The present invention relates to a process for the production of HCI gas from a chloride salt. More particularly, the present invention relates to a process for the co-production of gaseous HCI and a product salt from chloride salt, e.g., an alkali or ammonium chloride salt, and acids other than hydrochloride acid or acidic salts of such acid as well as to a process for the production of carbohydrates.

As used in the present application HCI denotes hydrogen chloride. HCI by itself forms a gas phase and is commonly described as "HCI gas". .

Alkali chlorides, primarily sodium chloride (NaCI) and potassium chloride (KCI), are the primary source chemicals for making alkali hydroxides (NaOH and KOH) and the corresponding bicarbonates and carbonates. These, in turn, are converted to an immense variety of inorganic and organic salts by neutralization with the corresponding inorganic or organic acids.

In the particular case of sodium sulfate Na ₂ SO ₄ and potassium sulfate K ₂ SO ₄ , it is possible to react the chloride directly with sulfuric acid (H ₂ SO ₄ ), at high temperature, to obtain the sulfate and hydrogen chloride HCI - according to the general reaction

2MCI + H ₂ SO ₄ → M ₂ SO ₄ + 2HCI _gas

where M denotes Na or K. In this particular case prior conversion of alkali chlorides to hydroxides or carbonates, by electrolysis or by reaction with lime, is profitably eliminated.

Such direct conversion to alkali salt and HCI is, however, restricted in practice to sulfuric acid that has the low volatility and the thermal stability required for reactions at high temperature.

It was surprisingly found that the aim of direct conversion of alkali chlorides (denoted MCI) to salts of inorganic or organic acids (which acids are denoted HX) can be achieved for a wide variety of acids that satisfy the conditions of being of weaker acidity than hydrochloric acid (as measured by a higher pKa value) and/or of higher hydrophilicity than hydrochloric acid (as measured e.g. by higher heat of dissolution) and of having some water solubility. A number of such weaker acids and their pKa values are tabulated below in the order of decreasing acid strength - by way of illustration: Table 1

This conversion takes place by contacting an aqueous solution of the chosen chloride salt and of the chosen acid and/or an acidic salt of such acid with an amine extractant that selectively extracts HCI whereby the desired product salt is formed as an aqueous solution from which it is optionally recovered by methods known per-se and wherein the HCI-carrying extractant is heated to distill-off HCI gas.

Thus according to the present invention, there is now provided a process for the co-production of gaseous HCI and a salt product comprising a cation and an anion, which process comprises the steps of: a. providing an aqueous solution comprising protons, chloride anions, and cations and anions of said salt product, b. bringing said solution into contact with a substantially immiscible extractant, said extractant comprising:

1) an oil soluble amine, which amine is substantially water insoluble both in free and in salt form; and

2) a carrier solvent for the amine; whereupon HCI selectively transfers to said extractant to form an HCI-carrying extractant and a chloride depleted aqueous solution containing said salt product; c. separating said HCI-carrying extractant from said chloride-depleted aqueous solution; and d. distilling HCI from said separated HCI-carrying extractant to form gaseous HCI and HCI depleted extractant.

Preferably said extractant further comprises an oil soluble organic acid, which acid is substantially water insoluble both in free and in salt form.

Preferably, the pKa of the organic acid is above 3.

In preferred embodiments of the present invention said extractant is characterized by a pHhn of less than 3.

Preferably said process further comprises: e. recovering said salt product of said separated chloride-depleted aqueous solution of step (b).

In preferred embodiments of the present invention, step a is carried out by combining a chloride salt of said cation with a compound selected from an acid of said anion and an acidic salt of said anion in the presence of water.

In some preferred embodiments of the present invention said recovery comprises crystallization to form crystals of said salt and a mother liquor.

In said some preferred embodiments, said mother liquor is preferably used for said providing of step a.

In especially preferred embodiments of the present invention, said cation is selected from the group consisting of alkali ions and ammonium.

Preferably said anion is selected from the group consisting of anions of acids that are weaker than HCI and anions that are more hydrophilic than chloride anions.

