Effect of Steam Treatment on the Catalytic Performance of ZSM-5 in the Co-conversion of Methanol and n-Hexane to Aromatics

Steam pretreatment is a widely used method for modifying the acidity and structure of zeolites,thereby enhancing their catalytic properties.This study systematically investigated the effects of steam treatment on ZSM-5 zeolites at varying treatment temperatures and durations.The structural evolution of the catalysts was monitored using N2 adsorptiondesorption,X-ray diffraction,inductively coupled plasma optical emission spectroscopy,scanning electron microscopy,NH3 temperature-programmed desorption,in situ pyridine infrared spectroscopy,and thermogravimetric analysis.The characterization results revealed that mesopores were introduced into the ZSM-5 zeolite catalysts through dealumination induced using steam treatment at moderate temperatures(400 and 500℃).Moreover,compared with the parent catalyst,the steam-treated catalysts exhibited a lower amount of acid sites and relative crystallinity,while the n(Si)/n(Al)ratio increased.In the co-conversion of methanol and n-hexane in a fixed bed reactor at 400℃and 0.5 MPa(N2 atmosphere),with a weight hourly space velocity of 1 h−1 and a stoichiometric ratio of 1:1(CH3OH to n-hexane),the steam-treated catalysts displayed a prolonged catalyst lifetime.Particularly,the parent zeolite had a lifetime of 96 h,while the catalyst treated at 500℃for 12 h had a lifetime of up to 240 h.Additionally,the steam-treated catalysts maintained stable n-hexane conversion and improved aromatic selectivity.Notably,these treated catalysts exhibited a lower deactivation rate than the parent catalyst,and would be conducive to industrial scale-up production.

Correlation between H-ZSM-5 crystal size and catalytic performance in the methanol-to-aromatics reaction

The porosity of H‐ZSM‐5zeolite is known to facilitate the diffusion of molecules in the methanol‐to‐aromatics(MTA)reaction.The activity and selectivity of the H‐ZSM‐5catalyst in the MTAreaction has been studied as a function of crystal size.ZSM‐5zeolites with different crystal sizeswere successfully synthesized by conventional hydrothermal methods.Tailoring ZSM‐5particle sizewas easily controlled by changes to the sol‐gel composition,and in particular,the deionized waterto tetrapropylammonium hydroxide ratio,and crystallization time.The structure of the H‐ZSM‐5zeolites were characterized by X‐ray diffraction and the morphology of the zeolite particles wasdetermined by scanning electron microscopy.N2adsorption‐desorption measurements establishedchanges to the textural properties,and compositional properties were characterized by X‐ray fluorescencespectroscopy.Acidity measurements of the catalysts were measured by pyridine‐adsorbedFourier transform infrared spectroscopy and the temperature‐programmed desorption of ammonia.After subjecting the catalysts to the MTA reaction,the total amount of coke formed on the spentdeactivated catalysts was determined by thermal gravimetric analysis.The results show that theSiO2/Al2O3molar ratios and acidic properties of the H‐ZSM‐5samples are similar,however,thenano‐sized hierarchical ZSM‐5zeolite with an additional level of auxiliary pores possesses a higher

Formaldehyde intermediate participating in the conversion of methanol to aromatics over zinc modified H-ZSM-5

Metal-modified H-ZSM-5 has a high selectivity of aromatics in methanol to aromatics(MTA)reaction,which is often attributed to the metal promoting the aromatization of intermediate olefins.However,the effect of methanol dehydrogenation on aromatics formation over these catalysts is rarely studied.Here,we report that HCHO,which is formed by methanol dehydrogenation over Zn/H-ZSM-5 prepared by Zn impregnation,can participate in the synthesis of aromatics.Methanol conversion can produce more aromatics than olefins(propylene or ethylene)conversion over Zn/H-ZSM-5,indicating the conventional MTA pathway including methanol-to-olefins and olefins-to-aromatics is not complete.Moreover,an MTA mechanism including the conventional pathway and the methanol and HCHO coupling pathway is systematically proposed.

