Process comprising two reaction zones and apparatus therefore

Abstract

In a process for carrying out a chemical reaction gaseous reactants are supplied to a first reaction zone including a first catalyst having a first particle equivalent diameter. The first reaction zone is operated such that when the reactants are contacted with the first catalyst a portion of the reactants is converted to the desired product. An intermediate stream of unreacted reactants and the desired product is removed and passed to a second reaction zone including a tubular reactor. Tubes of the reactor are catalyst carriers containing a second catalyst having a second particle equivalent diameter smaller than the first particle equivalent diameter. The second reaction zone is operated such that when the unreacted reactants are contacted with the second catalyst, at least some of the unreacted reactants are converted to the desired product. A product stream is then recovered. Apparatus for carrying out the process is also described.

Claims

1. A process for carrying out a chemical reaction comprising: supplying gaseous reactants to a first reaction zone comprising a first catalyst having a first catalyst particle equivalent diameter; operating said first reaction zone such that when the reactants are contacted with the first catalyst a portion of the reactants are converted to a desired product; removing an intermediate stream comprising unreacted reactants and the desired product and passing the intermediate stream to a second reaction zone comprising a tubular reactor which comprises tubes, wherein said tubes comprise a plurality of catalyst carriers containing a second catalyst having a second catalyst particle equivalent diameter which is smaller than the first catalyst particle equivalent diameter of the first catalyst; operating said second reaction zone such that when the unreacted reactants in the intermediate stream from the first reaction zone are contacted with the second catalyst, at least some of the unreacted reactants are converted to the desired product; and recovering a product stream, wherein each catalyst carrier comprises: an annular container for holding the second catalyst in use, said container having a perforated inner wall defining a tube, a perforated outer wall, a top surface closing the annular container and a bottom surface closing the annular container; a surface closing the bottom of said tube formed by the inner wall of the annular container; a skirt extending upwardly from the perforated outer wall of the annular container from a position at or near the bottom surface of said container to a position below the location of a seal; and a seal located at or near the top surface and extending from the container by a distance which extends beyond an outer surface of the skirt.

2. The process according to claim 1 wherein interstage cooling is provided between the first and second reaction zones.

3. The process according to claim 1 wherein the first reaction zone comprises a tubular fixed bed reactor.

4. The process according to claim 3 wherein the first and second zones are contiguous and each tube is packed with conventional catalyst in the first zone and with catalyst loaded into catalyst carriers in the second zone.

5. The process according to claim 1 wherein the first catalyst particle equivalent diameter is from about 1 mm to about 6 mm.

6. The process according to claim 1 wherein the second catalyst particle equivalent diameter is from about 0.1 mm to about 3 mm.

7. The process according to claim 1 wherein a portion of the product stream is recycled to at least one of the first and second reaction zones.

8. The process according to claim 1 wherein at least one reactant is one of a) added to the second reaction zone, and b) added to the intermediate stream before it is added to the second reaction zone.

9. The process according to claim 1 wherein the process is for the production of formaldehyde from methanol or methylal.

10. The process according to claim 9 wherein the first catalyst and the second catalyst is a silver catalyst.

11. The process according to claim 9 wherein the first catalyst and the second catalyst is an iron/molybdenum oxide based catalyst.

12. The process according to claim 9 wherein the first reaction zone is sized such that it terminates at a point when about 50% of the methanol or methylal will have been converted.

13. The process according to claim 9 wherein the reactor pressure is from about 1.1 bar(a) to about 10 bar(a).

14. The process according to claim 9 wherein the reactor temperature is from about 250 C. to about 450 C.

15. Apparatus for carrying out a chemical reaction comprising: means for supplying gaseous reactants to a first reaction zone comprising a first catalyst having a first catalyst particle equivalent diameter; means for removing an intermediate stream comprising unreacted reactants and a desired product and passing the intermediate stream to a second reaction zone comprising a tubular reactor comprising tubes, wherein said tubes comprise a plurality of catalyst carriers containing a second catalyst having a second catalyst particle equivalent diameter which is smaller than the first catalyst particle equivalent diameter of the first catalyst; and means for recovering a product stream, wherein each catalyst carrier comprises: an annular container for holding the second catalyst in use, said container having a perforated inner wall defining a tube, a perforated outer wall, a top surface closing the annular container and a bottom surface closing the annular container; a surface closing the bottom of said tube formed by the inner wall of the annular container; a skirt extending upwardly from the perforated outer wall of the annular container from a position at or near the bottom surface of said container to a position below the location of a seal; and a seal located at or near the top surface and extending from the container by a distance which extends beyond an outer surface of the skirt.

16. The apparatus according to claim 15 wherein interstage cooling is provided between the first and second reaction zones.

17. The apparatus according to claim 15 wherein the first reaction zone comprises a tubular fixed bed reactor.

18. The apparatus according to claim 15 further comprising means to recycle a portion of the product stream to at least one of the first and second reaction zones.

19. The apparatus according to claim 15 further comprising one of a) means for adding at least one reactant to the intermediate stream before it is added to the second reaction zone, and b) means for adding at least one reactant to the second reaction zone.

20. The apparatus according to claim 15 wherein the first reaction zone is sized such that it terminates at a point when about 50% of the gaseous reactants will have been converted.