In preferred embodiments of the present invention said anion is selected from the group consisting of phosphate, nitrate, sulfate, carbonate and bicarbonate.

Preferably said distilling is at a temperature lower than 25O ⁰ C. Preferably, said gaseous HCI comprises at least 90% of the chloride in said provided solution of step (a).

In especially preferred embodiments of the present invention there is provided a process for the production of gaseous HCI from an alkali or ammonium chloride salt comprising: a. combining an alkali or ammonium salt in solution with a water soluble acid or acidic salt having an acidity weaker than hydrochloric acid; b. bringing said solution into contact with a substantially immiscible extractant, said extractant comprising:

1) an oil soluble amine, which amine is substantially water insoluble both in free and in salt form;

2) an oil soluble weak organic acid having a pKa above 3, which acid is substantially water insoluble both in free and in salt form; and

3) a carrier solvent for the amine and organic acid; whereupon HCI selectively transfers to said extractant to form an HCI-carrying extractant and a chloride depleted solution containing the anion of said weak acid and the alkali or ammonium cation c. distilling HCI from said HCI-carrying extractant to form gaseous HCI and HCI depleted extractant.

In preferred embodiments of the present invention said process further comprises: d. recovering the salt of said anion of said weak acid and the alkali or ammonium cation from the chloride depleted solution of step b.

In a preferred embodiment of the present invention phosphoric acid is combined in solution with potassium chloride and there is obtained substantially pure gaseous HCI and potassium phosphate.

Preferably in these embodiments, said extractant is characterized by a pHhn of less than 3.

In especially preferred embodiments the pKa of the organic acid is above 3. Thus it will be realized that for example, according to preferred embodiments of the present invention potassium chloride could be combined with sulfuric acid to produce gaseous HCI as well as to produce the commercially valuable fertilizer potassium sulfate and that potassium chloride could be combined with phosphoric acid to produce HCI as well as to produce potassium phosphate. Similarly, H ₂ SO ₄ and NaCI could be used to produce HCI and Na ₂ SO ₄ .

The following combinations of salts and acids can be preferably used to produce gaseous HCI and desirable salts as set forth below:

1. Combining HaPO ₄ and KCI to produce gaseous HCI and KH ₂ PO ₄ (mono-potassium phosphate), K ₂ HPO ₄ (di-potassium phosphate) or their combination

2. Combining KH ₂ PO ₄ and KCI to produce gaseous HCI and K ₂ HPO ₄ (di-potassium phosphate)

3. Combining H ₃ PO ₄ and NaCI to produce gaseous HCI and NaH ₂ PO ₄ (mono-sodium phosphate), Na ₂ HPO ₄ (di-sodium phosphate) or their combination

4. Combining H ₃ PO ₄ andNH ₄ CI to produce gaseous HCI and NH ₄ H ₂ PO ₄ (mono-ammonium phosphate), (NH ₄ ) ₂ HPO ₄ (di-ammonium phosphate) or their combination

5. Combining NH ₄ H ₂ PO ₄ and KCI to produce gaseous HCI and (NH ₄ )2HPO ₄ (di-ammonium phosphate)

6. Combining H ₂ CO ₃ and KCI or (CO ₂ + H ₂ O) and KCI to produce gaseous HCI and KHCO ₃

7. Combining H ₂ CO ₃ and NaCI or (CO ₂ + H ₂ O) and NaCI to produce gaseous HCI and NaHCO ₃

8. Combining H ₂ CO ₃ and NH ₄ CI or (CO ₂ + H ₂ O) and NH ₄ CI to produce gaseous HCI and NH ₄ HCO ₃

9. Combining Acetic acid and NaCI or acetic acid and KCI to produce gaseous HCI and sodium acetate or potassium acetate.

Concentration of hydrochloric acid by distillation is a well-known technology practiced for many years. Its basic drawback is the high cost of the equipment and the inherent large energy consumption. If various impurities are present in the dilute hydrochloric acid, the concentration by distillation needs to be preceded by some separation step to prevent equipment fouling or contamination of the concentrated hydrochloric acid.

