22 Claims, 9 Drawing Sheets

Disclosed are methods for producing dimethyl ether (DME)frommethanol and for producing DME directly from syngas,suchas syngas frombiomass.Also disclosed are apparatus forDMEproduction. The disclosed processes generally functionat higher temperatures with lower contact times and at lowerpressures than conventionalprocesses so as to produce higherDMEyields than do conventionalprocesses. Certain embodi­ments of the processes are carried out in reactors providinggreater surface to volume ratios than the presently used DMEreactors. Certain embodiments of the processes are carriedout in systems comprising multiple microchannel reactors.

ABSTRACT(57)

Primary Examiner - Rosalynd Keys(74) Attorney, Agent, or Firm - Frank Rosenberg; Derek H.Maughan

* cited by examiner

Cao et al., "Kinetic studies of methanol stearn reforming overPD/ZnO catalyst using amicrochannel reactor,"Applied CatalysisA:General,vol. 262, pp. 19-29 (2004).Fu et al., "The Effect of Solvent and Mixed Method to Direct Syn­thesis ofDME from Biomass SyngasVia GasificationBi-FunctionalCatalyst Preparation," International ConferenceonEnergy,Environ­ment and Disasters, Charlotte, North Carolina, 1 pg. (Jul. 24-30,2005).Hu et al., "Conversion of Biomass Syngas to DME Using aMicrochannelReactor,"Ind. Eng. Chem.Res., vol. 44, pp. 1722-1727(2005).Nakato et al., "Changes of Surface Properties and Water-TolerantCatalytic Activity of Solid Acid CS2sHosPW12040 in Water,"Langmuir, vol. 14, pp. 319-325 (1998).Hofbauer,Hermann et al., "Biomass CHPPlant Giissing-A SuccessStory,"ExpertMeeting onPyrolysis and GasificationofBiomass andWaste,Strasbourg, France, Oct. 2002, 13pages.Hofbauer and Rauch, "Hydrogen-Rich Gas from Biomass Stearn­Gasification,"Publishable Final Report, Institute of Chemical Engi­neering Fuel and Environmental Technology, Getreidemark 9/159,A-I060 Wien, Mar. 31, 2001, 26 pages.

OTHER PUBLICATIONS

5181726112004 Empedocles et al.8/2005 Tonkovich et al.

1012005 Jarosch et al.

2004/0005723 Al2005/0176832 Al *2005/0239910 Al

3/1977 Zahner. 51817138/1986 Brake6/1993 Lewnard et al. 5181700

1011998 Gradyet al. 435/252.55/2003 Shikada et al. 4221223912003 Tonkovich et al.

1012003 Wu et al. 502/3071212002 Kibbyet al. 436/371112003 Wang et al.

4,011,275 A *4,605,788 A5,218,003 A *5,821,111 A *6,562,306 Bl *6,616,909 Bl6,638,892 Bl *

200210182735 Al *2003/0219903 Al

U.S. PATENTDOCUMENTS

References Cited(56)

(52) U.S. Cl.CPC C07C 41109 (2013.01); C07C 41101

(2013.01)USPC .......................................................... 568/698

(58) Field of Classification SearchUSPC 568/698See application file for complete search history.

(2006.01)(2006.01)

(51) Int. Cl.C07C 41109C07C 41101

Apr. 5,2007US 2007/0078285Al

Prior Publication Data(65)

Sep.30,2005(22) Filed:

( *) Notice: Subject to any disclaimer, the term of thispatent is extended or adjusted under 35U.S.C. 154(b)by 0 days.

(21) Appl. No.: 11/241,321

(73) Assignee: Battelle Memorial Institute, Richland,WA (US)

(75) Inventors: Robert A. Dagle, Richland, WA(US);YongWang, Richland, WA (US); EddieG. Baker, Pasco, WA(US); Jianli Hu,Kennewick,WA(US)

DIMETHYL ETHER PRODUCTION FROMMETHANOL AND/OR SYNGAS

(54)

US 8,957,259 B2Feb. 17,2015

(10) Patent No.:(45) Date of Patent:

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(12) United States PatentDagle et al.

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US 8,957,259 B2Sheet 1 of9Feb. 17,2015u.s. Patent

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US 8,957,259 B2Sheet 3 of9Feb. 17,2015u.s. Patent

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US 8,957,259 B2

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---- - .. P=3MPa

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US 8,957,259 B2Sheet 5 of9Feb. 17,2015

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US 8,957,259 B2Sheet 7 of9Feb. 17,2015

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US 8,957,259 B2Sheet 8 of9Feb. 17,2015

Fig. 12

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US 8,957,259 B2Sheet 9 of9Feb. 17,2015u.s. Patent

FIG. 2 illustrates an embodiment of amicrochannel device.FIG. 3a illustrates DME yields in certain embodiments of

the disclosed process for producing DME from methanol.FIG. 3b illustrates DME yields in certain embodiments of

the disclosed process for producing DME from methanol.FIG. 4a illustrates DME yields in certain embodiments of

the disclosed process for producing DME from methanol.FIG. 4b illustrates DME yields in certain embodiments of

the disclosed process for producing DME from methanol.FIG. 5 illustrates an embodiment of syngas conversion to

methanol: equilibrium CO conversionunder different condi­tions; equilibrium is calculated for the reaction CO+5H2+CO2=2CH30H+H20.FIG. 6 illustrates an embodiment of direct syngas conver-

55 sion to DME: CO equilibrium conversion under differentconditions; equilibrium is calculated for the reactionCO+5H2+C02~CH30CH3+2H20.FIG. 7 illustrates the effect of GHSY on methanol synthe­

sis in certain embodiments disclosed herein.FIG. 8 illustrates the effect of pressure on dehydration of

methanol in certain embodiments disclosed herein(H-ZSM-5 dehydration catalyst, T=234° c., GHSY=10 600h-1).

