GB2538940A - Process for the preparation of butadiene - Google Patents

Abstract

There is provided a method for producing butadiene comprising: (a) contacting a mixture of butanediol and an inert gas with a zirconia catalyst in a reactor at a temperature of at least about 350°C for from about 0.2 seconds to about 10.0 seconds; and (c) obtaining a reaction product comprising butadiene. The zirconia catalyst may further comprise one or more transition metals such as cobalt or nickel, more preferably in the form of cobalt oxide and/or nickel oxide.

Description

PROCESS FOR THE PREPARATION OF BUTADIENE

TECHNICAL FIELD

The present invention relates to a method for producing butadiene from butanediol. BACKGROUND ART Butadiene is an important intermediate widely used in the manufacture of synthetic rubbers, polymer resins and elastomers.

During the early twentieth century producers in Germany obtained butadiene from acetylene via 1,3-butanediol or 1,4-butanediol. In a first route, acetylene was hydrated to yield acetaldehyde which was converted into the aldol product and hydrogenated to give 1,3-butanediol which was subsequently dehydrated to butadiene. In a second route, known as the "Reppe" process, formaldehyde and acetylene were used to produce 1,4-butynediol, which was then hydrogenated to 1,4-butanediol and dehydrogenated partly via tetrahydrofuran to butadiene. Today these acetylene routes are largely abandoned and a large percentage of butadiene is obtained as a byproduct of cracking, or is produced via the catalytic dehydrogenation of n-butane and n-butenes.

The availability of bio-derived butanediols from renewable and waste feedstocks has resulted in a renewed interest in the production of butadiene from butanediol. However, the production of butadiene from butanediol is not straightforward. Firstly, a number of structural isomers of butanediol exists, including 1,4-butanediol, 1,3-butanediol, 1,2-butanediol and 2,3-butanediol. Each isomer can be dehydrated twice to give butadiene but the pathway for dehydration in each case differs and proceeds via different intermediates depending on the isomer. Thus, in a catalytic dehydration process, the catalyst and the reaction conditions generally differ depending on the position of the alcohol groups. For example, 2,3-butanediol predominantly undergoes a pinacol type dehydration to form butan-2-one (commonly known as methyl ethyl ketone or MEK) whereas 1,4-butanediol is known to undergo a cyclodehydration to form tetrahydrofuran (THF).

Production of butadiene from 1,4-butanediol is well established from the Reppe process mentioned above, in which 1,4-butanediol is converted to butadiene via tetrahydrofuran using a H2Pa4catalyst at 280°C. 1,3-butanediol can also be converted to butadiene using the Reppe H2PO4 catalyst but higher temperatures are required.

The acidic dehydration of 1,4-butanediol almost always leads primarily to the selective formation of the cyclic ether tetrahydrofuran. Butadiene can nonetheless be obtained in small amounts. To obtain satisfactory yields of butadiene it is necessary to separate the butadiene from the major tetrahydrofuran product and then recycle the tetrahydrofuran back into the process.

1,3-butanediol on the other hand undergoes classic 1,3-diol dehydration under appropriate conditions and various dehydrated enol intermediates are formed, such as 2-buten-1-ol, 3-buten-1-ol and 3-buten-2-ol. CeO2 has been used in a two-step process in which 2-buten-1-ol and 3-buten2-ol are selectively formed. The enols are then further dehydrated to butadiene in good yield using Si02-A1203.

Catalysts such as A1203 and CeO2 have been more recently studied for the dehydration of 1,4butanediol but high conversion rates are always accompanied by low selectivity with respect to butadiene. For example, A1203 has been used to obtain butadiene with a selectivity of about 70 mol% although the conversion in this method is typically around 15 mol%. Thus, a process which provides high overall yields for butadiene from 1,4-butanediol is unknown.

