Journal of Scientific & Industrial Research

Vol. 59 , October 2000, pp 765-790

Factors Affecting the Preparation of Highly Concentrated Coal-Water Slurry (HCCWS)

S K Mishra and S B Kanungo •

Regio nal Research Labo ratory, Bhubaneswar 751 0 13, India

Received: 28 February 2000; accepted: 15 May 2000

Various factors such as nature of coal, its chemical composition, surface chemistry, colloid-chemical properties in aqueous suspension, presence of inorganic compounds or ions, addition of surface act ive agents and particle size distributi on have considerable influence on the preparati on of hi ghly concentrated coal-water slurry. These factors have been critically examined in this review.

Introduction

Since the oil crisis in the mid-70s there has been a sign if icant progress on the use of coal as a substitute for precious oil. Out of the total reserve of oil, 80 per cent is found in the middle-east and many countries inc luding India which are scarce in thi s foss il fuel , spent a considerable amount of valuable foreign exchange in importing crude oil. On the other hand many countries inc luding India have a large reserve of coal which can be utilized for various combustion purposes. Attempts were, therefore, made first to make fine ly ground coal-o il mixture as a means for partial substitute for oi 11

'2

. This technology has been put into commercial practice for transportation and combustion of coal in utility boilers, espec iall y for power generati on3

·7

Since 1980 the interest of the investigators shows distinct shift from coal-oi l to coal-water mixture , thereby proposing complete replacement of o il with coal as fue l. Hi ghl y concentrated coal-water slurry (HCCWS) behaves like liquid fuel during combu stion and is economicall y more viable than either coal liquefaction or gas ificati on bes ides having the advantage of storability and transportability through pipe lines . The translation of thi s technological dream to reality has been poss ibl e due to tremendous amount of R & 0 work carri ed out worldover. As a result, several demonstration plants were set up during the last decade8

-10

.

One of the most important requirement to be met while preparing a coal-water slurry (CWS) is that coal concentration should be as high as possible, but the viscosity is to be kept at a minimum possible leve l (< 2000 cP) for ease of handling during preparation, storage, transfer and atomization. But the viscos ity of CWS increases with the coal concentration in the slurry and the stability of the suspension becomes poor if the viscosity is reduced 11

-13

• Hence, simultaneous maintenance of optimum vi scos ity and stabi lity at high solids concentration poses several problems which need to be addressed.

Coal is not a homogeneous substance, but a complex mixture of carbonaceous and mine ral matters. Hence, it has various surface properties . Earlier studies 11

-15 have revealed that the fl ow

characteristics of coa l-water suspensions depend on many factors, of which the following are the most important : (i) The physico-chemical properties of coal , ( ii ) The volume fraction (<j>) of the suspension, (iii ) The particle size range and its di stributi on , (iv) The temperature of the suspensi on, (v) The interparticle interaction s in the suspensions which are affected by the nature of the surface groups, (vi ) T he pH and the presence of e lectro lytes and che mi ca l additives. In general , coal partic les that have been rendered mutuall y repul sive form a well di spersed suspension which is affected by adsorpti on of ionic or non-Jontc surfactants. These suspensions are

766 J SCI IND RES VOL 59 OCTOB ER 2000

characterized by their low viscosity but form hard sediments that are difficult to redisperse when left to stand 16

. The addition of various di spersants, wetting agents, and rheo logy enhancers is essenti al in obtaining higher coal loadings that produce hi gher energy densities for continuous combusti on.

Some of the most important factors which govern the production of hi gh ly concentrated coal­water slurry are di scussed subsequentl y :

Surface Properties of Coal

An intrinsic difficulty in the preparation of HCCWS is the diversity of coals in their physical and chemical contents which depends largely on the geological setting of their deposits . An universal correlati on for all coal samples is quite difficult . Therefore, characterization of indi vidual coa l sample is necessary prior to the preparation of HCCWS.

Electrical Double Layer on Coal in Aqueous Medium

The on gm of charge and consequent development of electrical double layer on the surface of coal in aqueous suspension is a subj ect of considerable debate because of the heterogeneous composi ti on of coal which also varies from one source to another. When coal is powdered there occurs breakage of both physical (weak van der Waal) and chemical (cova lent and ionic) bonds leading to unequal electronic charge distribution on the surface. Thi s results in the adsorption of oxygen from air and therefore coal when suspended in water adsorbs ei ther H+ or OH·, depending on the pH of the medium, like any other insoluble ox ides/hydrox ides. Bes ides, coal , by its origin , contai ns hydroxyl (mostly

phenolic), carboxyl (-COOH) or cabonyl (>CO), and even etherial oxygen ( -0-) groups. Coal also contains various inorganic oxides/hydroxides like Fe20 :; , FeOOH, clays, and sulphide minerals like FeS2 and FeS which also contribute to the overall surface charge on coal in aqueous medium.

Extensive investigati on 17•21 has been carried out

on the characterization of surface charge by measuring electrophoretic mobility/zeta potenti al as a function of pH , electrolyte concentrat ion, and also in the presence of surface active agents. It has been found that isoelectric point (IEP) of coal lies between 2 and 5, depending upon the rank of coa l with respect to ash content . Generally, with increase in ash content IEP shifts to alkaline side. The negative charge on coal surface generally tends to increase with increase in pH and reaches maximum at pH 8-9. The IEP values of coa l also undergo change when coa l suspension is all owed to age, which is attributed to the ox idation of Fe2+ (released from pyrite) to Fe3+ (ref. 17).

In the light of the brief di scuss ion on the ori gin of charge on coa l particle surface, we may now consider the surface phenomena invo lved in the preparation of HCCWS . The well-known Derjaguin­Landau-Yerwey-Overbeek (DLVO) theory of colloidal stability can be in voked to exp lain the electrostatic phenomenon involved in the case of coal suspension. Without going into the detail s of the theory, it may be stated that if the potential energy due to repulsion is much higher than the potenti al energy due to attraction between two particles of identical double layer charge the colloidal suspension should be stable. The diffused atmosphere of counter ions screen the surface charge from each other while

Dr S K Mishra is presently working os a reseorch scientist at Regional Research Laboratory, Bhubaneswar. He obtained his B.Sc. and M.Sc. degree in inorgan ic chemistry fro m Utkal University. Bhubaneswar, India, in 1983 and 1985 respectively and was warded Ph. D. degree f iwn the same University in 1995. His present fie lds of interest are colloid and suiface chemist/)', and process metallurgy.

DrS. B. Kanungo is presently working as a research scientist at Regional Research Laboratory Bhubaneswar. He obtained the degree of B.Sc. and M. Sc. in physical chemistry fi·om Dacca University, Bangladesh, in 1962 and 1963 respectively, and was awarded the degree of Ph. D. ji-o111 th e University of Ca lcutta, India, in 1969. He spent the year 1974-75 at the Institute of Physical Chemistry, University of Munich, Germany. His present fields of interest are colloid and suJface chemistry, process metallurgy and solid state chemist I)'.

MISHRA & KANU GO.: PREPARATION OF HIGHLY CONCENTRATED COAL-WATER SLURRY 767

themselves being mutually repulsive although particle solvent affinity is also an important factor. The situation is generally achieved by increasing the negative surface charge (and consequently the surface potential) to such an extent that even if the double layer gets squeezed due to removal of counter ion between the two very close particles the repul sive force remains sufficiently strong. It has been observed that negative charge on coal particles is considerably enhanced and stable suspension is obtained by adding 1-3 or 2-3 electrolytes such as sodium tripolyphosphate, sod ium hexametaphosphate or

d · I I 22-24 Tl ff f . . . so mm p 1osp 1ate . 1e e ect o vanous morgan1c cations and anions on the viscosity of HCCWS has been discussed in detail by Kaji et a/?5

, who have also observed that the presence of cations of hi gher valence increases the viscosity of coal water slurry . This is attributed to the partial neutralization of negative charge on coal surface25

.

