WO2016092517A1

WO2016092517A1 - Process for the production of 1, 3-butadiene from 1, 4 -butanediol via tetrahydrofuran

Info

Publication number: WO2016092517A1
Application number: PCT/IB2015/059540
Authority: WO
Inventors: Nicola Vecchini; Armando Galeotti; Andrea PISANO
Original assignee: Versalis S.P.A.
Priority date: 2014-12-12
Filing date: 2015-12-11
Publication date: 2016-06-16

Abstract

Process for the production of 1,3-butadiene comprising: feeding a mixture (a) comprising 1,4-butanediol and water to an evaporator, said water being present in an amount of greater than or equal to 5% by weight, preferably ranging from 10% by weight to 85% by weight, more preferably ranging from 15% by weight to 30% by weight, relative to the total weight of said mixture (a), to obtain: (b) a gaseous stream comprising 1,4-butanediol exiting from the top of said evaporator; and, optionally, (c) a blowdown stream exiting from the bottom of said evaporator; feeding said gaseous stream (b) to a first reactor containing at least one dehydration catalyst to obtain (d) a stream comprising tetrahydrofuran, water and, optionally, impurities and/or unreacted 1,4-butanediol, exiting from said first reactor; optionally, feeding said stream (d) to a first purification section to obtain: (e) a stream comprising tetrahydrofuran, water, and, optionally, impurities; (f) a stream comprising water and, optionally, impurities and/or unreacted 1,4- butanediol; feeding said stream (d) or said stream (e) to a second reactor containing at least one dehydration catalyst to obtain (g) a stream comprising 1,3-butadiene, water and, optionally, impurities and/or unreacted tetrahydrofuran, exiting from said second reactor; feeding said stream (g) to a second purification section to obtain: (h) a stream comprising pure 1,3-butadiene; (i) a stream comprising water and, optionally, unreacted tetrahydrofuran; and, optionally, (I) a stream comprising impurities. Said 1,3-butadiene may advantageously be used as a monomer or intermediate in the production of elastomers and (co)polymers.

Description

PROCESS FOR THE PRODUCTION OF 1,3-BUTADIENE FROM 1,4-BUTANEDIOL VIA TETRAHYDROFURAN

DESCRIPTION

The present invention relates to a process for the production of 1 ,3-butadiene from 1 ,4- butanediol via tetrahydrofuran.

More particularly, the present invention relates to a process for the production of 1 ,3- butadiene comprising feeding a mixture comprising 1 ,4-butanediol and water to an evaporator, said water being present in an amount of greater than or equal to 5% by weight relative to the total weight of said mixture; feeding the gaseous stream comprising 1 ,4-butanediol exiting from the top of said evaporator to a first reactor containing at least one dehydration catalyst; optionally feeding the stream comprising tetrahydrofuran, water and, optionally, impurities and/or unreacted 1 ,4-butanediol, exiting from said first reactor to a purification section; feeding the, optionally purified, stream comprising tetrahydrofuran, water and, optionally, impurities and/or unreacted 1 ,4-butanediol, to a second reactor containing at least one dehydration catalyst to obtain a stream comprising 1 ,3-butadiene, water and, optionally, impurities and/or unreacted tetrahydrofuran; recovering the 1,3-butadiene from said stream. Preferably, said mixture comprising 1 ,4- butanediol and water is derived from the fermentation of sugars obtained from biomass. Said 1 ,3-butadiene may advantageously be used as a monomer or intermediate in the production of elastomers and (co)polymers.

It should also be noted that the tetrahydrofuran obtained from the above-stated process, i.e. from the dehydration of 1 ,4-butanediol in the first reactor, may advantageously be used, other than for the production of 1 ,3-butadiene, in the production of intermediates which are in turn usable in fine chemistry, agricultural chemistry, pharmaceutical chemistry, or in petrochemistry.

It is known that, at present, industrial production of 1 ,4-butanediol, 1 ,3-butadiene and tetrahydrofuran, is based on conventional petrochemical processes.

The reason for this is that, since diols having four carbon atoms, in general, and 1 ,4- butanediol (generally also denoted 1 ,4-BDO) in particular, are generally obtained by means of complex petrochemical processes as described, for example by Grafje H. et al. in "Butanediols, Butenediol, and Butynediol", "Ulmann's Encyclopedia of Industrial Chemistry" (2000).

1 ,3-Butadiene is a basic product of petrochemistry. Around ten million tonnes of 1 ,3- butadiene are produced annually and preferentially used in the production of various products such as, for example, synthetic rubbers, resins, acrylonitrile-butadiene-styrene (ABS) terpolymers, hexamethylenediamine, butanediols, in particular 1,4-butanediol. More than 95% of the 1,3-butadiene produced annually is a by-product derived from "steam cracking" processes for the production of ethylene and other olefins and is separated by extractive distillation. Production processes having such production as their "main purpose" which may be mentioned are, for example, the dehydrogenation of butane and/or butenes.

Processes for the production of tetrahydrofuran from aqueous solutions of 1 ,4-butanediol, such as processes for the production of 1 ,3-butadiene from tetrahydrofuran, have long been known.

For example, Weissermel K. et al. in "Industrial Organic Chemistry' (1994), pp. 111 , describe the conversion of 1 ,4-butanediol into tetrahydrofuran by the elimination of water, in the presence of an acidic catalyst selected from phosphoric acid, sulfuric acid, acidic ion-exchange materials. In said process, 1,4-butanediol mixed with the acidic catalyst is heated and subsequently further 1 ,4-butanediol is added in a quantity such that the tetrahydrofuran/water mixture is removed by distillation.

