Experimental determination of quantitative yields from polymethyl methacrylate (PMMA) flash pyrolysis in a fluidized bed reactor via online FTIR gas analysis
Stefan Pielsticker, Katja Hendricks, Christoph Knevels, Marcus S. Lehnertz, Regina Palkovits, Reinhold Kneer
Abstract
Chemical recycling processes, such as pyrolysis, have the potential to break down the polymer (e.g., polymethyl methacrylate, PMMA) into its main building blocks (monomers), and thus enable the preservation of full functionality in closed-loop recycling processes. In this study, products from flash pyrolysis of PMMA are quantitatively determined using an ex situ exhaust gas analysis by means of Fourier-transform infrared (FTIR) spectroscopy. To achieve this, the FTIR is additionally calibrated for methyl methacrylate (MMA) with an MMA/N 2 mixture of various concentrations. Flash pyrolysis conditions (heating rates approximately 10 3 K s − 1 ) are realized with a small-scale fluidized bed reactor operated with a nitrogen atmosphere and temperatures between 573 and 873 K with a continuous feed of PMMA granules. The experiments reveal MMA yields up to 90 % at 673 K. With increasing temperature, the MMA yield drops to approximately 50 % at 873 K. In return, the yields of the MMA decomposition products such as carbon dioxide (CO 2 ), methane (CH 4 ), carbon monoxide (CO), propylene (C 3 H 6 ), and formaldehyde (CH 2 O) increase. The approximated residence time of 20–30 s leads to a stronger decomposition of the MMA into its fragments (especially at higher temperatures) than in other studies, which can be well modeled with a single first-order decomposition mechanism. A detailed analysis of captured condensate reveals a high purity of MMA, which enables the feedback into the polymerization process. • New FTIR calibration enables precise quantitative detection of MMA in the gas phase. • Very good closure of mass and elemental balance is achieved for PMMA pyrolysis. • MMA yield drops from 0.9 to 0.5 by increasing the temperature from 673 to 873 K. • MMA yield is controlled by primary pyrolysis and secondary gas-phase reactions. • High MMA purity in the condensate highlights potential for closed-loop recycling.