Pretreatment of Slurries

Another Form of Pressure Dependence 315 Pretreatment of Slurries 315... 

When deciding on the type of the reactor required for a particular chemical or physical transformation, the first question that needs to be addresses is whether the cavitation enhancement is the result of an improved mechanical process (due to enhanced mixing). If this is the case, then cavitation pretreatment of a slurry may be all that is required before the system is subjected to conventional type transformation scheme and the scale up of the pretreatment vessel would be a relatively simpler task. 

Performance often is improved by appropriate pretreatment of the slurry with flocculants or other means. An operating practice that is finding increasing acceptance is the delaying of cake deposition by some mechanical means such as scraping, brushing, severe agitation, or vibration. In these ways most of the filtrate is... 

The pretreatment of the carbon disk UMEs (like a greater part of plane electrodes) is commonly based on mechanical procedures, i.e. polishing [118]. Initially, carbon disk UMEs are grounded down on emery paper (600 grit). Then, the electrode surface is polished with successively finer grades of alumina slurries (0.1- and 0.05-gm diameter particles) on respective cloths. Usually, that is enough to obtain a clean and adequate electroactive electrode surface. 

Pretreatment of contaminants with various reagents to produce degradates more amenable to microbial mineralization (Leeson et al, 1993) and treatment of soil slurries with microbial enzymes (Nelson and Jones, 1994) have been successful in remediation. 

The DM content of the steam-pretreated SFF was adjusted to 5% and the pH set to 5.0 with NaOH. Enzymatic hydrolysis was performed using a Celluclast + Ultraflo mixture (1 1) at a ratio of 2 g of enzyme/100 g of slurry (10). Hydrolysis was carried out for 72 h in 100-mL shake flasks maintained at 50°C and shaken at 200 rpm in a laboratory rotary shaker-incubator (LSR/L-V Adolf Kiihner AG) for 72 h. Samples were withdrawn after 0,2, 4.5, 7.5,11,14, 24,31, 38,48, 60, and 72 h for analysis of monosaccharides. Direct enzymatic hydrolysis of a 5% DM SFF slurry was also performed as a reference to evaluate the effect of steam pretreatment on the yield. 

Fig. 3. Ethanol yield from pilot-scale fermentation of pretreated DG. Starch and cellulose in the pretreated DG slurry (10% [w/w]) were saccharified using glucoamylase and cellulose enzymes for 24 h prior to fermentation to ethanol using S. cerevisiae D5A yeast at 32°C, pH 5.0, and 75-rpm agitation.

Nitayavardhana, S., Rakshit, S.K., Grewell, D., Pometto III, A.L., van Leeuwen, J., and Khanal, S.K. 2008. Ultrasound pretreatment of cassava chip slurry to enhance sugar release for subsequent ethanol production. Biotechnology and Bioengineering, 101(3) 487 96. 

Performance often is improved by appropriate pretreatment of the slurry with flocculants or other means. An operating practice that is receiving increased acceptance is the delaying of cake deposition by some mechanical means such as scraping, brushing, severe agitation, or vibration. In these ways most of the filtrate is expelled before the bulk of the cake is deposited. Moreover, when the cake is finally deposited from a thickened slurry, it does so with an open structure that allows rapid filtration. A similar factor is operative in belt or top feed drum filters in which the coarse particles drop out first and thus form the desirable open structure. A review of such methods of enhancement of filtration rates is by Svarovsky (1981). 

Although analytical chemists have shown little interest in the use of ultrasound, its potential usually surpasses that of other, conventional auxiliary energies. Thus, ultrasound is of great help in the pretreatment of solid samples as it facilitates and accelerates operations such as the extraction of organic and inorganic compounds [2,3], slurry dispersion [4], homogenization [5] and various others [6-8]. 

As shown above, pervaporation is a useful analytical tool that features simplicity, and automation and miniaturization capabilities [195-197]. The actual potential of this technique for the pretreatment of solid, liquid and slurry samples can readily be inferred from its intrinsic features and from available methods using a pervaporator. 

TIP Often hydrogenations require a second charge of catalyst (usually Pt/C or Pd/C). In effect, impurities are being absorbed to the carbon support. To avoid multiple charges of a valuable metal-based catalyst, pretreat by slurrying the reaction with charcoal. 

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