However, one disadvantage of the above-mentioned process resides in the fact that the 1 ,4-butanediol must be subjected to purification before being used. To this end, the 1 ,4- butanediol is generally subjected to multi-stage distillation in order to remove unwanted low-boiling and/or high-boiling compounds, including water, to obtain pure 1 ,4-butanediol. Subsequently, the pure anhydrous 1 ,4-butanediol is converted into tetrahydrofuran with formation of water and unwanted by-products: for this reason, the tetrahydrofuran obtained must also be subjected to purification by multi-stage distillation: consequently, process times are lengthened and process costs increased. Furthermore, using free acids is unfavourable from both an economic and an environmental standpoint because it requires: using specific, costly reactors in order to avoid reactor corrosion problems, removing or neutralising the spent acids and subsequently disposing of them with the problems associated therewith. Not least, consideration must also be given to issues relating to the health of the operators since said acids are harmful and difficult to handle. Efforts in the art have accordingly been made to overcome the above-stated drawbacks. For example, American patent US 6,204,399 describes a process for the production of tetrahydrofuran from an aqueous solution of butanediol contaminated by light volatile organic compounds, comprising: (a) removing the light volatile organic compounds present in the aqueous butanediol solution by distillation; (b) removing the water from aqueous butanediol solution until a total water content ranging from 2% by weight to 70% by weight is achieved; (c) dehydrating the aqueous pre-purified butanediol solution in the presence of an acidic catalyst based on aluminium oxide to obtain a fraction containing a large quantity of tetrahydrofuran; and (d) subjecting the fraction containing a large quantity of tetrahydrofuran to at least one distillation stage to obtain pure tetrahydrofuran.

American patent US 6,316,640 describes a process for the production of tetrahydrofuran by reacting a reaction mixture containing 1 ,4-butanediol, said reaction mixture being the product obtained by the hydrogenation of a maleic acid diester in the presence of an acidic catalyst, in which the reaction mixture comprises from 15% by weight to 60% by weight of 1 ,4-butanediol, from 15% by weight to 50% by weight of at least one (further) monohydric aliphatic alcohol having from 1 to 7 carbon atoms, up to 30% by weight of γ-butyrolactone and/or of a succinic acid diester, said quantity being no greater than half the quantity of 1 ,4-butanediol, and up to 30% by weight of tetrahydrofuran and, furthermore, taking the total content of all the other components of the above-stated reaction mixture to be equal to 100, a quantity of water of less than 2%.

With regard to the production of 1 ,3-butadiene from tetrahydrofuran, it is known in the art that it is possible to dehydrate the tetrahydrofuran to obtain 1 ,3-butadiene by removing a water molecule.

In this connection, for example, the German chemist Reppe W. has described a process, which starts from acetylene, for obtaining 1 ,3-butadiene from tetrahydrofuran. Said process comprises: reacting acetylene and formaldehyde to obtain 1 ,4-butynediol; subjecting the 1,4-butynediol to hydrogenation to obtain 1 ,4-butanediol; subjecting the 1 ,4- butanediol to dehydration in the presence of an acidic catalyst to obtain tetrahydrofuran; subjecting the tetrahydrofuran to further dehydration in the presence of a catalyst containing phosphorus to obtain 1 ,3-butadiene.

Further details relating to the above-described process may be found, for example, in "Nuovo dizionario di merceologia e chimica applicata" (1973), vol. 2, pp. 693-694; or in German patent DE 725532; or in "Annalen der Chemie, Justus Liebigs" (1955), vol. 596(1 ), pp. 80-83 and p. 110.

In particular, German patent DE 725532 describes the dehydration of tetrahydrofuran, in the gas phase, in the presence of monoammonium orthophosphate and water in a quantity of 40% by weight relative to the total weight of tetrahydrofuran and water with a yield of 1 ,3-butadiene of about 98%-99% (greater than 99% conversion of tetrahydrofuran).

However, all the above-stated processes relate to 1 ,4-butanediol of synthetic origin and may involve some drawbacks such as, for example, the need to remove light volatile organic compounds present in the aqueous 1 ,4-butanediol solution by distillation and, not least, the need to use mixtures containing essentially anhydrous 1 ,4-butanediol (i.e. quantity of water of less than 2%).

No optimised and integrated processes for synthesising tetrahydrofuran and/or 1 ,3 butadiene from renewable sources starting from 1 ,4-butanediol have thus been found in the prior art.

In recent years, new processes have been developed for synthesising butanediols, in particular 1 ,4-butanediol, starting from renewable sources. Said processes are based on the fermentation of sugars derived from renewable sources carried out in a fermentation broth, in the presence of at least one genetically modified microorganism for the purpose of producing 1 ,4-butanediol. Generally, said microorganism is genetically modified by introducing one or more exogenous genes which encode compounds belonging to the enzymatic pathway for producing 1 ,4-butanediol. Said microorganism may optionally also comprise gene disruption for the purpose of optimising the flow of carbon through the desired pathway for the production of 1 ,4-butanediol. Said renewable sources are, generally, biomass of vegetable origin: sugar cane and sugar beet may be used for this purpose as a source of sugars (sucrose), or maize and potato may be used as a source of starch and, hence, of dextrose. Of greater future interest are "non-food" biomasses such as, for example maize stalks, cereal straw, arundo, thistle stalks, guayule bagasse, etc., which may yield sugars by destructuration of the cellulose and hemicellulose. In general, biomass of vegetable origin is subjected to chemical and/or enzymatic hydrolysis in order to obtain substrates which may subsequently be processed biocatalytically in order to obtain the chemicals of interest. Said substrates include mixtures of carbohydrates, such as aromatic compounds and other products derived from the cellulose, hemicellulose and lignin present in the biomass. The carbohydrates obtained by hydrolysis of said biomass are a mixture rich in sugars with 5 and 6 carbon atoms which include, for example, sucrose, glucose, xylose, arabinose, galactose, mannose and fructose, which will be used during fermentation. Further details relating to the above-stated new processes for synthesising 1 ,4-butanediol starting from renewable sources may be found, for example, in American patent applications US 2009/0047719 and US 2011/0003355.