In U.S. Patent No: 4291007 by one of the present inventors, there is described and claimed a solvent extraction process for the separation of a strong mineral acid from other species present in an aqueous solution and the recovery thereof under reversible conditions utilizing an extractant phase that contains an acid-base-couple (hereinafter referred to as an "ABC extractant") which obviates the consumption of chemicals for regeneration, comprising the steps of: a) bringing an aqueous solution containing the mineral acid to be separated into contact with a substantially immiscible extractant phase, said extractant phase comprising:

1) a strong organic acid, which acid is oil-soluble and substantially water-immiscible, in both free and salt forms;

2) an oil-soluble amine, which amine is substantially water- insoluble, in both free and salt forms; and

3) a carrier solvent for said organic acid and said amine, wherein the molar ratio of said organic acid to said amine is between about 0.5:2 and 2:0.5, whereupon said predetermined mineral acid selectively and reversibly transfers to said extractant phase; b) separating said two phases; and c) backwashing said extractant phase with an aqueous system to recover substantially all the mineral acid contained in said extractant phase.

The strong organic acids envisioned for use in the extractant phase of said invention were organic acids which may be defined and characterized as follows: When 1 mol of the acid in a 0.2 molar or higher concentration is contacted with an equivalent amount of 1N NaCI, the pH of the sodium chloride solution decreases to below 3. Especially preferred for use in said invention were strong organic acids selected from the group consisting of aliphatic and aromatic sulfonic acids and alpha-, beta- and gamma-chloro and bromo-substituted carboxylic acids, e.g., hexadecylsulfonic acid, didodecylnaphthalene disulfonic acid, alpha-bromo lauric acid, beta, beta-dichloro decanoic acid and gamma dibromo octanoic acid, etc.

The amines of said invention are preferably primary, secondary and tertiary amines singly or in mixtures and characterized by having at least 10, and preferably at least 14, carbon atoms and at least one hydrophobic group. Such commercially available amines as Primene JM-5, and Primene JM-T (which are primary aliphatic amines in which the nitrogen atom is bonded directly to a tertiary carbon atom) and which commercial amines are sold by Rohm and Haas chemical Co.; Amberlite LA-1 and Amberlite LA-2, which are secondary amines sold by Rohm and Haas; Alamine 336, a tertiary thcaprylyl amine (TCA) and Alamine 304, a tertiary trilaurylamine (TLA), both sold by Cognis., can be used in the processes of said invention, as well as other well-known and available amines, including, e.g., those secondary and tertiary amines listed in U.S. Patent No:3,458,282.

The carrier solvents of said invention can be chosen from a wide range of organic liquids known to persons skilled in the art, which can serve as solvents for said acid-amine active components and which provide for greater ease in handling and extracting control. Said carrier solvents can be unsubstituted or substituted hydrocarbon solvents in which the organic acid and amine are known to be soluble and which are substantially water-insoluble, e.g., kerosene, mineral spirits, naphtha, benzene, xylene, toluene, nitrobenzene, carbon tetrachloride, chloroform, trichloroethylene, etc. Also higher oxygenated compounds such as alcohols, ketones, esters, ethers, etc., that may confer better homogeneity and fluidity and others that are not acids or amines, but which may confer an operationally useful characteristic, can also be included.

In the process of said invention, the essential operating extractant is believed to be the amine, balanced by a substantially equivalent amount of strong organic acid. An excess of acid acts as a modifier of the system, and so does an excess of amine, which obviously will be present as salts of acids present in the system. These modifiers are useful in optimization of the extractant, but are not essential.

Thus, as stated, the molar ratio between the two foregoing active constituents lies between 0.5 to 2 and 2 to 0.5, and preferably between about 0.5 to 1 and 1 to 0.5.

The process as exemplified in said patent was especially useful for use with acids such as nitric acid; however, the process as defined therein wherein the acid is recovered by backwashing is not practical or commercially viable for obtaining concentrated hydrochloric acid from dilute hydrochloric acid.

According to the invention described and claimed in PCT/IL2008/000278, it was surprisingly found that HCI can be distilled out of such an HCI-loaded extractant phase at temperatures below 250° C without noticeable solvent decomposition.

