Patent Publication Number: US-3875239-A

Title: Dehydrogenation of alcohols to ketones

Description:
I United States Patent 11 1 1111 3,875,239 Stouthamer et al. 1 Apr. 1, 1975 1 1 DEHYDROGENATION 0F ALCOHOLS T0 3.156.735 11/1964 Armstrong 260/680 KETONES 3 499938 3/1970 Hwang 260/617 [75] Inventors: Bernhard Stouthamer; Arien FOREIGN PATENTS OR APPLICATIONS Kwantes, both of Amsterdam 611481 12/1960 Canada 260/596 Netherland 823.514 11/1959 United Kingdom 260/596 [73] Assignee: Shell Oil Co., New Yo Primary Eraminer-Bernard Helfin [22] Filed: June 8, 1970 Assistant E.raminerW. B. Lone Attorney, Agent, or FirmHenry C. Geller; Norris E. [21] Appl. No.: 44,051 Faringer [30] Foreign Application Priority Data ABSTRACT June 11,1969 Netherlands 6908875 Controlling the average P diameter of aluminasupported platinum or rhodium catalysts used for de- 52 us. c1. 260/596 hydrogenating lower Secondary alcohol to kewnes [51] Int. Cl. C07c 45/16 fem the p d stri ution- A large pore diameter [58] Field of Search 260/596 gives g electivities t0 the ketone corresponding in carbon number to the alcohol feed, whereas a small [56] Refer Cit d pore diameter permits coproduction of this lower ke- UNITED STATES PATENTS tone and economically attractive amounts of higher 2.885.442 5/1959 McCulloch .1 260/596 ketone Condensano products 3.053 898 9/1962 Heuth ct a1 260/596 3 Claims, 1 Drawing Figure CRUDE AC ETONE ISOPROPANOL [ISOPROPANOL WATER 22 tZi LIGHT ENDS ATENTEBAFR 11975 r 30 CRUDE AC ETONE ISOPROPANOL JISOPROPANOL WATER r {-12} LIGHT ENDS 2o--g 2 3s METHYL ISOBUTYL KETONE 4| VI E THYL ISOBUTYL CARBINOL HEAVY ENDS J INVENTORS:  
 BERQJHARD STOUTHAMER ARIEN KWANTES XLOMGQ w M THEIR ATTORNEY DEHYDROGENATION OF ALCOHOLS T0 KETONES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to processes and catalysts for the dehydrogenation of alcohols to ketones, and/or for the condensation of lower ketones to higher ketones. More specifically, it relates to a method for controlling. maximizing or minimizing the formation of ketone condensation products when secondary alcohols are catalytically dehydrogenated to kctones.  
 2. The Prior Art Certain lower ketones, for example dimethyl ketone (acetone) and methyl ethyl ketone are prepared on commercial scale by dehydrogenating secondary alcohols, for example isopropanol and sec-butanol, with zinc, copper and brass catalysts. Conventionally, these lower ketones can be converted into higher ketones, for example acetone can be converted into methyl isobutyl ketone. by a three-step process: first, the ketone (acetone) is condensed in the presence of caustic to form a diketone alcohol (diacetone alcohol), then the diketone alcohol is dehydrated to an unsaturated oxide (mesityl oxide) with a suitable dehydrogenation catalyst. and finally the unsaturated oxide is hydrogenated to higher ketone (methyl isobutyl ketone).  
  These three reactions, condensation, dehydration, and hydrogenation often occur to very minor extents during the initial alcohol dehydrogenation reaction. The amounts of higher ketone, for example, the methyl isobutyl ketone formed during acetone production, are often large enough to be deleterious to the lower ketone product quality but are seldom large enough to be economically recoverable. It is clearly desirable to have a method to control the formation of higher ketones, either to minimize their formation and thus reduce lower ketone product contamination or more importantly to increase their production to a point where they can be economically recovered and thus avoid complicated three-step conventional higher ketone production methods.  