FIG. 9 illustrates the effect of catalyst ratio on CO conver-65 sion in certain embodiments disclosed herein (MeOH synthe­

sis catalyst: dehydration catalyst; T=260° C., P=3.8 MPa,H2/CO=3,GHSY=10 000 h-1).

FIG. 1 is a schematic diagram of a reactor system andmicrochannel reactor assembly that may comprise certain

40 embodiments of the disclosed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

milliseconds, at about 1 atm to about less than 9 atm, andproducing greater than about 70%yield (molar percent yield)of dimethyl ether. Certain embodiments of the processes arecarried out in a system comprising multiple microchannelreactors.Also disclosed are processes for producing dimethyl ether

comprising providing a source of syngas, providing a hybridcatalyst, reacting the syngas and the hybrid catalyst at atemperature from about 200° C. to about 400° C. with a

10 contact time offrom about 25milliseconds to less than about500 milliseconds, and producing greater than about 60%conversion of CO to dimethyl ether. Certain embodiments ofthe processes are carried out in reactors providing greater

15 surface to volume ratios than the presently used DME reac­tors. Certain embodiments of the processes are carried out insystems comprising multiple microchannel reactors.Also disclosed are systems for producing DME from

methanol wherein the system includes a module including a20 plurality ofmicrochannel reactors, a source that feedsmetha­

nol to amethanol dehydrationcatalyst, or a plurality ofmicro­channel reactors and a source that feeds syngas to a hybridcatalyst, and wherein the microchannel reactors are operableat temperatures of greater than about 250° C. and with a

25 contact time ofless than about 250milliseconds to produce aDME yield of greater than about 70% (molar percent yieldwhen referring to DME production from methanol and per­cent conversion of CO to DMEwhen referring to DME fromsyngas).An alternative application includes on-demand syn-

30 thesis ofDME from either syngas or methanolThe foregoing and other objects, features, and advantages

of the inventionwill become more apparent from the follow­ing detailed description,which proceedswith reference to theaccompanying figures.

2

Disclosed are methods for producing dimethyl ether(DME) frommethanol and for producing DME directly fromsyngas, such as syngas from biomass. Also disclosed areapparatus for DME production. The disclosed processes gen­erally function at higher temperatures with lower contact 60times and at lower pressures than conventional processes soas to produce higher DME yields than do conventional pro­cesses. For example, disclosed are processes for producingdimethyl ether comprising providing a source of methanol,providing a catalyst, reacting the methanol and the catalyst ata temperature from about 200° C. to about 500° C. with acontact time of from about 15 milliseconds to about 250

SUMMARY

Biomass feedstock, such as agriculture and forestry resi­dues, plays an important role in developing alternatives tofossil fuels.Although there are severalmethods of generatingenergy from biomass, gasification, in which a hydrogen-car­bon monoxide gas mixture (syngas) is produced, offers sev­eral advantages. For example, syngas, like natural gas, can beburned in gas turbines, which are more efficient than steamboilers.Another key feature of syngas is, likepetroleumprod­ucts' it can be converted to useful chemicals, including dim­ethyl ether (DME). Syngas is also an available "raw" fuelfrom sources other than biomass, such as from coal gasifica­tion and natural gas stem reforming and other sources.

DME can be used as building blocks for synthesizingimportant chemicals, including dimethyl sulfate, high valueoxygenated compounds, and lower olefins. Because of itsenvironmentally benign properties, it can also be used as anaerosol propellant in products such as hair spray and shaving 35

cream. Recently, DME has been suggested as an alternativefuel for diesel engines. Engineperformance tests indicate thatDME has thermal efficienciesequivalent to traditional dieselfuel. Other advantages of using DME as a diesel replacementinclude the reducedNOx emissions, near-zero smokeproduc­tion, and less engine noise. However, there are obstacles toproducing DME frombiomass syngas at an economical scale.For example, unlike petroleum, coal, and natural gas plants,which are established for central, large-scale applications,biomass feedstock and gasification systems are widely dis- 45

tributed geographically. If conventional DME process tech­nology is adopted, a scale of 2500 tid may be required forproduction economically comparable to conventional LPGfuel. Because it is difficult to deliver enough biomass tosatisfy this criterion using conventional technology, a more 50

compact and efficient portable process for converting thebiomass or other source of syngas to DME is needed.

BACKGROUND

Disclosed herein are processes and systems for producingdimethyl ether from syngas and/or methanol.

FIELD

This inventionwas made with Government support underContract DE-AC0576RL01830 awardedby theU.S. Depart­ment of Energy. The Government has certain rights in theinvention.

ACKNOWLEDGMENTOF GOYERNMENTSUPPORT

1DIMETHYL ETHER PRODUCTION FROM

METHANOL AND/OR SYNGAS

US 8,957,259 B2

Certain embodiments of the disclosed methods and appa­ratus comprise forming DME from methanol using a metha­nol dehydration reaction. In particular embodiments, the pro­cess parameters of temperature, contact time and catalystproduce a DME yield (molar percent yield) of greater about70% or about SO%or even about 90%. In various embodi-ments of the disclosed methods suitable catalysts are used inconjunction with contact times as low as about 15millisec­onds and at temperatures as high as greater than about 500°C., at pressures of from about 1 atm to about 40 atm or atpressures of less than about 9 atm.Catalysts for DME from MethanolCertain embodiments of the disclosedmethods includeuse

of a zeolite catalyst with a SilAl ratio of 12, 30, 60, or SO.Aparticularly suitable catalyst comprises H-ZSM-5 zeolitewith a Si/Al ratio of 30. A suitable catalyst for producingDME from MeOHmay include acidic catalysts, y-aluminas,

20 and palladium-doped y-aluminas. Palladium-doped y-alu­mina catalysts may be doped at a variety of concentrations,for example from about 0.1 to about 20%, such as 0.5, 1,2, or13%,by weight. Other suitable catalysts for producing DMEfrom MeOH may include, e.g., zeolites with various Si/Al

