| With the continuous optimization of enery structure, the proportion of natural gas in the whole energy structure have been gradually increasing becauce of its high efficiency, environmental friend, safety, less pollution and other advantages. Fosil fules, replaced by natural gas, can significantly reduce emissions of CO2, H2S, NOx, which contributes to improve the atmospheric environment and alleviates the greenhouse effect. Recently, natural gas exploited from CO2-rich gas fields faced with the requirements of gas quality standard and exhaust gas emissions standard. Therefore, it needs to remove CO2. Adsorption process has attracted widespread interests due to its advantages of equipments simplicity, wide application, low energy consumption and easily automation realization. In this paper, zeolite 5A,13X and 13X-APG as adsorbents were selected for adsorptive separation of CO2 from natural gas. The pure and binary experiments and the theoretical models fitting to explore the three types of absorbent’s performance of CH4/CO2 mixed gas under low temperature.The static volumetic method was adopted to measure the adsorption equilition isotherms of CO2 and CH4 on zeolite 5A,13X and 13X-APG. The effects of temperature and pressure on the adsorption capacity were discussed. It was found that the adsorption capacity of CO2 and CH4 was increased as the adsorption temperature decreasing and the adsorption pressure increasing. The adsorption capacity of CO2 on adsorbents is larger than CH4. At-30℃, the largest saturated adsorption capacity of CO2 on zeolite 5A,13X and 13X-APG were reaced 4.94 mmol/g,6.52 mmol/g and 6.35 mmol/g, respectively. Furthermore, the Langmuir model, Sips model, Toth model and DSL model were used to fit the experimental datas and achieved good results, respectively. The relative paraments of models were obtained by using the nonlinear fitting. Among all the models, Toth model shows the best fitting result, and the R2 of the two gases are very close to 1. The isosteric heats of CO2 and CH4 on the three kinds of adsorbents were calculated by experimental datas. It was found that the adsorption process was mainly physical adsorption and the adsorbent’s surface was non-uniform.The separation performance of zeolite 5A and 13X molecular sieves on CH4/CO2 mixture was measured by single column breakthrough curves. The effects of gas flow rate, adsorption pressure, adsorption temperature and packed height on the breakthrough curves and separation performance were investigated. The experimental results show that the separation capacity was reduced as the gas flow rate increasing and the adsorption pressure increasing. Decreasing the adsorption temperature and increasing the packed height wrer favorable for the separation. The binary adsorption model was established to predict the adsorption equilibrium of CH4/CO2 mixture gas on the zeolite 5A and 13X based on the better fit single adsorption model. Compared with the binary adsorption model and the experimental results, it was found that LRC model had better prediction results.The regeneration and stability after regeneration of the adsorbent were also studied. The regeneration performance of the zeolite 13X was investigated under different heating regeneration temperatures and vacuum regeneration, respectivedly. It was found that the effect of heating regeneration is better, and the adsorbent can be substantially complete regenerated after heating 180 min at 250℃. For the experiment of recycling the adsorbent several times, its results showed that the zeolite 13X molecular sieve still has a good separation capacity for CH4/CO2 mixture gas after reusing 5 times at-30℃. |
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