CA1151216A - Preparation of methanol from synthesis gas with promoted palladium catalysts - Google Patents

Abstract

12,430 PREPARATION OF METHANOL FROM SYNTHESIS
GAS WITH PROMOTED PALLADIUM CATALYSTS

ABSTRACT OF THE DISCLOSURE

An improved catalytic process for the production of methanol from hydrogen and carbon monoxide at a temperature of from about 200°C to about 400°C ant a pressure of from about 150 to about 20,000 psia which comprises effecting the reaction in the presence of a heterogeneous solid catalyst comprising palladium in combina-tion with a metal additive selected from the group con-sisting of lithium, magnesium, strontium, barium, molybdenum and mixtures thereof.

SPECIFICATION

1.

Description

11 5~ 12,430 CROSS-REFERENCE TO RELATED APPLICATION
cc~ d~cln This application i6 related to copending V~
application Serial No. ~ filed on even tate herewith which describes a process for produc~ng methanol from synthesis gas using a catalyst containing palladium and calcium.
BACKGROUND 0~ THE INVEN~ION
This invention relates, in general, to e catalytic process for producing methanol from synthesis gas. More part~cularly, the invention concerns reacting synthesis gas in the presence of a promoted palladium catalyst to form methanol at high carbon efficiencies and improved rates of production.
Methanol is an increasingly important feed-stock for the production of carbon-based chemicals.
Existing or proposed commercial processes using methanol include dehytrogenation to form formaldehyde, carbonyla-tion to form acetic acid, -homolog~tion to form ethanol and reactions over zeolitic materials to form gasoline- ~, grade fractions. The presently anticipated increase in commercial methanol manufacture has underscored the need for new and improved catslysts characterized by high carbon efficiencies and good productivity to methanol.
The use of catalysts to influence the product distfibution resulting from the hydrogenation of carbon monoxite is well known in the art. Among the vast array of products obtainable from the reaction of carbon monoxide and hydrogen, methane is thermodynamically the most favored, longer chain hydrocarbons are next followed by h~gh molecular weight alcohols with methanol being .

2. ~

~ 216 12,430 thermodynamically one of the lea6t stable products which can be formed. Hence, specific catalysts for methanol synthe6is are required in order to selectively produce methanol at high reaction efficiencies from synthesis gas.
The prevalent commercial catalysts today for methanol manufacture from a synthesis gas are composed of oxides and mixed oxides of chromium, zinc ~nd copper.
Palladium is also known in the art as an effective methanol catalyst. U. S. Patent No. 4,119,6S6 to Poutsma 1~ et al., datet October 10, 1978, discloses the formation of hydroxylatet hydrocarbons such as methanol and ethylene glycol from synthesis gas in the presence of a palladium catalyst. While the process of Poutsma et al is character-ized by very high selectivities of methanol, generally above 95 percent, the productivity of methanol is ~ub-stantially below that achieved in commercial methanol synthesis processes. Hence, it would be desirable to significantly improve the methanol production rate of the Poutsma et al process while maintaining its high process efficiency.
SUMMARY OF THE INVENTION
This invention describes a catalyst for the production of methanol from the reaction of carbon monoxide and hydrogen, such catalyst being an improvement of that disclosed in the aforementioned U. S. Patent 4,119,6~6. Thç process of the invention involves contact-ing a heterogeneous solid catalyst comprising palladium in combination with an effective amount of a metal additive ~elected from the group consisting of lithium, magnesium, stsontium, barium, molybdenum and mixtures of same with . . . . ... . . . ..

