Method and process of producing ammonia from methane hydrate

Abstract

The present invention discloses a method and a process of producing ammonia from methane extracted from methane-hydrate at the site of methane-hydrate extraction. The method and the process comprise coupled chemical reactions. During the first reaction, carbon dioxide reacts methane-hydrate to produce carbon-dioxide-hydrate and methane: carbon dioxide+methane-hydrate⇄carbon-dioxide-hydrate+methane (CO.sub.2+CH.sub.4-hydrate⇄CO.sub.2-hydrate+CH.sub.4). The produced methane is reacted with water to produced carbon dioxide and hydrogen via the second reaction: methane+water⇄carbon dioxide+hydrogen (CH.sub.4+2H.sub.2O⇄CO.sub.2+4H.sub.2). One embodiment of the second reaction is a combination of the methane steam reforming reaction (CH.sub.4+H.sub.2O⇄CO+3H.sub.2) and the water-gas shift reaction (CO+H.sub.2O⇄CO.sub.2+H.sub.2), both are widely known in the art. The carbon dioxide produced in the second reaction is recycled and used for the first reaction. The hydrogen produced in the second reaction is reacted with nitrogen produced from an air separation process that is known in the art to produce ammonia via the third reaction: nitrogen+hydrogen.fwdarw.ammonia (N.sub.2+3H.sub.2.fwdarw.2NH.sub.3). One embodiment of the third reaction is the well-known Haber-Bosch process. The current invention is related to co-locating the ammonia synthesis at the methane-hydrate extraction sites to minimize the cost of transporting both methane and carbon dioxide over long distances. The process and the associated method also have the advantage of on-site carbon sequestration. The ammonia product produced via the current invention is easily transportable in liquid form from the production sites to the end-use sites as a carbon-free liquid fuel, a fertilizer and a chemical feedstock.

Claims

1. A method for producing ammonia from methane-hydrate at the location of the methane-hydrate extraction, the method comprising: providing at said location of the methane-hydrate extraction carbon dioxide to react with methane-hydrate to produce methane and carbon-dioxide-hydrate via a first reaction, wherein the first reaction is: carbon dioxide+methane-hydrate⇄carbon-dioxide-hydrate+methane (CO.sub.2+CH.sub.4-hydrate⇄CO.sub.2-hydrate+CH.sub.4); providing methane produced from the first reaction to react with water to produce carbon dioxide and hydrogen via a second reaction, wherein the second reaction is: methane+water⇄carbon dioxide+hydrogen (CH.sub.4+2H.sub.2O⇄CO.sub.2+4H.sub.2), wherein the produced carbon dioxide is provided to the first reaction and when reaching a steady state the first reaction and the second reaction are occurring simultaneously and feeding off of each other; and providing nitrogen from an air separation process to react with the hydrogen produced from the second reaction to synthesize ammonia via a third reaction: nitrogen+hydrogen.fwdarw.ammonia (N.sub.2+3H.sub.2.fwdarw.2NH.sub.3).

2. A method for producing ammonia from methane-hydrate at the location of the methane-hydrate extraction as cited in claim 1, wherein the first reaction takes place in molten methane-hydrate.

3. A method for producing ammonia from methane-hydrate at the location of the methane-hydrate extraction as cited in claim 1, wherein the second reaction, methane+water⇄carbon dioxide+hydrogen (CH.sub.4+2H.sub.2O⇄CO.sub.2+4H.sub.2), is a combination of a methane steam reforming reaction (CH.sub.4+H.sub.2O⇄CO+3H.sub.2) and a water-gas shift reaction (CO+H.sub.2O⇄CO.sub.2+H.sub.2).

4. A method for producing ammonia from methane-hydrate at the location of the methane-hydrate extraction as cited in claim 1, wherein the third reaction, nitrogen+hydrogen.fwdarw.ammonia (N.sub.2+3H.sub.2.fwdarw.2NH.sub.3), is the widely used Haber-Bosch synthesis method.

5. A method for producing ammonia from methane hydrate at the location of the methane hydrate extraction as cited in claim 1, wherein both the processes of the second reaction and the third reaction take place on the same ocean platform.

6. A method for producing ammonia from methane hydrate at the location of the methane hydrate extraction as cited in claim 1, wherein the processes of the second reaction and the third reaction take place on separate ocean platforms which are within ten miles from one another.

7. A method for producing ammonia from methane hydrate at the location of the methane hydrate extraction as cited in claim 1, wherein the processes of the second reaction and the third reaction take place on separate ocean platforms which are linked together via pipes from one another to transport both methane and carbon dioxide among the platforms.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) For the purposes of promoting an understanding of the invention, the terminology used herein is for the purpose of description, not limitation. Specific reactions, methods and processes disclosed herein are meant to be used as examples. Various variants or embodiments should be considered as part of this invention.

(2) One embodiment of the invention is to have the ammonia synthesis apparatus located on the same ocean platform as the methane-hydrate extraction. Examples of ocean platforms include those currently used for off-shore gas or oil productions that are known to those skilled in the art.

