Method for diopat enrichment

Abstract

The present invention provides an improved process for enriching 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1,3,5-triazine (DIOPAT) from an aqueous alkaline mixture M comprising DIOPAT, 2,4-dihydroxybenzophenone, and aluminum salts, wherein the process comprises the steps of precipitating the DIOPAT by acidifying the mixture M to a pH ≤ 5; diluting the crude DIOPAT suspension with water; heating the diluted DIOPAT suspension to a temperature in the range of from more than 50 °C to 95 °C; optionally concentrating the precipitated DIOPAT by ultrafiltration to increase the concentration of the DIOPAT in the diluted DIOPAT suspension; and separating of the precipitated DIOPAT from the dissolved 2,4-dihydroxybenzophenone and the dissolved aluminum salts by diafiltration of the DIOPAT suspension with water.

Description

[0001] METHOD FOR DIOPAT ENRICHMENT

[0002] Field of the invention

[0003] The present invention lies in the field of chemical engineering and purification processes of organic chemicals and provides an improved process for isolating 2,4-bis-(2,4-dihydroxyphenyl)-6-(4- methoxyphenyl)-1 ,3,5-triazine (DIOPAT) from an aqueous alkaline mixture M comprising 2,4-bis-(2,4- dihydroxyphenyl)-6-(4-methoxyphenyl)-1 ,3,5-triazine, 2,4-dihydroxybenzophenone, and aluminum salts, wherein the process comprises the steps of precipitating the DIOPAT by acidifying the mixture M to a pH <5; diluting the crude DIOPAT suspension with water; heating the diluted DIOPAT suspension to a temperature in the range of from more than 50 °C to 95 °C; optionally concentrating the precipitated DIOPAT by ultrafiltration to increase the concentration of the DIOPAT in the diluted DIOPAT suspension; and separating of the precipitated DIOPAT from the dissolved 2,4-dihydroxybenzophenone and the dissolved aluminum salts by diafiltration of the DIOPAT suspension with water.

[0004] Background of the invention

[0005] 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1 ,3,5-triazine (DIOPAT) is the staring material for the preparation of the UV absorber Tinosorb® S (also known as 2,2'-[6-(4-methoxyphenyl)- 1 ,3,5-triazine-2,4- diyl] bis{5-[(2-ethylhexyl)oxy]phenol}, anisotriazine, bis-ethylhexyloxyphenol methoxyphenyl triazine, or bemotrizinol; CAS Number 187393-00-6) having the following chemical formula.

[0006] Tinosorb S

[0007] Tinosorb® S is a broad band UV absorber, absorbing UVB as well as UVA rays. Thus, Tinosorb® S is an important ingredient for sunscreen compositions and cosmetic applications.

[0008] One possible synthesis route to DIOPAT is performed via two steps, starting from 4-bromoanisole and cyanuric chloride under Grignard conditions to form the intermediate DICAT. In the second synthesis step, DICAT is reacted with resorcinol in a Friedel-Crafts reaction to form DIOPAT. In the following, the synthesis route to DIOPAT, starting from 4-bromoanisole and cyanuric chloride, is depicted, wherein the parameters a) Mg, THF, 65 °C; b) cyanuric chloride, THF, 0-5 °C; and c) resorcinol, toluene / benzonitrile, 45 °C, AlCh are typically applied.

[0009] To complete the syntheses to Tinosorb® S, a third step, the alkylation of DIOPAT with isooctyl chloride, is performed. In the following, the reaction to Tinosorb® S is depicted, wherein the parameters a) isooctyl chloride, base, DMF, 143 °C are typically applied.

[0010] In connection with the preparation of DIOPAT, the workup procedure and isolation of DIOPAT causes difficulties.

[0011] Typically, the reaction mixture comprising DIOPAT is quenched on a pre-charged sodium hydroxide solution. The product DIOPAT as well as the aluminum salts (Al-salts) from the Friedel-Crafts reaction are then dissolved in the alkaline aqueous sodium hydroxide solution. The organic reaction solvent (e.g. a mixture of toluene and benzonitrile) is separated by phase separation. Residual organic solvents may be stripped off to guarantee an organic solvent free aqueous phase. Then, the DIOPAT is precipitated from the alkaline DIOPAT / AI-salt solution by acidifying the mixture. If a low pH is established (pH < 1), the Al- salts are still dissolved in the aqueous phase while the DIOPAT is precipitated as a solid.

[0012] However, standard filtration processes, such as the use of a filter press, to separate the precipitated DIOPAT from the Al-salt solution have disadvantages. In particular, the filtration process is a manual, time consuming and open process, which is economically unattractive and causes safety issues on technical scale. Furthermore, the DIOPAT will be obtained together with the undesired organic impurity 2,4- dihydroxybenzophenone (2,4-DHBP), which is a byproduct of the DIOPAT preparation. Impurities of the undesired by-product of 2,4-DHBP in the DIOPAT, which is used for the final reaction step to Tinosorb® S, elevates the consumption of the expensive reactant isooctyl chloride and results in undesired side products, thus increasing the production costs.

[0013] An improved separation of the Al-salts from DIOPAT is challenging. Due to the low solubility of DIOPAT in organic solvents that have a complete miscibility gap between the aqueous and the organic phase, a separation of the Al-salts from DIOPAT by phase separation is not suitable. On the other hand, due to the corrosive behavior of acidic AICh / DIOPAT suspensions, most filtration equipment where metallic material is in contact with these suspensions is not suitable. However, the Al-salts, as well as organic by-products, obtained in the Friedel-Crafts reaction with AlCh are unfavorable for the following reaction to the final Tinosorb® S and need to be separated from DIOPAT.

[0014] Alternative and improved processes for the purification of DIOPAT have been described in international patent publication WO 2020 / 016366 A1 . However, said process is limited to comparably high temperatures and thus has a high energy consumption.

[0015] There is thus still need in the art for further improved processes for the purification and / or enrichment of DIOPAT.

[0016] Summary of the invention

[0017] It was the object of the present invention to provide a further improved process for isolating DIOPAT from the DIOPAT / AI-salt solution obtained after quenching the reaction mixture of the Friedel-Crafts reaction for preparing DIOPAT and removing the organic solvents.

[0018] It is a further object of the present invention to provide a process for isolating DIOPAT, which avoids a manual, time consuming and open filtration process.

[0019] It is another object of the present invention to provide an improved process for isolating DIOPAT, wherein not only aluminum salts but also organic by-products are simultaneously separated from the DIOPAT.

[0020] It has surprisingly been found that an improved DIOPAT enrichment process can be carried out at lower temperatures that were previously found to be insufficient for an efficient separation of organic byproducts, in particular 2, 4-dihydroxybenzophenone, if the crude DIOPAT suspension obtained after acidification and the thus induced precipitation of DIOPAT is diluted prior to the filtration step.

[0021] In a first aspect, the present invention thus relates to a process for enriching 2,4-bis-(2,4-dihydroxyphenyl)- 6-(4-methoxyphenyl)-1 ,3,5-triazine (DIOPAT) from an aqueous alkaline mixture M comprising

[0022] (i) 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1 ,3,5-triazine (DIOPAT);

[0023] (ii) 2, 4-dihydroxybenzophenone (2,4-DHBP); and

[0024] (iii) aluminum salts; wherein the process comprises the steps of a) precipitating the DIOPAT by acidifying the mixture M to a pH <5, preferably <4, more preferably <3, even more preferably <2, most preferably <1 to obtain a crude DIOPAT suspension; b) diluting the crude DIOPAT suspension with water

[0025] (b1) by a dilution factor in the range of 1 .2 to 1 .8, preferably 1 .3 to 1 .6,

[0026] (b2) to a pH increase of 0.1 to 1.0, preferably 0.1 to 0.6,

[0027] (b3) to a DIOPAT concentration of 1 .0 to 3.0 wt.-%, preferably 1 .5 to 2.5 wt.%, relative to the total weight of the suspension, and / or (b4) to a 2,4-DHBP concentration of less than 0.25 wt.-%, preferably 0.05 to 0.23 wt.-%, to obtain a diluted DIOPAT suspension; c) heating the diluted DIOPAT suspension to a temperature in the range of from more than 50 °C to 95 °C, preferably more than 50 °C to 90 °C, more preferably more than 60 °C to less than 80 °C; d) optionally concentrating the precipitated DIOPAT by ultrafiltration to increase the concentration of the DIOPAT in the diluted DIOPAT suspension by at least 0.1 wt.-%, preferably by 0.2 to 1 .5 wt.-%, relative to the total weight of the suspension, whereby the temperature is kept in the range of from more than 50 °C to 95 °C, preferably more than 50 °C to 90 °C, more preferably more than 60 °C to less than 80 °C; e) separating the precipitated DIOPAT from the dissolved 2,4-DHBP and the dissolved aluminum salts by diafiltration of the DIOPAT suspension of step c) or d) with water, preferably with a ceramic membrane, whereby the pH increases to at most 5.5, preferably at most 4.0 or at most 3.0, and the temperature is kept in the range of from more than 50 °C to 95 °C, preferably more than 50 °C to 90 °C, more preferably more than 60 °C to less than 80 °C, wherein the separation step e) provides the precipitated DIOPAT in the form of an aqueous suspension in the retentate.