As mentioned above, under dehydration conditions 2,3-butanediol undergoes a pinacol rearrangement and therefore butanone (MEK) is predominately formed. However, butanone can isomerise to 3-buten-2-ol and as noted above dehydration of this isomer gives butadiene. A Th02 catalyst has been described to selectively produce butadiene from 2,3-butanediol.

The selective double dehydration of butanediols to butadiene remains a challenge requiring specific catalysts. Furthermore, known methods suffer from either poor conversion or poor selectivity, therefore making it challenging to obtain butadiene selectively and in high yield.

It is therefore an object of the invention to provide a new process for selectively producing butadiene from butanediol in high yield.

It is a further object of the invention to provide a process which can be carried out continuously.

DISCLOSURE OF THE INVENTION

The present invention provides a method for producing butadiene comprising: (a) contacting a mixture of butanediol and an inert gas with a zirconia catalyst in a reactor at a temperature of at least about 350°C for from about 0.2 seconds to about 10.0 seconds; and (b) obtaining a reaction product comprising butadiene.

The present invention further provides a method for regenerating a zirconia catalyst in a reactor in a method for producing butadiene from butanediol, comprising: (a) feeding a gas comprising oxygen into a reactor comprising a zirconia catalyst; and (b) heating the gas in the reactor to at least about 400°C.

The method suitably comprises stopping the production of butadiene from butanediol prior to feeding the gas comprising oxygen into the reactor. In step (b), combustion of carbon degradation products on the zirconia catalyst suitably occurs, thus regenerating the zirconia catalyst (i.e. the catalyst is decoked).

Thus, the present invention further provides a method for producing butadiene comprising: (a) contacting a mixture of butanediol and an inert gas with a zirconia catalyst in a reactor at a temperature of at least about 350°C for from about 0.2 seconds to about 10.0 seconds; (b) obtaining a reaction product comprising butadiene; (c) stopping step (a); (d) feeding a gas comprising oxygen into the reactor comprising said zirconia catalyst; and (e) heating the gas in the reactor to at least about 400°C.

Surprisingly, it has been found that butadiene is obtained in good yield by using a zirconia catalyst in combination with a specific temperature and reaction time. In particular, in the method of the invention, almost quantitative conversion of the butanediol is observed and butadiene is preferably obtained as the major product. Thus, the method of the invention provides butadiene in surprisingly high yields without the need for recycling of the mono-dehydration products, such as THF, back into the reactor.

Preferably, the zirconia catalyst is a zirconia catalyst which is known for catalysing the conversion of N20 to nitrogen and oxygen. Preferably, the zirconia catalyst further comprises transition metals other than zirconium, preferably present in the form of transition metal oxides, which has been found to improve both the overall conversion of the butanediol and the selectivity with respect to butadiene formation.

It has been found that over time the zirconia catalyst becomes less effective and that formation of dehydration side products, such as the mono dehydration product, increase. To this end, when the process is carried out continuously it is desirable to periodically remove carbon degradation products (i.e. coke) deposited on the catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a reactor configuration for carrying out the method of the invention. Figure 2 shows a further configuration for carrying out the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the invention are described herein. It will be recognised that features specified in each embodiment may be combined with other specified features to provide further embodiments.

The method of the invention provides a method for producing butadiene from butanediol which is particularly suitable for being operated as a continuous process.

Contacting butanediol with an inert gas The method of the invention suitably comprises the step of contacting butanediol with an inert gas to form a mixture. The butanediol may be contacted with the inert gas to form the mixture and then fed into the reactor. Alternatively, the inert gas and the butanediol may be fed into the reactor as separate feeds, thus forming the mixture in the reactor. It is therefore possible in this configuration to stop the contacting of the butanediol with the inert gas by stopping the inert gas feed or by stopping the butanediol feed.

Any inert gas may be used in the method of the invention. However, from an economical point of view, nitrogen is the preferred inert gas.