Catalytic performance of imidazole modified HZSM-5 for methanol to aromatics reaction

A facile approach was developed for the preparation of nano-sized HZSM-5 with a hierarchical mesoporous structure by adding imidazole into conventional zeolite synthesis precursor solution. The physicochemical properties of modified HZSM-5 were characterized by X-ray diffraction（XRD）, N;adsorption–desorption isotherms, scanning electron microscopy（SEM）, NH;-temperature-programmed desorption（NH;-TPD） and pyridine adsorption infrared spectroscopy（Py-IR）. The coke in spent catalysts was characterized by thermogravimetry（TG）. The results showed that hierarchical HZSM-5 zeolites with excellent textural properties, such as abundant porous structure, uniform particle size and suitable acidity, could be synthesized by the recipe of one-pot synthesis routes. Moreover, the obtained HZSM-5 exhibited higher selectivity of total aromatics as well as longer lifetime in the catalytic conversion of methanol to aromatics, comparing with conventional HZSM-5. It is expected that the synthesis approach demonstrated here will be applicable to other zeolites with particular textural properties and controllable particle sizes, facilitating the emergence of new-type porous materials and their related applications in catalysis and separation.

Commercial Demonstration Unit for Manufacture of Aromatics from Toluene and Methanol with Coproduction of Low-Carbon Olefins Will Be Set Up

On November 29,2013 the Shaanxi Coal Chemicals Technology Engineering Center,Ltd.(SCCTEC),the CNOOC Huizhou Refining and Chemical Company and the SINOPEC Luoyang Engineering Company,Ltd.signed an agreement on cooperation in development of

Emergy evaluation of aromatics production from methanol and naphtha

Aromatics are traditionally produced by the catalytic reforming of naphtha.However,with the demand of aromatics increasing and the reserves of petroleum resources declining,measures should be made to reduce the dependence of aromatics production on petroleum resources.Methanol-to-aromatics is proved to be an effective way to replace traditional naphtha-to-aromatics path.In order to compare the economic and environmental performance of aromatics production from naphtha and methanol,this paper carries out an emergy evaluation for each system by sorting out the simulation and literature data.Based on the emergy data collected,the emergy indices of each system are calculated.The results show that the sustainabilities of methanol-to-aromatics systems are higher than that of the naphtha-toaromatics system,indicating the advantages of aromatics production from methanol.Among the methanol-to-aromatics systems,the aromatics from biomass-methanol system has the highest sustainability,indicating that the biomass based methanol-to-aromatics system is worth promoting.The sustainability indexes of methanol-to-aromatics systems based on coal and coke oven gas are less than 1,which means unsustainable.Meanwhile,the sustainability of natural gas based system is slightly higher than 1.The economic and environmental benefits of these systems can be optimized by improving resource utilization and reducing investment costs.Furthermore,the combination of different raw materials for methanol production should be considered.

Intensified shape selectivity and alkylation reaction for the two-step conversion of methanol aromatization to p-xylene

Two-step conversion of methanol to aromatics via light hydrocarbons can significantly improve the conversion stability compared with direct aromatization of methanol,but it remains a challenge to achieve a high p-xylene(PX)selectivity.Herein,silica coating was firstly used to passivate external acid sites of ZSM-5 catalyst for the aromatization of light hydrocarbons by the chemical liquid deposition method.With the increase of SiO_(2) deposition,the density of the external acid sites of the catalyst was decreased from 0.1 to 0.03 mmol·g^(-1),which inhibited the surface secondary reactions and increased the PX/X from 34.6% to 60.0%.In view of the fact that the aromatization process in the second step was partly inhibited as methanol was consumed in advance in the upper methanol-to-light hydrocarbons catalyst layer,part of methanol was directly introduced into the lower aromatization catalyst layer to promote the alkylation process during the aromatization,which decreased the toluene selectivity from 34.5% to 14.3% but increased the xylene selectivity from 40.0%to 55.3%.It was also found that an appropriate external acid density was needed for aromatization catalyst to strengthen the alkylation process and improve the selectivity of xylene under the conditions of methanol introduction.

