Note: Descriptions are shown in the official language in which they were submitted.
133983~
5396
POLYETHER GYCOL ESTERS OF
POLYCARBOXYLIC ACIDS AS RHEOLOGICAL
ADDITIVES FOR COAL-WATER SLURRIES
This invention relates to a coal-water slurry
having a rheological additive which is the reaction product
of a polycarboxylic organic acid and a polyether glycol. The
ester reaction product is employed in an amount from about
0.1 to about 4~ by weight of the coal-water slurry, the
slurry having from about 60 to about 80% by weight of solids,
the balance being water.
In recent years a great deal of interest has
developed in utilizing coal-water slurries in lieu of oil for
electric power generation not only because of the lower cost
of coal but also because of its availability.
Coal-water slurries have been produced with solids
contents of about 60 to about 75~ which are fluid and handle
in about the same way as petroleum fuels. These coal-water
slurries may be burned directly without need of dewatering
the mixture. The heat generated during combustion is suffi-
ciently high so that the water in the slurry does not prevent
it from being used to generate power. Naturally, as the
solids of the coal-water slurry increase, the fuel value of
the slurry also increases. For this reason, slurries having
less than about 50 to 55% solids are unsuitable primarily for
economic reasons.
One of the difficulties encountered with coal-water
slurries at a solid content of about 60% and higher is that
the dispersion of coal in water be~omes an immobile mass and
when burned it has to be handled in the same manner as lump
coal. Handling in this respect includes not only
~33983~
transportation of the coal from the mine source but also the
delivery of the coal to a combustion chamber such as the
firebox of a steam boiler. Unless coal-water slurries have
the same liquidity as oil at these high solids content so
that they may be transported by pipeline and injected into a
firebox by spraying, the advantage of using a liquid carrier
(i.e., water) for the coal is lost. Stated otherwise, the
particles of coal in the slurry at these higher solids levels
tend to convert the liquid carrier (water) into a plastic
mass whereby the advantage of employing a liquid carrier is
lost.
The prior art has overcome some of-these diffi-
culties by providing additives which may be used in relative-
ly small amounts to assure that the coal-water slurry at high
solids content is fluid. Examples of these additives are
given by Kovacs in U.S. Patent 4,435,306 Sakaria U.S. Patent
4,398,919 and in European Patent Application 0131558.
Coal-fuel oil slurries containing a dispersing agent are also
described by Schmolka et al. in U.S. Patent 4,288,232, Naka
et al. U.S. Patent 4,251,229 and Shimizu et al. U.S. Patent
4,187,078-
The present invention relates to a coal-water
slurry having a novel rheological additive comprising the
reaction of:
(a) a polycarboxylic organic acid having from
about 16 to 60 carbon atoms and form 2 up to 4 carboxyl
groups with
(b) a polyether glycol having recurring
oxyalkylene groups containing up to 4 carbon atoms and having
a molecular weight from about 1,000 to about 20,000; the mole
3~ ratio of said polyether glycol to said polycarboxylic acid
1339839
--3--
ranging from about 1:1 to n-1:1 where n is the number of
carboxyl groups in the polycarboxylic acid.
The polyether glycol is selected from the group
consisting of polyethylene glycol, polypropylene glycol, and
poly(ethylene-propylene) glycol and the polycarboxylic acid
is selected from the group consisting of dimer acids, trimer
acids, adducts of unsaturated monocarboxylic acids or dimer
acids with maleic anhydr~de in a molar ratio of about 1:1,
adducts of linoleic acid or similar unsaturated
monocarboxylic acids with acrylic-type acids in a molar ratio
about 1:1 and adducts of olefins having about 12 to about 40
carbon atoms with maleic acid or maleic anhydride in a molar
ratio of about 1:1. Polyethylene glycol having a molecular
weight from about 3,000 to 12,000 is particularly useful for
the preparation of the rheological additives of this in-
vention. The acid value of the rheological,additive istypically 25 to 75 percent of the acid value of the
polycarboxylic acid/polyether glycol mixture before reaction.
According to another feature of an embodiment of
the present invention all or a portion of the remaining
carboxyl groups are converted to a salt form. Salts of
ammonia and the group IA or IIA metals, especially sodium or
potassium are particularly useful for this purpose.