It is also known that, on completion of fermentation, the resultant fermentation broth also contains, in addition to the products of interest, i.e. 1 ,4-butanediol, a large quantity of water (for example, 90% by weight - 95% by weight of water relative to total weight of the fermentation broth) as well as other impurities such as, for example: inorganic salts (for example, sodium chloride, potassium chloride, calcium chloride, ammonium chloride, magnesium sulfate, ammonium sulfate; sodium, potassium or ammonium phosphates; sodium, potassium or ammonium citrates; sodium, potassium or ammonium acetates; sodium, potassium or ammonium borates); insoluble solid materials such as, for example, cellular debris, precipitated proteins. Said fermentation broth must thus be subjected to purification in order to obtain pure 1 ,4-butanediol with low water contents (i.e. water contents ranging from 1% by weight to 5% by weight of water relative to the total weight of the mixture obtained after purification).

In this connection, for example, the above-mentioned American patent application US 2011/0003355 describes a process for isolating 1 ,4-butanediol from the fermentation broth which includes removing a portion of solids by means of a disc centrifuge ("disc stack centrifugation") to obtain a liquid fraction; removing a further portion of solids from said liquid fraction by ultrafiltration; removing a portion of the salts from said liquid fraction by ion-exchange resins; evaporating a portion of the water and recovering the 1 ,4-butanediol by distillation.

However, the above-stated processes for isolating the 1 ,4-butanediol from the fermentation broth may have some problems. In particular, removing water by evaporation entails high energy consumption due to the heat required for removing substantially all the water (with the aim of ultimately having, as stated above, water contents ranging from 1 % by weight to 5% by weight of water relative to the total weight of the mixture obtained after purification), and for separating the other impurities which are present, in particular for separating the impurities having a boiling point approximately the same as that of 1 ,4- butanediol (for example, γ-butyrolactone).

Furthermore, even after purification, the 1 ,4-butanediol may contain traces of inorganic salts and/or of organic compounds containing sulfur and/or nitrogen, which, as is known, are poisons for the catalysts normally used in subsequent processes for the use thereof, such as, for example, 1 ,3-butadiene production processes.

The Applicant has thus set itself the problem of finding a process for the production of 1 ,3- butadiene starting from a mixture comprising 1 ,4-butanediol and water, said water being present in a quantity of greater than or equal to 5% by weight relative to the total weight of said mixture, preferably from a mixture comprising 1 ,4-butanediol and water derived from the fermentation of sugars obtained from biomass, which process is capable of overcoming the above-described drawbacks.

The Applicant has now found that feeding a mixture comprising 1 ,4-butanediol and water to an evaporator makes it possible to use said mixture in a process for the production of 1.3- butadiene and to overcome the above-stated drawbacks. In particular, the Applicant has found a process for the production of 1 ,3-butadiene comprising feeding a mixture comprising 1 ,4-butanediol and water to an evaporator, said water being present in an amount of greater than or equal to 5% by weight relative to the total weight of said mixture; feeding the gaseous stream comprising 1 ,4-butanediol exiting from the top of said evaporator to a first reactor containing at least one dehydration catalyst; optionally feeding the stream comprising tetrahydrofuran, water and, optionally, impurities and/or unreacted

1.4- butanediol, exiting from said first reactor to a purification section; feeding the, optionally purified, stream comprising tetrahydrofuran, water and, optionally, impurities and/or unreacted 1 ,4-butanediol, to a second reactor containing at least one dehydration catalyst to obtain a stream comprising 1,3-butadiene, water and, optionally, impurities and/or unreacted tetrahydrofuran; recovering the 1 ,3-butadiene from said stream. Preferably, said mixture comprising 1 ,4-butanediol and water is derived from the fermentation of sugars obtained from biomass.

Numerous advantages are obtained by the above-stated process. For example, said process surprisingly makes it possible to reduce energy consumption by at least 10% relative to a similar process using a feed of substantially pure 1 ,4-butanediol (i.e. with a purity of greater than or equal to 98%): this estimate was obtained using approaches known to a person skilled in the art (for example, by computer simulations combining, for example, Hysys and Excel software).

Furthermore, since the water present in said mixture acts as a thermal flywheel, said process may be carried out adiabatically so making it possible to use conventional fixed- bed reactors, into which the catalyst is charged, instead of tube bundle reactors. This permits simpler and less costly mechanical construction of the reactor.

Furthermore, said process, which takes advantage of the presence of water in said mixture, makes it possible to avoid having to remove substantially all of the water formed as a reaction product from the stream comprising tetrahydrofuran, water and, optionally, impurities and/or unreacted 1 ,4-butanediol exiting from said first reactor, before said stream is fed to the second reactor for the production of 1 ,3-butadiene. This is advantageous because the tetrahydrofuran and water form an azeotrope which makes it difficult and costly to remove the water from said stream (because water is generally separated from azeotropes by extractive distillation in the presence of solvents).

Furthermore, the optional purification of the stream comprising tetrahydrofuran, water and, optionally, impurities and/or unreacted 1 ,4-butanediol exiting from said first reactor is very much simpler than the purification of the mixture comprising 1 ,4-butanediol and water derived from the fermentation of sugars obtained from biomass because the impurities normally present therein, as stated above, have a boiling point approximately the same as that of 1 ,4-butanediol, but on the other hand have a boiling point which differs from that of tetrahydrofuran.

The present invention accordingly provides a process for the production of 1 ,3-butadiene comprising:

feeding a mixture (a) comprising 1 ,4-butanediol and water to an evaporator, said water being present in an amount of greater than or equal to 5% by weight, preferably ranging from 10% by weight to 85% by weight, more preferably ranging from 15% by weight to 30% by weight, relative to the total weight of said mixture (a), to obtain:

(b) a gaseous stream comprising 1 ,4-butanediol exiting from the top of said evaporator; and, optionally,

(c) a blowdown stream exiting from the bottom of said evaporator;

feeding said gaseous stream (b) to a first reactor containing at least one dehydration catalyst to obtain (d) a stream comprising tetrahydrofuran, water and, optionally, impurities and/or unreacted 1 ,4-butanediol, exiting from said first reactor;

optionally, feeding said stream (d) to a first purification section to obtain:

(e) a stream comprising tetrahydrofuran, water, and, optionally, impurities;

(f) a stream comprising water and, optionally, impurities and/or unreacted 1 ,4- butanediol;

feeding said stream (d) or said stream (e) to a second reactor containing at least one dehydration catalyst to obtain (g) a stream comprising 1 ,3-butadiene, water and, optionally, impurities and/or unreacted tetrahydrofuran, exiting from said second reactor;

feeding said stream (g) to a second purification section to obtain:

(h) a stream comprising pure 1 ,3-butadiene;

(i) a stream comprising water and, optionally, unreacted tetrahydrofuran; and, optionally,

(I) a stream comprising impurities.