Zn/ZSM-5催化剂在甲醇制芳烃(MTA)反应中的失活与再生

在固定床反应器中进行Zn/ZSM-5分子筛催化甲醇转化制芳烃反应的积炭失活实验,采用X射线衍射,傅里叶变换红外光谱,N_2吸附-脱附,氨气程序升温脱附,热重等方法对新鲜及失活催化剂进行了表征。结果表明,在甲醇制芳烃反应中,催化剂的失活主要是由于催化剂表面积炭导致的微孔堵塞引起的,据分析结果推测积炭物种主要是芳香族化合物或带有双键的聚合态化合物。失活催化剂经再生后,催化剂平均孔径增大,稳定性增强,在312h的反应过程中,甲醇转化率始终保持99.8%以上,但芳烃的收率及选择性下降。

锌改性HGaZSM-5分子筛催化甲醇制芳烃(MTA)反应性能

通过水热合成法制得GaZSM-5分子筛,经酸交换得到氢型分子筛HGaZSM-5。采用浸渍法、机械混合法和离子交换法制备出一系列Zn改性GaZSM-5分子筛,分别记作WI,PM,IE。采用XRD、SEM、FT-IR、XPS、ICP、低温氮气吸附-脱附、NH 3-TPD和Py-IR等技术对其进行物化性质表征,并在连续流动固定床反应器上进行甲醇制芳烃(MTA)反应性能评价。结果表明,改性方法对分子筛的晶体结构没有影响,对孔径分布数量有一定的调变作用。锌改性降低了强酸强度并减少强酸量,提高L酸比例。氧化锌和与骨架有强相互作用的锌均能提高芳烃选择性,浸渍改性的锌负载量(w)超过3.0%时会导致催化剂快速积炭失活。机械混合法所得分子筛的B酸和锌活性中心的协同作用最好,平均芳烃选择性达到44.39%,使用寿命为216 h。

ZnO/HZSM-5催化剂上甲醇制芳烃(MTA):ZnO负载量和压力的影响

制备Zn负载的HZSM-5催化剂并将其应用于甲醇制芳烃反应,研究了Zn负载量及反应压力对催化剂活性及稳定性的影响。实验结果表明,Zn改变了HZSM-5催化剂的酸性位点分布,可显著增强其芳构化性能并抑制低碳烃类生成,提高新鲜催化剂的初始芳烃产率。适当提高反应压力,可延缓芳烃产率下降,延长催化剂寿命。反应压力为0.5MPa时,在1%Zn/HZ催化剂上得到了最优的甲醇制芳烃反应催化性能,初始芳烃产率达到58.6%,催化剂寿命达到48h。

甲醇制芳烃(MTA)反应动力学的研究

在消除内、外扩散对反应过程的影响下,研究了甲醇制芳烃的反应动力学,采用基团集总的方法,按照MDOH、C1烃、烯烃、烷烃、芳烃等5个集总建立了动力学模型,并通过试验进行验证,模型的计算值与实验值偏差很小,说明建立的模型是真实可靠的,为该技术的工业应用提供了技术基础。

Coking kinetics and influence of reaction-regeneration on acidity, activity and deactivation of Zn/HZSM-5 catalyst during methanol aromatization

The coking kinetics and reaction-regeneration on Zn/HZSM-5 （Zn/HZ） catalyst in the conversion of methanol to aromatics were investigated. The highest initial benzene, toluene and xylene （BTX） yield of ca. 67.7% was obtained on fresh Zn/HZ catalyst, which showed the worst catalytic stability. The cycle of reaction-regeneration significantly modified the texture and acidity of Zn/HZ catalyst, which in turn affected its catalytic performance and coking behavior in methanol conversion to BTX. The residual carbon located on the surface of Zn/HZ catalyst led to the decrease of acid sites and the change on the acid sites distribution, which played an important roles on its activity and deactivation. It was found that the high B/L ratio and the low total acid sites concentration of the Zn/HZ catalyst favored to the high BTX yield and good catalytic stability in methanol conversion.

