Understanding Physicochemical Characterization And Pyrolysis Mechanism Of Biomass Tobacco Stems

As an important and widespread economic crop,tobacco not only supports national revenue but also drives social and economic development.This paper focuses on the value-added utilization of biomass tobacco stems,and uses waste tobacco stems（TS）from typical tobacco（Nicotiana tabacum L.）growing areas in Yunnan Province as the main research object.Liquid impregnation method,continuous flow analyzer and TG analysis were used to characterize the physicochemical properties and thermal degradability behavior of TS and the correlation between them,and to estimate the kinetic and thermodynamic parameters of the TS,and to investigate the distribution characteristics of the physicochemical properties,the decomposition mechanism,the pyrolysis mechanism,and the effect of component differences on the activation energy.This study is important for the industrial value-added applicability of TS as well as the value-added utilization of waste resources.The findings are as follows:（1）The porosity and bulk density of TS varied greatly from typical tobacco growing areas in Yunnan Province.And it was significantly affected by the interaction of growing areas,varieties and parts（P<0.05）.The moisture content of TS varies significantly with relative humidity when the relative humidity is greater than 60%during the hygroscopic-desiccation process.The GAB model and the H-H model are suitable for the hygroscopic-desiccation process of tobacco leaf.（2）The chemical composition and aroma components of TS in typical tobacco growing areas in Yunnan Province have obvious regional characteristics;the content of sugars,total nitrogen,cell wall material and aroma components in the TS gradually decreases from west to east,while the mass fraction of potassium ions,total plant alkali and chloride ions gradually increases from west to east;the TS of different varieties and parts have their own characteristics.Cluster analysis results indicated that according to stem form,TS could be mainly classified into three categories:stem head,long and short stems,and fragmentary stem.Long and short stems had higher mass fractions of sugar and potassium and lower alkali.The stem heads and fragmentary stems with higher mass fractions of alkali and aroma components.Most importantly,the middle and upper TS should be preferred to use and classified to process according to the tobacco growing areas,which is beneficial for promoting industrial applicability in cigarette preparation.This study provides a theoretical reference for the industrial value-added applicability of TS in the aspects of flavour extraction and cigarette preparation.（3）Pyrolysis of tobacco wastes is divided into three stages:moisture evaporation,devolatilisation,and charring.The apparent activation energy（E_α）of TS and tobacco leaves（TL）increased gradually,whereas the E_αvalues of reconstituted tobacco sheets（RTS）also increased and then decreased with the increase of conversion degree（α）.The average activation energies were RTS（207.18 k J/mol）≈TS（206.58 k J/mol）>TL（172.28 k J/mol）.The pyrolysis components of tobacco wastes are complex,with significant differences at different temperatures,and they mainly produce furan,N-containing compounds,alcohols,and ketones.The gas emission during pyrolysis mainly occurs at 150-500℃,and the maximum gas release intensity is around 300℃,where CO₂ is the main component of pyrolysis gas,which increases and then decreases with the increase of pyrolysis temperature.The devolatilisation stage of the tobacco material was divided into four substages by deconvolution,and their reaction mechanisms followed a multi-step reaction of the diffusion,geometrical contraction,and reaction order models.It provides theoretical support for optimising the pyrolysis process and promoting the development of the biorefinery industry using tobacco wastes resources as raw materials.（4）The pyrolytic behavior of biomass TS was strongly influenced by their chemical composition.The apparent activation energy was significantly and positively correlated with nicotine,chloride ion,cellulose and lignin,and highly significantly and positively correlated with total cell wall material（P<0.01）.This study has elucidated the pyrolytic reactivity of tobacco stems and provided theoretical support for the rational utilization of biomass stems and the development of low-hazard cigarettes.