Crystal structure of xylene·CuAlCl4 and measurement of solid-liquid equilibrium of binary system

doi:10.11949/0438-1157.20241262

Abstract

Abstract:

Para-xylene (PX) is an important basic chemical raw material. The separation of PX from mixed xylenes (mixture of meta-xylene (MX), ortho-xylene (OX), and PX) is a prerequisite for its utilization. The complex crystallization method, combining complexation with crystallization, has great potential for separating PX from mixed xylenes. Three new crystals including 2PX·CuAlCl₄, 2MX·CuAlCl₄, and 2OX·CuAlCl₄ were obtained by complexing the bimetallic halide CuAlCl₄ with xylene isomers by π-complexation as a complexing agent. The melting points of these crystals were 41.0℃, 15.1℃ and 55.7℃, respectively. The solid-liquid equilibrium data of the binary systems 2PX·CuAlCl₄/2MX·CuAlCl₄ and 2PX·CuAlCl₄/2OX·CuAlCl₄ were further determined. Both were simple eutectic systems. The mole fraction of 2PX·CuAlCl₄ at the eutectic point was 0.3969 and 0.6107, and the corresponding temperatures were -3.36℃ and 14.83℃, which were 49.2℃ and 47.7℃ higher than those of the pure arene binary system, respectively. The temperature required for the crystallization operation was greatly increased. The phase equilibrium data were fitted by the ideal solution model, and the results showed that the model could be used to relate the solid-liquid phase equilibrium of the binary system. This provided a thermodynamic basis for the separation of mixed xylenes by bimetallic halide complex crystallization. A purity of 98% PX was obtained through initial crystallization, verifying the feasibility of the method.

Key words: bimetallic halides, para-xylene, π complexation, complex crystallization, solid-liquid phase diagram

摘要：

对二甲苯（PX）作为基本化工原料，将其从二甲苯混合物中分离是化工利用的前提。络合结晶法通过耦合络合与结晶过程，对于分离相近沸点混合物具有很高的潜力。以双金属卤化物CuAlCl₄作为络合剂与二甲苯通过π-络合得到三种新晶体2PX·CuAlCl₄、2MX·CuAlCl₄和2OX·CuAlCl₄，熔点分别为41.0、15.1和55.7℃。测定了2PX·CuAlCl₄/2MX·CuAlCl₄和2PX·CuAlCl₄/2OX·CuAlCl₄二元体系的固液平衡数据，均为简单低共熔体系，低共熔点处2PX·CuAlCl₄摩尔分数分别为0.3969和0.6107，对应温度为-3.36℃和14.83℃，与纯芳烃二元体系相比分别提高了49.2℃和47.7℃，结晶操作所需温度大幅度提升。采用理想溶液模型进行拟合，发现该模型可较好地关联固液平衡数据，为双金属卤化物络合结晶分离混合二甲苯提供了热力学基础。通过初步结晶分离得到98%纯度的PX，证明了该方法的可行性。

关键词: 双金属卤化物, 对二甲苯, π络合, 络合结晶, 固液相图

CLC Number:

TQ 028

Han LIU, Jiaxin CUI, Mengfan YIN, Tao ZHENG, Rui ZHANG, Xianghai MENG, Zhichang LIU, Haiyan LIU, Chunming XU. Crystal structure of xylene·CuAlCl₄ and measurement of solid-liquid equilibrium of binary system[J]. CIESC Journal, 2025, 76(5): 2241-2250.

刘晗, 崔家馨, 殷梦凡, 郑涛, 张睿, 孟祥海, 刘植昌, 刘海燕, 徐春明. CuAlCl₄-二甲苯络合物晶体结构及二元固液相平衡测定[J]. 化工学报, 2025, 76(5): 2241-2250.

Figures/Tables 17

References 36

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Item	2PX·CuAlCl₄	2MX·CuAlCl₄	2OX·CuAlCl₄
empirical formula	C₁₆H₂₀CuAlCl₄	C₁₆H₂₀CuAlCl₄	C₁₆H₂₀CuAlCl₄
molecular weight	444.64	444.64	444.64
crystal system	monoclinic	triclinic	orthorhombic
space group	Pc	P-1	Pnma
a/nm	7.8018(2)	8.1933(7)	15.8666(5)
b/nm	27.2834(5)	8.5770(6)	19.1064(5)
c/nm	18.3534(4)	14.8398(7)	6.3201(2)
α/(°)	90	90.451(4)	90
β/(°)	96.112(2)	93.877(5)	90
γ/(°)	90	105.355(7)	90
volume/nm³	3884.49(15)	1002.96(12)	1915.96(10)
Z	8	2	4
calculated density ( g·cm^-3）	1.521	1.472	1.541
F(000)	1808	452	904
θ range/(°)	4.708—54.968	4.926—54.968	5.134—58.91
goodness-of-fit on F²	1.009	1.072	1.032
R₁,wR₂[I＞2σ(I)]*	R₁ = 0.0315, wR₂ = 0.0650	R₁= 0.0490, wR₂ = 0.1369	R₁ = 0.0263, wR₂ = 0.0797
R₁,wR₂(all data)*	R₁ = 0.0399, wR₂ = 0.0680	R₁ = 0.0610, wR₂ = 0.1465	R₁ = 0.0331, wR₂ = 0.0830

