Among the many clean energy sources, hydrogen is a clean, carbon-free, flexible and efficient new energy source, hydrogen energy has a good development prospect, which can be used directly as an energy source, and can also be used as a carrier for clean and efficient conversion between chemical energy and electrical energy, which makes hydrogen energy have great potential. Hydrogen has special physical properties, so it cannot be obtained directly from nature, and the current raw materials for hydrogen production mainly come from fossil energy, water and industrial exhaust gas.
With the continuous development of chemical technology, researchers have proposed a variety of hydrogen production methods, such as natural gas hydrogen production, methanol hydrogen production, coke oven gas hydrogen production, and water electrolysis hydrogen production, and the purity of hydrogen produced is respectively. 500%~99.999%, the main impurity gases are CH4 CO CO2 N2, CH3OH CO2 H2O, CH4 CO2 N2, O2 H2O hydrogen raw gas is usually used after purification, hydrogen purity is selected according to the requirements of the application, and adsorption separation technology is usually used to remove impurities in hydrogen. There are three main processes for hydrogen purification, namely pressure swing adsorption (PSA), low-temperature distillation and membrane separation, among which PSA hydrogen production technology has the characteristics of low cost, low energy consumption and high efficiency, and has a good prospect in industrial hydrogen production. PSA technology selects adsorption at relatively high pressure and desorption at low pressure according to the difference in adsorption capacity of adsorbents for different gas components under different pressure conditions, so as to achieve gas separation and purification.
The PSA process is mainly divided into vacuum pressure swing adsorption (VPSA) and fast pressure swing adsorption (RPSA). The PSA cycle typically includes steps such as adsorption, equalization, reverse discharge, regeneration (vacuum), and final charge. VPSA increases the vacuum step after reverse discharge to enhance the desorption and regeneration effect of absorbent adhesion. RPSA uses a higher rate of pressure change and shorter cycle times for faster adsorption and desorption. Therefore, it is necessary for the adsorbent to have high adsorption capacity and fast adsorption and desorption performance. In this study, activated carbon and 5A molecular sieve were used as adsorbents to simulate the hydrogen production process of the six-tower RPSA process, and the effects of feed flow, flushing flow ratio and adsorbent filling height ratio on RPSA performance were investigated. The results show that the RPSA process has a high hydrogen yield but a low recovery, and it needs to be paired with an adsorbent that can quickly adsorb and desorption to avoid resource waste. In addition, the process variables that affect the hydrogen production performance of PSA include feed time, inlet pressure, adsorption time, purge time, and number of adsorption beds.
Selection of adsorbents
The choice of adsorbent is critical to the performance of PSA hydrogen production, and the commonly used adsorbents are zeolite, activated carbon, carbon molecular sieve (CMS), metal-organic framework (MOFS) and activated alumina. The characteristics and adsorption characteristics of PSA hydrogen adsorption agent are shown in Table 2. Depending on the selectivity of the adsorbent for different gas components, researchers often use multiple adsorbents as laminar bed-filled adsorbents to process complex feedgases, such as the absorption of CO, N2 with zeolite and CO2 and CH4 with activated carbon
PSA hydrogen production industrial applications
In recent years, China's PSA hydrogen production technology has become increasingly mature. For example, the Southwest Chemical Research and Design Institute has built more than 1,000 sets of PSA purification hydrogen industrial plants, which is in a leading position in the field of PSA hydrogen production, providing strong support for the development of large-scale refining and chemical industry, modern coal chemical industry and hydrogen energy industry. PSA technology can be applied to distributed hydrogen production and hydrogenation integrated units.
PSA hydrogen production has broad application prospects, and will develop in the direction of high efficiency, low energy consumption, intelligence and new materials in the future.