WO2014092849A1

WO2014092849A1 - Process and catalyst for conversion of acetic acid to isobutene

Info

Publication number: WO2014092849A1
Application number: PCT/US2013/063968
Authority: WO
Inventors: Junming SUN; Changjun Liu; Yong Wang; Colin Smith; Kevin Martin; Padmesh Venkitasubramanian
Original assignee: Washington State University; Archer Daniels Midland Company
Priority date: 2012-12-14
Filing date: 2013-10-09
Publication date: 2014-06-19

Abstract

A process is disclosed for converting acetic acid to isobutene in the presence of a catalyst. In certain embodiments, a ZnxZryOz mixed oxide catalyst is used for carrying out a gas phase process for converting acetic acid to isobutene. In some embodiments, a ZnxZryOz mixed oxide catalyst made by an incipient wetness impregnation method is used and is indicated to be very stable for carrying out the conversion.

Description

PROCESS AND CATALYST FOR CONVERSION

OF ACETIC ACID TO ISOBUTENE

Technical Field

[0001] The present Invention relates generally to renewable process alternatives for the production of isobutene and to the catalysts used therein, but concerns the novel production of isobutene from acetic acid rather than from ethanol.

Background Art

[0002] Isobutene is widely used for the production of a variety of industrially important products, such as butyl rubber for example, Isobutene has been produced commercially to date through the catalytic or steam cracking of fossil feedstocks, and the development of a commercially viable process for the manufacture of isobutene from a renewable source-based feedstock would accordingly be of great interest as fossil resources are depleted and/or become more costly to use - especially in consideration of Increased demand for isobutene,

|0O03J Previous to the referenced application, a hard-template method had been described for synthesizing Zn_xZr_yC¾ mixed oxides for the direct and high yield conversion of ethanol (from the fermentation of carbohydrates from renewable source materials, Including biomass) to isobutene, wherein ZnO was added to Zr0₂ to selectively passivafe zirconia's strong Lewis acidic sites and weaken Bronsted acidic sites while simultaneously introducing basicity, The objectives of the hard template method were to suppress ethanol dehydration and acetone polymerization, while enabling a surface basic site- catalyzed ethanol dehydrogenation to acetaldehyde, an acetaldehyde to acetone conversion via aldol-condensatlon/dehydrogenation, and a Bronsted and Lewis acidic/basic site-catalyzed acetone~to-isobutene reaction pathway.

[0004] High isobutene yields were In fact realized, but unfortunately, as later experienced by tzuno et al. (Mteuno et a!., "One - path and Selective Conversion of Ethanol to Propene on Scandium -modified Indium Oxide Catalysts", C em. Lett, vol. 41 , pp. 892-894 (2012)} in their efforts to produce propylene from ethanol if was found that further improvements in the catalyst^'s stability were needed, [0005] The prior, related application concerns the discovery that these improvements couid be realized without adding mod Hying metals and without a reduction in the initial high activity (100 percent ethane! conversion) that had been observed in these mixed oxide catalysts.

.§ ¾g? ¥. Of The Invention

[0006] The present invention concerns the discovery that the mixed oxide catalysts we have been evaluating for converting ethanol to !sobutene are also able to catalyze the conversion of acetic acid to isobutene. Since acetic acid can be made by a variety of methods from a number of different starling materials, including through carbonylation of methanol derived from sequestered carbon dioxide, for example, the capability of these mixed oxide catalysts to catalyze the conversion of acetic acid to isobutene enables a number of improvements to be realized and a range of options for utilizing renewable resources more efficiently, ail as described in greater detail hereafter.

000?3 Accordingly, in its broadest aspect, the present invention concerns a process for converting acetic acid to isobutene in the presence of a catalyst.

[0008] In another more particular aspect, the catalyst Is a mixed oxide catalyst of the formula Zn_*Z?\A_;.

[0009] in another aspect, the catalyst is an Improved stability mixed oxide catalyst of the formula Z.n_>;Zr_yC¾, as made by the process of our related application.

