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.     

Comparison of Activity and Selectivity of SSZ-33 Based Catalyst with other Zeolites in Toluene Disproportionation

SSZ-33 based-catalyst, after modification with Mo and alumina binder, was evaluated in long-run tests in the toluene disproportionation in the presence of hydrogen as a carrier gas. The activity and selectivity of this catalyst were compared with those of ZSM-5 and mesoporous ZSM-5 prepared with the same concentration of Mo and alumina. Formation of the final catalysts decreased the void volume of micropores in order SSZ-33 > ZSM-5 > ZSM-5/Meso. Simultaneously, the concentration of Lewis acid sites increased due to the addition of alumina to the catalyst. The highest toluene conversion was achieved with SSZ-33 catalyst comprising 12-12-10-ring channels, which is the result of high acidity of this zeolite together with increased mass transport through large pores. ZSM-5 zeolite exhibited lower toluene conversion while only a low activity was found for mesoporous ZSM-5 probably due to the limitations of the access to the zeolite channels after modification with alumina.     

Aromatic Transformations Over Mesoporous ZSM-5: Advantages and Disadvantages

Catalytic behavior of mesoporous ZSM-5 was investigated in toluene disproportionation, toluene alkylation with isopropyl alcohol, and p-xylene alkylation with isopropyl alcohol to understand the effect of the presence of mesopores. Three ZSM-5 zeolites (conventional one and two mesoporous differing in the mesopore volume) having similar Si/Al ratio were synthesized and characterized as for their acidity (internal and external) as well as their micropore/mesopore volume. No substantial differences among three samples were observed as for the type and concentration of Brønsted and Lewis acid sites as well as their location in zeolite channels or on external surface of zeolite crystals. Conversions of toluene and p-xylene increased with increasing volume of mesopores in ZSM-5 zeolite while the selectivity to individual products depended on the type of reaction. In general, selectivity to sum of xylenes in toluene disproportionation, sum of isopropyltoluenes in toluene alkylation and to 1-isopropyl-2,5-dimethylbenzene in p-xylene alkylation increased due to a shorter contact time molecules spent in mesoporous ZSM-5 catalysts. In contrast, para-selectivity decreased as diffusion pathways were shorten due to the presence of mesopores.     

Post-Synthesis Modification of SSZ-35 Zeolite to Enhance the Selectivity in p-Xylene Alkylation with Isopropyl Alcohol

Modification of textural and chemical properties of SSZ-35 was investigated in respect to the catalytic behavior of this zeolite in p-xylene alkylation with isopropyl alcohol. Acidic treatment of the external surface of SSZ-35 crystals resulted in a decrease in the void volume of the zeolite and in the concentration of acid sites mainly located on the external surface. This was evidenced from the FTIR spectra of adsorbed pyridine and 2,6-di-tert-butylpyridine. The modification caused a significant increase in the selectivity to 2,5-dimethylcumene while the p-xylene conversion decreased only very slightly.     

Adsorption of CO<Subscript>2</Subscript> and CO on H-zeolites with different framework topologies and chemical compositions and a correlation to probing protonic sites using NH<Subscript>3</Subscript> adsorption

Adsorption of CO₂ and CO at 25 °C has been conducted using commercially-available (Y, ZSM-5) and laboratory-synthesized (SSZ-13, SAPO-34) H-zeolites with different framework topologies and chemical compositions, and their textual and surface properties have been characterized by N₂ sorption and NH₃ adsorption techniques. All the zeolites were microporous, although ZSM-5 and SSZ-13 apparently showed a mesoporous sorption behavior due to the interparticle spaces. The zeolites had Si/Al values in the order of SSZ-13 (16.44) > ZSM-5 (16.08) ? Y (2.82) ? SAPO-34 (0.19). Regardless, high CO₂ adsorption capacity was obtained for SSZ-13 and SAPO-34 with a CHA framework. The FAU zeolite Y with the highest micropore volume showed less CO₂ adsorption than the CHA zeolites and the MFI-type ZSM-5 yielded the poorest performance. Probing acid sites in the H-form zeolites using NH₃ disclosed that these all contain both weak and strong acid sites with significant dependence of their strengths and amounts on the topology. The acid strength of the weak acid sites in the CHA zeolites was the weakest, which might allow a stronger interaction with CO₂. The H-zeolites gave CO₂/CO selectivity factors that were in the range of 4.61–11.0, depending on the framework topology.     

