The present disclosure relates to a "hybrid" process for the production of conjugated dienes from a low valued feedstock.

More particularly, the present disclosure relates to a "hybrid" process for the production of 1 ,3 butadiene (BD) from a feed containing C ₄ hyrocarbon/s.

BACKGROUND

In petrochemical industries 1,3-Butadiene is an important raw material for the production of a range of valuable materials and chemicals like polybutadiene rubber, styrene-butadiene rubber etc. which find applications mostly in the automobile industries.

The primary source of Butadiene is steam cracking of liquid hydrocarbons which produces Butadiene as a byproduct. Commercially, Butadiene is produced as a byproduct during the production of ethylene from naptha cracking. In the present scenario there is an increased demand of Butadiene end products like rubber etc. However, the traditional Butadiene production route is incapable of satisfying the demand of Butadiene. This eventually increases the price of Butadiene. On the other hand, the shift of new and forthcoming refineries from catalytic to steam cracking, which give lower yields of C ₄ s also results in reduction of Butadiene supply. Due to such uncertainty of Butadiene supply, the Butadiene price fluctuates significantly.

Therefore, it is highly desirable to develop a dedicated "on-purpose" process for the production of Butadiene to meet the global market demand and supply as well as to have stable global Butadiene price.

The catalytic oxidative dehydrogenation (ODH) process provides an excellent platform for producing a variety of alkene and alkadienes from low-valued corresponding alkanes and alkenes. The n-butene olefin stream is also a valuable chemical and is useful for production of other higher value chemicals. Thus, there is also a need to find a process that can economically convert alkanes to alkenes.

Some methods suggest use of olefin as a feedstock for the preparation of conjugated dienes, however olefins being high value chemical compound, its availability and cost proposition becomes the hurdle.

Further, the Catadiene process claims production of BD from n-butane in two-step process. The Catadiene process suffers from frequent regeneration due to coking problems due to the high temperature operation. This frequent regeneration also mandates high capex investment due to utilization of multiple reactors. In view of the above, there is felt a need for a process for the production of conjugated diene such as butadiene from the low valued feedstock such as n- butane, which is highly selective and which does not compromise with the quality of the final diene product.

OBJECTS

Some of the objects of the present disclosure are discussed herein below:

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 an object of the present disclosure to provide an economic process for production of conjugated diene.

It is another object of the present disclosure to provide a process of production of conjugated diene which employs easily and abundantly available feed stock.

It is still another object of the present disclosure to provide a process for the production of 1, 3 butadiene.

It is yet another object of the present disclosure to provide a cost effective and energy efficient process for the production of 1, 3 butadiene. It is still another object of the present disclosure to provide high yielding process for the production of 1 , 3 butadiene.

It is a further object of the present disclosure to provide high purity 1, 3 butadiene.

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.

SUMMARY

The present disclosure provides a process for preparing 1,3 -butadiene; said process comprising the following steps:

- dehydrogenating a feed containing at least one C ₄ hydrocarbon in the presence of at least one pincer ligated iridium catalyst and at least one hydrogen acceptor in a non-reactive medium at a temperature in the range of fOCPC* to 250°C to obtain a first stream comprising a mixture of at least one butene, 1, 3 -butadiene and unreacted C ₄ hydrocarbon;

- separating 1,3 -butadiene from said stream to obtain a second stream comprising a mixture of at least one butene and unreacted C ₄ hydrocarbon; and - oxidative ^" dehydrogenating said second stream in the presence of at least one dehydrogenating agent arid at least one catalyst to obtain 1,3 -butadiene.

The C ₄ hydrocarbon can be n-butane.

Typically, the hydrogen acceptor is at least one selected from the group consisting of t-butyl ethylene, norbornene, isobutylene and diisobutylene.

Typically, the non-reactive medium is at least one selected from the group consisting of mesitylene, 1,2,4,5-tetramethylbenzene and 2,2,4,4,6,6,8,8- octamethylnonane.

Typically, the pincer ligated iridium catalyst is a compound of formula I or II;

(I)

Wherein A = 0, CH ₂ or a combination of 0 and CH ₂

R' = H, MeO and NR2,

R = tert-butyl, isopropyl, cylopentyl and cyclohexyl ,

n = 0 to 4,

X = halogen, and m= 0 to 2.

Typically, the catalyst is selected from the group consisting of bismuth molybdenum based oxide catalysts, ferrite based catalysts, pyrophosphate-based catalysts, vanadium-based catalysts, metal catalysts and mixtures thereof.

Typically, the catalyst is an extruded mixture containing oxides of zinc, iron and aluminium.

