Research On Physical Property Attenuation Of Silica Gel In Dynamic Adsorption Process

Water is necessary for the astronaut activities.Four-bed molecule sieve system is the principle method to maintain the stability of the water concentration inside the capsule,which could also remove carbon dioxide in the air effectively.Silica gel is the key adsorption material to separate and regenerate water,since it possesses faster water adsorption,lower weight and easier regeneration than the molecule sieve.The adsorption and regeneration properties,thermal stability,mechanical strength and corrosion resistance of silica gel are the key to ensure the long-time running of the four-bed molecule sieve system.The static and dynamic experiments using molecule sieve and silica gel as adsorption materials are carried out through building experimental apparatus in this paper.The adsorption and regeneration properties of adsorbent materials and the operation conditions of the four-bed molecular sieve system were studied.The main contents are as follows:The basic properties of two adsorbent materials were first investigated,the specific surface of the silica gel and molecule sieve is 728 m²/g and 811 m²/g respectively,the pore size is 2.35 nmis and 0.96 nm respectively.Through the static adsorption experiment,the effect of relative humidity on the properties of silica gel after multiple adsorption was studied under the condition of 1 atm and 20 ^oC.The results show that,the adsorption capacities of silica gel gradually decreased with the increase of the times of adsorption.The higher the humidity of the environment,the lower the adsorption capacity.After many static adsorption tests,silica gel can maintain good strength.Three dynamic adsorption devices were built to conduct the dynamic adsorption experiment.The effects of regeneration method and airspeed on the performances of silica gel after multiple dynamic adsorption tests were examined.The results indicate that after thirty adsorption and regeneration,the breakage rate of silica gel through situ regeneration,vacuum regeneration and oven regeneration were 0.05%,3.10%and3.08%,respectively.Under the condition of 1 atm and 25 ^oC,the adsorption capacity of silica gel using situ regeneration can reach up to 25%,while the vacuum regeneration and the oven regeneration are 20%and 18%,respectively.After multiple adsorption regeneration,the silica gel through situ regeneration method still has higher mechanic strength than that using other two methods.The breakthrough adsorption capacity of silica gel remains constant with the change of airspeed in the range of 1700⁴000 h^-1,while the breakthrough time is negatively correlated with airspeed.When the airspeed is higher than 4000 h^-1,the breakthrough adsorption capacity of silica gel decreases with the increase of airspeed.When the airspeed reaches 8000 h^-1,the breakthrough adsorption capacity is only half as much as the airspeed in the range of 1700⁴000 h^-1.According to the results of silica gel-water dynamic adsorption,a Fick unsteady diffusion model was established,and the orders of magnitude for the diffusion coefficient of silica gel-water was 10^-12.