25 ratios (e.g., H-ZSM-5 available from Zeolyst International)or the zeolitemordenite, phosphoric-acidmodified aluminas,titanates, tungsten oxide, supported heteropoly acid catalystspreferably with controlled acidities, or, e.g., titania or titaniamodified alumina or zirconia. Heteropoly acid catalysts may

30 have controlled acidities by treatments known to those ofordinary skill in the art such as shown for example inNakato, et al., "Changes of Surface Pro~erties and W;ter­Tolerant Catalytic Activity of Solid AcidCs2.5HO.5PWI2040", Langmuir, 14, 319-325 (199S),

35 which is incorporated herein by reference.Gas Hourly SpaceVelocity or Contact Time for DME fromMethanolIn particular embodiments the gas hourly space velocity

through the reaction zone ranges from about 240000 h-1 toabout 3600 h-1, preferably from about 240000 h-1 to about72,000 h-1. The gas hourly space velocity is defined as thevolume of reactants per time per reaction zone volume. Thevolume of reactant gases is at standard conditions of pressure(1 atm or 101kPa) and temperature (0° C. or 273.16 K). Thereaction zonevolume is definedby the portion of the reactionvessel volume where reaction takes place and which is occu-pied by a gaseous phase comprising reactants, products, and/or inerts; a liquid phase comprising aqueous and/or organicphases; and a solid phase comprising catalyst. Gas hourlyspace velocity is the inverse of contact time, and thus, thisprocess parameter may also be characterized in terms ofcontact time rather than gas hourly space velocity. Suitablecontact timesmaybe from about 15to about 250millisecondsor from about 15to about 50milliseconds or from about 15toabout 100milliseconds or less than about 150millisecondspreferably less than about 50 milliseconds. Conventionalmethods use much longer contact times as compared to theshort contact times used in the disclosed embodiments'shorter contact times were likely not used to date for produc-

60 ing DME due to the relatively poor heat transfer in conven­tional reactors with which such short contact times wouldhave resulted in low DME yields.Although contact times are set forth above for a number of

embodiments of the disclosed methods, preferred contact65 times will depend in part on the catalyst chosen and other

process parameters (e.g.,the process temperature andthe typeof reactor utilized for the reaction), as would be understood

4DME from Methanol

L\.W32T C. ~ -9.3 kcallmol (4)(hydrogenolysis) (5)

L\.W32T C. ~ -24.0 kcallmol (1)L\.W32T C. ~ -14.7 kcallmol (2)L\.W32T C. ~ -5.6 kcallmol (3)

co + 2H2 f-t CH30HCO2 + 3H2 f-t CH30H + H202CH30H f-t DME + H20(dehydration)CO + H20 f-t CO2 +H2 (WGS)DME + 2H2 ~ 2CH4 +H20

Disclosed are methods for producing dimethyl ether(DME) frommethanol and for producing DME directly fromsyngas, such as syngas from biomass. Also disclosed areapparatus for DME production.As used herein, the singular terms "a," "an," and "the"

include plural referents unless context clearly indicates oth­erwise. The word "comprises" indicates "includes." It is fur­ther to be understood that all molecular weight or molecularmass values given for compounds are approximate, and areprovided for description. In addition, all physical parameters,such as temperatures, pressures and amounts are approximateunless otherwise indicated, whether the parameter is pre­ceded by the word "about" or is not. Thematerials methodsand examples are illustrative only and not intedded to b~limiting. Unless otherwise indicated, description of compo­nents in chemical nomenclature refers to the components atthe time of addition to any combination specified in the 40

description, but does not necessarily preclude chemical inter­actions among the components of a mixture once mixed. Asused herein percent (%) or percent yield refers to molar per­cent yield when referring to DMEproduction frommethanol.Percent (%) values when referring to DME produced from 45

syngas refers to percent conversion of CO to DME.DME may be produced via a methanol dehydration reac­

tion, using acidic catalysts, such as phosphoric-acidmodifiedgammaA1203, in a fixed-bed reactor. The cost of producingDME frommethanol is influencedbyprice and availability,as 50

methanol itself is an expensive chemical feedstock. Produc­ing DME directly from syngas has many economic and tech­nical advantages over methanol dehydration. Thermody­namically, DME production from syngas is more favorablethan from methanol, and the cost for DME production from 55

syngas is lower with use of a suitable catalyst.Direct DME synthesis involves many competing reaction

pathways:

DETAILEDDESCRIPTION

FIG. 10 illustrates the effect of reaction temperature onsyngas conversionto DME in certain embodiments disclosedherein (mixtureofmethanol synthesis catalyst andH-ZSM-5;P=3.SMPa, GHSY=5000 h-r, H2/CO=3).

FIG. 11 illustrates the effect of pressure and H2/CO ratioon DME formation in certain embodiments disclosed herein(mixture of methanol synthesis catalyst and H-ZSM-5;GHSY=5000 h-1).

FIG. 12 illustrates the effect of GHSY on syngas conver­sion to DME in certain embodiments disclosed herein (mix- 10

ture of methanol synthesis catalyst and H-ZSM-5; P=3.SMPa, HiCO=2, T=2S6° C.).

FIG. 13 illustrates direct syngas conversion to DME incertain embodiments disclosed herein (with a mixture of 15methanol synthesis catalyst and H-ZSM-5; P=3.S MPa,GHSY=5000 h-r, H2/CO=3, T=2S0° C.).

FIG. 14 illustrates one possible embodiment of a modulardesign of commercial DMEproduction plant utilizing micro­channel reactors.

