Method for producing 1,2-cyclohexanedicarboxylic acid dialkyl esters

Abstract

The invention relates to a method for producing 1,2-cyclohexanedicarboxylic acid dialkyl esters by nuclear hydrogenation of the corresponding dialkyl phthalate which has a CO number of less than 0.1 mg KOH / g. The invention further relates to the use of the 1,2-cyclohexanedicarboxylic acid dialkyl esters produced in this way as plasticizers or as part of a plasticizer composition for plastics, in particular PVC.

Description

[0001] Process for the preparation of 1,2-cyclohexanedicarboxylic acid dialkyl esters

[0002] The present invention relates to a process for the preparation of 1,2-cyclohexanedicarboxylic acid dialkyl esters by ring hydrogenation of the corresponding dialkyl phthalate, which has a CO number of less than 0.1 mg KOH / g. The invention also relates to the use of the 1,2-cyclohexanedicarboxylic acid dialkyl esters thus prepared as plasticizers or as part of a plasticizer composition for plastics, in particular PVC.

[0003] Plasticizers are used in many technical areas to make plastics such as polyvinyl chloride (PVC) softer and more flexible. For many years, phthalates, i.e. the diesters of (ortho-)phthalic acid, have been the dominant plasticizer class. In recent years, however, the alkyl esters of cyclohexanedicarboxylic acids have also gained importance, not least due to the discussion about potential health concerns of phthalate-based plasticizers. In particular, the

[0004] 1,2-Cyclohexanedicarboxylic acid dialkyl esters and, more recently, 1,4-Cyclohexanedicarboxylic acid dialkyl esters play a role.

[0005] Dialkyl 1,2-, 1,3-, and 1,4-cyclohexanedicarboxylic acid esters can be produced by hydrogenation of the aromatic ring of the corresponding phthalates, isophthalates, or terephthalates (hereinafter: ring hydrogenation). Such ring hydrogenations are already carried out on an industrial scale, for example, for the production of DINCH, the diisononyl ester of 1,2-cyclohexanedicarboxylic acid.

[0006] The reaction rate of the nuclear hydrogenation plays an important role in the economic viability of the process, as it influences both the investment and operating costs.

[0007] The object of the present invention was therefore to provide a process for the preparation of 1,2-cyclohexanedicarboxylic acid dialkyl esters, with which the hydrogenation rate can be maintained at a higher level and thus the productivity of the hydrogenation process can be increased. Furthermore, catalyst deactivation should be reduced.

[0008] Surprisingly, it has now been discovered that dialkyl phthalates, in which the alkyl groups each have 8 or 9 carbon atoms, can be hydrogenated more easily and quickly if their carbonyl number (CO number) does not exceed a certain value. Therefore, if corresponding dialkyl phthalates are used in core hydrogenation, productivity and thus the economic efficiency of the process increase. Furthermore, the amount of components that deactivate the hydrogenation catalyst is reduced, allowing catalyst activity to be maintained at a higher level for a longer period.

[0009] The process according to the invention is accordingly a process for the preparation of 1,2-cyclohexanedicarboxylic acid dialkyl esters in which the two alkyl groups each have 8 or 9 carbon atoms, the process comprising at least the following steps: a) preparing a dialkyl phthalate by reacting phthalic anhydride or dimethyl phthalate with a C8 or C9 alcohol and discharging a portion of a low-boiling phase distilled off during the reaction by applying a reduced pressure in the range of 500 to 900 mbar absolute, which comprises at least unreacted alcohol and reaction by-products, b) core hydrogenation of the dialkyl phthalate prepared in step a), in which the two alkyl groups each have 8 or 9 carbon atoms, in the presence of a heterogeneous hydrogenation catalyst with a hydrogen-containing gas to give the corresponding 1,2-cyclohexanedicarboxylic acid dialkyl ester, characterized in thatthat the dialkyl phthalate used in the core hydrogenation in step b) has a CO number of less than 0.1 mg KOH / g, preferably less than 0.08 mg KOH / g, more preferably less than 0.07 mg KOH / g and particularly preferably less than 0.01 mg KOH / g.

