Heater, Use Thereof And Method For Preparing Isocyanate Using Heater

Abstract

A heater for heating and vaporizing droplets in gas stream, comprising a heater housing and a heater body located inside the heater housing, wherein the heater housing is provided with an airflow inlet and an airflow outlet, the airflow enters into the heater housing via the airflow inlet, flows through the heater body, and then is discharged via the airflow outlet; the heater body comprises a stereoscopic network structure formed by interweaving one or more electrical heating wires. The use of the heater and a method for preparing isocyanate using the heater. The heater has a simple structure, a low pressure loss, uniform heating and a high heat utilization ratio during preparing isocyanate.

Claims

1. A heater for heating and vaporizing droplets in a gas stream, comprising a heater housing and a heater body located inside the heater housing, the heater housing is provided with an airflow inlet and an airflow outlet, an airflow enters into the heater housing via the airflow inlet, flows through the heater body, and then is discharged via the airflow outlet; the heater body comprises a stereoscopic network structure formed by interweaving one or more electrical heating wires.

2. The heater according to claim 1, wherein the gas stream is an amine gas stream, and the droplets are amine droplets.

3. The heater according to claim 2, wherein the stereoscopic network structure formed by interweaving electrical heating wires is combined with the inner wall of the heater housing through sealing insulation packing.

4. The heater according to claim 3, wherein the height-to-diameter ratio of the heater body is 1:0.01-100, preferably 1:0.1-10, more preferably 1:1-10.

5. The heater according to claim 4, wherein the cross section of the electrical heating wire is in the shape of a convex polygon, a sector or an arch.

6. The heater according to claim 5, wherein the cross section of the electrical heating wire is in the shape of a convex polygon which has a smallest angle or two smallest angles that are equal, the angularity of the smallest angle is smaller than 90, preferably 1-15, more preferably 1-5.

7. The heater according to claim 6, wherein the electrical heating wires are configured such that the smallest angle of the convex polygon shape is opposite to the flowing direction of the amine gas stream inside the heater housing, and the bisector of the smallest angle is paralleled with the flowing direction of the amine gas stream inside the heater housing.

8. The heater according to claim 7, wherein the number of the sides of the convex polygon is 3-100.

9. The heater according to claim 5, wherein the cross section of the electrical heating wire is in the shape of an arch, the central angle corresponding to the arc of the arch is smaller than 180, preferably 1-30, more preferably 1-10.

10. The heater according to claim 5, wherein the cross section of the electrical heating wire is in the shape of a sector, the central angle of the sector is smaller than 90, preferably 1-15, more preferably 1-5.

11. The heater according to claim 10, wherein the electrical heating wires are configured such that the central angle of the sector is opposite to the flow direction of the amine gas stream inside the heater housing, and the bisector of the central angle is paralleled with the flowing direction of the amine gas stream inside the heater housing.

12. The heater according to claim 3, wherein the hydraulic diameter of the mesh of the stereoscopic network structure is smaller than 1 nm, preferably 0.01-0.5 mm, more preferably 0.01-0.25 mm.

13. The heater according to claim 12, wherein the porosity of the stereoscopic network structure is 75-99.5%, preferably 90-99.5%.

14. The heater according to claim 13, wherein the heat exchange area per unit volume of the stereoscopic network structure is 100-1000 m.sup.2/m.sup.3.

15. The heater according to claim 12, wherein the bottom of the heater housing is provided with a drain port.

16. The heater according to claim 3, wherein the electrical heating wires are made of inert inorganic nonmetallic materials that are conductive, and the inert inorganic nonmetallic materials are not doped with metals or doped with 1-15 wt % metals.

17. The heater according to claim 16, wherein the inert inorganic nonmetallic materials are selected from one or two or more of molybdenum disilicide, lanthanum chromate, ceramic, silicon carbide and tin oxides; the metals are selected from one or two or more of Ti, Ni, Fe, W, Mo, V, Al, Cu and Zn.

