Alkylation of benzene with carbon dioxide to low-carbon aromatic hydrocarbons over bifunctional Zn-Ti/HZSM-5 catalyst

Alkylation of benzene to value-added,high octane number and low toxic toluene and xylenes provides a way to lower benzene content in gasoline pool,and is hence a method to promote fuel quality.On the other hand,CO₂ accumulation in the atmosphere causes global warming and requires effective route for its valorization.Utilization of CO₂ as a carbon source for benzene alkylation could achieve both goals.Herein,alkylation of benzene with CO₂ and H2 was realized by a series of low-cost bifunctional catalysts containing zinc/titanium oxides(Zn/Ti oxides)and HZSM-5 molecular sieves in a fixed-bed reactor.By regulating and controlling oxygen vacancies of Zn/Ti oxides and the acidities of HZSM-5,benzene conversion and CO₂ conversion reached 28.7%and 29.9%respectively,along with a total selectivity of toluene and xylene higher than 90%.In this process,more than 25%CO₂ was effectively utilized and incorporated into the target products.Moreover,the mechanism of the reaction was analyzed and the course was simultaneously traced.CO₂ was transformed into methanol firstly,and then methanol reacted with benzene generating toluene and xylene.The innovation provides a new method for upgrading of fuels and upcycling the emissions of CO₂,which is of great environmental and economic benefits.     

Influence of the post-treatment of HZSM-5 zeolite on catalytic performance for alkylation of benzene with methanol

The porous material HZSM-5 zeolite with micro-mesopore hierarchical porosity was prepared by post-treatment (combined alkali treatment and acid leaching)of parent zeolite and its catalytic performance for benzene alkyl-ation with methanol was investigated.The effect of post-treatment on the textural properties was characterized by various techniques(including ICP-AES,XRD,nitrogen sorption isotherms,SEM,NH3-TPD,Py-IR and TG).The results indicated that the post-treatment could modify the structural and acidic properties of HZSM-5 zeolite.In this procedure,not only additional mesopores were created by selective extraction of silicon but also the acidity was tuned.Consequently,the modified HZSM-5 zeolite showed larger external surface area with less acid sites as compared to the parent zeolite.It was found out that the modified zeolite exhibited a higher benzene conversion and xylene selectivity for alkylation of benzene with methanol as well as excellent life span of the catalyst than conventional ones.This can be explained by the facts that the presence of additional mesopores improved the diffusion property in the reactions.Furthermore,the modified zeolite showed an appropriate Br?nsted acidity for effective suppression of the side reaction of methanol to olefins,thus reduced the accumulation of coke on the HZSM-5 zeolite,which was favorable for the catalyst stability.In comparison with the parent HZSM-5 zeolite, the modified zeolite by alkali treatment and acid leaching showed better performance for the benzene alkylation with methanol.     

Selective toluene ethylation in supercritical CO2 using chemical liquid deposition modified HZSM-5 pellets

Pellets consisting of the para-selective HZSM-5 crystals prepared by the chemical liquid deposition (CLD) with tetraethyl orthosilicate (TEOS) were used as the catalyst for alkylation of toluene with ethylene in supercritical carbon dioxide. The pellets were formed by compressing the CLD modified HZSM-5 crystals with and without addition of the binder alumina. When the binder was used, the CLD was applied again right after the compression. For the addition of 0.1 ml of TEOS per gram of pellet, p-ethyltoluene yield and selectivity were found to be sufficiently close to those using the modified crystals and the compressed pellets without containing the binder. The alkylation was carried out in a tubular reactor packed with the prepared HZSM-5 pellets. From a study of the operating variables including temperature, pressure, weight hourly space velocity of toluene, and molar ratio of toluene to ethylene, the highest yield and selectivity of p-ethyltoluene were determined as 70 and 97%, respectively, at a temperature of 623 K, a pressure of 13.1 MPa, a weight hourly space velocity of 5.0 (g of toluene)/(g of catalyst)/h and a molar ratio of toluene to ethylene of 5. The obtained results indicate a pronounced shape-screening effect of the prepared HZSM-5 pellets and an applicability of using supercritical CO₂ as the carrier.     