Adsorption of Carbon Dioxide on High-Silica Zeolites with Different Framework Topology

Adsorption isotherms of carbon dioxide were measured on six high-silica zeolites TNU-9, IM-5, SSZ-74, ferrierite, ZSM-5 and ZSM-11 comprising three-dimensional 10-ring (8-ring for ferrierite) at 273, 293, 313 and 333 K. Based on the known temperature dependence of CO₂ adsorption, isosteric heats of adsorption were calculated. The obtained adsorption capacities and isosteric adsorption heats related to the amount of CO₂ adsorbed have provided detailed insight into the carbon dioxide interaction with zeolites of different framework topology. The zeolites TNU-9 and ferrierite are characterized by pronounced energetic heterogeneity whereas due to the location of Na⁺ cations in the same positions the isosteric adsorption heats of CO₂ adsorption on IM-5, ZSM-5 and ZSM-11 zeolites are rather constant for molecular ratio CO₂/Na⁺ < 1. As IM-5 zeolite has a maximum adsorption capacity, it appears to have optimum properties for carbon dioxide separation.     

Hydroisomerization and cracking of n-octane and C8 isomers on Ni-containing zeolites

The hydrocracking and hydroisomerization of n-octane, 2,5-dimethylhexane and 2,2,4-trimethylpentane on Ni-containing ZSM-5, mordenite and beta catalysts was investigated at 20 bar hydrogen pressure and a temperature of 533 K. The activity decreased in the sequence ZSM-5≫BETA≈MOR for the n-octane conversion and increased in this sequence for the conversion of 2,5-dimethylhexane and 2,2,4-trimethylpentane. The selectivity for isomerization of n-octane and 2,5-dimethylhexane was the highest on NiHBETA and the lowest on NiHZSM-5. The trends in the activity and selectivity were explained by the accessibility of the acid sites, estimated by adsorption of probe molecules followed by IR spectroscopy, and by a simulation of the space available in the pores of these zeolites.     

ZSM-22分子筛催化甲苯甲醇烷基化反应的研究

通过浸渍法对ZSM-22分子筛进行SiO₂和La₂O₃改性,制备了一系列催化剂。采用固定床微型连续流反应器对催化剂的反应性能进行了评价。考察了ZSM-22、SiO₂和La₂O₃改性ZSM-22对甲苯甲醇烷基化反应性能的影响。实验发现,ZSM-22催化甲苯甲醇烷基化反应的产物中,对二甲苯的选择性远高于间位和邻位异构体的选择性,而改性后的催化剂上目标产物对二甲苯的选择性得到提高,但反应活性下降。随SiO₂和La₂O₃负载量的增加,甲苯的转化率逐渐降低,对二甲苯选择性逐渐提高,其中,以La₂O₃改性后对二甲苯选择性提高较明显。SiO₂和La₂O₃复合改性后,甲苯的转化率高于La₂O₃单独改性的结果,而对二甲苯选择性与La₂O₃单独改性结果相近,并且,二甲苯的选择性略有提高。     

Facile synthesis of HZSM-5 with controlled crystal morphology and size as efficient catalysts for chlorinated hydrocarbons oxidation and xylene isomerization

ZSM-5 zeolites with controllable crystal morphologies (microsphere self-assembled from nanorod crystals, round-boat and cross shape) were synthesized in extremely diluted solutions (H₂O/SiO₂ = 350) by only adjusting the tetrapropylammonium hydroxide concentration under dynamic or static condition. The synthesized ZSM-5 were characterized by X-ray diffraction, infrared spectra, scanning electron microscopy, transmission electron microscopy, N₂ sorption and NH₃ temperature programmed desorption, and compared with the commercial ZSM-5 zeolite. Catalytic tests for the formation of p-xylene from o-xylene isomerization and the catalytic oxidation of chlorinated hydrocarbons showed that ZSM-5 microsphere composed of nanorod crystals exhibited both high conversion and improved p-xylene selectivity, and high catalytic activities for 1,2-dichloroethane and chlorobenzene oxidation and low selectivity to chlorinated by-products, which were attributed to the existence of nanosized ZSM-5 crystals and mesopores, high internal surface area and total acidity.     

