Indian Journal of Chemistry Vol. 31 A. June 1992. pp. 355-360

Direct production of pure concentrated from its salts by electromembrane processes

R Audinos" & S Paci Ecole Nationale Superieure de Chimie. 118 route de Narbonne. F31 400, Toulouse

A concentrated tartaric acid solution is directly produced from oenological wastes by a double de- composition in electrochemical reactors fitted with ion exchange membranes. In the classical route of production of tartaric acid, a first set of neutralization-separations is used with a view to precipitating cal- cium . Then, the -.acid is produced by metathesis with an aqueous solution of sulfuric acid. The fi- nal solution obtained is generally a diluted mixture of tartaric and sulfuric acids which must be separat- ed.In the first step of the process described here, the wasted tartaric salts are treated with a base, in such a way that a soluble neutral salt is formed in an aqueous solution. Then, the solution is fed into an elec- tromembrane reactor where the metathesis of the neutral salt gives tartaric acid, and the corresponding salt or the neutralizing base according to the type of reaction used. In the case of an electrometathesis reactor, the reaction involved can be written as: tartrate + sulfuric ucid= tartaric acid+ In the case of an electrohydrolysis reactor, the reaction is: Potassium tartrate + water+ tartaric acid + In each case, the use of an electromembrane reactor allows one to obtain a pure solution of each of the products, tartaric acid, potassium sulfate or potassium hydroxide. For each kind of stack assembly involved, the influence of the DC voltage applied to the outer elec- trodes, the concentration of the feeding solutions to each of the four cells and the velocity of the four streams have been studied. The results obtained allow the process to be modelised. According to the op- erating conditions. a more or less concentrated tartaric acid solution is produced in the concentrating cells.

Introduction tats. As a complexing compound, it is used in con- Tartaric acid, C4H406H2, is encountered in juices crete or plaster with a view to reduce setting time. of many plants, particularly in grape juice. This di- The production of tartaric acid by traditional acid-dialcohol, COOH-CHOH-CHOH-COOH, is routes is inadequate. So, three alternatives are possi- at once an organic acid, a buffer, a reducing com- ble: to use another acid, such as citric acid; to pro- pound and a complexing compound of metallic ions. duce tartaric acid by synthetic methods from maleic It is mainly obtained from co-products of wine acid issued in petrochemistry; or to improve the production and less than one-tenth of its production yields of the usual routes. is based on synthesis from petroleum derivatives. The worldwide production is about 100,000 metric ton a year'. The classical route of producing tartaric acid Tartaric acid is a product ot common use. Its acid- Tartaric acid is mainly obtained from hydrogeno- ic properties are used in biscuit, candies or sweets tartrate of potassium, KHC4H406, known as cus- fabrications, in fruit juice or bewerage production; tard tart, and from precipitates containing calcium in jam manufacture to catalyze the hydrolysis of suc- tartrate. rose; and in oenology, for acidification of too mel- According to the process described in Fig. 1, hy- low grape. drogenotartrate of potassium contained in vinasses, As a buffer, tartaric acid is used whenever it is ne- a residue of wine production, is treated with calcium cessary to keep a constant pH; for example in carbonate to obtain the insoluble calcium tartrate pharmaceutical products, in some chemical reac- salt, CaC4H406• tions and in galvanoplasty. In the second -step, addition of calcium sulfate,

As a reducing agent, it is used in photographic de- CaS04, is necessary to change the remaining soluble velopers, in silvering of mirrors, in dyeing with me- potassium tartrate into the insoluble calcium salt. 356 INDIAN 1 CHEM, SEe. A, JUNE 1992

