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.     

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%。     

柠檬酸处理对FCC干气与苯烷基化催化剂的影响

采用ZSM-5/ZSM-11共结晶分子筛催化剂，在固定床反应装置上对催化裂化干气与苯制乙苯进行考察。 NH₃-TPD结果表明，随着水热处理条件的苛刻, 催化剂的酸量和酸强度均下降, 虽然这些催化剂上干气中乙烯转化率变化不明显, 但产物中二甲苯含量大幅度下降。 柠檬酸对分子筛催化剂进行改性处理后, 可明显降低催化裂化干气与苯制乙苯中二甲苯杂质含量, 原因可能为催化剂大的比表面积和孔容改善了原料的传质能力, 从而抑制了二甲苯的生成。     

过渡金属改性对MgO/ZSM-5催化剂苯-甲醇烷基化性能的影响

采用过渡金属对2.5%Mg O/ZSM-5催化剂进行负载改性,考察其苯-甲醇烷基化性能,结果表明,Ni和Fe改性催化剂因改性后弱酸量大幅增加,苯转化率提高,分别为56.6%和55.8%;W和Mn改性催化剂二甲苯选择性较高,约为35%;与其他改性催化剂相比,Co和Mo改性催化剂上的苯转化率和二甲苯选择性没有明显优势。选择改性效果较好的双金属催化剂进行苯-甲醇烷基化高空速(15 h-1)长时间运转实验,催化剂初始活性均大于57%,反应20 h时,苯转化率约50%,20 h后烷基化活性迅速下降,是由于催化剂积炭失活所致。     

Production of Xylenes from Toluene and 1,2,4‐Trimethylbenzene over ZSM‐5 and Mordenite Catalysts in a Fluidized‐Bed Reactor

The production of various xylenes from toluene, heavy aromatics such as 1,2,4‐trimethylbenzene (1,2,4‐TMB) and their mixture was investigated over H‐ZSM‐5 (H‐Z), H‐mordenite (H‐M) and a dual zeolitic catalyst comprising ZSM‐5 and mordenite (H‐ZM). The experiments were conducted in a riser‐simulator reactor under different operating conditions to study the effect of temperature, reaction time and feed composition on conversion and product yields. At 400 °C, the conversion of toluene over the three catalysts yielded mainly benzene and xylenes with maximum conversion at 25 % and a xylene yield of 12.5 wt % over the H‐M catalyst. The transformation of 1,2,4‐TMB doubled the conversion level and xylene yield and suppressed benzene formation. However, a considerable portion of the 1,2,4‐TMB feed was isomerized into 1,2,3‐TMB and 1,3,5‐TMB accompanied by the formation of tetramethylbenzenes (TeMBs). The conversion of an equimolar mixture of toluene and 1,2,4‐TMB over the three catalysts resulted in higher toluene conversion and double xylene yield in comparison with 1,2,4‐TMB alone. The advantage of using a dual zeolitic catalyst was observed at an equimolar feed of toluene and 1,2,4‐TMB, exhibiting maximum toluene conversion, higher xylene yield and the formation of lower levels of undesirable products.     

Ce0.75Cu0.25-xO2固溶体催化剂用于PVOCs催化燃烧

通过柠檬酸络合法制得Ce_0.75Cu0._25-xO₂固溶体催化剂，采用X射线衍射、X射线光电子能谱和H2-程序升温还原对催化剂性能进行研究，考察催化剂对苯基挥发性有机物的催化燃烧活性。结果表明，催化剂中大量CuO溶入CeO2晶格中形成Ce_0.75Cu0._25-xO₂固溶体，固溶体的形成削弱了催化剂中的Cu-O和Ce-O键，提高了相应氧化物的低温可还原性，也提高了催化剂表面活性氧物种含量，从而提高了催化剂上苯基挥发性有机物的催化燃烧活性。在反应温度250 ℃和275 ℃时，Ce_0.75Cu0._25-xO₂固溶体催化剂上甲苯和二甲苯的催化燃烧转化率分别为97.6%和95.0%。Ce_0.75Cu0._25-xO₂催化剂上苯在280 ℃时催化燃烧转化率仅为61.0%，这可归因于苯分子稳定的芳香环结构不易被破坏。     

USY分子筛上苯与多仲丁苯烷基转移反应

在微型固定床反应器上研究USY分子筛对苯与多仲丁苯烷基转移反应的催化性能,考察反应温度、原料配比和空速等工艺条件对反应的影响。采用NH₃-TPD、吡啶IR吸附和N2吸附-脱附等手段对USY分子筛酸性质和孔结构进行表征。结果表明,USY分子筛在烷基转移反应中具有较好的催化性能,二仲丁苯转化率为87.7%,三仲丁苯转化率为19.3%,仲丁苯选择性为91.38%,与USY分子筛的多级孔道和较多B酸位有关。多仲丁苯转化率和仲丁苯选择性随反应温度的提高而增大,原料中苯的增加可提高仲丁苯选择性,空速对二仲丁苯转化率影响较小,但对仲丁苯选择性和三仲丁苯转化率影响显著。USY分子筛上反应较适宜的工艺条件为：反应温度240 ℃,反应压力3 MPa,苯与二仲丁苯物质的量比16,二仲丁苯空速1.4 h^-1。     

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.     

