HZSM-5 zeolites undergoing the high-temperature process for boosting the bimolecular reaction in n-heptane catalytic cracking

High-temperature treatment is key to the preparation of zeolite catalysts.Herein,the effects of hightemperature treatment on the property and performance of HZSM-5 zeolites were studied in this work.X-Ray diffraction,N2physisorption,27Al magic angle spinning nuclear magnetic resonance(MAS NMR),and temperature-programmed desorption of ammonia results indicated that the hightemperature treatment at 650℃ hardly affected the inherent crystal and texture of HZSM-5zeolites but facilitated the conversion of framework Al to extra-framework Al,reducing the acid site and enhancing the acid strength.Moreover,the high-temperature treatment improved the performance of HZSM-5 zeolites in n-heptane catalytic cracking,promoting the conversion and light olefins yield while inhibiting coke formation.Based on the kinetic and mechanism analysis,the improvement of HZSM-5 performance caused by high-temperature treatment has been attributed to the formation of extra-framework Al,which enhanced the acid strength,facilitated the bimolecular reaction,and promoted the entropy change to overcome a higher energy barrier in n-heptane catalytic cracking.

Experiment and modeling of coke formation and catalyst deactivation in n-heptane catalytic cracking over HZSM-5 zeolites

Since paraffins catalytic cracking was of significant importance to light olefins and aromatics production,this work was intended to gain insights into the feature and model of coke formation and catalyst deactivation in n-heptane catalytic cracking over HZSM-5 zeolites. 18 tests of n-heptane catalytic cracking were designed and carried out over HZSM-5 zeolites in a wide range of operating conditions. A particular attention was paid to the measurement of the conversion, product distribution, coke content, and the porosity and acidity of the fresh and spent HZSM-5 zeolites. It was found that alkene and aromatic promoted coke formation, and it reduced the pore volume and acid site of HZSM-5 zeolites, tailoring its performance in n-heptane catalytic cracking. The specific relationship between HZSM-5 zeolites, n-heptane conversion, product distribution and coke formation was quantitively characterized by the exponential and linear function. Based on the reaction network, the coupled scheme of coke formation and catalyst deactivation were specified for n-heptane catalytic cracking. The dual-model was proposed for the process simulation of n-heptane catalytic cracking over HZSM-5 zeolites. It predicted not only the conversion and product distribution but also coke content with the acceptable errors.

Effects of Operating Conditions on the Catalytic Performance of HZSM-5 Zeolites in n-Pentane Cracking

In this work,n-pentane catalytic cracking over HZSM-5 zeolites was studied at 650°C under atmosphere pressure.A particular attention was paid to the measurement of n-pentane conversion,light olefins production,product distribution,coke deposit,etc.Several indexes were defined to evaluate the effects of operating conditions on the catalytic performance of HZSM-5 zeolites.It was found that decreasing the weight hourly space velocity,increasing the reactant partial pressure,and increasing the carrier gas flow rate could inhibit C-H bond breaking and enhance the C-C bond breaking and hydride transfer reactions,leading to reduced alkenes selectivity,which suppressed the formation of external coke and alleviated the deactivation of HZSM-5 zeolites.It was deduced that the catalytic stability of HZSM-5 zeolites was improved at the cost of alkenes selectivity.Compared with decreasing the weight hourly space velocity and increasing the reactant partial pressure,increasing the carrier gas flow rate could enhance the diffusion process and protect alkenes from being consumed in coke formation in order to improve the catalytic stability of HZSM-5 zeolites with less reduction of alkenes selectivity.

Secondary Crystallization of Na_2CO_3-Modified HZSM-5 Zeolites with Tetrapropylammonium Hydroxide and Their Catalytic Performance in Thiophene Alkylation Reaction

The Na2CO3-modified HZSM-5 zeolites were further treated by tetrapropylammonium hydroxide(TPAOH) solution. The effect of TPAOH concentration on the secondary crystallization process was investigated. The resulting samples were characterized by a complementary combination of X-ray diffraction, N2 adsorption/desorption, scanning electron microscopy, X-ray fluorescence spectroscopy, XPS, 27 Al and 29 Si magic-angle spinning nuclear magnetic resonance spectroscopy, BET and temperature-programmed desorption techniques. The results showed that the secondary crystallization of the HZSM-5 zeolite could result in migration of non-framework species from the internal channels to the zeolite surface and their transformation into framework species. The catalytic activity of these modified samples for thiophene alkylation was evaluated. Both the activity and stability of the catalysts were improved after secondary crystallization.

