METHOD FOR PRODUCING DERIVATIZED STARCH

Abstract

A method for producing high-purity derivatized starch which to used in the manufacture of paper and cardboard, a starch raw material is subjected to at least the following steps: purification, slurrying, derivatization, gelatinization, pH adjustment, wherein a slurry of the derivatized starch obtained after the slurrying and derivatization method steps carried out in any sequence is subjected to purification, preferably at an alkaline pH and that the purified and gelatinized derivatized starch obtained after gelatinization is mixed at least once with dilute acid as well as application.

Claims

1. Method for producing high-purity derivatized starch to be used in the manufacture of paper and cardboard, a starch raw material is subjected to at least the following steps: purification, slurrying, derivatization, gelatinization, pH adjustment, wherein a slurry of derivatized starch obtained after slurrying and derivatization method steps carried out in any sequence is subjected to purification, at an alkaline pH and the purified and gelatinized derivatized starch obtained after gelantinization is mixed at least once with dilute acid.

2. The method according to claim 1, wherein the purification of the slurry of derivatized starch is obtained by washing and concentrating in a container selected from a decanter, hydrocyclone or separators at an alkaline pH.

3. The method according to claim 2, wherein the slurry of derivatized starch is purified in at least two steps, a first alkaline washing step and a second step of washing and concentrating the slurry.

4. The method according to claim 2, wherein the second step of washing is carried out by adding at least one acid selected from mineral acids and/or organic acids at a pH between 7 to 9.

5. The method according to claim 1, wherein in the purification the slurry of derivatized starch is concentrated to a solid content of 2 to 42 wt. %.

6. The method according to claim 1, wherein the purified and gelatinized derivatized starch obtained after the gelatinization is subjected to a two-stage acidification.

7. The method according to claim 1, wherein as derivatization, a cationization is carried out with a base selected from the group of alkali hydroxides NaOH, KOH, LiOH, alkali carbonate Na.sub.2CO.sub.3 or alkaline earth oxide CaO, or alkaline earth hydroxide Ca(OH).sub.2 or NaOH, a cationization reagent 3-chloro-2-hydroxy-propyl-trimethylammonium chloride or an epoxidic cationization reagent 2,3 epoxy-propyl-trimethylammonium chloride and further substitution reagents and optional adjuvants selected from activators selected from silicates, calcium oxide or calcium hydroxide.

8. The method according to claim 7, wherein sodium hydroxide solution, recycled from a pulp production, is used in the cationization.

9. The method according to claim 1, wherein the cationization is performed to a degree of cationization between 0.02 and 0.5 required in the subsequent paper or cardboard production.

10. The method according to claim 1, wherein a native starch selected from potato starch or tapioca starch, cereal starch selected from maize starch, waxy maize starch, wheat starch, barley starch, rice starch or fruit starch selected from starch from legumes or mixtures of two or more thereof is used as starch raw material.

11. The method according to claim 1, wherein the starch is used immediately after its derivatization in lignin, pulp, paper or cardboard manufacture.

Description

DESCRIPTION OF THE DRAWING

[0023] The invention is explained in detail hereinafter with reference to a drawing and exemplary embodiment and in particular a comparison of the process management according to the prior art and the process management according to the invention is shown from which it can be seen that the derivatized starch which can be obtained by the method according to the invention has a significantly higher purity than that which can be obtained by the methods according to the prior art.

[0024] FIG. 1 shows a flow diagram which depicts the possible process sequences for producing derivatized starch according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] In FIG. 1 is a starch storage silo in which an arbitrary starch not purified previously, selected from a bulbous starch such as potato starch or tapioca starch, a cereal starch such as maize starch, wheat starch, barley starch or the like or a fruit starch such as a starch from legumes or mixtures thereof is stored. From this starch storage silo 1 the starch is either conveyed to a wet derivatisation generally designated by cycle 2 or to a dry derivatisation generally designated by cycle 3. In this case, in the wet derivatisation 2 starch from the starch storage silo 1 is conveyed by means of a conveyor screw into a slurry container 4 in which it is mixed with water to a starch suspension, with a starch concentration of 30 to 40 wt. % by agitating. A protective salt, for example, Na.sub.2SO.sub.4 is added to this starch suspension and agitated further. The wet derivatisation is then carried out either in the slurry container 4 itself or in a separate derivatisation container 5 by adding a cationization agent such as 2,3 epoxy-propyl-trimethyl-ammonium chloride, optionally activators or further substitution reagents such as salts for a phosphorisation. This mixture is further agitated for a period of about 20 minutes and then the pH is gradually increased to a pH of 11.8 by adding 4% NaOH and agitated further. In order to complete the cationization, the temperature is increased to about 40 C. and the reaction mixture is held at a pH of 11.8 over the total reaction time by adding sodium hydroxide solution as required. After the end of the reaction the pH of the reaction mixture is reduced to a pH of 9 by adding diluted mineral acid such as hydrochloric acid in a purification step 6 and held for a short time.