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.     

丝光沸石分子筛催化剂上C_9芳烃脱烷基的研究

将Bi、Ni、Mo、Pt负载在氢型丝光沸石(H/MOR)分子筛上,以异丙苯为模型化合物对分子筛催化剂加氢脱烷基性能进行了评价,考察了不同金属的活性和分子筛催化剂的稳定性。采用Pt/MOR分子筛催化剂时,催化剂的稳定性以及模型化合物的转化率和苯、甲苯、二甲苯(BTX)的产率有显著提高。当反应温度为420℃,压力为0.8MPa,空速为1h-1时,其转化率最高可达89.8%,BTX的产率可高达82.8%。分子筛酸性分布与金属之间的平衡对催化剂的活性至关重要。当w(Pt)=0.5%,总酸为0.825mmol/g时,酸与金属间的平衡协同作用对催化剂的活性和稳定性有明显促进作用。     

Benzene Alkylation with 1-Dodecene over H-Mordenite Zeolite

The alkylation of benzene with 1-dodecene was studied over solid-acid zeolites, such as H-mordenite, H-USY, HY, and H-ZSM-5, in a batch reactor at 140°C and 10 atm. H-mordenite showed the highest selectivity of 78.2% for 2-phenyldodecane with 100% conversion. Depending on the catalyst amount (from 0.5 to 1.0 g) and the molar ratio of benzene to 1-dodecene (from 7 to 10), the conversion of 1-dodecene varied in the range from 63.8 to 100%. Furthermore, modification of H-mordenite by dealumination using nitric acid and by solid ion exchange with Mg²⁺ and Fe³⁺ ions led to the improvement of the selectivity for 2-phenyldodecane, and simultaneously reduction of the conversion of 1-dodecene is observed. In addition, it was found by pyridine adsorption FT-IR study that both strong Brønsted and Lewis acid sites are closely related to the conversion.     

Catalytic Activity of Copper Oxide Impregnated HZSM‐5 in Methanol Conversion to Liquid Hydrocarbons

A number of CuO/HZSM‐5 catalysts have been studied in a small scale fixed bed reactor for the conversion of methanol to gasoline range hydrocarbons at 673 K and at one atmospheric pressure. All the catalysts were prepared by wet impregnation technique. The copper oxide loading over HZSM‐5 (Si/Al=45) catalyst was studied in the range of 0 to 9 wt%. XRD, surface area analyzer, metal trace analyzer, SEM techniques and TGA were used to characterize the catalysts. Incorporation of CuO onto HZSM‐5 zeolite significantly increased conversion and liquid hydrocarbon product yields. The major liquid products of the reactions were ethyl benzene, toluene, xylene, isopropyl benzene, ethyl toluene, trimethyl benzene and tetramethyl benzene. The maximum methanol conversion and hydrocarbon product yield was obtained at a copper oxide loading of 7 wt%. Effect of run time on conversion and product distribution was also investigated to compare the performance of these catalysts and coke on the catalyst was determined. Effect of space‐time and temperature on methanol conversion and products yield with 7 wt% CuO/HZSM‐5 has also been investigated and analyzed qualitatively.     

稳定焦化二甲苯产品质量的措施

通过对焦化二甲苯组成的分析,找出了乙基苯和苯乙烯是二甲苯变色的主要有害杂质。试验结果表明：加酸量应控制在4.5%～5.0%,最佳洗涤温度为45～50℃,酸洗时间宜控制在7min以上。还可采用在产品中加入抗氧化剂、进行二次处理和水洗等措施稳定二甲苯产品质量。     

Disproportionation and Methylation of Toluene with Methanol Over Zeolite Catalysts

Zeolites TNU-9, SSZ-33, mordenite (MOR) and ZSM-5 were evaluated for their activities in toluene disproportionation and methylation reaction of toluene with methanol. The medium-pore zeolite TNU-9 was found to possess the highest conversion in toluene disproportionation as compared with SSZ-33, mordenite and ZSM-5 based catalyst. Zeolite mordenite with the highest Si/Al ratio of 135.9 (the lowest concentration of active sites) exhibited the highest toluene conversion and maximum xylene yield in toluene methylation. On mordenite, the presence of channel intersections allows more reaction space for the formation of bulky intermediates and/or products and the 12-ring channels on the other hand, allow diffusion without trapping, since the channel diameter is large enough. In toluene methylation, xylene selectivity at the same conversion level follows the order: ZSM-5 > TNU-9 > MOR > SSZ-33, which implies that xylene selectivity is directly related to the size of channels from medium to large pore zeolites. The medium-pore zeolite ZSM-5, with 10-ring channels, shows the lowest reactivity for further alkylation of xylene, while mordenite with 12-ring channel shows the highest reactivity for further alkylation of xylene.     

