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Title:
SINGLE STEP CONVERSION OF ETHANOL TO BUTADIENE
Document Type and Number:
WIPO Patent Application WO/2018/147934
Kind Code:
A1
Abstract:
A process for producing 1,3-butadiene (BD) from ethanol in a single step by s7passing a mixture containing ethanol in a gas phase over a multifunctional catalyst having a transition metal dispersion of at least 30% on a silica metal oxide support. In some examples the multifunctional catalyst comprises a silica metal oxide having a surface area of at least 200 m^2/g. The multifunctional catalyst can include a transition metal oxide, a silica metal oxide made from a high purity silica gel, mesoporous silica and fumed silica, such as high purity SBA16, SBA15, or Davisil grade 646.

Inventors:
DAGLE VANESSA (US)
DAGLE ROBERT A (US)
Application Number:
PCT/US2017/066024
Publication Date:
August 16, 2018
Filing Date:
December 13, 2017
Export Citation:
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Assignee:
BATTELLE MEMORIAL INSTITUTE (US)
International Classes:
C07C1/20; C07C1/207; C07C11/167
Domestic Patent References:
WO2012015340A12012-02-02
WO2014129248A12014-08-28
Foreign References:
Other References:
VITALY L. SUSHKEVICH ET AL: "Design of a Metal-Promoted Oxide Catalyst for the Selective Synthesis of Butadiene from Ethanol", CHEMSUSCHEM, vol. 7, no. 9, 14 August 2014 (2014-08-14), DE, pages 2527 - 2536, XP055276670, ISSN: 1864-5631, DOI: 10.1002/cssc.201402346
SUSHKEVICH, V.; IVANOVA, I.; TAARNING, E.: "Ethanol conversion into butadiene over Zr-containing molecular sives doped with silver", GREEN CHEMISTRY, vol. 17, 16 February 2015 (2015-02-16), pages 2552 - 2559, XP002778350
None
Attorney, Agent or Firm:
MAUGHAN, Derek H. (US)
Download PDF:
Claims:
What is claimed is:

1 . A process for producing 1 ,3-butadiene (BD) from ethanol in a single step, comprising the step of passing a feed containing ethanol in a gas phase over a multi-functional catalyst having a transition metal dispersion of at least 30% on a metal oxide support.

2. The process of claim 1 wherein the multifunctional catalyst comprises a silica metal oxide having a surface area of at least 200 mA2/g.

3. The process of claim 2 wherein the multifunctional catalyst further

comprises a Group 1 1 metal.

4. The process of claim 3 wherein the Group 1 1 metal is selected from the group consisting of copper (Cu), silver (Ag), and gold (Au).

5. The process of claim 2 wherein the silica metal oxide support comprises a silica metal oxide selected from the group consisting of a high purity silica gel, mesoporous silica and fumed silica.

6. The process of claim 4 wherein the silica metal oxide is a high purity

SBA16.

7. The process of claim 4 wherein the silica metal oxide is high purity SBA15.

8. The process of claim 4 wherein the silica metal oxide is Davisil grade 646.

9. The process of claim 1 wherein hydrogen is added to the mixture.

10. The process of claim 1 wherein the feed is 100% ethanol.

1 1 . The process of claim 1 wherein the feed is a mixture containing at least 30 percent ethanol and includes water.

12. The process of claim 1 wherein the step of passing the mixture containing ethanol in a gas phase over a catalyst comprising a silica metal oxide is performed at a temperature between 200oC and 500oC.

13. A process for producing 1 ,3-butadiene (BD) from ethanol in a single step, comprising the step of passing a feed containing ethanol in a gas phase over a Ag/Zr02/Si02 catalyst having a transition metal dispersion of at least 30% on a silica metal oxide support.

14. The process of claim 13 wherein the catalyst is 1 %Ag/4%Zr02/Si02- SBA-16.

15. The process of claim 13 wherein the operating conditions include a

temperature of 325° C, pressure of 1 atm, and a flow rate of 0.23 hr-1 .

