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Process simulation and catalyst development for biodiesel production West, Alex Harris


Four continuous biodiesel processes were designed and simulated in HYSYS. The first two employed traditional homogeneous alkali and acid-catalysts. The third and fourth processes used a heterogeneous acid catalyst and a supercritical method, respectively, to convert a waste vegetable oil feedstock into biodiesel. While all processes were capable of producing biodiesel at high purity, the heterogeneous and supercritical processes were the least complex and had the smallest number of unit operations. Material and energy flows, as well as sized unit operation blocks, were used to conduct an economic assessment of each process. Total capital investment, total manufacturing cost and after tax rate-of-return (ATROR) were calculated for each process. The heterogeneous acid catalyst process had the lowest total capital investment and manufacturing costs, and had the only positive ATROR. Following the results of the process simulations, tin(II) oxide was investigated for use as a heterogeneous catalyst. Unfortunately, catalytic experiments showed no activity. Subsequently, a carbon-based acid catalyst was prepared by sulfonating pyrolysis char, and was studied for its ability to catalyze transesterification of vegetable oil. The catalyst showed only qualitative transesterification, but demonstrated good conversion in free fatty acid esterification. Experiments were designed to measure the effect of alcohol to oil (A:O) molar ratio, reaction time and catalyst loading on the sample. It was observed that free fatty acid (FFA) conversion increased with increasing A:O molar ratio, reaction time and catalyst loading. Conditions that yielded the greatest conversion were 18:1 A:O molar ratio, 3 hour reaction time, 5 wt.% catalyst, 76°C under reflux. The above conditions reduced the FFA content in a waste vegetable oil (WV0)-ethanol mixture from 4.25 wt.% to <0.5 wt.%. Under an 78:1 A:O molar ratio and identical conditions, the catalyst was able to reduce the FFA content of a WVO feedstock from 12.25 wt.% to 1 wt.%. The catalyst has potential to be used in a process converting a high FFA feedstock to biodiesel if the limitations to transesterification can be overcome. Otherwise, it will serve as an excellent catalyst for reducing the FFA content of feedstocks in a two-step acid and base conversion process.

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