System and method for ammonia synthesis

Abstract

Systems and methods are disclosed herein for synthesizing ammonia using nano-size metal or metal alloy catalyst particles. Hydrogen and nitrogen gases are passed through a system comprising, for example, a bed of magnetite supporting nano-size iron or iron alloy catalyst particles having an optional oxide layer that forms the catalyst.

Description

RELATED APPLICATION[0001]This application is a continuation-in-part of U.S. patent application Ser. No. 12 / 418,356, filed Apr. 3, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 12 / 266,477, filed on Nov. 6, 2008, which claims priority from Provisional Application No. 60 / 985,855, filed on Nov. 6, 2007, the entire contents of each of which are hereby incorporated by this express reference.BACKGROUND[0002]1. Technical Field[0003]The disclosure relates generally to the synthesis of useful chemical byproducts and, more specifically, to the synthesis of ammonia using nano-size metal catalyst particles.[0004]2. Related Art[0005]Ammonia synthesis is an important industrial process. Ammonia is produced in huge quantities worldwide, for use in the fertilizer industry, as a precursor for nitric acid and nitrates for the explosives industry, and as a raw material for various industrial chemicals.[0006]Despite an energy production cost of about 35 to 50 GJ per ton of am...

AI Technical Summary

Benefits of technology

"The invention is about a new method for making ammonia using nanoparticle catalysts on a support material. This method improves catalytic activity while reducing the pressure needed for the reaction. The nanoparticle catalysts can be made using a support material that separates the particles, reducing sintering and promoting interaction between the particles. The new method can operate at lower pressures than traditional methods and maintain catalytic efficiency over time. The invention also includes a reactor design that allows for the use of nano-sized metal catalyst particles in a traditional or new reactor bed design. The nanoparticle catalysts can be made using ferrous materials, such as iron, cobalt, ruthenium, alloys, and mixtures thereof. The support material can be magnetite or other ferrous materials, silicon nitride, silicon carbide, silicon dioxide, aluminum oxide, or cordierite. The invention also includes a NOx remediation system and a selective catalytic reduction system for reducing NOx emissions."

Problems solved by technology

However, in practice, both high pressures and temperatures are used due to a sluggish reaction rate.

Due to overall low reaction efficiency when hydrogen and nitrogen are first passed over the catalyst bed, most ammonia production plants utilize multiple adiabatically heated catalyst beds with cooling between beds, typically with axial or radial flow.

High pressure favors the adsorption process as well, but at a cost of increased operational and capital costs.

Nevertheless, due in part to high pressures used in the process, ammonia production requires reactors with heavily-reinforced walls, piping and fittings, as well as a series of powerful compressors, all with high capital cost.

In addition, generation of those high pressures during plant operation requires a large expenditure in energy.

Use of this catalyst allowed the reactor pressure to be reduced, but the high cost of the precious metal ruthenium catalyst and the sensitivity of the catalyst to impurities in the hydrogen feed stock have prevented widespread use for ammonia synthesis.

Other catalysts being studied include cobalt doped with ruthenium, but few encouraging results have been exhibited to date.

Suggestions of reducing the processing pressures have been made, but have not been achieved economically.

U.S. Pat. No. 3,653,831 describes the addition of platinum to improve reaction efficiency, however given the expense of platinum this may not be feasible at large scales.

Retrofit and reconstruction of these plants could be costly should there be a need to change design based on catalyst properties, such as space velocity.

Non-ferrous catalysts in the above referenced prior art do not overcome all of these constraints because 1) catalyst cost increases more than catalyst efficiency, 2) the catalyst may not have the same properties that allow for seamless operation in existing ammonia production plants, or 3) the catalyst may have high activity but do not meet long term durability requirements.

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