Technical Field

The invention is designated to the production of starch derivatives and use thereof in technology. Cationic starch derivatives are perspective flocculants for use in water treatment and dewatering of municipal wastewater sludge, as such derivatives are produced from cheap, biodegradable and naturally reproducible raw materials. Besides, such derivatives are nontoxic and biocompatible. Background Art of the Invention

Destabilization of disperse systems in biotechnology, metallurgy, mining, water treatment, in food and pharmaceutical industries is usually carried out to separate the solid phase from liquid. In these fields, cationic starch (HCS) with the high degree of substitution (DS) by cationic groups may be used. On the other side, in paper manufacture a cationic starch of various dispersity with low degree of substitution (LCS), containing small amounts of quaternary ammonium groups (£>S<0.1), is used. The efficiency of cationic starch depends on the amount of cationic groups, molecular mass and polyelectrolyte conditions.

Preparing the working flocculant paste - gelatinized starch - from soluble LCS [Thomas D.J., Atwell W.A. Starches. Eagan Press Handbook Series 0-891 127-01-2, 1999, 94 p.] it is usually dispersed in hot water or jet cooked. The easier methods for chemical-mechanical dispergation of starch and LCS are also known [as US4579944, etc.]. Here the stable suspension of starch or derivatives thereof are obtained upon acting polysaccharide aqueous suspensions, containing the added NaOH solution, with use of shear forces at room temperature from few tens of minutes to several hours, and afterwards neutralizing the alkalis. To improve mechanical and consumer properties of the product in paper manufacture, it is proposed to use cross-linked LCS [WO2012076163; WO2006007045; EP1061086; W09746591 ; CN102796202], grafted and cross-linked starch copolymers [EP1452552, etc.] or cross-linked ampholyte starch [US5523339], The technological properties of such aqueous suspensions are predetermined not only by the chemical composition of the target additive [EP1452552; EP0603727], origin of starch used in the manufacture of the product [WO2006007045; EP0139597], but also by condition of modified polysaccharide after dispergation, which condition is predetermined by the number of covalent bonds between macromolecules and the method for preparation of modified starch suspensions. For example, EP0603727 points out that increasing the amount of cross-linking agent - epichlorohydrin, the viscosity of gelatinized starch obtained after its jet-cooking decreases up to 85 percent of the initial value. Upon selection of optimal conditions for starch chemical modification with cationic cross-linking agents and of gelatinization conditions [WO0214602], it is possible to obtain the product in the form of microparticles of the desirable size and starch suspension of cross-linked LCS of required viscosity [EP 1061086]. Using the latter in paper formation the quality becomes improved as well as the production process.

Use of additives for cross-linked LCS aqueous suspension is also known in paper manufacture [WO0208516]. Said suspension is obtained by dispergation LCS with use of shear forces in the aqueous solution, containing compounds, bearing the hydroxyl groups, where said LCS is mixed with 0.01-7% by weight of the cross-linking agent. During such processing, discrete particles of cross-linked LCS are formed, which degree of substitution by cationic groups is not higher than 0.1. The obtained suspension, being added into the paper formation mass, improves the retention of ingredients contained as well as paper strength in dry condition. However, soluble LCS or cross-linked LCS has too low density of positive charges to be effective in the preparation of drinking water, water treatment in the wastewater sludge thickening or dewatering processes.

In water treatment, cationic starch with high degree of substitution (HCS) may act as a flocculant, where the degree of substitution of its hydroxyl groups by cationic substances is higher than 0.1. Such HCS flocculants are obtainable by one-step etherification method, acting the natural starch in the form of microgranules with glycidyltrimethylammonium chloride (GTAC) in the presence of organic or inorganic bases. As the result of such reaction, cationic starch - N-(2-hydroxy)propyl-3-trimethylammonium starch chloride - is formed. In this case, after removing the residual reagents, the aqueous suspension of the flocculant from cationic starch is prepared by mixing microgranular cationic starch for one hour in water at 20-60°C and further keeping for 8-24 hours at room temperature [Bratskaya S. Effect of Polyelectrolyte Structural Features on Flocculation Behavior: Cationic Polysaccharides vs. Synthetic Polycations // Schwarz S., Laube T., Liebert T., Heinze T., Krentz O. // Macromolecular materials and engineering. 2005, vol. 290, p. 778-785; Sableviciene D., Klimaviciute R., Bendoraitiene J., Zemaitaitis A. Flocculation properties of high-substituted cationic starches // Colloids and Surfaces A: Physicochemical and Engineering Aspects. ISSN 0927-7757. 2005, vol. 259, p. 23-30]. In the latter case a flocculant is obtained purified from impurities after etherification reaction by stirring for one hour of cationic starch in water at 20°C and thereafter keeping the suspension obtained for 8 hours at room temperature or additionally treatment in the autoclave at about 126°C temperature for not less than 30 minutes. The flocculation efficiency of N-(2-hydroxy)propyl-3-trimethylammonium starch chloride might be increased by dispergation of cationic starch in the solution of bivalent cation salts or in seawater [WO2004041732], By dispergation with use of shear forces of the starch etherification mixture, containing HCS, after reaction in the hydrogen peroxide solution, the accessibility level of N-(2-hydroxy)propyl-3-trimethylammonium groups of HCS not less than 73 percent can be reached [Lithuanian patent LT5926]. However, the flocculation window of this soluble HCS flocculant, obtained after processing using shear forces, is strongly narrowed (see Fig, curve 1), and it becomes complicated to maintain the stable flocculation process.

