Research On The Resource Utilization Technology Of Tobacco Stem Waste Based On Thermochemical Conversio

The tobacco industry in Yunnan Province has held a prominent position in China.However,as the industry develops,the management of waste generated during tobacco cultivation and processing has become an issue that cannot be ignored.Among them,tobacco stalks,which make up about 50%of the whole plant and are the largest residual waste in tobacco production,are still predominantly disposed of by direct return to the field or incineration,causing serious environmental pollution and resource wastage.In fact,tobacco stalks are a lignocellulose-rich biomass resource that boasts advantages such as wide distribution,low cost,and high regeneration potential,making them a potential high-quality raw material for biomass refining.Nevertheless,compared with corn straw and other grass straw materials,tobacco stalks have thicker and tougher stalks and higher lignification,which limits their comprehensive utilization.Therefore,developing efficient and clean tobacco stalk resource utilization technology is a key aspect of the sustainable development of the tobacco industry in Yunnan Province.Thermochemical conversion technologies,which mainly include combustion,pyrolysis,and solvent thermal conversion methods,have been considered an effective means of converting biomass resources into fuels or high-value bio-based chemicals.Among these methods,direct combustion methods are not considered due to their low utilization and high pollution.For tobacco stalks,preparing tobacco stalk-based biochar through high-temperature pyrolysis technology can convert the complex chemical components（nitrogen-and oxygen-containing compounds）within them into abundant surface functional groups,making them an excellent catalyst precursor.In addition,using solvent（water）thermal conversion technology can selectively separate the biomass components of tobacco stalks under low-temperature alkaline conditions,yielding high-purity cellulose,hemicellulose,and lignin,among other high-value chemicals.Thus,utilizing different thermochemical conversion technologies to treat tobacco stalk waste can diversify the utilization of tobacco stalk and improve the utilization of tobacco stalk biomass resources.Based on the above analysis,this paper examines the different resource utilization processes of tobacco stalks using the above two thermochemical conversion technologies.The details are as follows:Firstly,the tobacco stalks raw material was pyrolyzed at a charring temperature of500 ^oC and an activation temperature of 800 ^oC to prepare porous biochar with a specific surface area of 1801 m²/g,an average pore size of 4.33 nm,and a total pore volume of0.23 m³/g.Subsequently,Br?nsted and Lewis acid sites were introduced by loading a certain amount of-SO3H groups and Fe³⁺.The resulting bifunctional solid acid catalysts were used to catalyze the whole-component liquefaction of sucrose pith to furfural（FF）,5-hydroxymethylfurfural（5-HMF）and levulinic acid（LA）.Characterization of the catalysts revealed that during the loading of acidic sites,a partial dissolution and reorganization of the pore network occurred on the surface of the tobacco stalk biochar,resulting in an irregular structure similar to the thoracic skeleton.The acidic groups were mainly distributed in the microporous,small and medium mesoporous structures of the biochar,where the-SO3H group was primarily in the form of chemical bonding and Fe³⁺was mainly in the form of ligand bonding.Additionally,the role of the reaction solvent,a co-solvent system composed ofγ-pentyl lactone and water,was investigated.The highest sucrose pith liquefaction（94.53%）and FF,5-HMF,and LA yields of 105.3%,26.32%,and 28.06%,respectively,were obtained when the solvent ratio was 29:1.DFT calculations demonstrated that the presence of a small amount of water increased the interaction energy and solubility of the reaction system,promoting the reaction kinetics.Investigation of the catalytic mechanism showed that some six-carbon sugars were converted to five-carbon sugars and further to FF during the liquefaction process,resulting in ultra-high FF yields.Secondly,a multi-stage oxygen alkali hydrothermal treatment process was designed to achieve effective and clean separation of cellulose,hemicellulose and lignin fractions from tobacco stalks at 120 ^oC.Experimental results showed that cellulose yield（38.48%）and whiteness（42.0%ISO）were obtained from the new process with a relatively high yield compared to the conventional hot alkali process.In addition,the microscopic morphology and crystal structure of tobacco stalk fibers showed that severe exfoliation reactions and oxidative degradation of carbohydrate ends occurred in the oxygen/alkaline environment,which destroyed the cellulose crystal structure and facilitated the subsequent enzymatic saccharification utilization.In addition,major organic compounds such as hemicellulose,lignin and small molecule extracts were isolated from the reaction solution with yields of 22.3%,11.8%and 36.03%,respectively.Chemical characterization showed that the extracted lignin had relatively high molecular weight and abundantβ-aryl ether bonds,which could be used to produce polymeric materials or biofuels/chemicals through depolymerization strategies,while the small molecule extracts mainly consisted of lignin/polysaccharide degradation products and bioactive compounds from natural tobacco,which were able to obtain high-value functional chemicals or pharmaceutical ingredients after the refining process.