AU606311B2

AU606311B2 - Process for the preparation of very high purity sorbitol syrups

Info

Publication number: AU606311B2
Application number: AU44412/85A
Authority: AU
Inventors: Francis Devos; Michel Huchette
Original assignee: Roquette Freres SA
Current assignee: Roquette Freres SA
Priority date: 1984-06-29
Filing date: 1985-06-28
Publication date: 1991-02-07
Anticipated expiration: 2005-06-28
Also published as: DK296285A; FI85851B; AU4441285A; BR8503133A; FI852572A0; JPS6130543A; FI852572L; FR2566801A1; CN85105753A; DK296285D0; ATE36696T1; CA1311503C; FR2566801B1; EP0168315A1; FI85851C; EP0168315B1; DE3564563D1; KR860000311A

Abstract

1. Process for the preparation of very high purity sorbitol syrup, characterized by the fact that a starting material of which a first part is constituted by a starch hydrolysate, is subjected to a process comprising in combination - a catalytic hydrogenation step of the starting material, - a chromatographic separation step of the starting material which has undergone hydrogenation into a first fraction containing very pure sorbitol which is recovered and into a second fraction containing, besides sorbitol, non-hydrogenated sugars as well as hydrogenated di- and polysaccharides, - an acid hydrolysis step of the abovesaid second fraction, which provides a partially hydrogenated starch hydrolysate which is recirculated and which constitutes a second part of the starting material subjected to the hydrogenation step.

Description

zigmxture of Applicant (s) or Se al of Company andi S ignatures of Its Officers as Prescribed by its Articles of Association.

Paent tt~r~y 0 6C.43

I

Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: 'This do ,ineit conttins the Liii' ;W cisi correct for IPuldted Art: 4454 I S Name of Applicant: 0 Address of Applicant 4 ceia Inventor: Address for Service: ROQUETTE FRERES 62136 Lestrem, France FRANCIS DEVOS and MICHEL HUCHETTE EDWD. WATERS SONS, 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

Complete Specification for the invention entitled: PROCESS FOR THE PREPARATION OF VERY HIGH PURITY SORBITOL SYRUP S The following statement is a full description of this invention, including the best method of performing it known to: us 4. The basic application referred to in paragraph 2 of this Declaration the first application made in a Convention country in respect of the invention the subject of the application.

DECLARED trem.rance day of un 1- PROCESS FOR THE PREPARATION OF VERY HIGH PURITY SORBITOL SYRUPS The invention relates to a process for the preparation of very high purity sorbitol syrups.

At the present time, very high purity sorbitol syrups are obtained by hydrogenation of dextrose syrups prepared by dissolving crystalline dextrose in water.

The richness of sorbitol syrups so obtained which is sufficient, however rarely exceeds 98/ after purification.

The reason therefor is that in addition to traces of hydrogenated polyholosides originating in the raw material and traces of reducing substances which have escaped the hydrogenation, there are formed during the hydrogenation, isomers of sorbitol, namely particularly mannitol.

The presence of this group of products results in certain drawbacks in the matter of crystallisation operations of SI 20 the sorbitol from these syrups and has consequences on the characteristics of the crystalline soritol obtained, particularly from the point of view of its crystallinity.

In addition, the yield of the operation is not entirely satisfactory since, to obtain sorbitol syrups having this richness, which in any case rarely exceeds 98%, it is necessary to satisfy oneself with limited yields at Sthe level of the preceding step of preparation of the crystalline dextrose, which is used for the preparation of the subsequently hydrogenated dextrose syrup, and which is obtained by crystallisation in two or three crops from starch hydrolysates with a glucose content of the order of 94 to 967 by weight in fact, said yields of dextrose are generally limited to about 75 to 77% in two crops and to about 80 to 88/ after a third crop and the crystallisation mother liquors or hydrols have a sometimes difficult sale in commerce by reason of their color and their content of h? 9 to967 byweiht ;in act sad yeld of extoseare'!. .I impurities.

It has indeed already been proposed to suppress the intermediate crystallisation step of the dext::ose by subjecting directly, within the same reaction vessel, a cheaper raw material, namely a starch hydrolysate, not only to reducing conditions, but also to hydrolysis by means of a strong acid, which permits also to make use of the conversion known in itself, of polyholosides such as maltitol or isomaltitol into equimolecular amounts of sorbitol and of glucose under the action of the strong acid.

It is possible to mention in this respect French Patent N" 1 263 298 which proposes the use, as a catalyst, of reduced nickel on a support constituted of infusorial earth and according to which there is carried out in one and the same reaction vessel, in substantially neutral solution and at a moderately high temperature, a reduction of the major part of the reducing sugars, after which a strong inorganic acid such as phosphoric acid is added, in a proportion of 0.05 to 1.0. by weight on the basis of the saccharides initially employed, the mixture constituted by the thus acidified solution and the catalyst being subjected to higher pressure and temperature, by means of which the hydrolysis of the hydrogenated polyholosides present in the hydrolysate and the hydrogenation of the sugars then appearing are effected simultaneously.

Within the same order of ideas, but 15 years later, Belgian Patent N' 837 201 described the simultaneous hydrogenation-hydrolysis-hydrogenation of starch hydrolysates with use of a ruthenium catalyst supported on zeolite of type Y; the hydrogenation reaction is effected in two steps, the first being conducted at a temperature comprised between 100 and 175'C and the second at a temperature of about 170 to 200'C. The pH conditions in which the consecutive phases of the hydrogenation take place are specified, the pH of the product of the reaction having to It rr I I Ia I -i i: -cc~ i

I

L

i i p.' 3 be comprised between 3.5 and 4.

