Method for ring hydrogenation of dialkyl terephthalates with low by-product formation

Abstract

To provide a method for ring hydrogenation of dialkyl terephthalates in a hydrogenation unit which enables a more efficient production of the corresponding esters.SOLUTION: There is provided a process for ring hydrogenation of dialkyl terephthalates having C3- to C16-alkyl groups to give 1,4-cyclohexanedicarboxylic esters in a hydrogenation unit composed of two reaction units in series. Reactors in a second reaction unit are operated in a straight pass, wherein a heterogeneous hydrogenation catalyst is present in the reactors of each of the two reaction units of the hydrogenation unit. The process comprises a step of bringing an aromatic carboxylic ester used as feed into contact with a hydrogen-containing gas in the reactors of the reaction units and monitoring the reaction conversion in the first reaction unit, and at least one parameter in relation to the first reaction unit is controlled such that a reaction conversion in the range of 85 to 93% is achieved.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for ring hydrogenation of dialkyl terephthalates having C3-C16 alkyl groups in a hydrogenation unit having two reaction units connected in series. In the process according to the invention, a constant reaction conversion is achieved by adjusting the appropriate process parameters for the first reaction unit. [Background technology]

[0002] Plasticizers are used in many industrial applications to make plastics such as polyvinyl chloride (PVC) softer and more flexible. For many years, phthalates, i.e., diesters of (ortho)phthalic acid, have been the predominant plasticizers. However, in recent years, concerns about the health effects of phthalate plasticizers have emerged, and alkyl esters of cyclohexanedicarboxylic acids have also become important. In particular, dialkyl esters of 1,2-cyclohexanedicarboxylate and, more recently, dialkyl 1,4-cyclohexanedicarboxylate have played an important role.

[0003] Dialkyl 1,2- and 1,4-cyclohexanedicarboxylates can be prepared by hydrogenating the aromatic rings of the corresponding phthalates or terephthalates (hereinafter referred to as "ring hydrogenation"). The corresponding ring hydrogenation is already used on an industrial scale today for the conversion of phthalates, i.e., dialkyl phthalates, for example, from DINP (diisononyl phthalate) to DINCH (1,2-diisononyl cyclohexanedicarboxylate). Regarding the hydrogenation of terephthalates, i.e., dialkyl terephthalates, the reaction proceeds more slowly than the ring hydrogenation of dialkyl phthalates, resulting in the formation of many by-products, making such a process economically unattractive. Summary of the Invention [Problem to be solved by the invention]

[0004] The problem that the present disclosure seeks to solve was to provide an improved process for the ring hydrogenation of dialkyl terephthalates that may be more economically viable than the ring hydrogenation of dialkyl phthalates. It was therefore an object of the present invention to provide a process for the ring hydrogenation of dialkyl terephthalates in a hydrogenation unit that allows for more efficient production of the corresponding esters. [Means for solving the problem]

[0005] This object has been achieved by a method according to claim 1 for the ring hydrogenation of dialkyl terephthalates with C3- to C16-alkyl groups. Preferred embodiments of this process are set out in the dependent claims. DETAILED DESCRIPTION OF THE INVENTION

[0006] The method of the present invention therefore provides a process for ring-hydrogenating dialkyl terephthalates having C3 to C16 alkyl groups or dialkyl terephthalates having C4 to C11 alkyl groups to 1,4-cyclohexanedicarboxylic acid esters having the corresponding alkyl groups in a hydrogenation unit consisting of one reactor or two or more parallel reactors connected in series, wherein one or more reactors in the second reactor unit are operated in straight path, and a heterogeneous hydrogenation catalyst is present in each of the reactors of the two reactor units of the hydrogenation unit, wherein: contacting an aromatic carboxylic acid ester used as a feed with a hydrogen-containing gas in the reactor of the reaction unit and monitoring the reaction conversion in the first reaction unit; and The at least one parameter related to the first reaction unit is selected from the group consisting of: the amount of feed supplied to the first reaction unit (the sum of the fresh feed amount and the recycled amount), the amount of dialkyl terephthalate to be hydrogenated, the reactor temperature in the reactor of the first reaction unit, the temperature rise, the circulation volumetric flow rate, the feed / recycle ratio, the ratio of hydrogen to aromatic carboxylic acid ester, the reactor pressure, the feed composition, the catalyst amount, the amount of cooling water recycled if the catalyst composition is cooled, the product amount in the discharge of the first reaction unit, and combinations thereof, wherein the at least one parameter related to the first reaction unit is controlled to achieve a reaction conversion in the range of 85 to 93%, or 88 to 92%.

