U.S. patent number 3,904,685 [Application Number 05/381,190] was granted by the patent office on 1975-09-09 for polyacrylic acid having high chelation value and its production.
This patent grant is currently assigned to Celanese Corporation. Invention is credited to Jorge Alberto Blay, Iraj Khatib Shahidi.
United States Patent |
3,904,685 |
Shahidi , et al. |
September 9, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Polyacrylic acid having high chelation value and its production
Abstract
Polyacrylic acid having a high chelation value is produced by
polymerizing acrylic acid at elevated temperature in the presence
of an alkali metal or ammonium persulfate initiator and, in a
concentration of about 0.5 to 4% by weight of the acrylic acid, a
chain transfer agent selected from the group consisting of
alkanethiols, hydroxy alkanethiols, and carboxy alkanethiols.
Preferably the chain transfer agent is present in about 1% by
weight concentration and is octanethiol, butanethiol, thioglycolic
acid, or 2-thioethanol.
Inventors: |
Shahidi; Iraj Khatib (Florham
Park, NJ), Blay; Jorge Alberto (Corpus Christi, TX) |
Assignee: |
Celanese Corporation (New York,
NY)
|
Family
ID: |
23504058 |
Appl.
No.: |
05/381,190 |
Filed: |
July 20, 1973 |
Current U.S.
Class: |
562/594; 526/211;
526/215; 526/224; 510/245; 510/533; 510/476; 510/361; 510/230 |
Current CPC
Class: |
C08F
120/06 (20130101); C11D 3/3761 (20130101) |
Current International
Class: |
C08F
120/06 (20060101); C08F 120/00 (20060101); C11D
3/37 (20060101); C07C 055/24 () |
Field of
Search: |
;260/526N,537N |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
695,097 |
|
Aug 1940 |
|
DD |
|
167,857 |
|
Oct 1953 |
|
AU |
|
Other References
Jacobson Chem. Abstracts, V. 57(1962), V. 1037. .
Sakaguchi et al. Chem. Abstracts, V. 64(1966), p. 12822. .
Salutsky Chem. Abstracts, V. 70(1969), p. 248. .
Hwa et al. Chem. Abstracts, V. 71(1969), p. 216..
|
Primary Examiner: Patten; James A.
Attorney, Agent or Firm: Horn; Leonard Pritchett; Ralph
M.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. The process for producing a polyacrylic acid of high chelation
value at 80% chelation which comprises polymerizing acrylic acid in
aqueous solution at elevated temperature in the presence of an
alkali metal or ammonium persulfate as initiator and about 0.5 to
4% by weight of acrylic acid of a chain transfer agent selected
from the group consisting of an alkanethiol, a hydroxy alkanethiol
and a carboxy alkanethiol.
2. The process of claim 1, wherein the chain transfer agent is an
alkylmercaptan and is present in a concentration of about 1% by
weight of the acrylic acid, and wherein the polymerization is
conducted at about 95.degree. C for about 1 to 2 hours.
3. The process of claim 2, wherein the chain transfer agent is
octanethiol.
4. The process of claim 2, wherein the chain transfer agent is
butanethiol.
5. The process of claim 1 wherein the chain transfer agent is
thioglycolic acid.
6. The process of claim 1 wherein the chain transfer agent is
2-thioethanol.
7. Polyacrylic acid produced by the process of claim 2 and having a
chelation value at 80% chelation in excess of about 500 mg
CaCO.sub.3 per gram in an aqueous solution containing calcium ions
in a concentration equivalent to 200 ppm of CaCO.sub.3.
Description
BACKGROUND OF THE INVENTION
This invention relates to the production of polyacrylic acid having
a high chelation value, e.g., a chelation value which is in excess
of 500 milligrams of calcium carbonate per gram of chelant obtained
in water with a 200 ppm hardness, pH 9.5 and at the point at which
80% of the hardness has been sequestered. The significance of this
80% chelation level as an index for comparing various chelating
agents will be explained later hereinbelow.
Most common detergents, e.g. common household detergents, comprise,
in addition to other components, phosphates such as sodium
tripolyphosphate. These are inexpensive and effective, but their
use is now considered to present a water pollution problem in that
the phosphate component has the undesired effect of promoting
excessive growth of algae in lakes and streams
(eutrophication).
