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Design of epichlorohydrin-oriented quaternary system separation via hybrid extraction-distillation process Liu Yang, Xiangyang Li, Chao Yang, and Shaojun Yuan Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b06039 • Publication Date (Web): 01 Mar 2019 Downloaded from http://pubs.acs.org on March 3, 2019
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Industrial & Engineering Chemistry Research
Design of epichlorohydrin-oriented quaternary system separation via hybrid extraction-distillation process Liu Yang1,2, Xiangyang Li2*, Chao Yang2,3*, Shaojun Yuan1 1
2 CAS
College of Chemical Engieering, Sichuan University, Chengdu 610065, China
Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
3 College
of Chemical Engieering, University of Chinese Academy of Sciences, Beijing 100049, China
Abstract ALC (allyl chloride) epoxidation method for preparing ECH has outstanding advantages such as atom-efficiency and environmental-friendliness. However, the separation of ECH (epichlorohydrin) from the ECH/H2O/ALC/MET (methanol) quaternary system is still a great challenge for industrial interest. A hybrid extractiondistillation process is explored in this work to overcome the defects of high energy consumption and low efficiency in the process with separate extraction or distillation. At first, ALC is recommended as the solvent. Then the flow sheet of hybrid extractiondistillation process was designed and subsequently optimized using Aspen Plus according to the TAC (Total annual cost) minimum principle. At last, several different settings of distillation column were explored and an optimal combination with ECH purity of 0.998 and maximum savings of 37.26% TAC was found. The results show that the hybrid extraction-distillation process is feasible and beneficial to industrialization of the proposed ALC epoxidation method.
Key word: epichlorohydrin; extraction-distillation; quaternary system; azeotrope
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1. Introduction Epichlorohydrin (1,2-epoxy-3-chloropropane, ECH) is a useful and important organic intermediate in petrochemical industry. The main use of ECH is in the manufacture of epoxy resins, whose demand is at high growth rate. Furthermore, a number of surfactants (such as detergent, demulsifier), pharmaceuticals and plasticizers are also produced from ECH. Until now, most of ECH in China is industrially manufactured by dehydrochlorination of dichloropropanol (DCP, including 1,3-dichloro-2-propanol and 1,2-dichloro-3propanlol),1-4 which is derived from high temperature chlorination of propylene. An alternative technology is allyl acetate method.5 The common disadvantages of these two methods are severe equipment corrosion, serious environmental pollution, long process flowsheet and great investment.6,7 In recent years, the glycerol chlorination method using glycerol as raw material,8-10 has been industrialized in many countries. However, its shortcomings are that it is affected by the price of upstream glycerin products and the atomic utilization is not as high as that advertised.11 Many researchers have inspected a new approach for preparing ECH by direct epoxidation of ALC with hydrogen peroxide, namely the ALC epoxidation method,12-16 and it has become one hotspot in this field in recent years because of its outstanding advantages of atomefficiency and environmental-friendliness. Conventionally, this reaction is catalyzed by a titanium-silicon (TS) catalyst. Because ALC and hydrogen peroxide are immiscible, the reaction rate is too low. Therefore, a large amount of solvent (such as MET, acetonitrile, chloroform etc.) is added to dissolve ALC and hydrogen peroxide for a greater reaction rate. Pandey and Kumar17 discussed the effect of different solvents on the epoxidation of ALC using TS-1 to catalyze hydrogen peroxide (45 wt.%) and ALC epoxidation to ECH. The results, also confirmed by Liu et al.18, show that the use of MET as solvent can better compromise the ALC conversion rate and the ECH selectivity simultaneously. Moreover, Li et al.19 investigated the synthesis under solvent-free conditions and found that it is far worse than that of MET solvent. After TS-1 separated, the epoxidation
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product stream mainly consists of the excess reactant ALC, solvent MET, target product ECH and byproduct H2O. This ECH/H2O/ALC/MET quaternary system is a highly non-ideal one as it consists of three binary azcotropes, two of them being heterogeneous. How to separate ECH from this quaternary system is a topic of great academic and industrial interests. Some researchers had noticed this problem and made some meaningful attempts. For example, Joshi et al.20 reported the RCM (Residue curve map) analysis based on experimentally determined residue curves for the ternary ECH-H2OMET system for the first time. Many others2,13,15,21,22 discussed the reaction pathways and kinetics of the system, as shown in Figure 1. Although there is not a complete and effective separation process proposed up to now, all of these attempts are still beneficial and provide a solid foundation to design separation process for the quaternary system.
