1. Method for the preparation of an aqueous slurry of calcium hydroxide with a dry content of at least 40% by weight, the viscosity of the said aqueous slurry measured by a Brookfield DVIII viscometer at 10 RPM being between 25 and 1,000 mPa.s at 20°C, including the steps consisting of: a) the availability of a specific volume of an aqueous solution, b) the availability of a specific quantity of powdered calcium hydroxide, c) the availability of a specific quantity of a copolymer consisting: - of methacrylic acid monomers and/or any of its salts, - possibly of acrylic acid monomers and/or any of its salts, - monomers with the formula (I): R – X – R’ (I) according to which: R represents a polymerisable unsaturated group, notably acrylate, methacrylate, methacrylurethane, vinyl or allyl, R’ represents hydrogen or an alkyl group with from 1 to 4 carbon atoms, X represents a structure with n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide PO, arranged randomly or regularly, m and n are 2 non-zero integers and are between 1 and 150, d) to at least a part of said aqueous solution, at least a part of the quantity of the said copolymer is added under agitation, e) to the aqueous solution of step d), at least a part of the said quantity of the said calcium hydroxide is added under agitation, 37 f) a homogeneous shearing level greater than 50,000 s-1 is applied to the mixture resulting from step e), g) possibly, in the course of step f), the remaining quantity of the said copolymer and/or of the said calcium hydroxide is added.

2. Method according to claim 1, according to which the copolymer has a molecular mass between 30,000 and 200,000 g/mol as determined by Gel Permeation Chromatography (GPC).

3. Method according to any of the previous claims, according to which the said monomer of formula (I) is such that n and m are two non-zero integers, and n+m > 17.

4. Method according to any of the previous claims, according to which the R group of the said monomer of formula (I) represents the methacrylate group.

5. Method according to any of the previous claims, according to which the R' group of the said monomer of formula (I) represents H or CH3.

6. Method according to any of the previous claims, according to which the said monomer of formula (I) consists of, expressed as a percentage by weight of each of its components: - 5 to 30% by weight of methacrylic acid monomers and/or any of its salts, - 0 to 10% by weight of acrylic acid monomers and/or any of its salts, - 70 to 95% by weight of monomers of formula (I).

7. Method according to any of the previous claims, according to which a mixer of the rotor-stator type is used for step f).

8. Method according to any of the previous claims, according to which the device used to perform the step f) is equipped with a recirculating loop. 38

9. Method according to any of the previous claims, according to which a device configured to deliver a useful output of at least 1,000 W/m3 is used to carry out step f).

10. Aqueous slurry of calcium hydroxide with a dry content of at least 40% by weight, the viscosity of the said aqueous slurry measured by a Brookfield DVIII viscometer at 10 RPM being between 25 and 1,000 mPa.s at 20°C, the said slurry being likely to be obtained by the method according to any of claims 1 to 9.

11. Use of a slaked lime aqueous slurry according to claim 10 for the treatment of industrial smoke, including for the desulfurization of smoke, or for the treatment of domestic wastewater, including drinking, or industrial wastewater. ABSTRACT Title: AQUEOUS SUSPENSION OF CALCIUM HYDROXIDE, METHOD FOR THE PRODUCTION THEREOF, AND USES OF SAME The present invention concerns a lime-based slurry including a new additive as well as a method for the preparation of such a slurry. Such slurries are used in particular as chemical neutralization agents in domestic or industrial processes.

The present invention relates to the technical field of the preparation of aqueous slurries of
calcium dihydroxide. Specifically, the present invention concerns a lime-based slurry
including a new additive as well as a method for the preparation of such a slurry. Such
slurries are used in particular as a chemical neutralization agent in domestic or industrial
processes.
Calcium dihydroxide Ca(OH)2, also known as slaked lime or hydrated lime, is obtained by
hydration of calcium oxide CaO, also known as quicklime, according the following
exothermic reaction:
CaO + H2O �� Ca(OH)2
In the context of the present invention, the terms “calcium hydroxide” or the terms “calcium
dihydroxide” are used in an equivalent manner to designate particles of Ca(OH)2.
Calcium hydroxide-based products come in various forms: in the form of powder (dry
product in powdery form), in the form of plastic pastes, or in the form of aqueous
slurries/dispersions (milk-of-lime).
The present invention relates more specifically to a calcium hydroxide-based product which
is in the form of an aqueous slurry. Such aqueous slurries of slaked lime can be used as
chemical neutralization agents in many industrial processes. An example that can be cited is
the treatment of industrial effluents, for example gases such as acid smoke. The treatment of
potable water, wastewater or industrial water are also examples.
Aqueous slurries of slaked lime are characterized in particular by their dry solids content (%
by weight). The person skilled in the art typically seeks to increase the dry solids content in
aqueous slurries of slaked lime for reasons that are primarily economic: by increasing the dry
solids content of aqueous slurries of slaked lime, the relative cost of transport and handling
per tonne of product is thereby reduced. In addition, the nuisances due to the handling of
powders (hygiene, handling) is reduced, and implementation is facilitated.
3
To increase the dry solids content of aqueous slurries of slaked lime, a dispersing agent can
be used.
A “dispersing agent” means an agent that has the ability to improve the dispersion state of
Ca(OH)2 particles in an aqueous slurry.
Specifically, when these agents are used in aqueous slurries of mineral material, they induce
a decrease in viscosity. Thus, an aqueous slurry of mineral material containing a dispersing
agent will have a viscosity that is less than that of the same aqueous slurry of mineral
material that does not contain the said dispersing agent.
A certain number of documents of the prior art describe the use of dispersing agents.
Document EP 0 061 354 (Blue Circle) describes the implementation of anionic oligomeric
polyeletrolytes, for example, homopolymers of (meth)acrylic acid, carboxymethyl cellulose
or sulphonate, for making aqueous dispersions of slaked lime.
Document FR 2 677 351 (Italcementi) describes a concentrated aqueous slurry of calcium
hydrate that contains at least 40% solid hydrated lime obtained from powdered hydrated lime,
slaked lime or quicklime, and a water-soluble polymer that can be a polyacrylate of an alkali
or alkaline-earth metal.
Document EP 0 594 332 (Rohm & Haas) describes the use of anionic polymeric dispersing
agents to obtain aqueous dispersions of quicklime or slaked lime. These dispersing agents are
chosen from homopolymers, copolymers and terpolymers having carboxylic acid, sulphonic
acid or phosphonic acid functionalities. The monomers that confer such an acid functionality
include, for example, acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic
anhydride, itaconic acid, mesaconic acid, fumaric acid, citraconic acid, vinyl acetic acid,
acryloxy propionic acid, vinyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-
methylpropane sulfonic acid, allylsulfonic acid, allyl phosphonic acid, vinyl phosphonic acid
and vinyl sulfonic acid.
4
Document US 2008/0011201 (Ultimate Nominees) describes the combined use of a
polycarboxylate dispersant and a carbohydrate dispersant to prepare a milk-of-lime for
applications in the food and potable water field. In particular, according to this document, the
carbohydrate dispersant is a sugar, chosen notably from among the aldoses, saccharides,
disaccharides and polysaccharides. Also, examples of polycarboxylate dispersants are in
particular the styrene maleic anhydride copolymer salts or the polyether polycarboxylate
salts. In particular, this document describes the combined use of a comb-type copolymer,
namely Ethacryl® G (a polycarboxylate dispersant from the Coatex company) and a glucose
syrup (carbohydrate dispersant) to prepare a 50% hydrated lime slurry/dispersion.
