Catalytic Conversion of Ethanol and Hydrogen to a 1 -Butanol-Containing Reaction Product Using a Thermally Decomposed Hydrotalcite/Metal

Carbonate

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims benefit of priority from Provisional Application No. 61/062604, filed January 28, 2008.

FIELD OF THE INVENTION

The present invention relates to the catalytic conversion of ethanol and hydrogen to a 1 -butanol-containing reaction product. Various organic chemicals, including 1 -butanol itself, can be separated from the reaction product. The catalysts are combinations of hydrotalcites (optionally containing transition metals) and metal carbonates, which combinations have been thermally decomposed, either partially or fully, to form catalytically active species.

BACKGROUND Efforts directed at improving air quality and increasing energy production from renewable resources have resulted in renewed interest in alternative fuels, such as ethanol and butanol, that might replace gasoline and diesel fuel, or be used as additives in gasoline and diesel fuel.

It is known that 1-butanol can be prepared by condensation from ethanol over basic catalysts at high temperature using the so-called "Guerbet Reaction." See for example, J. Logsdon in Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley and Sons, Inc., New York, 2001.

Methods of using catalysts to convert ethanol to butanol are also discussed in the following references.

M. N. Dvornikoff and M. W. Farrar, J. of Organic Chemistry (1957), 11 , 540-542, disclose the use of MgO-K ₂ Cθ3-CuCrθ2 catalyst system to promote ethanol condensation to higher alcohols, including 1 -butanol.

The disclosed liquid phase reaction using this catalyst showed a 13% conversion of ethanol and 47% selectivity to 1 -butanol.

U.S. Patent No. 5,300,695, assigned to Amoco Corp., discloses processes in which an alcohol having X carbon atoms is reacted over an L-type zeolite catalyst to produce a higher molecular weight alcohol. In some embodiments, a first alcohol having X carbon atoms is condensed with a second alcohol having Y carbon atoms to produce an alcohol having X+Y carbons. In one specific embodiment, ethanol is used to produce butanol using a potassium L-type zeolite. J. I. DiCosimo, et al., in Journal of Catalysis (2000), 190(2), 261 -

275, describe the effect of composition and surface properties on alcohol- coupling reactions using Mg _y AIO _x catalysts for alcohol reactions, including ethanol. Also condensation reactions on Mg ₇ AIO _x samples involved the formation of products containing a new C-C bond, such as n-C ₄ H ₈ O (or n- C ₄ H ₉ OH) and iso-C ₄ H ₈ O (or iso-C ₄ H ₉ OH). They also describe, in Journal of Catalysis (1998), 178(2), 499-510, that the oxidation to acetaldehyde and the aldol condensation to n-butanol both involve initial surface ethoxide formation on a Lewis acid-strong base pair.

WO 2006059729 (assigned to Kabushiki Kaisha Sangi) describes a process for efficiently producing, from ethanol as a raw material, higher molecular weight alcohols having an even number of carbon atoms, such as 1 -butanol, hexanol and the like. The higher molecular weight alcohols are yielded from ethanol as a starting material with the aid of a calcium phosphate compound, e.g., hydroxyapatite Caio(PO ₄ )6(OH) ₂ , tricalcium phosphate Ca3(PO ₄ )2, calcium monohydrogen phosphate CaHPO ₄ X(O- 2)H ₂ O, calcium diphosphate Ca ₂ P ₂ O ₇ , octacalcium phosphate Ca ₈ H ₂ (PO ₄ ) ₆ ^χ 5H ₂ O, tetracalcium phosphate Ca ₄ (PO ₄ ) ₂ O, or amorphous calcium phosphate Ca ₃ (PO ₄ ) ₂ ^χ nH ₂ O, preferably hydroxyapatite, as a catalyst, the contact time being 0.4 second or longer. Carlini et al. describe a catalytic reaction of methanol with n- propanol to produce isobutyl alcohol. The involved catalyst is a calcined hydrotalcite in combination with copper chromite. See C. Carlini et al, Journal of Molecular Catalysis A: Chemical (2005), 232 (1 -2) 13-20. See

also C. Carlini, Journal of Molecular Catalysis A: Chemical (2004), 220 (2), 215-220, in which the catalyst is a mixture of a hydrotalcite with Pd, Ni, Rh, or Cu, with the mixture being calcined at 500 ⁰ C.

