DE69315833T2 - Hydrophobic polyelectrolyte coagulant for concentrating residues from coal processing - Google Patents

Description

The present invention relates generally to the use of novel hydrophobic polyelectrolyte compositions as coagulants for thickening or concentrating coal processing residues or coal sludges. These polyelectrolyte compositions are preferably hydrophobically associating copolymers of diallyldimethylammonium chloride (DADMAC) and either dimethylaminoethyl acrylate (DMAEA) or dimethylaminoethyl methacrylate (DMAEM).

Background of the invention

Coal is the most abundant natural energy source in the world. A significant portion of the energy needs in the United States are met by burning coal as a fossil fuel. Within the United States, several types of coal are found, i.e. anthracite, anthracite coal (semi-anthracite), low-volatile bituminous coal, medium- and high-volatile bituminous coal, brown coal (subbituminous coal), and lignite. Types of coal such as anthracite and bituminous coal usually have high ash and sulphur contents and therefore must be processed before use.

The main purpose of coal preparation is to reduce the content of non-combustible ash components in order to increase the heat content. Reducing the ash content leads to savings in terms of transportation and ash disposal costs. Sulfur, mainly in the form of pyrite, is also reduced.

Another important economic factor to consider in coal processing is the recovery and reuse of process water. Water is usually very expensive and is therefore often subject to restrictions on overall consumption. In addition, strict environmental controls prohibit or severely restrict the disposal of process water. It is therefore necessary that the solids are effectively removed from the process water and that the water is recycled into the process stream.

Coal processing is carried out by taking advantage of two main properties of coal, i.e. (1) by taking advantage of the differences in specific gravity between coal and its impurities and (2) by taking advantage of the differences in surface properties between coal and its impurities. Since the higher ash fractions are usually found in the finer coal particles, some coal processing plants only screen out these fines. However, as the amount of these fines increases, they must also be treated.

A coal processing plant can generally be divided into a section for separation using specific gravity and a section for fine coal treatment. In the separation according to specific gravity, use is made of the cleaning units of the Differentiate in specific gravity between coal and its impurities to effect separation. Normally, the specific gravity of clean coal is less than that of its impurities. Some commonly used equipment for specific gravity separation are vibrating screens, heavy liquid baths and cyclones, wash tables, water cyclones and circulators.

The fine coal treatment section includes one or more flotation cells, clean carbon filters and thickeners. In the flotation cell, a collector and a foaming agent are added to the flotation feed. The collector (e.g. diesel oil #2) makes the coal particles selectively hydrophobic. This increased hydrophobicity causes air bubbles to adhere better to the coal particles. The foaming agent (e.g. an alcohol-based product) lowers the surface tension of the air-water interface, thereby producing a stable foam.

The concentrate (i.e. the pure coal) from the flotation cells goes into the pure coal filter and is dewatered. The sludge (residues) from the flotation cell goes into the thickener, where it is thickened and discharged.

The thickener is treated with coagulants and flocculants to improve settling. Typically, the coagulants and flocculants are added at several points along the feed line into the thickener and in different sequences. Coagulation is the destabilization of stable negatively charged particles that are in suspension (i.e., settling or dispersed) by neutralizing the surface charge using inorganic salts or cationic polyelectrolytes. Flocculation is the aggregation of fine particles suspended in a liquid by using an enclosing agent (i.e., an inorganic flocculant) or a binder (i.e., an organic flocculant). which causes the particles to aggregate. Although some inorganic substances, mainly alum and iron salts, are still used as coagulants, water-soluble organic polymers are more commonly used as coagulants. Both naturally occurring and synthetic polymers are used as coagulants and flocculants in the mining industry. The main natural polymers used are starch and guar gum, both of which are polymers of simple sugars (i.e. polysaccharides) with a high molecular weight. Starch is a polymer of glucose and consists of a mixture of linear (amylose) and branched (amylopectin) segments.

Synthetic polymers have the advantage of being able to be tailored to a specific application. This has led to a wide range of commercially available coagulants and flocculants with varying charge, composition and molecular weight. The most commonly used synthetic coagulants are polydiallyldimethylammonium chloride (poly-DADMAC or DADMAC) and the condensation polymers of dimethylamine and epichlorohydrin (EPIIDMA). These structures vary widely in terms of molecular weight, which is in the range of 20,000 to 100,000.