< CaC-lH-lO(,> In the traditional method, tartaric acid and pota- ssium sulfate are mixed together in the same aque- [K S0-lJ 2 ous solution. The separation of these products by a After these two reactions, the tartrate anion is . classical procedure is not easy at all. On the other

present only as the calcium tartrate salt, CaC4H40f" hand, if the reaction occurs in a membrane reactor, which is not soluble. Then the tartaric acid is pro- using the selective means of electrodialysis the two duced from its calcium salt by adding a stronger ac- products are created in separate volumes: it is one of id, generally sulfuric acid. the advantage of an electrometathesis reaction with All these reactions are based on the fact that some membranes 3. salts of tartaric acid can precipitate easily. Such a Such a method is indicated in Fig. 2. It clearly ap- route is common in the classical chemistry. pears that this route is less complicated than a tradi- However, the increase in intermediary steps re- tional process, like that indicated in Fig. 1. quires control of many fluxes of matter, with various compositions. As a consequence, the operating pro- Materials and Methods cesses, although being safe, are complicated by a Use of a selective permeability artificial mem- great multiplicity of operations. brane technique (SPAMT) involves optimisation of a method and a process". Production of tartaric acid by {In electrometathesis The method consists of optimising theoretical con- reaction ditions for a separation based on properties of The use of calcium compounds allows one to ob- membranes, considerations of energy and of sub- tain precipitates, but leads to the formation of cal- stances". This is indicated in Fig. 3. cium sulfate as by-product. Generally, this by-pro- Membranes-As the metathesis reaction involved duct cannot be reused and is wasted. is a reaction between ions, membranes capable of On the other hand, it is well known that the neu- distinguishing ions are needed. In the study de- tral potassium salt of tartaric acid is very soluble, scribed here, only heterogeneous ion exchange whereas the acidic salt is only slightly soluble'. For example, this acidic salt contributes to the formation of a precipitate in wine bottles. Based on the use of soluble , the process consists of dissolving the tartaric ions in a neutral salt. by reaction with potash:

[KHC.jH.j0h] + < KOH > - [K2C-lH.P6] + [H20] Then, tartaric acid is directly produced from the potassium salt by a metathesis reaction with sulfuric acid. The double decomposition reaction is as fol- lows:

[K2C.jH.j0f,] + 2[H2SO.jl- [C.jH{,OIl+I [K2S041 Fig. 2-Production of tartaric acid from hydrogenopotassium tartrate by an electrometathesis with sulfuric acid [R I = neutrali- zation tank; EMT = electrometathesis stack ]..

K2S~

Fig. 3-Membrane technique at the intercept of membranes- Fig. 1- -Classical route for the production of tartaric acid (R I. R2. energies-substances [SPAMT= semi-permeable artificial mem- R3 = reacting vessels; Ft. F2. F3 = dead end filters]. branes technique]. AUDINOS et al.: PRODUCTION OF TARTARIC ACID BY ELECTROMEMBRANE PROCESS 357 membranes from the French company, Rhone Pou- The reaction may be written as: lenc were used. [CdH406K21d+ 2[H2S041g -[C4H406H21h Energy-A: is also clear that ions can easily be moved by an electric field. So, the driving force is +2[KHS041r the one created by the gradient of the difference of This way of production offers two main advan- an electrical continuous potential. In this study, the rages in comparison to the one used in classical electric field is always oriented in the same direc- reactors: tion, perpendicular to the surface of the flat mem- (1) Each compartment being separated, substances branes, as in an electrodialysis stack. are never in direct contact. As opposed to a tradi- Substances-In the present case, electrometathe- tional reactor, there is never mixing of reactants and sis needs the substances to be soluble, and to be ion- consequently of products. So, the difficult problem ized. This aspect demands that the physicochemical of separation of the products is avoided. properties of the medium be well known. (2) As products-are created in different vessels, it is Now, the practical fitting involves 4 channels for possible to use a volume appropriate to the desired the solutions, apart from the 2 channels necessary to concentration for each of them. In a traditional reac- wash the electrodes. tor, this operating mode is not possible as all the The study of the process aims at optimising con- substances are in the .same reacting vessel. ditions regarding the elementary cent', the stack, the The elementary cell insertion in the production mode, and the techno- The unit cell is already described by the method economic analysis 7. used. In practice, the separating frames used in this study make a tortuous path for the solution. The Results and Discussion channels of rectangular cross section of 3 mm x 10 The electrometathesis reaction mm are (7 times x 6) 42 cm long. Ion exchange membranes are heterogeneous ARP and CRP The electrometathesis reaction was carried out in membranes described in another publication. an apparatus similar to a classical electrodialysis Under the electric field, ions migrate and create stack, but it included 2 diluting and 2 concentrating concentration polarization layers near each of the 4 streams, in addition to the 2 needed by the elec- membranes of the unit cell, as indicated in Fig. 5. trodes, as indicated in Fig. 4. If the electric current is too high, the departure of Reactants were introduced as liquids in this mem- ions from the exporting channels can split water into brane reactor by means of separated aqueous solu- ions, near the membranes". As an elementary cell in- tions of dipotassium tartrate and sulfuric acid (chan- cludes the 2 diluting compartments d and g, 2 pos- nels d and g, in Fig. 4). sibilities arise. So, each case was studied separately, Products obtained were tartaric acid, C4H406H2, whereas in the other compartment the circulating and hydrogenopotassium sulfate, KHS04 (channels solution had a concentration high enough to avoid band f, Fig. 4). any ionolysis of water.

