Assessment of process conditions in the dry reforming of HDPE fast pyrolysis volatiles for syngas production

The joint valorization of CO 2 and high density polyethylene (HDPE) has been carried out by means of a two-stage process consisting of plastic fast pyrolysis and in-line dry reforming. The first step of pyrolysis was carried out in a conical spouted bed reactor (CSBR) by feeding plastics continuously and the volatiles formed were reformed in a second catalytic fluidized bed reactor (FBR), in which Ni commercial methane reforming catalyst has been used. The effect of reforming temperature (600–700 °C), space time (2–25 g cat min g HDPE −1 ) and CO 2 /C molar ratio (1−2) on the conversions of HDPE and CO 2 has been analyzed. Furthermore, their influence on the yield of carbon containing products and H 2 production has been analyzed. Thus, an increase in temperature and space time favors HDPE and CO 2 conversion, reaching full HDPE pyrolysis volatiles conversion into gaseous products at temperatures above 650 °C, with a space time of 20 g cat min g HDPE −1 and CO 2 /C molar ratio of 1.5. Nevertheless, although an increase in CO 2 /C molar ratio enhances HDPE conversion, it also leads to CO 2 conversion decrease due to excess CO 2 in the feed. In fact, an increase in all variables above the values corresponding to full conversion of HDPE enhances the reverse Water Gas Shift (WGS) reaction, and therefore increases the conversion of CO 2 to the detriment of H 2 production. Thus, a maximum H 2 production of 0.08 g H2 g HDPE −1 has been obtained at 650 °C with a space time of 25 g cat min g HDPE −1 and CO 2 /C molar ratio of 1.5, attaining a syngas production of 4.7 g syngas g HDPE −1 . • The process of pyrolysis-dry reforming allows jointly valorizing plastics and CO 2 . • An increase in temperature, space time and CO 2 /C ratio enhances process conversion. • Process conditions allow striking a balance between primary and secondary reactions. • HDPE pyrolysis-dry reforming produces a syngas with H2/CO ratio between 0.22 and 0.37.