Vapor recompressed dividing-wall distillation columns: Structure and performance

Due to the topological structure of double columns and multiple separating sections in dividing-wall distillation columns (DWDCs), the development of vapor recompressed dividing-wall distillation columns (DWDC-VRHPs) represents a challenging issue with great complexities and tediousness. For the separations of light-component dominated and wide boiling-point ternary mixtures, because the purification of the light-component from the intermediate-and heavy-components incurs the primary energy dissipation, the application of vapor recompressed heat pumps (VRHP) should be aimed to reduce the irreversibility and this leads to the generation of the optimum topological structures of the DWDC-VRHPs, i.e., a DWDC plus a two-stage VRHP. The first-stage VRHP is to preheat feed, not only taking the advantages of the small temperature elevation available but also favoring the mass transfer between the vapor and liquid phases through feed splitting. The second-stage VRHP is to reduce further separation irreversibility. The philosophy can be applied to any DWDCs no matter where the dividing wall locates. Two case studies on the separations of ternary mixtures of benzene, toluene, and o-xylene and n-pentane, n-hexane, and n-heptane demonstrate the economic optimality of the proposed DWDC-VRHPs and reveal the inherent interplay between internal and external process integration.     

Equilibrium theory of a pressure swing adsorption process

An equilibrium theory of the separation of two-component gaseous mixtures via the pressure swing adsorption process known as heatless adsorption is presented. Both components of the mixture are adsorbable. One is present at a trace level and is preferentially adsorbed.Principal predictions of the theory for the condition of complete removal of the trace component from the high pressure product stream when using the least possible amount of adsorbent are as follows. When the separation factor is large, high recovery of purified high pressure product is obtained and blowdown and purge losses are small. Recovery is increased and losses decreased by increasing the pressure ratio. Conversely, recovery of the purif high pressure product is small and blowdown and purge losses are large when the separation factor is small. In this case the use of high pressure ratio not improve performance.The trace level component in the combined blowdown and purge stream is derived increasingly from the blowdown as the pressure ratio is increased.     

中间气两步充压对快速真空变压吸附制氧的影响

针对快速变压吸附制氧浓度和回收率低问题,提出了用于提高产氧浓度和回收率的中间气两步充压的快速真空变压吸附流程,并对该流程进行了研究。结果表明：在快速真空变压吸附制氧过程中,中间气先在出气端充压可以有效提高产氧浓度,之后再在进气端充压可提高氧气回收率。出气端充压前中间气压力及氧浓度和进气端充压后床层压力是影响产氧浓度和回收率提高的关键参数。当吸附和解吸压力分别为240、60 kPa时,循环氧气回收率为34.57%,且每天产单位吨氧需吸附剂量为61.18 kg·TPD^-1。     

Understanding rate‐limiting processes for the sublimation of small molecule organic semiconductors

Organic small molecules continue to gain attention for application in light‐emitting devices in displays and solid‐state lighting. The purification of these materials by sublimation represents a critical obstacle for their high throughput processing. In this work, we find that the purification of the archetypical hole‐transporting material N,N′‐bis(naphthalen‐1‐yl)‐N,N′‐bis(phenyl)‐benzidine (α‐NPD) is controlled by a combination of viscous flow, Knudsen diffusion, and physical vapor deposition. In contrast with other commercially practiced sublimations, steps like diffusion within the solid feed, desorption from the feed particle surface, and mass transfer within the bed of feed particles, do not significantly affect the sublimation rate. This work provides guidelines for the large‐scale purification of organic semiconductor materials, and possibly for a broader range of high value small molecule specialty materials. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1347–1354, 2014     

The energy consumption in a batch stripper and a batch rectifier

The energy consumption in a batch rectifier and a batch stripper was investigated with a shortcut mathematical model. The minimum energy consumption of a batch stripper was compared to that of a batch rectifier under “general constant reflux” and “general constant distillate composition” with the ratio of minimum energy consumption E_S/E_R. When the feed contains a large amount of light component, the product purity specification is low and the relative volatility is small, the minimum energy consumption of a batch stripper is less than that of a batch rectifier under “general constant reflux” and “general constant distillate composition”. When the feed contains a small amount of light component, the product purity specification is very high and the relative volatility is low, a batch stripper can also consume less energy only in the “general constant distillate composition” operation mode. In other cases, a batch rectifier can consume less energy.     