[0010] In other more particular aspects, the present invention concerns certain integrated processes wherein the inventive step of converting acetic acid to isobutene in the presence of a catalyst is incorporated to enable a plurality of hiobased products to be made inclusive of isobutene and/or for improved renewable resource utilization. Brief _.Description Qf The Drawings

00111 Figure schematically depicts a process of converting acetic acid to isobufene in the presence of a catalyst, wherein various options fo obtaining the acetic acid are suggested.

[0012] Figure 2 shows the yields of the various products in a process according to the present invention over time, carried out as described in Example 1 below.

Description Of Embodiments

[0013] Referring now to Figure 1 , a process 10 is schematically illustrated wherein acetic acid 12 is converted to isobutene 14 in the presence of a catalyst, particularly; a Zn_xZr_yO_z mixed oxide catalyst.

[0014] In one embodiment, the Zn_xZr_y0₂ mixed oxide catalyst can be made by a "hard template" or "confined space synthesis" method generally of the character used by Jacobsen et al,₅ " esoporous Zeolite Single Crystals", Journal of the American Chemical Society, vol. 122_: pp. 7118-7117 (2000), wherein nanozeoiites were prepared.

[0O1S| v ore particularly, the same carbon black (BP 2000, Cabot

Corp.) may be used as a hard template for the synthesis of nanosized

n_xZf_y0₂ mixed oxides, rather than nanozeoiites as In Jacobsen et ai. Prior to use, the BP 2000 template is dried, for example, at 180 °C overnight.

Calculated amounts of zircony! nitrate hydrate (Sigma-A!drieh, greater than 99.8% purity) and Ζπ(Ν0₃)2·6Η₂0 (Sigma-Aldrich, greater than 99.8% purity) are dissolved in a given amount of water, and sonicated for 15 minutes to produce a clear solution with desired concentrations of Zn and Zr. In one preparation, about 25 grams of the obtained solution are then mixed with 6.0 grams of the preheated BP 2000 to achieve incipient wetness, and the mixture is transferred to a ceramic crucible and calcined at 400 degrees Celsius for 4 hours, followed by ramping the temperature to 650 degrees Celsius (at a ramp rate of 3 degrees Celsius/minute) and holding at 550 degrees Celsius for another 20 Iiours. Nanosized white powders are obtained, having a mean particle size of less than 10 nanometers.

[0016] The nanosized Zn_xZr_y0₇. mixed oxide catalysis made by a hard template method are further described in Sun et ai., "Direct Conversion of Bio - ethanoi to Isobutene on Nanosized Ζη_χΖ _ζ Mixed Oxides with Balanced Acid-Base Sites", Journal of the American Chemical Society, vol. 133, pp 11098-11099 (201 1), along with findings related to the character of the mixed oxide catalysts formed thereby and the performance of the catalysts for the ethanoi to isobutene conversion, given certain Zn/Zr ratios, residence times and reaction temperatures.

[0017J lternatively, the Zn*ZryO_z mixed oxide catalysts may be made as described in copending United States Patent Application Ser. No.

61/720433, filed October 31 , 2012 for "Stable Mixed Oxide Catalysts for Direct Conversion of Ethanoi to Isobutene and Process for Making", by a process broadly comprising, in certain embodiments, forming a solution of one or more Zn compounds, combining one or more zirconium-containing solids with the solution of one or more Zn compounds so that the solution wets the

zirconium-containing solids to a state of incipient wetness, drying the welted solids, then calcining the dried solids. In other embodiments, a solution is formed of one or more Zr compounds, the solution Is combined with one or more Zn-containing solids so that the solution wets the Zn-containing solids to a state of incipient wetness, the wetted solids are dried and then the dried solids are calcined.

[OOISJ In certain embodiments, the Zn_¾Zr_yO_?. mixed oxide cataiysts (whether made by the hard template or Incipient wetness methods) are characterized by a Zn/Zr ratio (x:y) of from 1 :100 to 10:1 , preferably from 1 :30 to 1 :1 , especially 1 :20 to 1 :5, and still more preferably 1 :12 to 1 :10.