[0028] In various embodiments, acidifying in step a) is performed with hydrogen chloride, preferably by adding the mixture M to an aqueous hydrogen chloride solution.

[0029] The dilution in step b) with water may, in various embodiments, be conducted to (b1) to a dilution factor of 1 .35 to 1 .50; (b2) to a pH increase of 0.15 to 0.6; (b3) to a DIOPAT concentration of 1 .8 to 2.5 wt.-% relative to the total weight of the suspension; and / or (b4) to a 2,4-DHBP concentration of 0.12 to 0.24 wt.-% relative to the total weight of the suspension.

[0030] In various embodiments, the temperature in steps c) and e) and, optionally, step d) is kept in the range of >60 to <80 °C, preferably 61 to 79 °C, 62 to 78 °C, 65 to 75°C, or more preferably 67 to 73 °C.

[0031] The ultrafiltration step d) and / or the diafiltration step e) may be carried out with a ceramic membrane, the ceramic membrane preferably being a TiC>2, ZrC>2, or AI2O3 membrane, preferably an (1-AI2O3 membrane. In various embodiments, (1) the ceramic membrane has a pore size in the range of from 20 to 500 nm, preferably from 50 to 100 nm; (2) the ceramic membrane is an (1-AI2O3 membrane having a pore size of 50 nm, preferable with 400 / 200 / 50 nm membrane layers; and / or (3) the ceramic membrane is provided in the form of a multi-channel element having a length of from 0.5 to 1 .5 m and a channel diameter of from 3 to 8 mm, preferably of 6 mm, wherein the multi-channel element preferably comprises from 7 to 19 channels.

[0032] The feed pressure in the diafiltration step e) may, in various embodiments, be from 1 .0 to 4.0 bar and / or the cross flow be from 2.0 to 5.0 m / s.

[0033] In some embodiments, the separation step e) involves continuous washing of the suspension in the retentate with water and removing of the permeate. In the processes of the invention, the diafiltration factor may be at least 3.0, preferably 3.5 to 5.0.

[0034] In some embodiments of the processes described above, the washing water (diluent) is heated to the process temperature before use, preferably by an external heat exchanger or direct steam injection.

[0035] In various embodiments, the volume concentration factor of the retentate in step e) relative to the diluted DIOPAT suspension of step b) is less than 3.0, preferably 1 .6 to 2.5.

[0036] The process of the invention may further comprise the step of f) concentrating the retentate obtained in step e) by ultrafiltration to increase the concentration of the DIOPAT in the enriched DIOPAT suspension by at least 0.1 wt.-%, preferably by 0.2 to 2.5 wt.-%, relative to the total weight of the suspension.

[0037] The process of the invention may, additionally or alternatively, further comprise the step of g) neutralizing the aqueous suspension of the retentate obtained in step e) orthe concentrated retentate obtained in step f) to obtain a pH of from 6 to 10, and optionally simultaneously concentrating the aqueous suspension.

[0038] Said neutralizing in step g) may be performed with sodium hydroxide or sodium carbonate, preferably with sodium hydroxide.

[0039] In some embodiments, the process further comprises the step of h) concentrating the neutralized aqueous suspension obtained in step g) by filtration, preferably by ultrafiltration or dynamic filtration, for example using a Dyno filter (Bokela), optionally after washing the neutralized aqueous suspension with water; and / or i) drying the suspension obtained in step e), step f), step g) or step h).

[0040] Detailed description

[0041] As indicated above, the main purpose of the process of the present invention is the removal of Al-salts and the organic byproduct 2,4-DHBP from the mixture M comprising DIOPAT, wherein said mixture is obtained after the Friedel-Crafts reaction, quenching and removal of the organic phase.

[0042] This object can be achieved by the diafiltration process of the present invention in an advantageous manner, as a closed system can be used, which does not require manual steps. Further, it has been found that the byproduct 2,4-dihydroxybenzophenone can be efficiently separated from the DIOPAT by the diafiltration process of the present invention at lower temperatures than previously considered if the DIOPAT suspension is diluted with water prior to the diafiltration. In this regard, the temperature during the filtration step could be lowered from the previously described range of from 80 °C to 95 °C to a range of more than 50 °C to less than 80°C, while still being high enough to keep the 2,4-DHBP in solution. Moreover, in said process the ceramic membranes previously found to be particularly advantageous, in order to avoid corrosion issues due to the acidic pH value of the suspension to be separated in the diafiltration process, which is required in order to keep the DIOPAT in precipitated form, are used.

[0043] The process of the invention allows enriching 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1 ,3,5- triazine (DIOPAT) from an aqueous alkaline mixture M comprising 2,4-bis-(2,4-dihydroxyphenyl)-6-(4- methoxyphenyl)-1 ,3,5-triazine (DIOPAT) and the undesired components 2,4-dihydroxybenzophenone (2,4- DHBP), which is an undesired byproduct of the reaction, and aluminum salts, which are used as catalysts in the reaction.

[0044] The process comprises the steps of a) precipitating the DIOPAT by acidifying the mixture M to a pH <5 to obtain a crude DIOPAT suspension; b) diluting the crude DIOPAT suspension with water

[0045] (b1) by a dilution factor in the range of 1 .2 to 1 .8, preferably 1 .3 to 1 .6,

[0046] (b2) to a pH increase of 0.1 to 1.0, preferably 0.15 to 0.6,

[0047] (b3) to a DIOPAT concentration of 1 .0 to 3.0 wt.-%, preferably 1 .5 to 2.5 wt.%, relative to the total weight of the suspension, and / or

[0048] (b4) to a 2,4-DHBP concentration of less than 0.25 wt.-%, preferably 0.05 to 0.23 wt.-%, to obtain a diluted DIOPAT suspension; c) heating the diluted DIOPAT suspension to a temperature in the range of from more than 50 °C to 95 °C, preferably more than 50 °C to 90 °C, more preferably more than 60 °C to less than 80 °C; d) optionally concentrating the precipitated DIOPAT by ultrafiltration to increase the concentration of the DIOPAT in the diluted DIOPAT suspension by at least 0.1 wt.-%, preferably by 0.2 to 1 .5 wt.-%, relative to the total weight of the suspension, whereby the temperature is kept in the range of from more than 50 °C to 95 °C, preferably more than 50 °C to 90 °C, more preferably more than 60 °C to less than 80 °C; e) separating the precipitated DIOPAT from the dissolved 2,4-DHBP and the dissolved aluminum salts by diafiltration of the DIOPAT suspension of step c) or d) with water, preferably with a ceramic membrane, whereby the pH increases to at most 5.5, preferably at most 4.0 or at most 3.0, and the temperature is kept in the range of from more than 50 °C to 95 °C, preferably more than 50 °C to 90 °C, more preferably more than 60 °C to less than 80 °C, wherein the separation step e) provides the precipitated DIOPAT in the form of an aqueous suspension in the retentate. The aluminum salts and the 2,4-DHBP may be enriched in the permeate, as they remain in solution under these conditions and can thus pass through the diafiltration membrane.

[0049] Preferred embodiments of the present invention can be found in the claims, the description and the examples. It is to be understood that the features mentioned above and those still to be illustrated below of the subject matter of the invention are preferred not only in the respective given combination but also in other combinations without leaving the scope of the invention. Before describing in detail exemplary embodiments of the present invention, definitions important for understanding the present invention are given.

[0050] As used in this specification and in the appended claims, the singular forms of "a" and "an" also include the respective plurals unless the context clearly dictates otherwise. In the context of the present invention, the term "about" or "approx." (approximately) denotes an interval of accuracy that a person skilled in the art will understand to still ensure the technical effect of the feature in question. The term typically indicates a deviation from the indicated numerical value of ±20 %, preferably ±15 %, more preferably ±10 %, and even more preferably ±5 %.

[0051] All numerical values given herein are rounded to the given integer, if any. A numerical value of 3 thus includes the range of from 2.5 to 3.4, while the value 3.0 includes the range of from 2.95 to 3.04.

[0052] All percentages given herein are weight percentages unless indicated otherwise and relate to the respective total weight of the subject composition or mixture, i.e. typically the total weight of the suspension.

