US2458895A

US2458895A - Electrolytic process for reducing sugars

Info

Publication number: US2458895A
Application number: US487870A
Authority: US
Inventors: Creighton Henry Jermain; Ralph A Hales
Original assignee: Atlas Powder Co
Current assignee: Atlas Powder Co
Priority date: 1943-05-21
Filing date: 1943-05-21
Publication date: 1949-01-11
Anticipated expiration: 1966-01-11

Description

Jan. 11, S1949.` H. J. CREIGHTQN ET AL 2,458,895

`ELECTROLYTIC PROCESSFOR REDUGING SUGARS mw ATTOR N E Jan- 11, 1949- H. J. cRElGHToN ET Al. 2,458,895

ELECTROLYTIG PROCESS FOR REDUCING SUGARS Filed May 21, 1943 2 Sheets-Sheet 2 ATTORN Y Patented `an. 11, 1949 ELECTROLYTIC PROCESS FOR REDUCING .SUGARS Henry Jermain Y Creighton, Swarthmore, and Ralph A. Hales, Tamaqua, Pa., assignors to Atlas Powder Company, Wilmington, Del., a

corporation of Delaware Application May 21, 1943, serial No. 487,870

The present invention relates to an improved process for electrolytically reducing sugars to polyhydric alcohols.

An object of the invention is to improve the eiciency oi the electrolytic reduction process by reducing greatly the time necessary to complete the reduction.

Another object is to increase the production of present electrolytic cell equipment by shortening the time of reduction.

A particular object is to improve the efficiency of the process forelectrolytically reducing glucose to one ormore polyhydric alcohols.

The reduction or hydrogenation of reducible sugars by the electrolytic process is a known and commercially practiced operation. Broadly the process involves the use of an electrolytic diaphragm cell providing separated anode and cathode compartments. The anolyte isa solution of an electrolyte, preferably sulfuric acid, in water. The catholyte is a solution of the sugar to be reduced together with a suitable 'electrolyte in Water. In the catholyte the electrolyte is preferably an alkali metal compound, like sodium sulfate, .to which is frequently added an alkali hydroxide. The anode in the process is an Velectrically conductive material resistant to thecorrosive'action of the anolyte. In commercial practicevthe cathode is a rigid plate'of lead or zinc. The cathode may also be made ofvany rigid material and covered with a layer of lead or Zinc. Lead cathodes'are amalgamatecl before use.v Zinc cathodes are used either amalgamated or unamalgam'ated. When the anode and cathode are connected to a source of direct current nascent hydrogen is formed at the cathode and sugar in the catholyte solution is thereby reduced to one or more polyhydric alcohols.

B y means of this electrolytic process a series of polyhydric alcohols can be made from reducible sugars. Conditions can be selected to produce the polyhydric alcohol which directly corresponds to the sugar, or to produce mixtures of polyhydric alcohols some of which do not correspond directly to the sugar. Thus, from glucose can be made sorbitolwhich is the corresponding hexitol, or a mixture of mannitol and sorbitol can be made, or theproduct can be composed of mannitol, sorbitol and other polyhydric alcohols such as hexane pentols. The last two types of products 4 Claims. (Cl. 2044-77) are produced when the catholyte solution is maintained at a` relatively high alkalinity while the first type is made at very low alkalinity or with the catholyte in a neutral or acid condition.

This process is more completely described in y the patentto H, J. Creighton, No, 1,990,582; and

in the patents to R. A. Hales, Nos. 2,289,189, 2,289,190, 2,300,218, and 2,303,210. In commercial practice the catholyte is circulated through the cathodecompartmentiand through a heat exchanger and receiver, as described in the patent to H. J'. Creighton, No. 1,990,582, so that the temperatureand rcomposition of. the catholyte can be controlled throughout the operation. y

While `the above-described process has been commercially successful it has been slow in operation, requiring reduction times in the neighborhood of 200 hours for completion of a large scale reduction. This long period of operation has Vthe effect of requiring large cell capacity for a given volunef 'of production.

Thepresent `invention resides ink an improvementof the' electrolytic process which greatly increases"- the rate of reduction thereby increasing the productivity ofcell equipment. Operating inaccordance'with theinvention results in increasing up to ten-iold'or more the rate of reduction of the process. Another advantage of the present process resides in operating economies made possible in temperature control by virtue of the fact that the process is conducted at a higher temperature than the known process.

