GB1570776A

GB1570776A - Desulphurizing fluid materials

Info

Publication number: GB1570776A
Application number: GB8315/78A
Authority: GB
Original assignee: Molycorp Inc
Current assignee: Molycorp Inc
Priority date: 1977-10-03
Filing date: 1978-03-02
Publication date: 1980-07-09
Also published as: DE2756201A1; FR2404676A2; DE2756201B2; IT7847733A0; CA1077682A; JPS5451976A; IT1155781B; DE2756201C3

Description

(54) DESULPHURIZING FLUID MATERIALS (71) We, MOLYCORP INC., a corporation organised and existing under the laws of the State of Delaware, United States of America, of 6 Corporate Park Drive White Plains, New York 10604, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to methods of desulphurizing fluid materials and particularly to a method of externally desulphurizing fluids such as molten iron and steel, stack gases, coal gases and coal liquification products using rare earth fluorocarbonates or rare earth oxyfluorides preferably in a substantially dry process.

This invention is an improvement in or modification of the invention described in our copending Application No. 46118/77 (Serial No. 1552507) which claims a method of desulphurizing iron or steel, comprising the steps of: (a) reacting the sulphur to be removed with a rare earth oxide in the presence of a separate deoxidizing agent or a deoxidizing atmosphere to form a rare earth sulphide and/or rare earth oxysulphide; and (b) removing the sulphide and/or oxysulphide.

The improvement or modification provided by this invention is based on the observation that instead of the rare earth oxide there may be used a rare earth fluorocarbonate or oxyfluoride, provided the desulphurization reaction is carried out at a low oxygen potential. Under those conditions the treatment is applicable to all sulphur-containing fluids.

This invention accordingly provides a method of desulphurizing a fluid material comprising the steps of: (a) reacting the sulphur in the fluid material with a rare earth fluorocarbonate and/or a rare earth oxyfluoride at low oxygen potential to form a rare earth sulphide and/or a rare earth oxysulphide; and (b) removing the sulphide and/or oxysulphide.

Although the method according to this invention is suited to the desulphurization of any fluid material, the following discussion is confined, for the purpose of illustration, to the two most pressing problems of desulphurization which industry presently faces, i.e. the desulphurization of molten iron and steel baths and the desulphurization of stack gases.

In the desulphurization of molten iron and steel by the process of this invention the rate earth oxyfluoride and/or the rare earth fluorocarbonate is preferably reacted with the sulphur in the molten metal in the presence of a deoxidizing agent. The rare earth oxyfluoride/ fluorocarbonate may be in the form of a Bastnasite concentrate.

Preferably, the hot metal is treated in a ladle or transfer car with the rare earth oxyfluoride or fluorocarbonate, by the simple addition and mixing of the rare earth oxyfluoride or fluorocarbonate, by an injection technique in which the rare earth oxyfluoride or fluorocarbonate is injected into the molten bath in a carrier gas such as an argon or nitrogen or by the use of an "active lining" i.e., a rare earth oxyfluoride or fluorocarbonate lining in the vessel. The techniques used are exactly the same as those taught in our copening Application No. 46118/77 (Serial No.

1552507). For example, when the deoxidizing agent is carbon the oxygen potential is preferably maintained at a low level by reducing the partial pressure of CO, advantageously to below 0.1 atmosphere.

This may be achieved by adding the rare earth fluorocarbonate and/or oxyfluoride to the fluid material subject to a vacuum sufficient to maintain the partial pressure of CO below 0.1 atmosphere or, in the injection technique described above, by using a stream of inert carrier gas sufficient to dilute CO formed in the reaction to below 0.1 atmosphere. Another method of controlling the oxygen potential is by controlling the CO/CO2 or H2/H20 ratios.

