GB2233320A - A method of conditioning decolorising clay minerals - Google Patents

Abstract

The invention relates to a method of conditioning activated decolorising clay materials which are used for the adsorption of colourings and other accompanying substances derived from oils or fats, for the bleaching or decolorising of edible oils and for the cleansing of oil products. The object of the invention is to improve the quality of the conditioned activated decolorising clay material and to achieve an increase in bleaching or decolorising power. According to the invention, the activated decolorising clay material which is present as a suspension is spread out in a layer in which an inert substance has a drying gas flowing through it, is simultaneously dried and is comminuted to a granulation diameter of less than 90 mu m. The reduction in flow velocity is brought about by a linear widening of the cross section.

Description

A METHOD OF CONDITIONING DECOLnRISINC. CLAY MATERIALS Field of application of the invention The invention relates to a method of conditioning activated decolorising clay materials or earths (Bleicherde), such as fullers earth, which are used for the adsorption of dyes and other accompanyina substances contained in oils or fats, particularly in the foodstuffs industry, for decolorising or bleaching edible oil and for cleaninq oil products in the chemicals industry.

Prior art By reason of inadequate activity, naturally occurrinq clay minerals for decolorising and cleaning oils or fats are processed by treatment with acids to produce activated decolorisinq clay materials.

Compared with crude clay material, the structural chanqes which occur in the process have not been fully explained. The activation of the crude clay material to produce a decolorising clay material achieved in various ways, mostly in a boiling process with acids, delivers a oroduct which, on account of its acid and water content and the coarse comminution which usually takes place, is a product which is aggressive in the bleaching or decolorising process and which is also harmful for the equipment used, the product being unsuitable for adsorption of the colourinq agents and other accompanying substances, and which furthermore has to be mechanically comminuted and then screened (DD-PS 339 919, DE-OS 2056 333 n-PS 998).

In known manner, the decolorising clay material activated by various acids is subjected to multiple washing and filtration and then dried to the required residual moisture content in a drying drum (Fette - Seifen - Anstrichmittel 68(1966), 8,651-659).

The outcome of such a drying process is a vastly differentiated particle spectrum, in which the small diameter fractions are overdried while the larger diameter fractions are underdried. Subsequent grinding to a desired particle spectrum of less than 100 rm, reqardless of the grinding mechanism chosen, results in an undesirably high level of fineness or agglomeration due to underdried particles. The decolorising clay material fraction with a diameter smaller than 5 ,um does not however bleach or decolorise more intensely than the fraction within a diameter range of 5 to 10 oum (Fette - Seifen - Anstrichmittel 83(1981),5,177-1 A4).

In order to improve the filtering capacity of the decolorisinq clay material, the resultant product is subsequently subjected to forced-air sifting and any fractions which fall outside the necessary particle spectrum are either put through the grinding and dryinq process again or have to be rejected. According to DE-AS 1 173 442, treatment of decolorising clay material activated in special process stages is proposed in the drying stage with a high speed drying process representinq brief action of a superheated atmosphere accompanied by movement or agitation. This method, too, requires subsequent grinding and siftinq, with the disadvantages of the above-mentioned procedures.

Also known is a method of producing montmorillonite (DE-nS 25 38 519). This suggested method incorporates the process staqes: preliminary comminution of the crude montmorillonite, drying of the precomminuted material with hot, dry gases during pneumatic transport, feeding of the stream of gas charged with pre-comminuted drv material to a mechanical comminuting stage in a suitable qrindinq mechanism followed by possibly twofold air grading to achieve the desired particle spectrum. It is true that with this procedure in comparison with the above-mentioned methods, there is a successful concentration of the particle spectrum for the product, although the necessary air grading demonstrates the unacceptability of the mechanical comminution staqe.

All in all, the previously proposed methods of processinq activated decolorising clay materials so that they are ready for use do exhibit a number of disadvantages, due above all to the need for at least two procedural stages, with the appropriate equipment, and the occurrence of undesired particle sizes and high acid contents as well as insufficient activity.

Aim of the invention An aim of the invention resides in the development of a method which conditions activated decolorising clay material which is in the form of a suspension, to produce in one procedural step a quality which is required for bleaching or decolorising oils, the drying time beinq considerably shortened, energy savings being possible in comparison with conventional methods, while the quality of the conditioned activated decolorising clay material in which there is no oversized or undersized fraction being improved by the maintenance of the necessary particle spectrum, accompanied by concentration of the residual moisture content distribution and a reduction in the acid content, the increase in activity resulting in increased bleaching or decolorising performance in conjunction with reduced use of activated decolorising clay material and a reduction in oil losses Summary of the invention The invention is based on the problem of providing a method of conditioning activated decolorisinq clay material which, in one procedural stage simultaneously combining the processes of drying at a hiqh rate of drying and permanent grading of the decolorising clay material particles along with clearly defined comminution, produces a conditioned activated decolorising clay material in the required granulation spectrum of preferably smaller than 90Xum and greater than 5jim.

The invention generally concerns the use of a bed of inert particles subjected to an upward current of drying qas for the simultaneous drying and comminution of decolorising clay material therein. More specifically the cross-section of the bed increases in the direction of gas flow so that the gas flow rate decreases and dry particles of decolorising clay material of appropriate size are carried out of the bed with the gas.

