Catalytic pyrolysis of tyres: influence of catalyst temperature

Two stage pyrolysis–catalysis of used tyres was undertaken to upgrade the derived oil to a highly aromatic oil suitable to be used as a chemical feedstock rather than a liquid fuel. The tyres were pyrolysed in a fixed bed reactor and the evolved pyrolysis gases were passed through a secondary fixed bed reactor containing zeolite catalyst. The pyrolysis reactor was maintained at 500 °C and the influence of catalyst temperature between 430 and 600 °C on the yield and composition of the derived oils was examined. Two zeolite catalysts were examined; a Y-type zeolite catalyst and zeolite ZSM-5 catalyst of differing pore size and surface activity. The influence of the catalyst was to reduce the yield of oil with a consequent increase in the gas yield and formation of coke on the catalyst. Single ring aromatic hydrocarbons, benzene, toluene and xylenes present in the oils showed a marked increase in the presence of the catalyst. Naphthalene and alkylated naphthalenes were also analysed and showed a similar marked increase in the concentration when a catalyst was present. The Y-type zeolite catalyst of larger pore size and higher surface activity was found to produce higher concentrations of aromatic compounds compared to the ZSM-5 catalyst. Increasing the catalyst temperature resulted in significant changes in the concentration of benzene, toluene, xylenes, naphthalene and the alkylated naphthalenes.     

Toluene removal from indoor air using a miniaturized photocatalytic air purifier including a preceding adsorption/desorption unit

The performance of the miniaturized photocatalytic air purifier including a continuous adsorption/desorption unit with a zeolite particles-loaded honeycomb rotor was investigated in the photocatalytic purification of 1 m³ air containing toluene at concentrations of 3-11 mg m⁻³ (about 1-3 ppmv). While operating the continuous adsorption/desorption unit only, and for desorption temperatures controlled within the range of 90-120 and 130-160 °C, the unit took approximately 10 min to reduce the toluene concentration in a 1 m³ room, to a value of almost zero. Almost the same time courses of toluene concentrations were obtained when the photocatalytic reactor was switched on. This result clearly shows that the rapid decrease in the toluene concentration in the 1 m³ room is mainly due to the adsorption of toluene onto the zeolite rotor. When the reactor was switched off, the concentration of toluene desorbed into the 0.022 m³ reactor box increased rapidly and then levelled off in 10 min. On the other hand when the reactor was switched on, the toluene concentration in the reactor box increased rapidly, passing through a maximum in 10-150 min, and then decreasing to a value near zero, leading to the toluene concentration in the 1 m³ room becoming negligible. The apparent rates of decomposition determined from the decreasing toluene concentration in the reactor box were 10-fold smaller than the intrinsic rate constant in the Langmuir-Hinshelwood equation, which would suggest that the desorption process of toluene from the rotor is the rate-limiting. All the decomposition experiments were performed using the same zeolite rotor and photocatalytic reactor over a six month period; and the runs were repeated more than one hundred times. Nevertheless, there was no distinct decrease in decomposition activity of the photocatalyst or any significant loss in ability for the zeolite rotor to adsorb toluene could be seen, indicating that these materials can perform constantly over a long period of time. However, as the rotor will sooner or later become saturated with toluene, it may become necessary to introduce a regeneration procedure in order to periodically remove toluene from the rotor.     

Alkylation of toluene with 1‐dodecene over HFAU zeolite. Deactivation and regeneration

The alkylation of toluene with 1dodecene was carried out over a HFAU zeolite (total and framework Si/Al ratio = 25) under the following conditions: fixedbed reactor, 90°C, molar toluene/dodecene ratio of 3, WHSV =10 h^–. Monododecyltoluenes are selectively formed, bidodecyltoluenes appearing only in low amounts at a complete conversion of dodecene. Tridodecyltoluenes are also formed inside the supercages but cannot desorb from the zeolite. These compounds, mainly located in the outer part of the crystallites are responsible for catalyst deactivation. However, tridodecyltoluenes can be completely removed by treatment under toluene flow, which allows a complete regeneration of the catalyst. This removal occurs by transalkylation between tridodecyltoluenes and toluene molecules with a final formation of monododecyltoluenes. At least, the first transalkylation steps occur between toluene in the liquid phase and tridodecyltoluenes in the zeolite pores (pore mouth catalysis).     