According to a particularly preferred embodiment of the present invention, said mixture (a) is derived from the fermentation of sugars obtained from biomass.

For the aim of the present description and of the following claims, unless stated otherwise, definitions of numerical ranges always include the extremes.

For the aim of the present description and of the following claims, the term "comprising" also encompasses the terms "which consists essentially of or "which consists of.

For the aim of the present description and of the following claims, the term "biomass" denotes any organic material of vegetable origin including: products derived from agriculture such as, for example, guayule, thistle, maize, soy, cotton, flax seeds, rape seeds, sugar cane, palm oil, including discards, residues and waste derived from said products or from the processing thereof; products derived from crops specifically grown for energy use such as, for example, miscanthus, panic grass, giant cane, including discards, residues and waste derived from said products or from the processing thereof; products derived from rom forestry or silviculture products, including discards, residues and waste derived from said products or from the processing thereof; discards from agricultural products intended for human food or animal feedstuffs; residues from the paper industry; waste originating from separate collection of solid urban waste, such as, for example, urban waste of vegetable origin, paper..

According to a particularly preferred embodiment of the present invention, said mixture (a) is derived from the fermentation of sugars obtained from guayule or thistle, including discards or residues derived from said guayule and/or thistle or from the processing thereof.

According to one still more preferred embodiment of the present invention, said mixture (a) is derived from the fermentation of sugars obtained from guayule, including discards or residues derived from said guayule or from the processing thereof.

The production of sugars from biomass may be performed by processes known in the art. For example, when biomass of vegetable origin (for example, lignocellulosic biomass) is used to produce sugars, said biomass is subjected to physical treatments (for example, extrusion, steam explosion, and the like), and/or to chemical and/or enzymatic hydrolysis, with mixtures of carbohydrates, aromatic compounds and other products derived from the cellulose, hemicellulose and lignin present in the biomass being obtained. In particular, the resultant carbohydrates are mixtures of sugars with 5 and 6 carbon atoms which include, for example, sucrose, glucose, xylose, arabinose, galactose, mannose and fructose, which will be used in fermentation. Further details relating to processes for the production of sugars from biomass may be found, for example, in Italian patent application MI2013A002069 in the name of the present Applicant. Said fermentation is generally performed by microorganisms, in particular by genetically modified microorganisms, capable of producing the alcohols of interest. Further details relating to the above-stated new processes for synthesising 1 ,4-butanediol starting from renewable sources may be found, for example, in the above-stated American patent applications US 2009/0047719 and US 2011/0003355.

In the case in which the mixture (a) is derived from the fermentation of sugars obtained from biomass, said mixture (a) may comprise impurities such as, for example: γ-butyrolactone, inorganic salts (for example, sodium chloride, potassium chloride, calcium chloride, ammonium chloride, magnesium sulfate, ammonium sulfate; sodium, potassium or ammonium phosphates; sodium, potassium or ammonium citrates; sodium, potassium or ammonium acetates; sodium, potassium or ammonium borates); insoluble solid materials such as, for example, cellular debris or precipitated proteins; unfermented sugars.

Any type of evaporator known in the art may advantageously be used for the aim of the present invention. Specific examples of evaporators which may advantageously be used are: "natural circulation" evaporators in which evaporation is brought about by motion induced solely by boiling, kettle type evaporators, evaporators in which evaporation is brought about by means of forced circulation in which velocity and turbulence are increased by using a circulation pump ("Forced-circulation Evaporators"), evaporators of the ME-EV ("Multi-Effect Evaporator") type, single or multiple stage evaporators, single effect evaporators, STV type evaporators ("Short Tube Vertical Evaporators"), LTV type evaporators ("Long Tube Vertical Evaporators"), "basket type" evaporators, horizontal tube evaporators, "Falling Film Evaporators", thin-film evaporators ("Wiped Film Evaporators"), and the like. A kettle type evaporator is preferably used.

Further details relating to the types of evaporators used may be found, for example, in "Process Heat Transfer", Donald Q. Kern, McGraw-Hill (1950), chapter 14, Evaporator, pp. 375-510; Perry's Chemical Engineers' Handbook, McGraw-Hill (7th ed. - 1997), section 11 , pp. 108-118.

According to a preferred embodiment of the present invention, said evaporator may operate at a temperature ranging from 95°C to 300°C, preferably ranging from 130°C to 280°C.

According to a preferred embodiment of the present invention, said evaporator may operate at a pressure ranging from 0.5 bara (bar absolute) to 5 bara (bar absolute), preferably ranging from 0.9 bara (bar absolute) to 3 bara (bar absolute).

It should be noted that, for the aim of the present invention, said mixture (a), before being fed to the evaporator, may be pre-heated in a heat exchanger (i.e. in the second heat exchanger as described below), by stream (g) which may be used entirely or in part for this aim, thus permitting heat recovery. On exiting from said heat exchanger, stream (g) is fed to said second purification section. It should furthermore be noted that, for the aim of the present invention, a small portion of the gaseous stream (b), once condensed, may be refluxed in the liquid phase to the top of said evaporator. Operating in this manner, the rising vapour and the descending liquid are brought into contact in the dome of the evaporator which is equipped with a contact apparatus so as to avoid entraining high-boiling impurities which may contain substances which poison the catalyst. The remaining portion, on the other hand, is fed to said first reactor.

