Claims:1) A process for production of butadiene comprising contacting a feed containing a heated oxidant, a diluent, super-heated steam and a hydrocarbon stream comprising n-butenes with a preheated oxidative dehydrogenation catalyst at a predetermined temperature and a predetermined gas hourly space velocity (GHSV) to obtain an oxidized product stream containing butadiene.
2) The process as claimed in claim 1, wherein the diluent is at least one gas selected from the group of carbon containing greenhouse gases consisting of methane and carbon dioxide.
3) The process as claimed in claim 1, wherein the preheating of the oxidative dehydrogenation catalyst is carried out with the help of a heated oxidant.
4) The process as claimed in claim 1, wherein the oxidative dehydrogenation catalyst is preheated to a temperature in the range of 400 ?C and 600 ?C; and the predetermined temperature is in the range of 330 ?C and 400 ?C.
5) The process as claimed in claim 1, wherein the predetermined gas hourly space velocity of the feed is in the range of 6000 per hour and 7000 per hour.
6) The process as claimed in claim 1, wherein the ratio of the amount of the hydrocarbon stream and the amount of the diluent in the feed ranges from 1:15 to 1:45.
7) The process as claimed in claim 1, wherein the oxidant is at least one selected from the group consisting of oxygen and air.
8) The process as claimed in claim 1, wherein the ratio of the amount of the oxidant and the amount of the hydrocarbon stream in the feed ranges from 0.1 to 5.0.
9) The process as claimed in claim 1, wherein the ratio of the amount of the hydrocarbon stream to the amount of the super-heated steam in the feed ranges from 1:10 to 1:100.
10) The process as claimed in claim 1, wherein the oxidative dehydrogenation catalyst comprises at least one metal oxide and at least one support; wherein the metal oxide is selected from a group consisting of zinc oxide and iron oxide; and the support is selected from a group consisting of alumina, silica and clay. , Description:FIELD
The present disclosure relates to a catalytic oxidative dehydrogenation (ODH) process for production of 1,3-butadiene in the presence of a diluent gas.
DEFINATIONS
As used in the present specification, the following words and phrases are generally intended to have the meanings as set forth below, except to the extent that the context in which they are used indicates otherwise.
The phrase “gas hourly space velocity” (GHSV) is used herein to refer to the volumetric flow rate of a feed in a reactor. GHSV is the quotient of the amount of feed entering in reactor divided by the reactor volume. The GHSV of the feed indicates the number of reactor volumes of the feed that can be treated in a unit time.
The phrase “super-heated steam” is used herein to refer to steam at a temperature higher than its vaporization (boiling) point at the absolute pressure, where the temperature is measured.
BACKGROUND
1,3-Butadiene, hereinafter referred to as butadiene, is an important industrial chemical used as a monomer in the production of synthetic rubbers such as poly-butadiene rubber (BR), styrene-butadiene (SBR), acrylonitrile butadiene styrene (ABS) and acrylonitrile butadiene (NBR).
At present, butadiene is mainly produced as a by-product of ethylene steam cracking of naphtha or gas oil feedstocks. Apart from naphtha cracking process, the catalytic oxidative dehydrogenation (ODH) of n-butenes is also an alternative “on-purpose” route to produce 1,3-butadiene from lighter feedstocks. When a hydrocarbon stream containing n-butenes is mixed with an oxidant in the presence of super-heated steam and passed over an oxidative dehydrogenation catalyst at high temperature, 2-butenes undergo dehydrogenation to produce butadiene.
During catalytic oxidative dehydrogenation, some amount of 2-butenes undergo side reactions such as cracking, complete oxidation (burning), isomerization and gets converted into unwanted or less desirable by-products such as carbon monoxide, carbon dioxide and 1-butene, which results in a lower yield of butadiene.
The art has developed and is continuing to develop a number of alternative methods for oxidative dehydrogenation process to produce butadiene in higher yield in commercial quantities. Further, it is desired that the hydrocarbon dehydrogenation produces maximum conversion of starting material into the desired product.
