LIGHT RICE BRAN WAX OXIDATES WITH A HIGH ESTATE CONTENT

Description

[0001] The invention relates to light-colored rice bran wax oxidates with a high ester content and a medium acid number, a process for producing these oxidation products of rice bran wax, and their use for agricultural or forestry purposes, as an additive in plastics processing, in personal care products, in printing inks, and / or in varnishes. Saponified rice bran wax oxidates produced by the saponification of the rice bran wax oxidates according to the invention are also related.

[0002] The oxidation of fossil and non-fossil natural waxes with chromic acid has been known since the beginning of the 20th century and has been carried out industrially using fossil montan waxes since 1927 in the still-operated "Gersthofen process." Besides fossil montan wax, renewable natural waxes such as carnauba wax and candelilla wax can also be oxidized using these chromic acid-based processes. A process for the chromic acid oxidation of carnauba wax was described in 2004 by DE-A 10231886. However, natural carnauba waxes (grease gray, type 4; medium yellow, prima yellow, and flor, types 3 to 1) and crude montan wax (black) are distinctly dark in color. Oxidation with chromic acid leads to lighter wax products. However, depending on the amount of chromic acid used, the chromic acid bleaching of these natural waxes usually leads to high acid values, typically in the range of 130 to 160 mg KOH / g.

[0003] Oxidation with chromic acid essentially involves the cleavage of wax esters and the in-situ oxidation of the resulting wax alcohols to wax acids. The acid number is a measure of the content of free wax acids. Typical conversions of such oxidations range from 50% to 90% with respect to the ester groups. Natural waxes bleached in this way, in addition to the desired lightening, possess a higher saponification number and acid number than unbleached waxes, which is undesirable in some applications. However, rice bran wax oxidates with a higher acid number can be more easily derivatized, for example, by esterification.

[0004] For some applications, it is advantageous for the acid number to remain relatively low, but still high enough to allow derivatization to a significant extent. The acid number of wax oxidates can be reduced, for example, by esterifying the acids contained in the wax and / or wax oxidate with alcohols.

[0005] This esterification is often carried out with polyvalent alcohols, such as ethylene glycol, butylene glycol, or glycerin. However, this involves an additional step, which is disadvantageous from a process economics perspective.

[0006] Rice bran wax is an economically valuable natural wax, produced in large quantities as a byproduct of raw rice (Oryza sativa) processing. After the threshing of the ripe rice plants, the husks adhering to the grains are removed, and other husk components, along with other impurities, are separated in the rice mill. The rice grains still contain the germ and are enclosed by the bran. In a further processing step, the germ and bran are removed by milling, yielding rice bran along with the milled rice. Rice bran contains lipids, consisting predominantly of fatty oils and a smaller percentage of waxy components. These waxy components are found in the oil obtained from the bran by pressing or solvent extraction. Due to their low solubility at low temperatures, they can be isolated, for example, by freezing.According to the Journal of Scientific & Industrial Research, 2005, Vol. 64, 866-882, the calculated potential availability of rice bran wax, if the entire world rice production were used to obtain rice bran wax in addition to rice oil, is approximately 300,000 tons per year.

[0007] According to Ullmann's Encyclopedia of Industrial Chemistry, 5th ed. 1996, Vol. A28, p. 117, rice bran wax belongs to a group of waxes that have so far only been considered to have local significance or to be of purely academic interest.

[0008] The use of rice bran wax in cosmetics (EP-A 1343454; Bräutigam, Lexikon derkosmetikn Rohstoffe, Norderstedt 2010, p. 77), as a processing aid in plastics (JP-A H10-007862 (1998); JP-A S60-011553 (1985); JP-A S49-090739 (1974)) and in printing inks and electrophotographic toners (JP-A 2010-020304; 2010) has been described.

[0009] Despite numerous analytical investigations with conflicting results, the chemical composition of rice bran wax is apparently not fully understood. However, the composition of the wax body as wax esters is certain.

[0010] Rice bran wax esters consist mainly of monoesters of long-chain, saturated, unbranched monocarboxylic acids with long-chain, unbranched, aliphatic monoalcohols (hereinafter also referred to as "genuine esters"). The predominant acid components of rice bran wax esters are behenic and lignoceric acid, with chain lengths of C22 and C24, respectively, while the predominant alcohol components are chain lengths of C26, C28, C30, C32, and C34. The wax may also contain free fatty acids and other constituents such as squalene, phospholipids, and steryl esters.

