Conversion of biomass-derived oil over promoted ZSM-5 based catalysts

Abstract

Crude canola oil was thermo-catalytically converted to unsaturated hydrocarbons and aromatics. The major products were: 1,5-Heptadien-3-yne, 1,3-Hexadien-5-yne, 1- ethenyl-3-methylene-cyclopentene and Xylenes for Ni-ZSM-5, Benzene, Toluene, and other Aromatics including Ethylbenzene for Sn-ZSM-5 samples. The preparation of Ni and Sn-HZSM-5 was achieved by calcining the commercial NH4-ZSM-5, Si/Al ratio of 50, and promoting the material with Ni and Sn chlorides. Various techniques were used to promote the catalysts, namely, mechanical mixing promotion (MM), incipient wetness promotion (IW) and aqueous promotion (AQ). All the reactions were carried out at a WHSV of 10.6 hr-1 and temperature of 450°C. A fixed bed reactor system was used. To understand the reactions involved in the process, the characterization of the feed was done by GC-FID to identify the fatty acid composition of the Canola oil. The analysis showed that the feed was mainly composed of C18-16 fatty acids. The Gas products were characterized by GC-TCD and revealed the presence of C1 gases: CO, CO2 and CH4. No H2 was detected in the gas products. The selectivity in the gas fraction was barely influenced by the composition of the HZSM-5 based samples and the results show a mean difference within ±1.0%. A fractional conversion of close to 100% for all the tested Ni-loaded samples was observed, no fatty acids were detected in the OLP. Since the detected C18-16 fatty acids are liquids at room temperature, it was concluded that the amount of C18 fatty acids in the gas product was zero. When the HZSM-5 was loaded with Sn (atomic radius = 145pm), at higher loading %, (2.99 and 3.82%) of Sn, the conversion was lowered up to 77.9 and 91.4% from 100% that was observed for lower loading of 0.25 – 1.77%. The organic liquid product fraction was characterized using GC-MS. An analysis was done for the thermo-catalytic products of six different groups of catalysts, namely: Ni- Aqueous promotion; Ni-AQ, Ni-Incipient Wetness promotion Ni-IW; Ni-Mechanical Mixing promotion; Ni-MM; Sn-Aqueous promotion; Sn-AQ, Sn-Incipient Wetness promotion; Sn-IW, and Sn-Mechanical Mixing promotion; Sn-MM. Each of these different metal loading/ promotions were done to understand how the products were affected by increasing the Metal Loading/ promotion. For each of the product streams, the metal loading/ promotion targets of 0.5%, 1%, 3%, 5% and 7% were used. Trends to relate the Metal loading/ promotion to the product output and fractional conversion were done for each metal for comparison of the different product streams. It was observed that for Ni-AQ, Ni-IW and Ni-MM the average amount of aromatics in the organic liquid product for the Metal loading/ promotion was 68.3%, 80.6% and 63.3% respectively. From results it was observed that the activity of the Sn loaded samples increases in the production of various products groups such as Benzene, Toluene and Xylene (BTX) among other aromatics and, Ni activity was more towards Cyclopentane derivatives and Alkynes (XCA). The unpromoted commercial HZSM-5 catalyst produced 7.18% Xylenes, with no Cyclopentane Deravatives and Alkynes detected. Ni-loading exhibited increased catalytic activity towards XCA production for samples loaded using AQ and MM techniques. The samples loaded by IW technique showed activity towards producing Xylene but not Cyclopentane Derivatives or Alkynes. The introduction of Ni has increased the production of unsaturated hydrocarbons lighter than the C18 hydrocarbons such as: 1,5-Heptadien-3-yne, 1,3-Hexadien-5-yne, and 1- ethenyl-3-methylene-cyclopentene. The results obtained from this study show the selectivity toward BTX and other aromatics was lifted when HZSM-5 was promoted with Sn in comparison to the unpromoted HZSM-5 and Ni-HZSM-5. No Cyclopentane Derivatives and Alkynes were detected in any of the products of the Sn loaded samples.