1 ,3-BUTADIENE

Description

The present invention falls within the scope of the production of 1 ,3-butadiene from a mixture of unsaturated hydrocarbons having from 2 to 10 carbon atoms (described as “C2-C10 unsaturates” in this text), preferably unsaturated hydrocarbons having 4 carbon atoms (described as“C4 unsaturates” in this text), or mixtures of saturated and unsaturated hydrocarbons having from 2 to 10 carbon atoms (described as“mixtures of saturated and unsaturated C2-C10” in this text), preferably saturated and unsaturated hydrocarbons having 4 carbon atoms (described as“mixtures of saturated and unsaturated C4” in this text) originating from cracking plants that are either stand-alone, or incorporated into a selective extraction plant or the entire cycle for the utilization of said hydrocarbons.

The present invention relates in particular to a dual catalyst composition which can be used in the process for the production of 1 ,3-butadiene.

The present invention may advantageously be applied where there is an existing butadiene extraction plant or where such plant is newly constructed.

In the present patent application, by the term Raffinate 1 or extraction raffinate is meant the resulting mixture after the starting materials have been treated with solvent for the extraction of 1 ,3-butadiene.

In the present patent application all the operating conditions described in the text are to be understood as preferred conditions, even if not expressly stated.

For the purposes of this description the term“comprises” or“includes” also comprises the terms“consists of” or“essentially consists of“.

For the purposes of the present description definitions of intervals always comprise the end members unless specified otherwise.

Throughout the world more than 95% of butadiene is currently obtained industrially through extractive distillation of the hydrocarbon fraction having four carbon atoms (C4 butanes) produced in steam crackers. As an alternative, commercial processes for the dehydrogenation of butanes (CB & I Lummus Technology’s Catadiene™ process) or C4 olefins (Texas Petrochemicals’ Oxo-DTM process), with subsequent extractive distillation of the effluent obtained. A description of the various technologies mentioned is included in Perp Report Nexant Chem Systems: On-Purpose Butadiene, PERP 2012S3.

Any isobutene present in the C4 charge is almost inert with regard to dehydrogenation to 1 ,3-butadiene and is generally separated out by esterification of ethanol or methanol to obtain ETBE or MTBE. No applications providing for its conversion to butadiene are known.

The production of butadiene by extractive distillation has as its intrinsic limit the availability of the charge of saturated and unsaturated C2-C10 hydrocarbons, in particular saturated and unsaturated hydrocarbons having four carbon atoms (C4) originating from the cracking furnaces. Butadiene yields depend on the operating conditions of the cracking process, which is generally optimized for the production of lighter olefins.

Furthermore, except in special contexts, dehydrogenation technologies are economically uncompetitive in comparison with selective extraction of the C4 hydrocarbons fraction from cracking and are only capable of converting linear C4 compounds. In all the cases known in the state of the art isobutene cannot be converted into butadiene and has to be separated out using a dedicated process, with not always acceptable economic returns, or are isomerized to linear C4 hydrocarbons before being fed to a dehydrogenation plant for the production of 1 ,3-butadiene.

The article“Dehydroisomerization of n-Butane over Pt-ZSM5 (I): Effect of the metal loading and acid site concentration” by the authors G.D. Pirngruber, K. Seshan, J.A. Lercher (Journal of Catalysis 186, 188-200, 1999) describes the dehydroisomerization of n-butane to isobutene on Pt-ZSM5 catalyst in which the Pt concentration ranges from 0.1 to 1 % and the Si/AI ratio is 480, 125 or 80.

The article“Catalytic dehydroisomerization of n-alkanes to isoalkenes” by the authors Xuebing Li, Enrique Iglesia (Journal of Catalysis 255 (2008) 134-137) describes the dehydrogenation of C2-C4 alkanes, in particular n-pentane, on Pt/Na-[Fe]ZSM-5 catalyst. Patent GB 2246524 describes a catalyst for the production of isobutene via the dehydroisomerization of n-butane. The catalyst comprises a solid support of porous gamma-alumina on the surface of which catalytic quantities of Pt, silica and optionally Sn and/or In are deposited as promoters. In a preferred embodiment said catalyst is used with a second catalyst comprising Boralite B or a granular support of porous gamma- alumina on the surface of which silica is deposited. Tin is present in quantities ranging from 0.1% to 1% by weight, indium is present in quantities ranging from 0.05% to 1%. Platinum/indium ratios by weight range from 0.3:1 to 1.5:1. Platinum/tin ratios range from 0.5:1 to 2:1.

The Applicant has identified a dual catalyst composition capable of simultaneously promoting both isomerization of the chains of saturated and unsaturated hydrocarbons, having from 4 to 10 carbon atoms (C4-C10), including when mixed, preferably saturated and unsaturated hydrocarbons having from 4 to 6 carbon atoms (C4-C6), more preferably isobutene, including when mixed, in such a way that the branched isomers are converted into hydrocarbons having a linear structure, and dehydrogenation of the saturated and unsaturated linear hydrocarbons having from 2 to 10 carbon atoms (C2-C10), including when mixed, preferably saturated and unsaturated hydrocarbons having 4 carbon atoms (C4), including when mixed, to form 1 ,3-butadiene. Said dual catalyst composition comprises a component with acid moiety and a component with dehydrogenating moiety mechanically mixed or chemically bound together in a dual way.