[0026] In order to separate the excess cationization agent, the reaction by-products, the salts that have been added and formed as well as the dissolved proteins and raw material impurities, the suspension of the cationized starch is purified by adding further water using a decanter, hydrocyclone or separators. The purification step can possibly be carried out twice or several times to remove remaining impurities.

[0027] If this is necessary, the cationized starch thus produced can be stored at a temperature between 4 and 25 C., a pH of 7.1 to 9 which is optionally set by adding dilute acid. In this case, the starch has a density between 12 Beaum and 21 Beaum or 15 wt. % to 39 wt. % of starch in the slurry. Naturally the starch can be further processed immediately without storage.

[0028] An alternative model is dry derivatisation which is carried out according to cycle 3. For this purpose non-pre-purified starch from the starch storage silo 1 is introduced into the mixing area 7 by means of a conveyer screw where it is mixed and blended with solid calcium hydroxide, an activator such as silicates and the like. In order to carry out the derivatisation, a small quantity of water and sodium hydroxide solution is sprayed onto the dry starch mixture and mixed, the cationization agent such as 2,3-epoxy propyl trimethyl ammonium chloride is then sprayed on and mixed and then the temperature is gradually increased to a reaction temperature of 30 to 80 C. and left to stand at the reaction temperature for 24 hours to 120 hours for completion of the reaction in order to reach the desired degree of substitution of the starch. The cationized starch is then slurried with dilute mineral acid in slurring area 8 until the pH has dropped to about 7 to 10. The thus cationized starch is then fed to purification area 6 for removal of excess cationization agent, reaction by-products, salts which have been added and formed, raw material impurities, dissolved proteins and the like whereby water was added and the starch is purified using the decanter, hydrocyclone or separators. After the purification step the starch can optionally be stored or fed directly to gelatinization. Such a cationized starch is stored at temperatures between 4 C. and 25 C., a pH of 7.1 to 9 which has been set by adding dilute mineral acid, a density between 12 and 21 Beaum or 15 wt. % to 39 wt. % of starch in the slurry.

[0029] The cationized starch is then fed directly from the purification stage or from a storage tank to a gelatinization area 9, whereby it is boiled in a steam injection boiler at about 125 C. for 1 to 20 minutes with a concentration of the starch suspension in the boiler between 4 wt. % and 38 wt. %.

[0030] The starch thus gelatinized can then be stored either in a stacking tank 10 at about 70 C. and a pH of 7 to 8.5 which is achieved by adding dilute mineral acid and then further diluted for the respective use in the paper and pulp industry or the pH can be set. In the stacking tank the gelatinized starch has a temperature of about 70 C., a concentration of 3 to 35 wt. % and a pH between 7 and 8.5.

[0031] In the stacking tank 10 the starch can then be re-used in an alkenyl succinic acid anhydride (ASA) method 11 in which the gelatinized starch (1 to 4 wt. %) is set to a pH of 2 to 6.5 by adding dilute acid, in particular mineral acid. A further possible use in the application of the gelatinized starch as the bulk starch in thick matter as indicated at 12. Here the content of gelatinized starch in the suspension is 1 to 4 wt. %, the pH is again between 2 to 6.5 which is adjusted by adding dilute mineral acid, which pH can optionally be adjusted depending on the desired pH of the of the paper pulp thick matter. The third possible use is the application of the gelatinized starch as bulk starch in thin matter as is indicated at 13, wherein the concentration of the starch suspension is substantially the same as that of the ASA or the thick matter application although the pH is selected to be somewhat higher, namely 5 to 7 which pH is also set by using dilute mineral acid.

