Preparation Of Rice Husk Based Porous Material And Its Application Research

Agricultural biomass waste rice husk,a by-product of rice processing,can pollute the ecological environment if discarded directly or burnt on site.Rice husk is cheap,abundant and rich in cellulose and hemicellulose,and has great potential for high value biomass resources.This paper explores the preparation of modified rice husk adsorbents,rice husk biochar adsorbents and rice husk-based solid acid catalysts using rice husk as raw material and using impregnation modification,oxygen-limited pyrolysis and carbonisation sulfonation,respectively,for the adsorption of organic pollutants,carbon dioxide capture and catalytic hemicellulose hydrolysis.Various aspects have been explored based on rice husk,providing a useful reference for the high-value utilization of rice husk.The main studies are as follows:（1）NaOH and KMnO₄ were used to modify rice husk to prepare two modified rice husk adsorbents,NaOH-modified rice husk（N-RH）and KMnO₄-modified rice husk（K-RH）,respectively.By evaluating the adsorption performance of methylene blue,the conditions such as the concentration of NaOH and KMnO₄ in the modification process were optimized,while the structure and morphology were analysed by means of scanning electron microscopy（SEM）,Fourier infrared（FTIR）and specific surface area determination（BET）characterisation.Static adsorption experiments were carried out to investigate the adsorption performance of methylene blue（MB）on rice husk before and after modification at different adsorbent dosage,contact time,p H and temperature,and the data were fitted and analysed using kinetic and isothermal models.The results showed that the modified rice hulls showed good adsorption of MB with a loose and porous surface and increased specific surface area,with the maximum adsorption capacity of 100 mg·g^-1 for N-RH and 50 mg·g^-1 for K-RH,which were 107%and27%higher than those of unmodified rice hulls,respectively.Freundlich isotherm model.In addition,the regeneration experiments of N-RH showed that the removal rate of MB by N-RH was still greater than 90%after four regenerations and the regeneration effect was good.（2）KOH alone activated rice husk biochar（K-AC）and combined KOH-NaOH activated rice husk biochar（KN-AC）were prepared using KOH and NaOH as activators.The conditions for the preparation of rice husk biochar were optimised by evaluating the adsorption performance of MB,while the structure and morphology were analysed using SEM,FTIR,BET and TG characterisation.The adsorption performance of KN-AC and unactivated rice husk biochar for MB was investigated at different adsorbent dosages,contact times,p H and temperatures,and the data were fitted and analysed using kinetic and isothermal models.The results showed that the activated rice husk biochar had high specific surface area and rich pore structure,and the adsorption effect of combined KOH-NaOH activation was better than that of KOH alone;under better adsorption conditions,the adsorption capacity of KN-AC for methylene blue could reach 359.9 mg·g^-1,which was 24 times higher compared with that of unactivated rice husk biochar.The adsorption experiments on different dyes showed that KN-AC had the best adsorption effect on cationic dyes;KN-AC was more consistent with the quasi-secondary kinetic model and the Langmuir isotherm model,and the adsorption process was spontaneous.In addition,desorption and regeneration experiments showed that KN-AC has no significant loss of activity after four regenerations and can be reused,which is expected to be an ideal adsorbent for water treatment.（3）CO₂ activated rice husk biochar,KOH activated rice husk biochar,NaOH activated rice husk biochar and combined KOH-NaOH activated rice husk biochar（i.e.KN-AC）were prepared by physical activation and chemical activation,respectively.The CO₂ adsorption performance was tested to investigate the effect of activation method and adsorption temperature on the adsorption performance,and the data were fitted and analysed using a kinetic model.SEM and BET were used to analyse the structure and morphology of the rice husk biochar.The results showed that compared with the physically activated and unactivated rice husk biochar,the chemically activated rice husk biochar had a higher specific surface area and developed surface pores;the effect of chemical activation was better than that of physical activation,in which KN-AC was more effective than KOH-activated rice husk biochar and NaOH-activated rice husk biochar for CO₂ adsorption.Under better adsorption conditions,the adsorption capacity of KN-AC was 1.30 mmol·g^-1,which was 76%and 145%higher than that of commercially available charcoal and unactivated rice husk biochar,respectively.The results of the kinetic fitting showed that the adsorption of CO₂ on rice husk biochar and commercially available charcoal was more in line with the quasi primary kinetic model,and the adsorption was mainly physical.The adsorption-desorption cycle showed that the adsorption effect of the best KN-AC did not decrease significantly after ten cycles and was stable enough to be reused.This indicates that KN-AC can be used not only for the adsorption process of organic pollutants by liquids,but also for the adsorption separation of gaseous mixtures.（4）The rice husk-based solid acid catalysts were prepared from rice husk as raw material.The char-sulphonation conditions were optimised by its performance test on catalytic hemicellulose waste hydrolysis,while its structure and morphology were analysed using SEM,FTIR,BET and TG characterisation.The effects of hydrolysis temperature,hydrolysis time and solid acid dosage on the hydrolysis effect were investigated.The results showed that the charred-sulphonated rice husk showed a dense lamellar structure with a specific surface area55-91 times that of the raw rice husk,and the sulphonic acid groups were successfully loaded on the rice husk biochar;under better hydrolysis conditions,the yield of reducing sugars and xylose could reach 484.152 mg·g^-1,and the rice husk-based solid acids showed good catalytic performance.This provides an experimental basis for the treatment of hemicellulose waste generated from chemical fibre mills,while realizing the high value utilization of rice husk and hemicellulose waste.