NL2000790C2 - Cleaning equipment e.g. membrane filter for processing liquids containing organic matter involves contacting equipment with solution of periodate compound having defined pH value - Google Patents

Abstract

Cleaning equipment for processing liquids containing organic matter involves contacting the equipment with a solution of a periodate compound, where one of the following steps is performed, (A) where the solution has a pH value of = 6, the method further involves contacting the equipment with a solution having a pH value of >= 6; and (B) where a solution of a periodate is used at a pH value of >= 6, the method involves an additional oxidizing agent such as peroxydisulphate, hydrogen peroxide or a peracid.

Description

Method for cleaning filter membranes

The present invention relates to a method according to the preamble of claim 1. The invention relates in particular to a method for cleaning process equipment, in particular filters, such as membrane flashers, used for producing of liquid foods such as milk (milk products), fruit juices, beer, soft drinks (such as lemonade), cider, wine, sherry, port, distilled beverages and the like. These filters are contaminated during the filtration processes.

In the food industry and in sewage treatment plants, membrane flashers, in particular polymeric membranes such as polysulfone, polyethersulfone (with or without polyvinylpyrrolidone) and certain types of polyamides, and ceramic membranes for the removal of -soluble material from drinks and other liquids. Such membranes ensure suitable removal of undesirable components, in particular microorganisms such as algae, fungi, yeast and bacteria (exudates).

However, the permeability of such membrane flashers, also referred to by the term flux, decreases with the passage of time and the membranes can become blocked even after a relatively short time, that is, sometimes even within less than one hour, because components of the material to be treated are adsorbed or absorbed or deposited on surfaces of the equipment, which is undesirable. The result is that the process must be stopped in order to be able to clean the membranes. The blocked filters can be restored, for example, by flushing them in the opposite direction, a method known as back-flushing. This can be seen as a mechanical solution. However, it is a complicated process and is only a temporary solution and not a satisfactory solution, because after each step the original flux (at the same transmembrane pressure) is lower than before and in the long run the contamination accumulates to such an extent that the filter is completely blocked. In addition, it is difficult to remove some persistent organic contaminants in this way.

2000790 2

The invention is applicable to the cleaning of filters used for generally known processes, such as for the filtration of soft drinks, milk (milk products), wine, sherry, port, distilled drinks, fruit juices, lemonades, beer, such as cleared beer, residual beer, but also the wort / used grain separation, hot trub separation and cold trub separation.

In the case of beer brewing, the invention relates, inter alia, to the apparatus used during the preparation of the malt, the conversion of the malt and / or unmalted grains into wort and the further processing of the wort, with or without the addition of additional components, such as hops, by fermentation into beer, as well as all associated devices that are used and come into contact with the main streams or secondary streams from these processes.

There is therefore a need for an efficient cleaning system for cleaning liquid food production equipment, as defined above, wherein the system is capable of providing suitable cleaning that should preferably be carried out in a relatively short time (preferably in less than 120 minutes) and during which substantially all contaminants are removed during the cleaning.

A further investigation has shown that the equipment, and more particularly the filters, are contaminated during production by a combination of all types of compounds, of which polysaccharides, oligosaccharide, proteins, β-glucan, fats and polyphenols are important compounds .

Enzymatic processes have already been proposed for cleaning membranes. For example, the international patent application with publication number WO 98/45029 describes the use of cellulases and amylases for cleaning beer filtering membranes, after an alkaline pre-treatment of the membrane. Similarly, Japanese Patent Application Publication No. JP-A 4-267933 discloses using proteases and cellulases for the cleaning of separation membranes.

However, these non-oxidative processes are generally not fully satisfactory because substantial reaction times seem to be necessary to achieve effective removal of those components.

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The international patent application with publication number WO 97/45523 describes the use of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) as a nitroxyl compound and hypochlorite or hypobromite as a reoxidizing agent for the cleaning of beer-settling modules. However, the presence of halogen residues, in particular bromine residues, is very undesirable in the equipment due to their corrosive nature.

The international patent application with publication number WO 03/060052 describes a method in which filters can be cleaned in a bromine-free process by using a cyclic nitroxyl compound such as TEMPO or a 4-acetamido or 4-acetoxy derivative thereof and a halogen-free oxidizing system. The nitroxyl compound can be oxidized to the corresponding ion by enzymatic means with oxygen or hydrogen peroxide as co-substrate or by metal-catalyzed oxidation in combination with peracids, such as peracetic acid, persulfuric acid (Caro's acid), permanganoic acid or hydrogen peroxide.

