Patent Description:
Oils, such as mineral oils, vegetable oils or synthetic oils prepared for instance by Fischer-Tropsch synthesis, are an important raw material in various industries in a plurality of applications and chemical processes. However, such oils are usually contaminated with a significant amount of waxes, which have to be removed, in order to improve the quality of the oil, such as in order to reduce its setting point. Oil is defined in this connection as a hydrocarbon, mainly as an alkanes including composition, which is liquid at ambient temperature, which has a kinematic viscosity at <NUM> of at most <NUM> cSt and which is highly soluble in methyl ethyl ketone. In contrast thereto, wax is defined in this connection as a hydrocarbon, mainly as an alkanes including composition, which is plastic at ambient temperature, which has a kinematic viscosity at <NUM> of <NUM> cSt or higher and which is not soluble in methyl ethyl ketone when determined in accordance with ASTM D721 or DIN <NUM>.

Several techniques are known for dewaxing crude oil being contaminated with wax. Namely, among others crystallization of the waxes from the oil fraction, selective dissolution of the oil fraction in a solvent, which does not dissolve the wax, and microbiological methods.

Crystallization based dewaxing processes have gained in importance during the last years, because they are suitable to dewax oil quite efficiently and with a quite low energy demand. Such crystallization based dewaxing processes can be roughly divided into two groups, namely into solvent-free crystallization methods and into crystallization methods making use of solvents.

The latter methods making use of solvents are useable for crude oils including all kind of waxes independent from their molecular weight and are typically performed by mixing the crude oil with a sufficiently high volume of solvent, such as methyl ethyl ketone, which dissolves the oil fraction, and by then cooling the mixture in a crystallizer so that the wax fraction crystallizes, which is then separated from the liquid solvent-oil phase. However, these methods are disadvantageous because they require the addition of a high volume of solvent, which has to be removed afterwards from the oil fraction, which makes the whole method energetically expensive and necessitates a complex plant.

In contrast thereto, the crude mixture is crystallized without addition of a solvent in the solvent-free crystallization methods. Such a process is for example described in <CIT>. However, such processes are only suitable for oils including exclusively waxes having a comparable short carbon chain length, so that it cannot be used for fractionating crude oil including waxes having a comparable long carbon chain length.

Moreover, a more severe disadvantage is that all these processes only achieve a comparable low yield.

<CIT> discloses a method for dewaxing hydrocarbon oils, in which waxy oil is combined with a straight chain paraffin additive and n dewaxing solvent in a mixer, whereafter the so obtained solution is passed to a chiller, in which the solution is cooled to a dewaxing temperature. The chilled mixture containing precipitating waxes is then sent to a filter for separation of wax from dewaxed oil.

<CIT> relates to a method for the purification of (meth)acrylic acid by fractional crystallisation of a liquid mixture using a combination suspension crystallization and falling film crystallisation.

In view of this, the object underlying the present invention is to provide a method for fractionating a crude mixture, which comprises at least one oil and at least one wax, wherein the method is also suitable to fractionate crude oil including waxes having a comparable long carbon chain length to a certain amount, and wherein the method separates the crude mixture - with a high yield - to an oil fraction and to a wax fraction, wherein both fractions have an excellent purity.

In accordance with the present invention, this object is satisfied by providing a method for fractionating a crude mixture comprising at least one oil and at least one wax, which comprises the following steps:.

wherein the crude mixture includes <NUM> to <NUM>% by weight of oil and <NUM> to <NUM>% by weight of wax.

