WO2016037258A1

WO2016037258A1 - Integrated process for producing calcium sulfate and methanol

Info

Publication number: WO2016037258A1
Application number: PCT/CA2014/050860
Authority: WO
Inventors: Frank Steven ZEMEN
Original assignee: Minister of National Defence of Canada
Current assignee: Minister of National Defence of Canada
Priority date: 2014-09-11
Filing date: 2014-09-11
Publication date: 2016-03-17
Anticipated expiration: 2017-03-11

Abstract

A process for producing calcium sulfate involves reacting sulfur or hydrogen sulfide with calcium carbonate under anhydrous conditions in the presence of a source of oxygen at a temperature of 200°C or greater. The process for producing calcium sulfate may be integrated into a process that also produces methanol involving desulfurizing a sulfur-contaminated hydrocarbon mixture to obtain hydrogen sulfide and a desulfurized hydrocarbon mixture, reacting the hydrogen sulfide or elemental sulfur obtained from the hydrogen sulfide with calcium carbonate under anhydrous conditions in the presence of an oxygen source at a temperature of 200°C or greater to obtain calcium sulfate and carbon dioxide, and converting the carbon dioxide to methanol. The integrated process permits desulfurization and enhancement of a fuel (e.g. jet fuel) using fewer external inputs by recycling reaction products produced at each step of the process.

Description

INTEGRATED PROCESS FOR PRODUCING CALCIUM SULFATE AND METHANOL

Field

This application relates to chemical processes, in particular to an integrated process for producing calcium sulfate and methanol. Background

The emission to the atmosphere of sulfur found naturally in fossil fuel deposits (coal, oil, natural gas) leads to "acid rain" and the subsequent destruction of natural habitat. As a result, environmental regulations have reduced the allowable emissions of sulfur compounds and the sulfur content of transportation fuels. However, the standards for sulfur content are not uniform with some fuels, particularly jet fuel and bunker oil (marine transportation). Presently, jet fuel and bunker oil are allowed to have higher sulfur emissions because dispersion in the atmosphere reduces the risk of concentrated environmental damage. It would still be desirable to have a single low- or no-sulfur fuel for all transportation requirements. Presently, sulfur is removed from liquid fuels by reacting the sulfur-containing fuel with gaseous hydrogen to form gaseous hydrogen sulfide. The hydrogen sulfide is then treated, via the Claus process, to produce elemental sulfur. The sulfur is then formed into briquettes and stockpiled outdoors. Gaseous sulfur, usually in the form of hydrogen sulfide, is also injected underground in a process known as "sour gas injection". The stockpiling of elemental sulfur creates large piles of hazardous waste. Elemental sulfur is highly flammable, a dust hazard and forms sulfuric acid upon contact with water. As such, these stockpiles must be constantly monitored and maintained to prevent any of these occurrences, essentially in perpetuity. In current practice, there is essentially no solution other than storage for elemental sulfur or hydrogen sulfide, although there have been suggestions of storing sulfur in the form of sulfates (Rappold 2010).

There remains a need for efficient processes where a fuel may be desulfurized and the sulfur product produced thereby utilized to produce less troublesome products.

Summary

There is provided a process comprising desulfurizing a sulfur-contaminated hydrocarbon mixture to obtain hydrogen sulfide and a desulfurized hydrocarbon mixture; reacting the hydrogen sulfide or elemental sulfur obtained from the hydrogen sulfide with calcium carbonate under anhydrous conditions in the presence of an oxygen source at a temperature of 200°C or greater to obtain calcium sulfate and carbon dioxide; and, converting the carbon dioxide to methanol.

There is further provided a process for producing calcium sulfate comprising reacting sulfur or hydrogen sulfide with calcium carbonate under anhydrous conditions in the presence of a source of oxygen at a temperature of 200°C or greater.

The process to produce calcium sulfate permits the formation of gypsum by hydration of the calcium sulfate with water, but without using sulfuric acid to form the calcium sulfate, sulfuric acid being highly corrosive, toxic and environmentally detrimental. The integrated process permits desulfurization and enhancement of a hydrocarbon mixture (e.g. a fuel) using fewer external inputs by recycling reaction products produced at each step of the process. Overall, the processes may permit more environmentally friendly, lower cost production of high quality, sulfur-reduced hydrocarbon mixtures. Careful mass and energy balance in the integrated process reduces the number of external inputs required to operate the integrated process and results in commercially relevant outputs thereby reducing or eliminating waste products.