Other oxidative methods are also described. The international patent application with publication number WO

2006/012691 describes the formation of hydroxyl radicals to clean the membranes. This method is particularly suitable when the membranes are of the fluorinated polymer type and are therefore very inert to chemical reagents.

The international patent application with publication number WO 03/095078 describes a process which is also based on oxidation and which appears to be very effective when a backwashing is used, intended to convert the polyphenols. This method is based on the assumption that polyphenols initially adhere to the membrane surface and are responsible for the initiation of the contaminating layer. However, it appears from the data shown that of the oxidation chemicals mentioned, only hydrogen peroxide with a manganese catalyst is effective.

The present invention is based on the use of periodic acid or its salts as set forth in claim 2. The invention is based on the surprising effect that it appears to be possible to clean equipment appropriately, for example, filtration membranes and process equipment, and which are used during the production of foodstuffs and the cleaning of water by exposing the contaminated equipment to a solution containing periodic acid (H5I06) or its salts. The preferred material is sodium metaperiodate (NaIO 4). When dissolved in water, it reacts to form salts, known as para periodates, to be considered as salts derived from H5106. The term "periodate" as used in this specification includes all of these salts.

An overview of the general use of periodate 10 as an oxidizing agent is given in an article by Alexander J. Fatiadi, New Applications of Periodic Acid and Periodicals in Organic and Bio-organic Chemistry, Synthesis, 229, 1974, and in the "Handbook for reagents ", Oxidation and Reduction, biz. 440, Ed. S.D. Burke and R.L. Danheiser, John Wiley & Sons, New York 15 (2000). One of the first publications on periodate refers to the conversion of vicinal diols that leads to binding cleavage and the formation of two carbonyl groups (also known as the Malapradian oxidation). The general reaction is as follows: R-C (H) OH-C (H) OH-R '+ Na10 4 - RC (H) 0 + R'C (H) 0 + Na 10a

This reaction has found a wide application. In particular in the field of all types of saccharides, the reaction has been examined in a very broad way (for an overview, see the article in Advances in Carbohydrate Chemistry, R.D. Guthrie, ed.,

Full. XVI, pp. 105-158, 1961, Associated Press, New York). An important application has been found in the preparation of dialdehyde starch and dialdehyde cellulose. Other groups of interest that can be oxidized by periodates are sulfides, leading to sulfoxides, and dihydroxybenzene, leading to quinones.

A further explanation of the invention will be given with reference to the cleaning of equipment used for the filtration of beer. Of the most important components of beer, the reaction of periodate with polysaccharides is the most likely. Due to the addition of periodate that reacts with polysaccharides, an excess of aldehydes will be present. However, due to the presence of proteins, problems can be expected which makes the contamination process more serious. Proteins will also react with aldehydes, for example those that come from a reduction of sugar compounds that are present, and which takes place in an equilibrium reaction. The product released from the reaction with polysaccharides is the so-called dialdehyde polysaccharides. The Mail-5 lard reaction, which takes place between sugars (aldehyde groups) and proteins (amino groups), may be (partially) responsible for the contamination of membranes. The materials to be obtained are highly cross-linked products from the reaction between aldehydes and alcohols that lead to hemiacetals or, at a higher level of oxidation, to hemi-aldalen, or are highly cross-linked protein-saccharide complexes. Due to such a cascade-like reaction sequence, one could expect the contaminating layer to form a film that is difficult to degrade. The reaction results from the condensation of the amine group 15 with a carbonyl group. This primary reaction is reversible but the product has a tendency to rearrange in accordance with the so-called Amadori rearrangement. These products that originate from such a state are stable.

It has now surprisingly been found that these problems can also be solved by exposing the contaminating layer to a periodate salt, preferably in the presence of a chemical agent capable of further reacting with the products which released from the periodate reaction or followed by exposure to those chemicals, under neutral or alkaline conditions. A person skilled in the art would have no tendency to use a periodate compound because of the aforementioned cascade reactions. Although it is not intended to be bound by theory, it can be argued that due to the neutral or alkaline conditions, which are usually not used for the oxidation of polysaccharides with periodate, the oxidation may be followed by a positive side reaction . A first possible side reaction that is considered is the Cannizarro disproportionation (described by Veelaert, dissertation, pp. 88, 1995-1996, University 35 of Ghent, Belgium). Under the influence of OH ', two aldehyde groups will react to produce an alcohol (reduced form) as well as a carboxylic acid (oxidized form). The net result (under these alkaline conditions in accordance with the preferred embodiment of the present invention) is the formation of carboxylate groups. When the final product is less cross-linked, it can be expected that due to the higher solubility and the charges, the product can be removed more easily.