Thermal and hydrothermal stabilities of the alkali-treated HZSM-5 zeolites

有 micro-mesopore 的 HZSM-5 沸石层次孔被准备了由碱处理，和他们的热、热水的稳定性合成以后用 DTA， XRD，和 NH 3-TPD 描述技术被学习。比作未修改的沸石，因为 desilication 引起的中央毛孔的介绍，对待碱的 ZSM-5 沸石的热、热水的稳定性稍微被败坏。不过，对待碱的沸石框架能被维持直到温度增加了到 1175 ° C。

Properties and Characterization of Modified HZSM-5 Zeolites

Physicochemical and catalytic properties of phosphorus and boron modified HZSM-5 zeolites treated with 100% steam at 673 K were investigated. The acidity and distribution of acidic sites were studied by infrared spectroscopy using pyridine as probe molecule and temperature programmed desorption (TPD) of ammonia. The structure of the samples was characterized by XRD, and the textural properties of the catalysts were determined by nitrogen isothermal adsorption-desorption measurements and scanning electron microscopy (SEM). The XRD results show that the modified samples have no novel crystalline phase, indicating a high dispersion of phosphorus and boron species. After treatment, the microporous volume and surface area of the samples markedly decrease, implying the blockage of the channel. The nitrogen adsorption-desorption measurements suggest that the isothermal type of all samples is a combination of isothermal type I and IV, and all hysteresis loops resemble the H4-type in the IUPAC classification. The total acidity of the modified samples, determined by pyridine adsorption IR and TPD of ammonia, decreases in contrast to that of the parent HZSM-5. The conversion of n-heptane over P and B steam-modified HZSM-5 is higher than that of P and B-modified HZSM-5 zeolites but lower than that of the parent HZSM-5.

Dual-template synthesis of HZSM-5 zeolites with tailored activity in toluene methylation with CH3Br

Shape-selective zeolites(UZ-x/y) were synthesized by a one-pot method using TPAOH(y) and/or MeEt3 N^+I^-(x) as templates.The use of MeEt3 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 CH3 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.

Ce改性HZSM-5分子筛催化甲醇与丁烯耦合转化制丙烯性能研究

为了进一步提高HZSM-5分子筛在甲醇与丁烯耦合转化制丙烯反应中的催化性能,采用浸渍法对HZSM-5分子筛进行Ce改性,得到了一系列具有不同Ce负载量的x Ce/HZSM-5催化剂。考察了Ce负载量和反应条件(甲醇与丁烯物质的量之比、反应温度和空时)对催化性能的影响,并结合催化剂表征结果,分析了Ce改性对催化性能和物化性质的影响,探讨了x Ce/HZSM-5催化剂的构效关系。结果表明,在温度550℃、压力0.1 MPa、甲醇与丁烯物质的量之比0.8、空时2.3(g cat·h)mol CH_(2)的最佳反应条件下,Ce负载量(w)为2.5%的2.5Ce HZSM-5催化剂具有最高的丙烯收率,为41.9%。Ce与HZSM-5分子筛上羟基官能团(OH)发生相互作用,降低了B酸酸量,同时生成新的L酸中心Ce(OH)^(2+),调变了催化剂表面酸中心密度和酸类型分布,提高了丙烯选择性和收率。

Ni-MgO复合改性对HZSM-5分子筛催化性能的影响

采用等体积浸渍法制备了Ni和MgO改性的HZSM-5催化剂,考察Ni和MgO含量对甲醇制备丙烯的影响,并利用XRD、SEM、BET、NH 3-TPD等方法考察了Ni和MgO对HZSM-5分子筛的酸强度和结构的影响,结果表明,少量的Ni-Mg复合改性的HZSM-5分子筛MFI结构没有改变,但有效改变了催化剂的酸强度和孔径结构,显著降低催化剂中强酸含量,微孔孔径由0.5105 nm降为0.5016 nm,0.5%Ni-0.5%Mg/HZSM-5分子筛表现出较佳的丙烯选择性,丙烯的选择性提高了11.5%。

