US2289189A - Process of reducing sugars - Google Patents

Description

y 1942- RIA. HALES 2,289,189

I PROCESS OF REDUCING SUGARS Filed Oct. 20, 1959 RALPH A.HALES.

- mmvrox TTORNEY.

ical lead or other suitable material.

Fatente July 7, E42

PRGCESS F REDUCING SUG Ralph A. Hales, Tamaqna, Pa, assignor to Atlas I Powder Company, Wiln, Del, accrporation of Delaware Application October 20, 1939, Serial No. 303,376

6 Claims. (Cl. 204-47) The present invention relates to improvements in an electrolytic process and more particularly in the process of reducing sugars to polyhydric alcohols, andto a cell for use therein.

An object of the invention is to provide a process employing a novel cathode. I

Another object is to provide a process for electrolytically reducing glucose with the production of little. or no mannitol.

A further object is to provide a novel electrolytic cell.

The above and other objects will become apparent from the'following description.

The invention is broadly concerned with an improvement in the electrolytic process for reducing reducible sugars such as glucose and the like .in accordance with the teachings of the patent to Creighton No. 1,990,582, In this process an electrolytic diaphragm cell is employed in which the cathode compartment is separated by a permeable diaphragm from the anode compartment. As described in this patent, the cathode comprises an amalgamated lead plate. The catholyte which is in contact with the cathode is an aqueous solution of the sugar to be reduced and a suitable electrolyte. The electrolyte is preferably an alkali metal salt such as sodium sulfate although other alkali metal salts can be used provided that the anions are not injurious to the reduction or to the cell equipment. In addition to the electrolyte, it is customary in present practice of the process to add alkali or acid to the catholyte at the start of the reduction. The amount of alkali or acid used is a factor in determining the nature of the product to be produced. The catholyte tends to become alkaline in the course of a reduction, and, if desired, no alkali or acid need be added at the start.of the reduction.

The anolyte comprises an aqueous solution of an acid or other suitable electrolyte and is in contact with an anode which is formed of chem- In the operation of the process current is passed between the electrodes and the sugar in the catholyte is reduced at the cathode.

In accordance with the process just described, glucose can be reduced to sorbitol, which is the corresponding heidtol. Under some conditions such as in the'p'resence of alkali, glucose can be reduced partly to mannitol which is the reduction product of an isomer of glucose. In addition to sorbitol and mannitol, glucose reduction isalso attended 'withthe formation of various side-reactions taking place during the process. For many purposes a reduction syrup which contains large quantities of, these non-hexltol polyhydric bodies is preferable to a purer sorbitol syrup. A syrup which is high in sorbitol and low in these other componentshas a strong tendis substituted for lead as the cathode material.

The cathode "is composed of asheet of metallic.

zinc and is used otherwise .in the same manner as the lead cathode. Zinc has a much more satisfactory mechanical strength than lead and does not require strengthening as does the lead. In addition to this, zinc has higher conductivity than lead, being about 3.5 time as conductive. Furthermore, metallic zone is a relatively cheap element and is readily obtainable.

In accordance with this invention also, the cathodes are not amalgamated but plain zinc surfaces are used. Amalgamation in the case I of the lead cathodes is an expensive and time washed and then amalgamated by rubbing liquid.

consuming operation which. must be repeated before each run. Also, amalgamation of the lead cathodes causes a marked decrease in their mechanical strength. The cathode to be amalgamated would first have .to be cleaned and mercury on their outer surfaces. The use of a zinc cathode in accordance with this invention renders it unnecessary to amalgamate before use.

The zinc cathodes of the present invention are therefore cheaper initially because of less complicated cathode construction and are more emcient in use from the standpoint of elimimating the operation of amalgamation. The zinc is not subject to the defect of changing shape as are lead cathodes and they are alsolighter to handle 'and require less support. Due to their lower resistance there is also a lowering of the resistance of the complete electrolytic cell which results in a saving of electricity.

The invention offers particular advantages in non-hexitol polyhydric bodies which result from the processor reducing glucose in that it enables glucose to be reduced without substantial uction of mannitol. By further selecting conditions of reduction the product will not only be very low in mannitol or'free from mannitol, but will also contain relatively large quantities of the ncn-hexitol bodies referred to which constitute the reduction syrup of particular value for many applications.

Inthe'drawingtheflgureisadiagrammatic representation of an electrolytic cell embodying the present invention, the cell body and receiver being shown in vertical section.