[0019] Parenthetically, in the present application where any range of values is given for an aspect or feature of the catalysts of the present invention or any process described for using the catalysts of the present invention, the given ranges will be understood as disclosing and describing all subranges of values included within the broader range. Thus, for example, the range of 1 :100 to 10:1 will be understood as disclosing and describing not only the specific preferred and more preferred subranges given above, but also every other subrange including a value for x between 1 and 10 and every other subrange including a value for y between 1 and 00, [0020] The catalysts made by the as'ternaiive, incipient wetness method are consistent in their particle size with the catalysts described in the journal article, namely, comprising aggregates of less than 10 nm-sized particles with a highly crystalline structure. The Zn oxide component is again highly dispersed on the Zr oxide component.

[0021] In certain embodiments, the Zn_;<Zr_y<¾ mixed oxide catalysts are characterized as low sulfur catalysts, containing less than 0.14 percent by weight of sulfur. In the related copending application, it was reported in this regard that catalysts made by the incipient wetness method would desirably be substantially sulfur- free, preferably including less than 0.01 percent by weight of sulfur and more preferably including less than 0.001 weight percent of sulfur. In the prior related application, it was postulated thai the reduced sulfur content enabled by the incipient wetness method as compared to the hard template method contributed significantly to the much improved stability observed for the incipient wetness method catalysts of the prior related application for the ethanoi to isobutene process.

[00221 In the present context of a process for converting acetic acid to isobutene, however, in at least some embodiments and under certain process conditions some sulfur does appear to be beneficial, though as just indicated, it is expected that the amount of sulfur will preferably be such that the catalysts are characterized as low sulfur catalysts. Such low sulfur catalysts are most readily made by the incipient wetness method described briefly above and in greater detail In the prior related application.

[0023] In principle, provided the zinc and zirconium compounds and solids In these embodiments have a sufficiently low sulfur content in order to produce a low sulfur content when combined according to the incipient wetness method, an combination of zinc and zirconium materials and any solvent can be used that will permit the zinc and zirconium components to mix- homogeneously whereby., through incipient wetness impregnation, one of the zinc or zirconium components are well dispersed on a solid of the other component for subsequent drying and conversion to the oxide forms through calcining. As exemplified below, low sulfur catalysts can also be made by the incipient wetness method starting with zinc and zirconium compounds that are sulfur-free or substantially sulfur-free, then doping in a desired sulfur content into the Zr^ZfyOz mixed oxide catalysts used in certain embodiments of the inventive process,

[0024] The conditions and times for the drying and calcining steps of an incipient wetness preparation will depend, of course, on the particular zinc and zirconium materials and solvent used, but in general terms, the drying step can be accomplished in a temperature range of from 80 degrees Celsius to 200 degrees Celsius over at least 3 hours, while the calcining ca s take place at a temperature of from 300 degrees Celsius to 1500 degrees Celsius, but more preferably a temperature of from 400 to 600 degrees Ceisius is used, The calcination time can be from 10 minutes to 48 hours, with from 2 to 10 hours being preferred.

[002S] In stiii other embodiments, low sulfur catalysts as described herein could be prepared by a hard template method as described in the earlier incorporated publication, except that a suitably very low sulfur content carbon is used for the hard template to realize a low sulfur content in the finished catalyst,

[002631η certain embodiments, the process can be conducted continuously In the gas phase, using a fixed bed reactor or flow bed reactor. The reaction temperature may be in a range from 350 to 700 degrees Celsius, preferably, in a range from 400 to 500 degrees Celsius, and the VVHSV can be in a range from 0.01 hr^" to 10 hr^"1, preferably from 0.05 hr^"1 to 2 hr^"1.