Hydrotalcites are layered, double hydroxides of the general formula (M ² Y _x M ³⁺ _x (OH) ₂ )(A ⁿ - _x/n ) • yH ₂ O

The M ²⁺ ions can be a variety of divalent cations (e.g., Mg, Ni, Pt, Pd, Zn, Co, Fe, Cu) and the M ³⁺ ions can be trivalent Al, Fe or Cr. Some hydrotalcites are described by V. K. Diez, CR. Apesteguia, and J.I. DiCosimo {Latin American Applied Research, 33, 79-86 (2003)) and N.N. Das and S.C. Shvastava {Bull. Mater. Sci. 25, (4), 283-289 (2002)). It has been found that partially or fully thermally decomposed combinations of hydrotalcites (particularly those that incorporate transition metals) and metal carbonates can yield catalysts that are effective for the conversion of ethanol and hydrogen to a reaction product that comprises (i.e., contains, among other things) 1-butanol.

SUMMARY OF THE INVENTION

Certain combinations of hydrotalcites and metal carbonates, as described herein, are partially or fully thermally decomposed to provide catalysts useful for the conversion of ethanol, in the presence of hydrogen, to a reaction product comprising 1 -butanol.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 shows the powder X-ray diffraction pattern of the hydrotalcite material of the Examples before calcination, and indicates reflections typical of a hydrotalcite phase.

Figure 2 shows a powder X-ray diffraction pattern of the material of Figure 1 after calcination, showing decomposition of the hydrotalcite phase by the substantial loss of those reflections that are typical of a hydrotalcite phase.

DESCRIPTION

A stream of gas phase ethanol (that may contain water, and may be diluted with an inert gas such as nitrogen, carbon dioxide, and mixtures thereof) is contacted in the presence of hydrogen with at least one thermally decomposed hydrotalcite catalyst at a temperature and pressure sufficient to produce a reaction product comprising water, unreacted ethanol (if less than complete ethanol conversion), butanol, higher alcohols and other organic species. The butanol is predominantly 1 - butanol. Suitable temperatures are in the range of about 150 ⁰ C to 500 ⁰ C, for example about 200 ⁰ C to about 500 ⁰ C. Suitable pressures are from about 0.1 MPa to about 20.7 MPa. Hydrogen is supplied to the reactor at a feed rate of at least 5 percent by volume relative to the volume of feed gas.

The catalysts that are useful in the present invention are partially or fully thermally decomposed hydrotalcite/metal carbonate combinations of a hydrotalcite of the formula [(M ²⁺ i _-x M ³⁺ _x (OH) ₂ ) (A ^n" χ/ _n ) • yH ₂ O ] and a metal carbonate of the formula [M ¹ A']. The combinations, prior to thermal decomposition, have the empirical formula below:

[[(M ²⁺ _1-x M ³⁺ _x (OH) ₂ ) (A ⁿ - _x/n )] • yH ₂ O ][M'A'] _Z

wherein

M ²⁺ is divalent Mg, or a combination of Mg and at least one divalent member selected from the group consisting of Pd, Pt, Co and Cu;

M ³⁺ is trivalent Al, or a combination of trivalent Al and at least one thvalent member selected from the group consisting of Fe and Cr; x is 0.66 to 0.1 ;

A ^n~ is CO ₃ ^2" with n = 2, or OH ^" with n = 1 ;

M ¹ A' is a carbonate of at least one divalent metal M ¹ selected from the group consisting of Pd, Pt, Co and Cu; and A ¹ is carbonate; z is any number between 0.001 and 0.5, inclusive (i.e., including the endpoints of the range); and y is 0 to 4.

In a preferred embodiment of this invention, in the empirical formula M ²⁺ is divalent Mg; M ³⁺ is thvalent Al; A ^n~ is CO ₃ ^2" or OH ^" ; z is any number between 0.001 and 0.5; and M' is selected from the group consisting of Pd, Pt, Co and Cu. Preferred values for M' are Co and Cu. Preferred values for z are in the range between 0.01 and 0.25, including the endpoints of the range.

The catalysts that are useful in the present invention are derived from a hydrotalcite of the formula as defined above by a process comprising heating the hydrotalcite for a time and at a temperature sufficient to cause a diminution in the hydrotalcite powder X-ray diffraction pattern peak intensities between 2θ angles of 10 degrees and 70 degrees using CuKa radiation.