[0011] The wax ester content in refined and defatted rice bran wax is generally greater than 96% by weight. In non-defatted rice bran wax, the wax ester content can be as low as 50% by weight, depending on the rice bran oil content. Other variable components of rice bran wax, considered to be present in trace amounts, include unspecified dark substances, squalene, and the so-called "gum content." These components usually result in product quality that varies in color and usability and is difficult to reproduce consistently.

[0012] The classic technique for lightening brown rice bran waxes is bleaching with hydrogen peroxide. Hydrogen peroxide-bleached rice bran waxes are yellowish and largely correspond to the original waxes in their ester content and acid value. These types are predominantly offered on the market as defatted and refined rice bran waxes, but because the minor components remain in the product, they also exhibit fluctuating product quality.

[0013] CN-A 108048222, CN-A 108129302, and CN-A 108191602 from 2018 describe rice bran wax oxidates produced from defatted rice bran wax by oxidation with sodium dichromate, esterified with a polyhydric alcohol (CN-A 108129302 and CN-A 108191602), and subsequently saponified (CN-A 108191602). However, no product properties are specified. Due to the esterification, it can be assumed that the acid numbers must be high.

[0014] EP-A 2909273 from 2015 discloses oxidation products of rice bran wax produced by oxidation with chromic acid in the presence of oxidation promoters such as fluorinated alkylsulfonic acids, aluminum trichloride, or hydrochloric acid, or under particularly vigorous stirring. This aims to achieve high acid numbers. EP-A 2909274 describes rice bran wax oxidates that are saponified prior to oxidation. High acid numbers are also achieved in this case.

[0015] JP-B S36-005526 (1961) describes the production of solvent-based polishing compounds containing a chemically modified wax derived from rice bran wax. The modification is achieved by oxidizing crude rice bran wax with chromic acid or dichromate salts, resulting in acid values ​​of 40-45 mg KOH / g.

[0016] DE 102018116113 discloses rice bran wax oxidates with acid numbers in the range of 45mg to 70mg KOH / g.

[0017] There is a need for a method to selectively provide rice bran wax oxidates with average acid numbers in the range of greater than 45 mg KOH / g and less than 70 mg KOH / g.

[0018] It has now been surprisingly found that, by appropriately selecting the process parameters for the oxidation of rice bran wax, acid values, measured according to DIN ISO 2114 (from 2002), of greater than 45 mg KOH / g and less than 70 mg KOH / g, often greater than 45 mg KOH / g and less than 65 mg KOH / g, can be achieved when the proportion of multiple esters, formed from polyhydric alcohols and aliphatic carboxylic acids with 8 to 20 carbon atoms, in the rice bran wax is less than 5 wt.%.

[0019] The ester waxes possess the desired acid number without the need for an additional esterification step. Such compounds could previously only be obtained by oxidizing rice bran wax to acid numbers in the range of approximately 140 mg KOH / g and subsequent esterification with polyalcohols (EP-A 2909274).

[0020] An object of the invention is therefore a process for the production of rice bran wax oxidates (O) with an acid number greater than 45 mg KOH / g and less than 70 mg KOH / g and a needle penetration number less than 3 mm -1< comprising the steps: i) Providing a rice bran wax (R) containing less than 5 wt%, based on the total weight of the rice bran wax (R), of multiple esters formed from polyhydric alcohols and aliphatic carboxylic acids with 8 to 20 carbon atoms; ii) Providing a mixture (M) of chromium trioxide and sulfuric acid; iii) Carrying out the oxidation of the rice bran wax (R) by reacting the rice bran wax (R) with the mixture (M) under stirring and at a temperature of 90 to 150 °C to obtain a rice bran wax oxidate (O); iv) Stopping the reaction and allowing the reaction mixture obtained in step iii) to stand until the organic phase is separated from the aqueous phase; v) Separating the organic phase;vi) optional removal of residues containing chromium compounds from the organic phase to obtain the rice bran wax oxidate (O) in purified form, vii) optional repetition of the sequence of steps ii) to vi) up to two times, using the rice bran wax oxidate (O), optionally in purified form, instead of the rice bran wax (R), ; wherein the oxidation in step iii) is carried out over a period of 1 to 8 hours, and wherein the weight ratio of total chromium trioxide used to rice bran wax (R) used is from 5:4 to 9:6 (1.25 to 1.5).

