Direct observation of induction period of MTO process with consecutive pulse reaction system

The initial transformation of methanol over HZSM-5 catalyst was investigated by a consecutive pulse reaction system. The reactant–catalyst contact time influenced the initial methanol transformation and the performances implied methanol reaction in induction period or under steady-state condition. The induction period, in which an organic-free HZSM-5 catalyst could be transferred to a working catalyst, were directly observed. The analysis result of the product stream predicted hydrogen-deficient species deposition over catalyst surface at the beginning of MTO reaction. The hydrogen transfer level of steady-state MTO reaction also varied with reaction contact time.     

MTO分离新工艺技术研究

MTO分离的核心是杂质脱除和分离流程的开发和设计。文章介绍了典型的MTO分离工艺技术,并根据MTO反应气组成特点,推荐了二种新的工艺节能技术。     

Preparation of SAPO-34 catalyst and presentation of a kinetic model for methanol to olefin process (MTO)

Conversion of methanol to light olefins (MTO) using acidic SAPO-34 molecular-sieve as the reaction catalyst was studied in a differential fixed bed reactor within the temperature range of 375-425 °C and under 4 bar pressure. The importance of MTO process is due to the increasing demand for light olefins in recent years. SAPO-34 was synthesized by hydrothermal method, applying morpholine as the template. The latter compound was then changed into protonated form by ion exchange method with ammonium chloride at 80 °C. A simple stoichiometric scheme has been presented for MTO. In addition a mechanism for this process based on Langmuir-Hinshelwood formulation has been put forward and the kinetic parameters have been evaluated as functions of temperature.     

RAFT polymerization of N,N-diethylacrylamide: Influence of chain transfer agent and solvent on kinetics and induction period

RAFT polymerization of N,N-diethylacrylamide was achieved using three different chain transfer agents bringing cyanoisopropyl, cumyl, or tert-butyl R groups, in different solvents (dioxane, toluene), or in bulk. Reactions were controlled and allowed the synthesis of poly(N,N-diethylacrylamide) with targeted molecular weights. Best results were obtained with cyanoisopropyl dithiobenzoate at 80 °C in toluene. This chain transfer agent (CTA) led to the highest efficiency with a very short induction period. On the reverse, cumyl and tert-butyl dithiobenzoates led to relatively high induction periods which were explained by the slow fragmentation of the intermediate radicals and/or the presence of irreversible termination reactions. Initialization process was also discussed. Cumyl dithiobenzoate surprisingly gave the highest induction in comparison with other CTAs and the slowest polymerization rate in all reactional media. Finally, we demonstrated that the induction period was influenced by the solvent.     

Conformational changes in the induction period of crystallization as measured by FT-IR

The isothermal crystallization behaviors of poly(bisphenol A-co-decane ether) (BA-C10) at different temperatures were studied in situ by means of Fourier transform infrared spectroscopic (FT-IR) measurements. Conformational changes during the induction period were investigated in details. The results suggest that conformational changes of polymer chains always take place before the start of changes in the characteristic FT-IR peaks of the crystalline phase.     

Shelf‐life prediction of perilla oil by considering the induction period of lipid oxidation

Kinetic models for the induction period (IP) of lipid oxidation were developed to predict the shelf‐life of perilla oil during storage. The degree of lipid oxidation was measured in terms of peroxide values (PV). The perilla oil was stored in the dark at various temperatures. The IP was measured at the intersection point of two linear lines and in terms of time and PV at the IP. The IP was expressed by an Arrhenius‐like relationship. Before and after the IP, the reaction followed pseudo‐zero‐order kinetics. The oxidation degrees according to storage times were computed by considering the variables, IP and reaction rate constants. The prediction model equation that was developed to determine shelf‐life is more accurate than in previous studies. Conclusively, considering the IP of lipid oxidation is essential for predicting the shelf‐life of perilla oil and is expected to be applicable to other vegetable oils. Practical applications : In kinetic modeling for shelf‐life estimation in terms of lipid oxidation, induction period (IP) is rarely considered. Thus the estimation of peroxide values (PV) from such models might be inaccurate. The IP was observed in perilla oil oxidation and kinetic models involving the IP were developed. This work enables a better estimation of oxidation. Besides, a shelf‐life diagram of perilla oil has been constructed as a valuable tool for quality control in the food industry.     

