Study Of Tar Removal During Pyrolysis Carbonization Of Tobacco Waste

The depletion of China’s fossil fuel reserves and worsening environmental pollution have emerged as major challenges in recent times.Thus,the need to harness renewable energy sources has become imperative.Every year,the cigarette industry produces a large amount of tobacco waste.Tobacco waste is abundant in lignin,cellulose,hemicellulose,pectin and inorganic metal elements with high content of K,Na,Ca,Al,etc.It is a high-quality biomass raw material.Tobacco waste can be pyrolyzed to acquire pyrolysis gas,biochar and pyrolysis tar.Pyrolysis gas contains H₂,CO,CH₄and other small molecules of hydrocarbons,which have high caloric value.Biochar not only can sequester carbon and reduce emissions,but also can be returned to farmland to be used as fertilizer.However,pyrolysis tar has a high content and complex composition,which is difficult to use and can easily lead to equipment coking and stranding or poor operation.In addition,the melting and volatilization of potassium elements from the tobacco waste during pyrolysis at high temperatures can easily lead to equipment coking and corrosion.Therefore,it is an important technical problem to solve the problem of equipment coking and corrosion slagging caused by the escape of tar and potassium elements in the process of tobacco waste pyrolysis and carbonization.In this study,tobacco leaves and stems were used as biomass feedstock for comparative study.A two-stage fixed bed reactor was chosen.The first section of the reactor was applied as pyrolysis of tobacco waste（300-650°C）and the second section was used as cracking of volatile（650-800°C）or catalytic cracking of volatile.The catalysts used include oxide catalysts（Ti O₂）and molecular sieve catalysts（β（60H）,HY,HZSM-5）.This paper investigates the gas and liquid product yields under different process conditions and discusses the pyrolysis products（gas/liquid/solid）in detail.The following are the primary findings obtained from this research paper:（1）The regulations of gas-liquid-solid yields of tobacco stems and tobacco leaves were same,and the liquid yields of tobacco stems were lower（30-32 wt.%）.The main products of inorganic gases were CO and CO₂.The main products of organic gases were methane and ethane.At the temperature of 650℃,the tar yield of tobacco stem was observed to be the lowest,measuring at 8.3 wt.%.The maximum yield of light tar was only 1.0 wt.%.Most of the tar was still present in the form of heavy fraction.（2）Raising the temperature for volatile cracking（ranging from 600℃to800℃）was found to facilitate the production of gas products.Furthermore,an elevation in the pyrolysis temperature from 450℃to 600℃resulted in a rise of the gas yield,which increased from 30.0 wt.%to 43.8 wt.%.,the gas yield saw an increase from 30.0 wt.%to 43.8 wt.%.However,pyrolysis at high temperature may lead to volatilization of potassium element.Therefore,low temperature pyrolysis conditions（300-450℃）need to be controlled.The high-temperature cracking of volatiles facilitated the production of methane and ethylene,and the tar produced by low-temperature pyrolysis at 300°C versus 800°C cracking of volatiles was only 0.9 wt.%.The tar yield was reduced to below 1.0 wt.%,and the best tar removal effect was achieved.（3）The molecular sieve catalysts（HZSM-5/HY/β（60H））and oxide catalysts Ti O₂generally have little effect on gas generation from tobacco volatiles.Among the catalysts used,HZSM-5 and HY catalysts were relatively effective for tar removal,andβ（60H）with Ti O₂was not effective for tar removal.HZSM-5 and HY-type catalysts could reduce the tar yield by about1.0-1.2 wt.%under the same conditions.In tandem,the total tar content was reduced by 25.0%and 30.9%,respectively.（4）The variation of organic/inorganic elements and functional groups of the solid residual char of tobacco stem with the pyrolysis temperature was analyzed.With the rise of pyrolysis temperature in the first stage,the H/C in the char after the reaction gradually descended from 1.8 to 0.3,while the volatilization of carbonate（KCO₃/Ca CO₃）and the liberation of potassium elements from solid residual char were found to increase.Potassium release below 10%at 300-500°C and the release of potassium elements exceeded20%at 750℃.Therefore,the one-stage pyrolysis should be carried out at a lower pyrolysis temperature（≤500℃）to avoid the volatilization of metal elements.