EP1853522A1 - Method for separating solid materials suspended in aqueous systems by means of colloidal flocculants - Google Patents

Abstract

The invention relates to a method for separating solid materials suspended in aqueous systems consisting in adding a flocculant, which consists of polymer colloidal particles with cationic surface charge, into said system and in subsequently separating flocculated materials therefrom.

Description

Process for separating suspended solids from aqueous systems with colloidal flocculants

The invention relates to a process for the separation of suspended solids from aqueous systems, in which this is mixed with a flocculant of polymeric colloid particles with cationic surface charge and then the flocculated material is separated from the aqueous system.

The separation of suspended solids, which can range in size from a few nm to a few 100 μm, is not only essential in water treatment and wastewater technologies. Even in numerous technical processes, such as papermaking, this process step is an integral part of the respective process. The rational implementation of such separation processes requires the use of flocculants as adjuvants, which have gained importance here in terms of technology. By adding flocculants, the finely divided particles of technical spoilage found in many industries (water, metal, paper, food, ceramics, printing, biotechnology, pharmaceutical and cosmetics, etc.) can become large and rapid. sedimenting flakes and thus significantly increases the effectiveness of mechanical solid-liquid separations ("Polyelectrolytes, Formation, Characterization, Application", Carl Hanser Verlag, Munich, 1994).

In some cases, inorganic compounds such as iron or aluminum salts are used as flocculants. Under application conditions these usually form large-volume flakes, which include the material to be separated. A decisive disadvantage is that the amounts of inorganic salts used are comparatively high and, as a result, large volumes of sludge are formed. Most flocculation processes therefore use water-soluble, organic polymers as flocculants. Both naturally occurring and synthetic polymers are used. The natural polymers are predominantly based on starch as the main body and have the disadvantage that these flocculants are usually applicable in relatively large quantities and then only for a limited number of processes.

Flocculants based on synthetic polymers have the advantage that they can be produced very specifically with regard to chemical structure and molecular parameters for the particular application. This has resulted in a larger number of flocculants being commercially available. That's in usually cationic or anionic polyelectrolytes which vary with regard to the charge density, the molecular weight and the composition. Typical examples of cationic polyelectrolytes are the condensation products of dimethylamine and epichlorohydrin, the poly (diallyldimethyl-ammonium chloride) and the copolymers of acrylamide and quaternary esters or amides of acrylic acid or methacrylic acid. A typical example of an anionic polyelectrolyte are copolymers of acrylamide and acrylic acid.

The polyelectrolytes which are technically used as flocculants are linear macromolecules, which are molecularly dissolved under conditions of application. These polyelectrolyte flocculants can be used in very different technologies. These include the one-time or sequential addition of the polymers. In addition, anionic and cationic polyelectrolytes can be applied one after the other in a single process. Well proven technologies are now available for most technical separation processes and it is possible to stably manage a number of flocculation processes. This concerns e.g. municipal wastewater treatment as well as production processes such as papermaking.

In addition, particulate complexes of polycations and polyanions which are present as colloids are described as flocculants (H.M. Buchhammer, M. Oelmann, G. Petzold: Melliand Textile Reports 5 (2001) 391-394; G. Petzold, A Nebel, H. -M. Buchhammer, K. Lunkwitz: Colloid Polym, p. 276 (1998) 125-130). These colloids can carry both anionic and cationic charges. The production conditions of the particulate complexes are used to adjust the charge and, to a limited extent, the size of these particles. The disadvantage is the comparatively larger polymer requirement, which has hitherto prevented a technical application. Furthermore, the particle density is relatively small, which is also disadvantageous for the application as a flocculant.

In the totality of the flocculation processes, however, two major deficits still exist. On the one hand, this concerns the width of the flocculation area (flocculation window) in numerous technically implemented processes, ie the range between the minimum and maximum amount of polyelectrolyte, the addition of which enables optimal separation. The larger this flocculation window is, the lower is e.g. the risk of re-stabilization of the particles

Reloading and the safer the separation process is to master. In practice, only in water molecularly soluble polyelectrolytes of different charge density and molecular weight are used, in which this flocculation window is usually small (W. -M. Kulicke, Chemie-Ingenieur-Technik 61 (1989) 10).

