Use of sulfated lime derived from dry desulfurization of flue gas as a polymer filler

The invention relates to the use of particles of sulfated lime (containing up to 80% CaSO.sub.4) as a polymer filler which can be derived from dry desulfurization of flue gas. Such sulfated lime can advantageously be incorporated into an elastomer such as ethylene propylene diene monomer rubber (EPDM) or styrene-butadiene rubber (SBR).

BACKGROUND OF INVENTION 
The present invention relates to the use of sulfated lime (mainly calcium 
sulfate) derived from dry desulfurization of flue gas as a polymer filler. 
It is known that flue gas produced by fuels containing sulfur compounds 
must be purified to remove the sulfur oxides it contains before it can be 
released into the atmosphere. 
Different methods have been proposed in the prior art to achieve this goal. 
The desulfurization processes currently in use include those comprising 
contacting the flue gas with particles of an absorbing material containing 
at least one basic compound of an alkaline earth metal (see, for example, 
French Patent [FR] A-2 636 720). The most frequently used absorbents are, 
in particular, limestones (CaCO.sub.3), slaked lime (Ca(OH).sub.2) and the 
dolomites (CaMg(CO.sub.3).sub.2). The absorbents usually have a particle 
size of 1 to 100 microns. 
The flue gas desulfurization is carried out at an elevated temperature 
above 700.degree. C. and, at this temperature, the above-said compounds 
are at least partly converted into quicklime with elimination of water and 
carbon dioxide. 
Upon contact with flue gas, the quicklime particles react with the sulfur 
oxides present therein with formation of calcium sulfate and, thereafter, 
they contain a large amount of this compound. 
In the present description and the attached claims, said particles 
containing a large amount of calcium sulfate, typically derived from the 
desulfurization of flue gas, shall be referred to by the term "sulfated 
lime". 
Sulfated lime usually contains in weight percent 40 to 80% of calcium 
sulfate, CaSO.sub.4, and 10 to 50% of quicklime, CaO, the remainder 
consisting essentially of 0 to 10% of calcium carbonate, CaCO.sub.3, and 0 
to 15% of slaked lime, Ca(OH).sub.2. These, of course, are average 
compositions, it being possible to use within the scope of the invention 
sulfated lime of a different composition. 
Sulfated limes usually have a bulk density of 0.35 to 0.80 g/cm.sup.3. The 
particle size is usually between 1.times.10.sup.-6 and 100.times.10.sup.-6 
m, with an average of 2.times.10.sup.-6 to 40.times.10.sup.-6 m. 
The large-scale use of such absorbents for the desulfurization of flue gas 
can produce annually about ten thousand metric tons of sulfated lime per 
desulfurization unit. Said sulfated lime is thus an available material. 
Applicant and others have for a long time been studying the possible use of 
these desulfurization by-products and unexpectedly has now found that the 
sulfated lime derived from the desulfurization of flue gas can 
advantageously replace the fillers incorporated into polymers. 
It is known to incorporate different powdered fillers into polymers such as 
polyvinyl chloride and, more particularly, into elastomers such as natural 
or synthetic rubbers. Usually one distinguishes between inert fillers, 
namely those that are used simply to reduce the amount of polymer in a 
formulation by incorporating into said polymer a low-cost material, for 
example chalk, and reinforcing or semi-reinforcing fillers capable of 
modifying the properties of the polymer. The latter kinds of fillers 
include carbon black, precipitated silica and kaolin which when 
incorporated, for example, into elastomers enables said elastomers to meet 
certain industrial specifications. 
SUMMARY OF THE INVENTION 
Work carried out by applicant has led to the conclusion that sulfated lime 
not only can be used for such applications, but that, when replacing inert 
fillers in certain polymers, said sulfated lime has an appreciable effect 
on certain properties of said polymers. 
A first advantage of the invention is therefore to upgrade the usefulness 
of sulfated lime from a waste by-product derived from the desulfurization 
of flue gas by using it as a filler in polymers. 
Another advantage of the invention is to replace the inert polymer fillers 
of the prior art with sulfated lime, the cost of which is usually lower 
and the use of which exerts beneficial effects on the properties of 
certain polymers. 
