| In view of the secondary pollution caused by chlorine in the utilization of chlorine-containing waste plastics and the alkali corrosion during the thermal utilization of high-alkali solid fuels,the research group proposed that polyvinyl chloride（PVC）and high-alkali solid fuels synergize with hydrothermal（HTC）simultaneous dehydration,a method for removing chlorine and alkali and alkaline earth metal elements（AAEMs）to improve the quality of hydrochar.In this paper,we study the thermal conversion performance of hydrochar produced by this method,investigated the influence law of relevant factors on the thermal conversion of hydrochar,studied the distribution and characteristics of each phase product,and evaluated the adsorption performance of the solid phase product char after thermal conversion,in order to realize the efficient disposal and high-value recycling of organic solid waste through hydrothermal-thermal conversion process.（1）The pyrolysis characteristics of hydrochar were studied based on the thermogravimetric analysis method（TG）,and the kinetic parameters of the pyrolysis process of four samples:raw coal,raw coal hydrochar,hydrochar with a PVC to raw coal mass ratio of 0.08 and hydrochar with a PVC to raw coal mass ratio of 0.16（Raw coal,R0,R0.08,R0.16）,were solved using the Coats-Redfern integration method.The results showed that the pyrolysis process in the range of 30-900°C was mainly divided into the stages of moisture removal and adsorbed gas escape at 80-200°C and the stages of decomposition of volatile,residual carbon and inorganic salts at more than 200°C.For R0.16,an additional decomposition peak belonging to PVC appeared at the pyrolysis temperature of 325°C.The maximum weight loss rate of hydrochar and the temperature Tmax corresponding to the the increase of the pyrolysis heating rate.As for the kinetics of pyrolysis of coal and hydrochar,the activation energy（E）increased with the increase in temperature of the pyrolysis process for both coal and hydrochar.（2）Combined with thermogravimetric-infrared（TG-FTIR）,the product precipitation pattern during hydrochar pyrolysis was revealed,and the results showed that the pyrolysis weight loss rate of coal and hydrochar was maximum at 450-500°C,and the pyrolysis products were dominated by H2O,hydrocarbons/CH4,CO and carbonyl,while the overall H2O and CO2 precipitation in the hydrochar pyrolysis gas products showed a decreasing trend.（3）The thermal conversion characteristics of hydrochar under nitrogen and nitrogen with steam were investigated by using a downdraft fixed bed,and the laws of HTC process and thermal conversion process temperature on product distribution and characteristics were explored.The main indicators were the hydrogen yield of synthesis gas,the content of aromatic tar and the surface area of the char,which were limited by the catalytic effect of AAEMs,the amount of PVC added and the degree of hydrochar cross-linking,etc.Due to the depolymerization of small molecule compounds in the HTC process,the pyrolysis char yield after hydrochar of raw coal increased,but the yield of pyrolysis char from hydrochar made by synergistic HTC addition of PVC decreased with the increase of PVC addition,and the overall four samples showed the law of R0>Raw coal>R0.08>R0.16 for pyrolysis char yield.At the same pyrolysis temperature,the pyrolysis H2 yield of hydrochar obtained by synergistic HTC showed a trend of first decreasing and then increasing,which was attributed to the fact that the hydrocarbon straight chains contained in PVC itself produced a large amount of hydrogen during the pyrolysis process while strengthening the dealkalization,which offset the decrease in the catalytic hydrogen production effect of AAEMs caused by dealkalization,resulting in the decrease of hydrogen yield.（4）Exploring the application potential of char in the treatment of printing and dyeing wastewater based on the structural characteristics of char after hydrochar thermal conversion and using malachite green（MG）as the adsorption object.The results showed that the adsorption capacity of char for malachite green was 570 mg/g at a concentration of 500 mg/L,which was better than the adsorption performance of some activated carbon made by carbonization and chemical activation of biomass.The results showed that the surface area of char followed the variation pattern of R0>R0.08>R0.16>Raw coal,while the content of functional groups on the surface of char showed an overall decreasing trend.The comparison of the surface area,the content of functional groups and the adsorption capacity showed that the adsorption of MG was highly consistent with the change of surface area,indicating that the specific surface area played a dominant role in the adsorption of MG,and the adsorption of MG by char was surface adsorption. |
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