Separation of n-octane and o-xylene by liquid-liquid extraction with ionic liquids

doi:10.11949/0438-1157.20211073

Abstract

Abstract:

Separating straight-run naphtha into aliphatic hydrocarbons and aromatic hydrocarbons helps to optimize the utilization of naphtha resource. Solvent extraction is an important way to separate aromatic hydrocarbons and aliphatic hydrocarbons. The design and optimization of extractants are crucial to the extraction process. The effects of various ionic liquids on the extraction and separation performance of n-octane/o-xylene mixtures were studied, and the ionic liquid 1-butyl-2,3-dimethylimidazole ferric tetrachloride ([Bm₂im][FeCl₄]) was selected with extraction selectivity, distribution coefficient and extraction performance index as evaluation indicators. For low and medium concentration of aromatic hydrocarbons in naphtha (<33%), the extraction selectivity of o-xylene was above 45, the distribution coefficient was in the range of 0.38—0.40, the extraction performance index was above 18, and the dearomatization rate of single extraction reached above 60% at the temperature of 30℃ and the mass ratio of solvent to feed of 4. Compared with traditional solvent (sulfolane), the system had a larger two-phase zone with [Bm₂im][FeCl₄], which was helpful to separate n-octane and o-xylene. The weak interaction and the binding energy between [Bm₂im][FeCl₄] and n-octane/o-xylene were investigated with quantum chemistry software, and the results explained the reason why the ionic liquid could extract o-xylene with high selectivity.

Key words: ionic liquids, extraction, separation, n-octane, o-xylene

摘要：

将直馏石脑油分离为脂肪烃和芳烃有助于实现石脑油资源的优化利用，溶剂萃取是芳烃/脂肪烃分离的重要途径，萃取剂的设计与优选对萃取过程至关重要。实验探究了多种离子液体对正辛烷/邻二甲苯混合物萃取分离的效果，以萃取选择性、分配系数和萃取性能指数作为评价指标优选出1-丁基-2，3-二甲基咪唑四氯化铁([Bm₂im][FeCl₄])萃取剂。对于中低浓度芳烃体系(<33%)，在30℃、溶剂质量比为4时，邻二甲苯萃取选择性在45以上，分配系数在0.38~0.40，萃取性能指数在18以上，单次萃取脱芳率可达60%以上。相比传统的环丁砜萃取剂，[Bm₂im][FeCl₄]萃取剂可以使体系具有更大的两相区，易于正辛烷/邻二甲苯的分离。利用量子化学软件探究[Bm₂im][FeCl₄]与正辛烷/邻二甲苯的弱相互作用，并计算其结合能，解释离子液体高选择性萃取邻二甲苯的原因。

关键词: 离子液体, 萃取, 分离, 正辛烷, 邻二甲苯

CLC Number:

TQ 028.3

Mengfan YIN, Zheng TANG, Rui ZHANG, Zhichang LIU, Haiyan LIU, Chunming XU, Xianghai MENG. Separation of n-octane and o-xylene by liquid-liquid extraction with ionic liquids[J]. CIESC Journal, 2021, 72(12): 6282-6290.

殷梦凡, 唐政, 张睿, 刘植昌, 刘海燕, 徐春明, 孟祥海. 离子液体液液萃取分离正辛烷/邻二甲苯[J]. 化工学报, 2021, 72(12): 6282-6290.

Figures/Tables 13

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阳离子影响因素	萃取剂	分配系数		选择性	PI
阳离子影响因素	萃取剂	邻二甲苯	正辛烷	选择性	PI
烷基侧链长度	[Emim][FeCl₄]	0.3150	0.0062	51.21	16.13
	[Bmim][FeCl₄]	0.3600	0.0114	31.69	11.41
	[Hmim][FeCl₄]	0.4667	0.0242	19.26	8.99
	[Omim][FeCl₄]	0.5303	0.0323	16.43	8.71
烷基侧链数量	[Bm₂im][FeCl₄]	0.3400	0.0083	41.00	13.94
极性基团	[HOEtmim][FeCl₄]	0.1043	0.0012	90.26	9.41
	[Bzmim][FeCl₄]	0.2577	0.0062	41.38	10.66
	[Amim][FeCl₄]	0.2900	0.0072	40.34	11.70

