Microwave Conversion of High-density Polyethylene to Hydrogen
Bibliographic record
Abstract
Out of the 35 million tonnes of Canadian solid waste collected in 2018, only 29% was diverted (away from landfill). One of the roadblocks to increasing the diversion rate is the lack of knowledge about the potential of solid waste for thermochemical conversion. The total energy potential was quantified at 193 PJ/y if all solid waste were converted to heat, exceeding the total annual energy consumption of both the cement and steel industries in Canada. Plastic waste is the third-largest component of waste, accounting for 10% of total Canadian solid waste collected. The higher heating value of plastic waste—30 MJ/kg on an as-received basis—and its low moisture content—10 wt% on an as-received basis—resulted in the highest energy potential—58 PJ/y—among waste types. Polyethylene waste alone accounts for 27 wt% of total plastic waste, and its energy potential contributes 40% of the total plastic waste energy potential due to its high heating value of 44 MJ/kg. Approximately 89% of Canadian plastic waste is currently being landfilled, despite its high energy content and abundance. One way to valorize plastic waste is to convert it into gaseous fuel using microwave technology. Some plastics, such as high-density polyethylene (HDPE), are transparent to microwaves. Therefore, a microwave absorber, such as carbon material, must be mixed with the plastic before treatment. However, the active properties of carbon material for the microwave conversion of HDPE to hydrogen are not well understood. This thesis investigated the surface oxygen groups of carbon materials that affect hydrogen production in the microwave conversion of HDPE. Heat treatment and hydrogen peroxide treatment were performed on two different activated carbon materials. Quinone was identified as an impactful surface oxygen group (promoted by 14 mmol H2/gHDPE) for hydrogen production. In addition, the most active activated carbon material (reaching 15 mmol H2/gHDPE) can be reused for five cycles, maintaining more than 80% of its fresh hydrogen yield. The experimental setup significantly affected hydrogen yield, with the feed-to-absorber ratio and sample bed height as critical parameters. Hydrogen production reached a local maximum with changes in the feed-to-absorber ratio varied by more than threefold. Additionally, hydrogen yield decreased by a factor of two with increasing sample bed height. The impact of oxygen in metal oxides on hydrogen production in microwave conversion of HDPE is not well understood. This thesis uses cobalt oxide, both on and off an alumina support, and cerium oxide to explore the role of oxygen in metal oxides on hydrogen yield. The oxygen in the cobalt oxide reacted with hydrogen to produce water, which then reacted with hydrocarbons via steam reforming and subsequent water-gas shift reactions to produce hydrogen. The findings identified the potential for solid waste diversion in Canada through thermochemical conversion. Additionally, the experimental results will aid in designing a bifunctional carbon material that can serve as both a microwave absorber and a catalyst to enhance hydrogen production in the microwave conversion of high-density polyethylene plastic waste. Moreover, metal oxides can be incorporated into the carbon-HDPE system, further enhancing hydrogen production for the microwave conversion of HDPE.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".