The drawbacks of these processes reside not only in the rapid deactivation of the catalysts and in the denaturation of the structure of the zeolites, but also in the fact that the syrups so obtained include numerous impurities.

Thus, there occur partial anhydrysation reaction and isomerisation of the polyols, the hydrolysis of the hydrogenated polyholoside fraction is incomplete and manifested by a high value of "total sugars", -the proportions of "hexitans", of mannitol, of "total non-sugar impurities" are large, the content of true sorbitol being finally at the most equal to 947, which is, for example, very insufficient for the preparation of a crystalline sorbitol of suitable quality.

Another process suitable for the preparation of St sorbitol syrup without passage through the crystallisation of the dextrose is that described in French Patent N' 2 052 202 filed by the Assignee. According to this process, in which recourse is also had, as starting material, to a starch hydrolysate which is hydrogenated, a fractionation of the hydrogenated starch hydrolysate is carried out by passage over a resin or a cationic molecular sieve, preferably in calcium form, which permits the isolation of 7. a fraction containing sorbitol of richness greater than 997..

This technique therefore leads to a sorbitol of 30 very high purity, but it proves however to be unsatisfactory in practice. It results, in fact, in a very partial yield of sorbitol, strictly dependant on the true dextrose content of the starting starch hydrolysate, the latter having for this reason to be as high as possible.

It follows that a priori none of the known processes permits at the same time the manufacture of sorbitol S4 syrup of high purity, suitable particularly for the preparation of crystalline sorbitol, and an easy access to high yield whose influence on the cost price of the final product is readily seen.

It is to this problem that the Applicants have had the merit of proposing a particularly effective solution, according to which a raw material of which a first part is constituted by a starch hydrolysate, is subjected to a process comprising in combination a catalytic hydrogenation step of the raw material, a step of chromatographic separation of the raw material which has undergone hydrogenation into a first i fraction containing very pure sorbitol and which is recovered and into a second fraction containing, besides sorbitol, non-hydrogenated sugars as well as hydrogenated diand polysaccharides, an acid hydrolysis step of the abovesaid second fraction, which provides a partially hydrogenated starch n 20 hydrolysate which is recycled and which constitutes a second part of the raw material subjected to the hydrogenation step.

m s The process thus defined may be carried out by Smeans of the installation shown diagramatically in Figure 1 and which comprises a vessel 201 within which the catalytic hydrogenation step is carried out a chromatographic separation installation 202 and a reaction vessel 203 within which the hydroly- S, sis step is carried out.

The vessel 201 is supplied with raw material through a pipe 204 formed by the junction at 205 of a pipe 204a bringing in the starch hydrolysate from a tank (not shown) ard a pipe 204b connected to the outlet of the vessel 203 and introducing the partially hydrogenated

I

hydrolysate.

The outlet of the vessel 201 is connected to the inlet of the vessel 202 through a pipe 207.

From the outlet of the vessel 202, are conducted the first fraction containing very pure sorbitol through a pipe 208 to a storage tank (not shown) and -the second fraction containing sorbitol, nonhydrogenated sugars as well as hydrogenated di- and polysaccharides through a pipe 209 to the inlet of the vessel 203.

The means proper to ensure the circulation of the various syrups within the installation are not shown.

The starch hydrolysate which is part of the constitution of the raw material has, preferably, a true dextrose content comprised between 65 and 977 and, more preferably still, between 70 and 95%. Particularly advantageous starch hydrolysates are constituted by hydrols of the first and of the second crop obtained in the crystalt t r lisation of the dextrose.

t 20 In the foregoing and in the following, the percentages indicated are understood, except when stated to the contrary, with respect to the dry matter of the syrups.

The catalytic hydrogenation step is carried out in t manner known in itself, particularly on ruthenium or Raney 25 .nickel catalysts. Preferably, it is carried out on a Raney nickel catalyst, at a hydrogen pressure comprised between 70 kg/cm 2 and at a temperature.of about 100 to 150'C.

The chromatographic separation step can be effect- S ,ed, in manner known in itself, discontinously or continuously (simulated mobile bed), on strongly acid absorbants of the cationic resin type, charged with alkaline or alkaline earth ions or of the zeolite type, charged with ammonium, sodium, potassium calcium, strontium, or barium ions.

Examples of such chromotographic separation processes are described in patents US 3 044 904, US 3 416 961, •i 6 US 3 692 582, FR 2 391 754, FR 2 099 336, US 2 985 589, US 4 024 331, US 4 226 977, US 4 293 346, US 4 157 267, US 4 182 633, US 4 332 633, US 4 405 445, US4 412 866, and US 4 442 881.

In a preferred embodiment, the chromatographic separation step is carried out by employing the process and the installation disclosed in US Patent N° 4 442 881 and its corresponding French Application N° 79 10563 which is in the name of the Applicants Company.

Whatever the chromatographic separation process adopted, recourse is had, preferably, as adsorbant, to a strong cationic resin placed in the calcium form and having a proportion of divinyl-benzene from about 4 to about 107.

Preferably, the acid hydrolysis step of the abovesaid second fraction is carried out on a fixed acid catalyst and it is conducted so that more than 40% by weight of the hydrogenated disaccharides and polysaccharides present are hydrolysed.

20 It is possible to use, to do this, any type of reaction vessel and any reagent or acid catalysts capable of ensuring the hydrolysis of hydrogenated disaccharides and polysaccharides.