[0021] The rice bran wax (R) provided in step i) can be any rice bran wax, provided that it has a proportion of multiple esters formed from polyhydric alcohols and aliphatic carboxylic acids with 8 to 20 carbon atoms of less than 5 wt.%, preferably less than 2 wt.%, particularly preferably 0.1 to 2 wt.%, based on the total weight of the rice bran wax (R).

[0022] The desired proportion of polyhydric esters formed from polyhydric alcohols and aliphatic carboxylic acids with 8 to 20 carbon atoms can already be present in the raw rice bran wax, but can also be adjusted by pretreating the rice bran wax. Preferably, the proportion is already present in the raw rice bran wax (R). In this case, it is preferred that the rice bran wax (R) is not pretreated.

[0023] However, if the rice bran wax (R) contains proportions of multiple esters formed from polyhydric alcohols and aliphatic carboxylic acids with 8 to 20 carbon atoms, at a wt% or higher, it must be pretreated before being provided in step i). In this case, it is advantageous if the pretreatment does not include saponification of the esters contained in the rice bran wax (R).

[0024] Instead, extraction of the polyesters formed from polyhydric alcohols and aliphatic carboxylic acids with 8 to 20 carbon atoms using one or more organic solvents is preferred, wherein the extraction is carried out until the desired proportion of polyesters formed from polyhydric alcohols and aliphatic carboxylic acids with 8 to 20 carbon atoms of less than 5 wt% is reached. Any organic solvent capable of dissolving oils and fats is suitable, for example, ethyl acetate or acetone, preferably ethyl acetate.

[0025] The multiple esters formed from polyhydric alcohols and aliphatic carboxylic acids with 8 to 20 carbon atoms are preferably di- and triglycerides of aliphatic carboxylic acids with 8 to 20 carbon atoms, in particular oils naturally present in rice bran, especially rice bran oil. Accordingly, extraction with an organic solvent can result in de-oiling.

[0026] In this case, the proportion of multiple esters, formed from polyhydric alcohols and aliphatic carboxylic acids with 8 to 20 carbon atoms, of less than 5 wt% can also be referred to as the oil content of the rice bran wax.

[0027] Preferably, the rice bran wax (R), regardless of the proportion of multiple esters, is formed from polyhydric alcohols and aliphatic carboxylic acids with 8 to 20 carbon atoms in the crude state and is not pretreated at any time prior to oxidation by saponification.

[0028] The mixture (M) of chromium trioxide and sulfuric acid provided in step ii) can be any mixture capable of oxidizing oxidizable components of rice bran wax. Such mixtures of chromium trioxide and sulfuric acid are often referred to as chromium sulfuric acid. The sulfuric acid is concentrated sulfuric acid with a sulfur content of at least 90 wt.%, preferably at least 96 wt.%, and particularly preferably at least 99 wt.%. This can optionally be fuming sulfuric acid, i.e., containing additional sulfur trioxide. The concentration of chromium trioxide in the mixture (M) is preferably 50 to 200 g / L, particularly preferably 70 to 150 g / L, and most preferably 80 to 120 g / L.

[0029] In step iii) of the process according to the invention, the oxidation of the rice bran wax (R) is carried out by reacting the rice bran wax (R) with the mixture (M) under stirring and at a temperature of 80 to 150 °C, preferably 90 to 140 °C, particularly preferably 105 to 130 °C, to obtain a rice bran wax oxidate (O).

[0030] The weight ratio of total chromium trioxide to rice bran wax (R) used is preferably from 13:10 to 9:6 (1.3 to 1.5). If the ratio is less than 5:4, the acid values ​​will be too low. If the ratio is greater than 2:1, the acid values ​​will be too high.

[0031] This step can optionally be subdivided into several steps. For example, step iii) can include adding the mixture (M) and then adding the rice bran wax (R). Alternatively, step iii) can include adding the rice bran wax (R) and then adding the mixture (M). In these cases, the addition of the second component (R) or (M) can, for example, be carried out portion by portion, continuously, or in a batch, preferably portion by portion or continuously, and particularly preferably portion by portion.

