Biaohua Chen

Extractive Distillation: A Review

Extractive distillation is more and more commonly applied in industry, and becomes an important separation method in chemical engineering. This paper provides an in‐depth review for extractive distillation. Separation sequence of the columns, combination with other separation processes, tray configuration and operation policy are included in process of extractive distillation. Since the solvent plays an important role in the design of extractive distillation, such conventional and novel separating agents as solid salt, liquid solvent, the combination of liquid solvent and solid salt, and ionic liquid are concerned. The prominent characteristics of extractive distillation is that one new solvent with high boiling‐point, i.e. separating agent, is added to the components to be separated, so as to increase their relative volatility. Selection of a suitable solvent is fundamental to ensure an effective and economical design. CAMD as a useful tool is applied for screening the solvents and thus reducing the experimental work. Theories from molecular thermodynamics, which can interpret the microscale mechanism of selecting the solvents, are also collected. To accurately describe the extractive distillation process, mathematical model is necessary. There are two types of mathematical models to simulate extractive distillation process, i.e. equilibrium (EQ) stage model and non‐equilibrium (NEQ) stage model. The EQ stage model as an old method is widely used, but the NEQ stage model should be pay more attention. In the end comparison of extractive distillation and adsorption distillation, both of which belong to special distillation suitable for separating close boiling point or azeotropic components, is done, and it is shown that extractive distillation is more advantageous.

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.

Kinetics of benzene alkylation with 1-dodecene over a supported tungstophosphoric acid catalyst

Abstract The prepared catalyst of tungstophosphoric acid supported on SiO 2 has shown high activity, good selectivity of producing linear alkylbenzene (LAB) and 2-phenyl isomer and sufficient catalytic stability. Kinetics of benzene alkylation with 1-dodecene over this catalyst was investigated in a fixed-bed reactor after eliminating the influence of internal and external transport. Rate models of formation of different isomers of LAB were derived based on some simplifying assumptions. Kinetic parameters were determined.

Selective oxidation of CO in hydrogen rich gas over platinum-gold catalyst supported on zinc oxide for potential application in fuel cell

A series of gold zinc oxide catalysts were prepared using a coprecipitation procedure, and their performance for catalytic oxidation removal of CO from H-2 rich gas was investigated in a fixed bed reactor. The results showed that its optimum content of Au was 1.5 wt.% in ZnO, Au(1.5)/ZnO. The effect of calcining temperatures on Au(1.5)/ZnO performance for removal of CO showed that the ideal calcining. temperature was 300 degreesC, Au(1.5)/ZnO-300. During 500 h continuous experimental investigation for Au(1.5)/ZnO-300 to remove CO selectively at 80 degreesC, its performance was slightly decreased when the time on stream was over 350 h. When small amounts of platinum were added to Au(1.5)/ZnO-300, its stability was improved. However, when the content of platinum in Au(1.5)/ZnO-300 was over 1.0 wt.%, the selectivity for removal of CO for Au(1.5)-Pt/ZnO-300 was lowered with increasing content of Pt. The ideal composition for Au(1.5)-Pt/ZnO-300 was 1.0 wt.% Pt, Au(1.5)-Pt(1.0)/ZnO-300

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.

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.

Re-oxidation kinetics of a VPO catalyst

Oxidation of vanadium pyrophosphate (VPO) to the orthophosphate was investigated by temperature programmed oxidation (TPO) and by weight gain measurements in a TGA unit as a model for the re-oxidation of a catalyst in a two-bed process in the partial oxidation of butane to maleic anhydride (MA). It was demonstrated by FTIR observations that the weight gain corresponds to the VPO oxidation. The results of separate measurements of a catalyst alternatively exposed to oxygen and to a stream containing butane should also be applicable to a VPO catalyst employed in a two-bed process. The VPO oxidation measurements demonstrate that re-oxidation of a VPO catalyst in a two-bed process should be carried out at a higher temperature than the butane partial oxidation. When this is carried out, significant performance improvements in the two-bed process are observed.

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.

Modeling and Simulation of Ethylene Polymerization in Industrial Slurry Reactor Series

Abstract A five-site comprehensive mathematical model was developed to simulate the steady-state behavior of industrial slurry polymerization of ethylene in multistage continuous stirred tank reactors. More specifically, the effects of various operating conditions ( i.e ., inflow rates of catalyst, hydrogen and comonomer) on the molecular structure and properties of polyethylene ( i.e ., M w , M n , polydispersity index ( I PD ), melt index, density, etc .) are fully assessed. It is shown that the proposed comprehensive model is capable of simulating the steady-state operation of an industrial slurry stirred tank reactor series. It is demonstrated that changing the catalyst flow rate, changes simultaneously the mean residence-time in both reactors, which plays a significant role on the establishment of polyethylene architecture properties such as molecular mass and I PD . The melt index and density of polyethylene are mainly controlled by hydrogen and comonomer concentration, respectively.

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