Accordingly, there has been much research aimed at developing
detergents which contain little or no phosphate but which will
still be safe and effective. In particular, this research has been
aimed at developing detergent components which can sequester
calcium, magnesium, and like ions found in hard water and which
have an economically feasible price/performance ratio. Aside from
effectiveness and economic feasibility, it is also important that
these detergent components be free from health hazard and that they
have no adverse effects on mechanical equipment used in laundering.
For example, highly alkaline detergent components such as washing
soda have effective detergent action but are hazardous household
substances because of their high alkalinity (pH 11 or higher).
There is also a question as to whether they may cause mechanical
problems in, for example, washing machines. Likewise
nitrilotriacetic acid and ethylenediaminetetraacetic acid are very
effective in sequestering a large amount of calcium but are
relatively expensive and, in addition, have recently been
questioned from the health standpoint inasmuch as a question has
arisen as to whether they are potentially carcinogenic.
Finally, polyacrylic acid, as such or in the salt form, has also
been proposed as a chelant or sequestering agent which does not
cause eutrophication, but this material as known heretofore has
been of only mediocre effectiveness.
It has now been discovered, however, that polyacrylic acid, when
made by a certain procedure which will be described hereinbelow,
can be made to have an unexpectedly high chelating value. It is,
accordingly, an object of the present invention to provide a method
for producing a polyacrylic acid chelating agent which is
unexpectedly effective as compared with similar materials known to
the prior art and which will be free from the drawbacks which are
associated with those alternative detergent components known to the
art.
SUMMARY OF THE INVENTION
In accordance with the present invention it has been found that
polyacrylic acid having an unexpectedly high chelating value (which
will be defined hereinbelow) can be produced by polymerizing
acrylic acid at elevated temperature in the presence of an alkali
metal or ammonium persulfate initiator and also in the presence of
about 0.5 to 4% (calculated on the basis of the weight of the
acrylic acid) of a chain transfer agent selected from the group
consisting of alkanethiols, hydroxy alkanethiols, and carboxy
alkanethiols. Preferably the chain transfer agent is present in a
concentration of about 1% by weight based on the acrylic acid and
is a member of the group consisting of octanethiol, butanethiol,
thioglycolic acid, and 2-thioethanol. Other thiols which can be
employed include methanethiol, ethanethiol, propanethiol,
pentanethiol, hexanethiol, heptanethiol, nonanethiol, decanethiol,
dodecanethiol, and their branched isomers, e.g. sec.-butanethiol,
isopropanethiol, tert.-butanethiol, and the like, as well as their
hydroxy and carboxy substitution products, e.g.,
3-mercaptopropanol, 3-mercaptopropionic acid, 6-mercaptohexanoic
acid and the like.
The initiators may be present in amounts ranging from as little as
about 0.5 up to 10% or more by weight of acrylic acid although
preferably they are present in about 0.5 to 4%. A concentration of
about 1% is especially useful. Preferred initiators include sodium,
potassium, or ammonium persulfates or mixtures thereof.
The polymerization can be conducted in bulk but it is preferably
conducted in aqueous solution at a concentration of about 5 to 40%
and preferably about 10 to 30% acrylic acid by weight. The
temperature may be room temperature or lower but, since
polymerization rate increases with temperature, the temperature is
desirably elevated but below the boiling point so that special
equipment will not be required, e.g. about 95.degree.C. The time
will typically run about 1 to 2 hours until there is substantially
no residual free acrylic acid.
The molecular weight will directly determine the viscosity of the
resulting solution, and the viscosity may range from about 25
centipoise or lower up to 200 or more although preferably it is
about 50 to 150 centipoise for a 20-25% polyacrylic acid solution
by weight.
The solutions may if desired be concentrated to any desired degree,
including completely to dryness, optionally after neutralization to
form sodium and/or potassium polyacrylate. Alternatively, the
solution may be blended with one or more other ingredients of a
detergent composition in dry or liquid state and the mixture spray
or drum dried.