Promoted effect of zinc–nickel bimetallic oxides supported on HZSM-5 catalysts in aromatization of methanol

Zn/ZSM-5（NZ2） and Zn/Ni/ZSM-5（NZ3） as the catalysts for methanol to aromatics（MTA） were synthesized by a simple ultrasonic impregnation. The textural and acid properties of all catalysts were characterized using XRD, HRTEM, NH;-TPD, Py-IR, XPS, XRF and TG techniques. The XRD and HRTEM results showed that the basic zeolite structures were not affected much with the incorporation of Zn and Ni species. However, great changes have taken place in acid properties. The Py-IR and XPS results indicated that the Zn-Lewis acid sites（ZnOH;species）, which have stronger interaction with the zeolite framework compared with ZnO species, were generated at the expense of B acid sites with the incorporation of zinc species. Moreover, the product analysis results showed that the incorporation of zinc species promoted the primary aromatization by enhancing the dehydroaromatization and suppressing the cracking and subsequent H-transfer reaction. Furthermore, the addition of Ni species well inhibited the loss of zinc species by converting partial ZnO species to ZnOH;species, and thus improved the aromatization activity and catalyst stability. The catalytic performance results showed that the NZ3 possess higher conversion of methanol in a longer time and lower average rate of coke formation compared with NZ2. In addition,the NZ3 also exhibited the highest yield of BTX as the reaction proceeds.

Aromatization of Methanol over La/Zn/HZSM-5 Catalysts

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.

Enhancement of catalytic and anti-carbon deposition performance of SAPO-34/ZSM-5/quartz films in MTA reaction by Si/Al ratio regulation

In order to further improve the catalytic performance of zeolite catalyst for methanol to aromatics(MTA)technology, the double-tier SAPO-34/ZSM-5/quartz composite zeolite films were successfully synthesized via hydrothermal crystallization. The Si/Al ratio of SAPO-34 film was used as the only variable to study this material. The composite zeolite material with 0.6Si/Al ratio of SAPO-34 has the largest mesoporous specific surface area and the most suitable acid distribution. The catalytic performance for the MTA process showed that 0.6-SAPO-34/ZSM-5/quartz film has as high as 50.3% benzene-toluenexylene selectivity and 670 min lifetime. The MTA reaction is carried out through the path we designed to effectively avoid the hydrocarbon pool circulation of ZSM-5 zeolite, so as to improve the aromatics selectivity and inhibit the occurrence of deep side reactions to a great extent. The coke deposition behavior was monitored by thermogravimetric analysis and gas chromatograph/mass spectrometer, it is found that with the increase of Si/Al ratio, the active intermediates changed from low-substituted methylbenzene to high-substituted methylbenzene, which led to the rapid deactivation of the catalyst. This work provides a possibility to employ the synergy effect of composite zeolite film synthesizing anti-carbon deposition catalyst in MTA reaction.

甲醇制芳烃(MTA)催化剂再生动力学的研究

采用热重分析对甲醇制芳烃结焦失活的ZSM-5分子筛催化剂进行再生动力学的研究,实验考察了再生温度、氧分压和不同再生气体流量对再生效果的影响,计算得到积炭质量分数为18.7%的催化剂的再生动力学参数,回归得到ZSM-5分子筛催化剂的再生动力学模型。结果表明:适宜的再生烧炭温度在550℃左右,氧分压在14.89k Pa,再生气的流量100m L/min。并用不同的试验数据验证模型,表明动力学模型是可靠的。