The rheological additive is employed in an amount
from about 0.1 percent to about 4 percent and, more pref-
erably, from 0.25 to 1.5 percent in slurries containing from
about 60 to about 80 percent by weight solids.
The rheological additives of this invention are
utilized in coal-water slurries and are obtained by reacting
a polycarboxylic organic acid with a polyether glycol to rorm
3~ an ester. The acids have form about 16 to about 60 carbon
133~8~9
atoms, especially from 21 to 54 carbon atoms, and from 2 up
to about 4 carboxyl groups. The acids may be either dimer
acids, trimer acids, adducts of unsaturated monocarboxylic
acids or dimer acids with maleic anhydride in a molar ratio
of about 1:1, adducts of linoleic acid and similar unsatura-
ted monocarboxylic acids with acrylic-type acids in a molar
ratio of about 1:1 or adducts of olefins having about 12 to
about 40 carbon atoms with maleic acid or maleic anhydride in
a molar ratio of about 1:1.
Dimer acids are known in the art and described by
Barret et al. in U.S. Patent 2,793,220 and Myers et al. U.S.
patent 2,955,121. Trimer acids are also known in the art and
are described by Barrett et al. in U.S. Patent 3,097,220.
The dimer acid is obtained by oligomerizing an unsaturated 18
carbon atom naturally occurring unsaturated acyclic
monocarboxylic fatty acid such as oleic acid, linoleic acid,
linolenic acid and the like to obtain a 36 carbon atom
dicarboxylic acid whereas the trimer acid is obtained by
oligomerizing the foregoing unsaturated monocarboxylic acids
to obtain a 54 carbon acid tricarboxylic acid. In both of
these reactions, other products are obtained; however, the
reaction is conducted in a manner so that the reaction
product is principally the dimer acid or the trimer acid.
other unsaturated acyclic monocarboxlyic acids having at
least one ethylenically unsaturated position and from about
lO to about 22 carbon atoms can also be used to make the
polycarboxylic acids of the present invention. These include
decenoic, undecenoic, pentadecenoic, hexadecenoic acids and
the like. unsaturated acyclic monocarboxylic acids of the
above types may be obtained from natural fats and oils such
as tall oil, linseed oil, tung oil, soy oil, rapeseed oil,
corn oil, fish oil, beef tallow and mixtures thereof.
Dimer acid prepared as described in the foregoing
references containing 75~ or more of dimer acid is preferred
whereas trimer acid prepared according to the foregoing
references having 60% of more of trimer acids is preferred.
Mixtures of dimer acid and trimer acid are also useful and
advantageously employed.
- 4 -
Adducts of maleic anhydride (or acid) with unsa~ 9839
ated monocarboxylic acid and dimer acids are known in the art
and are described in U.S. Patents 2,902,499 and 2,975,133.
These adducts are prepared by heating maleic anhydride and an
5 unsaturated acid at a temperature from about 100~C to about
300 C until the addition reaction is completed. The molar
ratio of the maleic anhydride to unsaturated acid is
generally about 1:1.
A 21 carbon atom dicarboxylic acid designated
lO Westvaco 1550 (trademark) may be employed as the polycarboxy-
lic acid and comprises the addition product of an 18 carbon
atom monocarboxylic unsaturated acid and acrylic acid. Equi-
valent unsaturated monocarboxylic acid having at least two
ethylenically unsaturated positions and from about 10 to
15 about 22 carbon atoms reacted with an acrylic-~ype acid to
produce a dicarboxylic acid may also be employed as the
polycarboxylic acid. The acrylic-type acids, as referred to
herein, include angelic acid, tiglic acid, senecioic acid,
crotonic acid, isocrotonic acid, vinylacetic acid, methacry-
20 lic acid and the like mixtures thereof. The
-- 5 --
-6- 1~39~39
polycarboxylic acid can also be an adduct of maleic acid or
maleic anhyride with an olefin, where the olefin has from 12
to 40 carbon atoms and one or two unsaturated positions.
Polyether glycols reacted with the above-described
polycarboxylic acids to obtain the reaction product of the
present invention comprise higher molecular weight poly
(lower oxyalkylene) glycols. The molecular weight of the
polyether glycol ranges from about l,000 to about 20,000
and, more preferably, from about 3,000 to about 12,000.