Thus, said PCT specification describes and claims a process for the recovery of HCI from a dilute solution thereof, comprising: a) bringing a dilute aqueous HCI solution into contact with a substantially immiscible extractant, said extractant comprising:

1) an oil soluble amine, which amine is substantially water- insoluble, in both free and salt forms;

2) an oil soluble organic acid, which acid is substantially water- insoluble, in both free and salt forms; and

3) a solvent for the amine and organic acid; whereupon HCI selectively transfers to said extractant to form an HCI-carrying extractant; and b) distilling HCI from said separated HCI-carrying extractant to form gaseous HCI and HCI depleted extractant.

In Israel Patent Application 190,703, there is described and claimed a process for the recovery of HCI from a dilute solution thereof, comprising: a) bringing a dilute aqueous HCI solution into contact with a substantially immiscible extractant, said extractant comprising: 1) an oil soluble amine which amine is substantially water insoluble both in free and in salt form;

2) an oil soluble weak organic acid having a pka above 3 which acid is substantially water insoluble both in free and in salt form; and

3) a solvent for the amine and organic acid; whereupon HCI selectively transfers to said extractant to form an HCI-carrying extractant; and b) treating said HCI-carrying extractant to obtain gaseous HCI. In Israel Patent Application 190,704 there is described and claimed a process for the recovery of HCI from a dilute solution thereof, comprising: a) bringing a dilute aqueous HCI solution into contact with a substantially immiscible extractant, said extractant comprising:

1) an oil soluble amine, which amine is substantially water insoluble both in free and in salt form;

2) an oil soluble organic acid, which acid is substantially water insoluble both in free and in salt form; and

3) a solvent for the amine and organic acid; whereupon HCI selectively transfers to said extractant to form an HCI-carrying extractant; and b) treating said HCI-carrying extractant to obtain a mixture comprising HCI and a hydrocarbon in vapor phase for conveying the HCI from said extractant phase and for obtaining gaseous HCI.

The relevant descriptions and teachings of both of said applications are incorporated herein by reference.

As will be realized, the process of the present invention is based on a modification and improvement of the process described in said PCT specification and in said two later Israeli specifications, in that it utilizes the extraction and distillation steps thereof for the production of HCI gas from readily available chloride salts according to the equation:

MCIaq + HX _aq + EXTRACTANT _org → MX _aq + EXTRACTANT. HCI _org EXTRACTANT. HCIorg → EXTRACTANTorg + HCI _gas The sum of these two stages:

MCIaq + HX _aq → MX _aq + HCI _gas wherein in these formulas, M represents the cation of the product salt and X the anion of that product salt.

As stated hereinbefore with reference to basic U.S. Patent No: 4291007:

(1) "The strong organic acids envisioned for use in the extractant phase of said invention were organic acids which may be defined and characterized as follows: When 1 mol of the acid in a 0.2 molar or higher concentration is contacted with an equivalent amount of 1N NaCI, the pH of the sodium chloride solution decreases to below 3.

(2) Especially preferred for use in said invention were strong organic acids selected from the group consisting of aliphatic and aromatic sulfonic acids and alpha-, beta- and gamma-chloro and bromo-substituted carboxylic acids, e.g., hexadecylsulfonic acid, didodecylnaphthalene disulfonic acid, alpha-bromo lauric acid, beta, beta-dichloro decanoic acid and gamma dibromo octanoic acid, etc."

In contradistinction to the teachings of said prior art patent, and the expectations from the above rules, it was surprisingly observed that weak acids, having a pKa above 3 and even very weak acids such as aliphatic carboxylic acids, can provide for effective stripping of part or the whole of HCI carried in an extractant of which the ABC extractant couples a weak acid with an amine.