When the catalyst composition is a mechanical mixture the active part having acid moiety and the active part having dehydrogenating moiety are located on separate catalyst elements, typically separate catalyst particles.

When the components of the catalyst composition, which is the subject matter of the present patent application are chemically bound it is meant that the active part having acid moiety and the active part having dehydrogenating moiety are located on the same element.

In the latter case the active parts may either interact physically or establish bonds of the ionic type.

The dual catalyst composition described and claimed in the present patent application is very active, mechanically strong, and is suitable for operating with short contact times in fluidized bed or moving bed reactors, and in particular in reactors of the“Fast Riser Reactor” type which are more suitable for operating at shorter residence times to minimize parasitic reactions.

The object of the present patent application thus constitutes a dual catalyst composition comprising:

a component with acid moiety selected from oxides and mixed oxides of aluminum, preferably selected from aluminosilicates, aluminum oxides or zeolites;

a component with dehydrogenating moiety selected from oxides of a metal of Group IMA or IVA in the Periodic Table, said oxides having added noble metals belonging to Group VIIIB of the Periodic Table in a quantity ranging from 20 ppm to 500 ppm, preferably from 30 ppm to 200 ppm, more preferably from 30 ppm to 180 ppm, even more preferably from 30 ppm to 150 ppm of metal with respect to the total composition;

a support.

A further object of the present invention constitutes a process for the production of 1 ,3- butadiene from mixtures of unsaturated hydrocarbons having from 2 to 10 carbon atoms, or mixtures of saturated and unsaturated hydrocarbons having from 2 to 10 carbon atoms, said process comprising the following stages:

a) feeding C2-C10 unsaturated compounds or mixtures of saturated and unsaturated C2-C10 compounds, possibly coming from steam cracking or from petrochemical industry processes or refining processes, to an extractor;

b) extracting a final product containing 1 ,3-butadiene and an extraction raffinate

referred to as Raffinate 1 in this text, by extractive distillation in an extraction unit; c) subsequently to step (b), mixing Extraction Raffinate 1 with a reaction inert and sending such mixture to a non-oxidative isomerization and dehydrogenation reaction unit placed downstream of the extraction unit, wherein the mixture is simultaneously subjected to a non-oxidative dehydrogenation reaction and an isomerization reaction in a single-stage in the presence of a dual catalyst composition so as to form a reaction effluent containing from 4% to 25% by weight of 1 ,3-butadiene and possibly from 40% to 90% by weight of a mixture of unreacted unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain or a mixture of unreacted saturated and unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain, so as to form a stream of unreacted hydrocarbons containing unsaturated and saturated hydrocarbons having from 2 to 10 carbon atoms in the chain;

d) then sending the reaction effluent to a physical separation section to separate the following streams:

• the reaction inert,

• a stream of unreacted hydrocarbons containing unsaturated and saturated hydrocarbons having from 2 to 10 carbon atoms in the chain,

• a stream containing from 13% to 30% by weight of 1 ,3-butadiene, and

possibly a mixture of unreacted unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain or a mixture of unreacted saturated and unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain; e) recirculating said stream containing from 13% to 30% by weight of 1 ,3-butadiene to the extraction unit, without further and subsequent reaction or conversion stages, feeding it to the extraction unit;

f) possibly recirculating said mixture of unreacted unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain or a mixture of unreacted saturated and unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain directly to the non-oxidative isomerization and dehydrogenation unit.

The catalyst composition constituting the subject matter of the present patent application is very active, non-toxic, and is used in a fluidized bed or“fast-riser” type reactor; it also performs the function of a heat transfer agent. In this way it supports the endothermic nature of the non-oxidative dehydrogenation reaction, which can thus maintain itself thermally, doing without auxiliary furnaces external to the plant. Through this aspect it overcomes the critical factor in present commercial technologies.

One special feature of Fast Riser reactor technology comprises continuous catalyst regeneration as reaction volumes reduce, for the same productivity, at the same time avoiding the safety problems associated with air-hydrocarbon mixtures, in that regeneration of the catalyst system takes place in an operating unit, which is suitably intended for regeneration.

Use of the dual catalyst composition which is the subject matter of the present invention makes it possible to overcome the constraints associated with the methods for the supply of butadiene at present in existence, due essentially to the availability of light olefins originating from naphtha-fed steam cracking, and increasing 1 ,3-butadiene recovery from the same available unsaturated and saturated C2-C10 hydrocarbons, also converting the saturated and unsaturated hydrocarbons containing 4 to 10 carbon atoms, and in particular isobutene, which would otherwise be intended for other markets, into 1 ,3- butadiene. The addition of a section downstream from extractive distillation in which an isomerization reaction and a non-oxidative dehydrogenation reaction take place simultaneously in a single stage makes it possible to maximize 1 ,3-butadiene yield, through converting saturated and unsaturated hydrocarbons containing 4 to 10 carbon atoms, in particular isobutene, into linear isomers and at the same time dehydrogenating these non-oxidatively into 1 ,3-butadiene.

