Preparation Of Biomass Activated Carbon And Its Adsorption Properties

Activated carbon,as a widely used adsorbent,is rich in raw material sources.Among them,the biomass plant raw materials can be prepared with activated carbon with large specific surface area,developed porosity,low ash content,and high me-chanical strength due to the porous structure of the capillary system and high natural carbon content.Activated carbon prepared by phosphoric acid activation method has the advantages of simple process,lower activation temperature,less pollution and low cost,and is more conducive to preparation of activated carbon with more mesopore than alkaline activation method,which is beneficial to adsorb condensable gas.Bio-mass activated carbon containing more mesopore is prepared by efficient utilization of agricultural forestry waste as raw material and phosphoric acid as activator,which not only has a good development prospect but also meets the sustainable development strategy of our country.Four kinds of agricultural and forest waste biomass materials were selected and divided into compact group?coconut shell and walnut shell?and loose group?bamboo and corn cob?according to the different degree of natural structure density.The for-mer are based on the mesopore volume of activated carbon as an optimization index,followed by single variable principle to optimize the activation conditions of phos-phoric acid and obtain the suitable preparation conditions.Coconut shell activated carbon has a specific surface area of 1498 m²·g^-1 and a mesopore ratio of 28%.The activated carbon of walnut shell has a maximum specific surface area of 1710 m²·g^-1and a mesopore ratio of 27%.The activation conditions of bamboo and corn cob refer to pre laboratory work.The specific surface areas of obtained activated carbons were1454 m²·g^-1 and 1029 m²·g^-1 and the mesopore ratios were as high as 47%and 51%,respectively.It can be seen that the loose carbon material is easier to get the activated carbon with higher mesopores.In addition,actived carbon was prepared by dry and wet mixing method with corn core powder as raw material,and six kinds of mixing activators were ammonium persulfate,sodium hydroxide,boric acid,phosphotungstic acid,silicotungstic acid,and phospho molybdate acid,respectively.Compared with the final characteristic parameters of activated carbon products,boric acid has the best effect.The specific surface area of wet mixed grinding is 709 m²·g^-1,the pore volume reaches 0.51 cm³·g^-1,the specific surface area of dry mixed grinding is 511 m²·g^-1,and the pore volume reaches 0.32 cm³·g^-1.Therefore,boric acid as an activator has bright prospects for the preparation of activated carbonThe adsorption isotherms of CO₂?C₂H₆ and C₂H₄ under the critical temperature on the above four products were determined.The adsorption equilibrium data were fitted by Langmuir equation and Langmuir-Freundlich equation respectively,and iso-steric heat of adsorption was calculated.The results showed that the adsorption capac-ity of four activated carbons for three condensable gases increased with the decrease of temperature and the increase of pressure.The Langmuir-Freundlich model was more accurate than Langmuir model to describe the adsorption behavior of four kinds of biomass activated carbon on CO₂?C₂H₆ and C₂H₄.The applicability of Lang-muir-Freundlich equation on microporous carbon is higher than that of mesoporous carbon.The isosteric heat of adsorption value decreased basically as the adsorption capacity of ethane on four activated carbons increased from 0.5 mmol·g^-1 to 5mmol·g^-1,which reflected the surface heterogeneity of activated carbon.The selection of four kinds of activated carbon for three kinds of gas adsorption at different temper-atures is CO₂?coconut shell>walnut shell>bamboo>corn core?;C₂H₆?coconut shell,walnut shell>bamboo>corn core?;C₂H₄?walnut shell,coconut shell>bam-boo>corn cob?.