Preparation of high-purity H2 and CO by efficient separation of CO/H2 using dual-reflux pressure swing adsorption process

doi:10.11949/0438-1157.20240535

Abstract

Abstract:

Double reflux (DR) pressure swing adsorption (PSA) process has the advantage of not being affected by pressure ratio, and is expected to break through the thermodynamic limitations of traditional pressure swing adsorption (PSA) to obtain two high-purity gases at the same time. In this work, based on the two-bed four-step DR PSA process, we investigated the separation effects of activated carbon (AC), 13X and 5A molecular sieve composite adsorbents, and Cu(Ⅰ)/AC single adsorbent, achieving the simultaneous preparation of high-purity H₂ and CO products. A non-isothermal adsorption model consisting of mass, momentum and energy balance equations was developed using the Aspen Adsorption simulation platform, and its reliability was verified through fixed-bed adsorption experiments. The results demonstrated that the DR PSA process with AC, 13X, and 5A molecular sieve composite adsorbents exhibited unsatisfactory separation efficiency, but exhibited stronger CO desorption ability; using Cu(Ⅰ)/AC alone as the adsorbent can significantly enhance the separation efficiency, that is, using CO/H₂=0.5/0.5 (volume ratio) synthesis gas as the raw material, H₂ product with a purity of >99.999% could be obtained, the CO content is <0.20 ml/m³, and the yield is 96.69%. At the same time, the purity of CO product attains >97.00%, and the yield reaches 99.16%. Increasing the reflux ratio of light and heavy components could further improve the purity of H₂ and CO product gases, respectively.

Key words: dual-reflux, pressure swing adsorption, carbon monoxide, Cu(Ⅰ)/AC, numerical simulation

摘要：

双回流（DR）变压吸附（PSA）工艺具有不受压力比影响的优势，有望突破传统PSA的热力学限制同时获得两种高纯气体。基于两塔四步DR PSA工艺，分别考察了活性炭（AC）、13X和5A分子筛复合吸附剂以及Cu（Ⅰ）/AC单吸附剂的分离效果，实现了同时制备高纯H₂和CO产品。利用Aspen Adsorption模拟平台开发了一个由质量、动量和能量平衡方程组成的非等温吸附模型，并通过固定床吸附实验验证了模型的可靠性。结果表明，AC、13X和5A分子筛复合吸附剂的DR PSA工艺分离效率欠佳，但表现出更强的CO解吸能力；而单独以Cu（Ⅰ）/AC为吸附剂，可以显著提升分离效率，即以CO/H₂=0.5/0.5（体积比）合成气为原料，获得纯度>99.999%的H₂产品，其中CO含量<0.20 ml/m³，收率达96.69%；同时CO产品纯度>97.00%，收率达99.16%。增大轻、重组分回流比可以进一步提高H₂和CO产品气的纯度。

关键词: 双回流, 变压吸附, 一氧化碳, Cu（Ⅰ）/AC, 数值模拟

CLC Number:

TQ 028.1

Qiang GUO, Qidong ZHAO, Yonghou XIAO. Preparation of high-purity H₂ and CO by efficient separation of CO/H₂ using dual-reflux pressure swing adsorption process[J]. CIESC Journal, 2024, 75(11): 4298-4308.

郭强, 肇启东, 肖永厚. 双回流变压吸附高效分离CO/H₂制备高纯H₂和CO[J]. 化工学报, 2024, 75(11): 4298-4308.

Figures/Tables 17

Fig.1 Schematic diagram of pilot CO adsorption breakthrough experimental device

Table 1 Properties of the adsorption bed and operating conditions

Parameters	AC/13X/5A	Cu(Ⅰ)/AC
height of adsorbent layer/m	0.50/0.50/0.80	2.0
diameter of adsorbent layer/m	0.13	0.20
thickness of bed wall	0.0050	0.0020
inter-particle voidage	0.43/0.35/0.35	0.35
intra-particle voidage	0.61/0.65/0.65	0.33
bulk solid density of adsorbent/ (kg/m³)	708.00/851.29/715.70	625.00
adsorbent particle radius/mm	2.0	1.4
feed gas pressure/bar	5.0	5.0
feed flow rate/(L/min)	33.33	33.33

Fig.2 Fitting curves of adsorption isotherms for each component over AC, 13X, 5A and Cu(Ⅰ)/AC

Table 2 The equations used in DR PSA model

Model equation	Expression	Equation
mass balance	$- ε b D a x, i ∂ 2 c i ∂ z 2 + ε b ∂ v g c i ∂ z + ε b + 1 - ε b ε p ∂ c i ∂ t + ρ s 1 - ε b ∂ q i ∂ t = 0$	(1)
energy balance	gas phase $- ε b k g ∂ 2 T g ∂ z 2 + C v g v g ρ g ∂ T g ∂ z + ε b C v g ρ g ∂ T g ∂ t + P ∂ v g ∂ z + h f a p T g - T s + 4 h w T g - T 0 D b = 0$	(2)
	solid phase $- k s ∂ 2 T s ∂ z 2 + C p s ρ s ∂ T s ∂ t + ρ s ∑ i = 1 n C p a, i q i ∂ T s ∂ t + ρ s ∑ i = 1 n ∆ H i ∂ q i ∂ t - h f a p T g - T s = 0$	(3)
	bed wall $k w ∂ 2 T w ∂ z 2 + C p w ρ w ∂ T w ∂ t - h w 4 D b D b + W t 2 - D b 2 T g - T w + h a m b 4 D b + W t 2 D b + W t 2 - D b 2 T w - T a m b = 0$	(4)
	$N u f = 2 + 1.1 P r 1 / 3 R e 0.6$	(5)
	$N u w = 12.5 + 0.048 R e$	(6)
	$N u 0 = 0.1 R a 1 / 3$	(7)
momentum balance	$- ∂ p ∂ z = 150 μ 1 - ε b 2 ε b 3 2 r p ψ 2 v g + 1.75 1 - ε b 2 r p ψ ε b 3 ρ g v g v g$	(8)
LDF	$∂ q i ∂ t = k L D F, i (q i * - q i)$	(9)
LDF	$k L D F, i = 15 D p, i R p 2$	(10)
ideal gas law	$p V i = n i R T$	(11)