The dual catalyst composition described and claimed in this text makes it possible to bring about the conversion of all unsaturated and saturated C2-C10 hydrocarbons (which may originate from steam cracking, petrochemical industry processes or refining processes) into 1 ,3-butadiene in a single stage, thus maximizing 1 ,3-butadiene yields, with overall investment costs and operating costs that are competitive in comparison with ordinary commercial dehydrogenation processes which otherwise require that said C4- C10 hydrocarbons or isobutene must first be removed or isomerized in a plant built for that purpose.

Further objects and advantages of the present invention will be more apparent from the following description and the appended figures, provided purely by way of example and without limitation, illustrating preferred embodiments of the present invention. Figure 1 illustrates a preferred embodiment of the process for the production of 1 ,3- butadiene. A mixture of hydrocarbons having 4 carbon atoms (1 ) is fed to an extractive distillation unit (A) which produces a Raffinate 1 (2) and 1 ,3-butadiene (3). Raffinate 1 (2) is fed directly to a unit in which an isomerization and non-oxidative dehydrogenation reaction (B) takes place in a single stage. A fraction (6) which is sent to other applications can be extracted from Raffinate 1. A mixture containing unreacted butenes and butanes (4) which is recycled to B, and a mixture containing concentrated 1 ,3-butadiene (5) which is recycled to the extractive distillation unit without further subsequent conversion or reaction stages is produced from reaction unit (B).

Detailed description

The present invention is a dual catalyst composition comprising:

a component with acid moiety selected from oxides and mixed oxides of aluminum, preferably selected from aluminosilicates, aluminum oxides or zeolites;

a component with dehydrogenating moiety selected from metal oxides of a metal in Group IMA or IVA of the Periodic Table, said oxides having added noble metals belonging to Group VIIIB of the Periodic Table in a quantity ranging from 20 ppm to 500 ppm of metal with respect to the total composition;

a support

Preferred oxides may be aluminum oxides, aluminosilicates or zeolites; microspheroidal alumina having a specific surface area of between 50 m ² /g and 150 m ² /g measured according to the method in ASTM D-3037/89 (Brunauer, Emmett, Teller or BET method) and having an acidity of between 100 pmols/g and 500 pmols/g of pyridine adsorbed at 25°C may be more preferred.

The noble metals belonging to Group VIIIB of the Periodic Table may be added in a quantity preferably ranging from 30 ppm to 200 ppm, more preferably from 30 ppm to 180 ppm, and even more preferably from 30 ppm to 150 ppm of metal with respect to the total composition.

The oxides of metals in Group IMA in the Periodic Table may be selected from aluminum oxides, gallium oxides, indium oxides or thallium oxides; more preferably they may be selected from aluminum oxides or gallium oxides, even more preferably they may be AI2O3 or Ga ₂ 0 ₃ because they ensure a surprising balance in acidity values and at the same time have mechanical properties suitable for a Fast Riser type reactor.

The oxides of metals in Group IVA of the Periodic Table may be selected from silicon oxides, tin oxides, lead oxides or germanium oxides; tin oxides SnO and/or Sn0 ₂ may be more preferred because they promote dehydrogenating catalytic activity.

The concentrations of the oxides of metals in Group IIIA of the Periodic Table, and in particular Al ₂ 0 ₃ or Ga ₂ 0 ₃ , may range from 0.1 % by weight to 34% by weight, more preferably they may range from 0.2% by weight to 3.8% by weight in comparison with the total weight of the catalyst composition.

The concentrations of the oxides of metals in Group IVA of the Periodic Table, and in particular the Sn oxides, may range from 0.001 % by weight to 1 % by weight, more preferably they may range from 0.05% by weight to 0.4% by weight with respect to the total weight of the catalyst composition.

The metals in Group VIIIB of the Periodic Table may be selected from iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium or platinum; more preferably, they may be selected from ruthenium, rhodium, palladium, platinum, nickel; even more preferably it may be platinum, which enables the function promoting regeneration and reactivation of the dehydrogenating moiety.

The catalyst composition described and claimed has to be supported. Supports suitable for the present invention may be selected from alumina or microspheroidal aluminosilicates, preferably they may be microspheroidal aluminas having a d (Delta) and/or Q (Theta) crystalline phase and aluminosilicates in the form of ZSM-5 zeolites.

A support may be in the form of microspheroidal particles having the morphology below: mean particle diameter (D ₅ o) ranging from 70 microns to 90 microns, measured using the Light Scattering technique according to ASTM standard D4464-15.

surface area less than or equal to 150 m ² /g, measured according to the ASTM D-3037/89 method (Brunauer, Emmett, Teller or BET method).

The quantity of silica present in the support and/or the component having acid moiety ranges from 0.05% by weight to 10% by weight with respect to the support only, the remainder being alumina.

The components having acid and dehydrogenating moieties may be located on separate and different catalyst particles, or on the same catalyst particle in a single bifunctional system.

The microspheroidal particles render the catalyst system described and claimed suitable for use in fluidized bed, moving bed or“Fast Riser” technology reactors.

When the two components are present on the same particle the oxides of the metals in Group IMA or IVA in the Periodic Table are deposited on a support having an acidity of between 100 pmols/g and 500 pmols/g of pyridine adsorbed at 25°C. The acidity of the support so obtained may optionally be suitably modulated through the addition of a quantity of alkali metal oxides which may range from 10 ppm to 5000 ppm, preferably from 50 ppm to 700 ppm, more preferably from 70 ppm to 200 ppm of metal with respect to the total composition in order to minimize parasitic reactions and maximize butadiene yield.