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%。     

Exergy and exergoeconomic analyses for integration of aromatics separation with aromatics upgrading

Methanol to aromatics produces multiple products, resulting in a limited selectivity of xylene. Aromatics upgrading is an effective way to produce more valuable xylene product, and different feed ratios generate discrepant product distributions. This work integrates the aromatics separation with toluene disproportionation, transalkylation of toluene and trimethylbenzene, and isomerization of xylene and trimethylbenzene. Exergy and exergoeconomic analyses are conducted to give insights in the splitting ratios of benzene, toluene and heavy aromatics for aromatics upgrading. First, a detailed simulation model is developed in Aspen HYSYS. Then, 300 splitting ratio sets of benzene and toluene for conversion are studied to investigate the process performances. The results indicate that there are different preferences for the splitting ratios of benzene and toluene in terms of exergy and exergoeconomic performances. The process generates lower total exergy destruction when the splitting ratio of toluene varies between 0.07 and 0.18, and that of benzene fluctuates between 0.55 and 0.6. Nevertheless, the process presents lower total product unit cost with the splitting ratio of toluene less than 0.18 and that of benzene fluctuating between 0.44 and 0.89. Besides, it is found that distillation is the biggest contributor to the total exergy destruction, accounting for 94.97%.     

Benzene,Toluene and p‐xylene Interactions and the Role of Microbial Communities in Remediation Using Bioventing

Aromatic hydrocarbons, particularly benzene, toluene and xylene (BTX), are major contaminants at many hazardous waste sites. We studied volatilization and biodegradation of BTX from unsaturated soil through bioventing. Following inoculation with indigenous soil microorganisms obtained from the Dagang Oil Field in Tianjin, China, varying amounts of BTX were added to soil in a stainless steel column provided with a constant flow of CO₂‐ free air and pure N₂. Volatilization‐to‐biodegradation ratios of benzene, toluene and p‐xylene were 6:1, 2:1 and 2:1 respectively. Final concentrations recorded in soil gas after three weeks were 0.128 mg/L benzene, 0.377 mg/L toluene and 0.143 mg/L p‐xylene. Interactions between the contaminants occurred: benzene and p‐xylene degradation were accelerated while toluene was being degraded, and the presence of p‐xylene increased the lag period for benzene degradation.     

Structure and acidity modification of mordenite through isomorphous Fe substitution

A series of Fe-modified mordenite were hydrothermally synthesized. The effects of substrate composition, aging time, reaction temperature, and reaction time upon the crystallization of the mordenite were investigated. Isomorphous substitution of Fe was confirmed by FT-IR and EPR analysis. Acid strength and acid sites distribution of each catalyst were measured by pyridine TPD, which showed that the number of strong acid sites in H-Fe-mordenite are smaller than in H-Al-mordenite. Structural characteristics and thermal stability were also examined using XRD, SEM and TG. Fe-substitution into the mordenite structure have resulted in substantial decrease in thermal stability. H-Fe-mordenite catalysts showed high selectivity towards p-xylene in toluene alkylation and in xylene isomerization reaction, compared with those obtained using H-Al-mordenite because of lower concentration of strong acid sites. In addition, these H-Fe-modified mordenite showed little hexane cracking activity. Deactivation in both toluene alkylation and xylene isomerization reaction and coke formation over H-Fe-mordenite in these reactions were negligible.     

复合分子筛催化剂上C9芳烃脱烷基的研究

将Ni负载在H-ZSM-5和H-MOR分子筛催化剂上，以异丙苯为模型化合物对分子筛催化剂加氢脱烷基性能进行评价。考察了分子筛复配比例、金属含量和酸浓度对催化剂活性的影响。结果表明，酸处理后的分子筛催化剂，异丙苯转化率和苯、甲苯、二甲苯(BTX)的收率有明显提高。当反应温度为340 ℃、压力0.8 MP和空速1 h^-1时，其转化率为81.5％，BTX收率为72.8％，选择性可达89.2％。     

SEB-08催化剂在干气制乙苯装置的工业应用

中国石油化工股份有限公司广州分公司采用新一代SGEB气相法干气（稀乙烯）制乙苯技术,建成一套年产85 kt干气制乙苯装置。烷基化催化剂使用中国石油化工股份有限公司上海石油化工研究院研制的SEB-08稀乙烯制乙苯催化剂。运行结果表明,SEB-08催化剂可适用不同浓度的稀乙烯原料,具有较强的抗工艺波动能力,原料循环苯中甲苯含量对二甲苯的产生有较大影响,必须严格控制循环苯中甲苯含量;标定结果表明,在反应器入口温度344 ℃、入口压力0.86 MPa、苯与乙烯物质的量比6.71、乙烯质量空速0.297 h^-1和装置反应负荷109%条件下,乙烯转化率为99.73%,乙基选择性为99.65%,二甲苯含量为848×10^-6。SEB-08催化剂具有处理量大、活性高、选择性和稳定性好等优点,有利于提供现有干气制乙苯装置的生产能力。