.Acetic acid/water solutions with steam to carbon ratios from 0 to 20, preferably from 2 to 5 can be used to provide acetic acid to the catalyst. An inert carrier gas, such as nitrogen, can be used as in Example 1

[0027] As shown schematically in Figure 1 , the acetic acid 12 can be obtained by various methods from a number of starting materials, which in turn permits a number of Integrated processes to be considered for producing other products in addition to isobutene and/or for providing Improved utilization of renewable resources.

[00283 For example, acetic acid can be produced from a source of five and six carbon sugars 18 by fermentation. US 6,509,180 and US 8,252,567 seek to improve upon known processes for making eihanoi and butanol/hexanoi, respectively, by means including the fermentation of five and six carbon sugars into acetic acid. In US 6,509,180, the acetic acid is esterified to form an acetate ester which may then be hydrogenated (using hydrogen from, e.g., steam reforming of natural gas, electrolysis of water, gasification of biomass or partial oxidation of hydrocarbons generally) to ethanol. In US 8,252,587, the eihanol formed In this manner can be used to .make bufanol and hexanol, by subjecting the eihanol with acetate, acetic acid or mixtures thereof to an acidogenic fermentation using, for example, species of the bacteria Clostridium (Clostridium kluyveri is mentioned), to produce but rate, butyric acid, caproate, caproic acid or mixtures thereof. These materials then in turn are acidified to convert butyrate and caproate to butyric acid and caproic acid, the butyric and caproic acids are esferified and then the butyric and caproic acid esters undergo reduction by hydrogenation, hydrogenolysls or reduction by carbon monoxide to provide bufanol and ethanol.

[00291 As related In these two patents and as well known to those skilled in the fermentation art, the fermentation of five and six carbon sugars to form acetic acid can be accomplished by various organisms.. More particularly, homoacetogenic microorganisms are able through fermentation to produce acetic acid with 100% carbon yield; these microorganisms internally convert carbon dioxide to acetate, In contrast to a process for producing eihanol from sugars obtained from biomass (the starting point fo isobutene syntheses reported in the prior related application and in the earlier journal article (Sun et a!., "Direct Conversion of Bio-eihanol to isobutene on

Nanosized Zn_>:Zr_yi¾ Mixed Oxides with Balanced Acid-Base Sites", Journal of the American Chemical Society, vol. 133, pp 1 1096-11099 (201 1)) wherein carbon dioxide is produced as a byproduct.

[0030] Examples of homoacetogens given by US 8,252,56? are microorganisms of the genus Moo lia and Clostridium, especially

microorganisms of the species Moorelia thermoaceiicum (described as formerly classified as Clostridium thermoaceiicum) or Clostridium

formicoaceticum. US 8,252,567 represents that about one hundred known acetogens in twenty-two genera were known as of 2009, and cross- references Drake, et aL Ann, NY Acad. Sol. 1125: 100-128 (2008) for a review of acetogenic microorganisms.

[0031] Other references describing fermentation methods for producing acetic acid from five and six carbon sugars include US 4,935, 360; US

8,236,534; US 4,513,084; US 4,371,619 and US 4,506,012; both one-step fermentation processes from the sugars to acetic acid, acetates or both are disclosed, as well as two-step processes involving a first fermentation to lactic acid (by iactobaci!ius or known methods of homolactic fermentation, preferably) followed b a second fermentation to convert lactic acid to acetic acid, for example, using Clostridium formicoaceticum.

[0032] Any of the known fermentation methods may, in short, be used to produce acetic acid for conversion to isobufene In the presence of the mixed oxide catalysts of the present invention, but homoacetogenic

fermentation methods are considered preferable in that carbon dioxide is not produced as a byproduct -^■ the carbon dioxide represents a yield loss from the overall process to make isobutene and as a greenhouse gas is

undesirable particularly In the context of a process to make a needed product more sustainably from renewable resources.