Any isomer of butanediol may be used as the starting material in the method of the present invention. The butanediol may be selected from the group consisting of 1,4-butanediol, 2,3butanediol, 1,3-butanediol, and 1,2-butanediol. The use of bio-derived butanediols is also considered. Bio-derived butanediols are from renewable or waste feedstocks via fermentation of biomass. The bio-derived butanediols may be selected from the group consisting of 1,4-bio-butanediol, 2,3-bio-butanediol, 1,3-bio-butanediol, and 1,2-bio-butanediol.

Preferably, the butanediol used in the method of the invention is 1,4-butanediol. The butanediol may be a bio-derived butanediol, preferably 1,4-bio-butanediol.

The butanediol is suitably vaporised before being fed into the reactor. The butanediol may be vaporised by heating it, typically to the temperature of the contacting step, for example to at least about 350°C, before it is fed into the reactor. The heated vapour may be mixed with the inert gas. The heating is suitably carried out using one or more gas:gas or gas:liquid shell and tube heat exchangers. The butanediol vapour may comprise water. Suitably, the butanediol is provided as a solution in water containing at least about 10wt.% (of the total weight of the solution) butanediol and then vaporised. The solution may comprise at least about 20wt.°/0, at least about 30wt.%, at least about 40wt.%, at least about 50wt.%, at least about 60wt.%, at least about 70wt.%, at least about 80wt.%, and up to about 85wt.%, or up to about 90wt.%, or up to about 99wt.% butanediol.

Step (a) -Contacting the butanediol and inert gas mixture with a catalyst The method of the invention comprises the step of contacting a mixture of butanediol and an inert gas with a zirconia catalyst in a reactor at a temperature of at least about 350°C for from about 0.2 seconds to about 10.0 seconds.

Suitably, the mixture is formed by contacting the butanediol with the inert gas as described above.

The butanediol and/or the mixture may be heated, typically to the temperature of the contacting step, for example to at least about 350°C, before being fed into the reactor.

Suitably, the reactor is a packed bed reactor or a plug flow reactor.

The contacting step is carried out at a temperature of at least about 350°C. More particularly, the contacting step may be carried out at a temperature of from about 350°C to about 500°C.

Alternatively, the contacting step may be carried out at a temperature of from about 360°C to about 440°C, of from about 370°C to about 430°C, of from about 380°C to about 420°C, or of from about 390°C to about 410°C. The mixture is suitably contacted with the zirconia catalyst at a temperature in the range from about 350°C to about 450°C.

The reaction time for the method of the invention (i.e. the time over which the contacting step is carried out) is suitably from about 0.2 seconds to about 10.0 seconds. Reaction time corresponds to the gas contact time which is the actual flow of the gas (at the reactor temperature and pressure) divided by the reactor volume. The reaction time for the method of the invention may be from about 0.3 seconds to about 8.0 seconds, or from about 0.4 seconds to about 6.0 seconds, or from about 0.5 seconds to about 4.0 seconds, or from about 0.6 seconds to about 2.0 seconds.

The reaction time for the method of the invention is typically from about 0.2 seconds to about 4.0 seconds.

The reaction time can alternatively be expressed in terms of the catalyst contact time expressed as gh/ml (catalyst weight [g])/(reactant flow rate [ml/h]). The catalyst contact time in step (a) is suitably greater than 1.2 gh/ml, or greater than about 2.0 gh/ml, or greater than about 5.0 gh/ml, or greater than about 10 gh/ml, or greater than about 15 gh/ml, or greater than about 20 gh/ml, and less than about 100 gh/ml, or less than about 50 gh/ml, or less than about 30 gh/ml.

The method of the invention typically provides a high conversion of butanediol. In particular, the conversion of butanediol may be at least about 90mol%, at least about 95mo1% and up to about 100mork.

Zirconia Catalyst The catalyst used in the method of the present invention is a zirconia (ZrO2) catalyst. In particular, the zirconia catalyst is a zirconia catalyst which is known for catalysing the conversion of N20 to nitrogen and oxygen. The zirconia catalyst may be a zirconia catalyst such as that described in US 5,314,673, which is incorporated herein by reference.

