Process for the preparation of 1,4-cyclohexanedicarboxylic acid dialkyl esters

Abstract

The invention provides a process for the preparation of 1,4-cyclohexanedicarboxylic acid dialkyl esters by ring hydrogenation of the corresponding phthalic acid dialkyl esters having a CO number of less than 0.3 mg KOH / g. The invention also provides the use of the thus prepared 1,4-cyclohexanedicarboxylic acid dialkyl esters as plasticizers or as components of plasticizer compositions in plastics, in particular in PVC.

Description

Technical Field

[0001] This invention relates to a method for preparing 1,4-cyclohexanedicarboxylic acid dialkyl esters by cyclohydrogenation of corresponding dialkyl terephthalate esters with a CO value less than 0.3 mg KOH / g. The invention also provides the use of the resulting 1,4-cyclohexanedicarboxylic acid dialkyl esters as plasticizers or as components of plasticizer compositions in plastics, particularly PVC. Background Technology

[0002] Plasticizers are used in many industrial sectors to make plastics such as polyvinyl chloride (PVC) softer and more flexible. Phthalate esters, the diesters of (o)phthalic acid, have been the dominant type of plasticizer for many years. However, in recent years, the importance of alkyl esters of cyclohexanedicarboxylic acid has also increased, especially due to the controversy surrounding the potential health problems of phthalate-based plasticizers. Dialkyl 1,2-cyclohexanedicarboxylic acid plays a major role here, and recently, 1,4-cyclohexanedicarboxylic acid has also become the dominant agent.

[0003] Dialkyl esters of 1,2-, 1,3-, and 1,4-cyclohexanedicarboxylic acid can be prepared by hydrogenation of the aromatic rings of the corresponding phthalates, isophthalates, or terephthalates (hereinafter referred to as cyclohydrogenation). In some cases, such cyclohydrogenation has been carried out on an industrial scale, for example, for the preparation of DINCH (diisononyl ester of 1,2-cyclohexanedicarboxylic acid).

[0004] The reaction rate of cyclohydrogenation is a key factor in the profitability of this method, as it affects both investment and operating costs. Summary of the Invention

[0005] Therefore, the object of the present invention is to provide a method for preparing dialkyl 1,4-cyclohexanedicarboxylate, which allows the hydrogenation rate to be maintained at a high level and the yield of the hydrogenation method to be increased accordingly.

[0006] It has now been surprisingly discovered that dialkyl terephthalates, in which each alkyl group has at least two carbon atoms (preferably at least four carbon atoms), can be readily and rapidly hydrogenated when their carbonyl value (CO value) does not exceed a specified value. The use of suitable dialkyl terephthalates in cyclohydrogenation has also correspondingly increased productivity, thereby improving process yield.

[0007] Therefore, the method of the present invention is a method for preparing a dialkyl 1,4-cyclohexanedicarboxylate, wherein both alkyl groups have at least 2 carbon atoms, preferably at least 4 carbon atoms. The method includes at least cyclohydrogenating a dialkyl terephthalate with a hydrogen-containing gas, wherein both alkyl groups have at least 2 carbon atoms, preferably at least 4 carbon atoms, to form the corresponding dialkyl 1,4-cyclohexanedicarboxylate. The CO value of the dialkyl terephthalate used in the cyclohydrogenation is less than 0.3 mg KOH / g, preferably less than 0.2 mg KOH / g, and more preferably less than 0.1 mg KOH / g.

[0008] The CO value is defined as the amount of hydroxylamine required to oxime 1g of a substance, expressed in mg of KOH. This CO value is determined as follows: the substance dissolved in a carbonyl alcohol reacts with excess hydroxylamine to form the corresponding oxime, and then the unused hydroxylamine is back-titrated with hydrochloric acid.

[0009] To determine the CO value, the equivalence point must first be determined using a calibration solution. For this purpose, calibration solutions containing varying amounts of cyclohexanone are prepared in a suitable solvent (e.g., carbonyl-free methanol). The theoretical CO value is then calculated using the following formula:

[0010]

[0011] The prepared calibration solution was titrated with 0.1 mol / L hydrochloric acid. The measured pH values ​​were then plotted as a function of the volume of hydrochloric acid consumed in each case, and equivalence points were determined. This yielded the system calibration.