The alkali metal oxides may be selected from lithium oxides, sodium oxides, potassium oxides, rubidium oxides, cesium oxides or francium oxides; sodium oxide Na ₂ 0 or potassium oxide K ₂ 0 may be more preferred. Potassium oxide K ₂ O may be even more preferred.

Preferably the quantity of alkali metal oxides, and in particular of the quantity of K ₂ O oxide may range from 0.01% by weight to 5% by weight, more preferably from 0.01% by weight to 3% by weight with respect to the total weight of the catalyst composition.

The dual catalyst composition or the dehydrogenating fraction of the catalyst mixture described and claimed in the present text is obtained by a process comprising dispersing the precursors of the active metals on microspheres of modified alumina. This dispersion treatment may be:

the technique of impregnating said support with a solution containing precursors of the active metals, followed by drying and calcination; or

the technique of ion absorption, followed by separation of the liquid and activation; or

the technique of surface adsorption of volatile species of the precursors, and possible calcination of the solid.

A preferred technique is impregnation of the support with a volume of solution equal to that provided by the pores (the pore volume being calculated as the specific porosity of the support [cc/g] multiplied by the grams of support being impregnated) as appropriate for the quantity of support, which has to be treated. This impregnation procedure is known in the common state of the art as the“incipient wetness” procedure. Another preferred technique is immersion of the support in a volume of solution in excess with respect to that appropriate for the pores, in which the precursors of the active metals are dissolved, followed by evaporation and subsequent calcination. The active metal precursors may be dispersed simultaneously on the silica modified support in a single stage, or in several stages: • in the first stage the support, preferably modified with silica, is impregnated with a solution containing a precursor of the active metal, for example gallium and potassium, followed by drying and calcination; or the modified support, preferably modified with silica, is impregnated with a solution containing a precursor of the active metal, for example gallium, potassium and tin, followed by drying and calcination;

• in the second stage the calcinate originating from the first stage is impregnated with a solution containing a precursor of platinum and tin, the impregnate being dried and finally calcined.

Another object of the present invention is a process for the production of 1 ,3-butadiene. The starting materials used in the process for the production of 1 ,3-butadiene may be unsaturated C2-C10 or mixtures of saturated and unsaturated C2-C10.

Preferably, the starting materials may be mixtures of C4 unsaturates (“C4 butenes”), or mixtures of saturated and unsaturated C4 hydrocarbons (“mixtures of C4 butanes and butenes”).

Preferably, the starting materials may be mixtures of unsaturated hydrocarbons having from 2 to 8 carbon atoms, described as“C2-C8 unsaturates”; more preferably

unsaturated hydrocarbons having from 2 to 5 carbon atoms, described as“C2-C5 unsaturates”.

Preferably, the starting materials may be mixtures of unsaturated and saturated hydrocarbons having from 2 to 8 carbon atoms, described as“mixtures of unsaturated and saturated C2-C8”; more preferably unsaturated and saturated hydrocarbons having from 2 to 5 carbon atoms, described as“mixtures of unsaturated and saturated C2-C5”. Preferred mixtures suitable for the purposes of the present invention contain from 1% to 18% of saturated C2-C10 components, more preferably from 4% to 13% of saturated C2- C10 components, and from 82% to 99% of unsaturated C2-C10 components, more preferably from 87% to 96% of unsaturated C2-C10 components calculated with respect to the mixture as a whole. As is obvious, the sum of the components must always be 100%.

Saturated C2-C10 present in the starting mixtures may be selected from ethane, propane, n-butane, isobutane and their mixtures. Unsaturated C2-C10 present in the preferred starting mixtures may be selected from ethene, propene, 1 -butene, 2-butenes, isobutene and their mixtures.

More preferred may be mixtures of saturated and unsaturated C4 containing n-butane, isobutane, 1 -butene, 2-butenes, isobutene.

Even more preferred may be mixtures of saturated and unsaturated C4 containing n-butane, isobutane, 1 -butene, 2-butene, isobutene and 1 ,3-butadiene having the following composition:

hydrocarbons having fewer than 4 carbon atoms, in a quantity of 0.1 % w/w n-butane = 3.8% w/w

isobutane = 0.8% w/w

1-butene = 14.1 % w/w

2-butenes = 9.7% w/w

isobutene = 25.4% w/w

1 ,3-butadiene = 46% w/w

hydrocarbons having more than 4 carbon atoms, in a quantity of 0.1 % w/w.

The starting hydrocarbon mixtures are fed to an extractive distillation unit as separate flows.

Such extraction units may comprise one or more extractors in series or in parallel.

After extractive distillation a final product containing 1 ,3-butadiene and an extraction raffinate described in this text as Raffinate 1 is extracted.

Raffinate 1 is a flow, which may comprise hydrocarbons having fewer than 4 carbon atoms, n-butane, isobutane, 1 -butene, 2-butenes, isobutene, and hydrocarbons having more than 4 carbon atoms.