Since, butadiene is produced in very large amounts, even a small increase in the yield and/or selectivity of a butadiene production process leads to large economic benefits. Similarly, even a small decrease in the amount of the by-products has a significant environmental and economic effect.
Accordingly, there is felt a need to provide a process for improving the yield and selectivity of butadiene production during the catalytic oxidative dehydrogenation of a hydrocarbon feed comprising n-butenes.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a process for production of butadiene by catalytic oxidative dehydrogenation of a hydrocarbon stream comprising n-butenes in high selectivity and high yield.
Another object of the present disclosure is to provide a cost-effective process for production of butadiene by catalytic oxidative dehydrogenation of a hydrocarbon stream comprising n-butenes.
Another object of the present disclosure is to provide an environment-friendly process for production of butadiene by catalytic oxidative dehydrogenation of a hydrocarbon stream comprising n-butenes.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The process of the present disclosure relates to the use of at least one greenhouse gas as a diluent for improving the yield of butadiene during catalytic oxidative dehydrogenation of a hydrocarbon stream comprising n-butenes.
The process of the present disclosure is environment-friendly as it uses carbon-containing greenhouse gases such as methane and carbon dioxide, as diluents. The use of a diluent during the oxidative dehydrogenation process of the present disclosure led to an increase in the yield and selectivity for butadiene production from the n-butenes present in the hydrocarbon feed.
The process of the present disclosure involves contacting a feed containing a heated oxidant, a hydrocarbon stream comprising n-butenes, a diluent and super-heated steam with a preheated oxidative dehydrogenation catalyst at a predetermined temperature and a predetermined gas hourly space velocity (GHSV) to obtain an oxidized product stream containing butadiene.
The preheating of the oxidative dehydrogenation catalyst is carried out with the help of a heated oxidant. The oxidative dehydrogenation catalyst is preheated to a temperature in the range of 400 ?C and 600 ?C.
The predetermined temperature is in the range of 330 ?C and 400 ?C. The predetermined gas hourly space velocity of the feed is in the range of 6000 per hour and 7000 per hour.
The ratio of the amount of the hydrocarbon stream and the amount of the diluent in the feed ranges from 1:15 to 1:45.
The oxidant is at least one selected from the group consisting of oxygen and air. The ratio of the amount of the oxidant and the amount of the hydrocarbon stream in the feed ranges from 0.1 to 5.0. The ratio of the amount of the hydrocarbon stream to the amount of the super-heated steam in the feed ranges from 1:10 to 1:100. The oxidative dehydrogenation catalyst comprises at least one metal oxide and at least one support. The metal oxide is selected from a group consisting of zinc oxide and iron oxide. The support is selected from a group consisting of alumina, silica and clay.

DETAILED DESCRIPTION
The disclosure will now be described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The processes for the production of butadiene by catalytic oxidative dehydrogenation (ODH) of 2-butenes present in a hydrocarbon stream are associated with drawbacks such as formation of by-products leading to a lower conversion and a lower yield. It is desired that the catalytic oxidative dehydrogenation produces butadiene in commercial quantities with maximum conversion of 2-butenes to butadiene.
In the conventional catalytic oxidative dehydrogenation, a mixture of a hydrocarbon stream comprising n-butenes, an oxidant and super-heated steam is fed to a reactor. In the process of the present disclosure, the feed comprises at least one carbon-containing greenhouse gas as a diluent along with the mixture.
The carbon-containing greenhouse gas used as a diluent is selected from a group consisting of methane and carbon dioxide. Some industrial processes, such as the processes in petrochemical and refinery industry, generate these greenhouse gases in large amounts. It is desired that these greenhouse gases are used for value generation purposes instead of being liberated into the atmosphere, since the accumulation of such greenhouse gases in the earth’s atmosphere is harmful to the environment. Since, the process of the present disclosure, utilizes these carbon-containing greenhouse gases, it is environment friendly.