花生秸秆热解挥发分在HZSM-5负载Ga催化剂上的裂解特性

生物质热解能够将木质纤维素类生物质转化为生物油,但粗油含氧量高、热值低。利用负载Ga的HZSM-5催化剂对生物质热解挥发分进行催化裂解,可以促进生物油的选择性脱氧和芳构化,实现生物油提质。分别采用离子交换法和水热法制备了两种负载Ga的HZSM-5催化剂(Ga-H5-E和Ga-H5-H),采用两段式固定床反应器进行了花生秸秆热解在线联合热解挥发分催化裂解实验。花生秸秆在反应器下段以10℃/min的加热速率从室温升温至700℃,其间逸出的挥发分通过保持在600℃的上段催化剂层进行催化裂解。结果表明,相比无负载的HZSM-5,Ga-H5-E和Ga-H5-H使BTX(苯、甲苯和二甲苯)产率分别提高了77%和93%,其中甲苯和二甲苯的增加尤为明显。采用热重分析仪、电感耦合等离子发射光谱仪、X射线衍射仪、扫描电子显微镜、能量色散X射线光谱仪、比表面积分析仪和化学吸附仪等对催化剂进行了表征分析。结果表明,两种Ga负载催化剂的积炭产率显著低于原催化剂(HZSM-5);Ga负载使催化剂强酸位显著增多,有利于增加脱氧反应的催化活性中心;相比于Ga-H5-E,Ga-H5-H含有容积较大的介孔和较小的平均孔径,而且更多Ga浸入了颗粒内部,这些差异可能促进乙烯和丙烯在介孔内发生芳香化反应,从而提高了单环芳香烃产量。

Study of the Conversion of Postconsumer Polystyrene on CeO2/HZSM-5 Type Materials

The catalytic conversion of polystyrene (PS) was studied in the presence of the materials type HZSM-5, CeO2, 10% CeO2/HZSM-5 and 20% CeO2/HZSM-5, which were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and nitrogen adsorption at 77K. The catalytic tests were performed via thermogravimetric analysis (TG) at heating rates of 5, 10 and 20˚C min−1 in a temperature range from 30˚C to 900˚C. For the tests, a ratio of 30% by mass of each catalytic material mixed with PS was used and the activation energy of the degradation process was determined by the Vyazovkin method. The obtained results showed that the addition of the catalyst to the PS in general reduced its degradation temperature. The 10% CeO2/HZSM-5 catalyst showed greater efficiency, as it resulted in lower activation energy for PS degradation. Thus, the combination of CeO2 with HZSM-5 resulted in materials with potential for application in the catalytic degradation of polystyrene and the results indicate that the production of a composite material can be a good strategy to generate an increase in catalytic activity and a decrease in energy process activation.

HZSM-5分子筛一步法绿色合成

ZSM-5分子筛在吸附、催化中用途广泛,随着环保政策越来越严格,传统生产中面临的高耗能、高耗水及长流程给分子筛的应用带来阻碍。本文研究了以大孔硅胶、硝酸铝、正丙胺为原料一步法合成HZSM-5分子筛,考察了晶化时间的影响。结果表明,随着晶化时间延长,分子筛结构逐步生长,晶化36 h后成功制备出晶体呈棒状相互交错的高结晶度ZSM-5分子筛,其BET比表面积达到421 m^(2)/g,铝以四配位状态全部进入分子筛骨架。该合成方法流程简单,耗水量低,同时不添加高腐蚀性氟化氢,不需要铵交换,是一种有高效节能的分子筛绿色合成方法。

改性HZSM-5催化玉米秸秆与HDPE共热解制轻质芳烃

为提高生物质与聚乙烯共热解中苯、甲苯、乙苯、二甲苯和萘(简称)BTEXN和轻烯烃的产量,同时抑制C^(+)_(21)蜡的形成,通过TG-MS/FTIR和Py-GC/MS探究催化共热解中HZSM-5和改性HZSM-5对玉米秸秆和HDPE相互作用的影响,并对BTEXN进行定量分析。结果表明,在HZSM-5的催化共热解中,HZSM-5可促进玉米秸秆与HDPE之间的相互反应,芳烃和轻烃产率增加。相比HZSM-5,在改性HZSM-5的催化共热解中,改性HZSM-5可促进轻烯烃、C_(5)-C_(11)脂肪烃和芳烃的析出,并抑制C^(+)_(21)蜡的形成。Cu、Fe和Ce改性可促进单环芳烃的形成,同时提高BTEXN产量,相比HZSM-5分别提高20.99、25.43和20.89 mg/g,而P改性会抑制BTEXN形成。对于形成芳烃的Diels-Alder反应,Fe和Ce改性表现出较强的催化效果,而Cu改性对烃池反应催化效果较强。此外积碳分析表明,Fe和P改性具有较强的抗积碳能力。