Table 2 The equations used in DR PSA model

Model equation	Expression	Equation
mass balance	$- ε b D a x, i ∂ 2 c i ∂ z 2 + ε b ∂ v g c i ∂ z + ε b + 1 - ε b ε p ∂ c i ∂ t + ρ s 1 - ε b ∂ q i ∂ t = 0$	(1)
energy balance	gas phase $- ε b k g ∂ 2 T g ∂ z 2 + C v g v g ρ g ∂ T g ∂ z + ε b C v g ρ g ∂ T g ∂ t + P ∂ v g ∂ z + h f a p T g - T s + 4 h w T g - T 0 D b = 0$	(2)
	solid phase $- k s ∂ 2 T s ∂ z 2 + C p s ρ s ∂ T s ∂ t + ρ s ∑ i = 1 n C p a, i q i ∂ T s ∂ t + ρ s ∑ i = 1 n ∆ H i ∂ q i ∂ t - h f a p T g - T s = 0$	(3)
	bed wall $k w ∂ 2 T w ∂ z 2 + C p w ρ w ∂ T w ∂ t - h w 4 D b D b + W t 2 - D b 2 T g - T w + h a m b 4 D b + W t 2 D b + W t 2 - D b 2 T w - T a m b = 0$	(4)
	$N u f = 2 + 1.1 P r 1 / 3 R e 0.6$	(5)
	$N u w = 12.5 + 0.048 R e$	(6)
	$N u 0 = 0.1 R a 1 / 3$	(7)
momentum balance	$- ∂ p ∂ z = 150 μ 1 - ε b 2 ε b 3 2 r p ψ 2 v g + 1.75 1 - ε b 2 r p ψ ε b 3 ρ g v g v g$	(8)
LDF	$∂ q i ∂ t = k L D F, i (q i * - q i)$	(9)
LDF	$k L D F, i = 15 D p, i R p 2$	(10)
ideal gas law	$p V i = n i R T$	(11)

Table 3 Fitting parameters of extended Langmuir adsorption models for AC， 13X and 5A

Adsorbent	Parameters	H₂	Ar	CO
AC	Q_m/(mmol/g)	10.68	7.00	6.82
	b₀/bar^-1	2.16×10^-5	1.76×10^-4	9.05×10^-6
	ΔH/(kJ/mol)	-12.84	-13.53	-22.58
13X	Q_m/(mmol/g)	6.50	4.41	3.18
	b₀/bar^-1	1.33×10^-4	2.92×10^-4	8.49×10^-5
	ΔH/(kJ/mol)	-8.00	-11.00	-21.00
5A	Q_m/(mmol/g)	1.15	4.24	2.24
	b₀/bar^-1	2.82×10^-4	1.67×10^-4	6.14×10^-6
	ΔH/(kJ/mol)	-9.23	-13.30	-29.77

Table 4 Fitting parameters of extended Langmuir adsorption model for Cu（Ⅰ）/AC

Parameters	H₂	Ar	CO	CH₄	N₂	CO₂
Q_m/(mmol/g)	38.87	6.56	2.00	3.23	7.18	5.38
b₀/bar^-1	1.0×10^-5	1.8×10^-4	1.0×10^-5	5.0×10^-5	1.9×10^-5	7.5×10^-6
ΔH/(kJ/mol)	-8.50	-13.74	-31.45	-20.60	-15.87	-26.83

Fig.3 Constructed DR PSA model based on the Aspen Adsorption platform

Fig.4 Schematic diagram of the DR PSA process for half a cycle

Table 5 Cycle time of DR PSA process

Bed	Duration/s
Bed	100	20	100	20
1	AD	VU	PU	PR
2	PU	PR	AD	VU

Fig.5 The influence of different equilibrium gases on CO breakthrough curves

Fig.6 Pressure and temperature distribution across the bed within one cycle

Fig.7 Axial concentration distribution of CO in AC, 13X and 5A composite adsorbent and Cu(Ⅰ)/AC adsorption beds after each step within a cycle

Fig.8 The influence of different light to heavy reflux ratios on the purity of product gas on AC, 13X and 5A composite and Cu(Ⅰ)/AC adsorbents

Fig.9 The effect of different light to heavy reflux ratios on axial CO loading amounts after AD step

Fig.10 The influence of different feed gas concentrations on the purity of product gas in Cu(Ⅰ)/AC adsorbent bed

Fig.11 Solid phase concentration distribution at the end of each cycle of H2/CO/CO2/CH4/N2 synthesis gas under multi-component competitive adsorption conditions

Fig.12 Effects of different feed positions on the solid phase concentration distribution of each component after AD step

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Preparation of high-purity H₂ and CO by efficient separation of CO/H₂ using dual-reflux pressure swing adsorption process

双回流变压吸附高效分离CO/H₂制备高纯H₂和CO

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