Document EP 0 848 647 (Chemical Lime Company) describes the use of a dispersing agent
of the anionic polyelectrolyte type in combination with an alkali metal hydroxide to prepare a
lime slurry which can be of quicklime or slaked lime. The anionic polyelectrolyte is chosen
from among polyacrylic acid, polycarboxylic acid, and polyphosphoric acid, the copolymers
of polyacrylic acid, polycarboxylic acid and polyphosphoric acid and their alkali metal salts.
Document FR 6 687 396 (Lhoist) describes a calcium oxide or magnesium oxide quenching
process that takes place in the presence of SO3
-, SO4
2-, or Cl- ions and in which, in the course
of the reaction or at the end of the reaction, a polymer or copolymer is added that includes
monomers chosen from among acrylic acid and its salts, methacrylic acid and its salts,
vinylbenzylsulfonic acid and its salts, acrylamido-2-methylpropane-sulphonic acid and its
salts, methacrylate of 2-sulfoethyl and its salts.
Document JP 09 122471 (Nippon Shokubai) describes the use of copolymers consisting of a
carboxylic monomer and a monomer of the polyalkylene glycol (meth)acrylate type as a
dispersing agent for obtaining aqueous dispersions of slaked lime with a low viscosity.
This document illustrates the use for this purpose of copolymers whose molecular weight is
less than 20,000 g/mol.
Document WO 2010/106111 (Lhoist) refers to compositions including slaked lime and/or
quicklime and an organic polymer incorporated in the solid phase of the slaked lime. The
polymers described in this document can be non-ionic, anionic, cationic or amphoteric, and
of a highly varied nature. They can be obtained from monomers chosen from among the
anionic monomers with a carboxylic group or with a sulfonic acid group, the non-ionic
5
monomers (acrylamide, methacrylamide, N-vinyl pyrrolidone, vinyl acetate, vinyl alcohol,
acrylate esters, allyl alcohol, N-vinyl acetamide,
N-vinylformamide), the cationic monomers (ADAME, MADAME quaternized or salified,
DADMAC, APTAC, MAPTAC), possibly in association with one or more hydrophobic
monomers preferentially chosen from the group including the (meth)acrylic acid esters with
an alkyl, arylalkyl and/or ethoxylated chain, the allylic cationic derivatives, the anionic or
cationic hydrophobic (meth)acryloyl derivatives, or the anionic and/or cationic monomers
(meth)acrylamide derivatives with a hydrophobic chain.
When using the polymers of the prior art, the inventors have nevertheless found a
sedimentation problem when slurries are stored without agitation for a period exceeding 3
days, especially during their transport.
A paste is then formed at the bottom of tanks containing the slurries which makes their
pumping difficult or even impossible.
In addition, the inventors have also noted that this problem of sedimentation was due to a
poorly adapted rheology of the currently available slurries, and to a bad disagglomeration of
lime particles.
The processes and dispersing agents available at present do not allow aqueous slurries of lime
to be obtained that provide total satisfaction, particularly in terms of sedimentation and
rheological properties.
An object of the present invention is to avoid the problem of sedimentation when lime
slurries are stored without agitation.
Another object of the present invention is to provide aqueous slurries of lime that are as
concentrated as possible and that exhibit a rheology that is adapted to their uses in industrial
processes.
An object of the present invention is to provide a process for the preparation of an aqueous
slurry of slaked lime that can easily be implemented.
6
Unexpectedly, the inventors have revealed that by submitting a concentrated aqueous slurry
of lime to a shearing operation under specific conditions in the presence of a polymer with a
particular structure, it was possible to obtain concentrated and stable aqueous slurries over
time.
More specifically, the objective of the present invention is a process for the preparation of an
aqueous slurry of calcium hydroxide with a dry content of at least 40% by weight, with the
viscosity of the said aqueous slurry measured by a Brookfield DVIII viscometer at 10 RPM
being between 25 and 1,000 mPa.s at 20°C, including the steps consisting of:
a) the availability of a specific volume of an aqueous solution,
b) the availability of a specific quantity of powdered calcium hydroxide,
c) the availability of a specific quantity of a copolymer consisting:
- of methacrylic acid monomers and/or any of its salts,
- possibly of acrylic acid monomers and/or any of its salts,
- monomers with the formula (I):
R – X – R’
(I)
according to which:
R represents a polymerisable unsaturated group, notably acrylate, methacrylate,
methacrylurethane, vinyl or allyl,
R’ represents hydrogen or an alkyl group with from 1 to 4 carbon atoms,
X represents a structure with n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide
PO, arranged randomly or regularly,
m and n are 2 non-zero integers and are between 1 and 150,
d) to at least a portion of said aqueous solution, at least part of the amount of the said
copolymer is added under agitation.
e) to the aqueous solution of step d), at least a part of the said quantity of the said calcium
hydroxide is added under agitation.
f) a homogeneous shearing level greater than 50,000 s-1 is applied to the mixture resulting
from step e),
7
g) possibly, in the course of phase f), the remaining quantity of the said copolymer and/or of
the said calcium hydroxide is added.
In fact, the inventors realized that for aqueous slurries with the properties of stability over
time and the concentration expected, it was necessary:
- to disperse the particles of calcium hydroxide in the presence of a water-soluble
copolymer of the comb type with a (meth)acrylic acid skeleton and poly(alkyleneglycol)
side chains with a particular structure,
- to apply a shearing with a level higher than a critical shear threshold,
- to use a shearing device such that the entire aqueous slurry is subject to the critical shear
threshold, and
- that the said aqueous slurry has concentrations of calcium hydroxide and copolymer that
are such as to allow the application of a mechanical stress that is sufficient to deflocculate
the particles of calcium hydroxide during shearing.
To be more precise, a homogeneous shearing is applied to the said aqueous slurry.
“Homogeneous shearing” means a shearing which has the effect of applying the same
mechanical stress to all parts of the aqueous slurry thus treated.
In fact, some shearing devices have a configuration such that they can ensure that the entire
aqueous slurry of lime is subjected to the mechanical stress of the expected shearing.
The present invention is based on the combination of a specific process and a particular
(meth)acrylic copolymer.
In general, it is noted that in the context of the present invention, all the methods of
embodiment of the invention can be combined.
According to the present invention, the term “slurry”, or alternatively, in an equivalent
manner, “dispersion”, means an aqueous slurry containing solids and at least one additive.
8
According to the present invention, the aqueous slurry has a viscosity measured by a
Brookfield DVIII viscometer at 10 RPM which is between 25 and 1,000 mPa.s at 20°C.
It should be noted that at viscosity values higher than 1,000 mPa.s, slurries are likely to
present difficulties in handling (for example, pumping and filtration of the slurry).
Moreover, an object of the present invention is to maintain the viscosity of the slurry, as
measured by a Brookfield DVIII viscometer at 100 RPM after agitation, below
1,000 mPa.s over time, for example after a storage of 7 days, 20 days, or 1 month.
“Stable aqueous slurry” means an aqueous slurry that has a viscosity at 7 days, 20 days or 1
month which is less than 1,000 mPa.s as measured by a Brookfield DVIII viscometer at 100
RPM after agitation.
“Aqueous solution” preferentially means water according to the invention. This solution can
possibly contain other liquids that are miscible with water or solids that are soluble in water.
“Powdered calcium hydroxide” means particles of slaked lime. Slaked lime is lime consisting
of a collection of solid particles, mainly of calcium dihydroxide, Ca(OH)2 which is the result
of the reaction of quicklime particles with water, a reaction called hydration or quenching.