Hence, the invention has for a preferred embodiment the utilization of 
particles of sulfated lime derived from the dry desulfurization of flue 
gas as a polymer filler. It will be understood that sulfated lime can be 
used in combination with other fillers, such as carbon black, silica or 
kaolin, without thereby exceeding the scope of the invention. 
In this definition of the invention, by "polymers" we mean all polymers in 
which it is known to use inert fillers. 
Polymers containing sulfated lime as an inert filler constitute another 
embodiment of the present invention. 
In fact, applicant's studies have shown that sulfated lime particles 
disperse uniformly and in a large amount in polymers in which inert 
fillers are usually employed. Moreover, sulfated lime modifies the 
physicochemical properties of said polymers to a lesser degree than do 
conventional fillers. 
Sulfated lime can be added to the polymer in an amount of up to 1000 parts 
by weight of sulfated lime per 100 parts of polymer, depending on the 
nature of the polymer. 
Applicant has discovered that when sulfated lime is incorporated into an 
elastomer it increases the vulcanization rate of said elastomer in the 
presence of the usual vulcanization additives and under the usual 
vulcanization conditions. Moreover, sulfated lime improves the elastic 
properties of the elastomer without altering the other physical 
properties. 
Hence, still another embodiment of the present invention is the utilization 
of sulfated lime particles as a filler in elastomers. 
The beneficial effects of said sulfated lime become particularly evident 
when said sulfated lime is incorporated into ethylene propylene diene 
monomer rubber (EPDM) or styrene-butadiene rubber (SBR). 
In such an application, sulfated lime will preferably be used in an amount 
of 100 to 1000 parts by weight per 100 parts of elastomer. 
Although it is this incorporation of sulfated lime into elastomers that 
will be described in greater detail hereinbelow because it is 
advantageous, the invention, of course, applies to all polymers wherein 
inert or non-inert fillers are commonly used. 
It will be recalled that a rubber composition usually contains a base 
rubber (for example EPDM or SBR), one or more fillers, a plasticizer, a 
vulcanization agent (for example sulfur), one or more vulcanization 
activators (zinc oxide and/or stearic acid) and one or more vulcanization 
accelerators. The filler preferably has a particle size below 
100.times.10.sup.-6 m, a low water content and preferably a basic pH. 
The possibility of making such blends depends on the quantity of filler and 
plasticizer added. In fact, if the relative quantity of plasticizer is too 
high, the product obtained will have the consistency of a putty, and if 
the quantity of filler is too high, a powdered product will result. 
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
The following was used in all tests described hereinbelow. 
Rubbers: EPDM, commercially supplied by "SOCABU," derived from about 9% of 
5-ethylidene-2-norbornene, about 52% of ethylene and about 39% of 
propylene, with a Mooney viscosity (ML 1+8) of 82.+-.5 at 125.degree. C. 
and which has good cohesion in the uncured state, good low-temperature 
resistance and good extrudability. 
Plasticizers: a paraffin oil, supplied commercially by "TOTAL" under the 
name "PLAXENE 6110." 
Vulcanization agent: sulfur. 
Vulcanization activator: zinc oxide and stearic acid, used in combination. 
Vulcanization accelerator: mercapto benzo thiazole and dithio carbamate of 
zinc, supplied commercially by "VULNAX" under the name "VULCAFOR 2." 
Optional lubricant: zinc stearate. The sulfated lime, CS1 , used in these 
examples had the following characteristics: 
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Composition (wt %) 
H.sub.2 O 0.3 
CaCO.sub.3 3.3 
CaSO.sub.4 48.6 
Ca(OH).sub.2 6.6 
CaO 41.2 
Bulk density 0.41 g/cm.sup.3 
Particle size 2-30 .times. 10.sup.-6 
m 
Average diameter 9 .times. 10.sup.-6 
m 
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In the tests, the hardness, expressed in INTERNATIONAL SHORE A degrees, was 
determined in accordance with AFNOR (Association Francaise de 
Normalisation [French Association for Standardization]) standard method 
46003. 
The rheometric curves were recorded in accordance with AFNOR standard 
method 43015 using a "MONSANTO" rheometer. 