According to a preferred embodiment of the present invention, said blowdown stream (c) may exit from the evaporator at a flow rate such as to remove a quantity of mixture (a) fed to said evaporator ranging from 0.5% by weight to 5% by weight, preferably ranging from 1% by weight to 4% by weight, relative to the total weight of said mixture (a) fed to the evaporator in one hour.

It should be noted that said blowdown stream is particularly useful in the case in which mixture (a) is derived from the fermentation of sugars obtained from biomass: in this case, as has been stated above, said mixture (a) may comprise impurities which may be eliminated in this manner (entirely or at least in part).

According to a preferred embodiment of the present invention, the catalyst contained in said first reactor may be selected from among acidic catalysts such as, for example, aluminium oxide (γ-ΑΙ₂0₃), aluminium silicate (S1O2-AI2O3), sulfonated resins, ion- exchange resins, acidic earths (for example, lanthanum oxide, zirconium oxide). Said catalysts may optionally be supported on inert carriers such as, for example, pumice, graphite, silica. Aluminium oxide (γ-ΑΙ₂0₃) is preferred.

According to a preferred embodiment of the present invention, said first reactor may operate at a temperature ranging from 190°C to 350°C, preferably ranging from 240°C to 300°C.

According to a preferred embodiment of the present invention, said first reactor may operate at a pressure ranging from 0.3 bara (bar absolute) to 2 bara (bar absolute), preferably ranging from 0.8 bara (bar absolute) to 1.8 bara (bar absolute).

According to a preferred embodiment of the present invention, the gaseous stream (b) may be fed to said first reactor operating at a "Weight Hourly Space Velocity" (WHSV), i.e. at a ratio of between the weight of the gas stream (b) fed in one hour and the weight of the catalyst, said ratio being measured in h^"1, ranging from 0.5 h^"1 to 30 h^"1, preferably ranging from 1 h^"1 to 20 h^"1, more preferably ranging from 2 h^" to 15 h^" .

It should be noted that, with the aim of avoiding catalyst fluidisation phenomena, said first reactor is preferably fed with a downflow configuration. A gaseous stream (d) exits from said first reactor, said stream comprising tetrahydrofuran, water and, optionally, impurities (for example, γ-butyrolactone) and/or unreacted 1 ,4- butanediol. In general, assuming 1 ,4-butanediol conversion to be greater than or equal to 90%, preferably equal to 100%, said stream (d) comprises: tetrahydrofuran in a quantity of greater than or equal to 50% by weight, water in a quantity of greater than or equal to 20% by weight, unreacted 1 ,4-butanediol and optional impurities (for example, γ-butyrolactone) in a quantity of less than or equal to 15% by weight, said quantity being expressed in % by weight relative to the total weight of said stream (d).

Preferably, said first purification section may comprise a distillation column. Preferably, stream (d) exiting from said first reactor may be fed to said distillation column to obtain a gaseous stream (e) exiting from the top of said distillation column comprising tetrahydrofuran, water and, optionally, light impurities (for example, acetaldehyde, butenes), and a stream (f), exiting from the bottom of said distillation column, comprising water and, optionally, heavy impurities (for example, γ-butyrolactone) and/or unreacted 1 ,4-butanediol, said unreacted 1 ,4-butanediol generally being present in a quantity of less than or equal to 95% by weight relative to the total weight of said stream (f). Generally, said stream (e) comprises: tetrahydrofuran in a quantity of greater than or equal to 50% by weight, water in a quantity of greater than or equal to 30% by weight, and optional light impurities (for example, acetaldehyde, butenes) in a quantity of less than or equal to 5% by weight, preferably of less than or equal to 1 % by weight, relative to the total weight of said stream (e).

According to a preferred embodiment of the present invention, the catalyst present in said second reactor may be selected from among acidic catalysts such as, for example, aluminium oxide (γ-ΑΙ₂0₃), aluminium silicate (S1O2-AI2O3), aluminas, zeolites, sulfonated resins, ion-exchange resins, metal phosphates (for example, boron phosphate, aluminium phosphate, calcium phosphate, sodium phosphate, cerium phosphate), or mixtures comprising at least one of said metal phosphates and phosphoric acid (for example, a mixture of sodium phosphate and phosphoric acid), ammonium phosphate, acidic earths (for example, lanthanum oxide, zirconium oxide). Said catalysts may optionally be supported on inert carriers such as, for example, pumice, graphite, silica. Metal phosphates, preferably calcium phosphate, sodium phosphate, or mixtures comprising at least one of said metal phosphates and phosphoric acid, optionally supported on inert carriers such as, for example, pumice, graphite, silica are preferred. A mixture of sodium phosphate and phosphoric acid supported on graphite, is still more preferred.

For the aim of the present invention and of the following claims, the term "zeolites" is taken to have its widest meaning, i.e. also comprising those materials conventionally known, for example, as "zeolite-like", "zeotype", and the like.

According to a preferred embodiment of the present invention, said second reactor may operate at a temperature ranging from 250°C to 450°C, preferably ranging from 350°C to 400°C.

According to a preferred embodiment of the present invention, said second reactor may operate at a pressure ranging from 0.3 bara (bar absolute) to 2 bara (bar absolute), preferably ranging from 0.8 bara (bar absolute) to 1.8 bara (bar absolute).

According to a preferred embodiment of the present invention, said stream (d) or said stream (e) may be fed to said second reactor operating at a "Weight Hourly Space Velocity" (WHSV), i.e. at a ratio between the weight of said stream (d) or of said stream (e) fed in one hour, and the weight of the catalyst, said ratio being measured in h^~\ ranging from 0.5 h^"1 to 20 h^"1, preferably ranging from 1 h^"1 to 10 h^"1.