Interpreting the effects of operating variables on the induction period of CaCl2-Na2CO3 system by a cluster coagulation model

In this article the effects of several operating variables, including supersaturation, temperature, and the presence of additive and seeds on the induction period of CaCO₃ were studied experimentally and theoretically. In experimental, the induction period was measured by a conductivity method so that the induction period was well identified. The results show that the induction period increases with decreasing supersaturation and temperature. The presence of Mg²⁺ in solution prolongs the induction period and the addition of seeds reduces the induction period. In theoretical, a cluster coagulation model, which brings together the current nucleation models and the theories describing the behavior of colloidal suspensions, was applied to estimate the induction period under various operating variables. A comparison between the two results shows that the present model is a suitable one to interpret the effects of various operating variables on the induction period of aqueous CaCl₂-Na₂CO₃ solution.     

超临界水氧化布雷顿封闭循环系统反应热模拟计算

超临界水氧化技术(SCWO)主要应用于低浓度有机废水的研究。文中在超临界热力条件下对超临界水氧化过程进行模拟,力求实现能量的自补偿过程。通过应用Aspen P lus模拟软件建立模型对SCWO过程进行模拟,采用布雷顿封闭循环(CBC)系统来实现SCWO的能量自补偿过程。计算结果表明:SCWO能量自补偿过程损失的能量要远小于产生的能量(QR-QH>p),超临界水氧化CBC系统的能量自补偿过程是可以实现的,此过程环己烷的能量平衡点为2.4%。     

The nucleation period for crystallization of colloidal TPA-silicalite-1 with varying silica source

The effect of varying silica source on the nucleation and crystallization of TPA-silicalite-1 was investigated. A direct experimental method, involving a two-stage varying-temperature synthesis, was used to determine the nucleation period for colloidal crystals of TPA-silicalite-1 with different silica sources, including tetraethoxysilane (TEOS) and amorphous silica (Ludox TM and Ludox LS). For syntheses performed at 60°C with TEOS as silica source, the duration of the nucleation was about 72 h, and a very rapid increase in the crystal population occurred during the initial crystallization time. However, with the amorphous silica sources (Ludox TM or Ludox LS), the duration of the nucleation period was extended to about 120 h, and the nucleation profile consisted of a self-accelerating nucleation rate at the beginning of the nucleation period. The two-stage synthesis method could be used to determine the nucleation profile for the various silica sources. However, this technique overestimated the crystal concentration at the earliest stage of nucleation with amorphous silica. The use of amorphous silica gave rise to a broader crystal size distribution compared to that of TEOS. However, it was found that for both TEOS and amorphous silica the vast majority of the nucleation occurred during an induction period when little or no crystal growth was observed. In addition, Raman spectroscopy revealed structural differences between Ludox TM and Ludox LS which may account for differences in the nucleation processes observed for these two amorphous silicas.     

Study of induction period over K2CO3/MoS2 catalyst for higher alcohols synthesis

The K₂CO₃/MoS₂ catalyst for higher alcohols synthesis with synthesis gas as feedstock was prepared. The catalyst was characterized by TPR, in-situ XPS, XRD and SEM. Effects of pretreatment with H₂, CO or synthesis gas on activity and selectivity of the catalyst were investigated. Results showed that there was a remarkable induction period about 180 h at the initial reaction stage for the un-treated catalyst. The catalytic performances for alcohols synthesis changed notably during the induction period. The induction period was confirmed to be resulted primarily from the sulfur losing and K element dispersion on the surface of ADM catalysts. Pretreatment of the catalyst could remarkably shorten the time of induction period as well as promote the catalytic activity. Furthermore, the higher alcohols (C₂ + OH) content in the liquid products were enhanced after the catalyst pretreated by CO or synthesis gas which could be ascribed to the increasing of Mo⁴⁺ content on the surface of the catalyst.     