US 8,957,259 B23

Certain useful dehydration catalysts for performing par-ticular embodiments of the disclosed methods are shown inTable 1. Although the acid strengths of these catalysts aredifferent,A1203,F-AI203' and ZSM-5 yield the same con­version and selectivity.The USY zeolite (ultra stableY-zeo-

40 lite) exhibits the lowest dehydration activity.A CO conver­sionof about 40% is obtained,which is the sameasmethanol­only synthesis. LowDME selectivity (10%) further confirmsthat the loss of dehydration activity is responsible for lowCOconversion as discussed below. Without being tied to any

45 particular theory, it is believed that the nnexpected phenom­enon might be associated with the blocking of acid sites bywater. Y-zeolite contains less acid sites but higher acidstrength than H-ZSM-5. It is plausible that water producedfrom the reaction strongly adsorbed on acid sites, therefore

50 inhibiting the dehydration reaction rate. Thus, direct DMEsynthesis does not require strong solid acid and the acidity(number of acid sites) of the dehydration catalyst is moreimportant than the acid strength.The hybrid catalyst system used in certain embodiments

55 disclosed herein include DME synthesis performed underconditions of280° C., 3.8MPaandGHSVof5000h-1. Ithasbeen fonnd that stability of the catalysts is affected by thepresence of water. One particular embodiment comprises ahybrid catalyst system combining commercialmethanol syn-

60 thesis catalysts and a ZSM-5 zeolite. As shown in FIG. 13,initial CO conversion of about 88% is obtained. As the pro­cess proceeds a slowdecrease in CO conversion is produced.Throughout the process in this embodiment, selectivity toCO2 increases slightly, but methane selectivity remains

65 unchanged. From a carbon utilization point of view, the for­mation of CO2 from the water-gas shift (WGS) reactionappears to have negative effect on DME yield. However,the

USY-25 CATALYSTS ZSM-5 F-AL203 ACIDICAL203 ZEOLITE

conversion 80.0 79.3 79.7 no dehydrationselectivity activityDME 60.2 63.4 62.7MeOR 10.3 10.2 7.4CO2 27.0 22.7 22.3

30 CR4 2.5 3.7 7.6C2+Oxy

total 100 100 100

DehydrationActivity of SolidAcid Catalysts under DMESynthesis Conditions (Pressure 3.8 MPa. Temperatnre 280 gO C.)

TABLE 1

6The syngas useful for performing the disclosed methodsincludes any suitable syngas source, such as syngas frombiomass, coal, and/or natural gas. A hybrid catalyst systemincluding methanol synthesis from syngas and methanoldehydrationcatalysts are used to directly produceDME. Suit­able catalyst hybrids are used in conjnnction with relativelyshort contact times and at relatively high temperatures.Catalysts for DME from SyngasCertain embodiments of the disclosedmethods includeuse

of the following catalysts: a combination of a methanol syn­thesis catalysts (e.g., copper-based or palladium-based syn­thesis catalysts) such as F51-8PPT (available from KatacoCorp., formerly ICI India Ltd.), and dehydration catalysts,ZSM-5zeolitewith a SilAl ratio oBO (availablefromZeolystInternational) and acidic AI203 (available from EngelhardCorp.), solid acid AI203 containing 4 wt % fluoride(F-AI203 available from Engelhard).

Another embodiment of the disclosed methods comprisesforming DME from syngas using a hybrid catalyst system.

DME from Syngas

For particular embodiments of the disclosed methods forproducing DME frommethanol, the reaction zone pressure istypically at atmospheric pressure but the pressure could bevaried to be in the range of about 1 atm to about 10 atm.

by one of ordinary skill in the art. It is to be understood thatother "short" contact times may be suitable for a particularcatalyst-any given catalyst requires sufficient "contacttime" for the reaction of methanol-to-DME to occur. How­ever,if toomuch contact time occurs (if the contact time is toohigh), undesired reactions occur resulting in unwantedbyproducts instead of DME. Certain embodiments of thedisclosed methods utilize short contact times in part due tooperation of the disclosed methods in microchannel deviceswhich provide relatively high surface to volume ratios as 10compared to conventional reactors.Process Temperatures for DME from Methanol

The embodiments of the disclosedmethods operate attem­peratures much higher than conventionally used to produceDME. Themethods as disclosed herein benefit from carryingout the processes in microchannel devices so as to allow the 15process to operate at substantially or near isothermal condi­tions. Conventional reactors for DME production have notprovided the benefit of isothermal or near isothermal reactionenvironments. Fastkinetics (high turnover rates achievable atrelatively short contact times) and isothermal conditions 20(temperature control) favor the DME production. In certainembodiments of the disclosed methods the reaction zonetemperature is typically in the range of from about 2000 C. to5000 C. Preferably, the reaction zone is operated at tempera­tures of from about 2500 C. to 3500 C., or at temperatures ofabout 3000 C.As can be seen by reference to FIG. 3a, a DME yield of

about 70% was obtained when using a y-alumina catalyst (ay-alumina catalyst with no additives, purchased from Engel­hard) at a temperature of 4500 C.with a contact time of about100milliseconds and about an 80%methanol feed.As shown in FIG. 3b, a DME yield of about 90% was

achieved at a contact time of about 25 milliseconds withzeolite catalyst having a SilAl ratio of 30 was used and theprocess took place at about 3000 C. with a 20% methanolfeed. A DME yield of about 75% was achieved at a contact 35time of about 25 milliseconds when zeolite catalyst having aSilAl ratio oBO was used and the process took place at about2500 C. with a 20% methanol feed. At a contact time of 50milliseconds, a DME yield of about 75%was achievedwhenzeolite catalyst having a SilAl ratio of 30 was used and theprocess took place at about 3000 C. with a 20% methanolfeed.As can be seen with reference to FIG. 4a, when using

catalyst 12Bor 30A (12B is a Si/AI=12 zeolite and 30A is aSilAI=30 zeolite, both available from Zeolyst International)at about 3000C.with a 20%methanol feedwith contact timesvarying from about 15 to about 50 milliseconds, good DMEyields were generally achieved, especially at contact times ofabout 25milliseconds. As shown in FIG. 4b, a DME yield ofabout 90%was achieved at a contact time of about 25 milli­seconds when zeolite catalyst having a SilAl ratio of 30 wasused and the process took place at about 3000 C. with a 20%methanol feed. Although higher temperatures (i.e., 2750C.-4200C.) have been reported as used in conventionalDMEproductionmethods, suchhigher temperatures had to be usedin conjnnction with relatively high pressures (i.e., from 1000kPa-1700 kPa (-10-15 atm)).Process Pressures for DME from Methanol

