Spray drying solids levels

Fig. 1. Effect on solids level on the retention of volatiles during spray drying. (Reproduced with permission from ref. 37. Copyright 1969 American Dairy Science Association.)...

Impurities such as solvents and a variety of reactants can be removed from a polymer product to a very low (10 - 50 ppm) level via Supercritical Extraction (See chapter 9.6.) or Rapid Expansion Technology (See chapter 6.5.). In both methods, a compressed gas is used to extract undesired impurities out of the solid polymer (SCE), or as a compressed solvent for the polymer in a spray-drying operation. Several successes have been reported [48,49] and patented. 

Spray-dried powders are formulated to give the best overall cleaning performance and flow characteristics at the lowest possible formulation costs. Typical spray-dried detergent formulations are shown in Table 36.6. Slurry preparation is considered to be the single most important factor in spray drying. Control of the raw material order of addition, slurry solids level, slurry temperature, viscosity, and aeration enable manufacturers to deliver the desired final product characteristics. The spray tower itself is simply a contained heat source that removes moisture at a uniform rate dependent upon the quality and the quantity of feed to the dryer. If feed variables are not controlled, variability in the... 

This chapter is devoted to the other ceramic powder fabrication processes not easily classified in the solid, liquid, and gas phase sjmthe-sis schemes of Chapters 5, 6, and 7. These methods include spray drying, spray roasting, freeze drying, metalorganic decomposition, sol-gel sjmthesis, and melt and fiux solidification. Each of these techniques is described in various levels of detail. 

The last method of producing a yeast extract is via acid hydrolysis. This yields a product more similar to an HVP. Like HVPs, a yeast is initially slurried at 65 to 80% solids, concentrated HCl added, and the mixture is held at 100°C (or higher, under pressure) for 6 to 12 hrs. The mixture is cooled once the desired hydrolysis level has been achieved, is neutralized with NaOH to pH 5-7, filtered, concentrated to 35 to 40% solids and finally spray dried. These products have considerable MSG contents but are more expensive than those produced by autolysis due to high capital costs (acid and pressure). They also are high in salt. These two latter factors limit the market for acid hydrolyzed yeast extracts. 

Once a carrier (or blend of carriers) has been selected, it (or they) must be rehydrated in water. It is desirable to use a particular infeed solids level that is optimum for each carrier or combination of carriers. Research has shown that infeed solids level is the most important determinant of flavor retention during spray drying (Figure 13.9). While most research has suggested that one should use as high an infeed soUds level as possible, other work has shown that there is an optimum infeed solids level for each carrier system [68]. The existence of an optimum in solids content may be due to either the possibiUty that adding solids beyond their solubility... 

Poly(vinyl acetate) emulsions for adhesives contain preferably poly(vinyl alcohol) as a protective colloid. Spray-dried poly(vinyl acetate) emulsions, known as redispersion powders, are used in combination with cellulose ethers as binders in floor-leveling compositions and for increasing solids content in emulsion-based adhesives. Polyfvinyl acetates) are used as solid polymers for formulating solvent adhesives. 

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