塑料催化热解制备高附加值产品的研究进展

塑料催化热解技术可定向或联产制备低碳烯烃、单环芳烃、碳纳米管（CNTs）和氢气等能源产品,其调控过程简单,且产物选择性好、附加值高,因而受到了广泛的关注。在较短的停留时间（＜1 s）和较高的反应温度（＞800℃）下,塑料热解可得到较高产率的烯烃单体,而芳烃产物的形成更依赖催化剂的酸位点和孔结构。Fe、Co、Ni基催化剂可将塑料热解产生的含碳挥发分转为CNTs和富氢气,其CNTs产率和氢转化效率可分别达到30%（质量）和90%以上。总结了塑料催化热解制备高附加值能源化工产品的研究进展,讨论总结了温度、停留时间、催化剂等因素对产物分布和品质的作用机制,并对各类产物形成机理和制备方法分别进行了回顾与展望。     

生物质与塑料催化共热解制芳烃研究进展

芳烃是多用途的化学品,主要来源于石油和煤焦油等。以生物质和塑料为原料制取芳烃,可以缓解能源短缺和环境污染,实现生物质和塑料的资源化利用。催化剂能够增强共热解的协同效应,生物质与塑料进行催化共热解可以提高产物品质,改善热解产物分布,提高轻质芳烃的产率和选择性,抑制焦炭的生成。本文综述了生物质与塑料催化共热解制取芳烃的协同热解机理及影响因素,总结了不同种类催化剂的共热解研究进展,以期为生物质与塑料催化共热解定向调控制备芳烃工艺的改进和优化提供参考。     

生物质与废塑料催化热解制芳烃(Ⅰ):协同作用的强化

采用两段式固定床对比研究了纤维素与高密度聚乙烯（HDPE）的单独物料催化热解、混合物催化热解和分段催化热解,对热解产物分布、目标产物产率及选择性以及催化剂积炭量等参数进行考察,拟从模型化合物水平探索生物质与塑料催化热解制芳烃过程强化协同作用的可能性。结果表明,纤维素与HDPE的共催化热解（混合和分段催化热解）对芳烃的形成具有协同作用,且分段催化热解较混合催化热解表现出更显著的协同作用,可获得更高的芳烃产率及选择性,提高纤维素热解转化率并降低催化剂的积炭,其协同作用符合"双烯合成"反应理论。并结合HDPE催化热解验证实验对分段催化热解制芳烃过程协同作用的强化机理进行阐述。     

Fe-Zn共改性ZSM-5催化作用下生物质快速热解特性研究

选取木屑和花生壳作为原料进行生物质热解,研究有机产物分布,催化剂使用Fe、Zn两种金属元素进行改性。通过X射线衍射（XRD）、扫描电镜（SEM）、傅里叶红外（FT-IR）、比表面积测试（BET）对Fe-Zn改性的ZSM-5进行分析。使用闪速裂解-气质联用仪（PY-GC/MS）对原料进行热解,探究生物质催化热解的产物分布变化。催化剂的使用使得芳烃类产物产率获得较大提升,在木屑热解中,Fe负载的分子筛催化获得了酚类的最高产率,比ZSM-5催化热解产率提升18.30%。金属改性催化剂在花生壳热解中,大幅提升了芳烃类产物产率,其中Zn负载催化剂芳烃类产物产率最高,Zn负载催化热解比直接热解的酚类产率降低了18.92%。Zn负载催化获得了最低的酮类产率,与直接热解相比酮类产率降低19.74%,显示出较强的脱羟基效果。此外Zn负载催化和Fe-Zn双金属负载催化在花生壳热解中都大幅降低了酸类产物产率,与直接热解相比酸类产率分别降低了30.46%、36.71%。     

生物质三组分与低密度聚乙烯共催化热解制取轻质芳烃的协同作用机理

生物质与废塑料共催化快速热解是制取轻质芳烃的重要途径。 采用不同种类的分子筛催化剂,首先研究了分子筛种类对杨木、生物质三组分和低密度聚乙烯（LDPE）单独催化快速热解轻质芳烃产率的影响,其次研究了生物质三组分与LDPE在共催化热解过程中的协同作用机理。结果表明：在杨木、生物质三组分和LDPE单独催化快速热解时,HZSM-5（25）催化剂体现出最高的轻质芳烃产率;在杨木和LDPE共催化快速热解时,随着LDPE质量的增加,轻质芳烃的产率呈先升高后降低趋势;在生物质三组分和LDPE共催化快速热解时,纤维素和半纤维素热解的呋喃类中间产物与LDPE热解的轻烯烃中间产物易发生“双烯合成”反应,表现出较强的协同催化作用,促进轻质芳烃的生成,而木质素则抑制轻质芳烃生成。     