改性HZSM-5催化剂上甲苯-甲醇的烷基化反应的研究

采用浸渍法制得了P、B、Cu、Mg单组分及Mg、P、Si多组分复合改性的HZSM-5催化剂,通过XRD、BET、NH3-TPD等手段对改性前后催化剂的结晶度、孔结构及表面酸性进行了表征,在常压连续流动固定床反应装置上考察了改性HZSM-5在甲苯-甲醇烷基化制备对二甲苯反应中的催化性能,并对其微结构、表面酸性与择形选择性进行了关联。结果表明,P、B、Cu、Mg单组分改性的HZSM-5催化剂中,质量分数20%MgO改性使HZSM-5催化剂微孔面积和微孔容大幅下降,强酸显著降低,目标产物对二甲苯选择性明显提高(>60%);Mg、P、Si复合改性的HZSM-5催化剂中,改性剂之间的酸碱等相互作用对改性催化剂的开孔和表面酸性位的影响较大,与单组分改性相比复合改性效果不明显。     

ZnxZr/HZSM-5 as efficient catalysts for alkylation of benzene with carbon dioxide

Alkylation of benzene with carbon dioxide and hydrogen to produce toluene and xylene could increase the added-value of surplus benzene as well as relieve environmental problems like green-house effect. In this work, the alkylation benzene with carbon dioxide and hydrogen reaction was proceeded by using the mixture of zinc-zirconium oxide and HZSM-5 as bifunctional catalyst. The equivalent of Zn/Zr = 1 displays the best catalytic performance at 425 °C and 3.0 MPa, and benzene conversion reaches 42.9% with a selectivity of 90% towards toluene and xylene. Moreover, the carbon dioxide conversion achieves 23.3% and the carbon monoxide selectivity is lower than 35%, indicating that more than 50% carbon dioxide has been effectively incorporated into the target product, which is the best result as far as we know. Combined with characterizations, it indicated that the Zn and Zr formed a solid solution under specific conditions (Zn/Zr = 1). The as-formed solid solution not only possesses a high surface area but also provides a large amount of oxygen vacancies. Additionally, the bifunctional catalyst has excellent stabilities that could keep operating without deactivation for at least 80 h. This work provides promising industrial applications for the upgrading of aromatics.     

苯与合成气在ZnAlCrO x &HZSM-5双功能催化剂上一步法制甲苯/二甲苯

与传统的甲醇和苯烷基化反应相比,合成气和苯一步法制甲苯/二甲苯具有苯转化率高,催化剂稳定性好,经济性高等优点。本研究将系列Zn基的金属氧化物与H-ZSM-5分子筛组成双功能催化剂,实现了合成气与苯高效转化为甲苯/二甲苯,并筛选出最优的双功能催化剂为ZnAlCrO _x &H-ZSM-5。原位红外实验发现,单独的合成气在催化剂上的转化较弱,但加入苯之后,苯与甲氧基等中间体的烷基化反应可以有效拉动合成气的转化。这表明,双功能催化剂中金属组分和分子筛组分间的协同作用拉动了该反应的高效进行。通过Zn、Mg、Ga等元素改性H-ZSM-5分子筛,使得分子筛B酸酸量与L酸酸量的比值降低,发现比值的降低有助于苯的转化。其中Zn改性后B酸与L酸的比值降低最为显著,苯转化率增加的也最多。调变反应温度、原料空速、合成气氢碳比可以控制苯的烷基化程度,调节苯烷基化各产物的选择性。ZnAlCrO _x &H-ZSM-5双功能催化剂在压力3MPa、温度400℃的反应条件下,兼具高的苯转化率（90.6%）和甲苯/二甲苯选择性（74.3%）,同时CO有效利用率为33.7%。     

Benzene Alkylation with Propane over Mo Modified HZSM-5

Benzene alkylation with propane has been studied over HZSM-5 loading 3.1–15.4 wt% Mo in continuous-flow microreactor under 350 °C and atmospheric pressure with the highest activity obtained at 6.7 wt% Mo loading. C_7–9 aromatics were obtained as main products while the total amount of benzene rings kept unchanged. i-Propylbenzene and n-propylbenzene are formed primarily, while toluene, ethylbenzene, and ethyl-toluene are formed secondly from the propylbenzenes. Catalytic performance of 6.7 wt% Mo/HZSM-5(38) partially poisoned by NH₃ shows that the strong acid sites play a crucial role in the alkylation. Low SiO₂/Al₂O₃ ratio of HZSM-5 in the Mo modified catalysts gives high propane conversion. Two hydrothermal treatment methods were applied to the 6.7 wt% Mo/HZSM-5(38) catalyst, caused decrease of propane conversion but result in different product distribution. A possible reaction mechanism concerning bifunctional active centers resulted from combination of loaded Mo species and strong acid centers on HZSM-5 is proposed.     

