Experimental Study On Co-Production Of Phenol And CO By Catalytic Pyrolysis Of Rice Husk Via Activated Carbon Catalyst

As the only renewable carbon sources in this world,biomass is the fourth largest energy source with rich reserves and wide distribution.Rapid pyrolysis technology is such a thermochemical conversion method that aims at the acquisition of liquid bio-oil.However,the bio-oil from direct pyrolysis was high oxygen contained and chemically unstable.It seems that further upgrading before usage is essential.Besides,current researches mainly focused on the liquid chemical quality,but the efforts on gaseous by-products is insufficient.In this paper,activated carbon prepared by phosphoric acid activation was employed as solid acid catalyst,the typical agricultural waste rice husks was employed as feedstock,and then the experiment of selectively catalytic enrichment of phenol was carried out.After the investigation of the effects of activated carbon preparation parameters and catalytic pyrolysis parameters on the enrichment of phenol,the transformation law of main components in biomass to gaseous and liquid products was studied experimentally.On this basis,the feasibility of simultaneous enrichment of phenol and CO by the coupling of pretreatment and activated carbon catalysis was explored.In aspect of activated carbon catalyst preparation:Three activated carbon catalyst named P-AC,Z-AC and K-AC was prepared by KOH,ZnCl₂ and H₃PO₄,respectively.And then they were applied in catalytic pyrolysis experiment.Results indicated that P-AC is the best catalyst.Further investigation on the basic parameters of activation process showed that feedstock/H₃PO₄ mass ratio of 1:1,activation temperature of 500?and activation time of 90 min is the optimum preparation condition for catalytic experiment.Afterwards,the experiments of catalytic reforming process showed the optimum phenol output was obtained at the catalyst/rice husk mass ratio of 0.8 and the catalytic temperature of 500?.Catalytic cycle properties of activated carbon catalyst was carried out for 9 times under the optimum catalysis condition.Results showed that bio-oil in 1th-3th cycles was mainly composed of high-purity phenol and alkyl phenol,in which the first cycle included phenol and a small amount of 2/3-methyl phenol.A large amount of 4-ethylphenol was arisen in 2th and 3th cycles.After the 4th cycle,the actual peak area of phenolic compounds decreased significantly,so its value is limited.The characterization of deactivated catalysts revealed that the deactivation of activated carbon catalyst was mainly derived from the filamentous carbon deposition,which due to the covering of phosphorous functional groups on catalyst surface and the blockage of pores between 2-3 nm.In the catalytic experiment of main components from biomass,it was found that the optimal catalytic conversion conditions for hemi-cellulose and cellulose were obtained at the catalyst/rice husk mass ratio of 1:1 and the catalytic pyrolysis temperature of 450?.Phenols and CO were dominated in liquid and gas products,respectively.However,at 500?,the optimum temperature for biomass conversion,the enrichment degree and concentration of phenol and CO in hemicellulose decreased significantly.But the increasement of temperature had little effects on cellulose.Phenol and CO were still the main products in the gas and liquid products.Whereas,the optimum catalytic pyrolysis conditions for lignin was obtained at the catalyst mass ratio of 1:1 and the catalytic temperature of 500?.High content of phenol was enriched in bio-oil.In pyrolytic gas,CO,H₂,CO₂ and CH₄ were all obviously observed.Potassium acetate was employed as the molding compound of ash to investigate the effects of AAEMs on catalytic products.On the whole,the existence of ash content is not conducive to catalytic products.On the basis of components experiment,we employed pretreatment technologies,including the acid washing-torrefaction,hydrothermal pretreatment and acidic pretreatment to upgrade fuel properties of rice husk.Experimental results showed that the phenol and CO concentration were improved from pretreated rice husks.Specific experimental results are as follows:For the rice husk pretreated with acid washing and torrefaction at 240?,via catalytic pyrolysis,CO concentration in gas products rose to 61.86%,and the volume yield was 174.34 m L/g.Relative peak area of phenol in bio-oil was 71.72%,and the mass yield was 1.41 times of direct pyrolysis of rice husk(RH-N)and 0.97 times of catalytic pyrolysis of raw rice husk(RH).For the rice husk pretreated with hydrothermal pretreatment at 150?,via catalytic pyrolysis,CO concentration in gas products was66.68 vol.%,and the volume yield was 272.19 m L/g.Relative peak area of phenol in bio-oil was74.67%,and the mass yield was 1.45 times of RH-N and 1.05 times of RH.For the rice husk pretreated with acidic pretreatment at 100?,via catalytic pyrolysis,CO concentration in gas products was 63.23 vol.%,and the volume yield was 163.59 m L/g.Relative peak area of phenol in bio-oil was 67.14%,and the mass yield was 2.02 times of RH-N and 1.41 times of RH.Results above indicated that the combination of appropriate pretreatment methods and catalytic reforming with activated carbon significantly improved both the gas and liquid products from catalytic pyrolysis,and the simultaneous enrichment of phenol in liquid phase and CO in gas phase was successfully achieved in this work.