Tensile strength and elongation were determined in accordance with AFNOR 
standard method 46002. 
By means of appropriate formulas, the results obtained for EPDM can be 
transposed to SBR.

EXAMPLE 1 
The purpose of this example is to compare the properties of black 
compositions containing carbon black as the reinforcing filler (FEF black 
[fast-extruding furnace black]-ASTM standard N 550). Said compositions, 
respectively, contained the following: 
Composition A: sulfated lime; 
Composition B: a high-quality commercial chalk, sold by "OMYA" under the 
name "OMYA BSH Chalk (Special Hydrophobic White)"; 
Composition C: a chalk, used as a reference standard, sold by "OMYA" under 
the name "OMYA Violet Chalk." 
The amounts of the constituents and the properties of said compositions are 
collected in the following Table I. 
TABLE I 
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A B C 
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COMPOSITION (wt %) 
EPDM 100 100 100 
FEF Black 70 70 70 
Sulfated lime CS1 
80 -- -- 
Omya BSH Chalk -- 80 -- 
(Hydrophobic) 
Omya Violet Chalk 
-- -- 80 
Plaxene 6110 50 50 50 
ZnO 5 5 5 
Stearic acid 1 1 1 
Sulfur 2 2 2 
Vulcafor 2 5 5 5 
PROPERTIES 
Vulcanization time 
3 mn 30 s 
4 mn 04 s 3 mn 04 s 
rheometer T90, 
(180.degree. C.) 
Vulcanization curve 
Minimum torque, Nm 
10 9.5 12 
Maximum torque, Nm 
83 76 68 
Tensile strength, MPa 
8.8 9.7 7.1 
Elongation at break, % 
400 320 270 
100% modulus, MPa 
2.4 2.6 2.6 
300% modulus, MPa 
6.6 8.4 -- 
Hardness, internat'l 
64 63 66 
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The results presented in Table I indicate that at virtually equal hardness 
(64.degree.-66.degree. Shore), the sulfated lime replacing commercial 
chalk in Composition A increased the elongation at break of the elastomer 
composition while the tensile strength remained close to that of the 
composition containing the high-quality chalk (Composition B). 
EXAMPLE 2 
The purpose of this example is to compare the properties of a light-colored 
composition containing a light-colored reinforcing filler consisting of 
high-quality kaolin, sold under the name "WHITETEX No. 2" (Composition D) 
and optionally containing an additional filler of sulfated lime; according 
to the present invention (Composition E), "OMYA BSH Chalk" (Composition F) 
and "OMYA Violet Chalk" (Composition G). 
The amounts of the constituents and the properties of said compositions are 
collected in the following Table II. 
TABLE II 
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D E F G 
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COMPOSITION (wt %) 
EPDM 100 100 100 100 
Whitetex 175 87.5 87.5 87.5 
Sulfated lime -- 87.5 -- -- 
Omya BSH Chalk -- -- 87.5 -- 
Omya Violet Chalk 
-- -- -- 87.5 
Plaxene 6110 60 60 60 60 
Zno 5 5 5 5 
Stearic acid 1 1 1 1 
Sulfur 2 2 2 2 
Vulcafor 2 5 5 5 5 
PROPERTIES 
Vulcanization time 
6 mn 2 mn 54 s 
4 mn 54 s 
5 mn 
40 s rheometer T90, 
(180.degree. C.) 
Vulcanization curve 
Minimum torque, Nm 
8 9 6 7 
Maximum torque, Nm 
67 55 52 63 
Tensile strength, MPa 
6.3 4.7 3.6 2.3 
Elongation at break, % 
480 640 450 380 
100% modulus, MPa 
2.2 1.2 1.2 1.2 
300% modulus, MPa 
4 2 2.4 1.9 
Hardness, internat'l 
58 52 53 55 
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Table II shows that sulfated lime-containing Composition E, with a slightly 
lower hardness than Composition D which contains only the reinforcing 
"WHITETEX" filler, contains one half the amount of said reinforcing 
filler; furthermore, Composition E has a higher elongation than all the 
other compositions and a higher tensile strength than Compositions F and G 
which contain a chalk filler. 