Stated differently, weak acids such as carboxylic acids were not considered of interest in the practice of the invention as described in U.S. Patent No:4291007 or even as described in more recent application PCT/IL2008/000278, as constituents of ABC extractants or as constituents of extractants for HCI. Such extractants, when equilibrated with an aqueous HCI phase provide for powerful distribution in favor of the extractant, which distribution is only marginally affected by temperature. Stripping i.e. distribution of HCI at higher temperatures in favor of the gas phase that generally parallels the distribution in favor of the aqueous phase was naturally expected to be ineffective in case of weak acids as component of ABC extractants. Surprisingly it has now been found that this parallelism breaks in the case of carboxylic acids and similar weak acids having a pKa above 3 and that effective stripping obtains. Furthermore, the effective extraction of HCI from an aqueous phase, which results in high loading of the extractant, provides for an economically beneficial reduction of the amount of extractant required per unit of HCI.

Thus in contradistinction to the definition of strong organic acids presented in U.S. Patent No: 4291007, the weak organic acids envisioned for use in the extractant phase of the present invention are organic acids which may be defined and characterized as follows: when 1 mol of the acid in a 0.2 molar or higher concentration in an organic solvent is contacted with an equivalent amount of NaCI in 1 N aqueous solution, the pH of the sodium chloride solution is greater than about 4 more preferably greater than about 5.

Thus a weak acids according to the present invention, e.g. carboxylic acids such as lauric acid, when tested according to the above definition, reduces pH to about 6.

With regard to the pKa values of the acids mentioned in U.S. Patent No: 4291007 as opposed to those envisioned for use in the present invention, said patent refers to

> "aromatic sulfonic acids" e.g. Naphtalenesulfonic acid the pKa is 0.17; and

> "alpha-, beta- and gamma-chloro and bromo-substituted carboxylic acids". The following table sets forth the pKa values of these acids as opposed to those of the present invention: Table 2

Thus the weak acids measure 2 or more pKa units higher than the acids previously described and claimed, which corresponds to two orders of magnitude lower acidity.

Thus it was surprisingly observed that weak acids, even very weak acids such as aliphatic carboxylic acids can provide for effective stripping of part or the whole of HCI carried in an extractant of which the ABC extractant couples a weak acid with an amine.

It is to be noted that the term "carrier solvent" as used herein is intended to denote the solvent component of the extractant used in the present invention.

The amines of the present invention are preferably primary, secondary and tertiary amines singly or in mixtures and characterized by having at least 10, preferably at least 14, carbon atoms and at least one hydrophobic group. Such commercially available amines as Primene JM-5, and Primene JM-T (which are primary aliphatic amines in which the nitrogen atom is bonded directly to a tertiary carbon atom) sold by Rohm and Haas Chemical Co.; Amberlite LA-1 and Amberlite LA-2, which are secondary amines sold by Rohm and Haas; Alamine 336, a tertiary tricaprylyl amine (TCA) and Alamine 304, a tertiary trilaurylamine (TLA), both sold by Cognis, Inc., can be used in the processes of the present invention, as well as other well known and available amines including, e.g., those secondary and tertiary amines listed in U.S. Patent No:3,458,282. According to a preferred embodiment, tris(2-ethyl hexyl) amine is used as an amine of the ABC extractant of the present invention.

The term "pH half neutralization (pHhn)," as used herein refers to the pH of an aqueous solution, which is in equilibrium with the extractant carrying HCI at an HCI-to-amine molar/molar ratio of 1 :2.

According to other aspects of the invention, carbohydrates are formed by hydrolysis of polysaccharides such as cellulose and hemicellulose as found in lignocellulosic material, such as wood, sugarcane bagasse, straw and switch grass. Hydrolysis is conducted by contact with HCI solution. HCI is not consumed in the process, but rather acts as a catalyst. The product of hydrolysis, also referred to as hydrolyzate is an aqueous solution comprising carbohydrates and HCI. According to the process of the present invention, the hydrolyzate is treated for the separation of carbohydrates from HCI. The separated carbohydrates could then be used for various applications, e.g. as fermentation feedstock, while the separated acid is preferably reused for hydrolysis.