Properties of the HCS flocculant undergo changes after cross-linking macromolecules thereof. The cross-linked HCS may be obtained by a graft copolymerization method [CN 102898666] · or during the reaction between cationic starch and cross-linking agents, such as difunctional epoxides, dialdehydes, triazine, N-methylol derivatives and epichlorohydrin [CN101700922]. According to China patent CN101700922 mentioned cross-linked HCS flocculants are obtained by reacting the starch simultaneously with both reagents, containing cationic groups, and cross-linking agents, or by cationization of already cros,s-linked starch. Epichlorohydrin, difunctional epoxides, aldehydes, triazine derivatives and compounds, containing N-methylol groups, are used for cross-linking. Thus modified starch becomes an environment-friendly flocculant, which is able to bind soluble anionic dyes. According to the invention description, in the production of cross-linked HCS epichlorohydrin is used in the amount of not less than 0.02% by weight (0.04 mol/AGU). Therefore, when processing this cross-linked HCS using shear forces, it is not possible to achieve the accessibility of cationic groups higher than 15 percent and to obtain the effective flocculant, suitable for water treatment. A method to obtain cross-linked ampholyte polysaccharide with high degree of substitution according to cationic groups from tapioca starch is known [CN 102898666], A synthesis is carried out by grafting of dimethylammonium chloride, acrylic acid or derivatives thereof to the starch macromolecules and cross-linking with difunctional reagents, then drying and milling. Thus obtained material of cross-linked macromolecules with ampholyte properties is resistant to acids, heating and the impact of shear forces. However, due to the latter property, such cationic starch has the low flocculation efficiency.

The above-mentioned cross-linked HCS products due to the high amount of cross bonds cannot be processed using shear forces to the degree, when the amount of cationic groups accessible for polyanions could exceed 15 percent of the total. Therefore, using them in the processes of separation of dispersed solid substances, the flocculant input increases by at least a few times. In water preparation and water treatment, in processing the surface water, in wastewater treatment and in sludge processing by separating the solid particles from water, it would be expedient to use a flocculant, a small amount of which would cause a rapid and complete destabilization of aqueous suspension, while restabilization would start later, in the presence of as large as possible quantities of a flocculant. Such flocculant would be especially distinguished for its broad flocculation window. The broader the flocculation window, the lower is risk of restabilization of solid particles, including impurities, and the safer is the process of separation of impurities. Using the flocculant of above-mentioned properties it would be possible to flocculate both the diluted and concentrated suspensions, containing the solid particles of various sizes; to reduce the impact of changes of such factors of the process as pH of the suspension, ionic strength, concentration of solid substances and particle size thereof, while destabilization of such disperse system would be quite stable. Moreover, in expanding the possibilities of the application of flocculants, the flocculants which are able not only to settle down the solid particles of impurities, but also to bind water-soluble anionic substances (detergents, dyes, stabilizers, etc.) are needed. Then after flocculation the more clean water can be obtained. The composition of cationic starch flocculants in the present description is characterized by the amount of cationic groups (a degree of substitution, DS) and accessibility thereof for polyanions (AP). The quality of starch flocculants is characterized by the minimum amount of the flocculant C (parts of flocculant mass per mille parts of the dispersed phase), for example, mg/g of kaolin, in the presence of which the suspension destabilization occurs up to 10% of the residual turbidity (RT) and by the width of the flocculation window (W). The flocculation window (W) is defined as a difference between maximum and minimum (C) amounts of cross-linked cationic starch amounts, at which presence the residual turbidity (RT) is less than 10%. W value is expressed as amount of cross-linked cationic starch in parts of flocculant mass per mille parts of the dispersed phase- The larger W, the less dangerous is the restabilization of suspension particles and the safer is the process of separation of solid particles from liquid.

