EP4642815A1 - Method for producing cationized starch - Google Patents

Method for producing cationized starch

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Publication number
EP4642815A1
EP4642815A1 EP23833846.1A EP23833846A EP4642815A1 EP 4642815 A1 EP4642815 A1 EP 4642815A1 EP 23833846 A EP23833846 A EP 23833846A EP 4642815 A1 EP4642815 A1 EP 4642815A1
Authority
EP
European Patent Office
Prior art keywords
weight
liquid
washing
medium
starch
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23833846.1A
Other languages
German (de)
French (fr)
Inventor
Jonni Ahlgren
Jussi Nikkarinen
Jouni Touronen
Pia WILLBERG-KEYRILÄINEN
Pauliina KIVINEN
Juha Kokkonen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Kemira Oyj
Original Assignee
Kemira Oyj
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kemira Oyj filed Critical Kemira Oyj
Publication of EP4642815A1 publication Critical patent/EP4642815A1/en
Pending legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B31/00—Preparation of derivatives of starch
    • C08B31/08—Ethers
    • C08B31/12—Ethers having alkyl or cycloalkyl radicals substituted by heteroatoms, e.g. hydroxyalkyl or carboxyalkyl starch
    • C08B31/125—Ethers having alkyl or cycloalkyl radicals substituted by heteroatoms, e.g. hydroxyalkyl or carboxyalkyl starch having a substituent containing at least one nitrogen atom, e.g. cationic starch

Definitions

  • the present invention relates to a method for producing cationized starch according to the preamble of the enclosed independent claim.
  • Cationized starch is widely used chemical substance in various industries, especially in the manufacture of paper, board or the like, where cationized starch is commonly used to improve water drainage and retention. It is known that cationized starch may be used to improve the quality of produced paper or board, such as by improving its strength.
  • the current trend to reduce the use of petroleum-based chemicals and to replace them with renewable biobased alternatives has increased the interest in cationized starch in general, and in finding new industrial applications for cationized starch.
  • highly cationized starch which is easier to dissolve in water.
  • it is desirable that the cationized starch has a high purity.
  • Cationization of starch is conventionally performed by slurrying starch in water at an alkaline pH and allowing the starch to react under mixing with a cationizing agent which is added to the slurry.
  • a cationizing agent which is added to the slurry.
  • EPTAC 2,3-epoxypropyltrimethylammonium chloride
  • CHPTAC 3-chloro-2-hydroxypropyltrimethylammonium chloride
  • the process mixture remains throughout the process in slurry form, which means that the granular structure of the starch is maintained during the cationization step.
  • the problem with the conventional cationization method is that with an increasing cationization degree the water-solubility of the starch increases rapidly.
  • the conventional cationization methods generate side reactions, which provide inactive by-products, such as (2,3-dihydroxypropyl)trimethylammonium chloride (DHPTAC) and/or 3- hydroxypropenyltrimethylammonium chloride (HPTAC).
  • DHPTAC (2,3-dihydroxypropyl)trimethylammonium chloride
  • HPTAC 3- hydroxypropenyltrimethylammonium chloride
  • the amount of these byproducts may be significant, and they reduce the purity of the produced cationized starch.
  • the by-products may decrease the efficiency of the cationized starch when it is used e.g. as flocculant and may cause extra load to the flocculation system.
  • An object of this invention is to minimise or possibly even eliminate the disadvantages existing in the prior art.
  • Another object of the present invention is a method of producing cationized starch with high cationicity and low amount of by-products.
  • a typical method according to the present invention for producing cationized starch having a degree of substitution of at least 0.2 comprises at least the process steps of:
  • the process mixture comprises cationized starch dispersed in the liquid process medium comprising reaction by-products formed during the cationization step
  • the present invention also provides efficient recirculating of the organic liquid within the process, which makes the process both economical and sustainable, as the consumption of the organic liquid can be minimised. Furthermore, the undesired reaction by-products can be easily and efficiently removed from the produced cationized starch and from the cationization process, as they remain dissolved in the water phase. In this manner the waste flows from the cationization process can be kept as low as possible, which is environmentally beneficial. Especially, the organic liquid waste can be minimized.
  • the method according to present invention is intended for producing cationized starch having a degree of substitution of at least 0.2, preferably at least 0.3, more preferably at least 0.4.
  • the cationized starch may have the degree of substitution in a range of 0.2 - 1 .0, preferably 0.3 - 0.9, more preferably 0.4 - 0.8 or 0.5 - 0.8.
  • the degree of substitution defines how many substituted groups are contained in the cationized starch, calculated per one anhydroglucose unit of starch.
  • the present invention is thus intended for production of cationized starch with a high cationicity or very high cationicity. With the present method it is possible to produce, for example, cationized starch which is water-soluble at temperature of ⁇ 60 °C, preferably ⁇ 50 °C.
  • the starch which may be used in the present invention for cationization, can be any available starch, such as potato starch, waxy potato starch, rice starch, corn starch, waxy corn starch, wheat starch, barley starch, pea starch or tapioca starch.
  • the used starch is selected from potato starch, corn starch and tapioca starch.
  • Reaction by-products formed during the cationization step include (2,3-dihydroxy- propyl)trimethylammonium chloride (DHPTAC) and 3-hydroxypropenyltrimethyl- ammonium chloride (HPTAC).
  • the total amount of the reaction by-products, especially (2,3-dihydroxypropyl)trimethylammonium chloride (DHPTAC) and 3- hydroxypropenyltrimethylammonium chloride (HPTAC) in the cationized starch produced by the present method may be less than 5 weight-%, preferably less than 4 weight-%, more preferably less than 3 weight-%, sometimes even less than 1 weigh-%, calculated from the total dry weight, after drying of the produced cationized starch.
  • the total amount of the said by-products may be 0.1 - 5 weight-%, preferably 0.3 - 4 weight-% , more preferably 0.5 - 3 weight-%, calculated from the total dry weight, after drying of the produced cationized starch.
  • the cationization of the starch occurs in a cationization step, where the cationizing agent is allowed to interact with the starch in a process mixture.
  • the cationization step is performed in an elevated temperature.
  • the temperature of the process mixture during cationization step may be in a range of 40 - 70 °C, preferably 45 - 60 °C.
  • the process mixture comprises starch to be cationized, a cationizing agent and a liquid process medium comprising water and an organic liquid.
  • the process mixture can be prepared in a separate preparation step preceding the cationization step or the process mixture may be prepared directly to the cationization reactor employed in the cationization step.
  • the process mixture is in form of a slurry or a dispersion, formed by mixing the individual components of the process mixture together.