18. (canceled)

19. A method for preparing isocyanate, comprising: (1) vaporizing amine into amine gas stream that contains amine droplets; (2) eliminating the amine droplets contained in the amine gas stream to obtain amine gas stream that almost does not contain amine droplets; (3) allowing the gas phase phosgenation reaction to be carried out between the amine gas stream that almost does not contain amine droplets and phosgene to obtain isocyanate; wherein in step (2), the heater according to claims 1-17 is used to eliminate the amine droplets in the amine gas stream.

20. The method according to claim 19, wherein the pressure loss in the heater in step (2) is lower than 5 KPa, preferably lower than 2 KPa, more preferably lower than 1 KPa.

21. The method according to claim 20, wherein the temperature difference between any two or more points on the surface of the electrical heating wires of the heater body in step (2) is lower than 1 C., preferably lower than 0.2 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0078] FIG. 1 is a schematic view of a preferred embodiment of the heater of the present invention, wherein,

[0079] 1inlet of amine gas stream, 2outlet of amine gas stream, 3drain port, 4heater housing, 5sealing fastening nut, 6heater body, 7electrode leads, 8sealing insulation packing, F1amine gas stream with droplets that are not vaporized, F2amine gas stream without droplets, F3discharged liquid material.

DETAILED DESCRIPTION

[0080] The heater and the method for preparing isocyanate using the heater of the present invention are further illustrated below; however, the present invention is not limited to the following examples.

Example 1

[0081] A preferred embodiment of the heater of the present invention is shown in FIG. 1. The heater is a vertical tank that comprises a cylinder heater housing 4 and a cylinder heater body 6 that is provided inside the heater housing 4. The diameter of the heater body 6 is slightly smaller than that of the heater housing, and sealing insulation packing 8 is provided between the heater body 6 and the heater housing 4. An amine gas stream inlet 1 is provided on the side wall of the heater housing 4, an amine gas stream outlet 2 is provided on the top of the heater housing 4, and a drain port 3 is provided at the bottom of the heater housing 4. An external power source (not shown) applies a voltage to the heater body 6 through electrode leads 7, and controls the power and heating temperature of the heater body 6 through adjusting the voltage of the power source. A sealing fastening nut 5 is provided between the electrode leads 7 and the heater housing 4 to insulate the electrode leads 7 and the heater housing 4.

[0082] The heater body 6 is composed of a stereoscopic network structure that is formed by interweaving electrical heating wears and the thickness of the network structure is 15 cm, the diameter is 40 cm.

[0083] The heater body 6 is a stereoscopic network structure that is formed by irregularly interweaving electrical heating wires, and the meshes are of irregular shapes. The electrical heating wires are made of inert silicon carbide conductive materials that are doped with 2 wt % Ni. The cross sections of the electrical heating wires are sector shapes with the central angularity of 10.

[0084] When the heater is used to eliminate the amine droplets that are not vaporized in the amine gas stream, the amine gas stream F1 that contained the droplets that are not vaporized enters into the heater housing 4 via the amine gas stream inlet 1, When the amine gas stream passes through the heater body 6, the amine droplets are cut into smaller droplets by the electrical heating wires, which are heated and vaporized by the electrical heating wires, and then discharged from the heater via the amine gas stream outlet 2. Thus, amine gas stream that basically does not contain amine droplets F2 is obtained, which enters into the subsequent phosgenation reactor to react with phosgene to obtain isocyanate.

[0085] If the content of amine droplets in the amine gas stream F1 that enters into the heater is too high, for example, higher than 20 wt %, some of the amine droplets that are not vaporized would be separated from the amine gas stream during the process of heating and vaporization and are combined into a flow which drop and are discharged from the drain port 3. The discharged liquid material F3 can return to the amine vaporizer to revaporize to increase the vaporization rate of amine.

[0086] The method for preparing isocyanate using the heater of the present invention will be further illustrated by the following examples.

[0087] In the examples, the content of heavy component in the phosgenation reaction liquid is determined by Shimadzu GC2010 gas chromatograph with DB-5 type chromatographic column (FID detector, the temperature of the injection port: 290 C., the column temperature is raised according to the following steps: the temperature is maintained at 160 C. for 1 minute, then it is increased to 300 C. at the rate of 10 C./min and it is maintained at 300 C. for 11 minutes; the temperature of the detector is 320 C.), peak area normalization method is used to obtain the results.