Preferably, the acid used for hydrolysis is relatively pure in the sense that it is not a mixture of two acids. Working with such mixture, e.g. a mixture of HCI and H2SO4, would increase the cost of the production of the carbohydrates and add complications. Thus, recovery and recycle of such acid mixture is more expensive, e.g. not enabling the use of relatively low cost HCI evaporation. It is also difficult to maintain the ratio between the acids through repeated use of the acid mixture (the acid is a catalyst in hydrolysis and is not consumed in the hydrolysis process), which could changes the conditions as the process continues and complicates control and optimization of process conditions. Having sulfate and phosphate ions in the hydrolyzing acid may also lead to the formation of water-immiscible salts, e.g. gypsum, which further complicates acid recovery and contaminate the product carbohydrate. Thus, hydrolysis with HCI, that is essentially free of sulfate and phosphate anions and recovery of such pure HCI for further use, is of high importance.

The recovered hydrochloric acid is reused for the hydrolysis of polysaccharides to carbohydrates. Various methods are known for the recovery of HCI from aqueous solutions and are also applicable for its recovery from the hydrolyzate formed on the hydrolysis of polysaccharides. In case the acid concentration in the hydrolyzate is high enough, part of the acid is recovered by distillation. Yet, HCI and water have an azeotrope at about 22%. Recovery of all the HCI by distillation requires essentially drying the carbohydrates in the hydrolyzate and relatively high temperatures at which those carbohydrates start to degrade.

Solvent extraction was found to provide efficient separation of the non- distilled HCI. The extractant used needs to be selected so that the acid is extracted efficiently and selectively, i.e. with no carbohydrates and no other acids. Furthermore, the extracted acid needs to be recovered from the HCI- containing extractant in an acid form at a concentration high enough to enable reformation of the hydrolyzing acid solution at the required concentration, which according to a preferred embodiment is quite high, e.g., greater than 37%wt., andmore preferably greater than 40%wt.

HCI recovery yield according to the process of the preset invention is high, preferably greater than 95%, and more preferably greater than 97%. Yet, some HCI loss could not be avoided and acid makeup is required. As indicated, that make up should be of pure HCI, rather than a mixture of HCI and another acid. There is the possibility of purchasing an HCI solution for that makeup. According to the process of the present invention, the makeup acid is formed by reacting a chloride salt (MCI) and another acid (HX), which acid is weaker and or more hydrophilic than HCI. Acidic salts of such acids are also suitable. Thus, according to an embodiment of the invention, such MCI is combined with such HX or acidic salt thereof to form an aqueous solution containing chloride anions and X anions, protons and the cations (M) of MCI. The formed solution is contacted with an extractant that selectively extracts HCI from the mixture to form HCI-carrying extractant and a chloride depleted aqueous solution. Those are separated and the aqueous solution is preferably treated for the recovery of MX, as explained above. The separated HCI-carrying extractant is then treated for the recovery of HCI therefrom, forming an HCI solution that could be reused in hydrolysis.

As indicated, the recovered HCI for reuse in hydrolysis should be substantially pure as hereinafter defined, especially low in phosphate and sulfate, so that extraction from the aqueous solution formed on the combination of MCI and HX will be selective, preferably extracting very little of HX along with HCI. The recovered pure HCI is reused in the hydrolysis of carbohydrate to form a hydrolyzate and that step is followed by HCI recovery of HCI from the hydrolyzate.

Thus in an aspect of the present invention, there is also provided a process for the production of carbohydrates comprising: a. combining an alkali or ammonium salt in solution with a water soluble acid or acidic salt having an acidity weaker than hydrochloric acid; b. bringing said solution into contact with a substantially immiscible extractant, said extractant comprising: 1) an oil soluble amine, which amine is substantially water insoluble both in free and in salt form;

2) an oil soluble weak organic acid which acid is substantially water insoluble both in free and in salt form; and

