FI91642C - Cationic lignin useful as a flocculant and wastewater purification process - Google Patents

Description

91642

The present invention relates to the use of cationic lignin as a flocculant as a flocculant and to a process for the purification of wastewater.

Lignin is a natural polymer that is produced in large quantities as a by-product of the wood processing industry. When isolating cellulose, lignin enters the broths, from which, after stabilization, the heat obtained by wet combustion is an energy advantage (sulphate process). Lignin can be precipitated from the broth by acidification, as can black liquor, which can also be purified and fractionated by ultrafiltration, thus enabling chemical modification of the ultrafiltration fractions.

The lignin isolated from the sulphate broth has an average molecular weight of about 1500 to 5000, but can be fractionated, for example, by ultrafiltration or solvent treatment of black liquor, so that the molecular weight distribution is greater than 5000 for 50%.

In the past, cationic lignins have only been prepared from acid-precipitated lignins and have been incompletely tested in wastewater treatment (see, e.g., U.S. Patent Nos. 4,775,744 and 3,718,639).

In the preparation of the cationic lignin according to the invention, the ultrafiltered fraction of the waste liquor has the advantage that the acid precipitation step of the lignin from the previous methods is separated. The Tate method, in which cationic lignin is prepared from the above-mentioned material, also offers a more economical alternative to the previously known methods. Thus, a cheap cationic flocculant is obtained, which makes the treatment of large volumes of wastewater meaningful.

Ultrafiltration of black liquor also has the advantage that ultrafiltration avoids the small-molecular fraction of black liquor and obtains a fraction advantageous for flocculation of effluent colloidal substances with a molecular weight of> 2,000,642. The advantages of ultrafiltration include the naturally occurring hardening of the black liquor, whereby the stability required for cationization 5 is already achieved by this process.

In this invention, the hydroxyl groups of lignin are modified with epoxyammonium or chlorohydrin ammonium salts in "Preparation and Testing of Cationic Flocculants from Kraft Lignin", ACS Symposium Series 397, 195th National Meeting of the American Chemical Society, Toronto, Ontario, Canada, 5-11. .1988, as shown in the following diagram:

NaOH

lignin-OH + CH 2 CHCl 3 N 2 C 2 Cl 9 'slow O glycidyltrimethylammonium chloride lignin-OCH 2 CHCH 3 N 2 FCH 3 JClO

GTAK Reagent I

λ. OH

NaOH

^ NaCl + O- fast ^ CH2CHCH2N® (CH3) 3Cl2, + NaOH (chlorohydrin reagent)

:. 25 I I

QJOH N (3-chloro-2-hydroxypropyl) trimethylammonium chloride In U.S. Patent No. 3,718,639, lignin amines 30 are prepared by reacting lignin in the same manner with the reaction product of epichlorohydrin and a tertiary amine. This patent does not specify the yield in which the epoxy reagent is attached to the hydroxyl groups. The aforementioned "Preparation and Testing of 35 Cationic Flocculants from Kraft Lignin" discloses that with 91642 3 glycidyltrimethylammonium chloride, this yield can be greater than 50% for purified typical softwood soup isolated from blackheads (Indulin AT, manufactured by Westwaco Corp.). In contrast, N- (3-chloro-2-hydroxy-5-cipropyl) trimethylammonium chloride (GTAK-HCl reagent) does not give more than 50% reagent yield.

It has now surprisingly been found that starting from the ultrafiltered fraction of black and white with GTAK-HCl reagent yields more than 50% reagent yield. Reacting the black-10 alkaline lignin with the GTAK-HCl reagent also provides the advantage that the reagent neutralizes the alkali contained in the black-lip. It is essential to achieve a high reagent yield that the progress of the reaction is monitored by periodically determining the flocculation efficiency of a sample of the reaction mixture with respect to a colloidal silica standard.

At the same time, the excess NaOH relative to the chlorohydrin reagent converted to the epoxy reagent is kept low (about 10% of the reagent weight) by continuously neutralizing some of the NaOH.

The invention relates to a cationic lignin usable as a flocculant, characterized in that it is prepared from an ultrafiltered fraction of black liquor by first ultrafiltrating the black liquor, after which the ultrafiltered fraction obtained is cationized with glycine. . 25 with tritriaminonium chloride or N- (3-chloro-2-hydroxypropyl) trimethylammonium chloride.

