Co-reaction of Ethene and Methylation Agents over SAPO-34 and ZSM-22

Co-reaction of ethene and different methylation agents (i.e. methanol and chloromethane) was carried out over SAPO-34 and ZSM-22 and the results are compared. It was found that the enhancement of ethene conversion was achieved by co-feeding it with methylation agents. In the ethene–chloromethane system, the methylation of ethene by chloromethane was more prominent compared with that of the co-reaction of ethene and methanol. The reasons for the differences between ethene–methanol and ethene–chloromethane co-reaction system are discussed. Complete suppress of direct conversion of methanol or ethene could be achieved over ZSM-22 by pre-coking, and propene selectivity higher than 80% was obtained at lower conversions.     

Synergistic effects of tungsten and phosphorus on catalytic cracking of butene to propene over HZSM-5

Synergistic catalysis effects among tungsten, phosphorus and HZSM-5 on 1-butene cracking to propene and ethene have been demonstrated by catalytic tests. The tungsten–phosphorus-modified HZSM-5 (W–P/HZSM-5) catalyst, with very low density of acid sites, offers a fairly high conversion rate of butene and selectivity to propene. The status of doped tungsten is characterized by using techniques of D₂/OH exchange, NH₃ adsorption microcalorimetry, FT-IR spectroscopy, Raman spectroscopy, N₂ adsorption and X-ray photoelectron spectroscopy. The tungsten would be monotungstate that interacted with phosphorus before steam treatment and partly congregated to polytungstate species during steaming process at high temperature. The enhanced performance of the catalyst for 1-butene cracking to propene and ethene can be correlated to the synergistic effect between the doped tungsten and phosphorous on the reaction network of the cracking process. The W–P/HZSM-5 is a promising catalyst for the 1-butene cracking to propene and ethene.     

Metathesis of Ethene and Decene to Propene over a WO3/SiO2 Catalyst

Metathesis between decene and ethene to propene over a WO₃/SiO₂ catalyst was studied. The dependency of the conversion of decene, selectivity to propene, and working lifetime of the catalyst on ethane‐to‐decene molar ratio and temperature was evaluated. Low temperature was found to be favorable to the production of C₆–C₉ olefins, while high temperature enhanced C₁₀₊ olefins. The working lifetime of the catalyst decreased with the weight hourly space velocity. The optimum reaction conditions for the metathesis process of decene and ethene to propene were determined. An obvious induction period was found to exist in the metathesis reaction.     

ZSM-5催化剂上的甲醇转化研究

利用固定流化床反应器,考察了甲醇在改性ZSM-5分子筛催化剂上转化过程。实验结果表明:反应温度增加,甲醇转化率上升;乙烯和丙烯碳基选择性随温度增加而增加,且丙烯选择性的增加速率大于乙烯选择性的增加速率;油相产物的碳基选择性随温度增加而降低,而油相中芳烃浓度随温度的增加而增加;芳烃产物主要为C8芳烃,且C6芳烃、C7芳烃、C8芳烃随温度的增加而降低。由于分子筛酸性随温度的增加而变弱,降低了丙烯的氢转移反应速率,故丙烷/丙烯比随温度的增加而降低。     

甲醇与戊烯耦合制丙烯的实验研究

在等温固定床反应器中使用高硅铝比的H-ZSM-5分子筛催化剂,考察了温度、空时和进料比例3个反应条件对甲醇与戊烯耦合反应制丙烯的影响。适宜的温度范围为420~500℃,此时甲醇转化率可达到100%,升高温度可提高甲醇转化率和丙烯选择性,并减少副产物烷烃和芳烃的生成;减小空时可减少副产物的产生并提高丙烯与乙烯生成比例,但当空时减小到1~5(g·h)/mol,丙烯生成量减小;耦合反应相比甲醇和戊烯各自单独进料,可明显减少副产物生成,甲醇进料比例的增大能够使丙烯的选择性升高,但戊烯的转化率会降低。n(甲醇)/n(戊烯)为2时,副产物的生成量最小。     

