US2289190A - Reducing sugars - Google Patents

Description

July 7, 1942. R A HALES 2,289,190

REDUCING SUGARS Filed 0G13. 20, 1959 IIIIIIIIIHHPF www:

RALPH A. HALES.

IN V EN TGR.

E@ TTORNEY.

Patented July 7, 1942 REDUCING SUGABS Ralph A. Hales, Tamaqua, Pa., asslgnor toAtlas Powder Company, tion of Delaware Wilmington, Del., a corpora- Application October 20, 1939, Serial'No. 300,377

6 Claims.. (Cl. 204'i7) 'Ihe present invention relates to a process i'oi` reducing sugars and a cell for use therein. An object of the invention is to improve the electrolytic sugar reducing process by providing a novel cathode.

' Another object of the invention is to increase the rate of the electrolytic reduction process under conditions of low alkalinity as compared to the rate of reduction obtained under similar conditions with the cathodes formerly employed.

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.' The catholyte which is in contact with the cathode is an aqueous solution oi. 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 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 oi' 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 chemical lead or other suitable material.

The amalgamated lead cathode employed in 'accordance with the teaching o'f the Creighton patent has a vnumber of defects. In the first place, lead lacks mechanical strength so that a cathode of any substantial size has to be fabricated with some re-enforcing means such as bars of iron, which `fabrication involves considerable expense. A further feature of thel lead cathode is that due to its mechanical weakness it is subject to changing shape and for that reason the distance between the cathode surface and the diaphragm of the cell cannot be kept constant. This variation in distance from the diaphragm produces variations in the resistance of the cell andresults in irregularity in the character of the reduction and hence in the product.

,tage which is of great importance.

is substituted for lead as a cathode material. The cathode is composed oi a sheet of metallic zinc which is amalgamated and 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. 1n addition to this, zinc has higher conductivity than lead, being about 3.5 times as conductive. Furthermore, metallic zinc is a relatively cheap element and is readily obtainable.

Ihe zinc cathodes of the present invention are therefore cheaper initially, are not subject to changing shape as are the lead cathodes, are lighter to handle and require less support. Due to their lower resistance there is also a lowering of the resistance f the complete electrolytic cell which results in a saving of electricity.

The zinc cathodes have also a further advan- In reductions at low alkalinities, that is, where the catholyte contains a small amount of alkali, under 'about 10 g. NaOH per liter of catholyte or its equivalent and particularly Where it contains less than 5 g. NaOH per liter or its equivalent, it has been found that an amalgamated zinc cathode possesses the property of reducing the sugar at a rate which is much higher than the rate in a corresponding reduction at an amalgamated lead cathode. A similar superiority vof eficiency is` noted in reductions at low acidity, for example, 1.5 g. H2SO4 per liter of catholyte or its equivalent. In some cases the rate of reduction is improved as much as 100%. The character of the product of the reduction at an amalgamated zinc cathode compares very favorably to that produced at an amalgamated lead cathode. This dierence in the rate of reduction is particularly notable in comparing a 'reduction at an amalgamated zinc cathode with a reduction at a new or relatively new amalgamated lead cathode. A new amalgamated zinc cathode is very greatly superior in rate of reduction to a new amalgamated lead cathode or even one which has seen considerable service. It appears that particularly with amalgamated lead cathodes a modification occurs with extended use in reductions which imparts to it the property of reducing at a faster rate. Probably this modification is connected in some way with the surface structure of the metal but the reason for the phenomenon is not yet understood. The fact is, however, that with a new or a relatively new amalgamated lead cathode very low rates of reduction are In accordance with the present invention, zinc noted at low alkalinities as compared with an zinc cathode even of similar age. The time of change in activity is shorter than with amalgamated lead cathodes. Accordingly,

much higher current eillciencies and much more satisfactory reductions are obtained at low alkalinities with amalgamated zinc cathodes.

The advantages of shortening the time of reduction through increasing the rate are, rst oi all, to accomplish a substantial saving in electricity. Then, also, the production from a given set of cell equipment is greatly increased.

The amalgamated zinc cathodes can be substituted for amalgamated lead cathodes in all of the usual type reductions. Thus the cathodes o! the invention can be used in reductions under conditions in which the catholyte has high, medium or low alkalinity or in which the catholyte is acid. The other conditions of the electrolytic process can be varied with the amalgamated zinc cathodes to the same extent that they can be varied with the amalgamated lead cathodes. Under a given set oi conditions the products may be of slightly different composition when one type of cathode is substituted for the` other, but it is possible to produce substantially the same product with either of the types of cathodes by adjusting other conditions of the reduction as will be apparent to those skilled in this art. For example, in the case of the reduction of glucose wherein the catholyte is maintained in an alkaline condition, the proportion of mannitol to sorbitol in the product may be different for the two types of cathodes. However, by varying the temperature oi the reduction, the current density, sugar concentration in the catholyte or one or more of the other variables of the process.- substantially the same composition can be produced with one type of cathode as with the other.

In the drawing the ligure is a diagrammatic representation of an electrolytic cell embodying the present invention, the cell body and receiver being shown in vertical section.

