Concentrated acid pretreatment

Acid pretreatment of the ore before flotation had a positive effect on ilmenite flotation. Figure 25.3 shows the effect of different acids used in the pretreatment on ilmenite recovery in the rougher concentrate. The best metallurgical results were achieved using sulphuric acid in the pretreatment stage. 

Thus, it was observed that the first-order rate constants (/q) for nitrate reduction by untreated Fe° increase due to the pretreatment of iron metal with HC1 however, observed increases in the rate constant for nitrite reduction have been relatively small under similar acid pretreatment conditions. During the first 12 hr, the rate constant for nitrate reduction showed a gradual decline, and this decline seems to have been clearly influenced by the presence of chloride. The reaction rate constants for nitrate and nitrite reduction by untreated Fe° turnings are directly dependent on the concentration of Fe° used, ranging between 69.4 and 208.2 g/L thus /c, and k, increase linearly with increases in the surface area of the untreated iron. Table 13.8 demonstrates that acid-treated Fe° is more reactive than its untreated counterpart. 

Corn stover, a well-known example of lignocellulosic biomass, is a potential renewable feed for bioethanol production. Dilute sulfuric acid pretreatment removes hemicellulose and makes the cellulose more susceptible to bacterial digestion. The rheologic properties of corn stover pretreated in such a manner were studied. The Power Law parameters were sensitive to corn stover suspension concentration becoming more non-Newtonian with slope n, ranging from 0.92 to 0.05 between 5 and 30% solids. The Casson and the Power Law models described the experimental data with correlation coefficients ranging from 0.90 to 0.99 and 0.85 to 0.99, respectively. The yield stress predicted by direct data extrapolation and by the Herschel-Bulkley model was similar for each concentration of corn stover tested. 

Predicted Effects of Mineral Neutralization and Bisulfate Formation on Hydrogen Ion Concentration for Dilute Sulfuric Acid Pretreatment... 

Experimental results for carbonic acid pretreatment have been generated at low solids concentration (6,8,9), but no data are available for pretreatment conversions at higher solids concentrations, as are available for dilute H2S04. The equipment costs for carbonic acid pretreatment were calculated for different solids concentrations (Fig. 2), and it canbe seen that equipment costs are highly sensitive to solids concentration. For comparison to the dilute-acid system, a high reactor solids concentration of 40% was chosen to enable direct comparison with the NREF model. 

Fig. 9. Total sugar concentrations during combined hydrolysis (10% acetic acid-pretreated softwood substrate with prehydrolysate).

Typical properties of alkah-refined, bleached canola oil and of acid-water-degummed, acid pretreated, bleached canola oil ready for hydrogenation or steam refining/deodorization are given in Table 16. With the exception of the concentration of free fatty acids, the two process routes produce the same bleached oil quality. 

Most seed oils contain 0.2-0.8% nonhydratable phospholipids (5), specifically the magnesium (Mg) and calcium (Ca) salts of phospholipids, which cannot be removed by water degumming. For many years, a common way for nonlecithin producers to degum edible oil was to treat the oil with 0.02-1% of concentrated phosphoric acid at 70-90°C, after water degumming. Then, without the removal of any precipitated solids, the oil is caustically refined. Phosphoric acid chelates the Ca and Mg in the oil so that the nonhydratable phospholipids are converted into the hydratable form. The phosphoric acid pretreatment produces a darker lecithin with lower purity (5). 

Pretreatments prior to extraction have been used to lower the paramagnetic concentration or to increase the phosphorus concentration. Such pretreatments include acid (Tate and Newman, 1982 Hinedi et al., 1988 Adams and Byrne, 1989 Makarov et al., 2002a) and dithionite (Ingall et al., 1990 Carman et al., 2000). Post-extraction treatments include dialysis (Rubaek et al., 1999 Amelung et al., 2001) or exchange resins such as Chelex (Bishop et al., 1994 Robinson et al., 1998 Preston and Trofymow, 2000 Rheinheimer et al., 2002) and Sephadex (Pant et al., 1999, 2002). 

The pretreatment of any lignocellulosic biomass is cmcial before enzymatic hydrolysis. The objective of pretreatment is to decrease the crystallinity of cellulose which enhances the hydrolysis of cellulose by cellulases (17). Various pretreatment options are available to fractionate, solubilize, hydrolyze and separate cellulose, hemicellulose and lignin components (1,18-20). These include concentrated acid (27), dilute acid (22), SOj (25), alkali (24, 25), hydrogen peroxide (26), wet-oxidation (27), steam explosion (autohydrolysis) (28), ammonia fiber explosion (AFEX) (29), CO2 explosion (30), liquid hot water (31) and organic solvent treatments (52). In each option, the biomass is reduced in size and its physical structure is opened. Some methods of pretreatment of Lignocellulose is given in Table I. 

In preparation for steam refining, the crude oil must be very thoroughly degummed to a phosphorus concentration of less than 5 ppm, and bleached. Degumming with an acid and water (instead of the conventional degumming with water alone), followed by bleaching, with an acid pretreatment stage, achieves the required removal of phosphatides and other, heat-sensitive materials. 

On the other hand, an acidic pretreatment will hydrolyze the hemiceUulose but the cellulose and lignin remains intact (21). An acidic pretreatment may also result in high concentrations of furfural compounds in the liquid phase (13). Such compmmds may act as fermentation inhibitors. 

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