Optimization of process for preparation of furan compounds by pyrolysis catalytic conversion of corncob

Abstract: Catalytic upgrading of biomass pyrolysis products was an important way for converting biomass to high-value chemicals. Catalytic pyrolysis process produced a higher-oxygenated containing bio-oil over 100 compounds. Furan compounds (furans) were important green platform chemicals in organic synthesis. In order to find a new route for production of furans from catalytic pyrolysis of lignocellulosic biomass by gas-solid heterogeneous catalyst, catalytic conversion of biomass into furan yield and selectivity with catalytic pyrolysis vapor upgrading over different types of catalysts (Al2O3, MCM-41, AC (Activated Carbon), HZSM-5 (Si/Al=38, 46, 80), TiO2 and ZrO2) were investigated. Simultaneously, the response surface methodology was used to determine the optimum process conditions of catalytic pyrolysis of corncob by using MCM-41, AC and TiO2 as catalysts. The results showed that MCM-41 and AC catalysts had the largest specific surface area, followed by HZSM-5, while Al2O3, ZrO2 and TiO2 had the opposite results. In addition, all the catalyst belonged to mesoporous catalysts with the average pore size of 3-16 nm. The main components of corncob with non-catalytic pyrolysis were aldehydes and ketones (17.62%), furans (22.55%) and aromatic compounds (25.18%). Moreover, 4-hydroxy-3-methylacetophenone, 2,3-dihydro-benzofuran and catechol had the highest contents, which were 8.65%, 13.1% and 4.01% respectively. All catalysts inhibited the formation of acid compounds, especially, when AC and HZSM-5(80) were added, the acidic compounds disappeared. The formation of aldehydes and ketones was not significant with the presence of ZrO2, and was inhibited by other types of catalysts. And, HZSM-5 (38), HZSM-5 (46) and AC enhanced the formation of aromatic hydrocarbon, which increased by 1.82%, 14.12% and 12.64% respectively. However, other catalysts were facilitating the formation of furans, which increased by 7.89% (TiO2), 8.88 %( MCM-41), 6.23 %( AC) and 4.95 %( ZrO2), respectively compared with non-catalytic pyrolysis. The maximum yield of furfural of 3.46% was obtained (catalyst is AC) under the conditions of catalytic pyrolysis temperature of 500 ℃ and mass ratio of corncob to catalyst of 2:1. Both TiO2 and HZSM-5 catalysts promoted the formation of furfural, but the effect was not significant. The other catalysts inhibited the formation of furfural. The influence of HZSM-5 catalyst on 2 (5H) -furanone was small, while the other catalysts promoted the production of 2 (5H) -furanone, the maximum yield was obtained with the presence of MCM-41, which increased by 5.45%. And the addition of catalyst inhibited the formation of -benzofuran-2,3-dihydrogen and 5-hydroxymethylfurfural. All the catalysts promoted the production of 5-methyl-2(3H) -furanone except for Al2O3. A highly fitting regression equation was obtained by using the response surface methodology to optimize the preparation process of furans compounds produced by catalytic pyrolysis of corncob, which could effectively predict the yield of furans. The order of effect parameters on the yield of furans was as follows: catalyst > catalytic pyrolysis temperature > mass ratio of corncob to catalyst. The yield of furans could reach 35.30% at the optimum process conditions of catalytic pyrolysis temperature of 550℃ and the mass ratio of corncob to catalyst of 1:1 by using AC catalyst. It would provide a basis for the catalytic pyrolysis of lignocellulosic biomass for production of high value-added chemicals by using heterogeneous catalysts at gas-solid catalytic reaction conditions. And it would provide a new pathway for furans production.