This solution bases on the surprising finding that by combining a solvent based dewaxing step (b) carried out in at least one crystallization stage and downstream thereof an at least essentially solvent-free deoiling step (c) carried out in at least one crystallization stage with the slack wax obtained in the dewaxing step (b), a very pure oil fraction and a very pure wax fraction are obtained in a comparable simple and energy-efficient method in a surprisingly high yield, when at least a part of the soft wax obtained in the deoiling step (c) is recirculated back into the dewaxing step (b). During the dewaxing step (b), the wax fraction crystallizes and is separated from the liquid solvent-oil mixture, which is then further processed by removing the solvent, e.g. by evaporation, to obtain a very pure oil fraction having an oil content of up to more than <NUM>% by weight as first product. The wax fraction obtained during the dewaxing step (b) often contains significant amounts of solvent, for example, typically <NUM> to <NUM>% by weight of the wax fraction. One skilled in the art will understand that it is generally be preferred to remove this solvent from the wax fraction in order to simplify further processing and minimize any environmental, health and safety issues. The wax fraction is then subjected to the solvent-free or at least essentially solvent-free deoiling step (c), in which a wax-rich, nearly solvent free hard wax fraction crystallizes and is thus obtained as second product. The non-crystallizing and the sweatened out soft wax fraction is at least partially and preferably mostly recirculated into the dewaxing step (b), in order to thus increase the total yield of the process, surprisingly without negatively affecting the quality of the two products. Advantageously, the method in accordance with the present invention requires only comparable low amounts of solvent based on the total amount of produced hard wax. A further particular advantage of this process is that it is in particular suitable to fractionate crude oil including up to <NUM>% by weight of waxes having a comparable long carbon chain length based on the total weight of the waxes. All in all, the method in accordance with the present invention leads in a high yield to an oil fraction and to a wax fraction, wherein both fractions have an excellent purity.

The term slack wax denotes the crude wax fraction obtained after the dewaxing step (b). Slack wax comprising hydrocarbons having a comparable short carbon chain length is denoted as light slack wax and is defined in accordance with the present invention as slack wax having a kinematic viscosity of at most <NUM> cSt. In contrast thereto, slack wax comprising hydrocarbons having a comparable long carbon chain length is denoted as heavy slack wax and is defined in accordance with the present invention as slack wax having a kinematic viscosity of more than <NUM> cSt.

In addition, the term hard wax is defined in accordance with the present invention as wax having an oil content of at most <NUM>% by weight, whereas the term soft wax is defined in accordance with the present invention as wax having an oil content of more than <NUM>% by weight and typically of <NUM> to <NUM>% by weight.

Finally, in accordance with the present invention a solvent-free crystallization step is one, in which no solvent is added to the mixture before introducing it into the crystallizer and in which the mixture introduced into the crystallizer does - apart from unavoidable impurities - not contain solvent and in particular not more than <NUM>% by weight of solvent relative to the weight of the mixture. In contrast thereto, in accordance with the present invention an essentially solvent-free crystallization step is one, in which the mixture introduced into the crystallizer includes at most <NUM>% by weight of solvent relative to the weight of the mixture, wherein the included solvent has been either intentionally added to the mixture and/or is contained in the mixture from an earlier process step.

In principle, any crude mixture including at least one oil and at least one wax can be used as starting mixture of the method in accordance with the present invention. Particular good results are in particular obtained, when the crude mixture comprises oil as main ingredient. According to the present invention, the crude mixture includes <NUM> to <NUM>% by weight of oil and <NUM> to <NUM>% by weight of wax, preferably <NUM> to <NUM>% by weight of oil and <NUM> to <NUM>% by weight of wax and most preferably <NUM> to <NUM>% by weight of oil and <NUM> to <NUM>% by weight of wax.

As noted above, the method in accordance with the present invention is particularly suitable for processing crude oil mixtures including exclusively light wax as wax component or a mixture of light wax and up to <NUM>% by weight of heavy wax based on the total weight of waxes included in the crude mixture.

Accordingly, it is preferred that the crude mixture includes, based on the total weight of wax, at least <NUM>% by weight, more preferably at least <NUM>% by weight, even more preferably at least <NUM>% by weight, still more preferably at least <NUM>% by weight and most preferably <NUM>% by weight of light wax having a viscosity at <NUM> of at most <NUM> cSt.

In particular, the method in accordance with the present invention is particularly suitable to fractionate a cut of a waxy oil obtained from a distillation step in a distillation column as crude mixture. Apart from that, all known oils, particularly mineral oils, vegetable oils and synthetic oils prepared for instance by Fischer-Tropsch synthesis, which are contaminated with wax, may be used as crude mixture.