[0010] The CO number is defined as the amount of KOH in milligrams equivalent to the amount of hydroxylamine required to oximate 1 g of substance. The CO number is determined by reacting the substance dissolved in carbonyl-free alcohol with an excess of hydroxylamine to form the corresponding oxime, and back-titrating the unused hydroxylamine with hydrochloric acid.

[0011] To determine the CO number, the equivalence point must first be determined using a calibration solution. Calibration solutions are prepared with different amounts of cyclohexanone in a suitable solvent, e.g., carbonyl-free methanol. The theoretical CO number is calculated using the following formula:

[0012] Molar mass KOH ■ Purity Cyclohexanone CO number (theoretical) = - - - — -

[0013] Molar mass of cyclohexanone

[0014] The prepared calibration solutions are each titrated with 0.1 mol / l hydrochloric acid. The measured pH value is then plotted as a function of the respective hydrochloric acid consumption, and the equivalence point is determined. The system is then calibrated.

[0015] The CO number of an unknown sample can then be determined as follows: First, an appropriate amount of sample is placed in a reaction vessel and dissolved in 50 ml of a suitable solvent, e.g.

[0016] B. carbonyl-free methanol. With the solvent used, e.g. methanol, a blank value determination must first be carried out without a sample as described below. The solution of the sample in the solvent, e.g. methanol, is mixed with bromophenol blue and the pH is adjusted - if necessary - by adding hydrochloric acid or sodium hydroxide solution until the solution has a green-yellow color (corresponds to a pH of approximately 3). Then 20 ml of hydroxylamine solution (c = 0.24 mol / l) are added and the resulting solution is refluxed in the reaction vessel for 1 h. After cooling to room temperature, the reflux condenser is rinsed with 10 ml of the solvent, e.g. carbonyl-free methanol, and the reaction solution is then titrated with 0.1 mol / l hydrochloric acid to the equivalence point.

[0017] The CO number can then be calculated using the following formula:

[0018] ~ ~

[0019] CO number (mg where VB is the hydrochloric acid consumption in the blank value determination in ml, VH is the hydrochloric acid consumption in the sample to be examined in ml, FHCI is the titer of hydrochloric acid, CHCI is the concentration of hydrochloric acid in mol / l, MKOH is the molar mass of KOH = 56.11 g / mol and Ep is the sample weight in g.

[0020] If care is taken to ensure that the dialkyl phthalate used in the ring hydrogenation in step b) has a CO number of less than 0.1, the ring hydrogenation can be carried out more quickly. Of the 1,2-cyclohexanedicarboxylic acid dialkyl esters produced in this way, in which the alkyl groups each have 8 or 9 carbon atoms, the 1,2-cyclohexanedicarboxylic acid dialkyl esters in which the alkyl groups are 2-ethylhexyl or isononyl are preferred. Also preferred are dialkyl phthalates in which the two alkyl groups have the same number of carbon atoms. Therefore, preference is given to using di-2-ethylhexyl phthalate or diisononyl phthalate, which, in the ring hydrogenation, produce di-2-ethylhexyl 1,2-cyclohexanedicarboxylate or diisononyl 1,2-cyclohexanedicarboxylate (DINCH). The product particularly preferably formed in the core hydrogenation according to the invention is 1,2-cyclohexanedicarboxylic acid diisononyl ester (DINCH).

[0021] To obtain corresponding dialkyl phthalates for the ring hydrogenation in step b), the preparation process according to step a) of the present invention is used. The dialkyl phthalate is prepared by reacting phthalic anhydride or dimethyl phthalate with a C8 or C9 alcohol and discharging a portion of a low-boiling phase distilled off during the reaction by applying a reduced pressure in the range of 500 to 900 mbar absolute, which comprises at least unreacted alcohol and reaction by-products. Discharging the reaction by-products can ensure a reduction in the CO number.