 STATEMENT OF THE INVENTION It has now been found that platinum or rhodium on a porous alumina support are effective catalysts for the dehydrogenation of lower alcohols to ketones, and/or for the condensation of lower ketones to higher ketones, and that by varying the average pore diameter of the porous alumina support the amount of ketone condensation products formed can be maximized or minimized. In general terms. as the average pore diameter of a porous platinum rhodium or alumina catalyst is raised. the specificity of the dehydrogenation to the corresponding ketone is increased, and as the pore diameter is lowered, the proportion of higher ketones is increased. Thus, for example, when isopropanol is dehydrogenated wtih a small pore diameter aluminasupported catalyst. methyl isobutyl ketone is coproduced with acetone in economically recoverable high yields. When a large pore diameter aluminasupported platinum or rhodium catalyst is employed, high selectivity to acetone is achieved.  
  The invention will be described with reference to the accompanying drawing, wherein the sole FIGURE illustrates diagramatically an elevational view of one form of apparatus suitable for carrying out the process of the invention.  
 DETAILED DESCRIPTION OF THE INVENTION Catalyst Platinum or rhodium on alumina catalysts are employed in this invention. The platinum or rhodium content of the catalysts is suitably selected in the range of from 0.0l% by weight platinum or rhodium (calculated as the respective metal based on the entire weight of catalyst) to about l.O% by weight. with platinum or rhodium contents of 0.02% by weight to 0.75% by weight being preferred and platinum or rhodium contents of from 0.04% by weight to 050% by weight being most preferred. Higher and lower amounts of platinum or rhodium may be employed but higher amounts are unsuitably expensive and lower amounts give lower catalyst activity.  
  The platinum or rhodium is applied to the catalyst by conventional methods. One very suitable method is by impregnating a suitable aluminous support with a solution, preferably an aqueous solution, of a platinum compound, for example chloroplatinic acid (H PICI or tetrammine platinum hydroxide (PHNHUJOHJ or of a rhodium compound, for example rhodium nitrate (RI1(NO;,) If desired, the support can simultaneously or separately be impregnated with solutions of other metals. Thus, impregnation with a titanium compound gives very favourable results in combination with platinum or rhodium. Impregnation with titanium isopropoxide (Ti(OC;,H from an anhydrous solution has proved very useful. After impregnation, the solvent can be removed by evaporation. When the platinum or rhodium is applied to the support as a compound, it is desirable to convert the said metal of the compound in question to a metallic state, as by reduction with hydrogen at a temperature above I50C, and preferably above 250C.  
  It should be noted that in the preparation of the catalyst one or more basic components may be added to the support. e.g., after the platinum or rhodium has been applied. It is more advantageous, however, to carry out the impregnation of the carrier in one single operation by applying the basic and noble metal components simultaneously.  
  The nature of the catalyst support employed is important. Suitable supports include the porous, nonacidic aluminas. The acidity of a catalyst support can be determined by the following procedure. A sample of catalyst support is contacted with isopropanol/water azeotrope vapor (87% IPA, 13% water) at a space velocity of 4 liters of liquid isopropanol azeotrope per liter of support per hour at a temperature of 370C and a pressure of 6 atmospheres. After 20 hours, a sample is taken from the gas stream which had just passed over the support and the hydrocarbon content of the sample of the gas stream is determined. A support is regarded as non-acidic ifless than l()% by weight ofthe total isopropanol component of the sample has been dehydrated to olefin. Catalyst supports which dehydrate less than 5% by weight of the isopropanol are preferred with supports which dehydrate less than 2% of the isopropanol being most preferred.  
  The average pore diameter of the porous alumina catalyst support is critical. The average pore diameter can be calculated using the formula:  
 average pore diameter (A) 4 X pore volume (ml/g)/specific surface area (m /g) l The specific surface area can be determined according to the BET method as explained by Paul H. Emmett in the second chapter of the book Catalysisf Volume I (Reinhold Publishing Corporation, New YOrk, 1954). The pore volume can be determined as described by A. Wheeler in the second chapter of Volume ll of the book Catalysis (Reinhold Publishing Corporation, New York, 1955 by means of the BET method for pores of not too large diameters (up to about 100 A), and for larger pores by means of the mercuryporosimeter method likewise described in that latter chapter.  
