二氯乙烷裂解过程研究

研究了二氯乙烷裂解制氯乙烯过程的影响因素。确定了二氯乙烷裂解生成氯乙烯及副产物的反应过程为串连反应模型，研究结果可用于工业裂解炉操作优化分析，为裂解炉模拟计算提供基础数据。     

乙炔与二氯乙烷反应体系热力学分析

对乙炔与1,2-二氯乙烷反应体系进行了热力学计算,使用AspenPlus11.0中的RGibbs反应器模块,并结合灵敏度分析工具,对不同情况下各产物在100～450℃下的平衡收率进行了计算;采用REquil反应器模块并结合灵敏度分析工具对1,2-二氯乙烷裂解反应、乙炔氢氯化反应以及二者协同反应在100～600℃下的平衡收率进行了计算。结果表明,1,2-二氯乙烷裂解反应为强吸热反应,在标准状态下不能自发进行。乙炔与1,2-二氯乙烷协同反应为微放热反应,反应在标准状态下能自发进行;乙炔平衡转化率随温度提高逐渐降低。非聚合副反应对氯乙烯收率影响很小,但聚合副反应对氯乙烯收率影响很大,主要生成氯丁二烯。二氯乙烷裂解与乙炔氢氯化协同反应氯乙烯收率随着温度上升而降低。     

影响二氯乙烷裂解反应的因素

1　 1 ,2 -二氯乙烷转化率在裂解的工艺操作中 ,提高二氯乙烷的转化率 ,必须提高反应温度 ,但是 ,过高的反应温度会使副反应和结焦加剧 ,导致氯乙烯产品收率下降、生产周期缩短、消耗增加及氯乙烯产品质量的下降。为满足 VCM产品纯度高、副产物少、裂解生产周期长及消耗低的要求 ,1 ,2 -二氯乙烷裂解的最佳转化率为 55%左右。但随着 EDC裂解转化率的增加 ,VCM产品中的杂质量也随着增加。其杂质主要是乙炔、氯甲烷、氯乙烷、1 ,3 -丁二烯和氯丁二烯等。二氯乙烷转化率过高 ,裂解炉炉管结焦加剧、裂解炉的使用周期缩短。2　原料纯度原料纯…     

管式裂解炉二维模型两种不同计算方法的对比

用两种不同的求解方法建立了乙烯裂解炉的二维工艺数学模型。该模型包括有49个组分、49个反应的复杂分子反应体系,通过对轴向和径向流体流动、传热及管壁处结焦反应等过程的描述,可以较完整地模拟轻烃裂解炉管内的流体流动、反应、传热、结焦等过程。用此两种方法和一维模型分别对大庆W型轻烃炉的同一工况进行了模拟计算。结果表明,两种计算方法对径向温度、速度和浓度分布描述比一维模型更加符合工业炉裂解的实际情况,在靠近管壁处径向速度、温度以及浓度的变化趋势与工业实际相吻合,其它主要计算结果与工业数据和一维模型的计算结果一致,两种计算方法各有优缺点,适用于不同目的的计算。     

多组扭曲片排布方式对乙烯裂解炉管内产物收率的影响

针对乙烯裂解炉炉管内置入不同组数扭曲片对裂解产物收率的影响进行数值模拟,选用石脑油为裂解原料,得到不同管型的温度分布、乙烯等产物质量分数的分布情况.结果 表明,扭曲片可有效降低管壁与核心流体间的温度梯度,且出口段置入3组扭曲片的炉管换热效果最佳;炉管中乙烯与丁二烯的产率沿轴向距离线性增加,丙烯产率在反应后期的出口段下降...     

1,1,2-三氯乙烷裂解反应体系热力学分析

为探索温度对1,1,2-三氯乙烷裂解反应体系的影响,对该体系进行了热力学模拟计算。采用Aspen Plus V11中的反应器模块RGibbs并结合灵敏度模型分析工具,分别计算了单组分、无聚合反应以及发生聚合反应3种条件下各生成物在150～300℃下的平衡收率。热力学模拟结果表明：在标准状况下,1,1,2-三氯乙烷脱氯化氢生成偏二氯乙烯的主反应与生成顺-1,2-二氯乙烯、反-1,2-二氯乙烯的副反应均无法自发进行。主副反应均是吸热反应,当温度为150℃时,生成反-1,2-二氯乙烯和顺-1,2-二氯乙烯的副反应平衡转化率分别为最低和最高,1,1,2-三氯乙烷裂解反应的平衡转化率与温度成正比。当温度达到300℃时,平衡转化率均接近100%。通过Materials Studio的DMol-3模块对相关物质的热力学特性进行了验证。     