Slaked lime is also called hydrated lime. In general, slaked lime can contain impurities which
are mainly issues from quicklime, for example, magnesia, magnesium oxide, Al2O3, Fe2O3,
MgO, S, SiO2, Mn3O4, silicates etc. Slaked lime can occur in the powdery form or in the form
of an aqueous slurry called milk-of-lime.
In the context of the present invention, slaked lime is dispersed as a powder in an aqueous
solution in order to obtain a milk-of-lime that is concentrated and stable over time. For
example, commercially available slaked lime in powder form is used as a starting mineral
material. For example, slaked lime sold under the names
Supercalco® 97, Supercalco® 97/20, Sorbacal® SP, Standard Hydrated Lime, MicroCal®
HF are cited.
9
The particular (meth)acrylic copolymer according to the invention is a water-soluble comb
type copolymer with a methacrylic acid and possibly an acrylic acid skeleton, and
poly(alkyleneglycol) side chains.
“Poly(alkylene glycol)” means an alkylene glycol polymer derived from an olefinic oxide.
The poly(alkylene glycol) chains of the copolymer according to the present invention
contain a proportion of oxyethylene groups and a proportion of oxypropylene groups.
The poly(alkylene glycol) chains according to the present invention may for example include
a dominant proportion of the oxyethylene group in association with a secondary proportion of
the oxypropylene group. Some specific examples of alkylene glycol polymers include: the
poly(alkylene glycols) having an average molecular weight of 1,000, 4,000, 6,000, 10,000
and 20,000 g/mol; the polyethylene polypropylene glycols having an ethylene oxide
percentage between 20 and 80% by weight, and a propylene oxide percentage between 20
and 80% by weight.
It should be noted that the oxyethylene and oxypropylene groups of the copolymer side
chains can be arranged randomly, on a regular basis or in a block.
To be more precise, the polymer according to the present invention consists:
- of methacrylic acid monomers and/or any of its salts,
- possibly of acrylic acid monomers and/or any of its salts,
- monomers with the formula (I):
R – X – R’
(I)
according to which:
R represents a polymerisable unsaturated group, notably acrylate, methacrylate,
methacrylurethane, vinyl or allyl,
R’ represents hydrogen or an alkyl group with from 1 to 4 carbon atoms,
10
X represents a structure with n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide
PO, arranged randomly or regularly,
m and n are 2 non-zero integers and are between 1 and 150.
Thus, the copolymer according to the invention has a skeleton consisting of methacrylic acid
monomers, and possibly acrylic acid monomers. Indeed, the inventors realized that the
presence of methacrylic acid monomers in the skeleton of the copolymer according to the
invention was indispensable in order to solve the technical problem at the origin of the
present invention.
According to one method of embodiment of the invention, the copolymer has a skeleton
consisting of methacrylic acid monomers exclusively.
According to another method of embodiment of the invention, the copolymer has a skeleton
consisting of methacrylic acid monomers and acrylic acid monomers.
Thus, excluded from the context of the present invention is the use of a copolymer with a
skeleton consisting exclusively of acrylic acid monomers.
The inventors also found that the use in the context of the present invention of the comb-type
copolymer marketed under the name Ethacryl® G (polycarboxylate dispersant of the Coatex
company, which does not contain methacrylic acid monomers) is not suitable for solving the
technical problem at the origin of the present invention.
The said copolymer is obtained by known conventional free radical copolymerization
processes in solution, in bulk, in direct or inverse emulsion, in suspension or by precipitation
in suitable solvents, in the presence of known catalytic systems and transfer agents, or again,
by controlled radical polymerization processes such as the process known as reversible
addition-fragmentation chain transfer (RAFT), the process known as atom transfer radical
polymerization (ATRP), the process known as nitroxide-mediated polymerization (NMP), or
again, the process known as cobalt-oxime mediated radical polymerization.
11
It is obtained in an acid and possibly distilled form. It can also be partially or totally
neutralized by one or more neutralization agents chosen from among the hydroxides of
sodium, calcium, magnesium and potassium and their mixtures, or chosen from the amines.
According to one method of embodiment of the present invention, the said copolymer is
100% neutralized with sodium hydroxide.
According to another method of embodiment of the present invention, the said copolymer is
partially neutralized with sodium hydroxide.
According to steps a), b) and c) of the process according to the invention, there is
respectively a specific volume of an aqueous solution, a specific quantity of powdered
calcium hydroxide and a specific quantity of a copolymer as described above.
According to step d) of the process, at least part of the amount of the said copolymer is added
under agitation to at least part of said aqueous solution.
In the present description, in general, “part”, means a proportion of the total amount required,
or alternatively, a proportion of the total volume required.
As an example, one part of the aqueous solution can for example correspond to 40% of the
total amount of water needed for the final dilution.
At the end of step d) of the process, a total aqueous solution or a primary aqueous solution is
obtained.
“Total aqueous solution”, means that the entire aqueous solution is subject to the following
steps of the process.
“Primary aqueous solution” means that, as a first step, only a part of the aqueous solution is
subject to shearing, the rest of the aqueous solution being implemented during the shearing
and/or its terminal phase.
12
According to one method of embodiment, step d) of the process consists of adding under
agitation at least one part of the amount of the said copolymer to the entire said aqueous
solution (total aqueous solution).
According to another method of embodiment, step d) of the process consists of adding under
agitation the entire amount of the said copolymer to the entire said aqueous solution (total
aqueous solution).
According to still another method of embodiment, step d) of the process consists of adding
under agitation a part of the necessary total quantity of the said copolymer to part of the total
volume of the said aqueous solution (primary aqueous solution).
According to still another method of embodiment, step d) of the process consists of adding
under agitation the entire necessary total quantity of the said copolymer to part of the total
volume of the said aqueous solution (primary aqueous solution).
According to step e) of the process, at least a part of the said quantity of the said calcium
hydroxide is added under agitation to the aqueous solution of step d).
Thus, the total quantity of slaked lime can be added in a single step, or alternatively, in
increments.
The slaked lime can also be introduced into the aqueous solution in a continuous manner, i.e.
at a constant or variable speed, but without stopping the introduction.
According to one method of embodiment, all of the said quantity of the said calcium
hydroxide is added under agitation to the aqueous solution of step d).
According to one method of embodiment, a part of the said total required quantity of the said
calcium hydroxide is added under agitation to the aqueous solution of step d). This method of
embodiment has the advantage of increasing the flow of the apparatus by separating the
addition of the lime into two steps: pre-dispersion and then final dispersion during shearing.
13
According to step f) of the process of the invention, a homogeneous shearing with a shearing
level greater than 50,000 s-1 is applied to the mixture resulting from step e).
The inventors demonstrate in fact that there is a critical homogeneous shear threshold
required to achieve the objectives of the present invention, namely, elevated slaked lime
content of the slurry, absence of sedimentation and stability of the slurry over time.
Applying such a shearing level to slaked lime slurries in combination with the use of a watersoluble
copolymer with a particular chemical structure results in the achievement of these
objectives. The rheological properties of the resulting dispersion are thus significantly
optimized over time.
According to one method of embodiment, a homogeneous shearing with a shearing level
greater than 60,000 s-1, in particular greater than 70,000 s-1 is applied to the mixture resulting
from step e).
According to the process of the present invention, a homogeneous shearing, which has the
effect of applying the same minimum mechanical stresses to all parts of the aqueous slurry
thus treated is applied to the said aqueous slurry.
The homogeneous shearing required according to the present invention can be obtained
according to several variants.
According to a first variant, subjecting the mixture resulting from step e) to a constant
shearing rate can be envisaged.
However, the invention is not limited to this particular method of embodiment.