In the drawing the cell l, which may be constructed of glass, rubber-lined metal or the like, contains the cathodes 2, the diaphragms 3 and anodes 4. The cathodes 2 are zinc plates amalgamated by rubbing metallic mercury onto their faces. The anodes 4 are preferably chemical lead plates although other materials resistant to the analyte can be employed. For operating the cell the electrodes are connected to a suitable source ot direct current. The diaphragms shown are in the form of open top boxes and are tllled with the anolyte 5, 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 now 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 6 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 othersuitable electrolyte, and in addition, may contain either acid or alkali. In the form of the device shown, the cathoiyte is circulated through the cell l. I'he catholyte is withdrawn continuously through the pipe 1 into the receiver B in which it can be ad- .iusted as to pH and concentration as required.

From the receiver 8 the catholyte is pumped through the cooling coils 9 after which it is returned to the cell I through the return pipe I0.

It is to be understoo'd that the invention can be practiced in other cell equipment than that shown in the drawing. For example, the catholyte need not be circulated and no receiver need be used. However, this is the preferred set up for large scale operation of the process.

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. The alkalinity or acidity indicated in the examples was maintained by the addition of suitable quantities of alkali or acid from time to time during the reduction. The

cathodes used for the examples shown in Table' 1 were amalgamated zinc plates while those used for the examples in Table 2 were amalgamated lead plates. 'I'he respective cathodes used for Examples l and 5 had not been used previously while those used in the other examples had been used for many previous reductions.

In the tables which follow, the data are listed under abbreviated headings which refer to the following:

Conc. is the initial concentration of sugar in the catholyte in grams per liter and unless otherwise noted will 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 effeet.

Ratio is the quotient of the area of the cathode in square decimeters divided by the number of liters of catholyte. 1

"C. D. is the current density in amperes per square decimeter of cathode area.

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

S. R." is the time in hours after the start of the reduction at which 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 total polyhydric alcohol produced.

By P. N. as used herein is meant an index of sorbitol content of sorbitol-containing material. This index is determined by crystallizing sorbital 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 sorbital, driving oi the pyridine by vacuum distillation with water, dehydrating the sorbitol residue and weighing it as sorbitol. The procedure is specific for sorbitol since no other polyhydric material, such as sugar, mannitol, ete., 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 sorbitol-containing product is an index of its crystallizing tendency from relatively highly concentrated aqueous solutions. The higher the pyridine knumber the greater the crystallizing tendency. 'Ihe greater the complexity of the sorbitol-containlng product the less its crystallizlng tendency and vice versa.

C.` E. is the current eiiciency up to 99% sugar reduced corrected for the yield of polyhydric alcohol.

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 The above Examples l and 2 illustrate the use of amalgamated zinc cathodes at low alkalinity. Example 3 shows the use of similar cathodes at high alkalinity while Example 4 shows the use of these cathodes in an acid catholyte.

By way of comparison with the invention the following four examples illustrate the reduction amalgamated 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 salt as electrolyte; and passing an electric current between said anode and cathode and through said glucose solution to reduce the glucose to of glucose at amalgamated lead cathodes. polyhydric 9,1c0hg1,

Table 2 ax. c0115. 111k. aan@ c. D. T. 90% aa. gf M1111. P. N. c E.

l/ 5 325 0.5-1.5 2.o 1.0 css-70 171 250 0 58.5 15.1 5 325 0.5-1.5 2.o 1.0 1s-70 105 182 0 71.5 24.3 7 325 10-20 1.21 1.0 1s-7o 105 154 14.0 51.5 47.0 s 325 0.5-1.5g. 2.42 1.1 55% 67-59 87% sa. 0 80.5 26.8 H3804 S. R. tlieg 1n200hours at 87% S. R.

gamated zinc cathodes, as shown in Examples 3 and 7, although the zinc cathodes give very good results. Y For reductions at low acidity Examples 4 and 8 show amalgamated zinc cathodes to be markedly superior to amalgamated lead cathodes.

All of the reductions using amalgamated zinc cathodes exhibit the advantages of improved mechanical strength, constant shape, lighter weight, lower resistance, and initial economy described above.

The invention is not to be taken as limited to the specific examples or other details set forth in the above description but is to be 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 diaphragm, and an anode in the anode compartment: which comprises providing a cathode of amalgamated 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 salt as electrolyte; and passing an electric current between said anode and cathode 3. A process for the production of polyhydric alcohols in an electrolytlc cell having anode and cathode compartments separated by a permeable diaphragm, and an anode in the anode compartment: which comprises providing a cathode of amalgamated zinc in the cathode compartment of the cell; maintaining in the cathode compartment and in contact with said cathode an aqueous solution of glucose, an alkali metal salt as electrolyte, and sodium hydroxide in an amount not more than 10 grams per liter of solution; and passing an electric current between said anode and cathode and through said glucose solution to reduce the glucose 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 amalgamated zinc in the cathode compartment of the cell; maintaining in the cathode compart` ment and in contact with said cathode an aqueous solution of glucose, an alkali metal sulfate as electrolyte, and from about 0.5 to 1.5 grams lof sodium hydroxide per liter of solution; and

passing an electric current between said anode and cathode and through said glucose solution 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 compartment: which comprises providing a cathode of amalgamated zinc in the cathode compartment of the cell; maintaining in the cathode compartment and in contact with said cathode an aqueous solution of glucose, an alkali metal sullate, and sulfuric acid in an amount equivalent to not more than about 1.5 grams per lir of solution; and passing an electric current between said anode and cathode and through said glucose solution to reduce the glucose to polyhydric alcohol.

RALPH A. HALES.

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