Preferably, said stream (d) or said stream (e), may be pre-heated in a first heat exchanger by stream (g) which may be used entirely or in part for this purpose, thus permitting a first heat recovery. On exiting from said first heat exchanger, stream (g) may be fed, entirely or in part, to a second heat exchanger for the purpose, as stated above, of pre-heating mixture (a) before it is fed to the evaporator, thus permitting a second heat recovery. On exiting from said second heat exchanger, stream (g) is fed to said second purification section. Said pre-heated stream (d) or said pre-heated stream (e), may be fed to a third heat exchanger so as to achieve the input temperature into said second reactor, said temperature being ranging from 250°C to 450°C, preferably ranging from 350°C to 400°C. In the case in which stream (d) is fed to said first purification section, said stream (d), before being fed to said first purification section, may optionally be pre-cooled in a further heat exchanger which is part of said first purification section (as shown in Figure 2).

It should be noted that, with the aim of avoiding catalyst fluidisation phenomena, said second reactor is preferably fed with a downflow configuration.

Stream (g) is fed to a second purification section in order to obtain a stream (h) comprising pure 1 ,3-butadiene (purity > 90%, preferably > 99%), a stream (i) comprising water and, optionally, unreacted tetrahydrofuran, said unreacted tetrahydrofuran generally being present in a quantity of less than or equal to 60% by weight relative to the total weight of said stream (i), and, optionally, a stream (I) comprising impurities (for example, aldehydes, ketones having 4 carbon atoms, or compounds derived from the condensation thereof). Said second purification section may comprise one or more distillation columns. For the aim of the present invention, said process for the production of 1 ,3-butadiene is preferably carried out continuously. Said first reactor and said second reactor may be fixed-bed, or fluidised-bed, preferably fixed-bed. Said first reactor and said second reactor may be adiabatic, isothermal, or a combination of the two, preferably adiabatic.

As stated above, said 1 ,3-butadiene may advantageously be used as a monomer or as an intermediate in the production of elastomers and (co)polymers.

Furthermore, as stated above, the tetrahydrofuran obtained from the above-stated process, i.e. from the dehydration of 1 ,4-butanediol in the first reactor, may advantageously also be used, other than for the production of 1 ,3-butadiene, in the production of intermediates which are in turn usable in fine chemistry, agricultural chemistry, pharmaceutical chemistry, or in petrochemistry.

The present invention will now be illustrated in greater detail by an embodiment with reference to Figure 1 shown below.

The process provided by the present invention may be carried out as shown, for example, in Figure 1.

In this connection, a mixture (a) comprising 1 ,4-butanediol and water, said mixture (a) preferably being derived from the fermentation of sugars obtained from biomass, is fed to an evaporator (A) to obtain a gaseous stream (b) comprising 1 ,4-butanediol exiting from the top of said evaporator (A) and a blowdown stream (c) exiting from the bottom of said evaporator (A). Said gaseous stream (b) is fed to a first reactor (B) containing at least one dehydration catalyst to obtain a stream (d) comprising tetrahydrofuran, water and, optionally, impurities and/or unreacted 1 ,4-butanediol, exiting from said first reactor (B). Said stream (d) is fed to a first purification section (C) to obtain a stream (e) comprising tetrahydrofuran, water and, optionally, impurities, and a stream (f) comprising water and, optionally, impurities and/or unreacted 1 ,4-butanediol. Said stream (e) is fed to a second reactor (D) containing at least one dehydration catalyst to obtain a stream (g) comprising 1 ,3-butadiene, water and, optionally, impurities and/or unreacted tetrahydrofuran, exiting from said second reactor (D). Said stream (g) is fed to a second purification section (E) to obtain a stream (h) comprising pure 1 ,3-butadiene, a stream (i) comprising water and, optionally, unreacted tetrahydrofuran which is fed to said first purification section (C), and a stream (I) comprising impurities.

Figure 2 shows a setup of the first purification section (C) to which stream (d) may be fed. To this end, said stream (d) is fed to a heat exchanger (S1 ) to obtain a stream (d1 ) at a lower temperature which is fed to a non refluxing distillation column (C1 ) equipped with a reboiler (R) having 8 theoretical stages. Said distillation column (C1 ) is fed, apart from with said stream (d1 ) (fed to the 5th stage), with demineralised water [fed at the top (ml ) and to the 4th stage (m2)] with the aim of promoting separation of the heavy impurities (for example, γ-butyrolactone). A gaseous stream (e1 ) comprising tetrahydrofuran, water and, optionally, impurities exits from the top of said distillation column (C1 ) and is sent to said heat exchanger (S1 ) to obtain a stream (e) heated by said stream (d) which may be fed to a second reactor (D) (not shown in Figure 2), and a stream (f) exiting from the bottom of said distillation column (C1 ) comprising water and, optionally, heavy impurities (in particular, γ-butyrolactone) and/or unreacted 1 ,4-butanediol.

Some illustrative, non-limiting examples of the present invention are provided below to assist in understanding the present invention and the implementation thereof.

EXAMPLE 1

The description of the present example makes reference to Figure 1 and Figure 2 shown below.

Table 2 shows the results obtained in terms of conversion (C%), selectivity (S ) and yield (Y%), expressed by calculating the conversion of 1 ,4-butanediol (1 ,4-BDO) {CI_:4-BDO), selectivity for tetrahydrofuran (THF) (S,) and yield of tetrahydrofuran ( Y_THF), conversion of tetrahydrofuran (THF) (C_THF), selectivity for 1 ,3-butadiene (1 ,3-BDE) (SU-BDE) and yield of 1 ,3-but to the formulae shown below.

(moles_THF\

_{BDE =} ^moles _{1 QQ} .

moles_THF)_in - {moles_THF)_out

in which:

(molesi_i4._BDo)in = input moles of 1 ,4-butanediol;

(moles 4-BDo)out = output moles of 1 ,4-butanediol;

molesTHF = total moles of tetrahydrofuran;

(molesTHF)in = input moles of tetrahydrofuran; (molesTHF)out - output moles of tetrahydrofuran;

moles_{1 3}._BDE = total moles of 1 ,3-butadiene.