In a preferred embodiment, the lignin can also be crosslinked with formaldehyde, whereby the network of the lignin molecule expands all the way to gelation. It has been found that as crosslinking increases, the optimum blocking dose of the corresponding cationic lignins with respect to colloidal materials decreases. At the same time, the consumption of the cationization reagent can be reduced without a decrease in the nitrogen contents of the cationized lignins.

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The effect of cationic polymers on effluents is known to adhere, alone or with inorganic coagulants, to the surface of negatively charged colloidal particles contained in effluents and to neutralize the surface charge and to remove the interparticle removal force. In this case, the colloidal components precipitate.

If a high molecular weight (MP several million) linear, cationic, anionic or neutral water-soluble polymer is present in the flocculation dose, the long flexible polymer chains bind the contaminant particles into bundles that settle as large flocs.

Iron and aluminum salts also contain, in the typical pH range (pH 6-8) of effluents, cationic molecular species that neutralize the negative surface charges of colloidal particles and rapidly polymerize into hydroxyl gels, while enclosing the harmful fraction. Often, however, coagulant doses are high and the resulting sludges do not settle well.

It is an object of the present invention to reduce the amount of inorganic sludges and to improve their settling and stability properties. This is generally accomplished with composite flocculants that include a cationic polyelectrolyte, an inorganic coagulant, and possibly a neutral or anionic high molecular weight polymer. It has now been found that in several combination doses, the cationic polyelectrolyte can be replaced by cheaper cationic lignin without compromising the flocculation efficiency.

Several experiments with phosphorus-containing effluents show that the cationic polyelectrolyte together with the Al and Fe salts not only removes colloidal solids but also significantly reduces the amount of phosphorus. In these cases, the high cost of the cationic polyelectrolyte often precludes the use of a combination dose. It has now been found that 91642 5 good results can be obtained when the cationic polyelectrolyte is replaced by cationic lignin. When replacing the potassium cationic polymer in a component dose with a cheaper cationic lignin, the removal of the phosphorus-containing colloidal fraction also becomes economical.

The flocculation efficiency of cationic polyelectrolytes and cationic lignins can be compared by preliminary tests. In the vessel test, the colloidal dispersion is precipitated at different maximum flocculant doses, whereby, after settling of the precipitate 10, the lowest residual suppression in the series indicates the optimum flocculation dose. Tests performed with a dispersion analyzer show relative floc size. By performing this test at different stirring speeds, the durations of the flocs can be compared. Microcrystalline silica and microcrystalline cellulose have been used as colloidal standard dispersions in the vessel test and analyzer tests. A pre-test for flock permeability has been used for a period of time in which the colloidal dispersion or effluent sample leaches into the same volume in a pressure filter with a 0.45 μιη: η acetate membrane and a pressure of two bar. The pores of the membrane clog quickly if there are colloidal constituents in the slurry. The settling of the flock is tested in a measuring cylinder, whereby the settling time and the volume to which the flock 25 lands are compared.

The following examples illustrate the preparation of cationic lignins from ultrafiltered black liquor.

Example 1 In this example, the ultrafiltered fraction of black liquor (Metså-Serla Oy) is started, whereby lignin is first crosslinked with formaldehyde in three different ways and then the products are cationized. The initial state is shown in Table 1.

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table 1

Initial situation for cross-precipitation and cationisation of ultrafiltered black liquor 5 _ _Grams of Molar

Markana Dry Dry Mole ratio

Lignin 10 In ultrafiltered black liquor dry matter (ka) 18.6% 100 18.6 Organic fraction 15 88.6% of ka 16.5

Reagent GTAK-HCl 53.3%, MP 188.1 48.58 21.63 0.115 l

NaOH

20 In black liquor (11.4%) 2.12

Dry matter: 42.8 X 100 = 27.9% 25 153.58

Added (as 5 M solution) 1-batch 3 ml 0.60 2-batch 10 ml 2.00 30 Total 13 4.72 0.118 1.03

The amount is 153.58 42.85

The first batch of NaOH was added before cross-linking, the second batch after cross-linking.

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Cross-linking was performed in a water bath in three 200 ml centrifuge tubes with efficient mixing. To the tubes were added 100 g of ultrafiltered blackhead (ca. 18.6%) and 3 ml of 5 N NaOH as well as 0.6, 1.0 and 1.5 ml of 37% HCHO solution and the reaction mixture was stirred at 95- At 100 ° C for 1.5 hours. Calculated per 100 g of lignin, the formaldehyde concentrations in moles were 0.049, 0.081 and 0.121, respectively.