Oxidation of volatile organic compounds by using a microwave-induced plasma process

A microwave plasma system using a 2.45 GHz magnetron was applied to the decomposition of volatile organic compounds such as toluene and trichloroethylene. Designed for producing plasma at atmospheric pressure, this microwave plasma system consists of a magnetron detached from a household microwave oven, a directional coupler, a three-stub tuner, a tapered waveguide, and plasma flame section where a quartz tube with a nozzle is located. In this system, the organic compounds can be decomposed by thermal incineration as well as by reactions with various active species formed during plasma discharge. The effect of feed gas flow rate on the decomposition was significant due to the decrease in the gas temperature, but the initial concentration in the range of 210-2,100 ppm did not largely affect the decomposition efficiency. The principal byproduct was nitrogen oxides because this system was operated at high temperature. To improve the decomposition of the organic compounds, argon was used as a plasma-assisting gas, together with the air-like feed gas mixture. Large enhancement in the decomposition efficiency was achieved by the use of argon.     

TEOS-化学液相沉积法改性ZSM-5催化剂上的高选择性甲苯择形歧化反应

Shape-selective catalysts for the disproportionation of toluene were prepared by the modification of the cylinder-shaped ZSM-5 zeolite extrudates with chemical liquid deposition with TEOS (tetraethyl orthosilicate).Various parameters for preparing catalysts were changed to investigate the suitable conditions.The resulting cata-lysts were tested in a pressured fixed bed reactor and characterized by SEM (scanning electron microscopy).The conversion of toluene and para-xylene selectivity were influenced remarkably by the n(SiO2)/n(Al2O3) ratio of ZSM-5 zeolite,the type and amount of deposition agent,acid and solvent used,and the time and cycle of deposition treatment.TEOS was proved to be a more efficient agent than the conventional polysiloxanes when the deposition amount was low.The catalyst prepared at the suitable conditions exhibited a high para-xylene selectivity of 91.1% with considerable high conversion of 25.6%.SEM analyses confirmed the formation of a layer of amorphous silica on the external surface of ZSM-5 zeolie crystals,which was responsible for the highly enhanced shape-selectivity.     

利用Fluent软件对N_2O催化分解反应器数值模拟

为了设计N_2O催化分解反应器,运用Fluent软件对整体式分子筛催化剂进行数值模拟,考察孔密度和操作条件对整体式分子筛催化剂转化率的影响。结果表明,在相同温度下,N_2O的转化率随着催化剂孔密度的减小而降低。在反应器轴向距离120 mm处,气体反应最快;提高入口温度、浓度或降低空速,均有利于在较短的轴向距离内达到较高的N_2O转化率。在固定床反应器中,比较棒状催化剂和整体式催化剂中床层温度、反应转化率及轴向压降的变化规律,为整体式分子筛催化剂工业化设计提供理论基础。     

下行床气固传质及反应特性的实验研究

以臭氧催化分解为模型反应,对气固并流下行循环流化床反应器中气固传质与反应特性进行了研究. 制备了臭氧分解催化剂,并以它为循环物料在内径0.09 m、高度8.2 m的下行床中测定了颗粒浓度分布和臭氧浓度分布. 实验结果表明,臭氧在加速段分解率在45%左右,约占总分解率的90%,其随颗粒循环量(Gs)的增加略有上升. 当Gs从2.77 kg/(m2×s)增加到6.58 kg/(m2×s)时,全床分解率从50%上升至55%. 建立了平推流的传质模型,给出了有效传质系数和操作参数的关联式.     

Determination of decomposition rate constants of volatile organic compounds and nitric oxide in a pulsed corona discharge reactor

The decomposition of toluene, propylene and nitric oxide by using a pulsed corona discharge process was investigated. The performance equation of the pulsed corona reactor was derived with the assumption that the decomposition reaction rate is directly proportional to the concentration of the pollutant and the discharge power. From this model equation and the experimental data, the apparent decomposition rate constants of various gaseous organic compounds and nitric oxide were determined. Alkene and substituted alkene were found to have much larger decomposition rate constants than aromatic compounds and substituted alkane, which indicates that the derivatives of aromatics and alkane cannot readily be decomposed in this system. To verify the validity of the model derived, the experimental data in the present study and in the literature were compared with the calculation results using the decomposition rate constants. Despite the different reactor geometry and experimental condition, good agreement between the experimental data and the calculation results was shown.     

