Such a process is known from DE-A-28 55 860, in which soluble sulfates are added to organic peroxides in order to remove water by layer separation. This process has the disadvantage that traces of salt remain in the organic peroxide, which reduces its stability considerably.

US 4,995, 983 discloses a process where a peroxide waste stream is first freed of impurities in a first reverse osmosis or a nanofiltration step. Following the first step, the peroxide is first ionized by the addition of a base salt so as to increase the pH of the stream, and subsequently the stream is subjected to a second reverse osmosis step in order to remove water from the stream. Reverse osmosis depends heavily on the pressure of the stream; the higher the pressure, the higher the flux. Pressures of up to 60 bars are not uncommon, which is undesirable as this brings about the use of equipment specifically suitable for these high pressures. Another disadvantage is that traces of the base salt remain in the peroxide, which is detrimental to its stability and thus undesirable.

It is an object of the present invention to provide a process for removing water from a peroxygen formulation resulting in a more concentrated peroxygen formulation having an improved stability.

We have found that if water is removed from the formulation using pervaporation, a formulation with an improved stability with respect to the salt- containing formulations of the prior art can be obtained.

Accordingly, the invention is a process of removing water from a peroxygen formulation comprising a pervaporation or vapor permeation step wherein the water is transported through a semipermeable membrane. The techniques of pervaporation and vapor permeation enable the selective removal of water from the formulation, as the transport of water through the semipermeable membrane is faster than the transport through it of the peroxygen. Hence, with the process of the invention water can be removed without the addition of a salt to the peroxygen formulation, resulting in a more concentrated peroxygen formulation with a higher stability. A higher stability further enables storage in larger quantities. The high stability furthermore enables water removal at a higher temperature relative to conventional processes which improves the water flux through the membrane resulting in a higher productivity of the applied pervaporation or vapor permeation device. Another advantage is that the process of the invention can be applied to a wider range of peroxides, thus also the peroxides which cannot be dewatered by addition of salt due to stability problems.

In WO 99/59711 a process is disclosed for the preparation of an organic compound, not a peroxygen, by a condensation process at a temperature above 80°C. In this process, water formed during the condensation is removed by pervaporation. This water removal serves to shift the condensation equilibrium to the condensate side, thus effectively enhancing the reaction rate.

In the process of the present invention pervaporation is used to remove water from a peroxygen formulation, which is not disclosed in WO 99/59711.

Membranes of the process of the invention are semipermeable membranes which are as such known to the skilled person. These membranes are able to separate molecules through a difference in diffusive flux of the molecules.

Transport mechanisms of molecules through the membrane are commonly

known and may depend on a difference in adsorption onto the membrane between the molecules, a difference in diffusivity of the molecules, or on a difference in size of the molecules to be separated (viz. via molecular exclusion), for example. Through these properties a semipermeable membrane is clearly distinguished from conventional permeable membranes having for example relatively large pores (with sizes in the order of microns or even larger). Suitable semipermeable membranes are polymer-based membranes, inorganic membranes, and mixed-matrix membranes, for example. The polymer-based membranes generally are dense membranes. Such dense membranes may comprise a polymer matrix with a thin dense top layer, whereby the hydrophilic (or hydrophobic) properties of the matrix and the top layer may be the same or differ. The hydrophilicity of the polymer applied in the dense membrane is an important parameter which determines the size of the water flux through the membrane and the selectivity towards water relative to more hydrophobic components. Examples of polymers suitable for use in such polymer-based membranes are polyvinyl alcohol which can be cross-linked, cellulose, cellulose acetate, chitosan, mixed polymers, grafted polymers, polysulfone, and polyacrylonitrile. The polymer matrix and/or the dense top layer can be made from one or more of the aforementioned polymer materials.

Inorganic membranes generally are microporous membranes. Examples of such inorganic membranes are ceramic membranes comprising any type of zeolite, alumina, zirconia, titania, or amorphous materials such as silica, or a combination thereof. The inorganic membrane used in the process of the invention has a pore size of at least 0.2 nm, preferably at least 0.25 nm, and most preferably at least 0.3 nm, and at most 1.5 nm, preferably at most 1 nm, and most preferably at most 0.5 nm. The pore size distribution is an important parameter that determines the separation power of the membrane. If the membrane has a relatively large amount of larger pore sizes, larger molecules, i. e. molecules with a large kinetic diameter, can also pass the membrane and

the separation power will be relatively low. If, in contrast, the membrane has a relatively large amount of smaller pore sizes, predominantly water will pass the membrane and the separation power will be high.