[0007] Surprisingly, it has been found that limiting the reaction conversion in the first reaction unit allows reducing the amount of by-products and reactants in the final hydrogenated product (after passing through the second reaction unit), so that the resulting reaction product is purer and does not require more complex purification or is readily available in the required specifications without further purification efforts, making it available for sale or further use.

[0008] According to the present invention, the hydrogenation unit is composed of two reaction units connected in series, each of which consists of one reactor or two or more parallel reactors. One or more of the reactors in the second reaction unit are operated in a straight path. The reactors in the first reaction unit can be operated in various ways. However, if a reactor is present in the first reaction unit, it is preferably operated in a circulating manner. The input feed is then fed to the second reaction unit after adjusting the reaction conversion rate.

[0009] In the context of the present invention, the parameters controlled to limit the conversion in the parallel reactors of the first reaction unit are preferably selected from the group consisting of the amount of feed (the sum of the amount of fresh feed and the recycled amount) supplied to the circulation reactor, the amount of dialkyl terephthalate to be hydrogenated, the reactor temperature in at least one circulation reactor, the temperature rise (i.e., the difference between the reactor inlet temperature and the reactor outlet temperature), the circulation volumetric flow rate, the feed / recycle ratio, the reactor pressure, the amount of coolant circulated if cooled, the amount of product in the discharge of the first reaction unit, and combinations thereof. Suitable means for adjusting these parameters are known to those skilled in the art. In a particularly preferred embodiment, the parameters controlled to limit the conversion in the one or more parallel reactors of the first reaction unit are preferably selected from the group consisting of the amount of feed (the sum of the amount of fresh feed and the recycled amount) supplied to at least one circulation reactor, the amount of dialkyl terephthalate to be hydrogenated, the feed / recycle ratio, and combinations thereof. In particular, the reaction throughput is significantly improved, which has the advantage of producing more product in a shorter time with less by-products.

[0010] Regarding adjusting the amount of product in the effluent of the first reaction unit, a method for adjusting the reaction conversion can be achieved by routing a portion of the feed used around the first reaction unit, i.e., not passing through the reactor of the reaction unit and not hydrogenating it, thereby limiting the reaction conversion purely by calculation. The feed passed through the first reaction unit is then mixed with the reaction effluent of the first reaction unit to control the amount of product in the effluent of the first reaction unit, and the reactor is operated in a straight-through mode to convey it to the second reaction unit. The composition of the stream fed to the second reaction unit then corresponds to the composition of the reaction effluent from the first reaction unit, achieving a reaction conversion in the range of 85-93% or 88-92%. This can be very easily controlled by the amount of feed passed through the first reaction unit. In this embodiment, the desired conversion in the first reaction unit is simply devised in this way. The true reaction conversion of the first reaction unit is (significantly) high and is artificially reduced by the addition of feed.

[0011] The process according to the present invention can be carried out in principle discontinuously (batchwise) or continuously. A continuous process is preferred according to the present invention. Despite limiting the reaction conversion in the first reaction unit, the overall conversion of the process according to the present invention based on all the hydrogenation units is 99.7% or more, preferably 99.8% or more. The amount of by-products in the product of the ring hydrogenation process after the hydrogenation unit is preferably less than 1.3% by mass, more preferably less than 1.2% by mass.