Broadly the invention employs a higher operating catholyte temperature thanthat previously employed, plus a higher cathode current density than that previously employed, the temperature and current density values being correlated according to a definite plan which takes into account two other process variables, namely, the

concentration of sugarin the catholyteand theV relation of the area of the cathode to the volume of the catholyte. f f

' In` the prior practiceof the electrolytic process, the catholyte was maintained at a temperature of about' 68or 69 Fahrenheit vand the current densityl at the cathodev was about 1 ampere or less per squarev decimeter of cathode surface. Higher temperatures Were tried and found unsatisfactory. in the priorfprocess because they impaired.` the quality -oiz' the product through darkening lthe color, and producing organic acids in objectionable quantities. Raising the temperature alone did not improve the rate of reduction. A further eiect of raising temperature alone was to give products of different composition than the normal process. It had also been attempted to increase the rate of reduction by raising the current density at the cathode without making any change in the catholyte temperature. The result of this attempt was that no increase in the rate of reduction occurred and the current efficiency of the process dropped off sharply,

In the process'ofthel invention the catholyte is maintained at a temperature of at least '72,"

Fahrenheit and not over 135 Fahrenheit. Raising the temperature alone, vhowever, produces only the disadvantages just discussed. We have found it to be possible to compensate for 4this higher operating temperature by"increasing-the current density at the cathode tdafvalue `ofl'l ampere or higher per square'decimeter of cathode surface. The upper limit of current density is a practical one because extremely Thigh current densities involve excessive power costs. In general current densities should not exceed'lO amperes per square decimeter of cathode surface for this reason. It does not suice to select-any two valuesl of-temperature and current density at random but these variables -must be correlated to compensate for one another. `We -have further found that the particular values of teme perature and current-,density to be used'depends in a given case on Athe concentration of sugar in the catholyte-and-alsoon*the ratio of cathode area to catholytey volume.

`For convenience in presentation, vthe relationship of these four operating variables has been broken down into temperature as one-element and 'the expression grams vinitial vsugar per ampere as theother element. The expression grams initial sugar per ampere is derivedby factoring the fraction c., A exon wherein, Cu is the number ofigr-amsof vsugar perv literof catholyte, Ris the ratio =ofthe.cathode area in square decimeters Ato the volumevof the catholyte in liters,A andCD is the ,current density at'the cathode-in amperes per square decimeter -ofcathode surface. Supplyingthe values of the symbols inthe fraction gives grams sugar liter amperes dm.2 liter which on factoring becomes grams sugar amperes v` the cell will retain aqueous solutions without leakage and resist the corrosive actions of strong @electrolytes Disposed Within the body of the {ficell are diaphragme 26, which also are of box- Referring'now to .the` accompanying drawings l wherein like .numerals .designate corresponding Dalits,

`iFigure lisa diagrammatic representationfof -an like structure, open at the top. The diaphragms are made of "semiepermeable material so as to pm ,prevent .liquids on opposite sides thereof from ..,'fre,ely,intermixing but offering little resistance to the passage of charged ions through the walls. .Atsuitable material for the construction of the diaphragms is sintered aluminum oxide such as the material sold under the trade-mark Alundum. In the form of cell illustrated in Figure i; twodiaphragms lare employed. Suspended in the diaphragm-boxes 2-6 are the ano des2l,'which are preferably made of chemical ',lead, Aalthough other current conductive, corrosionresistantmaterials can tbe used. lOutside .of the diaphragm boxes "26 and iintthe main body-'of Athe 'cell"25 cathodes 28 areypositioned. The `cathodes are rigid k'plates `with metallic surfaces lsuch `vas lead orzinc. The cathodescan be made of solid metal or of suitable base material-coveredfbyya 'layer of such metal. Whenthe cathode surface is lead, itis amalgamated by dippingn or rubbing'with mercury or dipping in mercurio nitrate solution before using. `Wherethefsurface is of zinc, 'the cathode Acan; be usedl either with or withoutamalgarnation. 'jIt .vs/ill, thus,'be seen lthatjthe cell body 2 5 is divided bymeans ofthe diaphragms 2 6 "into -anode and cathode .compartments "The anode compartments are provided with. the anolyte'j vwhich is .an aqueous solution .of a current carrying electrolyte, preferably sulphuric acid.

he -,cathode `compartment, which is actually 'the body of the cell outside the Vdiaphragms 26, is provided with the catholyte 29, which is an aqueoussolutionl of the sugar to be reduced.A and a current carrying alkali metal electrolyte.

