Study on physical property model and enrichment process of trioxane system

doi:10.11949/0438-1157.20250139

Abstract

Abstract:

In this study, the UNIFAC method was employed in Aspen Plus to develop a vapor-liquid equilibrium model for the trioxane system. The model demonstrates high accuracy when temperature ranged from 343 K to 423 K, with formaldehyde concentrations below 65%(mass) and trioxane concentrations below 80%(mass), achieving a relative a0age deviation of less than 9.15%. The density, viscosity and phase change enthalpy of the system are fitted and estimated at the same time, and the maximum relative average deviation is no more than 8.17% compared with the literature value. Based on this model, the concentration column for trioxane production processes was designed and optimized, and the effect of feed methanol on the trioxymethylene concentration tower was discussed. The results indicated that the presence of methanol increases the energy consumption of the concentration column. Furthermore, a hydraulic verification of the concentration column was conducted to ensure its design integrity.

Key words: vapor-liquid equilibrium, simulation, optimization, trioxane, UNIFAC

摘要：

在Aspen Plus上采用UNIFAC方法构建了用于描述三聚甲醛体系的汽液平衡模型，结果表明本模型在温度处于343~423 K，甲醛浓度低于65%（质量分数，余同）以及三聚甲醛浓度低于80%时拥有良好的精度，相对平均偏差小于9.15%。同时拟合和估算了系统的密度、黏度和相变焓，与文献值相比，最大相对平均偏差不超过8.17%。在此基础上，对三聚甲醛生产工艺中的浓缩塔进行设计和优化，探讨了进料甲醇对三聚甲醛提浓塔的影响，发现含有甲醇时提浓塔的能耗更高。此外，对提浓塔进行水力学校核，以保证设计的完整性。

关键词: 汽液平衡, 模拟, 优化, 三聚甲醛, UNIFAC

CLC Number:

TQ 028.3

Zhihong JIANG, Qian LEI, Yinjun ZHU, Zhigang LEI, Honglin CHEN. Study on physical property model and enrichment process of trioxane system[J]. CIESC Journal, 2025, 76(9): 4872-4881.

蒋智洪, 雷骞, 朱引军, 雷志刚, 陈洪林. 三聚甲醛体系物性模型和提浓工艺研究[J]. 化工学报, 2025, 76(9): 4872-4881.

Figures/Tables 19

Table 1 Related parameters of chemical reaction equilibrium constant ki［19］

反应	A	B	C	D
式(2)	-30.946	4819.0	3.7410	-0.004534
式(3)（n=2）	-30.941	5653.0	3.7410	-0.004534
式(3)（n>2）	-30.933	5361.0	3.7410	-0.004534
式(4)	1129.7	-25100	-198.40	0.3160
式(5)（n=2）	1129.0	-25510	-198.40	0.3160
式(5)（n>2）	1129.0	-25630	-198.40	0.3160

Table 2 UNIFAC groups of components in trioxane solutions［13］

物质	拆分基团
CH₂O	1·CH₂O
H₂O	1·H₂O
HOCH₂OH	1·HOCH₂OH
HO(CH₂O) _n H，n>1	1·H₂O n·CH₂O
CH₃OH	1·CH₃OH
HOCH₂OCH₃	1·CH₃O 1·CH₂OH
HO(CH₂O) _n CH₃，n>1	1·CH₃O 1·CH₂OH n-1·CH₂O
(CH₂O)₃	1·(CH₂O)₃

Table 3 Size and surface parameters of UNIFAC group

基团	编号	R	Q	文献
—OH	1	1	1.2	[25]
—CH₂O—	2	0.9183	0.78	[25]
—CH₂—	3	0.6744	0.54	[25]
H₂O	4	0.92	1.4	[25]
HOCH₂OH	5	2.6744	2.94	[25]
(CH₂O)₃	6	2.754	3.3	[25]
CH₃OH	7	1.4311	1.432	[26]
—CH₃O	8	1.1459	1.088	[26]
—CH₂OH	9	1.2044	1.124	[26]

Table 4 UNIFAC group interaction parameters aij［19］

i	j
i	1	2	3	4	5	6	7	8	9
1	—	28.06	156.4	353.5	353.5	28.06	-137.1	112.8	-137.1
2	237.7	—	83.36	867.8	189.2	a₂₆	238.4	0	238.4
3	986.5	251.5	—	1318	1318	251.5	697.2	447.8	697.2
4	-229.1	-254.5	300	—	189.5	80.63	289.6	-219.3	a₄₉
5	-229.1	59.2	300	-191.8	—	80.63	289.6	-142.4	289.6
6	237.7	a₆₂	83.36	379.4	379.4	—	239.6	0	392.20
7	249.1	-128.6	16.5	-181.0	-181	-16.67	—	-128.6	0
8	1164.8	0	273	423.8	774.8	0	238.4	—	238.4
9	249.1	-128.6	16.5	a₉₄	-181	-187.7	0	-128.6	—

