Mississippi State Biodiesel Production Project (2008)

Biodiesel is a renewable fuel conventionally generated from vegetable oils and animal fats that conforms to ASTM D6751. Depending on the free fatty acid content of the feedstock, biodiesel is produced via transesterification, esterification, or a combination of these processes. Currently the cost of the feedstock accounts for more than 80% of biodiesel production cost. The main goal of this project was to evaluate and develop non-conventional feedstocks and novel processes for producing biodiesel. One of the most novel and promising feedstocks evaluated involves the use of readily available microorganisms as a lipid source. Municipal wastewater treatment facilities (MWWTF) in the USA produce (dry basis) of microbial sludge annually. This sludge is composed of a variety of organisms, which consume organic matter in wastewater. The content of phospholipids in these cells have been estimated at 24% to 25% of dry mass. Since phospholipids can be transesterified they could serve as a ready source of biodiesel. Examination of the various transesterification methods shows that in situ conversion of lipids to FAMEs provides the highest overall yield of biodiesel. If one assumes a 7.0% overall yield of FAMEs from dry sewage sludge on a weight basis, the cost per gallon of extracted lipid would be $3.11. Since the lipid is converted to FAMEs, also known as biodiesel, in the in Situ extraction process, the product can be used as is for renewable fuel. As transesterification efficiency increases the cost per gallon drops quickly, hitting $2.01 at 15.0% overall yield. An overall yield of 10.0% is required to obtain biodiesel at $2.50 per gallon, allowing it to compete with soybean oil in the marketplace. Twelve plant species with potential for oil production were tested at Mississippi State, MS. Of the species tested, canola, rapeseed and birdseed rape appear to have potential in Mississippi as winter annual crops because of yield. Two perennial crops were investigated, Chinese tallow tree and tung tree. High seed yields from these species are possible because, there stature allows for a third dimension in yield (up). Harvest regimes have already been worked out with tung, and the large seed makes shedding of the seed with tree shakers possible. While tallow tree seed yields can be mind boggling (12,000 kg seed/ha at 40% oil), genotypes that shed seed easily are currently not known. Efficient methods were developed to isolate polyunsaturated fatty acid methyl esters from bio-diesel. The hypothesis to isolate this class of fatty acids, which are used as popular dietary supplements and prescription medicine (OMACOR), was that they bind transition metal ions much stronger than their harmful saturated analogs. AgBF4 has the highest extraction ability among all the metal ions tested. Glycerol is a key product from the production of biodiesel. It is produced during the transesterification process by cleaving the fatty acids from the glycerol backbone (the fatty acids are used as part of the biodiesel, which is a fatty acid methyl ester). Glycerol is a non-toxic compound with many uses; however, if a surplus exists in the future, more uses for the produced glycerol needs to be found. Another phase of the project was to find an add-on process to the biodiesel production process that will convert the glycerol by-product into more valuable substances for end uses other than food or cosmetics, focusing at present on 1,3-propanediol and lactic acid.All three MSU cultures produced products at concentrations below that of the benchmark microorganisms. There was one notable isolate the caught the eye of the investigators and that was culture J6 due to the ability of this microorganism to co-produce both products and one in particularly high concentrations. This culture with more understanding of its metabolic pathways could prove a useful biological agent for the conversion of glycerol. Heterogeneous catalysis was examined as an alternative to overcome the disadvantages of homogeneous transesterification, such as the presence of salts in the glycerine phase and the continuous lost of catalyst. A maximum soy biodiesel yield of 85% was obtained by BaO in 14 minutes, whereas, PbO, MnO2, CaO and MgO gave a maximum yields of 84%, 80%, 78% and 66% respectively at 215°C. The overall reaction order of PbO, MnO2, BaO, CaO and MgO was found to be 1, 1, 3, 1 and 1 respectively. The highest rate constant was observed for BaO, which was 0.0085 g2.mole-2.min-1. The performance of biodiesel in terms of type (e.g., NOx, and CO) and quantity of emissions was tested using soy biodiesel, blends of biodiesel and ethanol, and differently aged diesel engines. It was determined that saturated methyl esters, and relatively high oxygen content in the fuel, caused by addition of ethanol, increased the NOx emissions from new diesel engines compared to petroleum diesel.