16. The process of claim 13 wherein the feed contains water.

17. The process of claim 13 wherein the feed contains water.

Description:
SINGLE STEP CONVERSION OF ETHANOL TO BUTADIENE

CLAIM TO PRIORITY

[0001] This invention claims priority from U.S. Non-provisional Patent Application No. 15/837,382, entitled Single Step Conversion of Ethanol to Butadiene, filed December 1 1 , 2017, which claims priority to U.S. Provisional Patent Application No. 62/455,768, entitled Single Step Conversion of Ethanol to Butadiene, filed February 7, 2017.

PRIORITY

[0002] This invention was made with Government support under Contract DE-AC05-76RL01830 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

[0003] 1 ,3-Butadiene (BD) is an important building block used in the polymer chemistry. It is used among other things in the production of styrene- butadiene rubbers that are primarily used in the fabrication of materials such as synthetic rubber or elastosmers which make up products such as production of polymers such as synthetic rubbers or elastomers including styrene-butadiene rubber (SBR), polybutadiene rubber (PBR), nitrile rubber (NR) and polychloropropene (Neoprene).

[0004] Currently, BD is typically primarily obtained as a by-product of the naphtha steam cracking process that serves to make ethylene. The production of ethylene from steam cracking is in decline due to the recent and drastic increase of shale gas production in the USA which offers another pathway for obtaining ethylene from ethane but does not result in the BD creation. In addition to the shift in lighter feedstocks, crude oil price swings have historically led to corresponding price fluctuations in the cost of butadiene, and this is not sustainable for the end users of this important building block. Thus, alternative technologies for producing butadiene are highly desired.

[0005] Ethanol conversion to butadiene (ETB) represents an attractive alternative technology. Ethanol can be sourced from a variety of locations including commercial production from renewable biomass or waste sources. In addition, the ethanol "blend wall" coupled with advancements in production efficiency and feedstock diversification will potentially lead to excess ethanol at competitive prices available for the production of a wide range of fuels and commodity chemicals. Furthermore a recent early-stage assessment method comparing the bioethanol-based pathway for butadiene production with the naphtha-based route suggests that the bioethanol pathway could be a promising alternative to the naphtha-based process.

[0006] Research on butadiene production from ethanol has existed for years however, achieving high yield to butadiene at industrially relevant process conditions has been challenging. There are a large number of catalyst systems capable of converting ethanol to butadiene in one step that have been reported however, in many of these instances low single pass conversion (< 45%) resulted. For the single-step process to be successful and viable higher per pass conversion and high selectivity (> 70%) are desirable. What is needed is a system for producing BD from ethanol that can achieve this higher selectivity in a single pass. The present disclosure provides examples of advances toward meeting this need.

[0007] Additional advantages and novel features of the present invention will be set forth as follows and will be readily apparent from the descriptions and demonstrations set forth herein. Accordingly, the following descriptions of the present invention should be seen as illustrative of the invention and not as limiting in any way.

SUMMARY

[0008] The present disclosure provides examples of a process for producing 1 ,3-butadiene (BD) from ethanol in a single step by passing a mixture containing ethanol in a gas phase over a multifunctional catalyst having a transition metal dispersion of at least 30% on a metal oxide support. In some examples the multifunctional catalyst is a ternary catalyst comprising a silica metal oxide having a surface area of at least 200 m A 2/g. The multifunctional catalyst could also be a transition metal oxide including for example; a silver (Ag) metal oxide, a silica metal oxide made from a high purity silica gel, mesoporous silica and fumed silica, such as high purity SBA16, SBA15, or Davisil grade 646.

[0009] In some examples, hydrogen can be added to the mixture. The mixture may also include water in addition to ethanol in a percentage ranging between 10 and 100 percent. In one particular example the mixture is 35% ethanol and includes water. The processing conditions in which the temperature ranges between 200°C and 500°C, the pressure between 1 atm and 20 atm and a weight-hour space velocity between 0.05 and 20 hr 1 . [00010] In one particular example a process for producing 1 ,3- butadiene (BD) from ethanol in a single step is described wherein a mixture containing ethanol in a gas phase is passed over a ternary Ag/Zr02/Si02 catalyst having a transition metal dispersion of at least 30% on a silica metal oxide support. In one example the ternary catalyst is 1 %Ag/4%Zr02/Si02- SBA-16. In other examples the operating conditions include a temperature of 325° C, pressure of 1 atm, and a flow rate of 0.23 hr-1 . In some other examples the mixture contains water and less than 50% ethanol.