A second possible side reaction is known as the β-alkoxy-carbonyl elimination, also referred to as the β-5 elimination. This reaction has been investigated by several authors. An overview of this reaction is presented in a publication already mentioned above (Advances in Carbohydrate Chemistry, R. D. Guthrie, ed., Vol. XVI, pp. 105-158, 1961, Associated Press, New York). Possible pathways for allowing this reaction to proceed are described by Floor et al. (Reel.

Trav. Chim. Pays-Bas, 107 (1989) 384), and by Veelaert (dissertation, 1995-1996, University of Ghent, Belgium as already mentioned above). The most important result of this reaction is that the polysaccharide-based molecules are split and that carboxylate-containing materials are formed. These products are more soluble in water than the original compounds and show less adsorption.

A typical condition is an elevated temperature, for example, higher than about 60 ° C, preferably higher than about 70 ° C, making it possible to perform a cleaning step in a relatively short time (in less than 60 minutes). The concentration of periodate to be used is 500-2000 ppm. The consumption of the reagent can be monitored by means of a UV-fish spectroscopy and the amount of reagent to be added can be based on this measurement.

The membrane is fully recovered after the treatment and further treatment with chemicals is not necessary.

Despite the rigorous conditions that are applied (high temperature and high pH), the membranes appear to be stable.

A second embodiment of the present invention relates to the regeneration of the reagent in situ.

Because periodate is an expensive chemical, its use for a large-scale process is very limited. A large-scale recovery method based on electrochemical in situ regeneration has already been described in various patents and articles (an overview is given in Starch, T_, 208 (1966) and in the US patent publication with number US 5 747 658), 40 methods developed for recovering this chemical after the reaction based on sodium hypochlorite, 7 have already been described in Die Starke, 2J3, (1971), pages 42-45 and in the US patent with publication number US 6 538 132 and are based on peroxomono sulfuric acid and ozone, as described in the European patent application with publication number EP 5 1 341 717 and by ozone (the international patent application with publication number WO 98/27118). This second embodiment involves carrying out the reaction with a very limited amount of, for example, sodium periodate (less than 250 ppm = 1.2 mM) in the presence of a second oxidizing agent, capable of reacting with the aldehyde groups resulting from the action of periodically to oxidize. It has been found to be an advantage that in this way the amount of the expensive periodate can be limited. Examples of such oxidizing agents are hydrogen peroxide and peroxodisulfate. While not wishing to be bound by any particular theory, it is expected that the good cleaning effect of periodate combined with another oxidizing agent is due to oxidation of the products formed by periodate under the alkaline conditions of the process. This reaction is carried out at a pH of greater than 6. Because the oxidation of polysaccharides is preferably carried out at a pH in the range of 1 to 6 and dialdehyde polysaccharides are reactive under alkaline conditions, an in situ regeneration is not possible. . An improved method is described in the European patent application with publication number EP 0 118 983. It has now been found that these regeneration methods can be used under the alkaline conditions applied during the cleaning procedure of the present invention.

A third embodiment involves performing the reaction with a very limited amount of periodate (of less than 1.2 mM) in the presence of a reagent capable of reacting with the products, such as peroxydisulphate, hydrogen peroxide, preferably at a relatively high pH value (of approximately greater than 6), which leads to degradation of the products by means of β-elimination and / or oxidation, or to perform the oxidation at a lower pH value (of approximately lower then 6) followed by treatment with a reagent capable of reacting with the products such as hydrogen peroxide, peracids, hypochlorous acid and sodium chlorite. Particularly at a lower pH (of about lower than 6) it may be advantageous to carry out the reaction in this way because an after-treatment will give very 8 highly soluble dicarboxy derivatives. Only limited quantities of periodate are then required.

The method according to the present invention can be used for cleaning membrane flashers used in the food and feed industry and for the purification of water. Production of dairy products, beer, wine, fruit juices (apple, pineapple, grapefruit, oranges), vegetable drinks (vegetable juices) and other drinks. The equipment includes pipes, tubes, mixing devices. The filter type can be of any type including those made from PVP, polysulfone, polyether sulfone and in particular polyamides and ceramic membranes.

