Upgrading Of White Pine Pyrolysis Oil In A Decoupled Dual Loop Reaction System

Biomass is an environmentally friendly renewable energy source,and it is also the only renewable carbon source which can produce fuel or valuable chemicals.It has the characteristics of carbon balance,wide sources,and low cost.In recent years,the situation of using biomass resources to replace traditional fossil energy has become very urgent.This measure has a particularly important significance for realizing self-supply of energy and building a beautiful China.Biomass rapid pyrolysis technology for oil production is a promising biomass utilization technology.Its process is simple,and the liquid fuels and high value-added chemicals produced can effectively alleviate the dilemma of shortage of petroleum resources in China.In this paper,using a decoupled dual-loop reaction system and a fixed-bed experimental device,the optimal process conditions for the pyrolysis of white pine sawdust to make oil and the catalytic pyrolysis behavior of pyrolysis oil model compounds weree explored with hematite as catalyst.The specific research content and conclusions are as follows:In a decoupled dual loop reaction system（DDLR）,the pyrolysis of white pine sawdust and the catalytic upgrading of pyrolysis oil were carried out with quartz sand-hematite as the bed material.The system consists of a fluidized bed pyrolyzer（FBP）,a radial flow moving bed upgrader（MBU）,a riser combustor（RC）and a particulate classifier（PC）.Through the PC,the circulated bed materials are separated into a fine quartz sand particle group and a coarse group composed of both quartz sand and hematite,that are distributed into the FBP and MBU,respectively.The both then enter into the RC and PC in series again,forming two independent and parallel reaction loops,i.e.a loop of raw material pyrolysis-char combustion and a loop of pyrolysis oil catalytic upgrading-bed material regeneration.In this way,these reactions could be decoupled and controlled individually.The effects of pyrolysis temperature,circulated hematite/biomass mass ratio（H/B）and catalytic upgrading temperature on the products were investigated.It has been indicated that increasing pyrolysis temperature is beneficial to the deoxidation of white pine sawdust,and the pyrolysis oil yield reaches its peak at 500℃.The increase of H/B promotes the decarboxylation and decarbonylation of pyrolysis oil,which effectively decreases the content of esters,acids,ketones,thus enriches high-value chemicals such as aromatics and furfurals.As the catalytic upgrading temperature increases,the content of various oxygenated compounds（except phenols）in the oil are all at a low level,while the content of aromatics raises,up to 35.6%.Acetic acid,ethyl acetate,acetone,furfural,and 2-methoxy-phenol were selected as pyrolysis oil model compounds in a fixed-bed experimental device.The effects of catalyst bed materials,pyrolysis temperature and liquid hourly space velocity（LHSV）on the catalytic pyrolysis behavior of model compounds were investigated.It is found that,compared with quartz sand,hematite promotes the deoxidation of the model compound and increases the CO content in the gas composition,and it also can promote the condensation polymerization of the model compound to a certain extent,so that the H₂content increases;While when the catalyst is the pre-reduced hematite,the deoxidation rate and gas yield are further increased,the water yield is reduced,and the main form of deoxidation is CO;The H₂content increases greatly,so the polycondensation reaction intensifies at this time.The increase of pyrolysis temperature is conducive to the deoxygenation of the model compound,and the CO content in the gas composition increases while the CO₂content decreases;In addition,the increase of the pyrolysis temperature promotes the migration of oxygen in hematite,but the direction of migration depends on the nature of the model compound itself.The experimental results of the change of liquid hourly space velocity not only show that the catalytic ability of hematite has a certain limit,but also show that the change law of the pyrolysis products of the model compound is also related to its autopyrolysis properties.