The energy consumption in a batch stripper and a batch rectifier

The energy consumption in a batch rectifier and a batch stripper was investigated with a shortcut mathematical model. The minimum energy consumption of a batch stripper was compared to that of a batch rectifier under “general constant reflux” and “general constant distillate composition” with the ratio of minimum energy consumption E _S /E _R . When the feed contains a large amount of light component, the product purity specification is low and the relative volatility is small, the minimum energy consumption of a batch stripper is less than that of a batch rectifier under “general constant reflux” and “general constant distillate composition”. When the feed contains a small amount of light component, the product purity specification is very high and the relative volatility is low, a batch stripper can also consume less energy only in the “general constant distillate composition” operation mode. In other cases, a batch rectifier can consume less energy.     

Analysis of solids densification during the pressurization of lock hoppers

Lock hoppers are used to feed solids into high pressure reactor vessels. During the gas pressurization phase of the operating cycle, gas pressure gradients add to the solids stresses caused by gravity, resulting in a gain of density and strength of the solid. The increase of strength may require a larger hopper outlet and, hence, a larger valve at the outlet in order to assure flow without obstructions thus increasing the initial cost and the cost and time of maintenance.Concentric pressurization of a compressible solid from the cylinder walls inward is analyzed. This is a coupled nonlinear diffusion and nonlinear elastic-plastic finite deformation problem in plane strain. The results suggest that the concentric method permits rapid pressurization with little densification.     

轻组分绝对占优的蒸汽再压缩隔离壁蒸馏塔的最优拓扑结构

隔离壁蒸馏塔（DWC）的双塔多段拓扑结构导致蒸汽再压缩热泵（VRHP）的应用具有多种可能性,包括单VRHP、多VRHP、多级VRHP以及它们的相互组合等复杂结构,这显著加剧了蒸汽再压缩隔离壁蒸馏塔（DWC-VRHP）综合与设计的复杂性与烦琐性。为解决这一问题,针对轻组分绝对占优的三元宽沸点物系的分离问题推演了DWC-VRHP的最优拓扑结构,由此能够有效回避系统综合与设计过程中的结构搜索问题并显著降低模型化与搜索计算的工作强度。轻组分绝对占优与宽沸点物性导致了塔顶冷凝器与预分离蒸馏塔的提馏段是主要的热源与热阱,也决定了DWC-VRHP的最优拓扑结构,即一个二级VRHP与DWC的耦合系统。第一级VRHP用于进料预热,既充分利用温度提升跨度小的特点,又可以通过进料分流强化气液相间的物质传递。第二级VRHP用于加热预分离蒸馏塔的提馏段（或公共提馏段）,能够最大限度地降低分离操作的非可逆性。采用苯/甲苯/邻二甲苯和正戊烷/正己烷/正庚烷两个物系的分离问题对所提出的DWC-VRHP的最优拓扑结构进行了分析与验证。通过与DWC以及DWC-VRHP其他潜在结构的系统性比较,显示了所提出系统结构在稳态性能方面的优越性。     

High‐pressure induced formation of isotactic polypropylene mesophase: Synergistic effect of pressure and pressurization rate

The crystallization induced by high pressures up to 2 GPa was studied for isotactic polypropylene (iPP) using wide angle X‐ray diffraction, small angle X‐ray scattering, and atomic force microscopy methods. The iPP mesophase can be induced at 200°C by high pressures with fast pressurization rate. A pressure–pressurization rate kinetic phase diagram of mesophase and γ‐phase was established to systematically analyze the influences of pressure and pressurization rate on crystallization polymorphism. Under pressure not higher than 0.75 GPa, only γ‐phase is formed, even the pressurization rate reaches 5 × 10³ MPa/s. With increasing pressure to 1.0 GPa, the mesophase is possible to be generated. As pressure further increases to 1.5 GPa and higher, the pure mesophase system can be obtained for pressurization rate above the critical values (about 10 MPa/s). Moreover, the structure of iPP mesophase obtained by rapid pressurization was analyzed and compared with that prepared by temperature quenching. Also interestingly, the pressure‐induced mesophase can transform into γ‐phase by annealing under pressure at 200°C, and the rate of this phase transition is slowed down with increasing annealing pressure. POLYM. ENG. SCI., 59:439–446, 2019. © 2018 Society of Plastics Engineers     