[00011] Various additional advantages and novel features of the present invention are described herein and will become further readily apparent to those skilled in this art from the following detailed description and attached presentations. In the preceding and following descriptions only a sampling of the embodiments of the invention are shown by way of illustration. Accordingly, the descriptions and presentations of the preferred embodiment are to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[00012] Figure 1 shows the generally accepted reaction pathway for the formation of butadiene from ethanol. By-products are not included.

[00013] Figure 2 shows the selectivities to butadiene, acetaldehyde and crotonaldehyde as a function of the conversion over 4Ag/4Zr02/Si02 (Davisil 646) catalyst. T = 325°C, P = 1 atmosphere, WHSV = 0.37-38.0 hr 1 , 50% ethanol/N2.

[00014] Figure 3 shows reactivity performance for various catalytic embodiments. [00015] Figure 4 shows effect of the Si02 support on the catalytic performance of 1Ag/4Zr02/Si02 catalysts.

[00016] Figure 5 shows BET Surface, pore volume, pores size, Lewis acid sites concentration, organic impurities contents for 1Ag/4Zr02/Si02 catalysts synthesized from different Si02 supports.

[00017] Figure 6 shows catalytic performance comparison between catalysts under similar reaction conditions (T= 320-350°C, WHSV = 0.2-0.5 hr 1 , P = 1 atmosphere).

[00018] Figure 7 shows effect of the nature of the metal Ag, Pt or Ir on the catalytic performance

[00019] Figure 8 shows effect of the Ag loading on the catalytic performance of Ag/4Zr02/Si02 catalysts.

[00020] Figure 9 shows effect of the Zr02 loading on the catalytic performance for 4Ag/yZr02/Si02 catalysts and Lewis acid sites concentration

[00021] Figure 10 shows evolution of the conversion with (a) the BET surface and (b) the Ag dispersion for 1Ag/4Zr02/Si02 catalysts prepared from different silicas. The dispersion was measured via TEM after reduction. T =325°C, WHSV = 0.23 hr 1 , P = 1 atmosphere, 24.3% ethanol in N2.

[00022] Figure 1 1 shows evolution of the butadiene selectivity with the Lewis acid sites concentration for 1Ag/4Zr02/Si02 catalysts. Lewis acid sites concentration determined after pyridine desorption at 150°C. Butadiene selectivity at 75-85% conversion.

[00023] Figure 12 shows infrared spectra recorded after pyridine adsorption at 50°C followed by desorption at 150°C for 4Ag/yZr02/Si02 (Davisil 646) catalysts; varying the Zr02 loading (y = 1 -10 wt. %). Spectra were normalized to a pellet of 20 mg and 2 cm2. (b) Evolution of the

butadiene selectivity with the concentration of Lewis acid sites determined after pyridine desorption at 150°C.

[00024] Figure 13 shows the results of experiments performed

particularly regarding to the stability and regenerability of 1Ag/4Zr02/Si02 (SBA-16).

[00025] Figure 14 presents the results of Zr02 on stability of the catalyst compositions

[00026] Figure 15 shows the results of washing to remove K on various example catalysts.

[00027] Figure 16 shows the results of hydrogen to the processing conditions. T =325°C, WHSV = 0.23 hr 1 , P = 1 atmosphere, 24.3% ethanol in N2 or N2/H2 mixture. S1O2 support: Davisil 646.

[00028] Figure 17 shows a set of data related to the addition of water to the process mixture feed and the effect of weight-hour space velocity. T =400°C, P = 1 atmosphere, 35% ethanol in H2O feed mixture.

4%Ag/4%Zr0 2 /Si0 2 (Davisil 646).

[00029] Figure 18 shows another data set related to the addition of water to a process mixture feed. T =400°C, WHSV=0.30-0.35 hr-1 , P = 1

atmosphere. 4%Ag/4%Zr02/Si02 (Davisil 646).

