Process for preparing chlorine from HCI

Abstract

Process for preparing chlorine by oxidation of hydrogen chloride by means of oxygen in the presence of a particulate catalyst in a fluidized-bed reactor, where the heat of reaction of the exothermic oxidation of hydrogen chloride is removed by means of water which circulates in the tubes of a shell-and-tube heat exchanger, where (i) the fluidized-bed reactor is heated up to an operating temperature in the range from 350 to 420 C. in a heating-up phase and (ii) hydrogen chloride is reacted with oxygen in an operating phase at the operating temperature, wherein (i-1) the fluidized-bed reactor is heated up to a temperature below the operating temperature in a first heating-up phase and (i-2) hydrogen chloride and oxygen are fed into the fluidized-bed reactor and reacted in a second heating-up phase in which the fluidized-bed reactor is heated up to the operating temperature by the heat of reaction of the exothermic oxidation of hydrogen chloride.

Claims

1. A process for preparing chlorine, the process comprising: introducing hot nitrogen into a fluidized-bed reactor to heat the fluidized-bed reactor to a first temperature in a first heating phase; feeding hydrogen chloride and oxygen into the fluidized-bed reactor and reacting the hydrogen chloride and oxygen, thereby heating the fluidized-bed reactor to an operating temperature of from 350 to 420 C. in a second heating phase; further reacting hydrogen chloride with oxygen in the presence of a particulate catalyst in the fluidized-bed reactor at the operating temperature in an operating phase; and circulating water in a tube of a shell-and-tube heat exchanger to remove heat from the fluidized-bed reactor, wherein: the first temperature is below the operating temperature; the operating temperature is increased during the operating phase to counter a decrease in HCl conversion due to progressive deactivation of the particulate catalyst; the first heating phase occurs before the hydrochloric acid and oxygen are introduced into the fluidized-bed reactor; and the first heating phase further comprises circulating a heat transfer medium in the tube of the shell-and-tube heat exchanger to heat the shell-and-tube heat exchanger, thereby heating the fluidized-bed reactor; wherein the HCl:O.sub.2 ratio is reduced during the operating phase to counter a decrease in HCl conversion due to progressive deactivation of the particulate catalyst.

2. The process of claim 1, wherein the first temperature is from 205 to 350 C.

3. The process of claim 1, wherein a temperature of the hot nitrogen is from 300 to 400 C. when the hot nitrogen is introduced into the fluidized-bed reactor.

4. The process of claim 1, wherein the heat transfer medium is steam having a pressure of from 16 to 165 bar and a temperature of from 205 to 350 C.

5. The process of claim 1, wherein the introducing of the hot nitrogen into the fluidized-bed reactor occurs after the circulating of the heat transfer medium.

6. The process of claim 1, wherein the fluidized-bed reactor comprises a heterogeneous particulate catalyst, comprising a metal component on an oxidic support.

7. The process of claim 6, wherein the particulate catalyst comprises, as the metal component, a ruthenium compound, a copper compound, or mixtures thereof.

8. The process of claim 6, wherein the particulate catalyst comprises, as the oxidic support, aluminum oxide, zirconium oxide, titanium oxide, or mixtures thereof.

9. The process of claim 1, wherein a pressure in the fluidized-bed reactor is from 1 to 11 bar absolute when oxidizing hydrogen chloride.

10. The process of claim 1, wherein a molar ratio of hydrogen chloride to O.sub.2 in the second heating phase is from 1:1 to 5:1.

11. The process of claim 1, wherein a feed gas mixture for feeding hydrogen chloride, oxygen, or both hydrogen chloride and oxygen into the fluidized-bed reactor in the second heating phase comprises nitrogen in a content of 20% or less by volume.

12. The process of claim 1, wherein a pressure in the fluidized-bed reactor is from 2 to 11 bar during the second heating phase.

13. The process of claim 1, wherein the fluidized-bed reactor comprises a particulate catalyst.

Description

EXAMPLES

Comparative Example

(1) The heating-up of a fluidized-bed reactor from an initial temperature of 0 C. to the operating temperature of 380 C. was simulated mathematically. Heating by means of nitrogen having a temperature of 400 C., which is introduced via the gas distributor plate, was assumed. The heat exchanger of the fluidized-bed reactor is not in operation and not filled with heat transfer medium or cooling medium.

(2) The calculation is additionally based on the following assumptions: mass of the catalyst particles: 70 t specific heat capacity of the catalyst particles: 0.9 kJ/kg/K particle density: 2400 kg/m.sup.3 mass of the reactor: 140 t specific heat capacity of the reactor: 0.44 kJ/kg/K mass flow of nitrogen: 15 t/h initial temperature: 0 C. target temperature: 380 C.

(3) Result: About 23.5 h are required for heating up the reactor including the catalyst.

Example

(4) The heating-up of the fluidized-bed reactor was simulated mathematically. The calculation was based on a three-stage heating-up procedure. Here, i) in a first stage, the reactor is heated up from 0 C. to about 250 C. by heating the heat exchanger with steam having a temperature of 265 C., ii) heating is subsequently continued to about 320 C. by means of nitrogen having a temperature of 400 C., with heat transfer medium no longer circulating in the tubes of the heat exchanger after a temperature of 265 C. has been reached, and iii) after a temperature of 320 C. has been reached, hydrogen chloride and oxygen are fed into the fluidized-bed reactor and reacted and the heat of reaction liberated is used for further heating-up to 380 C.

(5) The calculation was based on the following further assumptions: mass of the catalyst particles: 70 t specific heat capacity of the catalyst particles: 0.9 kJ/kg/K particle density: 2400 kg/m.sup.3 mass of the reactor: 140 t specific heat capacity of the reactor: 0.44 kJ/kg/K heat transfer area: 62 m.sup.2 heat transfer coefficient steamtube: 20 W/m.sup.2/K heat transfer coefficient tubefluidized bed: 750 W/m.sup.2/K resulting k value: 19.5 W/m.sup.2/K steam temperature: 265 C. amount of steam: 100 t/h specific heat capacity of the steam: 4.5 kJ/kg/K amount of hydrogen chloride: 8.8 t/h ratio of HCl:O.sub.2: 4 catalyst activity: 1 reactor pressure: 5 bar absolute

(6) Result: The heating-up i) to 250 C. by means of steam having a temperature of 265 C. takes about 4 hours, the further heating-up ii) to 320 C. by means of nitrogen having a temperature of 400 C. takes a further 5 hours and the further heating-up iii) to 380 C. utilizing the heat of reaction takes about 1 hour. The entire heating-up procedure takes a total of about 10.3 hours.