基于增压吸收的吸收式蓄能装置的性能分析

吸收式蓄能技术具有蓄能密度高、热损失小等特点,是一种具有发展潜力的蓄能技术,但目前的技术尚存在吸收效果差、效率不高等问题。提出基于增压吸收的吸收式蓄能方法,并阐述其装置的工作原理和特点,通过数学模型研究在不同工况下增压对其热力学性能的影响规律。结果表明：当蒸发温度与发生温度越低、冷凝温度越高时,增压器改善吸收式蓄能循环的性能系数（COP）越明显;与无增压吸收式蓄能循环相比,蓄能密度（ESD）得到提高,当增压比为3时,其ESD可提高30%～295%。     

Operation and control of batch extractive distillation for the separation of mixtures with minimum-boiling azeotrope

Batch distillation is commonly used in the fine chemicals, specialty polymer, biochemical, pharmaceutical, and food industries. For separating mixtures with minimum-boiling azeotrope, a heavy entrainer is frequently added to the top section of the batch column to aid in the separation. This process is called batch extractive distillation. Most of the papers in open literature have only studied the first operating step of the batch extractive distillation which is the recovery of the light component without mentioning the later steps for the recovery of the other component and entrainer. In this paper, two real chemical systems, one separating acetone and methanol using water as entrainer and the other separating isopropyl alcohol (IPA) and water using dimethyl sulfoxide (DMSO) as entrainer, are studied for the feasible operation of the complete batch distillation sequence. The operating variables, including the pre-load amount with the mixture, continuous feed rate of the entrainer, and reflux ratio at each operating step are determined in the operating sequence. The constant reflux ratio and constant entrainer feed rate operating policy and another policy to allow these two operating variables to be varied will be compared in order to further improve the batch operation. All dynamic simulations that are performed directly mimic industrial situations from an empty column using a rigorous dynamic simulator, Aspen Dynamics™.     

Effects of pressure drop in a PSA process

The effects of pressure drop on the dynamics of fixed-beds were theoretically studied. The system used was an H₂/CO mixture (70 vol% H₂, 30 vol% CO) in zeolite 5A. The pressure drop at the pressurization step affected the breakthrough time at an adsorption step in the PSA process. As a result, the combined effects of pressure drop during adsorption and pressurization steps led to earlier breakthrough compared to the case without a pressure drop. The effect of pressure drop at the adsorption step under the non-isothermal condition was slightly larger than that under the adiabatic condition. In the case of pressurization and blowdown steps with large pressure drop, the flow pattern near the open end during a short period of time had to be explained by the Ergun equation instead of Darcy’s law. However, there was only a slight difference in the results of a multi-bed PSA process depending on whether or not the pressure drops at the pressurization/depressurization steps as well as at the adsorption step were considered.     

基于双回流变压吸附工艺的空气分离模拟及分析

双回流变压吸附是一种在吸附塔中间位置进料,塔顶和塔底分别采用轻、重组分回流的变压吸附过程,能够同时生产两种高纯度、高回收率的产品气。以实验室自主合成的LiLSX分子筛为吸附剂,利用Aspen Adsorption模拟软件,对进料组成为78%N₂/21%O₂/1%Ar的实际空气进行了两塔双回流变压吸附的模拟研究。模拟结果表明：当原料气为78%N₂/21%O₂/1%Ar,吸附压力为2 bar(1 bar=10⁵ Pa),解吸压力为0.3 bar,进料量为0.4 m³/h,轻组分回流流量为0.095 L/min,重组分回流流量为5.22 L/min时,能够得到体积分数为95.67%的O₂和体积分数为98.25%的N₂,回收率分别为94.60%和99.91%。并且进一步探究了进料位置、吸附时间、轻组分回流流量、重组分产品气流量等因素对O₂和N₂两种产品气纯度和回收率的影响。     

Bifurcation analysis for MTBE synthesis in a suspension catalytic distillation column