Similarly, the problem of desulphurizing gases is one of the oldest recognized problems in environmental chemistry. It dates back to the beginning of the utilization of fossil fuels for home heating and for industrial power. Sulphur dioxide is the primary sulphur compound which has been recognized as the problem in environmental control. Sulphur dioxide is a constituent in many waste gases such as flue gases, off gases from various chemical manufacturing processes, stack gases from coal and oil burning furnaces and boilers, smelter gases, ore roaster gases, coke gases and the like. Contamination of the atmosphere by sulphur dioxide, whether present in dilute concentrations of 0.05 of 0.3 volume percent as in power plant flue gases or in higher amounts of up to 10% as in ore roaster gases, has been a public health and environmental problem for many years due to its effect on the respiratory system of animals and humans, its destructive effect on plant life and its corrosive attack on metals, fabrics and building materials.

The reduction or elimination of the sulphur dioxide from gases emitted into the atmosphere is an essential key to the successful use of the world's abundant fuels (coal and high sulphur oils). Thus many methods have been proposed for the desulphurization of gases. Most methods which have been proposed are technically feasible but their expense is in most cases completely prohibitive. The most commonly proposed methods involve scrubbing the gases with water and precipitation of the sulphur dioxide with lime as calcium sulphate or sulphite, depending upon the process involved. Unfortunately, the expense of scrubbing the vast amounts of gas involved and disposing of the resulting precipitate is extremely expensive.

The present invention lies in the discovery that rare earth fluorocarbonates are rare earth oxyfluorides will, at low oxygen potential, remove sulphur from gases and will in turn give up the sulphides at high oxygen potential so that they may be regenerated with the production of a gas high in sulphur oxides from which elemental sulphur, sulphuric acid and like useful products can be obtained.

The ability of Bastnasite concentrates (complex rare earth fluorocarbonates and rare earth oxyfluorides) to transform to oxysulphide and sulphide under conditions of low oxygen potential has been established thermodynamically and experimentally by us.

In all cases the chemical reactions are analogous to those disclosed in our copending Application No. 46118/77 (Serial No. 1552507) in connection with the use of rare earth oxides.

In the case of liquid reactions, such as in the treatment of molten iron or steel, the product sulphide or oxysulphide will either be fixed in an 'active' lining or removed by flotation and absorbed into the slag cover and vessel lining depending upon the process used for introducing the rare earth oxyfluoride or fluorocarbonate.

The products of desulphurization of carbon saturated iron with rare earth fluorocarbonates and oxyfluorides is dependent on the partial pressure of CO(pCO) and the Henrian sulphur activity in the metal (hs).

The rare earth compounds used in the method of the invention may be recovered and, if desired, re-used. For example the rare earth sulphide and/or oxysulphide reaction products may be removed from the fluid material, regenerated with oxygen and returned to the fluid system for further desulphurization. Regeneration of the reaction products may be achieved by converting the rare earth sulphides or oxysulphides at high oxygen potential to rare earth oxides.

WHAT WE CLAIM IS: 1. A method of desulphurizing a fluid material comprising the steps of: (a) reacting the sulphur in the fluid material with a rare earth fluorocarbonate and/or a rare earth oxyfluoride at low oxygen potential to form a rare earth sulphide and/or a rare earth oxysulphide; and (b) removing the sulphide and/or oxysulphide; 2. A method according to claim 1, wherein the sulphur in the fluid materials is reacted with a Bastnasite concentrate.

3. A method according to claim 1, wherein the oxygen potential is maintained at a low level by reducing the partial pressure of CO.

4. A method according to claim 3, wherein the partial pressure of CO is maintained below 0.1 atmosphere.

5. A method according to claim 1, wherein the rare earth fluorocarbonate and/or oxyfluoride is added to the fluid material by injecting the rare earth fluorocarbonate and/or oxyfluoride into the fluid material in a stream of inert gas sufficient to dilute carbon monoxide formed in the reaction to below 0.1

