Catalytic Fast Pyrolysis Of Biomass To Prepare High-value Chemicals

Fast pyrolysis is a promising technique to convert lignocellulosic biomass mainly into a liquid product known as bio-oil. However, conventional bio-oils were difficult for chemical recovery owing to the complex chemical composition. It was necessary to establish a new technology system for producing a stable quality bio-oil enriched of some high value-added chemical products. The relative simple bio-oil could be refineried by the existing refining system to achieve industrialization and practical application of chemicals, paving the way to further utilization biomass resource.The biomass feedstock and pyrolysis conditions had a great influence on the chemical composition of bio-oil. The composition of bio-oil obtained from cellulose was simpler than that from fast pyrolysis of lignocellulosic biomass. Some proper means were adopted to regular the process of fast pyrolysis. The target product would be obtained by promotion or inhibition certain specific reaction pathway. For obtaining high-value chemicals from selective catalytic pyrolysis of lignocellulosic biomass, this study was focused on the effect of various catalysts in a vertical flow fixed bed reactor.LGO can be produced with high selectivity and yield from fast pyrolysis of cellulose admixed with SO₄^2-/ZrO2. The introduction of SO₄^2-/ZrO2 could promote the cellulose conversion and LGO production. The proper temperature for preparation of levoglucosenone may be in the range of 320-350°C. The higher temperature and/or excess catalyst were not apt to LGO production. The SO₄^2-/ZrO2 was considered as a effective solid acid catalyst to replace of phosphoric acid. However, sulfated zirconia would be gradually deactivated by leaching of SO₄^2-. The effect of morphological structure (porosity and surface area) on catalytic activity of catalysts was discussed. Various metal oxides were screened as solid acid catalysts in fast pyrolysis of cellulose under optimized conditions. The LGO yield was affected by the nature of the catalyst and anatase titanium oxide exhibited optimum activity for LGO. A new technique was developed for the co-production of furfural and activated carbon from pyrolysis of biomass materials impregnated with ZnCl₂. During the fast pyrolysis process, the catalysis of ZnCl₂ would inhibit the devolatilization of lignin and pyrolytic ring scission of holocellulose, while promote the depolymerization and dehydration of holocellulose to form furfural. Fast pyrolysis of the corncob impregnated with at least 15wt% ZnCl₂ at around 340°C could obtain the furfural yield over 8wt%. The solid residues from the fast pyrolysis process can be further activated at 500°C to produce activated carbons.When the bagasse was pyrolyzed as raw material at lower temperature, 4-vinylphenol and 2-methoxy-4-vinylphenol were enriched in the bio-oil. Compared the conventional pyrolysis, the energy consumption was reduced. A two-step method for pyrolysis of bagasse was developed: 4-vinylphenol and 2-methoxy-4-vinylphenol were enriched at first. The high purity levoglucosenone was gained by further pyrolysis of solid residue after impregnated with phosphoric acid. Fast pyrolysis of ammonium dihydrogen phosphate, diammonium phosphate, phosphoric acid solution pretreatment bagasse at 350°C could prepare more simple composition of bio-oil, which enrich in levoglucosenone, furfural and acetic acid.The process of selective catalytic pyrolysis can be further extended to more extensive biomass feedstocks. In addition to acetic acid, furfural and other bulk chemicals, levoglucosenone and other high value-added chemicals could also be obtained. It would not only solve the higher economic cost of biomass utilization, but also achieve high-value utilization of biomass resources. Promotion of the process would have good economic and social benefits.