US 8,957,259 B25

In certain embodiments, processes are utilized (with aGHSV of about 5000 h-1), using different feed compositions(H2/CO) 3:1 and 2:1. Increasing the pressure exhibited apositive effect on DME formation. As shown in FIG. 11, at arelatively low pressure of about 1.0 MPa, low CO conversionoccurs. A sharp increase in CO conversion is observed whenpressure is increased from about 1.0 to about 3.8 MPa. Thiscounters conventional belief where it is indicated that in DMEsynthesis CO conversion increases with increased pressurebut levels off at 2 MPa, beyond which the impact of pressureon CO conversion was not significant. Without being tied to

because methanol synthesis is thermodynamically limited. Incontrast, as shown in FIG. 12, in one particular embodimentof direct DME synthesis, conversion increases significantlywith a decrease in GHSV. When GHSV is decreased from20,000 to 5,000 h-1, conversion is increased from 31% to80%. Even when GHSV is changed, selectivity to CO2remains fairly stable.Process Temperatures for DME from Syngas

The embodiments of the disclosed methods operate attem-10 peratures much higher than conventionally used to produce

DME. The ability to carry out the process of these embodi­ments at relatively high temperatures is due at least in part tothe use of microtech-sized reactors as described furtherbelow, and the ability to carry-out the reactions in a substan­tially isothermic enviroument. In certain embodiments of thedisclosed methods the reaction zone temperature is typicallyin the range of from about 2000 C. to about 4000 C. or fromabout 2000 C. to about 3500 C. Preferably, the reaction zoneis operated at temperatures of from about 2400 C. to about2900 C.

In one embodiment, a temperature range of from about2400 C. to about 2600 C. is used and the effect of the tem­perature on the catalytic activity of a methanol synthesiscatalyst and ZSM -5 catalyst combined is depicted in FIG. 10.In this particular embodiment a micro channel reactor sun asshown in FIG. 1 is operated in an isothermal mode. Twothermal couples are installed in a catalyst bed and a furnacetemperature is used to control the catalyst bed temperature.The temperature difference between the top and bottom cata­lyst bed may be controlled within about 20 C., indicatingexcellent heat removal capability of the micro channel reactor.Unlike methanol synthesis alone, where CO conversiondecreases with an increase in reaction temperature, FIG. 10shows that temperature has a positive effect on CO conversion

35 in direct syngas conversion to DME. The embodiments uti­lizing micro channel reactors can be operated at higher reac­tion temperatures (and lower pressures) than are conventionalreactors to achieve high space time yield but can still operatein the isothermal regime. At a GHSV of 5000 h-r, CO con-

40 version of about 80% is achieved but is below the equilibriumlimit ofDME synthesis (94%). Thus the dehydration reactionmay proceed at slower rate than the methanol synthesis reac­tion and only a relatively low GHSV is needed to approachequilibrium conversion.

A large amount of CO2 may be produced via the WGSreaction. Within the operating temperature range disclosedfor these embodiments selectivity to CO2 remains substan­tially constant. As a result of isothermal operation in micro­channel reactors, hot spots on the catalyst surface and

50 between catalyst particles are eliminated; therefore, negativeside reactions are not favored.Process Pressures for DME from Syngas

The reaction zone pressure is typically in the range of about0.5 MPa to about 40 MPa, more preferably from about 1MPa

55 to about 12 MPa, and still more preferably from about 2 MPato about 8 MPa.

WGS reaction is preferred in DME synthesis to keep waterconcentration low, so as to enhance the rate of the dehydrationreaction. This is especially useful for a CO-rich feedstock, asthe WGS reaction can also balance the ratio of CO and H2 bydepleting CO and forming H2.It has been reported that the presence of water inhibits

dehydration activity. However, as disclosed in certain meth­ods herein, with the use of the disclosed hybrid catalyst,deactivation is not significant. Excess water, upon formationin the reaction, may be removed via the WGS reaction. TheWGS reaction proceeds at faster reaction rates than as con­ventionally believed and reach equilibrium to yield 22% CO2,The WGS reaction depletes the water produced from thedehydration reaction, which may reduce the interactionbetween water and methanol catalyst, and therefore retard 15catalyst sintering.

In certain embodiments, the catalysts are pre-treated inmanners known to those of ordinary skill in the art to improveperformance. For example, the dehydration catalysts may becalcined in air at high temperatures (e.g., 5000 C.) to remove 20physically absorbed moisture for both the MeOH synthesisand dehydration catalysts may be crushed and sieved (e.g.,sieved into 70-100 mesh).

The hybrid catalyst may be prepared by mixing the syn­thesis and dehydration catalysts in any suitable fashion, such 25as by mechanically mixing the catalysts at a desired ratio. Ithas been discovered that an important parameter in the designof such a hybrid or dual catalyst system is the catalyst loadingratio, that is, the methanol dehydration to methanol formationactivity. Too high of a methanol dehydration activity com- 30

pared with WGS activity leads to a high water production.Results shown in FIG. 9 indicate that CO conversion isaffected by the catalyst ratio, but product selectivity is notsensitive to the change of catalyst ratio. A particularly usefulcatalyst ratio appears to be about 1: 1 by weight but otherratios, such as 2:1 may be used. Conventionally, ratios ofabout 4:1 and higher are used; although such ratios may beused in certain embodiments of the disclosed methods, lowerratios provide greater DME yields.Gas Hourly Space Velocity or Contact Time for DME fromSyngas

In particular embodiments the gas hourly space velocitythrough the reaction zone ranges from about 500 h-1 to about100,000 h-1, preferably from about 3,600 h-1 to about 36,000h-1. The gas hourly space velocity is defined as the volume of 45

reactants per time per reaction zone volume. The volume ofreactant gases is at standard conditions of pressure (1 atm or101 kPa) and temperature (00 C. or 273.16 K). The reactionzone volume is defined by the portion of the reaction vesselvolume where reaction takes place and which is occupied bya gaseous phase comprising reactants, products, and/or inerts;a liquid phase comprising liquid products and/or other liq­uids; and a solid phase comprising catalyst.