In the drawing the cell I, which may be constructed of glass, rubber-lined metal or the like, contains-the cathodes f, the diaphragms I and anodes 4. The cathodes 2 are zinc plates. The anodes l are preferably chemical lead plates although other materials resistant to the anolyte can be employed. For operating the cell the electrodes are connected to a suitable source of direct current. The diaphragms shown are in the form of open top boxes and are filled with the anolyte l, which can be an aqueous solution of sulfuric acid or the like. The material of the diaphragms is selected to permit passage of 'ions through the wall but not to permit substantial flow of the solutions therethrough. The diaphragms and other parts of the setup must of course be resistant to the action of the solutions employed. Alundum has been found to be a satisfactory diaphragm material although numerous other materials are operative. In the cell I the body of catholyte t is maintained around the cathodes 2 and diaphragms 3 The catholyte, as described, is an aqueous solution of the sugar and further contains sodium sulfate or other suitable electrolyte, and in addition. may contain either acid or alkali. In the form of the device shown, the catholyte is circulated through the cell I. The catholyte is withdrawn continuously through the pipe 1 into the receiver 8 in which it can be adjusted as to pH and concentration as required. From the receiver l the catholyte is pumped through the cooling coils I after which it is returned to the cell I through the return pipe ll.

It is to be understood that the process of the invention can be practised in other'equlpment than that shown. For instance. the catholyte need not be circulated and no receiver need be used. However, the setup shown is preferred for large scale operation.

The use of zinc cathodes does not require variation of the other details of the usual re-- duction process. Zinc cathodes can be used in catholytes of the usual alkali or acid concentrations, with varying sugar concentrations and the usual other variations of this type ofreduction.

The following specific examples of reductions at zinc cathodes areintendedtoillustrate some of the variations in which these cathodes can be used.

skilled in this art. In the following'tabl e of examples the reference items are as follows:

Conc." is the initial concentration of sugar in the catholyte and unless otherwise noted will 5 refer to the concentration of glucose.

Alk. is the alkalinity of the catholyte in grams NaOH per liter; acidity is also noted under this heading but with a note to that effect.

' l=2.atio" is the quotient of the area of the cathode in square decimeters divided by the number of liters of catholyte.

"C. D. is the current density in arnperes per square declmeter of cathode area,

T. is the temperature ,of the catholyte in degrees Fahrenheit.

90% S. R. is the time in hours after the I start of the reduction atwhich 90% of the sugar is reduced.

99% S. R."'is the time in hours after the start of the reduction at which 99% of the sugar is reduced.

Man. is the percentage of mannitol in the from sorbitol-containing products in the form of a sorbitol-pyridine complex, filtering the crystalline'complex, adding water to it to decompose the complex into pyridine and sorbitol, driving off the pyridine by vacuum distillation I with water, dehydrating the sorbitol residue and weighing it as sorbitol. The procedure is speciilc for sorbitol since no other polyhydric material, such as sugar, mannitol, etc., exhibits the same behavior with pyridine. The pyridine number is the weight of sorbitol crystallized from anhydrous pyridine as above multiplied by 100, and divided by the weight of the sample (ash, moisture and sugar free). The pyridine number for pure sorbitol is about 95. The preparation of the sorbitol pyridine complex and its treatment to free sorbitol therefrom is described by Strain in J. Am. Chem. Soc. vol. 56, page 1757 (1934) The pyridine number of a sorbitolcontaining product is an index of its crystallizing tendency from relatively highly concentrated aqueous solutions. The higher the pyridine number the greater the crystallizing tendency. The greater the complexity of the sorbitol-containing product the less its crystallizing tendency and vice versa.

In each of the following examples the catholyte was an aqueous solution of glucose and sodium sulfate. The anolyte was an aqueous solution of sulfuric acid. The anodes were chemical lead plates and the cathodes were zinc plates. The alkalinity or acidity indicated in the examples was maintained by the addition of suitable quantities of alkali from time to time duri the reduction.

Ex. Gone. .1115. Ratio 0. D. T. 90% s. R. fiz Man. I. N.

sas /1. 0.5-1.5 1. 21 1. 01-02 224 366 0 54.5 mos/I. so 1. 21 1. 0 99-10 195 266 o 39. mJl. -20 1.21 1.0 59-10 221 215 5. a 10 325m. 0.5-1.5 1.0 119-10 114 114 o 8L0 H5504 perliter 5 325gJl. in- 9-21 1.46 10 m 03-12 89.2% s. R. 13. 4 0

verted one B Rbtgen in 170 hrs.