Item	2PX·CuAlCl₄	2MX·CuAlCl₄	2OX·CuAlCl₄
empirical formula	C₁₆H₂₀CuAlCl₄	C₁₆H₂₀CuAlCl₄	C₁₆H₂₀CuAlCl₄
molecular weight	444.64	444.64	444.64
crystal system	monoclinic	triclinic	orthorhombic
space group	Pc	P-1	Pnma
a/nm	7.8018(2)	8.1933(7)	15.8666(5)
b/nm	27.2834(5)	8.5770(6)	19.1064(5)
c/nm	18.3534(4)	14.8398(7)	6.3201(2)
α/(°)	90	90.451(4)	90
β/(°)	96.112(2)	93.877(5)	90
γ/(°)	90	105.355(7)	90
volume/nm³	3884.49(15)	1002.96(12)	1915.96(10)
Z	8	2	4
calculated density ( g·cm^-3）	1.521	1.472	1.541
F(000)	1808	452	904
θ range/(°)	4.708—54.968	4.926—54.968	5.134—58.91
goodness-of-fit on F²	1.009	1.072	1.032
R₁,wR₂[I＞2σ(I)]*	R₁ = 0.0315, wR₂ = 0.0650	R₁= 0.0490, wR₂ = 0.1369	R₁ = 0.0263, wR₂ = 0.0797
R₁,wR₂(all data)*	R₁ = 0.0399, wR₂ = 0.0680	R₁ = 0.0610, wR₂ = 0.1465	R₁ = 0.0331, wR₂ = 0.0830

Bond	Bond length/Å
Bond	2PX·CuAlCl₄	2MX·CuAlCl₄	2OX·CuAlCl₄
Cu—C	2.251(4)	2.173(3)	2.152(15)
	2.364(4)	2.317(3)	2.152(15)
	2.218(4)	2.314(3)	2.415(18)
	2.255(4)	2.143(3)	2.415(18)
Cu—Cl	2.616(12)	2.354(7)	2.297(6)
Al—Cl	2.164(16)	2.191 (11)	2.177(7)
	2.161(16)	2.117(10)	2.127 (7)
	2.118(17)	2.104(12)	2.121 (5)
	2.108(16)	2.121(11)	2.121(5)

Bond	Bond length/Å
Bond	2PX·CuAlCl₄	2MX·CuAlCl₄	2OX·CuAlCl₄
Cu—C	2.251(4)	2.173(3)	2.152(15)
	2.364(4)	2.317(3)	2.152(15)
	2.218(4)	2.314(3)	2.415(18)
	2.255(4)	2.143(3)	2.415(18)
Cu—Cl	2.616(12)	2.354(7)	2.297(6)
Al—Cl	2.164(16)	2.191 (11)	2.177(7)
	2.161(16)	2.117(10)	2.127 (7)
	2.118(17)	2.104(12)	2.121 (5)
	2.108(16)	2.121(11)	2.121(5)

物质	熔点/℃	熔化焓/(kJ·mol^-1)
2PX·CuAlCl₄	41.0	14.36
2OX·CuAlCl₄	55.7	17.71
2MX·CuAlCl₄	15.1	17.80
PX	13.3^[32]	17.11^[32]
OX	-25.2^[32]	13.60^[32]
MX	-47.9^[32]	11.57^[32]

Crystal structure of xylene·CuAlCl₄ and measurement of solid-liquid equilibrium of binary system

CuAlCl₄-二甲苯络合物晶体结构及二元固液相平衡测定

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x₁	T_exp/℃	T_id/℃
0	15.17	15.10
0.0962	11.13	11.23
0.2082	7.07	6.32
0.3182	0.63	0.96
0.3969	-3.37	-3.27
0.4936	3.63	5.24
0.5976	12.73	14.09
0.6905	20.83	21.17
0.7849	28.77	27.74
0.8950	34.97	34.78
1.0000	40.93	40.99
D_AR/%	0.19

x₁	T_exp/℃	T_id/℃
0	55.53	55.65
0.0953	47.93	50.64
0.1915	43.33	45.21
0.3169	33.93	37.38
0.4076	29.33	31.07
0.5062	21.23	23.36
0.6107	14.83	13.86
0.7149	24.37	22.92
0.8021	27.73	28.88
0.9087	35.33	35.61
1.0000	40.93	40.99
D_AR/%	0.47

体系	原料组成/%		晶体组成/%
体系	PX	MX或OX	PX	MX或OX
2PX·CuAlCl₄/2MX·CuAlCl₄	20.82	79.18	1.55	98.45
2PX·CuAlCl₄/2MX·CuAlCl₄	78.49	21.51	97.94	2.06
2PX·CuAlCl₄/2OX·CuAlCl₄	19.15	79.18	1.88	98.12
2PX·CuAlCl₄/2OX·CuAlCl₄	80.21	21.51	98.73	1.26

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