[0032] Optionally, the temperature of the rice bran wax (R) and / or the mixture (M) can deviate from the reaction temperature during the addition and only be adjusted to the required value of 80 to 150 °C, preferably 90 to 140 °C, and particularly preferably 105 to 130 °C, after the addition of the second component. For example, the temperature at the time of addition can be 70 to 130 °C, preferably 80 to 110 °C. Preferably, the rice bran wax (R) is in molten form during the addition.

[0033] In one embodiment, the provided mixture (M) of chromium trioxide and sulfuric acid is placed and heated to a temperature of 70 to 130 °C, and the rice bran wax (R) is added in portions in solid form. After addition, the temperature is adjusted to 80 to 150 °C and the oxidation is carried out.

[0034] In another embodiment, the provided mixture (M) of chromium trioxide and sulfuric acid is placed and heated to a temperature of 70 to 130 °C, and the rice bran wax (R) is added in portions in a molten state, preferably at a temperature of 70 to 130 °C. After the addition, the temperature is adjusted to 80 to 150 °C and the oxidation is carried out.

[0035] In another embodiment, the rice bran wax (R) is placed and melted at a temperature of 70 to 130 °C, and the mixture (M) of chromium trioxide and sulfuric acid is added cold in portions.

[0036] After the addition, the temperature is set to 80 to 150 °C and the oxidation is carried out.

[0037] In another embodiment, the rice bran wax (R) is placed and melted at a temperature of 70 to 130 °C, and the mixture (M) of chromium trioxide and sulfuric acid is added portionwise while hot, preferably at a temperature of 70 to 130 °C. After addition, the temperature is adjusted to 80 to 150 °C and the oxidation is carried out.

[0038] In another embodiment, rice bran wax (R) and the mixture (M) of chromium trioxide and sulfuric acid are placed together at room temperature and slowly heated to a temperature of 80 to 150 °C, and the oxidation is carried out at this temperature.

[0039] At least the oxidation at 80 to 150 °C, and preferably also the addition of the rice bran wax (R) and / or the mixture (M), takes place under stirring. The stirring can be carried out in any manner, for example with a mechanically driven stirrer or a magnetically driven stirrer. Preferably, the stirring is carried out with a mechanically driven stirrer, particularly preferably with a mechanically driven stirrer comprising a KPG stirrer.

[0040] The stirring speed in step iii) is preferably in the range of 100 to 500 rpm (revolutions per minute), particularly preferably from 120 to 300 rpm, and most preferably from 170 to 250 rpm, since at a stirring speed below 100 rpm the mixing required for efficient oxidation is not achieved and at a stirring speed above 500 rpm there is an increased risk of the formation of an inseparable emulsion.

[0041] The oxidation of the rice bran wax in step iii) at a temperature of 90 to 150 °C takes place over a period of 1 to 8 hours, preferably 2 to 5 hours, particularly preferably 3 to 4.5 hours.

[0042] Furthermore, it is advantageous if no oxidation promoters are added to the reaction mixture of rice bran wax (R) and the mixture (M), as these can often lead to the cleavage of ester bonds and therefore increase the acid number in the rice bran wax oxidate (O). Preferably, therefore, no oxidation promoters are used in the oxidation, in particular no oxidation promoters such as emulsifiers (e.g., alkanesulfonates, fluorinated alkanesulfonates), surfactants, polymeric surfactants, nitrogen-containing cation surfactants, phase-transfer catalysts, Fenton reagents, metal salts, hydrochloric acid, or the like.

[0043] After the desired reaction time has been reached, the reaction is stopped in step iv) and the reaction mixture is allowed to stand until the organic phase separates from the aqueous phase. "Stopping the reaction" means that stirring is stopped and heating is discontinued. At this point, the separation of the floating organic phase, containing the rice bran wax oxide (O), from the sinking aqueous phase, containing sulfuric acid and chromium compounds, begins. Optionally, before being allowed to stand, the reaction mixture can be transferred to a device that facilitates the separation of the organic phase from the aqueous phase after its separation. An example of such a device is a separating funnel. Other devices for this purpose are known to those skilled in the art and are applicable here.

[0044] In step v), the organic phase containing the rice bran wax oxidate is separated. This can be done, for example, using a separatory funnel. Alternatively, the floating organic phase can be skimmed off using suitable technical means. Pouring the organic phase over the rim of a vessel is also possible. Methods for separating organic phases from aqueous phases after phase separation are generally known to those skilled in the art and applicable here.