A mixed-matrix membrane is a membrane comprising a combination of an inorganic and an organic material, such as a ceramic membrane coated with a polymer layer, or a polymer matrix impregnated with an inorganic material.

The membrane of the invention can be of any suitable shape depending on the application in which it is used. It can have the shape of a flat plate, of a tube, of a hollow fibre, a monolith and of a wound spiral.

The peroxygen formulation of the invention can be any type of compound comprising a peroxygen group. Preferably, the peroxygen compound is a hydrogen peroxide or an organic peroxide, of which the hydrogen peroxide is less preferred. Examples of organic peroxides are diacyl peroxides, peresters including percarbonates, peroxydicarbonates, perketals, ketone peroxides, dialkyl peroxides, hydroperoxides, peracids, or a combination of two or more organic peroxides.

The concentration of these peroxygen compounds in the formulation is at least 1 procent by weight (wt%), preferably at least 10 wt%, and most preferably at least 25 wt%, and at most 99 wt%, preferably at most 90 wt% and most preferably at most 75 wt% of the total formulation.

A skilled person will understand that. in the peroxygen formulation any conventional additive can be present in a desired amount. Such an additive may be for instance a non-ionic surfactant, a protective colloid, anti-freeze, pH- adjusting agents, sequestering agents, and, if desired, biocides.

The process of the invention is carried out at any suitable temperature.

Preferably, the temperature is at least 0°C, more preferably at least 10°C, and most preferably at least 20°C, and at most 200°C, preferably at most 150°C, more preferably at most 100 °C, and most preferably at most 80°C.

On one side the semipermeable membrane is brought into contact with the peroxygen formulation. On the other side of the membrane (permeate side) the partial pressure of water is lower than the partial vapor pressure on the formulation side, so as to create a driving force for transport of water through the membrane. In case pervaporation is used, the partial vapor pressure is defined as the product of the mole fraction of water, the activity coefficient of water, and the saturated vapor pressure of water at the applied temperature.

When vapor permeation is used, the partial pressure is defined as the product of the mole fraction of water in the vapor and the total vapor pressure.

Preferably, the pressure at the permeate side is chosen so low that the permeate (which is mainly water) is actively removed, i. e. the partial pressure of water on the permeate side is lower than the partial pressure of water on the formulation side. Such removal can be reached by evacuation, e. g. with a vacuum pump, or by flowing a gas along the membrane, e. g. an inert gas such as N2, He or Ar. Preferred absolute pressures at the permeate side are at least 1 mbar, preferably at least 2 mbar, and most preferably at least 5 mbar, and at most 1 bar, preferably at most 500 mbar, more preferably at most 100 mbar, even more preferably at most 75 mbar, and most preferably at most 50 mbar.

The peroxygen formulation can be dewatered with any conventional pervaporation or vapor permeation device. The formulation can be brought into contact with the membrane once. It is further contemplated to have a multitude of membranes set in series, so that the formulation will be in contact with all the membranes one after the other. It is also possible for the peroxygen formulation, once it has passed the membrane, to be recirculated in a circulation pervaporation or vapor permeation apparatus, after which the formulation may again be brought into contact with the same membrane.

The formulation from which water is at least partially removed after it has passed the membrane can be stored in a storage tank. The storage tank can

be a tank separated from the pervaporation or vapor permeation apparatus or it may be part of the circulation pervaporation or vapor permeation apparatus.

Also devices suitable for pervaporation or vapor permeation are envisaged comprising one or more separation elements comprising a first hollow tube which is surrounded by a second hollow tube which is in turn surrounded by a cooling and/or heating element. The first hollow tube is at least partially made of a tube-shaped semipermeable membrane in which the permeate is actively removed, e. g. by a vacuum or a flowing gas. Between the first and the second tube the peroxide formulation may be flown either in liquid or gaseous form. An example of a device having a plurality of separation elements is the PERVAPO SMS ex Sulzer Chemtech. An advantage of such a device is that the volume of the formulation which is present in the device, is relatively small, therewith reducing the danger of explosion considerably. Moreover, the temperature within each separating element can be controlled actively and accurately, whereby the temperature of the peroxide present in the element is easily adjusted in a relatively short period of time, reducing the explosion risk even more. This configuration also enables a large contact area of the formulation with the semipermeable membrane. Consequently, the water removal rate is relatively high, and dewatering can be performed in a short period of time relative to conventional pervaporation or vapor permeation devices.

