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Product Distribution for Heterogeneous Catalytic Cracking of Acylglycerides on Commercial Catalysts

Tracy J. Benson1, Rafael Hernandez1, William T French1, Earl E Alley2, and William E. Holmes2. (1) Chemical Engineering, Mississippi State University, Mississippi State, MS 39759, (2) Mississippi State Chemical Laboratory, Mississippi State University, Mississippi State, MS 39759

Renewable fuels will be essential to sustain future energy demand, as petroleum supplies decrease and economies of developing nations continue to grow at a fast pace. Green diesel and green gasoline could be produced via cracking of crude lipids using catalytic processes currently employed in the petroleum refining industry. In contrast to biodiesel, green fuels could be distributed via the petroleum pipelines. Also, its production does not generate glycerine as a by-product.

In this work, model unsaturated lipids were reacted over Zeolite Y and silica-alumina solid catalysts at 400C in a micro-bed reactor coupled with online GC/MS/TCD analysis. These model lipids were acylglycerols in which the fatty acid constituent was oleic acid, an unsaturated fatty acid commonly found in the fatty acid profile of many plant, animal, and microbial sources. Zeolite Y and silica-alumina are two commonly used catalysts within the petroleum industry.

The reactor used in this work was an in-house built cryogenic capillary catalytic cracker, called the Quatra C, which uses online mass spectrometry and thermal conductivity detectors. The online analysis via cryogenic oven cooling allowed for quick assessment of reaction products from C1 C30 hydrocarbons, as well as, CO and CO2.

Initial studies on H-ZSM-5, a highly acidic benchmark catalyst, indicated that cracking of the unsaturated acylglycerides (mono-, di-, and triolein) begins at the double bond within the carbon backbone of the fatty acid constituent and proceeds with cyclization to produce a multiplicity of aromatic hydrocarbons and several low molecular weight hydrocarbon gases (C2 C6). Cracking results using Zeolite Y showed a shift in the product yield and produced more low molecular weight unsaturated compounds and fewer aromatics. Silica-alumina, an amorphous catalyst, produced chiefly dienes (C5 C9) and very few aromatic compounds. Results from this work suggest that triglycerides crack at much lower temperatures and light olefin gas yields are higher than for crude petroleum cracking. Therefore, process conditions must be altered from what are currently employed in petroleum refineries.