Preferably, said hydrolysis is carried out conti- 25 nuously by passing the syrup containing the polyols to be hydrolysed over a fixed bed comprising acid catalysts of the alumino-silicate, silica, alumina or cationic resin type, at a temperature and for a time sufficient to achieve the above indicated desired result.

Advantageously, the hydrolysis is conducted on strong cationic resins in the acid form, at a temperature comprised between 50 and 120"C, the passage flow rate over the acid catalyst bed being regulated so as to obtain a hydrolysis ratio of the hydrogenated di- and polysaccharides at least equal to 607 and, preferably, at least equal to 7 I'The content of dry matter of the above-said second fraction which is subjected to the hydrolysis step and which is recycled is generally comprised between 1.57 and 307 and, preferably, between 2.5 and 207.

The process thus described permits sorbitol syrups to be obtained having a richness in sorbitol greater than 987, and even greater than 997, which are essentially characterised by a minimal content of reducing sugars. These -yrups, which have at the outlet from the vessel 202, a content of dry matter comprised between 207 and 50% and, preferably between 257 and 407, can then be evaporated to the dry matter content for marketing or be evaporated more completely for the production of crystalline sorbitol.

The invention will be still better understood by means of the examples which follow and of the illustrative figures appended hereto, said examples relating to preferred embodiments of the invention.

EXAMPLE 1 Preparation of pure sorbitol from a starch hydrolysate tt 20 prepared by a double enzymatic hydrolysis with a-amylase i and amyloglucosidase and having a richness in true dextrose equal to 94.5%, its composition being Dry Matter (DM) :74.0 7 Dextrose 94.5 7 DP 2 4. 0 DP 3 DP 3 it being understood that "DP" means the degree of polymerisation of a given constituent of the hydrolysate.

30 a) Hydrogenation step The above-said hydrolysate, after purification on ion exchanle resins and on active carbon, is hydrogenated on Raney nickel, at a hydrogen pressure of 45 kg/cm 2 and at a temperature of 125"C.

It shows, after conventional purification, the following composition DP 2 1.3 DP 2 5.6 Glycerin 0.2 Mannitol Other hexitols 0.4 Sorbitol 93.5 Reducing sugars 0.08 Total sugars 2.74 determined by the analytical method disclosed in the FOOD CHEMICAL CODEX, 2nd Edition, page 791.

b) Chromatographic separation step The above-said hydrogenated starch hydrolysate is then sent to a continuous chromatographic separation installation of which the details of constitution and of operation are those disclosed in US Patent N' 4 442 881 and in the corresponding French Patent N° 79 10563, which are incorporated by reference, the said details only being taken up again here to the extent that understanding of the present description requires it.

It includes, as shown in Figure 2 of the American patent (taken up again here as Figur 2 for the detailed explanation of which reference is made to the American patent), eight columns or stages C to C of 200 liters each, lined with adsorbant of the strong cationic resin 25 type in the calcium form and of fine granulometry (0.2 to 0.4 microns).

By adjustment of the electrovalves, there are formed a desorption zone I of two stages, an adsorption zone II of four stages and an enrichment zone III for the hydrogenated polyholosides of two stages.

A closing device maintains in the configuration adopted the total fluid-tightness between the zone III, enrichment zone at the end of which are recovered the hydrogenated polyholosides and the zone I or desorption zone of the sorbitol, at the head of which zone the desorption water is introduced.

;1 t 9 This closing device ensures the direction of passage of the liquid phase over the selective adsorbant and avoids especially contamination of the pure sorbitol by traces of polyholosides, whose migration speed within the resin is largely greater than that of the hydrogenated di- or triholosides.

I A timer (not shown) adjusted to 23 minutes Sseconds ensures for the flow rates indicated below a water I supply sufficient to carry out de-sugaring of the first stage of the desorption zone, and for the supply of a volume of hydrogenated starch hydrolysate or HSH compatible with the volume of adsorbant and its capacity of absorption, so as to obtain an extraction ratio of the hydrogenated polyholosides greater than 997 and an extraction ratio of the sorbitol at least equal to 907 of the sorbitol present in the supplied hydrogenated hydrolysate.

These proportions are kept constant by adjusting the flow rate of the extraction pump (not shown) of the adsorbed sorbitol. The outflow of the polyholoside frac- 20 tion is effected at atmospheric pressure and its flow rate, constant, results from the difference between the supply flow rates and the extraction flow rate.

The hydrogenated starch hydrolysate which is introduced into the installation at the head of the adsorption stage, has a dry matter content equal to 64.57.

The temperature inside the separation columns is kept at about In the schematic diagram of Figure 3 is shown the installation of Figure 2 diagramatically at 202 (the same references denoting the same elements for the common parts as in Figure The chromatography installation includes, J in addition to the constituent elements already shown in Figure 1,a pipe 210 for recirculating excess water and a pipe 211, through which are extracted from the circuit the polyholoside fractions of DP 4 extracted at a very low

DM.

LI s F Supply of the installation with water is effected by a pipe 212.

The arrows borne on the pipes indicate the direction of flow.

