Steeping press

Fig. 12.5. Flow diagram for manufacture of viscose yarn (1) cellulose sheets and caustic soda (2) steeping press (3) shredder (4) xanthating churn (5) dissolver (6) caustic supply (7) ripener (8) filtration (9) deaeration (10) filtration (11) continuous process (12) tire cord (13) pot spinning (14) staple spinning.

Steeping. Sheet, roU, or suitably milled flock pulp is metered into a pulper along with vigorously stirred 18% sodium hydroxide solution at 50°C. The resulting slurry, containing about 5% finely dispersed pulp, passes to a buffer tank from which it is metered to a slurry press that sieves out the swollen fiber and returns the pressings soda for concentration correction and reuse. The cellulose reacts with the soda as a complex alcohol to form the sodium salt or alk-ceU. 

In the manufacture of baker s yeast, the stock strain is inoculated into a medium that containing molasses and com steep liquor. The pH of the medium is adjusted to be slightly acidic at pH 4-5. The acidic pH may retard the bacterial growth. The inoculated medium is aerated during the incubation period. At the end, the cells are harvested by centrifuging out the fermentation broth, and they are recovered by filter press. A small amount of vegetable oil is added to act as plasticiser, and then the cell mass is moulded into blocks. The process is shown in Figure 1.2. 

Recently, the alkah-soluble hemicelluloses of hardwood dissolving pulps have been investigated [28]. Their composition and molecular properties depended on the pulp origin and steeping conditions. The MGX of the j8-fraction from press lye had a low uronic acid content (ratio of MeGlcA to Xyl is about 1 20). The molecular weight of the hemicellulose fractions varied between 5000 and lOOOOg/mol. 

Cotton linters or wood pulp, usually in the form of sheets, is steeped in strong alkali (18-50%). The swollen sheets are then pressed to force out most of the excess alkali solution. This alkali cellulose is then shredded, and aged if low viscosity is desired. The aging process is the one followed in the viscose industry and is fully explained in any discussion of that process. More alkali may be introduced during the shredding, either as a concentrated solution or as solid alkali.18 The alkali... 

Molecular mechanics calculations for disaccharides (7,18 Imberty, A. Tran, V. Perez S. J. Comp. Chem., in press also see below), not surprisingly, have shown that the assumption of rigid geometry leads to artificially steep potential energy surfaces. 

Uses and Physiological Properties of Carbon Disulphide.—Besides its employment as a solvent (see p. 260), carbon disulphide is used extensively in the manufacture of viscose silk. Viscose is a solution of the sodium salt of the cellulose ester of thiolthioncarbonic acid (p. 268) in water or dilute aqueous sodium hydroxide, or it may be described as an aqueous solution of the sodium salt of cellulose xanthic acid. For its production cellulose is steeped in concentrated sodium hydroxide solution and then pressed, the product being called alkali-cellulose and the formula CeH10O5.NaOH assigned to it. This is converted into viscose by treatment with carbon disulphide, when the colour changes to golden yellow ... 

For comparison, figure 3B shows results not only for the relatively most stable face of a single crystal (2) and a polycrystalline thin layer prepared by pasting 5), but also for a pressed pellet of CdSe (2). This last electrode shows stability behaviour intermediate between that of the two other electrodes. This behaviour is evident also in the decrease in output stability, which is less steep than that of the single crystal electrode. 

A procedure for starch production was given in some detail in a Roman treatise by Cato in 184 bce.5 Grain was steeped in water for ten days and then pressed. Fresh water was added. Mixing and filtration through linen cloth gave a slurry from which the starch was allowed to settle. It was washed with water and finally dried in the sun. 

The cellulose sheets are loaded vertically, but loosely, into a combination steeping bath and press (Fig. 12.6), which is slowly filled with a solution of 17-19 percent caustic, where they remain for about 1 hr. In the steeping, the alpha cellulose is converted into alkali or soda cellulose at the same time, as already mentioned, the caustic solution removes most of the beta and gamma cellu-... 

The excess caustic solution is drained off for reuse. Additional amounts are removed by forcing the sheets through a press. The sheets are still in a swollen state and retain from 2.7 to 3.0 parts of the alkali solution. The spent steeping solution squeezed out of the pulp is processed for recovering the caustic from the organic materials. 

Anderson then developed a second screw-press, this one designed to generate lower pressure and to operate at higher capacity. It was used to prepress oilseeds and animal scraps and to dewater steeped com germ and other wet materials. The high-pressure press (The No. 1 Press) had a 15.2-cm (6-in.) diameter barrel. 

Figure 7.1 Schematic diagram of interaction potential versus separation distance D for van der Waals and electrostatic double-layer interactions. The lower inset shows the collapse of the repulsive barrier as the electrolyte concentration is increased or the surface potential is decreased. At a separation distance of zero, there is an infinitely steep hard-core repulsive (or positive) interaction. (From Israelachvili 1991, reprinted with permission from Academic Press.)...

The alkali cellulose is obtained by treating the sheets of purified wood pulp with cold caustic soda solution of 17 -5 per cent concentration. For this purpose a combined steeping vessel and press (Fig. 6.7) is generally used, so that the excess of caustic soda can be removed without handling the sheets. In the steeping part of the operation no pressure is applied by the ram, and the cellulose is allowed to remain in contact with the caustic soda solution for about 2 hours. The a cellulose is converted into alkali cellulose and the hemicelluloses are dissolved. The vessel is then drained and pressure is applied by the ram which squeezes out the excess of alkali liquor. 

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