Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Phosphorus or compound containing same
Reexamination Certificate
1999-06-22
2001-01-16
Rotman, Alan L. (Department: 1625)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Phosphorus or compound containing same
C549S263000
Reexamination Certificate
active
06174833
ABSTRACT:
This application claims priority under 35 USC §119 from Belgian patent application 09800475 filed Jun. 23, 1998, incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
This invention relates to a method of producing vanadium-phosphorus mixed oxide catalyst for the manufacture of maleic anhydride. More particularly the present invention provides a process for producing mature, active catalysts suitable for commercial production of maleic anhydride by oxidation of aliphatic hydrocarbons, particularly n-butane, in the vapor phase, with a gas containing molecular oxygen, such as air, or oxygen, in a stream of exhaust gas recycled from the reaction effluent, following the recovery of maleic anhydride.
BACKGROUND OF THE INVENTION
Maleic anhydride is a substantial commercial product made throughout the word for over fifty years. It is used alone or in combination with other materials mostly as a precursor for other products, including resins, pharmaceuticals and food additives.
Hundreds of articles and patents have been published related to the vanadium phosphorus oxides catalysts since Bergman et al, U.S. Pat. No. 3,293,268, taught the process of oxidizing saturated aliphatic hydrocarbons to produce maleic anhydride using such catalysts, often referred to as mixed oxides of vanadium and phosphorus. Bulk analysis of the active, mature catalyst shows the catalyst to be generally crystalline vanadyl pyrophosphate. However, as yet there are many factors not clearly understood that are important to the making of active, mature catalysts giving commercially acceptable productivities, yields and lives.
Numerous methods of making the vanadium-phosphorus oxide catalysts with and without promoters are disclosed and taught in the prior art. Generally, such catalysts are made by contacting suitable vanadium compounds under conditions which result in the vanadium being in the +4 valence, and reacted with the phosphorus to form a catalyst precursor consisting essentially of hydrated vanadyl hydrogen phosphate. The catalyst precursor is subsequently recovered by techniques well know in the art, such as drying, filtering and centrifuging, and treated physically and thermally by several conventional practices to form “calcined” mature catalysts.
Very few methods don't use calcination as an integral part of the process of production of an active catalyst. U.S. Pat. No. 4,317,778, for instance, describes a process where the final activation of the catalyst precursor is claimed to occur by introducing the catalyst precursor into water to form an aqueous slurry and by spray drying the slurry to form microspheroidal catalyst particles to be used in fluid bed reactors.
The methods used for the calcination of the catalyst precursor may be divided into two broad categories
1) calcination performed in equipment other than the reactor (external calcination) and
2) calcination in the reactor tubes, under hydrocarbon and air, usually mild operating conditions (in-situ calcination).
An external calcination method which results in a good, competitive catalyst has many advantages over the in-situ procedure. Firstly, productive capacity is lost, usually for weeks, during the in-situ calcination operating at below normal feed concentrations and throughput. Secondly, since the calcination procedure is a very sensitive operation which, if done improperly, results in inferior catalysts, the total reactor charge is put at risk in the in-situ calcination procedure, since the whole catalyst charge is calcined at the same time. The external calcination has the advantage of calcining the catalyst in smaller increments, resulting not only in lower risk of inferior catalyst charged to the commercial reactor, but allowing known procedures for measuring and controlling the quality of the catalyst. Better performance in yield, productivity and life results.
Prior art teaches procedures for both in-situ and external calcination. In both methods the ultimate form of the mature catalyst, in the bulk, is crystalline vanadyl pyrophosphate with various degrees of activity and selectivity for the production of maleic anhydride. Usually in the in-situ method the catalyst in the precursor form is charged to the reactor and brought up to reacting conditions using a feed of hydrocarbon and air. After several days or weeks of producing maleic anhydride at low rate, the precursor is converted to the active vanadyl pyrophosphate with the bulk of the vanadium very close to a valence of +4.
Generally, in the external calcination procedures, the prior art teaches that the catalyst be partially oxidized during the calcination. For reason not totally understood, partial oxidation of vanadium is required to make catalysts with high performance. Vanadium oxidation levels of above 4.0 and below 4.8 are considered favorable. The external calcination procedures described in prior art are varied, using batch and continuous thermal systems. Gaseous atmospheres are controlled in many cases. Gaseous atmospheres containing a combination or mixture of hydrocarbon and oxygen are usually not used, because of the difficulty in controlling the exothermal oxidation.
U.S. Pat. No. 5,137,860 teaches a process for conversion of vanadium-phosphorus catalyst precursors to active catalysts by subjecting the catalyst precursor to elevated temperatures in three stages:
a) an initial heat-up stage in an atmosphere of air, steam and nitrogen,
b) a rapid heat-up stage at a programmed heat-up rate in an air/steam atmosphere and
c) a maintenance-finishing stage, using consecutively an oxygen containing and a non-oxidizing atmosphere.
U.S. Pat. No. 4,562,268 relates to a process for the production of maleic anhydride by oxidation of aliphatic hydrocarbons in the vapor phase using phosphorus-vanadium mixed oxide catalysts. The catalysts employed are normally prepared by introducing pentavalent vanadium compounds into an alcohol capable of reducing the vanadium and contacting the mixture with alcohol modifying agents. The patent discloses two basic modes of calcination.: (1) air calcination and (2) nitrogen/steam calcination. In the air calcination the catalyst precursors are subjected to heating in air, as in one embodiment, to 400° C. over a two hours period, then holding at this temperature for six hours. In the nitrogen/steam calcination the catalyst precursors are first calcined in air, at a temperature in the range from 325° C. to 350° C. for six hours, followed by calcination in nitrogen and steam at a temperature in the range from 250° C. to 600° C. for from two to ten hours. The nitrogen/steam calcination is preferred.
U.S. Pat. No. 4,392,986 discloses a process for preparing vanadium-phosphorus catalysts by reaction in isobutanol followed by water washing of the precursors. The precursors, after drying at 120° C. to 140° C., are activated in the reactor oxidizing butane in air to maleic anhydride, typifying the in-situ calcination type.
U.S. Pat. No. 4,336,198 relates to vanadium-phosphorus catalysts modified with uranium, in which the precursors are supported on inert porous media such as alundum shapes. Calcining of the coated particles is disclosed as “heating from 200° C. to 400° C. at a rate of 5°/minute with heating at 400° C. for one hour”.
U.S. Pat. No. 4,317,777 teaches the production of maleic anhydride using vanadium-phosphorus catalysts by oxidizing a mixture which comprises a hydrocarbon of at least 4 linear carbon atoms and an oxygen containing gas, which compositions are above the flammable limit. All of the catalysts described in the 18 examples were calcined as typified by the description: “The catalyst was calcined in-situ by heating to 385° C. at a rate of 9°/minute, whilst a 1.5% v/v n-butane/air mixture flowed through the bed at a GHSV of 1000 hr
−1
”. After several hundred hours of operation the performances of the catalysts were evaluated.
U.S. Pat. No. 4,315,864 teaches a process for preparing catalysts useful in the production of dicarboxylic acid anhydrides comprising the steps of:
a) introducing a penta
Bertola Aldo
Cassarino Salvatore
Nsunda Veron K.
Desai Rita
Pantochim S.A.
Rotman Alan L.
Stevens Davis Miller & Mosher LLP
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