An aspect of the present disclosure provides a process for production of butadiene comprises contacting a feed containing a heated oxidant, a diluent, superheated steam and a hydrocarbon stream comprising n-butenes with a preheated oxidative dehydrogenation catalyst at a predetermined temperature and a predetermined gas hourly space velocity (GHSV) to obtain an oxidized product stream containing butadiene.
In accordance with the embodiments of the present disclosure, the hydrocarbon stream can be a mixed-C4 stream comprising n-butane, trans-2-butene and cis-2-butene. The 2-butenes (a mixture of trans-2-butene and cis-2-butene) undergo catalytic oxidative dehydrogenation and produce butadiene. Some amount of 2-butenes undergoes complete oxidation and produce carbon dioxide and carbon monoxide (referred to as COx). Some amount of 2-butenes also undergoes isomerization and produce 1-butene. Thus, complete oxidation and isomerization result in the formation of by-products.
An increase in the yield and selectivity for the conversion of 2-butenes to butadiene present in the hydrocarbon feed was observed, when the oxidative catalytic dehydrogenation was carried out in the presence of a carbon-containing greenhouse gas as a diluent.
It was observed that to obtain high yield and selectivity of butadiene production in the process of the present disclosure, the components of the feed are to be used in a specific proportion/ratio and the reaction parameters are to be established.
In accordance with the embodiments of the present disclosure, the oxidative dehydrogenation catalyst is preheated to a temperature in the range of 400 ?C and 600 ?C.
In accordance with one embodiment of the present disclosure, the oxidative dehydrogenation catalyst is preheated to 500 ?C.
In accordance with the embodiments of the present disclosure, the predetermined temperature is in the range of 330 ?C and 400 ?C.
In accordance with one embodiment of the present disclosure, the predetermined temperature is 345 ?C.
In accordance with another embodiment of the present disclosure, the predetermined temperature is 355 ?C.
In accordance with yet another embodiment of the present disclosure, the predetermined temperature is 365 ?C.
In accordance with still another embodiment of the present disclosure, the predetermined temperature is 385 ?C.
In accordance with the embodiments of the present disclosure, the predetermined gas hourly space velocity (GHSV) is in the range of 6000 per hour and 7000 per hour.
In accordance with the embodiments of the present disclosure, the ratio of the amount of the hydrocarbon stream and the amount of the diluent used for the catalytic ODH ranges from 1:15 to 1:45.
In accordance with one embodiment of the present disclosure, the ratio of the amount of the hydrocarbon stream and the amount of the carbon-containing greenhouse gases as a diluent is 1:26.
In accordance with another embodiment of the present disclosure, the ratio of the amount of the hydrocarbon stream and the amount of the carbon- containing greenhouse gases as a diluent is 1:30.
In accordance with yet another embodiment of the present disclosure, the ratio of the amount of the hydrocarbon stream and the amount of the carbon- containing greenhouse gases as a diluent is 1:33.
In accordance with still another embodiment of the present disclosure, the ratio of the amount of the hydrocarbon stream and the amount of the carbon- containing greenhouse gases as a diluent is 1:41.
In accordance with the embodiments of the present disclosure, the oxidant used for the catalytic ODH is at least one selected from the group consisting of oxygen and air.
In accordance with the embodiments of the present disclosure, the ratio of the amount of the oxidant and the amount of the hydrocarbon stream used for the catalytic ODH ranges from 0.1 to 5.0.
In accordance with one embodiment of the present disclosure, the ratio of the amount of the oxidant and the amount of the hydrocarbon stream is 0.7.
In accordance with another embodiment of the present disclosure, the ratio of the amount of the oxidant and the amount of the hydrocarbon stream is 0.95.
In accordance with yet another embodiment of the present disclosure, the ratio of the amount of the oxidant and the amount of the hydrocarbon stream is 1.3.
In accordance with still another embodiment of the present disclosure, the ratio of the amount of the oxidant and the amount of the hydrocarbon stream is 1.4.
In accordance with the embodiments of the present disclosure, the ratio of the amount of the hydrocarbon stream to the amount of the super-heated steam ranges from 1:10 to 1:100.