乙酰丙酸改性对HZSM-5甲醇芳构化催化剂性能的影响

利用葡萄糖水解原位产生的乙酰丙酸对HZSM-5分子筛进行改性,通过X射线衍射、X射线荧光分析、N2吸附-脱附、扫描电子显微镜、NH3-TPD、Py-Fourier透射红外光谱、热分析等手段对催化剂进行表征,在固定床微型反应器上评价催化性能.结果表明:改性后的HZSM-5在保留完整晶相结构的基础上产生了微孔-介孔结构,酸...     

SELECTIVE FORMATION OF ALKYLAROMATICS OVER ZEOLITE CATALYSTS: ALKYLATION OF TOLUENE WITH ETHANOL

Selective formation of para-ethyltoluene by alkylation of toluene with ethanol was studied using as catalysts ZSM-8 Type zeolite which is another member of ZSM-5 family. Disproportionalion of toluene to produce xylenes increased with increasing reaction temperature, A temperature programmed desorption study snowed very strong acid sites were absent on Mg or Ba modified HZSM-8. Increased para-ethylloluene selectivity over modified ZSM-8 catalysts is interpreted in terms of a reduction in the strong acid sites and increased diffusional resistance.     

微孔-双介孔核壳型HZSM-5@BMMs催化甲醇芳构化

采用外延法,以HZSM-5为核,双介孔分子筛BMMs为壳制备了多级孔核壳型HZSM-5@BMMs甲醇芳构化(MTA)催化剂。采用XRD、BET、NH3-TPD、SEM和TEM对催化剂进行了表征。结果表明:HZSM-5@BMMs具有明显的核壳结构和微孔-双介孔多级孔孔道,孔径集中分布于0.9、2.2和5.3 nm,其比表面积(510.8 m2/g)和孔容(0.399 cm3/g)均高于HZSM-5的比表面积(408.4 m2/g)和孔容(0.190 cm3/g),而酸量(0.573 mmol/g)和酸强度均低于HZSM-5的酸量(0.883 mmol/g)和酸强度。相同反应条件下HZSM-5@BMMs寿命比HZSM-5增加38 h,最高芳烃收率为25.7%,最高BTX(轻质芳烃:苯、甲苯、二甲苯)选择性为55.3%。     

Improved selectivity in the toluene alkylation reaction through understanding and optimising the process variables

It has been demonstrated that it is possible to produce p-xylene with near-perfect selectivity by optimising the process variables of the toluene alkylation reaction over a B/ZSM-5 catalyst. This has been achieved specifically by minimising the undesirable isomerisation of p-xylene on the external acid sites of the catalyst by controlling the contact time. This offers a superior route to high selectivity compared to multiple pre-treatments of the catalyst to eliminate external acid sites (for example, by silanisation). Additionally, a high toluene:methanol feed ratio is beneficial because it minimises the methanol dehydration reaction. A further benefit is that the maximum theoretical conversion of toluene is limited, which diminishes p-xylene product inhibition. These findings confirm that toluene alkylation is best operated in a multistage reactor, but also highlight the need for removal of p-xylene as well as addition of methanol between stages. The method of catalyst preparation is not critical, provided that there is sufficient boron present (≥6.5 wt%) and any boron lost through sublimation during the reaction is replenished. It has been found that an active catalyst can be produced in situ by either loading a physical mixture of hydroboric acid and HZSM-5 into the reactor prior to reaction or even placing a bed of hydroboric acid upstream from a bed of HZSM-5. The in situ-formed catalyst readily achieves >99.9% selectivity to the desired p-xylene isomer, under optimised conditions.     

