Zhigang Lei

Influence of salt added to solvent on extractive distillation

Abstract The vapor–liquid equilibria (VLE) of the systems, ethanol–water, ethanol–water–ethylene glycol and ethanol–water–ethylene glycol–CaCl 2 , at finite concentration and normal pressure were measured. The experimental results showed that ethylene glycol with added salt was more effective than ethylene glycol without salt for separating ethanol and water by extractive distillation. A set of experimental apparatus has been established to measure the relative volatilities of C4 (including butane, 1-butene, 2- trans -butene, 2- cis -butene and 1,3-butadiene) at infinite dilution by the inert gas stripping and gas chromatography method. It is verified that adding a little salt to the solvents can improve the relative volatilities of C4, and the effect is apparent compared with other organic solvents. Either polar or non-polar systems can be separated by extractive distillation with salt, which is a convenient method for separations to be carried out in industry.

Process improvement on separating C4 by extractive distillation

Abstract C4 mixtures are usually separated by extractive distillation with acetonitrile (ACN) and N,N-dimethylformamide (DMF) methods in industry. These two methods were modified to improve the extractive distillation process in this work. Vapor–liquid equilibrium (VLE) models for the ACN and DMF methods were established with the Wilson equation. In terms of the models the extractive distillation processes were improved by means of a computer simulation software. The improvement to the ACN method was such that liquid load in the second extractive distillation column was significantly decreased and there were few changes on the equipment. Improvement to the DMF method was also made by replacing tray configuration and decreasing the times of butadiene phase changes. Both improvements are closely connected with the C4 practical production and are easily accomplished.

New process for separating propylene and propane by extractive distillation with aqueous acetonitrile

Abstract A new process for separating propylene and propane in ethylene production has been put forward in which the extractive distillation with aqueous acetonitrile (ACN) as entrainer is employed. A PRO/II software process simulation has been made with the selection of an appropriate vapor–liquid equilibrium model. The new process, extractive distillation, requires a small number of trays, less energety consumption and small column diameter. In the design of the distillation column a new type of multi-overflow compound slant-hole tray was adopted which has been widely used in the recent years. It is believed that with the new process the industrial separation of propylene and propane is greatly improved.

Separation of acetic acid and water by complex extractive distillation

A new separation method, complex extractive distillation, was put forward in this work for separating acetic acid and water. Tributylamine was selected as the separating agent. The reversible chemical interaction between acetic acid and tributylamine was verified through infrared spectra (IR) and mass chromatogram (MS) technique. The mathematics models of equilibrium (EQ) stage with and without incorporating chemical equilibrium equations were, respectively, established to simulate the extractive distillation column. From the comparison of simulated results with experimentally observed results, it was concluded that the EQ stage model was accurate whether chemical equilibrium equation was incorporated or not because the chemical equilibrium constant was small under the operation condition.

Application of scaled particle theory in extractive distillation with salt

Salt effect on the extractive distillation was discussed thoroughly in terms of scaled particle theory. A relationship of salting coefficient and relative volatilities at infinite dilution with salt and no salt was obtained. For the non-polar solute systems DMF/C4 and ACN/C3, we have calculated relative volatilities at infinite dilution with salt which were in agreement with experimental values. But the theory is unsatisfactory for the polar solute systems, glycol/ethanol/water and ethylene glycol/acetone/methanol, because in this case the interactions between polar solutes and solvents are very complicated. The salt effect on the relative volatilities can only be qualitatively analyzed in terms of scaled particle theory for the polar solute systems. But for separating non-polar systems or polar systems by extractive distillation, it is possible to optimize the solvents with salt. A set of experimental apparatus has been set-up to test the effect of adding salts. This work provides a way to optimize the solvents.

Study on the alkylation of benzene and 1-dodecene

Linear alkylation (LAB) is an important intermediate in the detergent industry. This work deals with the suspension catalytic distillation (SCD) column used for synthesis of C12 alkylbenzene with benzene and 1-dodecene. A novel solid catalyst, which is friendly to environment, was selected. The kinetic equations using this catalyst were measured in a fixed-bed reactor. The mathematical models of equilibrium (EQ) stage and nonequilibrium (NEQ) stage for alkylation of benzene and 1-dodecene were, respectively, established by incorporating the kinetic equations to simulate the SCD column. By comparison of the results from experiments, it was concluded that the NEQ stage model was more accurate than the EQ stage model for the simulation.