[0012] According to the present invention, dialkyl terephthalates having C3 to C16 alkyl groups are used for ring hydrogenation. The selection of the alkyl group length is not particularly critical and should not present a problem for those skilled in the art. However, it is preferred that the chain lengths of the two alkyl groups are the same. As dialkyl terephthalates, dialkyl terephthalates having C4 to C11 alkyl groups are preferred, dialkyl terephthalates having C4 to C10 alkyl groups are more preferred, dialkyl terephthalates having C5 to C9 alkyl groups are even more preferred, and dialkyl terephthalates having C8 or C9 alkyl groups are particularly preferred. The dialkyl terephthalates used are particularly preferably diethylhexyl terephthalate or diisononyl terephthalate.

[0013] The dialkyl terephthalates used in the ring hydrogenation can be prepared by transesterification of an ester of terephthalic acid, such as dimethyl terephthalate, with a suitable alcohol, or by transesterification of terephthalic acid with a suitable alcohol, the chain length of which corresponds to the chain length of the resulting ester.

[0014] According to the present invention, heterogeneous hydrogenation catalysts are generally used in the process of the present invention for the ring hydrogenation of dialkyl terephthalates or aromatic carboxylic acid esters. These may be catalysts containing a support material or unsupported catalysts (without a support material), such as Raney-Ni. Preferably, the heterogeneous hydrogenation catalysts used in the ring hydrogenation in at least two reactors of the hydrogenation unit contain or consist of at least one transition metal on a support material. However, suitable catalysts are known to those skilled in the art, and are described, for example, in WO 03 / 103830.

[0015] The transition metal of the heterogeneous hydrogenation catalyst is preferably a metal selected from Group 8 (iron group) of the periodic table, and is preferably selected from the group consisting of iron, ruthenium, cobalt, nickel, rhodium, platinum, palladium, or a mixture thereof. Ruthenium is particularly preferred as the transition metal of the catalyst used in the present invention. The content of the transition metal in the heterogeneous hydrogenation catalyst is preferably in the range of 0.1% to 10% by mass, particularly preferably 0.2% to 5%, and particularly preferably 0.5% to 3% by mass. When ruthenium is used as the transition metal, the content of ruthenium calculated as metal is preferably in the range of 0.1% to 10% by mass, particularly preferably 0.2% to 5%, and particularly preferably 0.5% to 3% by mass.

[0016] The support material on which the transition metal of the heterogeneous hydrogenation catalyst is present is preferably selected from the group consisting of activated carbon, silicon carbide, aluminum oxide, silicon dioxide, aluminosilicates, zeolites, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide, or mixtures thereof. Preferred support materials are aluminum oxide, silicon dioxide, titanium dioxide, and mixtures thereof, with titanium dioxide and aluminum oxide being particularly preferred. Furthermore, these support materials may contain alkali metals, alkaline earth metals, and / or sulfur components.

[0017] The heterogeneous hydrogenation catalysts in the reactors of both reaction units may have the same or different transition metal and support material compositions, and preferably the at least two heterogeneous hydrogenation catalysts have the same composition, i.e., the same transition metal and the same support material, but the transition metal, preferably ruthenium, content may be different.

[0018] According to the present invention, the ring hydrogenation is preferably carried out in the liquid phase. Ring hydrogenation can be carried out over a homogeneous hydrogenation catalyst or a heterogeneous hydrogenation catalyst arranged in suspension or bulk in a fixed bed. In the process of the present invention, continuous ring hydrogenation, in which the reaction mixture is mainly in the liquid state at the reaction conditions, is preferred over heterogeneous catalysts arranged in a fixed bed. Preferably, the reactor is operated in a mixed liquid / gas phase, for example as a trickle-bed reactor, which can be fully or partially submerged.

[0019] Various process variations can be selected for the ring hydrogenation. It can be carried out in one or more stages, adiabatically or polytropically. In the latter case, all reactors, preferably tubular reactors, can be operated adiabatically or polytropically, or one or more can be operated adiabatically and the others polytropically.