[0022] The preparation of the dialkyl phthalates according to the invention by esterification of phthalic anhydride with an alcohol or an alcohol mixture having 8 or 9 carbon atoms can be carried out by all known processes. However, the esterification is preferably carried out by a process in which the water of reaction is removed by azeotropic distillation with the alcohol, and the amount of liquid removed from the reaction by the azeotropic distillation is fully or partially replenished with the starting alcohol. The amount of liquid is referred to below as the volume of liquid removed from the reaction by azeotropic distillation, mainly consisting of water of reaction and alcohol. Complete replacement of the removed amount of liquid is preferred. The esterification with phthalic anhydride to give the dialkyl phthalates can be carried out according to the invention by autocatalysis or by acid or base catalysis.Lewis or Brønsted acids or organometallic substances can be used as esterification catalysts. Preferred esterification catalysts are alcoholates, sulfonic acids, carboxylic acid salts, or chelate compounds of titanium or zirconium, where the catalyst molecule may contain one or more metal atoms. Tetra(isopropyl) orthotitanate and tetra(butyl) orthotitanate are particularly used. The catalyst concentration depends on the type of catalyst. For the preferred titanium compounds, this is 0.005 to 1.0 wt.% based on the reaction mixture, in particular 0.01 to 0.3 wt.%.

[0023] The esterification according to the invention is preferably carried out in a reaction vessel in which the reaction mixture can be intensively mixed using a stirrer or a circulating pump. The reactants and the catalyst can be introduced into the reactor simultaneously or sequentially. The catalyst can be introduced in pure form or as a solution, preferably dissolved in one of the starting materials, at the beginning or only after the reaction temperature has been reached. The alcohol to be reacted, which serves as an entrainer, can be used in a stoichiometric excess. Preference is given to an excess of 5 to 50%, particularly preferably 10 to 30%, based on the phthalic anhydride used.

[0024] When using titanium catalysts, reaction temperatures during esterification are between 120 °C and 270 °C, preferably between 130 °C and 270 °C. The optimal temperatures depend on the feedstock, reaction progress, and catalyst concentration. They can be easily determined for each individual case through experimentation. Higher temperatures increase reaction rates and promote side reactions, such as dehydration from alcohols or the formation of colored by-products.

[0025] The transesterification of dimethyl phthalate with a C8 or C9 alcohol is also a known process and has already been described in the prior art, for example, in WO 2009 / 095126 A1. The transesterification typically takes place in the liquid phase. The dimethyl phthalate is reacted with the respective alcohol or alcohol mixtures in the presence of a suitable catalyst. The methanol formed during the transesterification is preferably separated during the reaction. Since the reaction temperatures are usually above the boiling point of methanol, the methanol can be easily separated in vapor form.

[0026] The alcohol used to produce the dialkyl phthalate in the esterification or transesterification is an alcohol or an alcohol mixture having 8 or 9 carbon atoms. The alcohol used in the esterification is preferably 2-ethylhexanol or isononanol. The alcohol is particularly preferred is isononanol. For the purposes of the present invention, isononanol is understood as a mixture of primary C9 alcohols, which may be either linear or branched. The esterification or transesterification according to the invention in step a) is preferably carried out discontinuously. The discontinuous operation preferred here is, in particular, batch production. Thus, a quantity limited by the reactor volume is produced, and then the reaction is terminated. After the reactor has been emptied, a new batch production can be started.

[0027] Suitable reactors are those known to those skilled in the art and which can be used for the synthesis of dialkyl phthalates. Suitable reactors comprise, in particular, a distillation column, via which the water or methanol formed and, after the reaction, also the unreacted alcohols are separated. The distillation column is preferably permanently connected to the reactor or reactors of the process according to the invention. The reactor essentially represents the bottom of the distillation column. Due to the prevailing reaction temperatures, water or methanol can pass into the gas phase even during the esterification or transesterification and be distilled off via the distillation column. The amount of liquid lost in this way can be replaced by adding the alcohol or alcohol mixture used.

[0028] The temperature during the production of dialkyl phthalates depends on various factors, for example, the reaction variant used, but is preferably between 150 °C and 260 °C. This temperature range is suitable for both esterification and transesterification. The pressure during esterification and transesterification is preferably in the range of 0.5 to 10 bar absolute. Temperature and pressure should preferably be adjusted so that the resulting water or methanol can be distilled off during the reaction.