The unit operates as follows: the hydrogenated starch hydrolysate or HSH intended for chromatographic fractionation is led through the pipe 207 at a flow rate of 120 1/hour and has a dry matter content of 64.5%, the water is introduced through pipe 212 with a flow rate of 330 I/hour, the pure sorbitol is recovered through the pipe 208 with a flow rate of 240 1/hour, its content of dry matter I being 34.157, the total amount of liquids extracted from the installation 202 is extracted with a total flow rate of 386 1/hour, comprising successively, .a fraction of excess water of 176 1/hour which is recirculated through the pipe 210 to the head 20 of the installation, a polyholoside fraction removed through the pipe 211, whose flow rate is 114 1/hour and the DM about 1%, Sa polyholoside fraction led through the pipe 209 to the hydrolysis installation with a flow rate of 96 1/hour, the contert of DM being Analyses of the outflows of sorbitol and of hydrogenated polyholosides are presented in Tables I and II.

I 7 7 l TABLE I OF THE SORBITOL ANALYS IS A 4 t Times Brix DP 2 Glycerin Mannitol Sorbitol (minutes 7.7Z 0 56.5 0.4 0.3 1.0 98.3 3 47.5 0.3 0.3 0.9 98.5 6 41.5 0.3 0.3 0.8 98.6 12 27.0 0.2 0.2 0.5 99.1 21.5 0.2 0.1 0.5 99.2 18 16.0 0.1 0.4 99.5 21 1 2 .5 0 0.1 0 .3 99. 6 23'50" 10.0 0.3 99.7 From examination of Table I, it is seen that sorbitol has been extracted for 23 minutes 50 seconds with an average purity higher than 987. and an average content of dry matter of 34.157.

The value of the "brix" gives the approximate percentage a-f dry matter it is determined by the refractive index.

20 TABLE II ANALYSIS OF THE POLYHOLOSIDES OUTFLOW Times Brix Rotatory OP 3 OP 3 OP 2 Sorbitol (minutes) power Z 7 7 7 0 0- 2- 4- 6- 8 12 +0 .166 14 0.7 +0.629 16 1.5 +1.038 35.9 30.9 22.6 10.6 18 2 +1.079 24.0 29.5 33.7 12.8 2.5 +2.209 21.0 26.0 43.7 9.3 22 3.4 +2.807 16.1 21.2 53.4 9.3 23'50" 4.0 +2.604 13.5 19.0 57.0 10.5

U

C,

hydrolysate which is recirculated and which constitutes a second part of the raw material subjected to the hydrogenation step.

/2 4 N, Ai i;

I.

The specific rotatary power (a)D is deduced from the angle of rotation read on a polarimeter.

Detailed analysis of the results collected in Table II and of the indications provided above with respect to Figure 3, as regards the hydrogenated polyholosides, shows in addition that: during the first 11 minutes, that is to say an equivalent of 176 1/h, the polyholosides outflow has been recyclable for the de-sugaring of the following stage, from minute 11 to minute 18, the extracted fraction, containing the major portion of the hydrogenated polyholosides of DP greater than or equal to 4 was eliminated from the system, that is to say 114 1/h with 17 of dry matter, then, from minute 18 to the moment corresponding to 23 minutes 50 seconds, the polyol fraction was recovered for the hydrolysis step, that is to say 96 liters with a dry matter of 3.6..

The overall balance, which appears on examining the 20 diagram of Figure 3 and Tables I and II, is summarised as indicated below.

The chromatographic separation system was supplied as follows: rice

I

~trr ctcr r r t r Hydrogenated starch hydrolysate Flow rate 120 1/h Density 1.269 7. dry matter 64.5 Flow rate by weight 98.22 kg/h There was drawn from this system Higher polyols Sorbitol discarded Flow rate 240 1/h 114 1/h Density 1.138 1.0 Z dry matter 34.15 1.0 Flow rate by weight 93.27 kg/h 1.14 kg/h Water 330 1/h

I'

Polyols recovered 96 1/h 1 .02 3.6 3.53 kg/h i -j 13 These results correspond to an extraction ratio of sorbitol present in the hydrogenated starch hydrolysate higher than 997..

c) Continuous hydrolysis step of the recovered polyols The fraction of polyols recovered is then led through the pipe 209 into a hydrolysis vessel 203 consti- Stuted by a column identical with that equiping the chromatographic separation installation illustrated by Figure 2.

This column is filled with a cationic resin of very fine granulometry (0.1 0.2 microns) placed in the H form.

The feed flow rate was adjusted to about 90 liters/ hour.

4* The hydrolysis vessel was kept at a temperature of about 110 C.

So Under these conditions, the hydrolysed syrup flows o 20 2 out from the vessel 203 with a proportion of reducing 'r sugars equal to 17.0 grams/liter glucose equivalent, which is equivalent to a hydrolysis ratio of 91.4X, since an assay test of the reducing sugars carried out after complete hydrolysis (effected after two hours under reflux in the 5 presence of normal H2SO 4 showed a glucose equivalent of l e 18.6 grams per liter.

c The chromatographic analyses of the syrup at the I inlet and at the outlet from the hydrolysis vessel 203 t c Ci gave the results indicated below.

The composition of the syrup led through the pipe 209 to the vessel 203 was as follows: Sorbitol 9 L E t Mannitol" 0.8 DP 2 DP 3 15.2 DP 3 i 1.

14 and that of the syrup emerging from the vessel 203 through the pipe 204b, determined on three samplings, as follows: Sorbitol 41 42 39.6 annitol 2.3 2.5 2.8 Glucose 46.4 52 45.6.

d) Recirculation through pipe 204b of the syrup thus hvdrnlvsed to the hvdrpingsntin vas s ~~thll hvrolucspr tn +hR hv/rrnnnatinn wespeco i ii

II

ii

I

I t I ,I I I LI 201, which corresponds to a dilution of the starting starch hvdrolvsate.

