Ammoximation reactor for cyclohexanone oxime production

Abstract

Ammoximation reactor for cyclohexanone oxime production comprising: (a) a reactor vessel provided with a stirrer; (b) an internal filtering system; (c) an internal liquid ammonia evaporation coil; (d) an internal gaseous ammonia toroidal distributor; (e) an external cyclohexanone toroidal distributor; (f) an internal hydrogen peroxide toroidal distributor; (g) an internal cylindrical draft tube; (h) an external cooling jacket. Said ammoximation reactor allows to obtain a better mixing of the components of the ammoximation reaction and to maximize both the heat-transfer coefficients and the mass-transfer coefficients. Moreover, said ammoximation reactor allows to increase the packing time of the catalyst used in the ammoximation reaction on the filtering system (i.e. the plugging phenomena) so as to avoid the necessity of carrying out the backwashings with nitrogen. Moreover, said ammoximation reactor does not require external downstream separation units to separate the catalyst from the reaction mixture obtained from the ammoximation reaction.

Claims

1. Ammoximation reactor for cyclohexanone oxime production, comprising: (a) a reactor vessel provided with a stirrer; (b) an internal filtering system; (c) an internal liquid ammonia evaporation coil installed at the bottom of the reactor vessel; (d) an internal gaseous ammonia toroidal distributor connected to the outlet end of the evaporation coil; (e) an external cyclohexanone toroidal distributor; (f) an internal hydrogen peroxide toroidal distributor; (g) an internal cylindrical draft tube; and (h) an external cooling jacket; wherein said internal filtering system comprises a set of tubular filters arranged in two concentric circular crowns, the bottoms of each tubular filter being connected together to form two continuous toroidal connecting tubes, each continuous toroidal connecting tube having an outlet end to collect and recover a liquid reaction mixture obtained from an ammoximation reaction and the tubular filters retain catalyst used in the ammoximation reaction in the reactor vessel; wherein said external toroidal cyclohexanone distributor is endowed with circularly arranged oriented feeding nozzles for tangential feeding of cyclohexanone into the reactor vessel and mixing of the cyclohexanone with the liquid reaction mixture, and the internal toroidal hydrogen peroxide distributor feeds an aqueous hydrogen peroxide solution to the liquid reaction mixture; and wherein: the ratio between the internal diameter of the cylindrical draft tube (D.sub.C) and the internal diameter of the reactor vessel (D.sub.R) ranges from 0.25 to 0.8; the distance (H.sub.DT) between the bottom of the reactor vessel (T.L.) and the bottom of the cylindrical draft tube ranges from 10 mm to 800 mm.

2. Ammoximation reactor according to claim 1, wherein said tubular filters are made of stainless steel which is selected from the following types: AISI 316L, AISI 316, and AISI 304.

3. Ammoximation reactor according to claim 1, wherein the total number of said tubular filters in each continuous toroidal connecting tube is ranging from 30 to 80.

4. Ammoximation reactor according to claim 1, wherein said tubular filters have a filtration rate ranging from 1 m to 10 m.

5. Ammoximation reactor according to claim 1, wherein said filtering system has a filtering rate (square meter of the filtering surface of the tubular filters per each cubic meter per hour of the obtained liquid filtered reaction mixture) which ranges from 0.7 (m.sup.2hour)/m.sup.3 to 3 (m.sup.2hour)/m.sup.3.

6. Ammoximation reactor according to claim 5, wherein said filtering system has a filtering rate (square meter of the filtering surface of the tubular filters per each cubic meter per hour of the obtained liquid filtered reaction mixture) which ranges from 1.5 (m.sup.2hour)/m.sup.3 to 2.5 (m.sup.2hour)/m.sup.3.

7. Ammoximation reactor according to claim 1, wherein said liquid ammonia evaporation coil is loop-shaped, or helicoidal-shaped.

8. Ammoximation reactor according to claim 1, wherein said gaseous ammonia toroidal distributor is directly connected to the outlet end of the evaporation coil.

9. Ammoximation reactor according to claim 1, wherein said hydrogen peroxide toroidal distributor is endowed with holes evenly arranged in both its bottom part and its upper part.

10. Ammoximation reactor according to claim 1, wherein said cylindrical draft tube is suspended, through supports, in the center of the reactor vessel.

11. Ammoximation reactor according to claim 1, wherein the ratio between the internal diameter of the cylindrical draft tube (D.sub.c) and the internal diameter of the reactor vessel (D.sub.r) ranges from 0.5 to 0.7.

12. Ammoximation reactor according to claim 1, wherein the distance (H.sub.DT) between the bottom of the reactor vessel (T.L.) and the bottom of said cylindrical draft tube ranges from 25 mm to 300 mm.

Description

(1) In particular, FIG. 1 schematically represents a longitudinal section of one embodiment of the ammoximation reactor according to the present invention.