Typically, the oxidative dehydrogenation is carried out a temperature ranging from 350 to 450°C.

Typically, the ratio of the pincef ligated iridium catalyst to~ said feed ranges from 1 :1000 to 1 : 10000.

Typically, the ratio of the hydrogen acceptor to the feed ranges from 2: 1 to 1 :3.

Typically, the ratio of the non-reactive medium to said feed ranges from 1 :1 to 1 :5.

Typically, the dehydrogenating agent is at least one selected from the group consisting of air, oxygen and C0 ₂ .

Typically, the separation of 1,3 -butadiene is carried out by extractive distillation. The process also includes a step of recovering and recycling at least one component selected from the group consisting of un-reacted C ₄ hydrocarbon, butene and catalyst.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

FIGURE 1 illustrates a schematic diagram of an apparatus for the production of 1,3 butadiene by selective dehydrogenation of C ₄ hydrocarbons; and

FIGURE 2 illustrates separation of 1,3 butadiene (BD).

DETAILED DESCRIPTION:

The present disclosure provides a simple and high yielding process for preparing

1,3 -butadiene from a feed containing at least one C ₄ hydrocarbon. The process involves two stage dehydrogenation of a feed using a combination of two types of catalysts, i.e. homogeneous catalyst and heterogeneous catalyst.

The present disclosure provides a "hybrid process" for the production of 1,3 butadiene (BD) from C ₄ hydrocarbon feed such as n-butane at low temperature using dehydrogenation homogeneous catalyst. C ₄ hydrocarbon feed (n-butane) is converted to olefin stream such as n-butenes and/or BD. Thus produced olefin stream was subjected to conjugated diene (BD) separation, if produced, before subjecting to oxidative dehydrogenation (ODH) reactor containing heterogeneous catalyst along with other gases e.g. oxidants and diluents at elevated temperature. The outlet stream of ODH reactor contains high yield of BD with unreacted n- butenes which can be recycle back.

The process involves the following steps:

In the first step, a feed containing at least one C ₄ hydrocarbon is dehydrogenated in the presence of at least one pincer ligated iridium catalyst and at least one hydrogen acceptor in a non-reactive medium at a temperature in the range of 100°C to 250°C to obtain a first stream comprising a mixture of at least one butene, 1,3- butadiene and unreacted C ₄ hydrocarbon.

In one embodiment the C ₄ hydrocarbon employed is n-butane.

In accordance with the present disclosure the hydrogen acceptor includes but is not limited to t-butyl ethylene, norbornene, isobutylene, diisobutylene and combinations thereof and the non-reactive medium is selected from the group consisting of mesitylene, 1,2,4,5-tetramethylbenzene, 2,2,4,4,6,6,8,8- octamethylnonane and combinations thereof.

The homogeneous catalyst employed for the first stage dehydrogenation is a pincer ligated iridium catalyst represented by a compound of formula I or II;

δ

(I)

Wherein A = O, CH ₂ or a combination of O and CH ₂

= H, MeO and NR2,

R = tert-butyl, isopropyl, cylopentyl and cyclohexyl ,

n = 0 to 4,

X = halogen, and

m= 0 to 2.

In accordance with the present disclosure the ratio of the pincer ligated iridium catalyst to said feed ranges from 1: 100.0 to 1 :10000; the ratio of the hydrogen acceptor to the feed ranges from 2: 1 to 1 :3; and the ratio of the non-reactive medium to said feed ranges from 1 : 1 to 1 :5.

1,3 -butadiene formed is then separated from the stream to obtain a second stream comprising a mixture of at least one butene and unreacted C ₄ hydrocarbon. In one embodiment the separation of 1,3 -butadiene is carried out by extractive distillation.

In the next step, the obtained second stream is subjected to oxidative dehydrogenation in the presence of at least one dehydrogenating agent and at least one catalyst to obtain 1,3-butadiene. The oxidative dehydrogenation is carried out a temperature ranging from 350 to 450°C. The heterogeneous catalyst employed for the second stage dehydrogenation is selected from the group consisting of bismuth molybdenum based oxide catalysts, ferrite based catalysts, pyrophosphate-based catalysts, vanadium-based catalysts, metal catalysts and mixtures thereof.

In accordance with the present disclosure the catalyst employed in oxidative dehydrogenation is an extruded mixture containing oxides of zinc, iron and aluminium.

The dehydrogenating agent employed is selected from the group consisting of air, oxygen, C0 ₂ and a combination thereof.

The process also includes a step of recovering and recycling at least one component selected from the group consisting of un-reacted C ₄ hydrocarbon, butene and catalyst.