The process of the invention can be performed at any suitable temperature. In common pervaporation or vapor permeation devices the temperature chosen for dewatering is generally below the self-accelerating temperature (SADT) of the formulation in said device. In the process of the invention the dewatering temperature can also be chosen below the SADT of the formulation in the pervaporation or vapor permeation device. The SADT of a peroxygen formulation depends on the type of peroxygen and the (storage) volume of the

formulation, for example, as can be learned from"Initiators for high polymers" from Akzo Nobel Chemicals bv.

However, the inventors have now found that, it is possible to dewater a peroxide formulation at a temperature at or above the SADT of the formulation in the device, while still securing safety. Preferably, dewatering at such high temperatures is performed in a device having one or a plurality of separation elements. At this relatively high temperature, the water flux through the membrane is improved even more resulting in an increased productivity of the pervaporation or vapor permeation device. Preferably, the temperature of the formulation in the process of the invention is at least 50 °C, preferably at least 60 °C, more preferably at least 70 °C, and most preferably at least 80 °C, and at most 200 °C, preferably at most 150 °C, more preferably at most 100 °C, and most preferably at most 90 °C. Preferably, the period of time during which the formulation is at a temperature at or above SADT, is shorter than the induction time of the formulation at that temperature. The heating and cooling of the formulation can be performed within the device itself or outside the device with a separate cooling and/or heating device.

The purity of the dewatered formulation is generally chosen such that formulation is stable. Preferably, the dewatered formulation comprises at least 10 wt%, preferably at least 20 wt%, more preferably at least 25 wt%, and most preferably at least 30 wt%, and at most 80 wt%, preferably at most 85 wt%, more preferably at most 90 wt%, and most preferably at most 99 wt%. The purity level of the peroxygen formulation that can be obtained depends on the stability of the dewatered formulation, which in turn depends on the type of peroxygen.

The permeated water that is obtained with the process of the invention has a relatively high level of purity. Purity levels of above 95 wt%, preferably above 98 wt%, and most preferably above 99 wt% of water in the permeate can be obtained.

It is also envisaged to remove at least partially a first peroxygen together with water from a peroxygen formulation comprising a second peroxygen. The first and second peroxygen must differ so much that it is possible to separate them with the process of the invention; the first peroxygen may be smaller in size than the second, or the first may be more hydrophobic than the second peroxygen (or vice versa), for example. The first peroxygen can be any type of peroxygen, and is preferably hydrogen peroxide or an organic peroxide.

Hydrogen peroxide is most preferred.

Hydrogen peroxide, hydroperoxide, and peracid formulations from which water is removed according to the process of the invention can be used to prepare an organic peroxide, such as an organic hydroperoxide. In other words, the dewatered formulation can be a raw material for the production of organic peroxides. The advantage of using dewatered formulations in this process is that the preparation of the organic peroxide is performed in a shorter time with a higher space-time yield as compared to conventional processes with water- containing formulations. For the process less of the formulation is required to obtain the same quantity of organic peroxide, which is also cost-saving.

These advantages are also apparent when the dewatered formulation is used in any other kind of conventional chemical process, such as a bleaching process or a polymerization reaction. A preferred example of such a process is the use of an organic hydroperoxide in peroxidation processes.

A further aspect of the invention is a process for cleaning a contaminated membrane with a peroxygen formulation using pervaporation and/or vapor permeation. The contaminated membrane can result from any process in which membranes according to the present invention can be used. In pervaporation or vapor permeation processes contaminants may adsorb or even react at the surface of the pore wall of the membrane, resulting in a lower separation power.

It is therefore desirable to keep the membrane clean. The inventors have now surprisingly found that peroxygen compounds, e. g. hydrogen peroxide and organic peroxides, are suitable to remove contaminants from the membrane pore wall, in particular when the contaminant is of an organic nature.

Preferably, hydrogen peroxide which is generally diluted with water, is used for this purpose. It is also contemplated to have a small amount of, e. g. , hydrogen peroxide present in the peroxygen formulation in order to increase the cleaning capability. Preferably, at most 10 wt%, more preferably at most 5 wt%, even more preferably at most 2 wt%, and most preferably at most 1 wt% of hydrogen peroxide will be present in the formulation.

It is further envisaged that water is removed simultaneously with the process of cleaning. In this way, the membrane can be kept clean during the removal of water. This has the advantage that the separation power of the membrane will remain unchanged during the dewatering process and can be used for a plurality of batches. It further enhances the lifetime of the membrane.

The invention as described above is illustrated with the following Figure and Examples.