Preparation of carbon micro-coils involving the decomposition of hydrocarbons using PACT (plasma and catalyst technology) reactor

Carbon micro-coils as well as carbon fibers with various morphologies were prepared by the decomposition of hydrocarbons, such as acetylene, methane, propane, ethylene, etc., at 770°C using a PACT (plasma and catalyst technology) reactor. The preparation conditions, growth mechanism and morphology of the carbon micro-coils were examined. The Ni electrode of the PACT reactor was used as the catalyst as well as a plasma source electrode. It was found that hydrocarbons, such as methane, propane and ethylene, decomposed under the plasma and catalyst atmosphere to form acetylene as the main decomposition product, and then this acetylene was further decomposed to form carbon micro-coils. Using a Ni powder catalyst dispersed on the substrate, the carbon micro-coils with a double helix structure, in which two pieces of carbon coils entwine each other in the same coiling direction, grew among the single straight carbon fibers and paired straight fibers. On the other hand, the carbon micro-coils with a single helix structure and wide coil pitch were obtained by the indirect decomposition of acetylene using the N₂ plasma formed by the PACT reactor.     

Co/RPSA系列催化剂在N2O分解中的应用

采用正交试验设计方法设计和浸渍法制备分子筛RPSA负载Co、K、Ba和Sr催化剂,使用微型反应器评价催化剂用于直接分解N₂O的催化活性,考察活性组分对催化剂活性的影响。采用XRD、H₂-TPR和NH₃-TPD等方法对催化剂进行表征。结果表明,金属Co和K对催化剂活性影响显著,Co对提高催化剂活性有促进作用,Co含量增加,催化剂活性提高,而K对催化剂活性有抑制作用。催化剂表征结果显示,Co物种主要以Co₃O₄形式存在于载体表面,催化剂的组成和配比影响催化剂活性、氧化还原性能和酸性,催化剂强酸的存在有利于催化剂活性的提高。
     

甲苯甲醇烷基化制对二甲苯催化剂中试反应性能研究

经过多步改性制备了负载二氧化硅（SiO₂）、氧化镁（MgO）、五氧化二磷（P₂O₅）、贵金属铂（Pt）的纳米ZSM-5分子筛催化剂,并在六段固定床反应器上分段装填该催化剂720 g进行甲苯、甲醇烷基化制对二甲苯反应活性评价。实验结果表明,通过调变甲醇和甲苯物质的量比可以使甲苯转化率在22%~30%可调,烷基化液相产物中二甲苯选择性保持在95%以上,二甲苯中对二甲苯选择性保持在95%以上;催化剂单程寿命达到1 300 h,随着反应时间延长催化剂的活性有所下降。通过X射线衍射（XRD）、热重分析（TG-DTG）和氮气吸附-脱附等手段对参加反应前后的催化剂进行了表征,结果表明反应中生成的积炭堵塞了分子筛的孔道或覆盖了催化剂的活性位;经过在反应器内原位再生,催化剂的反应活性基本恢复到新鲜催化剂水平。     

Catalytic Activity of Copper Oxide Impregnated HZSM‐5 in Methanol Conversion to Liquid Hydrocarbons

A number of CuO/HZSM‐5 catalysts have been studied in a small scale fixed bed reactor for the conversion of methanol to gasoline range hydrocarbons at 673 K and at one atmospheric pressure. All the catalysts were prepared by wet impregnation technique. The copper oxide loading over HZSM‐5 (Si/Al=45) catalyst was studied in the range of 0 to 9 wt%. XRD, surface area analyzer, metal trace analyzer, SEM techniques and TGA were used to characterize the catalysts. Incorporation of CuO onto HZSM‐5 zeolite significantly increased conversion and liquid hydrocarbon product yields. The major liquid products of the reactions were ethyl benzene, toluene, xylene, isopropyl benzene, ethyl toluene, trimethyl benzene and tetramethyl benzene. The maximum methanol conversion and hydrocarbon product yield was obtained at a copper oxide loading of 7 wt%. Effect of run time on conversion and product distribution was also investigated to compare the performance of these catalysts and coke on the catalyst was determined. Effect of space‐time and temperature on methanol conversion and products yield with 7 wt% CuO/HZSM‐5 has also been investigated and analyzed qualitatively.     