A process for production of conjugated diene, particularly 1, 3 butadiene in accordance with the present disclosure will now be explained in relation to the accompanying drawing, in which:

FIGURE 1 illustrates a schematic diagram of an apparatus for the production of 1,3 butadiene by selective dehydrogenation of C ₄ hydrocarbons. In Figure 1 the following reference numerals have been used to designate the elements mentioned alongside.

10: C ₄ hydrocarbon stream;

12:catalyst and solvent;

14: mixer;

16: first feed;

18: first reactor;

20: first mixture;

22: first separator;

23: gaseous mixture;

26: second separator;

28: second mixture;

30: drum;

32: fourth mixture;

36: gas mixer;

2: steam mixer;

44: steam;

6: second feed;

48: second reactor;

50: third mixture;

52: third separator; 54: water;

56:water collection;

58: mixture of air and C0 ₂ ;

60: air and C0 ₂ recycle drum;

62: air and C0 ₂ recycle stream;

64: solvent for extraction;

66:1, 3 -butadiene;

68:1, 3 -butadiene; and

70: crude 1, 3-butadiene.

The process for the production of butadiene is described herein below:

In the first step, C ₄ hydrocarbon stream 10 is mixed with at least one homogenous catalyst (pincer ligated iridium catalyst), at least one hydrogen acceptor and at least one inert vehicle (non-reactive medium) by means of a mixer 14 to obtain a first feed 16. Typically, hydrocarbon includes but is not limited to butane, 1-butene, trans-2-butene and cis-2-butene and mixtures thereof.

The first feed 16 is then introduced into a first reactor 18 wherein C ₄ hydrocarbon reacts with homogeneous catalyst at a temperature of 100°C to 250°C to obtain a first mixture/stream 20 containing 1,3 butadiene, at least one monoene, a homogenous catalyst and inert vehicle. Typically, the monoenes include but are not limited to 1-butene, trans-2-butene and cis-2-butene. The first mixture 20 may further comprise unreacted C ₄ hydrocarbons. The homogenous catalyst and inert vehicle present in the first mixture 20 are separated in a first separator 22 to obtain a gaseous mixture 23 containing 1, 3 -butadiene and at least one monoene. The gaseous mixture 23 may further comprises traces of the unreacted C ₄ hydrocarbons.

The gaseous mixture 23 is then fractionated using a solvent stream 64 by means of a second separator 26 into 1, 3-butadiene 66 and a second mixture/stream 28 containing at least one monoene and the unreacted C ₄ hydrocarbons. The second mixture 28 is then mixed with air and carbon dioxide (C02) in a gas mixer 36 and subsequently subjected to a steam mixer 42 to obtain a second feed 46. The steam mixer 42 is adapted to receive a steam 44.

In the second step, the second feed 46 containing monoene/s such as 1-butene, trans-2-butene, cis-2-butene and optionally, comprising unreacted C ₄ hydrocarbons undergoes oxidative dehydrogenation in the presence of air, carbon dioxide (C02) and at least one heterogeneous catalyst to obtain a third mixture 50 containing 1, 3- butadiene, at least one monoene and unreacted C ₄ hydrocarbons along with impurities of air and carbon dioxide. The abovementioned step of oxidative dehydrogenation of the second feed 46 is carried out in a second reactor 48. In one embodiment of the present disclosure the second reactor 48 is a fixed bed reactor.

The third mixture 50 is then introduced into a third separator 52 in order to separate crude 1, 3-butadiene 70, a mixture of air and C0 ₂ 58 and water 56. The crude 1, 3-butadiene 70 containing traces of unreacted C ₄ hydrocarbons and monoenes is then transferred to a second separator 26 in order to fractionate 1, 3- butadiene 66 and a fourth mixture 32 containing traces of unreacted C ₄ hydrocarbons and at least one monoene.

The fourth mixture 32 is recycled into a drum 30 and transferred into 36 via 34. The fractionated air and C0 ₂ 58 is collected in recycled drum 60. The air and C0 ₂ 62 is further recycled to steam mixer 42.

The details of the disclosure will further be explained by the way of examples which do not limit the scope of the disclosure.

Example 1: 50 ml Mesitylene and 80 ml t-butylethylene (TBE) and 125 mg of catalyst A were added to a 300 ml PARR reactor in the glove box. The reactor was brought out and 85 g of n-butane was charged into the reactor while cooling the reactor to -70 °C. The reaction mixture was heated to 190 °C under stirring for 2hours. Then the reaction mass was cooled and vented into a pressure vessel and about 84.8 g of the gas was collected. Analysis of the gas by GC showed the following composition.

