Sugar crystallisation

With very viscous or semi-solid liquids such as syrups, molasses and massecuite, the sample is taken by means of a cylindrical metal sampler in such a way that proportionate amounts are taken at different depths. With very dense products which may have crystallised sugar at the bottom, it is especially necessary to reach with the sampler the very bottom of the vessel. Several samples are withdrawn and mixed and the sample or samples for analysis (about 200 grams each) then stored in glass bottles with ground stoppers. 

Since these products are non-homogeneous and contain crystallised sugar in suspension, it is necessary, in order to obtain trustworthy results, to mix the sample well and to take as nearly as possible proportionate quantities of crystals and liquid. 

The use of a ternary mixture in the drying of a liquid (ethyl alcohol) has been described in Section 1,5 the following is an example of its application to the drying of a solid. Laevulose (fructose) is dissolved in warm absolute ethyl alcohol, benzene is added, and the mixture is fractionated. A ternary mixture, alcohol-benzene-water, b.p. 64°, distils first, and then the binary mixture, benzene-alcohol, b.p. 68-3°. The residual, dry alcoholic solution is partially distilled and the concentrated solution is allowed to crystallise the anhydrous sugar separates. 

High test molasses (invert molasses) is produced from cane sugar when sucrose manufacture is restricted because of overproduction. The cane sugar at ca 55 wt % solids is en2ymatically converted to invert symp to prevent crystallisation and evaporated to a symp. The product is used in the same applications as blackstrap molasses. 

Molasses from other sources include citms and com sugar (hydrol) molasses. Citms molasses is produced from citms waste and contains 60—75% sugars. Com sugar molasses is the mother liquor remaining after dextrose crystallisation and contains a minimum of 43% reducing sugars expressed as dextrose. 

If an impurity (copper, say) is dissolved in a metal or ceramic (aluminium, for instance) at a high temperature, and the alloy is cooled to room temperature, the impurity may precipitate as small particles, much as sugar will crystallise from a saturated solution when it is cooled. An alloy of A1 containing 4% Cu ( Duralumin ), treated in this way, gives very small, closely spaced precipitates of the hard compound CUAI2. Most steels are strengthened by precipitates of carbides, obtained in this way. ... 

Crystallisation is used for the production, purification and recovery of solids. Crystalline products have an attractive appearance, are free flowing, and easily handled and packaged. The process is used in a wide range of industries from the small-scale production of specialised chemicals, such as pharmaceutical products, to the tonnage production of products such as sugar, common salt and fertilisers. 

Invert sugar is only encountered as a syrup. The fructose in the mixture will not crystallise so attempts to crystallise invert sugar yield dextrose. Invert sugar overcomes one of the big drawbacks of sucrose. Invert... 

Fructose is a very soluble and hence very hygroscopic product. It is usually used as a syrup. For many years fructose was referred to as the uncrystallisable sugar. Attempts to crystallise it by normal methods do not work. Fructose in a form that is described as crystalline is now available commercially. The product could well be produced by spray drying. 

Semi-continuous crystallisation processes which often combine the best features of both batch and continuous operation are described by Nyvlt(35), Randolph(37), Robinson and Roberts(70) and Abbeg and Balakrishnam(7I ). It may be possible to use a series of tanks which can then be operated as individual units or in cascade. Mullin(3) suggests that for production rates in excess of 0.02 kg/s (70 kg/h) or liquor feeds in excess of 0.005 m3/s, continuous operation is preferable although sugar may be produced batch-wise at around 0.25 kg/s (900 kg/h) per crystalliser. 

Thijssen and Spicer1 1191 has given a general review of freeze concentration as an industrial separation process and Bushnell and Eagen(63) have discussed the status of freeze desalination. The potential of freeze crystallisation in the recycling and re-use of wastewater has been reviewed by Heist 120, and the kinetics of ice crystallisation in aqueous sugar solutions and fruit juice are considered by Omran and King(121). 

Liquid fluidization is the basis of both the Oslo (or Krystal) continuous crystalliser (Mullin, 1993) which is used in the production of, for example, sugar or citric acid, and the bioreactors in which immobilised cells or enzymes are fluidized by the reactant solution (Epstein, 2003). It is used in the leaching of vegetable oils from seeds (Rios et al, 1985 Epstein, 2003) and in physical operations such as the washing and preparation of vegetables. 

Co crystallisation is mainly done from supersaturated sugar solutions [15]. Aggregated particles (of 3-30 pm) of sugar crystals are formed which entrap guest molecules. The sugars form an oxygen barrier, thereby extending the shelf life of aroma chemicals. The procedure is simple and inexpensive, because relatively cheap encapsulation matrices can be used, such as sucrose. 

Of the eighteen to twenty-two per esnt. of sugar in the cane, it is generally believed that no more than eight is obtained crystallised. 

Glucose, Grape Sugar or Dextrose, C6H1206.—Glucose is readily soluble in water and crystallises therefrom in granules, containing 1 molecule of water of crystallisation, which melt at 86°. From alcohol the anhydrous... 

Sucrose, Cane Sugar or Saccharose, C12H22On.—Sucrose is very soluble in water from which it crystallises in large monoclinic prisms. It is sparingly soluble in alcohol. It is dextrorotatory, [a] °° = 66-5°... 

Trehalose is a relatively new bulk sweetener with potential for use in soft drinks. It is a di-glucose sugar and it occurs in nature in shellfish and mushrooms, where it confers a degree of protection to plant and animal cells in conditions causing dehydration. This led to its use as a cryoprotectant in freeze-drying systems in the pharmaceutical industry. In food markets, its potential use is as a bulk sweetener. It is manufactured using the Hayashibara patented process using starch as a raw material. The process involves enzymatic conversion and crystallisation to the trehalose dehydrate crystal (LFRA, 2001). 

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