[0029] At the end of the reaction, the dialkyl phthalates produced are present in a reaction solution that contains, in addition to the produced compounds, at least the unreacted alcohols or the unreacted alcohol mixture. Since byproducts with lower boiling points than the alcohols or alcohol mixtures used can be formed during esterification or transesterification, such reaction byproducts are usually also present in the reaction solution. Possible byproducts include alkenes formed by splitting off water groups or monocarboxylic acids (esters) formed by splitting off at least one acid or ester group, which can lead to an increase in the CO number.

[0030] As mentioned, a low-boiling phase is distilled off during the reaction, which primarily consists of water and alcohol, e.g. the unreacted alcohol in esterification or the unreacted alcohol and / or methanol in transesterification. Towards the end of the reaction, the amounts of water or methanol produced by the esterification or transesterification decrease due to the increasing conversion. Separation can be assisted by applying a vacuum of 500 to 800 mbar absolute, preferably 520 to 750 mbar absolute. This also has the advantage that any reaction by-products formed are transferred with the low-boiling phase. Therefore, at least a portion of the low-boiling phase is removed, thereby reducing the amount of reaction by-products in the (final) reaction solution.

[0031] The negative pressure is preferably applied only when a threshold reaction conversion is reached. In a preferred embodiment, the negative pressure is applied after a reaction conversion of at least 92%, particularly preferably at least 95%, has been reached. For this purpose, the reaction conversion is monitored during the reaction. However, it is also possible to monitor not the conversion but a single other parameter or several other parameters during the reaction, whereby the parameter(s), possibly after prior calibration, allows a conclusion to be drawn about the conversion or, more generally, the progress of the reaction.

[0032] The negative pressure can be applied using known devices or machines. An example of such a suitable device is a (vacuum) pump, which is used to create the negative pressure in the reactor. The temperature when the negative pressure is applied can correspond to the reaction temperature. If the negative pressure is applied only with a certain delay after the conversion threshold has been reached, the temperature can also be lower than the reaction temperature.

[0033] The portion of the low-boiling phase that first passes over during the distillation of the low-boiling phase, i.e., the portion of the low-boiling phase that is distilled off first after the application of the negative pressure, is at least partially discharged and discarded. Based on the total amount of the distilled low-boiling phase separated to produce the crude product, the amount of the discharged portion of the low-boiling phase is preferably 0.05 to 8 wt.%, preferably 0.1 to 4 wt.%.

[0034] The core hydrogenation of dialkyl phthalates according to step b) is generally known to those skilled in the art. The core hydrogenation is carried out using a hydrogen-containing gas. Any hydrogen-containing gas mixture that does not contain harmful amounts of catalyst poisons, such as carbon monoxide or hydrogen sulfide, can be used as the hydrogen-containing gas. Gas mixtures with inert gases can also be used. Hydrogen with a purity of > 95%, in particular > 98%, is preferably used as the hydrogen-containing gas. Inert gas components can be, for example, nitrogen or methane.The hydrogen-containing gas is preferably used in such a way that the hydrogen is present in excess, in particular in an excess of up to 200%, preferably in an excess of 5 to 100% and particularly preferably in an excess of 10 to 50%, based on the stoichiometric amount required to achieve the desired conversion.

[0035] In the core hydrogenation according to the invention in step b), heterogeneous hydrogenation catalysts are also used, which preferably contain at least one transition metal, particularly preferably a metal from Group 8 of the Periodic Table of the Elements. The transition metal used is preferably platinum, rhodium, palladium, cobalt, nickel, or ruthenium, or a mixture of two or more thereof, with ruthenium being used in particular as the active metal. In addition to the metals already mentioned, the catalysts may additionally contain at least one metal from Groups 7 and 11 of the Periodic Table of the Elements. Rhenium and / or copper are preferably used.

[0036] The content of transition metal in the hydrogenation catalyst according to the invention is preferably in the range from 0.1 to 10 wt.%, in particular in the range from 0.3 to 5 wt.%, very particularly in the range from 0.5 to 3 wt.%.