6 12,430 ~ynthesis gas comprising carbon monoxide ant hytrogen at a temperature of from about 200C to about 400C
and a pressure of from about 150 to about 20,000 psia to 6electively fcrm methanol The preferred reaction conditions are a temperature between about 250C and about 350C and a pressure between about 150 and about 3,000 psia.
The present invention ~s predicated on the discovery that the production rate of methanol in the aforementioned Poutsma et al process can be significantly enhanced by the addition sf a metal promoter or additive as herein described to a palladium catalyst such as utilized in the Poutsma et al process. Thus, up to a three-fold increase in methanol manufacture can be achieved in accordance with the invention relative to the process of U. S. Patent 4,119,656 without adversely affecting the very hi~h process efficiencies achieved with such process.
PROCESS DISCUSSION
In accordance with the invention, a æynthesis gas containin~ carbon monoxide and hydrogen is con-tacted with a palladlum catalyst containing one or more of the aforementioned metal promoters under reaction conditions ~f temperature and pressure which thermo-dyna~ically favor the $ormation of methanol relative to hydrocarbon3, 6uch as, methane. The selectivity of the resction to methanol is generally at lea6t 90 percent, more typically ~bout 95 percent or greater, and under preferred reaction conditions about 98 percent.
Molybdenum is the preferred metal promoter insofar ~ methanol production i8 concerned, albeit less 12,~30 ~ 6 preferred than lithium, magnesium, strontlum and/or barium with re~ard to reaction efficiency to methanol.
I~at is, the u6e of molybdenum in con~unction with palladium results in a 6ignificsnt increase in the manufacture of reaction products which although comprised primarily of methanol also include methane, two or more carbon atom hydrocarbons, and hydro~ylated com-pounds, such as, ethanol. In contrast thereto, the use of lithium, magnesium, 6trontium and/or barium in accordance with the invention re~ults in a generally higher reaction selectivity to methanol, typically above 95%, and under preferred reaction conditions about 98%, but a lower reaction productivity relative to the use of molybdenum.
Reaction selectivity, or efficiency, is -defined herein as the percentage of carbon atoms con-verted from carbon monoxide to a specified com~ound other than C02.
The promoted palladium catalyst of the invention comprises palladium in combination with one or more of the aforementioned metal additives employed in a fine dispersion or slurried in a high boiling point ~olvent, or alternatively, supportet upon an inert carrier material. ,The preferred mode of operation is to support the palladium catalyst and the desired metal additive(s~
on a particulate high surface area support and the 6upported combination then placed into the reaction zone.
In an alternate embodiment of the invention, the desired amount of metal additive is incorporated into the support during formulation so as to be an integral part of the fini~hed suppost, the palladium being thereafter deposited .
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... . . , . . .. ,~ . .. .. _ .. . , . . .. . . ~ .

~ Z ~6 12,430 upon ~uch 6upport. If de6~red, a portion of the metsl additive may be incorporated lnto the ~upport and the remainder deposited upon the 6upport with the pallad~um catalyst.
A 6upport having a ~urface area greater than 1.0 square meters per gram (BET low temperature nitro~en adsorption isotherm method) is generally preferred, A
surface area above 10 ~quare meters per gram being particularly desirable, although surface area i~ not the ~ole determinative variable. Silica gel is a preferred catalyst ~upport with alpha alumina, gamma alumina, magnesia, carbon, zirconia and titania being among the useful albeit less desirable catalyst supports.
For the purpose of this invention it is believed that palladium deposited on particles of a compound of one or more of the aforementioned metal additives such as the oxide or carbonate is substantially the same as palladium and such additive(s) deposited on any of the above support materials.
On the basis of experience to date, the amount of palladium on the support should range from about 0.1 wt. % to about 20 wt. %, based on the weight of the support material. Preferably, the amount of palladium is within the range of about 2 to about 5 wetght percent.
The amount of metal additive in the catalyst may vary depending upon the particular metal additlve; the catalyst 6upport employed and the method of catalyst preparation.
For a given additive, catalyst 6upport, and method of cataly~t preparation, the optimum concentration of additive is readily determined by ~imple experimentation. For . _ . _ .. ... _, . .. .. . . .. _ .. ... .. . . . . . . . . .

