萃取精馏生产高纯度环氧丙烷的工艺研究

doi:10.11949/j.issn.0438-1157.20181052

摘要/Abstract

摘要：

丙烯环氧化反应获得的粗环氧丙烷(PO)中含有乙醛、甲醇、甲酸甲酯和水等杂质，由于这些杂质与PO相对挥发度接近于1，普通精馏难以提纯PO；同时，分离过程中PO易发生水解生成1,2-丙二醇(PG)，而PG又导致萃取剂萃取性能下降。据此，结合萃取精馏和液液萃取技术，同时考虑PO水解反应，开发了水洗回收PO和侧线采出共沸物脱除PG流程，在有效脱除杂质的同时，提高了PO的回收率和萃取剂的萃取效率，获得了高纯度PO产品。采用流程模拟软件Aspen Plus对上述流程进行了全流程模拟计算，借助NRTL热力学方法，分析了萃取精馏塔的溶剂比、理论塔板数、原料进料位置、溶剂进料温度等主要工艺参数对分离过程的影响。结果表明该工艺流程合理、可靠，经济性优于现有工艺，可指导工业过程设计和操作优化。

关键词: 环氧丙烷, 萃取精馏, 共沸混合物, 分离, 优化设计

Abstract:

Crude propylene oxide (PO) produced from propylene epoxidation contains contaminations such as acetaldehyde, methanol, methyl formate, water and so on. It is difficult to remove them by using simple distillation because the relative volatilities of these components to PO are close to 1. Meanwhile, the PO is easy to react with water and 1,2-propanediol (PG) that will affect the extractive efficiency is then produced. Therefore, a process flowsheet combined extractive distillation and liquid-liquid extraction is proposed here to effectively remove these contaminations and improve PO product yield, in which the PO hydrolysis reaction (non-catalytic reactive distillation) and the processes of water washing for PO recover and side-drawing for the removal of PG are considered. The whole process is then simulated by using process simulation software Aspen Plus, in which the NRTL thermodynamic model is employed to character the thermodynamic properties. The effects of major design parameters of the separation process, such as the solvent ratio, the theoretical stage number of extractive distillation column, the location of feed, and the temperature of solvent, are investigated. The results show that the process is reasonable, reliable, and economical superior to existing processes, which can guide industrial process design and operation optimization.

Key words: propyleneoxide, extractive distillation, azeotrope, separation, optimal design

中图分类号:

TQ 028.13

胡松, 李进龙, 李木金, 杨卫胜. 萃取精馏生产高纯度环氧丙烷的工艺研究[J]. 化工学报, 2019, 70(2): 670-677.

Song HU, Jinlong LI, Mujin LI, Weisheng YANG. Extractive refining process for production of propylene oxide with high purification[J]. CIESC Journal, 2019, 70(2): 670-677.

图/表 16

表1 PO中杂质对PO相对挥发度的影响

Table 1 Effect of extractant on relative volatility of water，acetaldehyde, methanol, methyl acetate to PO (101.325 kPa)

Comp.	Relative volatility
Comp.	None Sol.	nC8	nC7
water	0.9	7.9	11.0
acetaldehyde	1.5	4.5	2.7
methanol	1.0	5.5	2.9
methyl formate	1.1	4.0	2.5

表2 烷烃萃取PO液液平衡数据

Table 2 LLE for nC7/nC8-water-PO mixture/%(mass)

Comp.	Waste water	nC7
Comp.	Waste water	Organic phase	Aqueous phase	Organic phase	Aqueous phase
water	40.0	1.14	59.06	1.20	58.25
acetaldehyde	5.0	3.45	4.74	3.32	4.82
methanol	5.0	0.83	6.84	0.86	6.73
methyl formate	10.0	11.28	5.98	11.77	5.67
PO	36.0	38.54	23.18	37.38	24.28
nC7/nC8	4.0	44.77	0.21	45.47	0.25

表3 PG对萃取过程的影响(101.325 kPa)[16]

Table 3 Effect of PG on extraction process[16]

PG/%(mass)	Relative volatility of listed components to PO
PG/%(mass)	Methanol	Water	Acetaldehyde
0 (without extractant)	0.7	0.9	1.5
0	2.9	11	2.7
13	1.2	1.2	1.3
36	0.5	0.4	0.9

图1 环氧丙烷精制工艺流程

Fig.1 Flow diagram of propylene oxide (PO) refining process

图2 PO-水(a)、PO-乙醛(b)体系T-x-y 图

Fig.2 T-x-y diagrams of PO-H2O (a)[17], PO-acetaldehyde (b)[18] binary system

图3 PG-nC8汽液液相平衡预测

Fig.3 Prediction of vapor-liquid-liquid equilibrium for PG and nC8 with UNIFAC and COSMO-SAC

图4 溶剂比与PO-乙醛相对挥发度的关系

Fig.4 Relationship diagram of solvent ratio and relative volatility of PO to acetaldehyde

图5 溶剂比对分离过程的影响

Fig.5 Effect of solvent ratio on separation process

图6 萃取精馏塔理论塔板数对分离过程的影响

Fig.6 Effect of number of theoretical stage on separation process

图7 粗PO进料位置对分离过程的影响

Fig.7 Effect of feed stage of crude PO on separation process

图8 萃取剂进料温度对分离过程的影响

Fig.8 Effect of temperature of solvent feed on separation process

表4 流程模拟优化工艺条件

Table 4 Optimization parameters for flowsheet simulation

Unit block	Parameter	Value	Unit
extractive distillation column (EDC)	theoretical stage	60	—
	operating pressure	200	kPa
	feed stage of crude PO	31	—
	temperature of solvent	50	℃
	solvent ratio	4.0	—
	flow rate of water	55.0	kg/h
PO production column (PPC)	theoretical stage	30	—
PO production column (PPC)	operating pressure	170	kPa
water wash column (WWC)	theoretical stage	10	—
	operating temperature	50	℃
	flow rate of solvent	120	kg/h
PG separator	temperature	40	℃

表5 PO产品及水洗塔废水组成

Table 5 Composition of PO product and waste water of water wash column(mass fraction)

Component	Waste water	PO production
water	0.8398	0
acetaldehyde	0.0693	<5×10^?6
methanol	0.0694	<5×10^?6
methyl formate	0.0069	<2 ×10^?6
PO	0.0135	>0.9999
nC8	0.0008	＜1 ×10^?6
PG	0.0003	0

图9 萃取精馏塔(a)和PO产品塔(b)温度和关键组分分布

Fig.9 Profiles of temperature and key components in extractive distillation(a) and PO production columns (b)

图10 全流程物料平衡图

Fig.10 Balance of mass flow for all key components

表6 经济性分析

Table 6 Economical analysis

Item	This work	Traditional process
PG content in recycle solvent	46×10^?6	2%(mass)
solvent ratio	4.0	6.0
energy consumption/(MW/(t PO))	0.721	0.775
solvent loss/(kg/h)	2.4	823.6
PO product yield/%	99.88	99.78

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