[0053] It is to be understood that the term "comprising" is not limiting. For the purposes of the present invention the term "consisting of is considered to be a preferred embodiment of the term "comprising".

[0054] “Enriching”, as used herein, relates to increasing the concentration of a given compound relative to other compounds that are also present in the same composition. In the present processes, it refers to increasing the concentration of DIOPAT relative to other components in the suspension, in particular the indicated 2,4- DHBP and aluminum salts, but also relative to salts that may be present due to the neutralization / acidification, such as NaCI. The term "isolating” may be used with a similar meaning, i.e. by referring to separating the subject compound from other undesired compounds at least to a certain degree. It is to be understood that a term such as “isolating” does not refer to achieving absolute purity but refers to increasing the purity in a given composition by increasing the proportion of the compound of interest relative to the totality of the components in said composition.

[0055] As used herein, the term “aqueous alkaline mixture M” refers to a mixture comprising components (i), (ii), and (iii) as defined herein, which is typically obtained after quenching the Friedel-Crafts reaction mixture to prepare DIOPAT, i.e. component (i), with an aqueous sodium hydroxide solution and removing the organic phase. The pH of the aqueous alkaline mixture M is preferably in a range of from 10 to 15, more preferably from 12 to 14.

[0056] As used herein “2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1 ,3,5-triazine” (DIOPAT) is the compound of interest in the process of the present invention, as it is the precursor for the preparation of Tinosorb® S, as explained above. 2,4-dihydroxybenzophenone is a by-product of its preparation. As used herein, the term “aluminum salts” (Al-salts) refers to aluminum salts including aluminum trichloride and / or aluminum hydroxide. These aluminum salts are obtained in the preparation of DIOPAT as aluminum trichloride is required for the Friedel-Crafts reaction. It is to be understood that the aqueous alkaline mixture M may also comprise further components, e.g. sodium chloride, as a result of the reaction of aluminum trichloride with sodium hydroxide, as well as sodium hydroxide. In addition, sodium aluminum oxide (NaAIC>2) may be formed and therefore be present in the aqueous alkaline mixture M. Furthermore, residual amounts of the starting materials DICAT and resorcinol may be present, if the conversion to DIOPAT was incomplete or an excess of DICAT or resorcinol was used.

[0057] As used herein, the term “acidified mixture M” refers to a mixture comprising components (i), (ii), and (iii) as defined herein, which is obtained from the aqueous alkaline mixture M after acidification. The acidified mixture M additionally comprises certain amounts of a salt, preferably sodium chloride, from the neutralization reaction. Preferred amounts of the salt obtained due to the neutralization reaction are in the range of from 5 % to 15 % by weight, based on the total weight of the acidified mixture M. Furthermore, instead of a base, such as sodium hydroxide, an acid will be present, preferably hydrogen chloride. The pH of the acidified mixture M is <5, preferably <4 or <3, more preferably <2 or <1 .

[0058] As used herein, the term “acidifying” refers to the addition of an acid. Preferred acids include strong inorganic acids, such as sulfuric acid or hydrochloric acid. Preferably, “acidifying” in step a) of the process of the invention is performed with hydrochloric acid, in particular an aqueous hydrogen chloride solution. Preferred concentrations of the hydrogen chloride solution are in the range of from 20 to 37 %, preferably in the range of from 36 to 37 %. As a result of the acidifying step a), sodium chloride may be formed by reaction of sodium hydroxide with hydrogen chloride.

[0059] As used herein, the term “pH <1 ” refers to a pH of below or equal 1 .0. Similarly, “pH <2”, “pH <3”, etc. relate to a pH of below or equal to 2.0, 3.0, etc. All pH values referred to herein are those measured under standard conditions, i.e. 20°C and 1013 mbar, unless indicated otherwise. The pH given is typically the pH of the respective composition, i.e. the suspension or other liquid phase, without further modification or processing, such as further dilution, unless indicated otherwise.

[0060] As used herein, the term “precipitating” refers to solids formation of a compound. According to the present invention, DIOPAT is precipitated from the mixture M by acidifying the mixture M to a pH <5, preferably <4, more preferably <3, even more preferably <2 or most preferably <1 , whereby the solubility of DIOPAT is significantly reduced, so that a suspension is formed.

[0061] As used herein, the term “dilution” refers to adding solvent, in the process of the present invention water, to the DIOPAT suspension thus lowering the concentrations of the components (i) to (iii) present in said suspension as well as all other compounds different than water that may also be present in the acidified / crude DIOPAT suspension. A “diluted DIOPAT suspension” is thus characterized by a lower DIOPAT concentration relative to the starting suspension prior to dilution. The water used for dilution is preferably as pure as possible, for example deionized water may be used, to keep the salt concentration as low as possible and not introduce additional solutes into the crude DIOPAT suspension. The term “dilution factor”, as used herein, has its common meaning as understood in the art, and refers to the volume ratio of the diluted suspension to the starting suspension.

[0062] As used herein, the term “ultrafiltration” (UF) refers to a process, wherein a suspension comprising a precipitated compound is separated from dissolved components, which are permeable through a membrane in view of their size. The suspension, which does not pass the membrane is referred to as the “retentate”, and the solution comprising the dissolved components, which passes the membrane is referred to as the “permeate”. The ultrafiltration may be conducted as a diafiltration, as described below, but is typically conducted without the addition of additional solvent, in contrast to the diafiltration which typically includes addition of additional solvent, unless indicated to the contrary herein. Step d) as described herein is intended as a concentration step and thus typically conducted without addition of additional solvent.

[0063] As used herein, the term “diafiltration” (DF) refers to a process, wherein a suspension comprising a precipitated compound is separated from dissolved components, which are permeable through a membrane in view of their size. The suspension, which does not pass the membrane is referred to as the “retentate”, and the solution comprising the dissolved components, which passes the membrane is referred to as the “permeate”. During the diafiltration, the suspension is preferably continuously pumped from the feed vessel to the membrane and from their back to the feed vessel. Typically, diafiltration is performed as a continuous process, wherein additional solvent is continuously added to the retentate, and the permeate is continuously removed. This results in washing of the precipitated compound in the retentate. In some embodiments, the diafiltration step e) includes washing with water with a washing factor of 3 to 6, such as 4 to 5, for example about 4.5, wherein the term “washing factor”, also known as “diafiltration factor”, refers to the amount of water, also called diafiltration solvent, relative to the suspension as used in step e).

[0064] As used herein, the expression that “the pH increases to at most 5.5, preferably at most 4.0 or at most 3.0” in the context of step e) of the process of the invention means that the pH may increase during the diafiltration step due to removal of HCI or other acids with additional solvent, in the present case preferably water. The amount of additional solvent will be selected accordingly. For example, starting from a pH <1 , a washing factor of 4.5 results in a pH in the range of from 2 to 3, preferably 2.3 to 2.8. Due to the acidic pH value, dissolution of the precipitated DIOPAT and thereby a decrease of the amount of isolated DIOPAT can be avoided. Of course, it is to be understood that the pH does not necessarily increase to a value as indicated above. The pH may also increase less significantly, if less diafiltration solvent is used. Further, as additional solvent is added in a continuous process over time, the pH value will only increase slowly with increasing amount of diafiltration solvent. It is also understood that the final pH value is dependent on the starting pH of the suspension, so that if, for example, the suspension pH is 4.0, the pH increase cannot be at most to 4.0 or to 3.0 but must then be to at most 5.5, at most 5.0 or at most 4.5. In various embodiments, the pH increase is to at most 5.5, preferably at most 5.0, more preferably at most 4.5 or 4.0, even more preferably at most 3.5 or 3.0. As used herein, the expression that “the temperature is kept in the range of from more than 50 °C to 95 °C” in the context of step e) of the process of the invention means that the temperature of mixture subjected to the diafiltration step, in particular the temperature of the retentate is kept at a temperature of from more than 50 °C to 95 °C, e.g., by using a heating device or by adding pre-heated washing water. It is important that the temperature remains in this range, in order to keep 2,4-dihydroxybenzophenone in solution, so that this byproduct can additionally be removed by the diafiltration step. It is to be understood that the temperature may vary within the range of more than 50 °C to 95 °C, when step e) of the process is performed. It is however understood that from the perspective of energy consumption, the lower end of this temperature range may be preferred. Preferably, the temperature is at the beginning of the diafiltration of step e) in a range of from more than 50 °C to 80 °C or less than 80°C, for example in the range of from more than 60 °C to less than 80 °C, in particular in the range of from 65 °C to 75 °C.

