J. Van Gerpen

BIODIESEL PRODUCTION FROM OILS AND FATS WITH HIGH FREE FATTY ACIDS

Biodiesel is an alternative fuel for diesel engines consisting of the alkyl monoesters of fatty acids from vegetable oils or animal fats. Most of the biodiesel that is currently made uses soybean oil, methanol, and an alkaline catalyst. The high value of soybean oil as a food product makes production of a cost–effective fuel very challenging. However, there are large amounts of low–cost oils and fats such as restaurant waste and animal fats that could be converted to biodiesel. The problem with processing these low cost oils and fats is that they often contain large amounts of free fatty acids (FFA) that cannot be converted to biodiesel using an alkaline catalyst. In this study, a technique is described to reduce the free fatty acids content of these feedstocks using an acid–catalyzed pretreatment to esterify the free fatty acids before transesterifying the triglycerides with an alkaline catalyst to complete the reaction. Initial process development was performed with synthetic mixtures containing 20% and 40% free fatty acids, prepared using palmitic acid. Process parameters such as the molar ratio of alcohol, type of alcohol, acid catalyst amount, reaction time, and free fatty acids level were investigated to determine the best strategy for converting the free fatty acids to usable esters. The work showed that the acid level of the high free fatty acids feedstocks could be reduced to less than 1% with a 2–step pretreatment reaction. The reaction mixture was allowed to settle between steps so that the water–containing alcohol phase could be removed. The 2–step pretreatment reaction was demonstrated with actual feedstocks, including yellow grease with 12% free fatty acids and brown grease with 33% free fatty acids. After reducing the acid levels of these feedstocks to less than 1%, the transesterification reaction was completed with an alkaline catalyst to produce fuel–grade biodiesel.

Biodiesel production via acid catalysis

Vegetable oils and animal fats can be transesterified to biodiesel for use as an alternative diesel fuel. Conversion of low cost feedstocks such as used frying oils is complicated if the oils contain large amounts of free fatty acids that will form soaps with alkaline catalysts. The soaps can prevent separation of the biodiesel from the glycerin fraction. Alternative processes are available that use an acid catalyst. The objective of this study was to investigate the effect of process variables on acid-catalyzed transesterification. The molar ratio of alcohol, reaction temperature, catalyst amount, reaction time, water content, and free fatty acids were investigated to determine the best strategy for producing biodiesel. Food grade soybean oil was used to prepare esters using excess methanol and sulfuric acid as a catalyst. To compare the effect of different alcohol types on ester formation, methanol, ethanol, 2-propanol, and n-butanol were compared. The American Oil Chemists’ Society Method Ca 14-56 was used to measure the biodiesel’s total glycerin amount as an indicator of the completeness of the reaction. It was found that acid catalysis can provide high conversion rates but much longer times are required than for alkaline catalysts. The acid catalyst also requires the concentration of water to be less than 0.5%, which is about the same as is required for alkaline catalysts. Water formed by the esterification of free fatty acids limited their presence in the oil to 5%.

The effect of timing and oxidation on emissions from biodiesel-fueled engines

The alkyl monoesters of fatty acids derived from vegetable oils or animal fats, known as biodiesel, are attracting considerable interest as an alternative fuel for diesel engines. Biodiesel-fueled engines produce less carbon monoxide, unburned hydrocarbons, and particulate emissions than diesel-fueled engines. However, biodiesel has different chemical and physical properties than diesel fuel, including a larger bulk modulus and a higher cetane number. Some of these properties can be affected by oxidation of the fuel during storage. These changes can affect the timing of the combustion process and potentially cause increases in emissions of oxides of nitrogen. The objective of this study was to evaluate the effect of injection and combustion timing on biodiesel combustion and exhaust emissions. A John Deere diesel engine was fueled with two different biodiesel fuels, one of which had been deliberately oxidized, and with their 20% blends with No. 2 diesel fuel. The engine was operated at three different timings and two loads at a single engine speed of 1400 rpm. The engine performance of the biodiesel was similar to that of No. 2 diesel fuel with nearly the same thermal efficiency. The range of injection timings studied produced changes of 50% and 34% in the CO and HC emissions, respectively. A reduction in NO x emissions of 35% to 43% was observed for a 3° retarded injection timing compared with a 3° advanced injection timing. A common linear relationship was found between the start of injection and the NO x emissions for all the fuels studied. When compared at the same start of combustion, the neat biodiesel produced lower NO x emissions than the No. 2 diesel fuel.