1~51Zi6 12,430 additives such as lithium, magnesium, strontium and/or barium supported on a 6ilica gel supp~rt, the preferred concentration of sddit~ve is from about .05% to about 1%
by weight of the catalyst ~upport. For molybdenum, con-centrations of from about 0.1 to 5.0% by weigbt of the support are 6ultable with c~ncentrations of from ~bout 0.2 to 3.0% by weight being preferred.
Palladium snd one or more of the ~forementioned additives may be deposited onto the catalyst base or support by any of the commonly accepted techniques for catalyst preparation, as for example, impregnation from a solution containing the galt6 of palladium ant the desired metal additive(s), precipitation, coprecipitation, or ion exchange. Typically, a 601ution of heat de-composable inorganic or organic palladium compound and a compound of lithium, magnesium, ~trontium, barium and/or molybdenum is contacted with the gupport material and then dried and heated, the latter under reducinR conditions to form the finely dispersed promoted palladium catalyst.
The metal additive and palladium metal catalyst may be deposited concurrently or sequentially.
That is, palladium may be codeposited with the metal additive of choice or it may be deposited upon the carrier either before or after such metal additive. Similarly, $f more than one metal adtitive is used, the additives themselves may be deposited concurrently or in any desired ~equence.
The palladium deposited $s typically in metal form, des~rably as fi~e discrete particles. The form of additive metal component is, however, not completely ~ Zl~ 12,430 l~der~to~d. It m~y ~e chemically 6soci~ted wlth the palladium or lt may be a physical dmixture. For example, the additive may be alloyed with the palladium or not, ~n the form of a met~l or an oxidized 6tate of the metal, or it m~y be a s~lic~te, carbonate, or the l$ke.
Conditions of temperature, of pressure, and of gas composition are within the ranges~thst are eseentially conventional for synthesis gas conver6ion to methanol for palladium catalysts. The reaction temperature markedly affects the productivity of the reaction with regard to methanol formation. Thus, an increase in reaction temperature results in an increa~ed co~version t~ methanol with the proviso that the reaction pressure is correspond-ingly increased to avoid thermodynamic limitations.
Increased pressure enhances the productivity of the reaction but mzy affect product distribution. Thus, for example, at increased pressures there may be an increased proportion of impurities, ~uch as, ethanol and methyl formate in the product mixture. For purposes of economy, the reaction pressure is preferably within the range of 150 - 3,000 psia although a reaction pressure of from sbout 150 - 20,000 psia i8 generally suitable.
The operable space velocities in the flow reactor may vary from about 102 to 106 per hour; space velocity being defined a~ volumes of reactant gas at O~C and 760 mm.
mercury pressure, per volume of catalyst, per hour.
Generally, the higher the 6pace velocity, the more economical the overall reaction, although at excessively high ~pace velocities the productivity of ~he reaction is adversely affected while excessively low space ~elocities ,, , .. , . . ... ~

~ 12,430 c~use the production of a more diverse spectrum of reaction products.
The mQlar rat$o of hydrogen to carbon monoxide in the synthesis gas m~y vary cxtensively from about 1:10 to 10:1. The preferred hydrogen to carbon monoxide ratio is within the range of at least 1:5 to 5:1, a ratio of about 2:1 being most preferred. Increas$ng the percentage of hydrogen relative to carbon monoxide ~n the g8S mixture increases the rate of the reaction, but adversely affects the economlcs of the overall process.
PREPARATION OF CATALYSTS
The catalysts cited ~n the examples below were all prepared by essentially the following sequence of steps: The tesired quantities of palladium (II) chloride, ammonium paramolybdate, and the nitrate salts of lithium, magnesium, strontium and barium, depending upon the desired catalyst composition, were dissolved in a 1:1 HCl/H20 (by volume) solution at ambient temperature. The ~olume of 601ution was chosen to ~ust fill the void volume ~pores) of the support sample being impregnated.
DavisonTM Grade 59 ~ilica gel (8-20 mesh - V. S. Sieves) was placed in a vacuum flask. The top of the flask was sealet with a rubber septum, and the flask was eva~uated through the side arm. A ~yringe needle was then ~sed to in~ec~ the solution onto the evacuated 6upport. When addition was complete, t~e impregnated support was allowed to stand at one atm~sphere for approximately 30 minutes.
It was then carefully dried in a nitrogen atmosphere using the following sequence: 80C. (for 1 hr.); 110C. (2 hrs.);
150~C. (2 hrs.); and about 300C. (2 hrs.). The dried, il~lZ 1~ 12,430 impregnated 6upport was placed ln a quartz tube through which hydrogen was cont~nuously passed. The temperature was raised from 100 to 500C., over R five hour period and then held at 500C. for 1 hour. The reduced catalyst was then cooled to amb~ent temper~ture cver a period of approxima~ely two hours in a flowing hydrogen atmosphere and finally flushed with nitrogen before being removed.
In order to remove signif$cant amounts of impurities which were present in the support material as received from the manufacturer, the DavisonTM Grade 59 silica support was initially `'washed" with oxalic acid prior to being used as the catalyst support. Such treatment consisted of passing a mixture of oxalic acid, glycerine, and water in proportions of 1:1.5:2.5 by weight, respectively, through a bed of 6upport material (length/diameter ratio of about 20 to 25) contained within a glass tube which drained through a 6topcock at its base. The contents of the tube were maintained at about 90C by means of resistance heating wire wrapped around the exterior of the tube. About 2.5 volumes of oxalic ac~d solution were used to wash one volume of 8-20 mesh silica gel over a three-hour period. The material was then washed with about 8iX volumes of distilled water at 90C over a period of about four hours ant then dried at 350C for about four hours.
The chemical ~nalysis of the silica gel for iron, aluminum, 60dium and calcium impurities following the above-described treatment was as follows:

