Dependence of biodiesel fuel properties on the structure of fatty acid alkyl esters

Production of liquid biofuels from renewable resources

Effect of biodiesel fuels on diesel engine emissions

Influence of fatty acid composition of raw materials on biodiesel properties.

Biodiesel is an alternative fuel for diesel engines consisting of the alkyl monoesters of fatty acids from vegetableoils or animal fats. Most of the biodiesel that is currently made uses soybean oil, methanol, and an alkaline catalyst. The highvalue of soybean oil as a food product makes production of a costeffective fuel very challenging. However, there are largeamounts of lowcost oils and fats such as restaurant waste and animal fats that could be converted to biodiesel. The problemwith processing these low cost oils and fats is that they often contain large amounts of free fatty acids (FFA) that cannot beconverted to biodiesel using an alkaline catalyst. In this study, a technique is described to reduce the free fatty acids contentof these feedstocks using an acidcatalyzed pretreatment to esterify the free fatty acids before transesterifying the triglycerideswith an alkaline catalyst to complete the reaction. Initial process development was performed with synthetic mixturescontaining 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 strategyfor converting the free fatty acids to usable esters. The work showed that the acid level of the high free fatty acids feedstockscould be reduced to less than 1% with a 2step pretreatment reaction. The reaction mixture was allowed to settle betweensteps so that the watercontaining alcohol phase could be removed. The 2step pretreatment reaction was demonstrated withactual feedstocks, including yellow grease with 12% free fatty acids and brown grease with 33% free fatty acids. After reducingthe acid levels of these feedstocks to less than 1%, the transesterification reaction was completed with an alkaline catalystto produce fuelgrade biodiesel.

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Biodiesel production from oils and fats with high free fatty acids

Glycerol is the principal by-product of biodiesel production. For each gallon of biodiesel produced, approximately
0.3 kg of crude glycerol accompanies. Such crude glycerol possesses very low value because of the impurities contained. As
the demand and production of biodiesel grow exponentially, the utilization of the glycerol becomes an urgent topic. The
make-up of crude glycerol varies depending on the parent feedstock and the biodiesel production process. Before the crude
glycerol could be considered for possible value-added utilizations, it is necessary to characterize it on its physical, chemical,
and nutritional properties. This article reports the characterization of crude glycerol obtained from different seed oil
feedstocks of mustard, rapeseed, canola, crambe, soybean, and waste cooking oils. Batch processes of biodiesel production
were used as the means of crude glycerol preparation using unrefined vegetable oils, methanol, and sodium methylate as the
catalyst. After separation from biodiesel, the crude glycerol from each of the oils was analyzed using ASTM and other standard
test methods. Elemental impurities, nutritional value, and other chemical properties were tested.

Characterization of crude glycerol from biodiesel production from multiple feedstocks.

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.

Process Optimization of Biodiesel Production Using Alkaline Catalysts

This article describes an in−depth follow−up to previous studies showing that an oil−methanol mixer prior to an RD reactor played an important role in enhancing the overall performance of the RD reactor system. An in−line static mixer was used for the purpose of providing initial mixing of the reactants, heating the mixture up to the desired operating temperature, and carrying out a substantial part of the transesterification reaction in the early stage. It performed three functions: a reactant mixer, a heat exchanger, and a pre−reactor. This article reports the systematic investigations of the pre−reactor performance by examining the effects of process variables on the process evaluating parameters, and the operating conditions for optimum operation. A wide range of results was observed under different operating conditions. The product yield was as high as 84.60% and as low as 1.63%. The soap formation was in the range of 2.80% to 10.37%. The feed molar ratio, reaction time, and catalyst concentration all contributed positively to the product yield and soap formation. Although an optimum condition produced a product yield of 80.46% and soap formation of 5.18% with a 1.33 min reaction time, the optimization should be based on the integration of the whole RD reactor system rather than a collection of individually optimized components. This study of the pre−reactor serves as an analysis tool for part of the RD reactor system.

Biodiesel Production

Methyl and ethyl esters, prepared from various vegetable oils by the process of transesterification, have shown
much promise as fuels for all types of diesel engines. Very limited information is available on possible deterioration of
biodiesel in storage. This project was designed to determine the extent of deterioration of Rape Methyl Ester (RME) and
Rape Ethyl Ester (REE) in storage. The study involved triplicate samples of RME and REE stored in glass and steel
containers at room temperature (inside) and at the local ambient outdoor temperatures (outside). The study was
conducted for 24 months. At the beginning of the study and at three-month intervals, samples were taken for measurement
of peroxide value, acid value, density, viscosity, and heat of combustion. At the conclusion of the study, engine
performance tests were conducted with the two year stored REE and RME, new REE and RME, and low sulfur diesel
reference fuel. On the average, the esters increased over time in all of the previously mentioned properties with the
exception of heat of combustion, which decreased. Regression models are presented to predict the deterioration with time.
Engine power varied less than 2% for both Biodiesel fuels compared to the stored counterparts while smoke density
decreased 3.2% for the stored RME and increased 17.5% for stored REE.

Two-year storage study with methyl and ethyl esters of rapeseed

Six different vegetable oil esters (coconut ethyl ester, used hydrogenated soy methyl ester, rapeseed ethyl ester,
mustard ethyl ester, safflower ethyl ester, and a commercial methyl ester of soy oil) were selected to represent a range of
iodine numbers from 7.88 to 133. These vegetable oil esters were tested neat and in 20% biodiesel/80% diesel blends in
comparison with low sulfur diesel fuel for the effect on regulated emissions. The test vehicle was a pickup truck with a
5.9 L turbo-charged and inter-cooled direct injection diesel engine. The emissions tests were conducted at the Los Angeles
County Metropolitan Transit Authority Emissions Testing Facility on a chassis dynamometer. It was found that lower
iodine numbers correlated with reduced nitrogen oxides (NOx). As iodine number increased from 7.88 to 129.5 the NOx
increased 29.3%. Fatty acids with two double bonds appeared to have more effect on increasing NOx emissions than did
fatty acids with one double bond. Changes in carbon monoxide (CO), hydrocarbons (HC), and particulate matter (PM)
were not linearly correlated with iodine number. It is apparent that the type of feedstock oil affects the characteristics of
the biodiesel fuel. The most obvious difference is that the pour point changes with fatty acid composition, however, other
fuel characteristics, some of which effect combustion, are also changed. This article reports on a study of biodiesel iodine
number on changes in regulated emissions. The results of this and similar studies provide information for developing
triglycerides specifically for optimum use in biodiesel. Modern chemical processes and/or plant breeding should make
this possible.

J. C. Thompson

Papers

Characterization of crude glycerol from biodiesel production from multiple feedstocks.

Process Optimization of Biodiesel Production Using Alkaline Catalysts

Biodiesel Production

Two-year storage study with methyl and ethyl esters of rapeseed

The effect of biodiesel feedstock on regulated emissions in chassis dynamometer tests of a pickup truck.