Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
1999-04-23
2002-04-09
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S248000
Reexamination Certificate
active
06369240
ABSTRACT:
FIELD OF TECHNOLOGY
This invention relates to a process for the vapor-phase oxidation of hydrocarbons such as naphthalene, xylene, benzene, toluene, durene, butene, anthracene, indene and their derivatives. This invention also relates to a process for preparing phthalic anhydride by the oxidation of naphthalene or xylene.
BACKGROUND TECHNOLOGY
It is known that the catalytic vapor-phase oxidation of naphthalene, ortho-xylene, indene and the like gives phthalic anhydride and, likewise, the process yields maleic anhydride from benzene or butene, benzoic acid from toluene, pyromellitic dianhydride from durene and phthalic anhydride or anthraquinone from anthracene.
The aforementioned process for the catalytic vapor-phase oxidation generates a large amount of heat in the reaction and a practice generally adopted for heat removal is to fill a reactor tube of relatively small diameter with a catalyst to form a fixed bed of catalyst and pass a gaseous mixture of a raw material and a molecular oxygen-containing gas such as air to the catalyst bed [Japan Tokkyo Koho Nos. Sho 44-24580 (1969) and Sho 46-13255 (1971)].
Catalysts useful for the process normally consist of active components, indispensable members of which are titanium oxide and vanadium pentoxide, deposited on inert carriers. A process is also known which utilizes two kinds of catalysts differing from each other in catalytic activity. For example, the specification of EP286448 discloses the following process for preparing phthalic anhydride. A catalyst bed is constructed of a layer of a first catalyst made by depositing catalytically active components containing 90 to 67% by weight of titanium dioxide, 8 to 30% by weight of vanadium pentoxide and 2 to 5% by weight of a compound of cesium (calculated as sulfate) and showing a specific surface area of 20 m
2
/g or more on a nonporous inert carrier and a layer of a second catalyst made by depositing catalytically active components containing no more than 0.1% by weight of a compound of alkali metal (calculated as sulfate), 94 to 67% by weight of titanium dioxide and 5 to 30% by weight of vanadium pentoxide on a nonporous inert carrier, with the first catalyst placed upstream and the second catalyst downstream in the flow of the gaseous mixture of raw materials. A gaseous mixture of naphthalene or ortho-xylene and a molecular oxygen-containing gas is then brought into contact with the catalyst bed to be oxidized to phthalic anhydride.
This process advantageously gives the intended product such as phthalic anhydride in high yields; still there is a strong demand for improvement of the productivity per unit catalyst volume.
The productivity can be increased by increasing the yield and also by increasing the flow rate of a gaseous mixture of a raw material and a molecular oxygen-containing gas, that is, by increasing GHSV, or by increasing the concentration of raw material in the gaseous mixture. There is, however, a theoretical limit to the increasing of the yield and it is difficult to look for a significant improvement here. There is also a limit to the increasing of GHSV as it increases the cost of motive power to drive air blowers. On the other hand, increasing the concentration of raw material creates problems such as readier occurrence of incomplete reaction accompanied by increased formation of by-products, execution of the reaction in the explosive range of raw material and generation of more heat per unit volume with easier formation of the so-called hot spots, but it offers an advantage of reducing the cost of equipment and utilities.
It is an object of this invention to provide a process for vapor-phase oxidation which is capable of giving the intended product not only in high yields but also with high productivity. In case phthalic anhydride is the intended product, it is an object of this invention to provide a process for preparing phthalic anhydride not only in high yields but also with high productivity.
DISCLOSURE OF THE INVENTION
Firstly, in executing the oxidation of hydrocarbons by passing a gaseous mixture comprising of a molecular oxygen-containing gas and hydrocarbons which may contain substituents to a fixed bed of catalyst, this invention relates to a process for vapor-phase oxidation which is characterized by passing said gaseous mixture to a fixed bed of catalyst which increases by stages in void ratio in one step or more from upstream downward in the flow of said gaseous mixture. In this case, the void ratio of a catalyst layer placed most upstream or V
1
and the void ratio of a catalyst layer placed most downstream or V
2
preferably satisfy the relationship V
1
/V
2
=0.6~0.9. Moreover, in construction of the catalyst bed, a given catalyst is preferably so arranged in layers that the oxidative activity increases by stages in one step or more from upstream downward.
Secondly, in preparing phthalic anhydride by passing a gaseous mixture comprising of a molecular oxygen-containing gas and naphthalene and/or ortho-xylene to a fixed bed of catalyst, this invention relates to a process for preparing phthalic anhydride which is characterized by utilizing a catalyst containing titanium dioxide and vanadium pentoxide as principal catalytically active components and also by passing said gaseous mixture to a fixed bed of catalyst which increases by stages in void ratio in one step or more from upstream downward in the flow of said gaseous mixture.
Thirdly, this invention relates to a process for preparing phthalic anhydride wherein the aforementioned catalyst comprises a catalyst placed upstream and a catalyst placed downstream in the flow of the gaseous mixture of raw materials; the aforementioned upstream catalyst is made by depositing catalytically active components containing 75 to 90% by weight of titanium dioxide, 10 to 20% by weight of vanadium pentoxide, 1.0 to 3.5% by weight of a compound of cesium (calculated as sulfate) and 0.1 to 1.8% by weight of a compound of at least one metal selected from barium, magnesium, yttrium, lanthanum and cerium (calculated as oxide of selected metal) and showing a specific surface area of 100 to 160 m
2
/g on a nonporous inert carrier while the aforementioned downstream catalyst is made by depositing catalytically active components containing less than 0.1% by weight of a compound of alkali metal (calculated as sulfate), 75 to 90% by weight of titanium dioxide, 10 to 20% by weight of vanadium pentoxide, 1.0 to 3.0% by weight of a compound of phosphorus (calculated as oxide) and 0.3 to 2.0% by weight of a compound of at least one metal selected from tungsten, molybdenum, tin, antimony and bismuth (calculated as oxide of selected metal) and showing a specific surface area of 70 to 100 m
2
/g on a nonporous inert carrier. The upstream catalyst may contain two kinds or more of catalysts and, if such is the case, the amount of cesium preferably decreases by stages from upstream downward within the aforementioned range.
Raw material hydrocarbons with or without substituents may be any hydrocarbons as long as they are oxidized in vapor phase to yield the intended and they include benzene, alkylbenzenes, naphthalene, alkylnaphthalenes, anthracene, indene, butene and alkylpyridines with or without substituents such as halogen, hydroxyl and carboxyl.
The category of oxidation reaction includes ordinary oxidation in which oxygen increases, oxidative dehydrogenation in which hydrogen decreases and ammoxidation in which other reactions take place together with oxidation. Examples of the intended products are acid anhydrides such as phthalic anhydride, maleic anhydride and pyromellitic dianhydride, carboxylic acids such as benzoic acid and a compound such as styrene to be obtained from ethylbenzene. The process of this invention is best suited for a reaction which is primarily directed for the preparation of carboxylic acids or acid anhydrides where the heat of reaction is relatively high and the reaction is carried out on a large scale. In particular, the process is suited for a reaction which is intended for the p
Hara Tadanori
Nakamura Nobuyoshi
Birch & Stewart Kolasch & Birch, LLP
Covington Raymond
Nippon Steel Chemical Co. Ltd.
Rotman Alan L.
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