环状ZSM-5分子筛在苯和乙醇烷基化反应中的应用

低温下采用水热晶化法合成了环状中空ZSM-5分子筛,并以磷酸二氢铵为前体,制备了不同磷负载量的环状中空ZSM-5催化剂,采用XRD,SEM,NH_(3)-TPD,Py-FTIR等方法对催化剂进行表征,并在气相连续流动固定床反应器上对苯和乙醇烷基化制乙苯进行性能评价和稳定性考察。实验结果表明,环状中空ZSM-5催化剂进行磷改性后,催化剂的酸强度降低,随着磷负载量的增加,乙苯选择性逐渐增加,甲苯和丙苯选择性逐渐降低;当磷负载量达到3%(w)后,催化剂外表面强酸位基本消失,此时乙苯选择性最高;在n(苯)∶n(乙醇)=8∶1、340℃、1.0 MPa、WHSV=1 h^(-1)条件下,对该催化剂进行了寿命考察,在300 h反应过程中,乙醇转化率超过99.9%,苯的转化率维持在11%左右,乙基苯的选择性最高达到98.4%,二甲苯相对含量最低达到0.11%。

过渡金属改性HZSM-5催化转化煤油共炼重油制轻质芳烃的研究

煤油共炼技术为煤炭和重质油清洁高效利用开辟了新途径,但其产品单一,附加值低。为实现煤油共炼液体产物的高值化利用,本研究以煤油共炼重油(H-CT)为原料,利用热裂解-气相色谱质谱联用仪(Py-GC/MS),通过单、双金属改性的HZSM-5对H-CT催化转化制苯、甲苯、乙苯、二甲苯和萘(BTEXN,B—苯,T—甲苯,E—乙苯,X—二甲苯,N—萘)的性能进行了考察,探究了裂解温度、升温速率和催化剂与原料的质量比对BTEXN峰面积和选择性的影响,利用红外快速加热炉对H-CT的Py-GC/MS结果进行了校正。结果表明:单、双金属负载使HZSM-5的强酸酸性减弱,中强酸酸性增强;Mo,Fe及双金属Mo-Fe的负载增大了HZSM-5介孔比表面积;H-CT裂解的最佳条件为温度700℃、升温速率5℃/ms,催化剂与原料的质量比8∶1,在此最优条件下,催化剂按转化效果由大到小依次为Mo-Fe,Mo-Ni,Mo,Ni,Fe,HZSM-5;HZSM-5和Mo-Fe/HZSM-5催化转化制备BTEXN的总选择性分别为39.78%和60.30%,修正后的BTEXN产率分别为197.3 mg/g与339.0 mg/g。过渡金属改性HZSM-5促进了BTEXN的生成,金属与HZSM-5的结合加速了催化转化过程中氢转移、脱羟基、开环、脱烷基和其他反应。

水热处理对HZSM-5分子筛乙苯/乙烯烷基化反应性能的影响

针对在保持高选择性的前提下抑制催化剂的快速积炭失活问题,利用X射线衍射(XRD)、氨气程序升温脱附(NH_(3)-TPD)、N_(2)物理吸附-脱附(BET)和吡啶吸附傅里叶变换红外光谱(Py-FT-IR)等手段对水热处理后的HZSM-5催化剂进行表征,并详细考察了水热处理条件对反应性能的影响。结果表明,水热处理温度和时间对催化剂稳定性有显著影响,最佳水热处理条件为T=550℃、t=3 h、MHSV H_(2)O=1 h^(-1)。其中HT-550-3-1催化剂稳定性表现最好,反应32 h后乙苯转化率仅降低了2.6百分点,热重分析发现其炭质量损失率(1.38%)远低于HZSM-5的炭质量损失率(5.08%)。在最佳水热处理条件下的HZSM-5分子筛经过硅(Si)、镧(La)复合改性制得的HT-9%Si-4%La催化剂,在反应温度340~370℃、压力101.325 kPa、乙苯质量空速5 h^(-1)、n(C_(8)H_(10))/n(C_(2)H_(4))=5、n(N_(2))/n(C_(2)H_(4))=11.3的反应条件下,乙苯转化率高于12.1%,对二乙苯选择性超过97.0%,催化剂稳定运行454 h。

