WO2015173740A2

WO2015173740A2 - A process for conjugated diene production from mixed c4 stream

Info

Publication number: WO2015173740A2
Application number: PCT/IB2015/053513
Authority: WO
Inventors: Basavaraj LONI; Vivek Kumar Srivastava; Raksh Vir Jasra; Nitin PAL; Ganesh C BASAK; Madhuchhanda MAITI; Nagesh Sharma; Laxmilal Jain
Original assignee: Reliance Industries Ltd
Current assignee: Reliance Industries Ltd
Priority date: 2014-05-13
Filing date: 2015-05-13
Publication date: 2015-11-19
Anticipated expiration: 2016-11-13
Also published as: WO2015173740A3

Abstract

The present disclosure provides a process for the preparation of butadiene from a mixed C4 feed stream comprising n-butane and n-butenes. The process involves separation of n-butane from the mixed C4 stream followed by oxidative dehydrogenation process. The water and fluid mediums are separated from the product C4 stream followed by separation of butadiene. The process of the present disclosure is cost effective, energy efficient, and provides high yield of butadiene.

Description

TITLE: A PROCESS FOR CONJUGATED DIENE PRODUCTION FROM MIXED C4 STREAM

FIELD OF DISCLOSURE

The process of the present disclosure relates to a process for producing conjugated dienes.

BACKGROUND

1,3-Butadiene, henceforth written as butadiene, is an important chemical for the petrochemical industry. Butadiene is used as a monomer in the production of a wide range of rubbers, polymers and copolymers; such as styrene-butadiene rubber (SBR), polybutadiene, styrene-butadiene latex, acrylonitrile-butadiene- styrene copolymers, nitrile rubber, styrene-butadiene block copolymers, and methyl methacrylate-butadiene-styrene copolymers. It is also used as an intermediate for the production of chemicals such as adiponitrile, hexamethylenediamine, chloroprene, 1,4-hexadiene, sulfolane and 1,5,9- cyclodecatriene.

Butadiene is produced commercially by steam cracking and by on-purpose processes such as direct oxidative dehydrogenation and catalytic oxidative dehydrogenation.

The steam cracking process has several limitations. During the steam cracking process, which is primarily used for the production of ethylene, butadiene is produced as one of the co-products. It is purified from crude C4 stream which contains butadiene, 2-methylpropene (isobutylene), n-butenes, and n-butane. The steam cracking process is a high temperature reaction and needs a large amount of energy. Further, the steam cracking process is not an independent process for producing butadiene. The investment and operation of a steam cracker cannot be optimally matched with the production and demand of butadiene. Furthermore, the yield of butadiene during the steam cracking process is low as other fractions are also produced in significant amounts. Therefore, an independent process for producing butadiene in high yield is required.

The process of producing butadiene by a direct dehydrogenation of n-butene and/or n-butane is an endothermic reactions which requires high-temperature and low-pressure reaction conditions. Further, due to thermodynamic limitation the yield of butadiene is low during the direct dehydrogenation. Thus, this process is not economically viable as a commercial process.

The catalytic oxidative dehydrogenation of n-butenes involves a reaction of n- butenes with an oxidant such as air or oxygen and steam to produce butadiene and water. The catalytic oxidative dehydrogenation process is an exothermic process which overcomes the thermodynamic limitation and provides a higher yield of butadiene even at low reaction temperature and normal pressure in contrast to the direct dehydrogenation process. Therefore, the process of producing butadiene using the catalytic oxidative dehydrogenation of n-butene is an effective independent commercially viable process capable of satisfying the increasing demand for butadiene. This process is also be used when a C4 mixture includes impurities such as n-butane. A cheap surplus C4 fraction such as a C4 raffinate mixture or a crude C4 mixture can be used as a feed and converted into a high value-added product by this process. However, side reactions taking place during the process decreases the yield of butadiene. One such side reaction is complete oxidation of the hydrocarbons leading to combustion which takes place due to the presence of oxidants in the reaction mixture.

Thus, there is felt a need to develop a feasible catalytic oxidative dehydrogenation process for preparing butadiene from C4 mixture which suppresses the side reactions and increases the yield of butadiene.

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.

It is another object of this disclosure to provide a feasible catalytic oxidative dehydrogenation process for preparing butadiene.