Preferably, Raffinate 1 may contain:

hydrocarbons having fewer than 4 carbon atoms, in a quantity of 0.2% w/w n-butane = 7.1 % w/w

isobutane = 1.5% w/w

1 -butene = 26.1 % w/w

2-butenes = 18% w/w

isobutene = 47% w/w

hydrocarbons having more than 4 carbon atoms, in a quantity of 0.1 % w/w

After the extraction stage extraction Raffinate 1 is mixed with a reaction inert and the mixture is sent to a reaction unit for isomerization and non-oxidative dehydrogenation located downstream from the extraction unit in which the mixture simultaneously undergoes a non-oxidative dehydrogenation reaction and an isomerization reaction in a single stage.

The reaction is carried out in the presence of a dual catalyst composition suitable for isomerization and non-oxidative dehydrogenation reactions to form a reaction effluent containing from 4% to 25% by weight of 1 ,3-butadiene and possibly 40 to 90% by weight for a mixture of unreacted unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain or a mixture of unreacted saturated and unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain, in such a way as to form a flow of unreacted hydrocarbons containing unsaturated and saturated hydrocarbons having from 2 to 10 carbon atoms in the chain. The catalyst composition used in the isomerization and non-oxidative dehydrogenation reaction unit is preferably the composition described and claimed in the present text. Preferably, the hydrogenation and isomerization reaction can take place at a temperature ranging from 500°C to 700°C. Preferably, the isomerization and dehydrogenation pressure may range from 0.2 atm to 2 atm absolute. The reaction inert/charge ratio (v/v) may range from 1 to 23, preferably from 1 to 9.

Said reaction unit may comprise one or more reactors in series or in parallel, each operating as a single reaction stage, meaning that the isomerization and dehydrogenation reactions take place simultaneously in each individual reactor.

The reactors, which may preferably be used in the process described and claimed may be selected from fluidized bed reactors or moving bed reactors or“Fast Riser” type reactors.

The inert has the function of lowering the partial pressure of the starting materials (reagents) and that of the reaction products with a view to increasing conversion and reducing the kinetics of parasitic reactions to preserve selectivity for the desired product. The inert may be selected from nitrogen, methane or another combustible gas having a maximum hydrogen content of 1% by weight and possibly oxygen. The latter may be present in traces as a typical residue of air distillation. The combustible gas offers the advantage in comparison with nitrogen that it can recover the calorific value of the hydrogen without the need for cryogenic separation.

The reaction effluent is then sent to a physical separation section to separate out the following flows:

the reaction inert,

a flow of unreacted hydrocarbons containing mixtures of unsaturates and saturates having from 2 to 10 carbon atoms in the chain, a flow containing from 13% to 30% by weight of 1 ,3-butadiene, and possibly a mixture of unreacted unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain or a mixture of unreacted saturated and unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain.

The flow containing from 13% to 30% by weight of 1 ,3-butadiene can be recirculated to the extraction unit without further subsequent reaction or processing stages, feeding it to the extraction unit separately from the starting materials (unsaturated C2-C10

compounds or mixtures of saturated and unsaturated C2-C10 compounds).

The mixture of unreacted unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain or a mixture of unreacted saturated and unsaturated hydrocarbons having from 3 to 6 carbon atoms in the chain can be recirculated directly to the isomerization and non- oxidative dehydrogenation unit.

Fast-Riser technology comprises a reactor in the upper part of which there is a zone for separation of the catalyst and a stripping zone fed with inert, and in the lower part of which a regenerator in which there is a stripping zone. The regenerator is fed with a comburant, a fuel and an inert. The reactor and regenerator are connected together by means of a conduit for the passage of partly exhausted catalyst. The isomerization- dehydrogenation reaction effluent leaves the gas-solid separator at the top of the reactor. The hot regenerated catalyst leaves from the bottom of the regenerator and is

transported to the reactor by gas (carrier gas). Some of the partly exhausted catalyst is directly recycled to the reactor.

Preferably, the part of the catalyst which is sent to the regenerator ranges from 50% to 80% and as a consequence the part which is not regenerated ranges from 50% to 20%. The same carrier gas may be used to dilute the charge entering the reactor. The inert to dilute the charge may be selected from nitrogen, methane or another combustible gas having a maximum hydrogen content of 1 % by weight, and possibly oxygen. The latter may be present in traces, possibly as a typical residue of air distillation.

Within the reactor the charge is mixed with the at least partly regenerated catalyst composition entering from the base of the reactor.

In the reactor of the Fast-Riser type the charge is progressively isomerized and dehydrogenated (by means of non-oxidative dehydrogenation) as it advances co- currently, until it passes through the entire reactor. At the top of the reactor the catalyst composition separates out from the gaseous effluent and at least part is sent to the regeneration device. The unregenerated part of the catalyst is directly recycled to the reactor. After regeneration the catalyst composition is recirculated to the reactor.

In a“Fast-Riser” reactor the residence time of the gas phase may be a minute or less, and preferably in a range from 0.2 sec to 5 sec.

In a“Fast-Riser” reactor the temperature may range from 450°C to 700°C. The pressure may preferably range from 0.2 atm absolute to 2 atm. The reaction inert/charge ratio (w/w) may range from 1 to 23, preferably from 1 to 9.