[0032] The method according to the invention differs compared with the conventional method for producing derivatized, gelatinized starch in respect of the purification step which is provided after the derivatisation, which purification step was hitherto unknown in the case of a dry-cationized starch since dry-cationized starch according to the prior art is used without any further purification and which differs from wet-cationized starch in that not only a simple rinsing with water is provided but a specially selected purification device such as a hydrocyclone, decanter or also separators is used by means of which it is surprisingly possible not only to separate water-soluble contaminants but also as a result of the basic conditions of the purification step to separate all alkalinically soluble proteins, starch impurities, reaction by-products such as glycols, residue reagents such as residual epoxides and also low-molecular starch decomposition products. With this process management it is therefore possible to obtain, starting from a non-pre-purified starch raw material, a high-purity derivatized starch by means of which a better swelling is then achieved in the gelatinization with the result that a higher-quality high-purity product can be achieved overall.

[0033] The method described above for producing high-purity derivatized starch is then compared by using various non-pre-purified initial starches with the conventional cationization methods, and specifically both wet and dry cationization methods. For the comparative tests the wet and dry cationization as described in the literature was carried out. In dry cationization, after the cationization process the reaction mixture is pre-dried in a warm air drier at 50 C. and fumaric acid is added until a 5% suspension of the powder obtained in water at a pH of 5.5 was obtained. In wet cationization according to the prior art, cationization was also carried out as known from the literature and after the end of the reaction the reaction mixture obtained was acidified with dilute hydrochloric acid to a pH of 5.5, filtered and washed twice with water and the filter cake was dried to a dry powder in a warm air drier at 50 C.

[0034] The dry cationization method or wet cationization method according to the invention was carried out as shown in the flow diagram, in the wet cationization the purification was carried out at the end of the reaction by adding dilute mineral acid until a pH of 9 was achieved and the suspension was concentrated in a hydrocyclone. The concentrated starch suspension thus obtained was adjusted to pH 7 by adding dilute mineral acid and dried in a warm air drier at 50 C. to obtain a sample for the subsequent analysis. In the case of dry cationization, after the end of the reaction water was added with pH 8 until a suspension having a content of 30 wt. % starch was obtained, the suspension was adjusted to pH 8 by adding further dilute mineral acid, the slurry was purified in a hydrocyclone and the concentrate thus obtained was adjusted to pH 7 with dilute mineral acid, filtered and the filter cake obtained was dried to a dry powder in a warm air drier at 50 C. to obtain a sample for the following analysis.

[0035] The experiments were carried out using potato starch and maize starch and when examining the efficiency of the method according to the invention, on the one hand the total nitrogen after purification was determined by the Kjeldahl method, wherein % N according to the standardized Kjeldahl method gives the total nitrogen present in the sample which corresponds to the % nitrogen which was actually substituted +% nitrogen from the reaction by-products +% nitrogen from the proteins obtained.

[0036] A second examination criterion related to the insoluble components in the dry substance. In this case, 100 g of sample after acid hydrolysis was left to react in 600 ml of 0.1 normal hydrochloric acid at 100 C. for 30 minutes and the insoluble residue was determined gravimetrically after filtration and washing twice with distilled water. The results are shown in the following Table 1.

TABLE-US-00001 TABLE 1 Experiment % N of dry substance according Number Starch type Prior art Invention to Kjeldahl Insoluble dry substance 1 Potato starch 1 Dry method 0.40 630 mg/kg 2 Potato starch 1 Dry method 0.26 100 mg/kg 3 Maize starch 1 Dry method 0.37 570 mg/kg 4 Maize starch 1 Dry method 0.29 120 mg/kg 5 Maize starch 2 Wet method 0.36 2400 mg/kg 6 Maize starch 2 Wet method 0.29 450 mg/kg 7 Maize starch 2 Wet method 0.22 630 mg/kg 8 Maize starch 2 Wet method 0.16 290 mg/kg 9 Maize starch 3 Dry method 0.42 330 mg/kg 10 Maize starch 3 Dry method 0.29 130 mg/kg 11 Potato starch 2 Wet method 0.41 910 mg/kg 12 Potato starch 2 Wet method 0.31 100 mg/kg

[0037] It can be seen from Table 1 that in all the experiments which were carried out according to the method of the present invention, the total Kjeldahl nitrogen after purification according to the invention is lower than that in a purification according to the prior art, likewise the content of insoluble substances in the dry substance could be reduced significantly compared with the method according to the prior art, in some cases even by about 90%.