The inventors have developed several new hydrophobic polyelectrolyte copolymers that can be used as coagulants in the thickening process during coal preparation. These hydrophobic monomers have improved performance or higher activity in thickening coal slurries than conventional inorganic and organic coagulants. In addition to hydrophobicity, the hydrophobic monomer used to synthesize the polyelectrolyte copolymers of the present invention yields copolymers with considerably higher molecular weights than the conventional synthetic DADMAC homopolymers prepared under the same conditions. In addition, by incorporating a quaternary group, such as the benzyl group, into the polyelectrolyte copolymer of the present invention, Copolymer reduces the volume viscosity of the resulting copolymer compared to the DADMAC homopolymers of comparable molecular weights. As such, the hydrophobic polyelectrolyte copolymers of the invention have higher polymer concentrations than the conventional organic coagulants. These hydrophobically associating copolymers also provide improved performance at replacement ratios (substitution ratios) on the order of 0.45 to 0.50.

The present invention also provides many additional advantages which will become apparent from the following description.

Summary of the invention

The invention relates to a process for concentrating coal tailings or coal slurries comprising liquid and colloidal particles. This process comprises the following steps: introducing the coal slurry into a thickener; treating the coal slurry with a hydrophobic polyelectrolyte copolymer coagulant comprising diallyldimethylammonium chloride (DADMAC) and a more hydrophobic monomer selected from the group consisting of quaternized dimethylaminoethyl acrylates (DMAEA) and quaternized dimethylaminoethyl methacrylates (DMAEM), the coagulant being added to the coal slurries in an amount between 22.5 and 112.5 ppm (about 0.05 to about 0.25 lb/ton), thereby reducing or neutralizing the charges on the surfaces of the colloidal particles; treating the coal slurry with a flocculant in an amount of between 22.5 and 112.5 ppm (about 0.05 to about 0.25 lb/ton) whereby the colloidal particles agglomerate and settle as concentrated slurry; discharging the substantially concentrated slurry; and withdrawing the substantially clarified liquor from the thickener.

The quaternized DMAEA and DMAEM monomers may include a quaternary methyl chloride (MCQ) or quaternary C4-C20 aliphatic and aromatic chlorides such as quaternary benzyl chloride (BCQ) or quaternary cetyl chloride (CCQ).

These hydrophobic polyelectrolyte copolymers are preferably prepared using a semi-batch process. The semi-batch process typically comprises the following steps: introducing diallyldimethylammonium chloride into a polymerization reactor vessel in an amount between about 1 and about 19 weight percent; heating the diallyldimethylammonium chloride to a temperature in the range between about 47 and about 57°C, depending on the initiator; adding a polymerization initiator dropwise to the diallyldimethylammonium chloride in an amount between about 0.05 and about 0.4 weight percent; adding a hydrophobic monomer dropwise to the diallyldimethylammonium chloride in an amount between about 3 and about 19 weight percent; and heating the mixture of diallyldimethylammonium chloride, polymerization initiator and more hydrophobic monomer to a temperature in the range between about 47 and about 82°C.

Other and further objects, advantages and features of the present invention will become apparent from the following description of the invention.

Short description of the drawing

The attached Fig. 1 shows a diagram in which the turbidity is plotted against the amount of addition (dosage) of various polyelectrolyte coagulants.

Description of preferred embodiments

The inventors have developed a new class of polyelectrolyte copolymer coagulants that offer improved performance (improved properties) in coal separation or coal slurry thickening. These coagulants are copolymers of DADMAC and a more hydrophobic monomer such as dimethylaminoethyl acrylate benzyl chloride quaternary (DMAEA.BCQ). These hydrophobically associating copolymers exhibit improved performance (improved properties) in terms of substitution ratios on the order of about 0.45 to about 0.50.

When processing fine coal, a collector and a foaming agent are added to a flotation feed. The concentrate, i.e. the clean coal from the flotation cells, goes into the pure coal filter and is dewatered. The sludge or residues from the flotation cells go into the thickener, where they are thickened and discharged.

The sludges or residues are preferably treated with coagulants and flocculants. It has been found that the neutralization of the surface charge of the colloidal particles in the sludge suspension can be improved by using a coagulant of poly(DADMAC) or DADMAC which has been modified to impart a certain degree of hydrophobicity. Such modification can be achieved by copolymerizing DADMAC with hydrophobic monomers such as DMAEA.BCQ, DMAEM.BCQ, DMAEA.CCQ, DMAEM.CCQ, DMAEA.MCQ and DMAEM.MCQ. Moreover, these copolymers are particularly effective in thickening coal sludges or coal dressing residues when prepared using a semi-batch process rather than a batch process.

