 I .a 20 3.65

13631 RF.0. w/2% Bio None 1.5 1.5 3 3 L2 5 6.6 960 L2.0 1.2 1.6 2.7

13632 #2F.O. w/2% Bio HiTech 4733 1.5 15 3 4 L2 5 7.6 960 L2.0 0.8 1.4 2.45

13633 #2F.O. w/2% BIO FOA 31A 1.5 15 2 3 2.5 5.0 960 L2.0 0.9 2.0 2.9

13634 #2F.O. w/2% Bio l/4% TBHQ 2.5 2.0 2 3 3.0 69.0 960 2.5 1.2 26 3.8

13635 #2F.O. w/2% Bio l/41 TBHQ B HiTech 4733 2.5 2.0 3 4 3.0 68.8 960 2.5 1.2 2.8 3.9

13636 #ZF.O. w/2% Bio 114% TBHQ a FOA 31A 2.5 L2.5 3 3 3.0 77.8 960 2.5 12 2.2 38

13637 #ZF.O. w/20% Bio None 1.5 1.5 2 4 2.0 2104 6 545 2.0 2.8 2.6 4.85

13638 #2F 0. w/20% Bio HiTech 4733 Ll 5 1.5 2 4 20 1583.0 a45 2.0 1.3 2.4 36

13639 #ZF.O. w/20% Bio FOA 31A L1.5 1.5 2 3 2.0 2555 8 485 2.0 1.7 2.6 4.1

13640 #ZF.O. w/20% Bio 114% TBHQ L2.0 L2.0 2 3 L3.0 157 6 960 2.5 0.8 36 5.15

13641 #ZF.O. w/20% Bio 114% TBHQ 8, HiTech 4733 L2.0 2.0 2 3 3.0 121.8 960 2.5 1.1 3.8 4.7

13642 #ZF.O. w/20% Bio l/4% TBHQ 8 FOA 31A L2.0 L2.0 3 3 2.5 I 55.8 960 L2.5 2.8 3.2 6.3 -

Oxidation Stability

I I I I DuPont F21 I Oxygen Overpressure I D 4625 (modified) I

Insolubles

Lab # Fuel Blend Additive Used Before After Before After 16hr Potential fnduction

Color Color Pad Pad Color Gum Period Color Filterable Adherent Total

13643 #2F.O ~140% Bto None 15 1.5 2 4 20 5788.8 245 1.5 50 36 9 05

13644 #2F 0 w/40% Bio HiTech 4733 15

13645 #2F.O w/40% Bio FOA 31A L1.5

13646 ( #2F 0 w/40% Bio 1 114% TBHQ I Ll 5

13647 1 #2FO w/40% BIO ) 114% TBHQ & HrTech 4733 1 1 0

’ L1.5 2 4 L2.5 5013.4 365 1.5 1.5 26 4 65

1.5 1 2 L2 5 5060.0 170 1.5 15.2 32 128

L2.0 2 3 2.5 3846.8 705 L2 0 19 34 505

L1.5 2 2 15 3987.0 960 2.0 30 30 6

13648 #2F 0 w/40% Bio 114% TBHQ 8, FOA 31A L1.5

13649 #2F.O. w/60% Bio None Li 5

13650 %2F 0 w/60% BIO HrTech 4733 LO.5 05 2 1 10 7964.6 125 Ll 5 64 3.4 8.1

13651 #2F 0 w/60% Bio FOA 31A 0.5 0.5 2 1 Ll 0 6472 2 185 Ll 5 197 2.8 20.95

1 13652 1 S2F.O w/60% Bio I l/4% TBHQ 1 L1.5 1 L1.5 / 2 1 2 ) IO 1 4162.2 1 600 1 1.5 1 3.7 1 14 ) 4.3 1

1 13653 I #2F 0 w/60% Bio 1 114% TBHQ & HiTech 4733 I Ll 5 I L1.5 I 2 ( 1 I 1.0 I 5493.4 1 635 1 1.5 1 4.5 ) 2.6 1 7.85 1

13654 g2F.O. w/60% BIO 114% TBHQ & FOA 31A 1 .o L1.5 2 1 15 69146 575 1.5 5.4 2.8 7

13655 Neat Brodresel None 1 .o L1 5 1 2 11.5 12135 0 95 0.5 51 3.2 8.3

15020 Neat Btodiesel HiTech 4733 1 .o L1.5 1 2 L1.5 11414.0 95 LO.5 98 2.0 10.3

15021 Neat Biodtesel FOA 31A LO.5 LO.5 2 2 Ll 5 12373.2 90 0.5 25.1 1.4 26 5

15022 Neat Biodresel l/4% TBHQ LO.5 LO.5 2 3 L1.5 10219.4 385 0.5 74 1.4 68

15023 Neat Brodresel 114% TBHQ & HiTech 4733 LO.5 LO 5 1 2 L1.5 11868.2 360 0.5 36 0.6 4.2

15024 Neat Biodresel 114% TBHQ & FOA 31A LO.5 LO.5 2 2 L1.5 13064.8 320 0.5 7.3 00 7.7

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Determination of Biodiesel Oxidation and Thermal Stabilitybiodiesel.org/reports/19970212_gen-230.pdf · DETERMINATION OF BIODIESEL OXIDATION AND THERMAL STABILITY ... Formation, 2