Table 5 Parameters of pure component vapor pressure

物质	A_i	B_i	C_i	文献
CH₂O	14.4625	-2204.13	-30.15	[26]
H₂O	16.2886	-3816.44	-46.13	[26]
CH₃OH	16.5725	-3626.55	-34.29	[26]
HOCH₂OH	17.4364	-4762.07	-51.2	[26]
HOCH₂OCH₃	19.5736	-5646.71	0	[26]
(CH₂O)₃	14.3796	-3099.47	-68.92	[5]

Fig.1 Vapor-liquid equilibrium diagram of trioxane system

Fig.2 Comparison of calculated value and literature value in vapor-liquid equilibrium of formaldehyde-water solution

Fig.3 Comparison of calculated value and literature value in vapor-liquid equilibrium of formaldehyde-water-methanol solution

Fig.4 Comparison of calculated value and literature value in vapor-liquid equilibrium of formaldehyde-water- trioxane solution

Table 6 Relative average deviation of different systems

模型	体系	Δ $y ˜ F A$ /%	Δ $y ˜ T O X$ /%	Δ $y ˜ M E$ /%	Δp/%
本模型	甲醛-水	4.64	—	—	0.81
	甲醛-水-甲醇	9.15	—	5.26	2.35
	甲醛-水-三聚甲醛	7.31	7.93	—	0.97
Bongartz等^[27]	甲醛-水	3.51	—	—	1.20
	甲醛-水-甲醇	14.04	—	10.97	3.03
	甲醛-水-三聚甲醛	19.38	31.16	—	5.95
Schemme等^[14]	甲醛-水	14.61	—	—	4.63
	甲醛-水-甲醇	5.91	—	7.09	3.59
	甲醛-水-三聚甲醛	11.91	8.72	—	2.08

Table 6 Relative average deviation of different systems

模型	体系	Δ $y ˜ F A$ /%	Δ $y ˜ T O X$ /%	Δ $y ˜ M E$ /%	Δp/%
本模型	甲醛-水	4.64	—	—	0.81
	甲醛-水-甲醇	9.15	—	5.26	2.35
	甲醛-水-三聚甲醛	7.31	7.93	—	0.97
Bongartz等^[27]	甲醛-水	3.51	—	—	1.20
	甲醛-水-甲醇	14.04	—	10.97	3.03
	甲醛-水-三聚甲醛	19.38	31.16	—	5.95
Schemme等^[14]	甲醛-水	14.61	—	—	4.63
	甲醛-水-甲醇	5.91	—	7.09	3.59
	甲醛-水-三聚甲醛	11.91	8.72	—	2.08

Fig.5 Relative deviation of calculated density and literature density[28] for the formaldehyde-water (293—383 K) and formaldehyde-water-methanol (283—333 K) systems

Fig.6 Relative deviation of calculated enthalpy of phase transition and literature values[29] for the formaldehyde-water (322—362 K) and formaldehyde-water-methanol (311—332 K) systems

Fig.7 Relative deviation of calculated viscosity and literature values for the formaldehyde-water (293—373 K) system

Fig.8 Concentration column of trioxane

Fig.9 Sensitivity analysis of column optimization

Table 7 Operating conditions of concentration column

进料	馏出物进料比/（g·g^-1）	回流比/（g·g^-1）	理论进料位置	理论塔板数	总能耗/kW
不含甲醇	0.30	0.28	2	14	18.92
含甲醇	0.30	0.39	2	13	21.61

Table 8 Inlet and outlet flow rates and compositions of the concentration column

条件		流量/(kg·h^-1)	甲醛浓度/(g·g^-1)	水浓度/(g·g^-1)	甲醇浓度/(g·g^-1)	三聚甲醛浓度/(g·g^-1)
含甲醇	进料	100	0.3933	0.4469	0.0107	0.1491
	塔顶	29.52	0.1445	0.3355	0.0199	0.5001
	塔底	70.48	0.4975	0.4935	0.0069	0.0021
不含甲醇	进料	100	0.3936	0.4548	—	0.1516
	塔顶	30.02	0.1512	0.3487	—	0.5001
	塔底	69.98	0.4976	0.5003	—	0.0021

Fig.10 Distribution of components in the vapor phase within the methanol-containing column

Table 9 Hydraulic design of concentration column

塔板	填料高度/m	液泛率/%	压降/kPa	持液量/L
2	0.5	77.45	0.14	9.90
3	1.0	75.78	0.13	9.80
4	1.5	73.91	0.12	9.70
5	2.0	72.02	0.11	9.60
6	2.5	70.23	0.10	9.51
7	3.0	68.69	0.09	9.44
8	3.5	67.43	0.09	9.37
9	4.0	66.45	0.08	9.33
10	4.5	65.72	0.08	9.29
11	5.0	65.15	0.08	9.27
12	5.5	64.65	0.08	9.27

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