Thus, the main object of present invention is obtaining of effective cationic starch flocculant for water treatment, which would distinguish by:

a) a broad flocculation window in the presence of small amounts of starch flocculants;

b) higher capability of binding of soluble anionic substances (such as dyes, residues of pharmaceutical preparations, heavy metals, especially salts of chromium anions, etc.).

With the use of a flocculant of the properties mentioned, the impact of changes of such process factors as pH of disperse system, ionic strength, concentration of solid substances and the size of particles thereof could be reduced; the suspension destabilization process could be stable; and the soluble anionic impurities could be removed during flocculation together with suspended particles.

Summary of the Invention

To achieve the object of present invention a new modified starch flocculant, based on a cationic starch, obtained by dispergation with use of shear forces is proposed, wherein said modified starch is cross-linked cationic starch of discrete particles, able to bind soluble anionic pollutants, and exhibiting a degree of substitution according to cationic groups not less than 0.15, preferably 0.15-0.28, an accessibility of cationic groups for polyanions from about 15% to about 40%, and a broad flocculation window, wherein said flocculation window means the difference between maximum and minimum flocculant amounts, necessary to destabilize the suspension up to 10% of residual turbidity. More specifically, the modified starch flocculant of the present invention is characterized in that for degree of substitution of the modified starch according to cationic groups being not less than 0.15, the flocculation window is not less than 35 parts by weight of the flocculant per mille parts of the dispersed phase. In one of preferred embodiments said modified starch is cross-linked N-(2-hydroxy)propyl-3-trimethylammonium starch chloride of no larger than submicron particles. The native starch is selected from the group, consisting of potato starch, tapioca starch, wheat starch, corn starch, rice starch, preferably is potato starch.

According to the main embodiment, the modified starch flocculant of present invention is designated for use in water treatment.

Another object is a disperse system, comprising the modified starch flocculant of present invention and the dispersion medium, wherein said system comprises 1-50% of said modified starch, and said dispersion medium comprises water or water mixture with multifunctional alcohols, such as ethanediol, glycerol, maltose, and sorbitol.

One of the embodiments of the invention is said disperse system in the form of paste, wherein the amount of said modified starch comprises preferably 15-40%.

A method of production of the modified starch flocculant according to present invention comprises steps of starch cationization and dispergation with use of shear forces, wherein during the processing starch cross-linking is carried out. In one of the preferred embodiments of the method of production of the modified starch flocculant said starch cross-linking step is carried out before cationization, during cationization or during dispergation with use of shear forces, the molar ratio of components starch anhydroglucoside unit (AGU) : cross-linking agent (CLA) : cationization agent (CA) : base : water being preferably 1 : (0.0005-0.005) : (0.17-0.40) : (0.006-0.048) : (3.5-10).

To produce the modified starch flocculant according to present invention said starch or cationic starch is cross-linked in the alkaline medium, using the cross-linking agent, selected from the group, consisting of epichlorohydrin, phosphates, difunctional epoxides, aldehydes, triazines and N-methylol derivatives.

Said dispergation with use of shear forces is carried out by milling, grinding and/or extruding of cross-linked cationic starch in the dispersion medium. In the preferred embodiment of present invention said dispergation with use of shear forces is carried out after swelling of cross-linked cationic starch in the dispersion medium up to the balance state. Brief Description of the Drawing

The substance of the invention is illustrated in the drawing (hereinafter Fig.), showing the dependence of residual turbidity (RT) of flocculated kaolin suspension on the amount of the flocculant from cationic starch, added to the suspension (mg/gk _ao iin): 1 - soluble cationic starch flocculant, obtained by dispergation with use of shear forces, wherein DS-0.2 and AP=77% (Example 6 of the description); 2 - cross-linked cationic starch flocculant, obtained by dispergation with use of shear forces, according to the present invention, wherein DS=0.19 and AP=29¾ (Example 1 of the description); 3 - soluble cationic starch flocculant, wherein DS=0.20 and AP=\ 8%, (Example 6 of the description).