[00030] Figure 19 shows the shows another data set related to the addition of water a process mixture feed. T = 325°C, WHSV = 0.30-0.35 hr-1 , P = 1 atmosphere. 4%Ag/4%Zr02/Si02 (Davisil 646). [00031] Figure 20 shows a data set related to the dilution of carrier gas nitrogen on conversion. T = 325°C, GHSV = 91 1 hr 1 , WHSVethanoi = 0.45-1.44 hr 1 , P = 1 atmosphere. 4%Ag/4%Zr02/Si02 (Davisil 646).

DETAILED DESCRIPTION OF THE INVENTION

[00032] The following description includes examples of various modes of the present disclosure. It will be clear from this description of the disclosure that the disclosure is not limited to these illustrated embodiments but that the disclosure also includes a variety of modifications and embodiments thereto. Therefore the present description should be seen as illustrative and not limiting. While the disclosure is susceptible of various modifications and alternative constructions, It should be understood, that there is no intention to limit the disclosure to the specific form disclosed, but, on the contrary, the disclosure is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the disclosure as defined in the claims.

[00033] The reaction mechanism for the conversion of ethanol to butadiene has generally been accepted as the reaction pathway presented in Figure 1 and involves ethanol dehydrogenation to acetaldehyde, followed by acetaldehyde condensation to 3-hydroxybutanal and its subsequent dehydration to crotonaldehyde, reduction of crotonaldehyde to crotyl alcohol, and finally its dehydration to butadiene. Figure 2 shows the evolution of selectivity curves for these various compounds in one particular example.

[00034] The table in Figure 3 shows a series of ternary Ag/Zr02/Si02 catalysts were studied for the single-step conversion of ethanol to butadiene (ETB). While Ag plays a major role in the ethanol conversion to acetaldehyde, the Lewis acid sites appeared to be responsible for the conversion of acetaldehyde to butadiene. Adding H2 to the feed gas does not affect the initial conversion, however, the selectivities to butadiene and butenes (i.e., 2-butene and 1 -butene) are impacted. While SBA-15 and SBA-16 demonstrated increased activity in achieving almost full conversion large differences in selectivities to the main products are observed between the two catalysts. The butadiene selectivity is equal to 46.6% and 70.5% for 1Ag/4Zr02/Si02 SBA-15 and 1Ag/4Zr02/Si02 SBA-16, respectively. The ethylene selectivity is quite high for the 1Ag/4Zr02/Si02 SBA-15 catalyst and equal to 29.4% whereas it is equal to 5.8% for 1Ag/4Zr02/Si02 SBA-16. Among all the catalysts tested, the 1Ag/4Zr02/Si02 SBA-16 is the most active toward butadiene formation and a butadiene yield equal to 70% was obtained. These experiments show the strong influence of the nature of the S1O2 support has on the catalytic performance of Ag/Zr02/Si02 catalysts for butadiene production from ethanol. Indeed, conversion between ~30 and 100% and butadiene yield between 0 and 70% can be obtained depending of the nature of the S1O2 support.

[00035] The table in Figure 4 shows the effect of SO2 support in the catalytic performance of 1Ag/4Zr02/Si02 catalysts. A total of 1 1 1 Ag/4Zr02/Si02 catalysts supported on different S1O2 were tested under similar reaction conditions. (T=325 degrees C, WHSV 0.23/hr, P=1 atm, 24.3% ethanol feed in N2). Differences in conversion and selectivities were observed depending on the choice of S1O2 support, and the surface area of the S1O2 appears to have a direct impact on the conversion which increases with the Si02/catalyst surface area due to increased Ag dispersion. The butadiene selectivity varies also greatly depending on the S1O2 support. The tables in Figures 5-9 as well as the graphs shown in Figures 10- 21 provide additional performance data regarding these catalysts.

[00036] The interaction between S 1O2 and Zr02 differs depending on the S 1O2 support which affects the catalyst acidity and consequently the butadiene selectivity. The catalysts were characterized by means of N2 adsorption, Pyridine adsorption/ desorption followed by FTIR spectroscopy and induced coupled plasma. These silica gels present different BET surface between 299 m 2 /g and 558 m 2 /g with a pore size decreasing from 120-170 Angstrom for the catalyst with the lowest BET surface to about 20-40 Angstrom for the catalysts with the highest BET surfaces. In comparison, the two fumed silicas present a lower surface area (i.e. < 270 m 2 /g) with large pores (i.e. > 200 angstrom). Both mesoporous S 1O2 have large BET surface (i.e., 656-728 m2/g) but different pore sizes (70 Angstrom for SBA-15 and 20 and 150 Angstrom for SBA-16). The acidity measurements indicate large differences between the catalysts as the one synthesized from the fumed silica Aerosil 390 has a concentration of Lewis acid sites equal to only 5 pmoles/g whereas the one supported on the Alfa Aeser silica gel presents a Lewis acid sites concentration of 35 pmoles/g.

