Title of Invention

"METHOD FOR FRACTIONAL CRYSTALIZATION OF SUBSTANCES AND A CRYSTALLIZER APPROPRIATE FOR CARRYING OUT THE METHOD"

Abstract A process for a fractional crystallization of substances comprising: filling a mixture of substances into a crystallizer, the crystallizer having vertical or inclined crystallization surfaces, said mixture containing (i) a substance which, when crystallized, does not adhere sufficiently to the vertical or inclined crystallization surfaces of the crystallizer, and (ii) fractions having a lower melting point than said substance, cooling said crystallization surfaces and thus, cooling the mixture and crystallizing said substance in layers on said crystallization surfaces, discharging remaining liquid from the crystallizer, heating said crystallization surfaces and thus sweating said crystallized substance, and characterized in that during said sweating, retaining crystals of the crystallized substance on a screen-like supporting structure disposed between the crystallization surfaces, said crystals due to their weight and their insufficient adhesion to the crystallization surfaces become detached from the crystallization surfaces, while permitting liquid fractions to flow through the screen-like supporting structure.
Full Text The invention relates to a process for the fractional crystallisation of substances which when crystallised have poor adhesion to the vertical or sloping crystallisation surfaces of a crystalliser.
In order to fractionate substances by crystallisation, a melt is cooled on crystallisation surfaces, forming crystals which contain the desired substance. The remaining liquid phase or mother liquor is run off. The crystals arc then heated so as to sweat out and run off fractions having lower melting-points. Crystals having a higher melting-point and high purity are left. The purified crystals are then melted, thus obtaining the substance. It has not hitherto been possible to fractionate substances such as paraffins, oils, fats or waxes by this process, since particularly in the "partial melting" or "sweating" phase, there is insufficient adhesion between the vertical -crystallisation surfaces and the crystallised substances, so that parts of the crystal layer or entire layers become detached and slide off. The sliding-off crystals will then lie on the bottom of the crystalliser and make it difficult or impossible to separate the crystals cleanly from the mother liquor. Even such poorly adhering substances, however, need to be fractionated by modern crystallisation techniques. Fractional crystallisation has the advantage, inter alia, that it can operate without solvents. It ,ig therefore less expensive and less of a danger to the environment or to human health. It is superior to comparable but outmoded techniques such as removing oil from paraffin by sweating, owing to its shorter working
cycles, called "batch times" or "stage times", and since it can be more accurately controlled.
An object of the invention therefore is to provide a process whereby substances which, when crystallised, can easily become detached from the crystallisation surfaces, can be fractionated by crystallisation in a crystalliser without crystals slipping off uncontrollably. The process should be faster than earlier processes and should give a higher yield of the desired fractions.
To this end, according to the invention, during sweating, crystals becoming detached from the crystallisation surfaces are held by a screen-like supporting structure such that crystals sliding down remain suspended in the screen-like supporting structure whereas liquid fractions flow through the screen-like supporting structure.
As a result of the supporting structures, only partial zones of the crystal layer can become detached and these partial zones remain suspended in the screen-like supporting structure. It is thus still possible to separate the liquid from the crystalline phase or fractions, since the layer of crystals does not slide down completely and consequently cannot clog the spaces between the crystallisation surfaces and the outlet for the melt. Since it is now permissible for the crystals to become detached from the crystallisation surfaces, the crystals can be uniformly heated more quickly, thus shortening the entire process. The screen-like supporting structure ensures that liquid fractions can flow away whereas the crystals are retained.
Advantageously the screen-like supporting structure inclines towards the crystallisation surfaces, since owing to the inclination, crystals detaching and resting on the inclined supporting structure are pressed by their own weight against the crystallisation surface and thus remain in thermal contact with the heat-exchanger surface or crystallisation surface.
Advantageously, the layers of crystals are held by the said supporting surfaces of the screen-like supporting structure, which divide the layers approximately horizontally into strips, liquid fractions being able to flow away through openings between the crystallisation surfaces and the supporting surfaces. The crystals can therefore become detached only in strips which are trapped by the supporting surfaces. The surfaces of the strips are horizontal or inclined, cox. responding to the supporting surfaces. The inclination helps sweated-out fractions to f-low away.
Advantageously, when the liquid fractions are sweated out, the crystal layer is heated so that it at. least partly becomes detached from the crystallisation surface and rests on the screen-like supporting structure. By this means the liquid fractions are also expelled by the weight of the crystals. The liquid phase flowu away between the two crystal layers and also between the crystal layer and the heated crystallisation surface.
Advantageously, the mother liquor obtained from the crystallisation process is purified at least once more by fractional crystallisation, by applying the above-
described process steps to the mother liquor. Advantageously also, the resulting purified fractions are additionally fractionated by conventional fractional crystallisation without screen-like supporting structures or by fractional crystallisation in accordance with the above-described process steps using screen-like supporting structures. Frequently the purified fractions, as soon as they reach a certain degree of purity, can be additionally purified in crystal Users without screen-like supporting structures. These purer fractions, if they adhere sufficiently to the crystallisation surfaces, can advantageously be additionally fractionated and purified by conventional fractional crystallisation without a supporting structure. Other less adhesive fractions can be additionally purified by the process according to the invention, using supporting structures in the crystalliser.
