Study On Catalytic Fast Pyrolysis Of Biomass By Modified ZSM-5

With the exhaustion of fossil resources, aromatics and olefins that mainly comefrom the petrochemical industry are increasingly difficult to satisfy the market demand.Biomass is abundant and inexpensive, which is regarded as the most attractive rawmaterials for producing renewable chemicals. Among kinds of biomass conversiontechnologies, biomass can be directly converted into aromatics and olefins and otherpetrochemicals during catalytic fast pyrolysis (CFP)，which therefore is regarded as apromising technology.Boron-modified ZSM-5zeolites were prepared by impregnating a conventionalZSM-5with different boron loadings. In addition, mesoporous bifunctional Zn/ZSM-5zeolites were prepared by desilication of ZSM-5zeolite with NaOH solutions andimpregnation of Zn．X ray diffraction, N2-adsorption/desorption and Pyridine-IR wereused to characterize the structure and acidity of catalysts. The catalytic properties oncatalytic fast pyrolysis of biomass and low-density polyethylene were investigated in aCurie-point pyrolyzer and Pyroprobe5200pyrolyzer.Due to boron deposition, the acidity and pore size of ZSM-5zeolites decreased.When impregnated with1wt.%boron, ZSM-5preserved sufficient catalytic activity forthe production of valuable monoaromatic hydrocarbons and decreased the formation ofundesired polyaromatic hydrocarbons in CFP of cellulose. Co-feeding of cellulose withlow-density polyethylene (LDPE) in CFP showed a positive synergistic effect thatenhanced aromatic production and further improved the product distribution. As a resultof boron modification and co-feeding, the monoaromatic yield increased from20.0C%for CFP of cellulose alone with the parent ZSM-5to24.6C%for co-feed CFP ofcellulose and LDPE mixture (mixing ratio of4:1) with the boron-modified ZSM-5,while the polyaromatic yield decreased from11.3C%to6.0C%. The yield for p-xylenealso increased from2.23C%to5.57C%while the selectivity increased from47.9%to75.2%. The results indicate that ZSM-5modification with boron and co-feeding ofplastics have a beneficial effect for improving aromatic product distribution in CFP ofbiomass.When ZSM-5zeolites were modified by impregnation of Zn and alkali treatment,Br nsted acid of the catalysts decreased while Lewis acid increased. This modificationconsiderably increased the catalytic performance of the zeolites for petrochemicalproduction in co-feed catalytic fast pryolysis of biomass and low-density polyethylenemixtures. Compared with the ZSM-5, the mesoporous Zn/ZSM-5increased the yields ofvaluable monoaromatic hydrocarbons and olefins by24.3%and decreased theundesirable polyaromatic hydrocarbons by50.8%in co-feed CFP. This improvement can be mainly due to the increased diffusion properties and dehydrogenation activity ofthe mesoporous Zn/ZSM-5. The results indicate that carefully controlled desilicationand Zn impregnation of ZSM-5have a beneficial effect on improving the conversionefficiency and production distribution from CFP of biomass and plastics.The results of this study indicate boron, zinc element and alkali treatmentmodification changed the acid and molecular sieve aperture size, which is a kind ofsimple and feasible method to change the product distribution and improve yield of highvalued products in CFP.