[00037] Large differences in conversion percentages were reported among the various materials. The conversion varied from 29.5% for the 1Ag/4Zr02 catalyst supported on Davisil 645 (before ion-exchange) to 100% conversion for the one supported on KSMG-GOST 3956-76. The products selectivities vary also greatly depending of the silica gel support. For instance, a butadiene selectivity as low as 29.3% was measured for the catalyst supported on the Alfa Aeser silica gel as opposed to 78.3% butadiene selectivity for the one supported on KSKG-GOST 3956-76. The catalysts prepared from the silica gel 645 and 646 present similar BET surface, pore volume, pore size and acid sites concentration. However, when tested under the same reaction conditions, the conversion and butadiene selectivities are significantly higher for the 1Ag/4Zr02/Si02 Davisil 646.

[00038] The Davisil 645 silica gel presents a higher content of K (i.e. 1850 ppm) as compared to the Davisil 646 (i.e. 260 ppm). To test the hypothesis that that the K impurity impedes the ethanol conversion an ion-exchange was done for the Davisil 645. The K level was decreased to ~100 ppm after ion-exchange. The 1Ag/4Zr02 catalysts supported on the ion-exchanged Davisil 645 presents a conversion of 79.6% and a selectivity to butadiene equal to 73.4% which is similar to the results obtained for the 1Ag/4Zr02/Si02 Davisil 646 catalysts. Hence, these results suggest that K impurity inhibits the ethanol conversion, by altering occupying locations that would otherwise form acid sites on the support.

[00039] As discussed above, acid sites are responsible for the acetaldehyde conversion to butadiene and intermediates. The Lewis acid sites concentration of the 1Ag/4Zr02/Si02 fumed silica Aerosil 380 is low and equal to 5 pmoles/g which can explain the high selectivity toward acetaldehyde.

[00040] The evidence in these tables reflects the fact that SBA-16 surpasses other S 1O2 support as evidenced by excellent catalytic performance attained over a 1Ag/4Zr02/Si02-SBA-16 catalyst thus resulting in a -70% butadiene yield and ~90% yield of total olefins at 99% ethanol conversion while operating under mild conditions (325°C, 1 atm, 0.23 hr 1 ). By varying independently the Ag loading and the Zr02 loading, it was found that the optimal composition for a silica gel supported catalyst is 4wt%Ag and 4wt%Zr02. In these experiments a direct relationship between butadiene selectivity and concentration of Lewis acid sites was also demonstrated. Butadiene selectivity appears to decrease with increasing Lewis acid sites concentration. Catalyst stability study shows a decrease of conversion over time due to coking. Efficient catalyst regenerability was successfully demonstrated for multiple cycles.

[00041] Figures 10(a) and 9(b) chart the effects of BET surface on ethanol to butane conversion over the Ag/4Zr02/Si02 catalysts prepared from different silicas. Addition of H2 to the feed gas favors hydrogenation reactions and can impede oligomerization reactions as well as dehydrogenation reactions leading to the formation of aromatics. Addition of Zr02 (metal oxide with acid sites) to Ag/Si02 did not appear to have a significant impact on the ETB conversion, however ETB conversion generally did tend to increase with the catalyst surface area. It is believed that this increase of the ETB conversion is attributed to a better dispersion of Ag with the increase of the surface area. Thus accounting for the direct relationship between the butadiene selectivity and the concentration of Lewis acid sites.

