In a study investigating the effect of the water and free fatty acid (FFA) content in waste chicken fat from poultry processing plants on the production of renewable diesel (not biodiesel), researchers in Thailand have found that both higher FFA and water content improved the biohydrogenated diesel (BHD) yield.
In their paper, published in the ACS journal Energy & Fuels, they reported that the presence of water accelerated the breakdown of the triglyceride molecules into FFAs, while the presence of more FFAs also increased yield. Therefore, they concluded, waste chicken fat from food industries containing a high degree of FFAs and water content can be used as a low-cost feedstock for renewable diesel production without requiring a pretreatment process.
In Thailand, chicken fat/oil and other wastes from the food industry have been used as important feed stocks for biodiesel production. However, the high content of free fatty acids (FFAs) and water in chicken fats/oil lead to an undesired reaction (i.e., a soap product from the saponification reaction of the fats/oil with methanol). Therefore, a pretreatment process is necessary to obtain a high purity biodiesel. Moreover, some of the properties of the biodiesel, such as the acidity, unsaturated carbon−carbon bonding, and oxygenated components in FAME [fatty acid methyl ester, i.e., biodiesel] molecules result in low thermal and oxidation stability relating to the high viscosity and low heating value.
… Because of these drawbacks, the deoxygenation of fats and oils using hydrogen has been proposed as an alternative and attractive method to convert fatty acids or triglycerides into a synthetic diesel, or so-called green diesel or biohydrogenated diesel (BHD) that contains straight-chain alkanes, which have molecular structures similar to those of petroleum diesel.
Generally, BHD production via deoxygenation undergoes three major reaction pathways including: hydrodeoxygenation (HDO), decarbonylation (DCO), and decarboxylation (DCO2). The alkane products obtained from the HDO of fatty acids retain the same number of carbon atoms with H2O as a byproduct, but one carbon atom is lost by DCO/DCO2 with CO/CO2 generation. Therefore, the choice of catalysts is clearly important for BHD product distribution.—Kaewmeesri et al.
|IFEU study: biodiesel from animal fat produces 85% fewer greenhouse gas emissions|
|Biodiesel made from animal fat reduces greenhouse gas emissions by 85% compared to fossil fuels, according to a recent study by the Institute for Energy and Environmental Research (IFEU) in Heidelberg, cited by the European Fat Processors and Renderers Association (EFPRA).|
|The methodology underlying this calculation was examined by the IFEU as part of a study commissioned by the European Fat Processors and Renderers Association (EFPRA). It specifically looked at how the greenhouse gas emissions resulting from the processing of animal by-products should be allocated. The study confirmed the accuracy of the calculation methods used.|
|Public health restrictions mean that animal by-products are subject to special disposal regulations and as a consequence have a negative market value. Therefore, according to the IFEU, all emissions relating to treatment necessary for compliance with public health requirements in sterilized preliminary products should not count towards the total amount of greenhouse gas emissions generated during production of the associated biofuel.|
For its study, the Thai team used a Ni/γ-Al2O3 catalyst under a liquid hourly space velocity (LHSV) of 0.5−2.0 h−1, a water content 0−4 wt %, and a free fatty acid content of 6−12 wt %. The chicken fat consisted of C8−C20 of fatty acids with majority of unsaturated C18. The researchers determined the differed contributions of HDO, DCO and DCO2 reactions by a molar balance method.
Among their findings was that the addition of water did not significantly affect HDO, but the contribution from DCO/DCO2 increased as similar to the product yield. The contribution of DCO/DCO2 was above 70%, while that of the HDO reaction was below 2%.
The major product was n-C17 alkane with an 80−90% composition, with the n-C18 alkane being only a very minor fraction. Light hydrocarbons (n-C8-n-C14) were les than 1%.
They also found that with the addition of additional FFAs (up to 12 wt % fatty acid chains) the major pathway again was DCO/DCO2, with a higher contribution from that pathway with the higher FFA content.
The BHD production from chicken fat is highly favored using a deoxygenation reaction over a Ni/γ-Al2O3 catalyst at reaction temperatures of 330 °C. The presence of water (4 wt %) in the chicken fat feed increased the BHD product yield by ca. 20 wt % due to the improved hydrogenation and/or hydrogenolysis of the triglycerides, whereas the major deoxygenation reaction pathway proceeded via DCO/DCO2 over the catalyst. In addition, the high free fatty acid content in the feed improved the selectivity of the DCO/DCO2, whereas the overall BHD yield was enhanced.
… The increase in the LHSV decreased the BHD yield due to the shorter contact time between the feed and the catalyst. The unique properties of the chicken fat obtained from food industrial waste containing a high degree of FFAs and water content can be used as a feedstock for green diesel production without requiring a pretreatment process.—Kaewmeesri et al.
Rungnapa Kaewmeesri, Atthapon Srifa, Vorranutch Itthibenchapong, and Kajornsak Faungnawakij (2014) “Deoxygenation of Waste Chicken Fats to Green Diesel over Ni/Al2O3: Effect of Water and Free Fatty Acid Content” Energy & Fuels doi: 10.1021/ef5023362