In accordance with one embodiment of the present disclosure, the ratio of the amount of the hydrocarbon stream to the amount of the super-heated steam is 1:26.
In accordance with another embodiment of the present disclosure, the ratio of the amount of the hydrocarbon stream to the amount of the super-heated steam is 1:35.
In accordance with yet another embodiment of the present disclosure, the ratio of the amount of the hydrocarbon stream to the amount of the super-heated steam is 1:54.
In accordance with still another embodiment of the present disclosure, the ratio of the amount of the hydrocarbon stream to the amount of the super-heated steam is 1:70.
In accordance with the embodiments of the present disclosure, the oxidative dehydrogenation catalyst comprises at least one metal oxide and at least one support. The metal oxide is at least one selected from a group consisting of zinc oxide and iron oxide. The support is at least one selected from a group consisting of alumina, silica and clay.
In accordance with one embodiment of the present disclosure, the oxidative dehydrogenation catalyst comprises a mixture of zinc oxide and iron oxide on alumina as support.
The diluent used during the process of the present application can be recovered and recycled.
The disclosure will now be described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The laboratory scale experiments provided herein can be scaled up to industrial or commercial scale.
Examples
The hydrocarbon stream used during the catalytic oxidative dehydrogenation of the present disclosure was a mixed-C4 feed comprising 30% n-butane; 43% cis-2-butene and 27% trans-2-butene.
Process for catalytic ODH of hydrocarbon stream
In a catalytic run, an oxidative dehydrogenation catalyst comprising an extruded mixture containing zinc oxide and iron oxide, and alumina (0.006 Liter) as support was charged into a tubular SS reactor. The catalyst was preheated at 500 ?C for 2 hours with an oxygen stream (20 LN/hour). The reactor temperature and oxygen gas flow rate was adjusted to the pre-decided reaction conditions provided herein below.
The oxygen stream was mixed with the hydrocarbon stream, super-heated steam and a diluent. The desired ratio of the hydrocarbon stream, oxygen, super-heated steam and diluent was maintained by controlling the individual gas flow rates using mass-flow controllers. The feed was continuously fed to the reactor at a desired gas hourly space velocity.
To evaluate the effect of diluents, catalytic oxidative dehydrogenation was also carried out without a diluent.
Product stream obtained from the reactor was periodically sampled and analyzed using on-line gas chromatography (GC) in FID and TCD detectors.
Conversion of 2-butenes (total amount of trans-2-butene and cis-2-butene) present in the hydrocarbon stream and selectivity of various products were calculated on the basis of carbon balance as follows:
1) Conversion of 2-butenes (total amount of trans-2-butene and cis-2-butene) = (moles of 2-butenes reacted) / (moles of 2-butenes supplied to the reactor)
2) Selectivity of 1,3-butadiene = (moles of 1,3-butadiene produced) / (moles of 2-butenes reacted)
3) Selectivity of 1-butene = (moles of 1-butene produced) / (moles of 2-butenes reacted)
4) Selectivity of COx = (moles of COx produced) / (4-moles of 2-butenes reacted)
Under the employed reaction condition the amount of n-butane present in the hydrocarbon stream remained unchanged, therefore the GC values of n-butane were not taken into consideration for calculations of the conversion and selectivity.
Example 1:
Catalytic oxidative dehydrogenation of the hydrocarbon stream was performed by the process described herein above. The catalytic oxidative dehydrogenation was carried out at 365 ?C at a total GHSV of 6300 per hour. In order to evaluate the effect of diluent, the process was carried without the use of a diluent. The results are provided below in the Table 1.
Table 1: Effect of diluent
Diluents No diluent CH¬4 as diluent CO2 as diluent
2-Butenes conversion; % 62 90 94
BD selectivity; % 81 93 90
1-Butene selectivity; % 10 4 4
COx selectivity; % 9 3 6
BD yield; % 50 84 85
BD = 1,3-butadiene, COx = total amount of carbon monoxide and carbon dioxide
It was found that, the yield and selectivity for butadiene production increased significantly in the presence of methane (CH4) and carbon dioxide (CO2) as a diluent. Further, the formation of unwanted by-products 1-butene and COx decreased.