(3) Another embodiment of the invention is to have the ammonia synthesis apparatus on a separate ocean platform but placed in close proximity to the methane-hydrate extraction platform. Here close proximity is defined as within ten miles from each other. One further embodiment of this invention is to have the two platforms tied together so pipes can be used to transfer chemicals such as carbon dioxide and methane between the platforms.

(4) The close proximity enables the following chemical reactions to take place without long-distance transport of both methane and carbon dioxide.

(5) In Reaction #1, carbon dioxide reacts methane-hydrate to produce carbon-dioxide-hydrate and methane: carbon dioxide+methane-hydrate⇄carbon-dioxide-hydrate+methane (CO.sub.2+CH.sub.4-hydrate⇄CO.sub.2-hydrate+CH.sub.4). Since carbon-dioxide-hydrate is more stable than methane-hydrate, Reaction #1 is thermodynamically favorable and has been experimentally demonstrated (For instance, N. Goel, “In situ methane hydrate dissociation with carbon dioxide sequestration: Current knowledge and issues.” Journal of Petroleum Science and Engineering, volume 51, no. 3-4, pages 169-184, 2006). Reaction #1 is also slightly exothermic, producing a small amount of heat during the reaction.

(6) Reaction #1 is kinetically sluggish when gaseous or liquid carbon dioxide is reacting with solid methane-hydrate (methane hydrate in solid ice). In one embodiment of the current invention, the gaseous or liquid carbon dioxide is reacting with a molten state of methane-hydrate (methane hydrate in liquid water) to accelerate the reaction rate. Such a liquid state of methane-hydrate exists according to the methane-hydrate phase diagram as shown in the publication of Jiafei Zhao, Kun Xu, Yongchen Song, Weiguo Liu, Weihaur Lam, Yu Liu, Kaihua Xue, Yiming Zhu, Xichong Yu, and Qingping Li: “A review on research on replacement of CH.sub.4 in natural gas hydrates by use of CO.sub.2”, Energies, volume 5, pages 399-419, 2012. In one further embodiment of the current invention, the exothermic heat of Reaction #1 is employed to locally melt the solid methane-hydrate (methane-hydrate in solid ice) to help create the state of molten methane-hydrate.

(7) The initial batch of carbon dioxide used for Reaction #1 can be provided by carbon dioxide sequestration from power plants or other sources and is transported to methane-hydrate extraction site. The initial batch of carbon dioxide can also be produced by converting methane on site using Reaction #2, whereas the initial methane is extracted from methane-hydrate using conventional processes such as heating and decompression of methane hydrate that is known in the art. Subsequent continuous carbon dioxide input for Reaction #1 will be provided by Reaction #2 on site.

(8) The methane produced in Reaction #1 is reacted with water (steam) to produce carbon dioxide and hydrogen via Reaction #2: methane+water⇄carbon dioxide+hydrogen (CH.sub.4+2 H.sub.2O⇄CO.sub.2+4 H.sub.2). This second reaction is a combination of the methane steam reforming reaction (CH.sub.4+H.sub.2O⇄CO+3H.sub.2) and the water-gas shift reaction (CO+H.sub.2O⇄CO.sub.2+H.sub.2), both are widely known in the art as described in the publication Jianguo Xu and Gilbert F. Froment, “Methane steam reforming, methanation and water-gas shift: 1. Intrinsic kinetics”, AIChE Journal, volume 35, no. 1, pages 88-96, 1989. The carbon dioxide produced in Reaction #2 is recycled to be used for Reaction #1; and when reaching a steady state, Reaction #1 and Reaction #2 are occurring simultaneously and feeding off of each other.

(9) The hydrogen produced in Reaction #2 is reacted with nitrogen extracted from air via an air separation process that is known in the art to produce ammonia via Reaction #3: nitrogen+hydrogen.fwdarw.ammonia (N.sub.2+3 H.sub.2.fwdarw.2 NH.sub.3). One embodiment of Reaction #3 is the Haber process which is also known as Haber-Bosch process that is used worldwide to produce ammonia as described by Max Appl in “Ammonia”, Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, 2005.

(10) The heat required for both Reaction #2 and Reaction #3 are produced by combustion of part of the methane produced on-site via Reaction #1. The electricity required for the operations of pumps and other necessary equipment can be generated using a gas turbine with part of the methane from Reaction #1. One embodiment of the invention is to use the oxygen separated from the air separation process (for ammonia production) as input to the gas turbine to produce high concentration of carbon dioxide that can also be captured and used as part of the input to Reaction #1. The exhaust heat generated by the gas turbines may further be used for the ammonia production and thus the gas turbine may serve the dual purpose of combined heat and power.

(11) Another embodiment of the invention is to use wind turbines installed or floating near the combined methane hydrate extraction and ammonia synthesis site to provide electricity required for the operations.

(12) Various embodiments of the invention have been described in fulfillment of the various needs that the invention meets. It should be recognized that these embodiments are merely illustrative of the principles of various embodiments of the present invention. Numerous modifications and adaptations thereof will be apparent to those skilled in the art without departing from the spirit and scope of the present invention. It is intended that the present invention cover all suitable modifications and variations as come within the scope of the appended claims and their equivalents.