Steeping in Sodium Hydroxide

Most rice starch is obtained from broken white kernels (Chapter 7). These broken kernels are treated with sodium hydroxide because most of the endosperm proteins 

Steep Solution with Soluble Solids 1 kg Solids 

FIG U RE 8.3 Flowchart of the wet-miUing process for the production of rice starch. 

---

Carboxymethylcelluloses (CMC). CarboxymethylceUulose [9004 2-6] (CMC) is the carboxymethyl ether of cellulose. To prepare CMC, cellulose is steeped in sodium hydroxide solution, and the so-called alkaU cellulose is treated under controlled conditions with sodium monochloroacetate to form the sodium salt of CarboxymethylceUulose and sodium chloride. Therefore, the CMC of commerce is actuaUy sodium CarboxymethylceUulose... 

To prepare croscarmellose sodium, crude cellulose is steeped in sodium hydroxide solution [1] and treated with sodium monochloroacetate to form carboxymethylcellu-lose sodium. After completion of the reaction, the excess sodium monochloroacetate slowly hydrolyzes to glycolic acid. The glycolic acid converts a few of the sodium earboxymethyl groups to the free acid and catalyzes the cross-linkage to form croscarmellose sodium. The by-products sodium chloride and sodium glycolate can be removed by extraction with alcohol to achieve 99.5% purity. Croscarmellose sodium may be milled to break the polymer fibers into shorter lengths and hence improve flow properties. 

Alkali cellulose is prepared by steeping cellulose obtained from wood pulp or cotton fibers in sodium hydroxide solution. The alkaline cellulose is then reacted with sodium monochloro-acetate to produce carboxymethylcellulose sodium. Sodium chloride and sodium glycolate are obtained as by-products of this etherification. 

SINI Also known as the Double Steeping process. A variation of the viscose process for making regenerated cellulose fibers, in which the treatment with sodium hydroxide is done in two stages, at different concentrations. Invented by H. Sihtola, around 1976. 

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 ... 

Although many columns and eluants can be used for gradient elution, the conditions used in Figs. 2.16 and 2.17 are recommended as a good starting point. The HPIC-ASSA (5 i) separator with sodium hydroxide eluant provides the optimum combination of efficiency, selectivity, and speed without an unacceptable baseline slope. If fewer ions than the 36 shown in Fig. 2.16 need to be separated, the gradient steepness can be increased to reduce the run time. 

In the alkali process, broken milled rice is steeped in 0.3-0.5% sodium hydroxide solution for up to 24 hours at temperatures that may vary from room temperature to 50°C. This steeping process softens the grain and effects solubilization of the proteins. Wet-milling of the steeped grain, in the presence of sodium hydroxide solution, releases the starch, producing a starch slurry. The starch is kept in suspension and stored for... 

Neutralization of the separator effluent is usually accomplished with sodium hydroxide however, lime or ammonia are occasionally used. A two-stage system using well-mixed tankage of suitable size is recommended. The neutralization invariably occurs on the steep part of the titration curve in these applications. Any inappropriate design, such as an excessively remote pH controllers, will result in a nonfunctional system. As a result, it is highly recommended that an individual experienced in designing pH control systems reviews the final design. 

Comparing the two titration curves one can recognize that the steepness of the titration curve at the equivalence point is much larger in case of the titration of ammonia with hydrochloric acid, than for the case of titration of ammonium ions with sodium hydroxide. This means that the random errors will be much smaller when ammonia is titrated with hydrochloric acid, and this titration is strongly to be preferred. 

The pulp is first steeped in an aqueous solution of sodium hydroxide (17 18%), which causes the fibers to swell and converts the cellulose to sodium cellulosate, commonly called alkali cellulose or white crumb. After steeping, the swollen mass is pressed to obtain a precise ratio of alkali to cellulose and then shredded to provide adequate surface area for uniform reaction in subsequent process steps. The alkali cellulose is aged under controlled conditions of time and temperature to depolymerize the cellulose by oxidation to the desired DP prior to reacting with carbon disulfide to form sodium cellulose xanthate. The xanthate, which is a yellow to orange crumb, is dissolved in dilute sodium hydroxide to yield a viscous orange-colored solution called viscose. The solution is filtered, deaerated, and ripened to the desired coagulation point (called salt index) appropriate for spinning. 

In commercial practice, pulp is steeped (soaked) in aqueous sodium hydroxide of about 18% concentration at ambient or slightly higher temperature ( 25°C). Because swelling of cellulose is temperature-dependent, less caustic is used at lower temperatures and more at higher... 

---