Conversion of waste palm kernel cake into value-added materials using subcritical water reaction

Waste palm kernel cake (PKC) is one of the oil palm biomasses with high potential for value-added materials. Waste PKC was characterized and the effect of reaction temperature of subcritical water treatment on the production of value-added materials was assessed. Next, the effect of reaction time on the production of value-added materials, especially sugar was investigated. Firstly, the subcritical water of waste PKC was carried out from 140 °C to 300 °C for 5 minutes. The highest residual oil yield was 48.52 mg/g dry matter at 230 °C. Thus, subcritical water treatment displayed maximum oil extraction at 230 °C. The dielectric constant was proved to be correlated with oil extraction with a correlation coefficient of -0.72. Total organic carbon (26.59 mg/g dry matter) and total sugar yield (302.73 mg/g dry matter) were the highest at 220 °C, as ion product was correlated with the total organic carbon yield with a correlation coefficient of +0.84. The monosaccharides detected were mannose, glucose, and arabinose. Tar yield showed an increasing trend from 220 °C to 300 °C with the highest tar yield of 136.92 mg/g dry matter at 300 °C; whereas, the total phenolic compound has the highest yield of 11.70 mg/g dry matter at 280 °C. Solid residue yield showed a decreasing trend as temperature increased with the lowest residue of 298.22 mg/g dry matter at 300 °C, due to the rapid degradation of waste PKC at higher temperatures. Secondly, the reaction temperature (220 °C) with the highest sugar yield was selected to investigate the effect of reaction time ranging from 1 to 15 min. The effect of reaction time was less signifi ant when compared to reaction temperature, especially for sugar production. Thus, the value-added materials could be selectively produced by varying reaction temperature whereas varying reaction time is less significant. Based on the results, the highest total sugar yield was obtained at 220 °C for 5 min. This study suggests the application of subcritical water treatment as a promising treatment medium for converting waste PKC into value-added materials.

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