| Fast pyrolysis is an efficient biomass utilization technology that can convert solid biomass into liquid bio-oil,which is highly promising.The composition of conventional bio-oil is extremely complex,mainly composed of various organic compounds such as acids,ketones.aldehydes,alcohols,phenols,esters,ethers,and water,which have disadvantages such as poor thermal stability,low calorific value,high corrosiveness,and easy aging,making it difficult to utilize bio-oil directly and efficiently.However,bio-oil contains a variety of value-added compounds,and the content of these value-added compounds under conventional pyrolysis conditions is usually low and the selectivity of the product is poor.The targeted preparation of specific value-added products can be achieved by introducing suitable catalysts in the fast pyrolysis process.At this stage,the commonly used solid catalysts for catalytic pyrolysis of biomass mainly include metal oxides,molecular sieves,and activated carbon.Metal oxides have the advantage of being both easy to obtain and cheap.Mixed metal oxides,which are compounded by two or more metal oxides,are multifaceted and structurally complex metal oxides with more excellent and unique catalytic properties than single metal oxides,and their applications in the catalytic pyrolysis of biomass have been rarely reported.Based on this,this paper carried out the study on the selective preparation of high-value products by catalytic fast pyrolysis of biomass with mixed metal oxides as catalysts,as follows.Firstly.nickel-tin layered double oxide(NiSn-LDO)catalysts were developed for the selective production of 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one(LAC)from the in-situ catalytic fast pyrolysis of cellulose.Microcrystalline cellulose was used as the experimental biomass material.and the effects of various layered double oxides,the Ni/Sn molar ratios in NiSn-LDO,pyrolysis temperatures,and catalyst-to-cellulose ratios on LAC generation were investigated by pyrolysis experiments on the pyrolysis-gas chromatography/mass spectrometry(Py-GC/MS).During the catalytic fast pyrolysis process,NiSn-LDO could effectively promote the conversion of LAC precursors to LAC.The selectivity of LAC was 27.92%at the pyrolysis temperature was 320℃,the Ni/Sn molar ratio was 2:1,and the catalyst-to-cellulose ratio was 1:1,while the yield was determined to be 9.11 wt%by the external standard method,which was more than 5 times that of non-catalytic pyrolysis of cellulose.Secondly,zirconium-tin mixed metal oxide(ZrO2-SnO2)catalysts were developed for the selective production of 5-hydroxymethylfurfural(5-HMF)from the in-situ catalytic fast pyrolysis of cellulose.Microcrystalline cellulose was used as the experimental biomass material,and the effects of pyrolysis temperature,Zr loading in ZrO2-SnO2,and catalyst-to-cellulose ratio on the selective catalytic fast pyrolysis for the preparation of 5HMF were investigated by Py-GC/MS pyrolysis experiments.The results showed that ZrO2-SnO2-15 with a Zr loading of 15 wt%was a weakly acidic catalyst that promoted the breakage of glycosidic bonds and the formation of reducing termini,while partially converting them to 5-HMF.under the optimal conditions of a pyrolysis temperature of 350℃ and a catalyst-to-cellulose ratio of 2:1,the yield of 5-HMF was 6.49 wt%,which was more than 4 times higher than that of 5-HMF during the non-catalytic pyrolysis of cellulose,meanwhile,its selectivity was as high as 23.50%.Then,phosphorus molybdenum tin mixed metal oxides(P-Mo/SnO2)catalysts were prepared for the selective production of levoglucosenone(LGO)from the in-situ catalytic fast pyrolysis of cellulose.Microcrystalline cellulose was used as the experimental biomass material,and the effects of phosphomolybdic acid loadings in P-Mo/SnO2,catalytic pyrolysis temperatures,and catalyst-to-cellulose ratios on the preparation of LGO by selective catalytic pyrolysis were investigated by Py-GC/MS pyrolysis experiments;the catalytic pyrolysis experiments with different catalyst contents and continuous regeneration of catalyst were carried out in a vertical lab-scale pyrolysis device.In the Py-GC/MS experiments,the highest yield of LGO of 17.98 wt%was achieved at the phosphomolybdate loading of 50 wt%in P-Mo/SnO2,the pyrolysis temperature of 300℃ and the catalyst-to-cellulose ratio of 1:1,and the corresponding LGO selectivity was 70.48%under these conditions.In the lab-scale pyrolysis experiments,the highest yield of LGO was 12.70 wt%and the content of LGO in the liquid product was 86.14%at a pyrolysis temperature of 300℃ and a catalyst-tocellulose ratio of 2:1.Furthermore,in six recycling experiments performed under this condition(catalysts were regenerated by roasting in the air),P-Mo/SnO2 exhibited good recycling stability,and the yield of LGO remained above 10 wt%after five regenerations.Finally,barium magnesium mixed metal oxide(BaMg-MMO)catalysts were developed and employed for the selective production of 4-VP from bagasse fast pyrolysis.The effects of Ba/Mg molar ratios in BaMg-MMO,pyrolysis temperatures,and catalystto-bagasse ratios on the preparation of 4-VP by selective catalytic pyrolysis were investigated via Py-GC/MS pyrolysis experiments using sugarcane bagasse as the experimental biomass material:catalytic pyrolysis experiments with different catalyst contents and pyrolysis temperatures were carried out using a horizontal lab-scale pyrolysis device.The results showed that BaMg-MMO could effectively increase the yield of 4-VP and inhibit the formation of other by-products such as 2-hydroxy-3-methyl2-cyclopenten-1-one to improve the selectivity of 4-VP.In the Py-GC/MS experiment,the yield of 4-VP was up to 7.3 wt%when the pyrolysis temperature was 300℃,the Ba/Mg metal molar ratio in BaMg-MMO was 1:1,and the catalyst-to-bagasse ratio was 4:1,and the corresponding selectivity of 4-VP under this condition was 44.4%.In the lab-scale scale catalytic fast pyrolysis experiments,the highest selectivity and yield of 4VP were 56.6%and 7.1 wt%,respectively,using BaMg-MMO with a Ba/Mg metal molar ratio of 1:1 as the catalyst,while the catalyst-to-bagasse ratio was reduced to 1:1.Catalytic fast pyrolysis of bagasse via BaMg-MMO also has the potential to co-produce 4-VP and biochar due to the higher carbon yield during the low-temperature catalytic pyrolysis. |