[0065] As used herein, the term “concentration factor” refers to the ratio of the starting volume of the suspension comprising the precipitated compound and the dissolved components to the final volume of the suspension comprising the precipitated compound (retentate), after the dissolved components and parts of the solvent (permeate) have been removed during the diafiltration process. It is to be understood that the concentration factor of the additional solvent, which may be continuously added to the retentate, does not affect the concentration factor, as the same amount of additional solvent, which is continuously added to the retentate, will be continuously removed from the system by removing the permeate.

[0066] As used herein, the term “suspension” denotes a heterogeneous mixture comprising a solvent and a precipitate. For the diafiltration process, the particles of the precipitate must be larger than the pore size of the membrane.

[0067] As used herein, the term “dissolution” denotes a homogeneous mixture comprising a solvent and dissolved components, for example ions of a salt. In the diafiltration process, the dissolved components must be sufficiently small that they can pass the membrane.

[0068] As used herein, the term “feed DIOPAT suspension” refers to the suspension comprising DIOPAT obtained after steps a) - c) and optionally step d) of the process according to the present invention.

[0069] As used herein, the term “cycle time” refers to the period of time required to complete one cycle of a process for isolating DIOPAT according to the present invention, comprising step a), step b), step c), optionally step d), step e), optionally step f), optionally step g), optionally step h), and optionally step i).

[0070] Preferred embodiments regarding the process of the invention are described hereinafter.

[0071] As already indicated above, the present invention relates to a process for enriching or isolating 2,4-bis-(2,4- dihydroxyphenyl)-6-(4-methoxyphenyl)-1 ,3,5-triazine (DIOPAT) from an aqueous alkaline mixture M comprising the 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1 ,3,5-triazine, 2,4- dihydroxybenzophenone, and aluminum salts, wherein the process comprises the steps of (a) precipitating the DIOPAT by acidifying the mixture M, for example to a pH <5, preferably <4, more preferably <3, even more preferably < 2, most preferably <1 .5 or <1 .0;

[0072] (b) diluting the crude DIOPAT suspension with water

[0073] (b1) by a dilution factor in the range of 1 .2 to 1 .8, preferably 1 .3 to 1 .6,

[0074] (b2) to a pH increase of 0.1 to 1.0, preferably 0.1 to 0.6,

[0075] (b3) to a DIOPAT concentration of 1 .0 to 3.0 wt.-%, preferably 1 .5 to 2.5 wt.%, relative to the total weight of the suspension, and / or

[0076] (b4) to a 2,4-DHBP concentration of less than 0.25 wt.-%, preferably 0.05 to 0.23 wt.-%, to obtain a diluted DIOPAT suspension

[0077] (c) heating the diluted DIOPAT suspension to a temperature in the range of from more than 50 °C to 95 °C;

[0078] (d) optionally concentrating the precipitated DIOPAT by ultrafiltration to increase the concentration of the DIOPAT in the diluted DIOPAT suspension by at least 0.1 wt.-% relative to the total weight of the suspension, whereby the temperature is kept in the range of from more than 50 °C to 95 °C; and

[0079] (e) separating the precipitated DIOPAT from the dissolved 2,4-DHBP and the dissolved aluminum salts by diafiltration of the DIOPAT suspension of step c) or d) with water, preferably with a ceramic membrane, whereby the pH increases to at most 5.5, preferably at most 4.0, more preferably at most 3.0, and the temperature is kept in the range of from more than 50 °C to 95 °C.

[0080] In step a) of the process according to the present invention, the acidifying to a pH below or equal to 5, preferably below or equal to 4, more preferably below or equal to 3, even more preferably below or equal to 2, still more preferably to 1 .5 or less, most preferably to less than or equal to 1 (less than or equal to 1 .0) may be performed by any suitable organic or inorganic acid. Preferred are inorganic acids, such as hydrogen chloride, hydrogen bromide, hydrogen iodine, sulfuric acid, or nitric acid. In particular, hydrogen chloride is used. Preferably, the acid is used in form of an aqueous solution.

[0081] Step a) may be performed by addition of the mixture M to an acid, preferably an acidic solution, or by addition of an acid, preferably an acidic solution, to the mixture M. Preferably, step a) is performed by addition of the mixture M to an acidic aqueous solution or by addition of an acidic aqueous solution to the mixture M.

[0082] In one embodiment, the invention relates to the process for isolating DIOPAT according to the present invention, wherein acidifying in step a) is performed with hydrogen chloride, preferably by adding the mixture M to an aqueous hydrogen chloride solution.

[0083] The low pH value is required to precipitate the DIOPAT and keep the DIOPAT in precipitated form and keep the aluminum (Al) in dissolved form. Thus, a DIOPAT suspension is obtained as acidified mixture M (=crude DIOPAT suspension) after step a), which comprises DIOPAT in precipitated form, and additionally comprises the 2,4-dihydroxybenzophenone (2,4-DHBP) and aluminum salts. Furthermore, the suspension comprises sodium chloride as neutralization product, if the alkaline aqueous mixture M contained sodium hydroxide and if hydrogen chloride was used for acidifying the mixture M. Typical sodium chloride concentrations are in the range of from 5 to 15 % by weight based on the total weight of acidified mixture M / crude DIOPAT suspension.

[0084] In step b) of the process according to the present invention, the acidified mixture M, also referred to as crude DIOPAT suspension, is diluted with water. The water used for dilution may be any water, such as deionized or distilled water or tap water, but is preferably as pure as possible and free of substantial amounts of salts and solutes.

[0085] The volume of water added in (b1) may be selected such that a dilution factor of 1 .2 to 1 .8, preferably 1 .3 to 1 .6, for example 1 .35 to 1 .55, such as 1 .40 to 1 .50, is achieved. The lower limit may be 1 .20, 1 .25, 1 .30, 1.35 or 1.40 and the upper limit may be 1.8, 1.7, 1.65, 1.60, 1.55 or 1.50. Lower dilution factors fail to provide for the desired effect of allowing a reduction of temperature during the filtration without impairing the separation from 2,4-DHBP, while higher dilution factors are disadvantageous with respect to energy and time consumption needed for later concentrating the DIOPAT.

[0086] Alternatively or additionally, the dilution with water in (b2) may be done to a pH increase of 0.1 to 1 .0. It is understood that by adding water to the acidified DIOPAT suspension, the pH will increase. Thus, the pH increase is another measure for the volume of water added. The addition of water is typically done to effect a pH increase of between 0.10 and 1 .00, such as 0.10 to 0.90, 0.10 to 0.80, 0.10 to 0.70, 0.10 to 0.60, 0.11 to 0.59, 0.12 to 0.58, 0.13 to 0.57, 0.14 to 0.56, 0.15 to 0.55, 0.16 to 0.54, 0.17 to 0.53, 0.18 to 0.52, 0.19 to 0.51 , 0.20 to 0.50, 0.11 to 0.39, 0.12 to 0.38, 0.13 to 0.37, 0.14 to 0.36, 0.15 to 0.35, 0.16 to 0.34, 0.17 to 0.33, 0.18 to 0.32, 0.19 to 0.31 , 0.20 to 0.30, 0.21 to 0.29, 0.22 to 0.28, 0.23 to 0.27, or 0.24 to 0.26. The pH increase is adjusted such that the pH of the suspension does not exceed a pH of 5.5, preferably does not exceed 5.0, 4.5, 4.0, 3.5 or 3.0, more preferably does not exceed 2.5, most preferably remains 2.0 or less. This ensures that the DIOPAT remains precipitated and the aluminum salts remain in solution.

[0087] Alternatively or additionally, the dilution with water in (b3) may be done to a target DIOPAT concentration. For example the dilution with water may effect a decrease of the DIOPAT concentration in the suspension of at least 0.1 wt.-%, relative to the total weight of the suspension, for example of at least 0.2 or at least 0.25 wt.-%. The target DIOPAT concentration may be in the range of 1 .0 to 3.0 wt.-%, for example 1 .1 to 2.9, 1 .2 to 2.8, 1 .3 to 2.7, 1 .4 to 2.6, 1 .5 to 2.5, 1 .6 to 2.4, 1 .7 to 2.3, or 1 .8 to 2.2 wt.-%, all relative to the total weight of the suspension. It is understood that if the starting concentration of DIOPAT in the crude DIOPAT suspension is already within the given target range, water is added to further lower its concentration, preferably by at least 0.1 wt.-%, relative to the total weight of the suspension, for example of at least 0.2 or at least 0.25 wt.-% or at least 0.3 wt.-% or at least 0.35 wt.-%, or at least 0.4 wt.-%, or at least 0.45 wt.-% or at least 0.50 wt.-%.