They are comprised of recurring oxyalkylene groups containing
up to about 4 carbon atoms and preferably from 2 to 3 carbon
atoms. Polyethylene glycol having a molecular weight from
about 3,000 to about 12,000 is particularly useful for the
preparation of the rheological additives of the present
invention, however, polypropylene glycol
poly(ethylene-propylene) glycols within the above-described
molecular weight ranges are also useful.
The various polyether glycols noted herein may have
either a broad or a narrow molecular weight distribution so
long as the molecular weight, on average, is within the
aforementioned ranges. These ranges apply not only to
polyether glycols falling within the range, but also to
polyether glycol mixtures having an average molecular weight
with the aforesaid range. The commercial glycols employed
according to the present invention are within the aforemen-
tioned molecular weight ranges and the molecular weights
thereof are average molecular weights. Some commercial
polyethylene glycols that may be employed according to the
present invention have average molecular weights of 1000,
3o
_7_ ~ 3983~
1 3350~ 8000, and 20000 and are sold under the trademark
Carbowax 1000, 3350, 8000 and 20000.
Lower alkoxy poly (lower oxyalkylene) glycols,
i.e., wherein one of the terminal hydroxyl groups is "capped"
with an alkyl group having from 1 to about 4 carbon atoms may
also be employed. These lower alkoxy poly (lower
oxyalkylene) glycols also are within the molecular weight
range as defined above for the polyether glycols. The
terminal hydroxyl group generally is "capped" with a methyl
group, such as methoxpolyethylene glycol.
Mixtures of any of the polyether glycols noted
herein may also be used.
Although the polycarboxylic acid and polyether
glycol may be reacted to almost completely esterify the acid,
in a preferred embodiment, the molar ratio of polyether
glycol to polycarboxylic acid is about 1:1 to n-l:l, wherein
n is the number of carboxyl groups in the polycarboxylic
acid. The polyether glycol and polycarboxylic acid are
reacted to form an ester in which the acid value (AV) of the
ester is 25 percent to 75 percent of the acid value of the
reactant mixture before esterification. Some unreacted
carboxyl groups remain in the ester which in some applica-
tions improves the performance as rheological additives.
The rheological additives of the present invention
are reaction products of the aforementioned polycarboxylic
acids and polyether glycols and are produced in accordance
with conventional esterification procedures. Some unreacted
glycol and acid remains~in the reaction product and are not
removed. Polymerization is avoided by the use of the afore-
mentioned molar ratios and controlled degree of reaction. By
13~9839
proceeding in this manner, the esters thus produced will haveunreacted carboxylic acid groups.
According to another feature of an embodiment of
the present invention, all or a portion of the remaining
carboxylic acid groups are converted to a salt form, These
salts of the partial ester are also useful as rheological
additives. salts of ammonia and the Group IA or Group IIA
Metals of the Periodic Table of the Elements, especially
sodium or potassium metals, are particularly useful. The
salts may be formed by reacting the partial ester with the
hydroxides of the aforementioned metals or with ammonium
hydroxide in an amount from about 50% to about 100% of the
free carboxylic acid groups of the partial ester,
Salts may also be obtained from alkanolamines or
heterocyclic nitrogen compounds having up to about 10 carbon
atoms and 1 or 2 nitrogen atoms by reacting the partial ester
with the alkanolamine or heterocyclic nitrogen compound in a
conventional manner, Various heterocyclic nitrogen compounds
that may be employed comprise pyridine, piperidine, pipera-
zine, morpholine, and alkyl-substituted imidazolines, useful
alkanolamines include ethanolamine, diethanolamine, trieth-
nolamine and the like.
Various rheological stabilizers in the preferred
embodiment of the invention comprise the following reaction
products:
I. Monoesters of a dimer acid with polyethylene
glycol having a molecular weight range from about 3,000 to
about 12,000. This particular monoester is one of the
especially preferred partial esters of the present invention;
II. A monoester or a diester of a trimer acid, or
mixtures thereof, and polyethylene glycol having a molecular
weight range of from about 3,000 to about 12,000;
III. A monoesters, diester, triester, or mixture
thereof of an essential 1:1 adduct of dimer acid with maleic
acid or maleic anhydride and a polyethylene glycol having a
molecular weight range of about 3,000 to about 12,000 and
~'.'~.