For example, the shearing rate can be separate, at a given time, for two points in the slurry. It
is thus that by varying the geometry of the device used to generate the shearing forces, it is
possible to modulate the shearing rate applied to the said dispersion over time and/or in
space.
The dispersion being fluid when it is subjected to shear, each part of it can thus be subjected
to a shearing rate which varies over time. The shearing is said to be homogeneous when,
regardless of the variation of the shearing rate over time, it passes through a minimum value
14
that is the same for all parts of the dispersion at a given time that may differ from one
location to another in the dispersion.
In the context of the present invention, the total aqueous slurry or the primary aqueous slurry
is introduced into an appropriate device in order to generate a homogeneous shearing.
This device can have varied configurations. The exact configuration is not essential
according to the invention, as long as on exiting this device, the entire dispersion has been
subjected to the same minimum shearing.
As an illustration, but one that is non-limiting, of the devices that can be used according to
the invention to apply a homogeneous shearing, the IKA® Magic Lab and the Dispax
Reactor® DR2000 mixers can in particular be cited.
According to one method of embodiment of the present invention, a rotor-stator type mixer is
used for step f).
According an another method of embodiment, a mixer consisting of several rotor-stator
couples in direct series is used for step f) of the process according to the invention.
According to one method of embodiment of the present invention, a mixer consisting of
cylindrical parts which have a tangential speed greater than 40 m/sec. Is used for step f).
A mixer of the rotor-stator type generally consists of two concentric disks creating a chamber
in which the primary dispersion circulates. One of the disks is stationary (stator) and the other
is driven with a uniform rotation around its axis (rotor). Such a device includes a product
supply line (in the case in point, the lime slurry) which goes through the upper disc to
discharge into the central part of the chamber. The slurry passes through the gap between the
stator and the rotor. The rotor (the part of the device driven by a motor) and stator (the fixed
part) are equipped respectively on their outer crowns with slots which allow the circulation of
the lime slurry to be sheared. Such a device also includes an outlet pipe connected to a tank
designed to receive the slurry thus sheared.
The shearing device can include a recirculation loop which allows a multiplication of the
passes through the shearing device.
15
Thus, according to one method of embodiment, the device used to perform step f) is equipped
with a recirculating loop.
Thus, according to one method of embodiment, the device configured to deliver a useful
output of at least 1,000 W/m3 is used to carry out step f).
According to optional step g) of the process according to the invention, the residual quantity
of the said copolymer and/or the said calcium hydroxide is added.
The said residual amount of the copolymer and/or the said residual quantity of the said
calcium hydroxide may be added in the form of a dilution or slurry made with the residual
part of the said aqueous solution (or at least a part of it).
This addition can, for example, be made in the course of step f), that is, during the shearing
step. The said addition can be made continuously for the entire duration of step f), during part
of it only, or in a single step, for example at the beginning of the shearing step, in the course
of it, or at the end of it.
According to one method of embodiment of the present invention, the process of the
invention does include the step consisting of the addition of an alkali metal hydroxide to the
aqueous solution or slurry. It is possible to dispose of a copolymer according to the invention
that is partially or totally neutralized by means of an alkali metal hydroxide. Nevertheless,
according this method of embodiment, the addition of an alkali metal hydroxide as such to
the aqueous solution or the aqueous slurry of lime is excluded.
According to one method of embodiment of the present invention, the process for the
preparation of an aqueous slurry of calcium hydroxide with a dry content of at least 40% by
weight, the viscosity of the said aqueous slurry measured by a Brookfield DVIII viscometer
at 10 RPM being between 25 and 1,000 mPa.s at 20°C, includes the steps consisting of:
a) the availability of a specific volume of an aqueous solution,
b) the availability of a specific quantity of powdered calcium hydroxide,
c) the availability of a specific quantity of a copolymer consisting:
- of methacrylic acid monomers and/or any of its salts,
- possibly of acrylic acid monomers and/or any of its salts,
16
- monomers with the formula (I):
R – X – R’
(I)
according to which:
R represents a polymerisable unsaturated group, notably acrylate, methacrylate,
methacrylurethane, vinyl or allyl,
R’ represents hydrogen or an alkyl group with from 1 to 4 carbon atoms,
X represents a structure with n unit(s) of ethylene oxide EO and m unit(s) of propylene oxide
PO, arranged randomly or regularly,
m and n are 2 non-zero integers and are between 1 and 150,
d) the entire amount of the said copolymer is added under agitation to the said aqueous
solution,
e) all of the said quantity of the said calcium hydroxide is added under agitation to the
aqueous solution of step d), and
f) a homogeneous shearing level greater than 50,000 s-1 is applied to the mixture resulting
from step e).
All the steps of the process of the invention can be carried out at room temperature, that is, at
about 20°C, or at lower temperatures, for example, 10°C. Heating can be introduced from an
external source. The introduction of slaked lime and/or the shearing of step e) are likely to
lead to a more or less significant increase in the temperature of the slurry. If necessary, a
device for cooling the slurry temperature can be provided.
According to one method of embodiment, the said specified quantity of copolymer varies
between 0.01 and 10% by weight based on the total weight of calcium hydroxide particles in
the slurry.
According to another method of embodiment, the said specified quantity of copolymer varies
between 0.05 and 5% by weight based on the total weight of calcium hydroxide particles in
the slurry.
17
According to still another method of embodiment, the said specified quantity of copolymer
varies between 0.1 and 3.0% by weight based on the total weight of calcium hydroxide
particles in the slurry.
According to another method of embodiment, the said specified quantity of copolymer varies
between 0.2 and 2.0% by weight based on the total weight of calcium hydroxide particles in
the slurry.
According to another method of embodiment, the aqueous slurry according to the present
invention consists of water, particles of calcium hydroxide and a copolymer according to the
present invention. According to this method of embodiment, the aqueous slurry contains no
additive other than the copolymer described in the present application, that is, it does not
contain another polymer or dispersant, for example.
According to one method of embodiment, the aqueous slurry is an aqueous slurry containing
a dry particle content of calcium hydroxide of at least 40% by weight based on the total
weight of the aqueous slurry.
According to another method of embodiment, the aqueous slurry according to the present
invention has a calcium hydroxide particle content between 40% and 60% by weight based
on the total weight of the aqueous slurry.
According to another method of embodiment, the aqueous slurry according to the present
invention has a calcium hydroxide particle content between 45% and 55% by weight based
on the total weight of the aqueous slurry.
According to one method of embodiment of the present invention, the said copolymer has a
molecular mass between 30,000 and 200,000 g/mol as determined by Gel Permeation
Chromatography (GPC).
According to another method of embodiment of the present invention, the copolymer has a
molecular mass between 30,000 and 160,000 g/mol as determined by Gel Permeation
Chromatography (GPC).
18
According to one method of embodiment of the present invention, in the said water-soluble
copolymer, the said monomer of formula (I) is such that n and m are two non-zero integers,
and n+m > 17.
According to one method of embodiment of the present invention, in the said water-soluble
copolymer, the R group of the said monomer of formula (I) represents the methacrylate
group.
According to one method of embodiment of the present invention, in the said copolymer, the
R’ group of the said monomer of formula (I) represents H or CH3.
According to one method of embodiment of the present invention, in the said copolymer, the
said monomer of formula (I) consists of, expressed as a percentage by weight of each of its
components:
- 5 to 30% by weight of methacrylic acid monomers and/or any of its salts,
- 0 to 10% by weight of acrylic acid monomers and/or any of its salts,
- 70 to 95% by weight of monomers of formula (I).
