US2091690A - Preparation of washed sugar - Google Patents

Description

Patented Aug. 31, 1937 PATENT OFFICE PREPARATION OF WASHED SUGAR Pedro Sanchez, New York, N. Y.

No Drawing.

Application November 13, 1934,

Serial No. 752,887

2 Claims.

This invention relates to the preparation of washed sugar from raw sugar and more particularly to the production of a washed sugar of high purity and low color with a minimum loss 5 of sucrose values.

In the preparation of sugar from sacchariferous plants such as cane, beet, and the like, the juice is generally expressed fromthe plant, defecated, filtered and evaporated to crystallize sugar values from the juice.

1 This type of sugar, generally designated as raw sugar, is of. low purity, dark in color, and must generally be refined in order to meet the specifications ordinarily required of white granulated sugar.

It has been the general practice heretofore to Wash or affmate the raw sugar prior to the refining treatment proper, whether the refining operations be carried out in accordance with the 0 procedures of the well-known bone-char process or the activated carbon" process. The usual affination procedure requires that the raw sugar be incorporated as a magma with a sugar solution of high Brix, the resulting magma being 25 thereafter purged in a centrifuge or other suitable filtering or draining'device and the sugar thereafter washed.

By operating in accordance with the methods of the present invention, it is possible to obtain 30 a washed or aflinated sugar of a high purity, a

purity of from 99 to 99.8, with a substantial decrease in the color, and with a loss of raw sugar of only from five to six per cent and yet with substantially complete removal of molasses. By so operating and maintaining a high washed sugar weight with respect to the initial quantity of raw sugar treated, considerable saving is effected by the process of the present invention since the remelting and reprocessing costs are 40' reduced considerably. Another advantage of the present invention is its operability in installations presently in use.

A further advantage of the invention resides in the fact that it is possible to produce sugar of the quality of 'Iurbinado from raw sugar, and a sugar that may be prepared upon the plantation and be suitable for immediate use for domestic consumption, or in the confectioners trade where colors approximating water white are not a prerequisite. The invention makes possible the removal of hardened molasses films often associated with raw sugar that has been stored for any considerable period of time, a procedure that has been attended heretofore With the greatest difiiculty and accomplished only with very great loss of sugar requiring reprocessing.

Raw sugar, as mentioned above, comprises substantially all material crystallized from the raw juice and carries, therefore, with the sucrose, non-sugar materials as well as pectins, bits of b-agasse, colloid coloring material, invert sugar, mineral material constituting ash, as Well as other materials of lesser importance, all constituting non-sugar values, and comprising the molasses. The raw sugar, therefore, consists of crystals of nearly pure sucrose carrying soluble coloring material, the sucrose crystal being coated and enveloped within an exterior film of molasses, colloid coloring material and the like which must be removed prior to the preparation of a white, substantially non-colored sugar crystal.

It is an object of the present invention, therefore, to remove the exterior coating of molasses surrounding the raw sugar crystal by softening and rubbing, and leave the interior clean crystal of nearly pure sucrose substantially unaffected, producing an improved washed or affinated sugar.

In the usual afrlnation procedure, the magma of raw sugar is mixed with a solution of molasses and sugar of low purity, centrifuged and washed. The sugar crystals in the centrifuge remain substantially stationary and present only one face to the washing operation whereby a large proportion of the molasses is still retained by the sugar. In general, the purity of the sugar is raised from about ninety-five to ninety-six to about ninety-eight to ninety-eight and one half, such sugar when melted being amenable to about three boils, whereas operating in accordance with the present invention, a sugar of a purity of from 99.5 to 99.8 is produced, which, upon melting and de-colorizing, may be subjected to four or five boils, thus decreasing subsequent operating procedures to recover sugar values in the final molasses. As molasses and colloid coloring matters are bleached and removed from solutions containing sugar only with great difiiculty and are largely responsible for the slow rate of filtration of sugar solutions containing them a material advantage of the instant process becomes apparent.