[0088] Alternatively or additionally, the dilution with water in (b4) may be done to a target 2,4-DHBP concentration. For example the dilution with water may effect a decrease of the 2,4-DHBP concentration in the suspension of at least 0.01 wt.-%, relative to the total weight of the suspension, for example of at least 0.02 or at least 0.025 wt.-%. The target 2,4-DHBP concentration may be less than 0.25 wt.-%, relative to the total weight of the suspension, for example in the range of 0.05 to 0.23 wt.-%, for example 0.06 to 0.22, 0.07 to 0.21 , 0.08 to 0.20, 0.09 to 0.19, 0.10 to 0.18, 0.11 to 0.17 or 0.12 to 0.16 wt.-%, all relative to the total weight of the suspension. It is understood that if the starting concentration of 2,4-DHBP in the crude DIOPAT suspension is already within the given target range, water is added to further lower its concentration, preferably by at least 0.01 wt.-%, relative to the total weight of the suspension, for example of at least 0.02 or at least 0.025 wt.-%.

[0089] It is understood that in determining the amount of water to be added, two or more of the above target parameters may be combined, so that, for example, water may be added to a dilution factor in the range of 1 .2 to 1 .8 (b1) and a pH increase of 0.1 to 1 .0 (b2).

[0090] Accordingly, in various embodiments, the dilution is such that the following conditions are satisfied, including the above preferred options: (b1) and (b2);

[0091] (b1) and (b3);

[0092] (b1) and (b4);

[0093] (b2) and (b3);

[0094] (b2) and (b4);

[0095] (b3) and (b4);

[0096] (b1), (b2) and (b3);

[0097] (b1), (b2) and (b4);

[0098] (b1), (b3) and (b4);

[0099] (b2), (b3) and (b4); and

[0100] (b1), (b2), (b3) and (b4).

[0101] In step c) of the process according to the present invention, the diluted DIOPAT suspension obtained in step b) is heated to a temperature in the range of from more than 50 °C to 95 °C. This may be done by a suitable heating device. Preferably, the diluted DIOPAT suspension is heated to a temperature in the range of from more than 50 °C to 90 °C, more preferably more than 60 °C to less than 80 °C. “More than 50°C” or “more than 60°C” as used herein relate to temperatures that are higher than 50.0 or higher than 60.0 °C, respectively. For example, a temperature of 50.1 would thus meet the requirement of being more than 50 °C. The same applies to the term “less than” in relation to a temperature. “Less than 80 °C” thus means less than 80.0 °C, for example 79.9 °C. Preferably the respective ranges are thus 50.1 to 79.9 °C or 60.1 to 79.9 °C. The lower limit is, in various embodiments, 51 , 52, 53, 54, 55, 56, 57, 58, 59, 60, 61 , 62, 63, or 64 °C. The upper limit is, in various embodiments, 79, 78, 77, 76, or 75 °C. In some embodiments the temperature may be about 70 °C, such as 68, 69, 70, 71 , or 72 °C. It may be generally preferred to keep temperatures below 90, preferably below 85 and more preferably below 80 °C to save energy. Surprisingly, it has been found that temperatures lower than 80° but higher than 50 °C, preferably higher than 55, or 60 °C are still high enough to provide 2,4-DHBP in dissolved form if the crude DIOPAT suspension is diluted as described herein above. The optional concentration step d) and the following separation step e) are therefore performed at elevated temperatures and a low pH value. This limits the possible materials to be used for the ultrafiltration / diafiltration. In particular, due to the elevated temperature of from more than 50 °C to 95 °C, the high NaCI load of from 5 % to 15 % by weight, and the acidic conditions (pH < 2 or pH <1) of the DIOPAT suspension, the DIOPAT suspension is very corrosive to steel.

[0102] Accordingly, for the filtration steps according to the present invention, any suitable ceramic membrane that can withstand these conditions may be used. Thereby, a suitable ceramic membrane needs to fulfill at least the criteria that i) no corrosion will take place, ii) the membrane is permeable for the dissolved components, in particular for sodium chloride, aluminum trichloride and also for the organic by-products, such as 2,4- DHBP, iii) the membrane is resistant to a pH below 1 , and iv) the membrane is suitable for applications at temperatures of up to 95 °C.

[0103] Suitable ceramic membrane materials are selected from the group consisting of TiC>2, ZrC>2, or AI2O3. The most preferred ceramic membrane material for membranes with pore sizes of 50 nm and more is AI2O3. Membranes with smaller pores are preferably made of ZrC>2.

[0104] The ceramic membrane may have, depending on the type of filtration it is used for, a pore size in the range of less than 50 nm for ultrafiltration membranes, typically having a cutoff in the range of 0.9 to 200 kDa. Typical pore sizes are up to 20 nm, for example 1 to 20 or 2 to 10 nm.

[0105] Greater pore sizes of 50 to 800 nm, preferably from 50 to 500 nm, more preferably from 50 to 400 nm, even more preferably from 50 to 200 nm, and especially preferably from 50 to 100 nm are used in case the membrane is used for microfiltration.

[0106] Preferably, the pore size of the ceramic membrane is provided as the mean pore size as determined by the bubble-rest described in American Society for Testing and Materials Standard (ASMT) Method F316.

[0107] The ceramic membrane may be provided in the form of a tubular, multi-channel or monolithic element, wherein a multi-channel element is preferred. Typically, the ceramic material has a multilayer structure with pore sizes ranging from larger pore sizes to smaller pore sizes, in order to provide, e.g. a macroporous support and a microporous top layer oriented to the retentate.

[0108] For example, a ceramic membrane having a pore size of 50 nm as the relevant value for the diafiltration step may comprise membrane layers with pore sizes of 400 nm, 200 nm, and 50 nm, wherein the smaller pore sizes will be on the side of the retentate. For the characterization of the ceramic membrane regarding the filtration properties, the smallest pore size oriented to the permeate is of relevance.

[0109] In a preferred embodiment, the ceramic membrane is an (1-AI2O3 membrane having a pore size of 50 nm with 400 / 200 / 50 nm membrane layers. In one embodiment of the present invention, the ceramic membrane is a tubular ceramic membrane, through which the retentate flows, while the permeate stream exits the tubular ceramic membrane laterally through the ceramic membrane.

[0110] In another embodiment of the present invention, the ceramic membrane is a multi-channel element comprising several channels within the ceramic membrane material, e.g. from 7 to 211 channels, preferably from 7 to 37 channels, wherein the retentate flows through the channels, while the permeate stream exits the multi-channel element laterally through the ceramic membrane. In a particular embodiment of the present invention, suitable multi-channel elements comprise 7, 19, 37, 61 , 85, or 211 channels, preferably

[0111] 7 or 19 channels.

[0112] The length of the multi-channel element is preferably in a range of from 0.5 to 2 m, preferably from 0.5 to 1 .5 m, more preferably from 1 .0 to 1 .5 m.

[0113] The inner diameter of the channels of the multi-channel element is preferably in the range of from 2 to

[0114] 8 mm. The overall diameter of the multi-channel element is preferably in the range of from 25 to 80 mm, preferably from 25 to 41 mm, more preferably 25.4 or 41 mm.

[0115] Thus, in a preferred embodiment of the invention, the ceramic membrane is provided in the form of a multichannel element having a length of from 0.5 to 1 .5 m and an inner channel diameter of from 1 .5 to 8 mm, preferably of 6 mm, wherein the multi-channel element preferably comprises from 7 to 19 channels. Particularly preferred is a multi-channel element having a length of from 1.0 to 1.5 m, an inner channel diameter of 6 mm, wherein the multi-channel element preferably comprises 7 or 19 channels. The overall diameter is then preferably from 25 or 41 mm.

[0116] The filter surface per element can be calculated from the length, the inner channel diameter and the number of channels of the element. In certain embodiments, the filter surface per element is from 0.02 to 3 m2, preferably from 0.02 to 2 m2, more preferably from 0.05 to 1 .5 m2, in particular from 0.1 to 0.6 m2.

[0117] According to the invention, a single-channel element may have, e.g., a 1 / 6 or a 1 / 16 geometry. Thereby, the 1 / 6 geometry denotes that the element has one channel and an inner channel diameter of 6 mm. A 1 / 16 geometry thus denotes that the element has one channel and an inner diameter of 16 mm.

[0118] According to the invention, the multi-channel element may have, e.g., a 7 / 6 (i.e. the element has seven channels and an inner channel diameter of 6 mm), a 19 / 3.3, a 37 / 2, a 19 / 4, a 19 / 6, a 37 / 3.8, a 61 / 2.5, a 19 / 8, a 85 / 3.3, or a 211 / 2 geometry. In one preferred embodiment, the multi-channel element has a 7 / 6 or 19 / 6 geometry and 1.2 to 1.5 m length. Particularly preferred is a multi-channel element with a 19 / 6 geometry and 1 .5 m length.

