Purification method for raw beet juice

Abstract: Purification method for raw juice obtained by diffusion from sugar beets, comprising the stages of pre-defecation and defecation with CaO, first carbonation, filtration, second carbonation and additional filtration; before said pre-defecation stage a great fraction of raw juice obtained by diffusion is taken out, subjected to a pre-filtration stage and subsequently to a stage of membrane filtration, the obtained permeate being mixed to the clear juice of first carbonation and said mixture being prepared for the second carbonation.

Description: The present invention relates to a purification method for raw juice of sugar beet. In the traditional purification process of raw juices obtained by diffusion from sugar beets, said juices undergo two treatments with CaO, called pre-defecation and defecation, and two following treatments with CO 2 , respectively first and second carbonation as described in prior art document WO 89 08635 A1. As universally known, said treatments are disadvantageous both from the environmental and from the energetic point of view. Still today said process is frequently used, above all because of its low operating costs. However, the present environmental regulations clearly tend to promote the development of technologies having low environmental impact. Object of the present invention is therefore a purification method for raw beet juices which can exploit the traditional process, though limiting the more invasive environmental aspects. Object of the present invention is therefore a purification method for raw juice obtained by diffusion from sugar beets, comprising the stages of pre-defecation and defecation with CaO, first carbonation, filtration, second carbonation and additional filtration, characterized in that, before said pre-defecation stage, a great fraction of the juice obtained by diffusion is taken out, subjected to a pre-filtration and subsequently to a membrane filtration, the obtained permeate being mixed with the clear juice of the first carbonation and said mixture being routed to the second carbonation. The fraction of raw juice which is taken out and prepared for the alternative treatment can reach 50% of the treated raw juice. In a form of embodiment the pre-filtration is carried out on meshed filters with openings in the range of 50-150 µm. The stage of membrane filtration generally consists of a microfiltration or tangential ultrafiltration, carried out with membranes showing a cut-off value ranging from 0,2 µm to 10 kDa; said membranes can be polymeric, ceramic, of the multi-channel type or spiral-shaped. Further advantages and features of the present invention will be evident from the following description of a form of embodiment of said invention, carried out as a mere non-limiting example, with reference to the only table of drawings enclosed, in which: Figure 1 is a schematic diagram of the method according to the present invention. The figure shows a flow-chart of the method according to the invention: the numeral 1 indicates the diffusion stage of the beets 101. The exhausted pulps 301 are routed to the pressing, whereas the raw juice 201 is destined to pre-defecation 2 with CaO. A fraction 108 of the raw juice 201, up to 50% of the total raw juice, is taken out in order to be treated in the working stages contained in square I of the Figure and being the novelty of the present method. The fraction 108 first undergoes a pre-filtration 8, which can be carried out with different types of filters, such as a filter with openings in the range of 100 µm, or two filters in series, a larger one with meshes in the range of 200-100 µm, and a thinner one with meshes in the range of 50-100 µm. After this pre-filtration 8 the filtered juice 308 undergoes a membrane microfiltration or ultrafiltration, while the suspended portions 208 are mixed with the exhausted pulps 301 and routed to the pressing. The membranes which can be used are tubular polymeric membranes, multi-channel ceramic membranes and spiral-module membranes, with a cut-off value which can range from 0,2 µm to 10 kDa. Quite satisfying results have been reached in particular with the latter type of membranes, and among these with those having a cut-off value around 30 kDa. The hold-up product 109 of the membrane filtration can undergo treatments, such as diafiltration or similar treatments, in order to retrieve the sucrose. On the other hand, the permeate 209 is mixed with the juice 105, that is to say, the juice of first carbonation obtained with the filtration 5 of the suspended portions 105. This juice results from the normal procedure of the traditional purification method. From pre-defecation 2 a juice 102 is obtained, said juice being treated again with CaO (defecation 3). The obtained juice 103 undergoes the first carbonation 4 and is then filtered (filtration 5). This clear juice 105, whose pH is in the range of 10,5-11,0, is then mixed with the permeate 209, whose pH ranges between 6,0 and 7,5, and said mixture undergoes the second carbonation 6. The resulting juice 106, whose pH ranges between 8,5 and 9,0, undergoes the filtration 7, which gives the purified juice 107 and the residual filtration products 207. Example 1 During a test the membrane filtration of the raw juice according to the method of the invention has given a permeate having the following composition: Qz = 84,7 pH = 6,3 Mg 2+ = 12,3 mmol/100 g of dry substance (DS) PO 4 3- = 4,5 mmol/100 g DS C 2 O 4 2- = 3,0 mmol/100 g DS This permeate has been mixed with a clear juice of first carbonation, obtained according to the traditional process, in different amounts, that is to say, a mixture consisting of 90% of juice of first carbonation and 10% of permeate, and a mixture consisting of 80% of juice of first carbonation and 20% of permeate. Both mixtures have then undergone the second carbonation. Table 1 shows the data referring to the purified juice obtained in both cases, compared with the data referring to the purified juice obtained from the treatment of the juice of first carbonation without the addition of permeate. Example 2: Another test has started from a raw juice with a far higher purity: Qz = 92,6 pH = 6,3 Mg 2+ = 3,1 mmol/100 g of dry substance (DS) PO 4 3- = 3,5 mmol/100 g DS C 2 O 4 2- = 1,2 mmol/100 g DS After a light alkalinisation with sodium carbonate and an ultrafiltration treatment on 30 kDa polymeric membranes, a permeated juice having the following composition has been obtained: Qz = 93,6 pH = 7,1 Mg 2+ = 3,0 mmol/100 g of dry substance (DS) PO 4 3- = 3,2 mmol/100 g DS C 2 O 4 2- = 1,4 mmol/100 g DS Table 2 shows the composition of the purified juices obtained by means of different additions of permeate to the clear juice of first carbonation. The mixtures of juice of first carbonation and permeated juice have been tested in the ratios 1+0, 4+1, 2+1. As evident from the example quoted, the purified juice obtained according to the method of the present invention does not show huge differences with respect to the juice obtained with the traditional method. As a matter of fact, data values such as purity, pH, color and alkalinity are in the same range. However, the purification potential of an equipment using the present method is greatly increased without increasing the use of lime, and therefore without increasing the environmental effects due to sludge. Moreover, the CO 2 consumption is reduced, which subsequently reduces emissions. Advantageously, a higher amount of Mg 2+ in the purified juice improves the characteristics of the juice for the treatments it will undergo later on.