  • Starch to be cationized may be provided in a form of dry particulate material, i.e. aggregates or powder, having a water content of 5 - 25 weight-%, preferably 10 - 20 weight-%.
  • the cationization agent used in the present invention may be any cationization agent conventionally used for cationization of polysaccharides.
  • the cationization agent is selected from 2,3- epoxypropyltrimethylammonium chloride (EPTAC) or 3-chloro-2- hydroxypropyltrimethylammonium chloride (CHPTAC) or any of their mixtures.
  • the cationization reaction between the starch and the cationizing agent occurs at alkaline pH.
  • the pH of the process mixture may be adjusted to the desired alkaline pH level by addition of an alkaline agent, for example strong base such as NaOH or KOH, to the process mixture.
  • an alkaline agent for example strong base such as NaOH or KOH
  • the alkaline agent such as NaOH
  • the organic liquid used in the liquid process medium is water-miscible and able to form a homogenous mixture with water.
  • the organic liquid is preferably an alcohol, for example a secondary or tertiary alcohol.
  • the organic liquid may be selected from a group comprising ethanol, n-propanol, isopropanol, butanol, tert-butanol, secbutanol, or any of their mixtures, preferably n-propanol, isopropanol, butanol, tertbutanol, sec-butanol, or any of their mixtures.
  • the organic liquid may be acetone; acetonitrile; or methyl ethyl ketone.
  • the liquid process medium may comprise 60 - 90 weight-%, preferably 65 - 85 weight-%, more preferably 70 - 80 weight-% of organic liquid, calculated from the total weight of the liquid process medium.
  • the liquid process medium may comprise 65 - 78 weight-% of organic liquid, calculated from the total weight of the liquid process medium.
  • the liquid process medium and thus the process mixture, comprises water in addition to the organic liquid. Water is required for the efficient reaction between the cationizing agent and starch.
  • the liquid process medium may comprise ⁇ 40 weight-%, preferably ⁇ 35 weight-%, more preferably ⁇ 30 weight- %, of water, and/or >5 weight-% or >10 weight-%, preferably >15 weight-%, more preferably >20 weight-%, of water, calculated from the total weight of the liquid process medium.
  • the liquid process medium may comprise 5 - 40 weight-% or 10 - 40 weight-%, preferably 15 - 35 weight-%, more preferably 20 - 30 weight-%, sometimes 22 - 35 weight-%, of water, calculated from the total weight of the liquid process medium.
  • the water forming a part of the liquid process medium may originate from the used raw materials, i.e. from starch, the organic solvent and/or cationizing agent. Alternatively, water can be added either to the process mixture or to the liquid process medium in an appropriate amount in order to obtain the desired water content in the process mixture.
  • the liquid process medium in the cationization step may comprise water and the organic liquid in a weight ratio from 2:3 to 1 :9, preferably from 2:4 to 1 :6, more preferably from 2:5 to 1 :4 (water:organic liquid). It has been found that these ratios of water to the organic liquid can provide an efficient cationization reaction while minimising the risk for starch dissolution during the cationization step.
  • the weight ratio of the other constituents of the process mixture, selected from starch, water, cationizing agent and optional alkaline agent, to the organic liquid can be from 2:1 to 1 :5, preferably 4:3 to 1 :3, more preferably 1 :1 to 1 :2 (other constituents:organic liquid).
  • the cationization step results in a dispersion of cationized starch, i.e. cationized starch particles or granules, which are dispersed in the liquid process medium.
  • the process mixture remains thus in form of a dispersion or a slurry throughout the cationization step.
  • the viscosity of the process mixture, at the end or after the cationization step may be ⁇ 1000 mPas, preferably ⁇ 500 mPas, more preferably ⁇ 200 mPas.
  • the viscosity may be, for example, in a range of 1 - 1000 mPas, preferably 5 - 500 mPas.
  • the cationized starch is in particle or granule form in the process mixture, even after the cationization step, the cationized starch can be easily separated from the liquid process medium.
  • the process mixture can be neutralized after the cationization step by an addition of an acidic agent, such as hydrochloric acid. After neutralization, the pH of the process mixture may be in a range of pH 5 - 9.
  • reaction by-products formed during the cationization step in the cationization reaction such as (2,3-dihydroxypropyl)trimethylammonium chloride (DHPTAC) and/or 3-hydroxypropenyltrimethylammonium chloride (HPTAC), are soluble in water and are present in the process mixture as dissolved in the liquid process medium. This means that when the cationized starch is separated from the liquid process medium, it is simultaneously separated from the reaction by-products.
  • DHPTAC (2,3-dihydroxypropyl)trimethylammonium chloride
  • HPTAC 3-hydroxypropenyltrimethylammonium chloride
  • the cationized starch may be separated from the liquid process medium in a separation step.
  • the separation step may employ any suitable solid-liquid separation technique, such as filtration, decantation or centrifuging.
  • the cationized starch is separated from the liquid process medium by filtration, decantation or centrifuging.
  • the liquid process medium After the liquid process medium is separated from the cationized starch in the separation step, it is transferred to a distillation step.
  • the liquid process medium In the distillation step the liquid process medium is divided into an organic liquid phase and a water phase by distillation.
  • the reaction by-products remain in the water phase, and thus they can be removed from the cationization process, whereas the organic liquid phase may be recirculated back to any process step of the cationization method where the organic liquid is present or used.
  • the present invention thus not only minimises the consumption of the fresh organic liquid in the process, but enables easy and efficient removal of undesired by-products, such as (2,3-dihydroxypropyl)trimethyl- ammonium chloride (DHPTAC) and 3-hydroxypropenyltrimethylammonium chloride (HPTAC) from the cationized starch, as well as from the cationization process.
  • DHPTAC (2,3-dihydroxypropyl)trimethyl- ammonium chloride
  • HPTAC 3-hydroxypropenyltrimethylammonium chloride
  • the cationized starch may be dried in a drying step.
  • the drying may be performed by evaporating the moisture from the cationized starch.
  • the cationized starch is usually dried to moisture content of at most 10 weight-%, preferably at most 7 weight-%.
  • Liquid process medium removed from the cationized starch in the drying step can be condensed, collected and recirculated.
  • the organic liquid evaporated during the drying step may be collected after the drying step, e.g. by using a condenser, and recirculated to the washing step.
  • the cationized starch may be further purified or washed in a washing step located after the cationization step and before the drying step, preferably before the separation step.
  • a washing medium comprising or consisting of organic liquid is added to the process mixture for purifying the obtained cationized starch.
  • the washing medium is mixed with the process mixture, including the cationized starch, whereby the washing medium becomes a part of the process mixture in the washing step. More specifically, the washing medium becomes a part of the liquid process medium of the process mixture.