A widening of the flocculation window would i.a. bring significant benefits: minimization of the influence of interfering factors, such as pH change, change in the ionic strength, change in the solids concentration.

Furthermore, there are a number of previously unresolved or not satisfactorily resolved separation problems. This concerns: Suspensions containing finely divided particles with low surface charge,

- suspensions with low solids concentration,

- suspensions containing high levels of accompanying substances (surfactants, stabilizers, dyes, oils) that interfere with the separation process,

- Concentrated suspensions (sludges) containing particles with a very broad distribution and whose fines are difficult to separate.

Typical examples can be found in the slurries of microelectronics and the wastewater from the pharmaceutical, food and textile industries.

In order to be able to carry out flocculation processes stably and safely and to be able to technically practice solid-liquid separations which have hitherto been impossible or unsatisfactory, the disadvantages of known materials and processes must be overcome.

The present invention is based on the underlying object to provide flocculants, which lead to flocculation to wide flocculation windows and continue to solve the hitherto unsolved separation problems in dilute or finely divided suspensions and suspensions with high levels of impurities and with very broad particle size distribution. Likewise, the task is to eliminate the disadvantages of the prior art mentioned.

This object is achieved by the method having the features of claim 1. In claim 11 uses according to the invention are given. The further dependent claims show advantageous further fertilize.

According to the invention, a process for separating suspended solids from aqueous media is provided, in which the aqueous medium is mixed with a flocculant of a polymeric colloid particle with cationic surface charge and then the flocculated material is separated from the aqueous medium.

Preferably, colloid particles are used which are formed by emulsion copolymerization of a hydrophobic vinyl monomer with a cationic vinyl monomer. The emulsion copolymerization is preferably carried out in the feed process. The preparation can also be done in a batch process.

Preference is given to using colloid particles consisting of styrene and / or its homologs, e.g. 3, 4-vinyltoluene or t-butylstyrene as hydrophobic monomers and N-methacryloyloxyethyl-N, N, N-trimethylammonium chloride (MADAM), N-methacryloyloxyethyl-N, N-dimethyl-N-benzylammonium chloride (MADAMBQ) and / or 4-vinylpyridine (4-VP) are formed as cationic monomers.

Essential in the flocculant according to the invention is the cationic surface charge, wherein both the cationic surface charge can be bound directly or via a spacer to the particle surface.

The colloid particles cm preferably have a charge density of 5 .mu.C / ² to 35 .mu.C / cm ^2, and particularly sawn vorzugt of 8 .mu.C / cm ² to 22 .mu.C / cm ^2. The size of the colloid particles according to the invention is preferably from 50 to 1000 nm, preferably from 100 to 150 nm.

For the separation process amounts of the flocculant are used, depending on the aqueous medium sufficient. Separation of the suspended solids allows. Preferably, 0.01 to 500 mg / l g of suspended solids are used.

In one embodiment of the method according to the invention, the ionic strength of the aqueous medium is increased. This can be done in particular by adding inorganic salts or changing the pH of the aqueous medium. The process is therefore preferably in a pH range of 1 to 14 and particularly preferably to 9 in a ^'pH range. 3

The invention also provides the use of cationic surface charge polymeric colloid particles for separating suspended solids from aqueous media. This includes all previously described flocculants which are based on the colloid particles according to the invention. As watery

Media come in particular slurries of microelectronics and wastewater of the pharmaceutical, food and textile industries in question.