[0020] The ring hydrogenation according to the invention can be carried out in a liquid / gas mixed phase or in a liquid phase in a three-phase reactor, whereby the hydrogenation gas phase is introduced into the liquid reactant / product stream in a manner known per se. In view of uniform liquid distribution, improved reaction heat removal and a high space-time yield, the reactor is preferably designed to have a cross-sectional area of ​​1 m per hour of empty reactor. 2 Per, 15-120, especially, 25-80m 3 When the reactors are operated in a straight path (series) configuration, the specific liquid hourly space velocity (LHSV) is 0.1 to 10 h ―1 It can take values ​​between .

[0021] In a preferred embodiment, the ring hydrogenation process can be carried out in the absence of a solvent or, preferably, in the presence of a solvent. The solvent used can be any liquid that forms a homogeneous solution with the reactants and product, is inert under the hydrogenation conditions, and can be easily removed from the product.

[0022] For example, linear or cyclic ethers such as tetrahydrofuran or dioxane, or aliphatic alcohols having an alkyl radical with 1 to 13 carbon atoms can be used as the solvent. Preferred examples of alcohols or alcohol mixtures that can be used include isopropanol, n-butanol, isobutanol, n-pentanol, 2-ethylhexanol, nonanol, technical-grade nonanol mixtures, decanol, technical-grade decanol mixtures, tridecanol, and the like.

[0023] When using an alcohol as a solvent, it may be appropriate to use the alcohol or alcohol mixture produced during the saponification of the product, thereby eliminating the production of by-products due to transesterification.More preferably, the solvent is the hydrogenated product, in this case the ring-hydrogenated dialkyl terephthalate itself.

[0024] The ring hydrogenation can be carried out at a pressure ranging from 3 to 300 bar, preferably from 20 to 200 bar. The hydrogenation temperature is preferably in the range of 50°C to 250°C, particularly preferably in the range of 60°C to 200°C.

[0025] The hydrogenation gas used may be any hydrogen-containing gas mixture that does not contain harmful catalyst poisons such as carbon monoxide or hydrogen sulfide. In addition to hydrogen, nitrogen and methane, such as CO, may also be present in the hydrogenation gas. Preferably, hydrogen is used with a purity of 95% or more, particularly 98% or more.

[0026] The present invention is further illustrated by the following examples, which merely disclose exemplary embodiments and should not be construed as limiting. [Example]

[0027] Hydrogenation experiments with diisononyl phthalate (DINP) and diisononyl terephthalate (DINT) were carried out in a hydrogenation unit consisting of a circulation reactor and a reactor operated in straight-pass mode as follows.

[0028] Ring hydrogenation of DINT or DINP was carried out in a tubular reactor in recycle mode and a second tubular reactor connected in straight-pass mode. The liquid phase (DINT or DINP and hydrogenated product) and the gas phase (hydrogen) were co-flowed through the trickle bed of the tubular reactor. Both reactors used a commercially available ruthenium catalyst (Specialist® 102: 1% Ru on a TiO support, Evonik Operations GmbH) as the hydrogenation catalyst. This was used in a 40 mm inner diameter, 479 mm long tubular reactor and a 20 mm inner diameter, 1076 mm long second reactor. The DINT or DINP feed rate for ring hydrogenation varied between approximately 180 and 800 g / h depending on the experiment, with the recycle flow always at 80 L / h. The feed rate was varied during the reaction to affect the reaction conversion. The hydrogen level was regulated in a constant exhaust gas circulation mode with an exhaust gas flow rate of 0.5 L / h. The experiments were carried out in one circulation reactor and one second reactor at 110°C, with a system pressure of 100 bar and a tubular reactor temperature of 105°C, respectively. The effluent from the hydrogenation unit was analyzed by gas chromatography (GC) for the presence and amount of by-products. The results are shown in Table 1.