Example 2

[0088] The structure of the heater was basically the same as that of example 1, wherein electrical heating wires made of inert silicon carbide conductive materials doped with 2 wt % Ni were used to form the heater body. The heater body was a cylinder stereoscopic network structure with the thickness of 15 cm and a diameter of 40 cm, the hydraulic diameter of the mesh of the stereoscopic network structure was 0.25 mm, the porosity was 97.5%, and the heat exchange area per unit volume was 550 m.sup.2/m.sup.3. The cross section of the electrical heating wire that composed the heater body was in the forms of a triangle, and the triangle had a smallest angle with the angularity of 2. The electrical resistivity of the heater body measured about 500 .Math.m. The heater body was encapsulated in a 316 L stainless steel heater housing, polyethylene sheath sealing pads were used for the sealing insulation packing.

[0089] HDA was preheated and vaporized in the amine vaporizer to obtain amine gas stream that contained about 10 wt % amine droplets that were not vaporized. The amine gas stream entered into the heater housing via the amine gas stream inlet of the heater of the present example. The external voltage of the heater body was 12V, the temperature of the heater body was 300 C. The amine gas stream that did not contain droplets and was discharged from the amine gas stream outlet of the heater, and the gas phase phosgene that was preheated to 300 C. were continuously added to the gas phase phosgenation reactor and were reacted under the temperature of 300 C., the absolute pressure of 0.13 MPa, wherein the feed rate of HDA was 100 kg/h, the feed rate of phosgene was 450 kg/h. The obtained reaction products were cooled quickly to 100 C. to 140 C. by a gas jet and absorption device with o-dichlorobenzene used as the solvent, and the reaction liquid that contained the product 1,6-hexamethylene diisocyanate (HDI) was obtained. The results are shown in table 1.

Comparative Example 2

[0090] HDA was preheated and vaporized in the amine vaporizer to obtain amine gas stream that contained about 10 wt % amine droplets that were not vaporized, the amine gas stream entered into the phosgenation reactor via an inlet pipe (the inlet pipe is a straight pipe, the same below) and was vaporized in the inlet pipe. The temperature of the inlet pipe was 305 C., the residence time of the amine gas stream in the inlet pipe was 0.3 s. The amine gas stream and the gas phase phosgene that was preheated to 300 C. were continuously added to the gas phase phosgenation reactor and reacted under the temperature of 300 C., the absolute pressure of 0.13 MPa, wherein the feed rate of HDA was 100 kg/h, the feed rate of phosgene was 450 kg/h. The obtained reaction products were cooled quickly to 100 C. to 140 C. by a gas jet and absorption device with o-dichlorobenzene used as the solvent, and the reaction liquid that contained the product HDI was obtained. The results are shown in table 1.

Example 3

[0091] The structure of the heater was basically the same as that of example 1, wherein electrical heating wires made of inert silicon carbide conductive materials doped with 2 wt % Ni were used to form the heater body. The heater body was a cylinder stereoscopic network structure with the dimensions as follows: a thickness of 15 cm and a diameter of 40 cm. The hydraulic diameter of the mesh of the stereoscopic network structure was 0.15 mm, the porosity was 98.5%, and the heat exchange area per unit volume was 650 m.sup.2/m.sup.3. The cross section of the electrical heating wire that composed the heater body was in the form of a convex pentagon, and the convex pentagon had a smallest angle that was 4. The electrical resistivity of the heater body measured about 500 .Math.m. The heater body was encapsulated in a 316 L stainless steel heater housing, and polyethylene sheath sealing pads were used for the sealing insulation packing.

[0092] IPDA was preheated and vaporized in the amine vaporizer to obtain amine gas stream that contained 15 wt % amine droplets that were not vaporized. The amine gas stream entered into the heater housing via the amine gas stream inlet of the heater of the present example. The external voltage of the heater body was 18V, and the temperature of the heater body was 330 C. The amine gas stream that did not contain droplets and was discharged from the amine gas stream outlet of the heater, and the gas phase phosgene that was preheated to 330 C. were continuously added to the gas phase phosgenation reactor and reacted under the temperature of 330 C., the absolute pressure of 0.13 MPa, wherein the feed rate of IPDA was 60 kg/h, the feed rate of phosgene was 150 kg/h. The obtained reaction products were cooled quickly to 100 C. to 140 C. by a gas jet and absorption device with o-dichlorobenzene used as the solvent, and the reaction liquid that contained the product isophorone diisocyanate (IPDI) was obtained. The results are shown in table 1.