ZSM-5分子筛对生物质热解特性影响

人类在面临能源短缺问题的同时面临着能源开发所引起的环境问题。而生物质作为一种具有强大的清洁性,可再生性的优势,得到了许多国内外研究者的重视。其中：利用气化、热解、和直接液化将生物质能转变为能源较为普遍。本实验通过TG-MS/FTIR和PY-GC/MS对催化共热解（CCP）中玉米秸秆衍生含氧化合物与HDPE衍生烯烃的相互反应和芳烃形成的影响机制进行研究,研究发现：玉米秸秆与HDPE在HZSM-5上的催化共热解,明显改善了产物分布：加入Cu改性的HZSM-5催化剂后,烷烃、烯烃的产率下降,芳香烃的产率提高,说明Cu改性过的催化剂使烷烃进一步向芳香烃和轻质芳烃转化。     

生物质与废塑料催化热解制芳烃(Ⅰ):协同作用的强化

采用两段式固定床对比研究了纤维素与高密度聚乙烯(HDPE)的单独物料催化热解、混合物催化热解和分段催化热解,对热解产物分布、目标产物产率及选择性以及催化剂积炭量等参数进行考察,拟从模型化合物水平探索生物质与塑料催化热解制芳烃过程强化协同作用的可能性。结果表明,纤维素与HDPE的共催化热解(混合和分段催化热解)对芳烃的形成具有协同作用,且分段催化热解较混合催化热解表现出更显著的协同作用,可获得更高的芳烃产率及选择性,提高纤维素热解转化率并降低催化剂的积炭,其协同作用符合"双烯合成"反应理论。并结合HDPE催化热解验证实验对分段催化热解制芳烃过程协同作用的强化机理进行阐述。     

生物质模化物催化热解制取烯烃和芳香烃

采用愈创木酚作为生物质模型化合物,以ZSM-5为催化剂,在固定床反应器中研究了反应温度、质量空速以及分压对热解产物产率、选择性的影响,并考察了催化剂的积炭情况。结果表明,愈创木酚催化热解的主要产物为酚类,其次是芳香烃。温度对产物分布有显著影响。催化剂适量的积炭有利于提高烯烃和芳香烃的产率。根据愈创木酚催化热解反应产物分布,推测其主要反应为脱除甲氧基形成酚类,进一步芳构化形成芳香烃。本文研究结果为研究生物质催化热解反应机理提供了理论依据。     

碱土金属氧化物基催化剂催化热解生物质研究进展

快速热解是生物质高效转化利用的重要方法之一,然而其目标产物生物油因含氧量高、组分复杂等不足而难以直接利用。通过在热解体系中引入碱土金属氧化物基催化剂,可以将热解产物中的氧元素以CO₂和H₂O等方式脱除,从而实现生物油品质的提升。总结了典型碱土金属氧化物基催化剂对生物质催化热解过程中发生的酮基化、羟醛缩合、开环和侧链断裂反应及机理,讨论了催化剂类型（CaO、MgO、基于碱土金属氧化物的分子筛和活性炭等）、生物质原料、温度、催化剂用量、停留时间、催化方式、催化剂失活等因素对生物油产率与品质的影响,并对生物质催化热解制备高品质生物油及其应用进行了展望。     

餐厨废油基活性炭负载Ni-Cu双金属催化裂解餐厨废油制备氢气的研究

以餐厨废油模型化合物为原料制备活性炭（AC）,并负载金属Ni、Cu组分制备系列催化剂,用于催化裂解餐厨废油模型化合物（MWCO）制取氢气和碳纳米管（CNTs）。通过ICP-OES、N₂-BET、XRD、H₂-TPR对催化剂进行结构和化学表征。研究了不同Ni和Cu质量分数催化剂、裂解温度、废油流量对产氢量的影响。结果表明,20%Ni-10%Cu/AC为催化剂时,反应活性最高,850℃时氢气瞬时体积分数可达41.1%,得到的CNTs产率最高为1 528%。CNTs主要为丝状多壁结构,且具有较高的氧化稳定性和石墨化程度。     

