Solid ammonia storage and delivery material

Abstract

A solid ammonia storage and delivery material A solid ammonia storage material comprising: an ammonia absorbing salt, wherein the ammonia absorbing salt is an ionic salt of the general formula: Ma(NH3)nXz, wherein M is one or more cations selected from alkaline earth metals, and / or one or more transition metals, such as Mn, Fe, Co, Ni, Cu, and / or Zn, X is one or more anions, a is the number of cations per salt molecule, z is the number of anions per salt molecule, and ri is the coordination number of 2 to 12, wherein M is Mg provides a safe, light-weight and cheap compact storage for ammonia to be used in the automotive industry.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to the storage of ammonia in a solid form using metal ammine complexes and delivery there from. The invention also relates to the use of ammonia stored in a solid form as the reducing agent in selective catalytic reduction (SCR) of NOx in exhaust gases from combustion processes, to methods for producing such complexes and to an ammonia delivery device comprising such complexes.[0003]2. Description of the Related Art[0004]Current environmental regulations necessitate the use of catalysts in the exhaust gas from automotive vehicles, boilers and furnaces for control of NOx emission leaving the system. Particularly, vehicles equipped with diesel engines or other lean burn engines offer the benefit of improved fuel economy, but suffer from the drawback of increased formation of NOx being noxious and which must be eliminated from the exhaust gas. However, catalytic reduction of NOx using conventi...

AI Technical Summary

Benefits of technology

[0012]In a third aspect the invention relates to a method for selective catalytic NOx reduction in waste gases containing oxygen, using ammonia and a reduction catalyst wherein gaseous ammonia is provided by heating a solid storage medium comprising one or more ionic ammonia absorbing salts of the general formula:

Problems solved by technology

Particularly, vehicles equipped with diesel engines or other lean burn engines offer the benefit of improved fuel economy, but suffer from the drawback of increased formation of NOx being noxious and which must be eliminated from the exhaust gas.

However, catalytic reduction of NOx using conventional so-called three-way exhaust catalysts for automobiles is impossible because of the high content of oxygen in the exhaust gas.

Injection of a too large amount of reducing agent will cause emission of ammonia with the exhaust gas whereas injection of a too small amount of reducing agent causes a less than optimum conversion of NOx.

However, there are several disadvantages related to the use of aqueous urea as the reducing agent.

Altogether, these difficulties may limit the possibilities of using SCR technology in abatement of pollution from NOx, particularly in connection with mobile units.

Transporting ammonia as a pressurized liquid is hazardous as the container may burst or a valve or tube might break in an accident giving a discharge of poisonous / lethal gaseous ammonia.

However, the use of the ammonia storage media known from WO 99 / 01205 suffers from various draw-backs hampering a wide-spread use in the automotive industry.

The vapour pressure of ammonia above a solid salt phase is e.g. about 1 bar at room temperature and atmospheric pressure for calcium octa ammine chloride and strontium octa ammine chloride complexes rendering the use somewhat complicated due to the high pressures that must be taken into account in view of the toxicity of ammonia.

Having such a high partial pressure of ammonia, the handling and transportation of the saturated storage material is still difficult and also dangerous.

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