133~83~
IV. Ammonium, alkali meal and alkanolamine salts of
I, II and III.
The coal-water slurries of the present invention
are made from pulverized or powdered coal which has a
particle size such about 60% to about 90% will pass through a
200 mesh U.S. standard screen (a 75 micron sieve). Powdered
or pulverized coal that may be converted into a water slurry
is generally described by Funk in U.S. Patents 4,282,006 and
4,416,666. The mixing of the powdered coal with water to
form a slurry is also described by Funk in U.S. patent
4,477,260 at column 21. The rheological additives of the
present invention are combined with water and the water in
turn is mixed with the coal in a mixer such as Hobart
(trademark) mixer or the various art known equivalents
thereof.
The coal slurry is made by adding about 0.1% to
about 4% and, more preferably, 0 25 to 1 5% by weight, based
on total slurry, of the rheological additive as defined here-
in to the water used in the coal-water slurry to form a coal-
water slurry having anywhere from about 60 to about 80%
solids by weight By used of the rheological additives of
the present invention the slurries are liquid at room temper-
ature and easily pourable. without the additives, the coal-
water slurry is a non-pourable mass that, at room tempera-
tures is solid The slurries containing the rheological
additives of
-lo- 133983~
the present invention should be maintained from about 0~C up
to about 95~C preferably from about 2~C to about 75~C and
most preferably less than 50~C.
The following Examples are illustrative.
EXAMPLE I
Preparation of C21 dibastic PEG monoester:
~estvaco 1550 (trademark) is a C21 diabasic acid produced at
220-250~C, for 2 hours through the addition of acrylic acid
to linoleic acid (AV 272-278; saponification value (SV) 300-
308; 88-90~ diabasic acid). For the reaction, 102.6g (0.254
mole) of the acid and 851.2g (0.254 mole) polyethylene glycol
having an average molecular weight of 3350 *(Carbowax 3350
were charged to a two-liter four neck round bottom fiask
equipped with a subsurface nitrogen inlet tube, therometer,
an Dean Stark trap for water of reaction removal. The
reactants were heated at 225~C for 19 hours resulting in a
drop in acid value of from 18.1 in the starting blend to 9.5
for the resulting partial ester product.
EXAMPLE II
Preparation of Trimer PEG monoester: Empol 1040
Trimer Acid (trademark), a trimerized linoleic acid produced
by Emery Chemicals AV 175-192; SV 192-200; 62% tribasic
acid, was reacted with polyethylene glycol having an average
molecular weight of 3350. For the reaction, 214.5g (0.7072
equivalent) of the trimer acid and 789.7g (0.4714 equivalent)
PEG 3350 were charged into a two-liter four-neck round bottom
3~ flask equipped with subsurface nitrogen inlet tube,
thermometer, and water trap. The reaction was run at 220~C
*Trade Mark
..,
.. ... . . . . . . .. . . . .
-11- 133~83~
for 7 hours resulting in a decrease in acid value from 39.5
to 25Ø The resulting partial ester product was a waxy
solid melting at about 55~C.
EXAMPLE III
Preparation of Dimer PEG monoester: Dimer acid (AV
189-197; SV 191-199; 77% biastic acid) was reacted with PEG
3350 at a 1:1 molar ratio. For the reaction, 176.7g (0.6142
equivalent) dimer acid and 1028.89 (0.6142 equivalent) of PEG
3350 were charged into a two-liter four-neck round bottom
flask equipped with nitrogen inlet tube, thermometer, and
water trap. The reaction was run at 200~C for 11 hours
resulting in a drop in the acid value of from 28.5 for the
starting blend to 15.8 for the resulting disperant product.
The product was found to have a hyroxyl value of 16.2;
viscosity at 210~F of 265.3, refractive index of 1.4632 at
54~C, and SV of 29.9.