聚烯烃塑料的热解和催化热解研究进展

通过热解和催化热解技术将废塑料转化为高附加值产品是一种有前途的回收途径,可解决废塑料对环境的污染问题并促进环境的可持续化,这种方法同时具有经济效益和明显的环境优势,为塑料的回收行业确立了未来的发展趋势。本文以石蜡、轻质芳烃（BTX）、低碳烯烃和苯乙烯等产品为出发点,阐述了不同聚烯烃塑料的热解特性,详细介绍了温度和停留时间对产品分布和收率的影响,然后基于聚烯烃空间结构的差异,讨论了不同催化剂作用下的热解机理,并对催化剂的酸强度和孔结构等影响因素进行了着重分析,以改善产品选择性。此外,文章简述了聚氯乙烯脱氯的三类过程,即热解脱氯、催化热解脱氯和吸附脱氯。最后指出催化热解过程中催化剂成本高、重复使用活性低等潜在问题,今后的研究应致力于优化工艺路线、开发价格低廉的新型催化剂。     

氢气流量和反应时间对焦化苯裂解制备碳纳米管的影响

以工业级焦化苯为碳源,以二茂铁为催化剂前躯体,以噻吩为生长促进剂,采用催化裂解(CVD)法制备碳纳米管,通过TEM进行形貌表征,着重探讨氢气流量和反应时间对碳纳米管形貌和产率的影响。结果分析表明:氢气流量和反应时间在一定范围内增加时,所得碳纳米管的管壁直,缺陷少,纯度高,且纯化后产率增加。因此,通过控制氢气流量和反应时间可以控制碳纳米管的形貌,而且能够提高碳纳米管的产率。     

Pyrolysis of Natural Gas: Effects of Process Variables and Reactor Materials on the Product Gas Composition

High‐temperature pyrolysis of natural gas is the basis of the standard method for the manufacture of acetylene. The study of methane pyrolysis was designed to find optimum process conditions that would produce high yields of acetylene with minimal carbon formation. High temperatures and short residence times enhanced the selectivity for acetylene, while hydrogen dilution was found to suppress the generation of carbonous products. Carbon formation on reactor surfaces over time may be mainly responsible for the misalignment of predicted and measured product gas compositions, as the mechanisms reported do not consider the surface chemistry. In essence, the pyrolysis system favors the highest possible temperature and shortest possible residence time, suggesting that the selection of reactor materials is the key for pyrolysis process optimization. The operating temperature is likely dictated by the physical properties of the reactor materials rather than the selection of optimal pyrolysis conditions.     

连续流动状态下纳米碳管负载镍催化剂催化苯乙炔选择加氢反应

采用浸渍法,以纳米碳管（CNT）为载体,制备了Ni负载量为3.91%（质量分数）的Ni/CNTs催化剂。利用X射线衍射（XRD）、拉曼光谱、电感耦合等离子体发射光谱（ICP-OES）以及透射电镜（TEM）等技术对Ni/CNTs催化剂进行了表征。在连续流动状态下通过一系列实验考察了温度、压力、氢气量以及流速对Ni/CNTs催化苯乙炔选择加氢性能的影响,利用高效液相色谱仪HPLC对产品进行定性和定量分析。实验结果表明,催化剂Ni/CNTs对苯乙炔选择加氢反应具有一定的催化活性;反应的最佳温度为20℃;压力对产品收率影响显著,微正压对反应有利;最佳氢气量为24mL/min;产品收率随着反应液流速的增加而增大。     

Carbon nanotube formation over plasma reduced Pd/HZSM-5

In this work, we reported a new plasma catalyst preparation method for carbon nanotube (CNT) formation. With this new method, argon glow discharge plasma was operated at room temperature and applied for the reduction of Pd/HZSM-5, instead of catalyst reduction thermally using hydrogen at elevated temperature. Such plasma reduced catalyst shows a high dispersion of metal particles. The multi-walled CNTs produced with this plasma reduced Pd/HZSM-5 exhibit structural graphene sheets in conical hollow shape, a typical structure observed in CNTs from catalytic methane decomposition. Some fiber fish bone type structures can be also observed. Compared to the hydrogen reduction (thermally), the reduction using argon plasma is feasible and effective for the preparation of catalyst for the CNTs formation. The glow discharge plasma catalyst reduction is very promising for the further development of green catalyst reduction technologies.     