[00042] Depending of the nature of the S1O2 support, the concentration of the acid sites responsible for the conversion of acetaldehyde to butadiene varies greatly for various catalysts including Ag/Zr02/Si02 catalysts. However, S 1O2 alone is not responsible for the catalyst acidity. The bare S 1O2 produced mainly acetaldehyde from ethanol and Zr02 is required to produce butadiene. The interaction between Zr02 and S1O2 varies greatly depending of the nature of the S 1O2 support which ultimately affects the catalyst acidity and butadiene selectivity. TEM imaging and XRD analysis demonstrate the presence of Zr widely dispersed over the S 1O2 support in the most effective catalysts. These results suggest that Zr is actually present as ZrOx patches interacting with S1O2 support modifying the catalyst acidity.

[00043] The catalysts acidity was investigated by pyridine adsorption/ desorption followed by Infrared spectroscopy to determine the nature and the concentration of the acid sites. The results of these studies did tend to show that acid sites play a role in the conversion of acetaldehyde to butadiene. The infrared spectra evidenced the presence of Lewis acid sites but no band characteristic of Bronsted acid sites was detected for any of the 1 Ag/4Zr02/Si02 catalysts prepared from silica gels, fumed silicas and mesoporous silicas. The relationship between the butadiene selectivity and the Lewis acid sites concentration for the 1Ag/4Zr02/Si02 catalysts presents a similar conversion between 75-85%. As shown in the figures, butadiene selectivity decreases from ~75% to ~30% as the Lewis acid sites concentration increases from ~22 umoles/g to ~35 umoles/g. These results suggest a relationship between butadiene selectivity and the amount of Lewis acid sites. In addition, they indicate that lower Lewis acid site concentrations are preferred to obtain higher selectivity to butadiene.

[00044] The catalytic performance of the 1Ag/4Zr02/Si02 (Davisil 646) catalyst was compared when promoting with either Pt or Ir precious metal, in lieu of Ag. Under the same reaction conditions, the activity is the highest for the supported Pt catalyst since full conversion was achieved. The table in Figure 7 shows the effect of Ag loading on the catalytic performance of Ag/4Zr02/Si02 catalysts. (The Ag dispersion was calculated from the Ag particle size using the formula D %= 100/d where D represents the dispersion and d stands for the Ag particle size. A total number of 100 particles was analyzed to determine the Ag particle size of each catalyst.) The conversion clearly increases from 71 % to 90.5% when the Ag loading increases from 1 to 4% but for Ag > 4% the conversion increases only slightly to 92.4%. The space velocity was varied for the 1Ag/4Zr02/Si02 catalyst to compare the main products selectivity at similar conversion (i.e., ~89-82%). The main reaction products include butadiene, ethylene, DEE, acetaldehyde and butenes (i.e., 1 -butene, 2-butene). At similar conversion, the butadiene selectivity is equal to ~66-67% for all three catalysts. Similarly, the butenes selectivity is quite similar for the three catalysts and between ~5.6-6.6%. Both ethylene and DEE selectivities decrease notably with the increase of the Ag loading from 1 to 4%.

[00045] Ethylene selectivity decreases from 14.1 % for 1Ag/4Zr02/Si02 to 10.5% for 4Ag/4Zr02/Si02. However, for Ag loading > 4% only a slight decrease of ethylene and DEE selectivities is observed. The acetaldehyde selectivity increases from 3% to 7.7% when the Ag loading increases from 1 to 8%. As demonstrated above, Ag is responsible for the dehydrogenation of ethanol to acetaldehyde. The increase of Ag loading leads to an increased amount of active sites for ethanol dehydrogenation. This can explain the increase of the acetaldehyde selectivity. Overall, 4Ag/4ZrO2/SiO2 is more active than 1Ag/4ZrO2/SiO2. The two catalysts with 4 and 8% Ag present similar activity and selectivity. Since lower metal loading reduces the cost of the catalyst we have chosen to investigate the effect of ZrO2 loading for a 4Ag/yZrO2/SiO2 catalyst.

[00046] Figure 12 (a) displays the normalized infrared spectra recorded after pyridine adsorption at 50°C followed by desorption at 150°C between 1410-1550 cm-1 for the 4Ag/yZrO2/SiO2 catalysts with ZrO2 loading between 1 and 10 wt.%. Two bands located at 1448 and 1491 cm-1 corresponding to coordinated pyridine and characteristic of Lewis acid sites are detected. The increase of the intensity of these bands with the Zr02 loading is indicative of an increase of the concentration of the Lewis acid sites. Note that the spectra do not evidence the presence of Bronsted acid sites since no band located at ~1540 cm-1 is detected. However, the presence of a minor amount of Bronsted acid sites cannot be completely ruled out. Indeed, the catalysts may contain a minor amount of Bronsted acid sites that are not sufficiently strong to protonate pyridine.