  • the composition of the liquid process medium in the washing stage may be altered from its composition in the cationization stage to ensure an effective transfer of the reaction by-products to the liquid process medium and obtainment of purified cationized starch. Simultaneously the dissolution of the cationized starch into the liquid process medium can be minimized.
  • the washing step may be performed at a temperature in a range of 0 - 60 °C , preferably 10 - 50 °C, more preferably 20 - 40 °C.
  • the washing medium added to the process mixture at the washing step comprises water and an organic liquid, which preferably is the same organic liquid which is used for the liquid process medium in the cationization step.
  • the washing medium may comprise ⁇ 35 weight-%, preferably ⁇ 30 weight-%, more preferably ⁇ 25 weight- %, of water, calculated from total weight of the washing medium.
  • the washing medium may comprise 1 - 35 weight-%, more preferably 2 - 30 weight-%, more preferably 5 - 25 weight-%, of water, calculated from total weight of the washing medium.
  • the washing medium may comprise 65 - 99 weight-%, more preferably 70 - 98 weight-%, more preferably 75 - 95 weight-%, of the organic liquid, calculated from total weight of the washing medium.
  • the organic liquid of the washing medium may be an alcohol, acetone; acetonitrile; or methyl ethyl ketone, preferably an alcohol selected from a group comprising ethanol, n-propanol, isopropanol, butanol, tert-butanol, sec-butanol, or any of their mixtures.
  • the washing medium and the liquid process medium comprise the same organic liquid.
  • the washing medium may comprise or consists of fresh organic liquid or preferably the washing medium comprises or consists of organic liquid recirculated from the other steps of the cationization process.
  • the washing medium may comprise both fresh and recirculated organic liquid.
  • At least a part of the organic liquid phase from the distillation step is recirculated to the washing step.
  • the organic liquid phase from the distillation step can be used to form a part of the washing medium or it can be used as the washing medium.
  • the process mixture may comprise cationized starch and liquid process medium, comprising water and organic liquid, in a weight ratio from 1 :1 to 1 :100, preferably 1 :4 to 1 :20, more preferably 1 :6 to 1 :10 (cationized starch:liquid process medium).
  • the liquid process medium during the washing step preferably comprises ⁇ 35 weight-%, preferably ⁇ 30 weight-%, more preferably ⁇ 25 weight-%, of water, calculated from the total weight of the liquid process medium.
  • the liquid process medium in the washing step may comprise 1 - 35 weight-%, more preferably 2 - 30 weight-%, more preferably 5 - 25 weight-%, of water, and/or 65 - 99 weight-%, more preferably 70 - 98 weight-%, more preferably 75 - 95 weight-%, of the organic liquid, calculated from the total weight of the liquid process medium.
  • the composition of the process mixture in the washing step ensures that the risk of dissolution of the cationized starch during the washing is minimised, while the effective removal of possible reaction by-products from the cationized starch is ensured.
  • the liquid process medium usually has a higher water content in the cationization step than in the washing step.
  • the process mixture is transferred to the separation step where the purified cationized starch is separated from the process liquid medium, as described above.
  • the purified cationized starch is separated from the process liquid medium by filtration, decantation or centrifuging.
  • the separated process liquid medium may be transferred to the distillation step, from where it may be recirculated back to any process step of the cationization method where the organic liquid is present or used, e.g. to washing step.
  • the purification or washing of the cationized starch may further comprise one or more, preferably a plurality of, additional washing stages, such as two, three or four consecutive additional washing stages.
  • Each individual additional washing stage comprises an addition of washing medium to the process mixture and separation of the cationized starch and liquid process medium, preferably by filtration, decantation or centrifuging.
  • the additional washing stages may work in counter-current fashion. For example, two or more washing stages can be arranged in a successive manner, where the separated cationic starch may be transferred to the consecutive additional washing stage, whereas the separated liquid process medium may be used in a preceding additional washing stage as the washing medium.
  • purification or washing may comprise, for example, at least two additional washing stages, including a first additional washing stage and a second additional washing stage, and optional intermediate additional washing stages between the first and the second washing stage.
  • the washing medium is first contacted with the process mixture in the second additional washing stage, and then led through the preceding intermediate additional washing stages to the first additional washing stage where it is contacted with the process mixture coming from the cationization step and entering the washing.
  • the process mixture it is first contacted with the washing medium in the first additional washing stage, and then led through the consecutive intermediate additional washing stages to the second additional washing stage.
  • the additional washing stage may be carried out by using a counter-current extractor, such as a screw extractor, where the cationized starch is fed to the extractor through an inlet at a first end of the extractor and removed through an outlet at a second end of the extractor.
  • the washing medium is fed to the extractor through an inlet at the second end of the extractor and removed through an outlet at the first end of the extractor.
  • the liquid process medium from the washing step or from the additional washing stages may be recirculated to in the cationization step to form a part of the process mixture.
  • the liquid process medium from the washing step/additional washing stage may be used for forming the process mixture without purification.
  • the amount of possible by-products is so low in the liquid process medium after washing step/additional washing stages that it does not have any negative impact on cationization reaction, when used for the process mixture.
  • the present method for producing cationized starch is a continuous method or at least part of the method is continuous.
  • the cationization step may be performed as a continuous process or as a batch process.
  • the purifying or washing, especially when comprising several additional washing stages, is usually performed as a continuous process.
  • Figure 1 shows an embodiment according to the present invention for producing cationized starch
  • Figure 2 shows schematically an embodiment of the purifying or washing of the cationized starch in counter-current fashion.
  • FIG. 1 shows one embodiment of the method for producing cationized starch according to the present invention.
  • a process mixture comprising starch granules or starch particles dispersed in a liquid process medium is prepared in a preparation step 11 .
  • a feed of starch, indicated with arrow A, a feed of liquid process medium comprising water and an organic liquid, indicated with arrow B, and a feed of a cationizing agent, indicated with arrow C, are fed to the preparation step 11 to form the process mixture.
  • the pH of the process mixture may be adjusted by a feed of alkaline agent, indicated with a dashed arrow aa.
  • the process mixture is then transferred to a cationization step 1.
  • the cationizing agent present in the liquid process medium interacts with the starch granules or particles, whereby a dispersion of cationized starch is obtained.
  • This dispersion may comprise reaction by-products, which are at least partly dissolved in the liquid process medium.
  • the feeds of starch, liquid process medium and cationization agent are fed directly to the cationization step 1 , i.e. the process mixture is formed directly to a cationization reactor without any preceding preparation step. It is also possible that the organic liquid and the water are fed as separate feeds to form the liquid process medium either in the preparation step 11 or the cationization step 1 .
  • washing step 3 a feed of washing medium comprising organic liquid is added to the process mixture.