According to one method of embodiment of the present invention, in the said copolymer, the
said monomer of formula (I) consists of, expressed as a percentage by weight of each of its
components:
- 7 to 22% by weight of methacrylic acid monomers and/or any of its salts,
- 0 to 5% by weight of acrylic acid monomers and/or any of its salts,
- 78 to 93% by weight of monomers of formula (I).
The present invention also concerns an aqueous slurry of calcium hydroxide with a dry
content of at least 40% by weight, the viscosity of the said aqueous slurry measured by a
Brookfield DVIII viscometer at 10 RPM being between 25 and 1,000 mPa.s at 20°C, the said
slurry likely to be obtained by the process of the present invention.
19
The present invention also concerns the use of the slaked lime aqueous slurry according to
the invention in the applications that follow.
Slurries can be used in the treatment of smoke from energy-producing plants that use
combustibles (including coal) containing sulphur and other impurities, for example, that
generate acid molecules (sulphur dioxide, sulphur trioxide, sulphuric acid, hydrochloric acid,
hydrofluoric acid, etc.) or pollutants (mercury, heavy metals, etc.).
They can also be used in household or industrial waste incineration plants which generate the
same type of pollutants, with dioxins as well.
The use of lime in a concentrated aqueous slurry, sprayed into the smoke, traps the pollutants
which are then eliminated in the solid residues produced by the reaction with lime, and the
partial or total drying of the reaction products.
Slurries can be used as acid reaction product neutralizing agents, allowing their removal in
the solid and/or neutralized form, or their use in the form of calcium salt (such as for example
sulfonates and phenates neutralized as additives of lubricating products). In a non-limiting
manner, the neutralization of acid sludges from the manufacture of titanium dioxide, the
neutralization of acidic solutions produced during chemical manufacturing processes, can be
cited.
The aqueous slurries of the present invention can be used as neutralizing agents of mine
effluents for the purpose of neutralizing acidity and/or separating heavy metals in solution
prior to the discharge of fluids into the natural environment or into a lagoon.
Slurries can be used in water decarbonation processes, a process for temporarily reducing
water hardness (partial or total elimination of alkaline earth metal bicarbonates). The water
thus treated is intended to be used as drinking water or industrial water, possibly after a
readjustment of the Ph using carbon dioxide or any other acid suitable for the final
application.
20
Drinking water, wastewater or industrial water purification treatments generate residues
called sludges. These sludges are first separated from the purified water and then processed
in order to stabilize and concentrate them. The treatment process of the sludges is usually
called conditioning and uses organic and/or mineral additives.
The present invention also concerns the use of the slaked lime aqueous slurry according to
the invention to package sludges from wastewater treatment plants. Slurried lime is used as a
first step to promote the flocculation of sludges, and in a second step for Ph sterilization of
the said sludges by maintenance of their Ph at 12 or higher for 24 to
72 hours or more.
Slurries can be used in the treatment of aggregates used in the bituminous coating production
process. The adhesion of bitumen emulsions to aggregates is greatly improved when these
aggregates are treated with lime beforehand. This better adhesion results in bituminous
coatings that are more wear and deformation-resistant and have an extended physical
integrity.
The aqueous slurries of the present invention can be used in the production of aerated
concrete type construction materials. Lime is mixed with cement, sand and aluminium
powder. The elevated Ph of the mixture causes a gaseous release of hydrogen by an attack of
the aluminium, and the resulting aerated paste produced is moulded and then autoclaved to
produce aerated concrete parts.
The aqueous slurries of the present invention can be used in the treatment of contaminated
soils in order to neutralize the acidity of these soils, to immobilize pollutants by
neutralization or flocculation, and thus avoid the driving of such pollutants into the
groundwater.
The aqueous slurries of the present invention can be used in the treatment of soils in
agriculture in order to correct the Ph of these soils, improve the said soils by providing a
source of calcium or of calcium and magnesium in the case of dolomitic limes, and make
these soils less impermeable by flocculation of clays they contain.
21
The aqueous slurries of the present invention can be used in the treatment of surface waters,
lakes, ponds and rivers in order to adjust the Ph of the water to reduce the impact of the
acidification of these waters, acidification of rain or animal origin in the case of fish farming.
The aqueous slurries of the present invention can be used in the production of food for
livestock or poultry, and among others, as a source of calcium or calcium and magnesium.
The aqueous slurries of the present invention can be used in the paper industry, for example,
as a constituent of papermaking pulp.
In addition, they can be used for the refining of sugar.
They can also be used for the production of precipitated calcium carbonate (PCC).
The present invention also concerns the use of slaked lime aqueous slurry according to the
invention for the treatment of industrial smoke, including the desulfurization of smoke, or for
the treatment of domestic wastewater, including drinking, or industrial wastewater.
The present invention also concerns a process for the treatment of gases or smoke, including
a step consisting of injecting/spraying an aqueous slurry of slaked lime according to the
invention into the gases or smoke to be treated in order to remove acidic compounds, oxides
of sulphur, hydrochloric acid, etc.
Examples
In all the tests that follow, the slurries are evaluated using the parameters described below.
The viscosity (expressed in mPa.s) of each slurry is measured at 20°C with a Brookfield
DVIII type viscometer. The indicated values of viscosities are measured before agitation or
after agitation at a speed of 10 RPM and 100 RPM, and at different storage times. The values
of viscosities after 1 month of storage and after agitation of the slurry (using equipment of the
Rayneri type, for example) are all particularly relevant in assessing the characteristics of the
invention (influence of the polymer, influence of the equipment, influence of the minimum
degree of shearing) with regard to the use of the slurries in industrial processes.
22
The sedimentation of each slurry is evaluated by a measurement of the height of the deposit
in the container. The sedimentation values are expressed in %, that is, the height of the
deposit compared to the total height of the slurry in the container, multiplied by 100.
EXAMPLE 1
This example illustrates the use of different polymers (prior art, invention, outside of the
invention) in a process for the preparation of an aqueous slurry of calcium hydroxide (slaked
lime) according to the invention.
Several aqueous slurries of calcium hydroxide, each having a 48±1% solids content, are
prepared in this example. 503 g of water are introduced into a container together with a
quantity of a polymer corresponding to 1.41% by dry weight (on the basis of the total weight
of the solids in the slurry), the said polymer being a polymer of the prior art or a polymer of
the present invention. Then, 485 g of slaked lime (Supercalco® 97, Carmeuse) are introduced
into the container under agitation.
A mixer of the IKA® Magic Lab type, adjusted to produce a shearing of 82,000 s-1 is then
supplied with the mixture obtained in the previous step. A recirculating loop allows several
passages through the gap formed by the rotor and the stator of the IKA mixer.
Once it is sheared, the slurry is stored for an evaluation of its parameters of viscosities,
sedimentation and stability at 1 month.
The polymers used in example 1 have the following characteristics:
Test 1-1:
This test demonstrates the use, in a process according to the invention, of a homopolymer
outside of the invention, available commercially under the name Rheosperse® 3010, Coatex,
France, and composed of acrylic acid monomers, 100% neutralized with sodium hydroxide
(molecular weight): 4,000 g/mol).
Test 1-2:
This test demonstrates the use, in a process according to the invention, of a copolymer
outside of the invention, commercially available and consisting of acrylic acid monomers and
23
of vinyl-PEG2000 structured macromonomers, i.e., of monomers having 46 units of ethylene
oxide.
Thus, this comb-structured polymer does not, on the one hand, have methacrylic acid
monomers, and on the other, propylene oxide units on its macromonomers.