[0012] The CO value of the unknown sample can then be determined as follows: First, add an appropriate amount of the sample to the reaction vessel and dissolve it in 50 ml of a suitable solvent (e.g., carbonyl-free methanol). The solvent used (e.g., methanol) must first be used in a blank determination without the sample, as described below. Add bromophenol blue to the sample solvent (e.g., methanol) solution, and adjust the pH by adding hydrochloric acid or sodium hydroxide solution if necessary, so that the solution turns yellow-green (corresponding to a pH of approximately 3). Then, quantitatively add 20 ml of hydroxylamine solution (c = 0.24 mol / L), and reflux the resulting solution in the reaction vessel for 1 h. After cooling to room temperature, rinse the reflux condenser with 10 ml of solvent (e.g., carbonyl-free methanol), and then titrate the reaction solution to the equivalence point with 0.1 mol / L hydrochloric acid.

[0013] The CO value can then be determined using the following formula:

[0014]

[0015] Where V B V is the volume of hydrochloric acid consumed in the blank assay (in ml). HThis is the volume of hydrochloric acid consumed in the analyzed sample (in ml), F HCl It's the titer of hydrochloric acid, c HCl This is the concentration of hydrochloric acid (in mol / L), M KOH The molar mass of KOH is 56.11 g / mol, and WS is the sample weight (in g).

[0016] If the CO value of the dialkyl terephthalate used in the cyclohydrogenation is ensured to be less than 0.3, the cyclohydrogenation can be carried out more quickly. In the resulting dialkyl 1,4-cyclohexanedicarboxylate, each alkyl group has at least 2 carbon atoms, preferably at least 4 carbon atoms. Preferably, in the dialkyl 1,4-cyclohexanedicarboxylate used, each alkyl group has 3 to 10 carbon atoms, more preferably 4 to 10 carbon atoms, more preferably 5 to 9 carbon atoms, particularly preferably 8 or 9 carbon atoms, and most preferably 9 carbon atoms.

[0017] In principle, the cyclohydrogenation of dialkyl terephthalates is known to those skilled in the art. Cyclohydrogenation is carried out using a hydrogen-containing gas. In principle, the hydrogen-containing gas used can be any hydrogen-containing mixture free of harmful amounts of catalyst poisons (such as carbon monoxide or hydrogen sulfide). A mixture of gases containing an inert gas can also be used. The hydrogen-containing gas used is preferably hydrogen with a purity ≥95%, particularly hydrogen with a purity ≥98%. For example, the inert gas component can be nitrogen or methane. Based on the stoichiometric amount required to achieve the desired conversion, it is preferable to use a hydrogen-containing gas in excess of hydrogen, particularly at most 200% excess, preferably 5 to 100% excess, and more preferably 10 to 50% excess.

[0018] The cyclic hydrogenation of the present invention also employs a heterogeneous hydrogenation catalyst, which preferably contains at least one transition metal, more preferably a metal from Group 8 of the periodic table. Preferred transition metals are platinum, rhodium, palladium, cobalt, nickel, or ruthenium, or mixtures of two or more thereof, with ruthenium being a particularly preferred active metal. In addition to the metals already mentioned, at least one metal from Groups 7 and 11 of the periodic table may also be present in the catalyst. Rhenium and / or copper are preferred.

[0019] The transition metal content in the hydrogenation catalyst of the present invention is preferably in the range of 0.1 wt% to 10 wt%, particularly in the range of 0.5 wt% to 5 wt%, and most preferably in the range of 0.5 wt% to 2 wt%.

[0020] The heterogeneous hydrogenation catalyst used is preferably a supported catalyst, i.e., it includes a support material. The support material can be activated carbon, silicon carbide, alumina, silica, aluminum silicate, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide, or mixtures thereof. Titanium dioxide or alumina is particularly preferred as the support material. Furthermore, these support materials may include alkali metals, alkaline earth metals, and / or sulfur.

[0021] The cyclic hydrogenation of dialkyl terephthalate according to the invention is preferably carried out in at least one hydrogenation unit. In this invention, a hydrogenation unit is understood to be a unit comprising one or more reactors that can be connected in parallel and / or in series; in other words, the reactor is a reactor or reactor assembly in which cyclic hydrogenation takes place. In a particularly preferred embodiment, cyclic hydrogenation is carried out in at least two hydrogenation units connected in series, wherein at least one of the two hydrogenation units operates in a cyclic mode, i.e., recovers a portion of the corresponding hydrogenation output. It can be advantageous when at least two hydrogenation units in the cyclic hydrogenation are operating in a cyclic mode. It is also advantageous when the final hydrogenation unit operates in a straight-through manner.

[0022] In a particularly preferred embodiment, cyclic hydrogenation is performed in at least three hydrogenation units connected in series, wherein at least the first two hydrogenation units operate in cyclic mode. The final hydrogenation unit may also operate in cyclic mode, corresponding to an embodiment where all at least three hydrogenation units operate in cyclic mode. The final hydrogenation unit may also operate in a through-flow manner.

[0023] Another particularly preferred embodiment is a parallel arrangement of reactors, such as in a tubular reactor.