TH2 KHSO, acid conc~nItot~d dilutt: salt 1Cl1TTlt:d mpa mpc t mpa mpc t mpa 07 ® f±} ® E3 !.

The critical current is indicated by the measure- [Salt]outlel= [salt]inkl- __ n_ Ze jerilsall ments of current density, j, of conductivity 0 and of I!zl! FY V pH of the diluting solution, as a 1'1 merion of the dif- ference in potential, ~ U, applied to the stack". The By eliminating the value of the concentration of results obtained are reported in Fig. 6. They show the salt at the outlet from the two previous equations that the critical current varies linearly with the initial we get the following relationship for the critical cur- concentration of dipotassium tartrate or with the in- rent: itial concentration of sulfuric acid, according to the . [salt];nlel case under study 10. Jerilsalt = a Z Its appears that for the same molar concentration, - n c -+---- the critical current is first reached in the compart- K_ IIzll FYv ment where the dipotassium tartrate flows. As a practical consequence, it is then-sufficient to use an So, it is possible to increase the value of the criti- aqueous sulfuric acid solution ofa concentration not cal current either by reducing Ze, the length of the less than that of the dipotassium tartrate. Then, from the water splitting point of view, it is 2 possible to ignore the sulfuric acid solution, calc parallel I The stack I I _ ----- In order to reduce investment costs, it is always ______----,-t------~lcS&rU necessary to transfer the maximum of matter in min- .,,' I »< I ~ imum time. So, it is necessary to increase the electric /" : 0 paraUd " I. = series current as far as possible without reaching its critical , I value. It is clear that this value is first reached at the I I outlet of the channel. 0(1) o·s 10 IS 20 H 3'0 H The straight line representing the critical current, v(cms') Jeril' is related to the concentration by the relation: Fig. 7-Influence of tangential velocity on the critical current, ie

Timc{m;n)

