Effects of catalyst acidity and HZSM-5 channel volume on polypropylene cracking

Effects of catalyst acidity and the restricted reaction volume afforded by HZSM-5 on the catalytic cracking of polypropylene are described. Polypropylene cracking by silica—alumina and HZSM-5 catalysts yields olefins as primary volatile products. In addition, HZSM-5 channels restrict carbenium ion rearrangements and facilitate formation of significant amounts of propene and alkyl aromatic volatile products. The higher acidity of sulfated zirconia compared to the other catalysts results in an increase in the frequency of hydride abstractions, resulting in the formation of significant yields of saturated hydrocarbons and organic residue for this catalyst. Primary polypropylene cracking products can be derived from carbenium ion reaction mechanisms. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 341–348, 1998     

Effects of catalyst acidity and HZSM-5 channel volume on the catalytic cracking of poly(ethylene)

The effects of catalyst acidity and the restricted reaction volume afforded by the HZSM-5 zeolite structure on the volatile cracking products derived from poly(ethylene) are investigated. The effectiveness of silica-alumina, HZSM-5, and sulfated zirconia acid catalysts for poly(ethylene) cracking are compared. When high catalyst to polymer ratios are employed and volatile products are rapidly removed during cracking, the most abundant volatile products generated by poly(ethylene) cracking are propene and isoalkenes. The relative amount of propene produced and the temperatures corresponding to the maximum rate of volatile hydrocarbon production are found to be related to catalyst acidity. The restricted volume inside HZSM-5 channels facilitates oligomerization and the production of small alkyl aromatics. © 1995 John Wiley & Sons, Inc.     

In situ analysis of volatiles obtained from the catalytic cracking of polyethylene

The effects of the solid‐acid‐catalyst pore size and acidity on polyethylene catalytic cracking were examined with a comparison of the temperature‐dependent volatile‐product‐slate changes when the polymer was cracked with HZSM‐5 and HY zeolites and the protonated form of MCM‐41. Volatile‐product distributions depended on the catalyst acidity and pore size. With HZSM‐5, paraffins were detected initially, and olefins were produced at somewhat higher temperatures. Aromatics were formed at temperatures 30–40°C higher than those required for olefin production. Small olefins (C₃–C₅) were the most abundant products when HZSM‐5 and MCM‐41 catalysts were employed for cracking polyethylene. In contrast, cracking with HY produced primarily paraffin volatile products (C₄–C₈). HY pores were large enough and the acid sites were strong enough to promote disproportionation reactions, which led to the formation of volatile paraffins. Compared with the other catalysts, HZSM‐5 with its smaller pores inhibited residue formation and facilitated the production of small alkyl aromatics. Volatile‐product variations could be rationalized by a consideration of the combined effects of catalyst acidity and pore size on carbenium ion reaction pathways. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3118–3125, 2001     

轻汽油在HZSM-5分子筛上催化裂解制丙烯的研究

以催化裂化轻汽油（≤75 ℃）为原料,在小型固定床反应器上,考察了反应温度、反应空速、催化剂不同硅铝物质的量比及载体Al₂O₃含量对轻汽油的催化裂解性能及丙烯选择性的影响。实验结果表明,反应温度和空速对催化裂解的产物分布和丙烯收率有较大的影响,高硅铝比催化剂的丙烯选择性比低硅铝比催化剂好,适量Al₂O₃的添加有助于提高丙烯收率。选择合适的反应条件可以有效提高催化剂的裂化性能并能很好抑制氢转移反应的进行,从而提高丙烯的选择性。在550 ℃、0.2 MPa和空速4 h^－1条件下,高硅铝比n(SiO₂)∶n(Al₂O₃)=200］催化剂的丙烯收率为37.56％,当添加30%的Al₂O₃时,丙烯收率增至38.26%。     