It is still another object of this disclosure to provide a feasible catalytic oxidative dehydrogenation process for providing higher yields of butadiene from a mixed-C4 stream. Other objects and advantages of the present disclosure will be more apparent from the following description when read in conjunction with the accompanying figures, which are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The process of the present disclosure will now be described with the help of the accompanying drawing, in which:

Figure-1 illustrates a flow diagram for the process of the present disclosure. SUMMARY

The present disclosure provides a process for the preparation of butadiene from a mixed C4 feed stream comprising n-butane and n-butenes.

n-Butenes are separated in high yield and high purity from the mixed C4 feed stream by extractive distillation using a first solvent. The separated stream containing n-butenes is diluted with CO₂, O₂ and steam such that the concentration of combustible substances is maintained below the flammability limits. CO₂ suppresses the combustion of hydrocarbons.

The diluted stream is subjected to catalytic oxidative dehydrogenation at a temperature in the range from 200 °C to 500 °C and a pressure in the range from 1 bar to 5 bars. Butadiene produced during oxidation is separated by extractive distillation using a second solvent selected from a group consisting of hydrocarbon solvents and ionic liquids. Butadiene is produced in high yield during the process; and the solvents, fluid mediums and energy are recovered and recycled.

DETAILED DESCRIPTION

Catalytic oxidative dehydrogenation of n-butenes to butadiene is associated with low yield due to combustion of the hydrocarbons such as n-butane and n- butenes. Further, the catalytic oxidative dehydrogenation is a costly process and requires high amount of energy. Apart from this, various fluid mediums and solvents are used during this process.

In the process of the present disclosure, the yield of butadiene is increased by suppression of combustion of the hydrocarbons. Further, the solvents, the fluid mediums and energy liberated during the process are recovered and recycled. The term 'recycle' in the context of this disclosure means the waste materials or energy generated during the process is used as raw materials or energy required during the process in order to prevent wastage of the potentially useful material or energy. Recycling reduces the consumption of fresh raw materials, reduces energy usage, and reduces air pollution and water pollution.

In accordance with one aspect of the present disclosure there is provided a process for the preparation of butadiene from a mixed C4 feed stream comprising n-butane and n-butenes. The n-butenes contain a mixture of cis-2- butene and tr /w-2-butene. The process of the present disclosure involves feed preparation, oxidative dehydrogenation and separation of the butadiene produced during the oxidation. The feed preparation involves removal of n-butane from the mixed C4 feed stream. n-Butane is removed before the oxidative dehydrogenation for the following reasons. The combustion of n-butane produces CO₂ which adds to the cost of the process in the form of cost incurred for separation of CO₂. Further, the combustion of n-butane produces coke which reduces the activity of the oxidation catalyst. Furthermore, extra cost is incurred for removal the heat generated during the combustion of n-butane. Still further, the separated n- butane can be used as LPG or can be dehydrogenated to n-butenes which can be used as a feed for the oxidative dehydrogenation process.

The feed preparation step involves subjecting the mixed C4 feed stream to extractive distillation using at least one first solvent selected from the group consisting of dimethylformamide (DMF), acetonitrile (ACN), n- methylpyrrolidone (NMP), methanol and ethanol with or without water to obtain a first C4 stream solution.

The term 'extractive distillation' relates to a process of separating components having a very low relative volatility (close to 1), which makes their separation difficult by normal distillation. Extractive distillation uses a separation solvent which interacts differently with these components, thereby causing their relative volatilities to differ sufficiently such that their separation by normal distillation becomes feasible. The component with higher volatility is obtained as the top product and the component with lower volatility is obtained as the bottom product in the form of a solution.

In accordance with the embodiments of the present disclosure, the first solvent is methanol, ethanol, n-methylpyrrolidone (NMP), ACN, DMF, a mixture of

DMF and ethanol and a mixture of acetonitrile and ethanol.

In accordance with one embodiment of the present disclosure the first solvent is

DMF.

The C4 stream is separated from the C4 stream solution by applying a combination of heat and pressure to obtain a first C4 stream comprising n- butenes.

In accordance with the embodiments of the present disclosure, the amount of n- butenes extracted in the first C4 stream from the mixed C4 stream is in the range from 75 to 99.9% on mass basis.

