Hydrogenation of aromatic compounds

Abstract

Process for hydrogenating aromatic compounds over a solid catalyst in the presence of a hydrogen-containing gas comprising a first reactor operated in loop mode, a second reactor operated in straight pass, at least part of the output of the first reactor is supplied to the second reactor, characterized in that the first reactor is configured as a trickle bed reactor and is operated in trickle bed mode and the second reactor is operated such that the catalyst present therein is partially flooded.

Claims

1. Process for hydrogenating an aromatic compound over a solid catalyst in the presence of a hydrogen-containing gas comprising supplying a fresh feed comprising the aromatic compound in a liquid form or in a solution in an inert solvent forming a continuous liquid phase and the hydrogen containing gas to a first reactor operated in loop mode, taking an output of the first reactor from the lower part of the first reactor, separating the output into a circulating current and a hydrogenation current, returning the circulating current to the first reactor, supplying the hydrogenation current to a second reactor operated in straight pass, wherein at least part of the output of the first reactor is supplied to the second reactor, and taking an output from the lower part of the second reactor comprising a product, wherein the catalyst is arranged in a fixed bed as a random bed or as a packing in the first and second reactors and the catalyst contains metals and/or metal oxides from subgroups VI to VIII of the Periodic Table of the Elements, the first reactor is configured as a trickle bed reactor and is operated in trickle bed mode, and the second reactor is operated such that the catalyst present therein is partially flooded.

2. The process according to claim 1, wherein a non-flooded part of the catalyst in the second reactor is operated in trickle bed mode.

3. The process according to claim 1, wherein a circulation ratio in the first reactor between the circulating current and the fresh feed is 1:1 to 20:1 (by mass).

4. The process according to claim 1, wherein a pressure in the first and second reactors is 50 to 500 bar.

5. The process according to claim 1, wherein a feed temperature for the first reactor is from 70 to 150° C. and a feed temperature for the second reactor is from 80 to 180° C.

6. The process according to claim 1, wherein 10 to 98 percent of a catalyst volume in the second reactor is surrounded by a continuous liquid phase.

7. The process according to claim 1, wherein the aromatic compound is an aromatic carboxylic acid ester and hydrogenated to the corresponding alicyclic carboxylic acid ester.

8. The process according to claim 7, wherein mono-, di- or polycarboxylic acid esters are used as the aromatic carboxylic acid ester.

9. The process according to claim 1, wherein the aromatic compound is diisononyl phthalate or di-2-ethylhexyl terepthalate.

10. The process according to claim 1, wherein the aromatic compound is isononyl benzoate or decyl benzoate.

11. The process according to claim 1, wherein the hydrogenation in the second reactor is 2 to 20 percent based on a total hydrogenation in the first and second reactors.

12. The process according to claim 7, wherein the catalyst comprises a metal of the eighth subgroup of the Periodic Table of the Elements.

13. The process according to claim 12, wherein the catalyst contains ruthenium.

14. The process according to claim 1, wherein the second reactor is a vertical tubular reactor and comprises a first compartment configured as an upwardly open cylinder that is essentially arranged concentrically in the second reactor comprising the catalyst and a second compartment configured as an annulus between the outer wall of the first compartment and the inner wall of the reactor comprising a liquid phase volume.

Description

EXAMPLE

(1) The examples are merely illustrative of the invention and are not intended to be limiting.

(2) In an industrial hydrogenation plant according to FIG. 1 or FIG. 2, diisononyl phthalate was hydrogenated to di-(isononyl)-1,2-cyclohexanedicarboxylate. Hydrogenation took place in two reactors connected in series. The catalyst was arranged in a fixed bed in both reactors. 72% of the total catalyst volume was in the first reactor; 28% of the total catalyst volume was in the second reactor. The catalyst used had a ruthenium content of 0.5 percent by weight based on the total weight of the carrier material, a specific surface area of 220 to 290 m.sup.2/g (BET, ISO9277) and a pore volume of 0.48 to 0.62 mL/g (Hg porosimetry, DIN 66133), the carrier material comprising alumina. The first reactor was operated in loop mode; the second reactor was operated in straight pass.

(3) The hydrogen pressure was 215 bar in both reactors. The hydrogenation plant was operated with a diisononyl phthalate fresh feed of 292 kg/(hour*m.sup.3 total catalyst volume). The circulation ratio in the first reactor between the circulating current and the fresh feed was 12:1. Hydrogenation was operated such that, in the output from the second reactor, the residual aromatic content based on di-(isononyl)-1,2-cyclohexanedicarboxylate was less than 100 ppm.

(4) Modes of Operation in Comparison:

(5) The first and the second reactors were operated in trickle bed mode. The following feed temperatures were set:

(6) First reactor: 97° C.

(7) Second reactor: 109° C.

(8) The hydrogen losses during this operation were 3 kg/t di-(isononyl)-1,2-cyclohexanedicarboxylate.

(9) Modes of Operation According to the Invention:

(10) The first reactor was operated in trickle bed mode. In the second reactor, the catalyst was 70% flooded. The following feed temperatures were set:

(11) First reactor: 92° C.

(12) Second reactor: 98° C.

(13) The hydrogen losses during this operation were 0.5 kg/t di-(isononyl)-1,2-cyclohexanedicarboxylate.

(14) Comparison of the Modes of Operation:

(15) Operating points are compared with the same load. By flooding the catalyst in the second reactor, the following advantages were achieved: Reduction of hydrogen losses Lowering of the feed temperature of the first reactor by 5° C. Lowering of the feed temperature of the second reactor by 11° C.

(16) A lower feed temperature increases the remaining service life of the catalyst.