磷改性ZSM-5沸石的催化裂化性能

用磷改性ZSM-5沸石,并将其制备成催化剂。初步考察了其物化性能的变化,并在固定床重油微反装置上考察了其催化裂化反应特性。研究发现,磷能显著改善ZSM-5沸石的活性、稳定性和选择性。ZSM-5沸石上不同的磷含量和其与不同的Y型分子筛配伍对催化裂化反应有着显著的影响。合理调配催化裂化催化剂的活性组分,适当控制其氢转移能力和烷基化能力,对增产丙烯有着积极的意义。     

Industrial Application of Shape-Selective Catalysis

In the 26 years since the term “shape-selective catalysis” was coined by P. B. Weisz and V. J. Frilette [1] to describe the unique catalytic properties of small pore molecular sieve zeolites, great strides in the use of shape-selective zeolites have been made, both scientifically and technologically. Since then, in addition to small pore zeolites, synthetic medium pore zeolites, such as ZSM-5 [2], ZSM-11 [3], ZSM-22 [4], ZSM-23 [5], ZSM-35 [6], ZSM-38 [7], ZSM-48 [8], etc., have been discovered. The availability of these synthetic medium pore zeolites has expanded the realm of “shape selectivity” beyond the original discovery of selective conversion of straight chain molecules to include certain branched molecules, single-ring aromatics, naphthenes, and nonhydrocarbons with a critical molecular dimension smaller than about 6 Å.     

Side-chain alkylation of 2,6-lutidine to 2,6-divinylpyridine over basic zeolites

Synthesis of 2,6-divinylpyridine (2,6-DVP) and 2-methyl-6-vinylpyridine (2M6VP) was achieved for the first time by side-chain alkylation of 2,6-lutidine using formaldehyde (37 wt/v) as alkylating agent in heterogeneous conditions at atmospheric pressure, and at a reaction temperature of 300 °C over alkali and alkaline metal ion modified zeolites. A mixture of 2,6-divinylpyridine and 2-methyl,6-vinylpyridine were formed by the alkylation of the 2,6-lutidine over Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba metal ion modified zeolites. The catalytic activity of 2,6-lutidine was studied over various potassium metal ion modified zeolite molecular sieves like ZSM-5 (30), X, Y, mordenite and MCM-41. Alkali modified ZSM-5 (30) catalyst was found more active in side-chain alkylation of 2,6-lutidine when compared to other zeolites. Among all these catalysts studied K modified ZSM-5 (30) gave best conversion of 2,6-lutidine and selectivity to 2-methyl,6-vinylpyridine. K-ZSM-5 (30) catalyst was employed to study the reaction parameters like reaction temperature, weight hourly space velocity, molar ratio, and time on stream for 2,6-lutidine. The effect of potassium metal ion content and precursors of potassium ion on catalytic activity in side-chain alkylation of 2,6-lutidine was studied. The bifunctional catalyst is required containing medium or weak acidic centers and basic centers in the side-chain alkylation, which is understood through proposed mechanism. The selectivities of 2,6-DVP were 45.2, 40.0, and 30.7% at 73.4, 66.0 and 60.5% conversion at 300 °C from 2,6-lutidine and formaldehyde over K-ZSM-5 (30), Rb-ZSM-5 (30) and Cs-K-ZSM-5 (30), respectively.     

甲苯甲醇烷基化制对二甲苯催化剂中试反应性能研究

经过多步改性制备了负载二氧化硅（SiO₂）、氧化镁（MgO）、五氧化二磷（P₂O₅）、贵金属铂（Pt）的纳米ZSM-5分子筛催化剂,并在六段固定床反应器上分段装填该催化剂720 g进行甲苯、甲醇烷基化制对二甲苯反应活性评价。实验结果表明,通过调变甲醇和甲苯物质的量比可以使甲苯转化率在22%~30%可调,烷基化液相产物中二甲苯选择性保持在95%以上,二甲苯中对二甲苯选择性保持在95%以上;催化剂单程寿命达到1 300 h,随着反应时间延长催化剂的活性有所下降。通过X射线衍射（XRD）、热重分析（TG-DTG）和氮气吸附-脱附等手段对参加反应前后的催化剂进行了表征,结果表明反应中生成的积炭堵塞了分子筛的孔道或覆盖了催化剂的活性位;经过在反应器内原位再生,催化剂的反应活性基本恢复到新鲜催化剂水平。     

