Experimental Study On The Pyrolysis And Adsorption Characteristics Of Mixed Biochar With Coal

Biochar is the pyrolysis product of biomass raw materials in the oxygen limited environment.It has the characteristics of large specific surface area,rich surface functional groups,low preparation cost,high stability and so on,so it has a broad application prospect.Biochar is often used to improve soil,absorb pollutants in the environment and so on.The co pyrolysis of biomass mixed with other substances can produce a certain synergistic effect to promote the optimization of the surface functional groups and pore structure of the products.In this paper,the typical biomass sawdust and its three components（cellulose,hemicellulose and lignin）are taken as the research object,and the influence of blended coal on its pyrolysis characteristics is studied by thermogravimetry.Through the comparison between the experimental weight loss curve and the calculated value based on the weight weighting of blending ratio,it is found that the two are not consistent,which indicates that there is a certain synergy.It was found that the pyrolysis of sawdust and its three components mixed with coal mainly experienced three stages:dehydration and degassing,intense pyrolysis and polycondensation.The addition of Menghuan coal is favorable for the pyrolysis of hemicellulose and cellulose to move to high temperature,and the yield of biochar is lower than the weighted value.There are two peaks in DTG curve of lignin pyrolysis at 220℃and 280℃.With the increase of coal content,the two peaks weaken and move to high temperature section.During the co pyrolysis of sawdust and coal,with the increase of coal content,the weight loss peak gradually moved to the high temperature section,and the peak value decreased,and the weight loss speed slowed down.When the coal content is 25%,the yield of the mixture is 24.25%,which is 4.39%lower than the weighted calculation value of 28.64%.It shows that mixing small proportion of coal can help biomass pyrolysis more thoroughly.Then the effects of different preparation and adsorption conditions on the adsorption of Cu²⁺on biochar were investigated.The adsorption of Cu²⁺by biochar and Menghuan coal at different mixing ratio was studied,and the adsorption results were analyzed by different adsorption models.It was found that when the pyrolysis temperature was lower than 600℃and the pyrolysis time was lower than 2h,increasing the pyrolysis time and pyrolysis temperature during the preparation of biochar could effectively optimize the pore structure of biochar and improve the adsorption effect to nearly 20mg/g.However,with the increase of pyrolysis temperature and time,the increase of adsorption capacity is not obvious because the pore opening reaction is close to saturation and pore destruction.Increasing pH value in acid atmosphere can weaken the competitive effect of protons and Cu²⁺in solution,and then improve the adsorption effect.When pH value is 7～9,the removal rate remains high,and the adsorption amount reaches 19.65mg/g.At this time,the pH value will continue to increase,because Cu²⁺will produce the trend of precipitation,which will affect the Cu²⁺degree of freedom,making the adsorption effect decline.Increasing the initial concentration of Cu²⁺can effectively improve the adsorption capacity of biochar.However,with the increase of equilibrium time,the removal rate also decreases due to the competitive adsorption of ions.When the initial solution is lower than 50ppm,the removal rate of biochar can reach more than 90%,the initial concentration rises to 300ppm,and the removal rate is less than 40%.When the coal content was 25%,the adsorption effect increased by 4.81%;when the blending ratio was 75%,the adsorption effect increased by 2.12%.Finally,the sawdust was carbonized into biochar at 600℃and 2h,then activated by KOH and CO₂ at 800℃,and the effects of different activation methods,activation temperature,activation time and the activated carbon treated by loaded ionic liquid on the adsorption of CO₂ were investigated.The adsorption of CO₂ by activated biochar and Menghuan coal at different mixing ratio and by adding ionic liquid were also studied Influence.It was found that the adsorption capacity of biochar on CO₂ was increased by 87%by CO₂ activation method and 134%by KOH activation method due to the K vapor generated at over 762℃.In a certain range,increasing activation temperature and activation time can effectively improve the adsorption performance of activated carbon for CO₂.When the activation temperature is 850℃and activation time is 3h,the adsorption capacity reaches the maximum value.At this time,continuing to increase activation temperature and time will cause the activated carbon to burn,resulting in the decrease of adsorption capacity.The co carbonization and activation of coal and sawdust in different proportion have a certain synergistic effect,which makes them generate more gas to escape,form more pores and increase the adsorption capacity by 5%～10%.The pore of activated carbon will be blocked and the specific surface area and pore volume will be reduced by ionic liquid loading,which will lead to a decrease of about 24%in the adsorption performance of CO₂ activated activated carbon at low pressure（0.1～0.8MPa）,33.72%～43.35%in the adsorption performance of KOH activated carbon,but an increase of about 3.91%in the adsorption capacity of CO₂activated carbon at high pressure（1.5MPa～2MPa）.With the increase of load,the trend is more obvious.The regeneration performance of activated carbon loaded with ionic liquid decreased slightly,but the regeneration loss was still less than 7%.