Hydrogen/Syngas Production from Different Types of Waste Plastics Using a Sacrificial Tire Char Catalyst via Pyrolysis–Catalytic Steam Reforming

Abstract

Single plastics and mixed waste plastics from different industrial and commercial sectors have been investigated in relation to the production of hydrogen and syngas using a pyrolysis–catalytic steam reforming process. The catalyst used was a carbonaceous char catalyst produced from the pyrolysis of waste tires. Total gas yields from the processing of single plastics were between 36.84 and 39.08 wt % (based on the input of plastic, reacted steam, and char gasification) but those in terms of the gas yield based only on the mass of plastic used were very high. For example, for low-density polyethylene (LDPE) processing at a catalyst temperature of 1000 °C, the gas yield was 445.07 wt % since both the reforming of the plastic and also the steam gasification of the char contributed to the gas yield. The product gas was largely composed of H2 and CO, i.e., syngas (∼80 vol %), and the yield was significantly increased as the char catalyst temperature was raised from 900 to 1000 °C. Hydrogen yields for the processing of the polyolefin single plastics were ∼130 mmol gplastic –1 at a catalyst temperature of 1000 °C. The pyrolysis–catalytic steam reforming of the industrial and commercial mixed plastics with the tire char catalyst produced hydrogen yields that ranged from 92.81 to 122.6 mmol gplastic –1 and was dependent on the compositional fraction of the individual plastics in their mixtures. The tire char catalyst in the process acted as both a catalyst for the steam reforming of the plastics pyrolysis volatiles to produce hydrogen and also as a reactant (“sacrificed”), via carbon-steam gasification to produce further hydrogen.

Catalytic Biochar and Refuse-Derived Char for the Steam Reforming of Waste Plastics Pyrolysis Volatiles for Hydrogen-Rich Syngas

“…HDPE, PP, and PS were obtained from Regain Polymers Limited, Castleford, U.K., while LDPE and PET were purchased from Sigma-Aldrich. All of the plastics were subjected to ultimate analysis and proximate analysis, and the results have been reported in our previous work …”

“…To address this problem, the use of pyrolysis char as a catalyst for the catalytic steam reforming process has been the topic of recent studies; for example, biochar, coal char, and tire char have been proposed as potential catalysts. − The advantages of pyrolysis chars as catalysts have been reported as their high surface area and pore volume, and the presence of abundant surface functional groups also regarded as low-cost catalysts. ,, In addition, the metals present, as the ash component of the char, can act as catalysts to enhance hydrogen and syngas yield via the reforming and water–gas shift reactions . For example, alkaline metals such as K, Na, and Ca found in biochars and transition metals such as Fe, Co, Cu, and Zn found in coal and tire chars have been reported as active metals for the promotion of steam reforming and water–gas shift reactions. − Yao et al investigated the use of biochar produced from the pyrolysis of different biomass types as a support for nickel and reported that the texture and compositional characteristics of the biochar catalysts promoted the reforming of pyrolysis volatiles derived from biomass. Liu et al used biochar from the pyrolysis and steam activation of biomass and also showed that the presence of O-containing functional groups in the biochar promoted the steam reforming process.…”

“…A further advantage of using pyrolysis chars as catalysts is the potential to use process conditions that allow the char to act as a reactant as well as a catalyst. , Thereby, the carbonaceous char is also gasified in the presence of steam to generate hydrogen and carbon monoxide and consequently increases the overall yield of hydrogen and syngas (eqs –)­ In summary, pyrolysis char (including biochar, coal char, and tire char) has been extensively studied in the process of catalytic steam reforming of biomass pyrolysis volatiles and has shown excellent catalytic properties. However, there is still limited investigation into the application of pyrolysis char in the catalytic steam reforming of waste plastics.…”

Oxygen-Vacancy-Rich Co–Ce/C for Highly Stable Catalytic Steam Reforming of Toluene at Low Temperature

“…Catalysts with excellent catalytic performance suitable for low-temperature biomass tar steam reforming generally have special characteristics, such as small and uniformly dispersed active metal particles, strong metal–support interaction (MSI), and good carbon-resistance. − For example, Ren and Liu et al − recently developed Ni/Mg–Al hydrotalcite and Ni/ZSM-5 catalysts and applied them to the steam reforming of toluene (SRT). They found that Ni/Mg–Al hydrotalcite with an average Ni size of 7.0 nm and a high reducibility of 96%, as well as Ni/ZSM-5 with an average Ni size of 15.2 nm, exhibited excellent catalytic performance with the toluene conversion reaching nearly 90% at 600 °C.…”