To the cationization-cooled reaction mixtures containing cross-linked lignin, 10 ml of 5 N NaOH (2 g, 0.05 mol) and 21.63 g of GTAK-HCl reagent as a 53.3% aqueous solution were added. The reaction time at 55 ° C was 6 hours. The reaction was quenched by neutralizing the mixture with dilute hydrochloric acid. Nitrogen percentages were determined from the ultrafiltered and dried-15 products, giving a yield of 32% for reagent consumption in all crosslinking / cationization experiments. The low yield can be attributed to the hydrolysis side reaction during both reagent preparation and cationization. It can be seen from Table 2 that cross-linking of formaldehyde across the alkali lignin prior to cationization actually causes a decrease in the optimal dosage in the vessel test. Experiments with a dispersion analyzer show cross-linking to improve flock resistance (compare 25 relative floc sizes at different agitation rates). The commercial Fennopol 194 K used in the experiment is a strongly cationic polyacrylamide with a molecular weight of about 4 million.

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Table 2

Effect of CH2 crosslinking of alkali lignin on silica precipitation efficiency of the corresponding cationic lignin in ast iatest isså <a 5 _

Crosslinking Dosage <b Relative flocculent size (c degree, moles% N (a% silica 64 rpm 200 rpm 300 rpm ch2o / ioo g 10 0 2.3 0.041 0.65 0.37 0.10 0.049 2.3 0.041 0, 82 0.38 0.10 0.081 2.3 0.039 0.99 0.45 0.10 0.121 2.3 0.030 1.6-2.0 0.87 0.20

Fennopol 194 K

0.033 1.8-2.2 1.20 0.38 e) The crude product was purified by ultrafiltration through a Diaflo YM2 membrane (Amicon Corp., exclusion limit 1,000). In vessel tests, the colloidal standard dispersion was 20 microcrystalline silica (Min-U-Sil 5; Pennsylvania Class and Sand Corp.) at a stability of 250 mg / 600 ml.

c) Relative floc size was determined with a photometric dispersion analyzer (PDA 2000 / Rank Brothers Ltd).

25 Example 2

This example demonstrates that cationic lignin with a nitrogen content (purified) of 3.0% and a reagent yield of 52% can be prepared from ultrafiltered black liquor with GTAK reagent. The cationic lignin thus prepared precipitated colloidal silica more efficiently in a vessel test than the commercial Fennopol K 1912 (a slightly cationic polyacrylamide-type polyelectrolyte having a molecular weight of about 4 million). The experiment used ultrafiltered black liquor (re-35 tentate) from Met-sa-Serla Oy with a dry matter content of 16.6%. The black lipstick was evaporated at 90 ° C in an oven until the dry matter content was 29.9%.

Table 3 5 Preparation of cationic lignin from ultrafiltered black liquor glycidyltrimethylammonium chloride (GTAK) reagent11a 10 Graroma Mole-Mårkåna Dry Mole ratio

The situation in the bay

Ultrasuod. black dry matter lye, also 29.9% 604.1 180.1 content was 43.3%

Lignin 163.08

Reagent 228.8 151.47 0.999 1 GTAK, ka 79% 100% epoxide epoxide 66.2% of 20 crude products 83.8% ka

NaOH 17.87 0.447 0.447

Reacted for 4 h at 35-40 ° C and then for 45 h at 55 ° C The purified product contained 3.0% nitrogen, based on which the reagent yield was 52%.

Example 3

This example describes experiments in which solids and phosphorus were removed from the water leaving the foot treatment plant of Metsa-30 pulp Oy's Åånekoski mills. The experiments were performed in a vessel test apparatus (Phipps & Bird) in which 600 ml of effluent was added to 800 ml beakers. Precipitators were added during rapid stirring (64 rpm), after which stirring was continued for 5 min. Prior to settling the flock, 91642 10 was stirred slowly for 5 minutes (30 rpm), after which the precipitate was allowed to settle without stirring for 30 minutes. After 30 minutes, a 100 ml sample of the clarified solution was pipetted. All chemical doses are calculated per liter of 5 effluents (ppm, mg / l, g / m3).

Experiments 1 and 3, respectively, show that at a dose of 37.5 ppm for Ansu 2 (commercial aluminum sulphate, manufactured by Kemira Oy) and 1.25 ppm for cationic lignin, the reduction in phosphorus content is of the same order of magnitude 10 (49% vs. 59%) the reduction in solids content is greater (81% vs. 68%) than with Ansu 2 at 35 ppm and cationic Fennopol at 2.2 ppm.