It is to be understood that the invention is not restricted to these particular examples but'that they are intended merely as suggestive to those From the above examples it will be seen that throughout the reductions the product from the treatment of glucose is substantially free from mannitol. Example 2 and particularly Example 3 show the production of syrups of low P. N. value, hence low crystallizing tendency, which is of particular value in uses where the physical characteristics of the syrup are sought, for example, in conditioning and humectant uses. Example 4 illustrates a reduction at low acidity in which a syrup of high sorbitol purity is obtained. Such a syrup would be suitable for processing to isolate pure sorbitol.

Example 5 illustrates a reduction of a sugar other than glucose at a zinc cathode. In this particular example inverted cane sugar which is a mixture of glucose and fructose was reduced.

Electrolytic reductions of sugars using unamalgamated zinc cathodes compare favorably as to rates of reduction and current emciences with amalgamated cathodes although the unamalgamated zinc cathode is somewhat less efiicient than the amalgamated ones. The production of reduction syrups low in mannitol from glucose is believed to be fully evident from the examples. Zinc cathodes therefore oifer this advantage over the amalgamated cathodes in the case of glucose reduction. In the case of reduction of invert and other reducible sugars, the zinc cathodes offer the advantages of lightness and the elimination of the expense and time loss incident to amalgamation.-

The inventionis not restricted to glucose and inverted sucrose reductions but is applicable to the reduction of other reducible sugars such as fructose, mannose, lactose, galactose and others. Some of the polysaccharides such as lactose can beinverted and reduced in'one operation under acid catholyte conditions and the invention is also applicable to this procedure.

While the invention has been described particularly with reference to the examples, it is not limited thereto but is to be taken as limited only by the scope of the following claims.

I claim:

l. A process for the production of polyhydric alcohols in an electrolytic cell having anode and cathode compartments separated by a permeable 1 diaphragm, and an anode in the anode compartment:. which comprises providing a cathode of metallic zinc in the cathode compartment of the cell; maintaining in the cathode compartment and in contact with said cathode an aqueous G solution of a reducible sugar and an alkali metal salt as electrolyte; and passing an electric current between said anode and cathode and through said sugar solution to reduce said sugar to polyhydric alcohol.

2. A process for the production of polyhydric alcohols in an electrolytic cell having anode and cathode compartments separated by a permeable diaphragm, and an anode in the anode compartment: which comprises providing a cathode of metallic zinc in the cathode compartment of the glucose solution to reduce the glucose to polycell; maintaining in the cathode compartment and in contact with said cathode an aqueous solution oi glucose and an alkali metal salt as electrolyte; and passing an electric current between said anode and cathode and through said glucose solution to reduce said glucose to polyhydric alcohol.

3. A process for the production of polyhydric alcohols in an electrolytic cell having anode and cathode compartments separated by a permeable diaphragm, and an anode in the anode compartment: which comprises providing a cathode of metallic zinc in the cathode compartment of the cell; maintaining in the cathode compartment and in contact with said cathode an aqueous solution of a reducible sugar and an alkali metal sulfate as electrolyte; and passing an electric current between said anode and cathode and through said sugar solution to reduce said sugar to polyhydric alcohol.

,4. A process for the production of polyhydric alcohols in an electrolytic cell having anode and cathode compartments separated by a permeable diaphragm, and an anode in the anode compartment: which comprises providing a cathode of metallic zinc in the cathode compartment of the cell; maintaining in the cathode compartment.

and in contact with said cathode an aqueous solution of glucose and an alkali metal sulfate as electrolyte; and passing an electric current between said anode and cathode and through said hydric alcohol.

5. A process for the production of 'polyhydric alcohols in an electrolytic cell having anode and cathode compartments separated by a permeable diaphragm, and an anode in the anode compartment: which comprises providing a cathode of metallic zinc in the cathode compartment of the cell; maintaining in the cathode compartment and in contact with said cathode an aqueous solution of glucose and sodium sulfate as electrolyte; and passing an electric current between said anode and cathode and through said glucose solution to reduce the glucose to polyhydric alcohol.

6. A process for the production of polyhydric alcohols in an electrolytic cell having anode and cathode compartments separated by a permeable diaphragm, and an anode in the anode compart ment: which comprises providing a cathode of metallic zinc in the cathode compartment of the cell; maintaining in the cathode compartment and in contact with said cathode an aqueous solu-,

tion of glucose, sodium sulfate as electrolyte, and r from 0.5 to 20 grams of sodium hydroxide per liter of solution; and passing an electric current between said anode and cathode and through said glucose solution to reduce said sugar to polyhydr ic alcohol.

RALPH A. I-IALES.

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