Put another way, suitable contact times for production ofDME directly from syngas may be from about from about0.025 s to about 7.2 s, or from about from about 0.036 s toabout 7.2 s less than about 1 s, or less than about 0.5 s.Conventional methods use much longer contact times thanthe short contact times used in the disclosed embodiments;shorter contact times were likely not used due to the relatively 60poorer heat transfer in conventional reactors, which severelylimit syngas conversion and selectivity at short contact times.

As shown in FIG. 7, methanol synthesis is conducted underconstant temperature of about 2500 C. and pressure of about3.8 MPa. When using decreasing GHSY, CO conversion 65increases first and begins to approach equilibrium conversionof about 50%. This response may be in large part occur

8US 8,957,259 B2

7

One embodiment of a commercial scaleplant designbased onuse of microchannel reactors is shown in FIG. 14. Utilizingmicrochannel technology intensifiesthe process by a factor ofabout 40 to about 1000 as compared to conventional reactortechnology and DME production processes.A module suitably sized to accommodate the desired pro­

ductivity and operational flexibilitymay contain many hun­dreds of micro-channels. An estimation of the number ofpotential modules and their sizes based on a productioncapacity of 120,000tons/yr ofDME are summarized in Table3. The system capacity can be adjusted by changing the num­ber of modules. As illustrated in the embodiment shown inFIG. 14, a commercial DME production systemmay operate

40 utilizing microchaunel modular devices. The total volumeoccupied by these modules is approximately 1500 to about2000 L. The disclosed embodiments of commercial-sizedDME production systems are about 300 times smaller thanwould be a conventional commercial scale reactor system for

45 converting syngas to DME reactor to achieve the same pro­ductivity as achievedby the disclosedmethods and apparatus.In general, as used herein, a microtech or microchaunel

device refers to a reactor wherein the reaction chamber has across-section ofless than about 5mm. Certain embodiments

50 of the disclosed commercial-scalemicrotech ormicrochannelsystemsmay comprise, for example, from about 100to about300modular reactors (modules)wherein the individualmod­ules include at least about 100microchaunels.As usedherein,

55 commercial-scalemicrotech ormicrochaunel systemmeans asystem having at least about 50 reactor modules with themodules having at least about 50 to about 100microchaunelreactors. A characteristic or feature of the microtech devicesas disclosed herein is the ability of such devices to operate

60 during the DMEproduction process in a substantially isother­mal enviroument. Put another way, the microtech devicesutilized with certain embodiments of the disclosed processesare devices capable of operating substantially isothermallywhen producing DME due to the devices' heat transfer abili-

65 ties. Thus, an advantage of using the disclosedmicrochaunelreactors for the exothermic DME synthesis reaction is thatreactor temperature is uniformly distributed in the reactor.

Amicrochaunel reactor is effectivefor achievinghigh pro­ductivity in direct DME synthesis. The performance of thehybrid bifunctionalized catalyst system is much higher thanthat in conventionalreactors, as a result of improvedheat andmass transfer. Heat transfer improvement eliminates hotspots,which improves catalyst stability and product selectiv-

20 ity.The improvedmass transfer capability of a microchaunelreactor is attributable to the shortening of bulk diffusionlength, minimizing back-mixing and increasing accessibilityfrom the gas phase to the catalyst surface, which leads to anenhanced space time yield.

Enhancement in space time yield is also attributed toimprovedmass transfer in amicrochannel reactor. Comparedwith the conventional fixed-bedreactors, the (bulk) diffusionlength from gas phase to catalyst surface is significantlyreduced. Furthermore, unlike the slurry reactors, there is noliquid holdup inside the microchannel reactor. Calculationsshow that in the microchannel reactor under reaction condi­tions, the internal diffusion limitation is significantlyreduced. In addition, a high linear velocity in the microchan­nel reactors facilitating the removal ofwater from the catalystsurface, releasing blocked acid sites and accelerating thedehydration reaction.

By way of example in FIG. 2, a possible embodiment of amicrochannel device is shown. The distance from the heatsource to heat sink is about 1centimeter or less. This distanceis a function of the heat duty, the selection of heat transferf1uid(s),and the effective thermal conductivity of a porouscatalyst insert. Thin sheets or tubes can be used to obtain highheat duties and short contact times. The thickness of the webbetween the reaction channel and the heat exchange channelcan vary, but is preferably between about 0.01 inches andabout 0.25 inches. The preferred thickness for the heatexchange channel preferably ranges from 100microns to 10millimeters. The preferred thickness is 250microns to 3 mil­limeter. Flow of the heat transfer fluidmay be either counter­current, cross-current, or co-current to the direction of theflow of reactants.A microchaunel reactor is preferably able to operate at

relatively severe conditions to obtain high productivity. Asshown in Table 2, DME synthesis may be conducted in amicrochannel reactor at GHSY=10 238 h-I, 2.2 times higherthan in the commercial slurryreactors. Side-by-sidecompari­son reveals excellent performance of microchannel reactors.A specificactivityof3.52 gofCO/(g,h) and a spacetimeyieldof 2.25 g1(g,h) are obtained, respectively. Even when themicrochannel reactor was operated under severe conditions,selectivity to byproducts produced from methanation andpyrolysis were negligible. It is generally believed that backmixing occurs in the conventional slurry reactor, whichaffects product selectivity, resulting in much lower DMEyields than the presently disclosedmethods. Backmixingwasnot present in the microchannel reactor.