According to the invention, the activated decolorisina clay material which, after acid treatment, the washing processes and preliminary draining, takes the form of a suspension with a water content of 1.2 to 3.3 kg water per kg dry decolorising clay material is conditioned in a jetted layer or fluidised bed (Strahischicht) with simultaneous dryino, comminution and grading. For this purpose, the suspension is applied to the inert bodies or particles present in the layer and havina a definite equivalent diameter in the range from 1.5 to 5 mm, the inert bodies or particles having a stream of drying gas passed throuqh them from the bottom upwards.The rate of flow of the drying gas is so adjusted that it is reduced from a value in the region of 42 to 53 m/s at the point at which the drying gas enters the layer, preferably linearly to a value in the ranae from 0.4 to 1.1 mis at the place where the drying gas emerqes from the layer.The suspension of activated decolorising clay material applied to the surface of the inert bodies or particles dries under the effect of the drying gas and the clearly diminishing velocity on the one hand ensures the delivery of conditioned activated decolorising clay material with the drying gas leaving the procedural stage while on the other it ensures that the abraded particles of decolorising clay material which have not been reduced sufficiently in size remain in the layer, exposed to the influence of the fluidised inert bodies or particles until they correspond to the preset particle spectrum size of less than 90sum. The ratio of inert bodies or particles to the throughput of conditioned activated decolorisinq clay material with a water content of less than 0.0527 kq water per kq of dry decolorising clay material ought thereby to fall within the range from 0.85 to 2.1 kgh/kg. To ensure a high drying rate in the decolorising clay material accompanied by simultaneous comminution to the required granulation spectrum, the temperature in the layer should be adjusted to a value between 80 and 1350C. The reduction in the flow velocity of dryina gas from the point of entry into the layer to the point of exit from the layer should be achieved by a preferably linear widening of the crosssection.

Preferred embodiment The invention will be explained in greater detail hereinafter with reference to a preferred embodiment.

In a layer or bed, 12 kg of glass balls with an equivalent diameter of 2.3 mm are fluidised as the inert bodies. The drying gas used is air heated to 2520C and injected into the layer at a velocitv of 48.1 mis.

The mass throughput of activated decolorisinq clay material (such as fuller's earth) suspension, of 43.2 kg/h, the water charge in the suspension representing 2.39 kg water per kg of dry decolorisina clav material, is contacted with drying gas in the layer, the inlet temperature being adjusted to 2520C while the temperature in the layer is 92or. Ry a conical widening of the cross-section of the layer, the drying gas, when it emerges from the layer, is flowing at a velocity of 0.44 m/s. For the given conditions, the proportion of the inert body mass in relation to the throughput of conditioned activated decolorising clay material with a water content of 0.0037 kg water per kg of dry decolorising clay material assumes a level of 0.907 kgh/kg.The conditioned activated decolorising clay material obtained in this way, in comparison with that produced hy the conventional method (drying in a drum drier followed hy qrindinq) has the following features: Conventional Method of Feature method the invention Granulation spectrum greater than 90um (%) 30 smaller than 5 - pm (%) 30 approx. an Less than 5,um (%) 30 smaller than 15 Bleaching power to TGL 38 594 (%) 87 94 free HC1 (%) 0.05 0.nl bonded HC1 (%) 0.4 n.15 Where the bleaching of vegetable oils is concerned, the decolorising clay material produced according to the invention, when compared with the product of conventional methods shows such a reduction in the amount of decolorising clay material used, a reduction in oil losses and a prolongation of the effective life of the filterina equipment.

Claims (5)

1. A method of conditioning activated decolorising clay material which is present as a suspension after acid treatment, a washing process and preliminary drainage, wherein the activated decolorising clay material, with a water content of 1.2 to 3.3 kg water per kg of dry decolorising clay material, is spread out in a jetted layer in which there are inert bodies with a definite equivalent diameter of between 1.5 and 5 mm, a drying gas being caused to flow upwards through the layer, its rate of flow diminishing from a level in the range from 42 to 53 m/s at the place at which the drying gas enters the layer to a level in the ranae n.4 to 1.1 m/s at the place at which the drying gas emerges from the layer, drying taking place simultaneously and at least 95% of the conditioned activated decolorising clay material being comminuted to a granulation of less than 90 um diameter, the ratio of the mass of inert bodies in relation to the throughput of conditioned activated decolorisinq clay material with a water content of less than 0.0527 kg water Der kg of dry decolorisino clay material being adjusted to a value in the range from 0.85 to 2.1 kgh/kg and the temperature in the layer being adjusted to a value in the range from 80 to 135 0C.

2. A method of conditioning activated decolorisinq clay material according to claim 1, wherein the reduction in the flow velocity of the drying gas from the point of entry into the layer to the point of emergence from the layer is brought about by preferably linear widenino of the cross-section.

3. A method according to claim 1, substantially as described in the Examples.

4. Use of a bed of inert particles subjected to an upward current of drying gas for the simultaneous dryinq and comminution of decolorisinq clay material therein.

5. Use according to claim 4, wherein the cross-section of the bed increases in the direction of gas flow so that the gas flow rate decreases and dry particles of decolorising clay material of appropriate size are carried out of the bed with the gas.