Study On The Catalytic Pyrolysis Characteristics Of Biomass With Carbide Slag-based CaO Additives

Catalytic pyrolysis of biomass is one of the most promising technologies in the conversion of biomass.Ca O-based catalysts have achieved good results in both yield and quality of products and reducing carbon emissions.However,the deoxidation activity and cyclical stability of conventional Ca O are poor,which limit its development.China has a wide range of high calcium solid waste resources.Preparing Ca O from high calcium solid waste and its application in biomass catalytic pyrolysis are expected to further improve the deoxidation effect and products quality and can promote the efficient resource utilization of high calcium solid waste and biomass.Clarifying the mechanism of Ca O obtained from high calcium solid waste in biomass pyrolysis process and optimizing its physical and chemical properties to improve the catalytic effect and stability are the key to expand the application prospect of high calcium solid waste-based Ca O in biomass catalytic pyrolysis.Based on this,the mechanism of carbide slag-based Ca O during biomass catalytic pyrolysis process was deeply studied.The preparation conditions and modification methods of catalysts which can realize efficient conversion of biomass were also investigated.The main conclusions are as follows:Firstly,the effect of carbide slag-based Ca O on catalytic pyrolysis of cotton stalk and the phase transition of catalysts before and after experiments were explored in a two-stage fixed-bed reactor.It was found that carbide slag-based Ca O could react with CO₂ to promote water-gas shift reaction and increase the yield of H₂ during pyrolysis,and the calorific value of pyrolysis gas could reach～17 MJ/m³.In addition,carbide slag-based Ca O could reduce the content of high oxygen-containing organic compounds in bio-oil by reacting with acids and catalyzing the dehydration of sugars and furans,so as to improve the quality of bio-oil.With the increase of carbide slag-based Ca O,the qualities of pyrolysis gas and bio-oil were enhanced.But excessive catalyst would lead to a large amount of coke deposition and reduce the utilization efficiency of the catalyst.Generally speaking,the optimal mass ratio of carbide slag-based Ca O catalyst to cotton stalk is 1:1.Then,the activity and stability of Ca O-based catalysts with different preparation temperature and precursor（inorganic calcium source:calcium carbonate（eggshell,conch,analytical pure Ca CO₃）,dicalcium silicate（steel slag）,calcium hydroxide（carbide slag）and organic calcium source（analytical pure calcium gluconate））were investigated.It was found that the Ca O catalyst prepared at lower calcination temperature had smaller and more uniform grain size,higher alkaline strength and more basic sites.0.146 g CO₂/g Ca O could be fixed by calcined carbide slag-based Ca O at the best condition.In terms of calcium precursor,CG-Ca O obtained from calcium gluconate was superior to that from inorganic calcium source in both physicochemical properties and catalytic effect.Carbide slag-based Ca O which prepared and regenerated at lower temperature（650℃）had stronger stability and its catalytic effect was superior to that of CG-Ca O after regeneration for 5 times.Finally,carbide slag-based Ca O was pretreated with organic acid by impregnation method and the physicochemical properties and catalytic activity of the modified catalysts were investigated.It was found that the types of organic acid（oxalic acid,citric acid,formic acid and acetic acid）had a significant effect on the alkaline strength and number of basic sites of Ca O catalyst,among which Ca O modified by oxalic acid had the most abundant basic sites and the effect on improving the quality of bio-oil and pyrolysis gas was the most obvious.Further investigation on the concentration of oxalic acid and the calcination temperature showed that when the molar ratio of oxalic acid to carbide slag was 1:1 with calcined at700℃,the Ca O-based catalyst had the smallest crystal size and a large number of basic sites.This made the CO₂ content in pyrolysis gas lowest（13.2 vol.%）and the gas calorific value（18.7 MJ/m³）highest.The content of acids（from 35.2%for cotton stalk alone to 10.3%）and high oxygen-containing compounds（from 91.5%to 75.1%）in bio-oil decreased significantly.Besides,the catalyst also showed good cyclic stability.This study not only enhances the quality of products obtained from biomass pyrolysis,but also realizes the fixation and emission reduction of carbon dioxide.It provides a new approach for the resource utilization of biomass and high calcium solid waste.