[0037] The heterogeneous hydrogenation catalysts used are preferably supported catalysts, i.e., they comprise a support material. Activated carbon, silicon carbide, aluminum oxide, silicon dioxide, aluminosilicate, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide, or mixtures thereof can be used as the support material. Particular preference is given to using titanium dioxide or aluminum oxide as the support material. These support materials may also contain alkali metals, alkaline earth metals, and / or sulfur.

[0038] The core hydrogenation of the dialkyl phthalates according to the invention is preferably carried out in at least one hydrogenation unit. In the present invention, a hydrogenation unit is understood to mean a unit which comprises one reactor or more reactors which may be connected in parallel and / or in series, i.e. a reactor or a reactor arrangement in which the core hydrogenation takes place. In a particularly preferred embodiment, the core hydrogenation is carried out in at least two hydrogenation units connected in series, with at least one of the two hydrogenation units being operated in loop mode, i.e. with recirculation of a portion of the respective hydrogenation output. It can be advantageous if all of the at least two hydrogenation units are operated in loop mode during the core hydrogenation. It can also be advantageous if the last hydrogenation unit is operated in straight pass.In a particularly preferred embodiment of the present invention, the core hydrogenation is carried out in two hydrogenation units connected in series, wherein the first hydrogenation unit is operated in loop mode and the last hydrogenation unit is operated in straight pass.

[0039] In an alternative embodiment, the core hydrogenation is carried out in at least three hydrogenation units arranged in series, with at least the first two hydrogenation units being operated in loop mode. The last hydrogenation unit can also be operated in loop mode, thus corresponding to an embodiment in which all of the at least three hydrogenation units are operated in loop mode. Likewise, the last hydrogenation unit can be operated in straight-through mode.

[0040] Another particularly preferred embodiment is the parallel arrangement of the reactors, for example in a tube bundle reactor.

[0041] The individual reactors can be operated adiabatically, polytropically or virtually isothermally, i.e. with a temperature rise (difference between the temperature at the inlet and the temperature at the outlet of the reactor) of typically less than 15 K. In particular, the reactors operated in loop mode are preferably operated quasi-isothermally, i.e. preferably with a temperature rise of less than 15 K. For reactors that are not operated in loop mode, the preferred temperature rise in the reactor is below 35 K, particularly preferably below 25 K. A cooling device can be installed between individual hydrogenation elements in order to lower the temperature before entry into the following hydrogenation unit.

[0042] The core hydrogenation of dialkyl phthalates according to the invention is preferably carried out in the liquid / gas mixed phase or liquid phase in three-phase reactors in cocurrent flow, the hydrogen-containing gas being distributed in the liquid reactant / product stream in a manner known per se. In the interest of uniform liquid distribution, improved reaction heat removal, and / or a high space-time yield, the reactors operated in loop mode are preferably operated with high liquid loadings of 10 to 400, preferably 20 to 200, and particularly preferably 40 to 150 m 3 per m 2Cross-section of the empty reactor and hourly operation. The liquid loadings can be the same or different in the reactors operated in loop mode. The liquid loading is preferably greatest in the first reactor and decreases in the subsequent reactors operated in loop mode. One or more reactors can be partially flooded with liquid or function entirely as trickle-bed reactors.

[0043] The ring hydrogenation of dialkyl phthalates can be carried out in the absence or presence of a solvent. Any liquid that forms a homogeneous solution with the reactant and product, is inert under hydrogenation conditions, and can be easily separated from the product can be used as solvents. The solvent can also be a mixture of several substances and may optionally contain water. The following substances can be used as solvents in the ring hydrogenation: straight-chain or cyclic ethers, such as tetrahydrofuran or dioxane, as well as aliphatic alcohols in which the alkyl radical has 1 to 13 carbon atoms. Preferred alcohols for use as solvents are isopropanol, n-butanol, isobutanol, n-pentanol, 2-ethylhexanol, nonanols, technical nonanol mixtures, decanol, technical decanol mixtures, and tridecanols.When using alcohols as solvents, it may be advantageous to use the alcohol or alcohol mixture that would be produced during saponification of the product. This would eliminate the formation of byproducts due to transesterification. Another preferred solvent is the hydrogenation product itself.