  • the washing step 3 may comprise one or more additional washing stages, as described more closely in Figure 2.
  • the process mixture comprising cationized starch is transferred to the separation step 2, where the cationized starch is separated from the liquid process medium comprising dissolved reaction by-products.
  • the separated purified cationized starch is transferred to a drying step 4. In the drying step, the residual liquid process medium remaining in the cationized starch after separation is removed by evaporation.
  • the liquid process medium comprising dissolved reaction by-products is transferred after the separation step 2 to a distillation step 5, where it is divided into an organic liquid phase and a water phase.
  • the water phase comprises the reaction by- products and is removed from the cationization process, as indicated by arrow E.
  • the organic liquid phase can be recirculated back to any process step, where the organic liquid is present.
  • the organic liquid can be recirculated back to the preparation step 11 for preparing the process mixture, to the cationization step 1 or to the washing step 3.
  • the organic liquid phase from the distillation step is transferred to a collection step 6 for collecting the recirculated organic liquid, as indicated by arrow F.
  • Organic liquid separated from the purified cationized starch by evaporation in the drying step 4 can also be transferred to the collection step 6.
  • recirculated organic liquids from different process stages are combined and recirculated back for preparation of the process mixture or for use in the washing stage. If needed, fresh organic liquid can be added to the recirculated organic liquids at the collection step 6, indicated by arrow G.
  • FIG 2 shows schematically an embodiment for purifying or washing of the cationized starch in a counter-current fashion between the cationization step 1 and the separation step 2, as indicated in Figure 1.
  • the process mixture coming from the cationization step enters a first additional washing stage 3a.
  • the process mixture is mixed with the washing medium coming from a consecutive second additional washing stage 3b, indicated by arrow Y2.
  • the cationized starch and the liquid process medium are separated from each other in the first additional washing stage 3a, whereby the process mixture comprising mainly cationized starch is transferred to the consecutive second additional washing stage 3b, as indicated by arrow X1 , and the liquid process medium is exited from the washing stages, indicated by arrow Y3.
  • the process mixture is mixed with the washing medium coming from a washing step 3, indicated by arrow Y1 .
  • the process mixture and the washing medium is mixed and separated in the similar manner as in the first additional washing stage 3a, whereafter the process mixture comprising mainly cationized starch is transferred to the washing step 3, indicated by arrow X2.
  • the washing medium enters the counter-current washing at the washing step 3 closest to the separation step 2, and is there mixed with the process mixture from the second additional washing stage 3b. This means that the cleanest washing medium entering the washing step 3 is used to wash process medium which have already gone through the preceding additional washing stages and contains already relatively pure cationized starch. From the washing step 3, the process mixture is transferred to the separation step 2.
  • a process mixture of 433 grams of 2,3-epoxypropyltrimethylammonium chloride, EPTAC (72 %), 749 grams of potato starch (dry content 80 %), 3000 grams of isopropanol and 301.5 grams of water were placed in a 10-liter Lodige reactor equipped with a plough mixer, a thermostated jacket and a thermometer. The reactor pressure was atmospheric throughout the whole synthesis. The process mixture was agitated with 150 rpm and heated to 50 °C, and then 16.84 ml of 50 % NaOH aqueous solution was added to start the cationization reaction.
  • the process mixture was kept in 50 °C for 24 hours, after which the process mixture was cooled to the room temperature (about 25 °C), neutralized with 10 % HCI and removed from the reactor.
  • the process mixture was poured into a Buchner funnel and the liquid phase was removed by filtering.
  • Reaction yield calculated from the formation of the process mixture was 81 .4 %.
  • the liquid phase contained 990 ppm of EPTAC, 10 ppm of CHPTAC, 1770 ppm of HPTAC and 3260 ppm of DHPTAC.
  • Example 2 Washing tests of cationized starch
  • cationized starch prepared in the same manner as Example 1 , were washed with different solvents or solvent-water mixtures as the washing medium. Before washing, the cationized starch contained following amounts of impurities, including reaction by-products: EPTAC 58 ppm, CHPTAC 4.2 ppm, HPTAC 5130 ppm and DHPTAC 22600 ppm.
  • Washing of dried and ground cationized starch was performed in Erlenmayer flasks with stirring with different solvent or solvent-water mixtures as the washing medium.
  • the washing time was 2 hours in room temperature (about 25 °C).
  • the samples were centrifuged, solids were analysed for impurities by UPLC-MS/MS analysis. Washing medium impurity contents are given in Table 1 .

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Abstract

The invention relates to a method for producing cationized starch having a degree of substitution of at least 0.2. The method comprises providing a process mixture comprising starch dispersed in a liquid process medium comprising water and an organic liquid, and allowing the starch to interact with a cationizing agent in a cationization step. After this the process mixture comprises cationized starch dispersed in the liquid process medium comprising reaction by-products formed. The cationized starch is separated from the liquid process medium in a separation step. The liquid process medium is divided in a distillation step into an organic liquid phase and a water phase, wherein the water phase comprises the reaction by-products. The organic liquid phase is recirculated back to any process step where the organic liquid is present.

Description

METHOD FOR PRODUCING CATIONIZED STARCH
The present invention relates to a method for producing cationized starch according to the preamble of the enclosed independent claim.
Cationized starch is widely used chemical substance in various industries, especially in the manufacture of paper, board or the like, where cationized starch is commonly used to improve water drainage and retention. It is known that cationized starch may be used to improve the quality of produced paper or board, such as by improving its strength. The current trend to reduce the use of petroleum-based chemicals and to replace them with renewable biobased alternatives has increased the interest in cationized starch in general, and in finding new industrial applications for cationized starch. There is special interest in highly cationized starch, which is easier to dissolve in water. In order to be able to use the cationized starch in demanding and/or regulated applications, e.g. involving food contact, it is desirable that the cationized starch has a high purity.
Cationization of starch is conventionally performed by slurrying starch in water at an alkaline pH and allowing the starch to react under mixing with a cationizing agent which is added to the slurry. Usually 2,3-epoxypropyltrimethylammonium chloride (EPTAC) or 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) are used as cationizing agents. The process mixture remains throughout the process in slurry form, which means that the granular structure of the starch is maintained during the cationization step. The problem with the conventional cationization method is that with an increasing cationization degree the water-solubility of the starch increases rapidly. This leads to partial or complete gelatinization of the starch, which transforms the original slurry in a dough-like paste, making the mixing and water separation hard or even impossible. Furthermore, the conventional cationization methods generate side reactions, which provide inactive by-products, such as (2,3-dihydroxypropyl)trimethylammonium chloride (DHPTAC) and/or 3- hydroxypropenyltrimethylammonium chloride (HPTAC). The amount of these byproducts may be significant, and they reduce the purity of the produced cationized starch. The by-products may decrease the efficiency of the cationized starch when it is used e.g. as flocculant and may cause extra load to the flocculation system.