[0024] In this configuration, individual reactors can operate adiabatic, multi-heated, or nearly isothermal (i.e., typically with a temperature rise of less than 15 K, the difference between the reactor inlet and outlet temperatures). Reactors operating in recirculation mode are particularly preferably operated in quasi-isothermal conditions, that is, preferably with a temperature rise of less than 15 K. In reactors operating in non-recirculation mode, the temperature rise within the reactor is preferably below 35 K, more preferably below 25 K. Cooling devices can be installed between individual hydrogenation elements to reduce the temperature before entering subsequent hydrogenation units.

[0025] The cyclohydrogenation of dialkyl terephthalate according to the present invention is preferably carried out simultaneously in a liquid / gas mixture or liquid phase of a three-phase reactor, wherein the hydrogen-containing gas is distributed in the liquid reactant / product stream in a known manner. To achieve uniform liquid distribution, improved heat dissipation of the reaction heat, and / or high space-time yield, the reactor operating in circulation mode is preferably at a temperature of 10-400, preferably 20-200, and particularly preferably 40-150 m³. 3 / Cross-section of empty reactor (m) 2 Operating at high liquid loads per hour. Liquid loads in reactors operating in circulation mode can be the same or different. The liquid load is preferably maximum in the first reactor and decreases in subsequent reactors operating in circulation mode. One or more reactors may be partially submerged in liquid or may function entirely as trickle bed reactors.

[0026] Cyclohydrogenation of dialkyl terephthalates can be carried out in the absence of a solvent or in the presence of a solvent. The solvent used can be any liquid that forms a homogeneous solution with the reactants and products, is inert under hydrogenation conditions, and can be readily removed from the product. The solvent can also be a mixture of two or more substances and may optionally include water. The following substances can be used as solvents for cyclohydrogenation: straight-chain or cyclic ethers, such as tetrahydrofuran or dioxane, and aliphatic alcohols in which the alkyl group has 1 to 13 carbon atoms. Alcohols that are preferably used as solvents include isopropanol, n-butanol, isobutanol, n-pentanol, 2-ethylhexanol, nonanol, industrial-grade nonanol mixtures, decanol, industrial-grade decanol mixtures, and tridecanol. When using an alcohol as a solvent, it is advantageous to use an alcohol or mixture of alcohols formed during the hydrolysis of the product. This will exclude byproducts formed through transesterification. Another preferred solvent is the hydrogenation product itself.

[0027] The use of solvents can limit the reactant concentration in the reactor feed, thereby enabling better temperature control within the reactor. This minimizes side reactions and thus increases product yield. The reactant content in the reactor feed is preferably between 1% and 70%. The required concentration range in reactors operating in recirculation mode can be adjusted by the recirculation ratio (the molar ratio of recovered hydrogenation output to reactants). The reactant concentration in the reactor feed preferably decreases from the first reactor to the last.

[0028] The cyclohydrogenation of dialkyl terephthalate according to the invention is preferably carried out in a pressure range of 3 to 300 bar, particularly 15 to 200 bar, and most preferably 50 to 200 bar. The pressure in individual reactors can be the same or different. The pressures are preferably the same or substantially the same, i.e., the difference between them is at most 10%.

[0029] The hydrogenation temperature in cyclic hydrogenation is preferably in the range of 50 to 250°C, and more preferably in the range of 80 to 200°C. The hydrogenation temperatures in a single reactor may be the same or different.

[0030] The product obtained in the method of the present invention is a corresponding composition, which depends on the feedstock and the conversion during hydrogenation. The composition formed in the cyclohydrogenation of the present invention preferably has a content of more than 96% by weight, particularly more than 98% by weight, and especially preferably more than 99% by weight of dialkyl 1,4-cyclohexanedicarboxylate. This mixture can be used directly or after purification. For example, byproducts can be removed by distillation or by stripping with steam or an inert gas (such as nitrogen). Steam stripping is preferably used in a temperature range of 120°C to 240°C, particularly 150 to 200°C, and preferably at a pressure of 0.05 to 0.1 bar, to preferably remove small amounts of low-boiling solvents.

[0031] The dialkyl terephthalate used in cyclohydrogenation, wherein one of the two alkyl groups has at least 2 carbon atoms, preferably at least 4 carbon atoms, can be prepared by transesterification of dimethyl terephthalate with an alcohol or mixture of alcohols having more than 2 carbon atoms, preferably 3 to 10 carbon atoms, more preferably 4 to 10 carbon atoms, even more preferably 5 to 9 carbon atoms, particularly preferably 8 or 9 carbon atoms, and most preferably 9 carbon atoms. Another option for preparing the dialkyl terephthalate used in cyclohydrogenation is to esterify terephthalic acid with an alcohol or mixture of alcohols having more than 2 carbon atoms, preferably 3 to 10 carbon atoms, more preferably 4 to 10 carbon atoms, even more preferably 5 to 9 carbon atoms, particularly preferably 8 or 9 carbon atoms, and most preferably 9 carbon atoms. In principle, both methods are well known to those skilled in the art.