Description

(1) The present invention will now be described, by way of example, with reference to the accompanying drawings in which:

(2) FIG. 1 is a schematic representation of the process of the present invention where the first and second reaction zones are located in separate vessels;

(3) FIG. 2 is a schematic representation of the process of the present invention where the first and second reaction zones are located in the same vessels;

(4) FIG. 3 is a perspective view from above of one example of a catalyst carrier which may be used in the second reaction zone;

(5) FIG. 4 is a perspective view of the catalyst carrier of FIG. 3 from below;

(6) FIG. 5 is a partial cross section viewed from the side;

(7) FIG. 6 is a simplified diagram of the catalyst carrier of FIG. 3;

(8) FIG. 7 is a schematic illustration of a carrier of the present invention from below when located within a tube;

(9) FIG. 8 is a schematic cross section of three catalyst carriers located within a tube; and

(10) FIG. 9 is an enlarged cross-section of Section A of FIG. 8.

(11) It will be understood by those skilled in the art that the drawings are diagrammatic and that further items of equipment such as reflux drums, pumps, vacuum pumps, compressors, gas recycle compressors, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, and the like may be required in a commercial plant. The provision of such ancillary items of equipment forms no part of the present invention and is in accordance with conventional chemical engineering practice.

(12) For convenience the present invention will be described by reference to the production of formaldehyde from methanol. However, it will be equally applicable to other reactions.

(13) One arrangement of the present invention is described in FIG. 1. A feed of methanol, nitrogen and oxygen is fed in line 101 to the first reaction zone 102. The first reaction zone is a fixed bed reactor 103. Any suitable configuration of fixed bed reactor may be used. Coolant is supplied to the shell of the reactor. The reactor tubes are packed with a first catalyst, generally an iron/molybdenum oxide catalyst, which will generally be of from about 1 mm to about 6 mm. As the reactants travel through the catalyst bed, reaction of some of the methanol occurs to the desired formaldehyde. The length of the reactor tubes is generally selected so that about 50% of the methanol is reacted in the first reactor zone. An intermediate stream comprising the unreacted methanol, nitrogen and oxygen and product formaldehyde is removed as intermediate stream 103 and passed to second reaction zone 104.

(14) The second reaction zone 104 is configured to allow a small catalyst particle equivalent diameter catalyst to be used. In a preferred arrangement, the reactor comprises a plurality of tubes packed with catalyst carriers containing a second catalyst of a second catalyst catalyst particle equivalent diameter which is smaller than that used in the first reaction zone 102. In one arrangement, the catalyst is an iron/molybdenum oxide catalyst of about 0.5 mm diameter. As the reactants travel through the catalyst beds in the carrier, reaction of remaining methanol occurs to the desired formaldehyde.

(15) The product stream is recovered in line 105.

(16) An alternative arrangement is illustrated in FIG. 2 where the first reaction zone 102 and the second reaction zone 104 are located in the same vessel.

(17) Any suitable catalyst carrier may be used in the second reaction zone 104. In one arrangement the catalyst carrier is of the kind illustrated in FIGS. 3 to 5. The carrier comprises an annular container 2 which has perforated walls 3, 4. The inner perforated wall 3 defines a tube 5. A top surface 6 is closes the annular container at the top. It is located at a point towards the top of the walls 3, 4 of the annular container 2 such that a lip 6 is formed. A bottom surface 7 closes the bottom of the annular container 2 and a surface 8 closes the bottom of tube 5. The surface 8 is located in a lower plane that that of the bottom surface 7. Spacer means in the form of a plurality of depressions 9 are located present on the bottom surface 7 of the annular container 2. Drain holes 10, 11 are located on the bottom surface 7 and the surface 8.

(18) A seal 12 extends from the upper surface 6 and an upstanding collar 13 is provided coaxial with the tube 5.

(19) A corrugated upstanding skirt 14 surrounds the container 2. The corrugations are flattened in the region L towards the base of the carrier 1.

(20) A catalyst carrier 1 of the present invention located in a reactor tube 15. The flow of gas is illustrated schematically in FIG. 6 by the arrows.

(21) When a plurality of catalyst carriers of the present invention are located within a reactor tube 15 they interlock as illustrated in FIGS. 8 and 9. The effect on the flow path is illustrated in the enlarged section shown in FIG. 9.

(22) The present invention will now be further described by reference to the accompanying examples.

EXAMPLE 1 AND COMPARATIVE EXAMPLE 1

(23) Two reactions for the production of formaldehyde from methanol in a reactor in accordance with the present invention (Example 1) and in a conventional reactor (Comparative Example 1) were carried out. In both reactions, the reactor was operated at 270 C. inlet temperature and at a pressure of 1.71 bar(a). The same inlet composition of 10 mol % methanol was used in each. The results are set out in Table 1.

(24) TABLE-US-00001 TABLE 1 CO Concentration Methanol (mol %) Yield Conversion Example 1 0.18 95.3% 99.1% Comparative 0.36 92.0% 98.1% Example 1

(25) The CO concentration is the CO content in the exhaust gas. The conversion is the % of methanol in the reactor feed that has been reacted to formaldehyde, carbon oxides or any other reaction product. Yield is the mols of formaldehyde formed divided by the mols of methanol in the reactor feed expressed as a %.