In view of the increased interest in the industry for cationized starch with high cationicity and high purity, there is a clear need for a simple and efficient process for its production.
An object of this invention is to minimise or possibly even eliminate the disadvantages existing in the prior art.
Another object of the present invention is a method of producing cationized starch with high cationicity and low amount of by-products.
These objects are achieved by the features disclosed in the independent claims. Some preferred embodiments of the present invention are presented in the dependent claims. The features recited in the dependent claims are mutually freely combinable unless otherwise explicitly stated.
The exemplary embodiments presented in this text and their advantages relate to all aspects of the present invention, even though this is not always separately mentioned.
A typical method according to the present invention for producing cationized starch having a degree of substitution of at least 0.2, comprises at least the process steps of:
- providing a process mixture comprising starch dispersed in a liquid process medium comprising water and an organic liquid,
- allowing the starch to interact with a cationizing agent in a cationization step, whereafter the process mixture comprises cationized starch dispersed in the liquid process medium comprising reaction by-products formed during the cationization step,
- separating the cationized starch from the liquid process medium in a separation step, - dividing in a distillation step the liquid process medium into an organic liquid phase and a water phase, wherein the water phase comprises the reaction by-products,
- recirculating the organic liquid phase back to any process step where the organic liquid is present, and
- drying the separated cationized starch in a drying step.
Now it has been surprisingly found that performing the cationization of starch in a presence of a liquid process medium comprising water and an organic liquid, it is possible to avoid many of the problems relating to the increased solubility of the starch during the cationization process. The present invention also provides efficient recirculating of the organic liquid within the process, which makes the process both economical and sustainable, as the consumption of the organic liquid can be minimised. Furthermore, the undesired reaction by-products can be easily and efficiently removed from the produced cationized starch and from the cationization process, as they remain dissolved in the water phase. In this manner the waste flows from the cationization process can be kept as low as possible, which is environmentally beneficial. Especially, the organic liquid waste can be minimized.
The method according to present invention is intended for producing cationized starch having a degree of substitution of at least 0.2, preferably at least 0.3, more preferably at least 0.4. The cationized starch may have the degree of substitution in a range of 0.2 - 1 .0, preferably 0.3 - 0.9, more preferably 0.4 - 0.8 or 0.5 - 0.8. In the present context, the degree of substitution defines how many substituted groups are contained in the cationized starch, calculated per one anhydroglucose unit of starch. The present invention is thus intended for production of cationized starch with a high cationicity or very high cationicity. With the present method it is possible to produce, for example, cationized starch which is water-soluble at temperature of <60 °C, preferably <50 °C.
The starch, which may be used in the present invention for cationization, can be any available starch, such as potato starch, waxy potato starch, rice starch, corn starch, waxy corn starch, wheat starch, barley starch, pea starch or tapioca starch. According to one preferable embodiment the used starch is selected from potato starch, corn starch and tapioca starch.
Reaction by-products formed during the cationization step include (2,3-dihydroxy- propyl)trimethylammonium chloride (DHPTAC) and 3-hydroxypropenyltrimethyl- ammonium chloride (HPTAC). The total amount of the reaction by-products, especially (2,3-dihydroxypropyl)trimethylammonium chloride (DHPTAC) and 3- hydroxypropenyltrimethylammonium chloride (HPTAC), in the cationized starch produced by the present method may be less than 5 weight-%, preferably less than 4 weight-%, more preferably less than 3 weight-%, sometimes even less than 1 weigh-%, calculated from the total dry weight, after drying of the produced cationized starch. In some embodiments the total amount of the said by-products may be 0.1 - 5 weight-%, preferably 0.3 - 4 weight-% , more preferably 0.5 - 3 weight-%, calculated from the total dry weight, after drying of the produced cationized starch.
The cationization of the starch occurs in a cationization step, where the cationizing agent is allowed to interact with the starch in a process mixture. Typically the cationization step is performed in an elevated temperature. The temperature of the process mixture during cationization step may be in a range of 40 - 70 °C, preferably 45 - 60 °C.
The process mixture comprises starch to be cationized, a cationizing agent and a liquid process medium comprising water and an organic liquid. The process mixture can be prepared in a separate preparation step preceding the cationization step or the process mixture may be prepared directly to the cationization reactor employed in the cationization step. The process mixture is in form of a slurry or a dispersion, formed by mixing the individual components of the process mixture together. Starch to be cationized may be provided in a form of dry particulate material, i.e. aggregates or powder, having a water content of 5 - 25 weight-%, preferably 10 - 20 weight-%.
The cationization agent used in the present invention may be any cationization agent conventionally used for cationization of polysaccharides. According to one preferable embodiment the cationization agent is selected from 2,3- epoxypropyltrimethylammonium chloride (EPTAC) or 3-chloro-2- hydroxypropyltrimethylammonium chloride (CHPTAC) or any of their mixtures.
The cationization reaction between the starch and the cationizing agent occurs at alkaline pH. The pH of the process mixture may be adjusted to the desired alkaline pH level by addition of an alkaline agent, for example strong base such as NaOH or KOH, to the process mixture. For example, the alkaline agent, such as NaOH, can be added to the process mixture in amount that is 3 - 30 mol-%, preferably 5 - 20 mol-%, more preferably 7 - 15 mol-%, of the amount of the cationizing agent.
The organic liquid used in the liquid process medium is water-miscible and able to form a homogenous mixture with water. The organic liquid is preferably an alcohol, for example a secondary or tertiary alcohol. The organic liquid may be selected from a group comprising ethanol, n-propanol, isopropanol, butanol, tert-butanol, secbutanol, or any of their mixtures, preferably n-propanol, isopropanol, butanol, tertbutanol, sec-butanol, or any of their mixtures. In some embodiments the organic liquid may be acetone; acetonitrile; or methyl ethyl ketone. In the cationization step the liquid process medium may comprise 60 - 90 weight-%, preferably 65 - 85 weight-%, more preferably 70 - 80 weight-% of organic liquid, calculated from the total weight of the liquid process medium. For example, in the cationization step the liquid process medium may comprise 65 - 78 weight-% of organic liquid, calculated from the total weight of the liquid process medium. The high amount of organic liquid in the liquid process medium reduces the solubility of the cationized starch and thus makes it possible to provide cationized starch with very high degree of cationic substitution without risk of gelatinization during the cationization step.