The catalyst may be in any form conventional in the art. The catalyst is suitably in the form of pellets. The pellets may be rods. Alternatively, the pellets may be cylinders, spherical, trilobal, or

tablet shaped.

Typically, the pellet has a mean particle size of less than about 1/4 inch (6.4 mm) in diameter. Suitably, the pellet has a mean particle size of greater than 1/64 inch (0.40mm). Preferably, the pellet has a particle size of about 1/8 inch (3.2 mm) in diameter. The "particle size" measurement refers to the longest dimension of the pellets.

The catalyst suitably has a surface area of less than about 40.0 m2/g. The catalyst may have a surface area of less than about 35.0 m2/g, or less than about 30.0 m2/g, or less than about 25.0 m2/9 and greater than about 20.0 m2/g. The catalyst may have a surface area of from about 20.0 m2/9 to about 35.0 m2/g, or about 27.4 m2/g. Suitably, surface area is measured using nitrogen B.E.T as described in BS4359-1996, IS09277:1995 'Determination of the specific surface area of powders Part 1: BET method of gas adsorption for solids (including porous materials)'.

Optionally, the zirconia catalyst may further comprise one or more transition metals and/or oxides of one or more transition metals, wherein said one or more transition metals are other than zirconium. The one or more transition metals are suitably selected from the group consisting of cobalt, nickel and a mixture thereof. When the zirconia catalyst comprises cobalt, the cobalt may be present in an amount of from about 0.1 to about 5.0 wt.%, or from about 0.5 to about 4.0 wt.%, or from about 1.0 to about 3.0 wt.%, wherein wt.% is relative to the total weight of the catalyst. When the zirconia catalyst comprises nickel, the nickel may be present in an amount of from about 0.1 to about 5.0 wt.%, or from about 0.5 to about 4.0 wt.%, or from about 1.0 to about 3.0 wt.%, wherein wt% is relative to the total weight of the catalyst. Suitably, the zirconia catalyst comprises both cobalt and nickel. For instance, the cobalt may be present in an amount of from about 0.5 to about 2.5 wt.% and the nickel may be present in an amount of from about 0.5 to about 2.5 wt.%. Suitably, the zirconia catalyst comprises about 0.9 wt.% cobalt and about 0.9 wt.% nickel, or about 1.0 wt.% cobalt and about 1.0 wt.% nickel.

Preferably, the zirconia catalyst comprises cobalt and nickel in the form of cobalt oxide and nickel oxide, respectively. The ratio of nickel oxide to cobalt oxide in the catalyst is suitably in the range of from about 0.5:1 to about 3:1, or from about 1:1 to about 2:1.

Step (b) -Obtaining the reaction product The method of the invention comprises the step of obtaining a reaction product that comprises butadiene. The method therefore suitably comprises the step of removing a reactor exit stream comprising the reaction product comprising butadiene from the reactor. The reactor exit stream is typically a vapour stream that is suitably condensed to provide a reaction product stream. Thus, the method of the invention suitably comprises cooling the reactor exit stream. For instance, the reactor exit stream may be passed through a first condensation stage in which water is condensed. The water may then be recirculated in the process. In particular, the water separated from the reactor exit stream may be contacted with butanediol to provide the solution of butanediol in water that is vaporised and combined with the inert gas to form the reaction mixture. The reactor exit stream may then be passed through a second condensation stage in which the reaction product comprising butadiene is condensed to provide a reaction product stream and an inert gas stream. The inert gas stream may be recirculated in the process. In particular, the inert gas separated from the reactor exit stream may be contacted with butanediol to form the reaction mixture of butanediol and the inert gas as described above. The recirculation of inert gas and water in this manner reduces the consumption of these raw materials by the process.