Methanol Conversion to Hydrocarbons (MTH) Over H-ITQ-13 (ITH) Zeolite

Product flexibility is key to meeting fluctuating chemicals demands in the future. In this contribution, the methanol to hydrocarbons (MTH) reaction was investigated over two Ge-containing H-ITQ-13 samples, one with needle-like (H-ITQ-13(N), with (Si+Ge)/Al) = 42) and another with plate-like (H-ITQ-13(P), with (Si+Ge)/Al > 100) morphology. The samples were characterised using XRD, BET, SEM/EDS and FTIR spectroscopy, and their MTH performance was compared with the performance of H-ZSM-5 and H-ZSM-22. Similar specific surface areas (413 and 455 m² g^?1 for H-ITQ-13(N) and (P), respectively) and similar acid strength (Δν ~ ?327(?310) cm^?1) was observed for the two H-ITQ-13 samples. Testing of H-ITQ-13(N) at weight hourly space velocity (WHSV) = 2–8 h^?1 at 350–450 °C revealed that C₅₊ alkenes were the main products (35–45 % selectivity at 400 °C), followed by propene and butene. A low but significant selectivity for aromatic products was observed (6–8 % selectivity at 400 °C). Product selectivity was found to be independent of deactivation. The methanol conversion capacity of H-ITQ-13(N) was 120–150 g methanol g^?1 catalyst at 400 °C. Testing H-ITQ-13 at high (30 atm) and ambient pressure, respectively, at 350 °C showed that a high pressure led to enhanced C₅₊ selectivity, but close to a tenfold decrease in methanol conversion capacity. H-ITQ-13(P) was tested at 400 °C and 2 h^?1. It gave lower conversion than H-ITQ-13(N). Furthermore, when compared at the same conversion level, H-ITQ-13(P) gave higher C₅₊ alkene selectivity, lower aromatics selectivity, and a higher propene to ethene ratio than H-ITQ-13(N). The H-ITQ-13 samples yielded a product spectrum intermediate of H-ZSM-22 and H-ZSM-5. The effluent product cut-off of H-ITQ-13 was similar to that of H-ZSM-5 with tetramethylbenzene as the largest significant product, while H-ZSM-22 produced mainly linear and branched alkenes. The lifetime of H-ITQ-13(N) was clearly enhanced compared to H-ZSM-22, but inferior to H-ZSM-5.     

Butene Catalytic Cracking to Propene and Ethene over Potassium Modified ZSM-5 Catalysts

Catalytic cracking of butene over potassium modified ZSM-5 catalysts was carried out in a fixed-bed microreactor. By increasing the K loading on the ZSM-5, butene conversion and ethene selectivity decreased almost linearly, while propene selectivity increased first, then passed through a maximum (about 50% selectivity) with the addition of ca. 0.7–1.0% K, and then decreased slowly with further increasing of the K loading. The reaction conditions were 620 °C, WHSV 3.5 h⁻¹, 0.1 MPa 1-butene partial pressure and 1 h of time on stream. Both by potassium modification of the ZSM-5 zeolite and by N₂ addition in the butene feed could enhance the selectivity towards propene effectively, but the catalyst stability did not show any improvement. On the other hand, addition of water to the butene feed could not only increase the butene conversion, but also improve the stability of the 0.7%K/ZSM-5 catalyst due to the effective removal of the coke formed, as demonstrated by the TPO spectra. XRD results indicated that the ZSM-5 structure of the 0.07% K/ZSM-5 catalyst was not destroyed even under this serious condition of adding water at 620 °C.     

甲醇制烯烃反应工艺、反应机理及其动力学研究进展

甲醇制烯烃工艺近年来已成为煤化工领域的研究热点。不同的甲醇制烯烃催化剂将导致不同的反应过程,以SAPO-34为催化剂时,甲醇主要遵循烃池机理,通过快速的平行反应直接生产乙烯和丙烯(MTO)等低碳烯烃;以ZSM-5为催化剂时,甲醇主要遵循双循环机理中的烯烃循环机理,通过甲基化-裂解等多步反应间接生产丙烯(MTP)。这种反应特征的不同也决定着反应器类型和工艺条件的不同:SAPO-34催化剂易失活的特性决定了工业MTO过程通常采用易再生的流化床反应器从甲醇一步生成乙烯和丙烯,而具有良好抗结焦能力的ZSM-5催化剂使得工业MTP过程通常选择易放大的固定床反应器,通过大量烯烃循环与分离逐步获得丙烯。针对SAPO-34催化剂上MTO过程以及ZSM-5催化剂上MTP过程的不同反应情况,综述了近年来甲醇制烯烃代表性的反应工艺、反应机理以及反应动力学等方面的研究进展,并根据其存在的问题提出了相应的发展方向。     