In this case, through the pipe 204 is conducted a starting material constituted by starch hydrolysate not yet treated and hydrolysed syrup emerging from the vessel 203.

In Figure 4, are shown diagramatically the principal elements of the corresponding installation, the same elements being denoted by the same reference figures as in Figures 1 and 3.

Two stages of purification 213 and of evaporation purification 214 are shown in respectively the pipes 205 and 207.

To bring the raw material introduced into the vessel 201 to a dry matter content of about 43%, which corresponds to the optimal conditions of the hydrogenation reaction, through the pipe 204a is led, at a flow rate of 140.4 kg/h, the starch hydrolysate not yet treated and having a content of dry matter of 707., which, after combining with the flow rate of 97.9 kg/h of syrup flowing from the vessel 203 with a dry matter content of 3.67. provides a raw material of dry matter content 42.7% with a flow rate of 238.3 kg/h.

After purification and evaporation at step 214, there is thus led to the installation 202, through the pipe 207, a hydrogenated syrup with a dry matter content of 64.5. at a flow rate of 120 1/h.

1 1> 1 As already indicated with respect to Figure 3: the installation 202 is fed with 330 1/hour of water coming through the pipe 212 to which is added the 176 1/ hour of excess water recycled through the pipe 210, i.e. a total of 506 1/hour from installation 202 is extracted: 114 1/hour of a fraction of higher polyols removed from the system through the pipe 211 and having a dry matter content of about 17., 96 1/hour with a dry matter content of 3.67 of polyols led to the hydrolysis vessel 203 through the pipe 209.

The whole of the device thus described was placed in continuous operation.

In Tables III, IV and V below, are collected the values recorded respectively with respect to the analyses of the hydroqenated starch hydrolysate before chromatographic separation with the analyses of the sorbitol fraction recovered and with the analyses of the fraction which have to be subjected to hydrolysis, in the course of five different successive samplings.

r TABLE III HYDROGENATED HYDROLYSATE BEFORE CHROMATOGRAPHY r r r r I I1 DP 2 1.6 1.6 1.65 1.5 1.7 DP 2 3.5 3.5 2.85 3.4 3.6 Glycerin 0.1 0.1 0.2 0.2 0.2 Mannitol 0.7 0.9 1.0 0.8 Other hexitols 0.3 0.3 0.4 0.2 0.4 SORBITOL 93.8 93.6 93.9 93.9 93.1 Reducing sugars 0.09 0.07 0.065 0.06 0.092 Total sugars 1.5 1.45 1.50 1.33 1.33 tt i i i

I

i l

L-

1- 1 L I i"

I

16 TABLEAU IV ANALYSIS OF THE SORBITOL FRACTION DP 2 DP 2 0.2 0.3 0.3 0.25 0.3 SORBITOL 98.6 98.2 98.4 98.45 98.1 Mannitol 0.7 0.9 0.9 0.8 Glycerin 0.2 0.2 0.2 0.2 0.2 Other hexitols 0.3 0.4 0.3 0.3 0.4 Reducing sugars 0.017 0.028 0.010 0.020 0.012 Total sugars 0.11 0.09 0.14 0.12 0.17 TABLE V ANALYSIS OF THE FRACTION SUBJECTED TO HYDROLYSIS DP 3 20.2 20.2 16.9 16.4 DP 3 18.4 16.1 14.1 13.8 DP 2 43.2 49.2 55.8 55.5 SORBITOL 17.6 13.5 12.1 13.3 Mannitol 0.6 1.0 1.1 Other hexitols Reducing sugars 0.83 0.30 0.25 0.35 Total sugars 26.4 28.0 33.5 30.5 3'

I

ri r

I-

The sorbitol fraction so obtained was compared with five liquid sorbitol grades obtained by hydrogenation of dextrose according to the prior art and of which the analyses are presented in Table VI below: i i i A, .7 Ir #44 *114c 444 14*4 4441r I oc 17 TABLE VI ANALYSES OF SORBITOL SYRUPS OBTAINED BY HYDROGENATION OF DEXTROSE ACCORDING TO THE PRIOR ART DP 2 0.06 0.15 0.40 0.25 0.30 DP 2 0.40 0.40 0.40 0.6 0.50 SORBITOL 97.84 98.8 97.55 97.35 97.40 Other hexitols 0.40 0.50 0.15 0.2 0.20 Mannitol 1.0 0.80 1.1 1.1 1.1 Glycerin 0.30 0.03 0.4 0.5 Reducing sugars 0.058 0.040 0.052 0.047 0.050 Total sugars 0.26 0.26 0.22 0.26 0.30 It can be observed, by comparing Tables IV and VI that the sorbitol quality obtained by the process according to the invention: has a higher average purity in sorbitol, has a content of products of DP equal or greater than 2 which is distinctly lower, and has a content of reducing sugars distinctly less (0.017 on the average against 0.050).

A ratio of reducing sugars, so low in the case of the process according to the invention, could only be obtained with great difficulty by direct hydrogenation.

This ratio would need in fact a degree of hydrogenation of 99.98Z, which can only be achieved with greatly prolonged and, consequently, uneconomic hydrogenation periods.

EXAMPLE 2 This example discloses the production of pure sorbitol from a hydrol from a frist crop of crystallation of dextrose, having a true dextrose content equal to 86.7%.

a) Step of catalytic hvdrogenation of the hydrol The hydrol, obtained after crystallisation from a first crop of dextrose monohydrate, has a dry matter coni 18 I i 1414 t(Il tent of 74. and the following composition: DP 3 2.7 DP 3 1.8 DP 2 Dextrose 86.70 Fructose 0.3.