Solvent improvement for separating C4 with ACN

This paper reports the work to find the best additives added to acetonitrile (ACN) for improving the separation of C4 mixtures with the help of computer-aided molecular design (CAMD). CAMD is programmed to provide necessary information for our search of the additives. The two types of additives we seek, liquid solvents and salts, are designed by CAMD. The selected additives are then tested by experiments. It is found that the addition of salt is more efficient than the addition of liquid solvents (including water) for improving the separation ability of ACN. After taking implicit properties into consideration, salts NaSCN and KSCN, are the best candidates to improve ACN. As a strong tool, CAMD greatly reduces experimental working in separating C4 by extractive distillation with ACN.

Suspension catalytic distillation of simultaneous alkylation and transalkylation for producing cumene

This work deals with the improvement of the suspension catalytic distillation (SCD) process. An improved process that alkylation and transalkylation reactions for producing cumene are carried out simultaneously in a SCD column, was put forward. The kinetic data of alkylation of benzene with propylene over a modified β-zeolite catalyst, YSBH-01, were determined in a fixed-bed laboratory micro-reactor. On this basis, the equilibrium stage (EQ) model (MESHR equations) is established to simulate the SCD column. The performance of the SCD column is discussed. The innovation present in this work for the SCD process is also suitable for the fixed-bed catalytic distillation (FCD) process for producing cumene.

Azeotropic Distillation: A Review of Mathematical Models

Abstract Azeotropic distillation as an early and important special distillation process is commonly used in laboratory and industry. It can be used for separating the mixture with close boiling point or forming azeotrope. This paper tries to provide a review on azeotropic distillation for general readers, focusing on entrainer selection and mathematical models. Since the 1950s, along with extractive distillation, azeotropic distillation has gained a wide attention. Like extractive distillation, the entrainer, i.e., the third component added to the system, is also the core of azeotropic distillation. In the process design and synthesis, the graphical method (in most cases refer to as triangular diagram) is often employed. But it is better to take on the results from graphical method as the initial values of rigorous equilibrium (EQ) stage/non‐equilibrium (NEQ) stage models. One outstanding characteristic of the EQ/NEQ stage models different from extractive distillation and catalytic distillation is to describe phase split for heterogeneous azeotropic distillation. In general, the operation process is very sensitive to some parameters in the case of more than one azeotrope formed, and thus the phenomenon of multiple steady states (MSS) tends to appear.

Comments on special distillation processes

The purpose of this letter is to offer some comments regarding the topic of special distillation processes. Distillation, with its unique advantages in operation and control, becomes a very powerful separation tool in laboratory and industry. Although many promising separation methods are constantly put forward by engineers and scientists, most of them cannot become alternatives of distillation on a large product scale. Among all distillation processes, special distillation processes possess an important position. Herein, a new term, “special distillation processes,” is proposed, that is, the distillation processes by means of which the mixtures with close boiling point or forming an azeotrope can be separated into their pure constituents. The other distillation processes are, therefore, called ordinary distillation processes. We are interested in the field of special distillation processes, and have been working on them for many years [Lei et al., 2003, 2005; Li et al., 2005]. Table 1 gives a distribution of 20 articles except one comment [Lei et al., 2003] with respect to ordinary distillation and special distillation processes in the Korean Journal of Chemical Engineering from 1984 to 2005 (April) by the title “distillation” search. The parenthesis denotes the number of articles. It can be seen that except for only four articles [Assabumrungrat et al., 2004; Kim et al., 1996; Seo et al., 1999; Ko et al., 2002] with respect to special distillation processes, the others are concerned with ordinary distillation processes. However, the situation is different in the regional journal, AIChE Journal, where just in the year 2004 there are up to nine articles with respect to special distillation processes. We feel that the future research hotspot in the field of distillation may be the special distillation processes. Special distillation processes can be divided into two types: one with mass separating agent (i.e., the third component or solvent added) and the other without mass separating agent. The former involves azeotropic distillation (liquid solvent as the separating agent), extractive distillation (liquid Table 1. Article distribution among distillation processes