Comparative Example 3

[0093] IPDA was preheated and vaporized in the amine vaporizer to obtain amine gas stream that contained 15 wt % amine droplets that were not vaporized. The amine gas stream was first passed through the gas liquid separator to decrease the amine droplets that were not vaporized to 5 wt %, then the amine gas stream entered into the phosgenation reactor via the inlet pipe in which remained amine droplets were vaporized. The temperature of the inlet pipe was 330 C., the residence time of the amine gas stream in the inlet pipe was 0.6 s. The amine gas stream and the gas phase phosgene that was preheated to 330 C. were continuously added to the gas phase phosgenation reactor and reacted under the temperature of 330 C., the absolute pressure of 0.13 MPa, wherein the feed rate of IPDA was 60 kg/h, the feed rate of phosgene was 150 kg/h. The obtained reaction products were cooled quickly to 100 C. to 140 C. by a gas jet and absorption device with o-dichlorobenzene used as the solvent, and the reaction liquid that contained the product IPDI was obtained. The results are shown in table 1.

Example 4

[0094] The structure of the heater was basically the same as that of example 1, wherein electrical heating wires made of inert silicon carbide conductive materials doped with 2 wt % Ni were used in the heater body. The heater body was a cylinder stereoscopic network structure with the dimensions as follows: a thickness of 15 cm and a diameter of 40 cm. The hydraulic diameter of the mesh of the stereoscopic network structure was 0.15 mm, the porosity was 98.5%, and the heat exchange area per unit volume was 650 m.sup.2/m.sup.3. The cross section of the electrical heating wires that composed the heater body was in the form of a convex quadrilateral, and the convex quadrilateral had a smallest angle with the angularity of 5. The electrical resistivity of the heater body measured about 500 .Math.m. The heater body was encapsulated in a 316 L stainless steel heater housing, and polyethylene sheath sealing pads were used for the sealing insulation packing.

[0095] TDA was preheated and vaporized in the amine vaporizer to obtain amine gas stream that contained 10 wt % amine droplets that were not vaporized. The amine gas stream entered into the heater housing via the amine gas stream inlet of the heater of the present example. The external voltage of the heater body was 24V, and the temperature of the heater body was 330 C. The amine gas stream that did not contain droplets and was discharged from the amine gas stream outlet of the heater, and the gas phase phosgene that was preheated to 320 C. were continuously added to the gas phase phosgenation reactor and reacted under the temperature of 350 C., the absolute pressure of 0.15 MPa, wherein the feed rate of TDA was 50 kg/h, the feed rate of phosgene was 200 kg/h. The obtained reaction products were cooled quickly to 100 C. to 140 C. by a gas jet and absorption device with toluene used as the solvent, the reaction liquid that contained the product toluene diisocynate (TDI) was obtained. The results are shown in table 1.

Comparative Example 4

[0096] TDA was preheated and vaporized in the amine vaporizer to obtain amine gas stream that contained 10 wt % amine droplets that were not vaporized. The amine gas stream entered into the phosgenation reactor via the inlet pipe in which the amine droplets were vaporized. The temperature of the inlet pipe was 310 C., the residence time of the amine gas stream in the inlet pipe was 0.5 s. The amine gas stream and the gas phase phosgene that was preheated to 320 C. were continuously added to the gas phase phosgenation reactor and reacted under the temperature of 350 C., the absolute pressure of 0.15 MPa, wherein the feed rate of TDA was 50 kg/h, the feed rate of phosgene was 200 kg/h. The obtained reaction products were cooled quickly to 100 C. to 140 C. by a gas jet and absorption device with o-dichlorobenzene used as the solvent, and the reaction liquid that contained the product TDI was obtained. The results are shown in table 1.