[0044] By using a solvent, the reactant concentration in the reactor feed can be limited, thereby achieving better temperature control in the reactor. This can minimize side reactions and thus increase the product yield. The reactant content in the reactor feed is preferably between 1 and 70%. For reactors operated in loop mode, the desired concentration range can be adjusted by the circulation ratio (ratio of recycled hydrogenation effluent to reactant). The reactant concentrations in the reactor feed preferably decrease from the first to the last reactor. Another possible temperature control option is the dilution of the hydrogen-containing gas used for hydrogenation, in particular the hydrogen, with an inert gas. The inert gas can be selected from the group consisting of nitrogen, helium, neon, argon, carbon dioxide, and mixtures thereof.Nitrogen or carbon dioxide are preferred, as they are the easiest and cheapest to obtain. Nitrogen is particularly preferred as the inert gas for the process according to the invention. By diluting the hydrogen-containing gas used for hydrogenation, the reaction can be slowed down and the temperature can be controlled. This process is also suitable for starting up the reactor after installation or regeneration of the catalyst when no suitable solvent is available.

[0045] According to the invention, the ring hydrogenation of the dialkyl phthalates is preferably carried out in a pressure range from 3 to 300 bar, in particular from 15 to 200 bar, very particularly preferably from 50 to 200 bar. The pressure in the individual reactors can be the same or different. Preferably, the pressures are the same or approximately the same, ie, they differ from one another by a maximum of 10%.

[0046] The hydrogenation temperatures during core hydrogenation are preferably in the range of 50 to 250 °C, preferably in the range of 80 to 200 °C. The hydrogenation temperatures can be the same or different in individual reactors.

[0047] The products obtained from the process according to the invention are corresponding compositions which depend on the starting materials and the conversion during the hydrogenation. The composition formed in the ring hydrogenation according to the invention preferably has a content of 1,2-cyclohexanedicarboxylic acid dialkyl esters of more than 96% by weight, in particular more than 98% by weight, particularly preferably more than 99% by weight. This mixture can be used directly or after purification. By-products can be separated off, for example, by distillation or by stripping with steam or with an inert gas such as nitrogen. Small amounts of low boilers are preferably separated off by stripping with steam in the temperature range from 120 °C to 240 °C, in particular in the range from 150 to 200 °C and preferably at a pressure of 0.05 to 0.1 bar.

[0048] The 1,2-cyclohexanedicarboxylic acid dialkyl esters prepared according to the invention, in which the two alkyl groups each have 8 or 9 carbon atoms, can advantageously be used as plasticizers or part of a plasticizer composition in plastics or plastic compositions, as additives in paints or varnishes, in adhesives or adhesive components, in sealants or as solvents.

[0049] The prepared 1,2-cyclohexanedicarboxylic acid dialkyl esters can also be used as plasticizers in mixtures with other plasticizers, in particular so-called rapid gelators. The proportion of 1,2-cyclohexanedicarboxylic acid alkyl esters according to the invention in the mixture with other plasticizers is preferably 15 to 95 wt. %, particularly preferably 20 to 90 wt. %, and very particularly preferably 25 to 85 wt. %, with the proportions of all plasticizers present adding up to 100 wt. The above-mentioned compositions of 1,2-cyclohexanedicarboxylic acid dialkyl esters and other plasticizers can be used as plasticizer compositions in plastics and plastic compositions, adhesives, sealants, varnishes, paints, plastisols, or inks.