With reference to the following examples, the inventive object is intended to be explained in more detail, without wishing to restrict it to the specific embodiments described here. example 1

Preparation of Polymeric Colloidal Particles with Cationic Surface Charge (Styrene / MADAMBQ)

In 156 ml of ultrapure water, 0.137 g of borax and 0.12 g of hexadecyltrimethylammonium bromide (CTAB) are dissolved. The solution is placed in a 250 ml double-jacketed glass reactor and stirred there with added 14 g of styrene at 350 / min to form an emulsion. Now the reactor contents are purged with nitrogen for 20 minutes. It is then heated to 60 ⁰ C and further rinsed. After 10 min at 60 ⁰ C, the polymerization by rapid feed of 2.4 g of V-50 (2,2'-azo-bis (2-amidinopropane) dihydrochloride from Wako Chemical) dissolved in 20 ml ultrapure water, from started a dropping funnel. At the same time, the pumping of an aqueous comonomer solution to the polymerization batch is started. For this, (1) 0.7 g and (2) 1.4 g and (3) 2.1 g and (4) 2.8 g and (5)

3.5 g of 75% aqueous MADAMBQ solution (ATOCHEM) diluted with ultrapure water to 20 ml and filled into an appropriate syringe. The contents are pressed into the reactor uniformly over 2.2 h by syringe pump (see Latices No. 1 - No. 5 in Tab. After 6 hours of polymerization, the latex is cooled and the nitrogen flow is interrupted. The latex is filtered using a fine metal sieve and dialyzed for precleaning in Visking dialysis tubing (SERVA) against deionized water for 3 days. The

Fine purification is carried out by ultrafiltration in stirred 400 ml cells (Berghof) on nuclear track membranes (Whatman) with 100 nm diameter of the cylinder pores. Molar concentration data (in moles per liter of water, with 0.196 liters of water):

Borax I, 83 * 10 ^"3 mol / l, CTAB I, 68 * 10 ^{" 3} mol / l, styrene 0.685 mol / l, V-50 4.52 * 10 ^{~ 2} mol / l, MADAMBQ 1) 9.44 * 10 ^{~ 3} mol / l, 2) l, 88 * 10 ^{~ 2} mol / l, 3) 2,83 * 10 ^"2 mol / l, 4) 3,76 * 10 ^{~ 2} mol / l, 5) 4 , 72 * 10 ^'2 mol / 1.

Example 2

(Styrene / MADAM) Following the procedure of Example 1, MADAM was used as the cationic comonomer. Additions of MADAM solution (75%) in 20 ml ultrapure water via the syringe pump: (6) 0.52 g and (7) 1.04 g and (8) 1.56 g and (9) 2.08, respectively g or (10) 2.60 g - Latices No. 6 - No. 10 in Tab.l.

Example 3

(Styrene / 4-vinylpyridine) Following the procedure of Example 1, the cationic comonomer 4-VP was used. Additions of 4-vinylpyridine in 20 ml of ultrapure water via the syringe pump: (11) 0.195 g and (12) 0.389 g and (13) 0.585 g and (14) 0.78 g and (15) 0.975 g-latices, respectively No. 11 - No. 15 in Tab. 1.

Characterization: The latex particles were examined for their size and surface charge. The particle size distribution was determined by means of dynamic light scattering (BI-90 or FOQELS / Brookhaven Inc.). The titration of the

Surface charge density was measured using a combination of a particle charge detector (PCD-03 pH / MÜTEK) and an autotitrator (Titrino 716 / Metrohm). With series of measurements of the electrophoretic mobility with increasing ionic strength, it was possible to prove that the surface of the surface is advantageous for flooding. The particles used are not smooth but hairy. Most of the charges are located on the water-soluble polymer chains, which protrude into the surrounding, aqueous medium. (Zetamaster S / Malvern Instruments).

A compilation of synthesized cationic latex particles is given in Table 1.