This hydrophobic polyelectrolyte copolymer coagulant preferably comprises a diallyldimethylammonium chloride and a hydrophobic monomer. The hydrophobic monomer is at least one monomer selected from the group consisting of quaternized dimethylaminoethyl acrylates and quaternized dimethylaminoethyl methacrylates. DMAEA and DMAEM are preferably quaternized using C4-C20 quaternary chlorides or quaternary methyl chlorides. The preferred C4-C20 quaternary chlorides are quaternary benzyl chloride and quaternary cetyl chloride.

The DADMAC can be prepared by any conventional method, such as the method described in U.S. Patent No. 4,151,202 (Hunter et al.), issued April 24, 1979, the contents of which are incorporated herein by reference.

The quaternized dimethylaminoethyl acrylate is selected from the group consisting of quaternary dimethylaminoethyl acrylate methyl chloride and quaternary dimethylaminoethyl acrylate C4-C20 chlorides. The dimethylaminoethyl acrylates with quaternary C4-C20 chloride are preferably either quaternary dimethylaminoethyl acrylate benzyl chloride or quaternary dimethylaminoethyl acrylate cetyl chloride.

The quaternized dimethylaminoethyl methacrylate is selected from the group consisting of quaternary dimethylaminoethyl methacrylate methyl chloride and quaternary dimethylaminoethyl methacrylate C4-C20 chlorides. The dimethylaminoethyl methacrylates with quaternary C4-C20 chloride are preferably either quaternary dimethylaminoethyl methacrylate benzyl chloride or quaternary dimethylaminoethyl methacrylate cetyl chloride.

The diallyldimethylammonium chloride and the hydrophobic monomer are preferably present in a molar ratio in the range of 20:80 to 99:1.

The novel semi-continuous process (semi-batch process) according to the invention for producing the hydrophobic polyelectrolyte copolymers according to the invention comprises the following steps:

a) introducing diallyldimethylammonium chloride into a polymerization reactor vessel in an amount between about 1 and about 19 wt.%;

b) heating the diallyldimethylammonium chloride to a temperature in the range between about 47 and about 57°C;

c) adding dropwise a polymerization initiator to the diallyldimethylammonium chloride in an amount between about 0.05 and about 0.4% by weight;

d) adding a hydrophobic monomer dropwise to the diallyldimethylammonium chloride in an amount between about 3 and about 19% by weight; and

e) heating the mixture of diallyldimethylammonium chloride, polymerization initiator and hydrophobic monomer to a temperature in the range between about 41 and about 82°C.

Typically, deionized water is added periodically as needed during the polymerization process in a total amount of between about 63 and about 80 weight percent. In some cases, it is preferred to mix the diallyldimethylammonium chloride with NaCl and deionized water to form a diallyldimethylammonium chloride solution before introducing it into the reaction vessel. The NaCl is added in an amount of between about 2 and about 3.5 weight percent and the deionized water is added in an amount of between about 1.0 and about 2.5 weight percent. This diallyldimethylammonium chloride solution has a concentration of diallyldimethylammonium chloride in the range of between about 54 and about 59 percent.

The diallyldimethylammonium chloride, polymer initiator and hydrophobic monomer are heated to a temperature in the range of between about 47 and about 57°C for a period of between about 4 and about 5 hours. Thereafter, the temperature of the reaction vessel is increased to about 72 to about 82°C for a period of between about 1 and about 4 hours. After polymerization is complete, the copolymer product is typically diluted with deionized water, cooled and stored.

The polymerization initiator is selected from the group consisting of V-50 (2,2'-azobis(2-amidinopropane) hydrochloride), VA-44 (2,2'-azobis(N,N'- dimethyleneisobutyramidine)dihydrochloride), ammonium persulfate and ammonium persulfate/sodium metabisulfite.

The flocculant causes aggregation of the neutralized colloidal particles suspended in the residue suspension. Aggregation is the result of either the inclusion agents (i.e., inorganic flocculants) or the binders (i.e., organic flocculants) bringing the neutralized particles together (aggregating them). A preferred flocculant is a copolymer of 78% acrylamide and 22% acrylic acid.

