Xianqiang Zhu1, 3, Yingshu Liu1, 2*, Xiong Yang1, Wenhai Liu1

Study of a novel rapid vacuum pressure swing adsorption process with intermediate gas pressurizationfor producing oxygen

Xianqiang Zhu1, 3, Yingshu Liu1, 2*, Xiong Yang1, Wenhai Liu1

1School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China

2Beijing Key Laboratory of Energy Saving and Emission Reduction for Metallurgical Industry, University of Science and Technology Beijing, Beijing 100083, China

3Jiangsu Oxtek Air Equipment & Technology Co., Ltd., Danyang 212300,China

*Corresponding author: .

Key words

miniature oxygen concentrator; rapid pressure swing adsorption; vacuum; pressurization; numerical simulation

Supporting Information

S.1 Dual-use tankInformation

Portability of oxygen concentrator is asignificantrequirement for personal medical application.The rapid vacuum pressure swing adsorption (RVPSA) concept originated from the miniature air scroll integrated vacuum and compressor as well as the need for appropriate oxygen concentrator at high altitudes.A truly oxygen concentrator product based the proposed RVPSA process should be portable and efficient. The approach of storing a gas in a separate vessel (tank 14 and tank 15) may increase the size of oxygen concentrator.However,a separate vessel is necessary because of different oxygen purity of the storing gas during the adsorption (AD) step and the recovery of intermediate gas (IPP) step. A dual-use tank (shown in FigureS1) should be designed to improve the utilization of the tank. As seen from FigureS1, the dual-use tank was featured by a movable plate or piston. The plate or piston moves up or down and then the dual-use tank support the space for storing product gas during the adsorption step or storing intermediate gas during the recovery of intermediate gas step.Although the idea has not been practically employed, but should be easy to implement.

Fig.S1Dual-use tank

S.2 Adsorption isothermdata

Isotherms for LiLSXpellets used in the present simulations are shown in Figure S2.

Fig. S2Adsorption isotherms of LiLSX pellets

S.3 Model validation

Figure S3 shows the pressure change of adsorption column at feed end during the RVPSA process without intermediate gas pressurization. As can be seen from Figure S3, the change of the pressure in experiment was consistent with the one in simulation in four steps (PR, AD, and RE step) except in the CD step. However, the pressure errors of the CD step were not caused large changes of the process performance because of same desorption pressure.

Fig. S3 Pressure histories of adsorption column at feed end during the RVPSA process without intermediate gas pressurization

S.4 Simulated bed profiles

Figures S4a–c show the simulated steady state column profiles of gasphase O2mole fraction, N2 mole fraction, and specific N2 loading at the end of each process stepas functionsof dimensionless column positions (z/l) for the RVPSA cycle with intermediate gas pressurization and without intermediate gas pressurization.

(a) Gas phase concentration distributionby the cycle without intermediate gas pressurization

(b) Gas phase concentration distribution by the cycle with intermediate gas pressurization from product end

Fig.S4Simulated gas phase concentrationdistributionat the end of each step during the cycle with and without intermediate gas pressurization: (a) gas phase concentration distribution by the cycle without intermediate gas pressurization; (b) gas phase concentration distribution by the cycle with intermediate gas pressurization from product end; (c) specific N2 loading distribution on adsorbent by the cycle with intermediate gas pressurization from product end

Figures S4a–c showed that the leading edges of the N2 masstransferzones were pushed back toward the feedend during the IPP step. Then the gasphase O2 mole fraction of the product end could be effectively improved, which was beneficial to produce high oxygen purity of the product during the AD step. The oxygenpurity ofthe product obtained by the cycle without intermediate gas pressurization was limitedto <90% because of high N2 loading near product end.

The effects of pressurization with different oxygen purities of intermediate gas on gas phase concentration and temperature distribution at the end of IPP step are shown as Figure S5.

(a) Gas phase concentration distribution

(b) Gas phase temperature distribution

Fig.S5 Effect of oxygen purity of intermediate gas ongas phase concentration and temperature distribution at the end of IPP step: (a) simulatedgas phase concentration distribution; (b) simulated gas phase temperature distribution

Figures S5a and S5b showed that the pressurization with higher oxygenpurity of intermediate gas can pushN2 masstransferzones closer to the feed end and make lower gas temperature at product end, which confirmed the more beneficial effects for oxygen purity of product by pressurization with higher oxygenpurity of intermediate gas.

The effects of intermediate gas pressure before pressurization on the gas phase concentration and temperaturedistribution at the end of IPP step are shown as Figure S6.

(b) Simulated gas phaseconcentration distribution

Fig.S6 Effect of intermediate gas pressure on simulatedgas phase concentration and temperature distribution at the end of IPP step; (a)gas phaseconcentration distribution; (b) gas phase temperature distribution

FiguresS6a and S6b showed thatthe N2 masstransferzones were pushed closer to the feed end and the gas phase temperature was higher at the feed end by pressurization with intermediate at P*. Then higher oxygen concentration and lower gas temperature was obtained near the product end, which was favorable to produce higheroxygen purity of the product.