Influence of carrier gas flow and heating rates in fixed bed hydropyrolysis of coal

Fixed bed hydropyrolysis experiments on a UK bituminous coal (82% dmmf C) at 580–650 °C and pressures up to 300 bar have indicated that tar yields depend strongly on the velocity of the hydrogen carrier gas relative to the static coal particles. Tar yields increase with increasing pressure provided that the superficial gas velocity is not reduced. Otherwise, tar yields can actually decrease because the beneficial hydrocracking reactions that occur are no longer sufficient to counter the increased char formation resulting from the slower rates of intra-particle diffusion and devolatilization of tar molecules. While raising the heating rate from 1 to 20 °C s⁻¹ had little effect on overall conversions, hydrocarbon gas yields increased significantly at the expense of tar. Moreover, the higher heating rate gave more aromatic tars, and the available evidence strongly suggests that the primary volatiles are hydrocracked before escaping from the coal particles as well as in the vapour phase.     

Fe/CaO催化剂对脱灰徐州烟煤热解特性的影响

煤热解是一种重要的煤炭分质利用技术，但热解过程中产生的副产物焦油危害极大，催化改质是高效清洁利用煤焦油的方法之一。本文采用溶胶凝胶法制备Fe/CaO催化剂，在管式炉反应器上对脱灰徐州烟煤进行了催化热解实验，对研究催化裂解煤焦油具有重要的意义。结果表明：Fe/CaO催化剂可以明显促进热解气的产生，热解气中CO₂、CO和CH₄的产量均不断增加。Fe/CaO催化剂促进了液体产物的催化裂解，导致液体产率明显下降。Fe/CaO催化剂促进焦油中的稠环芳烃向脂肪烃和轻质芳烃转化，此外，Fe/CaO催化剂还对萘类化合物的产生有促进作用。Fe/CaO催化剂催化后焦油中两环化合物的含量增多，三环及以上的化合物含量减少，焦油分子量呈减少的趋势。     

催化裂化轻汽油在ZSM-5分子筛催化剂上裂化反应的研究

以ZSM-5分子筛为催化剂，在小型固定床反应器上，进行了催化裂化轻汽油的裂化反应。考察了反应温度和空速对催化裂化轻汽油裂化反应气液相收率和产品分布的影响。实验结果表明，ZSM-5分子筛催化剂具有较强的裂化活性和氢转移活性。在保证裂化转化率的条件下，提高反应温度和空速可以抑制催化剂上氢转移反应的发生。以ZSM-5分子筛为催化剂上的催化裂化反应中，温度、空速是影响转化率和选择性的重要因素，因此可以通过改变温度、空速来提高目的产物的选择性。但是，单纯依靠改善反应条件，不能使目的产物的收率和选择性达到理想的程度，还必须对催化剂进行改性。ZSM-5分子筛催化剂上催化裂化反应的研究为ZSM-5分子筛催化剂的进一步改性，及ZSM-5分子筛催化剂在轻汽油催化裂解和汽油改质方面的进一步应用提供了试验依据。     

Hydrocracking of phenanthrene over bifunctional Pt catalysts

Hydrocracking of phenanthrene was studied in a fixed bed continuous flow reactor under 60 bar total pressure using a bifunctional catalyst constituted of Pt deposited on silica–alumina. GC–MS analysis was utilised in order to identify the numerous products formed during phenanthrene hydrocracking. Following a kinetic study, a reaction pathway was proposed based on a multi-step mechanism: hydrogenation of aromatic rings, isomerisation and cracking of naphtenic rings, and rearrangements. Reaction temperature showed a great effect in terms of selectivity and catalysts comparison was therefore done at a temperature of 300°C. Three bifunctional catalysts: platinum supported on silica–alumina, on H-Y zeolite and on H-β zeolite were compared in terms of activity and selectivity. A close examination of product distribution indicated that the major contributing factor was the pore structure of the support. Zeolite structures favoured overcracking because of the numerous collisions with acid sites that perhydrophenanthrene could undergo during its diffusion.     

Computational fluid dynamics modeling of biomass catalytic fast pyrolysis in bubbling fluidized reactor: Effects of catalyst parameters on process performance

In this study, a computational fluid dynamics mathematical model has been developed for catalytic fast pyrolysis (CFP) of biomass based on multiphase flow, transfer process, and biomass pyrolysis reactions in a bubbling fluidized bed reactor. The multiphase fluid flow, and the inter-phase momentum and energy transfer processes are modeled with Eulerian multiphase formulas, representing the flows of gases and solids (catalyst and biomass) within the reactor. The biomass CFP reactions are described by using a two-stage, semi-global model. Specified secondary tar catalytic cracking process, which considers both intrinsic reaction rates and mass-transfer process, is embedded to the developed model by user-defined function. The model simulation results of pyrolysis product yield and distribution are compared with the experimental data with close agreement. The model is then employed to investigate the effects of structural properties of catalyst, such as specific internal area, average size of active sites, pore diameter, and tortuosity, on products yields and composition. The tar cracking process by the selected catalyst is proposed and the influences of adsorption capability of tar molecule on catalyst surface and external film mass transfer are also analyzed. The developed model can be solved with short computational time and thus it can be employed for further research and engineering designs of the catalytic pyrolysis of carbonaceous materials.     