[00047] The concentration of Lewis acid increases from 17.3 pmoles/g for 4Ag/1 Zr02/Si02 to 28.4 pmoles/g for 4Ag/10ZrO2/SiO2. The results do not clearly evidence a relationship between the concentration of the acid sites and conversion. The conversion increases slightly from ~79 to ~86% when the Lewis acid sites concentration increases from 17.3 to 26 pmoles/g and further increase of the amount of acid sites results in a decrease of the conversion. Figure 6 (b) presents the evolution of the butadiene selectivity with the Lewis acid sites concentration. One can see that the butadiene selectivity decreases from about 71 % to 62% with the increase of the Lewis acid sites concentration. Among all the 4Ag/ZrO2 catalysts supported on S1O2 Davisil 646, 4Ag/4ZrO2/SiO2 (Davisil 646) presents the highest yield toward butadiene (59.4%).

[00048] To address potential concerns regarding coking various experiments and tests were performed particularly in regard to the stability and regenerability of 1 Ag/4ZrO2/SiO2 (SBA-16). The results are displayed in Figure 13. As shown in this figure, the conversion decreases from 98% (TOS= 5 hours) to 81 % after 22 hours on stream. However, the butadiene selectivity remains fairly stable at approximately 70%. The deactivation is likely due to coking from heavy compounds as aromatics liquid product were detected when notable drops of conversion occurred. Two successful regeneration cycles were conducted under flowing 5%02/He for 4-5 hours at 500°C followed by a reduction treatment at 325°C under 10% H2/N2 for 1 hour. Indeed, after the oxidation/reduction treatment the catalyst regains its initial conversion. This highlights the effectiveness of this oxidative treatment for complete regeneration of the Ag/ZrO2/SiO2 system.

[00049] Figure 13 presents the reactivity data obtained for a series of 4Ag/yZrO2/SiO2 catalysts with ZrO2 loading between 1 and 10 wt%. While the ZrO2 loading quadrupled from 1 to 4 % the conversion increases only slightly from ~79% to ~86%. In addition, when the ZrO2 loading increases further to 10 wt% the conversion decreases to 82.3%. The butadiene selectivity decreases from ~ 71 % to ~ 62% when the ZrO2 loading increases from 1 to 10 %. Similarly, the acetaldehyde selectivity decreases from about 14% to about 9% with the increase of the ZrO2 loading from 1 to 10 %. ZrO2 is acidic and varying its loading is expected to modify the catalyst acidity.

[00050] Figure 14 shows the effects of washing the catalyst to remove excess potassium K. As the data reflects, the reduction in K increases the conversion rate and selectivity for butadiene conversion. Figure 15 shows the effect of hydrogen addition in increasing the stability of the catalyst. Figure 16.

[00051] Figures 16-20 show the results of variations on flow rates and mixture compositions. These results demonstrate that aqueous ethanol feeds of varying concentrations could be used as source for butadiene production. Many times an ethanol feed coming out of a fermenter requires a significant amount of energy to separate ethanol from water. The present process can be used to convert ethanol to butadiene across a wide range of mixed feeds. These tests showed that mixtures such as ~30% ethanol/water mixtures (which represents something that might come directly from a standard fermenter "beer column") to be effective in this one step conversion process. While this example is shown, it is also to be understood that these examples are not limiting but are intended to show that the feedstock can be both ethanol and aqueous mixtures of ethanol. The ability to use various forms of ethanol mixtures ranging from 100 percent to 10 percent ethanol and even lower provides additional advantage in reducing the cost and complexity of converting ethanol to butadiene and provides significant economic advantage.

[00052] While various preferred embodiments of the invention are shown and described, it is to be distinctly understood that this invention is not limited thereto but may be variously embodied to practice within the scope of the following claims. From the foregoing description, it will be apparent that various changes may be made without departing from the spirit and scope of the invention as defined by the following claims.