[0032] The transesterification of dimethyl terephthalate is carried out under catalysis, preferably using an acid or base. (Or Lewis) can be used as a catalyst. Regardless of the catalyst used, a temperature-dependent equilibrium is always reached between the feed (dimethyl terephthalate and alcohol) and the products (dialkyl terephthalate and methanol released from the dimethyl terephthalate used). To shift the equilibrium in favor of dialkyl terephthalate, it may be advantageous to distill off the methanol formed from the dimethyl terephthalate reactants from the reaction mixture.

[0033] In transesterification, using an excess of alcohol in general can be additionally advantageous. The amount of alcohol used, having more than two carbon atoms, is preferably an excess of 5 to 50% of the molar amount required to form the dialkyl terephthalate of the present invention, more preferably an excess of 10 to 30%.

[0034] The transesterification catalyst used can be an acid, such as sulfuric acid, methanesulfonic acid, or p-toluenesulfonic acid, or a metal or a compound thereof. Examples of suitable metals or compounds thereof are tin, titanium, and zirconium, which are used in the form of metal powder or conveniently in the form of their salts, as oxides, or as soluble organic compounds. Compared to protic acid-based catalysts, these metal catalysts are typically high-temperature catalysts that only reach their full activity at temperatures above 180°C. However, to minimize or avoid the formation of byproducts, the use of metal-based catalysts or their compounds can be advantageous. Particularly preferred examples of metal catalysts are tin powder, tin(II) oxide, tin(II) oxalate, titanates (such as tetraisopropyl orthotitanate or tetrabutyl orthotitanate), and zirconates (such as tetrabutyl zirconate). Furthermore, basic catalysts, such as oxides, hydroxides, bicarbonates, carbonates, or alcohols of alkali metals or alkaline earth metals, can also be used. Among this group, alcohols, such as sodium methoxide, are preferred. Alcohols can also be generated in situ from alkali metals and alcohols (such as nonanol or a mixture of isononol). It is particularly preferred to use an alcohol derivative in which the alcohol residues participate in the reaction.

[0035] The catalyst concentration can vary over a wide range, and especially depending on the properties of the catalyst. Based on the reaction mixture, the catalyst concentration is preferably from 0.005 wt% to 2.0 wt%. The optimal concentration for each catalyst can be readily determined through preliminary experiments, and a trade-off is made between minimizing catalyst consumption (cost factor) and maximizing the reaction rate. In the case of the tetrabutyl titanate catalyst, which is particularly preferred according to the invention, for example, based on the dimethyl terephthalate used, the preferred concentration is in the range of 0.005 wt% to 1 wt%.

[0036] The transesterification is preferably carried out at a temperature between 100 and 240°C. The pressure during the transesterification can be between 0.1 and 10 bar. The selected temperature is particularly preferably high enough to distill off the alcohol formed from the ester reactants from the reaction mixture at a specified pressure. The resulting crude ester mixture can be treated in the same manner as the mixture produced by terephthalic acid esterification as described below.

[0037] According to all known methods, the preparation of dialkyl terephthalate of the present invention can be carried out by esterification of terephthalic acid with an alcohol or mixture of alcohols having at least 2 carbon atoms, preferably at least 4 carbon atoms. However, the esterification is preferably carried out by removing the reaction water using an alcohol via azeotropic distillation, and then replenishing all or part of the liquid volume removed from the reaction by azeotropic distillation with the alcohol used. The liquid volume, as described below, consists mainly of the reaction water and alcohol, removed from the reaction by azeotropic distillation. Complete replacement of the removed liquid volume is preferred. Esterification from terephthalic acid to dialkyl terephthalate can be carried out according to the present invention under autocatalysis or acid or base catalysis. The esterification catalyst used can be Lewis or... Acids or organometallic compounds. Preferred esterification catalysts are alkoxides, sulfonic acids, carboxylates, or chelates of titanium or zirconium, wherein the catalyst molecule may contain one or more metal atoms. Tetrapropyl titanate and tetrabutyl titanate are particularly used. The concentration of the catalyst depends on the nature of the catalyst. In the case of a titanium compound that is preferably used, the concentration is 0.005% to 1.0% by weight, particularly 0.01% to 0.3% by weight, based on the reaction mixture.