A'Ilxeanodes'l and cathodes '28 of 'the cell are connectedrespectively to the positiveand negative terminals of a source of direct current. When the-solutions are placed withinthe cell and anelectr-ic current is ,passed between the anodes andcathodes, the sugarin thevcatholyte is reduced .or rhydrogenated to .form `the ,polyhydric alcoholproduct.

L'Iheconcentration of sugar will depend upon its.solubnitymmeramente 2.9. In .the ease ,of glucose, the preferred,concentrationfis between 2 .0.and.'700.grams,per liter. The preferred sugar isi-,.glucose, because of-.the valuable products .,obtainedfrom-it, although other reducible monosaccharides .such :as fructose, Vmannose, -the .mixture of tglucose and fructose obtained .by theinversion of 4s ucroseLthe.mixture of glucose and4 galactose obtained by the inversion of lactose, andpentoses, andreducible disaccharides, ,such .as .-lactose, can bei-used.

{Ifhe .-ratio of cathode area to catholytefvolume is .-Lsusceptible ofx wide yvariation but forg practical purposesgthe range of,.0.25to {10 squarefdeoimeters of cathode surfacep'erliter of catholyte is preferred. This ratio can be controlled at a selected upper surface of the catholyte to prevent contact with air. Suitable means for this purpose are disclosed in the application of K. R. Brown, Serial Number 458,820, filed September 18, 1942,'"now n abandoned.

The temperature of the catholyte may be adjusted initially by heating or cooling, as required,

before starting the reduction. The reduction process results in the generation of heat in the solutions and during the operation of a cell the catholyte temperature is kept at the desired value by cooling. The temperature control may be accomplished by conventional means such as im'- mersing the cell in a bath of liquid, by owing a liquid through coils immersed in the cell solutions7 by circulating the cell 'solutions through external heat exchangers, etc. In large scale installations it is customary to employ external heat exchangers for temperature control, as described for example in the patent to H. J. Creighton', No. 1,990,582. [l

Referring now to Figure 3, the graph is of the semi-logarithmic type with temperature in degrees 'Fahrenheit represented arithmetically as the abscissa and grams initial sugar per ampere represented `logarithmically as` ordinate. The area bounded bythe line ABCDEA contains the pointswhich represent the range of operativeratios of temperature to grams initial sugar per ampere when current densities of at least 1.1 amperes per square decimeter of cathode surface are used. For a given set of conditions of sugar,

catholyte alkalinity (or acidity), and cathode material, substantially the same product can be made at the ratios of temperature to grams initial 3' sugar per ampere which lie on lines parallel to the line BC. For example, the line FG represents ratios of temperature to grams initial sugar per ampere for making Aa high vpurity sorbitol from` glucose with anamalgamated zinc cathodeand with a catholyte containing from 0 to 2.0 grams NaOH per liter.- Similarly, the lineI-II representsv ratios .for making mannitol anda noncrystallizing sorbitol syrupiromglucose with an amalgamated i lead cathode and Witha catholyte containing.

from l0 to20 grams NaOI-I per liter.A

two reductions employing ratios lying on diierent linesparallel to BC, that which is farther from BC 'will produce a product higher in polyhydric alcohol obtainable directly by hydrogenating the carbonyl group ofthe selected sugar to a carbinol group. Where the selected sugars are hexoses the directly obtainable polyhydric alcohols are hexahydric alcohols also called hexitols. An

aldo-hrexose yields only one hexitol by direct hydrogenfation under non-isomerizing kconditions while a keto-hexose yields two hex-itols bydirectIv vwFor the same sugar, catholyte alkalinityI (or acidity) and cathode` material, Variations in theV 6. hydrogenation. `lFor'convenience in description the polyhydric alcohols obtainable by direct reduction 'of a sugar are referred to as the specic hydrogenation products of that sugar to distinguish from so-called non-specic products which are polyhydric. alcohols obtainable only by more complex reactions which may include, for example, isomerization of the sugar,

hydrogenation of carbinol groups to hydrocarbon groups, and carbon chain cracking. From glucose, for example, the reduction using 4a ratio y falling on the line farther from BC Will give a product containing more sorbitol than an othery .wise identical reduction using a ratio falling on the line nearerfto BC. The reduction employing a ratio falling on the line nearer to BC will give relatively moreof the nonspeciiic hydrogenation products, which from glucose are mannitol and non-hexitol compounds chiefly hexane pentols. These effects Will become more apparent from a consideration of the examples.