The coagulants and flocculants can be added to the thickener at several points along the feed line and in different sequences. A typical thickener is a gravity sedimentation unit, which is a cylindrical continuous thickener with mechanical sludge agitation arms. The residual sludge (i.e., a solid/liquid dispersion) enters the thickener at the center shaft. The coagulants and/or flocculants are introduced at points in the feed line and/or the center shaft. The number of addition points, sequence, flocculant, coagulant, etc. are determined for each specific application by laboratory cylinder testing. The flocculated solids settle to the bottom of the thickener. The mechanical arms agitate the sludge and it is discharged. The clarified water flows into a channel that surrounds the upper section of the thickener.

The typical amount (dose) of coagulant added to the thickener is 22.5 to 112.5 ppm (about 0.05 to about 0.25 lb/ton) based on the flotation tailings. The flocculant is also added to the thickener in an amount between 22.5 to 112.5 ppm (about 0.05 to about 0.25 lb/ton) based on the flotation tailings.

After treating the flotation tailings with sufficient coagulants and flocculants, the thickener effluent or tailings (i.e. the concentrated tailings) are withdrawn from the bottom of the thickener, while water and/or other liquids are withdrawn overhead. The water can then be recycled as process water for reuse in the treatment process or discharged into public waterways. The concentrated tailings from the thickener can then be used primarily for land replenishment.

In most cases, adding a given amount of flocculant in two or more portions will result in better performance (better effect) than adding the same amount of flocculant in one portion. It is not uncommon that the amount of flocculant required can be reduced by as much as 30 to 40% by adding at many points and still achieve the required settling rate. Adding at many points will also result in improved clarification (i.e. lower suspended solids) at a given settling rate.

This practice is carried out in an industrial treatment process by adding the flocculant at various points in the feed line to the thickener. The improvement results from the reduction of the surface area with which the second or third portion of the flocculant actually comes into contact when it is added to the system.

In many applications, both coagulants and flocculants are often required. Classical theory suggests adding a coagulant first to minimize the zeta potential on the particles and then adding the flocculating agent to form a larger, faster settling floc. For relatively homogeneous solid/liquid dispersions, this is often the best order of addition.

However, many solid/liquid dispersions are heterogeneous. For example, a simple coal wash water that must be purified before reuse is generally a mixture of coal, clay and water. In this system, the clay has a cation requirement and the coal has no cation requirement (for all practical purposes). However, the coal adsorbs the coagulant. The treatment sequence begins with the addition of a flocculant that visibly agglomerates the coal with little or no effect on the clay. This is followed by the addition of a coagulant that coagulates the clay. Finally, additional flocculant is added to densify the coal and clay flocs. When the treatment sequence begins with the flocculant, the coal is flocculated and its surface area is reduced. Less coagulant is required to meet the coagulant needs of the clay because less is delivered to the coal. Using this order of addition, coagulant needs can often be reduced by 50% or more.

The present invention is best understood by reference to the following embodiments and comparative examples

example 1

A hydrophobic polyelectrolyte copolymer was prepared from 95% diallyldimethylammonium chloride (DADMAC) and 5% quaternary dimethylaminoethyl methacrylate cetyl chloride (DMAEM.CCQ) monomers. The following reagents were used:

250.62 g of a 62% DADMAC solution

30 150.00 g of a 20 % DMAEM.CCQ solution

0.30 g Versene

10.00 g adipic acid

15.00 g of a 25% ammonium persulfate solution

75.08 g deionized water

DADMAC was added to a mixture of DMAEM.CCQ, adipic acid, Versene, and deionized water. This reaction mixture was then heated to about 50°C and then the ammonium persulfate was added. The reactor vessel was purged with nitrogen and stirred at about 250 rpm. After 30 minutes, a precipitate began to form so an additional 154.76 g of a 62% DADMAC solution, 10 g of a 25% ammonium persulfate solution and 0.10 g of Versene were added to the reactor vessel. The temperature of the mixture was then raised to 65°C for 6 hours and then cooled to ambient temperature. The final molar ratio of DADMAC to DMAEM.CCQ was 96.68%:3.32%.