Table 2 shows the characterisation of the streams obtained, in which the weight percentages of the compound(s) are expressed relative to the total weight of the stream obtained, characterisation being carried out as described below.

(i) Preparation of tetrahydrofuran from a mixture of 1 ,4-butanediol

A mixture (a) comprising 1 ,4-butanediol and water having the following composition was used for this purpose: 17% by weight of water relative to the total weight of said mixture comprising 1 ,4-butanediol.

A first tubular reactor, with an internal diameter of 10 mm, was charged with 10 g of aluminium oxide (γ-ΑΙ₂0₃ as extruded pellets 1 mm in length). Said first tubular reactor was heated with an electrical oven and the temperature inside the reactor was maintained at 270°C during the test. The temperature of the evaporator was maintained at 250°C during the test. The pressure inside said first tubular reactor and the evaporator was maintained at atmospheric pressure (1 bara). The outlet from said first reactor was connected to a first condenser operating at 15°C in order to recover those products which are liquid at room temperature. The vent of the flask for collecting the condensed liquid was connected to a sampling system made up of a steel cylinder of a volume of 300 ml equipped with intercept valves at each of the two ends. The gas flowed through the steel cylinder and the outlet from the latter was connected to a volumetric meter which measured the quantity of gas which evolved.

The above-stated mixture (a) comprising 1 ,4-butanediol and water was fed to said evaporator operating under the above-stated conditions at a flow rate of 100 g/h, vaporised, and fed to said first reactor at a WHSV of 10 h^"1, said first reactor operating under the above-stated conditions. On exiting from said first reactor, the stream (d) obtained, the composition of which is shown in Table 1 , was condensed, weighed and analysed by gas chromatography. The gas which evolved was measured and likewise analysed by gas chromatography. Table 2 shows the obtained results.

(ii) Purification of Tstream (d)1

It should be noted that stream (b) exiting from the evaporator may contain compounds having a boiling point close to that of 1 ,4-butanediol (for example, γ-butyrolactone) originating from the fermentation process. In particular, as described, for example, in the above-mentioned American patent US 6,316,640, it is obvious from the literature that the presence of even high percentages of γ-butyrolactone has no impact on the activity of the dehydration catalyst used in the first reactor (B) and it may thus be separated after conversion of the 1 ,4-butanediol into tetrahydrofuran thanks to the difference between the boiling points (i.e. 1 ,4-butanediol = 228°C; tetrahydrofuran = 64°C; γ-butyrolactone = 204°C).

Since a mixture derived from the fermentation of sugars obtained from biomass containing Y-butyrolactone in a quantity ranging from 10% by weight to 30% by weight relative to the total weight of said mixture was unavailable, the first purification section (C) was modelled using ASPEN PLUS v8.0 software. The process setup used is that shown in Figure 2. To this end, the following simulation was carried out under the operating conditions shown in Table 3 and in Table 4. Said Table 3 and said Table 4 furthermore show the results obtained from said simulation on the basis of a stream (d) exiting from first reactor (B) respectively containing 10% by weight and 30% by weight of γ-butyrolactone relative to the total weight of the stream (d).

Said stream (d) is fed to a heat exchanger (S1 ) to obtain a stream (d1 ) at a lower temperature which is fed to a non refluxing distillation column (C1) equipped with a reboiler (R) having 8 theoretical stages. Said distillation column (C1 ) is fed, apart from with said stream (d1 ) (fed to the 5th stage), with demineralised water [fed at the top (ml) and to the 4th stage (m2)] with the aim of promoting separation of the heavy impurities (for example, γ-butyrolactone). A gaseous stream (e1) comprising tetrahydrofuran, water and, optionally, impurities exits from the top of said distillation column (C1 ) and is sent to said heat exchanger (S1 ) to obtain a stream (e) heated by said stream (d) and a stream (f) exiting from the bottom of said distillation column (C1 ) comprising water and, optionally, heavy impurities (in particular, γ-butyrolactone) and/or unreacted 1 ,4-butanediol.

A stream (e) and a stream (f), the composition of which is shown in Table 3 and in Table 4, are obtained from the above-stated simulation.

(iii) Preparation of 1 ,3 butadiene from stream (e)

A stream (e), the composition of which is shown in Table 2, was used for this purpose, said stream being obtained by adding water in proportion to stream (d) derived from the above-stated stage (i) [so simulating the composition which would have been obtained by subjecting said stream (d) to the above-stated stage (ii)].

A second reactor was used for this purpose. Said second reactor had the same characteristics as the above-described first reactor in stage (i) but was charged with 18 grams of a mixture of sodium phosphate and phosphoric acid supported on graphite which was obtained as described in the above-mentioned "Annalen der Chemie, Justus Liebigs" (1955), vol. 596(1 ), pp. 110.

Stream (e) was fed, in vapour form, at a WHSV of 1 h^"1 to said second reactor operating at atmospheric pressure (1 bara) and at a temperature of 375°C. On exiting from said second reactor, the stream (g) obtained, the composition of which is shown in Table 2, was condensed, weighed and analysed by gas chromatography. The gas which evolved was measured and likewise analysed by gas chromatography. Table 1 shows the obtained results.

TABLE 1

TABLE 2

TABLE 3

Pressure (bar) 1.7 1.6 1.5 1.5 1.55 3 3

Vapour fraction 1 1 1 1 0 0 0

Molar flow rate 13.068 13.068 15.361 15.361 2.106 2.2 2.2 (Kmol/h)

Mass flow rate 500 500 504.339 504.339 74.928 39.634 39.634 (Kg/h)

Volumetric flow 315.657 290.644 374.526 315.245 0.083 0.04 0.04 rate (m³/h)

Enthalpy -0.677 -0.691 -0.804 -0.818 -0.156 -0.15 -0.15 (Gcal/h)

Weight fraction ⁾ (%)

1 ,4-BDO 0 0 0 0 0 0 0 γ-Butyrolactone 0.1 0.1 0.006 0.006 0.624 0 0

Water 0.3 0.3 0.399 0.399 0.376 1 1

Tetrahydrofuran 0.6 0.6 0.595 0.595 35 0 0

(ppm)⁽²⁾

Molar flow rate

(Kmol/h)

1 ,4-BDO 0 0 0 0 0 0 0 γ-Butyrolactone 0.581 0.581 0.038 0.038 0.543 0 0

Water 8.326 8.326 11.163 11.163 1.563 2.2 2.2

Tetrahydrofuran 4.16 4.16 4.16 4.16 <0.001 0 0

': % by weight relative to total weight of the analysed stream;

': quantity stated in ppm (parts per million). TABLE 4

: % by weight relative to total weight of the analysed stream : quantity stated in ppm (parts per million).