The process according to the invention is particularly suitable for purifying paraffins, oils, fats and/or waxes, and other substances having similar physical properties.
The invention also relates to a crystalliser having crystallisation surfaces which can be cooled and heated by a heat transfer medium for fractionating substances which when crystallised have poor adhesion to vertical or inclined crystallisation surfaces.
The crystalliser according to the invention has a screen-like supporting structure, permeable to the liquid phase or liquid fractions, for trapping crystals which become detached from the crystallisation
surfaces. The crystalliser according to the invention
is therefore suitable for working the process according to the invention.
Advantageously, the screen-like supporting structures are inclined to the crystallisation surfaces. As a result of the inclination, the crystals becoming detached remain in thermal contact with the crystallisation surfaces or heat-exchanger surfaces. As a result, the heat transfer is of practically constant and uniform efficiency and the crystallisation process can be better controlled and completed more quickly.
Advantageously, the screen-like supporting structure has inclined surfaces which divide the space between the crystallisation surfaces approximately horizontally. These surfaces divide the crystal layers into strips. As a result, the crystal layer becomes detached from the crystallisation surface only in parts which have a predetermined maximum size. These parts remain suspended in the screen-like supporting structure, thus effectively preventing the spaces between the cystallisation surfaces from being clogged by falling crystals. In addition, the crystals on the surface, owing to their weight, expel liquid fractions. The mother liquor or liquid phase can continue to drip over the crystal portions and between them. The liquid phase can also flow away on the surfaces of the screen-like supporting structure, because, of the inclination of the surfaces.
Advantageously, superposed inclined surfaces of the screen-like supporting structure are inclined in
opposite directions. By this means, the crystals are uniformly assigned to both neighbouring crystallisation surfaces.
Advantageously a screen-like supporting structure of this kind is in thermal contact with the crystallisation surfaces, so that, particularly in the melting phase, there is optimum heat transfer from the crystallisation surfaces to the crystals becoming detached from the crystallisation surfaces and lying on the screen-like supporting structure.
Advantageously, the screen-like supporting structure is assembled in units which ran be installed between pairs of crystallisation surfaces. The structure is therefore easy to produce and install.
Preferably, the screen-like supporting structure is in the form of a metal element bent in a number of zigzags. Metal has the necessary thermal conductivity and is advantageously easy to work. The zigzaq shape can easily be produced by bending the element and has the preferred properties described hereinbefore. The metal element can be a bent perforated sheet. when the perforated sheet is bent, care should be taken that the edge extends across openings or perforations in the metal, so that when installed there are spaced-apart openings at the lowest point of the inclined supporting surface between the edge of the perforated sheet and the crystallisation surface, so that the liquid fractions can run out through the openings. Alternatively, the metal external fittings can be a rod lattice or a network or the like. Perforated sheets with a wide variety of perforations are available
commercially. Advantageously, the perforations are in an interlocking pattern such that in every possible arrangement of the fold line the fold line extends through openings in the screen-like supporting structvire.
In addition to the preferred embodiments described, the screen-like supporting structures can have a wide variety of forms, such as sponge-like or felt-like structures spaced lattices, fabrics, networks, expanded metal, brushes, Raschig rings or similar fillers. The supporting structures can also be made of various materials other than metal, e.g. ceramics, plastic, glass, carbon and/or textile fibres of animal or vegetable origin.
Advantageously, the crystallisation surfaces themselves can be inclined, thus as before maintaining contact between detaching crystals and the heat-exchanger surface and enabling the sweated-out fractions to flow away easily.
If it is desired to use only one crystalliser for the process according to the invention, the screen-like supporting structure can advantageously be formed by the crystallisation surfaces. As a result, the heat-transfer between the heat transfer medium and the screen-like supporting structure and thus to the melt or crystals Is better than if the crystallisation surfaces and the screen-like supporting structure are two independent parts.
The crystalliser according to the invention can be a falling-film crystalliser or a static crystalliser.
Static crystallisation is preferred for fractionating substances which when crystallised have poor adhesion to the crystallisation surfaces, more particularly for removing oil from paraffin.
The invention also relates to an arrangement of a number of crystallisers for multi-stage fractionation of substances which when crystallised can easily become detached from the vertical or inclined crystallisation surfaces of a crystalliser.
The arrangement of crystallisers according to the invention comprises at least one crystalliser having screen-like supporting structures. By this means, substances which in purified crystal form have sufficient adhesion for fractionation in conventional crystallisers can be purified in at least a first step in a crystalliser having the supporting structures according to the invention.
In particular, paraffins, fats, waxes, oils and other substances having similar physical properties can be fractionated or purified by the method described, the crystalliser described and the arrangement of crystallisers described.
Accordingly, there is provided a process for a fractional
crystallization of substances as herein described(comprising:
filling a mixture of substances into a crystallizer, the
crystallizer having vertical or inclined crystallization
