Study On Catalytic Biochemical Coupling Conversion Of CO₂ To Acetic Acid

The large-scale use of fossil energy has led to more and more CO₂ being emitted into the atmosphere,and the accumulation of CO₂ will lead to the greenhouse effect,bringing serious threats to the survival and development of all mankind.However,as a cheap and readily available carbon source,the efficient use of CO₂ has been neglected.If it can be converted into high value-added chemicals,it will achieve a win-win situation for both economy and environmental protection.The traditional CO₂ chemical conversion method has many drawbacks,and the green and low-carbon microbial fermentation method to convert CO₂ is gradually becoming a research hotspot in academia and enterprises.The use of microbial conversion of H₂ and CO₂ in anaerobic sludge to produce acetic acid has the advantages of mild reaction conditions,simple technical operation and low price,but there are also disadvantages such as low yield and slow rate of acetic acid production.In this study,a catalytic biochemical coupling conversion system was constructed by introducing solid catalysts into anaerobic fermentation systems,so as to realize the efficient production of acetic acid from anaerobic fermentation microorganisms using H₂and CO₂.Firstly,in order to ensure the stable and efficient operation of the CO₂anaerobic fermentation and conversion system,the effects of Na HCO₃,Mg CO₃,Na₂CO₃ and Ca CO₃ buffer solutions on acetic acid production by CO₂ microbial fermentation were explored.After 22 days of anaerobic fermentation,the reactor adding Na HCO₃ buffer solution achieved the highest acetic acid yield of 13587.56 mg/L,which was 18.52%higher than that of the blank control group.The addition of buffer solution enabled the daily acetic acid yield and acetic acid production rate of the anaerobic fermentation system to be stable for a long time,which ensured the normal progress of microbial acetic acid production metabolism.The reactor adding Na HCO₃ buffer solution achieved the highest acetic acid yield with the smallest total CO₂ consumption,obtained a molar yield of 64.95%carbon acetate,and the buffer capacity of Na HCO₃buffer solution was moderate,which could better ensure the p H stability of the reaction system,so Na HCO₃ was selected as the optimal buffer solution for the experiment of microbial conversion of H₂/CO₂ to acetic acid.Secondly,on the basis of adding Na HCO₃ buffer solution,the catalytic biochemical coupling conversion of H₂/CO₂ to acetic acid was studied.By comparing the acetic acid production capacity of the reactor adding Pt/Fe₂O₃,Pt/Al₂O₃,Ru/Fe₂O₃,Ru/Al₂O₃,Pd/Fe₂O₃ and Pd/Al₂O₃ catalysts,Pt/Fe₂O₃ and Pd/Al₂O₃ catalysts with better catalytic performance were screened.When the p H of the anaerobic fermentation system remained stable,the reactor with Pt/Fe₂O₃ catalyst had the highest acetic acid yield,followed by the reactor with Pd/Al₂O₃ catalyst.When anaerobic fermentation systems are affected by p H mutation shocks,Pd/Al₂O₃ catalysts show great advantages,and the system in which it is located can restore the normal gas consumption and acetic acid production capacity faster.After 38 days of anaerobic fermentation,the reactor adding Pd/Al₂O₃ catalyst obtained the highest acetic acid yield of 9803.16 mg/L,and the improvement compared to the blank control group is 125.32%.The reactor with Pt/Fe₂O₃ catalyst ranked second,and its acetic acid yield was7500.36 mg/L,which was 72.39%higher than that of the blank control group.In the process of catalyzing the production of acetic acid by microorganisms,the Pd/Al₂O₃ catalyst has the strongest ability to resist p H mutation impact,and can also ensure the high acetic acid yield of microorganisms when the p H of the reactor does not mutate,and finally the total yield of acetic acid is the highest and the comprehensive performance is the best.After the coupling conversion experiment,a series of characterization were carried out on Pt/Fe₂O₃,Pt/Al₂O₃,Pd/Fe₂O₃ and Pd/Al₂O₃ catalysts with good catalytic performance.Through SEM characterization,the binding morphology of microorganisms and catalysts was observed;The phase composition and surface structure of the catalyst were analyzed by XRD,H₂-TPR,and N₂ adsorption-desorption characterization.Through the characterization of In-situ DRIFTS,it was found that the surface of Pd/Al₂O₃ and Pt/Fe₂O₃ catalysts generated formate,carbonate,bicarbonate and other species,and the Pd/Al₂O₃ catalyst had stronger ability to generate formate.In order to determine the effect of different p H conditions on the performance of catalysts to promote acetic acid production by microorganisms,the catalytic effects of Pt/Fe₂O₃ and Pt/Al₂O₃ catalysts on acetic acid production by microorganisms were explored at p H 9,among which the Pt/Fe₂O₃ catalyst performed better,which prompted microorganisms to use more H₂/CO₂ for acetic acid production,and the yield of acetic acid increased by 133.54%compared with the blank control group.Finally,the microbiological analysis of the final sludge sample of the reactor was carried out to explore the deeper mechanism of catalyst promoting the production of acetic acid by microorganisms.Analysis of 16S r RNA microbial diversity on the samples revealed higher microbial community abundance of Firmicutes and Eubacterium with the distribution of homoacetogens in the reactor adding Pd/Al₂O₃ catalyst.In metagenomics and metaproteomics analysis,it was found that the addition of Pd/Al₂O₃ catalyst could change the microbial community structure of the fermentation reactor and achieve effective enrichment of the unclassified＿Eubacterium of homoacetogens,while the reactor adding Pt/Fe₂O₃ catalyst did not undergo significant changes in the microbial community structure.Based on the results of microbiological analysis and catalyst characterization,it is found that Pt/Fe₂O₃ catalyst mainly promotes the utilization of H₂ and CO₂ by microorganisms by strengthening the mass transfer process,so as to achieve the growth of acetic acid production.The Pd/Al₂O₃ catalyst mainly produces more formate intermediates for microorganisms to synthesize more acetic acid through the methyl branch of the W-L pathway,which significantly reduces the energy barrier of the fermentation process of acetic acid production.Based on the demonstration and analysis of experimental data and characterization results,this study successfully constructed a catalytic biochemical coupling system for the efficient production of acetic acid by using anaerobic fermentation microorganisms to convert H₂/CO₂,which provides a new solution for the green and efficient utilization of CO₂.