25reactor configurationsreaction conditions Air Products slurry micro channel

T, cC. 250 280P, atrn 52 38GHSV,h-1 4500 10238 30HiCO 0.7 2performance 37 80conversionCO2 selectivity 32 22specific activity, gCO/g . h 1.19 3.52liquid yield, g/(g, h) 0.79 2.25 35

Performance Comparison of Syngas Conversionto DME in Different Reactor Configurations

TABLE2

anyparticular theory, it is proposed that using syngas as a rawfuel source, and perhaps utilizing a microtech reactors con­figuration, and because the use of two functionally indepen­dent catalysts are closely interrelated, the performance ofDME synthesis in, e.g., a microchannel reactor is differentfrom conventional fixed-bed or slurry reactors allowing forgreater DME yield at higher pressures.

One embodiment for producing DME includes conversionofDME frommethanol or DME from syngas in a microtechsystem, such as microchannel reactor. Suitable microtech 10

systems are described in, e.g.,U.S. Pat.No. 6,616,909,whichis incorporated herein by reference. Microchannel reactorshave the advantage of improved heat and mass transfer, hav­ing larger surface to volume ratios than do conventional reac- 15

tors,which allowfor greater process intensification.Air Prod­ucts commercial demonstration results obtained from a slurryreactorwere comparedwith thehybrid catalystlmicrochannelreactor system as disclosed herein. The performance resultsare shown in Table 2.

10US 8,957,259 B2

9

To better nnderstand the performance of the combinedprocesses in the micro channel reactor, the methanol dehydra­tion reaction was carried out independently. Itwas speculatedthat the large quantity of water produced in both methanolsynthesis and methanol dehydration reactions might retardthe methanol dehydration activity. The inhibiting effect maybecome more severe at elevated pressure, because desorptionof water is suppressed at high pressure, and active sites maybe blocked for methanol absorption. Consequently, methanoldehydration was conducted at different pressures. As illus-trated in FIG. 8, on raising pressure from ambient to 3.8 MPa,conversion of methanol to DME decreases, but not dramati­cally.An important parameter in the design of a dual catalytic

system is the catalyst loading ratio, that is, the methanoldehydration to methanol formation activity. Too high amethanol dehydration activity compared with water-gas shiftactivity leads to a high water production. Results shown in

40 FIG. 9 indicate that CO conversion is affected by the catalystratio, but product selectivity is not sensitive to the change ofcatalyst ratio. A preferred catalyst ratio was found to be about1:1 by weight.

Experiments were also conducted at GHSV=5000 h-1,45 using two different feed compositions (H2/CO=3: 1 and 2: 1).

Pressure exhibited a positive effect on DME formation. Asshown in FIG. 11, at low pressure of 1.0 MPa, low COconversion occurs. A sharp increase in CO conversion isobserved when pressure is increased from 1.0 to 3.8 MPa. The

50 phenomenon observed in the study of pressure effect appearsdifferent from what has been reported in the literature whereit has been indicated that, in DME synthesis, CO conversionincreased with pressure but starts to level off at 2 MPa,beyond which the impact of pressure on CO conversion is not

55 significant. Because the source of syngas, especially the typeof reactor configuration, and the loading of two fnnctionallyindependent catalysts are closely interrelated, the perfor­mance ofDME synthesis in a microchannel reactor is differ-ent from conventional fixed-bed or slurry reactors.

In view of the many possible embodiments to which theprinciples of the disclosed invention may be applied, it shouldbe recognized that the illustrated embodiments are only pre­ferred examples of the invention and should not be taken aslimiting the scope of the invention. Rather, the scope of the

65 invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope andspirit of these claims.

FIG. 6 shows the results of integrating the two reactions.Synergy in total methanol production is obtained by effec­tively removing the products from the methanol synthesisreaction, i.e., by minimizing the reverse reaction. Conse-

10 quently, maximum synergy is obtained close to the equilib­rium limit for methanol synthesis where the reverse reactionrate is maximum.

A baseline test was conducted with the methanol synthesiscatalyst. For this baseline test, methanol synthesis was per-

15 formed over a commercial Cu-based catalyst at 3.8 MPa andGHSV=3000 to 15000 h'.Steady state was achieved within12 hours from startup. As shown in FIG. 7, CO conversion islower at high GHSV. It becomes clear in FIG. 7 that COconversion starts to level off and approaches equilibrium

20 when GHSV is decreased from about 15 000 to about 3400h-1.

7.2

12tion. The calculation was done by coupling reactions (1)through (4) together, The combined reaction is expressed as

reactor, silicone-coated stainless steel tubing was used in thehigh-temperature preheating zone, Experiments were con­ducted at temperatures from 220 to 320° C, and pressure from2 to 5 MPa, All the experiments were carried out nnder iso­thermal conditions as indicated by the uniform temperaturedistribution along catalyst bed, The hybrid catalyst (mixtureof methanol synthesis and ZSM-5) was reduced with 10%hydrogen in helium in the 220-350° C, temperature range atatmospheric pressure, A mixture of N2/H2 was fed duringstartup to establish steady-state flow and to heat the reactor tothe desired temperature, When the catalyst bed temperaturereached the target, premixed syngas at the desired ratio wasfed into the reactor,