Vertically aligned carbon nanotubes synthesized by the thermal pyrolysis with an ultrasonic evaporator

Thermal pyrolysis process is a catalytic chemical vapor deposition (CVD) based method, involving pyrolysis of mixed solution composed of liquid carbon sources and catalysts. This paper is focused on the synthesis of carbon nanotubes (CNTs) by the thermal pyrolysis process with an ultrasonic evaporator that atomizes the mixed liquid solution. The merit of this approach is that the apparatus can produce aligned and clean CNTs which can be easily controlled in a cost-effective manner. CNT samples synthesized by introducing the atomized solution into the pyrolysis furnace were analyzed to understand and characterize the growth mechanism. HRTEM and high magnification SEM analysis indicate that the samples are multiwalled carbon nanotubes (MWNTs) grown through tip growth mechanism. The results were confirmed by Raman spectrum curve. In addition, the effects of experimental parameters on the structure of CNTs were investigated by SEM images and themogravimetric analysis. The results reveal that synthesis time and temperature have a key influence on the size of CNTs, and the concentration of catalyst determines the amount of the filling yield in the inner part of CNTs.     

Noncatalytic and catalytic pyrolysis of toluene

Noncatalytic and catalytic pyrolysis of toluene has been studied at atmospheric pressure in the temperature range of 1043 to 1153 K using steam or nitrogen as the diluent. The catalyst used was potassium carbonate impregnated calcium aluminate. Compared to noncatalytic pyrolysis, the conversions were significantly higher in the presence of the catalyst although the product selectivities were not affected. With nitrogen as the diluent the main products were hydrogen, methane, benzene, bibenzyl and higher hydrocarbons. When steam was used as the diluent, in addition to the above products appreciable amounts of carbon monoxide and carbon dioxide were also produced. The overall reaction of toluene could be represented by two parallel paths; one for toluene decomposition and the other for the toluene-steam reaction. The kinetic constants of these two reactions for catalytic as well as noncatalytic pyrolysis were determined by nonlinear optimization. In the presence of the catalyst, the activation energy for toluene decompostion was significantly reduced, whereas there was only a marginal reduction in the activation energy of the toluene-steam reaction.     

Wood/plastic copyrolysis in an auger reactor: Chemical and physical analysis of the products

Previous studies observed that slow copyrolysis of wood and plastic in enclosed autoclaves produced an upgraded raw bio-oil with increased hydrogen content. We now demonstrate that fast simultaneous pyrolyses of 50:50, w/w, pine wood/waste plastics in a 2 kg/h lab scale auger-fed reactor at 1 atm, with a short vapor residence time, generates higher heating value upgraded bio-oils. Three plastics: polystyrene (PS), high density polyethylene (HDPE) and polypropylene (PP) were individually copyrolyzed with southern yellow pine wood at 525, 450 and 450 °C, respectively, to generate modified bio-oils upon condensation. These liquids exhibited higher carbon and hydrogen contents, significantly lower oxygen contents, higher heats of combustion and lower water contents, acid values and viscosities than pine bio-oil. The formation of cross-over wood/plastic reaction products was negligible in the oils. Simultaneous pyrolysis process design requires using a temperature at which the plastic’s thermal decomposition kinetics produce vapors rapidly enough to prevent vaporized plastic from condensing on wood chars and exiting the reactor.     

Pyrolysis of methane in the presence of hydrogen

The kinetics of methane pyrolysis were studied in a tubular flow reactor in the temperature range 1200 to 1500°C at atmospheric pressure. To avoid excessive carbon formation the reaction time was short and the methane feed was diluted with hydrogen. Ethene, ethyne, benzene and hydrogen were the main gaseous products. Ethane was observed as a product at very low conversions of methane. More than 90% selectivity was obtained for C₂ products. The ratio of ethyne to ethene increased with increasing temperature. The yield of C₂ products is limited by gas-phase equilibrium at lower temperatures. Formation of carbon was strongly depressed by hydrogen at higher temperatures. The maximum yield of ethyne was found to increase from about 10% to about 50% when the temperature was increased from 1200 to 1500°C, with hydrogen dilution H₂: CH₄ = 2: 1. A mechanistic reaction model was used to simulate the pyrolysis of methane at the actual conditions. A sensitivity analysis was performed to evaluate the elementary reactions which influence the formation and consumption of the species in the model system.