生物基呋喃与甲醇耦合催化热解制备芳烃化合物

为了提高芳烃的选择性产率和减少催化剂的积碳,以生物基呋喃为原料,以甲醇为耦合试剂进行催化共热解,探讨工艺条件对芳烃的选择性产率的影响,同时对其转化路径以及催化剂的积碳进行分析。结果表明:呋喃与甲醇耦合协同催化共热解可以有效的提高芳烃的选择性产率,二者具有明显的协同效应,甲醇的添加促进了甲醇制烯烃(methanol to olefin,MTO)反应、Diels-Alder环加成反应以及苯烷基化反应的发生,高温促使多烷基化合物以及萘及其同系物选择性产率的增加;强酸性促进了甲醇的脱水以及Diels-Alder环加成反应;同时,羰基抑制了呋喃环和烯烃的Diels-Alder反应,而羟基的存在有效的促进了甲苯以及二甲苯的生成,因此,当采用HZSM-5(SiO2/Al2O3=25)为催化剂,当热解温度为500℃,催化温度为550℃,MF∶甲醇=1∶5,物质的进样量为0.2 mL/min时,其芳烃的选择性产率达到99.73%,积碳量达到11.06%,苯、甲苯、二甲苯以及乙苯的总含量达到40.49%,萘及其同系物的含量仅为10.15%,有效的提高了烷基苯的选择性产率。

Coupling catalytic co-pyrolysis of bio-derived furans and methanol for enhancing aromatic production over HZSM-5 catalyst

The catalytic converter is an important approach to obtain high-value chemicals from biomass with HZSM-5 mesoporous catalyst.Furan can serve as a representative model compound for catalytic fast pyrolysis of raw woody biomass.A major drawback of the aromatization of bio-derived furans is how to improve aromatic yield and selectivity of specific aromatic production(e.g.,xylenes)and to reduce the formation of carbon deposits.So,to overcome its disadvantages,the effect of process conditions(pyrolysis temperature,catalytic temperature,weight hourly space velocity,furan species,2-Methylfuran(MF)to methanol ratio and silicon to aluminum ratio)on the product yield and selectivity of aromatics were investigated with bio-derived furans and methanol catalytic co-pyrolysis with HZSM-5 catalyst.Simultaneously,the catalytic conversion mechanism and catalyst deactivation was discussed with X-ray diffractometer(XRD),specific surface area and aperture distribution meter(BET)and scanning electron microscope(SEM).The coupling conversion of bio-derived furans and methanol was conducted in a continuous fixed bed reactor.MF was used as a probe molecule to identify the possible reaction pathways.The experimental results showed that the coupling catalytic co-pyrolysis of furan and methanol effectively improved the yield and selectivity of aromatic hydrocarbon.The aromatic yield from the coupling conversion of MF and methanol was about 1.45 times higher than that of the catalytic fast pyrolysis of only MF.There was a positive synergistic effect between furan and methanol.The addition of methanol promoted methanol-to-olefin(MTO)reaction,Diels-Alder cycloaddition reaction and alkylation of benzene/toluene.In the process of the reaction,dimethyl ether was the main intermediate product of methanol dehydration.The first dehydration of methanol produced dimethyl ether,and then dimethyl ether continued to dehydrate to produce ethylene.Ethylene and MF further underwent Diels alder cycloaddition reaction to produce aromatic hydrocarbons.Higher temperature enhanced the occurrence of polymerization and increased the selectivity of polyalkylated compounds as well as naphthalene and its derivatives.Benzene alkylation reaction and Diels-Alder cycloaddition reaction was a pair of competitive reactions.Benzene alkylation reaction was dominant at high temperature,so inhabited the degree of Diels-Alder cycloaddition reaction.Moreover,strong acidity promotes methanol dehydration and Diels-Alder cycloaddition reaction.Moreover,the comparative study of the coupling conversion of different bio-derived furans(2-methylfuran(MF),furfural(FF),furanol(FA),5-methylfural(MFF)and 5-hydroxymethylfurfural(HMF))and methanol were also considered in this study.It showed that MF gave out the highest yield of aromatics.Additionally,different functional groups did not change the formation mechanism of aromatics.Carbonyl functional groups inhibited the Diels-Alder reaction of furan rings and olefins,resulting in lower selectivity of monocyclic aromatics.The presence of hydroxyl groups effectively promoted the formation of toluene and xylene and increased the content of SBTXE and polyalkylbenzene.Maximum aromatics yield and SBTXE of 99.73%and 40.49%and minimum coke content of 11.06%were obtained over HZSM-5(SiO2/Al2O3=25)under the conditions of pyrolysis temperature of 500℃,the catalytic temperature of 550℃,MF to methanol molar ratio of 1:5 and the weight hourly space velocity of 0.2 mL/min.At this time,naphthalene and its derivatives content were only 10.15%,which effectively improved the selectivity of alkylbenzene and reduced the deactivation of the catalyst.Moreover,the deactivation mechanism showed that the specific surface area decreased from 308.18 to 229.90 m2/g and the average pore size decreased from 3.42 nm to 3.07 nm.The particles on the catalyst surface increased obviously,the agglomeration phenomenon between the catalyst grains was intensified,the surface structure was more compact,and the fuzzy area increased.These findings provided a simple,green,efficient and cost-effective way for simultaneously overcoming the existing bottlenecks in the catalytic fast pyrolysis of bio-derived furans and would help the understanding of the reaction chemistry of co-conversion of biomass and alcohol mixtures.