The liquid process medium, and thus the process mixture, comprises water in addition to the organic liquid. Water is required for the efficient reaction between the cationizing agent and starch. In the cationization step, the liquid process medium may comprise <40 weight-%, preferably <35 weight-%, more preferably <30 weight- %, of water, and/or >5 weight-% or >10 weight-%, preferably >15 weight-%, more preferably >20 weight-%, of water, calculated from the total weight of the liquid process medium. According to one embodiment, in the cationization step the liquid process medium may comprise 5 - 40 weight-% or 10 - 40 weight-%, preferably 15 - 35 weight-%, more preferably 20 - 30 weight-%, sometimes 22 - 35 weight-%, of water, calculated from the total weight of the liquid process medium. The water forming a part of the liquid process medium may originate from the used raw materials, i.e. from starch, the organic solvent and/or cationizing agent. Alternatively, water can be added either to the process mixture or to the liquid process medium in an appropriate amount in order to obtain the desired water content in the process mixture.
According to one embodiment of the present invention the liquid process medium in the cationization step may comprise water and the organic liquid in a weight ratio from 2:3 to 1 :9, preferably from 2:4 to 1 :6, more preferably from 2:5 to 1 :4 (water:organic liquid). It has been found that these ratios of water to the organic liquid can provide an efficient cationization reaction while minimising the risk for starch dissolution during the cationization step.
According to one embodiment, in the cationization step the weight ratio of the other constituents of the process mixture, selected from starch, water, cationizing agent and optional alkaline agent, to the organic liquid can be from 2:1 to 1 :5, preferably 4:3 to 1 :3, more preferably 1 :1 to 1 :2 (other constituents:organic liquid).
The cationization step results in a dispersion of cationized starch, i.e. cationized starch particles or granules, which are dispersed in the liquid process medium. The process mixture remains thus in form of a dispersion or a slurry throughout the cationization step. The viscosity of the process mixture, at the end or after the cationization step, may be <1000 mPas, preferably <500 mPas, more preferably <200 mPas. The viscosity may be, for example, in a range of 1 - 1000 mPas, preferably 5 - 500 mPas. As the cationized starch is in particle or granule form in the process mixture, even after the cationization step, the cationized starch can be easily separated from the liquid process medium. The process mixture can be neutralized after the cationization step by an addition of an acidic agent, such as hydrochloric acid. After neutralization, the pH of the process mixture may be in a range of pH 5 - 9.
The reaction by-products formed during the cationization step in the cationization reaction, such as (2,3-dihydroxypropyl)trimethylammonium chloride (DHPTAC) and/or 3-hydroxypropenyltrimethylammonium chloride (HPTAC), are soluble in water and are present in the process mixture as dissolved in the liquid process medium. This means that when the cationized starch is separated from the liquid process medium, it is simultaneously separated from the reaction by-products.
The cationized starch may be separated from the liquid process medium in a separation step. The separation step may employ any suitable solid-liquid separation technique, such as filtration, decantation or centrifuging. Preferably the cationized starch is separated from the liquid process medium by filtration, decantation or centrifuging.
After the liquid process medium is separated from the cationized starch in the separation step, it is transferred to a distillation step. In the distillation step the liquid process medium is divided into an organic liquid phase and a water phase by distillation. The reaction by-products remain in the water phase, and thus they can be removed from the cationization process, whereas the organic liquid phase may be recirculated back to any process step of the cationization method where the organic liquid is present or used. The present invention thus not only minimises the consumption of the fresh organic liquid in the process, but enables easy and efficient removal of undesired by-products, such as (2,3-dihydroxypropyl)trimethyl- ammonium chloride (DHPTAC) and 3-hydroxypropenyltrimethylammonium chloride (HPTAC) from the cationized starch, as well as from the cationization process.
The cationized starch may be dried in a drying step. The drying may be performed by evaporating the moisture from the cationized starch. The cationized starch is usually dried to moisture content of at most 10 weight-%, preferably at most 7 weight-%. Liquid process medium removed from the cationized starch in the drying step can be condensed, collected and recirculated. According to one preferable embodiment the organic liquid evaporated during the drying step may be collected after the drying step, e.g. by using a condenser, and recirculated to the washing step.
According to one preferable embodiment of the invention the cationized starch may be further purified or washed in a washing step located after the cationization step and before the drying step, preferably before the separation step. In the washing step, a washing medium comprising or consisting of organic liquid is added to the process mixture for purifying the obtained cationized starch. The washing medium is mixed with the process mixture, including the cationized starch, whereby the washing medium becomes a part of the process mixture in the washing step. More specifically, the washing medium becomes a part of the liquid process medium of the process mixture. In this manner the composition of the liquid process medium in the washing stage may be altered from its composition in the cationization stage to ensure an effective transfer of the reaction by-products to the liquid process medium and obtainment of purified cationized starch. Simultaneously the dissolution of the cationized starch into the liquid process medium can be minimized. The washing step may be performed at a temperature in a range of 0 - 60 °C , preferably 10 - 50 °C, more preferably 20 - 40 °C.
The washing medium added to the process mixture at the washing step comprises water and an organic liquid, which preferably is the same organic liquid which is used for the liquid process medium in the cationization step. The washing medium may comprise <35 weight-%, preferably <30 weight-%, more preferably <25 weight- %, of water, calculated from total weight of the washing medium. Typically the washing medium may comprise 1 - 35 weight-%, more preferably 2 - 30 weight-%, more preferably 5 - 25 weight-%, of water, calculated from total weight of the washing medium.
Typically the washing medium may comprise 65 - 99 weight-%, more preferably 70 - 98 weight-%, more preferably 75 - 95 weight-%, of the organic liquid, calculated from total weight of the washing medium. The organic liquid of the washing medium may be an alcohol, acetone; acetonitrile; or methyl ethyl ketone, preferably an alcohol selected from a group comprising ethanol, n-propanol, isopropanol, butanol, tert-butanol, sec-butanol, or any of their mixtures. As stated above, preferably the washing medium and the liquid process medium comprise the same organic liquid. The washing medium may comprise or consists of fresh organic liquid or preferably the washing medium comprises or consists of organic liquid recirculated from the other steps of the cationization process. The washing medium may comprise both fresh and recirculated organic liquid. The possibility to recirculate and reuse the organic liquid within the cationization process makes it economically and environmentally more feasible as the chemical consumption is minimised.
According to one preferable embodiment, at least a part of the organic liquid phase from the distillation step is recirculated to the washing step. The organic liquid phase from the distillation step can be used to form a part of the washing medium or it can be used as the washing medium.