In accordance with the present invention the raw sugar of a purity of about ninety-five to ninety-six, is mingled in the usual Way with a solution of greens of about seventy Brix, that is, a substantially saturated solution of either raw or preliminarily washed sugar, to produce a magma. This magma, in the course of the mingling operation is stirred vigorously to cause a rubbing action between adjacent crystals, and as the temperature of the greens is usually in the neighborhood of eighty to eighty-five degrees centigrade, the stirring and mixing is effected at elevated temperatures. The purpose of the mingling is, insofar as possible to rub off, soften and dissolve the molasses, making the same fluid and mobile, without dissolving any substantial proportion of the interior sugar crystal. That is to say, the exterior coating of molasses and nonsugars, including the colloid coloring material, is removed from the crystal of sugar leaving the same as an undissolved sugar crystal present in the magma, the liquid constituent of which comprises a solution substantially saturated with sucrose and carrying the molasses.

Subsequent to the mingling, the mobile liquid portion, including the molasses and colloid coloring material, is removed from the undissolved sugar crystals by any suitable method. In general, the magma is discharged into a centrifugal separator and the liquid discharged from the sugar. This aflinated sugar, having a purity generally of about 98.5 is still highly colored, the color naturally depending upon the type of sugar originally used, as well as its previous history; the color may range from about twelve to about twenty-four units of color on the Horner scale calculated per hundred Brix.

In accordance with the procedures of this invention, this preliminarily aifinated sugar is again mingled at elevated temperature with an aqueous solution substantially saturated with sucrose. Although this solution may be made from raw sugar, a substantially saturated solution prepared from sugar of high purity is preferred; the resulting magma is stirred so that there is a substantially complete removal of molasses and colloid coloring material by softening, and solution in the liquid used for the preparation of the magma. In general, this operation is eifected at elevated temperatures of from seventy-five to eighty degrees centigrade. By the term high purity is meant any sugar showing a purity of higher than about 90.0. The liquid and mobile portions of the magma are thereafter separated from the substantially pure sugar by any convenient method as for instance by centrifuging or draining with the production of a sugar of generally better than 99.5 purity. It will, of course, be understood that the discharged solution may be used again for the treatment of preliminarily aflinated sugar as above described.

The following examples are illustrative rather than limitative of the process and show the production of washed or affinated sugar in accordance with the procedures of this invention with the production of sugar of high purity and low color.

Example 1 1000 grams of ex-stores raw sugar of average polarization of 95.8 upon mingling with 750 cc. of greens of '70 Brix and at a temperature of 80 degrees C., upon centrifuging without subsequent washing, produced sugar of a purity of 98.61 and color of 20.3 units on the Horner scale calculated per hundred Brix. Upon mingling the above preliminarily treated sugar with '70 Brix solution of sugar of high purity, and at a temperature of from '75 to 80 degrees C., and centrifuging, the centrifuged sugar showed a purity of 99.75 with a color of only 9.91 units on the Horner scale per hundred Brix. A subsequent Water wash of this centrifuged sugar did not increase the purity and decreased the color to only 8.5 Horner units per hundred Brix. The loss of weight during affination was only 5%.

Example 2 Hawaiian raw sugar of average polarization of 98.0 upon mingling with greens of '70 degrees Brix at 80 C., and centrifuging, the centrifuged sugar then being treated with 70 degree Brix solution of sugar of high purity and at 85 C., produced, upon washing, a sugar of polarization 99.8, and a color of 6.5 Horner units of color per hundred Brix.

From the foregoing, it will be apparent that the present invention provides a method whereby substantially all the molasses and colloid coloring material can be removed from raw sugar with the production of washed sugar of high purity, and low color, sugar suitable for immediate consumption in certain specified uses and sugar which lends itself readily to subsequent decolorization by any ofthe methods of refining currently used.

What is claimed is:

1. The method of removing the exterior coating of molasses from raw sugar crystals which comprises mingling the raw sugar with a substantially saturated solution of sugar of a lesser purity than the raw sugar to produce a magma, separating the crystals from the magma, mingling the separated crystals with a substantially saturated solution of a sugar of purity greater than the sugar in the first solution but of less purity than said separated crystals and separating the crystals from the solution.

2. The method of removing the exterior coating of molasses from raw sugar crystals which comprises mingling the raw sugar with a syrup substantially saturated with sugar of lesser purity than the raw sugar to produce a magma, removing the mobile parts of the magma from the crystals with a loss of sugar of less than about 5%, mingling the so-treated crystals with a substantially saturated solution of a sugar of higher purity than the mingling syrup used in the first stage but of a lower purity than the crystals with which it is mingled and separating the crystals from the solution.

PEDRO SANCHEZ.