Detailed Description of the Invention

As mentioned above, the key object of the invention is effective cross-linked HCS flocculant (Table 1), able to precipitate particles of suspension in a broad interval of cross-linked HCS amounts (the flocculation window, W, being broad) and, additionally, able to remove soluble anionic substances from the suspension. This is achieved by etherification of microgranules of native potato, tapioca or cereal starch, for example, with glycidyltrimethylammonium chloride (GTAC) by introducing from 0.15 to 0.28 molls GTAC to starch anhydroglucoside unit (AGU) and cross-linking polysaccharide with difunctional cross-linking agents in the basic conditions in one or two stages (general scheme is given below), and then processing it using shear forces in the dispersion medium until from 15 to 40 percent of N-(2 -hydroxy )propyl-3- trimethylammonium (cationic) groups accessible for polyanions appear in cross-linked cationic starch. The size of discrete submicronparticles of obtained cross-linked cationic starch is less than 10 μιη, optimally is about 1 μιη.

Table 1

Quality parameters of effective cross-linked HCS flocculant

Flocculation window W >35

Minimum required amount C, mg/gkaoiin <15

Accessibility of cationic groups for polyanions AP, % 15-40 A general scheme of one- and two-stage synthesis is as follows:

Cross-linked cationic starch

R - -H or -CH ₂ -CH(OH)-CH ₂ -N ⁺ (CH ₃ )3 CI ^'

As can be seen from the synthesis scheme provided, in all cases cross-linked cationic starch is obtained, which during synthesis or afterwards is processed by dispergatioii with use of shear forces. It is possible to obtain cross-linked cationic starch in one-stage method by etherification of natural starch (including potato, wheat, corn, rice starches) with a cationization agent, such as glycidyltrimethylammonium chloride or other, and simultaneously cross-linking with a cross-linking agent, such as epichlorohydrin or phosphates, difunctional compounds, containing epoxy, aldehyde, triazine, N-methylol groups, etc. When obtaining cross-linked starch in two-stage method, the cationic starch is obtained first, which is then cross-linked with the selected cross-linking agent, or the cross- linked cationic starch is etherified with a cationization agent.

In producing the cross-linked microparticle HCS by One-stage method, an etherification mixture is prepared by mixing the solution of NaOH or of other base (for example* benzyltrimethylammonium hydroxide) with glycidyltrimethylammonium chloride (GTAC), adding to such mixture a cross-linking agent (CLA) (epichlorohydrin (EPI) or some other, for example, sodium trimetaphosphate (STMP)), air dried natural starch and stirring all thoroughly. The molar ratio of the reagents in the heterogeneous reaction mixture 1 is AGUstarch". CLA : GTAC : base : H ₂ 0 = 1 : (0.0005-0.00065) : (0.17-0.35) : (0.04-0.048) : (3.5-4.6). The reaction is carried out at 30-55°C temperature for 56-20 hours.

In producing the cross-linked microparticle HCS by a two-stage method, cross-linked starch is produced first and then cationized. Cross-linked starch is obtained by pouring epichlorohydrin (EPI), emulsified in the water-alkaline mixture, into 50% aqueous potato starch suspension and stirring well the mixture obtained with a magnetic stirrer at room temperature. The molar ratio of the reagents in the heterogeneous mixture 2 is AGU : EPI : NaOH : H ₂ 0 = 1 : 0.005 : 0.006 : 10. Reaction is carried out at 30-55°C temperature for 56-20 hours. Cationization is carried out by the etherification of cross-linked starch, for example, with glycidyltrimethylammonium chloride (GTAC), in the alkaline medium. To obtain cross- linked HCS, an etherification mixture is prepared by mixing NaOH solution with GTAC, adding cross-linked starch to such mixture and stirring components thoroughly. The molar ratio of the reagents in the heterogeneous mixture 3 is AGU : GTAC : NaOH : H ₂ 0 = 1 : 0.40 : 0.044 : 3.15. Reaction is carried out in the heterogeneous medium at 30-55°C temperature for 56-20 hours.

In preparing 1-50% flocculant suspension from cross-linked HCS, particles of the latter in the dispersion medium (for example ₄ in water or in the mixture of water and multifunctional alcohols, like ethanediol, glycerol, and sorbitol) are milled, grinded and/or pushed through a die (extruded) to be acted upon by a shear forces. For example, 1% cross-linked HCS aqueous suspension is processed for from 10 to 30 minutes with Digital Ultra-Turrax T25 dispergator applying a rate of 15,000 rpm.

