Development of simulation strategy based on molecular weight distribution in polyester production process

doi:10.11949/0438-1157.20190499

Abstract

Abstract:

A polyester industrial production process simulation method targeting molecular weight distribution was proposed. The general process simulation software Aspen Plus could not calculate the molecular weight distribution index and molecular weight distribution curve under the step-growth reaction mechanism._{To overcome this disadvantage, an external interface program was developed to calculate MWD and PDI with major data from the *.bkp/*.apw file running in the background. This strategy was validated by the pre-condensation process simulation of PBT industrial plant. The pre-condensation process model framework with rigorous process mechanism including phase equilibrium and reaction kinetics was established. The sensitivity analysis of the kinetic parameters to molecular weight and concentration of end carboxyl group was applied for the kinetic parameters tuning. Furthermore, the model was validated by process data and analysis data. The calculation errors of weight average molecular weight and PDI were 4.2% and 5.6%. The simulation strategy can be applied for molecular weight distribution in polyester industrial process.}

Key words: mathematical modeling, molecular weight distribution, polyester, reaction kinetics, modeling strategy

摘要：

提出一种以分子量分布为目标的聚酯工业生产过程流程模拟方法，针对通用流程模拟软件Aspen Plus在逐步聚合（step-growth）反应机理下不能计算分子量分布指数和分子量分布曲线的不足，通过外置接口程序从后台运行的Aspen源文件（*.bkp/*.apw）中读取数据，实现分子量分布曲线的可视化和其他质量指标的计算。以聚对苯二甲酸丁二醇酯（PBT）工业生产中的预缩聚过程为建模实例，在Aspen Polymers Plus软件平台上建立基于严格过程机理的聚酯工业预缩过程框架模型。根据分子量及端羧基浓度随动力学参数变化的灵敏度，利用工业操作参数及分析数据整定动力学参数，进一步通过外置接口程序计算PBT的分子量分布，重均分子量、分子量分布指数误差分别为4.2%、5.6%，为聚酯生产过程的分子量分布可视化提供基础。

关键词: 数学模拟, 分子量分布, 聚酯, 反应动力学, 建模方法

CLC Number:

TQ 316.3

Cheng CHANG, Liangfang FENG, Xueping GU, Xi CHEN, Cailiang ZHANG. Development of simulation strategy based on molecular weight distribution in polyester production process[J]. CIESC Journal, 2020, 71(2): 708-714.

常诚, 冯连芳, 顾雪萍, 陈曦, 张才亮. 基于分子量分布指标的聚酯生产过程模拟方法[J]. 化工学报, 2020, 71(2): 708-714.

Figures/Tables 8

Fig.1 Simulation strategy for polyester industrial process based on molecular weight distribution

Table 1 Kinetic reactions for polymerization process

No.	Reaction equations
main reactions
1	$T P A + B D O ? k 1 k 1 / K 1 t T P A + t B D O + H 2 O$
2	$t T P A + B D O ? k 2 k 2 / K 2 b T P A + t B D O + H 2 O$
3	$T P A + t B D O ? k 3 k 3 / K 3 t T P A + b B D O + H 2 O$
4	$t T P A + t B D O ? k 4 k 4 / K 4 b T P A + b B D O + H 2 O$
5	$t B D O ? + t T P A + t B D O ? k 5 k 5 / K 5 b B D O + t T P A + H 2 O$ $t B D O ? + b T P A + t B D O ? k 5 k 5 / K 5 b B D O + b T P A + H 2 O$
side reactions
6	$B D O → k s 1 T H F + H 2 O$
7	$t T P A + t B D O → k s 2 T H F + T P A$ $b T P A + t B D O → k s 2 T H F + t T P A$
8	$t T P A + b B D O → k s 3 T P A + t B U E N$ $b T P A + b B D O → k s 3 t T P A + t B U E N$
9	$b B D O - 1 + b T P A : t B D O - 2 → k s 4 b B D O - 2 + b T P A : t B D O - 1$

Table 1 Kinetic reactions for polymerization process

No.	Reaction equations
main reactions
1	$T P A + B D O ? k 1 k 1 / K 1 t T P A + t B D O + H 2 O$
2	$t T P A + B D O ? k 2 k 2 / K 2 b T P A + t B D O + H 2 O$
3	$T P A + t B D O ? k 3 k 3 / K 3 t T P A + b B D O + H 2 O$
4	$t T P A + t B D O ? k 4 k 4 / K 4 b T P A + b B D O + H 2 O$
5	$t B D O ? + t T P A + t B D O ? k 5 k 5 / K 5 b B D O + t T P A + H 2 O$ $t B D O ? + b T P A + t B D O ? k 5 k 5 / K 5 b B D O + b T P A + H 2 O$
side reactions
6	$B D O → k s 1 T H F + H 2 O$
7	$t T P A + t B D O → k s 2 T H F + T P A$ $b T P A + t B D O → k s 2 T H F + t T P A$
8	$t T P A + b B D O → k s 3 T P A + t B U E N$ $b T P A + b B D O → k s 3 t T P A + t B U E N$
9	$b B D O - 1 + b T P A : t B D O - 2 → k s 4 b B D O - 2 + b T P A : t B D O - 1$

Fig.2 Flowsheet for pre-condensation process

Fig.3 Influence of kinetic parameters on MWN

Fig.4 Influence of kinetic parameters on tTPA1concentration

Table 2 Comparison of data between analysis and simulation

Data	Concentration of carboxyl end group/（mol/t）	Number average molecular weight
analysis data	22.002	6292
simulation data	21.973	6302
relative error/%	-0.132	0.165

Fig.5 Comparison of MWD curve between calculated and analysis curve of pre-condensation product

Table 3 Comparison of MWD between simulation and analysis data

Data	Weight average molecular weight	Polymer dispersity index
analysis data	10346	1.644
simulation data	10778	1.736
relative error /%	4.2	5.6

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