Enhanced propene/ethene selectivity for methanol conversion over pure silica zeolite: Role of hydrogen-bonded silanol groups

Pure silica zeolite with MEL structure (Si-ZSM-11) was firstly reported as an efficient Methanol-to-Propene (MTP) catalyst in methanol conversion, with higher propene yield (14.0 wt.%) and propene/ethene ratio (5.9) than H-ZSM-11 zeolite with a Si/Al ratio of 26 (7.4 wt.% and 1.9, respectively). Hydrogen-bonded silanol groups in Si-ZSM-11 are weakly acidic and act as active sites in methanol conversion, predominantly promoting propene production and inhibiting side reactions.     

Use of isotopic labeling for mechanistic studies of the methanol-to-hydrocarbons reaction. Methylation of toluene with methanol over H-ZSM-5, H-mordenite and H-beta

Methylation of toluene (in one case benzene) with methanol has been investigated over four different zeolites: Small and large crystal ZSM-5, dealuminated mordenite and zeolite beta. The feed ratio methanol/arene was varied over a wide range, mostly >1, using nitrogen or helium as carrier gas. A rather high space velocity was employed (WHSV (methanol + arene): 5–35 h⁻¹). The reaction temperature was 350°C or 375°C. A parallel set of experiments was performed using ¹³C methanol (99% ¹³C). The products were analyzed by on-line gas chromatography using a GC–MS system allowing determination of isotopic composition of the more important products, i.e., ethene, propene and the arenes when ¹³C methanol was employed, otherwise a FID was used. The goal was to obtain mechanistic information, and no attempt has been made to optimize for any particular reaction product.

The experiments showed that ethene and propene were isotopically mixed, containing 50–75% ¹³C. The 25–50% ¹²C atoms coming from the reactant arene. Over all catalysts the arene was, when fed alone, essentially inert with 0.5% or less conversion, giving neither ethene nor propene in measurable quantities. The isotopic distribution in ethene was indistinguishable from a random distribution. Propene, although being close to, displayed some deviation from randomness. The ¹²C/¹³C isotopic ratio in propene was equal to that in ethene, and they both varied with the methanol/arene ratio in the feed, but much less so than the variation in feed composition.

The results support a pool mechanism where the catalytic activity for converting methanol to hydrocarbons is connected with the presence of adsorbates in the zeolite cavities which add methanol and split off product molecules, notably ethene and propene. Formation of ethene by reaction between C₁ species is at best a minor reaction. While formation of propene may take place by a homologation/cracking mechanism, this route was of minor importance here.

Polymethylbenzenes which were formed in many cases displayed a pronounced isotopic scrambling, containing up to six ¹³C atoms in the benzene ring. Molecules with fewer ¹³C atoms than the number of added methyl groups were also identified.     

Dominant reaction pathway for methanol conversion to propene over high silicon H-ZSM-5

The reaction pathway for propene formation in methanol to propene (MTP) process over a high silica H-ZSM-5 catalyst has been investigated in a fixed bed reactor by comparing the experimental results from three kinds of feeding: alkene only, methanol only and mixed alkene and methanol. The results show that alkene methylation with methanol is dominant for the case of methanol and individual C₃–C₆ alkenes co-feeding, C₂⁼ is almost un-reactive. C₇⁼ cracks to propene and butene immediately whether co-fed with methanol or not, and C₆⁼ cracks to propene readily when reacted alone. Oligomerization occurs but is suppressed by the co-fed methanol for light alkenes of C₂–C₅. Methylation-cracking has been verified as the main reaction mechanism of a typical MTP process in which recycling of C₂⁼ and C₄⁼–C₆⁼ to the reactor inlet is required. Based on the relative reactivities of alkenes towards methylation and inter-conversion, a reaction scheme has been presented including a cycle composed of a consecutive methylation from C₄⁼ through C₅⁼ to C₆⁼ and further to C₇⁼, the β-scission of hexene and heptene for propene, and the α-scission of hexene for ethene as well.     