In the washing step, the process mixture may comprise cationized starch and liquid process medium, comprising water and organic liquid, in a weight ratio from 1 :1 to 1 :100, preferably 1 :4 to 1 :20, more preferably 1 :6 to 1 :10 (cationized starch:liquid process medium). The liquid process medium during the washing step preferably comprises <35 weight-%, preferably <30 weight-%, more preferably <25 weight-%, of water, calculated from the total weight of the liquid process medium. For example, the liquid process medium in the washing step may comprise 1 - 35 weight-%, more preferably 2 - 30 weight-%, more preferably 5 - 25 weight-%, of water, and/or 65 - 99 weight-%, more preferably 70 - 98 weight-%, more preferably 75 - 95 weight-%, of the organic liquid, calculated from the total weight of the liquid process medium. The composition of the process mixture in the washing step ensures that the risk of dissolution of the cationized starch during the washing is minimised, while the effective removal of possible reaction by-products from the cationized starch is ensured.
The liquid process medium usually has a higher water content in the cationization step than in the washing step. After the washing step, the process mixture is transferred to the separation step where the purified cationized starch is separated from the process liquid medium, as described above. Preferably the purified cationized starch is separated from the process liquid medium by filtration, decantation or centrifuging. The separated process liquid medium may be transferred to the distillation step, from where it may be recirculated back to any process step of the cationization method where the organic liquid is present or used, e.g. to washing step.
In addition to the above-described washing step, the purification or washing of the cationized starch may further comprise one or more, preferably a plurality of, additional washing stages, such as two, three or four consecutive additional washing stages. Each individual additional washing stage comprises an addition of washing medium to the process mixture and separation of the cationized starch and liquid process medium, preferably by filtration, decantation or centrifuging. The additional washing stages may work in counter-current fashion. For example, two or more washing stages can be arranged in a successive manner, where the separated cationic starch may be transferred to the consecutive additional washing stage, whereas the separated liquid process medium may be used in a preceding additional washing stage as the washing medium. In this embodiment, purification or washing may comprise, for example, at least two additional washing stages, including a first additional washing stage and a second additional washing stage, and optional intermediate additional washing stages between the first and the second washing stage. The washing medium is first contacted with the process mixture in the second additional washing stage, and then led through the preceding intermediate additional washing stages to the first additional washing stage where it is contacted with the process mixture coming from the cationization step and entering the washing. As for the process mixture, it is first contacted with the washing medium in the first additional washing stage, and then led through the consecutive intermediate additional washing stages to the second additional washing stage. Alternatively, the additional washing stage may be carried out by using a counter-current extractor, such as a screw extractor, where the cationized starch is fed to the extractor through an inlet at a first end of the extractor and removed through an outlet at a second end of the extractor. The washing medium is fed to the extractor through an inlet at the second end of the extractor and removed through an outlet at the first end of the extractor.
According to one embodiment, the liquid process medium from the washing step or from the additional washing stages may be recirculated to in the cationization step to form a part of the process mixture. The liquid process medium from the washing step/additional washing stage may be used for forming the process mixture without purification. Usually the amount of possible by-products is so low in the liquid process medium after washing step/additional washing stages that it does not have any negative impact on cationization reaction, when used for the process mixture.
Preferably the present method for producing cationized starch is a continuous method or at least part of the method is continuous. For example, the cationization step may be performed as a continuous process or as a batch process. The purifying or washing, especially when comprising several additional washing stages, is usually performed as a continuous process.
In the following, some non-limiting embodiments of the invention will be described in detail. The appended schematic drawings form part of the description. In the drawings,
Figure 1 shows an embodiment according to the present invention for producing cationized starch, and
Figure 2 shows schematically an embodiment of the purifying or washing of the cationized starch in counter-current fashion.
Figure 1 shows one embodiment of the method for producing cationized starch according to the present invention. A process mixture comprising starch granules or starch particles dispersed in a liquid process medium is prepared in a preparation step 11 . A feed of starch, indicated with arrow A, a feed of liquid process medium comprising water and an organic liquid, indicated with arrow B, and a feed of a cationizing agent, indicated with arrow C, are fed to the preparation step 11 to form the process mixture. The pH of the process mixture may be adjusted by a feed of alkaline agent, indicated with a dashed arrow aa. The process mixture is then transferred to a cationization step 1. During the cationization step, the cationizing agent present in the liquid process medium interacts with the starch granules or particles, whereby a dispersion of cationized starch is obtained. This dispersion may comprise reaction by-products, which are at least partly dissolved in the liquid process medium.
It is possible that the feeds of starch, liquid process medium and cationization agent are fed directly to the cationization step 1 , i.e. the process mixture is formed directly to a cationization reactor without any preceding preparation step. It is also possible that the organic liquid and the water are fed as separate feeds to form the liquid process medium either in the preparation step 11 or the cationization step 1 .
After the cationization step 1 , it is possible to transfer the obtained process mixture comprising cationized starch directly to a separation step 2, indicated with dashed arrow D, but preferably the process mixture of cationized starch is transferred to a washing step 3, located between the cationization step 1 and the separation step 2.
In the washing step 3, a feed of washing medium comprising organic liquid is added to the process mixture. The washing step 3 may comprise one or more additional washing stages, as described more closely in Figure 2.
From the washing step 3, the process mixture comprising cationized starch is transferred to the separation step 2, where the cationized starch is separated from the liquid process medium comprising dissolved reaction by-products. The separated purified cationized starch is transferred to a drying step 4. In the drying step, the residual liquid process medium remaining in the cationized starch after separation is removed by evaporation.
The liquid process medium comprising dissolved reaction by-products is transferred after the separation step 2 to a distillation step 5, where it is divided into an organic liquid phase and a water phase. The water phase comprises the reaction by- products and is removed from the cationization process, as indicated by arrow E. The organic liquid phase can be recirculated back to any process step, where the organic liquid is present. For example, the organic liquid can be recirculated back to the preparation step 11 for preparing the process mixture, to the cationization step 1 or to the washing step 3.
In the embodiment of Figure 1 , the organic liquid phase from the distillation step is transferred to a collection step 6 for collecting the recirculated organic liquid, as indicated by arrow F. Organic liquid separated from the purified cationized starch by evaporation in the drying step 4 can also be transferred to the collection step 6. From the collection step 6, recirculated organic liquids from different process stages are combined and recirculated back for preparation of the process mixture or for use in the washing stage. If needed, fresh organic liquid can be added to the recirculated organic liquids at the collection step 6, indicated by arrow G.