After purification and hydrogenation, the composition of the syrup became: DP 2 4.6 DP 2 Glycerin Mannitol Other hexitols 0.2 Sorbitol 86.7.

b) Step of continuous liquid chromatographic separation This separation was carried out on the device and according to the process described in Example 1 with respect to Figure 3.

The chromatography installation was fed: -with hydrogenated hydrol through pipe 207 at a flow rate of 120 1/hour, the hydrol having a dry matter of 627. and a density d=1.267, i.e. 94.26 kg/hour, with water through the pipe 212 at a flow rate .of 330 1/hour, with a fraction of excess water recirculated through the pipe 210 at a flow rate of 176 1/hour.

There was withdrawn from this installation: pure sorbitol through the pipe 208 at a flow rate of 220 1/hour, the content of dry matter being 32.

and the density 1.137, that is to say 80 kg/hour, a polyol fraction, discarded through the pipe 211, at a flow rate of 100 1/hour, the dry matter content being 1.5% and the density 1.00, that is to say 1.5 kg/ hour, a fraction of polyols subjected to hydrolysis it ii ir 3j ij

I

S. 19 through the pipe 209 at a flow rate of 130 1/hour, with a dry matter content of 8.8% and a density of 1.02, that is to say 11.7 kg/hour.

The whole gave an extraction calculated on the sorbitol of 96.27.

c) Conti,uous hydrolysis step The streams of recovered polyols were conducted through the pipe 209 to the hydrolysis vessel 203 as described in Example 1. The temperature is kept at 115'C in side the said vessel 203. The degree of hydrolysis of the polyholosides measured by the reducing sugars in comparison with the product hydrolysed under reflux for two hours in the presence of normal sulfuric acid, was always higher than d) Dilution step, by means of the syrup flowing from vessel 203 and led through the pipe 204b, of the hydrol introduced through the pipe 204a before purification In the integrated circuit as presented in Example 20 1, the hydrolysed polyol fraction was used for the dilution of the hydrol before purification, the whole constituting the raw material subjected to hydrogenation.

From the practical point of view, 112 kg/h of hydrol with 747 of dry inatter are thus diluted with 130 1/h of the hydrolysed polyols. The solution thus diluted titrates 30.77 of dry matter.

After hydrogenation, purification and evaporation to 62% of dry matter, the syrup was sent to the continuous chromatography installation.

-o-0-o- After several days of operation, the results collected in Tables VII (for three samplings), VIII (for five *f samplings), and IX (for five samplings) were obtained.

i L I L r: I rl i -II

I

I r f'l

I;

irl i -C- TABLE VII ANALYSIS OF THE RAW MATERIAL CONSTITUTED BY THE HYDROL DILUTED BY THE HYDROGENATED POLYHOLOSIDES HYDROLYSED AND THEN HYDROGENATED Nature of the Content ir constituent in the sy: DP 2 4.6 2.9 DP 2 7.1 Glycerin 0. 0.2 Mannitol 1.1 0.9 Other hexitols 0.3 0.2 SORBITOL 86.8 88.3 Reducing sugars 0.08 0.06 Total sugars 4.36 4.7 rup TABLE VIII ANALYSIS OF THE SORBITOL OBTAINED r c trti Icrr I ii Nature of the Content in 7.

constituent in the sorbitol DP 3 DP 2 0.4 0.3 0.6 0.2 0.4 Mannitol 1.0 1.1 0.9 0.7 1.1 Other hexitols 0.3 0.2 0.2 0.3 0.1 Glycerin 0.15 0.1 0.1 0.2 0.1 SORBITOL 98.15 98.3 98.2 98.6 98.6 Reducing sugars 0.025 0.010 0.022 0.010 0.040 Total sugars 0.11 0.15 0.20 0.09 0.13

J

21 TABLE IX ANALYSIS OF THE POLYOLS INTRODUCED BEFORE HYDROLYSIS Nature of the Content in X constituent DP 3 18.7 20.2 21.3 16.9 16.4 DP 3 15.9 16.1 17.0 14.2 13.7 DP 2 48.0 49.2 51.9 55.8 57.4 SORBITOL 17.4 14.5 9.8 13.1 13.5 Reducing sugars 0.17 0.14 0.11 0.14 0.14 Total sugars 27.1 33.8 34.5 29.6 28.7 The more detailed composition of a sample of this polyol fraction before hydrolysis is given in Table X TABLE X ~4It I

I

001 1*14 Nature of the Content in X constituent Sorbitol 12.8 Mannitol 1.9 DP 2 50.4 DP 3 14.9 DP 4 DP 5 2.1 DP 6 2.9 DP 7 2.8 DP 9 1.1 DP 10 to DP 20 5.6 DP 20 0.9

I.

C i I I I' From all these analyses, it again emerges that the 3 quality of sorbitol produced under these conditions with a total yield from a hydrol from a first crystallisation of dextrose is at least equal to that obtained by hydrogenation of a pure dextrose.

Reference will be made, by way of comparison, with the compositions, given in Example 1, of sorbitol obtained by dextrose hydrogenation.

I:

OKI

-r 22 The polyols extracted throughout the balanced operation of the chromatography had a true sorbitol content less than 15., which indicates an effective extraction of the sorbitol, higher than 90Z of the content of sorbitol of the material processed.