... '0 Fig. 8-Comparison in the transport of tartrate ions in parallel 'I; « or series flow as a function of time. .;: ~- 5 Table I-Initial operating conditions [number of runs = IS, Temp. = 298K, Ll U= l Ov, v = 1.6 cm.s - IJ Stream Solution Initial Initial teneur volume conc. ~--L.---'------L-_....&..-_-:o"".o:-:-s----'L---'" Acid used H!SO. not 0.1 mol.l " ' concentration (mol dm - 3 ) recirculated Concentrate TH2 75ml 5.1O-4mol.l-' Fig. 0- Values of the critical current, icn, due to each reactant in Diluate treated TK2 lO liter 15 g.l-I the electrometathesis stack, as a function of the concentration [I, Resulting salt KHSO. 500ml 5.1O-4mol.l-' H,SO. (acid g); 2, dipotassium tartrate (TK2) (dilutedj], AUDINOS et (/1.: PRODUCTION OF TARTARIC ACID BY FLFCTRClMFI\1BRANF PROCFSS 3:;l) channel, or by increasing the tangential velocity v in tions of dipotassium tartrate. However, it gives po- the channel. tassium sulfate as waste. In the present case. this po- For a constant transfer area, the best way to pro- tassium sulfate can be used to fertilize the wine yard. ceed is to use a high tangential velocity in a stack Potassium is then recycled in byproducts of wine with compartments fed in parallel as shown in Fig. 7. making. Practically, the interest in using a parallel feeding This cycle can be shortened, and transportation centres on the quantity of matter transferred from avoided, by direct production of potash, from dipo- the diluting stream to the concentrating one. So, for tassium tartrate, by using an electrohydrolysis reac- identical operating conditions, the quantity of moles tion with membranes. of tartaric ion transported from the diluate to the As a matter of fact. among the acidic anions that concentrate, is greater for a parallel flow than that are suitable for displacing the tartaric acid from its for a serial flow, as indicated in Fig. 8. salts, the hydroxyl anion, OH -, is an interesting electron donor. For example, the oxhydryl ion can Inclusion in the production mode be produced by splitting water into its ions. Using the operating conditions described before, Then, the electrohydrolysis reaction with mem- some production of tartaric acid from dipotassium branes involves a metathesis reaction with mem- tatrate was carried out. The starting volumes and branes and the ionolysis of water, as indicated by the concentrations are indicated in Table 1. following equation: For example, if we start with an initial volume of [C4H40(jK21d + 2[H201hip -[C4H(j061h + 2[KOHlr the diluate as 10 litres and dissolve 15 g of In such a reaction, a bipolar membrane, bip, sub- C H 0 K per litre, the final concentration of the 4 4 6 2 stitutes the sulfuric acid compartment g, as indicated concentrate is about 125 ± 5 g of tartaric acid per li- in Fig. 10, and gives directly the protons and the hy- tre. droxyl ions. However, as indicated in Fig. 9, the concentration As noted earlier, the advantages of the electro- of the concentrated tartaric acid solution does not metathesis reaction with membranes include produc- always increases with time. The weakening is attri- tion of pure products in solution, and obtaining con- buted to the water transport. centrated solutions of tartaric acid, starting from a Even if the water flux is only about 13 diluted solution of dipotassium tartrate. mol.s - I.m- 2, i.e. 3000 time less than that of tartrate Moreover, the co-product formed is a potash so- ion, which is about 44,000 mol.s - I.m- 2, it is suffi- lution, which can be directly reused to dissolve the cient to check the increase in the concentration with hydrogenopotassium tartrate on the plant itself. time. Moreover, it is interesting to notice that for a seri- The process al flow, the value of the final concentration is 1.5 The stack used is similar to that fitted for the elec- times lower. trometathesis reaction with membranes, but every compartment, g, where the stream of aqueous sulfu- Electrohydrolysis reaction with bipolar membranes. ric acid solution flows, is now substituted by a bipo- The method lar membrane, bip. But, in order to obtain a suffi- The electro metathesis reaction permits to. pro- KOH duce concentrated tartaric acid from dilute solu- TH2 mpc bip bip mpa f t I \000 I K+ K+ I l- H+ ; 71 I 800 I I I 2- c,H,ol- ,OH---t E1 ':' I~,H, E 600 I dilute ~I • = [T~J Iconccntrat- I 1 I ed I 400 d a = [:~ I b t I 200 TK2

