Research On VOCs Adsorption Properties Of Modified Pyrolytic Carbon From High Ash Content Food Waste Components

Under the policy background of waste classification,the production amount of food waste is continuously increasing,and its efficient resource utilization is an important link in urban sustainable development.Making use of the characteristics of food waste containing animal bones,shells and other high ash content components,the preparation of pyrolytic carbon with hierarchical pore structure is a hot spot in the research of resource utilization of food waste.The prepared pyrolytic carbon can be widely used in the fields of pollutant adsorption.In this work,high ash content food waste components such as bones,shrimp shells,and crab shells were selected as raw materials.The structural and surface modification processes of pyrolysis carbon were studied based on the results of pyrolysis mechanism and characteristics of those components.The formation mechanism of hierarchical porous structure was revealed and the dynamic regulation mechanism of surface hydrophobicity of pyrolytic carbon was further explored.The prepared modified pyrolytic carbon materials were applied to the static/dynamic adsorption of aromatic VOCs,and the VOCs adsorption properties of the material were studied.The adsorption characteristics of hydrophobic modified pyrolysis porous carbon on VOCs under humidity conditions were explored.Finally,the adsorption effect of formaldehyde in indoor environments was verified by preparing formed adsorption materials.Firstly,the pyrolysis characteristics and mechanisms of components including bovine bone,crab shell,and shrimp shell were studied.A series of materials with hierarchical porous structure were obtained by pyrolysis under high-temperature conditions.By analyzing the characteristics of gas-phase products generated during the pyrolysis process of food waste components using thermogravimetric infrared spectroscopy（TG-FTIR）,it was found that the CO₂ generated during the decomposition of hydroxyapatite and calcium carbonate in the ash of food waste components was the main factor affecting the micropore structure of materials generated during the pyrolysis process.The pyrolytic carbon material obtained by pyrolysis of bovine bone at 900℃showed the best specific surface area and total pore volume among all pyrolytic carbon materials.Abundant nitrogen-containing functional groups were distributed on the materials’surfaces.The nitrogen-containing functional groups were mainly pyrrolic nitrogen.The material had promising dynamic adsorption performance for toluene（dynamic adsorption capacity:288.12 mg/g）.It was determined that the structural parameter with the highest correlation with adsorption performance during the dynamic adsorption process is the specific surface area.Based on the porous structural characteristics of pyrolytic carbons from different components,bovine bone was selected as the raw material to further explore the surface modification and structural modification process of pyrolytic carbon materials.Using potassium carbonate as activation agent and phosphoric acid as surface modification agent,the structural and surface properties of food waste-based pyrolytic carbon materials were modified,respectively.The results indicated that through the potassium carbonate activation process,carbon materials with a three-level hierarchical porous structure of"micropore-mesopore-macropore"could be obtained.After surface modification,the content of oxygen-containing functional groups on the surface of the material significantly increased.The structural modified material performed an ultra-high static toluene adsorption capacity（13.03 mmol/g）.The static toluene adsorption process can be mainly divided into three stages:（i）adsorption in microporous pores and monolayer adsorption in mesoporous pores,（ii）multi-layer adsorption and filling in mesoporous pores,and（iii）capillary condensation and adsorption in macropores.In addition,the phosphate radical in hydroxyapatite on the material surface and toluene are chemically adsorbed in the form of intermolecular hydrogen bond.Based on the structural modification results of the pyrolytic carbon,the pyrolytic carbon formation potential of actual food waste components was explored.Bovine bone was selected as a typical high ash content food waste component,and peptone was added as organic component.The mentioned components were mixed to simulate the actual animal-based food waste,and the structure of pyrolytic carbon was modified under high-temperature chemical activation conditions.The results showed that the hierarchical porous carbon with hierarchical structural properties could be obtained from mixed food waste components under high temperature activation conditions.With the increment of the modification temperature,the average pore size of the structures increased.During the pyrolysis and structural modification process,peptone provided the carbon source,while bovine bone provided the template and partial activation agent.The modified materials showed promising adsorption effects on benzene and toluene（benzene adsorption capacity:139.5 mg/g,toluene adsorption capacity:440.7 mg/g）.By analyzing the correlation relationship between the adsorption rate parameters and material structure parameters during the dynamic adsorption process,it was found that the total pore volume was the most important factor affecting the adsorption rate.Based on the research basis of the porous structural modification processes of the pyrolytic carbon,the hydrophobic modification process was further optimized by ammonium bicarbonate assisted PDMS.Compared with traditional PDMS modification processes,ammonium bicarbonate assisted PDMS modification required lower temperature（less than 100℃）.The ultra-pure water contact angle of the material increased from 92.7°to 132.2°at the same modification temperature.After the modification process,there was a certain degree of structural loss in the materials.With the surface Si content increased,more severe the structural lose.Under humidity conditions,the adsorption performance loss of materials with better surface hydrophobicity was significantly smaller.Lastly,the application potential of high ash content food waste components-based modified pyrolytic carbon was studied.Using pyrolytic carbon powder as the raw material and polyvinyl alcohol as the adhesive,granular modified pyrolytic carbon was prepared.The prepared granular modified pyrolytic carbon retained its original hierarchical porous structure.Compared with the raw powder materials,there was a certain loss of structure in the granular modified pyrolytic carbon.Formaldehyde removal experiments were conducted on the granular modified pyrolytic carbon and commercial activated carbon in a self-made simulated adsorption chamber.The results indicated that compared with commercial activated carbon,formed modified pyrolytic carbon showed better removal efficiency for formaldehyde.The maximum removal efficiency for formaldehyde reached 92%.The entire adsorption process of formed modified pyrolytic carbon was also faster.The conclusions of this study can provide theoretical and data support for the pyrolysis mechanism of high ash content food waste components and the parameter control of pyrolytic carbon modification process.The conclusions of this study also provide a feasible technical route for the treatment and high-value utilization of more than 100 million tons of food waste generated in China every year,which has satisfying application value.