EXAMPLE 3 This example illustrates the production of pure sorbitol from a H2 hydrol of a second crystallisation crop of dextrose, titrating about 78Z of true dextrose.

Reference is made again to Figures 1 and 3.

a) Hydrogenation step The syrup obtained after purification and hydrogenation had the composition indicated in Table XI: TABLE XI i i ti: i' rz rt: P 1 f IP;l.'( P I t ifl(

L

Nature of the Content in X constituent DP 3 DP 3 3.1 DP 2 11.1 20 Mannitol 1 .0 Other hexitols 0.3 Sorbitol 78.0 Reducing sugars 0.48 Total sugars 7.1 b) Chromatography step 25 The above-said syrup was supplied at a flow rate of 103.2 1/h for a content of dry matter of 63.57 through pipe 207 to the continuous liquid chromatography installation 202 described previously the density of the syrup was 1.264.

The feed flow rate of water through the pipe 212 of this installation was 341 1/h, to which must be added a flow rate of 166 1/h of recirculated water (excess water coming from the total de-sugaring during the preceeding sequence of the first pure sorbitol desorption stage) introduced through the pipe 210.

-II

-_.iiL.ili_ ~LL rCL)~ WIIII 23 The sorbitol extraction pump was regulated to 200 1/h to obtain at the same time excellent sorbitol quality as well as maximum extraction ratio.

Hence 200 1/h of sorbitol was extracted with a dry matter content of 28.2., namely 62.04 kg/hour through the pipe 208.

Through the pipe 209 was extracted a syrup which had to be subjected to hydrolysis, the flow rate being 134 1/hour, the density 1.04 and the dry matter content 13.7., namely 18.9 kg/hour.

Through the pipe 211 was extracted a discarded syrup with a flow rate of 160 1/hour, the dry matter content being 1.7Z, namely 1.87 kg/hour.

Analysis was made as a function of time of both te sorbitol extracted from the installation and the output of the polyol fraction.

The results are collected in Tablex XII and XIII.

TABLE XII ANALYSIS OF THE SORBITOL 00 0 o o 0 00 ao e 0 S0090 o 0 0i64 4 T Time Brix Other hexitols DP 3 DP 2 Mannitol Sorbitol heitl Sorbito 56 54 48 4.0 35.5 31 26 21 16 8 6 0.2 0.2 0.2 0.1 0.1 0.5 0.4 0.4 0.3 0.2 0.2 0.2 0.3 0.3 0.2 0.2 0.2 1 .1 1.0 1.0 1.0 1.0 1.0 0.9 0.9 0. 8 0.7 0.6 0.6 0.3 0.3 0.4 0.3 0.3 0.3 0 .4 0.3 0.3 0.3 0.3 0.3 97.9 98.0 97.9 98.1 98.4 98.5 98.5 98.4 98.6 98.9 98.9 98.9 I I t L

A~

i m i

LV.

L.XMf~~ i i f 24 TABLE XIII ANALYSIS OF THE POLYOLS FRACTION Other Time Brix DP 3 DP 3 DP 2 Mannitol hexitols Sorbitol 2 4 6 8 12 14 2 16 18 10.5 22 21.0 20 15.7 5.2 1.3 0.4 24 28.0 21 16.7 54.6 1.4 0.4 6 c) Continuous hydrolysis step The syrup recovered for the purposes of hydrolysis at the outflow of the installation 202 is led to the hydrolysis vessel as described in Example 1.

The temperature therein was kept at 110'C. The 2 degree of hydrolysis of the polyholosides for a flow rate of 130 1/h on a bed of 20 liters of adsorbant was always higher than 907..

The degree of hydrolysis was, as in the preceeding examples, obtained by comparing the ratio of reducing su- 2 gars expressed in glucose equivalents, found in the syrup flowing out from the hydrolysis vessel, with that found in a specimen subjected to the action of normal sulfuric acid under reflux.

d) Step of dilution of the hydrol H2 introduced through the pipe 204a, before hydrogenation with the syrup flowing from the hydrolysis vessel and conducted through the pipe 204b.

93.4 kg/hour of hydrol H2 with 74. of dry matter was diluted with 134 1/hour of hydrolysed polyols with 13.7. of dry matter, introduced through the pipe 204b, the solution obtained representing 230 kg/hour of a syrup with about 387. of dry matter.

j ;i i.

This syrup was hydrogenated, purified and evaporated to 63.5% of dry matter, then led to the continuous chromatography installation 202.

After several days of operation, analysis was carried out of five samplings of the raw material constituted by the hydrol diluted with the syrup introduced through 204b (Table XIV) and hydrogenated, five samplings of the sorbitol obtained (Table XV) and four samplings of the syrup introduced through the pipe 209 (Table XVI).

TABLE XIV HYDROL DILUTED WITH HYDROGENATED POLYHOLOSIDES HYDROLYSED AND THEN HYDROGENATED Nature of the Contents in 7 constituent DP 3 5.2 6.6 4.5 5.4 4.3 DP 3 3.3 4.3 3.1 2.8 3.2 DP 2 10.2 14.0 11.7 12.4 11.7 20 Mannitol 1.2 1.3 1.2 1.3 SORBITOL 79.8 75.4 79.2 79.0 79.0 Other hexitols 0.3 0.4 0.3 0.2 0.3 Reducing sugars 0.05 0.045 0.048 0.035 0.07 25 Total sugars 6.9 7.2 7.5 7.0 ii

U

ii 0 i i 26 TABLE XV

SORBITOL

Nature of tre Contents in 7.

const: t nt DP 3 0.1 0.05 0.05 0.1 DP 2 0.2 0.2 0.2 0.3 0.3 Mannitol 0.9 0.9 1.1 1.1 1.2 Other hexitols 0.5 0.2 0.2 0.3 0.1 SORBITOL 98.4 98.6 98.45 98.25 98.3 Reducing sugars 0.011 0.027 0.028 0.01 0.03 Total sugars 0.04 0.2 0.12 0.15 0.13 Results of analyses collected in Tables XIV and XV, show that the sorbitol quality produced under these conditions from hydrol H2 had a purity at least equal to that obtained by hydrogenation of a pure dextrose and is characterised by a very low content of reducing sugars.

