Abstract
Co-pyrolysis of biomass biopolymers (lignin and cellulose) with plastic wastes (polyethylene and polystyrene) coupled with downstream catalytic steam reforming of the pyrolysis gases for the production of a hydrogen-rich syngas is reported. The catalyst used was 10 wt.% nickel supported on MCM-41. The influence of the process parameters of temperature and the steam flow rate was examined to optimize hydrogen and syngas production. The cellulose/plastic mixtures produced higher hydrogen yields compared with the lignin/plastic mixtures. However, the impact of raising the catalytic steam reforming temperature from 750 to 850 °C was more marked for lignin addition. For example, the hydrogen yield for cellulose/polyethylene at a catalyst temperature of 750 °C was 50.3 mmol g−1 and increased to 60.0 mmol g−1 at a catalyst temperature of 850 °C. However, for the lignin/polyethylene mixture, the hydrogen yield increased from 25.0 to 50.0 mmol g−1 representing a twofold increase in hydrogen yield. The greater influence on hydrogen and yield for the lignin/plastic mixtures compared to the cellulose/plastic mixtures is suggested to be due to the overlapping thermal degradation profiles of lignin and the polyethylene and polystyrene. The input of steam to the catalyst reactor produced catalytic steam reforming conditions and a marked increase in hydrogen yield. The influence of increased steam input to the process was greater for the lignin/plastic mixtures compared to the cellulose/plastic mixtures, again linked to the overlapping thermal degradation profiles of the lignin and the plastics. A comparison of the Ni/MCM-41 catalyst with Ni/Al2O3 and Ni/Y-zeolite-supported catalysts showed that the Ni/Al2O3 catalyst gave higher yields of hydrogen and syngas.Graphic abstract
Highlights
Hydrogen is an important commodity that can be used to generate clean energy in fuel cells and hydrogen engines and is used in the petroleum and chemical industries,1 3 Vol.:(0123456789)Waste Disposal & Sustainable Energy (2020) 2:177–191 and iron and steel plants
The greater influence on total gas yield and hydrogen and syngas yield for the lignin/plastic mixtures compared to the cellulose/plastic mixtures is probably due to the overlapping thermal degradation profiles of lignin and the polyethylene and polystyrene (Fig. 2)
The results show that the influence of increased steam input to the process was greater for the lignin/plastic mixtures compared to the cellulose/plastic mixtures
Summary
Hydrogen is an important commodity that can be used to generate clean energy in fuel cells and hydrogen engines and is used in the petroleum and chemical industries,. The commercial production of hydrogen from natural gas involves catalytic steam reforming of the methane using nickel-based catalysts to produce hydrogen and carbon monoxide [5]. The most common catalysts used for hydrogen production from biomass [22] and waste plastics [23] are nickel-based, reflecting the main type of catalyst used for commercial methane catalytic steam reforming [24]. It is interesting to compare the Ni/MCM-41 catalyst with molybdenum as a transition metal-based catalyst for the pyrolysis–catalytic steam reforming of the biopolymer/plastic mixtures. In attempts to improve the stability of Ni-based catalysts, different support materials including highly porous zeolites and mesoporous MCM-41 have been investigated for hydrogen production from waste plastics [21, 30] and biomass [31]. The Ni/MCM-41 catalyst was compared with nickel catalysts supported on A l2O3 and Y-zeolite for comparison of hydrogen yield
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