Effect of Inorganic Mineral Matter in Coal

S I - . h b d h 26. ? 9 evera mvest1 gators ave o serve t at -increase in the pH values of coal/water slurry with su itable alkali metal hydroxide, carbonate or even with ammonium hydroxide helps in the preparation of HCCWS. This is attributed to the increase in the negative surface charge as supported by increase in the 'zeta potential' of coal in aqueous medium. Alkaline earth metal carbonates and hydroxides are found by some workers as having beneficial role for the reduction of viscosity of CWS. Kaj i et a/24 used two wt per cent ground calcium carbonate along with other dispersing agents for effecti vely reducing the viscos ity of CWS containing 50-75 wt per cent coal (particle diam < 300 mm). The presence of sulphur in coal leads to environmental pollution as sulphur dioxide is emitted from the same during combustion of CWS. Hence, CaC03, MgC03 and/or dolomite is chosen in ratio of Ca or Mg-S :: ( 1.5 - 3) as a desulphuriser which is added during the preparation of CWS. A highly concentrated aqueous suspension has been prepared by adding a desulphuriser also possessing capability to ra ise pH and having anti­corrosive properties such as MgO, Mg(OH)2, CaO and/or Ca(OH)2 in 0.04-0.4 wt per cent of the final suspension30

. However the tolerance limits of the presence of these alkaline earth meta l ions that are known to possess negative effect on the stabi I it y of coal-water slurry, has not been reported .

The effect of mineral impurities on the rheological properties of CWS has been investigated. Out of the total impurities, 65-90 per cent are clay mineral s, kaolinite being the main component. Montmorillonite and illite occur only as interlayer mineral s31

. Quartz, calcite and pyrite are also present in the solid phase of the slurries31

. The maximum concentration of coal in a slurry depends on the type and content of minerals . The presence of clay mjnerals and particularly montmorillonite and illite, negatively affect the fluidity of the slurr/2

. Kaoli nite decreases the rigidity of the coagulating structure of aqueous coal suspension , but, its stabilizing action is lower than those of other clay minerals. The presence of quartz in the so lid phase causes the slurry to separate33

. In general the apparent viscosity increases and viscosity power index decreases with increase in the ash content of coal 34

.

The rheological behaviour of coal slurries wit h different types of coal are found to be dependent on the solubility of the mineral matters. The solubilities of mineral matter vary greatly and depend on the type of coal and their composition. The ions extracted from the mineral matters are mainly : Ca2

+, Mg2+,

Al ' + F 2+ F >+ d s· b . . U d · , e or e· , an 1- eanng amons . n er certain specified conditions35 the slurries exh ibit shear thinning behaviour for fine so lubility of mineral matters in coal and shear-thickening behaviour for bad solubility . It is also reported 36 that the addition of stoichiometric quantity of soda ash and lime to precipitate Ca2

+ and Mg2+ ions naturally present in the

aqueous phase of the CWS leads to the marked reduction in viscosity.

Effect of Coal Macerals

The microscop ic constituents present in coal are called macerals by analogy with the minerals that occur in inorganic rocks . The three main group of macerals present in coal are vi trinite, exinite, and inertinite. The vitrinite maceral s are rich in oxygen, whereas the exinite macerals are relatively rich in hydrogen . On the otherhand the inertinite macerals are relatively rich in carbon or more in keeping with the two other macerai groups are, ac tuall y hydrogen deficient. On the basis of these significant differences in composition , it is observed that the three groups show differing behaviour in many of the technological processes in coal utilization . Higher vi trinite and semivitrinite contents and lower fusinite

768 J SCI INO RES VOL 59 OCTOBER 2000

(a subgroup of inertinite) content are beneficial to the ability of the coal to form slurries37

. Although the properties of coal maceral became clear with the progress of the separation techniques, systematic study on maceral and slurryability of coal has not been sufficiently made.

Effect of Oxygen Containing Functional Group

Coal was formed from partially decomposed plant debris that had collected in regions where water-logged conditions prevailed . When orgamc debris is buried under sedimentary cover, vanous physico-chemical processes occur as part of the metamorphosis. This leads to changes in the constituents of the debri s such as increase in the carbon content, alteration in the functional groups and various molecular stmctures. Oxygen containing functional groups, especially hydroxyl and carboxyl groups are the main factors in determining wettabilities of coal surface38

. The carboxyl groups on the coa l surface play a far more important role in determining coal slurry forming ability than the phenolic hydroxyl group. It is also reported that the phenolic -OH groups are harmful to coal s lurry formjng abilit/9

. A detailed study on Chinese coals40

established an important relationship between oxygen containing functional groups and other stmctural parameters for coal and aqueous s lurry characteristics. Air oxidation of coal increases the specific surface area, oxygen containing functional groups, wettabilities and equilibrium moisture content and slurry viscosity of coals39

.

According to another stud/ 1 the adsoption characteristics of anionic surfactants on coal surface and viscosity reducing capabilities are all hi ghly influenced by the content of the reactive oxygen­bearing functional groups, especially carboxyl groups on coal surface38

.41. Hence the adsorption of the

dispersant and its viscosity reduc ing capabi lity are weakened for low rank coals with hi gh content of these reactive groups . Decomposition of these reactive oxygen-bearing functional groups by low temperature thermal upgradi ng of coal (200°-300°C) enhance the viscosity reducing characteristic of dispersants . This a lso leads to the decrease in the moisture holding capabilities of coa ls. Viscosity of CWS increases with increase in oxygen/carbon ratio 42

·43

. It is earlier pointed out that hydroph i I ic oxygen-bearing groups and mineral matters on coal

surface increase the hydrophilicity and moi sture holding capacity of coal. Highly concentrated CWS can be prepared from hydrophobic coal more easily than from the hydrophilic particles, because the inner surface and pore stmcture of hydrophobic coal is not penetrated by water and water soluble adsorbate, so that more water remains outside the coal particles, i.e., in the inter particle spaces, thereby increasing the fluidity of the slurr/8

.41.4

4•45

.

Effect of Porosity vis-a-vis Water Content

Water is present within the coal matrix in more than one form. The natural bed moisture of coal is the amount of water a particular coal will ho ld when it is fully saturated at about 100 per cent relative humidity. It is considered to be an indication of the total pore volume of coal that is accessible to water. The inherent moisture content in coal depends on porosity. Kaji et a/. 46 have shown a good relationship between water holding capacity (equ ilibrium moi sture at complete saturation) and [0] x Sg. where [0] is the weight fraction of oxygen in the coal and Sg i the specific surface area. A detailed study on seventeen Chinese coals47 indicates that pore structure of coal plays an important rol e in determining coa l slurryability through governing the moisture holding capability which varies greatly from one coal to another because of great difference 1n coal hydrophilicity . Since water adsorbs on hydrophilic sites but not on hydrophobic ones the measured adsorption applies only to areas of hydrophilic sites48

.

Contact angle measurements show that the advancing contact angles reflect the most hydrophobic regions of the surface whi le the reced ing contact angles reflect the hydrophilic regions. The sessile drop contact angles of water on coal49 range from about 40° for sub-bituminous coal to about 70° for medium volatile bituminous coal. Any smooth coal surface having a water contact angle of less than I 00.5° contains various hydrophilic areas (polar functiona l grou ps, inorganic/mineral impurities, etc.) on the hydrophobic carbon matrix . The product of absolute pore volume V and coal-water contact angle 8, i.e., V.Cos (8/2) is a measure of the hydrophilicity of coa l surface and is defined as the effective pore volume of coal in slurr/ 7

. The static storage properties of s lurry are mainly related to the m1cropore whose hi gh effective volume may hasten coal water sl urry to form hard sediment which is difficult to be redispersed.