Figure 1 Schematic representation of a circulation pervaporation apparatus.

Examples In Examples 1-6 a 70 wt% tert-butyl hydroxy peroxide (TBHP) formulation, Trigono) e A-W70 ex Akzo Nobel N. V. , is dewatered using pervaporation.

Pervaporation as conducted in the examples is performed in a circulation pervaporation apparatus which is illustrated in Figure 1. TBHP is added to a circulation vessel 1, from which the peroxide is pumped through Teflone tubes by means of and via a pump 2 to a membrane module 3. The membrane module 3 is connected to a cold trap 4, which in turn is connected to a vacuum pump 5, and a tube 7 which is connected to the circulation vessel 1. From the tube 7 the formulation can be tapped, if desired, via an outlet 6.

The membrane module comprises a ceramic membrane (ex ECN, The Netherlands, code S9-5_Ti12-1) with an amorphous silica top layer with a thickness of about 150 nm coated on an alumina support layer. The main average pore diameter of the membrane is between 0.3 and 0.5 nm. The membrane is tubular in shape with the silica layer situated on the outside of the tube. The outer diameter of the membrane is 14 mm and the length of the membrane is 391 mm. The membrane area is 172 cm2. The TBHP formulation was pumped from the circulation vessel to the membrane module at a flow of 360 litres per hour at atmospheric pressure.

The permeate separated by the membrane module is collected using the cold trap 4, which is cooled by liquid nitrogen. The analysis of the permeate was performed by determination of the refractive index using a refractometer. The concentration in the feed was analyzed using a GLC.

Example 1 In this example Trigonoxe A-W70 was diluted in a glass circulation vessel to a TBHP weight fraction of 60 wt% and a water content of 40 wt%. At this concentration the mixture is a two-phase system consisting of an organic phase with 70% TBHP and an aqueous phase with about 85% water. The total starting weight of the mixture was 1.5 kilograms. The temperature of the solution was kept at 25°C during the whole experiment. The pressure applied on the permeate side was 2 mbar.

Table 1 Time Weight % Gram Weight % Total Flux Minutes H20 in feed Permeate H20 in Gram/sqmtr/h permeate 0 41.89 56 37.99 13.90 98.37 865 112 34.78 15.38 95.37 958 165 33.54 15.03 99.79 989 225 33.03 16.72 99.46 972 285 32.63 16.68 99.68 970 345 31.96 15.18 98.35 883 410 31. 32 18. 72 99. 50 1, 005 The results of Table 1 show that the water content in the formulation is decreased by about 10 wt% using the pervaporation technique at 25°C. The permeate has a purity of more than 99%, indicating that water is selectively removed from the formulation.

Example 2 In Example 2 Trigonox A-W70 was dewatered at 25 and 35°C. The average vacuum applied on the permeate side of the membrane was 11 mbar. The starting weight of the solutions was 1,327 grams.

Table 2 Time Weight % Gram Weight % Total Flux Minutes H20 in feed Permeate H20 in Gram/sqmtr/h permeate 0 30.1 45 29.88 10.67 98.62 827 105 29.11 14.38 98.93 836 170 28.48 14.93 98.97 801 232 27.99 14.88 99.10 837 300 27.49 15.20 99.08 780 375 26.52 18.27 99.21 850 406* 25.97 7.15 98.65 805 440 25.33 7.69 98.99 789 475 24.31 11.22 99.11 1,118 536 23.37 22.77 99.16 1,302 591 22.30 21.64 99.20 1,373 675 20.43 29.91 99.18 1,242 740 18.50 23.86 99.22 1,281 800 16.57 19.65 99.18 1,142 874 14. 70 24. 57 99. 17 1, 158 * Experiment was stopped for a short time; temperature reduced to 15°C ;

experiment continued at 35°C ; at t= 406 minutes the temperature was again 25°C ; only at t= 475 minutes the temperature was 35°C.

The formulation was dewatered from 70 wt% TBHP to 73 wt% at 25°C and was further dewatered to 85 wt% TBHP at 35°C. The purity of the permeate is about 99 wt% of water, indicating that water is selectively removed from the formulation.

Example 3 Trigonoxe A-W70 was dewatered at 45°C in Example 3. The average vacuum applied on the permeate side of the membrane was 18 mbar. The starting weight of the solutions was 1,379 grams.

