VPSA Plant for CO Separation from Syngas with CUCLl/Zeolite
Youchang Xie, Jiaping Zhang, and Wei Tang. College of Chemistry and Pioneer Technology Company, Peking University, Buld.18, No.4-302, Huaqingjiayuan, Haidian, Beijing, Beijing, 100083, China
Based on the principles that cuprous ions can form complex with carbon monoxide and salts can disperse onto the surface of supports as a monolayer spontaneously, a CuCl/Zeoilte adsorbent has been made by heating a mixture of CuCl and a zeolite at a suitable temperature to disperse the CuCl onto the surface of the zeolite. This adsorbent has high CO adsorption capacity (>50ml/g at 1 atm. and ambient temperature) and high CO selectivity over H2, N2, CH4 and CO2. In comparison with existed commercial, This adsorbent also has an advantage of no corrosion problem in industrial application., which often occurs in other existed commercial Cu+1adsorbents made by reducing supported CuCl2 which produce corrosive HCl.. By using this adsorbent, a large scale plant has been build in China to separate CO from syngas for production of acetic anhydride. The plant consists of two unit, a pre-treatment VPSA-1 unit to remove CO2, water and trace heavy components such as sulfur-containing compounds, followed by a VPSA-2 unit to produce CO. The first unit VPSA-1 has three beds filled with adsorbents which have high adsorption capacity for CO2 and H2O and poor adsorption for CO. Each bed passes through the following steps in cycle: adsorption, pressure-equalization, counter depressurization, purge with tail gas from VPSA-2 and evacuation (regeneration), partially pressurization (with gas from pressure equalization), re-pressurization (with purified gas from adsorption step). The second unit VPSA-2 has four beds filled with the CuCl/zeolite adsorbent working at about 70oC. Each bed passes through the following steps in cycle: adsorption, pressure-equalization, co-current depressurization, purge with CO product, counter depressurization to obtain CO product, evacuation to obtain CO product, partially pressurization (with gas from pressure equalization), re-pressurization (with tail gas from adsorption step). With a feed gas 6400m3/hour, composed of CO 30%, H2 41.1%, N2 17%, CH4 2.2%, O2 0.4%, CO2 8% and saturated water, working under the conditions: ambient temperature, pressure 8 bar, cycle time about 20 minutes for VPSA-1; feed temperature at about 70oC, pressure 7.5 bar, evacuating pressure 100-150 mmHg, purge pressure about 3 bar, purge ratio about 0.3, cycle time about 16 minutes for VPSA-2; the following results have been obtained: CO product 1700 m3/hour, yield 88%, purity 99.3%, impurity CH4<188ppm, CO2,10ppm, O2<5ppm. The plant has commissioned in Feb. 2003 and has been working smoothly until now and another larger scale plant (CO 4600m3/hour) is constructing.