surfaces, said mixture containing (i) a substance which, when
crystallized, does not adhere sufficiently to the vertical or
inclined crystallization surfaces of the crystallizer, and
(ii) fractions having a lower melting point than said
substance,
cooling said crystallization surfaces and thus, cooling the
mixture and crystallizing said substance in layers on said
crystallization surfaces,
discharging remaining liquid from the crystallizer,
heating said crystallization surfaces and thus sweating said
crystallized substance, and characterized in that
during said sweating, retaining crystals of the crystallized
substance on a screen-like supporting structure disposed
between the crystallization surfaces, said crystals due to
their weight and their insufficient adhesion to the
crystallization surfaces become detached from the
crystallization surfaces, while
permitting liquid fractions to flow through the screen-like
supporting structure.
Accordingly, there is also provided a crystallizer for the fractionating crystallization of substances, having substances which, when heated, have poor adhesion to crystallization surfaces of the crystallizer, the crystallizer comprising a plurality of vertical or inclined crystallization surfaces which are coolable or heatable by a heat transfer medium, a screen-like supporting structure disposed between the crystallization surfaces, the screen-like supporting structure
being impermeable to a solid phase, but permeable to a liquid phase, for trapping and suspending crystals between the crystallization surfaces when the crystals become detached from the crystallization surfaces, the screen-like supporting structure permitting a liquid fraction to flow therethrough.
Exemplified embodiments of the invention will not be described with reference to the drawings, in which:
Fig. 1 shows a prior-art crystallizer for static crystallization, in perspective and partly in section;
Fig. 2 is a diagrammatic vertical section through a crystallizer according to the invention;
Fig. 3 is a detail showing the point of contact between the external fittinqs and the crystallisation wall;
Fig. 4 is a top view of the place shown in Fig. 3;
Fig. 5 is a diagrammatic vertical section through a crystalliser according to the invention, rotated through 90° relative to the section in Fig. 2;
Fig. 6 shows a possible structure of the layer of crystals after crystallisation is complete;
Fig. 7 shows the crystal layer of Fiq. 6 during sweating;
Fig. 8 shows another possible structure of the crystal layer after crystallisation, and
Fig. 9 shows the crystal layer of Fig. 8 durinq sweating.
For clarity, corresponding parts of different crystallisers will hereinafter be denoted by the same reference numbers, even when the embodiments of the parts may be different.
As shown in Fig. 1, a crystalliser 11 for static crystallisation comprises a container 13 for holding the melt and containing a number of spaced-apart crystallisation walls 15 which can be cooled and heated. After the melt has been poured in, the crystallisation walls 15 arc completely surrounded by the melt. The crystallisation walls 15 have internal
ducts 17 through which a heat transfer medium can flow and which are connected to a distribution block 19.
A melt is fed through inlets 21 into the container 13, where it crystallises out in fractions on the cooled crystallisation walls 15. The liquid phase which always remains after crystallisation is run out through outlets 25, after which fractions and residues of undesired substances in the crystals are sweated out by heating the crystallisation walls 15 and are likewise run off, after which the crystals purified by this process are finally melted.
A preferred embodiment 27 of the crystalliser according to the invention is shown in simplified form in Figs. 2 and 5. Screen-like supporting structures 29 are disposed belween the crystallisation walls 15 inside the container 13. The supporting structures 29 are made from perforated metal sheets 31 (Figs. 3 and 4). The perforations 33, 35 in the perforated metal sheets 31 enable the liquid phase to flow through the screen-like supporting structures 29. The perforated sheet 29 is folded in a zigzaq, so that neighbouring edges 37 are in contact with opposite crystallisation surfaces 39. The edges 37 are practically horizontal (Fig. 5). One row of perforations 35 is disposed on the edge 31 of the perforated sheet, so that the liquid phase can run out even in the lowest regions of the triangular zones 41.
If, for example, oil is removed from paraffin in the said crystalliser, a layer of crystals 43 forms on the cooled crystallisation surfaces 39 as shown in Figs. 6, 7 or 8, 9. In some cases, depending on the product, an
open space 45 is left between the two crystallisation layers 43, through which the remaining mother liquor, which as a high oi1 content, can be discharged, or the two layers 43 grow together to form a single layer 44, in which case inclusions 46 can form between the layers (Figs. 9 and 10). During the sweating phase the oily fraction is first sweated out through the central surfaces 49 of the crystal layers 43. As soon as the crystal layer 43 has been softened by heating, its adhesion to the crystallisation surface 39 is reduced. Parts 53 of the crystal layer 43 become detached from the crystallisation surface 39 when or before the adhesive surface 49 of the crystal layer 43 has been melted by heating. The parts 53 remain suspended on the perforated sheet 31, which abuts the crystallisation surface 39 at an acute angle. By being detached from the crystallisation surface 39, the sweaf.able surface of the crystal layer 43 is enlarged. The liquid phase 55 can flow out at the central surface 47 and at the surface 49 on the crystallisation surface side. Expulsion of the liquid phase is facilitated by the pressure of the weight of crystals 53. The liquid phase 55 drips between the crystal parts 53. Part of the liquid phase 55 flows away on the crystallisation surfaces 39. The surface 49 of the crystal parts 53 on the crystallisation surface side is melted by the heat supply, so that the liquid phase 55 finds channels or melts freely between the crystallisation surface 39 and the crystal parts 53 and flows away through the openings 35 at the edges 37 of the perforated sheets 31 in contact with the crystallisation surfaces 39. Mother liquor 55 falling on to crystal parts 53 runs over the sloping surface 57 of the part 53 and drips through holes 33, 35 in the perforated sheet 31 into
the next-lowest triangular zone 41.