Further features will be described or will become apparent in the course of the following detailed description. It should be understood that each feature described herein may be utilized in any combination with any one or more of the other described features, and that each feature does not necessarily rely on the presence of another feature except where evident to one of skill in the art.

Brief Description of the Drawings

For clearer understanding, preferred embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is flow chart illustrating an integrated process for producing calcium sulfate and methanol. * links oxygen gas output from water electrolysis to oxygen gas input to the Claus process. ** links heat output from calcium sulfate synthesis to heat input to steam gasification.

Fig. 2 depicts a table illustrating mass and energy balance to produce 1 kg of gypsum in the integrated process of Fig. 1. Detailed Description

Referring to Fig. 1 , one embodiment of an integrated process for producing calcium sulfate and methanol involves several sub-processes including desulfurization of a hydrocarbon mixture 1 , synthesis of solid calcium sulfate (CaS0₄) 3 using sulfur product obtained from the desulfurization 1 , and synthesis of methanol (CH₃OH) 5 using the carbon dioxide gas obtained from the synthesis of calcium sulfate 3. The process may further comprise other sub-processes to provide inputs to and use outputs from the desulfurization of the hydrocarbon mixture and the syntheses of the calcium sulfate and the methanol. Desulfurization of Hydrocarbon Mixture (1)

Any sulfur-contaminated mixture of hydrocarbons may be desulfurized in the process. The hydrocarbon mixture may be, for example, natural gas, a petroleum product or the like. Preferably, the hydrocarbon mixture comprises a fuel, for example gasoline, jet fuel, bunker oil, kerosene, diesel fuel and fuel oils. Desulfurization preferably comprises hydrodesulfurization, which results in the production of hydrogen sulfide (H₂S) gas. Hydrodesulfurization involves hydrogenation of thiols in the hydrocarbon mixture to form hydrocarbons and hydrogen sulfide in accordance with Equation 1.

RSH + H₂→ RH + H₂S Eq. 1 Hydrogen gas needed for hydrodesulfurization may be obtained from one or more sub- processes, for example water electrolysis 6 or steam gasification of organic residue 7 as described below. Hydrodesulfurization is preferably catalyzed using metal-containing catalysts (e.g. molybdenum disulfide (MoS₂)) together with other metals. Heat used to conduct the hydrodesulfurization may be obtained from other sub-processes, for example calcium sulfate synthesis 3, or may be supplied as an external input. Hydrodesulfurization is a generally known process that is used in many industries including the petroleum industry.

After desulfurization, the hydrocarbon mixture, especially fuels, may be blended with liquid methanol produced in the methanol synthesis sub-process 5. Methanol in a fuel offers an increase in thermal efficiency, increased power output and high heat of vaporization. Claus Process (2)

Hydrogen sulfide gas produced in the desulfurization 1 may be used directly in the calcium sulfate synthesis 3, or may be used to produce solid elemental sulfur. Solid elemental sulfur may be produced by any number of sub-processes; however, the Claus process 2 is a well-known and industrially used process for producing elemental sulfur. The Claus process is a multistep process involving thermal combustion of hydrogen sulfide with oxygen gas (0₂) to form solid elemental sulfur (S), water vapor (H₂0) and sulfur dioxide gas (S0₂), followed by a catalytic step whereby remaining hydrogen sulfide reacts with the sulfur dioxide to form more elemental sulfur and water. Equations 2 and 3 illustrate the process.

10 H₂S + 5 O₂→2 H₂S + SO₂ + 7 S + 8 H₂O Eq. 2

2 H₂S + S0₂→ 3 S + 2 H₂0 Eq. 3

Water produced in the Claus process may be recycled into water source 8, which is used to supply water to various sub-processes. The elemental sulfur (S) may be stored and/or used to produce calcium sulfate in the calcium sulfate synthesis 3. Oxygen gas for the Claus process may be supplied as an external input, or may be supplied from a sub- process. Preferably, the oxygen gas is supplied from a sub-process of the integrated process, for example from water electrolysis 6.