In one of the embodiment variants the cross-linked starch gel before dispergation with shear forces is allowed to swell up to the balance swelling, for example, by keeping gel for 30-60 min at room temperature. Upon maximum swelling, the particles of flocculant according to the present invention, are distinguished for their lower polydispersity.

When processing the said cross-linked HCS by extrusion method, the disperse systems, containing, for example, 30-40% of the modified starch flocculant according to the invention, are obtained in the form of paste. Such pastes may be characterized by measuring the mechanical work (J) used in production thereof per gram of cross-linked HCS. In obtaining a flocculant according to present invention by extrusion method, the amount of the mechanical work performed is between 0.1 kJ/g and 0.5 kJ/gfi _0C cuiant- To characterize the flocculant, the following values are to be determined: amount of cationic groups in cross-linked HCS (DS) and accessibility (AP, %) thereof for dextran sulphate (DeSu); flocculant efficiency by residual turbidity, which is evaluated by the light absorption of model suspensions of kaolin or of real suspensions after flocculation (turbidimetric investigation of suspensions). Methods for determination of these parameters are generally known and are described, for example, in Lithuanian patent LT5926.

According to the determination methods mentioned, the amount of cationic groups in the modified starch is calculated as a degree of substitution (DS) from the formula (1):

162 - N

1400 - 151,5 - N wherein N is the amount of nitrogen in a sample, %, 162 - the mass of anhydroglucoside unit (AGU) of the starch.

The amount of cationic groups, bounded with polyanions (DeSu) AoeSu , g-eq/g in the cross- linked starch is calculated from the equation (2):

V · N

^A DeSu ⁼ ~^~ ^{> (2)}

wherein V is amount of DeSu, used for titration, ml; N - DeSu concentration, g-eq/ml; m - amount of cationic starch in the solution volume, used for analysis, g.

The amount of accessible cationic groups (AP), % in the cross-linked cationic starch is calculated from the equation (3):

AP = ApeSu 100; (3)

Anltrogen J wherein AoeS is the amount of quaternary ammonium groups bounded by DeSu, g-eq/g; Anitrogen - the total amount of quaternary ammonium groups, determined by the Kjeldahl method, g-eq/g.

For determination of flocculation efficiency of a flocculant, the finely dispersed kaolin, received from Sigma-Aldrich (USA), is used. The geometrical average of particle diameter, calculated from the curves of particle size distribution according to the volume (Delsa™ Nano C, Beckman Coulter, USA), was 0.7-0.85 μπι.

Suspensions of kaolin were prepared by ultrasonic treatment of the finely dispersed aqueous kaolin suspension of 1 g/1 concentration for 15 minutes.

Destabilization of kaolin suspension: destabilization treatment with kaolin suspensions is performed at room temperature. The required amount of flocculant is poured into a glass with 50 ml of the prepared kaolin suspension, stirring with the magnetic stirrer. Then suspensions are allowed to settle down, forming two fractions, and the light absorption of the upper fraction of suspension is measured at the wavelength of 500 nm (A500) with the spectrophotometer UNICAM UV3 UV/Vis. Residual turbidity (RT) is calculated from the formula (4):

ASOOf

RT = 100, %; (4)

A500 _P j wherein A500/ is light absorption of the suspension at the wavelength of 500 nm, after adding of flocculant, A500 _p - light absorption of the initial model suspension at the wavelength of 500 nm. The effective amount of cross'linked cationic starch C is calculated as the lowest amount of added cross-linked cationic starch mg/g of the dispersed phase, which induces the residual turbidity (RT) of 10%.

During the flocculation of suspension, containing the acid blue dye (Acid Blue 25) in addition to kaolin, the residual colour of suspension is determined. It is also calculated as the residual turbidity, the light absorption of suspension being measured at the wavelength of 600 nm. Description of Embodiments

The invention can be better understood from the examples provided below. This information is provided to illustrate the invention, it is not limiting the scope of protection.