正己烷在HZSM-5分子筛上的催化裂解研究

为筛选反应活性和烯烃选择性相对较高的催化剂用于研究吸热型碳氢燃料的催化裂解,以正己烷的催化裂解作为探针反应,探讨其在不同硅铝物质的量比HZSM-5［n(Si)∶n(Al)=25、36、100］分子筛上催化裂解的反应活性和产物分布。结果表明,正己烷在HZSM-5分子筛上的裂解转化率随温度的升高和分子筛中硅铝物质的量比的减小而增大;裂解产物中乙烯、丙烯和总烯烃的选择性均随裂解温度的升高和分子筛中硅铝物质的量比的增加而增加,在（300~550） ℃,HZSM-5［n（Si)∶n(Al)=36］上的总烯烃收率最高,芳烃含量随分子筛中硅铝物质的量比的增加而减小;基于裂解转化率、烯烃和芳烃收率等因素综合考虑,HZSM-5 n(Si)∶n(Al)=36］分子筛为优选催化剂。     

轻汽油催化裂解生产丙烯催化剂的研究

采用HZSM-5和改性的HZSM-5催化剂,以抚顺石油二厂初馏点约为75℃的催化裂化轻汽油馏份为原料,在实验室连续固定床反应装置上进行了催化裂化轻汽油的催化裂解反应,考察了反应条件对催化裂化轻汽油裂解及芳构化反应的影响和Al2O3作为催化剂载体对HZSM-5催化剂上催化裂解产品分布的影响。研究结果表明,当催化剂中载体组分为30％（wt）时,丙烯收率最高,为38．26％（wt）,芳烃收率为26．26％（wt）,同不使用载体相比,芳烃收率下降了5．1％。     

催化剂结构与焦油模型化合物裂解行为的关联性

以Ni（NO₃）₂·6H₂O为镍源,分别以HZSM-5（Si/Al=25）、HZSM-5（Si/Al=50）、HZSM-5（Si/Al=200）、USY、Al₂O₃为载体制备了5种镍基催化剂,采用XRD、H₂-TPR、BET、NH₃-TPD等方法对其进行了表征,在固定床反应器中考察了上述催化剂对煤焦油模型化合物甲苯+芘的催化裂解性能。结果表明,相比惰性载体石英砂,在催化剂作用下,液相产物中轻质芳烃种类明显增多。3种Ni/HZSM-5催化剂的比表面积和平均孔径较为接近,然而酸性中心数量最多的Ni/HZSM-5（Si/Al=25）,对甲苯+芘的裂解能力最强,体现为液体产物收率最低（仅为15.95%）,气产率和析碳率均最高,分别达16.73%和67.32%。在酸性中心数量相近的Ni/HZSM-5（Si/Al=200）与Ni/Al₂O₃作用下,液体产物收率差别较小,但后者的芘裂解率比前者高41.47%,主要是由于后者的平均孔径比前者高1.64倍,说明平均孔径大有利于重质组分芘的裂解。综合考虑液体产物收率、气产率、析碳率和芘的裂解率,Ni/Al₂O₃更适合甲苯+芘裂解反应体系。     

Recycling polystyrene into fuels by means of FCC: performance of various acidic catalysts

In accordance with the option of recycling plastics into fuels by dissolving them in standard feedstocks for the process of catalytic cracking of hydrocarbons, FCC, various acidic catalysts (zeolites ZSM-5, mordenite, Y, and a sulfur-promoted zirconia) were tested in the conversion of polystyrene dissolved into inert benzene at 550°C in a fluidized-bed batch reactor. Experiments were performed with very short contact times of up to 12 s. Main products were in the gasoline range, including benzene, toluene, ethylbenzene, styrene, and minor amounts of C_9–12 aromatics and light C₅₋ compounds. Coke was always produced in very significant amounts. All the products can be justified with basis on the properties of each catalyst and the various possible catalytic reaction pathways: cracking after protolytic attack on the polymer fragments, styrene oligomerization and subsequent cracking, or hydrogen transfer to styrene. Styrene would be mainly produced in this system from thermal cracking of the polymer as the initial step. If present, shape selectivity effects due to catalyst structure can influence significantly the prevalence of the various reactions, because they would interfere with those undergoing bulky transition states, like styrene oligomerization or hydrogen transfer. Even though sulfur-promoted zirconia is highly acidic, the low proportion of Brønsted-type acid sites does not allow the occurrence of secondary styrene reactions. It was shown that most favorable product distributions (higher yields of desirable products) are obtained on equilibrium commercial FCC catalysts.     