Claims

Process for the production of 1 ,3-butadiene comprising:

(c) a blowdown stream exiting from the bottom of said evaporator;

optionally, feeding said stream (d) to a first purification section to obtain:

(e) a stream comprising tetrahydrofuran, water, and, optionally, impurities;

(f) a stream comprising water and, optionally, impurities and/or unreacted 1,4-butanediol;

feeding said stream (d) or said stream (e) to a second reactor containing at least one dehydration catalyst to obtain (g) a stream comprising 1 ,3- butadiene, water and, optionally, impurities and/or unreacted tetrahydrofuran, exiting from said second reactor;

feeding said stream (g) to a second purification section to obtain:

(h) a stream comprising pure 1 ,3-butadiene;

(I) a stream comprising impurities.

Process for the production of 1 ,3-butadiene according to claim 1 , in which said mixture (a) is derived from the fermentation of sugars obtained from biomass.

Process for the production of 1 ,3-butadiene according to claim 1 or 2, in which said mixture (a) is derived from the fermentation of sugars obtained from guayule or thistle, including discards or residues derived from said guayule and/or thistle or from the processing thereof, preferably from the fermentation of sugars obtained from guayule, including discards or residues derived from said guayule or the processing thereof.

Process for the production of 1 ,3-butadiene according to any one of the preceding claims, in which said evaporator operates:

at a temperature ranging from 95°C to 300°C, preferably ranging from 130°C to 280°C; and/or

at a pressure ranging from 0.5 bara (bar absolute) to 5 bara (bar absolute), preferably ranging from 0.9 bara (bar absolute) to 3 bara (bar absolute).

Process for the production of 1 ,3-butadiene according to any one of the preceding claims, in which said blowdown stream (c) exits from the evaporator at a flow rate such as to remove a quantity of mixture (a) fed to said evaporator ranging from 0.5% by weight to 5% by weight, preferably ranging from 1% by weight to 4% by weight, relative to the total weight of said mixture (a) fed to the evaporator in one hour.

Process for the production of 1 ,3-butadiene according to any one of the preceding claims, in which the catalyst contained in said first reactor is selected from acidic catalysts such as aluminium oxide (γ-ΑΙ₂0₃), aluminium silicate (S1O2-AI2O3), sulfonated resins, ion-exchange resins, acidic earths (such as lanthanum oxide, zirconium oxide), said catalysts optionally being supported on inert carriers such as pumice, graphite, silica; aluminium oxide (γ-ΑΙ₂0₃) being preferred.

Process for the production of 1 ,3-butadiene according to any one of the preceding claims, in which said first reactor operates:

at a temperature ranging from 190°C to 350°C, preferably ranging from 240°C to 300°C; and/or

at a pressure ranging from 0.3 bara (bar absolute) to 2 bara (bar absolute), preferably ranging from 0.8 bara (bar absolute) to 1.8 bara (bar absolute). Process for the production of 1 ,3-butadiene according to any one of the preceding claims, in which the gaseous stream (b) is fed to said first reactor operating at a "Weight Hourly Space Velocity" (WHSV), i.e. at a ratio between the weight of the gaseous stream (b) fed in one hour, and the weight of the catalyst, said ratio being measured in h^"1, ranging from 0.5 h^" to 30 h^"1, preferably ranging from 1 h^"1 to 20 h^"1, more preferably ranging from 2 h^"1 to 15 h^~1.

Process for the production of 1 ,3-butadiene according to any one of the preceding claims, in which the catalyst contained in said second reactor is selected from acidic catalysts such as aluminium oxide (γ-ΑΙ₂0₃), aluminium silicate (S1O2-AI2O3), aluminas, zeolites, sulfonated resins, ion-exchange resins, metal phosphates (such as boron phosphate, aluminium phosphate, calcium phosphate, sodium phosphate, cerium phosphate), or mixtures comprising at least one of said metal phosphates and phosphoric acid (such as a mixture of sodium phosphate and phosphoric acid), ammonium phosphate, acidic earths (such as lanthanum oxide, zirconium oxide), said catalysts optionally being supported on inert carriers such as pumice, graphite, silica; preferably being selected from metal phosphates, more preferably calcium phosphate, sodium phosphate, or from mixtures comprising at least one of said metal phosphates and phosphoric acid, optionally supported on inert carriers such as pumice, graphite, silica; a mixture of sodium phosphate and phosphoric acid supported on graphite being still more preferred.

10. Process for the production of 1 ,3-butadiene according to any one of the preceding claims, in which said second reactor operates:

at a temperature ranging from 250°C to 450°C, preferably ranging from 350°C to 400°C; and/or

at a pressure ranging from 0.3 bara (bar absolute) to 2 bara (bar absolute), preferably ranging from 0.8 bara (bar absolute) to 1.8 bara (bar absolute).

11. Process for the production of 1 ,3-butadiene according to any one of the preceding claims, in which said stream (d) or said stream (e) is fed to said second reactor operating at a "Weight Hourly Space Velocity" (WHSV), i.e. at a ratio between the weight of said stream (d) or of said stream (e) fed in one hour, and the weight of the catalyst, said ratio being measured in h^"1, ranging from 0.5 h^"1 to 20 h^"1, preferably ranging from 1 h-¹ to 10 h-¹.