Table 3 Time Weight % Gram Weight % Total Flux Minutes H20 in feed Permeate H20 in Gram/sqmtr/h permeate 0 29.69 35 18.08 97.48 1,802 65 28.00 20.19 99.35 2,348 125 26.49 36.65 99.37 2,131 185 38.20 99.42 2.221 255 22.26 40.14 99.37 2,000 315 36.33 99.39 2,112 365 17.75 26.96 99.32 1,881 430 14.69 34.55 99.31 1,854 485 12.75 22.77 99.19 1,444 520* 11.10 10.22 95.74 1,019 563 9. 39 15. 49 98. 88 1, 257 * Experiment was stopped and continued the next day; temperature reduced to

15°C ; at t= 520 minutes the temperature was again 42. 8°C ; at t= 538 minutes the temperature was again 45°C.

The TBHP formulation was dewatered from 70.3 wt% TBHP to 90.6 wt%. Also in this example the permeate is relatively pure, as about 99 wt% is water.

Example 4 In this example dewatering of TrigonoxX A-W70 at 55°C is described. The average vacuum applied on the permeate side of the membrane was 25 mbar.

The starting weight of the solutions was 1,201 grams.

Table 4 Time Weight % Gram Weight % Total Flux Minutes H20 in feed Permeate H20 in Gram/sqmtr/h permeate 0 20.10 45 28.15 45.13 99.15 3,350 90 39.49 99.27 3,204 124 23.40 33.80 99.35 3,187 180 45.86 99.24 3,018 225 15.93 38.05 99.28 2,950 270 30.41 99.15 2,357 325 9. 77 32. 49 99. 12 2, 061 The formulation was dewatered from 69.9 wt% TBHP to 90.2 wt%. Again water is selectively removed from the formulation.

Example 5 Example 5 describes an experiment wherein Trigono) e A-W70 was dewatered at 65°C. The average vacuum applied on the permeate side of the membrane was 30 mbar. The starting weight of the solutions was 1,424 grams.

Table 5 Time Weight % Gram Weight % Total Flux Minutes Ha0 in feed Permeate H20 in Gram/sqmtr/h permeate 0 31.22 25 28.69 30.33 98.86 4,232 52 27.09 32.45 99.49 4,193 77 25.61 28.43 99.53 3,967 113 22.93 41.27 99.56 3,999 142 21.43 32.53 99.56 3,913 177 19.41 32.46 99.52 3,235 207 17.24 27.33 99.50 3,178 237 15.51 23.72 99.48 2,758 285 13.46 36.99 99.49 2,688 334 11.04 345 10. 39 36. 31 99. 45 2, 111 The TBHP was dewatered from 68.8 wt% TBHP to 89.6 wt%. The selectivity of the membrane for water appears to increase compared to the results of Examples 2-4. The purity of the permeate is now about 99.5 wt% of water.

Example 6 Dewatering of TrigonoxO A-W70 at 75°C is monitored in Example 6. The average vacuum applied on the permeate side of the membrane was 35 mbar.

The starting weight of the solutions was 1,358 grams.

Table 6 Time Weight % Gram Weight % Total Flux Minutes H20 in feed Permeate H20 in Gram/sqmtr/h permeate 0 29.27 10 15.46 98.21 5,393 33 27.66 39.00 99.57 5,915 63 24.61 45.84 99. 60 5,330 77 21.63 99.61 5,390 124 19.34 60.53 99.56 4,493 170 15.65 53.37 99.54 4,047 210 12.70 37.11 99.46 3,236 235 10.93 21. 19 99.43 2,957 267 9.56 21.31 99.35 2,323 290 8. 59 14. 35 99. 32 2, 176 The TBHP was dewatered from 70.7 wt% TBHP to 91.4 wt%. As in the case of the results of Example 5, the removal of water proceeds selectively, with the permeate containing about 99.5 wt% of water.

Example 7 In Example 7 the thermal stability of the formulations obtained in Examples 2-6 were determined using DSC-scans carried out in closed pyrex cups. The DSC was heated from 28 to 220°C at a rate of 2°C/min. The heat flow was recorded as a function of temperature. The temperature at which the heat flow is equal to 100 Watt/kg gives a good indication of the thermal stability of the sample.

These results are given in Table 7 below.

