Researchers from Xi’an Jiaotong University explored an oxidative liquefaction process using aqueous hydrogen peroxide to break down polymer layers in end-of-life crystalline silicon PV modules
The process achieved polymer degradation rates of up to 88.4% at around 245°C, significantly lower than temperatures typically used in pyrolysis recycling
Acetic acid emerged as the dominant recovered product, while fluoropolymer backsheet materials remained comparatively stable during processing
Deployment of solar PV systems is increasing worldwide, and is expected to generate large volumes of end-of-life solar panel waste over the coming decades. One of the challenges in recycling crystalline silicon modules is the crosslinked ethylene-vinyl acetate (EVA) encapsulant, which tightly bonds together the glass, solar cells, and backsheet layers while resisting chemical degradation.
Among the alternative PV recycling methods being explored in this area are pyrolysis, solvent-based delamination, and supercritical fluid processing. Pyrolysis can effectively remove EVA, but it usually requires temperatures above 450°C. Solvent-based approaches may involve hazardous chemicals, while supercritical processes operate under high pressure and add complexity to the system.
Researchers from Xi’an Jiaotong University in China investigated a lower-temperature chemical recycling route based on oxidative liquefaction. The process uses hydrogen peroxide at temperatures between 210°C and 310°C to chemically break down polymer materials in end-of-life PV modules. Instead of relying mainly on high heat, this method converts the EVA encapsulant into smaller liquid chemical compounds through oxidation reactions generated by hydrogen peroxide. It mainly targets EVA encapsulants, although some PE- and PP-based backsheet components were also degraded during processing. Fluoropolymer-based layers remained comparatively stable.
The researchers used degraded monocrystalline silicon modules sourced from a solar installation facility in Xi’an, China. The discarded 250 W modules showed visible cracking and delamination typical of end-of-life solar panels. Before processing, the panels were cut into progressively smaller chips and treated in a 510 mL laboratory-scale batch reactor. The study investigated how temperature, hydrogen peroxide concentration, and waste-to-liquid ratio influenced polymer degradation performance.
Thermogravimetric analysis showed that EVA degradation occurs in 2 major stages. The first stage, between approximately 305°C and 385°C, corresponds to the release of acetic acid from vinyl acetate groups. The second stage, between 385°C and 500°C, involves decomposition of the remaining EVA structure and other plastic materials within the module. Based on these findings, the oxidative liquefaction process was intentionally operated below the second decomposition stage to avoid complete combustion and instead recover liquid-phase chemical products.
Material analysis showed significant chemical changes in the polymer structure after treatment. The reduction in acetate-related signals and the appearance of broad O-H absorption bands indicated cleavage of EVA acetyl groups and formation of oxidized products such as acids and alcohols.
The recycling process produced several liquid chemical compounds, with acetic acid emerging as the dominant product. Other compounds such as formic acid, methanol, and glycolic acid were also detected. The study found that moderate temperatures helped maximize recovery of these liquid products, while higher temperatures promoted their further decomposition into CO₂ and water.
The optimized process conditions were identified as 245°C, 32% hydrogen peroxide concentration, and a 13% waste-to-liquid ratio. Under these conditions, the process achieved total polymer degradation of 88.4% and an oxygenated carbon compound yield of 52.8 mg/g PV waste. Normalized energy consumption was reported at 1.95 kWh/kg PV waste.
The study compares this energy demand with established PV recycling technologies. According to the authors, the oxidative liquefaction process reduced energy consumption by 46% compared with conventional pyrolysis and by around 65% relative to supercritical delamination approaches. The lower operating temperature and partial heat generation from hydrogen peroxide decomposition contributed to the reduced energy requirement.
The researchers also found that not all module materials degraded equally during processing. Fluoropolymer backsheet materials such as PVDF and Tedlar remained comparatively stable because of the high strength of carbon-fluorine bonds. Silicone adhesive layers also showed only partial degradation. This indicates that the process still requires additional downstream processing steps to achieve complete material recovery.
The research team also discussed requirements for scaling the process toward industrial use, including heat recovery and continuous reactor systems. However, the work remains at laboratory scale and would require further pilot-scale validation before commercialization.
The findings were reported in the paper titled Oxidative Liquefaction as a Sustainable Route for End-of-Life Photovoltaic Panel Recycling: Process Optimization, Ecological Indicators, and Scale-Up Assessment.