[0045] Furthermore, optionally in step vi) the separated organic phase containing the rice bran wax oxidate can be further processed to remove residues containing chromium compounds from the organic phase and thus obtain the rice bran wax oxidate in purified form.

[0046] The work-up can be carried out by any method suitable for separating polar and / or water-soluble substances from organic substances. For example, chromatographic purification of the organic phase or filtration over silica gel can be performed.

[0047] Preferably, residues containing chromium compounds are removed by washing the organic phase with an aqueous solution of oxalic acid and / or sulfuric acid.

[0048] Alternatively, the removal of residues containing chromium compounds can preferably be carried out by washing the organic phase with water. Alternatively, the removal of residues containing chromium compounds can preferably be carried out by centrifuging the organic phase. "Washing" in each case means mixing the organic phase with the respective washing agent and subsequent phase separation according to steps iv) and v).

[0049] In a preferred embodiment, the removal of residues containing chromium compounds is carried out by simply or repeatedly washing the organic phase with an aqueous solution of oxalic acid and sulfuric acid, followed by simply or repeatedly washing the organic phase with water.

[0050] In a further preferred embodiment, the removal of residues containing chromium compounds is carried out by simply or repeatedly washing the organic phase with an aqueous solution of oxalic acid and sulfuric acid, followed by centrifuging the organic phase.

[0051] In another preferred embodiment, the removal of residues containing chromium compounds is carried out by simply or repeatedly washing the organic phase with water, followed by centrifuging the organic phase.

[0052] In a particularly preferred embodiment, the removal of residues containing chromium compounds is carried out by simply or repeatedly washing the organic phase with an aqueous solution of oxalic acid and sulfuric acid, followed by simply or repeatedly washing the organic phase with water, followed by centrifuging the organic phase.

[0053] Optionally, in step vii), the sequence of steps ii) to vi) can be repeated up to two times, using rice bran wax oxidate (O), optionally in purified form, instead of rice bran wax (R). Preferably, in step vii), the sequence of steps ii) to vi) is repeated up to one time. In these cases, at least half of the total chromium trioxide provided is used in the first execution of steps ii) to vi), and the remaining portion in the repetitions of steps ii) to vi). Particularly preferably, the sequence of steps ii) to vi) is not repeated.

[0054] A further object of the invention is a rice bran wax oxidate (O) with an acid number (measured according to DIN ISO 2114 of 2002) greater than 45 mg KOH / g and less than 70 mg KOH / g and with a needle penetration number less than 3 mm - 1, produced according to the inventive process. Preferably, the rice bran wax oxidate has an acid number greater than 45 mg KOH / g and less than 65 mg KOH / g.

[0055] Also part of the invention is a rice bran wax oxidate (O) with an acid number greater than 45 mg KOH / g and less than 70 mg KOH / g, preferably less than 65 mg KOH / g, with a needle penetration number less than 3 mm -1< and with a proportion of multiple esters formed from polyhydric alcohols and aliphatic carboxylic acids with 22 to 36 carbon atoms less than 5 wt.%, based on the total weight of the rice bran wax oxidate (O).

[0056] The rice bran wax oxidate (O) according to the invention preferably has a proportion of multiple esters formed from polyhydric alcohols and aliphatic carboxylic acids with 22 to 36 carbon atoms less than 5 wt.%, particularly preferably less than 3 wt.%, and most particularly preferably less than 1 wt.%, based on the total weight of the rice bran wax oxidate (O).

[0057] In one embodiment, the rice bran wax oxide (O) contains a) 10 to 40 wt%, based on the total weight of rice bran wax oxidate (O), free aliphatic carboxylic acids with 8 to 36 carbon atoms; b) 0 to 5 wt%, based on the total weight of rice bran wax oxidate (O), free aliphatic alcohols with 24 to 36 carbon atoms; c) 0 to 10 wt%, based on the total weight of rice bran wax oxidate (O), free aliphatic dicarboxylic acids with 10 to 30 carbon atoms; d) 45 to 90 wt%, based on the total weight of rice bran wax oxidate (O), genuine esters with 42 to 64 carbon atoms; and e) 0 to 15 wt%, based on the total weight of rice bran wax oxidate (O), other natural constituents contained in rice bran wax.