0 400 500 600 0 \00 200 300 Fig. IO-Elementary cell for electrohydrolysis of potassium minub tartrate with a bipolar membrane [b = stream of tartaric acid produced TH;; d = diluting stream of dipotassium tartrate TK,; Fig. 9- Variation in concentrations (in mol.m - -')of dipotassium f = stream of hydrogenopotassium sulfate produced: mpa = an- tartrate, TK" and of tartaric acid, TH" with time (in min) in the ion exchange membrane : mpb = bipolar membrane: mpc = ca- electrometathesis reaction. tion exchange membrane]. 360 INDIAN J CHEM, SEe. A, JUNE 1992

1200

1000 ':'E eoo KOH ~ 600

1~-""""'-"I0000o;b:.----"--=±:::--....:i:- A.s

Fig. ll-Variation of concentration (in mol.m'] of dipotas- Fig. 12-Production of tartaric acid from hydrogenotartrate by sium tartrate, 'lKz, and tartaric acid, THz, with electric charge an electrohydrolysis with bipolar membranes [EHM = e~ect:?- (in coulombs (A.S)), used during the electrohydrolysis with bipo- hydrolysis stack with bipolar membranes; R = neutralization lar membranes. tank]. cient quantity of OH- ions from a bipolar mem- Such concentrations of tartaric acid are compati- brane, it is necessary to have the current density ble with the final evaporation, which gives the crys- high enough. Therefore, the critical current is first tals. In both routes, potassium appears as a co-pro- obtained in the diluting compartment (d) where the duct, either in the sulfate form, or as potash. It can aqueous solution of dipotassium tartrate flows. So, it be reused. But, the electrohydrolysis reaction with is sufficient to increase the content of dipotassium membranes has the advantage of recycling this pota- tartrate of the feeding solution. In fact, the increase ssium inside the process itself, on the plant. in C4H406K2 is economically favourable. As an example, starting with 1.21 litre of diluate d References containing 100 g of TK2 per litre, the final concen- 1 Mourgues J, Conte T & Roussel J, Recuperation des se/s de tration of concentrate b rises to 180 g of TH2 per li- racide tartrique, Revue des oenologues et des techniques viti- tre, as indicated in Fig. II. coles et oenologiques, 42 (1979) 17-20. At the same time, the potash solution produced 2 Landolt-Bornstein, Numerii cal data and junctional relation- overstays 0.8 mol per litre. Then, it can be reused to ship in science and technology (Springer Verlag, Berlin) neutralize the hydrogenopotassium tartrate incom- 1975. 3 Wilson J R, Demineralization by electrodialysis (Butter- ing to the plant. worth, London) 1960. As indicated in Fig. 12, the whole process is now 4 Audinos R, Membrane techniques in the chemical industry, very short. Chemie Ingenieur Technik, 53 (1981) 215. 5 Lakshminarayanaiah N, Transport phenomena in mem- Conclusion branes(Acadernic Press, New York) 1969. 6 Audinos R. Electrodialysis, Ch 10 in Water, waste water and Either by an electrometathesis reaction with sludge filtration, edited by S Winneswaran & R Ben Aim membranes, or by an electrohydrolysis reaction (CRC Press, Boca Raton) 1989. with membranes, an aqueous solution of pure tar- 7 Audinos R, Etude technico-economique des precedes Ii taric acid is obtained. In the first case this solution membranes, Ch 10 in Energetique des precedes; Coordina- contains more than 100 g of tartaric acid per litre, tor P Le Goff (Lavoisier, paris) 1989. 8 Lacey R E & Loeb S, Industrial processing with membranes and in the second case a solution with 180 g of tar- (Wiley Interscience, New York) 1972. taric acid per litre is easily produced from a solution 9 Audinos R. Determination du courant limite d elctrodialyse of hydrogenopotassium tartrate. This salt, of low par conductivite, Electrochimica Acta, 25 (1\180) 405-410. solubility, is collected as a waste in wine making. 10 Paci S, titre, Dr. Thesis, Toulouse III University, 1989.