Regeneration preferably takes place in a fluidized bed at a temperature higher than the operating temperature of the reaction section, preferably above 700°C. The pressure in the regeneration section may be equal to that in the isomerization and dehydrogenation section or atmospheric. The residence time of the catalyst composition during regeneration may range from 5 minutes to 60 minutes, preferably from 15 minutes to 40 minutes. During regeneration the gas phase hourly space velocity (GHSV in Nl/h of air per liter of catalyst) may range from 1000 h ¹ to 5000 h ¹ , preferably from 2000 h ¹ to 3000 h- ¹ .

The catalyst composition may be regenerated and the fuel gas may be burnt with a comburant selected from air, oxygen or any other gaseous comburant. The advantages of a“Fast-Riser” reactor can be isomerized as follows:

^■ smaller reaction volumes and consequent lower investment;

^■ the heat required by the reaction is transferred directly from the regenerated

catalyst, there are no furnaces in which the charge is preheated, so the formation of undesired combustion by-products is avoided;

^■ no specific treatment is necessary to reduce polluting gas emissions;

^■ reaction and regeneration take place in physically separate zones and there can be no mixing of hydrocarbon flows with flows containing oxygen;

^■ catalyst regeneration carried out in a fluidized bed prevents the formation of

hotspots due to the strong remixing of the bed, preventing thermal stress on the catalyst formulation;

^■ it is not necessary to stop operation of the plant to replace catalyst; portions of catalyst are periodically discharged and replaced with equal quantities of fresh catalyst.

The special feature of“Fast-Riser” technology is that it allows optimum conditions for use of the dual catalyst composition/catalyst mixture described and claimed in this text to be applied. Firstly, thanks to short contact times between the hydrocarbon charge and catalyst it is possible to minimize the inevitable parasitic cracking, oligomerization and polymerization reactions encouraged by the acid moiety, which would have an adverse effect on 1 ,3-butadiene yield, resulting in the formation of coke. Secondly, the use of a continually regenerated circulating catalyst composition makes it possible to have a catalyst, which is always active in the reaction environment, one thus capable of best performing its function.

The Applicant describes the benefits obtained using the embodiments according to the invention below. The composition described and claimed in the present patent application is very active and selective at low contact times for the isomerization of unsaturated C2-C10 hydrocarbons, in particular for the isomerization of isobutene, and for the

dehydrogenation of individual unsaturates or mixtures of saturates and unsaturates, including in particular butenes alone or mixtures of butenes with butanes.

The possibility of performing the isomerization reactions for unsaturated C2-C10 hydrocarbons, in particular isobutene, and the non-oxidative dehydrogenation reactions of unsaturated C2-C10 hydrocarbons, in particular linear butenes, simultaneously in a single reactor, in comparison with performing it in separate reactors, makes it possible to achieve competitive overall investment and operating costs. In fact, the reaction conditions and techniques for separation and recovery of the products for the separate isomerization and dehydrogenation stages are different and have a significant effect on process costs, while the possibility of performing both reactions in a single system offers significant savings. Furthermore, performing both the reactions in a single reactor requires a catalyst composition capable of promoting both without excessively penalizing selectivity. The operating conditions used are typical of dehydrogenation processes (500°C-700°C). However, use of the“Fast-Riser” technology and the catalyst composition described and claimed make it possible to perform the isomerization reaction under more severe temperature conditions than in normal isomerization processes without significantly penalizing selectivity thanks to short contact times and an appropriate ratio between the concentrations of dehydrogenation and isomerization sites.

In the process, which is the subject matter of the present invention, no provision is made for the use of furnaces to preheat the charge, thus reducing the formation and emission of NOx. The catalyst composition described and claimed in the present text constitutes the heat transfer agent for the isomerization and dehydrogenation reaction giving up sensible heat accumulated during regeneration.

Combustion of the coke present in the spent catalyst composition generates heat which is wholly recovered for the reaction and incorporated with the proportions of combustible gases added to the regenerator to be able to completely balance the endothermic reactions.

Natural gas or hydrogen, or combustible gas, including that obtained from a mixture of hydrogen and natural gas, can be used as combustible gas for the regeneration section.

A preferred process, which is the subject matter of the present patent application, will now be described with particular reference to Figure 1.

A mixture of C4 hydrocarbons comprising n-butane, isobutane, 1 -butene, 2-butene, isobutene, 1 ,3-butadiene (1 ) is fed separately to an extraction section (A) in which a flow containing 1 ,3-butadiene (3) and a Raffinate 1 (2) is extracted through extractive distillation. Raffinate 1 is fed directly to a reaction unit in which an isomerization reaction and a non-oxidative dehydrogenation reaction (B) which convert the C4 mixtures into a mixture containing 1 ,3-butadiene (5) in the presence of the catalyst system described and claimed take place simultaneously. Possibly some of Raffinate 1 is directed to other purposes (6). The unreacted flow (4) is recycled directly to the reaction section (B) feeding it as a separate flow, while the flow containing 1 ,3-butadiene (4) is recirculated directly to extractive distillation without further reaction and processing steps, feeding it separately.

Some examples of applications of the present invention which are purely for the purposes of description and are non-limiting and represent preferred embodiments according to the present invention will now be described.