[0033] As well or in the alternative, the acetic acid feedstock 12 can be made from ethanol 18, according to any of several known methods employing oxidative fermentation with acetic acid bacteria of the genus Acetobacter,

[0034|As well or in the alternative, the acetic acid feedstock 12 can be made from methanol 20 through combination with carbon monoxide according to the most Industrially used route for making acetic acid, for example, in the presence of a catalyst under conditions effective for the carbonylation of methanol. A variety of carbonylation catalysts are known in this regard, see, for example, US 5,672,743; US 5,728, 871 ; US 5,773,842; US 5,833,289; US 5,883,295.

[0035J Those skilled in the art will appreciate that making at least a portion of the acetic acid feedstock 12 from methanol 20 would enable other Integrated process options to be considered for making isobutene from a biomass. Thus, syngas may be produced by gasification of a biomass, and methanol then produced from the syngas with additional hydrogen provided, for example, through electrolysis of water. The electrical energy required for the electrolysis may In turn be generated from combustion of additional biomass, through steam from heat energy captured from the methanol synthesis or from combustion of a biomass fraction {ligmn, for example), with optional capture and recycle of carbon dioxide from the flue gas to be used in the methanol synthesis. A variety of options for producing methanol from biomass have been presented in the literature, see, for example. US

2007/0254969 A1 by Olah et al; US 6,645,442 and US 8,991 ,769, both by Kaneko et al; and US 8,340,581 to Gaddy.

[0038] Those skilled in the art will appreciate that still other options may be considered for producing acetic acid from biomass or from a biomass fraction, including by catalytic, thermochemical and biological means, and that the limited description of various embodiments provided above should by no means be construed as limiting of the ways in which the acetic acid feedstock 12 may be made using renewable resources inclusive fundamentally of biomass, carbon monoxide and carbon dioxide gases. For example, as is known, the required acetic acid may be made at least in some part by- anaerobic fermentation using carbon monoxide and carbon dioxide gases themselves for a carbon source.

[0037] The present invention is further illustrated by the following example:

[00383 E amstfej.

00391 Commercial zirconium hydroxide was dried at 120 degrees

Celsius for more than 5 hours, A calculated amount of Zn(NOs)2 (from Sigma- Aldrich, more than 99.8 percent purify) was dissolved in wafer, forming a clear solution. The dried zirconium hydroxide (which was also from Sigma-Aldrieh, more than 99.8 percent purity) was then mixed with the solution by Incipient wetness, in order to form wet powders impregnated with Zn. The wetted powder was then dried at 80 degrees Celsius for 4 hours, followed by calcination at 550 degrees Celsius for 3 hours, to obtain a ZniZr_sO., catalyst of the type described in the '433 application (though for converting ethanol to Isobutene) by an Incipient wetness impregnation method, [0040] An acetic acid to isobutene process was conducted with the catalyst thus prepared in a fixed-bed stainless steel reactor having an inside diameter of 5 millimeters, 100 mg of the catalyst was packed between quartz wool beds. A thermocouple was placed in the middle of the catalyst bed to monitor the reaction temperature. Before beginning the reaction, the catalyst bed was prefreafed by flowing 50 ml/minute of nitrogen at 450 degrees

Celsius through the catalyst over a half hour. A 25 weight percent solution of acetic acid in water was then introduced into an evaporator at 180 degrees Celsius by means of a syringe pump, and the vaporized steam/acetic acid was carried into the reactor by a flowing nitrogen carrier gas at an acetic acid concentration in the gas phase of 1.38 weight percent and a WHSV of 0.1 grams of acetic acid per gram of catalyst per hour. Meanwhile, the product line was heated to in excess of 150 degrees Celsius before a cold trap, to avoid condensing the liquid products in the product; line. A reaction

temperature of 415 degrees Celsius was employed.

[0041 J A Shimadzu 2400 gas chromatograph equipped with an auto sampling valve, HP-Plot O. column (30 m_« 0.53 mm, 40 pm) and flame ionization detector was connected to the line between the reactor outlet and cold trap to collect and analyze the products in the effluent gas. After the cold trap, an online micro-GC (MicroGC 3000A equipped with molecular sieves 5.A, plot U columns and thermal conductivity detectors) was used to analyze the product gases specifically, using nitrogen as a reference gas.