The removal of n-butane from mixed C4 feed stream results in an increase in the partial pressure of n-butenes in the first C4 stream which help in increasing per pass conversion of the catalyst and thereby increasing the yield of butadiene. The first C4 stream comprising n-butenes is diluted with at least one fluid medium selected from the group consisting of steam, oxygen and carbon dioxide to obtain a second C4 stream comprising n-butenes.

Typically, the fluid medium used for dilution is CO₂ which suppresses the combustion reactions as well as acts as a mild oxidant. In accordance with one embodiment of the present disclosure, the fluid mediums used for dilution are steam, carbon dioxide and oxygen.

In accordance with one embodiment of the present disclosure, the ratio of the amount of carbon dioxide, the amount of oxygen and the amount of steam is 1: 1: 15 on mass basis.

During the step of diluting, the ratio of the amount of the first C4 stream and the total amount of fluid mediums is in the range from 1:5 to 1:20 on mass basis. In accordance with one embodiment of the present disclosure, the ratio of the amount of the first C4 stream and the total amount of fluid mediums used for diluting is 1:10 on mass basis.

The dilution ratio is selected such that the concentration of combustible substances does not fall in the flammability limits.

The second C4 stream comprising n-butenes is then pre-heated to a temperature less than 355 °C before feeding to the oxidation reactor.

In the oxidation reactor, the second C4 stream comprising n-butenes is subjected to oxidative dehydrogenation in the presence of an oxidative dehydrogenation catalyst to obtain a fluid C4 stream comprising butadiene. In accordance with the embodiments of the present disclosure, the oxidative dehydrogenation catalyst comprises,

(a) oxide of at least one metal in an amount ranging from 0.1 to 15 weight %; wherein the metal selected from the group consisting of group I-b metals, group II-b metals, group IV -b metals, group V-b metals, group Vl-b metals, group Vll-b metals, group VIII metals and noble metals;

(b) at least one support in an amount ranging from 30 to 96 weight %; and

(c) at least one solubilizing agent in an amount ranging from 4 to 50 weight %. In accordance with the embodiments of the present disclosure, the oxidative dehydrogenation catalyst comprises oxide of at least one metal selected from the group consisting of nickel (Ni), molybdenum (Mo), cobalt (Co), zinc (Zn), zirconium (Zr), vanadium (V), tungsten (W), rhenium (Re), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh) and iron (Fe).

In accordance with one embodiment of the present disclosure, the oxidative dehydrogenation catalyst comprises a mixture of oxides of zinc and iron.

The support of the oxidative dehydrogenation catalyst comprises at least one carrier selected from the group consisting of alumina, silica, clays, zirconia, alumina- silica, zeolite and molecular sieves.

The support of the oxidative dehydrogenation catalyst may further comprise at least one binder selected from the group consisting of aluminophosphate, psuedoboehmite, alumina, silica, clays and ludox silica solution.

The support of the oxidative dehydrogenation catalyst can be in the form of extrudates, spheres, pellets and powder.

In accordance with the embodiments of the present disclosure the reactor contains catalyst in the form of extrudates. The solubilizing agent is selected from the group consisting of ammonia solution, piperidine, pyrrolidine, morpholine, piperazine hydrate, 2- methylcyclohexyl amine, cyclohexylamine and hexamethyleneimine.

The oxidative dehydrogenation is carried out at a temperature in the range from 200 °C to 500 °C.

The oxidative dehydrogenation is carried out at a pressure in the range from 1 bar to 5 bars.

The fluid C4 stream comprising butadiene obtained from the oxidation comprises butadiene, unreacted cw-2-butenes and tr ns-2-butenes, CO₂, O₂ and water.

In accordance with the embodiments of the present disclosure the conversion of butenes to butadiene is up to 85% with selectivity up to 92%.

The oxidative dehydrogenation of butene to butadiene is an exothermic reaction. It is essential to remove the heat produced during this conversion in order to avoid combustion and thereby avoid the loss of yield. In order to remove the heat produced in the reactor, the contents of the reactor are diluted with an inert material. High temperature oil or molten salt is used as a medium for removal of heat. Further, configuration of the reactor is chosen in such a way that hot spot is not generated in the reactor.

The fluid C4 stream comprising butadiene from the oxidation has a temperature in the range from 300 °C to 400 °C. The fluid C4 stream comprising butadiene is cooled to a temperature in the range from 40 °C to 70 °C. In accordance with one embodiment of the present disclosure, the fluid C4 stream comprising butadiene is cooled to 50 °C.