Catalysts derived from the hydrotalcite can be synthesized by the following method. An aqueous salt solution containing (a) magnesium and one or more divalent metals selected from the group consisting of palladium, platinum, cobalt and copper and (b) aluminum and, optionally, one or more trivalent metals selected from the group consisting of iron and chromium is prepared. Preferred salts are nitrates, chlorides, or acetates. Most preferred are nitrates. The salt solution is added to a basic, aqueous solution containing sodium or potassium carbonate (or bicarbonate), sodium, potassium or ammonium hydroxide, or a mixture of the foregoing carbonates, bicarbonates and hydroxides, thereby providing the carbonate ion or hydroxide ion for A ^n~ , as well as the carbonate ion for A'. The pH of this basic solution is typically adjusted to a pH of approximately 10 during the addition of the aqueous salt solution. The (a) magnesium and at least one other divalent metal and the (b) aluminum and optional trivalent metals should be in a molar ratio (a)/(b) between 0.5 and 9 inclusive (i.e., including the endpoints of the range) to satisfy the stoichiometry of the hydrotalcite component of the formula (i). In practice, however, the endpoints of the range should exceed 0.5 and 9 by an amount sufficient to satisfy the value of "z" for the [M ¹ A'] component of formula (i). This is because the metal M' is selected from the same group of metals as the metals that can substitute for divalent magnesium in the hydrotalcite

component of formula (i). (Alternatively, a plurality of individual metal salt solutions may be used, provided that they are added concurrently to the basic, aqueous solution containing the carbonate, bicarbonate, hydroxide or mixtures thereof.) The resulting suspension that is formed (i.e., a precipitate suspended in a liquid) can be aged, preferably for approximately 18 hours, at about 60 ⁰ C to 70 ⁰ C. The precipitate is then separated, generally by filtering, and subsequently dried (generally in a vacuum oven or in air). The dried precipitate can be analyzed by powder X-ray diffraction to confirm the presence of a hydrotalcite phase. This phase is isostructural with the hydrotalcite Mg ₆ AI ₂ (CO ₃ )(OH)I ₆ • 4H ₂ O (JCPDS card # 54-1030; Powder Diffraction Files, International Centre for Diffraction Data, 1601 Park Lane, Swarthmore, PA 19081 ). The dried precipitate is then calcined by heating it for a time and at a temperature sufficient to cause a diminution in the hydrotalcite powder X-ray diffraction pattern peak intensities between 2θ angles of 10 degrees and 70 degrees using CuKa radiation. The calcined material can be analyzed by powder X-ray diffraction to confirm the diminution (including the complete absence) in these peak intensities and the appearance of new peaks corresponding to a material which is isostructural with partially crystalline magnesium oxide (MgO, JCPDS card # 65-0476). It is preferred to calcine the dried precipitate for a time and at a temperature sufficient to substantially reduce the peak intensities characteristic of the hydrotalcite phase. Although any calcination protocol can be used, one that is particularly useful on a laboratory scale includes heating the hydrotalcite in a 2.5 centimeter (cm) (one inch) diameter tube furnace from about 25 ⁰ C to about 360 ⁰ C over 140 minutes (min) at 2.4 ⁰ C per minute, and then holding at 360 ⁰ C for about 2 to about 4 hours.

The catalysts usable in the process of the invention can be prepared as described above. The catalysts may be used in the form of powders, granules, or other particulate forms. Selection of an optimal average particle size for the catalyst will depend upon such process parameters as reactor residence time and desired reactor flow rates.

The catalytic conversion of ethanol and hydrogen to the reaction product comprising 1 -butanol can be run in either batch or continuous mode as described, for example, in H. Scott Fogler, (Elements of Chemical Reaction Engineering, 2 ^nd Edition, (1992) Prentice-Hall Inc, CA). Suitable reactors include fixed-bed, adiabatic, fluid-bed, transport bed, and moving bed.

It is preferable, but not essential, to treat the catalyst, prior to its use, with nitrogen or air at elevated temperatures, which is thought to remove unwanted carbonates from the catalyst surface. If the starting hydrotalcite contains Pd, Pt, Co or Cu, it is also preferred, but not essential, to treat the catalyst, prior to its use, with hydrogen at elevated temperatures. One protocol that has been found to be effective is described in more detail in the Example, below. If catalyst treatment is desired, the catalyst may be treated in situ in the reactor or ex situ and then introduced into the reactor.

During the course of the reaction, the catalyst may become fouled, and therefore it may be necessary to regenerate the catalyst. Preferred methods of catalyst regeneration include contacting the catalyst with a gas such as, but not limited to, air, steam, hydrogen, nitrogen or combinations thereof, at an elevated temperature, although care must be taken not to use a temperature that is so high that the regeneration results in a loss of surface area or other unwanted effects. If catalyst regeneration is desired, the catalyst may be regenerated in situ in the reactor or ex situ and then introduced into the reactor. One skilled in the art will know that conditions, such as temperature, catalytic metal, catalyst support, reactor configuration and time can affect the reaction kinetics, product yield and product selectivity. Standard experimentation can be used to optimize the yield of 1 -butanol from the reaction. 1 -Butanol can be separated from the reaction product by known chemical engineering methods, including distillation. Other specific chemicals (or combinations of chemicals) also can be removed from the reaction product using known chemical engineering methods. The specific

methods will be dependent on the nature of the reaction product, which, in turn, is dependent on the specific catalyst used and the reaction conditions, particularly the extent of ethanol conversion.