In assessing the effectiveness of chelating agents it is convenient
to employ a term referred to as the "chelating value", the
significance and determination of which are explained by J. A. Blay
and J. H. Ryland in "Analytical Letters", Vol. 4, No. 10, pp
653-663 (1971). Numerically, the "chelation value" (CV) is
expressed as the milligrams of calcium carbonate chelated or
sequestered per gram of chelating agent. The chelation reaction is,
in effect, a reversible chemical reaction so that the CV depends,
numerically, upon the concentration of hardness, e.g. calcium ions,
in the solution to which the chelating agent is added, the pH, and
also the amount of chelating agent which has been added to that
solution. This is particularly noticeable for chelants with a
formation constant (log K) smaller than 5 (K < 10.sup.5). For
these reasons it is desirable, in making practical comparisons of
one chelating agent with another, to test them at a constant level
of hardness at constant pH and to add each of the several chelants
being tested in an amount that the proportion of the hardness which
is chelated is the same in each of the several samples being
tested.
The polyacrylic acid produced by the present process has a
chelation value (CV) which is normally equal to, or in excess of,
about 500 milligrams of calcium carbonate per gram of the
polyacrylic acid at an 80% chelation level in an aqueous solution
containing a hardness equivalent to 200 ppm of calcium carbonate.
This is essentially as good as, if not better than, chelation
values characteristic of other chelants known to the prior art
which, however, have drawbacks of cost, water-pollution tendency,
health hazard, or adverse mechanical effects in washing
equipment.
The invention will be further illustrated in the following examples
wherein all parts are by weight unless otherwise expressed. It will
be understood that these examples are given by way of illustration,
rather than limitation, of the invention. The polyacrylic acid (or
its salts including especially alkali metal salts) to the
production of which this invention is directed will be seen to have
very broad applications in combination with surfactants, buffering
agents, scouring agents, and other ancillary substances well known
in the art, in all end-uses in which a sequestrant or chelant is
customarily employed and including specifically such applications
as laundry detergents, automatic dishwashing detergents, scouring
powders, boiler scale removal, metal degreasing and cleaning,
leather and textile treating solutions, ore leaching and
benefication, and ion-exchange operations to name a few.
EXAMPLE I
250 g of 92% acrylic acid, 3.0 g of potassium persulfate, and 2.3 g
octanethiol were reacted in a 1000 g total aqueous solution for 2
hours at 96.degree.-98.degree. C. The resulting aqueous polyacrylic
acid solution had a viscosity of 125 cps and contained 20.4 weight
percent solids. Only 0.4 g/l of this polyacrylic acid was required
to sequester 94% of Ca.sup.+.sup.2 ions present in a pH = 9.5
buffer containing 200 ppm of Ca.sup.+.sup.2 ions. Expressed
differently, the polyacrylic acid had the capacity to chelate 560
mg CaCO.sub.3 per gram of polyacrylic acid with 80% of the total
calcium present in the medium being sequestered. The chelation
power of some known sequestering agents under comparable conditions
were as follows: citric acid, 350 mg/g; tripolyphosphoric acid, 370
mg/g; ethylenediaminetetraacetic acid, 330 mg/g.
When evaluated under similar conditions, a typical commercial
polyacrylic acid (Versicol E5, from Allied Colloids Co.) required
1.1 g of polyacrylic acid to sequester 95% of the Ca.sup.+.sup.2
ions present in a pH = 9.5 buffer containing 200 ppm
Ca.sup.+.sup.2, corresponding to a chelation capacity of 390 mg
CaCO.sub.3 /g chelant when 80% of Ca.sup.+.sup.2 ions have been
chelated.
EXAMPLE II
250 g of 92% acrylic acid, 3.0 g of potassium persulfate, and 2.3 g
butanethiol were reacted in a 1000 g total aqueous solution for 2
hours at 96.degree.-98.degree. C. The resulting aqueous polyacrylic
acid solution had a viscosity of 70 cps and contained 23.9 weight
percent solids. Only 0.51 g/l of this polyacrylic acid was required
to sequester 95% of the Ca.sup.+.sup.2 ions present in a pH = 9.5
buffer containing 200 ppm of Ca.sup.+.sup.2 ions. Expressed
differently, the polyacrylic acid had the capacity to chelate 520
mg CaCO.sub.3 per gram of polyacrylic acid with 80% of the total
calcium present in the medium being sequestered.
EXAMPLE III
To evaluate the performance of sodium polyacrylate in detergent
compositions, formulations A-F listed below were prepared.