[0038] The esterification of the present invention is preferably carried out in a reaction vessel, wherein the reaction mixture can be vigorously mixed by means of a stirrer or a circulating pump. The reactants and catalyst can be added to the reactor simultaneously or sequentially. The catalyst can be introduced in pure form or as a solution, preferably dissolved in one of the raw materials, either at the beginning or only after the reaction temperature is reached. The alcohol to be used as an azeotropic agent can be used in stoichiometric excess. Preferably, an excess of 5% to 50%, more preferably 10% to 30%, is used based on the terephthalic acid used.

[0039] The reaction temperature using titanium catalysts is between 120°C and 270°C, preferably between 130°C and 270°C. The optimal temperature depends on the feedstock, reaction progress, and catalyst concentration. The results for each individual case can be easily determined experimentally. Higher temperatures increase the reaction rate and facilitate side reactions, such as the removal of water from the alcohol or the formation of colored byproducts.

[0040] The amount of liquid recycled into the reaction can consist of some or all of the alcohol obtained by treating the azeotropic distillate. Alternatively, treatment can be performed at a later time, replacing all or part of the removed liquid with fresh alcohol, i.e., alcohol available in a storage tank. In other embodiments of esterification, the removed liquid is treated with alcohol, preferably pure alcohol.

[0041] At the end of the reaction, the reaction mixture, mainly consisting of the target product dialkyl terephthalate and excess alcohol, also contains the catalyst and / or its conversion products and / or trace amounts of carboxylic acids. For the treatment of these crude mixtures, excess alcohol is removed, acidic compounds are neutralized, the catalyst is destroyed, and the resulting solid byproducts are separated. The main portion of the alcohol is removed by distillation under standard pressure or reduced pressure. For example, trace amounts of alcohol can be removed by steam distillation or nitrogen injection, particularly in the temperature range of 120 to 225 °C. Alcohol removal can be carried out as either the first or last step of the treatment.

[0042] Acidic substances, such as carboxylic acids, half-esters, or (if used) acidic catalysts, can be neutralized by adding basic compounds of alkali metals and / or alkaline earth metals. These compounds can be used in the form of carbonates, bicarbonates, or hydroxides thereof. The neutralizing agent can be used in solid form, or preferably in solution form, particularly as an aqueous solution. Neutralization can be carried out immediately after the esterification reaction is completed or after distillation to remove the bulk of the excess alcohol. After the esterification reaction at a temperature above 150°C, neutralization is preferably carried out immediately using a sodium hydroxide solution. The water added with the alkali can then be distilled off together with the alcohol.

[0043] Considering that terephthalic acid is only slightly soluble in the alcohol to be used for esterification, even at the boiling point, the solubility and thus the reaction rate can be further increased by an overpressure of up to 20 bar, preferably up to 10 bar, as a result of the higher boiling point. These problems do not exist when using dimethyl terephthalate for transesterification. If dimethyl terephthalate is used as the starting material, the corresponding terephthalic ester can generally be obtained in a shorter time than when terephthalic acid is used as the starting material. Therefore, it is particularly preferred to prepare dialkyl terephthalate esters used in cyclohydrogenation via transesterification starting with dimethyl terephthalate.

[0044] The alcohol used in transesterification or esterification to prepare dialkyl terephthalates is an alcohol or mixture of alcohols having at least 2 carbon atoms, preferably at least 4 carbon atoms. Preferably, alcohols having 3 to 10 carbon atoms are used, more preferably 4 to 10 carbon atoms, even more preferably 5 to 9 carbon atoms, particularly preferably 8 or 9 carbon atoms, and most preferably 9 carbon atoms. The alcohols used are particularly primary alcohols, especially ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol (preferably 2-ethylhexanol), nonanol (preferably a mixture of isononol / isononanol), 2-propylheptanol, or decanol. The alcohol used in esterification is particularly preferably 2-ethylhexanol or isononol.

[0045] Dialkyl 1,4-cyclohexanedicarboxylate prepared according to the present invention, wherein each of the two alkyl groups has at least 2 carbon atoms, preferably at least 4 carbon atoms, can be advantageously used as a plasticizer or component of a plasticizer composition in plastics or plastic compositions, as an additive in paints or varnishes, in adhesives or adhesive components, in sealants, or as a solvent.

[0046] The prepared dialkyl 1,4-cyclohexanedicarboxylate can also be used as a plasticizer in mixtures with other plasticizers (especially so-called fast fixers). In the mixture, the proportion of the 1,4-cyclohexanedicarboxylate of the present invention to other plasticizers is preferably 15% to 95% by weight, more preferably 20% to 90% by weight, and most preferably 25% to 85% by weight, with the total proportion of all plasticizers present being 100% by weight. The above-described composition of dialkyl 1,4-cyclohexanedicarboxylate and other plasticizers can be used as a plasticizer composition in plastics and plastic compositions, adhesives, sealants, varnishes, paints, plastisols, or inks.