Figure 2 shows schematically an embodiment for purifying or washing of the cationized starch in a counter-current fashion between the cationization step 1 and the separation step 2, as indicated in Figure 1. The process mixture coming from the cationization step, indicated by arrow X, enters a first additional washing stage 3a. In the first additional washing stage 3a, the process mixture is mixed with the washing medium coming from a consecutive second additional washing stage 3b, indicated by arrow Y2. After this, the cationized starch and the liquid process medium are separated from each other in the first additional washing stage 3a, whereby the process mixture comprising mainly cationized starch is transferred to the consecutive second additional washing stage 3b, as indicated by arrow X1 , and the liquid process medium is exited from the washing stages, indicated by arrow Y3. In the second additional washing stage 3b, the process mixture is mixed with the washing medium coming from a washing step 3, indicated by arrow Y1 . The process mixture and the washing medium is mixed and separated in the similar manner as in the first additional washing stage 3a, whereafter the process mixture comprising mainly cationized starch is transferred to the washing step 3, indicated by arrow X2. The washing medium, indicated by the arrow Y, enters the counter-current washing at the washing step 3 closest to the separation step 2, and is there mixed with the process mixture from the second additional washing stage 3b. This means that the cleanest washing medium entering the washing step 3 is used to wash process medium which have already gone through the preceding additional washing stages and contains already relatively pure cationized starch. From the washing step 3, the process mixture is transferred to the separation step 2.
EXPERIMENTAL
Some embodiments of the present invention are described in the following nonlimiting examples.
Example 1
A process mixture of 433 grams of 2,3-epoxypropyltrimethylammonium chloride, EPTAC (72 %), 749 grams of potato starch (dry content 80 %), 3000 grams of isopropanol and 301.5 grams of water were placed in a 10-liter Lodige reactor equipped with a plough mixer, a thermostated jacket and a thermometer. The reactor pressure was atmospheric throughout the whole synthesis. The process mixture was agitated with 150 rpm and heated to 50 °C, and then 16.84 ml of 50 % NaOH aqueous solution was added to start the cationization reaction. The process mixture was kept in 50 °C for 24 hours, after which the process mixture was cooled to the room temperature (about 25 °C), neutralized with 10 % HCI and removed from the reactor. The process mixture was poured into a Buchner funnel and the liquid phase was removed by filtering.
After drying the resulting cationized starch product had the following properties:
- Charge density by particle charge titration: 1 .71 meq/g
- Turbidity of 3 % water solution 34.5 NTU
- Viscosity of 3 % water solution ca. 19000 mPas
- EPTAC content 480 ppm
- CHPTAC content 330 ppm
- HPTAC content 4500 ppm
- DHPTAC content 8080 ppm.
Reaction yield calculated from the formation of the process mixture was 81 .4 %. After separation of the liquid and solid phases, the liquid phase contained 990 ppm of EPTAC, 10 ppm of CHPTAC, 1770 ppm of HPTAC and 3260 ppm of DHPTAC.
Example 2: Washing tests of cationized starch
Samples of cationized starch, prepared in the same manner as Example 1 , were washed with different solvents or solvent-water mixtures as the washing medium. Before washing, the cationized starch contained following amounts of impurities, including reaction by-products: EPTAC 58 ppm, CHPTAC 4.2 ppm, HPTAC 5130 ppm and DHPTAC 22600 ppm.
Washing of dried and ground cationized starch was performed in Erlenmayer flasks with stirring with different solvent or solvent-water mixtures as the washing medium. The washing time was 2 hours in room temperature (about 25 °C). After the washing, the samples were centrifuged, solids were analysed for impurities by UPLC-MS/MS analysis. Washing medium impurity contents are given in Table 1 .
Table 1 Washing medium impurities after washing.
Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.

Claims

1 . Method for producing cationized starch having a degree of substitution of at least 0.2, the method comprising at least process steps of:
- providing a process mixture comprising starch dispersed in a liquid process medium comprising water and an organic liquid,
- allowing the starch to interact with a cationizing agent in a cationization step, whereafter the process mixture comprises cationized starch dispersed in the liquid process medium comprising reaction by-products formed during the cationization step,
- separating the cationized starch from the liquid process medium in a separation step,
- dividing in a distillation step the liquid process medium into an organic liquid phase and a water phase, wherein the water phase comprises the reaction by-products,
- recirculating the organic liquid phase back to any process step where the organic liquid is present, and
- drying the separated cationized starch in a drying step.
2. Method according to claim 1 , characterized in that washing medium comprising organic liquid is added to the process mixture in a washing step for purifying the obtained cationized starch before the separation step.
3. Method according to claim 2, characterized in that the method comprises one or more additional washing stages, where each individual additional washing stage comprises an addition of washing medium to the process mixture, and a separation of the cationized starch and liquid process medium.
4. Method according to claim 2 or 3, characterized in that at least a part of the organic liquid phase from the distillation step is recirculated to the washing step.
5. Method according to any of the preceding claims 2 - 4, characterized in that the organic liquid is collected after the drying step and recirculated to the washing step.
6. Method according to any of preceding claims 1 - 5, characterized in that in the cationization step the liquid process medium comprises <40 weight-%, preferably <35 weight-%, more preferably <30 weight-%, of water, calculated from the total weight of the liquid process medium.
7. Method according to any of preceding claims 1 - 6, characterized in that in the cationization step the liquid process medium comprises >10 weight-%, preferably >15 weight-%, more preferably >20 weight-%, of water, calculated from the total weight of the liquid process medium.
8. Method according to any of preceding claims 2 - 7, characterized in that the washing medium comprises <35 weight-%, preferably <30 weight-%, more preferably <25 weight-%, of water.
9. Method according to any of preceding claims 2 - 8, characterized in that in the washing step the process mixture comprises cation ized starch and liquid process medium in a weight ratio from 1 :1 to 1 :100, preferably 1 :4 to 1 :20, more preferably 1 :6 to 1 :10 (cationized starch:liquid process medium).
10. Method according to any of preceding claims 2 - 9, characterized in that the liquid process medium has a higher water content in the cationization step than in the washing step.
11 . Method according to any of preceding claims 1 - 10, characterized in that the separation in the separation step is performed by a solid-liquid separation technique, such as filtering, decantation or centrifuging.
12. Method according to any of preceding claims 1 - 11 , characterized in that the organic liquid is an alcohol, preferably selected from ethanol, n-propanol, isopropanol, butanol or any of their mixtures; acetone; acetonitrile; or methyl ethyl ketone.
13. Method according to any of preceding claims 1 - 12, characterized in that the cationization agent is selected from 2,3-epoxypropyltrimethylammonium chloride (EPTAC), 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) or any of their mixtures.
14. Method according to any of preceding claims 1 - 13, characterized in that amount of reaction by-products in the cationized starch after the drying is less than 5 weight-%, preferably less than 4 weight-%, more preferably less than 3 weight-%, or 1 weight-%, calculated from the total dry weight, after drying of the produced cationized starch.
EP23833846.1A 2022-12-27 2023-12-22 Method for producing cationized starch Pending EP4642815A1 (en)

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