Test 1-3:
This test demonstrates the use, in a process according to the invention, of a commercially
available copolymer outside of the invention consisting of 15% by weight of acrylic acid
monomers and methacrylic acid monomers, as well as 85% by weight of MPEG5000
macromonomers (i.e. methoxy (EO)113 units).
Thus, this comb structured polymer does not have propylene oxide units on its
macromonomers.
Tests 1-4 to 1-8: copolymers with a particular structure, according to the invention or outside
of the invention.
These tests demonstrate the use of water-soluble copolymers according to the invention or
outside of the invention, having:
- a negatively charged skeleton consisting of randomly polymerized acrylic acid and/or
methacrylic acid monomers, and
- uncharged side chains consisting of poly(alkylene glycol) units.
* Test 1-4: outside of the invention
The copolymer has the following composition (in % by weight relative to the total weight of
the copolymer):
- 12.8% acrylic acid monomers,
- 87.2% monomers of formula (I): R – X – R’ in which R represents a methacrylate group, R’
designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units
of propylene oxide PO, arranged randomly.
Molecular mass: 38,000 – 52,000 g/mol.
Partial NaOH neutralization; Ph: 3-4.5.
24
This copolymer, not having methacrylic acid monomers, is a copolymer outside of the
invention.
* Test 1-5: according to the invention
The copolymer has the following composition (in % by weight relative to the total weight of
the copolymer):
- 7.44% methacrylic acid monomers,
- 92.56% monomers of formula (I): R – X – R’ in which R represents a methacrylate group,
R’ designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15
units of propylene oxide PO, arranged randomly.
Molecular mass: 110,000 – 150,000 g/mol.
Partial NaOH neutralization; Ph: 3-4.5.
* Test 1-6: according to the invention
The copolymer has the following composition (in % by weight relative to the total weight of
the copolymer):
- 19.8% methacrylic acid monomers,
- 3% acrylic acid monomers, and
- 77.2% monomers of formula (I): R – X – R’ in which R represents a methacrylate group, R’
designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units
of propylene oxide PO, arranged randomly.
Molecular mass: 34,000 – 44,000 g/mol.
Total NaOH neutralization; Ph: 7.7.
* Test 1-7: according to the invention
The copolymer has the following composition (in % by weight relative to the total weight of
the copolymer):
- 12.5% methacrylic acid monomers,
- 87.5% monomers of formula (I): R – X – R’ in which R represents a methacrylate group, R’
designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units
of propylene oxide PO, arranged randomly.
Molecular mass: 60,000 – 95,000 g/mol.
Total NaOH neutralization; Ph: 6.7-7.7.
25
* Test 1-8: outside of the invention
The copolymer has the following composition (in % by weight relative to the total weight of
the copolymer):
- 24% methacrylic acid monomers,
- 4.3% acrylic acid monomers, and
- 71.7% monomers of formula (I): R – X – R’ in which R represents a methacrylate group, R’
designates H, X represents a structure with 46 units of ethylene oxide EO.
Neutralization: 100% NaOH.
Molecular mass: 17,900 g/mol.
This copolymer, whose monomers of formula (I) do not have propylene oxide units, is a
copolymer outside of the invention.
The results of sedimentation and of the different measurements of viscosity are presented in
table 1 below:
Tests sedimentation T0
viscosity
aftag
T0
10 RPM
viscosity
aftag
T0
100
RPM
viscosity
befag
T0+1m
10RPM
viscosity
befag
T0+1m
100RPM
viscosity
aftag
T0+1m
10 RPM
viscosity
aftag
T0+1m
100 RPM
1-1 PA 15% 10 58 1000 124 2770 382
1-2 PA 0 9840 1140 21000 4550 11020 1146
1-3 PA 0 1940 386 17800 3820 7220 1000
1-4 OI 0 290 170 19000 3310 16460 1900
1-5 INV 0 300 159 4620 890 590 230
1-6 INV 0 250 152 1320 478 730 234
1-7 INV 0 170 114 1260 462 330 170
1-8 OI 30% 30 40 1900 802 470 202
Table 1
PA: prior art
OI: outside of the invention
INV: Invention
Aftag: after agitation
Befag: before agitation
26
Firstly, one can observe that the polymers of tests 1-1 (homopolymers of acrylic acid) and 1-
8 (copolymers with no propylene oxide in their side chains) do not avoid sedimentation. The
use of these polymers therefore does not solve the technical problem at the origin of the
present invention.
The measurement of viscosity at 10 RPM after agitation and at T0 shows that the polymers of
tests 1-2 and 1-3 do not create slaked lime slurries with rheological characteristics enabling
their uses in industrial processes, in particular the rheological characteristics specific to the
pumping of the slurries. The slurry obtained in test 1-2 using a polymer of the prior art in fact
has a viscosity of 9,840 mPa.s at T0 after agitation. The slurry obtained in test 1-3 using
another polymer of the prior art has a viscosity of 1,940 mPa.s at T0 after agitation. These
values, outside the range of viscosities claimed (between 25 and 1,000 mPa.s at 20°C) are
incompatible with the use of expected slurries.
The measurement of viscosity at 10 RPM after agitation at T0 + 1 month shows that the
polymer of test 1-4 does not produce a concentrated lime slurry that has a suitable viscosity.
In fact, this viscosity rises to 16,460 s-1.
The rheological profiles of the lime slurries of tests 1-5, 1-6 and 1-7 (use of a copolymer
according to the invention) are suitable for the use of slurries in industrial processes.
EXAMPLE 2
This example demonstrates the use of shearing equipments, identical or different, possibly
adjusted to different shearing levels to prepare an aqueous slurry of calcium hydroxide
(slaked lime) containing a copolymer according to the invention.
A first series of three aqueous slurries of calcium hydroxide (tests 2-1 to 2-3), each one
having a 48 ± 1% solids content, is prepared by the introduction into a container of
503 g of water and of a quantity of a polymer which corresponds to 1.41% by dry weight (on
the basis of the total weight of the solids in the slurry). The said polymer is the one of test 1-
5. Then, 485 g of slaked lime (Supercalco® 97, Carmeuse) are introduced into the container
under agitation.
27
A second series of three aqueous slurries of calcium hydroxide (tests 2-4 to 2-6), each one
having a 48 ± 1% solids content, are prepared by the introduction into a container of 503 g of
water and a quantity corresponding to 1.41% by dry weight of a polymer (on the basis of the
total weight of the solids in the slurry), the said polymer being that of test 1-6. Then, 485 g of
slaked lime (Supercalco® 97, Carmeuse) are introduced into the container under agitation.
Tests 2-1 and 2-4
A mixer of the Ultraturax® type (rotor-stator type) adjusted to produce a shearing of about
40,000 s-1, and which produces a homogeneous shearing according to the definition of the
present invention, is supplied with the mixture obtained in the previous step.
A recirculation loop allows several passes through the mixer. The recirculation time is set to
15 minutes.
Tests 2-2 and 2-5
A mixer of the Rayneri® type, adjusted to produce a shearing of about 3,000 s-1, (which does
not produce a homogeneous shearing according to the definition of the present invention), is
supplied with the mixture obtained in the previous step.
A recirculation loop allows several passes through the mixer. The recirculation time is set to
15 minutes.
Tests 2-3 and 2-6
A mixer of the IKA® Magic Lab type, adjusted to produce a shearing of about
82,000 s-1, and which produces a homogeneous shearing according to the definition of the
present invention, is then supplied with the mixture obtained in the previous step.
A recirculating loop allows several passages through the gap formed by the rotor and the
stator of the IKA mixer. The recirculation time is set to 15 minutes.
28
Once they are sheared, the slurries are stored for an evaluation of the parameters of
viscosities, sedimentation and stability at 1 month.