Example 1

Cross-linked HCS was obtained in one stage by etherification of potato starch with glycidyltrimethylammonium chloride (GTAC) and epichlorohydrin (EPI) in the alkaline medium. The etherification mixture was prepared by mixing NaOH water solution with GTAC and EPI, adding starch to such mixture and mixing the components thoroughly. The molar ratio in the mixture was AGU : EPI : GTAC : NaOH : H ₂ O = 1 : 0.0005 : 0.22 : 0.04 : 3.5. Reaction was carried out at 45°C temperature for 48 hours. A degree of substitution of the obtained product was DS=0.19, AP of cationic groups was 4%. Flocculation window W=362, minimum necessary amount of cross-linked cationic starch being C=138 mg/gkaoiin- When producing cross-linked cationic starch flocculant, 1% aqueous suspension of the product was processed by dispergation with use of shear forces with Digital Ultra-Turrax T25 dispergator at a rate of 15,000 rpm at room temperature for 20 minutes. AP of cationic groups of cross-linked cationic starch after dispergation was 29%. The flocculation window was

^=49, C=15 mg/g _k aolin.

Example 2

Cross-linked LCS and flocculant therefrom were produced as in Example 1, the difference being the molar ratio of reagents in the mixture AGU : EPI : GTAC : NaOH : H ₂ O = 1 : 0.0005 : 0.1 1 : 0.04 : 3.5. The degree of substitution of obtained cross-linked LCS was ASM).10. Dispergation with use of shear forces resulted in accessibility of cationic groups of cross-linked cationic starch for polyanions of 85%, W=2\ , C=9 mg/gkaoiin- Example 3

Cross-linked HCS and flocculant were produced as in Example 1 , the difference being the molar ratio of reagents in the mixture AGU : EPI : GTAC : NaOH : H ₂ 0 = 1 : 0.0005 : 0.17 : 0.04 : 3.5. The obtained cross-linked HCS had the degree of substitution DS=0A 5. After dispergation with use of shear forces, AP of cationic groups of cross-linked cationic starch was 15.5%, W=35, C=15 mg/g _kao i _in .

Example 4

Cross-linked HCS and flocculant were produced as in Example 1, the difference being the molar ratio of reagents in the mixture AGU: EPI : GTAC : NaOH : H ₂ 0 = 1 : 0.0005 : 0.33 : 0.04 : 3.5. The degree of substitution of obtained cross-linked HCS AS=0.28. After dispergation with use of shear forces, AP of cationic groups of cross-linked cationic starch was 18%, W=49, C= 14 mg/g _kao iin. Example 5

Cross-linked HCS and flocculant were produced as in Example 1, the difference being the molar ratio of reagents in the mixture AGU : EPI : GTAC : NaOH : H ₂ 0 = 1 : 0.0005 : 0.44 : 0.04 : 3.5. The degree of substitution of obtained cross-linked HCS DS=0.39. After dispergation with use of shear forces, AP of cationic groups of cross-linked cationic starch was 25%, W=26, C=9 mg/g _ka0 ii _n .

Example 6

Soluble HCS was produced as cross-linked HCS in Example 1 , but epichlorohydrin was not added into the reaction mixture. The degree of substitution of HCS obtained was 0.20, AP was 18%, W=26, C=28 mg/g _kao iin.

To produce a flocculant from this HCS, the gelatinized starch was processed by dispergation, using Digital Ultra-Turrax T25 dispergator at a rate of 15,000 rpm for 15 minutes at room temperature until formation of 1% opalescent solution of flocculant. AP of cationic groups of soluble cationic starch was 77%, W=$, C=2 mg/gk _ao iin- Example 7 (comparative, according to patent CN101700922)

Cross-linked HCS was produced as in Example 1, but the molar ratio of reagents in the mixture was AGU : EPI : GTAC : NaOH : H ₂ 0 = 1 : 0.01 : 0.22 : 0.05 : 3.5. The degree of substitution of cross-linked HCS obtained was DSH).19.

Cross-linked HCS flocculant was produced as in Example 1. AP of cationic groups of cross- linked cationic starch after dispergation was 1.4%, PF=2380, C=380 mg/gk _ao ij _n .

Example 8 (comparative, with the known synthetic cationic flocculant)

Polyacrylamide synthetic soluble cationic flocculant, namely poly(acrylamide-co-N,N,N,- trimethylammonium-ethylacrylate) chloride (Praestol K122L), was dissolved in water, and 0.1% aqueous solution thereof was used for flocculation of kaolin suspension. Accessibility of cationic groups for polyanions was 100%, W=l, C=1.2 mg/gkaoiin-

Table 2 presents C and ^ parameters of LCS (Example 2), of HCS (Examples 1, 3-7) and of synthetic cationic (Example 8) flocculants. Evaluating the efficiency of starch flocculants of various substitution degrees according to cationic groups by settling of kaolin suspensions, it can be seen that only discrete particles of cross-linked cationic starch, processed with use of shear forces, a degree of substitution of which according to cationic groups is from 0.15 to 0.28, were distinguished for the flocculation window, larger than W=35, the necessary minimum cross-linked cationic starch amount C being of 15 mg/gkaoiin or lower.

