Propylene oxide offgas recovery and purification process with methanol solvent

doi:10.11949/0438-1157.20191392

Abstract

Abstract:

Aiming at the difficulty of recovering the propylene oxide tail gas in the process of producing propylene oxide by the hydrogen peroxide method, a new propylene oxide recovery process using methanol in the reaction unit as the absorbent and extraction distillation column in the refining unit as the desorption tower was proposed. The reactions of both PO hydrolysis and PO and methanol reaction without catalyst were considered and the high-value product of propylene glycol monomethyl ether was additionally obtained through azeotropic distillation technology. The simulation and design optimization for the full process using Aspen Plus package with NRTL thermodynamic model was carried out, and the influence of the main technological parameters, such as solvent ratio, the number of theoretical plates, and the feed temperature of methanol was discussed. The calculations showed that the mass recovery yield of PO was up to 99.99%. The presented process would play an important role in product capacity improvement, energy saving and volatile organic compounds (VOCs) treatment in HPPO plant.

Key words: hydrogen peroxide process, propylene oxide, absorption, extractive distillation, azeotrope separation

摘要：

针对环氧丙烷生产中环氧丙烷尾气难回收问题，提出了甲醇吸收和环氧丙烷萃取精馏解吸回收的环氧丙烷回收新工艺。该工艺同时考虑无催化环氧丙烷水解和与甲醇反应，并采用共沸精馏分离获得高附加值产品丙二醇单甲醚。选用NRTL热力学方法，对上述流程进行了全流程模拟和优化设计，分析了溶剂比、理论塔板数、吸收剂进料温度等主要工艺参数对分离的影响规律，发现新工艺对环氧丙烷质量回收率达到99.99%。研究结果对环氧丙烷工业装置产能提升、节能降耗和挥发性有机物(VOC_S)治理具有指导作用。

关键词: 双氧水法, 环氧丙烷, 吸收, 萃取精馏, 共沸分离

CLC Number:

TQ 028.8

Song HU, Jinlong LI, Weisheng YANG. Propylene oxide offgas recovery and purification process with methanol solvent[J]. CIESC Journal, 2020, 71(4): 1657-1665.

胡松, 李进龙, 杨卫胜. 环氧丙烷尾气甲醇吸收及纯化工艺[J]. 化工学报, 2020, 71(4): 1657-1665.

Figures/Tables 16

Table 1 Binding energies of different components/(kJ/mol)

N₂-PO	N₂-CH₃OH	PO-CH₃OH	H₂O-CH₃OH	H₂O-PO	CH₃CHO-CH₃OH	CH₃OOCH-CH₃OH
-1.59	-0.42	-7.89	-15.35	-13.60	-13.47	-3.46

Fig.1 σ profiles for different molecules

Fig.2 Effect of water on relative volatility of PO to methanol

Fig.3 Flowsheet of propylene oxide (PO) offgas recovery and recycle methanol purification process

Fig.4 Distillation residue curves of research system

Fig.5 VLE for binary mixtures predicted from UNIFAC(line) and COSMO-SAC(dot) at 101.3 kPa

Fig.6 Effect of mass ratio of absorbent to offgas on absorption process

Fig.7 Effect of absorbent temperature on absorption process

Fig.8 Effect of OAC theoretical stages on absorption process

Fig.9 Effect of solvent ratio on separation process

Fig.10 Effect of number of theoretical stage on separation process

Fig.11 Effect of reflux ratio on PO product and reboiler heat duty

Fig.12 Effect of feed stage of solvent (a) and crude PO (b) on process

Table 2 Optimization parameters for flowsheet simulation

Unit block	Parameter	Value
absorption column (OAC)	operating pressure	180 kPa
	operating temperature	20.0℃
	theoretical stage	12
	feed stage of PO offgas	12
	temperature of solvent	20.0℃
	solvent ratio	1.0
extractive distillation column (EDC)	operating pressure	50 kPa
	theoretical stage	54
	feed stage of solvent	26
	feed stage of crude PO	44
	solvent ratio(mass)	0.12
	reflux ratio(mass)	2.9
methanol recovery column (MRC)	operating pressure	20 kPa
	theoretical stage	42
	feed stage of feeding	20
	stage of side product	24
	reflux ratio(mass)	2.2
azeotropic distillation column (ADC)	operating pressure	20 kPa
	theoretical stage	11
	stage of feeding	5
	solvent ratio(mass)	6.72

Fig.13 Profiles of temperature and key components in OAC(a), EDC(b), MRC(c) and ADC(d)

Fig.14 Balance of mass flow for all key components(F—mass flow, kg/h; unit of mass composition,%)

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