COMPARISON OF ENGINE PERFORMANCE AND EMISSIONS FOR PETROLEUM DIESEL FUEL, YELLOW GREASE BIODIESEL, AND SOYBEAN OIL BIODIESEL

Biodiesel is a non-toxic, biodegradable and renewable alternative fuel that can be used with little or no engine modifications. Biodiesel is currently expensive but would be more cost effective if it could be produced from low-cost oils (restaurant waste, frying oils, animal fats). These low-cost feedstocks are more challenging to process because they contain high levels of free fatty acids. A process for converting these feedstocks to fuel-grade biodiesel has been developed and described previously. The objective of this study was to investigate the effect of the biodiesel produced from high free fatty acid feedstocks on engine performance and emissions. Two different biodiesels were prepared from animal fat-based yellow grease with 9% free fatty acids and from soybean oil. The neat fuels and their 20% blends with No. 2 diesel fuel were studied at steady-state engine operating conditions in a four-cylinder turbocharged diesel engine. Although both biodiesel fuels provided significant reductions in particulates, carbon monoxide, and unburned hydrocarbons, the oxides of nitrogen increased by 11% and 13% for the yellow grease methyl ester and soybean oil methyl ester, respectively. The conversion of the biodiesel fuels energy to work was equal to that from diesel fuel.

A pilot plant to produce biodiesel from high free fatty acid feedstocks.

Biodiesel is an alternative diesel fuel consisting of the alkyl monoesters of fatty acids from vegetable oils or animal fats. Currently, most biodiesel is made from soybean oil, methanol, and an alkaline catalyst. However, there are large amounts of fats and oils that are unsuitable for human consumption that could be converted to biodiesel at lower cost. The problem with processing these waste oils is that they often contain large amounts of free fatty acids that cannot be converted to biodiesel using an alkaline catalyst. These free fatty acids react with the alkaline catalyst to produce soaps that inhibit the separation of the biodiesel, glycerin, and wash water. Previous research has developed a process for pretreating these high free fatty acid feedstocks using acid catalysts, which do not form soaps. The objective of this study was to construct a pilot plant to produce biodiesel from a wide variety of feedstocks including those with high free fatty acids. A 190 L batch pilot plant has been built that can process high free fatty acid feedstocks using an acid–catalyzed pretreatment followed by an alkaline–catalyzed transesterification. Case studies of pilot plant–scale production of biodiesel from soybean oil, yellow grease with 9% free fatty acids, and brown grease with 40% free fatty acids are presented. The effect of varying the reaction parameters is discussed, and the separation and washing processes are described. Estimates of the fuel cost using different feedstocks are also provided.

ACCELERATED OXIDATION PROCESSES IN BIODIESEL

Biodiesel is an alternative fuel for diesel engines that can be produced from renewable feedstocks such as vegetable oil and animal fats. These feedstocks are reacted with an alcohol to produce alkyl monoesters that can be used in conventional diesel engines with little or no modification. Biodiesel, especially if produced from highly unsaturated oils, oxidizes more rapidly than diesel fuel. This article reports the results of experiments to track the chemical and physical changes that occur in biodiesel as it oxidizes. These results show the impact of time, oxygen flow rate, temperature, metals, and feedstock type on the rate of oxidation. Blending with diesel fuel and the addition of antioxidants are explored also. The data indicate that without antioxidants, biodiesel will oxidize very quickly at temperatures typical of diesel engines. This oxidation results in increases in peroxide value, acid value, and viscosity. While the peroxide value generally reaches a plateau of about 350 meq/kg ester, the acid value and viscosity increase monotonically as oxidation proceeds.

THE ENERGY BALANCE OF SOYBEAN OIL BIODIESEL PRODUCTION : A REVIEW OF PAST STUDIES

Although several studies have found biodiesel to be a renewable source of energy, there has been a claim that it is not. This article investigates models used to calculate the net energy ratio (NER) of biodiesel production to point out the reasons for the contradictory results, compares their strengths and weaknesses, and proposes a uniform model for interpretation of the final result. Four commonly referenced models were compared for their assumptions and results. The analysis revealed that the most significant factors in altering the results were the proportions of energy allocated between biodiesel and its coproducts. The lack of consistency in defining system boundaries has apparently led to very different results. The definitions of NER used among the models were also found to be different. A unified model is proposed for biodiesel energy analysis to answer the renewability question. Using the unified boundary, a range of probable NERs was calculated using bootstrapping. The mean NER on a mass basis was 2.55 with a standard deviation of 0.38. The economic sustainability ratio (ESR) is defined as the monetary value ratio of biodiesel to biodiesels share of the energy inputs. The average ESR was found to be 4.43 with a standard deviation of 0.6.