[0050] The plastic compositions which can contain the produced 1,2-cyclohexanedicarboxylic acid dialkyl esters can be polymers selected from polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyacrylates, in particular polymethyl methacrylate (PMMA), polyalkyl methacrylate (PAMA), fluoropolymers, in particular polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate (PVAc, polyvinyl alcohol (PVA), polyvinyl acetals, in particular polyvinyl butyral (PVB), polystyrene polymers, in particular polystyrene (PS), expandable polystyrene (EPS), acrylonitrile-styrene-acrylate (ASA), styrene-acrylonitrile (SAN), acrylonitrile-butadiene-styrene (ABS), styrene-maleic anhydride copolymer (SMA), styrene-methacrylic acid copolymer, polyolefins, in particular polyethylene (PE) or polypropylene (PP), thermoplastic Polyolefins (TPO), polyethylene vinyl acetate (EVA), polycarbonates, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyoxymethylene (POM), polyamide (PA),Polyethylene glycol (PEG), polyurethane (PU), thermoplastic polyurethane (TPU), polysulfides (PSu), biopolymers, in particular polylactic acid (PLA), polyhydroxylbutyric acid (PHB), polyhydroxyvaleric acid (PHV), polyester, starch, cellulose and cellulose derivatives, in particular nitrocellulose (NC), ethylcellulose (EC), cellulose acetate (CA), cellulose acetate / butyrate (CAB), rubber or silicones as well as mixtures or copolymers of the aforementioned polymers or their monomeric units. The compositions according to the invention preferably comprise PVC or homo- or copolymers based on ethylene, propylene, butadiene, vinyl acetate, glycidyl acrylate, glycidyl methacrylate, methacrylates, acrylates, acrylates or methacrylates with alkyl radicals of branched or unbranched alcohols having one to ten carbon atoms, styrene, acrylonitrile or cyclic olefins bonded to the oxygen atom of the ester group.

[0051] The use of PVC is particularly preferred.

[0052] The plastic composition according to the invention preferably contains suspension, bulk, microsuspension, or emulsion PVC as the PVC type. Based on 100 parts by weight of polymer, the compositions according to the invention preferably contain from 5 to 200, preferably from 10 to 150 parts by weight of plasticizer according to the invention.

[0053] In addition to the components mentioned, the plastic compositions may contain other components, in particular, for example, additional plasticizers, fillers, pigments, stabilizers, co-stabilizers such as epoxidized soybean oil, lubricants, blowing agents, kickers, antioxidants, rheology additives or biocides.

[0054] The plastic compositions according to the invention comprising the 1,2-cyclohexanedicarboxylic acid dialkyl esters and the aforementioned polymer materials can be used as plastic compositions, adhesives, sealants, varnishes, paints, plastisols, artificial leather, floor coverings, underbody protection, fabric coatings, roof membranes, wallpapers, or inks, or for the production thereof. Plastic products produced with the plasticizer compositions can be, for example, profiles, seals, food packaging, films, toys, medical articles, roofing membranes, artificial leather, floor coverings, underbody protection, coated fabrics, roof membranes, wallpapers, cables, and wire sheathing. Preferred areas of application from this group are food packaging, toys, medical articles, wallpapers, roof membranes, fabric coatings, and floor coverings.

[0055] The invention will be illustrated below by examples. These examples are selected embodiments and do not constitute a limitation.

[0056] Example 1 : Nuclear hydrogenation of diisononyl phthalate (DINP)

[0057] Experiments were conducted on the core hydrogenation of DINP, in which the conversion of DINP was measured as a function of time. The following DINP samples were tested.

[0058] DINP-1 is the product VESTINOL® 9 from Evonik Oxeno GmbH & Co. KG. The CO number was determined using the method specified in the description and was 0.006 mg KOH / g.

[0059] DINP-2 is a product of a Korean company. The CO value was determined using the method described in the description and was 0.048 mg KOH / g.

[0060] DINP-3 is Kanatol-900 from the KLJ Group, India. The CO number was determined using the method described in the description and was 0.15 mg KOH / g.

[0061] Core hydrogenation of DINP samples

[0062] A batch hydrogenation of various DINP (diisononyl phthalate) samples was carried out in a tubular reactor with an internal diameter of 40 mm and a length of 250 mm in recirculating operation. The tubular reactor was flowed through in cocurrent flow by the liquid and gas phases in a trickle bed. The catalyst used in the hydrogenation was a coated catalyst consisting of 1 wt. % Ru supported on titanium dioxide (Aerolyst 7711, Evonik Operations GmbH). A mixture of 25 g each of hydrogenation catalyst and 25 g of inert material consisting of Y-Al2O3 (Spheralite 538E, Axens), each in the form of 1.5 mm extrudates, was introduced into the tubular reactor. The amount of DINP used in the hydrogenation was always 1000 g. The H2 control is carried out via an exhaust gas mode, whereby a constant exhaust gas flow of 1 L / h (47.8 m 3 m _2 h' 1). All experiments were conducted at a system pressure of 90 bar and a tubular reactor temperature of 110 °C. After passing through a heat exchanger below the reactor, gas-liquid separation was carried out using a separator. The gas phase was continuously released into the exhaust gas. Over a period of 8 hours, the liquid phase was continuously recirculated to the tubular reactor via a heated preheater. The reaction progress (conversion of DINP over time) in the reactor was recorded using inline Raman analysis. The results can be found in Table 1 below.