More particularly, the reaction product may comprise at least about 50 mol% butadiene (based on the total amount of reaction product), or at least about 60 mol%, or at least about 70 mol% butadiene. More preferably, the reaction product comprises at least about 80 mol% butadiene.

Accordingly, the yield of butadiene may be at least about 50 mol% (based on the amount of butanediol starting material), at least about 60 mol%, at least about 70 mol% or at least about 80 mol%.

Where the butanediol is 1,4-butanediol, the reaction product may contain tetrahydrofuran and/or 3-buten-1-ol. Preferably, where the butanediol is 1,4-butanediol, the reaction product comprises no more than about 50 mol% tetrahydrofuran, or no more than about 40 mol% tetrahydrofuran, or no more than about 30 mol% tetrahydrofuran, or no more than about 20 mol% tetrahydrofuran.

Where the butanediol is 2,3-butanediol, the reaction product may contain methyl ethyl ketone (MEK) and/or 3-buten-1-ol. Preferably, where the butanediol is 2,3-butanediol, the reaction product comprises at least about 40 mol% butadiene, or at least about 50 mol% butadiene. Accordingly, the yield of butadiene may be at least about 40 mol% (based on the amount of 2,3-butanediol starting material), or at least about 50 mol%. Preferably, where the butanediol is 2,3-butanediol, the reaction product comprises no more than about 60 mol% methyl ethyl ketone, or no more than about 50 mol% methyl ethyl ketone.

Where the butanediol is 1,3-butanediol, the reaction product preferably contains at least about 40 mol% butadiene. Accordingly, the yield of butadiene may be at least about 40 mol% (based on the amount of 1,3-butanediol starting material). Preferably, where the butanediol is 1,3-butanediol, the reaction product comprises no more than about 60 mol% of other products.

Regenerating the zirconia catalyst Optionally, carbon degradation products (e.g. coke) deposited on the catalyst are removed during the process. The method of regenerating the zirconia catalyst comprises: (a) feeding a gas comprising oxygen into a reactor comprising a zirconia catalyst; and (b) heating the gas in the reactor to at least about 400°C.

The method suitably comprises stopping the production of butadiene from butanediol prior to feeding the gas comprising oxygen into the reactor. The production of butadiene from butanediol can be stopped by stopping step (a) of the method for producing butadiene. More particularly, the production of butadiene from butanediol can be stopped by stopping the feed of butanediol into the reactor. The step of contacting the butanediol with the inert gas may also be stopped. Organic material, including starting material and reaction product comprising butadiene, is suitably removed from the reactor. After stopping the feed of butanediol into the reactor, the feeding of a gas comprising oxygen into the reactor typically purges residual butanediol from the reactor.

The gas comprising oxygen is suitably compressed air, and is suitably provided in the absence of butanediol. The gas is heated in the reactor to at least about 400°C, typically to a temperature in the range from about 400°C to about 600°C. In a continuous process, carbon degradation products may be periodically removed to regenerate (i.e. decoke) the zirconia catalyst. In the method for regenerating the zirconia catalyst, carbon degradation products on the catalyst combust, thereby re-exposing the pore structure of the catalyst. The method of regenerating the catalyst is preferably applied when deterioration in conversion or selectivity is observed. The method of producing butadiene may then recommence, i.e. steps (a) and (b) are restarted.

Figure 1 is a schematic of a process according to an embodiment of the present invention. A butanediol stream (10) is fed together with water into a reactor (100) containing the zirconia catalyst. An inert gas stream (20) is also fed into the reactor (100). The stream (30) exiting the reactor (100) comprising the butadiene reaction product passes into a first condenser (200). The water contained in the stream (30) exiting the reactor (100) is condensed in the first condenser (200) and is recirculated as stream (60). The gaseous stream (stream 40) exiting the first condenser (200) passes into a second condenser (300) and butadiene is obtained as a liquid stream (50). The inert gas exiting the second condenser (300) is recirculated as stream (20).