[0047] Plastic compositions that may contain the prepared dialkyl 1,4-cyclohexanedicarboxylate may include polymers selected from: polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyacrylates (especially polymethyl methacrylate (PMMA) and polyalkyl methacrylate (PAMA)), fluoropolymers (especially polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE)), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polyvinyl acetal (especially polyvinyl butyral (PVB)), polystyrene polymers (especially polystyrene (PS) and expandable polystyrene (EPS)), acrylonitrile-styrene acrylate (ASA), styrene-acrylonitrile (SAN), acrylonitrile-butadiene-styrene (ABS), styrene-maleic anhydride copolymer (SMA), styrene-ethylhexylene. olefin-methacrylic acid copolymers, polyolefins (especially polyethylene (PE) or polypropylene (PP), thermoplastic polyolefins (TPO)), polyethylene-vinyl acetate (EVA), polycarbonate, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyoxymethylene (POM), polyamide (PA), polyethylene glycol (PEG), polyurethane (PU), thermoplastic polyurethane (TPU), polysulfide (PSu), biopolymers (especially polylactic acid (PLA), polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV)), polyesters, starch, cellulose and cellulose derivatives (especially nitrocellulose (NC), ethyl cellulose (EC), cellulose acetate (CA), cellulose acetate / butyrate (CAB)), rubber or silicone, and mixtures or copolymers of the above polymers or their monomer units. The compositions of the present invention preferably comprise PVC or homopolymers or copolymers based on ethylene, propylene, butadiene, vinyl acetate, glycidyl acrylate, glycidyl methacrylate, methacrylate, acrylates, wherein an alkyl residue from a branched or unbranched alcohol having 1-10 carbon atoms is attached to an oxygen atom of an ester group, or styrene, acrylonitrile, or cycloolefin. PVC is particularly preferred.

[0048] As a type of PVC, the plastic composition of the present invention preferably includes suspension PVC, bulk PVC, microsuspension PVC, or emulsion PVC. Based on 100 parts by weight of polymer, the composition of the present invention preferably contains 5 to 200 parts by weight, more preferably 10 to 150 parts by weight of the plasticizer of the present invention.

[0049] In addition to the above-mentioned components, the plastic composition may also include other components, particularly plasticizers, fillers, pigments, stabilizers, co-stabilizers (such as epoxidized soybean oil), lubricants, blowing agents, kickers, antioxidants, rheological additives, or antimicrobial agents.

[0050] The plastic compositions of the present invention, derived from dialkyl 1,4-cyclohexanedicarboxylate and the above-mentioned polymer materials, can be used as plastic compositions, adhesives, sealants, varnishes, paints, plastisols, artificial leather, floor coverings, underbody protection, fabric coatings, roofing films, wallpapers, or inks, or their production.

[0051] For example, plastic products made using plasticizer compositions can be profiles, gaskets, food packaging, films, toys, medical devices, roofing sheets, artificial leather, floor coverings, bottom protection, coated fabrics, roofing membranes, wallpaper, wall coverings, and wire sheathing. This preferred group of applications includes food packaging, toys, medical devices, wallpaper, roofing membranes, fabric coatings, and floor coverings. Detailed Implementation

[0052] The present invention is illustrated below by way of examples. These examples are selected embodiments and do not constitute any limitation.

[0053] Example 1: Cyclohydrogenation of diisononyl terephthalate

[0054] To examine the dependence of diisononyl terephthalate cyclohydrogenation cyclization duration, various DINT samples were tested during cyclization. The following samples were used:

[0055] Sources of various DINT samples:

[0056] DINT-1

[0057] 2.318 g (16.1 mol) of isononol (INA, Evonik, purity > 99%), 1.358 g (7 mol) of dimethyl terephthalate (Oxxynova, purity > 99.9%), and 2.4 g of tetrabutyl titanate catalyst were placed in a 6 L glass flask equipped with a stirrer, a pipette, and a condenser connected to a Raschig ring column. The mixture was heated to 240 °C under a nitrogen atmosphere (nitrogen flow: 6 L / h), and the distillate was discarded while ensuring that the headspace temperature of the column did not rise above 65 °C. The reaction was monitored by gas chromatography, and the reaction was terminated once the residual concentration of methyl ester was < 0.5%. After 3 h of reaction time, the bottom temperature was lowered to 220 °C, and the pressure was gradually reduced to distill off excess alcohol.