It also follows from the data provided in Fig. and in Table 2 that suspension particles were effectively flocculated only by cross-linked HCS flocculants of optimal AP of cationic groups. Cross-linked HCS with DS of 0.15-0.30 acquired such quality due to mechanical processing with use of shear forces according to present invention, resulted in that in its particles from 15 to 40 percent of cationic groups accessible for polyanions appeared. The flocculation effect beyond the said limits of accessibility of cationic starch DS or its flocculant was worse. Table 2

* HCS, not processed by dispergation with use of shear forces Example 9

Cross-linked HCS was produced as in Example 1. In producing of cross-linked cationic starch flocculant, 15% aqueous suspension of the product was processed by dispergation for 4 minutes with use of shear forces using a hand stirrer Philips (power 700 W) at a rate 5. AP of cationic groups of cross-linked cationic starch after dispergation was 29%, W=40, C=10 mg/gkaolin-

Example 10

Cross _' linked HCS was obtained by the etherification of potato starch with glycidyltrimethylammonium chloride (GTAC) in the alkaline medium and adding sodium trimetaphosphate (STMP) into the reaction mixture. The etherification mixture was prepared by mixing STMP, dissolved in the water, with GTAC and NaOH solution, adding starch to such mixture and carefully mixing the components. The molar ratio of reagents in the mixture was AGU: STMP : GTAC : NaOH : H ₂ 0 = 1 : 0.00065 : 0.33 : 0.048 : 4.6. The reaction was carried out under heterogeneous conditions at a temperature of 55°C for 20 hours. A degree of substitution of the obtained cross-linked HCS was DS=0.28.

To produce cross-linked HCS flocculant, 1% aqueous suspension of the product was processed by dispergation with use of shear forces at room temperature for 10 minutes using Digital Ultra-Turrax T25 dispergator at a rate of 15,000 rpm. AP of cationic groups of cross- linked cationic starch after dispergation was 23%, ^=51, C=15 mg/gkaoiin Example 11

Cross-linked HCS was obtained in one-stage etherification of wheat starch with glycidyltrimethylammonium chloride (GTAC) and epichlorohydrin (EPI) in the alkaline medium. The etherification mixture was prepared by mixing NaOH solution with GTAC and EPI, adding starch to such mixture and carefully mixing the components. The molar ratio of reagents in the mixture was AGU : EPI : GTAC : NaOH : H ₂ 0 = 1 : 0.0005 : 0.22 : 0.04 : 3.5. The reaction was carried out under heterogeneous conditions at a temperature of 45 °C for 48 hours. A degree of substitution of the obtained cross-linked HCS DS ).19.

A cross-linked HCS flocculant was produced as in Example 10. AP of cationic groups of cross-linked cationic starch after dispergation was 29%, W=31, C=\ 1 mg/gkaoiin-

Example 12

Cross-linked HCS was produced by a two-stage method: first, cross-linked starch was obtained by pouring epichlorohydrin (EPI), emulsified in the water and alkaline mixture, into 50% aqueous potato starch suspension, and mixing well the obtained mixture at room temperature with a magnetic stirrer. The molar ratio of reagents in the mixture was AGU : EPI : NaOH : H ₂ 0 = 1 : 0.005 : 0.006 : 10. The reaction was carried out under heterogeneous conditions at a temperature of 45°C for 48 hours. Cross-linked HCS was obtained by etherification of cross-linked starch with glycidyltrimethylammonium chloride (GTAC) in the alkaline medium. The etherification mixture was prepared by mixing NaOH solution with GTAC, adding cross-linked starch to such mixture and mixing the components thoroughly. The molar ratio of reagents in the mixture was AGU : GTAC : NaOH : H ₂ 0 = 1 : 0.40 : 0.044 : 3.15. The reaction was carried out under heterogeneous conditions at a temperature of 45 °C for 48 hours. A degree of substitution of the obtained cross-linked ^* HCS £ ⁾ <S=0.28.