阳离子影响因素	萃取剂	分配系数		选择性	PI
阳离子影响因素	萃取剂	邻二甲苯	正辛烷	选择性	PI
烷基侧链长度	[Emim][FeCl₄]	0.3150	0.0062	51.21	16.13
	[Bmim][FeCl₄]	0.3600	0.0114	31.69	11.41
	[Hmim][FeCl₄]	0.4667	0.0242	19.26	8.99
	[Omim][FeCl₄]	0.5303	0.0323	16.43	8.71
烷基侧链数量	[Bm₂im][FeCl₄]	0.3400	0.0083	41.00	13.94
极性基团	[HOEtmim][FeCl₄]	0.1043	0.0012	90.26	9.41
	[Bzmim][FeCl₄]	0.2577	0.0062	41.38	10.66
	[Amim][FeCl₄]	0.2900	0.0072	40.34	11.70

溶剂比	萃余相			萃取相			分配系数		选择性	PI	脱芳率
溶剂比	x_o-_xylene	x_n-_octane	x_IL	x_o-_xylene	x_n-_octane	x_IL	邻二甲苯	正辛烷	选择性	PI	脱芳率
	m_n-_octane∶m_o-_xylene= 2∶1
0.5	0.3003	0.6997	0.0000	0.0873	0.0043	0.9084	0.2906	0.0062	46.87	13.62	14.41%
1	0.2622	0.7378	0.0000	0.0892	0.0061	0.9047	0.3400	0.0083	41.00	13.94	29.58%
2	0.2036	0.7964	0.0000	0.0761	0.0062	0.9177	0.3736	0.0078	47.97	17.92	49.83%
3	0.1666	0.8334	0.0000	0.0642	0.0088	0.9270	0.3843	0.0095	40.64	15.62	61.90%
4	0.1357	0.8643	0.0000	0.0545	0.0067	0.9388	0.4017	0.0087	46.32	18.61	69.71%
5	0.1204	0.8796	0.0000	0.0475	0.0073	0.9452	0.3942	0.0083	47.54	18.74	74.47%
	m_n-_octane∶m_o-_xylene= 4∶1
4	0.0819	0.9181	0.0000	0.0313	0.0052	0.9635	0.3824	0.0056	67.73	25.90	65.00%
	m_n-_octane∶m_o-_xylene= 9∶1
4	0.0408	0.9592	0.0000	0.0162	0.0068	0.9770	0.3964	0.0071	56.21	22.28	64.05%

溶剂比	萃余相			萃取相			分配系数		选择性	PI	脱芳率
溶剂比	x_o-_xylene	x_n-_octane	x_IL	x_o-_xylene	x_n-_octane	x_IL	邻二甲苯	正辛烷	选择性	PI	脱芳率
	m_n-_octane∶m_o-_xylene= 2∶1
0.5	0.3003	0.6997	0.0000	0.0873	0.0043	0.9084	0.2906	0.0062	46.87	13.62	14.41%
1	0.2622	0.7378	0.0000	0.0892	0.0061	0.9047	0.3400	0.0083	41.00	13.94	29.58%
2	0.2036	0.7964	0.0000	0.0761	0.0062	0.9177	0.3736	0.0078	47.97	17.92	49.83%
3	0.1666	0.8334	0.0000	0.0642	0.0088	0.9270	0.3843	0.0095	40.64	15.62	61.90%
4	0.1357	0.8643	0.0000	0.0545	0.0067	0.9388	0.4017	0.0087	46.32	18.61	69.71%
5	0.1204	0.8796	0.0000	0.0475	0.0073	0.9452	0.3942	0.0083	47.54	18.74	74.47%
	m_n-_octane∶m_o-_xylene= 4∶1
4	0.0819	0.9181	0.0000	0.0313	0.0052	0.9635	0.3824	0.0056	67.73	25.90	65.00%
	m_n-_octane∶m_o-_xylene= 9∶1
4	0.0408	0.9592	0.0000	0.0162	0.0068	0.9770	0.3964	0.0071	56.21	22.28	64.05%

能量	o-xylene	n-octane	[Bm₂im][FeCl₄]	sulfolane	[Bm₂im][FeCl₄]+o-xylene	[Bm₂im][FeCl₄]+n-octane	sulfolane+o-xylene	sulfolane+n-octane
E^①/hartree	-310.64	-315.46	-3566.45	-705.57	-3877.11	-3881.92	-1016.23	-1021.04
E^②/(kJ·mol^-1)	-815595.18	-828240.35	-9363701	-1852478.6	-10179343.99	-10191972.85	-2668110.29	-2680739.29
ΔE^③/(kJ·mol^-1)					-47.81	-31.5	-37.51	-21.34