| In recent years,CO2 emissions have continued to increase,and atmospheric CO2 concentrations have exceeded 400 ppm.As the largest energy consumer,China urgently needs CCUS technology to alleviate the sharp increase in CO2 emissions.Among all the CO2 capture technologies,the advantages of post-combustion capture are obvious,and solid adsorbents play an important role.Zeolite molecular sieves in solid adsorbents have attracted attention due to their regular pore structure and good hydrothermal stability.The raw materials used in the synthesis of the existing zeolite are mainly chemical materials,and it is necessary to add a toxic or environmentally harmful structure directing agent in the synthesis process,with a hydrothermal temperature of 423 K or more.Therefore,this paper explored the green synthesis method of ZSM-5 zeolite from the perspective of reducing the synthesis cost,reducing the environmental hazard and lowering the reaction temperature.The samples were systematically analyzed by XRD,SEM,FTIR,BET and other characterization methods,and the adsorption properties of CO2 were studied.This paper first used cheap rice husk ash and pseudo-boehmite as raw materials for the synthesis of ZSM-5 zeolite.The organic templating agent tetrapropylammonium hydroxide(TPAOH)was added to synthesize ZSM-5 zeolite seeds with a silica-alumina ratio of 20,30 and 40 at a crystallization temperature of 438 K.ZSM-5 zeolite samples(ZSM-5-H-20/30/40)corresponding to the silica-alumina ratio were synthesized at a crystallization temperature of 438 K by replacing the templating agent with ZSM-5 zeolite seeds crystal.Next,using ZSM-5 zeolite seeds,the effects of synthesis temperature,crystallization time and amount of seed crystal on low temperature synthesis of ZSM-5-L zeolite(ZSM-5L-20/30/40)were investigated.In this paper,363,378 and 393 K were used to explore the effect of crystallization temperature on the synthesis of ZSM-5 zeolite.The experimental results showed that the crystals synthesized at crystallization temperature of 393 K had the highest crystallinity and Zeolite growth was the most complete.The crystallization time was selected for 3,5,7 and 10 days.The experimental results showed that the zeolite with the crystallization time of 7 days had the best performance.The mass ratio of the seed crystals to the total feed was 0%,1%,2%and 5%,respectively.The experimental results showed that the zeolite with a higher crystallinity could be synthesized by using 1%of the seed crystal with a hydrothermal reaction temperature of 393 K.The samples synthesized at 393 K were tested for CO2 adsorption performance,CO2/N2 and CO2/O2 adsorption selectivity tests and regeneration performance tests.The CO2 adsorption isotherms of the samples were tested at temperatures of 273,303,and 333 K with a pressure of 15 bar.It was found that the CO2 adsorption amount of samples ZSM-5-L-20,ZSM-5-L-30 and ZSM-5-L-40 decreased with the increase of temperature and decreased with the increase of silicon to aluminum ratio.The experimental data were fitted and analyzed using Langmuir,Toth and Dual-Site Langmuir adsorption isotherm models.The CO2 adsorption isotherms of the samples ZSM-5-L-20,ZSM-5-L-30,and ZSM-5-L-40 were all fitted by the Toth model.The Toth model was used to fit the adsorption isotherms of O2 and N2 of the three samples.It was found that the adsorption of O2 by the sample was close to that of single layer adsorption.As the pressure reduced,the adsorption selectivity of CO2/O2 and CO2/N2 was greatly increased.The adsorption capacity of ZSM-5-L-20,ZSM-5-L-30 and ZSM-5-L-40 zeolite on CO2 at about 1 bar was about 8.0 times,5.8 times and 6.3 times of O2,respectively,about 3.8 times,3.4 times and 3.6 times of N2,respectively.Five times of CO2 cycle adsorption and desorption performance tests were performed on ZSM-5-L-20,ZSM-5-L-30 and ZSM-5-L-40 zeolites.After five cycles,the adsorption index of the sample could still reach 85.01%,82.69%and 83.43%which meant that the ZSM-5 zeolite synthesized at a low temperature had a good regeneration performance.In this paper,a method for green synthesis of ZSM-5 zeolite is proposed,which recycles the waste rice husk ash,effectively reduces the hydrothermal reaction temperature,and has good performance in synthetic products and broad application prospects. |
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