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. to the fluid material subject to a vacuum sufficient to maintain the partial pressure of CO below 0.1 atmosphere or, in the injection technique described above, by using a stream of inert carrier gas sufficient to dilute CO formed in the reaction to below 0.1 atmosphere. Another method of controlling the oxygen potential is by controlling the CO/CO2 or H2/H20 ratios. Similarly, the problem of desulphurizing gases is one of the oldest recognized problems in environmental chemistry. It dates back to the beginning of the utilization of fossil fuels for home heating and for industrial power. Sulphur dioxide is the primary sulphur compound which has been recognized as the problem in environmental control. Sulphur dioxide is a constituent in many waste gases such as flue gases, off gases from various chemical manufacturing processes, stack gases from coal and oil burning furnaces and boilers, smelter gases, ore roaster gases, coke gases and the like. Contamination of the atmosphere by sulphur dioxide, whether present in dilute concentrations of 0.05 of 0.3 volume percent as in power plant flue gases or in higher amounts of up to 10% as in ore roaster gases, has been a public health and environmental problem for many years due to its effect on the respiratory system of animals and humans, its destructive effect on plant life and its corrosive attack on metals, fabrics and building materials. The reduction or elimination of the sulphur dioxide from gases emitted into the atmosphere is an essential key to the successful use of the world's abundant fuels (coal and high sulphur oils). Thus many methods have been proposed for the desulphurization of gases. Most methods which have been proposed are technically feasible but their expense is in most cases completely prohibitive. The most commonly proposed methods involve scrubbing the gases with water and precipitation of the sulphur dioxide with lime as calcium sulphate or sulphite, depending upon the process involved. Unfortunately, the expense of scrubbing the vast amounts of gas involved and disposing of the resulting precipitate is extremely expensive. The present invention lies in the discovery that rare earth fluorocarbonates are rare earth oxyfluorides will, at low oxygen potential, remove sulphur from gases and will in turn give up the sulphides at high oxygen potential so that they may be regenerated with the production of a gas high in sulphur oxides from which elemental sulphur, sulphuric acid and like useful products can be obtained. The ability of Bastnasite concentrates (complex rare earth fluorocarbonates and rare earth oxyfluorides) to transform to oxysulphide and sulphide under conditions of low oxygen potential has been established thermodynamically and experimentally by us. In all cases the chemical reactions are analogous to those disclosed in our copending Application No. 46118/77 (Serial No. 1552507) in connection with the use of rare earth oxides. In the case of liquid reactions, such as in the treatment of molten iron or steel, the product sulphide or oxysulphide will either be fixed in an 'active' lining or removed by flotation and absorbed into the slag cover and vessel lining depending upon the process used for introducing the rare earth oxyfluoride or fluorocarbonate. The products of desulphurization of carbon saturated iron with rare earth fluorocarbonates and oxyfluorides is dependent on the partial pressure of CO(pCO) and the Henrian sulphur activity in the metal (hs). The rare earth compounds used in the method of the invention may be recovered and, if desired, re-used. For example the rare earth sulphide and/or oxysulphide reaction products may be removed from the fluid material, regenerated with oxygen and returned to the fluid system for further desulphurization. Regeneration of the reaction products may be achieved by converting the rare earth sulphides or oxysulphides at high oxygen potential to rare earth oxides. WHAT WE CLAIM IS:

1. A method of desulphurizing a fluid material comprising the steps of: (a) reacting the sulphur in the fluid material with a rare earth fluorocarbonate and/or a rare earth oxyfluoride at low oxygen potential to form a rare earth sulphide and/or a rare earth oxysulphide; and (b) removing the sulphide and/or oxysulphide;

2. A method according to claim 1, wherein the sulphur in the fluid materials is reacted with a Bastnasite concentrate.

atmosphere.

6. A method according to claim 5, wherein the inert gas is nitrogen.

7. A method according to claim 1, wherein the rare earth fluorocarbonate and/or oxyfluoride is added to the fluid material subject to a vacuum sufficient to maintain the partial pressure of carbon monoxide below 0.1 atmosphere.

8. A method according to any preceding claim, wherein the rare earth sulphide and/or oxysulphide is removed from the fluid material, regenerated with oxygen and returned to the fluid system for further desulphurization.

9. A method according to claim 1 for desulphurizing gases, wherein the oxygen potential is maintained at a low level by controlling the CO/CO2 or H2/H20 ratios.

10. A method according to claim 1 for desulphurizing gases, wherein the removed rare earth oxysulphides and sulphides are regenerated at high oxygen potential to rare earth oxides.