Formulation F consists of distilled water and serves as a control
only. Formulation E in which no builder is utilized contains the
surfactants and the auxiliary components used in a typical
heavy-duty laundry formulation. Formulations A-D have the builder
added to the basic formulation in E and provide a direct comparison
between sodium polyacrylate and other available builders.
Evaluation of the performance of the formulations was by the well
established procedure of Spangler, Journal of the American Oil
Chemists Society 42, 723-727 (1966). Cotton swatches were uniformly
soiled in a blend of synthetic sebum and particulate soil and
separated into groups with similar aggregate degree of soiling.
Measurements of soiling were performed with standard commercial
reflectometer (Colormaster Model V, Manufacturers Engineering and
Equipment Corporation).
The soiled swatches were washed in a standard laboratory
"Terg-O-Tometer" (trade name of U.S. Testing Company, Hoboken,
N.J.) operated at 100 rpm. Five swatches were used for each
formulation. One and one-half grams of each of the formulations A-F
were used in a liter of water containing 160 ppm hardness composed
of 85% Ca.sup.+.sup.2 and 15% Mg.sup.+.sup.2. After washing for ten
minutes at 120.degree.F, the swatches were hand squeezed and put
through a 5 minute rinse at 100.degree. F. The swatches were next
dried in a print dryer, and their reflectance determined again. The
operation was repeated three times (3 cycles). The performance of
the formulations in terms of changes in reflectance (.DELTA. Rd)
along with the compositions of formulations A-F are shown in the
table below: COMPOSITION WEIGHT % A B C D E F
__________________________________________________________________________
Linear alkylbenzene sulfonate 10 10 -- 10 10 -- Nonionic surfactant
(C.sub.12 -C.sub.18 -- alcohol ethoxylate "60%") 2 2 11 2 2 --
Tallow fatty acids soap 2 2 -- 2 2 -- Sodium silicate (SiO.sub.2
:Na.sub.2 O 2.4:1) 7 7 9 7 7 -- Sodium sulfate 40 40 -- 40 40 --
Distilled water 4 4 10 4 39 100 Sodium polyacrylate 35 -- -- -- --
-- Sodium tripolyphosphate -- 35 -- -- -- -- Sodium carbonate -- --
70 -- -- -- Sodium oxydiacetate -- -- -- 35 -- -- PERFORMANCE (3
cycles) Reflectance, Rd, of soiled swatches 61.4 60.6 55.0 58.9
58.6 61.2 Reflectance, Rd, of washed swatched 76.9 76.2 69.6 68.1
64.8 65.8 .DELTA. RD 15.5 15.6 14.6 9.2* 6.2 4.6
__________________________________________________________________________
*Performed in water of 200 ppm hardness, 60% Ca.sup.+.sup.2, 40%
Mg.sup.+.sup.2
As the detergency results above clearly indicate, sodium
polyacrylate is an excellent performer in heavy-duty laundry
composition. Its closest competition, sodium tripolyphosphate, is
suspected of contributing to eutrophication of lakes and rivers,
and its use in laundry detergents is thought by many to be
undesirable. Formulations with sodium carbonate (such as
Formulation C) are also disfavored since their high alkalinity
makes them hazardous for use in households and can also cause
damage to washing instruments. Thus, sodium polyacrylate provides a
high performance alternative in laundry detergents.
EXAMPLE IV
The formulation given below is suitable for cleaning metal parts
prior to use. It cleanses metal surfaces free of oil and grease and
removes surface scale and rust.
______________________________________ Composition Wt%
______________________________________ Sodium silicate (Na.sub.2
SiO.sub.3) 24.0 Sodium silicate (SiO.sub.2 :Na.sub.2 O 3.1:1) 48.0
Nonionic surfactant (C.sub.12 -C.sub.18 alcohol 1.5 ethoxylate,
"60%") Sodium polyacrylate 25.0 Sodium sulfite 1.5
______________________________________
EXAMPLE V
Formulation below is a low foaming dishwashing powder with
excellent grease removal and gentle scouring action.
______________________________________ Composition Wt%
______________________________________ Soda ash 50 Sodium meta
silicate 10 Trisodium phosphate 15 Sodium polyacrylate 20
Alkylbenzene sulfonate 5 ______________________________________
* * * * *