Europäisches Patentamt *EP001341717B1* (19) European Patent Office Office européen des brevets (11) EP 1 341 717 B1 (12) EUROPEAN PATENT SPECIFICATION (45) Date of publication and mention (51) Int Cl.7: C01B 11/22, C08B 31/18 of the grant of the patent: 26.05.2004 Bulletin 2004/22 (86) International application number: PCT/NL2001/000904 (21) Application number: 01270492.0 (87) International publication number: (22) Date of filing: 12.12.2001 WO 2002/048029 (20.06.2002 Gazette 2002/25) (54) RECOVERY PROCESS FOR SPENT PERIODATE RÜCKGEWINNUNGSPROZESS FÜR GEBRAUCHTES PERIODAT PROCEDE DE RECUPERATION DE PERIODATE EPUISE (84) Designated Contracting States: (74) Representative: Jorritsma, Ruurd AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU Nederlandsch Octrooibureau MC NL PT SE TR Postbus 29720 2502 LS Den Haag (NL) (30) Priority: 13.12.2000 EP 00204482 18.12.2000 US 255898 P (56) References cited: EP-A- 0 913 358 WO-A-98/27118 (43) Date of publication of application: US-A- 4 176 167 10.09.2003 Bulletin 2003/37 • T A MCGUIRE ET AL: "Chemical process for (73) Proprietor: SCA Hygiene Products Zeist B.V. making dialdehyde starch" STARCH 3700 AJ Zeist (NL) STARKE,DE,WILEY-VCH VERLAG, WEINHEIM, vol. 23, no. 2, 1971, pages 42-45, XP002121065 (72) Inventor: BESEMER, Arie, Cornelis ISSN: 0038-9056 cited in the application NL-3958 CC Amerongen (NL) Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 1 341 717 B1 Printed by Jouve, 75001 PARIS (FR) EP 1 341 717 B1 Description [0001] The invention relates to a process for regenerating periodic acid and to a process of oxidising carbohydrates with periodic acid with regeneration and recovery of the periodic acid. 5 [0002] Periodic acid is extensively used for oxidising vicinal diols resulting in dialdehydes according to the following reaction: 1 2 - 1 2 - R -CHOH-CHOH-R + IO4 → R -CH=O + O=CH-R + IO3 + H2O 10 - (5-n)- Instead of periodate (IO4 ), the actual oxidising species is para- or meta-periodate (HnIO6 ), which results from reaction of periodic acid with water: + - 15 HIO4 + 2 H2O → H5IO6 → H + H4IO6 In the present description, all such oxoiodate species of heptavalent iodine, whether in neutral or in deprotonated form, are referred to as periodate. Usually, the two groups R1 and R2 are part of the same ring system, such as in carbohy- drates. The most common process in which periodate is used as an oxidising agent is the oxidation of starch to dial- 20 dehyde starch (DAS), which is used as a wet strength additive for paper, or can be further oxidised to calcium-binding dicarboxy starch. [0003] As periodate is an expensive oxidising agent, the spent oxidising agent, i.e. iodate, should be regenerated to periodate. This is usually done by oxidation with hypochlorite, as described by McGuire and Mehltretter, Die Stärke, 23, (1971) 42-45. According to this method, spent iodate is treated with 1.5 mol equivalents (3.0 redox equivalents) of 25 sodium hypochlorite at pH 13-14 and at 90-95°C for 40 min, resulting in an average recovery of 97.6 % periodate. EP-A-913358 (DSM) discloses the preparation of sodium para-periodate from iodine, iodide or iodate using alkaline sodium hypochlorite in the presence of other ions such as chloride or sulphate. WO 98/27118 (Avebe) describes oxi- dation of starch with periodate, and recovery of periodate by oxidation of the iodate with ozone. [0004] The prior art methods for periodate recovery have drawbacks in that they are performed at high pH, so that 30 the product cannot be directly used in a process performed under acidic conditions. Moreover, processes using hypo- halite are undesired, since they produce substantial amounts of chlorinated by-products. [0005] It was found according to the invention that the regeneration of periodate can be improved using persulphuric acid as the oxidising species. The persulphuric acid or peroxosulphate may have any form, and is preferably a mixed salt such as commercially available Oxone® (2KHSO5.KHSO4.K2SO4). The regeneration proceeds not only for pro- 35 ducing periodate from iodate, preferably an iodate-containing solution, but also from iodide or other iodine species having lower oxidation states than the oxidation state in periodate (+7). [0006] The process of the invention allows short regeneration times and low temperatures (0-20 °C), although higher temperatures, up to about 60°C can be used as well. The process also avoids the formation of halogenated products of the periodate oxidation and the production of halide byproducts. Moreover, the oxidation can be carried out at acidic 40 pH, as low as pH 3, up to about pH 8. This is especially advantageous where the periodate is used in an oxidation process at low pH, such as the oxidation