TABLE XVI POLYOL SYRUP INTRODUCED THROUGH THE PIPE 209 S 20 u <as DP 3 19.2 21.7 21.0 20.7 DP 3 15.9 16.9 16.4 16.4 DP 2 51.6 56.1 54.6 54.8 Mannitol 3 2 1.8 2 SORBITOL 10 2.9 5.8 5.7 Reducing sugars 0.3 0.4 0.40 0.4 Total sugars 35.0 38.2 36.4 32.2 From the results collected in Table XVI, it is deduced that the polyols extracted throughout the balanced 27 operation of the chromatography installation had a sorbitol content below 10%, which indicated a very efficient extraction of the sorbitol, higher than about 94% of the content in sorbitol of the raw material.

As is self-evident and as emerges already besides from the foregoing, the invention is in no way limited to the embodiments and applications which have been more particularly envisaged it encompasses, on the contrary, all modifications.

I i

K'

Claims

1. Process for the preparation ofv j 1 1 puri- ty sorbitol syrup, wherein a starting material of which a first part is constituted by a starch hydrolysate, is subjected to a process comprising in combination a catalytic hydrogenation step of the starting material, a chromatographic separation step of the start- ing material which has undergone hydrogenation into a first fraction containing very pure sorbitol which is recovered and into a second fraction containing, besides sorbitol, non-hydrogenated sugars as well as hydrogenated di- and polysaccharides, an acid hydrolysis step of the abovesaid second fraction, which provides a partially hydrogenated starch hydrolysate which is recirculated and which constitutes a second part of the raw material subjected to the hydroge- S nation step.

2. Process according to claim 1, wherein the starch hydrolysate which is part of the constitution of the starting material shows, preferably, a true dextrose ,i content comprised between 65 and 977 and, more preferably still, between 70 and 95%, particularly advantageous starch hydrolysates being constituted by hydrols of the first and second crop obtained during crystallisation of the dextrose.

3. Process according to one -of claims 1 and 2, wherein the catalytic hydrogenation step is carried out on ruthenium or Ranay nickel catalysts, preferably on a Raney nickel catalyst, at a hydrogen pressure comprised between 2 and 70 kg/cm and at a temperature from aat 100 to S 35 150'C. :.lil~ULljmiWI-I 29

4. Process according to one of claims 1 to 3, wherein the chromatographic separation step is carried out discontinuously or continuously on adsorbants of the strongly acid cationic resin type, charged with alkaline or alkaline earth ions or of the zeolite type, charged with ammonium sodium, potassium, calcium, strontium or barium ions.

Process according to one of claims 1 to 3, wherein the chromatographic separation step employs seve- ral chromatography columns lined with adsorbant of the strong cationic resin type in the calcium form and of fine granulometry, a zone I of desorption, a zone II of adsorp- tion and a zone III of enrichment of the hydrogenated polyholosides being formed by the setting of the electro- valves located in the pipes connecting the outlet of any one column to the inlet of the following column, a closure device maintaining total fluid-tightness between zone III t at the end of which are recovered the hydrogenated poly- holosides and zone I for desorption of the sorbitol, at the head of which zone the desorption water is introduced, said closure device ensuring the direction of the passage of the liquid phase over the selective adsorbant and avoiding particularly contamination of the pure sorbitol by traces of polyholosides.

6. Process according to one of claims 1 to 4, wherein the acid hydrolysis step of the second fraction is carried out on a fixed acid catalyst and is conducted so that more than 40X by weight of the hydrogenated disaccha- rides and polysaccharides present are hydrolysed, said hy- drolysis being effected preferably continuously by passing the syrup containing the polyols to be hydrolysed over a fixed bed containing acid catalysts of the alumino- silicate, silica, alumina or cationic resin type. i. L~ ~I i I_

7. Process according to claim 6, wherein the hy- drolysis is conducted on strong cationic resins in the acid form, at a temperature comprised between 50 and 120'C, the passage flow rate over the acid catalytic bed being regulated so as to obtain a hydrolysis ratio of the hydrogenated di- and polysaccharides at least equal to and, preferably, at least equal to

8. Process according to one of claims 1 to 7, wherein the content of dry matter of the second fraction which is subjected to the hydrolysis step and which is recirculated is generally comprised between 1.5% and 307 and, preferably, between 2.5% and

9. Installation for carrying out the process according to one of claims 1 to 8, comprising: a vessel within which the catalytic hydrogena- tion step is carried out, 94 0 S- a chromatographic separation installation and o 20 a reaction vessel within which the hydrolysis step is carried out. 4 t

10. Very high purity sorbitol as obtained by oo employing the process according to one of claims 1 to 8. DATED this 27th day of June 1985. 4 ROQUETTE FRERES -EDWD. WATERS SONS PATENT ATTORNEYS QUEEN STREET MELBOURNE. VIC. 3000. tA c Cl