In Experiments 5, 6 and 7, in which Fe 3 O-sulfate was used in combination with cationic lignin, the amount of phosphorus could be reduced by the same amount as in Experiment using Ansu 2 and cationic lignin, respectively (Experiment 1). Although floc deposition was promoted by neutral Fennopol N-300 (a very slightly anionic polyacrylamide with a molecular weight of about 10 million), 20 solids could only be significantly reduced in Experiment 4 (85%), in other experiments containing Fe 3+ sulphate ( 5, 6 and 7) less than 50%.

1X 91642

Table 4

Removal of phosphorus and colloidal solids from pulp mill effluent at pH 7.5 using a co-dosage of inorganic coagulant and cationic lignin or cationic poly (acrylamide) or neutral poly (acrylamide)

Experiment Inorganic Cationic Reduction% 10 No. coagulant polyelectro-phosphorus (ppm) lithium (ppm) substance

Ansu 2 cat. lignin 1 37.5 1.25 81 49 15 2 37.5 3.75 80 52 cat. Fennopol 3 35 2.2 68 59

Fe3 + sulfate cat. Fennopol lignin N-300 20 4 31.3 1.56 - 85 54 5 31 1.25 1.25 40 58 6 31 1.90 1.90 40 58 7 31.3 1.56 1.90 48 58 25 Pulp mill the effluent contained 0.95 mg / l phosphorus and 97 mg / l solids. The solution for experiment 1 contained 3 g of Ansu 2 and 100 mg of cationic lignin per liter of water. In Experiment 2, the precipitation solution contained 3 g of Ansu 2 and 300 mg of cationic lignin per liter. In Experiment 3, a solution 30 containing 5 mg of ferric acid per milliliter was used. sulfate and 0.25 mg of cationic lignin. Ferrisulfate was commercial (70%) and dried in an oven at 120 ° C to constant weight.

Example 4 This example describes how, after crosslinking from ultrafiltered black liquor with GTAK-HCl reagent, cationic lignin is obtained in a reagent yield of 73.6%.

Table 5 5 Conditions for cross-linking and cationization of ultrafiltered black liquor with GTAK-HCl reagent-_Grammaa_ Moles- 10 Mars Dry Moles ratio

Lianiini

In ultrafiltered black liquor, 15 ka 27.5% 986 271.2

Organic part 241.4

NaOH (M 40.01) in black liquor 29.8

Additions 20 1-batch (before cross-linking) 13.8 2-batch (after cross-linking) 23.0 1.665 1.68

Crosslinking 80 ° C / 6 h 25 formaldehyde! (M 30.02) 37% solution 50 18.5 0.616

Etherification 65 ° C / 6.5 h GTAK-HCl (M 188.11) 62.3% solution of active substance 300 186.9 0.994 l

The dry matter was 28.9% when crosslinked and 38.4% when etherified. The reagent in the reaction mixture was 0.994 / 241.4 x 100 = 0.412 mol / 100 g of lignin. Formal-35 dehyde was used in 0.26 moles per 100 g of lignin.

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For crosslinking, the formaldehyde was stirred in alkali lignin at 50 ° C, after which the temperature was raised to 80 ° C and the mixture was stirred at this temperature for 6 hours.

To the cooled mixture at 65 ° C was added a second portion of NaOH and the cationization reagent with stirring over 0.5 h. Stirring was continued at room temperature for 2.5 hours, at which time the reaction mixture was completely water soluble. The reaction was allowed to proceed at 65 ° C for 3.5 hours, after which the mixture was neutralized with dilute hydrochloric acid. The ultra-filtered (Amicon PM 10 membrane, M> 10,000) and dried sample contained 2.9% nitrogen.

Calculation of reagent yield: per 100 g of pure cationic lignin was. 0.20714 x 152.64 = 31.62 g of GTAK reagent and 100.00-31.62 = 68.38 g of lignin. Reagent yield: 0.207 241.4 = 73 5% 68.38 0.994

Claims (3)

91642 Patent Claims Cationic lignin useful as a flocculant, characterized in that it is prepared from ultrafiltered fractions of 5 black liquors by first ultrafiltrating the black liquor, after which the resulting ultrafiltered fraction is cationized with glycidyltriammonium chloride-N- (3-chloro-2-chloro) chloride. Cationic ligene according to Claim 1, characterized in that the ultrafiltered fraction of the black liquor is crosslinked with formaldehyde before cationization. 3. A process for the purification of wastewater, characterized in that the wastewater is treated with a cationic lignin according to claim 1 or 2. il 91042