Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-02-19
2001-09-11
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S542000
Reexamination Certificate
active
06288274
ABSTRACT:
TECHNICAL FIELD
This invention relates to methods and devices for making intermediate oxidation products, and especially dibasic acids, by oxidizing a hydrocarbon under controlled conditions.
BACKGROUND OF THE INVENTION
There is a plethora of references (both patents and literature articles) dealing with the formation of intermediate oxidation products, such as for example acids, one of the most important being adipic acid, by oxidation of hydrocarbons. Adipic acid is used to produce Nylon 66 fibers and resins, polyesters, polyurethanes, and miscellaneous other compounds.
There are different processes of manufacturing adipic acid. The conventional process involves a first step of oxidizing cyclohexane with oxygen to a mixture of cyclohexanone and cyclohexanol (KA mixture), and then oxidation of the KA mixture with nitric acid to adipic acid. Other processes include, among others, the “Hydroperoxide Process,” the “Boric Acid Process,” and the “Direct Synthesis Process,” which involves direct oxidation of cyclohexane to adipic acid with oxygen in the presence of solvents, catalysts, and initiators or promoters.
The Direct Synthesis Process has been given attention for a long time. However, to this date it has found little commercial success. One of the reasons is that although it looks very simple at first glance, it is extremely complex in reality. Due to this complexity, one can find strikingly conflicting results, comments, and views in different references. It is also important to note that most studies on the Direct Oxidation have been conducted in a batch mode, literally or for all practical purposes.
There is a plethora of references dealing with oxidation of organic compounds to produce acids, such as, for example, adipic acid and/or other intermediate oxidation products, such as for example cyclohexanone, cyclohexanol, cyclohexylhydroperoxide, etc.
The following references, among the plethora of others, may be considered as representative of oxidation processes relative to the preparation of diacids and other intermediate oxidation products.
U.S. Pat. No. 5,463,119 (Kollar), U.S. Pat. No. 5,374,767 (Drinkard et al.), U.S. Pat. No. 5,321,157 (Kollar), U.S. Pat. No. 3,987,100 (Barnette et al.), U.S. Pat. No. 3,957,876 (Rapoport et al.), U.S. Pat. No. 3,932,513 (Russell), U.S. Pat. No. 3,530,185 (Pugi), U.S. Pat. No. 3,515,751 (Oberster et al.), U.S. Pat. No. 3,361,806 (Lidov et al.), U.S. Pat. No. 3,234,271 (Barker et al.), U.S. Pat. No. 3,231,608 (Kollar), U.S. Pat. No. 3,161,603 (Leyshon et al.), U.S. Pat. No. 2,565,087 (Porter et al.), U.S. Pat. No. 2,557,282 (Hamblet et al.), U.S. Pat. No. 2,439,513 (Hamblet et al.), U.S. Pat. No. 2,223,494 (Loder et al.), U.S. Pat. No. 2,223,493 (Loder et al.), German Patent DE 44 26 132 A1 (Kysela et al.), and PCT International Publication WO 96/03365 (Constantini et al.).
None of the above references, or any other references known to the inventors disclose, suggest or imply, singly or in combination, oxidation reactions to intermediate oxidation products under conditions subject to the intricate and critical controls and requirements of the instant invention as described and claimed.
Our U.S. Pat. Nos. 5,580,531, 5,558,842, 5,502,245, as well as our PCT International Publication WO 96/40610 describe methods and devices relative to controlling reactions in atomized liquids.
SUMMARY OF THE INVENTION
As aforementioned, this invention relates to methods and devices for making intermediate oxidation products, and especially dibasic acids, by oxidizing a hydrocarbon under controlled conditions. More particularly, it relates to a method of controlling the oxidation of a hydrocarbon to an intermediate oxidation product in a reaction zone, the method characterized by the steps of:
(a) contacting a gas comprising oxidant with a hydrocarbon by feeding the gas at a first flow rate, and the hydrocarbon into the reaction zone, at a first pressure, and at a first temperature adequately high to allow the oxidant to react with the hydrocarbon at a reaction rate and/or reactivity; and
(b) controlling consumption rate of the oxidant in a manner that the reaction rate and/or the reactivity is maintained within predetermined limits.
The consumption rate of the oxidant is defined as the amount of oxidant (preferably in weight units) consumed per unit of time.
According to this invention, reaction rate is defined as the molar oxidation of hydrocarbon per unit of time, and the reactivity is defined as the reaction rate divided by the total volume of non-gaseous mixture involved in the reaction. Also, according to this invention, reference to controlling or maintaining the reaction rate or the reactivity within a desired range, includes the case of controlling and/or maintaining both the reaction rate and the reactivity within desired ranges.
An intermediate oxidation product is defined as an oxidation product of a hydrocarbon, which is different than carbon monoxide or carbon dioxide.
The reaction rate may be determined very accurately, in a continuous reactor for example, by subtracting the amount of hydrocarbon exiting the system per unit of time from the hydrocarbon entering the system per unit of time. Depending on the configuration of a reactor system or device, amounts of hydrocarbon entering or exiting the system per unit time may be either known facts or facts, or may be determined by chemical analysis and stream flow rate data, or may be a combination of both. This type of information may be easily processed by a controller so that a predetermined program may be followed, as explained in detail hereinbelow.
The oxidant consumption rate may be arbitrarily considered as a variable proportional to the reaction rate, and/or as a variable proportional to pressure drop rates or proportional to differences of incoming and outgoing gas flows, or proportional to differences of incoming and outgoing oxidant flows, or proportional to differences of incoming and outgoing hydrocarbon flows, as described below.
In one embodiment of this invention, the consumption rate of the oxidant is determined by the difference of oxidant entering the reaction zone and oxidant leaving the reaction zone per unit of time. The consumption rate of the oxidant may also be indirectly determined by the difference of hydrocarbon entering the reaction zone and hydrocarbon leaving the reaction zone per unit of time.
It is evident that in all cases, matter recycled to the reaction zone has to be taken into account for determining consumption rates, reaction rates, reactivity, etc.
In another embodiment, the consumption rate of the oxidant is determined by conducting at least one step of the following, after stopping gas feed into the reaction zone and after stopping the removal of non-condensible off-gases from the reaction zone:
(i) determining the time it takes for the oxidant contained in the reaction zone to cause a reaction in a manner that the reaction zone attains a predetermined second pressure, lower than the first pressure; and
(ii) allowing the oxidant to cause a reaction, and measuring the pressure drop within a predetermined interval of time.
It is important that the oxidant is allowed to continue reacting, for example by being brought in contact with the hydrocarbon.
In still another embodiment, the consumption rate of the gaseous oxidant is determined by the difference between the first flow rate (flow rate of the incoming gases) and the flow rate of non-condensible off-gases.
The consumption rate of the oxidant may be controlled by regulating a variable selected from a group consisting of temperature, pressure, partial pressure of oxidant, flow rate of oxidant, sparging rate, recycled gas flow rate, flow rate of hydrocarbon, flow rate of solvent, flow rate of catalyst, flow rate of water, flow rate of initiator or promoter, and a combination thereof. Flow rates of the miscellaneous components determine the concentration of said components in the reaction zone, for all practical purposes. Thus, the consumption rate of the oxidant may also be controlled by determining a
Aldrich Sharon M.
Dassel Mark W.
DeCoster David C.
Rostami Ader M.
Vassiliou Eustathios
Geist Gary
Oh Taylor
RPC Inc.
Seed Intellectual Property Law Group PLLC
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