EXAMPLE IV
Preparation of Polybasic Acid PEG sesquiester:
21.0g (0.0933 equivalents) of a commercial polybasic acid
having an average carboxyl functionality of approximately
three obtained from the addition of dimer acid and maleic
anydride was reacted with 279.8g (0.0933 equivalents) of
polyethylene glycol having an average molecular weight of
6,000. The reactants were charged to a 500ml four-neck round
bottom flask equipped with nitrogen inlet tube, thermometer
and water trap. The reaction was run at 255~C for 4.5 hours.
3~ The acid value decreased from 17.4 to 8.7.
-12- ~39~3~
1 EXAMpLE V
Preparation of slurries containing rheological
additives of Ex. I-IV: 1.75g of disperant of the above
examples was dissolved in about 10 grams of water in a Hobart
mixins bowl. To the bowl were charge 240.35 grams (175 grams
DB) of OxlO0 mesh reclaim Western Pennsylvania coal fines
with a moisture content of 26.1%. This coal mixture had the
following analysis: Ash 6.92% DB [DB = dry basis]; sulfur
1.149% DB; BTU 14956, moisture and ash free; wet screen
analysis, 68.5~200 mesh, 65.8% ~230mesh, 54% ~325 mesh.
The dispersant solution and coal were allowed to mix at low
speed (No. 1) for approximately 1 hour. Small water
additions were made to account for evaporative losses.
The slurries were transferred to 8 ounce bottles
for viscosity determinations using a Brookfield Viscometer
LVF with a Helipath stand adaptor and F spindle. Viscosity
readings were made over a two inch high volume of the slurry
and averaged. The Brookfield viscometer was used to measure
a series of conventional viscosities using a number 4 spindle
without the Helipath stand. Viscosities are reported in
Table I and were obtained on slurries aged approximately 20
hours.
3o
TABLE I
DispersantTap Water Slurry Brookfield viscositY (cP)
ExamPle (q) % Solids HeliPath 6 rPm Conventional 60 rPm
I 14.80 68.8 21,320 700
II 12.58 69.4 53,560 1,100
III 6.49 71.1 43,160 750
IV 5.80 71.3 55,640 1,500
-14-
~39~39
EXA~IPLE VI
Preparation of Polybasic Acid PEG Diester: 39.lg (0.1732
equivalent) of the polybasic acid of Example IV and 932.8g
(0.2310 equivalent) polyethylene glycol (avg. mw = 8000),
were charged to a two-liter four-neck round bottom flask
equipped with nitrogen inlet tube, thermometer, and water
trap. The reaction was carried out between 210~C and 230~C
for 39.5 hours resulting in an acid value drop of from 9.7
for the starting blend to 3.5 for the resultant ester
product.
The blend of coal (Eastern Kentucky freshly
pulverized) was made from two grades of fines such that the
final blend contained 80 percent smaller than 200 mesh U.S.
standard sieve. In the blend, 47.32% of a coal 58.43%e 200
mesh was blended with 52.68% of a coal 99.4%~ 200 mesh.
1.75g of the disperant of Example VI was dissolved
in 73.25g tap water in a 500 ml stainless steel cup. The
disperant was mixed at moderate agitation and 175.0g of the
coal blend slowly added. The slurry (70.7% solids) was
allowed to mix for an additional 15 minutes after all of the
coal had been added resulting in a Brookfield model LVF
Helipath Stand viscosity of 71,700 cP at 6 rpm using F
spindle. No separation of the slurry was observed over 10
weeks storage.
EXAMPLE VII
Evaluation of Additional Rheological Additives in
Pulverized Coal Slurries: Utilizing the coal blend of
Example VI, slurries were prepared using 1% (based on coal
3~ weight) of the following rheological additives:
A. Tetra propenyl succinic anhyride monoester with
PEG 3350 (AV 15.6)
-15- ~33983~
B. Dimer acid-maleic anhyride adduct diester with
PEG 3350 (AV 7.8)
C. Dimer acid-maleic anhyride adduct diester with
PEG 1000 (AV 19.8)
D. Dimer acid (60%) monoester with PEG 4000 (AV
11.6)
E. Dimer acid-maleic anhyride adduct sesquiester
with PEG 6000 (AV 8.7)
F. C21 dibasic acid monoester with PEG 6000 (AV
8.5)
G. Dimer acid (77%) monoester with PEG 6000 (AV
9.6)
H. Dimer acid (77%) monoester with PEG 3350 (AV
15.9)
For preparation of the slurries, 1.75g dispersant
was dissolved in 73.25g tap water in a Hobart mixing bowl.