Producing the cross-linked HCS flocculant, 1% aqueous suspension of the product was processed by dispergation with use of shear forces using Digital Ultra-Turrax T25 dispergator at a rate of 15,000 rpm for 25 minutes at room temperature. AP of cationic groups of cross- linked cationic starch after dispergation was 20%, W=35, C=15 mg/gkaoiin- The efficient flocculant can be produced by various one- and two-stage methods (Table 3) by etherification of starch (Examples 1 and 12), using various cross-linking agents (Example 10) and raw materials of botanical origin (Example 1 1), processing by dispergation of suspensions of high HCS concentration (Example 9).

Table 3

Example 13

Polyacrylamide synthetic soluble cationic flocculant, namely, poly(acrylamide-co-N,N,N,- trimethylammonium-ethylacrylate) chloride (Praestol K122L) was dissolved in water as in Example 8 and 0.1% aqueous solution thereof was used in the thickening of 0.3% sludge from methantank (UAB "Kauno vandenys"). The flocculation window of flocculant W=36, C—2 mg/g of the dispersed phase. Example 14

Cross-linked HCS and flocculant were produced as in Example 9 and used in the thickening of 0.3% water treatment sludge from methantank (UAB "Kauno vandenys"). The flocculation window of cross-linked cationic starch W=5&, C=5 mg/g of the dispersed phase. Example 15

Polyacrylamide synthetic soluble cationic flocculant - poly(acrylamide-co-N,N,N,- trimethylammonium-ethylacrylate) chloride (Praestol K122L) was dissolved in water as in Example 8, and 0.1% aqueous solution thereof was used in the flocculation of kaolin suspension with 0.01 g/1 of acid blue dye (Acid Blue 25) added. Flocculant's W=5.5, C=5 mg/gkaoiin- The residual colour of clarified suspension (filtrate) was 16%. Example 16

Cross-linked LCS was prepared and processed by dispersgation with use of shear forces as described in Example 2. Flocculation was carried out as specified, except 0.01 g/1 of acid blue dye (Acid Blue 25) being added to the kaolin suspension. The product did not flocculate effectively this kaolin suspension with a dye as the residual turbidity was higher than 10%, and the residual colour of filtrate was 12%.

Example 17

Cross-linked HCS was prepared and processed by dispergation with use of shear forces as described in Example 1. Flocculation was carried out as specified except 0.01 g/1 of acid blue dye (Acid Blue 25) being added to the kaolin suspension. Cross-linked cationic starch had W-12, C=24 mg/gkaoiin, and residual colour of filtrate was 2%.

Table 4

Cross-linked LCS, HCS and synthetic cationic flocculants were all tested in the thickening of methantank sludge and in the flocculation of the kaolin suspensions with a dye Acid Blue 25 added. It can be seen from the data provided in Table 4, that the minimum amount of cross- linked HCS, required in the thickening of the methantank sludge, was some higher, however the flocculation window was considerably broader as compared with the industrial synthetic cationic flocculant. In the presence of aqueous soluble dye in the kaolin suspension, the flocculant from LHS was ineffective (Example 16), the synthetic cationic flocculant have flocculated quite effectively but with the narrow flocculation window (Example 15) and have bound the smaller amount of a dye than cross-linked HCS flocculant. The latter have perfectly flocculated the kaolin suspension with a dye added in the broad flocculation window (Example 17) and have bound the dye well. Example 18

Cross-linked HCS and its flocculant were produced as in Example 1, but benzyltrimethylammonium hydroxide (BTMAOH) was used as a catalyst, and the molar ratio of the reagents was AGU : EPI : GTAC : BTMAOH : H ₂ 0 = 1 : 0.0005 : 0.35 : 0.04 : 3.5. The reaction was carried out under heterogeneous conditions at 30°C temperature for 56 hours. The degree of substitution of the obtained cross-linked HCS DS=0.2$. After dispergation with use of shear forces the AP of cationic groups of cross-linked cationic starch was 19%, P =48,

C=15 mg/gkaolin-

In summary, the. present, invention as compared to the known prior art is characterized by the following main advantages:

1) the proposed flocculant flocculates suspensions effectively and has a broad flocculation window;

2) besides flocculating suspensions effectively, the proposed flocculant is also binding the soluble anionic pollutants, containing in the suspensions.

Industrial Applicability

From the experimental data provided in Examples 1-18 it should be concluded, that flocculants of the present invention may be used effectively in water treatment - including water treatment, wastewater treatment and sludge processing when separating solid particles and water soluble anionic pollutants to ensure the effective and stable process, less dependent on the pH of disperse system, ionic strength, concentration of solid substances and the size of particles thereof.