3) a carrier solvent for the amine and organic acid; whereupon HCI selectively transfers to said extractant to form an HCI-carrying extractant and a chloride depleted solution containing the anion of said weak acid and the alkali or ammonium cation c. separating said HCI-carrying extractant from said chloride-depleted aqueous solution; d. recovering high-purity HCI from said HCI-carrying extractant to form high-purity HCI stream and HCI-depleted extractant; e. hydrolyzing a lignocellulosic material with said high-purity HCI stream to form a carbohydrates-comprising and HCI-comprising hydrolyzate; and f. separating HCI from carbohydrates in said hydrolyzate. According to yet further aspect of the invention, pure HCI is used for the hydrolysis of polysaccharides to form HCI-comprising hydrolyzate and HCI is recovered from that hydrolyzate by means of solvent extraction. A first extractant is combined with the hydrolyzate whereupon pure HCI transfers into it to form HCI-depleted hydrolyzate and a first HCI-carrying extractant. Those are separated to form a separated HCI-depleted hydrolyzate comprising the formed carbohydrates and a separated first HCI-comprising extractant. The latter is then treated to recover pure HCI therefrom and to regenerate the first extractant. The recovered pure HCI is reused to hydrolyze polysaccharides. According to that aspect there is some HCI loss and HCI makeup is required. Such makeup HCI is formed by means of combing MCI and HX as above and separating HCI from that aqueous solution by extraction. Said separating is conducted by combining the aqueous solution with a second extractant whereupon pure HCI transfers selectively to the extractant to form chloride depleted aqueous solution and a second HCI-carrying extractant. The aqueous solution is then separated from the second HCI-carrying extractant and the latter is treated to recover pure HCI therefrom and to regenerate the second extractant. The recovered pure HCI is reused to hydrolyze polysaccharides.

According to said aspect, the first extractant used for the recovery of HCI from the hydrolyzate has a similar composition to the second extractant used for the production of the extractant makeup. Preferably the two extractants have the exact same composition. According to that embodiment, the first HCI-carrying extractant has a composition similar to that of the second HCI-carrying extractant, particularly in terms of the extractant components and the weight/weight ratios between the them. There could however be differences in HCI concentrations there and in the content of some other components, e.g. the concentration of co- extracted water. According to a further preferred embodiment, rather than separately treating the first and second HCI-carrying extractants for HCI- recovery, the two are combined to form a combined extract and that combined extract is treated for the recovery of HCI and for the regeneration of an extractant. The recovered HCI (comprising the HCI extracted from the hydrolyzate and the HCI recovered in the makeup production step) is used for hydrolysis of polysaccharides to form another hydrolyzate.

The inventors have found that ABC extractants as described above are efficient and selective in the extraction of pure HCI from the hydrolyzate of polysaccharides and that that extractant enables the recovery of the extracted HCI at a purity and concentration sufficiently high to be reused for hydrolysis of polysaccharides. The inventors have surprisingly found that the ABC extractant is also efficient in the separation of HCI from the aqueous solution formed for the production of HCI makeup from the mixture formed by combining MCI and HX. Furthermore, that extractant shows high selectivity in extraction from that aqueous solution, so that HCI is extracted with essentially no HX. Therefore, the HCI formed on recovery from that extractant is concentrated enough and pure enough for use in the hydrolysis of polysaccharides. It was further found that the same composition of the ABC extractant can be used for both the recovery from the hydrolyzate and the HCI makeup operation. The surprising finding that a given extractant combines efficient, reversible and selective recovery from the carbohydrates-comprising polysaccharides hydrolyzate and efficient, reversible and selective HCI recovery of HCI from the MX-comprising makeup production solution enables an economically attractive process of carbohydrates production from polysaccharides by hydrolysis with a pure HCI solution, recovery of the HCI for reuse, production of HCI makeup and all that with the same extractant and a single HCI recovery from the HCI-carrying extract.

Thus, in an aspect of the present invention there is provided a process for the production of carbohydrates comprising: a. hydrolyzing lignocellulosic material with high-purity HCI stream to form a carbohydrates-comprising and HCI-comprising hydrolyzate b. bringing said hydrolyzate into contact with a substantially immiscible extractant, said extractant comprising:

1) an oil soluble amine, which amine is substantially water insoluble both in free and in salt form;

2) an oil soluble weak organic acid which acid is substantially water insoluble both in free and in salt form; and