EXAMPLES

Examples 1 -2

[(M ²⁺ i _-x M ³⁺ x (OH) ₂ ) (A ⁿ -χ/ _n )] • yH ₂ O][M'A'] _z hydrotalcite M ²⁺ is Mg; M ³⁺ is Al; x is 0.25; A ^n" is CO ₃ ^2" with n = 2; M' is Cu ²⁺ ; A' is CO _j ^2' ; z = 0.013; and v = 0 to 4

Examples 1 -2 are comparative examples carried out at 300 ⁰ C and 350 ⁰ C, respectively, under a flow of nitrogen. Sodium bicarbonate (8.2 g; EMD Sciences, Gibbstown NJ) was dissolved in 250 milliliters (ml) water in a three neck, round bottom flask. The solution was heated to 65 ⁰ C, and the pH was adjusted to approximately 10 using 2 M sodium hydroxide solution (Baker). 27.5 g of aluminum nitrate (AI(NO ₃ )3 • 9H ₂ O (EMD Sciences AX0705-11 )), 57.6 g of magnesium nitrate (Mg(NO ₃ ) ₂ • 6H ₂ O (EMD Sciences MX0060-1 )) and 0.92 g of copper nitrate (Cu(NO ₃ ) ₂ • 2.5H ₂ O (Fisher, Lot#725840)) were dissolved in 100 ml of water and added drop-wise to the preheated solution containing sodium bicarbonate. After complete addition of the metal nitrates, the suspension was kept at 65 ⁰ C with stirring for 1 hour (hr) and then aged at this temperature for 18 hours without stirring.

The precipitate was separated from solution by filtering. The precipitate was dried in a vacuum oven at 90 ⁰ C for 48 hrs and calcined at 360 ⁰ C for 2 hours in nitrogen. The heating protocol was as follows: the precipitate was placed in a 2.5 cm (1 inch) diameter tube furnace, and the temperature was raised from 25 ⁰ C to 360 ⁰ C at 2.4 °C/minute over 140 minutes, and held at 360 ⁰ C for 2 hours. The catalyst was evaluated according to the following procedure.

Reactor Evaluation:

Approximately 2 cubic centimeters (cc) of catalyst was loaded on a stainless steel mesh support within a 45.7 cm x 1.3 cm (18 inch x ^λ A inch) outside diameter (o.d.) type 360 stainless steel tube reactor with inlets for

gas and liquid feeds. The catalyst was then pre-conditioned in situ by flowing nitrogen gas, initially at room temperature, raising the temperature to 350 ⁰ C, holding it there for one hour, lowering the temperature to 180 ⁰ C, flowing hydrogen gas at 15 cc/min for one hour, reintroducing nitrogen gas at a flow rate of 15 cc/min, and increasing the reactor temperature to that shown in Table 1 to introduce the ethanol to generate reaction data. At reaction temperature, nitrogen flow was set at 15 cc/min and ethanol flow at 1.03 ml/hr. The majority of the reaction off-gases were condensed throughout a 60 minute reaction time in cold N-methylpyrrolidone solvent, and the resultant solution was analyzed using an Agilent™ 5890 GC equipped with flame ionization and mass selective detectors. Results are shown in Table 1 below, wherein "EtOH" means ethanol, "BuOH" means 1 -butanol, "Conv." means conversion, and "SeI." means selectivity. Ethanol conversion (%) was calculated as follows: [(1 - carbon moles of unreacted ethanol)/carbon moles of total outlet gases] times 100. Selectivity (%) was calculated as follows: (carbon moles of product/carbon moles of ethanol reacted) times 100.

Table 1

Examples 3-4

[(iv /|r2+ _1-x IV .T3+ _x (OH) ₂ ) (A ⁿ - _x/n )] • yH ₂ O][M'A'] _z hydrotalcite

M ²⁺ is Mg; M ³⁺ is Al; x is 0.25; A ^n" is CO ₃ ^2" with n = 2; M' is Cu ²⁺ ;

A' is CQ ₃ ; z = 0.013; and v = 0 to 4

The catalyst was prepared and evaluated according to the procedure described in Examples 1 -2, except that the gas flow used in the reactor evaluation reaction with ethanol was hydrogen instead of nitrogen. The results are shown in Table 2.

Table 2

Although particular embodiments of the present invention have been described in the foregoing description, it will be understood by those skilled in the art that the invention is capable of numerous modifications, substitutions, and rearrangements without departing from the spirit or essential attributes of the invention. Reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.