EXAMPLES

Catalysts Various catalysts were evaluated including the NaH2PO4 catalyst as used in the Reppe process, a-alumina, y-alumina, ZrO2, and ZrO2 doped with CoO and NiO. The alumina catalysts were sourced from Dytech Catalyst Technologies, Sheffield, UK. The ZrO2 catalyst and Zr02+CoO/Ni0 catalyst (1wt% Co, 1 wt% Ni expressed as wt% of base metal relative to the total weight of the catalyst as measured by XRF, and having a surface area of 27.4 m2/9 as measured using nitrogen B.E.T) were sourced from BASF.

The Zr02+CoO/Ni0 catalyst may be prepared by the method described in US 5,314,673.

Specifically, 5 g cobalt nitrate (CO[NO3]2.6H20) and 5.3 g nickel nitrate (Ni[NO3]3.6H20) are dissolved in 20 ml H2O. ZrO2 pellets having dimensions of about 1/8 inch (3.2 mm) in diameter and 1/8 inch (3.2 mm) long are soaked in the cobalt/nickel solution for 2.5 hours with occasional stirring. The liquid is drained off the pellets and the pellets are dried overnight in a vacuum oven at 100°C. The dried pellets are heated in a 1 inch (25 mm) tube furnace at 700°C with air flow of 100 cc/min for 2 hours to convert the nickel nitrate and the cobalt nitrate to the respective oxides.

Test Method Experimental: Supporting experiments were carried out as described below using the apparatus shown in Figure 2. In a typical experiment, 10 wt.% 1,4 butanediol solution in water (wt.% based on the total weight of the solution) was pumped continuously at 0.25m1/min through a pre-heating coil at 350°C to vaporise the stream. This butanediol (BDO/H20) vapour stream was then mixed with a nitrogen stream, typically at 7nUmin, before entering a temperature-controlled sand bath containing the reactor. Within the sand bath, the combined stream was heated to the reactor temperature via a 6m x 6.4 mm (0.25inch) diameter coil. The combined stream then passed through a cylindrical reactor (20mm internal diameter (ID) and 150mm length) packed with 80g of the catalyst pellets under investigation. The exit stream from the reactor was directed through a water-jacketed cooling coil before entering a gas-liquid separator vessel (GLS), via a pressure let-down valve operating at ambient temperature and pressure. Butadiene, being a gas under these conditions, was transferred to the gas sampling area, whilst any unreacted butanediol, tetrahydrofuran and water were collected as a liquid stream from the base of the GLS. Both the liquid samples and the gas samples were analysed by gas chromatography.

Effect of Catalyst Various catalysts were evaluated using 1,4-butanediol as the reagent. The conditions were as described above, unless indicated otherwise. The percentage conversion of the butanediol and the amount of THF, 3-buten-1-ol (3Belol) and butadiene (BD) were determined using vapour phase sampling by gas bags to gas injection GC (gas chromatography, Agilent 6890 machine) or liquid sampling by liquid injection GC (Agilent 6890 machine).

The results are presented in Table 1 below. Table 1 Catalyst Reaction Temperature (°C) BDO BD Yield THF Weld 38e1o1 Yield (mol%) Converted (mol%) (mol%) (mol%) 1. NaH2PO4 350 100 3.9 94 2.1 on carbon 2. NaH2PO4 350 93.9 8 85 0.9 +CoO/Ni0 on carbon 3. a-alumina (fluted) 350 75 0 74.2 0 4. a-alumina (cylinders) 350 25 0 25 0 5. y-alumina (cylinders) 350 70 0 70 0 6. ZrO2* 350 100 42 56 2 7. ZrO2 350 100 56 23 16 +CoO/Ni0 *Experiment carried out at 0.49 seconds reaction time. All other experiments carried out at 0.2 seconds reaction time.