Example 1

A catalyst composition was prepared as a mechanical mixture by mixing an acid component and a dehydrogenation catalyst in a stirred vessel in a 1 : 1 ratio by weight.

The acid component was an aluminosilicate or microspheroidal alumina, modified with 5% by weight of silica, with average particles diameter (D50) equal to 70 pm and specific surface area of 120 m ² /g. The dehydrogenation catalyst was a composition comprising Ga2C>3, in which Ga was present in a quantity amounting to 1.6% by weight, K ₂ 0 in which K was present in a quantity corresponding to 0.8% by weight, the % being calculated with reference to the total composition, SnO and/or Sn0 ₂ in which Sn was present in a quantity corresponding to 700 ppm by weight of metal with respect to the total composition and platinum oxides in which Pt was present in a quantity corresponding to 200 ppm by weight of metal with respect to the total composition, supported on microspheroidal alumina modified with 1.5% by weight of silica with respect to the total composition.

The dehydrogenation catalyst was prepared in the following way.

A 300 g aliquot of microspheroidal alumina modified with 1.5% by weight of silica, with average particles diameter (D50) equal to 80 pm and specific surface area of 80 m ² /g, was impregnated using the“incipient wetness” technique with an aqueous solution comprising: 61 g of gallium nitrate solution (Ga concentration 7.9% by weight), 24.8 g of potassium nitrate solution (K concentration 10.04% by weight) and water to bring the volume of the solution to 87 cc. The impregnate was dried at 120°C for 4 hours and then calcined using the heating rate: from ambient temperature to 460°C in 530 minutes and an isothermal stage of 180 minutes at 460°C. 306 g of the calcined product comprising Ga ₂ 0 ₃ , in which Ga was present in a quantity amounting to 1.6% by weight, K2O in which K was present in a quantity corresponding to 0/8% by weight, the % being calculated with respect to the total composition, AI2O3 and S1O2 constituting the remainder were impregnated using the“incipient wetness” procedure with an aqueous solution containing in a dissolved state: 21 g of anhydrous citric acid, 4.2 g of tin tetrachloride solution (Sn concentration 5.6% by weight) and 3.6 g of ammonium tetrachloroplatinate solution (Pt concentration 1.84% by weight) and water sufficient to bring the volume of the solution to 83 cc. The impregnate was dried at 120°C for 4 hours and then calcined in accordance with the heating rate: from 20° (ambient temperature) to 120°C in 120 minutes, followed by an isothermal stage at 120°C for 120 minutes, then from 120°C to 250°C in 120 minutes, from 250°C to 730°C in 210 minutes, followed by an isothermal stage at 730°C for 90 minutes. The composition by weight of the catalyst system was: Ga ₂ 0 ₃ in which Ga was present in a quantity corresponding to 1.6% by weight, K ₂ 0 in which K was present in a quantity corresponding to 0.8%, the % being calculated with respect to the total composition, SnO and/or Sn0 ₂ in which Sn was present in a quantity corresponding to 700 ppm by weight of metal with respect to the total composition, and platinum oxides in which Pt was present in a quantity corresponding to 200 ppm by weight of metal with respect to the total composition, the remaining part being Al ₂ 0 ₃ and Si0 ₂ . The catalyst showes average particles diameter (D50) equal to 80 pm and specific surface area of 80 m ² /g,

Example 2

A catalyst composition comprising a bifunctional catalyst prepared by impregnation, using a microspheroidal alumina modified with 1.5% by weight of silica without the addition of potassium to modulate its acidity as a support and acid component was prepared by impregnation.

An aliquot of 300 g of microspheroidal alumina modified with 1.5% by weight of silica with average particles diameter (D50) equal to 80 pm and specific surface area of 80 m ² /g, was impregnated according to the“incipient wetness” technique with an aqueous solution comprising: 61 g of gallium nitrate solution (Ga concentration 7.9% by weight) and sufficient water to bring the volume of the solution to 87 cc. The impregnate was dried at 120°C for 4 hours and finally calcined using the heating rate: from ambient temperature to 460°C in 530 minutes and an isothermal stage of 180 minutes at 460°C. 306 g of calcined product comprising Ga ₂ 0 ₃ in which the Ga was present in a quantity corresponding to 1.6% by weight, the % calculated with respect to the total composition, with AI ₂ O ₃ and S1O ₂ for the remainder were impregnated using the“incipient wetness” procedure with an aqueous solution containing in a dissolved state: 21 g of anhydrous citric acid, 4.2 g of tin tetrachloride solution (Sn concentration 5.6% by weight) and 3.6 g of ammonium tetrachloroplatinate solution (Pt concentration 1.84% by weight) and water sufficient to bring the volume of the solution to 83 cc. The impregnate was dried at 120°C for 4 hours and finally calcined using the heating rate: from 20°C (ambient temperature) to 120°C in 120 minutes, followed by an isothermal stage at 120°C for 120 minutes, then from 120°C to 250°C in 120 minutes, from 250°C to 730°C in 210 minutes, followed by an isothermal stage at 730°C for 90 minutes. The composition by weight of the catalyst system was: Ga ₂ C> ₃ , in which Ga was present in a quantity corresponding to 1.6% by weight, the % being calculated with respect to the total composition, SnO and/or Sn0 ₂ in which Sn was present in a quantity corresponding to 700 ppm by weight of metal with respect to the total composition, and platinum oxides in which Pt was present in a quantity

corresponding to 200 ppm by weight of metal with respect to the total composition, the remainder being AI ₂ O ₃ and S1O ₂ . The catalyst showes average particles diameter (D50) equal to 80 pm and specific surface area of 80 m ² /g.