3) a carrier solvent for the amine and organic acid; whereupon HCI selectively transfers to said extractant to form a first HCI-carrying extractant and an HCI-depleted hydrolyzate c. separating said first HCI-carrying extractant from said hydrolyzate d. combining an alkali or ammonium salt in solution with a water soluble acid or acidic salt having an acidity weaker than hydrochloric acid; e. bringing said solution into contact with said extractant whereupon HCI selectively transfers to said extractant to form a second HCI- carrying extractant; and a chloride-depleted solution containing the anion of said weak acid and the alkali or ammonium cation f. separating said second HCI-carrying extractant from said chloride- depleted aqueous solution; g. combining at least a portion of said first HCI-carrying extractant and a portion of said second HCI-carrying extractant to form a combined extract; h. separating high-purity HCI from said combined extract to form separated high-purity HCI and a regenerated extractant; and i. using said high-purity HCI for hydrolyzing lignocellulosic material.

According to an embodiment of the invention, said regenerated extractant is then preferably divided into two portions. The first of those two portions is used for the recovery and separation of HCI from that other hydrolyzate and the second portion is used for generation of additional HCI makeup. According to an embodiment, the first portion is greater than the second portion, e.g. greater by 3 to 20 folds.

As used herein, the term pure HCI refers to both HCI gas and HCI aqueous solutions. The term "pure" here means according to various embodiments, purity greater than 90%, preferably greater than 95%, more preferably greater than 98%, and most preferably greater than 99% of the total acid in that stream in molar ratio. According to another embodiment, pure means HCI to (H ₂ SO ₄ + H ₃ PO ₄ ) molar ratio of greater than 10, preferably greater than 20, more preferably greater than 40, and most preferably greater than 50.

Any method of acid recovery from the first HCI-carrying extractant, second HCI-carrying extractant and extract is suitable. According to a preferred embodiment, recovery uses at least one of distillation to form a gaseous HCI stream and multiple-stage counter-current back extraction with water or with an aqueous solution to form an aqueous solution of HCI (also referred to as back- extract). According to a preferred embodiment, recovery uses multiple-stage counter-current back extraction with water wherein the number of stages is at least 3, preferably at least 4, more preferably at least 5. According to another preferred embodiment, the HCI concentration in the back-extract is at least 15%wt, preferably at least 20%wt, and more preferably at least 22%wt. According to still another embodiment, recovery uses counter-current back- extraction and said counter-current back-extraction is conducted at a temperature of at least 20 °C greater than the temperature of said combining with the hydrolyzate. While the invention will now be described in connection with certain preferred embodiments in the following examples so that aspects thereof may be more fully understood and appreciated, it is not intended to limit the invention to these particular embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the scope of the invention as defined by the appended claims. Thus, the following examples which include preferred embodiments will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purposes of illustrative discussion of preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of formulation procedures as well as of the principles and conceptual aspects of the invention. EXAMPLE 1

52grs of commercial 98% phosphoric acid were dissolved in 200ml of water. 38grs of fertilizer grade KCI (potash) were added. They dissolved with the help of a little stirring. The resulting, slightly clouded solution was contacted three successive times with 500grs, each time, of an extractant of a composition by weight: 14.6% n-octanoic acid; 35.3% tris(2-ethylhehyl)amine and 50.1% carrier solvent consisting of a hydrocarbons distillate boiling in the range 180/210 ⁰ C at atmospheric pressure - and these successive portions were combined. The concentration of chloride in the extracted aqueous solution was below 0.01% indicating a practically complete conversion of the potassium chloride to potassium phosphate. The combined extractant was boiled under vacuum at 160°C whereby HCI distilled and was collected in 0.1N NaOH for titration. 16.2grs of HCI were titrated - practically corresponding to complete conversion. EXAMPLE 2

HCI was mixed with sulfuric acid solutions to form aqueous solutions containing protons and ions of potassium chloride and sulfate. These solutions were contacted in vials with the extractant of Example 1. The vials were shaken at RT. Samples were taken to analysis and the results are presented in the following table. Table 3

The results show the very high selectivity of the extractant towards HCI when compared with extraction of sulfuric acid.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and that the present invention may be embodied in other specific forms without departing from the essential attributes thereof, and it is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive, reference being made to the appended claims, rather than to the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.