[0119] In one embodiment, the ultrafiltration step d) and / or the diafiltration step e) of the process according to the invention is performed at a feed pressure of from 0.5 to 5 bar, preferably from 1 .0 to 3.5 bar, and more preferably from 1 .5 to 3.0 bar. In this connection, the term “feed pressure” refers to the pressure with which the feed DIOPAT suspension, i.e. (I) the heated acidified diluted DIOPAT suspension obtained in step c) is provided to perform the ultrafiltration step d) or (II) the heated acidified and optionally concentrated diluted DIOPAT suspension obtained in step c) or d) is provided to perform the diafiltration step e), i.e. the pressure with which feed DIOPAT suspension is passed through the ceramic membrane element, in order to separate the precipitated DIOPAT from the dissolved 2,4-DHBP and the dissolved aluminum salts by means of ultrafiltration or diafiltration.

[0120] In the ultrafiltration step d) the precipitated DIOPAT is concentrated by reducing the volume of the continuous phase by the ultrafiltration. As the membrane used is permeable for the dissolved aluminum salts, 2,4-DHBP and other salts, such as NaCI, the concentration of these dissolved components remains essentially unchanged while the concentration of the precipitated DIOPAT increases.

[0121] This concentration step d) is typically carried out such that the concentration of the DIOPAT in the diluted DIOPAT suspension increases by at least 0.10 wt.-% relative to the total weight of the suspension. In various embodiments, the increase is by at least 0.15, O.2., 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 055, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.120, 1.25, 1.30, 1.35, 1.40, 1.45 or 1.50 wt.-% relative to the total weight of the suspension and relative to the starting concentration in the diluted DIOPAT suspension. The target DIOPAT concentration may be in the range of from 2.5 to 4.0 wt.-%, relative to the total weight of the suspension, for example 2.6 to 3.8, 2.7 to 3.5, 2.8 to 3.4 or 3.0 to 3.3 wt.- %. During said filtration step, the temperature is kept in the above-described elevated range of from more than 50 °C to 95 °C, preferably more than 50 °C to 90 °C, more preferably more than 60 °C to less than 80 °C. This ensures that the undesired components stay in solution and are not simultaneously enriched together with the DIOPAT.

[0122] In one embodiment, the ultrafiltration step d) and / or the diafiltration step e) of the process according to the invention, preferably both, are performed at a cross flow of from 1.5 to 5 m / s, preferably from 2 to 5 m / s, more preferably from 2.5 to 4 m / s, and in particular from 3 to 4 m / s. both steps are thus preferably carried out as crossflow filtration steps (also referred to as tangential flow filtration).

[0123] In one embodiment, the invention relates to the process for isolating DIOPAT according to the present invention, wherein, in the ultrafiltration step d) and / or the diafiltration step e), preferably both, the feed pressure is from 1 .0 to 3.5 bar and the cross flow is from 2 to 5 m / s.

[0124] The purity of the DIOPAT obtained in step e) of the process of the invention is typically increased by washing the suspension in the retentate of the diafiltration step with water. Preferably, washing water is continuously introduced into the diafiltration system on the retentate side, while the permeate is continuously removed. Due to the dilution with water, the pH value in the retentate may increase over time. However, the amount of water is adapted such that the pH value increases to a value of at most 5.5 or 4.0, preferably at most 3.0 or at most 2.5. Furthermore, it is required to preheat the washing water, in order to ensure that the temperature remains in the desired temperature range described above, such as more than 50 °C to 95 °C.

[0125] In a preferred embodiment, the separation step e) therefore involves continuous washing of the suspension in the retentate with water, and removing of the permeate, whereby the pH slowly increases to at most 5.5, preferably at most 4.0 or at most 3.0 and the temperature remains in the range of from more than 50 to 95 °C (or any other of the preferred ranges described above). Preferably, the overall volume of the retentate and the permeate is kept constant by removing the same volume of permeate as the volume of washing water that is introduced into the retentate.

[0126] During the washing process, the DIOPAT concentration remains constant. To separate the Al-salts and organic by-products, the DIOPAT suspension is pumped from the feed vessel to the ceramic membrane element and from there back to the feed vessel. In the ceramic membrane, the dissolved components (Al- salts and some organic components such as 2,4-DHBP) pass through the membrane. The DIOPAT particles stay in the suspension and go back to the feed vessel. The aqueous phase with the dissolved components (e.g. Al-salts and organic components such as 2,4-DHBP) passing through the membrane is called permeate, the suspension, comprising DIOPAT, that goes back to the feed vessel is called retentate.

[0127] The permeate is preferably sent to a wastewater treatment plant. Thus, the process may be performed as a batch process. Alternatively, the process may be performed as a continuous process. This would require that the ultrafiltration unit comprises 3 or 4 filtration loops, which are connected in series. The diafiltration water then has to be added to each filtration loop.

[0128] The feed DIOPAT suspension may be washed with a washing factor (diafiltration factor) of e.g. 2.0, meaning that the amount of water (volume) used for washing the DIOPAT suspension is equal to 2.0 times of the DIOPAT suspension amount (volumes). The higher the washing factor, the lower will be the Al-salt concentration in the retentate and the lower will be the 2,4-DHBP concentration.

[0129] It is preferred to wash with a washing factor of 2.5 or more, such as 3.0 or more, 3.5 or more, 4.0 or more, 4.5 or more or 5.0. In one preferred embodiment, the amount of washing water is at least three times as high as the amount of the suspension in the retentate. In another preferred embodiment, the amount of washing water is at most six times as high as the amount of the suspension in the retentate.

[0130] To keep the temperature of the retentate elevated during the whole washing process, it may be preferred to preheat the washing water by an external heat exchanger. Alternatively, the washing water may be heated before use by direct steam injection. Accordingly, in one embodiment, the washing water is heated before use, preferably by an external heat exchanger or direct steam injection.

[0131] The diafiltration step e) also results in concentrating the feed DIOPAT suspension to a certain extent, as the permeate is separated. The volume of the retentate is then kept constant during the washing with water as indicated above. The concentration factor defines the ratio of the volume of the feed DIOPAT suspension to the volume of the retentate comprising the precipitated DIOPAT.

[0132] In one embodiment, the concentration factor of the retentate is less than 2.5, preferably less than 1 .9, more preferably less than 1.8. In another embodiment, the concentration factor of the retentate is in a range of from 1 .4 to 2, preferably from 1 .5 to 1 .9, more preferably from 1 .6 to 1 .8.

[0133] In one embodiment, the concentration factor of the retentate is less than 2.5, preferably from 1 .6 to 1 .8.

[0134] In one embodiment, the total diafiltration factor, also referred to as washing factor, as defined above, is less than 6, preferably less than 5. In another embodiment, the total diafiltration factor is in the range of from 2 to 7, preferably from 3 to 6, in particular from 3.5 to 5.5, e.g. 4.5.

[0135] In summary, the process of the present invention comprising steps a), b), c), optionally d), and e) provides the DIOPAT in precipitated form in the form of an aqueous suspension in the retentate of the diafiltration. The obtained aqueous suspension of DIOPAT is concentrated in comparison to the alkaline mixture M.

[0136] Furthermore, 2,4-DIOPAT and aluminum salts as well as additional salts, which are, e.g., formed during acidifying the mixture M have been separated as the permeate from the aqueous DIOPAT suspension.

[0137] In one embodiment, the amount of Al-salts in the DIOPAT suspension after step e) is less than about 0.02 wt.-%, preferably less than about 0.015 wt.-%, more preferably less than about 0.01 wt.-%, in particular less than about 0.008 wt.-%, based on the total weight of the DIOPAT suspension after step e).

[0138] In one embodiment, the amount of 2,4-DHBP in the DIOPAT suspension after step e) is less than about 0.3 wt.-%, preferably less than about 0.2 wt.-%, more preferably less than about 0.15 wt.-%, in particular less than about 0.1 wt.-%, based on the total weight of the DIOPAT suspension after step e).

[0139] In one embodiment, the amount of DIOPAT in the DIOPAT suspension after step e) is at least about 1.5 wt.-%, preferably at least about 2 wt.-%, more preferably at least about 3 wt.-%, in particular at least about 4 wt.-%, based on the total weight of the DIOPAT suspension after step e).

[0140] In another embodiment, the amount of resorcinol in the DIOPAT suspension is reduced by at least about 80 %, preferably at least about 85 %, more preferably at least about 90 %, after step e), compared to the amount of resorcinol in the feed DIOPAT suspension.