[0058] In a preferred embodiment, the rice bran wax oxide (O) contains a) 13 to 35 wt%, based on the total weight of rice bran wax oxidate (O), free aliphatic carboxylic acids with 8 to 36 carbon atoms; b) 0 to 3 wt%, based on the total weight of rice bran wax oxidate (O), free aliphatic alcohols with 24 to 36 carbon atoms; c) 0 to 4 wt%, based on the total weight of rice bran wax oxidate (O), free aliphatic dicarboxylic acids with 10 to 30 carbon atoms; d) 50 to 87 wt%, based on the total weight of rice bran wax oxidate (O), genuine esters with 42 to 64 carbon atoms; and e) 0 to 15 wt%, based on the total weight of rice bran wax oxidate (O), other natural constituents contained in rice bran wax.

[0059] In a preferred embodiment, the rice bran wax oxide (O) contains a) 15 to 30 wt%, based on the total weight of rice bran wax oxidate (O), free aliphatic carboxylic acids with 8 to 36 carbon atoms; b) 0 to 1 wt%, based on the total weight of rice bran wax oxidate (O), free aliphatic alcohols with 24 to 36 carbon atoms; c) 0 to 3 wt%, based on the total weight of rice bran wax oxidate (O), free aliphatic dicarboxylic acids with 10 to 30 carbon atoms; d) 55 to 85 wt%, based on the total weight of rice bran wax oxidate (O), genuine esters with 42 to 64 carbon atoms; and e) 0 to 15 wt%, based on the total weight of rice bran wax oxidate (O), other natural constituents contained in rice bran wax.

[0060] Preferably, lignoceric acid is contained in the rice bran wax oxidate (O) to a maximum of 5 wt.%, particularly preferably to a maximum of 3 wt.%, based on the total weight of the rice bran wax oxidate (O).

[0061] The weight fractions and chain length distributions can be measured, for example, using gas chromatography.

[0062] Furthermore, the rice bran wax oxides according to the invention typically have a dropping point measured according to DIN ISO 2176 (1997) between 70°C and 90°C, preferably between 75°C and 80°C.

[0063] The rice bran wax oxidates according to the invention preferably have a particularly light to white color compared to conventional oxidates (e.g., montan wax-based). The color can be determined using the iodine color number measured according to DIN 6162 (2014). For the rice bran wax oxidates according to the invention, this number is less than 20, preferably less than 6, and particularly less than 2.

[0064] Preferably, the saponification value, measured according to DIN ISO 3681 (2007), increases by a maximum of 40% through the oxidation of the rice bran wax, more preferably by a maximum of 30%, and particularly preferably by a maximum of 20%. This increase in saponification value can be mechanistically explained by the cleavage of the wax esters and the subsequent oxidation of the wax alcohols to acids. Additionally, some unsaturated carbon-carbon bonds are cleaved by the oxidizing agent and also oxidized to acids.

[0065] The saponification value is thus also a measure of the actual oxidation that has taken place, in contrast to saponification, in which the saponification value is known to remain unchanged, and in contrast to other bleaching processes that merely result in a lightening of the product. For example, bleaching rice bran wax with hydrogen peroxide does not cause any chemical modification of the wax in the sense of the invention, since only discoloring impurities and minor components are removed without altering the actual wax structure.

[0066] The rice bran wax oxide (O) according to the invention is typically characterized by a particularly good thermal stability, measured according to DIN 51006 (2005) with a mass loss up to reaching a temperature of 300 °C (heating rate: 5 °C / min) of less than 25%, preferably less than 20%, particularly preferably less than 17%.

[0067] A further aspect of the invention is a saponified rice bran wax oxide (V) produced by saponifying the rice bran wax oxide (O) described above with a basic metal salt selected from the group consisting of metal hydroxides (e.g., NaOH, KOH, Ca(OH)₂ and Zn(OH)₂, etc.), metal oxides (e.g., CaO, etc.), metal carbonates (e.g., Na₂CO₃, CaCO₃, etc.) or aqueous alkalis (such as NaOH, KOH, etc.). Alkali metal hydroxides and / or alkaline earth metal hydroxides, in particular NaOH, KOH and / or Ca(OH)₂, are preferred.

[0068] Examples of corresponding manufacturing instructions can be found in DE4019167. In addition to being based on renewable raw materials, the saponified products are preferably characterized by particularly good thermal stability, measured according to DIN 51006, with a mass loss of less than 10%, preferably less than 5%, until a temperature of 300 °C (heating rate: 5 °C / min) is reached.