  [t has been found that a large specific surface area gives rise to the formation of a greater amount of oxygen-containing compounds having more carbon atoms per molecule than the starting alcohol which are re&#39; ferred to as condensation products) than a small specific surface area. lf, in general, the formation of condensation products is to be kept low, it is recommended to use alumina carriers with a specific surface area of 5 l00 m /g, in particular of 80 m /g. If, on the contrary. it is desired to produce a larger percentage of condensation products, such as methyl isobutyl ketone, the specific surface area should preferably exceed I00 m-&#39;/g, surface areas of up to 150 m /g having proved to be particularly favorable.  
  The type of ketone product mixture produced is dependent on the average pore diameter of catalyst support. Catalyst supports having an average pore diameter not greater than 250 A. preferably less than 200 A, and of at least 150 A, are employed when maximum proportions of ketone condensation products, espe cially those ketones having twice as many carbons the starting alcohols. are desired. Supports having an average pore diameter of greater than 250 A, preferably greater than 300 A and most suitably greater than 450 A are employed when it is desired to maximize the production of ketones of the same number of carbons as the starting alcohols. Many commercial aluminas generally have relatively small (less than 150 A) average pore diameters. The average pore diameter of such supports can be increased. if desired, by heating the support at a temperature above 900C (preferably from 1.000 to l,200C) if desired in the presence of a fluxing agent such as boric acid. The duration of this treatment depends upon the temperature. For instance, a commercially available gamma-alumina with a specific surface area of 3l l m jg and an average pore diameter of 57 A on being heated at l,l00C for 6 hours is converted to an alumina with a specific surface area of 22.5 m fg and an average pore diameter of 780 A.  
  Before or after the heating described, one or more of the basic catalyst components maybe added to the carrier, for instance by impregnation with a solution thereof and evaporation of the solvent.  
 Alcohol and/or ketone Feedstock Acyclic, aliphatic mono-alcohols, i.e., alkanols containing from 3 to 6 carbon atoms, and/or lower ketones, are suitable feedstocks in the process according to the invention. Particularly suitable are the secondary aliphatic mono-alcohols with the secondary alkanols, isopropanol and sec-butanol being most preferred, and- /or the corresponding ketones, particularly acetone and methyl ethyl ketone. The process according to the invention is particularly suitable for application to mixtures of alcohol and water, especially those mixtures of isopropanol and water, such as the azeotropic mixture of water and isopropanol l37r by weight water/87% by weight isopropanol) which is produced commercially. A somewhat more specialized feedstock which may be suitably used with the platinum or rhodium on alumina catalysts of the invention is the ketone-containing effluent of conventional zinc, copper or brass-catalyzed alcohol dehydrogenation, for example, the acetone, isopropanol/water mixture which results when isopropanol/water azeotrope is dehydrogenated with a brass catalyst. Such an effluent typically contains about 50 to 557: by weight acetone, to by weight isopropanol, 13 to 25% by weight water, and hydrogen. When such a ketone-containing feedstock is employed, very complete dehydrogenation of the isopropanol initially fed is achieved and either high selectivity to acetone is realized or an efficient co-production of acetone and methyl isobutyl ketone is achieved. Mixtures of alcohols and/or ketones, of course, can be used as starting materials.  
 Reaction Conditions The temperature at which the dehydrogenation reaction can be performed may vary within wide limits. Temperatures between 250C and 500C are generally preferred. The amount of condensation products increases as the temperature is raised and the amount of ketone formed having the same number as carbon atoms as the starting alcohol decreases accordingly. Therefore, when ketone monomers are being prepared, temperatures in the range of from 250C to about 400C are preferred and when condensation products are being maximized, temperatures in the range of from 350 to 500C are preferred.  
  The pressure employed during the reaction according to the invention may vary within wide limits. ln general, atmospheric pressures to pressures of 25 atmospheres are very suitable. At these pressures. the alcohol feedstock will be present as vapor. Pressures between 1 atmosphere and 10 atmospheres are preferred. At lower pressures. such as from atmospheric to 6 atmospheres, the selectivity to ketone monomers are somewhat greater than at higher pressures such as from 5 atmospheres to l0 atmospheres.  
  Catalyst activity is sustained if added hydrogen is present during the contact of the alcohol to be dehy drogenated with the catalyst. When the starting material, or one of the starting materials, is a ketone, the presence of hydrogen is, of course, essential.  