Promising zeolite-type hydrocarbon trap catalyst by a knowledge-based combinatorial approach

Libraries consisting of more than 100 zeolite samples were prepared and examined for developing a promising HC trap catalyst. Parallel adsorptions of toluene onto the catalyst samples were conducted over a 10 × 10 array reactor under dry and wet conditions with or without a heating process three knowledge-based conditions for developing an automotive catalyst during the cold-start period. FAU and BEA type zeolites revealed a high performance of toluene adsorption under the dry condition. However, FAU type zeolite significantly decreased the amount of toluene adsorbed in the presence of water in the feed gas stream, mainly due to the hydrophobicity of the catalyst surface. Over Beta type zeolites, the toluene adsorbed was found to be considerably preserved, even after forced desorption temperature-ramping to the warm-up condition of an automotive engine. Li, K, or Ag ion-exchanged Beta zeolites seem to be particularly promising as an HC trap catalyst.     

甲醇甲苯烷基化流化床反应器的数值模拟

利用甲醇甲苯烷基化工艺生产对二甲苯具有良好的应用前景。甲醇甲苯烷基化催化剂较易积炭失活,且反应存在明显热效应。流化床因传热传质性能好、易实现催化剂连续再生,适合用作甲醇甲苯烷基化反应器。本文采用离散颗粒模型,对甲醇甲苯烷基化流化床反应器进行了数值模拟研究,重点考察了进料比、反应压力、分段进料对反应特性的影响。结果表明,当甲苯进料量给定时：降低反应物中甲苯甲醇比可有效提升对二甲苯产率和选择性,但产物中对二甲苯和烯烃摩尔比值较低;提高反应压力可显著提升甲醇和甲苯转化率,但会降低对二甲苯选择性;在低苯醇比基础上采用甲醇分段进料方式不仅可有效提高甲苯利用率,还可灵活调节产物中对二甲苯和烯烃比率;流化床反应器气体返混不利于获得高对二甲苯选择性,且操作条件变化会造成流化床反应器内气固流动改变,导致气固接触效率或反应物局部分压发生改变,这亦将对反应转化特性造成显著影响。这些结果对于流化床反应器优化和放大具有一定的指导意义。     

介质阻挡放电协同复合碳材料去除VOCs

挥发性有机物（VOCs）是常见的空气污染物,实验研究低温等离子体催化技术去除以甲苯为代表的VOCs。采用炭粉末、酚醛树脂和致孔有机高分子聚合物的有机溶剂混合物作为前驱物,经过炭化、水汽活化和负载锰催化剂,制备一种基于发泡金属的复合碳材料。采用扫描电子显微镜、XRD、全自动比表面积及微孔孔隙分析仪对材料进行表征。两段式介质阻挡放电反应器结合复合碳材料降解甲苯,前段介质阻挡放电初步降解甲苯,后段复合碳材料利用介质阻挡放电产生的长寿命活性物种和臭氧进一步去除甲苯。输入电压为10 kV时,甲苯去除率约99.4％,CO₂选择性达72.2%,并且有效控制了副产物臭氧。实验结果表明,复合碳材料有望应用于如臭氧和VOCs等的污染控制。     

In situ synthesis of SAPO-34 crystals grown onto α-Al2O3 sphere supports as the catalyst for the fluidized bed conversion of dimethyl ether to olefins

SAPO-34 is an excellent catalyst for the conversion of dimethyl ether (DME) to olefins, but because conventionally synthesized SAPO-34 crystals are too small to be used directly in a fluidized bed, they have to be used as, and have the disadvantages of, a spray-dried catalyst. In this study, SAPO-34 crystals were synthesized in situ to grow on the surface of small α-Al₂O₃ spheres to produce a zeolite catalyst for a fluidized bed reactor. The influences of the composition of the crystal gel and surface structure of the support were investigated. The catalytic performance of the zeolite crystals grown on the support (surface zeolite) for the conversion of DME to olefins was investigated in a fixed bed microreactor and a fluidized bed reactor. The experiments showed that these surface SAPO-34 crystals gave the same activity and product selectivity as conventionally synthesized free SAPO-34 crystals and a higher reaction rate (normalized to the weight of SAPO-34) than the spray-dried catalyst. In situ synthesis is a simple and effective way to produce a SAPO-34 catalyst for a fluidized bed reactor.     