In step (a) of the method in accordance with the present invention, the crude mixture is mixed with a sufficiently high volume of a solvent, which is able to efficiently dissolve the oil component of the crude mixture at the operation temperature of step (a) and in particular also at the temperature, in which the wax component is crystallized in the crystallizer during step (b). Good results are in particular achieved with this regard, when the solvent is selected from the group consisting of methyl ethyl ketone, methyl isobutyl ketone, acetone, benzene, toluene, dichloromethane, dichloroethane, methylene dichloride, methanol, methyl tertiary butyl ether, N-methyl-pyrolidone and mixtures of two or more of the aforementioned solvents.

In a further development of the idea of the present invention, it is proposed to use in step (a) as solvent either a mixture of methyl ethyl ketone and toluene or a mixture of dichloroethane and methylene dichloride. These solvent mixtures particularly efficiently dissolve oil in particular at the temperature, in which the wax component is crystallized in the crystallizer during the later step (b).

Preferably, the crude mixture is mixed in step (a) with <NUM> to <NUM>,<NUM>% by weight, more preferably with <NUM> to <NUM>% by weight and most preferably with <NUM> to <NUM>% by weight of solvent based on the total weight of the crude mixture.

In accordance with a particular preferred embodiment of the present invention, in the method step (b) at least one suspension crystallization stage is carried out. This is due to the fact that suspension crystallization allows to efficiently crystallize wax and to efficiently separate wax crystals from a solvent containing crude oil mixture with oil being the main ingredient.

Preferably, the suspension crystallization stage is performed in a suspension crystallizer comprising two blocks, namely one first block for producing the crystals and comprising at least one scraped surface crystallizer for removing the crystallization heat, and as a second block a separation device, in which the produced crystals are separated from the mother liquor. The second block may comprise a filter, a centrifuge or any other known separation device.

In principle, only one crystallization and preferably suspension crystallization step may be performed in method step (b). However, in order to increase the fractionation efficiency between the wax component and the oil component, it is proposed in a further development of the idea of the present invention, to perform in method step (b) two to five, more preferably two to four and even more preferably two crystallization stages and most preferably two suspension crystallization stages.

If the method step (b) comprises two or more crystallization stages, the at least part of the fourth fraction is preferably circulated into the second crystallization stage.

Preferably, the crystallization stages in method step (b) are carried out so that the first oil fraction obtained after the at least one crystallization stage comprises less than <NUM>% by weight, preferably less than <NUM>% by weight, more preferably less than <NUM>% by weight, even more preferably less than <NUM>% by weight and most preferably less than <NUM>% by weight of wax. The more crystallization stages are performed, the more dewaxed oil can be separated and the lower is the oil concentration in the first wax fraction obtained after the final crystallization stage; however, the higher are the energy costs and the more complex is the required crystallization equipment. Due to this, a good compromise between both tendencies is obtained by performing in method step (b) two suspension crystallization stages. While in the first crystallization stage, depending on the composition of the crude mixture, at least <NUM>% by weight or even at least <NUM>% by weight of the oil in the crude mixture is separated, in the second crystallization stage at least <NUM>% by weight of the remaining oil after the first crystallization stage is separated, so that the oil fraction after the second crystallization stage contains less than <NUM>% by weight of wax and in particular less than <NUM>% by weight of wax.

Moreover, it is preferred that the crystallization stages in method step (b) are carried out so that the second slack wax fraction obtained after the at least one crystallization stage comprises less than <NUM>% by weight, preferably less than <NUM>% by weight, more preferably less than <NUM>% by weight and even more preferably less than <NUM>% by weight of oil. The more crystallization stages are performed, the lower is the oil concentration in the second slack wax fraction obtained after the final crystallization stage; however, the higher are the energy costs and the more complex is the required crystallization equipment. Due to this, a good compromise between both tendencies is obtained by performing in method step (b) two suspension crystallization stages.