Note also the excellent (short) vulcanization times of Composition E 
containing sulfated lime. 
EXAMPLE 3 
The purpose of this example is to study the effect of the addition of 
sulfated lime on the vulcanization of the elastomers. 
The first test was carried out with two compositions, H and J, containing 
respectively sulfated lime CS1 (characterized hereinabove) and sulfated 
chalk CS2 (derived from the sulfation of chalk, CaCO.sub.3, being within 
the broad definition of "sulfated lime," and having the following 
characteristics): 
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Bulk density 0.71 g/cm.sup.3 
Composition (wt %): 
H.sub.2 O 0.5 
Ca(OH).sub.2 12.3 
CaSO.sub.4 41.5 
CaCO.sub.3 4.8 
CaO 40.9 
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Tests were carried out by varying the amount of sulfur and vulcanization 
activator for these compositions. 
The characteristics of said compositions and the test results obtained are 
presented in the following Table III. 
TABLE III 
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H J 
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COMPOSITION 
(wt %) 
EPDM 100 100 
FEF Black 70 70 
Sulfated lime CS1 
80 -- 
Sulfated chalk CS2 
-- 80 
Plaxene 6110 50 50 
ZnO 5 5 
Stearic acid 1 1 
Sulfur 2 1 2 1 
Vulcafor 2 5 2.5 5 2.5 
PROPERTIES 
Tensile strength, MPa 
8.8 7.5 6.7 8 
Elongation, % 
400 440 280 415 
100% modulus, MPa 
2.4 1.7 2.4 2.1 
300% modulus, MPa 
6.6 5 -- 6 
Hardness, internat'l 
64 61 63 61 
Vulcanization time 
3 mn 30 s 
3 mn 44 s 
3 mn 42 s 
3 mn 54 s 
rheometer T90, 180.degree. C. 
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These tests indicate that it is possible to reduce the quantity of sulfur 
and vulcanization accelerator ("VULCAFOR 2") to one half without 
appreciably extending the vulcanization time. 
Another series of tests was carried out with three compositions, K, L and 
M, which contained the same amount of sulfated lime CS1, but variable 
amounts of sulfur and vulcanization accelerator. 
The amounts of the constituents and the properties of said compositions are 
collected in the following Table IV. 
TABLE IV 
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K L M 
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COMPOSITION wt % 
EPDM 100 100 100 
Sulfated lime CS1 
600 600 600 
Plaxene 6110 200 200 200 
ZnO 5 5 5 
Stearic acid 1 1 1 
Zinc stearate 10 10 10 
Sulfur 2 1 1 
Vulcafor 2 5 2.5 5 
PROPERTIES 
Tensile strength, MPa 
1.4 1.5 1.5 
Elongation, % 700 750 800 
100% modulus, MPa 
0.5 0.6 0.7 
Hardness, internat'l 
45 42 36 
Vulcanization time 
1 mn 48 s 
4 mn 09 s 3 mn 11 s 
rheometer T90, 180.degree. C. 
Rheometric curves 
Minimum torque, Nm 
1.58 1.47 1.32 
Maximum torque, Nm 
20.76 20.54 23.13 
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The results shown in this table indicate that if either the quantity of 
sulfur (Composition M) or the quantity of sulfur and vulcanization 
accelerator (Composition L) is halved, the torques indicated by the 
rheometric curves remain the same and only the vulcanization time is 
prolonged. 
Note the very large amount of sulfated lime used in Compositions K, L and M 
(600 parts by weight per 100 parts of rubber). It was not possible to 
carry out a comparative test with commercial limestone fillers, because it 
was not possible to devise compositions with such high amounts of filler 
while using the same amount of plasticizer. 
The tests described in the preceding examples thus show clearly that inert 
fillers in polymers can be replaced with sulfated lime and that in the 
case of elastomer compositions such a replacement has a beneficial effect 
on mechanical properties and the vulcanization of said compositions. 
Sulfated lime therefore constitutes a highly advantageous replacement for 
conventional polymer fillers. 
It is understood that the invention is not restricted to the detailed 
description of the invention, which may be modified without departure of 
the accompanying claims.