MISHRA & KANUNGO.: PREPARATION OF HIGHLY CONCENTRATED COAL-WATER SLURRY 769

Effect of Particle Size Distribution.

One of the key parameter required to obtain the CWS with high coal content and low viscosity is the particle size distribution (PSDi0 of coal. The main focus in this regard is to maintain an optimum distribution for achieving minimum viscosity with maximum packing density . According to some workers43 the optimum particle size distribution depends on the rank of coal, i.e., oxygen/carbon ratio. Generally, for low rank coal the range between minimum and maximum size in the products of grinding is smal ler than that obtained for high rank coal. The required average particle diameter shows a slight increase with increase in oxygen/carbon atomic ratio.

It may be noted that the rheological behaviour of coal-water mixture is largely dependent on solids concentration and particle size and size distribution . A polydisperse suspension with a particle distribution from a few micrometers to few hundreds of micrometers is treated as bimodal 51

. Such a type of particle size distribution provides maximum packing efficiency at constant solids concentration with less water occupying the interparticle void spaces, but available to increase the distance of separation between the particles. This reduces the viscosity of the slurr/ 2

. When the microstructure is random the contribution to the viscosity of the coarse fraction which is polymodal is characterized by lubrication concepts. It is also reported by other workers53 that slurries with optimum viscosities can be prepared by using the bimodal and continuous size di stribution of coal with two peaks at 1.3 11m and 140 11m. This is achieved by mixing 20-30 wt per cent of very fine particles with the coarse particles . A study on the rheological properties of south Australian coal water mixture54 reveals that there exists an optimum coarse (208-279 11m) to fine ( -45 11m) particle ratio of 40:60 at which the slurry is Newtonian with a maximum viscosity of several order of magnitude lower than the viscosity of a slurry containing only fine particles at the same solids concentration . A further reduction in the slurry viscosity was achieved by adding a second coarser coal particles to the bimodal slurry .

High concentration of coal-water slurry (70-80 wt per cent solid) can be prepared using polymodal particle size while keeping the pore volume less than 30 per cent. Thus , a CWS with 900 cP viscosity can

be prepared where the powdered coal consists of particles of size 2 per cent (w/w) < 25 11m, 8 per cent (w/w) < 38-43 11m, 30 per cent (w/w) < 88-104 11m and 60 per cent (w/w) < 701-8331-lm with -24 per cent pore volume and 0 .5 wt per cent addition of anionic surfactant55

. Some other investigators arrived at a suitable formula depicting the importance of PSD on the preparation of HCCWS . It is also reported that56 accumulated weight ratio of coal particles with diameter smaller than D (> 95 per cent passing 1000 11m) in 55 wt per cent coal-water s lurry is expressed as I 00/[ I + exp( -a log D/D50)], where 0 50 is D at 50 per cent in 5-500 11m. According to Kikkawa57

, a suitable CWS with 60-80 per cent solid and having _s 5000 cP can be prepared by adjusting the PSD (in the range of 0.005-1000 11m) which satisfies the following equation U(D) = [(D-05)/(De-Ds)] '~ x I 00 (where D = Diameter of coal particles, De = Maximum particle diameter of 44-1000 11m; Ds = Minimum particle diameter of 0.005-0. 1 11m, q = An index of 0.25-0.50) followed by addition of 0.3 wt per cent of an anionic dispersant and .s._3 wt per cent base.

Use of Surface Active Agents

. Surface active agents or surfactants have been extensively used to obtain charge distribution conducive to the preparation of HCCWS with optimum viscosity and sedimentation stability using coal of suitable PSD. This often involves use of one or more surfactants. The beneficial role of surfactants may be noted as follows :

(i) Control of relative hydrophilic/hydrophobic character,

(ii) It modifies surface charge on the coal particles and hence the slurry behaviour,

(iii) It forms 3-D structure to prevent sedimentation in a slurry with high surface charge,

(iv) It induces weak flocculation which holds small and medium particles, thus maximizing so lids concentration.

The essential criteria for the surfactant is that : (i) It must be non-foamir.g, (ii) Be water soluble, (iii) Have a structure compatible with flat adsorption on coal surface, (iv) Be compatible with the stabilizers, and (v) Be effective at low concentrations . The cho ic~ of surfactant depends on the nature of coal , its mineral composition, soluble matter present and its

770 J SCI IND RES VOL 59 OCTOBER 2000

surface properties. The thi cker the adsorpti on layer the more the preventi on o f coal parti c les from mutual inte rac ti ons; thus the dispers ion of parti c les IS

favoured and the vi scos ity of CWS is reduced.

Various types of surfactants have been used in the preparation o f stable hi gh concentrati on coal s lurry . These inc lude anionic, non-i onic polymers co­po lymers synthesized depending upon the ingenuity of the chemis t.

Anionic surfactants possess certa in di stinct advantages over cati oni c surfactants in the preparati on of HCCWS . First the hydrophobi c ' ta il ' porti on of surfactant genera ll y adsorbs in a fl at manner over the coal surface with negati ve ly charged ' head' protruding out from the surface, thereby prov iding more negati ve surface charge. It has been observed that adsorpti on o f sod ium dodecy l benzene sulphonate increases the zeta potenti a l o f coa l58

. The second ad vantage is that if coal conta ins inorgani c matte r o f high cati on vale nce (e.g. Al 3+, Fe3+) adsorpti on takes pl ace through the formation of stable sur face complex with such cati on again thereby increas ing net negati ve charge. T hirdl y the hyd rophilic end group gets hydrated at re lati ve ly low pH (< 5.0) to prov ide a thin layer of wa ter surround­ing coal parti c les, just suffici ent to impart des irabl e fl u id ity to the suspens ion. On the other hand the negati ve ly charged end groups (hydroxyl, carboxy l, etc.) do not get opportunity for ex tensive hydrat ion which would otherwise lead to increase in viscos ity of coal s lurry. T hi s is one of the most important reason why cati onic surfac tant which is adsorbed at high pH(> 9.0) o nto coal are not preferred .

Stab ili zat ion of coa l-water s lu rry can a lso be achieved th rough the addit ion of non-ionic surfactant. However the mechani sm of stabili zat ion in th is case is different from that of anionic surfactant . In a hig ly concentrated s lurry the part ic les are close to each other which tends to promote the forma ti on of aggregate cl ue to coa lescence of interparticle water and aided by the partial stabi I ization of surface charge by the counter ions disso lved in it. Thi s inte rparti c le bound water is derived from the hydrati on of hydrophilic organic end groups as well as hydrated cat ions. Therefore, one of the objectives of the use of surface active agents is to control ex tens ive su rface hydration by rendering it hydrophobi c, but at the .-ame t1me maintaining the repulsion between the:

parti c les. Thi s is performed in a bette r way by the non-ionic surfac tants through the princ iple of steric stabilization . S ince detailed discuss ion on the phenomenolog ica l aspects of ste ri c stabi I izati on is beyond the scope of this review the readers are re ferred to re levant and important literature on this subj ec t59

·60

. The principle, in brie f, is as fo llows :

The non-ioni c surfactant which is genera ll y a po lymeric macromolecule is supposed to contain two end groups. One whic h is nomina lly insoluble in the continuous phase, is generall y anchored on the coal surface the other whi ch is the stab ilizing moiety remain s in so luble state very c lose to the surface of the parti c le and surrounds it compl ete ly. It is the so luti on properties of these moiet ies and not the entire surfactant molecule, which govem the stab ili ty o f the dispersion. The partic le can approach one another onl y if inte rpenetrati on and/or co mpress ion of the stabilizing chains occur. The consequent free energy of repul s ion is g iven by :