[0069] The invention also relates to the use of the rice bran wax oxides (O) or the saponified rice bran wax oxides (V) according to the invention for agricultural or forestry purposes, as an additive in plastics processing, in care products, in printing inks and / or in varnishes.

[0070] The invention is explained in more detail by the following examples and claims. Substance characterization

[0071] The standard methods listed in Table 1, which are also used in the characterization of montan waxes and montan wax derivatives, serve to determine the characteristic values ​​of rice bran waxes, rice bran wax oxidates and other derivatives of rice bran waxes. Table 1 method Acid number (SN) [mg KOH / g] ISO 2114 Saponification number (VZ) [mg KOH / g] ISO 3681 Dropping point (TP) [°C] ISO 2176 Melting point (SP) [°C] DIN EN ISO 11357-1 Enthalpy of fusion (SE) [J / g] DIN EN ISO 11357-1 Oil content (OI) [wt.%] AOCS Yes 4-46 Thermogravimetric analysis (TGA) [wt%] DIN 51006 from 25 to 300°C at 5K / min, then 30 min at 300°C. Measurement of mass loss upon reaching 300 °C and after 30 min at 300 °C Iodine Colour Number (IFZ) DIN 6162 Calcium content [wt%] (CaG) DGF M-IV 4 Needle penetration number [mm -1< ] (NPZ) DIN 51579 Chain length distributions

[0072] The chain length distributions of the components of rice bran wax oxidates were determined by gas chromatography. Wax acids and wax alcohols with carbon chain lengths between C6 and C36 served as reference substances. Wax esters with carbon chain lengths from C44 to C58 were prepared by combining the model substances. To identify the peaks in the gas chromatograms of the rice bran waxes, a defined amount of each component was added to a wax sample, and a significant increase in the area of ​​the corresponding peak was observed. The measurement conditions are shown in Table 2. Table 2 column Agilent Technologies HP-1 (DB-1) Length 15m ID0.25mm Film 0.10µm detector 310°C FID injector 300°C Split 1:100 Carrier gas helium solvent toluene concentration 30mg / ml Injection quantity 1µl Temperature program 40 to 320°C 5K / min; hold at 320°C for 50 minutes

[0073] Raw rice bran wax (RBW 1) was used as the raw material. The properties of the raw rice bran wax are shown in Table 3. Table 3 (Methods, abbreviations and units in Table 1) raw material SZ VZ TP SP SE ÖG TGA RBW 1 1,3 83 77 79 -192 1,9 1,2 / 6,4 Examples 1 to 3

[0074] In a 3 L reaction vessel equipped with a stirrer, temperature sensor, dropping funnel, and reflux condenser, the amount of chromium trioxide specified in Table 4 was placed in sulfuric acid (concentration: 100 g CrO₃ / L) and heated to 100°C. Molten (90°C) raw rice bran wax was then added in portions. The temperature of the reaction mixture was adjusted to 110°C and stirred for 4 h at approximately 200 rpm using a KPG stirrer. Heating and stirring were then stopped. Once the phases had separated, the aqueous phase was removed.

[0075] The organic phase was freed from chromium residues by washing with an aqueous solution of oxalic acid and sulfuric acid and subsequently by washing with water, drained into warm centrifuge tubes and centrifuged.

[0076] The conditions of the oxidations and properties of the rice bran wax oxidates are given in Table 4. Table 4: Example 1 2 3 RBW 1 [g] 150 150 150 CrO 3 / H 2 SO 4 [L] 1,95 2,25 2,55 Reaction time [h] 4 4 4 Reaction temperature [°C] 110 110 110 Time [min] until phase separation 2 2 2 SZ 45,7 52,2 64,1 VZ 106 113 116 TP 77 78 76 SP 81 79 80 SE -229,69 -225,74 -227,14 TGA 11,21 / 28,91 14,61 / 35,22 16,51 / 39,13 IFZ 1,4 0,3 0,2 NPZ 2 3 3