175.0g anhyride pulverized coal blend was added and mixing
completed at speed Number 1 (lowest) in about one hour.
Small additions of water were made to maintain solids level
or improve flow when slurries were too viscous.
Viscosities were measured using a Brookfield
Helipath Stand with the LVF model viscometer using an F
spindle. Conventional viscosity determinations were also
made using the LVF viscometer but with Number 4 spindle.
Slurries were aged about 20 hours prior to viscosity
determination. Results are provided in Table II. Percent
solids were determined by drying a small amount of the
prepared slurry.
3o
-16- 133~8~9
l EXAMPLE VIII
Dimer acid reaction products with polyethylene
glycols in the molecular weight range of 3350 to 20,000 were
prepared using a weight ratio charge of 30~ dimerized
linoleic acid and 70~ polyglycol in accordance with procedure
of Example 8 of European Patent Application 0131558. These
dispersants (6-10), which are polyethylene glycol
di(dimerates) containing su~stantial amounts of unreacted
dimer acid, were compared with products prepared in
accordance with the present invention (1-5) wherein dimer is
reacted with the PEG at a 1:1 mole ratio.
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Details were as follows:
Dispersant Polyether AV of % Dimer AV of
No. Glycol M.W. Reactant Charge* In Charge Product
1 3350 28.5 14.7 15.8
2 4500 22.1 '11.4 11.9
3 6000 17.0 8.7 9.1
4 8000 13.1 6.7 7.1
20000 5.4 2.8 3.1
6 3350 ~8.5 30.0 35.5
7 4500 58.5 30.0 41.5
8 6000 58.5 30.0 45.2
9 8000 58.5 30.0 48.7
'0 20000 5~.5 30.0 48.6
*Calculated value when not miscible
The dispersants were evaluated by preparing
slurries in accordance with the procedure of Example V using
beneficiated silt pond coal
88.1~ passing 200 mesh U.S. Standard Sieve
82.7% passing 230 mesh U.S. Standard Sieve
73.8% passing 325 mesh U.S. Standard Sieve
Results are reported in Table III.
In a second evaluation, pulverized bituminous coal
from Stockton/Lewiston Seam, West Virginia
75% passing 200 mesh U.S. Standard Sieve
70.5% passing 230 mesh U.S. Standard Sieve
61% passing 325 mesh U.S. Standard Sieve
was employed for the slurry preparation in accordance with
the technique of Example VII and results are reported in
Table IV.
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I~ is readily apparent from the data that the rheological
additives (dispersants) obtained in accordance with the
pre~ent invention gave superior viscosity characteristics,
when compared at comparable solids levels, than the composi-
tions of European Patent Application 0131558 published
January 16, 1985.
EXAMPLE IX
various salts of the partial ester of Example III
(Dimer acid and PEG 3350 monoester) where prepared in situ
during slurry preparation, i e., the rheological additive was
dissolved in water and the basic material added thereto at
room temperature, dropwise, until a pH of 8.5 was reached.
Slurries were then prepared by the addition of Kanawha countY
West virginia Bituminous Coal (74.2% < 200 mesh, 68.1% ~ 230
mesh, 60.1% C 325 mesh; ash 7.14%; sulfur 0.65% DB) in accor-
dance with the usual procedure. For the preparation of these
slurries, 0.025% xanthan gum, 0.0125% formaldehyde and 0.1%
defoamer were also included. Results obtained for the
various salts were as follows:
20 % Salt
Based Slurry Viscosity (cp)
on % Helipath Conventional
coal Based used Solids 6 rpm 60 rpm
1.0 sodium Hydroxide 72.3 4,000 1,500
1.0 Triethylenetriamine 72.6 7,800 550
1.0 Diethanolamine 69.1 4,700 200
1.0 Morpholine 71.6 11,300 1,250
1.0 Ammonium Hydroxide72.4 11,400 1,200
1.0 Diethylenetriamine72.5 9,400 800
~ 21 -