Calcium Sulfate Synthesis (3) Combustion of hydrogen sulfide gas or solid elemental sulfur in the presence of an oxygen source and calcium carbonate (CaC0₃) under anhydrous conditions at a temperature of 200°C or greater produces solid calcium sulfate (CaS0₄) and carbon dioxide gas (C0₂). The reactions are illustrated in Equation 4 and Equation 5.

H₂S + CaC0₃ + 2 0₂→ CaS0₄ + H₂0 + C0₂ + 841.6 kJ/mol S Eq. 4 S + CaC0₃ + 3/2 0₂→ CaS0₄ + C0₂ + 630 kJ/mol S Eq. 5

Preferably, hydrogen sulfide is used directly from the desulfurization 1 to produce calcium sulfate, rather than converting the hydrogen sulfide to elemental sulfur. However, the process may be configured to accept elemental sulfur as an external input in replacement or partial replacement of the hydrogen sulfide. Combustion of hydrogen sulfide with oxygen is done at a temperature of about 200°C or greater, preferably about 400°C or greater, more preferably about 500°C or greater. The temperature is even more preferably in a range of from about 500°C to about 600°C. The temperature is higher than the boiling point of water, which facilitates performing calcium sulfate synthesis under anhydrous conditions. At that temperature, water produced during the reaction is driven off as a gas. Prior art syntheses of gypsum (hydrated calcium sulfate) from hydrogen sulfide involve acid catalyzed oxidation of hydrogen sulfide in aqueous slurries using sulfuric acid to generate sulfur oxides. Such "wet" methods use highly corrosive and toxic sulfuric acid, which requires special handling and disposal. The "dry" method of the present invention provides a cleaner, more efficient reaction without the problems associated with sulfuric acid. Any water vapor produced in the combustion of hydrogen sulfide (see Equation 4) may be recycled in gaseous form back to water source 8 for use in other sub-processes.

The oxygen source may be in the solid state, liquid state or gas state or a combination thereof. Solid state oxygen sources include, for example, metal oxides. Liquid state oxygen sources include, for example, pure liquefied oxygen or liquid air. Gas state oxygen sources include, for example, air or pure oxygen gas. Preferably the oxygen source comprises oxygen gas. In one embodiment, oxygen gas may be supplied by a sub-process that produces oxygen gas, for example water electrolysis 6 as described below.

Any suitable source of calcium carbonate may be utilized, for example limestone. Limestone is a sedimentary rock largely comprising calcite and aragonite, which are different crystal forms of calcium carbonate (CaC0₃). Pure calcite or aragonite may also be utilized as the source of calcium carbonate. Carbon dioxide produced in the synthesis of calcium sulfate may be recycled by using the carbon dioxide in methanol synthesis 5. Anhydrous solid calcium sulfate produced may be vended as a commercial product, or may be converted to gypsum as described below. Heat generated in the production of calcium sulfate may be used in other sub-processes (e.g. the desulfurization 1 or the steam gasification 7) or for some other purpose entirely (e.g. to heat buildings).

Gypsum Synthesis (4)

Anhydrous solid calcium sulfate produced in the synthesis of calcium sulfate 3 may be conveniently converted to gypsum (CaS0₄-2H₂0) by hydrating the calcium sulfate in water. The anhydrous calcium sulfate may be cooled and water may be supplied from water source 8. Gypsum synthesis 4 provides a sub-process into which water produced in other sub-processes (e.g. Claus process 2, calcium sulfate synthesis 4, methanol synthesis 5) may be recycled. Gypsum is a vendable product used in the construction industry for cement, wallboard and the like; therefore, the gypsum is a value-added output of the process.

Methanol Synthesis (5)

Carbon dioxide gas produced in the synthesis of calcium sulfate 3 is used in conjunction with hydrogen gas to produce methanol (CH₃OH) in accordance with Equation 6.