[0042] Figure 2 shows the results of a one-pass durability test of the ZriiZfaO* catalyst prepared by the incipient wetness impregnation method, in converting acetic acid to isobutene in a gas phase process as described. A consistent product of about 5 percent by weight of methane, about 10 percent by weight of acetone, about 33 percent by weight of carbon dioxide and more than about 50 percent by weight of the desired isobutene product, was obtained; in contrast to the ethanol to isobutene process using these same Zn«∑r_y(¾; mixed oxide catalysts, no ethylene or propylene was produced. The catalyst showed very high stability over the full duration of the run, with no signs of observable deactivation after more than 1400 minutes of time-on- stream operation. [00441 For these examples, additional Zn_:<Zr_v<¾ mixed oxide catalysts were prepared both by the incipient wetness method used In Example 1 (!W In Table 1 below) but also by the prior art hard template method (NT), and these were evaluated and the products analyzed using the same apparatus and method described in Example 1 but nd r different sets of reaction conditions (as summarized in Table 1 below).

Claims

CLAIMS:

1. A process for converting acetic acid to isobutene in the presence of a

cataiyst.

2. A process according to claim 1, wherein the cataiyst is a Zn_xZr_v(¾ mixed oxide catalyst.

3. A process according to claim 2, wherein the mixed oxide catalyst contains less than 0.14 percent by weight of sulfur.

4. A process according to claim 3. wherein the catalyst contains less than 0.01 percent by weight of sulfur.

5. A process according to claim 4, wherein the catalyst contains less than 0.001 percent by weight of sulfur,

6. A process according to am of claims 2-5, wherein x:y is from 1 : 100 to 10.1.

7. A process according to claim 6, wherein x.y is from 1 :30 to 1 :1.

8. A process according to claim 7, wherein x:y is from 1 :20 to 1 :5.

9. A process according to claim 8, wherein x:y is from 1 : 12 to 1 :10.

10. A process according to any of claims 1~5_: conducted continuously in the gas phase by vaporizing acetic acid or an acetic acid solution in water and then bringing the vaporized acetic acid and steam mixture into contact with the catalyst under reaction conditions which are effective for converting the acetic acid to isobutene.

1 1. A process according to claim 10, wherein acetic acid is supplied to the catalyst at a steam to carbon ratio of from 0 to 20 and a weight hourly space velocity of from 0.01 hr^{" ;} to 10 hr^"\ and Is converted to isobutene at a reaction temperature from 350 to 700 degrees Celsius.

12. A process according to claim 11 , wherein acetic acid is supplied at a

steam to carbon ratio of from 2 to 5 and a weight hourly space velocity of from 0.05 hf ¹ to 2 hr^"\ and is converted to isobutene at a reaction temperature of from 400 to 500 degrees Celsius.

1 . A process for making and using a catalyst, comprising: forming a solution of one or more Zn compounds: combining one or more∑r~contaming solids with the solution of one or more Zn compounds so that the solution wets the Zr-containing solids to a state of incipient wetness; drying the wetted solids; calcining the dried solids to form a Zn_KZt_yO_z mixed oxide catalyst; and contacting the catalyst with acetic acid at an elevated temperature for a time to convert acetic acid to isobutene.

4. A process according to either of claims 1 or 13,. wherein the acetic acid is obtained at least in part by fermentation of one or more of the five- and six- carbon sugars.

5. A process according to either of claims 1 or 13, wherein the acetic acid is obtained at least in part through an oxidative fermentation from ethanoi.

8. A process according to either of claims 1 or 13. wherein the acetic acid is obtained at least in part by carbony!ation of methanol.

7. A process according to claim 18, wherein the methanol is obtained at least in part by combining carbon dioxide generated from biomass and hydrogen under conditions which are effective for forming methanol.