[0141] In one embodiment, the amount of benzoic acid in the DIOPAT suspension is reduced by at least about 80 %, preferably at least about 90 %, more preferably at least about 95 %, after step e), compared to the amount of benzoic acid in the feed DIOPAT suspension. In one embodiment, the amount of 2,4-DHBP in the DIOPAT suspension is reduced by at least about 60 %, preferably at least about 70 %, more preferably at least about 80 %, after step e), compared to the amount of 2,4-DHBP in the feed DIOPAT suspension.

[0142] In one embodiment, the amount of Al-salts in the DIOPAT suspension is reduced by at least about 80 %, preferably at least about 90 %, more preferably at least about 95 %, after step e), compared to the amount of Al-salts in the feed DIOPAT suspension.

[0143] In one embodiment, the amount of NaCI in the DIOPAT suspension is reduced by at least about 80 %, preferably at least about 90 %, more preferably at least about 95 %, after step e), compared to the amount of NaCI in the feed DIOPAT suspension.

[0144] The process of the invention may further comprise neutralizing and concentrating the obtained aqueous suspension comprising DIOPAT of the retentate. It is to be understood that this step may also be part of step e).

[0145] In various embodiments, the process of the invention may further comprise a step f) of concentrating the retentate obtained in step e), preferably by ultrafiltration, preferably to increase the concentration of the DIOPAT in the enriched DIOPAT suspension by at least 0.1 wt.-%, preferably by 0.2 to 2.5 wt.-%, relative to the total weight of the suspension. Said step may thus be similarto step d) described above but is carried out after the diafiltration step e). All preferred embodiments described above in relation to step d) similarly apply to this step f). The target DIOPAT concentration may however be higher, for example as high as 6.0 or 5.0 wt.-%.

[0146] In one embodiment, the process according to the present invention further comprises the step g) of neutralizing the aqueous suspension of the retentate. Thereby, the suspension preferably is neutralized to obtain a pH of from 5.5 to 10, more preferably from 6 to 10, 7 to 10 or 8 to 10, in particular about 9.

[0147] Directly after the neutralization of step g), the DIOPAT suspension may typically have a solid content in the range of from about 3 % to about 6 %, preferably from about 3 % to about 5.5 %, more preferably from about 3.5 % to about 5 %, in particular from about 4.0 % to about 4.5 %, in each case based on the total weight of the DIOPAT suspension.

[0148] Optionally, the aqueous suspension of the retentate may simultaneously be concentrated while neutralizing, preferably neutralizing the aqueous suspension of the retentate to obtain a pH of from 5.5 to 10, more preferably from 7 to 10, in particular about 9.5. Said concentration may be done by combining steps f) and g) and may be carried out as described for step f) above. Alternatively, the aqueous suspension of the retentate may be concentrated after neutralizing (in a concentration step h)), preferably neutralizing the aqueous suspension of the retentate to obtain a pH of from 5.5 to 10, more preferably from 7 to 10, in particular about 9.5. Neutralizing in step g) may be performed by any suitable base known in the art. The base may be an inorganic or an organic base, preferably an inorganic base, more preferably sodium hydroxide or sodium carbonate, in particular sodium hydroxide.

[0149] In one embodiment, the invention relates to the process for isolating DIOPAT according to the present invention, wherein the process further comprises the step of g) neutralizing the aqueous suspension of the retentate obtained in step e) or the concentrated retentate obtained in step f) to obtain a pH of from 8 to 10, and optionally simultaneously concentrating the aqueous suspension, in particular if a separate concentration step f) has been omitted or further concentration after step f) is desired.

[0150] In one embodiment, the process according to the present invention further comprises the concentrating step h) of the aqueous suspension obtained in step g), which is also referred to as a de-watering process. Concentrating may be performed by any method known in the art such as evaporation or filtration, preferably filtration. It has been found that such filtration (for example at pH 9.0 to 9.5) is particularly advantageous with respect to the removal of organic side products and salts. With regard to concentrating by filtration, any known filter may be used, such as a Dyno Filter (Bokela).

[0151] The concentration step h) may be performed after washing the neutralized aqueous suspension with water. Alternatively, the concentration step h) may be performed without prior washing the neutralized aqueous suspension with water. In one preferred embodiment, the concentration step h) is performed after washing the neutralized aqueous suspension with water.

[0152] Generally, the concentrating results in an increase of the solid content in the aqueous suspension from about 2 % to about 6 % up to about 10 % to about 25 %, preferably from about 3 % to about 6 % up to about 12 % to about 20 %, more preferably from about 4 % to about 5 % up to about 15 % to about 16 %, in each case based on the total weight of the DIOPAT suspension.

[0153] In one embodiment, the invention relates to the process for isolating DIOPAT according to the present invention, wherein the process further comprises the step of h) concentrating the neutralized aqueous suspension by filtration, after optionally washing the neutralized aqueous suspension with water.

[0154] In one embodiment, the invention relates to the process for isolating DIOPAT according to the present invention, wherein the process further comprises the step of i) drying the concentrate obtained in step h). However, said drying may also be done after any of the earlier steps, such as in particular step g), for example if the neutralizing step is already combined with a concentration step.

[0155] Drying may be performed by any method known in the art such as spray drying, evaporation, air drying, under vacuum, filtration, centrifugation, freeze drying, or mixtures thereof, preferably spray drying. Suitable spray drier are jet or disc spray drier. In one embodiment, the amount of Al-salts in the dried DIOPAT mass is less than about 0.5 wt.-%, preferably less than about 0.4 wt.-%, more preferably less than about 0.3 wt.-%, in particular less than about 0.2 wt.-%, based on the total weight of the dried DIOPAT mass.

[0156] In one embodiment, the amount of 2,4-DHBP in the dried DIOPAT mass is less than about 5 wt.-%, preferably less than about 3 wt.-%, more preferably less than about 2 wt.-%, in particular less than about 1 .8 wt.-%, based on the total weight of the dried DIOPAT mass.

[0157] In one embodiment, the amount of DIOPAT in the dried DIOPAT mass is at least about 80 wt.-%, preferably at least about 83 wt.-%, more preferably at least about 85 wt.-%, in particular at least about 87 wt.-%, based on the total weight of the dried DIOPAT mass.

[0158] In a particular embodiment, the invention relates to the process for isolating DIOPAT according to the present invention, wherein the separation step e) involves continuous washing of the suspension in the retentate with water, and removing of the permeate, and wherein the process further comprises at least the steps of g) neutralizing the aqueous suspension of the retentate obtained in step e) to obtain a pH of from 6 to 8, and optionally simultaneously concentrating the aqueous suspension; h) concentrating the neutralized aqueous suspension obtained in step g) by filtration, optionally after washing the neutralized aqueous suspension with water; and i) drying the concentrate obtained in step e).

[0159] The process for isolation DIOPAT according to the present invention is especially advantageous in view of production costs, as due to unexpected removal of 2,4-DHBP from the DIOPAT suspension, the consumption of the expensive reactant isooctyl chloride in the last reaction step to Tinosorb® S is reduced significantly. Together with the reduced energy consumption for heating the suspension and washing water to lower temperatures than reported before in the art which already significantly reduces costs, this further reduces the costs of the final synthesis step to Tinosorb® S as well as the costs of product workup of Tinosorb® S to reach the final specification.

[0160] The diafiltration process according to the present invention further provides a much more stable and higher performance of the diafiltration and avoids unnecessary manual process steps.

[0161] The present invention is further illustrated by the following example. Examples

[0162] The crude DIOPAT suspension was transferred to the ultrafiltration (UF) unit during circulation of rinsing water (dilution step) at operational temperature. Rinse water pH was at about 3. Cross flow was at 3.5 m / s. There was no permeate flow. The transfer was carried out in a deep-pipe to avoid air bubbles.

[0163] Start DIOPAT concentration was about 2.3 wt.-%. The transfer was completed and operational temperature reached. Then the concentration was started and permeate flow controlled to reach about 300l / m2h permeate flux. The concentration step was considered completed at a DIOPAT concentration of 3.2 wt.-%.

[0164] Then the diafiltration (DF) step was started. The amount of diafiltration medium (water) was 4.5xthe amount of suspension in the UF system (DF factor = 4.5). The amount of produced permeate was identical to the amount of added DF water. Due to water addition at the same rate as permeate production, the volume in the system stayed constant. DIOPAT concentration was constant at 3.2 wt.-%.

[0165] Subsequently, a concentration step was conduced to achieve a DIOPAT concentration of 4.0 wt.-%.