The results in Table 1 show that formation of THE is the predominant product for all catalysts except the zirconia catalysts. The results also show that the zirconia catalyst comprising the transition metals shows an improvement in selectivity with respect to butadiene compared to the ZrO2 catalyst.

Effect of Temperature Using the zirconia catalyst comprising cobalt and nickel oxides (catalyst 7 in Table 1), the effect of reaction temperature was evaluated. The reaction time was approximately 0.2-0.25 seconds and 1,4-butanediol was used as the reagent. The percentage conversion of the butanediol, and the amount of THF, 3-buten-1-ol and butadiene were measured.

The results are presented in Table 2 below.

Table 2

Catalyst Reaction Temperature (°C) BDO BD Yield THF Yield 3Be1o1 Yield (mol%) Converted (mo/%) (mo/%) (mol%) ZrO2 350 100 56 23 16 +CoO/Ni0 ZrO2 400 100 70 22 5 +CoO/Ni0 ZrO2 450 100 62 16 2 +CoO/Ni0 The results in Table 2 show that formation of THF is reduced at higher temperature and that increasing the temperature above 350°C improves selectivity with respect to butadiene.

Further examples using different forms of butanediol The method was further evaluated against a number of alternative isomers of butanediol to determine whether the zirconia catalyst comprising cobalt and nickel oxides (catalyst 7 in Table 1), was effective in converting these isomers of butanediol into butadiene.

The results are presented in Table 3 below.

Table 3

Butanediol Reaction Time (s) Reaction Temperature (°C) BDO BD Yield (mol%) THE Yield (mol%) MEK Yield (mol%) 3Belol Yield (mol%) Converted (mol%) 1,4- 0.46 400 100 80 20 --- 0 butanediol 2,3- 0.46 400 100 48 52 butanediol 1,4 bio-butanediol 0.5 400 100 80 20 0 1,3- 0.5 400 100 40 --- --- ---butanediol 1,2- 0.5 400 100 8 5 - -butanediol Table 3 shows that the zirconia catalyst comprising cobalt and nickel oxides (catalyst 7 in Table 1), can be used for dehydration of bio-derived butanediol and the various isomers of butanediol.

Effect of Reaction Time Using the zirconia catalyst comprising cobalt and nickel oxides (catalyst 7 in Table 1), the effect of reaction time was evaluated. The reaction temperature was 400°C.

The results are presented in Table 4 below.

Table 4

Catalyst BDO isomer Reaction time BDO BD Yield (mol%) THE Yield (mol%) 38e1o1 Yield (mol%) (seconds) Converted (mol%) ZrO2 1,4-BDO 0.25 97 55 34 1 +CoO/NiO ZrO2 1,4-BDO 0.43 98 75 25 0 +CoO/Ni0 ZrO2 1,4-BDO 1.00 100 90 10 0 +CoO/Ni0 ZrO2 1,4-BDO 1.8* 100 97 3 0 +CoO/Ni0 ZrO2 2,3-BDO 1.8* 100 80 20(MEK) 0 +CoO/Ni0 *Reaction carried out in a larger reactor (cylindrical having a 40mm diameter (ID), 150mm length and containing 305 g of the catalyst) The results in Table 4 show that increasing reaction time improves conversion and selectivity with respect to butadiene.

Effect of extended running time The effect of running the method with the doped zirconia catalyst over an extended period of time in a continuous process was investigated. The process was run continuously for approximately 40 hours at 400°C with a reaction time of 0.2 seconds.

The results are presented in Table 5 below.

Table 5

Elapsed time BDO BD Yield THE Yield 3Belol Yield (hours) Converted (mol%) (mol%) (mol%) (mol%) 0 100 70 28 2 98 60 32 8 39 96 55 25 10 The results in Table 5 suggest that the catalyst becomes less effective over extended reaction times. Thus, while increasing temperature and reaction time may appear to improve selectivity with respect to butadiene, the catalyst is likely to become ineffective under certain conditions, potentially as a result of deposits of carbon degradation products on the catalyst (i.e. catalyst coking).