Light aromatics from the hydropyrolysis of coal

The hydropyrolysis of British coals was studied at hydrogen pressures of 5–15 MPa using heating rates of up to 30 K s^?1. In a single-stage reactor, hydropyrolysis of a high-volatile coal gave a maximum yield of 4.5 Wt % of single-ring aromatics. The results suggested that the evolution of volatiles and their cracking to benzene, toluene and xylenes were sequential reactions. This was confirmed using a two-stage reactor in which the coal was heated in one zone and the volatiles cracked in a separate, isothermally heated zone. Yields of up to 12 wt % benzene were then obtained from a high-volatile bituminous coal in hydrogen at 15 MPa, both the cracking temperature and the vapour residence time being separately optimized. Hydropyrolysis of model compounds showed that benzene was a major product of the cracking of polynuclear aromatics under hydrogen pressure.     

多级孔分子筛在重油加氢裂化催化剂的应用进展

分子筛是加氢裂化催化剂关键组分,其性质影响着加氢裂化反应效率和产品分布。微孔分子筛的孔结构降低了大分子反应物的扩散效率和酸中心的可及性,不宜直接用作加氢裂化催化剂的载体。本文从分子筛的孔结构和酸中心可及性的角度出发,介绍了具有多级孔体系的分子筛和具有核壳结构分子筛的加氢裂化性能。与相应的参比剂比较,分子筛的多级孔结构能大幅提高反应物种的扩散效率和酸中心的可及性,呈现出更好的催化活性、稳定性以及目标产物选择性。此外,金属加氢活性中心与分子筛裂化活性中心的合理调配,也是多级孔分子筛在重油加氢裂化应用中面临的挑战。     

煤多段加氢热解过程的研究(Ⅰ)反应条件对产物分布的影响

在 10g加压固定床上考察了 5℃·min^-1和 2 5℃·min^-1的升温速率下先锋褐煤的多段加氢热解过程 .详细考察了有关的工艺参数如停留时间、升温速率、气体流量、反应压力及反应气氛对多段加氢热解过程产物分布的影响 ,并与同等条件下的单段加氢热解过程进行了对比分析 .实验结果表明 :多段加氢热解过程明显优于同等反应条件下的单段加氢热解过程 ,采用快速升温、多段停留的手段基本可以达到慢速升温过程高的转化率及油收率 ;多段加氢热解过程中的停留作用随升温速率的增大、反应压力的增加、氢气流量的增大而显著增大 .另外还发现合成气气氛下的多段停留作用与氢气气氛下的相类似     

催化剂制备与研究 中低温煤焦油加氢裂化催化剂的表征与分析

通过对反应前后的煤焦油加氢裂化催化剂进行表征与分析,研究影响中低温煤焦油加氢催化剂失活的原因,以煤焦油组分特点为依据,分别考察加氢裂化催化剂的活性元素、积炭、金属沉淀、分散度和中心酸性等对催化剂寿命的影响。结果表明,煤焦油加氢催化剂的失活原因主要为积炭失活、金属沉积和水热失活;催化剂中较低的金属钙含量、良好的水热稳定性及较低的L酸含量有利于催化剂寿命的提高。     

工业加氢裂化催化剂失活原因分析

采用200 m L加氢评价装置对一种中油型加氢裂化催化剂和其在工业装置运转4年后的再生后催化剂进行对比评价。结果表明,失活催化剂经再生后加氢裂化活性明显降低,反应温度比新鲜催化剂高5℃,生成油产品分布和主要性能都略变差。采用XRD、IR和ICP等手段对再生前后催化剂性能进行表征,分析探讨催化剂的失活原因,结果表明,加氢裂化催化剂经工业应用后,炭的沉积使其暂时性失活,而重金属沉积、金属活性组分聚集和分子筛结构烧结使催化剂部分活性永久丧失。     