Example 5

[0097] The structure of the heater was basically the same as that of example 1, wherein electrical heating wires made of inert silicon carbide conductive materials doped with 2 wt % Ni were used in the heater body. The heater body was a cylinder stereoscopic network structure with the dimensions as follows: a thickness of 15 cm and a diameter of 40 cm. The hydraulic diameter of the mesh of the stereoscopic network structure was 0.35 mm, the porosity was 98.5%, and the heat exchange area per unit volume was 650 m.sup.2/m.sup.3. The cross section of the electrical heating wires that composed the heater body was in the form of a sector, and the central angle of the sector was 3. The electrical resistivity of the heater body measured about 500 .Math.m. The heater body was encapsulated in a 316 L stainless steel heater housing, and polyethylene sheath sealing pads were used for the sealing insulation packing.

[0098] TDA was preheated and vaporized in the amine vaporizer to obtain amine gas stream that contained 10 wt % amine droplets that were not vaporized. The amine gas stream entered into the heater housing via the amine gas stream inlet of the heater of the present example. The external voltage of the heater body was 24V, and the temperature of the heater body was 330 C. The amine gas stream that did not contain droplets and was discharged from the amine gas stream outlet of the heater, and the gas phase phosgene that was preheated to 320 C. were continuously added to the gas phase phosgenation reactor and reacted under the temperature of 350 C., the absolute pressure of 0.15 MPa, wherein the feed rate of TDA was 50 kg/h, the feed rate of phosgene was 200 kg/h. The obtained reaction products were cooled quickly to 100 C. to 140 C. by a gas jet and absorption device with toluene used as the solvent, and the reaction liquid that contained the product toluene diisocynate (TDI) was obtained. The results are shown in table 1.

Example 6

[0099] The structure of the heater was basically the same as that of example 1, wherein electrical heating wires made of inert silicon carbide conductive materials doped with 1 wt % Ni were used in the heater body. The heater body was a cylinder stereoscopic network structure with the dimensions as follows: a thickness of 15 cm and a diameter of 40 cm. The hydraulic diameter of the mesh of the stereoscopic network structure was 0.15 mm, the porosity was 98.5%, and the heat exchange area per unit volume was 850 m.sup.2/m.sup.3. The cross section of the electrical heating wires that composed the heater body was in the form of an arch, and the radian of the arch was 5. The electrical resistivity of the heater body measured about 600 .Math.m. The heater body was encapsulated in a 316 L stainless steel heater housing, polyethylene sheath sealing pads were used for the sealing insulation packing.

[0100] IPDA was preheated and vaporized in the amine vaporizer to obtain amine gas stream that contained 15 wt % amine droplets that were not vaporized. The amine gas stream entered into the heater housing via the amine gas stream inlet of the heater of the present example. The external voltage of the heater body was 16V, and the temperature of the heater body was 330 C. The amine gas stream that did not contain droplets and was discharged from the amine gas stream outlet of the heater, and the gas phase phosgene that was preheated to 330 C. were continuously added to the gas phase phosgenation reactor and reacted under the temperature of 330 C., the absolute pressure of 0.13 MPa, wherein the feed rate of IPDA was 60 kg/h, the feed rate of phosgene was 150 kg/h. The obtained reaction products were cooled quickly to 100 C. to 140 C. by a gas jet and absorption device with o-dichlorobenzene used as the solvent, and the reaction liquid that contained the product IPDI was obtained. The results are shown in table 1.

TABLE-US-00001 TABLE 1 The comparison of the technical effects of examples 2-6 and comparative examples 2-4 The content of the heavy Pressure loss Running component in the reaction (KPa) period (h) liquid (A/A %) Example 2 0.5 2280 0.6 Comparative 0.4 1296 1.9 example 2 Example 3 0.6 2250 0.7 Comparative 8.9 1574 2.5 example 3 Example 4 0.6 2550 0.4 Comparative 0.5 1274 2.1 example 4 Example 5 0.7 2790 0.5 Example 6 0.8 2990 0.6 * The pressure loss is the pressure drop inside the heater.

[0101] From the results of table 1, it can be seen that comparing with the comparative examples, after the heaters of the examples of the present invention were used, the running periods of the device, from the vaporization of the amine to the phosgenation reaction, were prolonged, and the contents of the heavy component impurities in the reaction liquid were significantly decreased.