Effect of Dissolved Carbon Dioxide on Accumulation of Organic Acids in Liquid Hot Water Pretreated Biomass Hydrolyzates

Hydrothermal hydrolysis of starch with CO2 and detoxification of the hydrolysates with activated carbon for bio-hydrogen fermentation

“…Therefore, the level of CO 2 used in the present work was effective in promoting hydrolysis but may have also enhanced the formation of 5-HMF as reported in previous studies [24][25][26]. Based on these results, HCW hydrolysis of starch at concentrations of 120 and 200 g.L -1 were performed at an optimal temperature of 200 °C.…”

“…The addition of CO 2 into HCW hydrolysis was shown to enhance the yield of sugars from starch [24] and to reduce the concentrations of organic acids (fermentation inhibitors) in lignocellulose hydrolysates [25]. This effect was attributed to the action of CO 2 as an acid catalyst [26] unlike traditional acids CO 2 is extremely benign as it can be largely neutralised by the release of reactor pressure [25]. Table 1 summarises the five previous studies on starch hydrolysis in HCW, with and without CO 2 , showing that previous reactors had very small volumes (3-80 ml).…”

Structural recognition of lignin isolated from bioenergy crops by subcritical water: ethanol extraction

“…For example, a mixture of subcritical water:ethanol:carbon dioxide (Sub-CW) was found to be effective in isolating lignin from various biomasses, such as miscanthus [9] and rice straw [10]. In fact, while ethanol boosts the capacity of water to dissolve nonpolar compounds [11] pressurised carbon dioxide forms carbonic acid in water, and contributes to hydrolyze ester linkages, such as those in carbohydrates and lignin [12]. Carbonic acid is again converted into carbon dioxide by releasing the reactor pressure at the end of extraction.…”

Accelerating wet torrefaction rate and ash removal by carbon dioxide addition

“…Moreover, due to the volatile nature of CO 2 , the catalyst recovery is almost complete at no cost. Similar to other catalysts, the addition of CO 2 was found to enhance the hydrothermal reaction [15][16][17]. However, most studies on CO 2 -enriched hydrothermal treatment focused on a hydrolysis process which aims at maximization of the water-soluble products (e.g., sugars) yield for chemicals production.…”