[0029] [Table 1] It can be seen that in the ring hydrogenation of terephthalate, limiting the conversion in the first reactor can significantly reduce the amount of by-products after the last reactor. However, for the corresponding phthalate esters, this change is negligible. Limiting the conversion of terephthalic acid has the added benefit of significantly increasing the feed rate. This means that more ring hydrogenated product can be produced with higher purity, thereby improving the economics of the process.

Claims

1. 1. A process for ring-hydrogenating dialkyl terephthalates having C3 to C16 alkyl groups to 1,4-cyclohexanedicarboxylic acid esters having the corresponding alkyl groups in a hydrogenation unit consisting of one reactor or two or more parallel reactors connected in series, wherein one or more reactors in the second reactor unit are operated in straight path and a heterogeneous hydrogenation catalyst is present in each of the reactors of the two reactor units of the hydrogenation unit, wherein the process comprises: contacting an aromatic carboxylic acid ester used as a feed to the reactor of the reaction unit with a hydrogen-containing gas and monitoring the reaction conversion in a first of the reaction units; and the at least one parameter related to the first reaction unit is selected from the group consisting of: the amount of feed supplied to the first reaction unit (the sum of the amount of fresh feed and the amount recycled), the amount of dialkyl terephthalate to be hydrogenated, the reactor temperature in the reactor of the first reaction unit, the temperature rise, the circulation volumetric flow rate, the feed / recycle ratio, the ratio of hydrogen to aromatic carboxylic acid ester, the reactor pressure, the feed composition, the catalyst amount, the catalyst composition, the amount of recycled cooling water, if any, the amount of product in the effluent of the first reaction unit, and combinations thereof, wherein the at least one parameter related to the first reaction unit is controlled to achieve a reaction conversion in the range of 85 to 93%; process.

2. 2. The process of claim 1, wherein in the first reaction unit, there is a reactor that is operated in a cyclic manner.

3. 2. The process of claim 1, wherein the amount of by-products in the product of the ring hydrogenation process after the hydrogenation unit is less than 1.3% by mass.

4. 10. The process of claim 1, wherein the overall conversion of the process, based on all of the hydrogenation units, is 99.7% or greater.

5. 2. The process of claim 1, wherein the dialkyl terephthalate used in ring hydrogenation is a dialkyl terephthalate having a C4 to C10 alkyl group.

6. 6. The process of claim 5, wherein the dialkyl terephthalate used in the ring hydrogenation is prepared by transesterification of dimethyl terephthalate with an alcohol having 4 to 10 carbon atoms, or by transesterification of terephthalic acid with an alcohol having 4 to 10 carbon atoms.

7. 6. The process of claim 5, wherein the dialkyl terephthalate used in the ring hydrogenation is diethylhexyl terephthalate or diisononyl terephthalate.

8. 8. The process according to any one of claims 1 to 7, wherein the heterogeneous hydrogenation catalyst used for ring hydrogenation in the reactors of the two reaction units of the hydrogenation unit comprises a transition metal on a support material.

9. 9. The process of claim 8, wherein the transition metal is a metal of Group 8 (iron group) of the periodic table of the elements.

10. 9. The process of claim 8, wherein the support material is selected from the group consisting of activated carbon, silicon carbide, aluminum oxide, silicon dioxide, aluminosilicates, zeolites, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide, or mixtures thereof.

11. 11. The process of claim 10, wherein the support material is titanium dioxide or aluminum oxide.

12. The process of claim 8, wherein the content of the transition metal in the heterogeneous hydrogenation catalyst is in the range of 0.1% to 10% by weight.

13. 9. The process of claim 8, wherein the hydrogenation catalysts in the reactors of at least two of the reaction units of the hydrogenation unit are of the same composition.

14. 2. The process of claim 1, wherein the hydrogenation temperature in the ring hydrogenation ranges from 50°C to 250°C.

15. 2. The process of claim 1, wherein the ring hydrogenation is carried out at a pressure ranging from 3 to 300 bar.