乙炔氢氯化反应体系热力学分析

对乙炔氢氯化反应体系主反应与副反应的热力学性质进行了计算。采用Aspen Plus11.1中的Gibbs反应器模块并结合Sensitivity工具对单一产物、不考虑聚合反应与考虑聚合反应3种情况下各产物在90~420℃下的平衡收率进行计算。结果表明:从热力学角度讲,各反应均为强放热反应,标准状态下能自发进行;210℃以下各反应单独进行时均能达到接近100%的转化率,随温度升高,各反应乙炔平衡转化率逐渐降低且非聚合副反应降低的最快;当考虑非聚合副反应时,氯乙烯收率仍能达到97%以上;但当考虑聚合反应时,氯乙烯收率最高仅为0.6%,主要生成氯丁二烯。表明生成的氯乙烯容易与乙炔发生串联聚合,实际反应过程中应及时将氯乙烯移除,并避免乙炔过量。反应过程中应考虑催化剂的积炭失活因素,降低积炭。     

大型乙苯脱氢轴径向反应器的研究与开发(Ⅱ) 反应器模拟与分析

在轴径向反应器二维流动模型的基础上导出了基于二维流动的二维拟均相反应器模型 ,应用有限差分法求解此模型 ,发现轴径向反应器反应转化率略高于相应的径向反应器 0 .1%～ 0 .6 % ,而选择性两者基本相同 ;同时得出催化剂封中流体的二维流动使得轴径向反应器的温度场和浓度场极其复杂 ,对于乙苯脱氢反应 ,在催化剂封区域存在一个低温区和高苯乙烯浓度区 .此反应器模型得到了年产 3万吨乙苯脱氢轴径向反应器的工业数据的证实 ,可用于指导轴径向反应器的设计     

节能的氯乙烯生产新方法

目前,氯乙烯的生产方法主要有两种,一是乙炔法,另一种是乙烯与氯气反应制得二氯乙烷,再裂解生成氯乙烯和氯化氢。氯气由食盐电解制得。由于电能涨价,氯气的价格变得比较贵了。荷兰阿克苏盐类化学公司(Akzo     

USC裂解炉出口温度、炉管构型对循环乙烷裂解性能的影响

在USC裂解炉上进行了不同乙烯原料、裂解炉出口温度、炉管构型的工业裂解标定试验,结果表明,循环乙烷易脱氢生成大量的乙烯(56.35%),丙烯、丁二烯、裂解液相产物收率极低,液化气通过断链反应可生成乙烯、丙烯、丁二烯以及少量的裂解液相产物,石脑油拔头油裂解乙烯收率低,但裂解液相产物(高附加值)收率较高;乙烷裂解炉出口温度宜控制在858℃左右;与U型炉管相比,乙烷在M型炉管裂解乙烷转化率、乙烯收率、丙烯收率、三烯收率高。     

CFD study on partial oxidation of methane in fixed-bed reactor

Partial oxidation of methane (POM) is a preferred method for synthesis gas, which usually occurs in fixed bed reactors. In this paper, the discrete element method (DEM) is used to reconstruct the structure of a reactor bed via simulating the process of filling the reactor with catalyst. The particle resolved CFD physical model with the detailed micro-kinetcis of the POM reaction was established to study the interaction among reactant flow, heat and mass transfer, and reaction in the fixed bed. The gas composition and temperature distribution in the reactor were obtained based on the simulation results. The effects of the space velocity and the reaction temperature on the CH₄ conversion, catalyst selectivity, and catalyst surface coke formation were analyzed. The simulation results show that the temperature hot spots of the catalyst in the bed occur at the inlet and the temperature increases further near the wall. With the increase in space velocity, the conversion rate of CH₄ decreases gradually, and the selectivity does not change significantly. As the temperature increases, the conversion rate of CH₄ gradually increases and the selectivity decreases. The risk of coke formation on the catalyst surface rises axially and the C species concentration is relatively higher near the outlet. Appropriately increasing the gas velocity and increasing the temperature helps to reduce the surface coke accumulation of the catalyst.     