  Although the reaction may be performed batchwise, preference is given to a continuous process, i.e., a vapor stream containing the reaction components is passed, at a certain rate, over or through the catalyst. It is one of the advantages of the process according to the invention that high space velocities, expressed in liters of liquid alcohol or alcohol-containing liquid per liter of catalyst per hour (LHSV) may be applied without the conversion of alcohol decreasing unsuitably. LHSVs of up to about 25 liters/liter/hour and even higher are very suitable.  
 Ketone Products The ketones prepared by this invention have a wide range of application as solvents, plasticizers, blending agents, wax substitutes, detergents, and numerous other uses. Typical solvent applications include: acetone as a solvent for nitrocellulose, methyl isobutyl ketone as a solvent for cellulose esters, and methyl ethyl kctone as a solvent for lacquer resins.  
  A description of an exemplary process for the production of methyl isobutyl ketone from isopropanol EXAMPLE l Three platinum on alumina catalysts (Catalysts A. B and C] were prepared. The following aluminas were used as carriers for the preparation of catalysts:  
 using a pore S in il l gt zfig ggg si g For catalyst A an alumina with a specific surface area i or r 9 mm 1 p of 3H m /g, a pore volume of 0.44 ml/g, an average nylng drawing. Referring to the FIGURE. isopropanollpore diameter of 57 A (calculated from these figures) water azeotrope (877: isopropanol) is Introduced as a v&#39;&#39; I&#39; H i t r &#34;t I 12 wherein it contacts a and a sodium comflm of a Id mt n 0 r T m For catalyst B an alumina with a specific area of 312 used catalyst bed 13. The non-acidic catalyst eontalns v t) 57 b wei ht of latin )r rhodium on an alumina nT/g a pore volume of 035 average pore d]- 3 g p um i ameter of 45 A (calculated from these figures) and a support having an average pore diameter of [50 A and Sodium content of 0 5%w f &#39;iiw -L i li fif i r fia g f f a The carrier for catalyst C was obtained by heating the *2 f a or i 9} pro l5 alumina described for catalyst A for 6 hours at fii i g g i mgen f &#39;g f 1,100C. it had a specific surface area of 30.4 m /g and i&#34; 3 fi 2 my giid an average pore diameter of 580 A. wi Tg 0 f i r The non-acidic character of the carriers was demonf um f; imere g3 i strated by means of an appropriate experiment as has hydrogm. are condense Hydrogen is remove \ld me been described in the text 17 and optionally recycled to line 14. Other products Catalysts containing 0257!, of platinum were are transferred via line 18 to fracttonator 19, where acpared by impregnating the three aluminas with a Calcw etone and unreaeted isopropanol and some water are med amount of an aqueous Solution of chloroplatinic taken ott as overhead through line 20 and elther passed acid followed by drying at lzooc for 6 hoursv The ch1o via l ne 2| to turthertractlonators not shown to recover mphmnic acid was the&#34; Converted into platinum by panned acetone, or are recycled via line 2 2 to dehyheating the catalyst in an atmosphere f hydrogen drogenation reactor 14. A bottoms product is removed The three catalysts were tested f alcohol d h from fractionator [9 via line 24 to separator 25 where gehahoh performance The akuhopcohmihihg f d a water phase B is separated and removed via line 2o. consisted f mixture of 37% isopropanol and 39; All Ul&#39;glll&#39;llC PhtlSL A 15 SLpill&#39;lllCLi and tl&#39;lll&#39;lSfClTBLi V12] 3 of water The pressure during the reaction was 3 1mgline 27 {U t&#39;ractionator 28, WhLTt? light ends ill&#39;L OYCF- pheres and the feed was passed ver the atalyst at a headed and removed via line 29. A methyl isobutyl space velocity of 4 liters of liquid per liter of catalyst ketonc/u&#39;ater azeotrope sidedraw is taken through line p r hour: The temperature during the reaction was 30. condensed. and passed to separator 31 where a about 270C. After reaction for 6 hours the composi methyl isobutyl ketone phase C is separated and return tion of the reaction product was determined. Table A as rellus via line 32 and a water phase D is separated shows that with catalyst C a high conversion of the isoand removed via line 33. Fractionator bottoms product propano] is attained with a high selectivity to acetone. is removed via line 34 and either passed directly to while with catalysts A and B. a large amount of higher fractionator via line 35 or optionally passed through ketones is formed.  