Feedstock recycling of agriculture plastic film wastes by catalytic cracking

Feedstock recycling by catalytic cracking of a real plastic film waste from Almeria greenhouses (Spain) towards valuable hydrocarbon mixtures has been studied over several acid catalysts. The plastic film waste was mostly made up of ambient degraded low-density polyethylene (LDPE) and ethylene-vinyl acetate (EVA) copolymer, the vinyl acetate content being around 4 wt.%. Nanocrystalline HZSM-5 zeolite (crystal size 60 nm) was the only catalyst capable of degrading completely the refuse at 420 °C despite using a very small amount of catalyst (plastic/catalyst mass ratio of 50). However, mesoporous catalysts (Al-SBA-15 and Al-MCM-41), unlike it occurred with virgin LDPE, showed fairly close conversions to that of thermal cracking. Nanocrystalline HZSM-5 zeolite led to 60 wt.% selectivity towards C₁---C₅ hydrocarbons, mostly valuable C₃---C₅ olefins, what would improve the profitability of a future industrial recycling process. The remarkable performance of nanocrystalline HZSM-5 zeolite was ascribed to its high content of strong external acid sites due to its nanometer dimension, which are very active for the cracking of bulky macromolecules. Hence, nanocrystalline HZSM-5 can be regarded as a promising catalyst for a feasible feedstock recycling process by catalytic cracking.     

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。     

Methane and ethane activation without adding oxygen: promotional effect of W in Mo-W/HZSM-5

The conversions of methane and ethane over Mo/HZSM-5 and W/HZSM-5 catalysts are compared. A reaction model for hydrocarbon formation over Mo/HZSM-5 catalysts is proposed, which involves heterolytic splitting of methane and a molybdenum-carbene intermediate. Ethene is shown to be the initial product of methane conversion, and it undergoes further reaction to form aromatics in a solid acid environment. The promotional effect of addition of tungsten in the Mo-W/HZSM-5 catalyst in methane conversion reaction suggests the formation of Mo-W mixed oxide. The product selectivity patterns of Mo/HZSM-5 and W/HZSM-5 catalysts in ethane conversion reaction are consistent with a dual-path model involving dehydrogenation and cracking (or hydrogenolysis) of ethane. The rates of both these reactions over Mo/HZSM-5 are higher than over W/HZSM-5.     

Simplex Lattice Approach to Optimize Yields of Light Oil Products from Catalytic Cracking of Bio-Oil with Mixed Catalysts

Bio-oil is a potential product from the fast pyrolysis of biomass. However, it should be upgraded before being used in subsequent applications and corrosion prevention. In this work, crude bio-oil from fast pyrolysis of Jatropha curcas residues, which has many long-chain compounds, and a high content of carboxylic acid, was catalytically upgraded over mechanically mixed catalysts (normal ZSM-5 and Y-Re-16) in a fixed-bed reactor. The effects of the key parameters on the yields of light oil products were analyzed, including cracking temperature (350–500°C), reaction time (15–60?min), catalyst loading (10–25%), and mixture ratio between Y-Re-16 and ZSM-5 (10–70%). Experimental test cases were based on a simplex lattice design. The gas chromatograph-mass spectrometer (GC-MS) analysis showed that the catalytic cracking of crude bio-oil using mixed catalysts resulted in the successful formation of short-chain acid methyls. The employed analytical fit of the experimental data gave R² and the adjusted R² of 0.902 and 0.843, respectively. The optimized operation conditions to produce aliphatic hydrocarbons from mechanically mixed catalysts were found to be at 400°C, 15?min of reaction time, 15% of catalyst loading, and a mixture ratio of about 1:5.     