[0166] Sampling: The sampling and the analysis were the same independent from the process step. Samples of permeate and retentate were taken for Dry content (DC) and NaCI content, Al content, DIOPAT content and content of side product 2,4-DHBP. DC was measured with DC scales. NaCI was measured by titration. DIOPAT and 2,4-DHBP were determined via HPLC using

[0167] Agilent 1 100 column material: EUROSPHER 100-C18 / 5 Knauer column length: 25 cm, column diameter: 4 mm column temperature: 20 °C injection volume: 5 pl mobile phase: eluent A: 900 Deionat (2) + 100 acetate buffer pH 4.65 (3) + 0.2 % TBAHS, eluent B: acetonitrile (1) + 0.2 % TBAHS method: flow: 1 .0 mL / min, pressure: max. 400 bar, stop time: 30 min

[0168] Timetable:

[0169] The results are shown in Table 1 below. Table 1 : Summary of the analytical data of DHBP, DIOPAT and the salts for trials conducted at different temperatures (Ret.=Retentate after second concentration step, elim.=Elimination of component) '

[0170] Control experiments were carried out as follows:

[0171] The crude DIOPAT suspension was transferred to the ultrafiltration (UF) unit without dilution at operational temperature. Cross flow was at 3.5 m / s. There was no permeate flow. pH of the crude DIOPAT suspension was -0.3 to 0.

[0172] Start DIOPAT concentration was about 3.00±0,05 wt.-%. The transfer was completed and operational temperature reached. Then the concentration was started and permeate flow controlled to reach about 300l / m2h permeate flux. The concentration step was considered completed at a DIOPAT concentration of 3.2 ±0,05 wt.-%.

[0173] Then the diafiltration (DF) step was started. The amount of diafiltration medium (water) was 4.5xthe amount of suspension in the UF system (DF factor = 4.5). The amount of produced permeate was identical to the amount of added DF water. Due to water addition at the same rate as permeate production, the volume in the system stayed constant. DIOPAT concentration was constant at 3.2 wt.-%.

[0174] Subsequently, a concentration step was conduced to achieve a DIOPAT concentration of 5.0 wt.-%.

[0175] Results are shown in Table 2 below. Table 2: Summary of the analytical data of DHBP, DIOPAT and NaCI for trials conducted at different temperatures according to old procedure (Ret.=Retentate after second concentration step, elim.=Elimination of component) The following problems were encountered during these control experiments: viscosity increased with increasing temperature. Above 90-92°C the viscosity increase was significant. The viscosity increased with low shear rate. There was a high energy demand to heat up the high volume of DF water. Lower temperatures resulted in significantly lower removal of 2,4-DHBP. In contrast to these controls, the inventive processes had the following advantages: The viscosity was significantly lower and an operational temperature about 20°C below the temperature where a significant increase in viscosity was observed could be used without compromising 2,4-DHBP removal. This provides for a high safety temperature margin and a more stable procedure. The energy consumption was significantly lower due to a lower temperature of the DF water needed for achieving the same level of removal of side products and salts.

Claims

1. Claims1 . A process for enriching 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1 ,3,5-triazine (DIOPAT) from an aqueous alkaline mixture M comprising(i) 2,4-bis-(2,4-dihydroxyphenyl)-6-(4-methoxyphenyl)-1 ,3,5-triazine (DIOPAT);(ii) 2,4-dihydroxybenzophenone (2,4-DHBP); and(iii) aluminum salts; wherein the process comprises the steps of a) precipitating the DIOPAT by acidifying the mixture M to a pH <5, preferably <4, more preferably <3, even more preferably <2, most preferably <1 , to obtain a crude DIOPAT suspension; b) diluting the crude DIOPAT suspension with water(b1) by a dilution factor in the range of 1 .2 to 1 .8, preferably 1 .3 to 1 .6,(b2) to a pH increase of 0.1 to 1.0, preferably 0.1 to 0.6,(b3) to a DIOPAT concentration of 1 .0 to 3.0 wt.-%, preferably 1 .5 to 2.5 wt.%, relative to the total weight of the suspension, and / or(b4) to a 2,4-DHBP concentration of less than 0.25 wt.-%, preferably 0.05 to 0.23 wt.-%, to obtain a diluted DIOPAT suspension; c) heating the diluted DIOPAT suspension to a temperature in the range of from more than 50 °C to 95 °C, preferably more than 50 °C to 90 °C, more preferably more than 60 °C to less than 80 °C; d) optionally concentrating the precipitated DIOPAT by ultrafiltration to increase the concentration of the DIOPAT in the diluted DIOPAT suspension by at least 0.1 wt.-%, preferably by 0.2 to 1 .5 wt.-%, relative to the total weight of the suspension, whereby the temperature is kept in the range of from more than 50 °C to 95 °C, preferably more than 50 °C to 90 °C, more preferably more than 60 °C to less than 80 °C; e) separating the precipitated DIOPAT from the dissolved 2,4-DHBP and the dissolved aluminum salts by diafiltration of the DIOPAT suspension of step c) or d) with water, preferably with a ceramic membrane, whereby the pH increases to at most 5.5, preferably at most 4.0 or at most 3.0, and the temperature is kept in the range of from more than 50 °C to 95 °C, preferably more than 50 °C to 90 °C, more preferably more than 60 °C to less than 80 °C, wherein the separation step e) provides the precipitated DIOPAT in the form of an aqueous suspension in the retentate.

2. The process of claim 1 , wherein acidifying in step a) is performed with hydrogen chloride, preferably by adding the mixture M to an aqueous hydrogen chloride solution.

3. The process of claim 1 or 2, wherein in step b) the dilution is with water(b1) to a dilution factor of 1 .35 to 1 .50;(b2) to a pH increase of 0.15 to 0.6;(b3) to a DIOPAT concentration of 1 .8 to 2.5 wt.-% relative to the total weight of the suspension; and / or (b4) to a 2,4-DHBP concentration of 0.12 to 0.24 wt.-% relative to the total weight of the suspension.

4. The process of any one of claims 1 to 3, wherein the temperature in steps c) and e) and, optionally, step d) is kept in the range of >60 to <80 °C, preferably 61 to 79 °C, 62 to 78 °C, 65 to 75°C, or more preferably 67 to 73 °C.

5. The process of any one of claims 1 to 4, wherein the ultrafiltration step d) and / or the diafiltration step e) are carried out with a ceramic membrane, the ceramic membrane preferably being a TiC>2, ZrC>2, or AI2O3 membrane, preferably an (1-AI2O3 membrane.

6. The process of claim 5, wherein(1) the ceramic membrane has a pore size in the range of from 20 to 500 nm, preferably from 50 to 100 nm;(2) the ceramic membrane is an (1-AI2O3 membrane having a pore size of 50 nm, preferable with 400 / 200 / 50 nm membrane layers; and / or(3) the ceramic membrane is provided in the form of a multi-channel element having a length of from 0.5 to 1 .5 m and a channel diameter of from 3 to 8 mm, preferably of 6 mm, wherein the multi-channel element preferably comprises from 7 to 19 channels.

7. The process of any one of claims 1 to 6, wherein the feed pressure in the diafiltration step e) is from 1 .0 to 4 bar and the cross flow is from 2 to 5 m / s.

8. The process of any one of claims 1 to 7, wherein the separation step e) involves continuous washing of the suspension in the retentate with water and removing of the permeate.

9. The process of claim 8, wherein the diafiltration factor is at least 3.0, preferably 3.5 to 5.0.

10. The process of claim 8 or 9, wherein the washing water (diluent) is heated to the process temperature before use, preferably by an external heat exchanger or direct steam injection.11 . The process of any one of claims 1 to 10, wherein the volume concentration factor of the retentate in step e) relative to the diluted DIOPAT suspension of step b) is less than 3.0, preferably 1 .6 to 2.5.

12. The process of any one of claims 1 to 11 , wherein the process further comprises the step of f) concentrating the retentate obtained in step e) by ultrafiltration to increase the concentration of the DIOPAT in the enriched DIOPAT suspension by at least 0.1 wt.-%, preferably by 0.2 to 2.5 wt.-%, relative to the total weight of the suspension.

13. The process of any one of claims 1 to 12, wherein the process further comprises the step of g) neutralizing the aqueous suspension of the retentate obtained in step e) or the concentrated retentate obtained in step f) to obtain a pH of from 6 to 10, and optionally simultaneously concentrating the aqueous suspension.

14. The process of claim 13, wherein neutralizing in step g) is performed with sodium hydroxide or sodium carbonate, preferably with sodium hydroxide.

15. The process of claim 13 or 14, wherein the process further comprises the step of h) concentrating the neutralized aqueous suspension obtained in step g) by filtration, preferably by ultrafiltration, optionally after washing the neutralized aqueous suspension with water; and / or i) drying the suspension obtained in step e), step f), step g) or step h).

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