HZSM-5分子筛上吸附苯和甲醇的TPSR-MS研究

对不同硅铝比HZSM-5分子筛进行程序升温表面反应-质谱(TPSR-MS)实验和原位程序升温氧化(TPO)。结果表明,苯在HZSM-5分子筛上于60℃下吸附后程序升温脱附的过程中检测到乙烯,硅铝比越低,检测到的乙烯越多,HZSM-5分子筛上的残碳量越大。甲醇在HZSM-5分子筛上于60℃下吸附后程序升温脱附的过程中检测到甲苯,但未检测到苯,硅铝比越低,检测到的甲苯量越大;同时检测到氢气,硅铝比越低,氢气量越小,TPO检测到的残炭量越小。吸附温度越高,甲醇越易转化成甲苯。     

ZnZr/HZSM-5双功能催化剂在合成气与苯烷基化反应中的催化性能

将系列锌锆金属氧化物与HZSM-5分子筛耦合制备成双功能复合催化剂,并将其应用于合成气与苯烷基化反应。研究结果表明,ZnO是合成甲醇的主要活性组分,ZrO₂的加入能够促进ZnO分散,同时其表面具有的氧空位可促进CO的活化,二者结合方式显著影响反应活性。SEM、XPS、CO-TPD等表征结果表明,ZnO与ZrO₂相结合不仅能够提高ZnO的分散度,而且能调控氧化物表面的氧空位浓度,当二者形成固溶体时,锌在氧化锆中的分散度最大,表面氧空位浓度最高,CO吸附量最大,催化活性最高。锌锆结合方式一定时,锌含量是影响催化活性的另一重要因素,n(Zr)/n(Zn)=2的锌锆固溶体与HZSM-5以质量比1∶2耦合表现出最高的催化活性,CO和苯的转化率为34.65%和35.82%时,甲苯和二甲苯的总选择性高达85.24%。     

La/Zn/HZSM-5催化剂上的甲醇芳构化研究

Aromatization of methanol over co-impregnated La/Zn/HZSM-5 zeolite catalyst was studied.The selectivity of aromatics and BTX(benzene,toluene,and xylene)reached 64.0%and 56.6%,respectively,using La/Zn/HZSM-5 at 437°C,0.1 MPa and methanol WHSV(weight hourly space velocity)=0.8 h-1.Catalytic results showed that the La species was a very good promoter,increased selectivity of aromatics,and prolonged the catalyst lifetime on stream.The effects of the SiO2/Al2O3 ratio in zeolite,Zn and La loading,WHSV,reaction temperature, water content in the feed and H2 pretreatment of catalysts on the catalytic performance were studied in detail. Characterizations of the catalysts by thermogravimetric analysis(TGA),NH3-TPD(temperature programmed desorption),SEM(scanning electron micrograph),N2 adsorption-desorption,XRD(X-ray diffraction)and XRF (X-ray fluorescence),were carried out to understand the structure and discuss the aromatization performance of La/Zn/HZSM-5 zeolite catalyst.     

Efficient conversion of benzene and syngas to toluene and xylene over ZnO-ZrO2&H-ZSM-5 bifunctional catalysts

A series of ZnO-ZrO₂ solid solutions with different Zn contents were synthesized by the urea co-precipitation method, which were coupled with H-ZSM-5 zeolite to form bifunctional catalysts. As a new benzene alkylation reagent, syngas was used instead of methanol to realize the efficient conversion of syngas and benzene into toluene and xylene. A suitable ratio of ZnO-ZrO₂ led to the significant improvement in the catalytic performance, and a suitable amount of acid helped to increase the selectivity of toluene/xylene and reduce the selectivity of the by-products ethylbenzene and C₉⁺ aromatics. The highest benzene conversion of 89.2% and toluene/xylene selectivity of 88.7% were achieved over 10% ZnO-ZrO₂&H-ZSM-5 (Si/Al = 23) at a pressure of 3 MPa and a temperature of 450 ℃. In addition, the effect of the zeolite framework structure on product distribution was examined. Similar to the molecular dynamics of aromatic hydrocarbons, H-ZSM-5 zeolites comprise 10-membered-ring pores, which are beneficial to the activation of benzene; hence, the conversion of benzene is higher. H-ZSM-35 and H-MOR zeolites exhibited small eight-membered-ring channels, which were not conducive to the passage of benzene; hence, the by-product ethylbenzene exhibits a higher selectivity. The distance between the active centers of the bifunctional catalysts was the main factor affecting the catalytic performance, and the powder mixing method was more conducive to the conversion of syngas and benzene.     