... ( I )

If LlGR is negati ve, then such inte rpenetrati on of po lymeri c chains will lead to f locc ul at ion. O n the other hand , if LlCR is pos iti ve, stab ilizati on o f the suspens ion will occur. The pos iti ve value of LlCR can be attained by three different ways. F irst, both the entropy (LlSR ) and entha lpy (LlHR) are negati ve but the entropy of inte rpenetrati on outweighs that of the entha lpy. It is therefore ca lled e ntropy stabili zation. The second poss ibility envi sages the reversal of the s igns of both LlHR and LlSR but the enthalpy fac tor outweighs the des tabili z ing fac tor o f e ntropy. It is therefore called enthalpic stabi li zati on . T he third poss ibility is that LlHR is positi ve and LlSR is negative, bu t the combined effect of both leads to pos iti ve LlCR. Ent rop icall y stab il ized suspensions a re therefore floccul ated by cooling, whereas entha lpica ll y stab il ized suspens ions are destab ili zed by heati ng.

Conclusions

From the above discussions it is therefore ev ident that selection of proper solvent is very important in the steric stabi li zation by non-ionic surfactant. Entropic repuls ion originates in the loss of entropy of mixing of polymer segments with the molecules of dispersion medium when the interpenetrat ion and/or compression betwecr the adsorbed polymer or surfactant molecules Jccur. This

MISHRA & KANUNGO.: PREPARATION OF HIGHLY CONCENTRATED COAL-WATER SLURRY 771

phenomenon generally takes place in non-aqueous di sper:-. ion. On the other hand, when enthalpic stabilization occurs, some of the dispersion medium arising from the non-ideality of mixing is exc luded from the compression zone. The released di spersion medium or water in this case is associated either with the surfactant polymeric chain or formed during its adsorption on hydrophilic part of the coal through hydrogen bonding. The amount of energy required to release thi s water, provides the positive enthalpy of interpenetration/compression , capable of imparting stabilit/9

. The released water which l'tas now a greater degree of freedom, imparts fluidity to the suspensiOn. The salient aspects of surfactant stabilized coal-water s lurry may briefly be summarized as follows :

( I) Adsorption of both anionic and non-ionic surfactants at low surface coverage takes pl ace through hydrophobic interaction or weak physical bonding. At high surface coverage adsorption of surface, especially of ethoxy non-ionic types takes place possibl y through hydrogen bonding or surface complex formation with cations on coal surface. In all the cases water is displaced from the surface of coal.

(2) The polar end group of adsorbed anionic surfactant, usually remains away from the surface. However, at higher pH or at high surface coverage or in solution of higher ionic strength, lateral interaction between polar groups takes place, leading to the decrease in net surface charge and consequently the repulsive force between particles. Therefore, for anionic surfactant , stabilization of coal­water slurry, ash content in coal is a very critical factor.

(3) For steric stabilizati on of coal-water slurry with non-ionic surfactant, complete or near complete coverage of surface is essentia l. At low surface coverage, parti al flocculation of coal partic les may occur through bridging action of dangling disso lved filaments of polymer segment.

(4) The interpenetration/compress ion of the adsorbed surfactant polymer chains is essenti al to achieve mutual repul sion between coal particles. This is most ly controlled by solution

thermodynamics of polymer molecules and therefore is sensitive to temperature variat ion.

Most of the literature on the use of various types of surfactants in the preparati on of HCCWS are reported in the form of patents. These inc lude, different types of inorganic compounds, anionic and non-ionic surfactants , polymers and co-polymers synthesized for the purpose. In Tables 1-3, literature references on the use of various anionic and non-i onic surfactants in the preparation of highly concentrated coal-water slurry have been li sted.

Acknowledgements

The authors wish to express their thanks to the Director, Regional Research Laboratory, Bhuba­neswar for hi s kind permiss ion to publi sh thi s paper. One of the authors (SKM) is grateful to CSIR, New Delhi , for the award of Research Associateship.

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MISHRA & KANUNGO.: PREPARATION OF HIGHLY CONCENTRATED COAL-WATER SLURRY 773

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74 Lion Corp Jpn , lap Pat 60 32,893 (20 February 1985); Chem Abstr, 103( 1985)56634.

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118 Shinohara H, Yamahara N & Yoshida Y (to Japan Synthetic Rubber Co Ltd Jpn); .lap Pat 61 152,796 ( II July 1986) (to Japan Synthetic Rubber Co Ltd Jpn); Chem Abstr: lOS( 1986) 175770.

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774 J SC I IND RES VOL 59 OCTOBER 2000

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Chem Abstr; 110( 1989) 19622 1. 125 Nakayama M, Kyonaga Y & Ito K, l ap Pat 63 260,987 (27

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Chem Abstr, 110( 1989) 196222. 126 Naka A, Murakami 0, Sugiyama H & Ito K, l ap Pat OJ

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127 Ni shimura K & Tani guchi H, l ap Pat 09 40,979 ( I 0

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128 Ito H, Tatsumi S, Kajihata Y & Takao S, l ap Pat 62 43,487 (25 Febru ary 1987) (to Kawasaki Heavy lnd Ltd Jpn) ; Chem Abstr, 106(1 987) 199075.

129 Arquette R E & Maske F J , Eur Pat 224,183 (03 June 1987)

US Pat 799,767, ( 19 November 1985) (to Henkel Corp);

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130 Taguchi J & Mori K, lap Pat 62 J49,793 (03 July 1987) (to Daicel Chem lnd Ltd Jpn) ; Chem Abstr, 107( 1987) 137446.

13 1 Okada Y & Shi buya Y, lap Pat 62 192, 491 (24 August 1987) (to Telnite Co Ltd Jpn) ; Chem Abstr, 1 08(1988)78577.

132 Echtl er J P , US Pat 4,440,543 (03 April 1984) (to Conco Inc US); Chem Abstr, 101 ( 1984)9905 .

133 Zaidan H, lap Pat 58, 96,693 (08 June 1983) (to S G K S Co

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134 San yo Chemical Indu stries Ltd Jpn, lap Pat 60 120,794 (23

June 1985); Chem Abstr, 103( 1985) 144674.

135 Ito, H. , Tatsumi S , Kajihata Y & Takao S, lap Pat 62 43, 488 (25 February 1987) (to Kawasaki Heavy lnd Ltd , Jpn); Chem Abstr, 106(1 987) 179649 .

136 Ito, H, Tatsumi S , Kajihata Y & T akao S , lap Pat OJ 04,697 (09 January 1989) (to Kawasaki Heavy lnd Ltd, Japan

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137 Naka A, Murakami 0 , Sugiyama H & Ito K, lap Pat OJ 87,693 (3 1 March 1989) (to Daiichi Kogyo Seiyaku Co Ltd ,

Nippon Komu K K, Jpn); Chem Abstr, 112( 1990) I 01 985

138 Usui N to Ajino moto K K, Jpn , lap Pat 09 J3,053 ( 14 January 1997); Chern Abstr, 126(1 997)20 1561.

139 Taguchi J & Fukuda T , lap Pat 60 J66,393 (29 August 1985) (to Sanyo Chemicals lnd Ltd Jpn); Chem Abstr, 104(1 986)71598 .

In r-­r--

>-0:: 0:: ::> .....:1 en 0::

~ ~ ..J ~ 0 u Cl

~ ~ z ~ u z 0 u ~ ::c: 2 ::c: IJ,.