Table 1

Comonomer in -> MADAMBQ -> MADAM -> 4 - vinylpyridine feed

Matrix Monomer No. D LD No. D LD No. D LD

[nm] [μC / cm ² ] [nm] [μC / cm ² ] [nm] [μC / cm ² ]

Styrene 1 149.3 8.0 6 131 6.5 11 177 3.8

Styrene 2 117.5 10.7 7 129 9.2 12 156 6.2

Styrene 3 111.3 17.0 8 126 11.1 13 138 8.3

Styrene 4 130.2 15.1 9 127 13.7 14 143 9.9

Styren 5 114,2 21,6 10 124 15,4 15 • 151 11,7

Example 4

Flocculation of suspensions

The flocculation was monitored by measuring the optical density (OD) of the aqueous systems to be assessed at 500 nm (OD ₅₀₀ ) using a Lambda 900 UV / VIS spectrometer (Perkin-Elmer). The flocculation is considered good if the supernatant is clear. Optically clear supernatants are achieved at OD ₅₀₀ values equal to or less than 0.3.

To 50 ml of a stable silica suspension (10 g / l) in water at pH 10 with stirring (JAR test system) different volumes of the respective cationic Latices (solids content 4.2-5.4%) added. After a sedimentation time of 1 hour, samples of the supernatant were taken and the optical density was measured. The flocculation window (optimal flocculation area with clear supernatant) was determined as the ratio of mg of latex to substrate concentration. The results are summarized in Table 2.

Table 2. Flocculation of silica with cationic latices

Latex flocculation window

No . mg / g

1 110-170

2 60-80

3 10-25

4 8-25

5 2-9

6 120-170

7 70-90

8 50-70

9 10-30

10 7-25

1150-210

12 130-190

13 70-100

14 60-90

15 40-65

Example 5

A low charge, low solids disperse dye of 80 mg / l was dispersed in water. To 50 ml of this dye dispersion were added, while stirring, different volumes of a catalyst. No. 5 latex, the subsequent stirring time being 15 minutes. After a sedimentation time of 1 hour, samples of the supernatant were taken and the optical density was measured. The supernatant was clear and completely colorless. The FIO ckungsfenster was C _Par b _S toff / Cp _o iymer of 20 mg / 1 without re-stabilization in the investigated range up to 200 mg /. 1

Comparative example

A low charge, low solids disperse dye of 40 mg / l was treated with commercial cationic polyacrylamides according to the procedure of Example 3. It was not possible to achieve a flocculation without remaining strong residual color.

Claims

claims 1. A process for the separation of suspended solids from aqueous media, in which the aqueous medium is treated with a flocculant of a polymeric colloid particles with cationic surface charge and then the flocculated material is separated from the aqueous medium. 2. Method according to claim '1, characterized in that the colloid particles are formed by emulsion copolymerization of a hydrophobic vinyl monomer with a cationic vinyl monomer. 3. Method according to the preceding claim, characterized in that the emulsion copolymerization is carried out in the feed process. 4. The method according to any one of claims 2 or 3, characterized in that the colloid particles of styrene and / or its homologs, in particular 3, 4-vinyltoluene or t-butylstyrene, as hydrophobic monomers and N-methacryloyloxyethyl- N, N, N-trimethylammonium chloride, N- Methacryloyloxyethyl-N, N-dimethyl-N-benzylammonium chloride and / or 4-vinylpyridine can be prepared as cationic monomers. 5. Method according to the preceding claim, characterized in that the cationic charge is bonded directly or via spacers to the particle surface. 6. Method according to the preceding claim, characterized in that the charge density of the colloid particles of 5 .mu.C / cm ² to 35 microns / cm ^2, in particular from 8 .mu.C / cm ² to 22 .mu.C / cm ^2. 7. The method according to any one of the preceding claims, characterized in that the size of the colloid particles is from 100 nm to 150 nm. 8. The method according to any one of the preceding claims, characterized in that the flocculant is used in amounts of from 0.01 to 500 mg per 1 g of suspended solid. 9. The method according to any one of the preceding claims, characterized in that the ionic strength of the aqueous medium, in particular by adding inorganic salts or changing the pH is increased. 10. The method according to any one of the preceding claims, characterized in that the process is carried out in a pH range of 1 to 14, in particular in a pH range of 3 to 9. 11. Use of cationic surface charge polymeric colloid particles for separating suspended solids from aqueous media. 12. Use according to claim 11, characterized in that the aqueous media are slurries of microelectronics or waste waters of the pharmaceutical, food or textile industries.