Experimental study on hydrogen production from waste polystyrene plastics by two-step low-temperature thermal conversion
Published:
- Research project at Zhejiang University, China
- Nov. 2021 - Aug. 2022
- Supervisor: Prof. Shurong Wang
- Keywords: microbial electrofermentation, biomass energy, decarbonization
Introduction
This is a research project during my bachelor in Zhejiang University. The project is to produce hydrogen from waste plastics by liquid phase reforming. Basically when talking about the traditional ways about how to deal with waste plastics, there are several solutions, but they all have their own pros and cons:
- Landfill:
- Simple operation and management, low processing cost;
- More waste of resources, easy to cause secondary pollution to the environment.
- Burning:
- High calorific value, high efficiency, can achieve rapid reduction
- Easy to cause air pollution and greenhouse effect
- Regeneration granulation:
- Simple technology, low cost and high efficiency
- New product quality is reduced and plastic sorting capabilities are not mature enough
From the perspective of cost saving and carbon emission reduction, recycled granulation seems to be the most suitable option. However, due to the deficiencies of recycled plastics in physical properties, organizational structure and mechanical properties, liquid phase reforming to produce hydrogen has become a better choice.
Polystyrene liquid phase reforming technology refers to the production of hydrogen-rich synthesis gas through a series of thermochemical reactions under hydrothermal conditions at low temperature (200-260℃) and low pressure (1-5MPa). R1-R6 as shown in the table describe the liquid phase reforming reactions. Among them, the reforming reaction (R1) and the water-gas shift reaction (R2) are the main reactions for hydrogen production during the liquid phase reforming process. Methanation (R3, R4) and Fischer-Tropsch reaction (R5, R6) are side reactions that consume hydrogen to produce alkanes.
| Thermo-chemical reactions type | Stoichiometric reaction equation | ΔH(kJ/mol) | Reaction number |
|---|---|---|---|
| Reforming reaction | CₓH₂ₓ₊₂Oᵧ + x H₂O ↔ x CO + (2n+2) H₂ | ΔH > 0 | R1 |
| Water-gas shift reaction | CO + H₂O ↔ H₂ + CO₂ | -41.2 | R2 |
| Methanation reaction of CO₂ | CO₂ + 4H₂ ↔ CH₄ + 2H₂O | -165 | R3 |
| Methanation reaction of CO | CO + 3H₂ ↔ CH₄ + H₂O | -206.1 | R4 |
| Fischer-Tropsch (1) | (2x+1) H₂ + x CO ↔ CₓH₂ₓ₊₂ + nH₂O | ΔH < 0 | R5 |
| Fischer-Tropsch (2) | (2x) H₂ + x CO ↔ CₓH₂ₓ + nH₂O | ΔH < 0 | R6 |
Acheievements
- Verify the feasibility of the “low-temperature (<250℃) hydrothermal directional depolymerization + low-temperature (<260℃) liquid phase reforming two-step method”. The optimal operating temperature of the overall process is below 260℃, realizing mild hydrogen production from polystyrene plastics.
- Prepare hydrothermal oxidation catalysts to improve the selectivity of small molecular acids such as acetic acid and formic acid in the liquid phase products of depolymerization products that are suitable for liquid phase reforming hydrogen production.
- Achieve efficient and stable catalysis of liquid phase reforming catalysts.
Part of results