0 z 0 1= ~ 0:: ~ 0.. ~ 0:: 0..

0 0 z ::> z ~ :>C o(!

~ 0:: ::c: en :2:

Table 1 -Some important anionic surfactant used for the preparation of highly concentrated coal water slurry (HCCWS)

Nature of the anionic surfactant

or its combination with other

surfactant

1 EDTA at pH 10

2 Calcium lignosulphonate (pH 5-8) with

an inorganic alkali metal buffer salt

3 Ammonium lignosulphonate-calcium

lignosulphonate and sufficient amount

NH40H to have slightly basic pH

4 Sodium lignosulphonate (I) and

montmorillonite (II)

5 Sodium lignosulphonate (I) and

Sodium tripolyphosphate (II)

6 Sodium tripolyphosphate(I) and

Lignosulphonate (II)

Dosage (per cent

by weight

of coal)

0.5

One part/hundred

parts coal in the

ratio 0 .2 : 0 .8

(I) 7.0

(II) 10.0

0.3 part composed

of 96 wt per cent I

and 4 wt per cent II

(I) : (II) = 1 : 1.9

Concentration (wt per

cent) of coal slurry and

particle size range

72.0 (97 wt per cent

diameter < 60 mesh)

Mixing ultrafine particles

of< 10 J..tm MMD in an amount of 10-30 percent by

weight of slurry with larger coal

particles within 20-200 J..lm MMD

A blend of finely ground

coal particles (MMD 7.8 J..tm)

and coarser particles (MMD

37 J..tm) 19.5 & 45.5 wt per cent

on slurry weight respectively

70.0

64.0

80 wt per cent < 200 mesh

75.0

Effect on Stability Reference decrease in

apparent

viscosity

Six man 61

62

370 cP at 100 s·1 - 63

shear rate with

thixotropic yield

point of 1 dyne/cm2

One man 64

One man 65 ,66

1900 cP > Two man 22,67

0 0 0 N

0:: u..l o:l 0 f-u 0 0\ V)

....l 0 > (I)

u..l 0:: 0 z tJ (I)

\0 r­r-

Table I -Some important anionic surfactant used for the preparation of highl y concentrated coal water slurry (HCCWS)- (Contd)

Nature of the anionic surfactant Dosage (per cent Concentration (wt per Effect on Stability

or its combination with other by weight cent) of coal slurry and decrease in

surfactant of coal) particle size range apparent viscosity

7 Sodium lignosulphonate (I) (I) : 0.5 64.0 11 30 cP at -

Ammonium lignosulphonate (II) (II) : 0.5 (5 - 25 per cent < 2 ~m 10 s·1 shear

Polyalkylene ox ide (III) (III) : 0.2 50 - 80 per cent < 50 ~m rate

90- 100 per cent < 125 ~m 95 - 100 per cent < 300 ~m I 00 per cent< 400 ~m)

8 Poly (sodium styrene sulphonate) (I) 0.1 77 .0 2100 cP against -

mol wt 7,50,000 (80 per cent passing 20,000 cP

200 mesh) without I

9 Poly (sodium styrene sulphonate) (A) 0.7 wt per cent mixture 70.0 2200 cP -

and poly(acrylic ac id ) (B) of A and B in the 67.6 wt per cent passing at 25 °C

rati o of 4: 6 325 mesh

(wt ratio)

to A copolymer (av mol wt. 20,000) - 70.0 1750 cP -

composed of sodium styrene sulphonate at 25 °C

and sodium allyl sulphonate mixed for

10 min at 3000 rpm

Reference

68

69

70

71

- Contd

Table I - Some important anionic surfac tant used fo r the preparation of highly concentrated coal water slurry (HCCWS)- (Contd)

Nature of the anionic surfactant or its combination with other

surfactant

II Allyl alcohol - sodium styrene sulphonate

copolymer (av mol wt 20,000) is di ssolved in water and graduall y added to coal. The mixture is agitated for I 0 min at 3000 rpm

12 A copolymer (av mol wt 20,000) of sodium styrene sul phonate and sodium ac rylate is di sso lved in water and then added to coal. The mixture is agitated for 10 min

at 3000 rpm

13 A copolymer (av mol wt 20,000) of

sodium styrene sulphonate and aery! amide is dissolved in water and is added to coal water slurry. The mixture is agitated

fo r 10 min at 3000 rpm

14 An aqueous mixture of poly(sodium acrylate) and poly(sodium styrene sulphonate)

15 I: I w.t. rati o of styrene sui phonic ac id polymer ammonium salt (mol wt 1 0,000) and acrylamide-N-methylol

acrylamide copolymer (mol wt 30,000)

Dosage (per cent

by weight of coal)

0.5

Concentration (wt per cent) of coal slurry and

particle size range

70.0

70.0

70.0 + 200 mesh 19.3 wt per cent 200 mesh 80.7 wt per cent

70.0

Effect on

decrease in apparent viscos ity

Stability Reference

2500 cP at 25 °C

2300 cP at 25 °C

2400 cP at 25 °C

980 cP Prevents flocc ulation

650 cP at 25 °C against

5400 cP for a commercial di spersant containing

polyacryli c acid Na salt

72

73

74

75

76

-Contd

0 0 0 N

~ P-l co 0 E-u 0 a, V)

....J 0 > en P-l ~

0 z u en

00 r-­r--

Table I -Some important anionic surfactant used for the preparation of highly concentrated coal water slurry (HCCWS)- (Contd)

Nature of the anionic surfactant Dosage (per cent Concentration (wt per Effec t on Stability Reference

or its combination with other by weight cent) of coal slurry and decrease in

surfactant of coal) particle size range apparent

viscosity

16 Dispersant containing 65 :35 wt ratio 0.6 72.0 770 cP at 25°C against >One mon 77

of calcium polystyrene sulphonate (mol 5400 cP for a commercial

wt 15,000) and polyoxyethylene nonyl dispersant containing

phenol ether (mol wt 4,000) sodium polyacrylate

17 Sodium polystyrene suphonate prepared 0.6 68.0 - - 78

by sulphonating polystyrene by so) in

ClCH2CH2CI in the presence of

polyethylene glycol at 45°C and then

neutralizing with NaOH to give the product of mol wt 16,800

18 Sulphonated benzene sodium salt-! ,2,- 1.0 70.0 - - 79

dich1oroethane (l: 1.3 mol) (70 per cent~ 200 mesh)

19 90 : lO acrylic acid - vinyl sulphonic 0.25 72.0 900 cP Good shear 80

acid copolymer sod ium salt (no av mol (70 per cent < 200 mesh) at 25°C stability

wt 4000) is added under slow (300-500

rpm) agi tation.

20 A polymer of formaldehyde with mono- 0.1 60.0 1240 cP and in the - 81

styrenated phenol sulphonic acid absence of dispersant

ammonium salt > 23,000 cP

- Contd

0\ r-­r--

>-0:: ~ :.::J .....l Ul

0::

t:: <(

?; ...J <( 0 u Cl

~ ~ z u.J u :z: 0 u >­.....l :I: (.J

:I: u... 0 z 0

~ 0:: <( 0.. u.J 0:: 0..

0 (.J z ::J z <( ~ o(!