Benzene selective hydrogenation over supported Ni (nano-) particles catalysts: Catalytic and kinetics studies

This report aims to reduce the benzene in a mixture of benzene and toluene as a model reaction using catalytic hydrogenation. In this research, we developed a series of catalysts with different supports such as Ni/HMS, Ni/HZSM-5, Ni/HZSM5-HMS, Ni/Al_2O_3 and Ni/SiO_2. Kinetic of this reaction was investigated under various hydrogen and benzene pressures. For more study, two kinetic models have also been selected and tested to describe the kinetics for this reaction. Both used models, the power law and Langmuir–Hinshelwood, provided a good fit toward the experimental data and allowed to determine the kinetic parameters. Among these catalysts, Ni/Al_2O_3 showed the maximum benzene conversion(99.19%) at 130 °C for benzene hydrogenation. The lowest toluene conversion was observed for Ni/SiO_2. Furthermore, this catalyst presented high selectivity to benzene(75.26%)at 130 °C. The catalytic performance(activity, selectivity and stability) and kinetics evaluations were shown that the Ni/SiO_2 is an effective catalyst to hydrogenate benzene. It seems that the surface properties particularly pore size are effective parameter compared to other factors such as acidity and metal dispersion in this process.     

Solid-state NMR studies of methanol-to-aromatics reaction over silver exchanged HZSM-5 zeolite

Solid-state NMR spectroscopy was used to study the conversion of methanol to aromatics (MTA) over silver exchanged HZSM-5 zeolites. It is the silver oxide rather than silver cation that plays a crucial role for the MTA reaction. The aromatic products (mainly toluene and benzene) are formed at the expense of the small alkanes (mainly propane and isobutane). AgZSM-5 zeolite calcined in air shows much higher activity and selectivity for the MTA conversion compared with AgZSM-5 zeolite calcined in vacuum or HZSM-5 zeolite. A possible reaction mechanism is proposed for the MTA conversion on the AgZSM-5 zeolite.     

Synthesis of ethylbenzene by alkylation of benzene with diethyl oxalate over HZSM-5

Catalytic synthesis of ethylbenzene by alkylation of benzene with diethyl oxalate was carried out over HZSM-5 with Si/Al ratios from 50 to 250. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ammonia temperature-programmed desorption (NH₃-TPD) and pyridine IR techniques. As revealed by the results of NH₃-TPD and pyridine IR spectra, a significant decrease in acidic strength and the number of acidic sites is observed with increasing Si/Al ratio from 50 to 250. The benzene conversion and ethylbenzene selectivity increases obviously with increasing Si/Al ratio from 50 to 200. With a further increase in Si/Al ratios, a slight decrease in the conversion of benzene and selectivity for ethylbenzene is detected, indicating that a proper acidic strength was required in this reaction. In addition, the effects of temperature and feed ratio on the catalytic activity and product distributions are also investigated in this study.     

The study of methanol aromatization on transition metal modified ZSM-5 catalyst

In this article, transition metals of Cu, La and Zn were used as adjuvant to prepare modified HZSM-5 by impregnation method. The catalysts were characterized by XRD, BET, NH₃-TPD and Py-IR to reveal the microstructure and acid property. The catalysis performances of methanol aromatization of catalysts were investigated in a fixed-bed reactor. The results show that the strength and distribution of acid center of these catalysts are significantly influenced by the species of transition metal. There are more mediate strong Lewis acid center in Zn modified HZSM-5 catalyst and therefore exhibits higher selectivity to aromatic, benzene, toluene and xylenes in the MTA reaction..     

苯和乙烯一步法合成苯乙烯反应研究

首次采用苯和乙烯在无氧存在下, 于多种固体酸和金属负载HZSM-5分子筛催化剂上反应直接得到苯乙烯与其它固体酸相比, HZSM-5分子筛催化剂表现出最高的反应活性和较高的对苯乙烯的选择性。HZSM-5分子筛负载不同金属后, 苯乙烯的选择性均有明显提高, 其中以Co/HZSM-5、Fe/HZSM-5和Pd/HZSM-5催化剂显示出较高的反应活性和苯乙烯选择性。反应温度、苯烯比、金属负载量、液空速、催化剂的焙烧及还原温度均会不同程度地影响反应转化率和产物分布。