The method of this invention can be carried out by oxidation, whereby a better solubility and / or degradation of polysaccharides and proteins is obtained. The method can be carried out as a static (batchwise) method. The time required for cleaning is preferably between 5 minutes and 120 minutes.

A continuous or semi-continuous method is also possible in which the liquid is circulated through the system. After cleaning, the chemical aid can be removed by rinsing with a suitable liquid, which is preferably water.

The pH value in Examples 1, 2, 4, 6 and 7 is between about 11 and 13.

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Examples

General The membranes that are used are of the hollow fiber type, made of polyether sulfone / PVP type; 20 fibers with a length of 300 mm are included in a module, with a surface area of 0.0235 m2. Beer is pumped through the fibers at an initial pressure of 1 bar.

35 1. Standard contamination procedure for membranes

Beer with a temperature of 0 (± 1) ° C is filtered through the membranes at a constant flux of 107 1 .m "2 .hr" 1 .bar "1 under cross flow conditions (speed is 40 2 m / s). The procedure is continued until the transmembrane pressure is higher than 1.6 bar (usually it takes 4 hours). After the 9 contamination, the clean water flux is at a value between 7500-15000 1 .m ~ 2 .hr "1.bar -1.

2. Washing steps before and / or after the oxidative cleaning step (for example with periodate, periodate / persulphate, periodate / permanganate) can include one or more of the following procedures: a. A backwash flow consisting of the following steps: a backwash with reverse osmosis water for 10 seconds, followed by a flush with 0.01 M NaOH solution for 180 seconds and finally with reverse osmosis water for 140 seconds.

b. Alkali treatment carried out with a NaOH solution at a pH of 12 and at a temperature of 60 ° C.

C. An acid treatment carried out with nitric acid at a pH of 2 for 10 minutes at room temperature.

d. (alternative) An oxidative treatment is carried out with hydrogen peroxide and NaOH.

The flux of a membrane module that has never been used is 50000-55000 1 .m "2. Hr-1. Bar'1.

Examples of the invention will be given below without, however, limiting its scope. The determination of the clean water flux in each example simultaneously forms a wash step with clean water. The time during which the cleaning step with the periodate solution is carried out in the examples is up to about 45 minutes, unless otherwise indicated. When this time has elapsed, the concentration of the periodate solution can be reduced. Generally speaking, the lowest effective concentration of the periodate solution is approximately between 8 * 10 "5 - 0.5 M. The concentration of a regenerating agent (oxidizing agent such as hypochlorite, hypobromite or a peracid) generally varies at about 35 value from 2 * 10'4 - 2 M, preferably at a value between 5 * 10'4 and 2 M.

Example 1. Cleaning with periodate / sodium hydroxide

A contaminated membrane is cleaned by a backwash as described above. The clean water flux after this treatment is 10,000 µm "z.hr-1.bar" 1. Subsequently, a solution is circulated through the module which contains periodate (0.024 M) and sodium hydroxide (0.04 M). The temperature of the solution is kept at a value of 70 ° C during this entire procedure. After 45 minutes the module is removed and washed with an alkaline solution. The clean water flux after this treatment is 49000 l.m ”2.hr '_1. bar 1.

Example 2 Cleaning with periodate / sodium hydroxide / sodium perdisulphate 10 A contaminated membrane module, which has been pre-cleaned by backwashing, circulates an aqueous solution containing periodate (0.46 mM), sodium perisulphate (0.008 M) and sodium hydroxide (0.01) 11 M). The temperature of the treatment is kept at a value of 70 ° C during the entire procedure. The module is removed from the solution after 45 minutes. The clean water flux after this treatment is 48800 1 .m'2 .hr-1.bar "1.

Example 3 Cleaning with periodate at a pH of 3.

Through a contaminated membrane module, which is pre-cleaned by backwashing, an aqueous solution of periodate (in a concentration of 9.4 mM) is circulated at a temperature of 25 ° C and a pH of 3. After an exposure that has 45 minutes the module is removed from the solution and washed with an alkaline solution. The clean water flux is 41800 l.m "2.hr-1.bar-1.

Example 4 Cleaning with iodate / permanganate.

