Chemistry of inorganic compounds – Nitrogen or compound thereof – Carbon containing
Reexamination Certificate
1998-11-10
2001-11-13
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Nitrogen or compound thereof
Carbon containing
C204S157460
Reexamination Certificate
active
06315972
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to elevated temperature, gas phase, catalyzed reactions in which induction heating is used as a source of energy. While the invention relates to improvements in processes and catalysts for elevated temperature, gas phase, catalyzed reactions in general, it is particularly illustrated herein by reference to the manufacture of hydrogen cyanide.
BACKGROUND OF THE INVENTION
Induction heating is a non-contact method of selectively heating inducing a magnetic field into the material to be heated. Because induction heating uses alternating magnetic fields, it is only capable of heating electrically-conductive materials; i.e. the eddy current effect. Induction heating has been used in industry for may years, mainly for the purpose of heating metals, e.g. in annealing and soldering. However, figures of merit for induction heating of solid pieces of metal are significantly different from those for heating typical catalysts.
Hydrogen cyanide, hereinafter HCN, is an important chemical with many uses in the chemical and mining industries. For example, HCN is a raw material for the manufacture of adiponitrile for use in nylon; acetone cyanohydrin to make methyl methacrylate for acrylic plastics; sodium cyanide for use in gold recovery; and intermediates in the manufacture of pesticides, agricultural products, chelating agents, and animal feed. HCN is a highly toxic liquid boiling at 26 degrees C. and as such, is subject to stringent packaging and transportation regulations. In some applications, HCN is needed at remote locations distant from large scale HCN manufacturing facilities. For example, it is used in preparing cyanide derivatives on sites at which the derivatives will be used. Shipment of HCN to such locations involves major hazards. Local production of the HCN at sites at which it is used avoids the transportation hazards. However, this clearly requires the installation of a large number of small production facilities and is an expensive option.
As a rule, HCN is produced when compounds containing hydrogen, nitrogen, and carbon are brought together at high temperatures, with or without a catalyst. HCN is most commonly produced industrially by either the exothermic Andrussow process and the endothermic Degussa process or, to a lesser extent, the endothermic Shawinigan process. Other processes for making HCN that have not been significantly exploited commercially, due primarily to unsatisfactory economics, include formamide decomposition, methanol ammonolysis, and reaction of acid with sodium cyanide. HCN is also produced as a by-product in the Sohio process for the synthesis of acrylonitrile from propene and ammonia.
In all of the foregoing processes, the emerging product stream must be promptly cooled below about 300 degrees C. to prevent thermal degradation from occurring. Additionally, unreacted ammonia, termed “ammonia breakthrough”, must be removed since it can catalyze the polymerization of HCN, a process that can lead to explosions. In large plants the ammonia is recovered and recycled, in smaller units it may be burned or removed as ammonium sulfate, although the disposal processes involve environmental concerns over nitrogen oxide emissions and ammonium sulfate disposal respectively.
While it is known that HCN can be produced by the reaction of CH
4
and NH
3
in the presence of a Pt group metal catalyst, there is still a need to improve the efficiency of that process and related ones so as to improve the economics of HCN production, especially small scale production. It is particularly important to minimize energy use and ammonia breakthrough while maximizing the HCN production rate versus the amount of precious metal catalyst. Furthermore it is desired to improve activity and life of catalysts used in this process. Significantly, a large part of the investment in production of HCN is in the platinum group catalyst. The present invention accomplishes these desiderata.
SUMMARY OF THE INVENTION
This invention relates to a catalyst and process for conducting elevated temperature, gas phase, catalyzed reactions in which the catalyst is heated by induction heating, whereby the heated catalyst provides the reactants with the heat needed for the reaction. By relying on inductive heating of the catalyst, rather than the prior art processes directed to heating the reaction vessel or a portion thereof or the like and thereby heating the catalyst by conduction, radiation and/or convection, considerable advantages are realized.
DETAILED DESCRIPTION OF THE INVENTION
In the process of this invention, one or more reactants are contacted with a catalyst bed comprising a substantially uniformly distributed multiplicity of discrete substantially uniform susceptor entities. Preferably said multiplicity of susceptor entities is substantially uniformly distributed in a three dimensional array. The susceptor entities are heated by induction heating at a frequency between 50 Hz to 30 MHz to a temperature sufficient to effect reaction of said reactants. The improved catalyst of this invention comprises multiple susceptor entities that function as independent induction heating susceptors while providing a large catalytic surface area. By “susceptor entity” as used hereinafter, is meant pellets, rings, or rods, containing a core externally coated with a substantially uniform and complete catalytic metal wrap, coating, or surface impregnation, or containing the catalytic metal as a foam. The susceptor entities are distributed subsantially uniformly within the reaction zone volume, physically disposed such that electrical conduction between the susceptor entities is minimal and to allow uniform and turbulent flow of gas between them, and are positioned such that the largest eddy current path formed on them is substantially in the same plane as the current flow in the induction coil. The susceptor entities comprise one or more metals from Groups Ib, IIb, IIIa, IVa & b, Vb, VIb, VIIb, or VIII, hereinafter sometimes referred to as “catalytic metals”. The term “catalytic metal” is also used hereinafter to describe the above-described metals or alloys thereof, particularly platinum, platinum-iridium alloy, or platinum-rhodium alloy. The electrical conductivity between susceptor entities is substantially less than the surface conductivity of such entities. The susceptor entities must have sufficient electrical conductivity, and the size and geometry of said entities must be such that during heating by induction, said entities would include a sufficiently large eddy current path in the plane of the the coil current to have sufficient induction heating efficiency and sufficient surface area efficiently to promote catalytic activity. Preferably, induction heating is carried out at a frequency between 3 KHz to 30 MHz, and most preferably between 3 KHz to 450 KHz.
The process of this invention involves the inductively heating the susceptor entities of this invention to an elevated temperature sufficient to effect gas phase reactions. The process is suitable for reactions in which additional heat must be provided to the catalyst zone to maintain the reaction, and particularly to endothermic reactions. A convenient example reaction for the application of the process of this invention is an improved process for the production of hydrogen cyanide, the improvement comprising a reaction zone containing susceptor entities in the form of one or more of the aforesaid catalytic metals, particularly a Group VIII or platinum group metal catalyst, coated on or applied to the outside of a refractory support structure. The dimensions and electrical properties of the catalyst are designed for inductive heating of the susceptor entities and maximum electrical efficiency.
The core or support structure is comprised of pellets, rings, or rods of a conductive or non-conductive refractory material selected from materials that minimize the decomposition of ammonia at the reaction temperatures. The support structure is externally covered with, coated with, or impregnated with platinum or
Blackwell Benny Earl
Koch Theodore A.
Krause Karl Robert
Mehdizadeh Mehrdad
Sengupta Sourav Kumar
E.I. Du Pont de Nemours and Company
Hendrickson Stuart L.
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