甲醇制MTG技改石脑油制MTA装置工艺浅见

介绍了一起石脑油制MTA装置,其主要特点是:生产流程短、产品收率较高,此工艺主要是针对国际原油价格大幅下降,甲醇制MTG装置出现亏损,尤其当甲醇市场价格上涨,更是让这些装置长期处于停产状态。2017年全年开工率不足30%。目前国内甲醇制MTG、甲醇制MTA装置有近20套之多,其运行情况不尽相同。

二氧化碳催化转化生产化学品相关技术进展

CO_(2)直接生产烃类、醇类和酯类等化学品是CO_(2)减排及利用的有效措施。由于CO_(2)直接生产烃类、醇类化合物的过程中生成水,原子利用率低,氢气未被有效利用。通过CO_(2)在催化剂作用下直接生产甲醇和多元醇类化合物,在获取廉价“绿氢”的情况下才具有经济效益和环保效益;利用太阳能、风能等新能源来生产“绿氢”,并通过技术进步有效降低“绿氢”生产成本,在高效催化剂作用下将CO_(2)直接转化为烯烃和芳烃,才能实现CO_(2)加氢制低碳烯烃、轻质芳烃等烃类物质的真正突破。CO_(2)直接生产酯类化合物原子利用率最高,反应条件缓和,是典型的绿色化工过程,具有良好的工业应用前景。

Recent progress in the deactivation mechanism of zeolite catalysts in methanol to olefins

Methanol to olefins(MTO)as an important reaction in C1 chemistry can effectively transform non-petroleum carbon resources into value-added chemicals.Zeolites have been widely used as MTO catalysts.However,they usually suffer from a rapid deactivation due to bulky coke species production,and thus require continuous regenerations in industrial application.The key to design and develop highly stable zeolite catalysts for MTO process is to unravel the deactivation mechanism and clarify the structure–performance relationship of catalysts.Here,in this mini-review,we investigate the critical intermediate species inducing zeolite deactivation and analyze the formation and evolution pathways of polycyclic aromatic hydrocarbons(PAHs)that are the precursors of carbonaceous deposits.In addition,some methods to alleviate the coking mainly including acid regulation,morphology modification and process optimization,are also summarized.

Co-conversion of methanol and n-hexane into aromatics using intergrown ZSM-5/ZSM-11 as a catalyst

The conversion of n-hexane and methanol into value-added aromatic compounds is a promising method for their industrially relevant utilization.In this study,intergrown ZSM-5/ZSM-11 crystals were synthesized and their resulting catalytic performance was investigated and compared to those of the isolated ZSM-5 and ZSM-1I zeolites.The physicochemical properties of ZSM-5/ZSM-l1 intergrown zeolite were analyzed using X-ray diffrac-tion,N2 isothermal adsorption-desorption,the tempera-ture-programmed desorption of ammonium,scanning clectron microscopy,Fourier transform infrared spectra of adsorbed pyridine,and nuclear magnetic resonance of 27AI,and compared with those of the ZSM-5 and ZSM-11 zeolites.The catalytic performances of the materials were evaluated during the co-feeding reaction of methanol and n-hexane under the fixed bed conditions of 400℃,0.5 MPa(N2),methanol:n-hexane=7:3(mass ratio),and weight hourly space velocity=1 h 1(methanol).Com-pared to the ZSM-5 and ZSM-11 zeolites,the ZSM-5/ZSM-11 zeolite exhibited the largest specific surface area,a unique crystal structure,moderate acidity,and suitable Brensted/Lewis acid ratio.The evaluation results showed that ZSM-5/ZSM-11 catalyst exhibited better catalytic reactivity than the ZSM-5 and ZSM-11 catalysts in terms of methanol conversion rate,n-hexane conversion rate,and aromatic selectivity.The outstanding catalytic property of the intergrown ZSM-5/ZSM-11 was attributed to the enhanced diffusion associated with its unique crystal.structure.The benefit of using zeolite intergrowth in the co-conversion of methanol and alkanes offers a novel route for future catalyst development.