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llSlZl~ 12 ~ 430 Iron as Fe203 0.01% + 0.004%
Aluminum ~ A1203 0.01% ~ 0.004%
Sod~um as Na20 0.01% + 0.004%
Calcium as CaO 0.02% + 0.01%
DESCRIPTION OF TEST REACTOR
The re~ctor used in the following Examples was an internally silver-plated 316 6tainless steel, bottom-agitated "Magnedrive" autoclave with a centrally positionet catalyst basket and a 6ide protuct effluent line. It is of the type depicted in Flgure 1 of the paper by Berty, Hambrick, Malone and Ullock, entitled "Reactor for Vapor-Phase Catalytic Studies", presented as Preprint 42E at the Symposium on Advances in High-Pressure Technology - Part II, Sixty Fourth National Meeting of the American Institute of Chemical Engineers (AIChE), at New Orleans, Louisiana, on March 16-20, 1969 and obtainable from AIChe at 345 East 47th. Street, New York, New York 10017. A
~ariable speed, magnetically driven fan continuously recirculated the reaction mixture over the catalyst bed.
The following modifications were found to facilitate operation:
1. Hytrogen feed gas was introtuced continu-ously at the bottom of the autoclave through the well for the shaft of the Magnedrive agitator.
2. Carbon monoxide feed gas was introduced continuously thsough ~ separate port at the bottom of the autoclave, in order to avoid a hydrogen-rich zone in the autoclave.

12 ,430 Effluent gases were removed through a port in the ~ide of the re~ctor. 'Contensable liqu~d products were removed from the exit stream in a brine-cooled con-te'n~er at ca. 5 to lO~C and were collected ln a holding t~nk under pressure. The non-condensable com~onents of the exit 6tream were vented through a wet test meter at atmospheric pressure to determine their total volume. A
rubber 6eptum in the atmospheric pre6sure l$ne permitted syringe sampling of the non-contensable gases. No external recycle was employed.
DESCRIPTION OF THE TEST PROCEDURE
The weight of a given volume of catalyst sample was determined and the sample was placed in the catalyst basket. The quantity of catalyst charged was from about lS to about 50 cc. depending upon the particular 6ample. Silver-plated screens and thin layers of glass wool were placed above and below the catalyst bed to prevent circulation of solid fines. The catalyst basket was charged to the reactor, and the reactor then sealed.
The 6ealed reactor and the process lines were pressure ~'tested at operating pressure. Nitrogen, hydrogen, or a mixture of the two was used for this test.
When the reactor was shown to'be leak free, pure hydrogen was passed through the reactor, and the temperature raised to about 240C. The hydrogen and carbon monoxide flows were then ad~usted at the'desired molar ratio to give a.total purge rate of approximately 500 STP*
literslhr. This corresponds to a space velocity of from about lO,OOO to about 33,000 STP volumes of gas per ~olume of catalyst per hour depending upon the volume of *~"STP" means standard temperature and pressure defined as 0C and l atm. pressure.