The heat liberated during the above cooling process is recovered. The recovered heat is used for preheating the second C4 stream comprising n-butenes.

Water is removed from the cooled fluid C4 stream comprising butadiene followed by extractive distillation using at least one second solvent to obtain a C4 stream solution comprising butadiene; and separating the C4 stream from the C4 stream solution to obtain a predominantly gaseous C4 stream comprising butadiene.

CO₂ and water present in the oxidation reactor outlet can react together and form carbonic acid which causes corrosion of the metallurgy. To avoid this issue, water is removed from the reactor outlet stream. A flash separator is used in the process of the present disclosure to remove the condensed water from the fluid C4 stream comprising butadiene and the remaining water is removed by a molecular sieve dryer. After removal of water, the resultant C4 stream is sent to the product separation unit for removal of other fluid mediums.

The product separation unit consists of an absorber unit and a distillation section. In the absorber unit, butadiene, unreacted cw-2-butenes and trans-2- butenes, and other hydrocarbons present in the fluid C4 stream are separated by extractive distillation using a second solvent to obtain a predominantly gaseous C4 stream solution comprising butadiene. In accordance with the embodiments of the present disclosure, the second solvent is at least one selected from the group consisting of hydrocarbon solvents and ionic liquids.

In accordance with one embodiment of the present disclosure, the second solvent is hexane.

The non-hydrocarbon gases (CO₂ and O₂) separate out and are recovered from the top of the absorber unit. The top stream from absorber unit containing CO₂ and O₂ is recovered and recycled to the mixing section for mixing with the first C4 stream. The rest of CO₂ and O₂ can be purged off.

The C4 stream solution comprising butadiene in the second solvent is removed from absorber bottom and is fed to the distillation unit.

In the distillation unit, predominantly gaseous C4 stream comprising butadiene is separated from the second solvent by applying a combination of heat and pressure. The second solvent from the distillation unit is recovered and recycled to the absorber unit.

The predominantly gaseous C4 steam comprising butadiene separating from the top of the distillation unit contains butadiene along with unreacted cw-2-butenes and tr ns-2-butenes. This predominantly gaseous C4 stream solution comprising butadiene is further processed in extraction unit to recover pure butadiene.

In accordance with the embodiments of the present disclosure, the recovered solvent/s, fluid mediums and energy are recycled. In accordance with the embodiments of the present disclosure, the amount of butadiene in the predominantly gaseous C4 stream comprising butadiene ranges from 70% to 99.9% on mass basis.

In accordance with the embodiments of the present disclosure, the predominantly gaseous C4 stream comprising butadiene further contains unreacted n-butenes in an amount less than 20% on mass basis.

An exemplary embodiment of the present disclosure is provided in Figure 1. The process of the present disclosure involves feed preparation, oxidative dehydrogenation and separation of the butadiene produced during the oxidation. The feed preparation unit involves a first extractive distillation section (A) to separate n-butane from the crude C4 stream using the first solvent, a solvent recovery section (B), the mixing section (C) for diluting the first C4 stream with fluid mediums and a heater (D).

Oxidative dehydrogenation takes place in the oxidation section (E) and the fluid C4 stream comprising butadiene (12) is cooled with the help of the cooler (F), followed by removal of water with the help of the flash purifier (G) and the water recovery section (H). Separated water is sent to a water holding section (I). The resultant C4 stream is heated in the heater (J) and is subjected to the second extractive distillation with the second solvent in the absorber section (K) followed by separation of fluid C4 stream containing butadiene from the second solvent in recovery section (L). In the first extractive distillation section (A), the mixed C4 feed stream (1) is introduced and heated while the first solvent (2) is continuously introduced from the top. The first C4 stream solution comprising n-butenes (4) is obtained at the bottom of A, whereas a stream containing n-butane (3) is separated from the top of A.

The C4 stream is separated in the solvent recovery section (B) from 4 to provide the first C4 stream comprising n-butenes (6). The separated first solvent (5) is recovered and recycled to A for extractive distillation.

6 is diluted with fluid mediums [7 (CO₂) and/or 8 (O₂) and/or 9 (steam)] in mixing unit (C) to obtain a mixture (10) which is heated with a heater (D) to obtain a second C4 stream comprising n-butenes (11).