3 H₂ + C0₂→ CH₃OH + H₂0 Eq. 6

This production of methanol by the reaction of Equation 6 is generally known in the art. The reaction may be catalyzed with a catalyst, for example a metal catalyst (e.g. copper oxides). Hydrogen gas may be supplied as an external input or from another sub-process.

Preferably, the hydrogen has is supplied from another sub-process, for example water electrolysis 6 and/or steam gasification 7. If steam gasification is used as a sub-process, carbon dioxide produced in steam gasification may also be used in the methanol synthesis 5. Water produced in methanol synthesis may be recycled back to water source 8 for use in other sub-processes. The methanol produced is a vendable product in and of itself, or the methanol may be blended into the desulfurized hydrocarbon mixture (e.g. fuel).

Water Electrolysis (6)

Water electrolysis may form a sub-process to produce oxygen gas and hydrogen gas, which are used in other sub-processes. The oxygen gas may be used in Claus process 2 and/or calcium sulfate synthesis 4. The hydrogen gas may be used in desulfurization of hydrocarbon mixture 1 and/or methanol synthesis 3. In water electrolysis, liquid water is subjected to an electric current at a sufficient voltage to break hydrogen-oxygen bonds. Oxygen and hydrogen gas are thereby formed. Water electrolysis is a well-known reaction and is illustrated in Equation 7.

2 H₂0→ 2 H₂ + 0₂ Eq. 7 Water electrolysis also provides a sub-process into which water produced by other sub-processes (e.g. Claus process 2, calcium sulfate synthesis 4, methanol synthesis 5) may be recycled.

Steam Gasification of Organics (7) If desired, hydrogen gas and carbon dioxide gas (or carbon monoxide gas) may be produced for use in other sub-processes (e.g. desulfurization of hydrocarbon mixture 1 and/or methanol synthesis 3) by steam gasification of organic residues. The organic residue may be any biomass in which the carbonaceous material is convertible to syn gases (hydrogen and carbon monoxide), for example waste from agricultural operations or waste from pollution control plants.

Steam gasification is well-known and generally involves drying of a biomass followed by pyrolysis of the dried biomass to form a char and gasification of the char with oxygen/air and steam (H₂0) to form hydrogen gas and carbon monoxide (CO) gas. The carbon monoxide may be further converted to carbon dioxide and hydrogen through the action of steam in a water-gas shift reaction. Equation 8 and Equation 9 illustrate steam gasification.

C + H₂0→ H₂ + CO Eq. 8

CO + H₂0→ H₂ + C0₂ Eq. 9

Steam for steam gasification may be supplied by heating water from water source 8 and the heat to make the steam from liquid water may be supplied from an external input or from heat generated by another sub-process, for example the synthesis of calcium sulfate 3. Oxygen may be supplied from ambient air or from a source of oxygen gas (e.g. water electrolysis 6).

Water Source (8) Water is produced in some of the sub-processes of the integrated process and is used by others of the sub-processes. Water may be recycled throughout the integrated process. Where more water is produced than is needed for the process, excess water may be disposed of or may be used for an external purpose. Where the process does not produce enough water for the sub-processes that require water, or design factors prevent using the water produced elsewhere in the process, external inputs of water may be utilized. The present integrated process efficiently uses the outputs of some sub- processes as the inputs for other sub-processes. In a process where the mass and energy balances are carefully managed, few external inputs are required and many of the outputs that are not used as inputs in other sub-processes are value-added products. External inputs can be largely limited to input of energy (heat, electricity), hydrocarbon mixture (e.g. fuel) and calcium carbonate (limestone), and organic residue where steam gasification is used. Outputs can be largely limited to value-added products (desulfurized hydrocarbon mixture, methanol and calcium sulfate (or gypsum).

Mass and Energy Balance A sulfur mass and energy balance illustrates how an integrated process may be developed from the sub-processes described above. Fig. 2 provides examples of sub- processes 1 to 8 showing the mass balance to produce 1 kg of gypsum, and the energy involved in each of the sub-processes.