(2) According to FIG. 1, the ammoximation reactor (A) comprises: a reactor vessel (B) provided with a stirrer (F); an internal filtering system (E) comprising a set of tubular filters (candles) arranged in two concentric circular crowns, the bottoms of each tubular filter (candle) being connected together to form two continuous toroidal connecting tubes, from the outlet ends of said two continuous toroidal connecting tubes the liquid filtered reaction mixture (I), obtained from the ammoximation reaction, is collected and recovered; an internal liquid ammonia evaporation coil (C) installed at the bottom of said reactor vessel (B); an internal gaseous ammonia toroidal distributor (D1) directly connected to the outlet end of the evaporation coil (C); an external cyclohexanone toroidal distributor (not represented in FIG. 1) with circularly arranged oriented feeding nozzles [(D2) represents one feeding nozzle] through which the cyclohexanone is fed to the reactor vessel (B); an internal hydrogen peroxide toroidal distributor (D3); an internal cylindrical draft tube (G); an external cooling jacket (L).

(3) As reported above, in FIG. 1: (D.sub.R) indicates the internal diameter of the reactor vessel (B); (D.sub.C) indicates the internal diameter of the cylindrical draft tube (G); (H.sub.DT) indicates the distance between the bottom (T.L.) of the reactor vessel (B) and the bottom of the cylindrical draft tube (G).

(4) The present invention will be further illustrated below by means of a an applicative example, which is given for purely indicative purposes and without any limitation of this invention.

(5) The analyses of cyclohexanone and of cyclohexanone oxime were carried out by using gas chromatography and, based on the analyses results, the conversion of cyclohexanone, the selectivity of cyclohexanone oxime and the yield of hydrogen peroxide, were calculated.

EXAMPLE 1

(6) The ammoximation reactor used in the Example is as schematically show in FIG. 1.

(7) To the reactor vessel (B) the following components were continuously fed: liquid ammonia (NH.sub.3) (405 kg/hour) through the liquid ammonia evaporation coil (C) and the gaseous ammonia toroidal distributor (D1); cyclohexanone (1300 kg/hour) by means of the external cyclohexanone toroidal distributor (not represented in FIG. 1) through circularly arranged oriented feeding nozzles [(D2) represents one feeding nozzle)]; 50% w/w of an hydrogen peroxide (H.sub.2O.sub.2) aqueous solution (993 kg/hour) by means of the hydrogen peroxide toroidal distributor (D3).

(8) The continuous ammoximation reaction was carried out, under vigorous stirring, at a temperature of 85 C., at a pressure of 2.5 barg and at a residence time ranging from 1.2 to 1.3 hours while continuosly discharging the liquid filtered reaction mixture (I), obtained from the ammoximation reaction, from the outlet ends of the two continuous toroidal connecting tubes.

(9) The tert-butyl alcohol (TBA) was continuosly fed to the reaction vessel (B) in order to maintain its concentration equal to 55% by weight in the reaction mixture. During the ammoximation reaction, the catalyst (i.e titanium silicalite TS-1 from Polimeri Europa) was present in the reactor vessel (B), in a concentration ranging from 2% by weight to 6% by weight in the reaction mixture.

(10) The obtained liquid filtered reaction mixture (I), continuosly discharged from the reaction vessel (B), was analyzed obtaining the following data: conversion of cyclohexanone: 98.5%; selectivity of cyclohexanone oxime: 99.4%; yield of hydrogen peroxide on cyclohexanone oxime basis: 88.8%; concentration of ammonia: 2%.

(11) The data obtained shows that the ammoximation reactor according to the present invention is endowed with high productivity levels.

(12) In order to support the high reduction of the production costs, the following tests were carried out.

(13) The conventional ammoximation reactor needs a nitrogen backwashing every month, with a relative productivity loss equivalent to 10 hours/month.

(14) In addition, due to the packing of the catalyst on the internal filtering system (i.e. the plugging phenomena) which increases with time, two mechanical cleanings a year (one every 6 months), are normally required for the internal filtering system, typically involving a shut-down periods of 10 days for each cleaning, with a relative productivity loss equivalent to 480 hours/year. As a result, for a conventional reactor the overall productivity loss is equivalent to 600 hours/year.

(15) Experimental tests carried out in the ammoximation reactor as schematically show in FIG. 1, have demonstrated that the backwashing operations are completely eliminated and the ammoximation reactor was continuously run for 1 year without stopping. As a result, the total productivity loss was decreased to 240 hours/year.

(16) The difference () between the productivity using a traditional ammoximation reactor and the productivity using the ammoximation reactor according to the present invention, was equal to 360 hours/year. Said difference (), in a traditional plant for -caprolactam production having a nominal hourly capacity of 12.5 Mton/hours of -caprolactam, means a difference () in the -caprolactam production equal to 4500 Mton/year. Assuming for -caprolactam a variable cost margin of 600 $/Mton, the ammoximation reactor according to the present invention may allow to obtain a profit increase of 2.7 million $ per year compared to the conventional ammoximation reactor technology.