ATheinvention provides a range of novel operating conditions throughout which the advantages of faster rate of reduction and improved eiciency in temperature control are obtained. Furthermore, the invention provides a series of operating ratios of temperature to grams initial sugar per ampere for making products of like composition at xed conditions of sugar, catholyte alkalinity (or acidity) and cathode material.

For convenience in presentation and for better comparison the following examples are tabulated.

'Glucose solutions Were reduced in each example,

75 g. of sodium sulfate per liter being added to carry the current. An Alundum diaphragm separated the catholyte from the anolyte which was a dilute aqueous solution of sulfuric acid.

The tabulated items are:

Ratto-' The ratio of the surface area of the cathode, in square decimeters, to the volume of the cathode, in liters.

C. D.-The current density in amperes per square decimeter of cathode area.

Temp-The temperature in degrees Fahrenheit of the catholyte during reduction.

P. N.-The pyridine number of the product.

` This value is a measure of the sorbitol content is a measure of the time efficiency of the reduction. The gures are computed with reference to 99% sugar.'l reduction except where otherwise noted.

@wmp- Grams initial sugar per ampere, the value of the expression Gramsy initial sugar per liter of catholyte Ratio XC.1D.

Examples. 1 to' 10 inclusive employed amalgamated ylead cathodes, floats on the catholyte in the receiver, and an alkali concentration initially 10 g. NaOH .per liter which Was allowed to increase :togv 20:g."d'uring `the reduction and Was 1f maintained thereafter at the*I latter-1 value1-z by:` neutralization asrequiredz.

The following table givesexamples of reduc tions` :according to the inventiom` I n: Examples. 1- andV 2 the catholyte contained initially 500 g. glucose per liter While in vtheotherf. examples the tions of .theiother `variable:ffactonszoif. the-faccinea tiem.

time?l following tahteff. the-2 threei' reductions' according? tosth'e? inventiom .weref alla* carried: ont

with; catholytesr. atiY an' initials: concentra-tion`4 of;A

325: e. .glucoseoperr liter: The.;- threeif examplesa catholyte contained-initially. 325; g.: glucose per"y (11; ,12. and 13) were reductionsin'iwhichranvinieliter. l tial alkalinityof 5.0 g. NaOH per litemofcatho'- Table-I Example Ratio C, D. Temp. PxN. lMan Yield g./dm.*/hr. gjamp 1.21 4.0 si 40.55 1714# ses 4.75 10aA 1.21 10.0 100 18; 14.9.; 90.5 13.2; f ,i A411.13.

1.21` 4.o se 52 17.6 l 93.1 5.2i'.- Y 01.2

1.121 2.0 75 4a zozo 9120 2.40 `134.

2.0` 2.o s1. 54.A 17.11` 011.13 2.60 81.3

2.0 6.oV 11o 12.. 1 .5- Saiz-g 9.43 27.1.

For comparison with theexamples in..Tab-le-I which are in accordance withthe presentimien tion.. the following-table givestwo.examplesoil reductions atvaluesof temperature and-.currentdensity outside of the values contemplated byithis lyte was allowedatoincrease to...10.'0. g perv liter. at which. valueet .was kept.. b'yf neutralization ras required... Examples.,11..and.; 12.- were conducted:- with amalgamatedzinc cathodes:while:ineExamV ple .131 anam-alganrated .lead cathode was used..

invention. Example 95 had acatholyteconcentration of 5602-g.. glucose per liter-ai'id'th'ecatho` lyte in Example 10 hadf 325g. glucosecper liter. These reductions were both conducted at thesarne Notable.: in: the foregoing:A examplesf. are -.th"e.. sharp. riseffinzxfate' ofireductiom andE thewra'dicali change :iny the. composition :of'fthe prodncti oExe Y ampleI2:asecomparedztoExamplel1I: These two alkalinity as the examples in Tablel I'. 40 examples-awei:efsi'rnilar;inallirespects:excepixtelri Table II t Y Example Ratio C. D. Temp. I. N. Man. Yield. gJdm/hr.V g-Jamp.