Referring to Fig. 2, the base unit of mass in this analysis is the production of 1 kg of gypsum. For 1 kg of gypsum, 0.79 kg CaS0₄ needs to be reacted with 0.105 kg of water by process 4. CaS0₄ is produced through process 3 with co-production of 0.26 kg of C0₂. CaS0₄ is produced either directly from H₂S or from S produced through process 2 (the Claus process). In both, an initial mass of 0.198 kg of H₂S is required. H₂S is produced through process 1 , and therefore 0.012 kg of hydrogen is required. H₂ can be produced from processes 6 and 7. If all hydrogen is produced from process 6, 0.210 kg of water is required for the water electrolysis reaction. If hydrogen is all produced from process 7, 0.072 kg of carbon would be required. 0.26 kg of C0₂ is produced from process 3 that can be used to produce methanol through process 5. Additional hydrogen required can be produced from process 6 instead of process 7 producing less C0₂. References: The contents of the entirety of each of which are incorporated by this reference.

Lackner KS, Rappold TA. (2010) Systems and Methods for Generating Sulfuric Acid. US Patent 7,799,310 issued September 21 , 2010.

Rappold T, Lackner K. (2010) Large scale disposal of waste sulfur: From sulfide fuels to sulfate sequestration. Energy. 35(3), 1368-1380.

Suda T, et al. (1998) Method of Producing Gypsum. US Patent 5,798,087 issued August 25, 1998. Tatani A, et al. Production of Gypsum Hemihydrate from Hydrogen Sulfide. Abstract if JPH07237921 published September 12, 1995.

Tatani A, et al. (2005) Gas Refining System. US Patent 6,896,858 issued May 24, 2005.

Yamamoto M, et al. (1993) Production of Gypsum. Abstract of JPH05208815 published August 20, 1993.

Zeman F, Lackner K. (2008) The Reduced Oxygen Kiln. A White Paper Report for the Cement Sustainability Initiative of the World Business Council on Sustainable Development. Lenfest Center for Sustainable Energy Columbia University in New York Report No. 2008.01 , especially page 66. The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments, but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.

Claims

Claims:

1. A process comprising: desulfurizing a sulfur-contaminated hydrocarbon mixture to obtain hydrogen sulfide and a desulfurized hydrocarbon mixture; reacting the hydrogen sulfide or elemental sulfur obtained from the hydrogen sulfide with calcium carbonate under anhydrous conditions in the presence of an oxygen source at a temperature of 200°C or greater to obtain calcium sulfate and carbon dioxide; and, converting the carbon dioxide to methanol.

2. The process according to claim 1 , wherein the calcium carbonate is reacted with hydrogen sulfide.

3. The process according to any one of claims 1 to 2 further comprising blending the methanol with the desulfurized hydrocarbon mixture.

4. The process according to any one of claims 1 to 3 further comprising converting the calcium sulfate to gypsum by hydrating the calcium sulfate.

5. The process according to any one of claims 1 to 4, wherein the oxygen source is oxygen gas.

6. The process according to claim 5, wherein at least a portion of the oxygen gas is obtained by electrolyzing water.

7. The process according to any one of claims 1 to 6, wherein the carbon dioxide is converted to methanol by reacting the carbon dioxide with hydrogen gas.

8. The process according to claim 7, wherein at least a portion of the hydrogen gas is obtained by electrolyzing water.

9. The process according to claim 7, wherein at least a portion of the hydrogen gas is obtained by steam gasifying organic residue.

10. The process according to claim 9, wherein the steam gasifying produces carbon dioxide gas and the carbon dioxide gas produced by the steam gasifying is converted to methanol.

1 1. The process according to any one of claims 1 to 10, wherein the hydrocarbon mixture comprises a fuel.

12. The process according to claim 1 1 , wherein the fuel is a jet fuel.

13. A process for producing calcium sulfate comprising reacting sulfur or hydrogen sulfide with calcium carbonate under anhydrous conditions in the presence of a source of oxygen at a temperature of 200°C or greater.

14. The process according to claim 13, wherein the source of oxygen is oxygen gas.

15. The process according to any one of claims 1 to 14, wherein the temperature is 400°C or greater.

16. The process according to any one of claims 1 to 14, wherein the temperature is 500°C or greater.

17. The process according to any one of claims 1 to 14, wherein the temperature is in a range of from 500°C to 600°C.