甲苯甲醇烷基化合成对二甲苯催化剂研究进展

甲苯甲醇烷基化是新型高选择性合成对二甲苯的方法,可以解决石化行业甲苯和甲醇过剩问题,具有较高的工业开发价值。在具有B酸中心及特殊孔结构的分子筛催化下,甲苯甲醇发生苯环上亲电取代反应得到对二甲苯。甲苯甲醇烷基化催化剂主要有Y沸石催化剂、SAPO及MCM-22和ZSM-5分子筛催化剂等,研究较多的是ZSM-5分子筛催化剂。通过对ZSM-5分子筛进行金属、非金属或复合改性后,可以显著提高烷基化反应转化率和选择性。未来研究的主要目标是获得选择性高且稳定性好的催化剂。     

Side chain alkylation of 2-picoline with formaldehyde over alkali modified zeolites

The catalytic side-chain alkylation of 2-picoline with formaldehyde (37 wt/v) was studied over alkali and alkaline earth metal ion modified zeolites in vapor phase conditions at atmospheric pressure, and at a reaction temperature of 300°C. A mixture of vinylpyridine and ethylpyridine were formed by the alkylation of the corresponding picoline over Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba metal ion modified zeolites. The catalytic activity of side-chain alkylation of 2-picoline was studied over various alkali modified zeolite molecular sieves like ZSM-5 (SiO₂/Al₂O₃ = 30), X, Y, Mordenite and MCM-41. Alkali modified ZSM-5 (30) catalyst was found more active in side-chain alkylation of 2-picoline when compared to other zeolites. Among all these catalysts studied K modified ZSM-5 (30) and K-Cs-ZSM-5 (30) gave best conversion of 2-picoline and selectivity to vinylpyridine. Cs-ZSM-5 (30) and K-ZSM-5 (30) were employed to study the reaction parameters like reaction temperature, weight hourly space velocity, molar ratio, and time on stream for 2-picoline independently. The effects of alkali metal ion content (K, Cs) and precursors of potassium ion on catalytic activity in side-chain alkylation was studied. An attempt has been made to correlate between the basicity with the activity of side-chain alkylation. The bifunctional catalyst is required containing medium or weak acidic centers and basic centers in the side-chain alkylation, which is understood through proposed reaction mechanism. The selectivities of 2-vinylpyridine were 81.7, 90.8, and 94.8% at 65.4, 62.1 and 57.2% conversions at 300°C from 2-picoline and formaldehyde over K-ZSM-5 (30), Rb-ZSM-5 (30) and K-Cs-ZSM-5 (30) respectively. Indian Institute of Chemical technology (IICT) communication no: 020707     

Methanol-to-Olefins Reaction over Large-Pore Zeolites: Impact of Pore Structure on Catalytic Performance

In the methanol-to-olefins (MTO) reaction, product flexibility is important for meeting the fluctuating chemicals demands. In this paper, the catalytic performance of recently reported zeolites having 12-ring pores, such as boroaluminosilicate CON-type zeolite ([Al,B]-CON), MCM-68, and YNU-5 zeolites, in the MTO reaction was compared to understand the relationship between zeolite framework and product selectivity. The catalytic performance of the synthesized zeolites was compared with that of Beta, mordenite, and ZSM-5. The highest selectivities for propylene and butylenes were achieved over MCM-68. The highest propylene-to-ethylene ratio in the products was obtained over [Al,B]-CON. ZSM-5 and [Al,B]-CON exhibited a superior ability to suppress coke formation compared to Beta, mordenite, MCM-68, and YNU-5.     