of polysaccharides to produce dialdehyde polysaccharides, as this avoids the need for a pH adjustment between oxidation and regeneration. This allows both steps to be performed simultane- ously and/or using the same reactor, if the reaction product of the oxidation is compatible with the peroxosulphate. [0007] Thus, according to an embodiment of the present invention, the process can be carried out in the same reactor 45 as the process in which the periodate is used for oxidising a substrate, in particular a α,β-diol. In another embodiment of the invention, the regeneration reaction is carried out simultaneously with the oxidation reaction but physically sep- arated from it. For example, a two-compartment system can be designed, comprising a reaction compartment and a regeneration compartment, with a filter being provided between the two compartments. The filter can e.g. be a polymeric membrane, and can serve to keep the (insoluble) reaction product of the oxidation reaction, such as dialdehyde starch, 50 in the reaction compartment and the peroxosulphate in the regeneration compartment. In these embodiments, the reaction can be performed continuously or semi-continuously, and the periodate can be used in substoichiometric (catalytic) amounts, e.g. 0.05 - 0.5 equivalents. These embodiments require a careful control of peroxosulphate ad- ddition so as to avoid an excess of peroxosulphate to be present with the substrate. [0008] Alternatively, the process can be performed batch-wise. A stoichiometrical or near-stoichiometrical amount 55 of periodate can then be used. The iodate produced in the oxidation reaction can be separated from the reaction mixture by precipitation, if necessary by increasing the pH, and the iodate can then be regenerated in a separate reactor following the process of the invention. If the substrate and the reaction product are insoluble, such as with cellulose fibres, the can be simply separated from the reaction mixture by filtration or decanting, before optional precipitation of 2 EP 1 341 717 B1 the spent iodate. [0009] The regenerated periodate is particularly suitable for the oxidation of carbohydrates to produce carbohydrate dialdehydes, such as members of the starch family (starch, amylose, amylopectin, hydrolysates and derivatives there- of), cellulose, other glucans, galactomannans (guar, locust bean gum), fructans (inulin), xylans, and the like, and alkylat- 5 ed, carboxyalkylated, hydroxyalkylated and other derivatives thereof, provided they contain vicinal diol groups (-CHOH-CHOH-). Starch and starch derivatives and cellulose are especially preferred. It is observed that where the carbohydrate oxidation product is soluble in the reaction medium such as with low molecular weight carbohydrate dialdehydes, an effective separation of oxidation product (dialdehyde) and iodate can be achieved by precipitating the iodate, e.g. by addition of potassium or magnesium ions or an organic solvent such as ethanol. The precipitated iodate 10 is then reoxidised by redissolution and oxidation as described above. When the oxidation and regeneration are carried out simultaneously, the pH is preferably between 3.5 and 6, most preferably between 4 and 5. The temperature can be kept low, e.g. between 0 and 10°C. [0010] The dialdehyde oxidation products thus obtained can be used for various purposes, e.g. as a crosslinking agent, as an additive e.g. in glues, coatings, thickeners, and the like, or as a carrier material e.g. for proteins. The 15 dialdehydes are also suitable as wet strength agents, optionally after partial further oxidation to products having both aldehyde and carboxyl groups (see WO 00/26257). They may also be used as starting material for producing dicarboxy carbohydrates, which are suitable e.g. as calcium binding agents and as a raw material for producing superabsorbent materials. The dicarboxy carbohydrates can be conveniently prepared from the dialdehyde carbohydrates by oxidation with usual oxidising agents, in particular sodium chlorite: 20 [0011] The dicarboxy starches that can be obtained from the dialdehyde starches prepared by using extended peri- odate oxidation periods (e.g. 4-8 days) have an unexpectedly high calcium-binding power, as measured by their se- questering capacity (SC) of at least 2.8, especially at least 3.0 mmol Ca/g. Examples 25 Example 1: Preparation of dialdehyde starch [0012] In 2l water 110 g potato starch (AVEBE, dry weight 92.4 g, 0.57 mol) was suspended. The mixture was cooled to approximately 5 °C and then 123 g periodate (Aldrich, 99%, 0.57 mol ACS) was added. The mixture was stirred in 30 the dark for 6 days. Then stirring was stopped and the dialdehyde starch was allowed to precipitate.