Catalytic cracking of 1-butene to propene and ethene on MCM-22 zeolite

Catalytic cracking of butene to propene and ethene was investigated over HMCM-22 zeolite. The performance of HMCM-22 zeolite was markedly influenced by time-on-stream (TOS) and reaction conditions. A rapid deactivation during the first 1 h reaction, followed by a quasi-plateau in activity, was observed in the process along with significant changes in product distributions, which can be attributed to the fast coking process occurring in the large supercages of MCM-22.

Properly selected reaction conditions can suppress the secondary reactions and enhance the production of propene and ethene. According to the product distribution under different butene conversion, we propose a simple reaction pathway for forming the propene, ethene and by-products from butene cracking.

HMCM-22 exhibited similar product distribution with the mostly used high silica ZSM-5 zeolite under the same conversion levels. High selectivities of propene and ethene were obtained, indicating that the 10-member ring of MCM-22 zeolite played the dominant role after 1 h of TOS. However, MCM-22 exhibited lower activity and stability than that on high silica ZSM-5 zeolite with longer time-on-stream.     

Selective cracking of natural gasoline over HZSM-5 zeolite

This work presents a study on the catalytic cracking of natural gasoline (extracted from natural gas) over HZSM-5 zeolite. A factorial planning was carried out to evaluate the effect of temperature and W/F ratio on the cracking of natural gasoline, analyzing their effects on conversion and product distribution using an analysis based on surface response methodology. The process was optimized focusing on the maximization of the mass fractions and the production of specific products such as ethene, propene and butanes. The results have shown that the maximum selectivity and hourly mass production of ethene is obtained at high temperature (450 °C) and low catalyst weight to flow rate ratio (W/F) (7.2 to 8.2 g_cat h/mol). Maximum selectivity of propene is obtained at 350 °C and 7.0 g_cat h/mol, while the best condition for maximum mass production is found at 421 °C and 5.7 g_cat h/mol. The highest mass production of butanes is favored by high temperature (450 °C) and mid range W/F ratios (12.1 g_cat h/mol), while the highest selectivity is found at low temperature (350 °C).     

New aspects for heterogeneous cobalt-catalyzed hydroamination of ethanol

Gas-phase hydroamination of ethanol and ammonia over supported cobalt on silica catalysts was investigated at 103 kPa. Besides the desired products, mono-, di- and triethylamine, acetonitrile, diethylimine, and hydrocarbons (methane, ethene, ethane, propane, and propene) were identified as byproducts. The formation of hydrocarbons was found to depend on the cobalt loading of the catalyst and on the pretreatment of the catalyst. Guaranteeing a sufficient reduction of the cobalt catalyst allows a reduction in the selectivity of hydrocarbons from 25 to 10 mol% at a constant conversion of 90%. In addition, rapid deactivation of the catalyst was observed in the absence of hydrogen. The deactivation was ascribed to the interaction of ammonia with the catalyst and is largely reversible. Carbonaceous species are present on the spent catalyst, as shown by temperature-programmed reduction. These species are thought to be responsible for a slow deactivation in the presence of hydrogen.     

Converting olefins to propene: Ethene to propene and olefin cracking

Demand for propene as a petrochemical building block keeps growing, while its availability has been decreased by the adoption of shale gas resources, among others. Efforts to optimize its production by conventional means (including modified fluid catalytic cracking) and new on-purpose production technologies (including ethene to propene (ETP) and olefin cracking) are being pursued. This work reviews the progress made on olefin conversion processes, including the ETP reaction, which is still under development, and the cracking of butenes and higher olefins (C₅–C₈). The factors analyzed include the catalytic performance of different zeolite materials and their modifications to increase catalyst stability, yield, and selectivity to propene, as well as the effect of operating conditions, reaction thermodynamics, and mechanisms involved. The work is complemented by a survey of commercial technologies and developments on olefin conversion processes.     