Hydro-thermal cracking of heavy oils and its model compound

Liquid-phase cracking of vacuum gas oil (VGO) was performed over NiMo supported nonacidic catalysts under 713 K and 8.0 MPa of hydrogen in a batch reactor, which is termed hydro-thermal cracking. Compared with VGO thermal cracking under the same reaction conditions the new process showed the suppressed naphtha yield (from 22.4 to 13.5 wt.%) and VGO conversion (from 65.7 to 64.0 wt.%) and increased the middle distillate yield (from 44.3 to 49.3 wt.%). At the same conversion level, the yield ratio of middle distillates to naphtha for this new process was two times higher than that for VGO hydrocracking. The VGO hydrocracking over USY-supported NiMo proceeded at much lower temperatures but gave higher naphtha yields. Both the thermal cracking and the hydro-thermal cracking of n-dodecyl benzene (C₆H₅(CH₂)₁₁CH₃) yielded toluene as the major aromatic product, whereas its hydrocracking over NiMo/USY yielded benzene as the major aromatic product. The reaction mechanism of this new process was assumed to consist of thermal cracking of hydrocarbon molecules via the free radical chain mechanism and the catalytic hydroquenching of free radicals.     

Combined effects of pressure and ion-exchangeable metallic species on pyrolysis of Victorian lignite

A set of ion-exchanged samples prepared from Loy Yang lignite was pyrolyzed in a wire-mesh reactor at elevated pressures from 1 to 36 bar. The tar yields from the pyrolysis of H-form (acid-washed) sample at a fast heating rate of 1000 °C s⁻¹ were drastically reduced by increasing pressure to 6 bar and then remained unchanged with further increase in pressure to 36 bar. This behavior of the tar yield was in sharp contrast to that from the raw lignite which showed a minimum with increasing pressure. The sensitivities of the tar yields to changes in the heating rate were also suppressed by increasing pressure. The tar yields from Ca-form and Na-form samples (prepared by ion-exchanging Ca and Na on the H-form sample, respectively) were not very sensitive to changes in the heating rate and pressure up to 11 bar. At 20 bar, the tar yields from the Na-from sample nearly doubled whereas from the Ca-form sample nearly halved compared to those respective values at 1 bar. Although increasing pressure is thought to cause changes in the intra-particle mass transfer processes of volatile precursors, the rate of formation of volatile precursors tends to dictate the kind of mass transfer process responsible for the release of volatiles. Therefore, depending on the pyrolysis condition, bulk diffusion or forced flow would dominate the mass transfer processes for the release of volatiles. The introduction of cations is thought to result in irreversible changes in the lignite structure and not only control the process of formation but also the amount of volatile precursors and in turn alter the effects of pressure. Valence and catalytic activity of cations seem to play important roles in determining pyrolysis products distribution at elevated pressures.     

Industrielle Anwendung von zeolithischen Katalysatoren beim Hydrocracken

Industrial application of zeolitic catalysts in hydrocracking . For maximum production of gasoline by hydrocracking using zeolite type catalysts two cracking schemes are presented and the operation conditions, feedstocks, yields, and material balances are discussed. The advantages of zeolitic hydrocracking catalysts are outlined. The main catalyst parameters controlling activity and selectivity are described and a scheme for the preparation of zeolitic catalysts is given, which illustrates the superiority of zeolitic hydrocracking catalysts over amorphous ones. Finally, the hydrocracking of residues is reviewed and a typical process together with the product characteristics and yields obtained is described.     

Combustion of methane lean mixtures in reverse flow reactors: Comparison between packed and structured catalyst beds

The scope of this work is to compare systematically the performance of particle beds and monolithic beds in catalytic reverse flow reactors used for combustion of lean methane/air mixtures, using alumina-supported palladium as catalyst. Different values of gas surface velocity (0.1–0.3 m/s), particle diameter (3–6 mm, for particle bed), cell density (200–400 cpsi, for structured bed) and catalyst/inert ratio (0.4–1) were used for the simulation of the combustion of 3500 ppm methane in both kinds of reverse flow reactor. An unsteady one-dimensional heterogeneous model has been developed and solved using a MATLAB code. The model, physical parameters and transport properties used had been experimentally validated in a previous work, operating with a particle bed reverse flow reactor. Results obtained indicate that the reverse flow reactor is more stable when the catalyst particle beds are use, although the difference with the monolith bed decreases as surface velocity increases. In contrast, pressure drops in the bed are higher for the particle bed.     