Example 2

A hydrophobic polyelectrolyte copolymer was prepared from 70% DAD- MAC and 30% dimethylaminoethyl acrylate benzyl chloride quaternary (DMAEA.BCQ) monomers. The following reagents were used:

188.03 g of a 62% DADMAC solution

104.28 g of an 80% DMAEM.BCQ solution

0.20 g Versene

15.00 g of a 25% ammonium persulfate solution

692.49 g deionized water

The DADMAC and 100 g of deionized water were introduced into a polymerization reactor vessel which was flushed with nitrogen. The ammonium persulfate was then added dropwise into the reactor vessel using a syringe pump over a period of 2 h. At the same time, DMAEA.BCQ was added dropwise into the reactor contents using a syringe pump over a period of 2 h. The DMAEA.BCQ was mixed with 100 g of deionized water before being added to the syringe pump. water. The remaining deionized water and Versene were then added to the reactor vessel, which was then heated to 65ºC for 6 h.

Example 3

A hydrophobic polyelectrolyte copolymer was prepared from 70% DADMAC and 30% quaternary dimethylaminoethyl acrylate benzyl chloride (DMAEA. BCQ) monomers. The following reagents were used:

188.03 g of a 62% DADMAC solution

104.28 g of an 80% DMAEA.BCQ solution

0.20 g Versene

1.179 V-50

706.00 g deionized water

0.329 H₂SO₄

The DADMAC was introduced into a polymerization reactor vessel which was purged with nitrogen and stirred at 300 rpm with a torque of 350 dynes/cm. The pH was adjusted by adding H2SO4. After 40 min, the torque gradually increased to 2240 dynes/cm. Then 100 g of deionized water was added to the DAD MAC, decreasing the torque to 850 dynes/cm. Then V-50 and DMAEA.BCQ were added dropwise using syringe pumps over 2 h. The DMAEA.BCQ was diluted with 100 g of deionized water. The reactor vessel was then heated to 65°C for 5 h. After 2 h and 20 min, the torque reached a value of 2920 dynes/cm. Another 100 g of deionized water was added, reducing the torque to 1180 dyn.cm. After 3 h and 15 min, another 100 g of deionized water was added to the polymerizing product. After 5 h, another 100 g of deionized water was added to the reactor vessel and the temperature was raised to 80ºC for 1 h. After that, the resulting Polymer diluted with the remaining deionized water, cooled and stored.

Example 4

A hydrophobic polyelectrolyte copolymer was prepared from 80% DADMAC and 20% dimethylaminoethyl methacrylate quaternary cetyl chloride (DMAEM.CCQ) monomers. The following reagents were used.

188.02 g of a 62% DADMAC solution

83.43 g of a 100 % DMAEM.CCQ solution

0.209 Versene

1.179 V-50

727.03 g deionized water

0.159 H₂SO₄

The DADMAC was introduced into a polymerization reactor vessel that was purged with nitrogen and stirred at 300 rpm. The pH was adjusted by adding H2SO4. 150 mL of deionized water was added to the DADMAC. V-50 and DMAEM.CCQ were then added dropwise using separate syringe pumps over 2 h. The DMAEM.CCQ was diluted with 100 g of deionized water. The reactor vessel was then heated to 65°C for 4.5 h. Between 1.5 and 2 h, 180 mL of deionized water was added. After 4.5 h, the temperature was increased to 70°C for 0.5 h. The resulting polymer was then diluted with the remaining deionized water, cooled, and stored.

Example 5

A hydrophobic polyelectrolyte copolymer was prepared using the same procedure as described in Example 4 above from 80% DADMAC and 20% dimethylaminoethyl acrylate benzyl chloride quaternary (DMAEA.BCQ) monomers. The following reagents were used:

227.52 g of a 62% DADMAC solution

73.68 g of an 80% DMAEA.BCQ solution

0.40 g Versene

1.429 V-50

696.63 g deionized water

0.359 H₂SO₄

Water was added as needed. The table below shows the timing of adding deionized water while carrying out the semi-continuous polymerization process. Table 1

Example 6

A hydrophobic polyelectrolyte copolymer was prepared from 90% DADMAC and 10% quaternary dimethylaminoethyl acrylate benzyl chloride (DMAEA.BCQ) monomers. The following reagents were used:

251.79 g of a 67% DADMAC solution

39.13 g of an 80% DMAEA.BCQ solution

0.409 Versene

3.369 V-50

678.00 g deionized water

27,529 NaCl

The semi-continuous process was carried out as follows:

(1) A solution containing 251.79 g of 67% DADMAC solution, 27.52 g of NaCl and 16.6 g of deionized water was added to a polymerization reactor vessel.

