Preparation Of Biomass Based Porous Carbon Material And Its CO₂ Adsorption Performance

CO₂ is the main greenhouse gas,and its massive emissions have led to aggravation of global warming.Finding an achievable and environmentally friendly way to reduce CO₂emissions is a concern today.At present,CO₂ capture and storage technology is an effective way to reduce CO₂ emissions.Among all CO₂ capture methods,the adsorption method has received widespread attention due to its simple preparation process,no equipment corrosion,and low regeneration energy consumption.Among many adsorbents,porous carbon materials are considered to be the most promising adsorbents because of their high specific surface area,rich porous structure,and environmental friendliness.Biomass materials are considered to be effective carbon precursors for the preparation of CO₂ adsorbents due to the advantages of low price and wide sources.In this thesis,a series of biomass-based porous carbon materials were prepared with poplar wood chips as the precursor of biomass carbon,K₂C₂O₄ as the activator,and different heteroatoms doping.The pore structure of the materials and N,P,S,and O were discussed.The effect of heteroatom doping on CO₂ adsorption performance.The main conclusions are as follows:1.A porous carbon adsorbent was prepared with poplar wood chips as carbon precursor and K₂C₂O₄ as activator.The influence of the ratio of K₂C₂O₄ activator,the immersion time of K₂C₂O₄ activator,the activation temperature and the activation time on the CO₂ adsorption performance of the material was explored through orthogonal experiment design.It is determined that the optimal combination level of each influencing factor is a K/C ratio of 3,an immersion time of 6 h,an activation temperature of 800°C,and an activation time of 1.5 h.The best sample PC-800-2 has a CO₂ adsorption capacity of 5.33 mmol/g at 0°C and 1 bar,and its narrow micropore volume accounts for the largest ratio of micropore volume（V_n/V_m=81%）.It shows that the CO₂ adsorption performance of the adsorbent is closely related to the pore structure.2.Using poplar wood chips as the carbon precursor,ammonium phosphate as the modifier,and K₂C₂O₄ as the activator,a series of N and P co-doped biomass-based porous carbon material adsorbents were successfully prepared.The effects of the doping amount of ammonium phosphate and the amount of activator on the surface structure and properties of the adsorbent and the CO₂ adsorption performance were investigated.When the doping amount of ammonium phosphate is 10 g and the amount of activator is 3 times the mass of wood chips after carbonization,the prepared adsorbent CNPK-10-3 has the highest CO₂ adsorption capacity,at 1 bar,0,25°C The adsorption capacity of CO₂ was 5.49 and 3.73mmol/g,respectively.This is due to its optimal V_n/V_m value（77%）and the second highest surface effective nitrogen and phosphorus groups（N-5 and P-C groups）content.In addition,the CO₂/N₂ selectivity is 15;the initial isosteric heat of adsorption Q_st=29 k J/mol;the adsorption capacity can still be maintained at 97%of the original adsorption capacity after five adsorption and desorption cycles,indicating that the regeneration process of the adsorbent is simple Energy saving,with good recyclability.3.Using poplar wood chips as raw materials,sulfur-containing waste liquid（SCWL）as modifier,and K₂C₂O₄ as activator,a new type of N,S,and O co-doped porous carbon material adsorbent was successfully prepared.When the addition amount of SCWL is 2 m L,the amount of activator is 3 times the mass of wood chips after carbonization,and the sample PCSK-2-3-800 prepared at an activation temperature of 800°C has excellent CO₂ adsorption capacity.At 0/25°C and 1 bar,the CO₂ adsorption capacity was 5.61/3.82 mmol/g,the adsorption heat was 27.13 k J/mol,the CO₂/N₂ selectivity was 13,and the CO₂ adsorption capacity decreased by only 3.80%after 5 cycles.This is because the material that has undergone both SCWL modification and K₂C₂O₄ activation treatment has the highest content of micropores,and the surface of the material is doped with effective N,S,and O atoms.The CO₂ adsorption performance of the adsorbent is determined by the pore structure characteristics of porous carbon(S_BET,S_m,V_t,V_m,V_n),PSDs and effective heteroatom content.In addition,the possible mechanism of the reaction between the active ingredients of SCWL（ammonium thiosulfate and ammonium thiocyanate）and biochar was also determined.4.Through the response surface method and the Box-Behnken experimental principle,the adsorption conditions of the adsorbent for CO₂ at room temperature are optimized.The process parameters for the maximum CO₂ adsorption capacity are determined by taking the amount of sulfur-containing waste liquid,the amount of K₂C₂O₄ and the activation temperature as independent variables.The results showed that:（1）The amount of sulfur-containing waste liquid,the amount of K₂C₂O₄ and the activation temperature all have a significant effect on CO₂ adsorption.（2）Optimal preparation conditions:the sulfur-containing waste liquid volume is 2.8 m L,the K/C ratio is 3.3,the activation temperature is 786°C,and the optimal prediction value of the CO₂ adsorption capacity of the adsorbent at 1 bar and25°C 3.98 mmol/g,the actual value of CO₂ adsorption of the adsorbent OPCSK prepared under the above conditions at 1 bar and 25°C is 4.00 mmol/g,and the fitting deviation between the experimental results and the predicted value is less than 0.5%,indicating The significance of the model.（3）Compared with the PCSK-2-3-800 sample prepared in the previous chapter,the adsorbent OPCSK has better CO₂ adsorption capacity,cycle regeneration,CO₂/N₂ selectivity（15）and initial adsorption heat(Q_st=29.17 k J/mol).