In Example 9 both temperaturefandcurrent f density were below the values used in vfollowingthe present invention. Therate 4of reductionof sugar is markedly lower than 'thef'rates-in any of' the examples in Table I. For instanceExample 2 shows :a rate of reduction over eight times-that of Example 9. Note the increase in the'rate -of reduction obtained even loy` concurrently raising-f' the temperaturer to 75 F. and thecurerntden sity to 2.0 as in Example Las compared to the rate obtained at 69 F. and 1.0 ampereein-Example 9. Example 10 shows a decreasefwinethew rate of reduction compared to ExampleuQ'when the temperature is raised to 8P' FL and the current density held at 1.0 ampere. the 0 P. N. and 1.2% mannitol ofthe productof Example 10. I

Examples 1 and 6 following theA invention and Example 9 following the previous practice all produced substantially the same product, as far as sorbitol (determined as P. N.) and mannitol are concerned,1 although the temperatures. and current densities. of these` examplesanwererwidely" dierent. These examples'are `illustrativef-of'ithef.k variation of .temperature and current-density tot produce. similary products. under :various rcaomiiI Noteazaflsofv peratnrei: Iii-Example.` 11 the temperature-was Qilf'fli; whiiefin Example-12 the-terrip'erature"was 1.00%?? The; dlii'lererireein--methodes` is *strikingly* showmimExampl'es `12and^I` i otherwisesimilar;l where 'hef change from== air amalgamatedv zincvv sariify'show"complete` absence. of' sorbitol lit' does'- shovwvery low sorb'itol content... Example-13"ex liiltsa great increaseinheth .scribi-tol and. man.-

. nitoloonterit oil. theprbduct...

` Table.. gives further .examp1es--ofreductionsY' ing. accordance witl-rf the.V invention,- inwV which z a'. catholyteccont-ainingi:325i-g. gilucosefrfper .literf was reducerlnat, an 'alleaiimityfinitiailyzeg: NaQHrip-er: litertwhiclm wasnaliowedrto'frise to:1.51g;.per liter-'imA the.` course.: of reduction: ande was keptf between these vval-'frese105V` neutralizationw-as. required; Inr- Examplesee 144 to; 17 amalgamated' zi'noj-l -catl'iodesf' were used*lw11il irrExample-f lli-"ank ama-lga-mat'edl' learlcathodewaslused Table IV Example Ratio C. D. Temp. P. N. Man. Yield gJdm/hr. gJamp 2.0 4.0 si 76 0 93.3 ls 40.6

Examples 14 and 17 gave a product with sub- The improvement in the rate of reduction of stantially the same P. N. and mannitol content Example y.as compared with Example 21 is atalthough Example 14 was run with a catholyte tributable to the increase of'temperature from temperature of 81 F. and -at a current density 68 F., in Example 21, to 90 F., in Example 20, of 4 amperes while Example 17 was run at 90 F. V and to the simultaneous increase in current denand 6 amperes. However, Example 17 shows a l" sity from 1.0 in Example 21,' to 2.6 to 2.7 in Exrate of reduction over higher than Example ample 20. f 14. Example 18 shows a relatively low rate of The examples of reductions following the lOesrreduction attributable to the use of an amalent invention show a few of the possible temperagamated lead cathode at the low alkalinity unture and current'density values. It is preferred der which this run was conducted. Example 16 29 to conduct the reductions with the temperature shows the use of 120 F. as the catholyte temperbetween 80 and 110 F. and with the current ature along with a current density of 4.0,k the density between 2 to 10. At temperaturesV above product having a, low P. N. value and a low 110 F. the organic acid and color of the product mannitol content and being composed largely of .W are higher and the product is thereby rendered other hexitols and related materials. ff less desirable for many purposes than one pro- The following example of a run at ordinary duced at a lower temperature. Further increases temperature and current density shows the rein current density are generally undesirable besults of a low alkalinity reduction (0.5-1.5 g. cause of the increase in power cost andthe fall- NaOI-I per liter of catholyte as in Examples 14 l ing off of current efficiency. to 18) with an amalgamated zinc cathode and "U The foregoing 21 examples have been plotted a glucose concentration of 325 g. per liter of on the graph of Figure 3, the points represen-ting catholyte. the values of temperature and grams initial sugar Table V Example Ratio C. D. Temp. P. N. Man. Yield g./dm2/hr. gJamp.