<( 0:: :I: Ul

2

Table I - Some important anionic surfactant used fo r the preparation of highl y concentrated coal water slurry (HCCWS)- (Contd)

Nature of the ani onic surfactant Dosage (per cent

or its combinati on with other by weight

surfactant of coal)

2 1 An aqueous solution of thinner consi sting 0.3

of formaldehyde-naphthalene sulphonic ac id-

phenol sulphonic acid copolymer sodium salt

(I) [(naphthalene sulphonic ac id )- (phenol

sulphonic ac id) wt rat io 9.6 : 0 .4 av dp 22] and

sodium tripolyphosphate[I - tripolyphosphate

wt ratio 97 : 3]

22 Synergistic surfactant mi xture consisting of 0 .2 (I)

naphthalene sulphonic ac id (I) sodium salt and and

hexametaphosphori c ac id sodium salt (II) 0.2 (II)

23 Soap prepared by reacting NaOH with 5.0- 7.0

tall ow

24 Sodium alkyl naphthalene sulphonate

25 Acrylamide-ethylene-male ic anhydride 0.25

copolymer sodium sa lt (50:45:5 units) .

The dispersant is added to the CWS and

the mixture is then agitated at 500 rpm

for IOmin

Concentration (wt per

cent) of coal slurry and

partic le size range

74 .0

(80 per cent ~ 200 mesh)

65.0

(80 wt.per cent pass ing

200 mesh)

50.0 - 70.0

7 1.9

70.0

Effect on

decrease in

apparent

viscos ity

Stability Reference

Improved flu idi ty 82

and storage stab il ity

one month after

preparation

< 500 cP at room temp The viscosity produced

by the addition of e ither

surfactant at 0.4 wt.per cent

is 1500-2000 cP at room temp

83

Good stab ility 84

590 cP - 85

900 cP - 86

0 0 0 N

c.:: UJ co 0 f-u 0 o-V)

....J 0 > (/)

UJ c.:: Cl z 0 (/)

0 00 r-

Table I -Some important anionic surfactant used for the preparation of highly concentrated coal water slurry (HCCWS)- (Contd)

Nature of the anionic surfactant Dosage (per cent Concentration (wt per Effect on Stability Reference or its combination with other by weight cent) of coal slurry and decrease in surfadaut of coal) particle s1ze range a.pparent

viscosity

26 Mixture of I: I (mol. ratio) HCHO- 0.4 70.0 - Stable for 87 naphthalene sulphonic acid copolymer (70 wt per cent < 200 mesh) > 14 d sodium salt- di-i sobutylene-maleic

anhydride copolymer sodium salt

27 Acryiamide-acrylic acid-methyl acry late 0.3 70.0 9100cPvs. Stable for 88 copolymer sodium salt 2000 cP using I week

polyacrylate

28 Poly(maleic ac id ) sodium salt - - - - 89

29 ( I) Formaldehyde-lignosulphonic acid- 0.3 74.0 One month 90 naphthalene su lphonic acid copolymer (80 per cent~ 200 mesh) after prepar-sodium salt (I)[(Iignosulphonic acid- ation naphthalene sulphonic acid) wt ratio I :9,

d p 1.3] & (2) sodium tripolyphosphate

(I - tripolyphosphate wt. ratio 97:3)

30 Isobutylene-male ic anhydride (I) : 0.2 62.0 2000 cP Stable for 91 copolymer triethanolamine salt (I) (II) : 0.1 (70 wt per cent passing at 25°C > 1 week NaOH (II) 200 mesh)

3 1 Mixture of lignosulphonic sodium (I) : 0.1 70.5 1900 cP Stable for 92 salt (I) , carboxymethyl cellulose Na (II ) : 0.03 at room > 10 d

sa lt (II) and triphosphoric acid Na salt (III) (III) : 0.05 temperature

- Contd

00 r--

:>-0:: 0:: ;::) -l Cl"l

0:: LlJ f--< 3: ...J <1: 0 u Cl

t:: -< ~ z LlJ u z 0 u >--l :I: c.J :I: [J...

0 z 0 1= -< 0:: -< 0... LlJ 0:: 0...

0 c.J z ;::)

z -< ~

o(l

-< 0:: :c Cl"l

~

Table I - Some important anionic sur fac tant used fo r the preparation of highl y concentrated coal water slurry (HCCWS)- (Contd)

Nature of the anionic sur factant Dosage (per cent Concentration (wt per Effec t on Stability Reference

or its combination with other by weight cent) of coal slurry and decrease in

surfac tant of coal) parti cle size range apparent

viscos ity

32 Mi xture of 4 : I (wt rati o) formaldehyde 0 .5 70.0 772 cP - 93

naphthalene sulphonic acid copolymer (70 wt per cent passing at 25°C

sodium salt-poly(acrylic ac id) Na salt 200 mesh)

33 Lignosulphonic ac id - ammonium 0.36 77.0 (ash 12 per cent) 350 cP Stable for 94

persulphate reaction product at 25°C > 60 d

34 Naphthalene sulphonate (I), NH40H (II) (I) : 0 .4 70.0 750 cP Completely 95 and CaC1 2 so as to have a total hardness stable

of 330 ppm expressed as Ca2+ ions (II) : 0. 1

35 25 :75 wt. ratio of styrene sui phonic ac id 0.7 72.0 780 cP (25°C) vs Stable for 96 polymer sodium salt (av mol wt I 000) 5400 cP for a comm- >one mon

and a ( l : l ) styrene sulphonic ac id-a -methyl ercial di spersant contg

styrene sulphonic ac id copolymer calcium acrylic acid styrene

salt (av mol wt 25,000) copolymer sodium salt

36 Mixture of polyethylene glycol nonyl 0.8 65.0 820 cP at 5°C, 800 cP - 97

phenyl ether 20 , formalin-isopropyl at 50 °C vs I 020 and

naphthalene sulphonic ac id condensate > 4000 cP respecti vely

sodium salt (I) 75 and sodium ligno- for a slurry wi thout

sulphonate (II) 5 parts (I) and (II)

37 Acrylic ac id - hexaethylene glycol 0.6 69.5 1030 cP Coagulated 98

methacrylate- hexaethylene glycol phenyl (85 .5 per cent with 4 per cent

ether acrylate- sodium styrene sulphonate diam ~ 74 1-J.m) when stored

copolymer (wt av mol wt 9000) for one mon

-Contd

0

8 N

0:: t.Ll o::l

§ 0 o-,

"' ....l 0 > U)

t.Ll 0:: 0 z 0 U)

("' , 00 r--

Table I - Some important anionic surfac tant used for the preparation of highl y concentrated coal water slurry (HCCWS)- (Contd)

Nature of the anionic surfactant

or its combination with other

surfac tant

38 Sodium humate prepared by extrac tion

of brown coal with NaOH at I 00°C

39 Sulphonated ammonium humate(!)

prepared by heating a bituminous coal

NH40H mi xture at 50°C for I h to

obtain an ammonium salt fo llowed

by sulphonati on with so3.

40 Potassium nitrohumate

Dosage (per cent

by weight

o f coal)

0.4

1.5

0.5

Concentrati on (wt per

cent) o f coal slurry and

particle size range

65.0

( ~ 300 mm coal)

6 1.43

70.0

Effect on

decrease in

apparent

viscos ity

500 cP compared to

5000 cP fo r a di spersing

agent contg Na dodecy l

sulphonate

475 cP at sher rate 10.2 s·1

compared with 2000 cP

contg no I

Stability

11 50 cP Upon settling the

coal, concn in the

Reference

99

100

10 1

upper, middle and lower

layers are 69. 1, 70.4 and

70.5 per cent respecti vely

M 00 r--

>-Q:: Q:: :J ....l Cl)

Q::

~ <!: ~ ...J <!: 0 u a UJ f-<!: Q:: f-z UJ u z 0 u >-....l :I: S2 :I: u.. 0 z 0 [:::: <!: Q:: <!: 0.. UJ Q:: 0..