[0058] The column was then replaced with a distillation bridge, and 4 g of 10% NaOH solution and 20 ml of deionized water were added at 80 °C. The mixture was stirred for 15 min to degrade the catalyst. The reaction mixture was then heated to 180 °C and dried under full vacuum for 40 min, followed by stripping with 20 mbar nitrogen for 2 h. After checking the residual alcohol content by GC, the mixture was cooled to 80 °C and filtered.

[0059] The reaction product, diisononyl terephthalate (DINT), with a purity of 99.96% was obtained. The CO value was determined according to the method given in the instructions, and it was 0.03 mg KOH / g.

[0060] DINT-2

[0061] 2.318 g (16.1 mol) of isononol (INA, Evonik, purity >99%), 1.163 g (7 mol) of terephthalic acid (Acros Organics, purity >99%), and 2.4 g of tetrabutyl titanate catalyst were placed in a 6 L glass flask equipped with a stirrer, a pipette, a condenser, and a water separator, and heated to 240 °C under a nitrogen atmosphere (nitrogen flow: 6 L / h). To accelerate the removal of water from the reaction system, 140 mL of cyclohexane was added as an azeotropic agent. Esterification was terminated after 11.5 h.

[0062] After the reaction was complete and cooled to room temperature, the water separator was replaced with a distillation bridge, and residual alcohol was removed by distillation under full vacuum (approximately 1-3 mbar) at 180 °C. Then, 1.9 g of 10% NaOH solution and 20 ml of deionized water were added at 80 °C, and the mixture was stirred for 15 min to degrade the catalyst. The reaction mixture was then heated to 180 °C and dried under full vacuum for 40 min, followed by stripping with nitrogen at 20 mbar for 2 h. After checking the residual alcohol content by GC, the mixture was cooled to 80 °C and filtered.

[0063] The reaction product, diisononyl terephthalate (DINT), with a purity of 99.75% was obtained. The CO value was determined according to the method given in the instructions, and it was 0.06 mg KOH / g.

[0064] DINT-3

[0065] With a capacity of approximately 50m 3In an industrial-scale nitrogen-filled reactor, 27 tons of isononol (INA, Evonik, purity >99%) were preheated to approximately 145°C, followed by the addition of 5 kg of tetrabutyl titanate catalyst and 18 tons of dimethyl terephthalate (Oxxynova, purity >99.9%). The reaction mixture was further heated to a maximum of 220°C, during which methanol was removed by distillation. The reaction was monitored by gas chromatography, and the reaction was terminated once the residual concentration of methyl terephthalate was <0.5%.

[0066] Once the reaction is complete, immediately stop the reflux at the top of the column and apply a vacuum (approximately 50-100 mbar) to the reactor. In the next step, which proceeds in parallel, the catalyst is destroyed with a 25% NaOH solution, and the free acid is neutralized.

[0067] The generated DINT was dried under full vacuum (approximately 50 mbar) at approximately 130 °C and then filtered. The reaction product, diisononyl terephthalate (DINT), was obtained with a purity of 99.7%. The CO value was determined according to the method given in the instructions and was 0.07 mg KOH / g.

[0068] DINT-4 was purchased from UPC in Taiwan, China, product UN499. The CO value was determined according to the method given in the instructions, and it was 0.21 mg KOH / g.

[0069] DINT-5 is a mixture of DINT-4 (60 wt%) and DINT-6 (40 wt%). The CO value was determined according to the method given in the instructions, and it was 0.43 mg KOH / g.

[0070] DINT-6 was a product of Kanatol-9090 purchased from the Indian KLJ Group. The CO value was determined according to the method given in the instructions, and it was 0.57 mg KOH / g.

[0071] Cyclohydride of DINT samples

[0072] Batch hydrogenation of various DINT (diisononyl terephthalate) samples was performed in a tubular reactor with an inner diameter of 40 mm and a length of 190 mm, using a circulating operation. In this method, the liquid and gas phases flowed concurrently through the tubular reactor in a trickle bed. The catalyst used for hydrogenation was a shell catalyst consisting of 1% by weight Ru loaded on titanium dioxide (Aerolyst 7711). In all cases, 25 g of hydrogenation catalyst and 25 g of inert material (composed of Al2O3) were used in the tubular reactor in the form of a 1.5 mm extrusion. The amount of DINT used in hydrogenation was always 1000 g. H2 was regulated by a constant exhaust gas operation mode, where degassing was set at a constant flow rate of 1 L / h (47.8 m). 3m -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 performed by a separator. The gas phase was continuously released into the exhaust gas. The liquid phase was recirculated back into the tubular reactor via a heated preheater, where it could be re-hydrogenated with H2. The change in DINT concentration over time was recorded by online Raman analysis.

[0073] The results are shown in Table 1 below.