Note that the rate of reduction of Example 18, with an amalgamated lead cathode, is 90% higher than the rate attained in this Example 19 in spite of the fact that the latter run was made 'with an amalgamated zinc cathode. It is also vinteresting to observe that substantially the same P. N. and mannitol content were found in the product of Example 19 as were found in the products of Examples 14 and 17.

Two further examples follow to show the comparative results in Example 20, a run according to the invention, and Example 21, a run at ordinary temperature and current density. The two examples were lconducted in non-circulated cells, at 325 g. glucose per liter of catholy-te, 20 g. NaOH per liter of catholyte, and with amalgamated zinc cathodes. The cathodes were corrugated Or scored on their surfaces and the actual active cathode area was substantially double 'the area of a smooth (plane) cathode `of similar dimensions. The values given for Ratio and C. D. are based on the plane surface areas of the corrugated cathodes. Throughout this speccation and in the claims the term cathode area is used to signify the plane area of the cathode. Reduction was carried to a point at which 90% of the initial glucose had been reduced. v

per ampere being indicated by the respective example numbers.

While glucose was reduced in each of the foregoing examples the invention is not limited in this respect but may be applied to the reduction of other reducible sugars and mixtures of reducible sugars. e w

It is further to be understood Vas within the concept of this invention to maintain the conditions of high temperature and current density either throughout a reduction or during a substantial part thereof. Moreover, it is not necessary to keep either temperature or current density at a constant value in practicing the invention and desirable eiects and economies can be obtained in many instances by runningcertain parts of a reductionk under different conditions of temperature and current density than the rest of the reduction. p p

Having now described the invention what is claimed is:

1. In the process of electrolytically reducing glucose in a cell provided with a metalplate cathode and an anode in cathodeand anode compartpartment, the steps comprisingemployi'ng a soluantenas *1l tion of glucose and an alkali metal electrolyte in Water as the catholyte solution in the cathode compartment oi' the cell, said solution containing from 200 to '700 grams glucose per liter, the ratio of the area of the cathode of the cell to the volume of said catholyte solution being from 0.25 to square decimeters per liter, passing anfelectric current between said anode and said cathode and through said catholyte solution to reduce the glu- -cosetherein to polyhydric alcohol, maintaining acurrent densityof from `2 to 10 amperes per square .decimeter @surface of said cathodev duringasubstantial part of. the reduction, and simul-- taneouslymaintaining said ,catholyte solution vat ,ai-temperature Yof rfrom 80.to 11.0 F.; said current density and catholyte temperature being correlated;y taking into account the initial .concentrationofglucose in said catholyte, and the ratio of. area of `said cathode to thevolume of catholyte, so that the point dened by plotting the arithmetic value of the temperature in degrees Fahrenheit .as abscissa against `an ordinate which isthe logarithmic value of the expression wherein Cois-the initial `concentration of glucose in the catholyte solution in grams per liter R is the ratio of cathode'area to the volumesof Acatholyte solution insquare decimeters per liter CDis the current density at the cathode in amperes per square decimeter of cathode surface,

falls within the area ABCDEA in the accompanying graph Figure 3.