11 undergoes oxidative dehydrogenation in the oxidation section (E) to obtain a fluid C4 stream comprising butadiene (12) which is cooled with the help of the cooler (F) to obtain stream 13.

The flash purifier (G) partially removes water (14) from 13 and provide stream 15, which is sent to a water recovery section (H) that separates most of the remaining water and provides stream (18). Separated water (16) is sent to a water holding section (I). Water from I is recycled (17) to the step of diluting. The stream 18 is heated in the heater (J) to obtain the heated stream 19 which is subjected to the second extractive distillation in the absorber section (K). The second solvent (20) is continuously fed to K. The second solvent separates the hydrocarbons and provides the C4 stream solution comprising butadiene in the second solvent (22) in K. A stream containing the non-hydrocarbon gases such as CO₂ and O₂ (21) is obtained at the top of K. 21 is recovered and recycled to C for the step of diluting.

L separates the C4 stream from 22 and provides predominantly gaseous C4 stream comprising butadiene (23). The second solvent (24) is recovered and recycled to for extractive distillation in K.

The recovered first solvent (5) and recovered second solvent (24), recovered water (16) as well as recovered non-condensable gases (21) are recycled during the process of the present disclosure.

The present disclosure is further described in light of the following examples which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure.

Example 1:

Separation of n-butane from mixed C4 stream by extractive distillation

A mixed C4 feed stream was subjected to extractive distillation at 10000 Kg/h. Extractive distillation was carried out using different solvents. The results are provided herein below in Table 1.

Table 1: Results of the extractive distillation of mixed C4 feed stream with different solvents

Solvent Methanol Ethanol NMP Acetonitrile DMF DMF Acetonitrile

(92%) + (92%) +

Ethanol Ethanol (8%) (8%)

Solvent 30000 30000 30000 30000 30000 30000 30000 flow rate

(cum/h)

No. of 50 50 50 50 50 50 50 stages

Reflux ratio 8 8 8 8 8 8 8

(Molar)

Feed stage 24 24 24 24 24 24 24

Condenser 41.69 42 42.17 42.54 42 42 42 temp (°C)

Condenser 4 4 4 4 4 4 4

Press (Bar)

Reboiler 56.58 65.7 65.18 83.65 65.71 65.31 82.5 temp (°C)

Cond duty 2457 2391 2327 2297 2243 2244 2310

(Mcal/h)

Reboiler 2886 2908 2424 3103 2499 2512 3105 duty

Butane 51.3 60 81 97.36 98.98 98 97.1 recovery

(%)

Butene 77 80.3 90 98.6 99.4 99 99.8 recovery

(%)

Butane 51.3 60 81.2 97.4 99 98 97

Purity (%)

Butene 73 79 90.4 98.6 99.5 99 98.5

Purity (%) High recovery and high purity of n-butane and n-butenes was obtained using DMF as solvent during the extractive distillation. Excellent recovery and purity of n-butane and n-butenes was displayed by acetonitrile also.

Example 2

Oxidative dehydrogenation of the mixed-C4 feed stream was carried out in continuous flow fixed-bed reactor.

In a catalytic run, 0.05 Liter of an extruded catalyst containing oxides of zinc and iron, and alumina was charged into a tubular stainless steel reactor. The catalyst was preheated at 500 °C for 2 hours with air/oxygen stream (20 L_N/hour).

After preheating the catalyst, experiments were conducted at various feed compositions, temperatures and GHSV (gas hourly space velocity) on the basis of the mixed C4 feed stream. The C4 stream at various locations was periodically sampled and analyzed using on-line gas chromatography (GC). A flow diagram for the process of the present disclosure is shown in Figure-1. The mixed C4 feed stream was subjected to extractive distillation using DMF as a solvent. The material balance of the feed preparation unit is provided in Table 2. The stream numbers are in accordance with the flow diagram shown in Figure-1.

