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Fractionation Strategies to Obtain Multiple Products from the Hydrocarbon Stream of Fatty Acid Pyrolysis
- Author / Creator
- Sea-Nduka, Uche E.
A biorefinery concept defined as the sustainable processing of biomass into a spectrum of products has been proposed to achieve the true sustainability goals of a bio-based economy. Lipid pyrolysis is the thermal decomposition of lipids (triglycerides or fatty acids) into gas, liquid, and solid products. Typically, the complexity of the lipid pyrolytic liquid restricts its direct use for fuel and chemical production. A biorefinery can be established by separating the pyrolytic liquid into fractions to be processed into high-grade products. The aim of this research was to demonstrate a biorefinery concept by developing fractionation strategies for a liquid hydrocarbon feed gotten from the pyrolysis of fatty acids to obtain multiple high-value products such as renewable fuels, solvents, and mid-chain fatty acid compounds.
The first fractionation step done was acid-base extraction using 3 M NaOH to remove the fatty acids present in the feed and 3 M HCl to recover the extracted fatty acids as a separate mixture. The acid-base extraction successfully removed the fatty acids from the feed, creating an acid-free hydrocarbon fraction composed mainly of n-alkanes (about 48 %wt) and a fatty acid fraction of about 70 %wt fatty acids.
The second fractionation process explored was distillation. Atmospheric distillation was used to recover n-pentane and n-hexane solvents from the hydrocarbon fraction. This was done using a 90cm spinning band distillation unit with up to 100 theoretical plates. A naphtha fraction obtained from an initial distillation of the hydrocarbon fraction was also explored as a starting material for recovering the renewable n-pentane and n-hexane solvents. The effect of reflux ratio on the purity and recovery of the solvent fractions was studied by varying the reflux ratio between 90:1 to 240:1. n-Pentane solvent with percentage purity between 70 – 80 % was obtained from all the experiments. The amount of n-pentane present in the feed recovered in the n-pentane fraction was between 33 – 43 %wt. For n-hexane, the percentage purity was 80 % from all the experiments, and the amount of n-hexane in the feed recovered was 21 – 35 %wt for all the distillation runs. For both solvents, the major contaminants were the alkene compounds of the corresponding carbon number. Neither starting material nor reflux ratio influenced the solvents' purity and recovery under the distillation conditions used in this study. Drop-in diesel equivalent cut was obtained as the bottom product of the hydrocarbon fraction distillation and analyzed for conformity to Canadian diesel fuel standards: CAN/CGSB – 3.517-2020. The drop-in diesel equivalent cut met the CAN/CGSB – 3.517-2020 for acid number, kinematic viscosity, cetane number, flashpoint, distillation range and was comparable to the commercial diesel analyzed. On the other hand, the cold flow properties were not comparable to that of the commercially obtained diesel.
Vacuum distillation at 133.3 Pa was used to obtain individual fatty acid cut from the fatty acid extract, using the same spinning band distillation equipment at a reflux ratio of 60:1. Individual fatty acids between C5:0 and C10:0 carbon number was obtained during the distillation process. The purity of the recovered fatty acids ranged between 60 – 80 %, while the recovery was > 60 %wt for all the fatty acids except C10:0. The significant impurities of the fatty acid cuts were higher n-alkane compounds and the unsaturated fatty acids of the corresponding carbon number.
This is the first study demonstrating the combined recovery of renewable fuels and solvents together with the valorization of the fatty acids present in the liquid product of the pyrolysis of fatty acids or any other lipid feedstock.
- Graduation date
- Fall 2021
- Type of Item
- Master of Science
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