WE CLAIM;
1. A process for a fractional crystallization of substances as herein described comprising:
filling a mixture of substances into a crystallizer, the crystallizer having vertical or inclined crystallization surfaces, said mixture containing (i) a substance which, when crystallized, does not adhere sufficiently to the vertical or inclined crystallization surfaces of the crystallizer, and (ii) fractions having a lower melting point than said substance,
cooling said crystallization surfaces and thus, cooling the mixture
and crystallizing said substance in layers on said crystallization surfaces,
discharging remaining liquid from the crystallizer,
heating said crystallization surfaces and thus sweating said crystallized substance, and characterized in that
during said sweating, retaining crystals of the crystallized substance on a screen-like supporting structure disposed between the crystallization surfaces, said crystals due to their weight and their insufficient adhesion to the crystallization surfaces become detached from the crystallization surfaces, while
permitting liquid fractions to flow through the screen-like supporting structure.
2. The process as claimed in claim 1, wherein the screen-like
supporting structure is at an angle so as to be inclined to the
crystallization surfaces; and
comprising holding crystals becoming detached on said screen-like supporting structure.
3. The process as claimed in claim 1, dividing the layers substantially
horizontally into strips.
4. The process as claimed in claim 1, wherein during said heating
and sweating the crystals detached from the crystallization surfaces so
that the crystals slide down the crystallization surfaces and then rest on
the screen-like supporting structure.
5. The process as claimed in claim 1, having the steps of purifying the
resultant mother liquor thus obtained at least once by fractional
crystallization, by repeating the steps of claim 1.
6. The process as claimed in claim 1, repeating the steps of claim 1;
and then
fractionating the resulting purified fractions by a fractional crystallization without a screen-like supporting structure, or by a fractionalization.
7. The process as claimed in claim 1, wherein said substances
comprise paraffins, and at least one substance selected from the group
consisting of oils, fats, waxes and other organic products having similar
physical properties.
8. A crystallizer comprising a plurality of vertical or inclined
crystallization surfaces which are coolable or heatable by a heat transfer
medium,
a screen-like supporting structure disposed between the crystallization surfaces, the screen-like supporting structure being impermeable to a solid phase, but permeable to a liquid phase.
9. The crystallizer as claimed in claim 8, wherein the screen-like
supporting structure is positioned at an angle to be inclined to the
crystallization surfaces.
10. The crystallizer as claimed in claim 8, wherein the crystallizer
comprises at least two spaced apart crystallization surfaces; and
the screen-like supporting structure has surfaces which divide the space
between the crystallization surfaces approximately horizontally.
11. The crystallizer as claimed in claim 9, wherein the surfaces of the
screen-like supporting structure have superposed inclined surfaces
which slope in opposite directions.
12. The crystallizer as claimed in claim 8, wherein the screen-like
supporting structure is in thermal contact with the crystallization
surfaces.
13. The crystallizer as claimed in claim 10, wherein the screen-like
supporting structure is assembled in installation units as herein
described which are disposed between pairs of crystallization surfaces.
14. The crystallizer as claimed in claim 13, wherein the installation
unit has a repeated zig-zag shape.
15. The crystallizer as claimed in claim 8, wherein solid parts as herein
described of the screen-like supporting structure form the crystallization
surfaces.
16. The crystallizer as claimed in claim 8, wherein the crystallization
surfaces are inclined.
17. The crystallizer as claimed in claim 8, wherein said screen-like
supporting structure is made of metal sheets, and is in thermal heat
transfer contact with said heat transfer medium.
18. The crystallizer as claimed in claim 8, which is a static crystallizer.
19. The crystallizer as claimed in claim 8, which is a falling-film
crystallizer.
20. A crystalliser as claimed in one of claims 8 to 19 wherein the
crystalliser is arranged together with at least a second crystalliser, the
crystallisers forming an arrangement of crystallisers for multi-stage
fractionation of substances which when crystallized easily become
detached from the vertical or inclined crystallization surfaces of a
crystallizer.
21. A process for a fractional crystallization of substances
substantially as hereinbefore described with reference to and as
illustrated in the accompanying drawings.
22. A crystallizer for the fractionating crystallization of substances substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.