Table 2: Material balance of the feed preparation unit

I Feed preparation Section Stream no. 1 2 3 4 5

Temperature (°C) 25 25 41.9 65.8 208

Pressure (bar) 4 4 4 4 3.8

Vapor Fraction 0 0 1 0 0

Mass Flow (kg/h) 10000 30000 3400 36600 30004

Volume Flow cum/h 16.807 31.738 383.225 44.803 40.304

Enthalpy (Gcal/h) -2.932 -23.389 -1.722 -23.436 -20.208

Density (kg/cum) 594.987 945.226 8.872 816.909 744.445

Mass Flow kg/h

Butane 3400 3375.784 24.216 trace cis-2-butene 2600 18.016 2581.984 1.807 trans -2-butene 4000 6.199 3993.801 2.193

DMF 30000 0.001 30000 30000

By comparing of the compositions of stream- 1 and stream-4 from Table-1 it is evident that, when DMF was used as solvent, the n-butenes recovery was 99% from the mixed C4 feed stream.

DMF was separated and the first C4 stream comprising n-butenes, thus obtained, was sent to the mixing section. The second C4 stream comprising n- butenes was heated and then sent to the oxidation reactor. The composition of various streams at inlet and outlet of various parts of the mixing section and the reactor section are shown in Table-3. The stream numbers are in accordance with the flow diagram shown in Figure- 1.

Table 3: The composition of various streams at inlet and outlet of various parts of the mixing section and the reactor section

Reactor Section

Stream no. 6 7 8 (0₂) 9 10 11 12

The crude C4 feed stream containing 66% n-butenes and 34% n-butane was fed to the distillation unit. After the extractive distillation step and separation of DMF, the content of n-butane in the C4 stream reduced to less than 1% and the content of n-butenes increased to 99.6%.

The second C4 stream comprising n-butenes was converted to a fluid C4 stream comprising butadiene during oxidation; wherein 78% n-butenes were converted to butadiene. 15% of the n-butenes from the second C4 stream remained unreacted. Apart from this, water, CO₂ and 1-butene were produced during the oxidation process.

The fluid C4 stream comprising butadiene also contains unreacted cw-2-butenes and tr ns-2-butenes, CO₂ and O₂. The fluid C4 stream comprising butadiene was fed to a product separation unit consisting of an absorber unit and a distillation section. ASPEN simulation studies for separation of butadiene, cis- 2-butenes and tr /w-2-butenes, from the reactor outlet stream using hexane as the second solvent are provided herein below in Tables 4 and 5. The stream numbers are in accordance with the flow diagram shown in Figure-1.

Table 4: ASPEN simulation studies for separation of hydrocarbons from fluid stream comprising butadiene

Product Separation section

13 14 15 18 16 19 20

Temp (^UC) 50 50 50 50 50 212.7 25

Pressure bar 1.5 1 1 1 1 6 1.013

Vapor Fraction 0.494 0 1 1 0 1 0

Mass Flow kg/h 69021 19790.4 49230.5 46632.0 2598.5 46632.0 100000

Volume Flow cum/h 20049.1 20.342 31626.2 27750.7 2.68 6953.1 152.0

Enthalpy Gcal/h -166.7 -73.97 -92.19 -83.89 -9.78 -81.94 -55.01

Density kg/cum 3.44 972.8 1.557 1.68 969.5 6.7 657.6

Mass Flow (kg/h)

Butane 24.2 0.011 24.2 24.2 24.2

cis-2-butene 387.0 0.234 386.7 386.7 386.7

trans -2-butene 598.7 0.33 598.4 598.4 598.4

DMF

Water 22008.8 19410.2 2598.5 2598.5

«-hexane 100000 butadiene 4954.4 3.1 4951.3 4951.3 4951.3

Butene 167.5 0.071 167.5 167.5 167.5

co₂ 40876.3 376.3 40499.9 40499.9 40499.9

Oxygen 3.8 0.003 3.80 3.80 3.80 Table 5: ASPEN simulation studies for separation of hydrocarbons from fluid stream comprising butadiene

After the oxidative dehydrogenation and purification, a predominantly gaseous C4 stream containing 80.2% butadiene and 16.5% n-butenes was obtained. ECONOMIC SIGNIFICANCE AND TECHNICAL ADVANCEMENT

The process of the present disclosure described herein above has several technical advantages including, but not limited to, the realization of:

- a feasible catalytic oxidative dehydrogenation process for preparing butadiene from mixed-C4 feed stream comprising n-butane and n-butenes,

- higher yield of butadiene from the mixed-C4 feed stream, and

- recovering and recycling of the solvents and fluid mediums used during the process, thereby rendering the process economical and environment friendly.

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 specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment 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.