Isomerization and disproportionation of m-xylene : Selectivities Induced by the Void Structure of the Zeolite Framework

The conversion of m-xylene was performed on acid zeolites with ten- or twelve-membered rings, such as ZSM-5, ZSM-12, ZSM-48, OFF, MOR, FAU, Ω, β and L. All of these zeolites have distinctly different crystallographic structures with different shapes and dimensions of the intracrystalline cavities. This diversity of pore structures allowed to determine to what extent the pore shape and dimensions influence the selectivity of the reaction of m-xylene. The p/o selectivity in the isomerization of m-xylene is always high for ten-membered ring zeolites with crystals bigger than 1 μm. The moderate selectivity for p-xylene formation in some zeolites with twelve-membered rings is due to transition-state shape selectivity. The selectivity for disproportionation versus isomerization is very low for ten-membered ring zeolites and allows them to be distinguished easily from the twelve-membered ring zeolites, which show much more disproportionation. In the group of twelve-membered ring zeolites the disproportionation/isomerization selectivity does not correlate at all with the effective size of the intracrystalline cavities. The disproportionation/ isomerization selectivity is determined by the strong isolated acid sites which are present in cavities that allow the formation of at least one of the possible bimolecular transition-state complexes for disproportionation. The distribution of the trimethylbenzene isomers reflects important features of the shape of the pores, the presence and the position of larger spaces in lobes, cages or intersections adjacent to the twelve-membered ring channels of large pore zeolites.     

改性介微孔ZSM-5分子筛催化剂制备及催化甲苯甲醇烷基化反应性能

将微孔ZSM-5分子筛通过不同浓度的氢氧化钠溶液处理不同的时间制备不同的介微孔ZSM-5分子筛,然后负载五氧化二磷制备介微孔ZSM-5分子筛催化剂,对介微孔ZSM-5分子筛负载五氧化二磷催化剂进行甲苯甲醇烷基化反应评价。其中氢氧化钠溶液浓度为1.0 mol/L、处理时间为30 min得到的介微孔ZSM-5分子筛负载五氧化二磷催化剂催化甲苯甲醇烷基化反应的活性较高。对介微孔ZSM-5分子筛负载五氧化二磷催化剂进一步采用铂进行改性,将制备的催化剂用于甲苯甲醇烷基化反应,在460 ℃条件下连续反应505 h,甲苯转化率保持在10.9%,二甲苯中对二甲苯的选择性保持在96%以上。研究结果表明,五氧化二磷、铂改性的介微孔ZSM-5分子筛催化剂具有优异的甲苯甲醇烷基化反应性能。     

模板剂对ZSM-5分子筛甲醛环化制三聚甲醛性能的影响

以四丙基氢氧化铵、四丙基溴化铵、正丁胺和季戊四醇为模板剂水热合成ZSM-5分子筛,采用XRF、XRD、SEM、NH₃-TPD、Py-FTIR和²⁷Al MAS NMR等进行了表征,研究了模板剂对ZSM-5分子筛性质及甲醛制三聚甲醛催化性能的影响。结果表明,通过改变模板剂可改变ZSM-5分子筛的酸中心分布、表面酸性质和粒径;较大空间的孔道交叉位置的酸性中心、小催化剂粒径和高表面B酸/L酸比值有利于提高三聚甲醛选择性。以四丙基氢氧化铵为模板剂合成的ZSM-5分子筛的颗粒尺寸为240nm×240nm×150nm,分布于直形孔道和S形孔道的孔道交叉处的Br?nsted酸中心较多,甲醛转化率和三聚甲醛的选择性分别为30.15%和88.35%。     

Dual-template synthesis of HZSM-5 zeolites with tailored activity in toluene methylation with CH_3Br

Shape-selective zeolites(UZ-x/y) were synthesized by a one-pot method using TPAOH(y) and/or MeEt_3 N+I~-(x) as templates.The use of MeEt_3 N~+I~-affects the crystal growth and the distribution of acid sites on the external surface of the zeolites.The catalysts show excellent catalytic activity towards toluene alkylation with CH_3 Br.With toluene conversion of 36.3% and p-xylene selectivity of 66.2%,HZ-40/0 is the most effective among the prepared catalysts,showing a p-xylene yield of 21.2%.The improved para-selectivity is mainly due to the decrease of acid sites on the external surface of the catalysts.