.. .. .. , .. , . ...... . .. . ... , .. . .. . _ ... . .. . . .. . .. . . .. .

12,430 ~ 21~

catalyst charged in the part~cular example. The hydrogen-carbon monoxide ratlo was de~ermined by gas chromatographic analysi6 of an effluent gas aliquot.
When the appropriate gas composition was obtained, the reactor temperature was raised to 300C. ~ period from about 0.5 hour to sbout one hour was allowed for the reactor to reach a steady-state at this temperature. The liqu~d product trap was then drained, a wet test meter reading was taken, and the time was noted as the beginning of a run. During the course of a run, one or more effluent gas samples were analyzed fox hydrogen, carbon monoxide, methane, C2 and C3 hydrocarbons, methanol, ethanol, methyl formate, dimethyl ether and acetaldehyde. At the end of a run, the liquid product was collected, and the volume of effluent gas was noted. The liquid product was analyzed by gas chro~tography.
The results of the tests are shown in Tables I
and II. Examples B to L of Table I demonstrate the effect of the various promoters on the rate of methanol ,~
production relstive to the unpromoted catalyst of Example A.
Examples M to P of Table II démonstrate the efficacy of the invent$on wi~h ~lpha and gamma alumina catalyst 6upports. In addition, the examples demonstrate that an increase in methanol productivity can be achieved in accordance with the invention by depositing the metal additi~e upon the support prior to the deposition of the palladium catalyst rather than concurrently therewith as ln the e~amples of Table I.

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12, 430 TABLE I
METHANOL PRODUCTION DATA (fl ) FOR
SUPPORTED PALLADIUM CATALYSTS (b) CONTAINING LIT~IUM, ~AGNESIUM, STRONTIUM, BARIUM OR MOLYBDENUM

EXAMPLE PROMOTERRAll~ TO METHANOL(C) A None 9 . 2 B 0.1% Li 16.3 C 0.2% Li 19.3 D 0.4% Li 11.2 E 0.1% Mg 11.8 F 0.2% Mg 16.8 G 0.4% Mg 12.4 H 0.2% Sr 20.2 0.2% Ba 16.1 J 0.69% Ba 15.3 K 0.2%Mo 14.9 L 2.0% Mo 28 Ca~ Catalysts were tested at 300C and a reaction pressure of 2,500 psia using a 1:1 molar ratio of H2:CO
synthesis gas composition at a ~p4ce velocity of 1-0,000 hr -1.
(b) The catalysts consist of 5 weight percent Pd plus the inticAted weight percent of promoter supported on Da~i~onTM Grade 59 silica gel support. The weight pércent of each component is based on the weight of the support.
Cc) 'iRate" is the rate of synthesis of methanol in pounds of product per cubic foot of catalyst per hour.

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Claims (7)

12,430 WHAT IS CLAIMED IS:

1. In a heterogeneous catalytic process for the production of methanol by the reaction of hydrogen and carbon monoxide in the presence of a palladium-containing catalyst at a temperature of from about 200°C to about 400°C and a pressure of from about 150 to about 20,000 psia, the improvement for enhancing the production of methanol which comprises effecting said reaction in the presence of a heterogeneous solid catalyst containing palladium in combination with a metal additive selected from the group consisting of lithium, magnesium, strontium, barium, molybdenum and mixtures thereof.

2. The process of claim 1 wherein said catalyst is supported on silica gel.

3. The process of claim 2 wherein the palladium concentration on the catalyst support is from about 2-5%
by weight, of the catalyst support.

4. The process of claim 1 wherein said metal additive comprises molybdenum.

5. The process of claim 4 wherein the molybdenum concentration on the catalyst support is from about 0.2%
to about 3.0% by weight of the catalyst support.

6. The process of claim 1 wherein the reaction temperature is from about 250°C to about 350°C and the reaction pressure is from about 150 psia to about 3000 psia.

7. The process of claim 1 wherein said gaseous mixture contains hydrogen and carbon monoxide in a volume ratio of from about 1:5 to about 5:1.