Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-12-14
2001-08-14
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S607000
Reexamination Certificate
active
06274764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improved catalytic systems, including MoVNbPd, MoVLaPd and combinations thereof, and to improved catalytic processes for the low temperature selective oxygenation of ethylene to acetic acid. More specifically, the invention relates to a single stage catalytic process using novel catalysts for providing high ethylene conversions and acetic acid yields.
2. Description of the Related Art
Several publications are referenced in this application. These references describe the state of the art to which this invention pertains, and are incorporated herein by reference.
Acetic acid is generally produced by methanol carbonylation using an expensive rhodium catalyst in a liquid phase homogeneous reaction. This method requires complicated procedures for the recovery of the catalyst and the isolation of the products. Moreover, the presence of iodine at ppm levels in the final product has a negative impact on the usage of the acetic acid produced by the method.
Acetic acid is also produced by a two stage acetaldehyde process using manganese catalysts Such processes are disclosed in U.S. Pat. Nos. 3,131,223; 3,057,915; 3,301,905; and 3,240,805. The first stage of this process involves the production of acetaldehyde from ethylene. The economics of the process is not favored due to the costs arising from the two stages. Furthermore, these processes produce a large amount of acetaldehyde as a by-product. In addition, a large amount of ethylene may be lost by complete oxidation into carbon dioxide.
More recently, Showa Denko [EP 0 62 0205 Al] relates to a catalytic process for converting ethylene to acetic acid using catalysts containing heteropoly acids of phosphorus, silicon, boron, aluminum, germanium, titanium, zirconium, cerium, cobalt, chromium and metal palladium with at least one element selected from groups XI, XIV, XV, and XVI of the periodic table. The single pass conversion of ethylene was reported to be very low over these heteropoly catalysts and produces a significant amount of acetaldehyde, which can have a great impact on the separation cost. The catalytic systems used in the present invention are different from the Showa Denko catalysts.
EP A 0 29 4845 relates to a process for the higher selective production of acetic acid by the oxidation of ethane or ethylene with oxygen in contact with a physical mixture of at least two catalyst systems consisting of (A) a catalyst for oxydehydrogenation of ethane to ethylene and (B) a catalyst for hydration/oxidation of ethylene. The ethane oxydehydrogenation catalyst is represented by the formula Mo
x
V
y
Z
z
, wherein Z can be one or more of the metals Nb, Sb, Ta, Ca, Sr, Ti, W, Li, Na, Be, Mg, Zn, Cd, Hg, Sc, Fe and Ni. The catalyst for hydration/oxidation is selected from a molecular sieve catalyst, a palladium-containing oxide catalyst, tungsten-phosphorus oxide catalyst, or tin or molybdenum containing oxide catalyst. EP A 0 29 4845 employs the catalyst prepared by the physical mixing of the two types of catalysts.
Japanese Patent No. 46-6763 relates to the catalytic oxidation of ethylene to acetic acid using specific catalysts disclosed in the examples containing the following combination of metal atoms: V—Pd—Sb, V—Rh—Sb, V—Pd—P, V—Rh—P, V—Rh—As, V—Pd—As, Mo—Pd—Sb, Mo—Rh—Sb, Mo—Rh—As, and Mo—P—W—Pd—Rh—Sb. Japanese Patent No. 54-57488 relates to the use of NaPdH
2
-PMoV catalysts for the oxidation of ethylene to acetic acid.
Syoji Tan et al. [
J.Catal
., vol. 17, pp. 132-142, 1970]reported that olefins oxidize to ketones over the binary catalyst systems Co
3
O
4
-MoO
3
and SnO
2
-MoO
3
. The article discloses the formation of acetic acid as a by-product together with other compounds and product of specifically ethylene was only carbon dioxide.
Thus, none of the prior art discloses or suggests the advantages of the catalytic system disclosed in present invention for the selective production of acetic acid from ethylene using a catalyst which is a dual function catalyst and is designed in such way that it enhances the activation function as well as the selectivity to the desired product acetic acid.
OBJECTS OF THE INVENTION
It is an object of the invention to overcome the above-identified deficiencies.
It is another object of the invention to provide improved catalyst systems for the production of acetic acid.
It is yet another object of the invention to provide an improved method of making acetic acid with enhanced selectivity and yield of the desired product acetic acid.
It is a still further object of the invention to provide a method of making improved catalysts for the production of acetic acid.
The foregoing and other objects and advantages of the invention will be set forth in or apparent from the following description.
SUMMARY OF THE INVENTION
The present invention relates to the selective oxidation of ethylene with molecular oxygen to acetic acid in a gas phase reaction at relatively high levels of conversion, selectivity and productivity at temperatures ranging from 150° C. to 450° C. and at pressures of 1-50 bar. This is achieved by using a mixed metal oxides including MoVNbPd or MoVLaPd oxide catalysts, supported or unsupported, such as those disclosed in related U.S. application Ser. No. 08/997,913 filed Dec. 24, 1997, now U.S. Pat. No. 6,030,920, and U.S. application Ser. No. 09/107,115, filed concurrently herewith, now U.S. Pat. No. 6,087,297.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
For oxidation catalysts, the selectivity behavior to desired partial oxidation products depends on the types of active centers in the catalysts in addition to other physical reaction parameters, such as (a) hydrocarbon to oxygen ratio, (b) pressure, (c) reaction temperature, and (d) contact time.
Generally, it is well known that selectivity to mild oxygenated products such as acetic acid increases as reaction temperature decreases, whereas yield is decreased on account of total conversion. Active sites involved in the reaction play a key role in the direction of the reactions. Furthermore, the selectivity for the partial oxidation products depends on the reactivity of lattice oxygen to form C—O bonds with the adsorbed hydrocarbon. For example, alkenes are more reactive and adsorb preferentially as compared to alkanes over metal oxide/acidic catalysts. Mixed metal oxide phases of MoV are known to be responsible for the activation of hydrocarbon and the activity of the catalyst depends on the relative number of V
+4
and V
+5
over the surface of the catalyst. Moreover, palladium is known as a total oxidation metal, as well as a metal that helps to facilitate the oxygenation of alkene. An optimum amount of Pd with a high degree of dispersion of metal over mixed metal oxide catalyst results in a high selectivity to acetic acid.
Furthermore, it has been discovered that the addition of water as a co-feed plays an important role as a reaction diluent and as a heat moderator for the reaction and also acts as a desorption accelerator of the reaction product in the vapor phase oxidation reaction or masking the sites responsible for the total oxidation resulting in an increased yield of acetic acid.
In carrying out the partial oxidation of ethylene process, the reaction mixture preferably contains one mole of ethylene, 0.01 to 2.0 moles of molecular oxygen (either as pure oxygen or in the form of air), and zero to 5.0 moles of water in the form of steam. Other gases may be used as reaction diluents or heat moderators such as helium, nitrogen, and carbon dioxide.
The gaseous components of the reaction mixture preferably include ethylene, oxygen and a diluent, and these components may be uniformly admixed prior to being introduced into the reaction zone. The components may also be preheated, individually or after being admixed prior to being introduced into the reaction zone, which reaction zone should have a temperature of from about 150° C. to about 450° C. The reaction zone preferably has a pressure of from 1 to 50 bar, more preferably from
Karim Khalid
Sheikh Kareemudin
Deemie Robert W.
Killos Paul J.
Kramer Levin Naftalis & Frankel LLP
Saudi Basic Industries Corporation
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