After the method step (b), the obtained oil-solvent mixture is further processed so as to remove the solvent. The solvent removal may be effected by any technique known to a person skilled in the art, such as by evaporation, to obtain a pure oil fraction as first product of the method. The final oil fraction has preferably an oil concentration of at least <NUM>% by weight and more preferably of more than <NUM>% by weight.

As set out above, the method in accordance with the present invention is particularly suitable for processing crude mixtures including exclusively light wax as wax component. However, it may be also used for processing a crude mixture including, based on the total weight of the wax included in the crude mixture, <NUM>% by weight of a light wax having a viscosity at <NUM> of at most <NUM> cSt and up to <NUM>% by weight of a heavy wax having a viscosity at <NUM> of more than <NUM> cSt. If, as preferred, the crude mixture exclusively includes light wax as wax component, the deoiling step (c) is preferably preformed solvent-free, i.e. without adding any solvent to the slack wax obtained in step (b). However, if the crude mixture comprises a mixture of light wax and heavy wax, depending on the precise formulation of the slack wax a small amount of a solvent may be added to the slack wax, in order to improve the efficiency of the deoiling step (c). However, if solvent is added, the solvent is added in an amount that the solvent content of the slack wax mixture introduced into the crystallization stage of step (c) is, relative to the weight of the second fraction, at most <NUM>% by weight, preferably at most <NUM>% by weight, more preferably at most <NUM>% by weight and even more preferably at most <NUM>% by weight. If a solvent is added, the solvent is preferably selected from the group consisting of methyl ethyl ketone, methyl isobutyl ketone, acetone, benzene, toluene, dichloromethane, dichloroethane, methylene dichloride, methanol, methyl tertiary butyl ether, N-methyl-pyrolidone and arbitrary mixtures of two or more of the aforementioned solvents.

However, as set out above, most preferably no solvent at all is added to the second slack wax fraction obtained in step (b) prior to the crystallization in step (c).

Optional, if necessary the slack wax fraction may be heated to a temperature above <NUM>, preferably to a temperature between <NUM> and <NUM> before introducing it to the first of the at least one crystallization step (c), in order to melt the wax crystals.

In accordance with a particular preferred embodiment of the present invention, in the method step (c) at least one static crystallization stage is carried out. This is due to the fact that static crystallization allows to efficiently crystallize hard wax and to efficiently separate hard wax crystals from the oil containing soft wax fraction. In contrast to for example dynamic crystallization, static crystallization is suitable for crystallizing comparable highly viscous liquids, such as solvent-free slack wax mixtures. Furthermore, static crystallization has the advantage of high flexibility, of wide operating range, of easy operation since there is no crystal slurry handling and no filtration, of high reliability and of low operation costs due to the lack of moving parts. In a static crystallizer, the crystallizer is filled with mother liquid, which contacts cooled crystallization plates, which hang in vertical direction in the crystallizer. An essential feature of static crystallization is that the mother liquid is not stirred or otherwise agitated during the crystallization.

In order to improve the separation effect and its efficiency, after the static crystallization stage, when the mother liquid is removed from the static crystallizer, the crystal layers deposited on the cooled plates may be further purified by sweating, i.e. by partially melting the crystals by gently heating the crystals close to their melting point. This effects that impurities trapped in and adhered to the crystal layers will be removed from the crystals.

In principle, only one layer crystallization and preferably static crystallization step may be performed in method step (c). However, in order to increase the fractionation effect and its efficiency between the oil-free hard wax component and the oil containing soft wax component, it is proposed in a further development of the idea of the present invention, to perform in method step (c) two to five, more preferably two to four and even more preferably three layer crystallization stages, preferably static crystallization stages, and most preferably three static crystallization stages.

Preferably, the crystallization stages in method step (c) are carried out so that the third hard wax fraction obtained after the last crystallization stage comprises less than <NUM>% by weight, preferably less than <NUM>% by weight, more preferably less than <NUM>% by weight and most preferably less than <NUM>% by weight of oil. The more crystallization stages are performed, the lower is the oil concentration in the third hard wax fraction obtained after the final crystallization stage and/or the higher the yield of hard wax in method step (c); however, the higher are the energy costs and the more complex is the required crystallization equipment. Due to this, a good compromise between both tendencies is obtained by performing in method step (c) three static crystallization stages. While in the first crystallization stage, depending on the composition of the crude mixture, at least <NUM>% by weight of the included oil are separated, in the second crystallization stage at least <NUM>% by weight of the remaining oil are separated, so that the hard wax fraction after the second crystallization stage contains less than <NUM>% by weight of wax, in particular less than <NUM>% by weight of oil or even less than <NUM>% by weight of oil. In contrast thereto, the fourth soft wax fraction contains more than <NUM>% by weight, typically more than <NUM>% by weight, even more typically more than <NUM>% by weight and in particular <NUM> to <NUM>% by weight of oil.

An essential feature of the method in accordance with the present invention is that in method step (d) at least a part of the fourth soft wax fraction is circulated back to the dewaxing step (b), in order to increase the yield of the process, surprisingly without negatively affecting the purity of the both obtained products, namely of the dewaxed oil fraction and of the hard wax fraction. Good results are in particular obtained with this regard, when in step (d) <NUM> to <NUM>%, more preferably <NUM> to <NUM>% and most preferably <NUM> to <NUM>% of the fourth soft wax fraction are circulated into the at least one (dewaxing) crystallization stage of step (b).

The aforementioned method may be performed in a plant for fractionating a crude mixture comprising at least one oil and at least one wax, wherein the plant comprises:.

wherein the first crystallization section comprises a line for feeding solvent into the at least one suspension crystallizer.

Preferably, the circulation line connects the outlet of the at least one layer crystallizer iii) directly, i.e. without any further device there between, with the inlet of the at least one suspension crystallizer ii).

In typical embodiments of the plant, the source of the crude mixture is a storage or buffer tank or tanks, preferably filled with the crude mixture to be fractionated. In several preferred embodiments of the plant, the tank(s) are in fluid connection with one or more oil or wax processing units, such as extraction and/or distillation units.

In one specific embodiment, the oil or wax processing unit is part of a petrochemical refinery. In other less preferred embodiments of the plant, the tank(s) are in indirect fluid communication with the oil or wax processing units by means of intermediate transport vessels such as a tanker or railway or truck tank.

In accordance with a particular preferred embodiment of the present invention, the first crystallization section ii) of the plant comprises two to five suspension crystallizers.

Moreover, it is preferred that the second crystallization section iii) of the plant comprises one to thirty, preferably two to ten and more preferably two to five layer crystallizers, preferably static crystallizers.

If required, the second crystallization section of the plant may comprise a line for feeding solvent into the at least one layer crystallizer.

Specific embodiments in accordance with the present invention are now described with reference to the appended drawings and by an example.

<FIG> shows a plant <NUM> for conducting the method for fractionating a crude mixture comprising at least one oil and at least one wax in accordance with an embodiment of the present invention. The plant <NUM> includes a first crystallization section <NUM> comprising two suspension crystallizers <NUM>, <NUM>', which are in fluid communication with each other via line <NUM>. While the first suspension crystallizer <NUM> comprises a slack wax removal line <NUM>, the second suspension crystallizer <NUM>' comprises a slack wax removal line <NUM>.

Downstream of both suspension crystallizers <NUM> and <NUM>', an evaporator <NUM> is arranged, which is connected with the suspension crystallizers <NUM> and <NUM>' via lines <NUM> and <NUM>'. The evaporator <NUM> comprises a solvent removal line <NUM> as well as an oil product removal line <NUM>.

The inlet of the first suspension crystallizer <NUM> is in fluid communication with a feed line <NUM>, which is in fluid communication with an inlet line for crude mixture <NUM> and an inlet line for solvent <NUM>.

The inlet of the second suspension crystallizer <NUM>' is in fluid communication with the slack wax removal line <NUM>, which is in fluid communication with an inlet line for crude mixture <NUM>', an inlet line for solvent <NUM>' and the circulation line <NUM>.

It is noted that the crude feed inlet line <NUM>' and the below described slack wax inlet line <NUM> are optional, and it is preferable, if possible to feed streams having higher wax content and lower oil content to crystallizer located progressively downstream in the plant.

Downstream of the second suspension crystallizer <NUM>', a second evaporator <NUM>' is arranged, which is connected with the suspension crystallizer <NUM>' via the slack wax removal line <NUM>. The evaporator <NUM>' comprises a solvent removal line <NUM>' as well as a slack wax removal line <NUM>.

Moreover, the plant <NUM> comprises a second crystallization section <NUM> comprising three layer crystallizers, preferably static crystallizers <NUM>, <NUM>', <NUM>" which are in fluid communication with each other via lines <NUM> and <NUM>' for deoiled wax and via lines <NUM> and <NUM>' for soft wax. The first static crystallizer <NUM> comprises a deoiled wax removal line <NUM> leading to third crystallizer <NUM>" and a soft wax removal line <NUM> leading to the second crystallizer <NUM>'. The second static crystallizer <NUM>' comprises a deoiled wax removal line <NUM>', which leads to the first crystallizer <NUM> and a soft wax outlet line <NUM>. The third crystallizer <NUM>" comprises a hard wax removal line <NUM>" and a soft wax removal line <NUM>' leading to the first crystallizer <NUM>.

The hard wax removal line <NUM>" from the third crystallizer <NUM>" leads to a third evaporator <NUM>". The third evaporator <NUM>" comprises a solvent removal line <NUM>" as well as a hard wax removal line <NUM>.

In the case of solvent free deoiling (embodiment not shown in the figure), the line <NUM>" and the third evaporator <NUM>" are not necessary, and instead the hard wax would be directly removed from the third crystallizer <NUM>" in that embodiment by means of line <NUM>.

The soft wax outlet line <NUM> of the second static crystallizer <NUM> splits into a soft wax removal line <NUM> and the circulation line <NUM>, which leads into the slack wax removal line <NUM>.

In operation, a crude mixture comprising at least one oil and at least one wax, as well as solvent are fed through line <NUM> into the first suspension crystallizer <NUM>. While a solvent-wax rich fraction crystallizes on the scraped cooled surface of the first suspension crystallizer <NUM>, the solvent-oil rich fraction not crystallizing is withdrawn from the first suspension crystallizer <NUM> via line <NUM> and is fed into the evaporator <NUM>. The solvent-wax rich fraction including all crystallized wax from the first suspension crystallizer <NUM> is separated from solvent-oil fraction, is at least partially molten and is fed into slack wax removal line <NUM>.

The at least partially molten solvent-wax rich fraction from crystallizer <NUM> via slack wax removal line <NUM>, solvent via line <NUM>', crude mixture via line <NUM>' and the part of soft wax fraction recirculated via line <NUM> are all fed together into the second suspension crystallizer <NUM>'. Again, a solvent-wax rich fraction crystallizes on the scraped cooled surface of the second suspension crystallizer <NUM>', whereas the solvent-oil rich fraction not crystallizing is withdrawn from the second suspension crystallizer <NUM>' and is introduced into the evaporator <NUM> via line <NUM>'. In the evaporator <NUM>, the mixture is heated so as to evaporate the solvent included in the solvent-oil fraction, wherein via the solvent removal line <NUM> separated solvent is drawn off and the purified oil fraction with an oil content of more than <NUM>% by weight is drawn off via the oil product removal line <NUM>.

The solvent-wax rich fraction from the second suspension crystallizer <NUM>' including all crystallized wax is separated from solvent-oil fraction, at least partially molten and fed into the slack wax removal line <NUM> and introduced into the evaporator <NUM>'. In the evaporator <NUM>', the mixture is heated so as to evaporate the solvent included in the solvent-wax rich fraction, wherein via the solvent removal line <NUM>' separated solvent is drawn off and the pre-purified wax fraction, now called slack wax, is drawn off via line <NUM> to the second crystallization section <NUM>.

Optionally, a further solvent inlet line <NUM> leading to line <NUM> is provided and allows to add solvent to the slack wax rich fraction led to the first layer crystallizer <NUM>, preferably static crystallizer <NUM> of the second crystallization section <NUM>. Furthermore, optionally a further slack wax inlet line <NUM> leading to line <NUM> is provided and allows to add slack wax having a reasonable less oil content than the crude mixture streams added via lines <NUM> and / or <NUM>' before, to the slack wax rich fraction led to the first layer crystallizer, preferably static crystallizer <NUM> of the second crystallization section <NUM>. In the first static crystallizer <NUM>, oil-free or at least essentially oil-free hard wax crystallizes, whereas oil-rich soft wax remains liquid or becomes liquid by sweating the crystallized fraction.

The oil-rich soft wax is drawn off from the first static crystallizer <NUM> and conducted into the second static crystallizer <NUM>' via line <NUM>. At least essentially oil-free hard wax crystallizes in the second static crystallizer <NUM>', whereas oil-rich soft wax remains liquid or becomes liquid by sweating and is drawn off from the second static crystallizer <NUM>' via the soft wax outlet line <NUM>. While a part of the soft wax fraction is removed from the plant via line <NUM>, the remaining part of the soft wax fraction is recirculated into the second suspension crystallizer <NUM>' via circulation line <NUM>.

The crystallized hard wax fraction in the first static crystallizer <NUM> is heated up, molten and fed via line <NUM> to the third static crystallizer <NUM>". The crystallized hard wax fraction in the second static crystallizer <NUM>' is heated up, molten and fed via line <NUM>' and <NUM>' to the first static crystallizer <NUM>.

In case solvent has been added to the slack wax in line <NUM>' via line <NUM>, the remolten hard wax-solvent mixture from third static crystallizer <NUM>" is fed via line <NUM>" into the evaporator <NUM>". In the evaporator <NUM>", the mixture is heated so as to evaporate the solvent from the hard wax, whereas via the solvent removal line <NUM>" separated solvent is drawn off and the deoiled hard wax fraction is drawn off from the plant via line <NUM>.

In case no solvent has been added to the slack wax in line <NUM>' via line <NUM> (embodiment not shown), the molten hard wax from the third static crystallizer <NUM>" is drawn off from the plant via line <NUM>.

Subsequently, the present invention is illustrated by means of an example, which, however, does not delimit the present invention.

Unless stated otherwise, all parts and percentages are by weight.

Three different soft wax samples originating from a solvent-free crystallization stage and having an oil content of more than <NUM>% by weight were processed in a plant as shown in <FIG>. More specifically, the three different soft wax samples were mixed with a mixture of methylethylketone and toluene as solvent and circulated into a suspension crystallization stage to prepare a first fraction containing dewaxed oil and a second fraction containing slack wax. The slack waxes obtained had a <NUM> to <NUM> times lower oil content than the soft wax, as shown in the following table.

Claim 1:
A method for fractionating a crude mixture comprising at least one oil and at least one wax, which comprises the following steps:
(a) mixing the crude mixture with a solvent to obtain a crude solvent-mixture,
(b) carrying out at least one crystallization stage with the solvent-mixture obtained in step (a) to prepare a first fraction containing dewaxed oil and a second fraction containing slack wax,
(c) carrying out at least one crystallization stage with the second fraction obtained in step (b) in a layer crystallizer, wherein to the second fraction prior to the crystallization in step (c) no solvent or at most <NUM>% by weight of solvent relative to the weight of the second fraction are added, to prepare a third fraction containing hard wax having an oil content of at most <NUM>% by weight and a fourth fraction containing soft wax having an oil content of more than <NUM>% by weight and
(d) circulating at least a part of the fourth fraction into at least one of the at least one crystallization stage of step (b),
wherein the crude mixture includes <NUM> to <NUM>% by weight of oil and <NUM> to <NUM>% by weight of wax.