A rigorous bifurcation study is presented of methyl tert-butyl ether synthesis by suspension catalytic distillation (SCD). SCD is a new development of catalytic distillation (CD) in which fine catalyst particles are suspended in liquid, not only inherits advantages of CD but overcomes transfer limitations in catalyst bed. A complete equilibrium stage model is developed. Analysis results show that this system is sensitive to the operating parameters: the reflux ratio, the bottom flowrate, the methanol feed, the n-butane feed and the operation pressure, and the characteristic parameter for SCD: the solid/liquid separator ratio. The bifurcation diagram displays very intricate and highly nonlinear steady-state behavior, which can results in as many as seven steady-state solutions for identical column specifications. Especially, the results reveal that the superior column performance can be reached under practical operating conditions because the upper bound of the multiplicity range for the solid/liquid separation ratio is very small.     

双氧水法制水合肼中间体提纯的数值模拟

在双氧水法制水合肼的过程中,通过研究产物的分离工艺流程,采用隔壁塔完成杂质的采出。用Aspen Plus软件对组分的分离与提纯进行计算机模拟,同时考察进料位置、进料温度、回流比和塔压等因素对结果的影响,得到最佳工艺操作参数,为实际生产提供理论依据。从隔壁塔塔顶采出的杂质和丁酮的摩尔比为0.023<0.03,符合回收的标准。同时,优化后冷凝器的能耗节省了14.1%,再沸器的能耗节省了10.8%。隔壁塔的主塔理论板数为42块,副塔理论板数为14块,进料位置为副塔第13块板,回流比为7,操作压力为0.101 MPa。塔底分离出的丁酮连氮百分数为98.2%。     

顺丁橡胶装置回收单元溶剂油脱水塔换热的优化设计

溶剂油回收是多组分精馏过程,利用混合液中各组分的挥发度不同,在一定压力、温度下,在塔中经多次部分冷凝和部分蒸发,从而达到各组份分离的目的。粗溶剂油脱水采用非均相共沸,水与部分溶剂及丁二烯在一定温度、压力下产生共沸从塔顶蒸出,经冷凝器冷凝后,水与物料在回流罐中分层,水从设备底部排放掉,达到脱水的目的。溶剂油脱水塔,现塔顶温度约为100℃气相用循环水冷凝、冷却到40℃左右,而进料约40℃溶剂油用低压蒸汽加热。改为塔顶气相与进料两者进行换热,不但能节能低压蒸气、而且能减少循环水用量。     

等高压甲醇甲烷化技术在小氮肥装置改造中的应用

针对合成氨规模在40~60 kt/a的小氮肥企业的特点,提出合成氨原料气净化采用等高压甲醇甲烷化技术进行改造。结合浙江绍兴化工有限公司改造经验,阐述该技术具有工艺流程简单、操作方便、催化剂时空产率高、CO单程转化率高、出口气相中(CO CO2)含量低、醇氨比调节幅度大、生产稳定等特点。     

浓度极稀物中回收微量重组分的精馏操作策略-准间歇精馏

A new operation policy-quasi-batch distillation for recovering infinitesimal amounts species existing in a mixture is presented. In quasi-batch distillation operation, feed is introduced with a constant flow rate onto the feed stage of the column, and the flow rate of the distillate is the same as that of the feed, whereas the bottom product is withdrawn periodically. The behavior of quasi-batch distillation is simulated and analyzed through an example on heavy water separation. Comparing with continuous or batch distillation, the new operation policy is more reliable and efficient to achieve higher recovery of dilute component. This is especially suitable for separating small amount of precious species from large amount of raw material.     

浓度极稀物中回收微量重组分的精馏操作策略—准间歇精馏

A new operation policy--quasi-batch distillation for recovering infinitesimal amounts species existing in a mixture is presented. In quasi-batch distillation operation, feed is introduced with a constant flow rate onto the feed stage of the column, and the flow rate of the distillate is the same as that of the feed, whereas the bottom product is withdrawn periodically. The behavior of quasi-batch distillation is simulated and analyzed through an example on heavy water separation. Comparing with continuous or batch distillation, the new operation policy is more reliable and efficient to achieve higher recovery of dilute component. This is especially suitable for separating small amount of precious species from large amount of raw material.