[0038] The purified derivatized starch thus produced was then used in thick matter, in thin matter and sizing agent in the following concentrations or under the following conditions and possible improvements or savings of chemical were investigated.

EXAMPLES

Application in Thick Matter

[0039] The high-purity derivatized starch, in particular maize starch, potato starch or mixtures thereof which can be used cationically, anionically or amphoterically, was used in the mass in the thick matter in the consistency range from 3 to 35 wt. % (corresponds to 30 to 350 g of pulp atro/I water), in particular 4-30 wt. % in a quantity of 0.05-2.5% relative to the dry pulp or the paper to increase the paper strengths, in particular the paper dry strengths but also for fixing impurities. The application which is carried out at pH values of 5 to 9, optionally by adding other process adjuvants and temperatures of 30 to 80 C. is usually carried out by using already ground fibrous material which is mixed with high-purity derivatized starch. Optionally non-ground fibrous material can also be used. Furthermore, the fibrous material can have previously been subjected to a high-consistency and/or a medium-consistency and/or a low-consistency grinding (fibrous material contents: high-consistency grinding: 20-35%, medium-consistency grinding: 10-20%, low-consistency grinding: 3-10%).

[0040] Since high-purity derivatized starch was used in the thick matter, it is possible to reduce the amount of aluminium sulphate by about 30% since on the one hand, starch acidified to the special desired intended usage could be used (as a result of the on-site manufacture of the high-purity derivatized starch) and on the other hand, it was only necessary to add significantly reduced amounts of defoamer in the thick matter, which can be attributed to the fact that the non-starch-bound nitrogen content in the derivatized starch could be significantly reduced, with the result that the foaming could be reduced without adding defoamer.

Application in Thin Matter

[0041] The high-purity derivatized starch, in particular maize starch, potato starch or mixtures thereof which can be used cationically, anionically or amphoterically, is used in the mass in the thin matter in the consistency range from 0.15 to 3%, in particular 0.18-2% in a quantity of 0.05-0.5% relative to the dry pulp or the paper to increase the fine material retention and for fixing impurities. The application is carried out at pH values of 5 to 8, temperatures of 30 to 80 C. and optionally whilst adding further process adjuvants.

[0042] Since the high-purity derivatized starch was used in the thin matter, it is possible to improve the reaction behaviour and in particular the white water can be adjusted to the optimal desired pH with the result that on the one hand, the fine material fibre load can be controlled and on the other hand, savings of retention agents can be brought about. Furthermore, it was only necessary to add reduced quantities of a defoamer in the thin matter which can be attributed to the fact that the non-starch-bound nitrogen content in the derivatized starch could be reduced significantly with the result that the foaming could be reduced without adding defoamers.

Application in ASA Sizing Method

[0043] The high-purity derivatized starches, in particular maize starch, potato starch or mixtures thereof which can be used cationically, anionically or amphoterically are preferably used in an acid-washed state with a pH of 2 to <7 in the manufacture of emulsions with sizing agent such as ASA (alkenyl succinic acid anhydride). In this case, the starches are used as protective colloid in a quantity of 0.05-0.3% relative to the dry pulp or paper to produce a stable sizing agent emulsion. The temperatures used are max. 60 C. and the pH values are preferably a maximum of 8, preferably a maximum of 7, particularly preferably in the range between pH 2 and pH since otherwise decomposition products from the sizing agent must be expected which is overall inefficient and furthermore, the formation of deposits and deposition of these decomposition products on various plant parts in the paper machine is unfavourable for operation of the paper machine since in this case, it is necessary to clean the machine using cleaning chemicals.

[0044] Since a high-purity derivatized starch was used, it is possible to adjust the pH to the lowest possible and therefore ideal pH which prevents the starch from hydrolysing and therefore a better sizing effect can be achieved. Experiments have shown that when using high-purity derivatized starch, Cobb values according to ISO 535:2014 could be achieved which corresponded to those of conventional sizing methods but for which less than 10% more ASA must be used to achieve the corresponding Cobb values.

[0045] In each of these types of use, it has been shown that when using the high-purity derivatized starch produced according to the invention, substantially a saving of chemicals such as aluminium sulphate could be achieved and in addition in this process management a pH adjustment of the pulp fibre mixture treated with the starch could be omitted.