2. In the process of electrolytically reducing glucose in a cell provided with an amalgamated lead cathode and an anode in cathode and'anode compartments .respectively` separated .by a .diaphragm, and having an electrolyte .solution in the 39de vcompartment, the steps. comprising employinga @water solution. of. 20.0 to '700 grams. glucoselpalliter, Sodium sulfaterand from .10 13020 gramsperliter o isodllm. hydroxide. as the catholyte solution in the cathodecompartment of said cell, .thematic ofthearea offthe cathode of the cellto thavolume of said catholyte solution being from .-0125, to v10v square. decimeters. per liter, passing .an electr-ic .currentbetween saidenodeand cathode and through 4'said catholytesoluton to reduce the. glucose therein. to amiXture of polyhydrc. alcholslof.10W- sorbitol contentr maintaining .a .current density of 2 to 10 ,amperes per squareldecimeter .of surface of said cathode, during asubstantalpart .of thereduction, andsimultaneously maintaining said catholyteV solution at a temperature of 80 to 110 F.; .saidcurrent density and ...catholyte temperature being correlated, taking into account the initial concentration .or glucosein thecatholyte and the ratioy of areaofsaid cathode to the Vyolume of catholyte, so. that. the pointdefined by Aplotting-.the arithmetic .value ofthe temperature inA degreesFahrenheit `as Vabscissa` againstan. ordinateY which. is; the logarithmicvalue of. the expression wherein Co is the initial concentration of glucose inthe catholyte solution in grams per liter R is the ratio of cathode area to the volume of v catholyte solution in square decimeters per liter l2 CD is the current-density at the cathode in amperes per square decimeter of cathode surface,

falls substantially on the line HI in the accompanying graph Figure 3.

3. In the process of electrolytically reducing glucose in a cell provided with an amalgamated zinc cathode and an anode in anode and cathode compartments respectively separated by a diaphragm, and having an electrolyte solution in the anode compartment, the steps comprising employing a water solution of 260 to 700 grams glucose per liter, sodium sulfate, and from 0 to 2 grams-per liter of sodium hydroxide as the catholyte solution in the cathode compartment of said cell, the ratio of the area of the cathode of the cell. to the volume of said catholyte solution being from 0.25 to 10 square decimeters per liter, passing an electric current between said anode and cathode .and through said catholyte solution to reduce the glucose therein to a polyhydric alcohol product of highl sorbitol content, maintaining a current density of 2 to 10 amperes per square decimeter vof surface of said cathode during a substantialpart of the reduction, and simultaneously maintaining said catholyte solution at a temperature of to 110 F.; said current density and catholyte temperature being correlated, taking into account the initial concentration of glucose in the catholyte and the ratio of area oi said cathode to the Volume of catholyte, so that the pointdened .by plotting the arithmetic Value of the temperature in degrees Fahrenheit as abscissa against an ordinate which is the logarithmic value of the expression wherein,

-Goisthe initial concentration of glucose in the .catholytesolution in grams per liter R. is the ratio of cathode area to the volume of catholyte solution in square decimeters per liter CD isthe current density at the cathode in amperes per square decimeter of cathode surface,

falls substantially on the line FG in the accompanying graph Figure 3.

4, In the process of electrolytically reducing a reducible sugar selected from the class consisting of monosaccharides and disaccharides in a cell provided with a metal plate cathode and an anode in cathode and anode compartments respectively separated by a diaphragm, and having an electrolyte solution in the anode compartment, the steps comprising employing a solution of the reducible sugar and an electrolyte in water as the catholyte solution in the cathode compartment of said cell, said solution containing from 200 to 700 grams of the sugar per liter, the ratio oi the area of the cathode of the .cell to the volume of said catholyte solution being from 0.25 to .l0 square'decimeters per liter, passing an electric current between said anode and said cathode and through said catholyte solution to reduce the sugar therein to polyhydric alcohol, maintaining a current density oi from 2 to 1G ampercs per square decimeter of surface of said cathode during at least a substantial part of the reduction, and simultaneously maintaining said catholyte solution at a temperature of 80 to.110 E.; said ,current density and catholyte temperature being correlated, taking into account the initialconcentration of sugar in the catholyte and the ratio of area of said cathode to the volume of -catholytaso that the point dened by plotting 13 the arithmetic value of the temperature in degrees Fahrenheit as abscissa against an ordinate which is the logarithmic value of the expression,

falls within the area ABCDEA in the accompany- 15 ing graph Figure 3.

HENRY JERMAIN CREIGHTON. RALPH A. HALES.

14 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,612,361 Creighton Dec. 28, 1926 2,289,189 Hales July 7, 1942 2,289,190 Hales July 7, 1942 2,300,218 Hales Oct. 27, 1942 OTHER REFERENCES Transactions of The Electrochemical Society, vol. '75, pp. 289-307 (1939).

Transactions of The Faraday Society, vol. 1'7, pp. 453-456 (1921).