Claims: Purification method for raw juice obtained by diffusion from sugar beets, comprising the stages of pre-defecation and defecation with CaO, first carbonation, filtration, second carbonation and additional filtration, characterized in that before said pre-defecation stage a fraction up to 50% of the raw juice obtained by diffusion is taken out, subjected to a pre-filtration stage and subsequently to a stage of membrane filtration, the obtained permeate being mixed to the filtered juice of first carbonation and said mixture being routed to the second carbonation. Method according to claim 1, in which the pre-filtration stage is carried out on a filter with openings in the range of 50-100 µm. Method according to claim 1, in which the pre-filtration stage is carried out on a set of filters consisting of a coarse-meshed filter, with openings in the range of 200-100 µm, in series with a filter with openings in the range of 50-100 µm. Method according to claim 1, in which said filtration stage consists of microfiltration or tangential ultrafiltration of said juice on membranes. Method according to claim 4, in which said membranes show a cut-off value ranging from 0,2 µm to 10 kDa, and preferably 30 kD. Method according to claim 5, in which said membranes are spiral-module membranes.

Inventors: PEZZI GIORGIO, PEZZI, GIORGIO
Applicants: ERIDANIA S P A, TECNIMONT SPA, ERIDANIA S.P.A., TECNIMONT S.P.A.
Application year: 2000
Main classification: C13D3
IPC codes: C13D3