Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2000-12-19
2002-10-15
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S651000, C210S490000, C210S500250
Reexamination Certificate
active
06464881
ABSTRACT:
The present invention relates to an inorganic nanofiltration membrane which can be used especially in the sugar industry, in particular in the refining of cane sugar.
Membranes have been known for many years for their separation properties and are rapidly expanding with respect to conventional separative techniques in many fields of activity, in particular the farm-produce industry, biotechnology, the chemical, pharmaceutical and nuclear industries and the environment, in particular the treatment of drinking water and industrial effluents.
This transfer in technology towards membrane separative techniques has appeared in a rather marked way in the fields of tangential microfiltration (mean diameter of the pores of the membrane of between 0.1 and 5 &mgr;m) and of tangential ultrafiltration (mean diameter of the pores of the membrane of between 2 and 150 nm).
In tangential filtration techniques, the fluid to be treated moves parallel to the membrane.
The first membranes used were organic membranes which, in the fields of microfiltration and of ultrafiltration, are increasingly being replaced by inorganic membranes; the latter generally exhibit better mechanical strength and better chemical, biological and thermal stability.
Nanofiltration membranes which most often operate under tangential flow (mean diameter of the pores of the membrane of between 0.5 and 2 nm, generally of the order of 1 nm), in particular for the separation of organic compounds and of multivalent ions contained in water or effluents, have recently been developed. However, these membranes are still organic or mixed organic/inorganic membranes, the mechanical strength and the chemical, biological and thermal inertia of which are not as satisfactory as those which would be desired, which may not always operate efficiently under extreme conditions of use (pH, temperature, pressure, and the like).
In the same way, the use is known in the process for refining cane sugar of an operation for the purification of the sugar, in general in two stages, in order to decolour it and to remove certain organic impurities, such as polysaccharides.
The colouring is mainly due to the decomposition of glucose and fructose at temperatures not greatly exceeding 100° C.
The first purification stage (or decolouring stage), which most often comprises a carbonatation or a phosphatation, is often followed by a second purification stage (or decolouring stage) in which the sugar liquor passes, generally at a temperature of 80 to 90° C. (in order to reduce its viscosity), into one or a number of ion-exchange resins. The colorants and other impurities contained in the sugar liquor are then adsorbed on the resin (the goal is often for almost 90% of these colorants to thus be removed).
After a certain period of time, it proves necessary to regenerate the laden resin. Desorption of the colorants (and other impurities) is then carried out by using a brine or basic sodium chloride solution (pH generally of the order of 12), at a temperature usually of between 80 and 90° C.
The saline effluent resulting from the regeneration of the ion-exchange resins contains essentially sodium chloride but also organic matter (colorants and other impurities).
The Applicant Company has developed, with the aim in particular of recovering this saline effluent, a new filtration membrane, in this case a specific inorganic nanofiltration membrane.
This membrane, which meets the requirements of thermal and chemical resistance which follow from the conditions of use of a process for refining cane sugar, makes possible efficient separation of the organic matter (colorants and other impurities) from the saline effluent, which is thus regenerated and can subsequently be reused for the desorption of the colorants (and other impurities) adsorbed on the resins.
The use of this membrane thus makes possible efficient recycling of the saline effluent resulting from the regeneration of the ion-exchange resins and thus a significant reduction in the amounts of sodium chloride and of water necessary for the manufacture of the solutions for the regeneration of the resins.
In addition to its thermal and chemical resistance, the membrane according to the invention exhibits very good mechanical strength and thus a very long lifetime of use.
Thus, one of the subjects of the invention is an inorganic nanofiltration membrane containing:
a multichannel monolithic ceramic support composed of a mixture of Al
2
O
3
and of TiO
2
and exhibiting a mean equivalent pore diameter Ds of between 1 and 20 &mgr;m, preferably between 5 and 15 &mgr;m,
a microfiltration membrane separating layer situated at the surface of the channels and composed of sintered particles of metal oxide(s), the mean equivalent pore diameter Do of which before sintering is between 0.1 and 3.0 &mgr;m, according to a Ds/Do ratio such that 0.3<Ds/Do<200, preferably 1<Ds/Do<150, the said microfiltration membrane layer exhibiting a mean equivalent pore diameter Dm of between 0.05 and 1.5 &mgr;m,
an ultrafiltration membrane separating layer situated on the said microfiltration membrane layer and composed of sintered particles of metal oxide(s), the mean equivalent pore diameter Du of which before sintering is between 2 and 100 nm, according to a Dm/Du ratio such that 0.5<Dm/Du<750,
a nanofiltration membrane separating layer situated on the said ultrafiltration membrane layer and composed of sintered particles of metal oxide(s), the mean equivalent pore diameter Dn of which before sintering is between 0.5 and 1.5 nm,
the said inorganic nanofiltration membrane exhibiting a cutoff threshold of between 100 and 2000 daltons.
The monolithic support advantageously exhibits a high porosity, generally greater than 30% and preferably greater than 40% (measured using a mercury porosimeter).
It is preferentially composed of a ceramic of Al
2
O
3
grains coated at least in part with TiO
2
grains, the TiO
2
/(Al
2
O
3
+TiO
2
) ratio by weight being between 1 and 75%, in particular between 20 and 50%, for example between 20 and 40%.
The Al
2
O
3
grains generally exhibit a mean particle size of between 3 and 500 &mgr;m, preferably between 10 and 100 &mgr;m and more preferentially still between 20 and 30 &mgr;m. The TiO
2
grains usually exhibit a mean particle size of between 0.01 and 7 &mgr;m, preferably between 0.1 and 1 &mgr;m.
Generally, the alumina is essentially of corundum type (it being possible for the grains to have a tabular shape) and the titanium oxide is essentially of rutile type.
The monolithic support is preferably prepared by the process described in Patent Application EP-A-0,585,152 (column 3, line 24 to column 4, line 11).
The monolithic support is generally described as macroporous.
This support can exhibit a diameter of between 15 and 30 mm, for example 20 mm, and a length of between 800 and 1300 mm, for example of the order of 860 mm.
The number of channels in the monolithic support is generally between 5 and 52, in particular 7 or 19. Their diameter can in particular lie between 1.5 and 7 mm, in particular between 2.5 and 4.5 mm.
A particularly advantageous support consists of a monolithic support employed in the Kerasep® membranes sold by the Applicant Company.
The metals of the metal oxides forming the various membrane separating layers can be, for example, chosen from beryllium, magnesium, calcium, aluminium, titanium, strontium, yttrium, lanthanum, zirconium, hafnium, thorium, iron, manganese, silicon and their various possible mixtures.
However, the metal oxide(s) of the microfiltration membrane layer is (are) generally alumina, zirconia or, preferably, titanium oxide.
The microfiltration membrane layer is usually deposited on the support by the known process called slip casting, according to which generally a slip of the metal oxide is deposited on the support and then an appropriate sintering is carried out. The sintered membrane layer preferably has a thickness of between 5 and 50 &mgr;m.
The sintering temperature must be compatible with the maximum sintering temperature of the support. T
Fortuna Ana
Orelis
LandOfFree
Inorganic nanofiltration membrane and its application in the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Inorganic nanofiltration membrane and its application in the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Inorganic nanofiltration membrane and its application in the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2995834