Modeling of naphtha pyrolysis in swaged coils

Pyrolysis of naphtha in uniform diameter and swaged reactors has been modeled. Pyrolysis and coking models available for naphtha cracking were used to calculate the reactor profiles of pressure, process gas temperature, tube metal temperature, conversion and the product yields. For the swaged coil, not only was the inlet pressure and maximum tube wall temperature in the clean condition lower than for a uniform diameter reactor, but the increase in the inlet pressure and maximum tube wall temperature due to coke deposition was also less. Swaging the reactor can result in a significant increase in the run length between decokings.     

SIMULATION AND OPTIMIZATION OF COIL DECOKING IN ETHANE PYROLYSIS FURNACE

A detailed model of coupled heat transfer in the firebox and coke oxidation in the coils of a commercial ethane pyrolysis furnace was developed to simulate the decoking process. The model was created by combining a plug flow reactor model, the shrinking core model, and the zonal approach method to approximately describe the fluid flow in the coils, the gas-solid heterogeneous reactions of coke gasification, and the heat transfer in the furnace. The simulation accurately modeled the decoking time and CO₂ mole fraction at the coil outlets. The model may be used to evaluate existing decoking processes, and new decoking procedures can be investigated by iterative approximation. The model can be used to validate the following steady-state operating conditions: coil outlet temperature, coil inlet temperature, decoking time, coil outlet CO₂ mole fraction, and the maximum external tube wall temperature, resulting in lower consumption of steam and air and a reduction in residual coke. This work has provided essential information for the development of advanced on-line coke-burning procedures for ethylene production.     

模拟乙烷裂解炉管中流体返混对烧焦过程的影响

针对裂解炉管弯头处流体运动状态变化的特点,采用柱塞流反应器(PFR)与串联全混流反应器(CSTR)组合的反应器模型,耦合计算了炉膛传热和辐射段炉管内的烧焦过程.将烧焦时焦炭表面氧分压、烧焦速率、炉管出口气体温度和碳氧化物含量、焦炭层厚度等影响的模拟结果与无返混的PFR模型的模拟结果进行了比较.结果表明:两种模型模拟的炉管出口气体温度和碳氧化物含量均与生产实际基本相合,但有返混的模型能更准确地描述烧焦结束时残碳在管内的分布特点.     

基于CFD的强化裂解炉管设计

通过计算流体力学（CFD）的方法,将丙烷裂解反应动力学与流动方程、能量方程耦合,考察了在普通裂解炉管中加装中空立交盘（hollow cross-disk,HCD）内构件对管内流动及裂解反应的影响。结果发现,HCD内构件通过壁面几何形状变化重布了流场结构,以合理的压力损失为代价产生径向速度,并诱导产生纵向涡剪切破坏边界层,强化了流体的湍动程度,降低热阻,提高了温度分布均匀性。相比于普通炉管,加入中空立交盘后,裂解管丙烷转化率提高7.24%,烯烃选择性提高3.67%,乙烯收率降低0.87%,但丙烯收率大幅上升16.50%,烯烃总收率上升6.94%。此外发现,纵向涡产生的径向流动促进了近壁区高温流体和管中心区相对低温流体的换位,流体温度最高下降了0.7℃;与普通炉管相比,新型裂解管出口处重组分浓度下降了28.33%,说明加入中空立交盘可防止近壁面高温区域过度裂解,有助于抑制结焦。在此基础上,结合模拟所得的场分布数据,定量分析了HCD强化传热和传质的机理,并就阻力损失和强化效果做出综合评价。     

Détermination de constantes cinétiques du craquage catalytique par la modélisation du test de microactivité (MAT)

The microactivity test (MAT) for cracking catalyst test works with an approximately plug flow isothermal reactor. The yields at the outlet of such a reactor is numerically computed in the case of lumped kinetic with large molecular expansion and rapid catalyst deactivation expressed versus poison concentration. The poison (coke in cracking reaction) is considered as a product formed by several reaction routes. The results are applied to catalytic cracking kinetic with a four lump model (feedstock, gasoline, gas, coke). The comparison between experimental and computed yields, permits the adjustment of kinetic constants with a set of experimental results obtained from a laboratory scale reactor derived from the MAT. The simulation of concentration profile in the reactor permits a better understanding of the reaction courses.     