(2) The polymerization reactor vessel was then purged with nitrogen, stirred at 200 rpm and heated to 57ºC.

(3) Then 400 mg of Versene was added to the reactor vessel. (4) 39.13 g of DMAEA.BCQ was diluted with 15.87 g of deionized water, then 160 mg of Versene was added, stirred and filled into a syringe pump.

(5) 500 g of water was added to an addition funnel placed on top of the reactor vessel and continuously purged with nitrogen.

(6) 1.68 g of V-50 was dissolved in 45.16 g of deionized water and the solution was filled into another syringe pump.

(7) At 57ºC, 11.7 g of the V-50 solution was added to the reactor vessel while the DMAEA.BCQ was added dropwise.

(8) Additional deionized water was added from time to time as needed.

(9) After 5 h, the temperature was increased to 82ºC for 1 h.

(10) The resulting polymer was then diluted with the remaining deionized water, cooled and stored.

Example 7

A hydrophobic polyelectrolyte copolymer was prepared from 90% DADMAC and 10% quaternary dimethylaminoethyl acrylate benzyl chloride (DMAEA.BCQ) monomers. The following reagents were used in the semi-continuous process:

185.10 g of a 67% DADMAC solution

28.77 g of an 80% DMAEA.BCQ solution

0.159 Versene

2.489 V-50

498.42 g deionized water

20.23 g NaCl

DADMAC, NaCl and 12.20 g of deionized water were added to a reaction vessel and heated to 57°C in a nitrogen atmosphere. The DMAEA.BCQ and 1.24 g of V-50 were then added dropwise to the mixture of DADMAC, NaCl and water using separate syringe pumps over 4 hours. 500 mL of deionized water was added to an addition funnel, purged with nitrogen and added from time to time as needed. The Versene was then added and the reaction vessel was heated to 57°C for an additional 5 hours. 1.24 g of V-50 was added and the reaction vessel was heated to 82°C for 4.5 hours. The resulting polymer product was diluted with the remaining deionized water, cooled and stored.

Example 8

A hydrophobic polyelectrolyte copolymer was prepared from 90% DADMAC and 10% quaternary dimethylaminoethyl acrylate benzyl chloride (DMAEA.BCQ) monomers. The following reagents were used:

251.79 g of a 67% DADMAC solution

39.13 g of an 80% DMAEA.BCQ solution

0.20 g Versene

3.369 V-50

705.52 g deionized water

DADMAC and deionized water were added to a reaction vessel and heated to 57°C in a nitrogen atmosphere. The DMAEA.BCQ and 1.68 g of V-50 were then added dropwise to the mixture of DADMAC, NaCl and water over 4 hours using separate syringe pumps. 500 mL of deionized water was added to an addition funnel, flushed with nitrogen and added from time to time as needed. The Versene was then added and the reaction vessel was heated to 57°C for an additional 5 hours. 1.68 g of V-50 was added and the reaction vessel was heated to 82°C for 4.5 hours. The resulting polymer product was diluted with the remaining deionized water, cooled and stored.

Example 9

A hydrophobic polyelectrolyte copolymer was prepared from 85% DADMAC and 15% quaternary dimethylaminoethyl acrylate benzyl chloride (DMAEA. BCQ) monomers. The following reagents were used:

308.35g a 72.5% DADMAC solution

85.15 g of an 80% DMAEA.BCQ solution

0.20 g Versene

3,609 V-50

548.70 g deionized water

54.00 g NaCl

DADMAC, NaCl and deionized water were mixed together and heated to 57°C in a nitrogen atmosphere. The DMAEA.BCQ and 1.80 g of V-50 were then added dropwise to the mixture of DADMAC₃ NaCl and water over 4 hours using separate syringe pumps. 500 mL of deionized water was introduced into an addition funnel, purged with nitrogen and added from time to time as needed. The Versene was then added and the reaction vessel heated to 57°C for an additional 5 hours. 1.80 g of V-50 was added and the reaction vessel was heated to 82°C for 4.5 hours. The resulting polymer product was diluted with the remaining deionized water, cooled and stored.