Selective formation of light olefin by n-heptane cracking over HZSM-5 at high temperatures

The catalytic cracking of n-heptane has been performed over HZSM-5 catalysts with various Si/Al ratios at 723-923 K to form light olefins selectively. The HZSM-5 zeolites with various acid site densities exhibited almost the same selectivity at the same conversion. The ethylene + propylene selectivity increased, while the propylene/ethylene ratio decreased with an increase in reaction temperatures. It is found that a high temperature is required to obtain a high ethylene + propylene yield. The highest ethylene + propylene yield obtained in this study was 59.7 C-% with a propylene/ethylene ratio of ca. 0.72 at 99.6% conversion over HZSM-5 (Si/Al = 31) at 923 K. Moreover, it is concluded from the selectivities and activation energies that the monomolecular cracking is predominant at a high temperature as 923 K.     

Highly effective P-modified HZSM-5 catalyst for the cracking of C4 alkanes to produce light olefins

A series of HZSM-5 zeolites modified by different amounts of phosphorus (P/HZSM-5) were prepared. The physicochemical features of P/HZSM-5 catalysts were characterized by means of XRD, BET, NH₃-TPD, FT-IR spectra of adsorbed pyridine, etc., and their performances for the catalytic cracking of the mixed C₄ alkanes to produce light olefins were investigated. The results indicated that phosphorus (P) modification not only modulated the amount of acidic sites and the percentage of weak acidic sites in total acidic sites, but also regulated the acid type, i.e., the ratio of L/B (Lewis acid/Brönsted acid). The introduction of P also altered the basic characteristics of HZSM-5 which was evidenced by CO₂-TPD analysis. Consequently, P modification with suitable amount was favorable for enhancing the selectivity to light olefins, especially to propene. At the temperature of 650 °C, the maximum yields of propene and ethene were achieved 25.6 and 33.9%, which were higher than those over parent HZSM-5 by 7 and 4.5%, respectively. Aromatics yield was found to be decreased with the increasing P loading due to the reduction of strong acid and the formation of new basic site which inhibited the hydrogen transfer reaction. All this indicates that P-modified HZSM-5 zeolites are effective catalysts for the cracking of mixed C₄ alkanes to produce more light olefins.     

CrHZSM-5 Zeolites – Highly Efficient Catalysts for Catalytic Cracking of Isobutane to Produce Light Olefins

The CrHZSM-5 catalysts with trace amount of Cr were firstly used for catalytic cracking of isobutane, and the effect of Cr-loading on the catalytic performances of CrHZSM-5 catalysts for the cracking of isobutane was also studied. The results suggested that when the loading of Cr in the CrHZSM-5 catalysts was less than 0.038 mmol/g Cr, especially at Cr loading of 0.004 mmol/g, both the reactivity of isobutane cracking and the selectivity to light olefins of CrHZSM-5 samples were greatly enhanced compared with the unpromoted HZSM-5, and very high yields of olefins(C₂+C₃) and ethylene were obtained. For instance, the yield of olefins(C₂+C₃) and ethylene reached 56.1% and 30.8%, respectively, at 625 °C when 0.004 mmol/g Cr was loaded on HZSM-5 sample.     

轻汽油催化裂解生产丙烯催化剂的研究

采用HZSM-5和改性的HZSM-5催化剂,以抚顺石油二厂初馏点~75℃的催化裂化轻汽油馏分为原料,在实验室连续固定床反应装置上进行了催化裂化轻汽油的催化裂解反应,考察了反应条件对催化裂化轻汽油裂解及芳构化反应的影响和A l2O3作为催化剂的载体对HZSM-5催化剂上催化裂解产品分部的影响,并且考察了载镧HZSM-5催化剂上主要产品分布的影响。研究结果表明,在载镧量5%左右的催化剂上,丙烯产率比改性前下降5%、芳烃产率下降15%;当催化剂中载体组分为30%时,丙烯产率最高为38.26%,芳烃产率为26.26%,同不使用载体相比,芳烃产率下降了5.1%。     