 Table A Reaction Products Catalyst Selectivity towards Specific Average Conversion Methyl- Oxygen surface pore diaof lsopropisobutyl Comarea of meter of anal. 72 ketone pounds carrier. carrier -carbinol with 9 Hydro m lg carbon carbons Type A Acetone atoms A 31 57 70 5O 26 I! 3 B 312 55 30 [5 0.5 C 30.4 580 97 2 l 0.4  
 lines 36 and 39 through hydrogenator 37, which hydro- EXAMPLE gen-ates any traces ot&#39;mcsityl oxide present. In fraction- Ah alumina as described as Carrier f cata|yst B i ator 40. an overhead traction of purified methyl isobu- Example was h ated at l,l0OC for 6 hours. After this tyl ketone is removed via line 41. A bottoms product i d h Surface area was 3 and the average of fractionator 40 is transferred to t&#39;ractionator 44 via pore diameter 070 A the amount f hydmwrbohs line 42 where heavy ends are separated as bottoms and f d i h determinaticn f h idi or idi remmed via line 45 and an overhead of methyl isobutyl 60 Character f h carrier was 7 hi Carrier was i carhinol is either removed via line 46 or optionally pregnated i h an aqueo s solution of chloroplatinic passed via line 47 to dehydrogenator 49 where the a id and dried at 120C for 2 hours. The catalyst conmethyl isobutyl carhinol is converted into methyl isomin d 0,05% platinum, The catalyst was heated to butyl ketone and then recycled to line 35 via line 50. about 370C under a stream of hydrogen, and, subse- The following examples are illustrative of the prac- 6i quently. a mixture of 87%w isopropanol and l37rw watice of the invention. It is to be understood that these examples are given only for illustration and are not to be construed as limiting the invention in any way.  
 ter. together with hydrogen (5 liters of hydrogen (calculated at 0C and 1 atm) per grams of isopropanol/water mixture) was passed over the catalyst at a pressure of 6 atm. Table 8 shows the composition of the reaction product at various times.  
 and a pore volume of 0.65 ml/g was heated in air at l,l00C for 6 hours. After this treatment the material Table C Reaction. Hours Temp. at  
  Comersion. end of 4 Selectivity towards Methyl oxygen com ounds with carbon atoms ethyl cat. bed.  
 (&#39; ketone Space thus obtained had a specific surface area of 85.9 m /g and a pore volume of 0.33 ml/g. The average pore diameter. determined with the aid of a mercury porosimeter. was found to be 200 A.  
  This carrier material was subsequently charged with 0.25% of rhodium and 1.5% w of sodium by impregnation with the calculated amounts of an aqueous solution containing rhodium nitrate and sodium nitrate. in such a way that the pores were just filled. followed by drying at 120C and heating in air at 500C for 3 hours.  
  Over the catalyst thus obtained a feed was passed which consisted of 57.5 /(w of acetone, 25 &#39;ilw of isopropyl alcohol and 17.5 Uiw of water. together with such a quantity of hydrogen that the H /acetone molar ratio was l.0. During the reaction the pressure was maintained at (1 atm abs. In two experiments the space velocities (LHSV) amounted to 5 and 10 liters of feed per liter of catalyst per hour. respectively. The results are given in Table E.  
 Table E conversion of isopropyl alcoho in feed. l  
 temp. at end of cat.bed. C  
 EXAMPLE IV A catalyst as described in Example ll was prepared with the difference that the amount of platinum was 0.259;: A mixture of 52.9%w acetone. 24.07rw isopropanol and 23. Wh water and hydrogen. obtained by dehydrogenation of an isopropanol/water mixture (weight ratio 87/l3) over a copper-zinc alloy, was passed over this catalyst at a space velocity of 23 liters of liquid per liter of catalyst per hour. Table D shows the results.  