[0074] Table 1: Functional relationship between DINT concentration and time during hydrogenation

[0075]

[0076] * Concentration c(DINT) was normalized to 100%.

[0077] As can be seen from the table, cyclohydrogenation is significantly faster when using DINT with a CO value within the range required for protection.

Claims

1. A method for preparing a dialkyl 1,4-cyclohexanedicarboxylate wherein both alkyl groups have at least two carbon atoms, said method comprising at least: In the presence of a heterogeneous hydrogenation catalyst, a dialkyl terephthalate in which both alkyl groups have at least two carbon atoms is cyclohydrogenated with a hydrogen-containing gas to form the corresponding dialkyl 1,4-cyclohexanedicarboxylate, characterized in that: The dialkyl terephthalate used in the cyclohydrogenation has a CO value of less than 0.2 mg KOH / g.

2. The method according to claim 1, wherein both alkyl groups of the 1,4-cyclohexanedicarboxylic acid dialkyl ester have at least 4 carbon atoms.

3. The method according to claim 1, wherein the CO value of the dialkyl terephthalate used in the cyclohydrogenation is less than 0.1 mg KOH / g.

4. The method according to claim 1, wherein the two alkyl groups of the 1,4-cyclohexanedicarboxylic acid dialkyl ester have 3 to 10 carbon atoms.

5. The method according to claim 4, wherein the two alkyl groups of the 1,4-cyclohexanedicarboxylic acid dialkyl ester have 4 to 10 carbon atoms.

6. The method of claim 4, wherein the two alkyl groups of the 1,4-cyclohexanedicarboxylic acid dialkyl ester have 5 to 9 carbon atoms.

7. The method according to claim 4, wherein the two alkyl groups of the 1,4-cyclohexanedicarboxylic acid dialkyl ester have 8 to 9 carbon atoms.

8. The method according to claim 4, wherein the two alkyl groups of the 1,4-cyclohexanedicarboxylic acid dialkyl ester have nine carbon atoms.

9. The method according to any one of claims 1 to 8, wherein the dialkyl terephthalate used in the cyclohydrogenation is prepared by transesterification of dimethyl terephthalate with an alcohol having at least two carbon atoms or by esterification of terephthalic acid with an alcohol having at least two carbon atoms.

10. The method of claim 9, wherein the alcohol used in the transesterification or esterification is an alcohol having 3 to 10 carbon atoms.

11. The method of claim 9, wherein the alcohol used in the transesterification or esterification is an alcohol having 4 to 10 carbon atoms.

12. The method of claim 9, wherein the alcohol used in the transesterification or esterification is an alcohol having 5 to 9 carbon atoms.

13. The method of claim 9, wherein the alcohol used in the ester exchange or the esterification is an alcohol having 8 or 9 carbon atoms.

14. The method of claim 9, wherein the alcohol used in the transesterification or esterification is an alcohol having nine carbon atoms.

15. The method according to claim 4 or 10, wherein the dialkyl 1,4-cyclohexanedicarboxylate is diisononyl 1,4-cyclohexanedicarboxylate or di(2-ethylhexyl) 1,4-cyclohexanedicarboxylate.

16. The method according to any one of claims 1 to 8, wherein the heterogeneous hydrogenation catalyst used in the cyclic hydrogenation comprises a transition metal on a support material.

17. The method according to claim 16, wherein the transition metal is a metal of group 8 of the periodic table.

18. The method of claim 17, wherein the transition metal is ruthenium.

19. The method of claim 16, wherein the carrier material is selected from activated carbon, silicon carbide, alumina, silicon dioxide, aluminum silicate, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide, or mixtures thereof.

20. The method of claim 19, wherein the carrier material is titanium dioxide or aluminum oxide.

21. The method according to claim 16, wherein the content of the transition metal in the heterogeneous hydrogenation catalyst is from 0.1% to 10% by weight.

22. The method according to claim 21, wherein the content of the transition metal in the heterogeneous hydrogenation catalyst is from 0.5% to 5% by weight.

23. The method according to claim 21, wherein the content of the transition metal in the heterogeneous hydrogenation catalyst is from 1% to 3% by weight.

24. The method according to any one of claims 1 to 8, wherein the cyclic hydrogenation is carried out in at least one hydrogenation unit.

25. The method according to any one of claims 1 to 8, wherein the cyclic hydrogenation is carried out in at least two hydrogenation units in series, wherein at least one of the at least two hydrogenation units operates in a cyclic mode.

26. The method according to any one of claims 1 to 8, wherein the hydrogenation temperature of 8 in the cyclic hydrogenation is 50 to 250 °C.

27. The method according to any one of claims 1 to 8, wherein the cyclic hydrogenation is carried out at a pressure of 3 to 300 bar.

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