游离细胞膜生物反应器法与固定化细胞法在丙烯酰胺微生物转化中的比较

研究和介绍了一种新的分离方法———游离细胞法 ,并用膜生物反应器分离细胞和产品 ,使其在丙烯酰胺微生物转化中得到了成功的应用。比较了它和固定细胞法的生产工艺、生产效率、产品质量以及生产成本等因素。研究表明 ,在丙烯酰胺微生物转化中 ,游离细胞法优于固定化细胞法。     

Organosilane surfactant-assisted synthesis of mesoporous SSZ-39 zeolite with enhanced catalytic performance in the methanol-to-olefins reaction

SSZ-39 zeolite with AEI framework structure is a good catalyst candidate for the methanol-to-olefins (MTO) reaction. However, the diffusion limitation and coke formation often results in fast deactivation of the SSZ-39 zeolite catalyst. One solution for this challenge is to introduce mesoporosity in the SSZ-39 zeolite. Herein, we report the synthesis of mesoporous SSZ-39 zeolite using an organosilane surfactant, N,N-dimethyl-N-(3-(trimethoxysilyl)propyl)octan-1-aminium chloride, as a mesopore template and N,N-dimethyl-cis-2,6-dimethylpiperidinium as a micropore template. The obtained zeolites were characterized by X-ray diffraction, N₂ sorption, scanning electron microscopy, temperature programmed desorption of ammonia, and magic angle spinning nuclear magnetic resonance of ²⁷Al. The results show that the mesoporous SSZ-39 zeolite has high crystallinity, meso/microporosity, high surface area, cuboid morphology, and abundant acidic sites. More importantly, this mesoporous SSZ-39 zeolite exhibits enhanced catalyst lifetime in the MTO reaction due to the presence of mesoporosity for fast mass transfer, compared with a conventional SSZ-39 zeolite without mesoporosity.     

联箱式陶瓷滤管排的脉冲喷吹系统的研究

对共用一个喷嘴和引射器的联箱式陶瓷滤管排的喷吹性能进行了实验研究并得出结论,认为扩压管式引射器动态性能优于文氏管引射器和直管引射器,且喷嘴至引射器有一最佳距离     

The transient nature of maximum maleic anhydride grafting of polypropylene: A mechanistic approach based on a consecutive reaction model Part 1: Batch solution process

This article reports the chemical modification of an atactic polypropylene performed in solution. To model the process, a Box‐Wilson experimental design was used, taking in to consideration the concentrations of maleic anhydride and dycumile peroxide, as well as reaction time, as independent variables. The dynamic character of the process is proposed on the basis of model forecasts supported by experimental results. The proposed kinetic pathway agrees with the fact that short reaction times are not only sufficient but necessary for the greatest graft yields to be attained, while preventing degradative processes in the system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1182–1190, 2006.     

石墨烯化学气相沉积法可控制备的催化反应体系研究

石墨烯的化学气相沉积(CVD)法制备是一个复杂的多相催化反应过程。如何从催化反应角度理解此过程中的诸多科学问题对石墨烯的精准结构控制以及石墨烯产品的标准化和实用化至关重要。结合最新研究进展,系统分析了CVD反应体系所包含的碳源、反应气氛、催化金属及其内部碳杂质、反应中间碳物种对石墨烯生长的热、动力学以及石墨烯宏、微观结构特性(层数、质量、形状、晶畴等)的影响机制和调控策略,挖掘不同石墨烯CVD反应体系背后的共性科学规律。简介了增强型CVD技术的发展,展望和建议基元反应步骤和含碳反应中间物种对于石墨烯控制制备的重要作用,为未来无缺陷、超洁净、低成本、快速、宏量化的大面积石墨烯薄膜及特定石墨烯衍生结构的定制化制备提供参考。     

