The objective of this work was to evaluate the effect of operation conditions on sub/supercritical waterhydrolysis (SWH) of sugarcane bagasse and coconut husk adding carbon dioxide (CO2) as acid catalyst. The assays were carried out in semi-bath unit equipped with a 50 mL reaction vessel. The process was conducted at 250°C for 30 min, with water and carbon dioxide 20 MPa. The results of SWH of sugarcane with the addition of carbon dioxide indicate that there was no change in the content of

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... ing sugars in the hydrolysate (13.5%). However, for coconut husk the total reducing sugars recovered increased 15% in the hydrolysate more effectively and showed greater percentages of sugars compared to sugarcane. The pH varied indicating that other compounds were degraded by the addition of carbon dioxide to water at both raw materials. The phenolic compound analysis indicated that the fermentation inhibitors increased with carbon dioxide addition for sugarcane bagasse, and decreased for coconut husk. Therefore, the addition of carbon dioxide as an acid catalyst in the SWH of sugarcane bagasse did not improve the process, but it did improve the sub/supercritical water hydrolysis of coconut husk. Therefore, sub/supercritical water hydrolysis should be optimized individually for each raw material.