Thermodynamic analysis for NH3 separation using ionic liquids/deep eutectic solvents

doi:10.11949/0438-1157.20200894

Abstract

Abstract:

Ammonia (NH₃) is a harmful gas, and there are so many defects for traditional NH₃ absorption technologies. It is urgent to find ammonia absorbent with superior performance to develop new NH₃ separation technology. Ionic liquids and deep eutectic solvents are potential absorbents in gas separation process. They have attracted more and more attentions due to their low volatility, good thermal stability and flexible controllability. However, there are so large amount of ionic liquids and deep eutectic solvents that it is difficult to screen the one with superior performance. The thermodynamic analysis is used to analyze NH₃ separation process using ionic liquids and deep eutectic solvents as NH₃ absorbents. On the basis of the Gibbs free energy change, the optimal operational conditions of the NH₃ separation process were fitted. The energy use and the amount of absorbents considered as the criteria and [Omim][BF₄] was screened with good performance. The performance of [Omim][BF₄] is compared with that of water, which is a traditional NH₃ absorbents, and it can be concluded that [Omim][BF₄] shows lower energy use. Finally, the law between the screening criteria and the critical properties of ionic liquids/deep eutectic solvents is fitted, which can be used as the basis to develop new NH₃ absorbents and new NH₃ separation technology.

Key words: NH₃ separation, ionic liquids, deep eutectic solvents, thermodynamic analysis

摘要：

氨气（NH₃）作为一种有害气体，其传统吸收技术存在诸多缺陷，亟需开发性能优越的NH₃吸收剂，以开发新型NH₃分离技术。离子液体和低共熔溶剂作为气体分离过程的潜在吸收剂，因低挥发性、良好的热稳定性以及灵活的可调控性等特点受到越来越多的关注。但离子液体和低共熔溶剂数量众多，筛选困难。采用热力学分析方法分析离子液体和低共熔溶剂用于NH₃分离过程，基于Gibbs自由能变，拟合出分离过程的最佳操作条件，将总能耗和离子液体用量作为筛选标准，筛选出性能良好的[Omim][BF₄]。将[Omim][BF₄]与传统NH₃吸收剂水对比，发现[Omim][BF₄]具有更低的能耗。最后，拟合出筛选标准与离子液体/低共熔溶剂的临界性质间的规律，为开发新的NH₃吸收剂和新的分离技术提供依据。

关键词: NH₃分离, 离子液体, 低共熔溶剂, 热力学分析

CLC Number:

ZHANG Yingying, GUO Shuna, SONG Shuailong, YANG Xuzhao, WU Shide, TIAN Junfeng, HAN Guanglu, ZHANG Jingjing, LI Yakun, ZHANG Jianqiang. Thermodynamic analysis for NH₃ separation using ionic liquids/deep eutectic solvents[J]. CIESC Journal, 2021, 72(3): 1264-1274.

张盈盈, 郭淑娜, 宋帅龙, 杨许召, 吴诗德, 田俊峰, 韩光鲁, 张静静, 李亚坤, 张建强. 离子液体/低共熔溶剂用于NH₃分离过程的热力学分析[J]. 化工学报, 2021, 72(3): 1264-1274.

Figures/Tables 13

Table 1 The composition of synthetic ammonia purge gas[15-16]

氨气（NH₃）	氢气（H₂）	氮气（N₂）	甲烷（CH₄）
43.8%~50%	25%~36.3%	9.5%~15.8%	3.6%~9.2%

Fig.1 Simplified process flow diagram of NH3 separation process

Fig.2 Thermodynamic framework for of NH3 separation from synthetic ammonia purge gas with ILs/DESs

Fig.3 The process coupling thermodynamic analysis of NH3 separation from synthetic ammonia purge gas with ILs/DESs

Table 2 The molecular weight, NH3 solubility, density, isobaric heat capacity and critical properties of 8 ILs/DESs

离子液体/低共熔溶剂	M/ (g?mol^-1)	$x N H 3$			ρ/(g?cm^-3)	c_p/(J?mol^-1?K^-1)	T_c/K	P_c/bar
离子液体/低共熔溶剂	M/ (g?mol^-1)	T/K	P/bar	$x N H 3$	ρ/(g?cm^-3)	c_p/(J?mol^-1?K^-1)	T_c/K	P_c/bar
[Emim][BF₄]	197.97	313.15~333.15	1.2~6.3	0.084~0.526^[23]	1.280^[26]	311.5~316.8^[34]	585.3^[39]	23.60^[39]
[Bmim][BF₄]	226.02	313.15~333.15	0.7~8.3	0.061~0.562^[23]	1.201^[27]	371.7~377.7^[35]	632.3^[39]	20.40^[39]
[Hmim][BF₄]	254.08	313.15~333.15	1.4~7.1	0.128~0.624^[23]	1.145^[28]	436.2~444.0^[36]	679.1^[39]	17.90^[39]
[Omim][BF₄]	282.13	313.15~333.15	1.0~6.0	0.132~0.644^[23]	1.104^[29]	505.4~514.2^[36]	726.1^[39]	16.00^[39]
[Bmim][PF₆]	284.18	298.60~347.20	1.8~7.7	0.253~0.737^[9]	1.368^[30]	402.0~409.0^[37]	708.9^[39]	17.30^[39]
ChCl/urea(1∶2)	86.58	313.20~333.20	0.1~3.0	0.017~0.241^[24]	1.206^[31]	182.2~184.5^[38]	644.4^[40]	49.54^[40]
ChCl/gly(1∶2)	107.94	313.15~333.15	0.1~5.7	0.030~0.556^[25]	1.192^[32]	239.1~243.5^[38]	680.7^[40]	33.46^[40]
ChCl/EG(1∶2)	87.92	313.15~333.15	0.1~5.5	0.035~0.511^[25]	1.117^[33]	192.2~196.4^[38]	602.0^[40]	40.99^[40]