Claims

1. Process for the preparation of rice bran wax oxidates (O) having an acid value of greater than 45 mg KOH / g and less than 70 mg KOH / g and a needle penetration number of less than 3 mm-1 comprising the steps of: i) providing a rice bran wax (R) containing less than 5% by weight, based on the total weight of the rice bran wax (R), of polyesters formed from polyhydric alcohols and aliphatic carboxylic acids having 8 to 20 carbon atoms; ii) providing of a mixture (M) of chromium trioxide and sulphuric acid; iii) performing the oxidation of the rice bran wax (R) by reacting the rice bran wax (R) with the mixture (M) while stirring and at a temperature of 90 to 150°C to obtain a rice bran wax oxidate (O); iv) stopping the reaction and allowing the reaction mixture obtained in step iii) to stand until the organic phase hs separated from the aqueous phase; v) separating off the organic phase; vi) optionally removing residues containing chromium compounds from the organic phase to obtain the rice bran wax oxidate (O) in purified form, vii) optionally repeating the sequence of steps ii) to vi) up to two times, wherein the rice bran wax oxidate (O), optionally in purified form, is used instead of the rice bran wax (R), wherein the oxidation in step iii) is performed over a period of 1 to 8 hours, and wherein the weight ratio of the total amount of chromium trioxide used to rice bran wax (R) used is from 5:4 to 9:6.

2. Process according to claim 1, wherein the removal of residues containing chromium compounds is performed in step vi) and comprises washing the organic phase with an aqueous solution of oxalic acid and / or sulfuric acid.

3. Process according to at least one of claims 1 or 2, wherein the removal of residues containing chromium compounds is carried out in step vi) and comprises washing the organic phase with water.

4. Process according to at least one of claims 1 to 3, wherein the removal of residues containing chromium compounds is carried out in step vi) and comprises centrifuging the organic phase.

5. Process according to at least one of claims 1 to 4, wherein the concentration of chromium trioxide in the mixture (M) is from 50 to 200 g / L.

6. Process according to at least one of claims 1 to 5, wherein the oxidation in step iii) is carried out over a period of 2 to 5 hours.

7. Process according to at least one of claims 1 to 6, wherein the stirring speed in step iii) is between 100 and 500 rpm.

8. Process according to at least one of claims 1 to 7, wherein no additional oxidation promoters are added to the reaction mixture.

9. Rice bran wax oxidate (O) having an acid value of greater than 45 mg KOH / g and less than 70 mg KOH / g and a needle penetration number of less than 3 mm-1, prepared by the process according to at least one of claims 1 to 8.

10. Rice bran wax oxidate (O) according to claim 9 with a proportion of polyesters formed from polyhydric alcohols and aliphatic carboxylic acids with 22 to 36 carbon atoms of less than 5% by weight, based on the total weight of the rice bran wax oxidate (O).

11. Rice bran wax oxidate (O) having an acid number of greater than 45 mg KOH / g and less than 70 mg KOH / g, a needle penetration number of less than 3 mm-1and having a proportion of multiple esters formed from polyhydric alcohols and aliphatic carboxylic acids having 22 to 36 carbon atoms of less than 5% by weight, based on the total weight of the rice bran wax oxidate (O).

12. Rice bran wax oxidate (O) according to claim 10 or 11: a) 10 to 40% by weight, based on the total weight of the rice bran wax oxidate (O), of free aliphatic carboxylic acids having 8 to 36 carbon atoms; b) 0 to 5 % by weight, based on the total weight of the rice bran wax oxidate (O), of free aliphatic alcohols having 24 to 36 carbon atoms; c) 0 to 10 % by weight, based on the total weight of the rice bran wax oxidate (O), of free aliphatic dicarboxylic acids having 10 to 30 carbon atoms; d) from 45 to 90% by weight, based on the total weight of the rice bran wax oxidate (O), of genuine esters having from 42 to 64 carbon atoms; and e) 0 to 15 % by weight, based on the total weight of the rice bran wax oxidate (O), of other natural constituents contained in the rice bran wax.

13. Rice bran wax oxidate (O) according to at least one of claims 9 to 12, containing at most 10% by weight, based on the total weight of the rice bran wax oxidate (O), of lignoceric acid.

14. Saponified rice bran wax oxidate prepared by saponifying the rice bran wax oxidate (O) according to any one of claims 1 to 13 with a basic metal salt, preferably an alkali metal hydroxide and / or alkaline earth metal hydroxide.

15. Use of the rice bran wax oxidate (O) according to at least one of claims 9 to 13 or of a saponified rice bran wax oxidate (V) according to claim 14 for agricultural or forestry purposes, as an additive in plastics processing, in care products, in printing inks and / or in paints.