0 (.J z :J z <!: ~

a<:! <!: Q:: :I: Cl)

2:

Table 2- Some important non-ionic surfac tant used fo r the preparation of highl y concentrated coal water slurry (HCCWS)

Nature of the anionic surfactant Dosage (per cent Concentration (wt per Effect on Stability Reference

or its combination with other by weight cent) of coal slurry and decrease in

surfactant of coal) particle size range apparent

viscosity

I Poly( ethylene-propylene) glycol 0.5 70.0 810 cP compared to - 102

laurylether (mol wt 3000 e) (80 per cent< 200 mesh) ;:::. 20,000 cP in the

absence of the surfac tant

2 General formula of the di spersant I.d 70.0 - The slurry is 103

A[(C3H60 )y(C2H20 )2H], where A Ratio of (I) : (II) (- 200 mesh) stable for

is an anion or hydroxyl compound = 30:70 > 90 d

contg. acti ve H and x,y,z are integers

(>2, >I and >I respecti vely).

e .g. A mixture of polyethylene-poly

propylene glycol-trimethyl propane

ether (I) and oxypropylene-oxyethylene

(II) mol wt 20,000)

3. A mixture of polyethylene glyco l 0.3 76.0 1600 cP vs. > 20,000 cP - 104

methyl ether (mol wt 6500) (I) Ratio of (I) and (II) (80 per cent -200 mesh) in the absence of this

and tributyl phosphate (II) in the mixture= 55:45 additi ve mixture

4 15:35 polyethylene glyco l octyl ether 0.3 76.0 1380 cP vs. > 20,000 cP - 105

(mol wt 6500)-polyethylene glycol (80 per cent - 200 mesh) in the absence of the

Iaury! ether phosphate mixture di spersant

5 Polyethylene glyco l-polypropy lene (I) : 0.5 72.0 560 cP Stable for 106

glycol glycero l ether (I) and 2-ethyl (II) : 0.05 (80 per cent -200 mesh) at 25°C > 60 d

hexanol (II)

- Contd.

0 0 0 N

0::: ilJ co 0 f-u 0 a-V)

....l 0 > en ilJ 0::: 0 z u U)

'<j-00 r-

Table 2- Some important non- ionic surfactant used for the preparation of highl y concentrated coal water slurry (HCCWS)- (Contd)

Nature of the anionic surfactant Dosage (per cent Concentration (wt per Effect on Stability Reference or its combination with other by weight cent) of coal slurry and decrease in surfactant of coai) panicle size range apparent

viscosi ty

6 Ethoxylated and/or propoxylated 7l.O 1300 cP - 107 alcohols

7 A mi xture of 350 : 20 ethylene oxide- 1.0-2.0 65.0 630 cP - 108 propylene oxide copolymer Iaury! ether at 25°C 70, 48 per cent aqueous maleic anhydride-polyethylene glycol monomethyl ether copolymer (pH 9.5 , viscosity 203cP) 20 and polyethylenimine I 0 parts

8 A 70 : 30 mixture of ethylene diamine- 0.2 76.0 980 cP vs . 20,000 cP - 109 ethylene oxide-butylene oxide-propylene (80 per cent -200 mesh) in the absence of this oxide condensate (mol wt 15000) and dispersant butanetriol phosphate potassium salt

9 Alkylene ox ide copolymer amine ethers 0.5 7 1.0 1400 cP at > 30d 110 (contg >5 active H) e.g. ethylene ox ide- (70-90 wt per cent passes room temperature propylene oxide copolymer diethylene -200 mesh) triamine ether

I 0 Alkyl phenyl decaethylene glycol ether (I) (I) : 0 .005-0.5 63.0 500 cP - Ill and brown coal polycarboxylic acid (II) (II) : 0. 1

-Contd

<n 00 r-

>-0::: 0::: ~ .J (/)

0:::

~ <(

~ ...J <( 0 u 0 UJ f-<( 0::: f-z UJ u z 0 u >-.J :c S2 :c t.I.. 0 z 0 E= <( 0::: <( a. UJ 0::: a.

ci 0 z ~ z <( ~

o(l <( 0::: :c (/)

~

I

Table 2- Some important non-ionic surfac tant used for the preparation of highl y concentrated coal water slurry (HCCWS)- (Contd)

Nature of the anionic surfactant Dosage (per cent Concentration (wt per Effect on Stability or its combination with other by weight cent) of coal slurry and decrease in

surfactant of coal) particle size range apparent viscosity

II Mixtures containing 70 wt per cent propylene 0 .2 77 .0 1700 cP Stahle for oxide copolymer sorbitol ether having a (-200 mesh) at 25°C five mon 6 acti vated H 's (av mol wt 25,000) and 24 wt per cent hydroxymethyl starch

12 A 60:40 polyethylene glycol olelyl ether 0.3 74.0 Addition of the di spersant -

(mol wt 6500)-hydroxy propyl cellulose (80 per cent -200 mesh) leads to the decrease of mixture viscosity from >20,000

to 2200 cP

13 Polyethyleneimine (mol wt - 70,000) 1.0 65 .0 610 cPvs IO,OOO cP -

(79 per cent -200 mesh) without the dispersant

14 Ethylene oxide-propylene oxide-phenol 0.5 74.0 2700 cP Stable for butyl naphthalene-formaldehyde (80 wt per cent passing at 25°C > one mon copolymer 200 mesh)

15 Mixture of 70:10:20 (wt ratio) butylene 0.9 60.7 390 cP -

oxide-propylene ox ide copolymer, at 25°C

methacrylic ac id-polyethylene glycol methyl ether methacrylate copolymer

sodium salt

Reference

112

11 3

11 4

115

11 6

-Contd

0 0 c "' 0::: u..l co 0 f-u 0

"' <r.

....l 0 > C/l u..l 0::: 0 z

0 C/l .....,

'-0 00 r-

'

Table 2- Some important non-ionic surfactant used for the preparation o f highly concentrated coal water slurry (HCCWS)- (Contd)

Nature of the anionic surfactant Dosage (per cent Concentration (wt per Effect on Stability Reference

or its cumuination with othel uy weight cent) o f coal slurry and decrease in

surfactant of coal) particle size range apparent

viscosity

16 Mixture of 50:50 (wt per cent unit ratio) 1.5 69.5 1600 cP Stable 117 acrylic ac id-acrylonitrile copolymer for 3d (mol. wt 1550)

17 Sulphonated dicyclopentadiene male ic 0.5 70.0 730 cP 30 d 11 8

an hydride copolymer (av mol wt 5380)

18 Non-ionic dispersant of general formula 0.1-1.5 70.0 380-520 cP at 20°C - 11 9

RO(CH zCHzO)nH (n= 180-230; R=C12 0. 1-2. and 20°C & 220 s·'

C14 3.0-6.0, C16 20-35, C 18 55-75 & C20-allyl hear speed vs > I 150

0.5-3 wt per cent). Thus a dspersant contg. Iaury! cP for indi vidual

ale 0.5 , myrystyl ale 4 , cetyl ale 28, stearyl ethoxylated alcohol

ale 66 and eicosyl ale 1.5 wt per cent dispersant

19 80:20 wt. ratio naphthalene sulphonic acid 1.0 60.0 970 cP vs 2000 cP - 120

forma ldehyde copolymer sodium salt (I) for di spersant contg

and ethoxylated nonyl phenol (II) I alone

20 Mixture of 65 parts sodium lignosulphonate 1.0 63 .0 I 080 cP at 40°C - 121

(av mol wt 3500-5000) and 35 parts. compared to 4000 cP

polyethylene glyco l nonyl phenyl ether for the slurry without I

( 150 mol adduct) (I)

-Contd

r-00 r-

Table 2- Some important non-ionic surfactant used for the preparation of highly concentrated coal water slurry (HCCWS)- (Contd)

>-0::: Nature of the anionic surfactant Dosage (per cent Concentration (wt per Effect on Stability Reference 0::: ;:l or its combination with other by weight cent) of coal slurry and decrease in .....) en surfactant of coal) particle size range apparent 0:::

~ viscosity <t: 3:

21 Mixture of 10 parts butyric acid Iaury! 0.8 67.0 470 cP vs > 4000 cP and 122 ...J -<t: ethylene diamine salt and 90 parts ethylene poor fluidity for CWS 0 u oxide-propylene oxide copolymer nonyl without I 0 UJ phenyl ether-formaldehyde condensate (I) f-<t:

!= 22 95 :5 wt. ratio of naphthalene sulphonate- 0.2 73.0 700 cP (25°C) vs. ~one mon 123 z UJ formaldehyde condensate sodium salt ~ 2000 cP for the u z (I av polymerization degree 70) and dispersant contg. 0 u >-

sorbitan-ethylene oxide copolymer I alone .....) :r:: 23 50:20:30 wt. ratio of an a-methyl styrene 0.6 75.0 830 cP (25°C) after 124 0 -

5: sulphonic acid-styrene copolymer mono- 30 days of storage vs {.I..