[0063] Table 1 : DINP conversion (%) to DINCH as a function of time

[0064] The table shows that when using DINP with a CO number within the claimed range (DINP-1 and DINP-2), core hydrogenation occurs significantly faster.

Claims

Patent claims 1. A process for the preparation of 1,2-cyclohexanedicarboxylic acid dialkyl esters in which the two alkyl groups each have 8 or 9 carbon atoms, the process comprising at least the following steps: a) preparing a dialkyl phthalate by reacting phthalic anhydride or dimethyl phthalate with a C8 or C9 alcohol and discharging a portion of a low-boiling phase distilled off during the reaction by applying a reduced pressure in the range of 500 to 900 mbar absolute, which comprises at least unreacted alcohol and reaction by-products, b) core hydrogenation of the dialkyl phthalate prepared in step a), in which the two alkyl groups each have 8 or 9 carbon atoms, in the presence of a heterogeneous hydrogenation catalyst with a hydrogen-containing gas to give the corresponding 1,2-cyclohexanedicarboxylic acid dialkyl ester, characterized in thatthat the dialkyl phthalate used in the core hydrogenation in step b) has a CO number of less than 0.1 mg KOH / g, preferably less than 0.08 mg KOH / g, more preferably less than 0.07 mg KOH / g and particularly preferably less than 0.01 mg KOH / g.

2. The process according to claim 1, wherein the two alkyl groups of the 1,2-cyclohexanedicarboxylic acid dialkyl ester are each 2-ethylhexyl or isononyl.

3. The process according to claim 2, wherein the 1,2-cyclohexanedicarboxylic acid dialkyl ester is a 1,2-cyclohexanedicarboxylic acid diisononyl ester or a 1,2-cyclohexanedicarboxylic acid di-2-ethylhexyl ester.

4. The process according to any one of claims 1 to 5, wherein the heterogeneous hydrogenation catalyst used in the core hydrogenation comprises a transition metal on a support material.

5. The process according to claim 4, wherein the transition metal is a metal of group 8 of the periodic table of elements (iron group), preferably ruthenium.

6. The method according to claim 4, wherein the support material is selected from the group consisting of activated carbon, silicon carbide, alumina, silicon dioxide, aluminosilicate, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide or mixtures thereof.

7. The method according to claim 6, wherein the support material is titanium dioxide or aluminum oxide.

8. Process according to one of claims 4 to 7, wherein the content of transition metal in the heterogeneous hydrogenation catalyst is in the range from 0.1 to 10 wt.%, preferably in particular in the range from 0.3 to 5 wt.%, especially in the range from 0.5 to 3 wt.%.

9. Process according to one of the preceding claims, wherein the core hydrogenation is carried out in at least one hydrogenation unit, preferably in at least two hydrogenation units connected in series, wherein at least one of the at least two hydrogenation units is operated in loop mode.

10. Process according to one of the preceding claims, wherein the hydrogenation temperature in the core hydrogenation is in the range from 50 to 250 °C.

11. Process according to one of the preceding claims, wherein the core hydrogenation is carried out in a pressure range of 3 to 300 bar.

12. Use of the 1,2-cyclohexanedicarboxylic acid dialkyl esters prepared according to any one of claims 1 to 11 as plasticizers or as part of a plasticizer composition in plastics or plastic compositions.

13. Use of the 1,2-cyclohexanedicarboxylic acid dialkyl esters prepared according to any one of claims 1 to 11 as an additive in paints or varnishes, in adhesives or adhesive components, in sealing compounds or as solvents.

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