Table 7 Sample Content Temp. at which Q = 100 (%) W/kg (°C) Starting material TBHP-70 ex. 70 119 Pervaporation exp. Example 2 Sample 1 after pervap. at 25°C 73 121 Sample 2, after pervap. at 35°C 78 121 Sample3, afterpervap. at35°C 85 116 Pervap. Exp. Example 3 Sample 1, after pervap. At 45°C 85 115 Sample 2, after pervap. At 45°C 90.6 110 Pervap. Exp. Example 4 Sample 1, after pervap. at 55°C 90.2 111 Pervap. Exp. Example 5 Sample 1, after pervap. at 65°C 89.6 110.6 Pervap. Exp. Example 6 Sample 1, after pervap. at 75°C 91. 4 104. 5 The decrease in stability by pervaporation was only around 10°C for most of the samples, while the concentration was increased from 70 to 90 wt%. This is much better than is reached for comparable samples prepared in a traditional process. Such a traditional process of concentrating a TBHP formulation is by the addition of CaC12. The thermal stabilities of the formulations dewatered with CaCtz and pervaporation were determined using DSC. The results are tabulated in Table 8.

Table 8 Sample Predicted SADT from a DSC Real SADT scan (°C) (°C) TBHP-70% or Tx AW-70 70 80 TBHP-92% dried with 30 35 Caca2 60 65 TBHP-90% ex.

Pervaporation The thermal stability of TBHP-90% prepared by pervaporation is only decreased by about 15°C compared to the original TBHP-70 (i. e. Trigonox A- W70). Concentrating the peroxide by using CaC12 gives a reduction of 45°C.

These results indicate that dewatering by using pervaporation gives a TBHP formulation with a considerably higher stability. This more stable formulation can hence be stored in larger quantities.

Example 8 Example 8 describes a process of cleaning an amorphous silica pervaporation membrane with hydrogen peroxide.

The membrane was first intentionally contaminated with an organic compound according to the following procedure. The amorphous silica coated ceramic membrane (ex Sulzer Chemtech) with an effective membrane area of 57 CM2 was used for the dewatering of an ethanol/water mixture containing several ppm monochloroacetic acid. The mixture contained 12 wt% water on the total weight of the mixture. The measurement conditions were: 70°C feed temperature, 2 mbar permeate pressure, and a feed flow of 200 litres of mixture per hour. The water flux through the membrane decreased by a factor of two and the process selectivity increased by a factor of three.

For comparison reasons, a standard characterization test was performed with a clean butanol/water mixture on a non-contaminated amorphous silica pervaporation membrane. The mixture contained 5 wt% water and the measurement conditions were: feed temperature 75°C, permeate pressure 3 mbar, and feed flow 200 litres of mixture per hour. The average water flux measured was 1,558 grams/ (mz. h) with an average process selectivity of 693.

Cleaning of the silica membrane was performed by flushing the membrane with a solution of 2 wt% hydrogen peroxide at 30°C for 4 hours.

Following this cleaning step, a standard characterization test was performed with a clean butanol/water mixture. The mixture contained 5 wt% water and the measurement conditions were: feed temperature 75°C, permeate pressure 4 mbar, and feed flow 200 litres of mixture per hour. The average water flux measured was 2,173 grams/ (m2. h) at 5 wt% water in the feed with an average process selectivity of 960.

These results indicate that the amorphous silica membrane can be cleaned, in which process the productivity of the membrane and its selectivity are restored.

It is noted that an effective cleaning of the membrane surface depends on the properties of the adsorbed components. The use of specific organic peroxides can improve the efficiency of cleaning. Additionally, the concentration of the peroxide, the cleaning temperature, or the flow conditions can influence the effectiveness of the cleaning. The example given is not optimized, and a person skilled in the art can easily assess the optimal cleaning conditions.

Example 9 As opposed to the ceramic membrane as used in the previous examples, the membrane module comprises a polymer-based membrane (GFTO 1510 ex GFT). In this example Trigone A-W70 was dewatered at 40 °C for 400 minutes (0 to 400 minutes in Table 9). After 400 minutes of dewatering 80 g of water was added to the formulation, and the dewatering temperature was set at 30 °C. The flow rate of the formulation was 96 I/h. The pressure applied on the permeate side was 16 mbar.

Table 9 Time Weight % Gram Weight% Total Flux Minutes H20 in feed Permeate H20 in Gram/sqmtr/h permeate 0 31.57 15 20.52 4830 100 30.38 32.23 77.71 1340 167 29.85 19.51 94.76 1030 230 28.33 12.22 95.82 680 265 28.06 12.32 95.81 1240 308 36.98 16.07 97.46 1320 355 26.15 16.61 97.58 1250 400 19.16 98.20 1500 1345 17. 88 In Table 9 it is shown that the TBHP formulation can be dewatered at 40 °C and at 30 °C. The purity of the permeate is about 95 wt% of water and higher indicating that water is selectively removed from the formulation.