Example 10

The following Table 2 presents the results of a comparative test conducted to evaluate the performance of the hydrophobic polyelectrolyte copolymer coagulants of the present invention in comparison with various conventional organic coagulants. Table 2

40 * Footnote: the DADMAC was prepared in a NaCl solution

In Table 2 above, the inventors compared the settling rate of the hydrophobic polymers of the invention with that in poly(DADMAC) systems. For example, a poly(DADMAC) and acrylamide/acrylic acid system at a 1.5/6 add-on rate was compared with a DADMAC/DMAEA.BCQ and acrylamide/acrylic acid system at a 1.5/6 add-on rate. A poly(DADMAC) add-on rate of 135 ppm gave a settling rate of 17.8 cm (7.0 inches)/min and a turbidity of 68 NTU, while the hydrophobic polymer system (i.e., DADMAC/DMAEA.BCQ) gave a higher settling rate at the same polymer add-on rate (i.e., 17.8 cm (7.0 inches)/min) and a turbidity of 58 NTU.

Additionally, a poly(DADMAC) and acrylamide/acrylic acid system at a 3/6 addition rate was compared to a DADMAC/DMAEM.CCQ and acrylamide/acrylic acid system and a DADMAC/DMAEA.BCQ and acrylamide/acrylic acid system at similar addition rates. The poly(DADMAC) addition rate of 3 ppm resulted in a settling rate of 11.4 cm (4.5 inches)/min and a turbidity of 90 NTU, while the hydrophobic polymer systems resulted in an equal or higher settling rate at the same polymer addition rate and lower turbidity.

As can be seen from Table 2 above and Figure 1, the hydrophobic polymers of the present invention can achieve better clarity (i.e., lower turbidity) and similar or higher settling rates compared to conventional poly(DADMAC)-based systems.

In the attached Fig. 1, the turbidity is plotted in the form of a diagram against the amount of poly(DAD MAC), DADMAC/DMAEA. BCQ (90:10) added, prepared in a NaCl solution, and DADMAC/DMAEA.BCQ (90:10). From the diagram in Fig. 1, it is quite clear that the inventive hydrophobic polymers provide better clarity (ie, lower turbidity) at similar addition levels than poly(DADMAC).

Example 11

Various coagulants were evaluated for their performance when applied to low cation demand coal. Each coagulant was used in conjunction with a flocculant, ie acrylamide/acrylic acid (AaAm/AA) at a molar ratio of 78:22. The results are given in Table 3 below. Table 3

* Footnote: the DADMAC was prepared in a NaCl solution.

Table 3 above shows that approximately 0.5 parts of the hydrophobic polymer (ie DADMAC/DMAEA.BCQ) are required to achieve the same clarity (ie haze) as 1.0 part poly(DADMAC). Comparable are the DADMAC/DMAEA.BCQ and DADMAC/DMAEA.BCQ (prepared with a NaCl solution) systems at 1.5 ppm active material addition levels with the poly(DADMAC) system at 3.0 ppm active material addition levels. The hydrophobic polymer systems had similar turbidity values to the poly(DADMAC) system using only half the poly(DADMAC) system addition level (i.e., 1.5 ppm versus 3.0 ppm active material addition level). When the same active material addition level was used for each system, the hydrophobic polymer gave much better clarity (i.e., lower turbidity values).

Although the invention has been shown and described above using several embodiments, it is clear that these can be subject to numerous modifications that will be obvious to those skilled in the art. The invention is therefore not limited to the details given and described, but also includes all changes and modifications that are within the scope of the following patent claims.

Claims (19)