A contaminated membrane is cleaned by a backwash as described above. The clean water flux after this treatment is 9700 1 .m ~ 2. hr ”1 .bar'1. The module is then cleaned by circulating a solution containing iodate (1.2 mM) and also potassium permanganate (0.032 M) and NaOH (0.08 M). The temperature of the solution is kept at a value of 60 ° C. After 4 minutes, the membrane is washed with a solution containing ascorbic acid (0.5%) and oxalic acid (0.5%) to remove manganese dioxide (MnO 2). The clean water flux after this treatment is 48500 1 .m "2.hr" 1 .bar "1.

Alternatively, this method can also be carried out using a combination of iodate and monoperoxoper sulfate, wherein the amounts of these compounds required to obtain corresponding results can be suitably selected by a skilled in the art.

Example 5 Cleaning with sodium iodate and persulfate

A contaminated membrane module, pre-cleaned by backwashing, circulates an aqueous solution of iodate (0.010 M) and 0.011 M NaOH at a temperature of 70 ° C and at a pH of 7. After 45 minutes of exposure the module is removed from the solution and washed with an acid solution. The clean water flux then amounts to 16000 l.m_2.hr ”1.bar” 1. This implies that iodate does not contribute to the cleaning and that the cleaning as described in Examples 1 to 4 can be attributed to the operation. of periodate.

Example 6 Cleaning with periodate / sodium hydroxide / hydrogen peroxide

A contaminated membrane module, pre-cleaned by backwashing, recirculates an aqueous solution containing periodate (1.2 mM), sodium hydroxide (0.11 M). Hydrogen peroxide is dosed during the cleaning procedure (total amount is 45 mmol / liter). The temperature of this treatment is kept at a value of 70 ° C during the entire procedure. The module is removed from the solution after 45 minutes. The clean water flux after this treatment is 40700 1 .m-2 .hr-1 .bar-1.

Example 7 Cleaning with periodate / sodium hydroxide The procedure as described in Example 6 was repeated, but now without the addition of hydrogen peroxide. The clean water flux of this treatment is 34200 1 .rrf2. hr ”1. bar 1.

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Claims (15)

A method for cleaning equipment for processing liquids containing organic materials, comprising contacting the equipment with a solution of a periodate compound. A method according to claim 1, wherein the solution has a pH of about 6 or less and wherein the method further comprises the step of contacting the equipment with a solution having a pH of about 6 or higher. The method according to claim 1, wherein a solution of a periodate is used at a pH value of about 6 or higher and further comprising an additional oxidizing agent, for example peroxydisulphate, hydrogen peroxide or a peracid. A method according to claim 1, wherein the method is carried out at a temperature that is between 15 ° C and 95 ° C, preferably between 60 ° C and 95 ° C, more preferably between 7 ° C ° C and 95 ° C. 5. A method according to claim 1, wherein the periodate compound is used at a concentration that is between 8 * 10 -5 and 0.5 M, preferably between 4 * 10 -4 and 0.5 M. 6. A method according to claim 2, wherein the concentration of the periodate compound is at a value between approximately 2 and approximately 9 mM. The method according to claim 3, wherein the concentration of the periodate compound is less than 1.2 mM, preferably 1.1 mM. 8. A method according to claim 1, wherein the periodate that has reacted in the cleaning process is regenerated by an oxidizing agent at a pH of about 6 or higher. 9. A method according to claim 3, wherein the additional oxidizing agent is a peroxydisulfate, preferably a soluble salt thereof. The method according to claim 8, wherein the regenerating oxidizing agent is added in a concentration of 3 to 20 mM, preferably 6 to 15 mM and with 2000790 more preferably 6 to 12 mM. The method of claim 10, wherein the regenerating oxidizing agent is a hypochlorite, a hypobromite, or ozone. The method according to claim 2, wherein in the periodate treatment is followed by treatment with an oxidizing agent which is reactive to dialdehyde polysaccharides. The method according to claim 12, wherein the regeneration is carried out by an oxidizing agent selected from any of a hypochlorite, monoperoxy sulfate or a peracid, or by electrochemical means. 14. A method according to claim 12, wherein the regenerating oxidizing agent is used in an aqueous solution in a concentration that is in the range of 2 * 10 ~ 4 to 2 M, preferably in the range of 5 * 10 ~ 4 to 2 M, more preferably in the range of 5 * 10 -3 to 1 M. The method of claim 1, wherein the process equipment is a filter, preferably a membrane filter. 2000790