Role of reaction time in batch process modification of atactic polypropylene by maleic anhydride in melt

Following our studies on chemical modification proceses of polypropylenes by maleic anhydride, some new experimental works are shown here that check the possibilities of processing atactic polypropylene in the melt by a batch process. A modified polymer that is supposed to be useful as an interfacial agent if used in heterogeneous systems based on polypropylene is also clearly obtained. The favorable effect of the nonstereoregularity of the polymer can be noted. This polymer has a higher level of modification than the stereoregular polymer (isotactic polypropylene), despite the lower processing temperature used that causes a decrease in the initiator activity. Otherwise, this article deals with the role played by the reaction time during the process. A mechanism of chemisorption and some considerations about the fractal nature of the reaction kinetics are proposed to explain the results obtained. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1333–1347, 1997     

利用光度法监控焦性没食子酸三乙酸酯的合成过程

采用双波长分光光度法对焦性没食子酸三乙酸酯的反应进程进行化学分析监控。结果表明,双波长紫外分光光度法测定焦性没食子酸和焦性没食子酸三乙酸酯的精密度分别在0.59%～1.37%和1.41%～1.61%,相对误差均不大于1%,工作曲线分别为y1=261.61x＋0.004,r=0.999 12,y2=194.99x-0.000 2,r=0.998 85,回收率均在92%左右,所以采用双波长紫外分光光度法作为此反应的进程及终点的监控方法效果比较理想。     

旋流吸收器气液吸收传质过程研究

根据旋流吸收器中分散液相不同的运动形态建立了伴有化学反应的气液吸收传质模型,且该模型的表达形式与Danckwerts的表面更新理论一致。从模型上看,液侧传质系数kL正比于扩散系数DA和表面更新率S的平方根,这一正比关系还得到了实验结果的部分验证。根据实验结果可以看出,与其他吸收器相比,作为一种结构简单的静态设备,旋流吸收器同样可以提供一个强化传热、传质的流体力学环境。     

气固两相流内中空多孔催化剂性能的数值模拟

气固流态化过程中流体和颗粒分别聚集,形成稀密两相,严重限制其传质效率和反应速率的提高。针对此问题,本工作设计了一种中空多孔结构的催化剂颗粒,通过模拟方法研究该颗粒对稀密两相气相传质与反应的影响,及其在稀密相间转换的时间尺度。结果表明,一定的流动强度时,在颗粒稀密相转换的时间尺度内,中空多孔结构的颗粒能够有效地在稀相存储反应气体,并在密相释放,为密相提供额外的反应气体,增强体系的整体反应效率。当催化反应速率高于传质速率时,在所研究的流动条件下中空多孔颗粒体系的反应效率比实心球形颗粒体系高出26.92%~29.55%。可以预见在稀密相分布更广的大型气固流化床反应器中,中空多孔结构的催化剂颗粒能够更为有效地提高反应器的整体效率。     

生物质合成气甲烷化与变换反应串联偶合新工艺

以模拟生物质合成气为原料,在固定床反应器中,对合成气甲烷化反应工艺条件进行优化,并在此反应中串联偶合水煤气变换反应,以此提高生物质合成气中碳氢的比例,从而弥补生物质合成气碳氢比较低的不足,使生物质合成气甲烷化反应更彻底,进而提高甲烷的收率。实验结果表明,在水煤气变换空速为15 000 h~(-1)、进水量0.02 m L·min~(-1)和还原温度为450℃条件下,甲烷化催化剂的性能最优,CO转化率100%,甲烷选择性对于整个偶合反应为50%,但就单一甲烷化反应高达99%。