Thus, the use of diluents resulted in higher yield and higher conversion of butadiene as compared to the process carried out without the use of a diluent.
Example 2:
To study the effect of temperature on the catalytic oxidative dehydrogenation of the present disclosure, reactions were carried out at different temperatures using methane as a diluent, by the process described herein above. The catalytic oxidative dehydrogenation was carried out at a GHSV of 6723 per hour. The results are provided in Table 2.
Table 2: Effect of reaction temperature in the presence of methane as diluent
Reaction temperature (0C) 345 355 365 385
2-Butenes conversion; % 88 89 88 87
BD selectivity; % 93 92 91 74
1-Butene selectivity; % 4 4 4 5
COx selectivity; % 3 3 4 21
BD yield; % 82 82 80 64
BD = 1,3-butadiene, COx = total amount of carbon monoxide and carbon dioxide
The yield and selectivity for butadiene production was high at 345 ?C, 355 ?C and 365 ?C. A decrease in the yield and selectivity for butadiene production was observed with a further increase in the temperature of the oxidation.
Example 3:
To study the effect of the amount of diluent on the process of the present disclosure, reactions were carried out, by the process described herein above, at different dilutions. The reactions were carried out at 365 ?C. The results are provided in Table 3.
Table 3: Effect of the amount of diluent
CH4/mixed-C4 ratio 26 30 33 41
2-Butenes conversion; % 70 73 90 85
BD selectivity; % 75 83 93 79
1-Butene selectivity; % 9 4 4 6
COx selectivity; % 17 12 3 16
BD yield; % 53 61 84 67
BD = 1,3-butadiene, COx = total amount of carbon monoxide and carbon dioxide
It was found that the yield and selectivity for butadiene production during ODH increased with increasing the dilution of the feed from 26 to 33.
Example 4:
To study the effect of the ratio of the amount of oxidant to the amount of mixed C4 stream in the process of the present disclosure, reactions were carried out at different ratios of the oxidant to the hydrocarbon stream, by the process described herein above. The reactions were carried out with an oxidant to hydrocarbon stream ratio in the range from 0.7 to 1.4 at a GHSV of 6560 per hour. The results are provided in Table 4.
Table 4: Effect of amount of oxidant
O2/mixed-C4 ratio 0.7 0.95 1.3 1.4
2-Butenes conversion; % 62 77 90 90
BD selectivity; % 78 80 93 93
1-Butene selectivity; % 10 7 4 4
COx selectivity; % 12 13 3 3
BD yield; % 48 62 84 84
BD = 1,3-butadiene, COx = total amount of carbon monoxide and carbon dioxide
It was observed that the yield and selectivity for butadiene production during catalytic ODH increased with an increase in the ratio of the amount of oxygen to the amount of hydrocarbon stream in the range from 0.7 to 1.4.
Example 5:
To study the effect of the amount of super-heated steam in the process of the present disclosure, reactions were carried out at different ratio of the amount of super-heated steam to the amount of the hydrocarbon stream. The reactions were carried out at 365 ?C. The results are provided in Table 5.
Table 5: Effect of amount of super-heated steam
Super-heated steam/mixed-C4 ratio 26 35 54 70
2-Butenes conversion; % 86 86 82 90
BD selectivity; % 82 82 83 93
1-Butene selectivity; % 5 5 6 4
COx selectivity; % 13 13 11 3
BD yield; % 71 71 68 84
BD = 1,3-butadiene, COx = total amount of carbon monoxide and carbon dioxide
It was observed that the yield and selectivity for butadiene production formation increased as the amount of the super-heated steam increased.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The process of the present disclosure described herein above has several technical advantages including but not limited to the realization of:
? a process for production of butadiene providing high yield;
? a process for production of butadiene with high conversion of 2-butenes to butadiene;
? a cost-effective process; and
? an environment-friendly process.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.