Acetic acid production via the catalytic conversion of triacetin over Al-MCM-41 and the pyrolysis of cellulose acetate in waste cigarette filters

This study was conducted to establish the optimal pyrolysis process for producing high-yield and high-purity acetic acid (AA) from waste cigarette butts (CBs). The waste cigarette filters (CFs) were collected from CBs by shredding and sieving before pyrolysis. The non-isothermal pyrolysis of waste CF was studied using evolved gas analysis-mass spectrometry (EGA-MS) and double-shot pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) with tandem μ-reactor-GC/MS (TMR-GC/MS). EGA-MS of waste CF could differentiate the thermal desorption zones of tobacco additives, such as triacetin and glycerol tricaprylate, from the AA generation zone via cellulose acetate (CA) pyrolysis. The non-isothermal pyrolysis of CA, fresh CF, and waste CF from 100 °C to 400 °C at 20 °C/min resulted in AA as the primary product, with yields of 39.2 %, 34.8 %, and 36.2 %, respectively, along with the formation of additives, such as triacetin (8.8 wt% from waste CF) and glycerol tricaprylate as the main impurity. Despite the potential catalytic conversion of triacetin to AA using a mesoporous catalyst, Al-MCM-41 (SiO₂/Al₂O₃: 25), the catalytic pyrolysis of waste CF did not enhance the high AA yield because of the additional conversion of AA, produced from CA in waste CF, into light hydrocarbons, reducing the AA yield. Finally, the optimized conditions for the highest quantity and quality AA production, achieving a total yield of 40.0 %, were determined to be a two-step selective catalytic conversion: 1) catalytic thermal desorption up to 300 °C using Al-MCM-41 at 350 °C and 2) non-catalytic pyrolysis for CA conversion from 301 °C to 400 °C of waste CF.