Effect of catalyst regeneration (de-coking) The method was run continuously at 400°C with a reaction time of 0.46 seconds for over 100 hours while monitoring the proportion of reaction products. A drop in selectivity with respect to butadiene was observed. Following the drop in selectivity, compressed air was passed through the reactor for 15 minutes while maintaining the temperature at 400 °C. Following the treatment with compressed air the catalyst performance was restored.

Table 6

Elapsed time BDO BD Yield THE Yield 3Bel of Yield (hours) Converted (mol%) (mol%) (mol%) (mol%) 0 100 80 20 0 (prior to regeneration) 100 60 38 2 (after regeneration) 100 78 23 0

Claims (21)

1. CLAIMS1. A method for producing butadiene comprising: (a) contacting a mixture of butanediol and an inert gas with a zirconia catalyst in a reactor at a temperature of at least about 350°C for from about 0.2 seconds to about 10.0 seconds; and (b) obtaining a reaction product comprising butadiene.
2. 2. The method of claim 1, wherein the contacting is carried out at a temperature in the range from about 350°C to about 450°C.
3. The method of claim 1 or claim 2, wherein the contacting is carried out for from about 0.2 seconds to about 4.0 seconds.
4. 4. The method of any one of the preceding claims, wherein the butanediol is selected from the group consisting of 1,4-butanediol, 2,3-butanediol, 1,3-butanediol, and 1,2-butanediol.
5. 5. The method of any one of the preceding claims, wherein the butanediol is 1,4-butanediol.
6. 6. The method of claim 4, wherein the butanediol is selected from the group consisting of 1,4-bio-butanediol, 2,3-bio-butanediol, 1,3-bio-butanediol, and 1,2-bio-butanediol.
7. 7. The method of claim 6, wherein the 1,4-butanediol is 1,4-bio-butanediol.
8. 8. The method of any one of the preceding claims, wherein the reaction product comprises at least about 50mork butadiene.
9. The method of any one of the preceding claims, wherein the reaction product comprises no more than about 50mol% tetrahydrofuran.
10. 10. The method of any one of the preceding claims, wherein the reaction product comprises from about 80mol% to about 97mo1% butadiene, and preferably no more than about 0.3mol% to about 20mol% tetrahydrofuran.
11. 11. The method of claim 1, wherein the butanediol is 2,3-butanediol or 2,3-bio-butanediol.
12. 12. The method of claim 11, wherein the reaction product comprises at least about 40mol% butadiene.
13. 13. The method of claim 11 or claim 12, wherein the reaction product comprises no more than about 60mol% methyl ethyl ketone.
14. 14. The method of any one of the preceding claims, wherein the zirconia catalyst further comprises one or more transition metals other than zirconium.
15. 15. The method of claim 14, wherein the one or more transition metals are selected from the group consisting of cobalt, nickel and a mixture thereof.
16. 16. The method of claim 15, wherein the zirconia catalyst comprises cobalt in an amount from about 0.1 to about 5.0 wt.% and/or nickel in an amount from about 0.1 to about 5.0 wt.%.
17. 17. The method of claim 16, wherein the cobalt is present in an amount of about 1 wt.% and/or the nickel is present in an amount of about 1 wt.%.
18. 18. The method of claim 16 or claim 17, wherein the zirconia catalyst comprises both nickel and cobalt.
19. 19. The method of any one of claims 15-18, wherein the cobalt and/or nickel are present in the form of cobalt oxide and/or nickel oxide.
20. 20. The method of any one of the preceding claims, further comprising cooling said reaction product comprising butadiene.
21. 21. The method of any one of the preceding claims further comprising steps (c) and (d) for regenerating the zirconia catalyst: (c) feeding a gas comprising oxygen into a reactor comprising said zirconia catalyst; and (d) heating the gas in the reactor to at least about 400°C.