Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Reexamination Certificate
2000-10-05
2003-04-15
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
C423S518000, C423S551000, C423S556000, C423S592100, C423S593100, C423S625000, C423S626000, C423S641000, C423S642000
Reexamination Certificate
active
06548037
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to new aluminium polychlorosulphates having high basicity and stability, low sulphate content, and high coagulating and flocculating power, and to an improved production process thereof, easy to perform, carried out at room temperature, and free from any contamination and residue.
STATE OF THE ART
Aluminium polychlorosulphates are used in drinking and waste water treatment, in paper industry and in many industrial clarification processes. The performance and the applications of these aluminium polychlorosulphates depend not only on their chemical characteristics, but in particular on the process used for their manufacture. In most different fields of application it has been observed that aluminium polychlorosulphates with a very similar empirical formula can present completely different performances, depending on the method used for their preparation. The reason of this behaviour is attributed to the presence in solution of ionic polycondensed species, whose constitution and structure depend on the manufacturing process.
To the several applications of aluminium polychlorides and polychlorosulphates belong the manufacture of antiperspirant compositions, the production of catalyst supports, the sizing treatment of paper in paper industry and the treatment of water and waste water.
In water and waste water treatment the aluminium polychlorides and polychlorosulphates have been gaining strength to the detriment of other traditionally used compounds, like iron salts and aluminium sulphate, owing to the greater coagulating and flocculating power of these basic aluminium salts. The coagulating and flocculating properties can be improved by addition of sulphate ions (SO
4
2−
), whose synergy is well known since a long time.
Unlike aluminium sulphate solutions which are very stable, aluminium polychlorosulphate solutions are stable only in certain conditions of concentration, basicity and sulphate content.
The aluminium polychlorosulphates suitable for water treatment, especially for the treatment of drinking water, must exhibit a sufficiently high basicity and a sufficiently low sulphate content to guarantee a low level of residual aluminium in the treated water. On the other hand, the level of sulphate must be sufficiently high to guarantee good coagulating/flocculating properties. Too high basicities impair the coagulating/flocculating power. Low basification temperatures promote a good coagulation/flocculation. High basicities associated with high levels of sulphate impair the stability of aluminium polychlorosulphates.
In order to obtain aluminium polychlorosulphates suitable for water treatment, especially for drinking water treatment, a balance must be found between a sufficiently high level of sulphate to favour good coagulating/flocculating properties, without increasing the soluble aluminium content in treated water, and a sufficiently high basicity to guarantee low levels of residual aluminium, without impairing the coagulating/flocculating properties. Further the product must be stable, the preparation process must be simple and must not release any type of pollutant.
Aluminium polychlorosulphates that satisfy some of the above-mentioned requirements are known:
a) The French Patent Application No. FR-A-2317227 describes the process, carried out at a temperature lower than 50° C., for the preparation of aluminium hydroxychloride having the general formula:
Al(OH)
a
Cl
b
Y
c/z1
M
d/z2
where:
Y represents an anion with valency Z1, typically SO
4
2−
M represents a cation with valency Z2, such as ammonium, an alkali metal or an alkaline-earth metal and
1.2<a<1.7,
0<c<0.6,
0.2<d<1.7, and
a+b+c=3+d.
Nevertheless the basicities of above-mentioned aluminium polychlorides are lower than 57% and not high enough for some applications, as in water treatment.
b) The Japanese Patent No. JP 52113384 describes a process for the preparation of aluminium polychlorosulphate having high basicity in which an alkaline reagent, such as CaCO
3
, NaHCO
3
, Na
2
CO
3
, Mg(OH)
2
or MgO, is added at a temperature lower than 60° C. to a solution of an aluminium compound previously prepared by reacting a low basicity aluminium polychlorosulphate with CaCO
3
, thus obtaining gypsum as by-product, which is then separated. The major drawbacks of this process are the following: the basicity of this intermediate aluminium compound is 50%, the residual aluminium levels are too high and a considerable production as by-product of gypsum, which is of difficult disposal, occurs.
c) The Japanese Patent No. JP 53001699 describes a process for the preparation of high basicity aluminium polychlorosulphate, where first a medium basicity aluminium polychlorosulphate is reacted with CaCO
3
in equimolecular amount with respect to sulphate, thus obtaining gypsum, which is then separated. In the next step, the so obtained product with a basicity ranging between 55% and 58%, is reacted with a compound chosen among CaCO
3
, NaHCO
3
, Na
2
CO
3
, Mg(OH)
2
and MgO.
Nevertheless, even if these processes lead to high basicity compounds (basicity lower than 70%), they present the major drawback of a large acidic gypsum coproduction, of difficult disposal.
d) The European Patent No. EP-327419 describes a process for the preparation of aluminium polychlorosulphate having the general formula
Al
n
Cl
m
(OH)
3n+2K−m−2p
(SO
4
)
p
X
k
where
X represents an alkaline-earth metal, preferably calcium,
n, m, p, q represent the molar concentrations (mole/litre) of the ions in solution, [(3n+2K−m−2p)/3n]·100 represents the basicity.
The basicity of the products described in EP-327419 ranges between 45% and 70%, thus being high enough, and the products satisfy the above described requirements for water treatment; nevertheless, they present the major drawback of generating acidic gypsum as a by-product, whose disposal represents an ecological problem difficult to solve. Furthermore, the production process is complicated, including a filtration step, the washing of the filter cake and the recovery of active principle. A cooking phase at high temperature is also necessary. The investment and manufacturing costs are therefore elevated.
e) The European Patent No. EP-0557153 describes a process for the preparation of aluminium polychlorosulphates with a high basicity ranging between 65% and 75%, and low effluent production. Nevertheless a big disadvantage of this process is its scarce reproducibility. This lack of reproducibility is shown by the presence of high levels of residual aluminium in treated water in 80% of cases.
f) The European Patent No. EP-0794153 describes aluminium polychlorosulphates having the general formula:
Al(OH)
a
Cl
b
Y
c/d
M′Cl
2/e
M″Cl
where
Y represents an anion with valency 2, such as SO
4
2−
,
M′ represents a cation with valency 2, such as an alkaline-earth metal,
M″ represents a cation with valency 1, such as an alkali metal or ammonium,
a, b, c, d are non-zero positive integers or non-zero positive fractions,
e can be zero or a positive integer or a positive fraction,
where:
1.8<a<2.25
0.001<c<0.15
b=3−2c−a
2d+e+b≦3.
The process described in EP-0794153 reduces but does not eliminate the co-production of gypsum illustrated in the above mentioned patent EP-327419. The process is complicated because it includes a filtering operation and a cooking step at high temperature.
On the other hand, according to the above-mentioned process, the use of an alkaline-earth metal compound in the basification step is necessary, which can cause the precipitation of alkaline-earth metals sulphates, typically of calcium, scarcely soluble in an aqueous salt solution.
SUMMARY OF THE INVENTION
Now the Applicant has found an advantageous process for the preparation of new aluminium polychlorosulphates having high basicity and stability, a low sulphate content, and a high flocculating and coagulating power, corresponding to
Bos Steven
Hedman & Costigan ,P.C.
Vanoy Timothy C
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