Example 3

A catalyst composition comprising a bifunctional catalyst prepared by impregnation using a microspheroidal alumina modified with 1.2% by weight of silica, with the addition of potassium to modulate its acidity, being used as a support and acid component, was prepared.

A 300 g aliquot of microspheroidal alumina modified with 1.5% by weight of silica with average particles diameter (D50) equal to 80 pm and specific surface area of 80 m ² /g, was impregnated using the“incipient wetness” technique with an aqueous solution comprising: 61 g of gallium nitrate solution (Ga concentration 7.9% by weight), 0.7 g of potassium nitrate solution (K concentration 6.9% by weight) and water sufficient to bring the volume of the solution to 87 cc. The impregnate was dried at 120°C for 4 hours and finally calcined using the heating rate: from ambient temperature to 460°C in 530 minutes and an isothermal stage of 180 minutes at 460°C. 306 g of the calcined product comprising Ga ₂ C> ₃ , in which Ga was present in a quantity corresponding to 1.6% by weight, K ₂ 0 in which K was present in a quantity corresponding to 0.025% by weight, the % being calculated with respect to the total composition, AI ₂ O ₃ and S1O ₂ for the remainder, were impregnated using the“incipient wetness” procedure with an aqueous solution containing in a dissolved state: 21 g anhydrous citric acid, 4.2 g of tin

tetrachloride solution (Sn concentration 5.6% by weight) and 3.6 g of ammonium tetrachloroplatinate solution (Pt concentration 1.84% by weight) and water sufficient to bring the volume of the solution to 83 cc. The impregnate was dried at 120°C for 4 hours and finally calcined using the heating rate: from 20°C (ambient temperature) to 120°C in 120 minutes, followed by an isothermal stage at 120°C for 120 minutes, then from 120°C to 250°C in 120 minutes, from 250°C to 730°C in 210 minutes, followed by an isothermal stage at 730°C for 90 minutes. The composition by weight of the catalyst system was: Ga ₂ 0 ₃ in which Ga was present in a quantity corresponding to 1.6% by weight, K ₂ O in which K was present in a quantity corresponding to 0.025% by weight, the % being calculated with respect to the total composition, SnO and/or Sn0 ₂ in which Sn was present in a quantity corresponding to 700 ppm by weight of metal with respect to the total composition, and platinum oxides in which Pt was present in a quantity

corresponding to 200 ppm by weight of metal with respect to the total composition, the remainder being AI ₂ O ₃ and S1O ₂ . The catalyst showes average particles diameter (D50) equal to 80 pm and specific surface area of 80 m ² /g.

Example 4

The catalyst systems prepared in Examples 1-3 were tested for the isomerization and non-oxidative dehydrogenation reaction of a mixture of isobutene, linear butenes and n- butane (Raffinate 1 ) in a fixed bed laboratory microreactor, monitoring catalyst performance. All the tests were performed charging 0.5 cc catalyst, with a throughput of Raffinate 1 feed of 25 Nl/h diluted in nitrogen with a hydrocarbon concentration entering the reactor of 50% by weight; temperatures of 600°C and operating pressures of 0.6 and 1.1 atm absolute.

Catalyst performance is shown in Table 2, where isobutene conversion (A), total C4 conversion (B), selectivity for 1 ,3-butadiene (C), and 1 ,3-butadiene yield (D) have been calculated using the following formulae:

ISOBUTENE CONVERSION (A):

[(isobutene)reactor inlet - (iSObutene)reactor outlet] / (iSObutene)reactor inlet] *100

TOTAL 4 CONVERSION (B):

[(åbutanes+åbutenes+isobutene)reactor inlet -(åbutanes+åbutenes+isobutene) _reactor outlet]/ [(åbutanes+åbutenes+isobutene)reactor inlet ]*100

SELECTIVITY FOR 1 ,3-BUTADIENE (B):

[(1 ,3-butadiene reactor outlet - 1 ,3-butadiene reactor inlet)/

/[(Xbutanes+åbutenes+isobutene)reactor inlet -(åbutanes+åbutenes+isobutene)reactor outlet] ^x 1 00

1 ,3-BUTADIENE YIELD (B): [(1 ,3-butadiene reactor outlet - 1 ,3-butadiene reactor inlet)/

/[(åbutanes+åbutenes+isobutene) _{reactor miet} ] ^x 100

The composition of the charge treated in the Examples is shown in Table 1.

Table 1 : Charge (Raffinate 1 )

Table 2: Catalyst performance

The data shown in Table 2 reveal that through operating in the presence of the dual catalyst composition both as a mechanical mixture (Example 1 ) and in the case where the active part with acid moiety and the active part with dehydrogenated moiety are located on the same element (Examples 2 and 3) it is possible to convert the isobutene present in the charge and at the same time dehydrogenate the linear butenes already present in the charge or formed by the conversion of isobutene into 1 ,3-butadiene.