Investigation of Biodiesel Thermal Stability Under Simulated In-use Conditions

Biodiesel is an alternative diesel fuel produced by transesterification of vegetable oils or animal fats. While biodiesel provides numerous environmental benefits such as reduced exhaust emissions, it is more prone to oxidation than petroleum-based diesel fuel and this can alter its properties. When oxidation occurs at ordinary temperatures, the initial products are hydroperoxides. As the oxidation continues, the peroxides may split and form aldehydes, ketones, and short chain acids that produce unpleasant odors. Sediment and gums are formed through polymerization of the peroxides and can cause fuel filter plugging. The objective of this study was to relate the chemical and physical processes associated with biodiesel oxidation to the conditions that affect diesel fuel system performance. A relationship was sought between the test that is used by the engine industry to define engine fuel stability requirements (ASTM D2274) and the tests used by the fats and oils industry to characterize oxidation (Peroxide Value and Acid Value). It was found during the course of this study that the ASTM fuel stability method is not suitable for biodiesel. While oxidation causes the fuel viscosity to increase, fuel filter plugging was not necessarily a natural consequence of biodiesel oxidation even when the fuel was oxidized to a level beyond what would be observed in practice. The effect of fuel temperature and blending with diesel fuel on the oxidation was investigated and the interrelationship between the fuel’s acid value and viscosity is shown.

Process optimization of biodiesel production using alkaline catalysts.

The most commonly used method for biodiesel preparation is via transesterification of vegetable oil using alkaline catalysts. Biodiesel yield and oil conversion are affected by operating conditions including the catalyst formulation and concentration. Application of alkaline catalysts can also lead to undesired soap formation. This study evaluated the alkaline catalyst effects on biodiesel yield and soap formation in transesterifying methanol and canola oil at different catalyst concentrations, reaction temperatures, and methanol-to-oil molar ratios. Four different alkaline catalysts, i.e., potassium hydroxide, sodium hydroxide, potassium methoxide, and sodium methoxide, were studied and compared on molar basis through a 4-factor 3-level experimental design. It was observed that methoxide catalysts led to better biodiesel yields than hydroxide catalysts. The methoxide catalysts not only accelerated the reaction but also elevated the conversion equilibrium. Based on statistical optimization, the operating conditions for maximizing biodiesel yield and minimizing soap formation were potassium methoxide as catalyst at 0.2 mol/mol (1.59%wt), reaction temperature of 50.C, and methanol-to-oil molar ratio of 4.5:1. Experimental verification gave 95.8% biodiesel yield and 0.75%wt soap.

Fuel Property Effects on Injection Timing, Ignition Timing, and Oxides of Nitrogen Emissions from Biodiesel-Fueled Engines

Biodiesel is an environmentally friendly alternative diesel fuel consisting of the alkyl monoesters of fatty acids. It is obtained from triglycerides through the transesterification process. Biodiesel has been observed to reduce most engine exhaust pollutant emissions with the exception of oxides of nitrogen (NOx), which generally increase by 5% to 15%. The objective of this research was to determine the relationship between changes in combustion timing caused by differences in the fuel properties between diesel fuel and biodiesel and the NOx increase. The properties investigated in this research included the lower heating value, density, speed of sound, bulk modulus, and cetane number of biodiesel. It was found that half of the start of combustion advance associated with biodiesel originated from a start of injection advance that was split approximately evenly between the automatic timing advance of the pump as it injects more fuel to compensate for the lower heating value of biodiesel and the effect of the bulk modulus, viscosity, and density of the fuel. At the same temperature, the fuel delivery of biodiesel was higher than for petroleum-based diesel fuel because of the higher viscosity of biodiesel. At the same viscosity level, it was found that the fuel delivery of petroleum-based diesel fuel was higher than for biodiesel. This was attributed to the metering orifices in the fuel injection pumps restricting the amount of fuel flow for denser fuels. The other half of the start of combustion timing advance was due to the higher cetane number of the biodiesel.