MgO修饰的HZSM-5分子筛对甲苯甲醇烷基化反应性能的影响

采用浸渍法制备了系列MgO修饰的HZSM-5分子筛催化剂,通过X射线衍射(XRD)、扫描电子显微镜(SEM)、NH_(3)程序升温脱附(NH_(3)-TPD)、吡啶红外(Py-IR)等方法对修饰前后的HZSM-5分子筛催化剂进行表征,并在固定床反应器上对催化剂的性能进行评价.结果表明:MgO的修饰并未对HZSM-5分子筛的晶体结构有明显影响,但是部分MgO优先覆盖了分子筛表面的强酸位,从而降低了分子筛的酸强度,并改变了B酸/L酸比例;同时由于MgO堵塞部分孔道造成分子筛比表面积降低,进一步降低了分子筛表面酸性位的数量,影响甲苯甲醇烷基化反应性能和产物分布.MgO修饰后的HZSM-5分子筛,虽然使甲苯转化率降低,抑制了甲苯歧化反应、深度烷基化反应和缩聚反应的发生,但是有利于对二甲苯和乙基甲苯的生成,表现出一定的择形催化性能.

ZnZr/HZSM-5复合催化剂上CO_(2)加氢制备C_(5+)异构烷烃

本研究将锌锆氧化物(ZnZr)与HZSM-5分子筛有效耦合制得系列ZnZr/HZSM-5复合催化剂,考察了HZSM-5硅铝比及Zn/Zr比对复合催化剂上CO_(2)加氢制备C5+异构烷烃性能的影响。结果表明,SiO_(2)/Al_(2)O_(3)=130,Zn/Zr=1∶5制得的ZnZr-4/HZSM-5复合催化剂表现出最优的CO_(2)加氢制C_(5+)异构烷烃性能,CO_(2)转化率为17%,CO选择性抑制到25%,C_(5+)烃及C_(5+)烃中异构烷烃选择性分别达60%及89%。该复合催化剂稳定性良好,连续运转120 h未出现失活现象。ZnZr氧化物与HZSM-5分子筛的良好匹配对CO_(2)加氢高选择性合成C5+异构烷烃至关重要。

不同硅铝比微米级HZSM-5分子筛的合成及催化甲苯甲醇烷基化反应性能

HZSM-5分子筛是甲苯甲醇烷基化制对二甲苯技术中常用的催化剂之一。本研究在引入晶种调节HZSM-5分子筛形貌的同时,改变分子筛合成前驱体溶液硅铝比调控分子筛酸性位,采用一步法直接制备孔结构和酸性质均适宜的微米级HZSM-5催化剂。通过X射线衍射、N2吸附-脱附、扫描电子显微镜、NH3程序升温脱附、吡啶红外等手段对HZSM-5分子筛的物相组成、孔结构参数、微观形貌、酸性质进行表征分析,考察了其在甲苯甲醇烷基化制对二甲苯反应中的催化性能,探讨了孔结构和酸性质对催化性能的影响。结果表明:在水热晶化方法中,合成溶液中的晶种和铝含量对分子筛的酸性质和形貌结构有显著的影响,其中5μm晶粒的HZSM-5(150)分子筛催化剂因具有更长的扩散路径和更适宜的酸性位,在甲苯甲醇烷基化评价反应中表现出60%的对二甲苯选择性和11%的甲苯转化率。通过对HZSM-5分子筛的孔道和酸性位的精细调节有效提高了对二甲苯选择性,为择形催化剂的设计提供新的方法和思路。

Ni改性HZSM-5催化剂对混合C_(4)中异丁烯齐聚的影响

近年来,乙醇汽油全面推广导致甲基叔丁基醚(MTBE)的应用受限,作为其原料之一的异丁烯需要另寻出路。异丁烯主要来源于催化裂化和蒸气裂解所产生的混合C_(4)馏分,其通过选择性二聚反应可以生产高辛烷值的汽油添加剂。以Ni为助剂对HZSM-5进行改性,考察不同Ni负载量对催化性能的影响,并对一系列催化剂进行相关表征。结果表明,当Ni负载质量分数为0.25%时,综合效果最好,C_(8)^(=)收率为45.4%。表征结果表明,HZSM-5经Ni改性后,强酸位点的Lewis酸(L酸)和Bronsted酸(B酸)比值增加,对提高产物C_(8)^(=)选择性具有重要作用,该L酸中心可能来源于Ni物种与HZSM-5中的铝相互作用所生成的NiAl_(2)O_(4)。