Documents:

1914-del-1998-abstract.pdf

1914-del-1998-claims.pdf

1914-DEL-1998-Correspondence-Others-(17-03-2011).pdf

1914-del-1998-correspondence-others.pdf

1914-del-1998-correspondence-po.pdf

1914-del-1998-description (complete).pdf

1914-del-1998-drawings.pdf

1914-del-1998-form-1.pdf

1914-del-1998-form-13.pdf

1914-del-1998-form-19.pdf

1914-del-1998-form-2.pdf

1914-DEL-1998-Form-27-(17-03-2011).pdf

1914-del-1998-form-3.pdf

1914-del-1998-form-4.pdf

1914-del-1998-gpa.pdf

1914-del-1998-petition-137.pdf

1914-del-1998-petition-138.pdf


Patent Number 216549
Indian Patent Application Number 1914/DEL/1998
PG Journal Number 13/2008
Publication Date 28-Mar-2008
Grant Date 14-Mar-2008
Date of Filing 06-Jul-1998
Name of Patentee SULZER CHEMTECH AG,
Applicant Address HEGIFELDSTRASSE 10, CH-8404 WINTERTHUR, SWITZERLAND.
Inventors:
# Inventor's Name Inventor's Address
1 MANFRED STEPANSKI ERLENGRUND 5, CH-9470 BUCHS, SWITZERLND
2 BERNHARD JOSEPH JEANS AEULISTRASSE 25, CH-9470, BUCHS, SWITZERLAND
PCT International Classification Number B01D 9/02
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA