EP0524534A2 - Process and device for the adsorptive purification of vegetable and/or mineral oils and fats - Google Patents

Abstract

A process for the adsorptive purification of vegetable oils and/or mineral oils and fats operates using a multi-stage counter-current process. At least a part of the solid phase leaving the first separation stage is mixed batchwise or continuously with a part-quantity of the purified oil or fat leaving the last separation stage. The mixture produced as a result is fed to a downstream filter. <IMAGE>

Description

The invention relates to a method for the adsorptive purification of vegetable and / or mineral oils and fats in a multi-stage countercurrent process. The invention further relates to an apparatus for performing this method.

Processes for the adsorptive cleaning of oils and fats have been known for a long time. Examples include the extraction and purification of oils for food production, in particular using bleaching earth or activated carbon. These processes are such that an adsorbent is contacted with the oil to be cleaned. The adsorbent, which has many fine pores, takes up the dye and dirt particles to be extracted from the oil and is removed from the oil after the contacting process, which is thereby cleaned and bleached.

Cleaning is often carried out batchwise or continuously according to the direct current principle, i.e. oil and fresh adsorbent are mixed continuously or discontinuously and then separated again. The separated adsorbent still has free adsorption capacities.

It would be much more effective in itself, the countercurrent principle to use. This means that initially not fresh adsorbent, but rather an already used adsorbent originating from a later cleaning stage is supplied to the oil still to be cleaned. In relation to the oil, which is still unpurified here, it still has enough potential to absorb dirt particles. After this first cleaning step, consisting of contacting and subsequent separation, the pre-cleaned oil is now treated in a further course with fresh adsorbent, which is able to absorb the smaller number of dirt and paint particles that are still present and then still enough free ones Has capacity for a second mission. This adsorbent, which is now used, can then, as indicated above, be added to the first contacting stage at a later point in time, while the oil which has already been cleaned by two stages can be further processed.

In principle, it is also possible to provide more than two such separation stages.

Despite the inherent advantage, the countercurrent principle is not used in practice due to the considerable expenditure on equipment. The benefit, namely the saving of adsorbent, is disproportionate to the requirement of the additional multiple stages and the countercurrent flow.

Attempts to make the countercurrent principle more effective by means of clever solutions by means of continuous, simple solid or liquid phases flowing against one another are known, for example, from DD 238 924 A1. Rotating liquid columns and ascending or descending heavy and light phases are used there. There was no lack of attempts, with columns rotating internals to use the centrifugal field to improve the separation effect. A fluid flow is generated in a cylindrical tube, as a result of which heavy particles dispersed in the fluid form into rings of any length that rotate about the main axis of the chamber. These particles can be liquid particles or solid particles. Another alternative to this is known from CH-PS 382 716.

The disadvantage of centrifugal extraction is the high investment and operating costs. The opposite transport of oil and bleaching earth in this column leads to a significant loss of driving force due to insufficient stage separation and reduces the maximum bleaching earth savings possible through the countercurrent principle.

In contrast, the object of the invention is to propose a generic method and a device for its implementation, with which the effectiveness of the countercurrent processes can be improved.

This object is achieved in a method in that at least a portion of the adsorbate leaving the first separation stage of the multi-stage process is mixed batchwise or continuously with a portion of the purified oil or fat leaving the last separation stage and the resulting mash is fed to a downstream filter becomes.

This solution to the problem is very unexpected for the person skilled in the art, since it prompts him to include at least part of the freshly cleaned oil which is already suitable for further processing to mix the adsorbate, i.e. the solid particles of the entire process that are most contaminated with dirt and paint particles, and to feed them to a downstream filter.

It is precisely this measure, which at first glance appears to be nonsensical, which makes it possible to make a significant improvement and simplification in the filter stage which is always necessary after the adsorptive cleaning process. So far, the extraordinarily fine particles, which are still contained in the oil that has already passed through all cleaning stages, have tended to build up an impermeable filter layer in front of the filter membranes very quickly. There was a rapid increase in pressure, which reduced the filtering effect of the cake and forced it to change the filter constantly.

As a result of the measure according to the invention, however, the relatively large particles of the adsorbate are also found in the oil which has been cleaned per se. These also come into contact with the filter membrane of the filter stage and prevent it from becoming blocked.

In addition, use is made of an additional surprising effect which has shown that the contaminants and dyes contained in the adsorbate almost do not return from the adsorbate into the cleaned oil. The periods in which this occurs are extremely long in relation to the other contact times, so that it is reasonable to add the adsorbate back to the cleaned oil. The effect can be particularly enhanced by a drop in temperature for the pre-soiled adsorbate, in practice, for example, from 130 ° C 80 ° C. As a result, the pores of the adsorbate particles that have already been provided with dirt and color particles are closed from the tendency and do not allow the dye contained in them to escape. This drop in temperature can be supported by appropriate measures in the cleaning cycle.

Practice has shown that the process can save 40% of the bleaching earth used.

In a preferred embodiment, this addition occurs only to a part of the cleaned oil. The mash that forms is not fed to the filter continuously, but rather in batches or batches, specifically for floating, after a new or cleaned filter is used. This prevents the new filter from clogging with the very fine particles at the very beginning.

The continuous production of cleaned oil in the outlet of the filter stage can be ensured in that the turbid oil accumulating in the precoat phase is returned to the unpurified oil before the multi-stage countercurrent process.

With this measure, one of the two parallel filter stages is always in normal operation, while the other is cleaned and then washed with the mash.

An additional advantage, which is ensured by the invention, is that the fine adsorbate particles of the clarified oil can now be disposed of together with the adsorbate leaving the process. So far, it has been necessary to deal with this To remove waste materials or adsorbents separately from the process, while they can now all be produced in the filter. This increases the effectiveness of the counterflow process considerably and thus also makes it economical. Not only the amount of the adsorbent required, but also the corresponding amount of waste or adsorbate is drastically reduced, since the advantages of the countercurrent process mentioned at the beginning can now be used and the adsorption capacity of the individual adsorbent particles can be better utilized and thus only in a smaller number than waste attack.

As an alternative to use only during the precoat, it is also preferred that two filter stages connected in parallel be carried out after the last separation stage and alternately switched off, cleaned and resuspended, so that a continuous outflow of cleaned oil or fat takes place.

Here, too, there is the advantage that the fine adsorbate particles can be disposed of together with the main amount of adsorbate.

From GB-PS 700 234 a method for cleaning or bleaching oils is known, in which an already largely cleaned mixture of oil and adsorbent is passed over a press covered with filter cake. Partially used adsorbents are already in the filter cake. The cleaned oil flows through the channels and pores of the filter cake, whereby almost no mass exchange can take place and thus also a backmixing of the impurities from the filter cake with the cleaned oil is eliminated from the outset, but likewise all the advantages achievable with the present invention.

A device for performing the method is characterized in that at least two contact stages, two separation stages and a mixer are provided, that the contact stages and the separation stages are connected to one another according to the countercurrent principle, and that the solids outlet of the first separation stage and the liquid fraction outlet of the second separation stage are each connected to the input of the mixer and that the output of the mixer is connected to the input of a downstream filter.

It is particularly preferred if the solids outlet of the first separation stage is arranged directly above the mixer.

It is also preferred if the solids outlet of the second separation stage is arranged directly above the first contact stage.

The arrangement of the outputs of the separation stages directly above the contact stages or the mixer prevents blockages, oxidative air contact and complex transport routes. The resulting solids fall directly from the separation stage, such as the decanter, into the mixer or the next contact stage due to gravity alone. This additionally increases the effectiveness of the entire process and, above all, reduces the equipment costs.

Such a structure is also possible because the mixed, liquid / solid phases can now be transported upwards if necessary, since this is possible with them.

The process has proven particularly useful for dark starting oils that are heavily contaminated with mucilages and soaps, as well as oils that do not require low final color values after bleaching. This would be the case for bleaching before physical refining.

The separation stages are preferably formed by decanters, hydrocyclones or separators. Decanters have proven particularly suitable and reliable in the first test attempts; With hydrocyclones, an increased effectiveness can be achieved under certain circumstances.

Fig. 1

Eine schematische Darstellung einer ersten Ausführungsform einer Vorrichtung zur Durchführung des Verfahrens;

Fig. 2

eine schematische Darstellung einer zweiten Ausführungsform zur Durchführung einer anderen Alternative des Verfahrens;

Fig. 3

eine schematische Darstellung einer dritten Ausführungsform zur Durchführung einer weiteren Alternative des Verfahrens; und

Fig. 4

eine schematische Darstellung einer vierten Ausführungsform zur Durchführung einer weiteren Alternative des Verfahrens.

Four exemplary embodiments of the invention are described in detail below with reference to the drawing.
Show it:

Fig. 1

A schematic representation of a first embodiment of an apparatus for performing the method;

Fig. 2

a schematic representation of a second embodiment for performing another alternative of the method;

Fig. 3

a schematic representation of a third embodiment for performing a further alternative of the method; and

Fig. 4

is a schematic representation of a fourth embodiment for performing a further alternative of the method.

In the two embodiments of Figures 1 and 2, a two-stage adsorptive cleaning is provided; three-step processes can also be effective under certain circumstances. In principle, the method also has advantages with even more stages, but these are consumed again due to the high expenditure on equipment.

In Fig. 1, the unpurified oil reaches the heat exchanger 2 by means of a pump 1 and is heated there to earth bleaching temperature. The heated oil enters the bleaching apparatus, contact level 3.

There it is contacted with oil-containing adsorbent from a later procedure.

Contact time, temperature and a desired vacuum in contact level 3, the bleaching apparatus, are optimally set according to the type of oil used.

The suspension leaving contact stage 3 is fed to a decanter 5 by means of pump 4. The decanter 5 separates the suspension into a solid and a liquid phase. The desired separation effect is set by regulating a cutting disc, a drum speed, a screw speed and the throughput (not shown). The decanter 5 has 2 outputs for the two phases leaving it.

The solid phase passes directly through a vertically arranged chute into the mixing container or mixer 6 arranged under the decanter 5. The solid phase is mixed in the mixing container 6 with clarified oil from a later process step onto a suspension which is easy to pump. This mash is fed to one of the two filters 8 or 9 by means of a pump 7. The switchover is only indicated schematically. In this way, the filter used is washed up, i.e. built up a filter layer. The entire content of the mixing container or mixer 6 is preferably fed to the filter 8 or 9 used in each case.

The liquid phase leaving the decanter, that is to say the separation stage 5, that is to say the oil which has already been clarified to a certain extent, is brought back to the contacting temperature in a heat exchanger 16 heated and fed to a contact stage 12, again a bleaching apparatus.

At the same time, the contact stage 12 is supplied with fresh adsorbent from the adsorbent container 11. Bleaching temperature, amount of adsorbent, contacting temperature and contacting time are selected according to the type of oil used.

The suspension leaving the second contact stage 12 is fed to a decanter, the separation stage 14, by means of a pump 13. The separation stage 14 separates into a solid and a liquid phase. Cutting disc, drum speed, screw speed and throughput are selected according to the desired separation effect.

The solid phase reaches the first contact stage 3 via a vertically arranged chute directly into the bleaching apparatus below. It is mixed as described above, here with the still unpurified oil and then processed further.

In contrast, the liquid phase from the separation stage 14 is adjusted to the optimum temperature in a heat exchanger 15.

It or a subset of it is either fed to the filter 8 or 9 for the final filtering or clarification or, if necessary, conveyed into the mixing container or mixer 6 for the formation of mash for the precoating process.

The bleaching apparatus or contact stages 3 and 12 can be operated according to the requirements under normal pressure, vacuum or protective gas.

The procedure described allows the adsorbent to be used twice, so that the adsorption power can be better utilized. Depending on the type of oil and bleaching earth type, adsorbent savings of up to 50% are achieved.

The method makes it possible to mix the solid phase leaving the decanter or the separation stage 5 in batches with clarified oil from the decanter or the separation stage 14 and to use it in the filters 8 and 9 as a precoat. This phase can then be subjected to the usual deoiling in the filter. At the same time, the filter effect for the clarified oil from the decanter or the separation stage 14, which mainly contains fine adsorbent particles, is considerably improved.

By mixing the adsorbent loaded with contaminants with oil clarified in a decanter and tempered according to the type of oil, the equilibrium status of the loaded adsorbent remains almost unchanged. This means that the impurities do not desorb into the oil. The equilibrium status of the oil-containing adsorbent washed up in the filter hardly changes due to the contamination with the cleaned oil and is therefore receptive to further impurities.

This enables filtration of the solid phase of the first stage and the liquid phase of the last stage in the same filter. The solid phase of the first stage can be reduced to the desired residual oil content in the same filter by special treatment of the filter layer.

Furthermore, it is possible to use the known countercurrent principle with little outlay on equipment and to achieve high savings.

The use of the countercurrent principle in the bleaching of vegetable and mineral oils and fats was achieved with considerable savings in bleaching earth. The second alternative embodiment is also discussed below with examples. The entire system is continuously fed with a pump 1 rapeseed oil (carotene content 32.3 mg / kg, phaeophin content 13.8 mg / kg, iodine color number 46). While flowing through a heat exchanger or heat exchanger 2, the rapeseed oil is heated to 90 ° C. In the reaction container or the contact stage 3, the rapeseed oil is mixed with the solid phase from the decanter or the separation stage 14. In contact stage 3, an agitator (a motor is indicated) contacts both phases, so that a partial adsorption is realized.

The bleaching earth / oil mixture leaving contact stage 3 is partially separated in a decanter or separation stage 5. The phase enriched with solids is brought together with the low solids phase from another separation stage 14 and fed to a heat exchanger 15. The low solids phase is fed to the mixer 6. The mixer 6 mixes the thin phase from the decanter or separation stage 5 and 7.5 kg of bleaching earth per ton of rapeseed oil from the storage or adsorbent container 11.

A pump 7 conveys the bleaching earth-oil mixture into the vacuum dryer 17, where the mixture is dried and degassed.

The dried and degassed bleaching earth oil suspension is continuously conveyed through the downstream apparatus by means of a pump 13. A heat exchanger 16 heats the suspension to 100 ° C. In the second Contact stage 12, another reaction vessel, another reaction vessel, the second bleaching stage is realized in such a way that the bleached rapeseed oil has a content of only 1.47 mg / kg carotene, 1.41 mg / kg phaeophetin and iodine color number 8.5. If, in comparison, rapeseed oil of the same starting quality with 7.5 kg / t bleaching earth is bleached in a batch process under vacuum conditions (50 hPa) at 100 ° C until equilibrium is reached, the corresponding values for carotene with 1.53 mg / kg, pheophetin, are also included 1.49 mg / kg and the iodine color number at 9.6 is comparatively high. In order to obtain the same iodine color number value with batch bleaching as with the continuous step-wise countercurrent process according to the invention, a bleaching earth amount of 8.2 kg / t is required.

The bleaching earth rapeseed oil suspension coming from the reaction container, the contact stage 12, is separated by means of a decanter or separation stage 14 in a phase enriched with solid and a phase low in solids.

While the phase enriched with solids is fed to the previous bleaching stage in the reaction vessel or separation stage 3, the low-solids phase from separation stage 14, which is mixed with the solid-rich phase from separation tower 5, leaves the process.

As an example, it should also be stated that the oils (bel 14), which have already been largely cleaned, have a carotene content of 30 mg / kg, while the uncleaned oils entering the contact stage 3 from the pump 1 via the heat exchanger 2 have a carotene content of 30,000 mg / kg.

FIG. 3 schematically represents a flow diagram of a plant for the continuous counter-current bleaching of vegetable oil.

The unbleached oil is continuously fed to the system and preheated to the oil-oil heat exchanger 21 by the finished bleached oil. In the dryer 22, the water content of the oil is reduced by means of a vacuum.

Before the pump 23 conveys the oil from the dryer 22 into a bleacher 25, it heats an oil preheater 24 to the bleaching temperature. The bleacher 25 is designed as a centrifugal countercurrent column.

Bleaching earth from the bleaching earth storage container 29 is also dorsed into the bleacher 25.

While the cloudy run is drawn off at the foot of the bleacher 25, the clear run leaves the bleacher 25 at the top of the column. The clearing is pumped by means of a pump 28 through the oil-oil heat exchanger 21 and an oil cooler 27 for the purpose of cooling.

A pump 26 sucks the turbid run from the bleacher 25. Before the clear and turbid run of the bleacher 25 leave the system for common filtration, they are brought together.

FIG. 4 shows a plant for the two-stage, continuous countercurrent bleaching of vegetable oils in the form of a flow diagram. The unbleached oil is preheated in an oil-oil heat exchanger 31 by the finished bleached oil. Before the oil gels into a bleacher 33, it is heated to process temperature in an oil preheater 32.

In the bleacher 33, the oil is pre-bleached from a centrifuge 48 with bleaching earth that has been used once.

A pump 34 feeds the oil-bleaching earth suspension from the bleacher 33 to a centrifuge 47. The turbid run of the centrifuge 47 enters the mixer 36. The clear run is cooled in an oil cooler 38, and citric acid is added before it is mixed with fresh bleaching earth in the mixer 39.

The metering device 46 ensures a continuous supply of bleaching earth.

The suspension is conveyed from the mixer 39 into an oil dryer 41 by means of a pump 40. A pump 42 pumps the suspension into the bleacher 44 via the oil preheater 43. The pump 45 feeds the suspension to the centrifuge 48.

The turbid run from the centrifuge 48 falls into the bleacher 33 for the purpose of oil pre-bleaching.

The bleached oil is in the clear run. After cooling with the unbleached oil in the oil-oil heat exchanger 31, it is passed through the oil cooler 35 into the mixer 36. The mixer 36 mixes the bleached oil with the twice-used bleaching earth from the centrifuge 47. With the help of the pump 35, the suspension leaves the bleaching process in the direction of the filtration.

Claims (10)

Process for the adsorptive purification of vegetable and / or mineral oils and fats in a multi-stage countercurrent process, characterized in that at least a part of the adsorbate leaving the first separation stage (5) of the multi-stage process is carried out batchwise or continuously with a subset of the last separation stage (14) leaving cleaned oil or fat is mixed and that the resulting mash is fed to a downstream filter (8,9). Method according to Claim 1, characterized in that the mash is fed to the downstream filter (8, 9) as a precoat after each filter cleaning. A method according to claim 2, characterized in that the turbid oil obtained in the precoat phase is returned to the unpurified oil before the multi-stage countercurrent process. Method according to Claim 2 or 3, characterized in that two filter stages (8, 9) connected in parallel are carried out after the last separation stage (14) and are alternately switched off, cleaned and resuspended, so that a continuous outflow of cleaned oil or fat he follows. Method according to claim 1, characterized in that the solid phase leaving the first separation stage (15) is continuously combined with the cleaned oil or fat of the last separation stage (14) and fed to the downstream filter (8,9). Device for carrying out the method according to one of the preceding claims, characterized in that at least two contact stages (3.12), two separation stages (5.14) and a mixer (6) are provided, that the contact stages (3.12) and the Separation stages (5,14) are connected to each other according to the countercurrent principle, and that the solids outlet of the first separation stage (5) and the liquid fraction outlet of the second separation stage (14) are each connected to the input of the mixer (6) and that the output of the mixer ( 6) is connected to the input of a downstream filter (8,9). Apparatus according to claim 6, characterized in that the solids outlet of the first separation stage (5) is arranged directly above the mixer (6). Apparatus according to claim 6 or 7, characterized in that the solids outlet of the second separation stage (14) is arranged directly above the first contact stage (3). Device according to one of claims 6 to 8, characterized in that two downstream filters (8, 9) are provided which can be connected alternately to the output of the mixer (6). Device according to one of claims 6 to 9, characterized in that the separation stages (5, 14) are decanters, hydrocyclones or separators.

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