硅源对ZSM-5分子筛合成和催化性能的影响

为了考察硅源对ZSM-5分子筛合成和催化性能的影响,分别采用白炭黑、硅胶、硅溶胶和单分散SiO₂为硅源合成ZSM-5分子筛,对合成的ZSM-5分子筛进行XRD、SEM、BET和NH₃-TPD表征,并以C₄烯烃为原料评价合成的ZSM-5分子筛的催化裂解性能。结果表明,以硅溶胶为硅源合成的ZSM-5分子筛具有较好的结晶度和催化活性。水热处理使分子筛酸量减少,孔容缩小,改善了分子筛的乙烯丙烯选择性。经600 ℃水热处理4 h的ZSM-5分子筛在常压、580 ℃和空速9 h^-1反应条件下,丁烯催化裂解为乙烯和丙烯平均转化率为90.2%,乙烯和丙烯总收率达61.1%。     

Oxidative dehydrogenation of propane to propene in the presence of H2S at short contact times

The oxidative dehydrogenation of propane to propene at short contact times over V₂O₅/A1₂O₃ was remarkably enhanced by the introduction of H₂S in the feed mixture. Overall conversion of propane over this catalyst at 700 °C and 5 ms contact time was 53.7% with selectivity to propene of 56.5%, providing a net propene yield of 30.4%.     

HZSM-5催化剂上甲醇制丙烯反应条件的研究

以HZSM-5分子筛为催化剂,在固定床反应器中考察了反应温度和原料空速对甲醇制丙烯性能的影响。结果表明,随着反应温度的升高,乙烯和丙烯选择性均增加,但温度过高容易引起催化剂的失活;而随原料空速的增大,甲醇转化率、乙烯和丙烯的选择性均呈下降趋势。最佳的反应条件为反应温度为460°C,原料液时空速为1.4 kg(Methanol)/kg(cat.).h。对添加粘结剂与未添加粘结剂成型后的催化剂性能比较,表明添加粘结剂成型后,甲醇转化率和丙烯选择性有所下降。     

Bi2SiO5/SiO2的合成及催化丙烯气相环氧化反应

水热法合成了具有介孔特征的系列Bi2SiO5/SiO2催化剂（记为SBn,n为Si与Bi物质的量比,n=0.5、5、10、20、50）,并通过X射线粉末衍射、N2物理吸附-脱附和扫描电镜等技术对SBn催化剂进行表征。结果表明,以O2为氧源,SBn催化剂在气相丙烯环氧化反应中具有良好的催化活性。在温度330 ℃,SB20催化剂上环氧丙烷选择性达50%,对应丙烯转化率为0.6%;而在温度470 ℃时,SB20催化剂上丙烯转化率接近20%,但环氧丙烷选择性降至20%。     

ZSM-5分子筛的磷改性及其碳四烯烃催化裂解性能

ZSM-5分子筛的磷改性及其碳四烯烃催化裂解性能
薛扬,袁桂梅*,陈胜利,李淑娟,袁锐
（中国石油大学（北京）重质油国家重点实验室,北京 102249） 为了提高丙烯和乙烯产率,增强催化剂的稳定性,采用等体积浸渍法对硅铝物质的量比为38的ZSM-5分子筛进行磷改性,对制备的催化剂进行SEM、XRD、N2吸附-脱附和NH3-TPD表征,考察不同磷含量ZSM-5分子筛对C4烯烃催化裂解反应性能的影响。表征结果表明,随着磷含量的升高,磷改性后的ZSM-5分子筛晶体结构变化不大,比表面积和孔容逐渐减小,结晶度降低,酸强度减弱,酸量减小。性能评价结果表明,随着磷含量的升高,丁烯转化率逐渐下降,丙烯和乙烯选择性、收率先升后降,磷质量分数为2%时,ZSM-5分子筛催化性能较好,相对结晶度为84.66%,平均孔径2.334 nm,孔容0.154 cm3·g-1,微孔孔容0.082 8 cm3·g-1,比表面积264.1 m2·g-1,总酸量0.559 mmol-NH3·g-1,丙烯选择性约40%,乙烯和丙烯总收率约57%。