CH3OH
CH2CH Cl
CH2
OH
OCH3
1-chloro-3methoxypropan-2-ol H2O2/TS-1 CH2CH2
CH3
CH3OH
Cl
1-chloropropane
CH2CH Cl
CH2
H 2O Cl
O
2-(chloromethyl)oxirane
OH
OH
3-chloropropane-1,2-diol H 2O 2 Cl
Main Reaction
CH2
CH2CH
Side Reactions
CH2CH
C
OH
O
OH
3-chloro-2-hydroxypropanoic acid
Figure 1. Reaction pathways in epoxidation of ALC Starting from existing knowledge, there are two available approaches probably used to separate ECH from the quaternary system. The frequently used one is to distillate the liquid phase after solid-liquid separation.23-25 However, since H2O and ECH can form azeotrope, the existence of another two azeotropes, as shown in Table 1, makes this system more complex. Additionally, the mere distillation approach will consume more energy and need more investment. Alternative one is by extracting the epoxidation reaction product stream.26-28 However, a large amount of extraction solvent is
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introduced, which results in that some MET is also extracted together with ECH. Thus, distillation is still required to separate MET and ECH. Even more unfortunately, ECH can react with MET to produce some by-products such as chloropropanediol monomethyl ether and chloropropanediol during the distillation, which will reduce the yield of ECH. For the separation of complex heterogeneous systems like epichlorohydrin-oriented quaternary system, a single separation approach is difficult to achieve economically the goal of thorough separation. Naturally, hybrid separation methods are targeted by some scholars. For example, Kraemer et al.29 recommended an extraction-distillation hybrid process with acetone/butanol/ethanol extracted in the outer column to promote efficient and energy efficient product removal. The results show that the TAC (Total annual cost) of the new process is much lower than that of mere distillation process. Skiborowski et al.30 reviewed the distillation-based hybrid separation processes and pointed out that the use of hybrid separation methods for specific systems is more energy-saving. Chang and Chien31 studied the process of dehydration of n-propanol and also found that the method combining extraction and rectification can save energy. Liu et al.32 preferred that extraction in combination with distillation can save more energy. Some other works33,34 had confirmed this judgment too. In recent years, process simulation has been increasingly used as a powerful tool to provide help in efficient process design. Kurooka et al.35 simulated the separation of a ternary mixture of H2O/n-butyl acetate/acetic acid using heterogeneous azeotropic distillation. Zhu et al.36 proposed a procedure for separating a minimum-boiling azeotrope of toluene and ethanol via heat integration pressure-swing distillation (PSD) by means of Aspen Plus simulation. Recently Luyben37 also proposed an eloquent optimization method on the separation of tetrahydrofuran (THF) and H2O using PSD. Additionally, Luyben38 used benzene/cyclohexane as an example to compare the extractive distillation of a conventional three-column process with an extractive distillation process consisted of thermally coupled column/rectifier. So far, to the best of our knowledge, the efficient separation of ECH from the
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ECH/H2O/ALC/MET quaternary system is still a major challenge to industrialize ALC epoxidation process. The purpose of this work is to explore a new hybrid extractiondistillation process to separate this quaternary system by process simulation using Aspen Plus software. Therefore, the works on solvent choice, hybrid separation process flow sheet design and process optimization are conducted systematically. The newly developed hybrid extraction-distillation process is optimized giving consideration to economy and separation completeness. It will benefit significantly the industrialization of ALC epoxidation method in the future.
2. Solvent choice and simulation details description 2.1 Features of ECH/ALC/MET/H2O system Once the system to be separated has been identified, the system can be analyzed to find a suitable separation process. After repeat experiments, it is found that the extracted organic phase contains almost no MET (wt%
