| According to the 13th Five-Year Plan for biomass energy,the technology for the production of bio-oil and natural gas from biomass needs to be vigorously developed.At present,fast pyrolysis of biomass is the main process for producing crude bio-oil,which is then refined by catalytic hydroconversion.This process is carried out step by step,and the equipment is more numerous.Moreover,the low quality crude bio-oil will lead to deterioration during storage and transportation.Biomass catalytic hydropyrolysis can produce high quality bio-oil in one step,which has been studied a lot in recent 10 years.In-situ biomass hydropyrolysis study account for the majority,but the quality or yield of bio-oil isn’t perfect.Ex-situ biomass catalytic hydrogenation research is less because of using complex two-stage reactors,and most of them use microreactors,which can not obtain accurate quantification of bio-oil and gas products.Recently,the US GTI proposed a process called integrated catalytic hydropyrolysis of biomass and catalytic hydroconversion of volatile matter(IH2),in which a two-stage reactor was used for producing high quality and quantity bio-oil.However,the catalyst was not report.So far there are a few IH2 research,it is necessary to study a new IH2 process and develop new efficient catalyst.This work developed a novel IH2 process using a two-stage fixed-bed reactor,in which Fe(NO3)3 catalyst was selected for biomass catalytic hydropyrolysis,and iron-loaded charcoal catalyst(Fe/CC-s)was used to refine volatile matter to obtain the highest yield of high quality bio-oil and gaseous hydrocarbons.Meanwhile,the catalytic mechanism of catalytic hydropyrolysis of biomass and catalytic hydropyrolysis of volatile matter was was investigated.This work provides new technological ideas and basic experimental data for biomass production of liquid fuels and natural gas.The main contents of this paper are as follows:(1)Non-catalytic two-stage hydropyrolysis.The effects of atmosphere(nitrogen,hydrogen),single-stage or two-stage bed,cracking temperature(600-750℃)and pressure(1-5 MPa)for refining volatile matter in two-stage fixed bed reactor were investigated.33.2%(all dry ash-free groups,the same as below)gaseous hydrocarbons(C1-C3),5.3%BTXEN(benzene,toluene,xylene,ethylbenzene and naphthalene)were produced under 5 MPa H2 and 750℃ hydrocracking temperature,but the bio-oil yield was only 12.4%.Meanwhile,the effects of three main fiber components(hemicellulose neutral extract,cellulose and lignin)in biomass were also investigated,and it was found that each fiber component played a significant contribution to the target products under hydrogen atmosphere.The hydrogen consumption in system was also discussed.In general,the hydrocracking of volatile matter with no catalyst can improve the quality of bio-oil and produce more light aromatics,but it leaded to a large decrease in bio-oil yield.(2)Ex-situ catalytic hydropyrolysis(catalyst for refining volatile matter).The catalytic effect of two self-prepared iron-loaded charcoal catalysts(Fe/CC-s and Fe/CC-n)was investigated.It was found that Fe/CC-s could inhibit the decomposition of bio-oil into gas.The Fe/CC-s can produce 21.0-24.6%bio-oil at 550-600℃,higher than around 6%using no catalyst.The bio-oil quality was improved and its oxygen content was only 1.9%(oxygen basis).Fe/CC-n showed a high selectivity for methane production,and produced 30.0%gaseous hydrocarbons.The two catalysts showed distinct catalytic effects.The study of catalytic mechanism indicates that the volatile components cross-linked with charcoal and form intermediates.Fe/CC-n formed the fine and dispersed α-Fe,breaking the intermediates into small molecules,which were hydrogenated into methane;Fe/CC-s formed the agglomeration α-Fe,and break the intermediates into macromolecules,which were hydrogenated into bio-oil.(3)In-situ catalytic hydropyrolysis(catalyst for biomass hydropyrolysis).The catalytic effects of two iron salts(iron nitrate and ferrous sulfate)on biomass hydropyrolysis were investigated.It was found that iron nitrate had a strong catalytic hydrogenation ability at the final temperature of 600-700℃.The biomass carbon conversion reached 97.4%,and 21.2%methane,31.5%bio-oil was produced at 700℃ under 5 MPa H2.The light aromatics in bio-oil increased and oxygen content decreased slightly.Ferrous sulfate inhibit the formation of gaseous hydrocarbons and light aromatics.Catalyst characterization showed that Fe(NO3)3 was reduced and formed Fe3O4 at 400℃,which subsequently reacted with char and form α-Fe,releasing CO and leading to char structure fragmentation,which facilitated hydrogenation into methane as well as BTX;FeSO4 formed Fe2S3 at high temperatures,which may inhibit the formation of gaseous hydrocarbons and light aromatics.(4)Integrated catalytic hydropyrolysis and catalytic hydroconversion(IH2).The new IH2 process conditions were determined according to the research above.Fe(NO3)3 was used for biomass hydropyrolysis until the final temperature reach 700℃,while Fe/CC-s was used for refining the volatile matter at 600℃ under 5 MPa H2.The IH2 of pinewood produced 27.4%bio-oil,34.1%gaseous hydrocarbons and 5.9%BTXEN.Various agricultural waste biomass raw materials(peanut straw,sorghum straw,cotton pole,corn pole)were also used for IH2,producing 38.1-45.8%bio-oil,18.1-18.8%gaseous hydrocarbons and 2.3-3.8%BTXEN,lower than pinewood results.The reason is that the KCl in agricultural waste biomass restrained the catalytic effect of external catalyst α-Fe on hydrogenation of char. |