The results of sedimentation and of the different measurements of viscosity are presented in
table 2 below:
Tests sedimentation
T0
viscosity
Aftag
T0
10 RPM
viscosity
Aftag
T0
100RPM
viscosity
befag
T0+1m
10 RPM
viscosity
befag
T0+1m
100RPM
viscosity
aftag
T0+1m
10 RPM
viscosity
aftag
T0+1m
100RPM
2-1 OI 30% 70 107 3300 560 430 168
2-2 OI 20% 50 98 2400 236 790 220
2-3 INV 0 300 159 4620 890 590 230
24 OI 30% 650 162 1600 580 1890 380
2-5 OI 30% 260 107 19300 1800 1000 240
2-6 INV 0 250 152 1320 478 730 234
Table 2
OI: outside of the invention
INV: Invention
Aftag: after agitation
Befag: before agitation
It is immediately apparent that the shearing level used in tests 2-1 and 2-4 (Ultraturax
adjusted to 40,000 s-1) and tests 2-2 and 2-5 (3,000 s-1 mixer) do not avoid sedimentation.
On the other hand, the shearing level of tests 2-3 and 2-6 (IKA adjusted to 82,000 s-1),
combined with the use of a polymer with a particular structure, not only avoids the problem
of sedimentation, but in addition, enables the production of slurries whose rheological profile
is adapted to the expected use.
EXAMPLE 3
29
This example illustrates the use of two polymers according to the invention in a process for
the preparation of an aqueous slurry of calcium hydroxide (slaked lime) with a high dry
extract content (> 50% by weight).
Two aqueous slurries of calcium hydroxide, each having a 50 to 51% solids content, are
prepared in this example. 478 g of water are introduced into a container together with a
quantity of a polymer corresponding to 1.41% by dry weight, on the basis of the total weight
of the solids in the slurry. Then, 505 g of slaked lime (Supercalco® 97, Carmeuse) are
introduced into the container under agitation.
A mixer of the IKA® Magic Lab type, adjusted to produce a shearing of 82,000 s-1 is then
supplied with the mixture obtained in the previous step. A recirculating loop allows several
passages through the gap formed by the rotor and the stator of the IKA mixer.
Once it is sheared, the slurry is stored for an evaluation of its parameters of viscosity,
sedimentation and stability at 1 month.
The polymers used in this example have the following characteristics:
Test 3-1: according to the invention
The copolymer has the following composition (in % by weight relative to the total weight of
the copolymer):
- 7.44% methacrylic acid monomers,
- 92.56% monomers of formula (I): R – X – R’ in which R represents a methacrylate group,
R’ designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15
units of propylene oxide PO, arranged randomly.
Molecular mass: 110,000 – 150,000 g/mol.
Partial NaOH neutralization; Ph: 3-4.5.
Test 3-2: according to the invention
The copolymer has the following composition (in % by weight relative to the total weight of
the copolymer):
- 19.8% methacrylic acid monomers,
- 3% acrylic acid monomers, and
30
- 77.2% monomers of formula (I): R – X – R’ in which R represents a methacrylate group, R’
designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units
of propylene oxide PO, arranged randomly.
Molecular mass: 34,000 – 44,000 g/mol.
Total NaOH neutralization; Ph: 7.7.
The results of sedimentation and of the different measurements of viscosity are presented in
table 3 below:
viscosity viscosity viscosity viscosity viscosity viscosity
Tests sedimentation aftag aftag befag befag aftag aftag
T0
T0 T0 T0+1m T0+1m T0+1m T0+1m
10 RPM 100 RPM 10 RPM 100 RPM 10 RPM 100 RPM
3-1 50.4%
lime
0% 980 393 4900 1980 1930 687
50.56%
3-2 lime 0% 530 261 13600 3048 3300 839
Table 3
Aftag: after agitation
Befag: before agitation
The results demonstrate that it is possible, according to the process of the present invention,
and using water-soluble copolymers with a particular structure, to prepare high concentration
slaked lime slurries that remain stable over time.
EXAMPLE 4
This example demonstrates the use of two polymers according to the invention in a process
for the preparation of an aqueous slurry of calcium hydroxide starting with two different
types of slaked lime, namely, a lime with an average particle diameter between 4 and 5 μm
(Supercalco® 97, Carmeuse), and a lime with an average particle diameter between 2 and 3
μm (Supercalco® 97/20, Carmeuse).
31
Several aqueous slurries of calcium hydroxide, each having a 48±1% solids content, are
prepared in this example. 503 g of water are introduced into a container together with a
quantity of a polymer corresponding to 1.41% by dry weight (on the basis of the total weight
of the solids in the slurry). Then, 485 g of slaked lime, specifically,
Supercalco® 97 (Carmeuse) in tests 4-1 and 4-3, or Supercalco® 97/20 (Carmeuse) in tests
4-2 and 4-4, are introduced into the container under agitation.
A mixer of the IKA® Magic Lab type, adjusted to produce a shearing of 82,000 s-1 is then
supplied with the mixture obtained in the previous step.
A recirculating loop allows several passages through the gap formed by the rotor and the
stator of the IKA mixer.
Once it is sheared, the slurry is stored for an evaluation of its parameters of viscosities,
sedimentation and stability at 1 month.
The polymers used in this example have the following characteristics:
Tests 4-1 and 4-2: according to the invention
The copolymer has the following composition (in % by weight relative to the total weight of
the copolymer):
- 7.44% methacrylic acid monomers,
- 92.56% monomers of formula (I): R – X – R’ in which R represents a methacrylate group,
R’ designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15
units of propylene oxide PO, arranged randomly.
Molecular mass: 110,000 – 150,000 g/mol.
Partial NaOH neutralization; Ph: 3-4.5.
Tests 4-3 and 4-4: according to the invention
The copolymer has the following composition (in % by weight relative to the total weight of
the copolymer):
- 19.8% methacrylic acid monomers,
- 3% acrylic acid monomers, and
- 77.2% monomers of formula (I): R – X – R’ in which R represents a methacrylate group, R’
designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units
of propylene oxide PO, arranged randomly.
32
Molecular mass: 34,000 – 44,000 g/mol.
Total NaOH neutralization; Ph: 7.7.
The results of sedimentation and of the different measurements of viscosity are presented in
table 4 below:
Tests Sedimentation
T0
Viscosity
AFTAG T0
10 RPM
Viscosity
AFTAG T0
100 RPM
4-1 INV 0% 300 159
4-2 INV 0% 280 203
4-3 INV 0 250 152
4-4 INV 0% 190 126
Table 4
Aftag: after agitation
Befag: before agitation
The results demonstrate that it is possible, according to the method of the present invention,
by using water-soluble copolymers with a particular structure, to prepare high concentration
slaked lime slurries that remain stable over time, regardless of the starting particle size
distribution of the slaked lime.
EXAMPLE 5
The purpose of this example is to illustrate the levels of organic carbon (TOC or Total
Organic Carbon) present in the aqueous phase of lime slurries dispersed with the polymer of
the prior art or with the polymers of the invention, and thus determine the concentrations of
free polymer in the aqueous phase.
This example helps to illustrate the levels of soluble Ca2+ ions present in the aqueous phase
of lime slurries dispersed with polymers of the prior art or with polymers of the invention.
33
Process for the preparation of slurries
Several aqueous slurries of calcium hydroxide, each having a 48±1% solids content, are
prepared in this example. 503 g of water are introduced into a container together with a
quantity of a polymer corresponding to 1.41% by dry weight (on the basis of the total weight
of the solids in the slurry), the said polymer being according to the prior art or according to
the present invention. Then, 485 g of slaked lime (Supercalco® 97, Carmeuse) are introduced
into the container under agitation.