Table 2 The molecular weight, NH3 solubility, density, isobaric heat capacity and critical properties of 8 ILs/DESs

离子液体/低共熔溶剂	M/ (g?mol^-1)	$x N H 3$			ρ/(g?cm^-3)	c_p/(J?mol^-1?K^-1)	T_c/K	P_c/bar
离子液体/低共熔溶剂	M/ (g?mol^-1)	T/K	P/bar	$x N H 3$	ρ/(g?cm^-3)	c_p/(J?mol^-1?K^-1)	T_c/K	P_c/bar
[Emim][BF₄]	197.97	313.15~333.15	1.2~6.3	0.084~0.526^[23]	1.280^[26]	311.5~316.8^[34]	585.3^[39]	23.60^[39]
[Bmim][BF₄]	226.02	313.15~333.15	0.7~8.3	0.061~0.562^[23]	1.201^[27]	371.7~377.7^[35]	632.3^[39]	20.40^[39]
[Hmim][BF₄]	254.08	313.15~333.15	1.4~7.1	0.128~0.624^[23]	1.145^[28]	436.2~444.0^[36]	679.1^[39]	17.90^[39]
[Omim][BF₄]	282.13	313.15~333.15	1.0~6.0	0.132~0.644^[23]	1.104^[29]	505.4~514.2^[36]	726.1^[39]	16.00^[39]
[Bmim][PF₆]	284.18	298.60~347.20	1.8~7.7	0.253~0.737^[9]	1.368^[30]	402.0~409.0^[37]	708.9^[39]	17.30^[39]
ChCl/urea(1∶2)	86.58	313.20~333.20	0.1~3.0	0.017~0.241^[24]	1.206^[31]	182.2~184.5^[38]	644.4^[40]	49.54^[40]
ChCl/gly(1∶2)	107.94	313.15~333.15	0.1~5.7	0.030~0.556^[25]	1.192^[32]	239.1~243.5^[38]	680.7^[40]	33.46^[40]
ChCl/EG(1∶2)	87.92	313.15~333.15	0.1~5.5	0.035~0.511^[25]	1.117^[33]	192.2~196.4^[38]	602.0^[40]	40.99^[40]

Fig.4 The relationship between absorption pressures, the amounts of ILs needed, the energy uses and desorption temperature of [Bmim][BF4]

Fig.5 The relationship between absorption pressures and desorption temperature of 8 ILs/DESs

Fig.6 The relationship between amounts of absorbents needed and desorption temperature of 8 ILs/DESs

Fig.7 The relationship between total energy uses and desorption temperature of 8 ILs/DESs

Table 3 The desorption temperature, absorption pressure, amounts of absorbents needed and total energy uses of the screened ILs/DESs

离子液体/低共熔溶剂	T_s/K	P_a/bar	m_IL/DES/(g?g^-1)	Q_tot/(GJ?t^-1)
[Bmim][BF₄]	299.15~314.85	3.06~8.58	25.75~269.40	1.54~2.29
[Hmim][BF₄]	299.15~319.15	3.29~11.31	21.05~264.70	1.39~1.85
[Omim][BF₄]	299.15~319.15	3.31~11.06	20.12~257.05	1.05~1.91
ChCl/EG(1∶2)	314.85~319.15	2.34~2.38	15.18~17.72	2.37~2.40

Table 4 The molecular weight, density, NH3 solubility and isobaric heat capacity of water

参数	数值
分子量M_IL/(g?mol^-1)	18
溶解度 $x N H 3$	0.253~0.290^[41]
密度ρ/(g?cm^-3)	0.997^[20]
比热容c_p/(J?mol^-1?K^-1)	75.3~75.4^[20]

Table 4 The molecular weight, density, NH3 solubility and isobaric heat capacity of water

参数	数值
分子量M_IL/(g?mol^-1)	18
溶解度 $x N H 3$	0.253~0.290^[41]
密度ρ/(g?cm^-3)	0.997^[20]
比热容c_p/(J?mol^-1?K^-1)	75.3~75.4^[20]

Fig.8 The relationship between the amounts of absorbents needed, the total energy uses and desorption temperature of [Omim][BF4] and water

Table 5 The fitting coefficients and average absolute relative deviation of the law

体系	P_a			m_IL/DES				Q_tot
体系	a	b	AARD/%	c×10^-5	d	e	AARD/%	f	g	h×10³	AARD/%
[Emim][BF₄]	191.99	-78.94	4.73	25.84	0.27	-6.96	0.61	-17.07	921.53	-12.44	1.38
[Bmim][BF₄]	272.41	-155.94	5.05	9.02	0.36	-9.30	0.03	-7.70	527.65	-9.03	3.20
[Hmim][BF₄]	309.51	-224.34	5.48	-1.76	0.43	-10.50	0.09	-3.60	310.54	-6.69	6.96
[Omim][BF₄]	299.36	-262.65	5.77	-7.78	0.39	-11.70	0.11	-1.55	163.35	-4.31	8.03
[Bmim][PF₆]	340.73	-215.43	5.51	-7.09	0.48	-11.11	0.08	-2.48	232.74	-5.47	5.60
ChCl/urea(1∶2)	31.58	-0.29	0.14	0.83	-0.01	23.59	7.47	-9.35	253.40	-1.71	2.47
ChCl/gly(1∶2)								6.82	-298.99	3.28	2.02
ChCl/EG(1∶2)								11.76	-365.08	2.84	2.10

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Thermodynamic analysis for NH₃ separation using ionic liquids/deep eutectic solvents

离子液体/低共熔溶剂用于NH₃分离过程的热力学分析

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