Effective combination of non-thermal plasma and catalyst for removal of volatile organic compounds and NOx

A plasma/catalyst hybrid reactor was designed to overcome the limits of plasma and catalyst technologies. A two-plasma/catalyst hybrid system was used to decompose VOCs (toluene) and NOx at temperature lower than 150 °C. The single-stage type (Plasma-driven catalyst process) is the system in which catalysts are installed in a non-thermal plasma reactor. And the two-stage type (Plasma-enhanced process) is the system in which a plasma and a catalyst reactor are connected in series. The catalysts prepared in this experiment were Pt/TiO₂ and Pt/Al₂O₃ of powder type and Pd/ZrO₂, Pt/ZrO₂ and Pt/Al₂O₃ which were catalysts of honeycomb type. When a plasma-driven catalyst reactor with Pt/Al₂O₃ decomposed only toluene, it removed just more 20% than the only plasma reactor but the selectivity of CO₂ was remarkably elevated as compared with only the plasma reactor. In case of decomposing VOCs (toluene) and NOx using plasma-enhanced catalyst reactor with Pt/ZrO₂ or Pt/Al₂O₃, the conversion of toluene to CO₂ was nearly 100% and about 80% of NOx was removed. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

碱处理HZSM-5分子筛对神东煤热解产物分布的影响

使用NaOH溶液对HZSM-5分子筛进行处理,利用粉-粒流化床快速热解实验装置,考察了经过不同时间碱处理的HZSM-5分子筛对神东煤热解产物分布的影响。结果表明：适当的碱处理能够在不破坏HZSM-5分子筛晶相结构的情况下在晶体内部引入介孔,且随着碱处理时间的延长,分子筛的介孔孔容、介孔比表面积增加,孔径分布变宽,总酸量先增大后减小。碱处理0.5h的HZSM-5分子筛催化时焦油中苯、甲苯含量最大,较原煤热解分别增加了268%、296%;碱处理2h的HZSM-5分子筛催化下热解气体总含量达到最大,较原煤热解增加了24.8%;碱处理4h的HZSM-5催化时焦油中萘及萘的同系物、多环芳烃（除萘类）含量最大,分别较原煤增加了92%、192%。     

硅改性HZSM-5沸石上甲苯与甲醇选择性甲基化的研究

采用硅油化学液相沉积法,焙烧后在HZSM-5沸石外表面上形成SiO2涂层,可有效地调控HZSM-5沸石的孔口尺寸。制备了一系列SiO2沉积量不同的Si/HZSM-5催化剂,并进行了甲苯与甲醇选择性甲基化反应。随着SiO2沉积量增加,沸石骨架结构和内表面性质变化不大,而孔口尺寸逐渐缩小,反应中产物对二甲苯的选择性明显提高。     

VPT法制备MCM-22分子筛催化剂颗粒及其烷基化性能

采用汽相法（VPT）制备了以成型干胶颗粒为基体的MCM-22分子筛催化剂.利用XRD、SEM和BET测试技术对所制备催化剂进行了物相表征、形貌观察和织构分析,并以苯和丙烯烷基化合成异丙苯为模型反应,在液-固固定床反应器上对所制备催化剂的性能进行了评价.结果表明：汽相法制备的MCM-22分子筛催化剂不仅具有较好的结晶度和较高的微孔表面积,而且具有更好的晶体生长取向性和更加致密的结构;在烷基化反应中也具有很好的活性、选择性和稳定性,特别是对目的产物异丙苯的选择性明显高于水热法（HTS）合成的催化剂,在异丙苯合成上具有很好的应用前景.