不同载体负载的Ni基加氢催化剂对生物油加氢裂化制备芳香烃的影响研究

Effect of Ni-based hydrogenation catalysts with different supports on the hydrogenation-cracking of bio-oil to aromatic hydrocarbons

文章对一个两段式生物油加氢裂化过程进行研究,考察了不同载体(SiO_(2),ZrO_(2),CeO_(2)和Al_(2)O_(3))负载的Ni基催化剂的影响。反应过程中引入协同反应物甲醇,在裂化阶段进行二次供氢,与温和加氢的供氢作用联合抑制生物油加氢裂化的结焦。研究发现,Ni/金属氧化物催化剂上的酸性位能够与Ni协同作用促进生物油中酚类的加氢转化,从而使其在低生物油水相/甲醇掺混比下具有较好表现;过多的酸性位会强化气化反应,同时较强的酸性位会促进结焦,这都会降低目标产物芳香烃的产率。受这些因素的影响,当生物油水相/甲醇掺混比为2∶1时,基于Ni/SiO_(2)和Ni/Al_(2)O_(3)的加氢裂化过程的油相产率均约为13.4%,Ni/CeO_(2)加氢裂化过程的油相产率约为16.2%。Ni/ZrO_(2)具有合适的酸性位数量,使其在提高整体加氢效率的同时尽可能削弱了气化和结焦副反应,在生物油水相/甲醇掺混比为2∶1时具有最佳表现,油相产物产率约为19.3%,且油相产物中芳香烃的含量在95%以上。

Mild hydrogenation can improve the hydrogen-lacking characteristics of bio-oil, and hence it is a significant pretreatment step for bio-oil upgrading processes such as catalytic cracking. In this paper, a two-stage hydrogenation-cracking process for bio-oil upgrading was studied, and the influence of Ni-based hydrogenation catalysts with different supports(SiO_(2), ZrO_(2), CeO_(2)and Al_(2)O_(3))was investigated. The co-reactant methanol was added for secondary hydrogen supply in the cracking stage, which combined the hydrogen supply of mild hydrogenation to suppress coking during bio-oil cracking. Results showed that the acid sites on the catalyst could work synergistically with Ni to promote the hydrogenation of phenols in the bio-oil, which could reduce the amount of methanol blending;so that it had better performance under the conditions of low bio-oil/methanol ratio;while too many acid sites would enhance the gasification reaction and strong aicd sites would particularly promoted coking, which both reduced the ultimate yield of the target product aromatic hydrocarbons.Therefore, when the ratio of bio-oil to methanol was 2∶1, the yield of oil phase was 13.4%, based on the Ni/SiO_(2)or Ni/Al_(2)O_(3)hydrocracking process, and the oil phase yield was 16.2% based on the Ni/CeO_(2)hydrocracking process. Ni/ZrO_(2)had a suitable amount of acidic sites, which improved the overall hydrogenation efficiency and meanwhile weakened the gasification and coking reactions as far as possible. As a result, Bio-oil hydrogenation-cracking with Ni/ZrO_(2)as the hydrogenation catalyst is the most effective in producing aromatic hydrocarbons under the low methanol blending ratio. When the ratio of bio-oil to methanol was 2∶1, Ni/ZrO_(2)had the best performance. The rate of oil phase was 19.3%,and the content of aromatic hydrocarbons in the oil phase product accounted for about 95%.