A mixer of the IKA® Magic Lab type, adjusted to produce a shearing of 82,000 s-1 is then
supplied with the mixture obtained in the previous step. A recirculating loop allows several
passages through the gap formed by the rotor and the stator of the IKA mixer.
Test 5-1
The copolymer has the following composition (in % by weight relative to the total weight of
the copolymer):
- 7.44% methacrylic acid monomers,
- 92.56% monomers of formula (I): R – X – R’ in which R represents a methacrylate group,
R’ designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15
units of propylene oxide PO, arranged randomly.
Molecular mass: 110,000 – 150,000 g/mol.
Partial NaOH neutralization; Ph: 3-4.5.
Test 5-2
The copolymer has the following composition (in % by weight relative to the total weight of
the copolymer):
- 12.8% acrylic acid monomers,
- 87.2% monomers of formula (I): R – X – R’ in which R represents a methacrylate group, R’
designates hydrogen, X represents a structure with 46 units of ethylene oxide EO and 15 units
of propylene oxide PO, arranged randomly.
Molecular mass: 38,000 – 52,000 g/mol.
Partial NaOH neutralization; Ph: 3-4.5.
This copolymer, not having methacrylic acid monomers, is a copolymer outside of the
invention.
34
Test 5-3
The polymer used is a homopolymer outside of the invention available commercially under
the name Rheosperse® 3010, Coatex, France, and composed of acrylic acid monomers, 100%
neutralized with sodium hydroxide (molecular weight:
4,000 g/mol).
The slurries obtained are filtered.
A sample of the filtrate is taken and analysed according to the methods described below.
Measurement of TOC:
The TOC (Total Organic Carbon) is measured using a Shimadzu TOC-V CSH by means of a
method based on a catalytic oxidation by combustion method at 680°C.
The carbon atoms of the samples are oxidized into CO2. The gas eluent pushes the CO2 into a
system that enables the removal of H2O molecules and halogenated compounds. An IR
detector measures the CO2 concentration. A calibration curve is used to determine the carbon
concentration in the sample.
Assay of ions:
The ion content is evaluated by means of ion chromatography using Metrohm 761 Compact
IC type equipment. Separation of ions and polar molecules is based on their charge.
The results of TOC and free Ca2+ ion concentration measurements are given in table 5 below:
Tests Ca2+ ppm TOC ppm polymer concentration ppm
5-1 INV 1064 1640 396
5-2 OI 995 3900 856
5-3 PA 291 100 17
Table 5
It is observed firstly that the levels of free Ca2+ ions vary significantly depending on the
nature of the polymer used. This free Ca2+ ion content in a lime slurry dispersed with an
acrylic acid homopolymer (test 5-3) is low compared to that of an aqueous slurry of lime
35
dispersed with a copolymer with a (meth)acrylic acid skeleton and poly(alkyleneglycol) side
chains (tests 5-1 and 5-2).
In addition, although the starting quantities of polymer (1.41% by dry weight) are identical
for each of the slurries, it is noted that the concentrations of polymer in the filtrate of each
slurry vary significantly depending on the polymer used. When the polymer used is an acrylic
acid homopolymer, the concentration of soluble polymer in the aqueous phase is almost zero.
In addition, there is less free copolymer in the lime slurry filtrate when using a copolymer
according to the invention. Without being bound to any theory, one can think that the
particular structure of the copolymer according to the invention is adapted to the chemical
nature of lime, which improves the chemical interactions between the copolymer and the
particles of Ca(OH)2. There is less free copolymer in the lime slurries prepared according to
the process of the invention by using a copolymer with a particular structure, because a
greater quantity of it is adsorbed on the surface of the slaked lime particles. It is thus shown
that submitting a concentrated aqueous lime slurry to a shearing operation under specific
conditions in the presence of a copolymer according to the invention produces a
concentrated, stable lime slurry which is novel compared to lime slurries of the prior art by
virtue of the specific chemical interactions between the copolymers and lime particles.
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WE CLAIM:
1. Method for the preparation of an aqueous slurry of calcium hydroxide with a dry
content of at least 40% by weight, the viscosity of the said aqueous slurry measured
by a Brookfield DVIII viscometer at 10 RPM being between 25 and
1,000 mPa.s at 20°C, including the steps consisting of:
a) the availability of a specific volume of an aqueous solution,
b) the availability of a specific quantity of powdered calcium hydroxide,
c) the availability of a specific quantity of a copolymer consisting:
- of methacrylic acid monomers and/or any of its salts,
- possibly of acrylic acid monomers and/or any of its salts,
- monomers with the formula (I):
R – X – R’
(I)
according to which:
R represents a polymerisable unsaturated group, notably acrylate, methacrylate,
methacrylurethane, vinyl or allyl,
R’ represents hydrogen or an alkyl group with from 1 to 4 carbon atoms,
X represents a structure with n unit(s) of ethylene oxide EO and m unit(s) of
propylene oxide PO, arranged randomly or regularly,
m and n are 2 non-zero integers and are between 1 and 150,
d) to at least a part of said aqueous solution, at least a part of the quantity of the said
copolymer is added under agitation,
e) to the aqueous solution of step d), at least a part of the said quantity of the said
calcium hydroxide is added under agitation,
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f) a homogeneous shearing level greater than 50,000 s-1 is applied to the mixture
resulting from step e),
g) possibly, in the course of step f), the remaining quantity of the said copolymer
and/or of the said calcium hydroxide is added.
2. Method according to claim 1, according to which the copolymer has a molecular mass
between 30,000 and 200,000 g/mol as determined by Gel Permeation
Chromatography (GPC).
3. Method according to any of the previous claims, according to which the said
monomer of formula (I) is such that n and m are two non-zero integers, and n+m > 17.
4. Method according to any of the previous claims, according to which the R group of
the said monomer of formula (I) represents the methacrylate group.
5. Method according to any of the previous claims, according to which the R' group of
the said monomer of formula (I) represents H or CH3.
6. Method according to any of the previous claims, according to which the said
monomer of formula (I) consists of, expressed as a percentage by weight of each of its
components:
- 5 to 30% by weight of methacrylic acid monomers and/or any of its salts,
- 0 to 10% by weight of acrylic acid monomers and/or any of its salts,
- 70 to 95% by weight of monomers of formula (I).
7. Method according to any of the previous claims, according to which a mixer of the
rotor-stator type is used for step f).
8. Method according to any of the previous claims, according to which the device used
to perform the step f) is equipped with a recirculating loop.
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9. Method according to any of the previous claims, according to which a device
configured to deliver a useful output of at least 1,000 W/m3 is used to carry out step
f).
10. Aqueous slurry of calcium hydroxide with a dry content of at least 40% by weight, the
viscosity of the said aqueous slurry measured by a Brookfield DVIII viscometer at 10
RPM being between 25 and 1,000 mPa.s at 20°C, the said slurry being likely to be
obtained by the method according to any of claims 1 to 9.
11. Use of a slaked lime aqueous slurry according to claim 10 for the treatment of
industrial smoke, including for the desulfurization of smoke, or for the treatment of
domestic wastewater, including drinking, or industrial wastewater.

ABSTRACT
Title: AQUEOUS SUSPENSION OF CALCIUM HYDROXIDE, METHOD FOR THE
PRODUCTION THEREOF, AND USES OF SAME
The present invention concerns a lime-based slurry including a new additive as well as a
method for the preparation of such a slurry. Such slurries are used in particular as chemical
neutralization agents in domestic or industrial processes.