 EXAMPLE VI A carrier material as described in Example V was charged with 2 7(w of titanium (as titanium tetraisopropoxide dissolved in n-hexane). After drying at 120C the impregnated carrier was heated for 3 hours at 500C. Subsequently. this material was charged with 0.25 7(w of platinum and 1.5 %w of sodium by impregnation with the calculated amounts of an aqueous solution containing sodium hexachloroplatinate and sodium hydroxide in such a way that the pores were just An alumina with a specific surface area of 256 m lg filled. followed by drying at 120C and heating in air at 500C for 3 hours.  
  Over this catalyst a feed was passed which consisted of 94.8 72w of acetone, 4.3 7(w of isopropylalcohol and 0.9% of water, together with such a quantity of hydrogen that the intake molar ratio H,jacetone was 1.0. The working pressure of the reactor system was 6 atm abs. The space velocity (LHSV) was adjusted at 10 liters feedstock (1 cat. 11)&#34;. The reactor inlet temperature was 260C, resulting in an outlet temperature of 300C. The liquid reaction product excluding water consisted of 60 %w of acetone, 8 7cw ofisopropyl alcohol, 23 72w of methyl isobutyl ketone, 1.8 [7(W of mesityl oxide and methyl isobutyl carbinol, and 7.2% of C oxygen containing compounds.  
 EXAMPLE VI] The catalyst described in Example VI was contacted with a feedstock having the composition: 61.3 %w of acetone, 23.85 71W of isopropyl alcohol. 0.2 %w of methyl isobutyl ketone and 14.7 7(w of water, together with such a quantity of hydrogen that the intake molar ratio H /acetone was 1.0. The working pressure of the reactor system was again 6 atm abs. The feed rate was l liters liquid feed per liter of catalyst per hour (LHSV). The reactor inlet temperature was 354C, the reactor outlet temperature 380C. The composition of the liquid reaction product (excluding water) was 68 /1w of acetone. 40 7(w of isopropyl alcohol, 2L0 7zw of methyl isobutyl ketone. 1.3 71w of mesityl oxide and methyl isobutyl carbinol, and 5.7 %w of C oxygen containing compounds.  
 EXAMPLE Vlll A carrier prepared as described in Example V was charged with 0.25 7( of platinum and L 7r of sodium by impregnation with the calculated amounts of an aqueous solution containing sodium hexachloroplatinate and sodium hydroxide in such a way that the pores were just filled, followed by drying at lC and calcining in air for 3 hours at 500C. Over this catalyst the same feed as in Example VI] was passed at the same LHSV of 10, together with the same amount of hydrogen (molar ratio H lacetone 1.0). Also the pressure was the same. The reactor inlet temperature was 365C. The reactor outlet temperature 380C.  
 Acetone 80.4 lsopro yl alcohol 7.l Methy isobutyl ketone 10.5 Mcsityl oxide and 0.9  
 Methyl isobutyl carbinol C oxy compounds We claim as our invention:  
  1. A process for producing ketones by conversion of acyclic aliphatic secondary monoalcohols having from 3 to 6 carbon atoms to a mixture of aliphatic ketones comprising ketones having the same number of carbon atoms as the secondary monoalcohols and ketones having twice as many carbon atoms as the secondary monoalcohols which comprises passing l a mixture of a said monoalcohol and water or (2) a mixture of a said monoalcohol, water, hydrogen and a lower alkanone over a catalyst consisting essentially of from 0.0l7r by weight to l7r by weight of platinum or rhodium on a non-acidic porous alumina support having an average pore diameter of between [50 and 250A. at a temperature of from 350C to 500C and a pressure of from S atmospheres to 10 atmospheres, and recovering from the resulting dehydrogenation product the aliphatic ketones having the same number of carbon atoms as the secondary monoalcohols and the aliphatic ketones having twice as many carbon atoms as the secondary monoalcohols.  
  2. The process in accordance with claim 1 wherein the aliphatic alcohol is isopropanol, the aliphatic ketone produced having the same number of carbon atoms as the secondary monoalcohol is acetone and the aliphatic ketone having twice as many carbon atoms as the secondary alcohol is methyl isobutyl ketone.  
  3. The process in accordance with claim 2 wherein the catalyst contains from 0.02% by weight to 0.75% by weight of platinum and wherein the porous non-acidic alumina support has an average pore diameter of less than 200 A.