Catalytic cracking of tricyclo [5.2.1.0] decane over HZSM-5 molecular sieves

The catalytic cracking of a high density hydrocarbon fuel, tricyclo [5.2.1.0^2.6] decane (JP-10) over HZSM-5 molecular sieves with different Si/Al mole ratios of 25, 38, and 50 was investigated at the temperature range from 773 to 873 K. Compared with the thermal cracking and the catalytic cracking over ZSM-5, conversions of JP-10 from the catalytic cracking over HZSM-5 molecular sieves at the same temperature were evidently heightened. The predominant hydrocarbon products from the catalytic cracking, checked at room temperature and atmospheric pressure, were methane, ethane, ethene, propane and propylene in the gaseous phase and benzene, indene, naphthalene and their homologues in the liquid phase. The contents of ethane, propane and propene decrease with increasing Si/Al mole ratio of a catalyst while those of methane and ethene increase simultaneously with the increase of Si/Al mole ratio of HZSM-5. The contents of the main components in the liquid products produced on the catalyst surface at a given temperature also decreased with the increase of Si/Al mole ratio. To keep high yields of alkenes, the HZSM-5 catalyst with high Si/Al mole ratio could be chosen.     

Core-shell structured HZSM-5@mesoSiO2 catalysts with tunable shell thickness for efficient n-butane catalytic cracking

A series of core-shell HZSM-5@mesoSiO₂ with tunable shell thickness from 10 to 70 nm was prepared and studied for n-butane catalytic cracking. With introducing of SiO₂ shell, the catalytic performance of HZSM-5@mesoSiO₂ was largely enhanced, and n-butane conversion rate per Al site reached to 2.43 min⁻¹ over HZSM-5@mesoSiO₂(1:4) at 675°C which is nearly twice to that of HZSM-5 (1.34 min⁻¹). The diffusion property of n-butane over as-prepared sample was quantified by measuring the diffusional time constants using zero length column chromatography technique (ZLC). Combining with chemical reaction kinetic analysis, the quantitative relationship between diffusion property and catalytic performance was effectively established for the first time in n-butane catalytic cracking. Positive linear correlation between diffusional time constant (D/R²) and n-butane conversion rate per Al site could be found, which confirms that diffusion enhancement by hierarchical structure is an effective strategy to improve the activity of HZSM-5 in catalytic cracking.     

锯末快速热解气的在线催化裂解

采用Py-GC/MS装置对锯末进行快速热解并对热解气进行在线检测,研究了HZSM-5分子筛和SBA-15介孔催化剂对热解气进行在线催化裂解的效果。结果表明,热解气经HZSM-5催化裂解后,乙酸、羟基乙醛、呋喃类以及酚类物质的产率都大幅降低,同时形成了大量的芳香烃产物,主要是甲苯和二甲苯;而热解气经SBA-15催化裂解后,乙酸产率降低、羟基乙醛产率稍有降低、呋喃类和酚类物质的产率增加,只检测到了极少的烃类产物。由此可知,这两种催化剂对热解气有着不同的催化裂解效果：HZSM-5具有较好的催化脱氧功效;而SBA-15则基本不具有催化脱氧形成烃类产物的能力,但其介孔结构能够允许生物质裂解过程中形成的分子较大的低聚物进入其中并发生二次裂解,从而形成小分子产物。     

Influence of Catalyst Type and Regeneration on Upgrading of Crude Bio-oil through Catalytical Thermal Cracking

Catalysts, such as HZSM-5(Si/Al=50), HZSM-5(25), zeolite 5A, CaHZSM-5(50), ZnHZSM-5(50), and Kaolin were used in upgrading of crude biomass oil from pyrolysis in a fixed-bed reactor under atmospheric pressure, in order to investigate the effects of catalyst type on the yield of desired product. A blank test was carried out in a bed of inert packings to determine the extent of non-catalytical thermal cracking. The gas produced in the reaction was analyzed by the chemical absorption method. Among those catalysts, HZSM-5(50) gave the highest yield of the desired organic distillate while Kaolin gave the least formation of coke. Regeneration of deactivated HZSM-5(50) was studied. In terms of yield of organic distillate and formation rate of coke, the catalytic activity did not change much during the first 3 times of regeneration.