1. Process for concentrating (reducing) coal processing residues comprising liquid and colloidal particles, comprising the following stages: (a) introducing the abovementioned coal preparation residues into a thickening facility; b) treating said coal dressing residues with a hydrophobic polymer electrolyte copolymer coagulant comprising diallyldimethylammonium chloride and a hydrophobic monomer selected from the group consisting of quaternized dimethylaminoethyl acrylates and quaternized dimethylaminoethyl methacrylates, said coagulant being added to the coal dressing residues in an amount between 22.5 and 112.5 ppm (0.05-0.25 lb/ton); (c) treating the abovementioned coal preparation residues with a flocculant in an amount of between 22.5 and 112.5 ppm (0.05-0.25 ibiton) which causes the colloidal particles to agglomerate and settle as concentrated residues; (d) discharging the substantially concentrated residues from the mentioned thickening device; and e) withdrawing the substantially clarified liquid from said thickening device. 2. A process according to claim 1, wherein said coagulant is added to said coal dressing residues prior to said flocculant. 3. A process according to claim 1, wherein a portion of said flocculant is added to the coal dressing residues both before and after adding said coagulant to the coal dressing residues. 4. The process of claim 1 wherein said quaternized dimethylaminoethyl acrylate is selected from the group consisting of quaternary dimethylaminoethyl acrylate methyl chloride and the quaternary dimethylaminoethyl acrylate C4 -C20 chlorides. 5. A process according to claim 4, wherein said quaternary dimethylaminoethyl acrylate C4 -C20 chlorides are either quaternary dimethylaminoethyl acrylate benzyl chloride or quaternary dimethylaminoethyl acrylate cetyl chloride. 6. The process of claim 1 wherein said quaternized dimethylaminoethyl methacrylate is selected from the group consisting of quaternary dimethylaminoethyl methacrylate methyl chloride and quaternary dimethylaminoethyl methacrylate C4 -C20 chlorides. 7. A process according to claim 6, wherein said quaternary dimethylaminoethyl methacrylate C4 -C20 chlorides are either quaternary dimethylaminoethyl methacrylate benzyl chloride or quaternary dimethylaminoethyl methacrylate cetyl chloride. 8. The process of claim 1 wherein said diallyldimethylammonium chloride and said hydrophobic monomer are present in a molar ratio in the range of 20:80 to 99:1. 9. The process of claim 1, wherein said hydrophobic polyelectrolyte copolymer coagulant is formed by a semi-continuous process comprising the following steps: introducing diallyldimethylammonium chloride into a polymerization reaction vessel in an amount between about 1 and about 19 weight percent; heating the diallyldimethylammonium chloride to a temperature in the range between about 47 and about 57°C; Adding a polymer initiator dropwise to said diallyldimethylammonium chloride in an amount between about 0.05 and about 0.40 weight percent; adding a hydrophobic monomer dropwise to said diallyldimethylammonium chloride in an amount between about 3 and about 19 weight percent; and heating the mixture of diallyldimethylammonium chloride, polymer initiator and hydrophobic monomer to a temperature in the range between about 47 and about 82°C. 10. The method of claim 91, wherein deionized water is periodically added during the polymerization process to the extent required in a total amount of between about 63 and about 80 weight percent. 11. The method of claim 9 wherein said diallyldimethylammonium chloride is mixed with NaCl and deionized water to form a diallyldimethylammonium chloride solution prior to introduction into said reaction vessel, said NaCl being added in an amount between about 2.0 and about 3.5 weight percent and said deionized water being added in an amount between about 1.0 and about 2.5 weight percent. 12. The method of claim 11, wherein said diallyldimethylammonium chloride solution has a diallyldimethylammonium chloride concentration in the range between about 54 and about 59%. 13. The process of claim 9, wherein said polymer initiator is selected from the group consisting of 2,2'-azobis(2-amidinopropane) hydrochloride, 2,2'-azobis(N,N'-dimethyleneisobutyramidine) dihydrochloride, ammonium persulfate, and ammonium persulfate sodium metabisulfite. 14. A coagulant for use in concentrating coal preparation residues, comprising a hydrophobic polyelectrolyte copolymer of diallyldimethylammonium chloride and a hydrophobic Monomer selected from the group consisting of quaternized dimethylaminoethyl acrylates and quaternized dimethylaminoethyl methacrylates. 15. The coagulant of claim 14, wherein said quaternized dimethylaminoethyl acrylate is selected from the group consisting of quaternary dimethylaminoethyl acrylate methyl chloride and quaternary dimethylaminoethyl acrylate C4 -C20 chlorides. 16. A coagulant according to claim 15, wherein said quaternary dimethylaminoethyl acrylate C4 -C20 chlorides are either quaternary dimethylaminoethyl acrylate benzyl chloride or quaternary dimethylaminoethyl acrylate cetyl chloride. 17. The coagulant of claim 14, wherein said quaternized dimethylaminoethyl methacrylate is selected from the group consisting of quaternary dimethylaminoethyl methacrylate methyl chloride and quaternary dimethylaminoethyl methacrylate C4 -C20 chlorides. 18. A coagulant according to claim 17, wherein said dimethylaminoethyl methacrylate C4 -C20 chlorides are either quaternary dimethylaminoethyl methacrylate benzyl chloride or quaternary dimethylaminoethyl methacrylate cetyl chloride. 19. A coagulant according to claim 14, wherein said diallyldimethylammonium chloride and said hydrophobic monomer are present in a molar ratio in the range of 20:80 to 99:1.