Study of Coke and Coke Precursors During Catalytic Cracking of n-Hexane and 1-Hexene over Ultrastable Y Zeolite

In this paper we report about coke formation during catalytic cracking of n-hexane and 1-hexene over acidic ultrastable Y zeolite in a fixed-bed reactor. The study is based on a classification between coke precursors, whose amount is estimated through volatilisation by nitrogen purging, and coke, large formed coke molecules that remain during nitrogen purging even at 873 K and whose amount is estimated by oxidation at that temperature. The role of coke precursors on the coking process and catalytic cracking reaction is discussed as well as differences in coking tendencies between the two reactants. The results show that the amount of coke precursors and/or coke may decrease with reaction temperature resulting into a reversal of the coking dependence upon temperature.     

Computational fluid dynamics‐based steam cracking furnace optimization using feedstock flow distribution

Nonuniform temperature fields in steam cracking furnaces caused by geometry factors such as burner positions, shadow effects, and asymmetry of the reactor coil layout are detrimental for product yields and run lengths. The techniques of adjusting burner firing (zone firing) and feedstock mass flow rate (pass balancing) have been practiced industrially to mitigate these effects but could only reduce the nonuniformities between the so‐called modules (a group of many coils). An extension of the pass balancing methodology is presented to further minimize the intra‐module nonuniformities, that is, variation between the coils within a module, in floor fired furnaces. Coupled furnace‐reactor computational fluid dynamics‐based simulations of an industrial ultraselective conversion (USC) furnace were performed to evaluate four different feedstock flow distribution schemes, realizing equal values for coil outlet temperature, propene/ethene mass ratio, maximum coking rate and maximum tube metal temperature (TMT), respectively, over all the reactor coils. It is shown that feedstock flow distribution creates a larger operating window and extends the run length. Out of the four cases, the coking rate as criterion leads to the highest yearly production capacity for ethene and propene. Uniform maximum coking rates boost the annual production capacity of the USC furnace with a nameplate ethene capacity of 130 10³ metric tons per year with 1000 metric tons for ethene and 730 metric tons for propene. For industrial application, achieving uniform maximum TMT is more practical due to its measurability by advanced laser‐based techniques. Most steam cracking furnaces can be retrofitted by optimizing the dimensions of venturi nozzles that regulate the feedstock flow to the coils. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3199–3213, 2017     

Kinetic investigations of the deactivation by coking of a noble metal catalyst in the catalytic hydrogenation of nitrobenzene using a catalytic wall reactor

The vapour phase hydrogenation of nitrobenzene to aniline is a highly exothermic reaction deactivated by coking of the palladium catalyst supported on -alumina carrier. For studying the deactivation of the catalyst a catalytic wall reactor was used in order to ensure isothermal reaction conditions for the kinetic measurements. Furthermore, the catalytic wall reactor allowed the determination of axial coke profiles by total carbon analysis of different wall segments. On the assumption that the main reaction and the deactivation of the catalyst can be assumed separable both the steady state and the unsteady state kinetics were studied. Nitrobenzene was identified as the relevant coke precursor whereas aniline has neither an influence on the main reaction nor on the deactivation. It could be shown that the hydrogenation of nitrobenzene to aniline follows a Langmuir–Hinshelwood mechanism considering the surface reaction of the adsorbed nitrobenzene molecule and one adsorbed hydrogen atom as the rate determining step. The differentiation of coke on the active sites and coke on the support must be taken into account to model the kinetics of coke formation with sufficient accuracy.     

基于精细自由基反应机理的丙烷裂解炉炉管CFD模拟(英文)

In the radiant section of cracking furnace, the thermal cracking process is highly coupled with turbulent flow, heat transfer and mass transfer. In this paper, a three-dimensional simulation of propane pyrolysis reactor tube is performed based on a detailed kinetic radical cracking scheme, combined with a comprehensive rigorous computational fluid dynamics（CFD） model. The eddy-dissipation-concept（EDC） model is introduced to deal with turbulence-chemistry interaction of cracking gas, especially for the multi-step radical kinetics. Considering the high aspect ratio and severe gradient phenomenon, numerical strategies such as grid resolution and refinement, stepping method and relaxation technique at different levels are employed to accelerate convergence. Large scale of radial nonuniformity in the vicinity of the tube wall is investigated. Spatial distributions of each radical reaction rate are first studied, and made it possible to identify the dominant elementary reactions. Additionally, a series of operating conditions including the feedstock feed rate, wall temperature profile and heat flux profile towards the reactor tubes are investigated. The obtained results can be used as scientific guide for further technical retrofit and operation optimization aiming at high conversion and selectivity of pyrolysis process.