0 ethanol-amine salt-ethylene oxide-lauryl 31 00 cP for a comrn-z ale . copolymer-nontronite ercial dispersant 0 f= <t:

24 70:30 wt ratio of an a-methyl styrene 0 .6 73.0 860 cP after stored 125 0::: -<t:

sulphonic-styrene copolymer monoethanol at 25°C for 30 d 0.. w 0::: amine salt (mol wt 5000) and montmo- vs 31 00 cP for a 0..

0 rillonite (a smectite group mineral) commercial dospersant 0 z

25 95:5 (weight ratio) mixture of sulphonated (I) : 0.2 78 .0 900 cP (initial) at 25°C Coagulation 126 ;:l z

polystyrene sodium salt (mol wt 4000, (80 per cent< 200 mesh) and I 00 s·1 & 900 cP amount 0 <t: ~

degree of sapond 85 per cent) and ethoxylated (II) : 0.3 after I month vs I 080 Od per cent <t: nonyl phenol (adduct mol. no. 75) I and cP, 4500 cP for a coal 0::: :r:: bentonite (II) slurry contg polystyrene Coagulation en ~ (mixed with coal and water in a ball mill) sulphonic acid only amount 80

per cent

0 0 0 N

0::: u..l o:l 0 E-u 0 0\ ll")

-l 0 > Ul u..l 0::: Q z u Ul

00 ~ r-

T able 3 - Some important polysaccharides used fo r the preparati on of highl y concentrated coal water s lurry (HCCWS)

Nature o f the anionic surfactant Dosage (per cent Concentrati on (wt per Effect on Stability Reference

or its combination with other by weight cent) of coal slurry 1'\nd decrease in

surfactant o f coal) particle size range apparent

viscosity

Carboxymethyl cellulose or its salt - 65.0 - 80.0 - - 127 and alkali s

2 Sodium carboxymethyl cellulose 1.0 64.5 At shear > 20 s·1 1900 cP - 128 at shear < I 00 s-1

, 800 cP

3 Cellulose is added to l 00 wt parts 0.6 - Addition of 0.6 wt. parts to - 129 carboxymethyl cellul ose stabili zed I 00 wt parts CMC stabili zed

coal-water slurry CWS results in the dec rease

of viscosity from 1290 cP to

230 cP after 16 h

4 Carboxymethyl hydroxyethyl ce llulose (I) 0.0 1 65.0 1500 cP vs 25,000 cP fo r ;::>:_ two mon 130 (I) and sodium lignosulphonate (II) (II) 0.3 a slurry contg no I

5 An aqueous soluti on contg. humic ac id (I) 0.4 70.0 - Did not settl e 13 1 sodium salt (I) and carboxymethyl (II ) 0 .1 (av part icle size after 60 d of

cellulose a lkali metal sa lt (II) 45 J..tm) storage

6 Wood particles small er than -50 Tyler 1.0 - 10.0 - - - 132 mesh

7 A polysaccharide (uronic ac id) I (I) : 0.0 I 65.0 Good flui d ity Good stability 133 Tamol L (an anionic surfac tant) II (II) : 1.0

-Contd .

"' 00 r-

>-0::: 0::: :::> ....l Ul

0:::

t:: <(

~ ...J <( 0 u 0 Ul f-<(

~ z Ul u z 0 u >-....l :r: 2 :r: t.L.. 0 z 0 f= <( 0::: <( 0.. Ul 0::: 0..

0 0 z :::> z <( ~

o(! <( 0::: :r: Ul

2:

Table 3 -Some important polysaccharides used fo r the preparation of highl y concentrated coal water slurry (HCCWS) - (Contd)

Nature of the anionic surfac tant Dosage (per cent Concentration (wt per Effect on Stability Reference or its combination with other by weight cent) of coal slurry and decrease in

surfac tant of coal) partic le size range apparent

viscosi ty

8 Mixture of 10:85 :5 (wt per cent) sodium- 1.0 70 .0 1530 cP Stable for 134 kumarate-ethylene oxide-propylene at 20 °C > 2 weeks ox ide copolymer pentaerythritol ether-

hydroxy propyl methyl cellulose

9 A mixture contg sodium naphthalene (I) : 0.6 66.8 - Stable for > I 0 135 sulphonate-formaldehyde copolymer (I), (II ): 0 .0 15 weeks compared naphthalene sulphonate formaldehyde (III) : 0 .015 to < one week for copolymer (II) and carboxymethyl ce llulose the slurry contg no sodium salt (III) NaCMC

I 0 Maleic anhydride-dicyc lopentadiene 0.48 65.0 - Stable for> nine 136 copolymer sulphate Na salt (I) and week vs one week fo r polyoxyethylene carboxy methyl a CWS contg. I alone cellulose Na salt

II Sulphonate polystyrene sodium salt (I) : 0.2 77.0 At 25°C and 100 s·1 Coagulati on 137 (mol wt 6000, degree of sulphonation (80 per cent parti cles of 850 cP (initiall y) amount 0 per cent 80 per cent) I, hydroxypropyl cellulose (II ) : 0.05 size 200 mesh) 850 cP (a fter one

(11 20,000 cP) II month and I 000 cP

(mi xed in a ball mill ) (initi ally) , 3900 cP

(after I mon) for a

composition contg Coagulation polystyrene sulphonic amount 80 per cent ac id sodium salt

- Contd

0 0 0 ('l

0:: Ul ill

~ u 0 0\ V)

.....l 0 > C/)

Ul 0:: Ci z 0 C/)

0 0\ r-

Table 3- Some important polysaccharides used for the preparation of hi ghl y concentrated coal water slurry (HCCWS) - (Contd)

Nature of the anionic surfactant

or its combination with other

surfactant

12 Lipomyces microorganisms capable of

generating polysaccharose

13 Water soluble cellulose ether (I) selected

from methyl cellulose (II) and hydroxy

propyl methyl cellulose and a polyoxyalkene

surfactant of formula

Z[O(CHzCHzO)x(C3H60 )yH] 11 (III , z = mono­

or polyfunctional active H-contg comound,

x;:::. 0, y;::: 5 , n;:::_l ) at I- III (atomic ratio)

(20-80) : (0.5 - 99.5)

Dosage (per cent

by weight

of coal)

0.05- 0.5

3. 0 parts (II)

97.0 parts (III)

Concentration (wt per

cent) of coa l slurry and

parti cle size range

~ 200 J . .Un av

particle size

68.0

Effect on

decrease in

apparent

viscosity

1070 cP

at 20°C

Stabi li~y

;:::. Two weeks

Reference

138

139