Claims

1. A process for the preparation of butadiene from a mixed C4 feed stream comprising n-butane and n-butenes, said process comprising:

a) subjecting the mixed C4 feed stream to extractive distillation using at least one first solvent selected from the group consisting of dimethylformamide (DMF), acetonitrile (ACN), n-methylpyrrolidone (NMP), methanol and ethanol with or without water to obtain a first C4 stream solution; followed by separation of the C4 stream from said C4 stream solution to obtain a first C4 stream comprising n-butenes;

b) diluting the first C4 stream comprising n-butenes with at least one fluid medium selected from the group consisting of steam, oxygen and carbon dioxide, to obtain a second C4 stream comprising n-butenes;

c) subjecting the second C4 stream comprising n-butenes to oxidative dehydrogenation in the presence of an oxidative dehydrogenation catalyst to obtain a fluid C4 stream comprising butadiene; and

d) removing water from the fluid C4 stream comprising butadiene followed by extractive distillation using at least one second solvent to obtain a C4 stream solution comprising butadiene; and separating the C4 stream from said C4 stream solution to obtain a predominantly gaseous C4 stream comprising butadiene.

2. The process as claimed in claim 1, wherein the first solvent, the second solvent and the fluid mediums are recovered.

3. The process as claimed in claim 1, wherein the n-butenes comprise cis-2- butene and trans- 2-butene.

4. The process as claimed in claim 1, wherein the amount of n-butenes extracted from the mixed C4 feed stream in the first C4 stream in step (a) is in the range from 75 to 99.9% on mass basis.

5. The process as claimed in claim 1, wherein in the diluting step (b) the ratio of the amount of the first C4 stream and the amount of fluid mediums is in the range from 1:5 to 1:20 on mass basis.

6. The process as claimed in claim 1, wherein the oxidative dehydrogenation is carried out at a temperature in the range from 200 °C to 500 °C.

7. The process as claimed in claim 1, wherein the oxidative dehydrogenation is carried out at a pressure in the range from 1 bar to 5 bars.

8. The process as claimed in claim 1, wherein the second solvent is at least one selected from the group consisting of hydrocarbons and ionic liquids.

9. The process as claimed in claim 1, wherein the second solvent is hexane.

10. The process as claimed in claim 2, further comprises a step of recycling the recovered solvents and fluid mediums.

11. The process as claimed in claim 1, wherein the amount of butadiene in the predominantly gaseous C4 stream comprising butadiene is in the range from 70 to 99.9% on mass basis.

12. The process as claimed in claim 1, wherein the predominantly gaseous C4 stream comprising butadiene further comprises unreacted n-butenes in an amount less than 20% on mass basis.

13. The process as claimed in claim 1, wherein the oxidative dehydrogenation catalyst comprises:

(a) oxide of at least one metal in an amount ranging from 0.1 to 15 weight %; wherein the metal is selected from the group consisting of group I-b metals, group Il-b metals, group IV-b metals, group V-b metals, group Vl-b metals, group Vll-b metals, group VIII metals and noble metals;

(b) at least one support in an amount ranging from 30 to 96 weight %; and

(c) at least one solubilizing agent in an amount ranging from 4 to 50 weight %, said solubilizing agent is selected from the group consisting of ammonia solution, piperidine, pyrrolidine, morpholine, piperazine hydrate, 2- methylcyclohexyl amine, cyclohexylamine and hexamethyleneimine.

14. The process as claimed in claim 13, wherein the metal is selected from a group consisting of nickel (Ni), molybdenum (Mo), cobalt (Co), zinc (Zn), zirconium (Zr), vanadium (V), tungsten (W), rhenium (Re), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh) and iron (Fe).

15. The process as claimed in claim 13, wherein the support comprises at least one carrier selected from the group consisting of alumina, silica, clays, zirconia, alumina- silica, zeolite and molecular sieves.

16. The process as claimed in claim 13, wherein the support further comprises at least one binder selected from the group consisting of aluminophosphate, psuedoboehmite, alumina, silica and ludox silica solution.

17. The process as claimed in claim 13, wherein the support is in the form of at least one form selected from the group consisting of extrudates, spheres, pellets and powder.

18. The process as claimed in claim 13, wherein the oxidative dehydrogenation catalyst is an extruded catalyst comprising a mixture of oxides of zinc and iron.