The resultant mixture/gas was used as a feed for next stage of the reaction.

Example 2: 72 gm of t-butylethylene, 375 mg of pincer ligated catalyst A were mixed together in presence of 15 ml of mesitylene into a 300 ml PARR reactor. 25 gm of n-butane was charged into the mixture. The mixture was then heated at 190 °C for 24 hours. Then the reaction mass was cooled and vented into a pressure vessel and about 24.9 g of the gas was collected. Analysis of the gas by GC showed the following composition.

Component Percentage n-butane 36.8

trans-2 butene 32.6

1-butene 6.9

cis-2 butene 17.7

1 ,3 butadiene 6.0

Example 3:

The outlet stream of Example 2 was subjected to for BD (butadiene) separation. The schematic representation for the same is illustrated in figure 2, wherein

102: C ₄ feed; 104:NMP (N-methylpyrrolidone); 106 -.butane extractive distillation; 108: 2-butene + 1-butene + butadiene; 110: 2- butene extractive distillation; 112: 1-butene + butadiene; 114: 1-butene extractive distillation; and 1 16:butadiene.

The compositions of the streams (1-4) are provided herein below:

Example 4:

The outlet feed of Example 1 and Example 3 are feedstock for oxidative dehydrogenation (ODH) reactor. The oxidative dehydrogenation reaction of C ₄ feed was conducted by using an extruded catalyst comprising a mixture of oxides of zinc and iron with a binder selected from the group consisting of alumina, silica, clays or combinations thereof, and air/oxygen, C0 ₂ and steam.

Oxidative dehydrogenation of C ₄ feed to 1,3-Butadiene was carried out in a continuous flow fixed-bed reactor. In a catalytic run, 0.05 Liter of an extruded mixture containing oxides of zinc and iron, and aluminum was charged into a tubular SS (stainless steel) reactor. The catalyst was preheated at 500°C fpr 2hrs with air/oxygen stream (20 L _N /hour). A superheated steam was prepared from water by passing it through a pre-heated zone (at 180°C) and was continuously fed into the reactor together with C ₄ feed, air/oxygen and carbon dioxide. Air was used as an oxygen source and nitrogen present in air served as a carrier gas. Experiments were conducted at various feed compositions, temperatures and GHSV (gas hourly space velocity) on the basis of C ₄ feed. Reaction products were periodically sampled and analyzed using on-line gas chromatography (GC). Conversion of C ₄ feed and selectivity of various products were calculated on the basis of carbon balance as described below. Yield of 1,3-Butadiene was calculated by multiplying conversion and selectivity. Conversion of 1-butene = (moles of C ₄ feed such as normal-butane, 1-butene, trans-2-butene, cis-2-butene and a mixture of thereof reacted)/(moles of C ₄ feed such as normal-butane, 1-butene, trans-2-butene, cis-2-butene and a mixture thereof supplied)

Selectivity of 1,3-Butadiene = (moles of 1,3-Butadiene formed)/(moles of C ₄ feed such as normal-butane, 1-butene, trans-2-butene, cis-2-butene and a mixture thereof reacted)

Selectivity of 2-butenes = (moles of 2-butenes formed)/(moles of C ₄ feed such as normal-butane, 1-butene, trans-2-butene, cis-2-butene and a mixture thereof reacted)

Selectivity of carbon dioxide = (moles of carbon dioxide)/(moles of C ₄ feed such as normal-butane, 1-butene, trans-2-butene, cis-2-butene and a mixture thereof reacted)

Auto-generated reaction Pressure

(maximum) 1.8 kg/cm ²

Results

Values

Reaction temperature °C 372

% average conversion of 70

2-Butenes

% Selectivity of 1,3- 90

Butadiene

% yield of 1,3 -Butadiene 63

% Selectivity of COx 10

*GHSV: Gas Hourly Space Velocity; NTP: Normal temperature and pressure

Technical advance:

• The present disclosure provides hitherto unknown a hybrid process which involves dehydrogenation of n-butane to olefin stream rich with n-butenes and /or BD using a homogeneous catalyst at mild reaction temperature.

• The produced olefin stream is subjected to BD separation, if produced.

• The olefin stream after BD separation is subjected to oxidative dehydrogenation (ODH) reactor containing a heterogeneous catalyst along with other gases for e.g. oxidants and diluents at elevated temperature.

• The present disclosure provides highly selective process for the production of 1 ,3 butadiene from low valued feed stock such as n-butane. 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 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 foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.