全结晶ZSM-5分子筛催化剂研究及工业应用

制备了全结晶ZSM-5分子筛催化剂,采用XRD、SEM、N2物理吸附-脱附及NH3-TPD等对催化剂进行表征,并考察其用于碳四烯烃催化裂解制丙烯(OCC)反应的催化性能。结果表明,制备的全结晶ZSM-5分子筛催化剂比常规成型的催化剂具有更高的结晶度、更大的比表面积、更丰富的孔结构以及更多的活性中心。高空速有利于反应的进行,提高压力对反应不利,升高温度有利于提高产物丙烯收率。在实验室研究的基础上,将全结晶ZSM-5分子筛催化剂用于OCC工业装置,取得良好的应用效果。     

Experimental study on the coal tar hydrocracking process in supercritical solvents

In order to find the optimal operating parameters in high-temperature and low-temperature coal tar hydrocracking processes and to maximize the light oil yields, experimental studies have been carried out in a one-stage reactor in supercritical solvents. Xylene and gasoline were used as supercritical solvents to investigate their effects on the light oil yields. The results show that gasoline was more suitable as a supercritical solvent and that a suitable ratio of gasoline solvent to coal tar could result in higher light oil yields in both high- and low-temperature coal tar hydrocracking processes. The effects of different operating parameters, including temperature, hydrogen pressure, catalyst, and residence time, on light oil yield were tested. It was found that the yields of light oil from the two coal tar hydrocracking processes varied with the operating parameters in a similar manner. However, different values of the operating parameters gave rise to the maximum yields of light oil from the respective processes.     

Ni-Mo/Y-β催化正辛烷加氢裂化的研究

以双微孔复合分子筛Y-β为载体，制备了双功能催化剂Ni-Mo/Y-β。表征发现， 浸渍后Ni-Mo/Y-β催化剂的比表面积、孔容、总酸量和结晶度均有所下降。并在固定床不锈钢反应器上考察了Ni-Mo/Y-β催化剂对正辛烷加氢裂化反应的催化性能，结果表明，在反应温度230 ℃、压力3.0 MPa、体积空速1.5 h-1和氢油体积比1 000∶1条件下，反应转化率为83.9%，裂解率82.28%，对异丁烷的选择性为37.49%。     

NiMo/HY催化剂上四氢萘加氢裂化反应网络与热力学平衡分析

采用固定床反应器对四氢萘在NiMo/HY工业催化剂上的加氢裂化反应过程进行了研究,考察了反应温度对产物分布的影响,提出了四氢萘加氢裂化反应网络。该网络包含加氢、异构、脱氢、开环、脱烷基等12个反应,通过热力学计算,得到了这些反应的平衡常数,并据此求得各类产物的平衡收率及其随温度、压力和氢气/四氢萘（摩尔比）的变化规律。由热力学平衡分析得到的产物收率随反应条件的变化规律与实验结果较为吻合,表明本文构建的反应网络可以较好地描述NiMo/HY催化剂上的四氢萘加氢裂化反应体系。     

Decomposition and gasification of pyrolysis volatiles from pine wood through a bed of hot char

Pine wood was pyrolyzed in a fixed bed reactor at a heating rate of 10 °C and a final temperature of 700 °C, and the resultant volatiles were allowed to be secondarily cracked through a tubular reactor in a temperature range of 500-700 °C with and without packing a bed of char. The thermal effect and the catalytic effect of char on the cracking of tar were investigated. An attempt was made to deconvolute the intermingled contributions of the char-catalyzed tar cracking and the char gasification to the yields of gaseous and liquid products. It was found that the wood char (charcoal) was catalytically active for the tar cracking at 500-600 °C, while at 650-700 °C, the thermal effect became a dominant mode of the tar cracking. Above 600 °C, the autogenerated steam gasified the charcoal, resulting in a marked increase in the yield of gaseous product and a significant change in the gas composition. An anthracite char (A-char), a bituminous coal char (B-char), a lignite char (L-char) and graphite also behaved with catalytic activities towards the tar cracking at lower temperature, but only L-char showed reactivity for gasification at higher temperature.     

Alkylation of benzene with ethane over platinum-loaded zeolite catalyst

Alkylation of benzene with ethane was carried out using various zeolite catalysts at temperature ranges of 400–550°C. Loading of platinum onto zeolite greatly enhanced the yield of ethylbenzene. Among the zeolites tested, H-ZSM5 and H-MCM22 showed catalytic activities. By contrast, mordenite did not yield ethylbenzene. Moderate acid strength distribution is the key factor of zeolite catalysts. Optimum catalyst and conditions for this reaction are as follows. The platinum-loaded H-ZSM5 catalyst containing 6.8 wt% Pt, at a reaction temperature of 500°C, afforded ethylbenzene and styrene formation rates of 14.2 and 0.8 mmolh^–1g-cat^–1, respectively (benzene-based yields 7.3 and 0.4%). In the alkylation of benzene with ethane over platinum-loaded H-ZSM5, ethene was initially formed from ethane over the metallic platinum. Then the alkylation proceeded over the acid sites of H-ZSM5.