The typical feed composition was CO:H2:C02:Ar=30:62:4:4, The presence of Ar served as the internal standard forconversion and selectivity calculation purposes, Total feedflow rate was set to achieve the desired gas hourly spacevelocity (GHSV), The reaction products were analyzed byon-line gas chromatography (HP 5890 GC) equipped withboth TCD and FID detectors, GC column used is GS-Q 30 mmanufactured by JW Scientific, A temperature program of 5°CJmin to 300° C, was chosen for the analysis, Liquid prod­ucts were collected in a cold trap at _3° C, and were alsoanalyzed by GC-mass spectrometry, Carbon monoxide con­version and product selectivity were calculated on the basis of 60feed and product flow rates and carbon balance,

Methanol synthesis is a thermodynamically limited pro­cess, As shown in FIG, 5, CO conversion decreases as thereaction temperature rises; yet it increases with higher pres­sure, Calculating the chemical equilibrium shows that theoverall methanol yield can be increased, in principle, bycombining the methanol synthesis with methanol dehydra-

A hybrid catalyst system, including methanol synthesisand dehydration catalysts, was developed to test direct syn­thesis of biomass syngas to produce DMK The experimentswere carried out in a micro channel reactor (316 stainlesssteel), with the dimensions 5,08 cmxO,94 cmxu, 15 ern. Threecommercial catalysts were used: a methanol synthesis cata­lyst, F51-8PPT (Kataco Corp.); and two dehydration cata­lysts, ZSM-5 zeolite with a Si/Al ratio oBO (Zeolyst Inter­national) and acidic Al203 (Engelhard Corp.). Solid acidAl203 containing 4 wt % fluoride was also used as dehydra­tion catalyst (F-AI203) Prior to reaction, the zeolite andacidic catalysts were calcined in air at 500° C, to remove 25physically absorbed moisture, Both the methanol synthesiscatalyst and the dehydration catalyst were crushed and sievedinto 70-100 mesh, The hybrid catalyst was prepared bymechanically mixing the two types of catalysts in a transpar- 30ent vial at a desired ratio and charged in the micro channelreactor, This is high pressure down flow fixed-bed type ofreactor, The schematic diagram of the reactor system andmicrochannel reactor assembly were as shown in FIG, 1,

To minimize methanation reaction in the stainless steel 35

EXAMPLES

100-600

120,000100,00050-90100-300

Plant Capacity, tonsiyrGHSV,h-1Syngas single pass conversion,%TotalmodulesEstimated physical volume of each module(total), litersNumber of channels in a module

Embodiment of a DME Syntbesis Plant Utilizing Microchannel Modules

11TABLE 3

US 8,957,259 B2

* * * * *

1416.The process of claim 12,wherein the methanol synthe­

sis and dehydration catalyst comprise a copper-based metha­nol synthesis catalyst and a zeolite catalyst present in a weightratio of about 2: 1 to about 1:1.

17. The process of claim 12,wherein the contact time isless than about SOO milliseconds and the pressure is fromabout 2 to about 8 MPa.. 1~.The process of claim 12,wherein the source of syngasIS biomass.

19. A method of producing dimethyl ether, comprising:providing a syngas source;

combining the syngas source with a hybrid catalyst com­prising a methanol synthesis catalyst and a methanoldehydration catalyst; and

reacting the syngas in the presence of the catalyst in amicro channel reactor under substantially isothermalconditions at a temperature of from about 2000 C. toabout 3S0° C. with a contact time of from about 2Smilliseconds to about SOOmilliseconds to produce DMEwith greater than about 60% CO conversion to dimethylether and methanol.

20. A method of producing dimethyl ether, comprising:providing a biomass syngas source;

combining the biomass syngas source with a methanolsynthesis catalyst and dehydration catalyst, in a micro­channel reactor, each microchannel at a single tempera­ture of from about 2000 C. to about 3S0° C. and with acontact time of less than about 1 second' and

producing greater than about 60% CO con~ersion to dim-ethyl ether and methanol.

21.A method of producing dimethyl ether, comprising:providing a biomass syngas source;combining the biomass syngas source with a methanol

synthesis catalyst and zeolite catalyst present in a weightratio of about 1:1; and reacting the biomass syngas in thepresence of the catalyst in a microchannel reactor, at atemperature of from about 2400 C. to about 2900 c., thetemperature varying less than about 20 C. while thebiomass syngas is reacting in the micro channel reactor,and with a contact time ofless than about SOO millisec­onds;and

producing greater than about 60% CO conversion to dim­ethyl ether and methanol.

22. The process of claim 1further comprising:providing the syngas and the bydrid catalyst to a module

including a plurality of micro channel reactors; andreacting the syngas and the hybrid catalyst in the micro­

channel reactors at temperatures of from about 2000 C.to about 3S0° C. and with a contact time of less thanabout 1 second to obtain greater than about 70% COconversion to dimethyl ether and methanol.

We claim:1.A ~rocess for. producing dimethyl ether comprising:reactmg syngas in contact with a hybrid catalyst in a micro-

channel reactor at a temperature from about 2000 C. toabout 4000 C. with a contact time of from about 2Smilliseconds to less than about 1 second; and convertingmore than about 60% of CO in the syngas to dimethylether and methanol.

2. The process of claim 1comprising converting more thanabout 60% of CO in the syngas to dimethyl ether. 10

3. The process of claim 1,wherein there is no liquid holdupinside the microchannel reactor.

4. The process of claim 1, wherein the hybrid catalystcomprises a methanol synthesis catalyst and a methanoldehydration catalyst present in a weight ratio of about 1:1. 15

5. The process of claim 1, wherein the hybrid catalystcomprises a methanol synthesis catalyst and a zeolite catalystpresent in a weight ratio of about 1:1 to about 2: 1.

6. ~he process of claim 1, wherein the hybrid catalystcompnses FSI-8PPT and ZSM-S zeolite with a Si/AI ratio ofabout 30. 20

7. The process of claim 6, wherein the FSI-8PPT andZSM-S zeolite are present in a weight ratio of about 1:1.

8. The process of claim 1,wherein the process is carried outin multiple micro channel reactors to produce greater thanb

25a out 70% CO conversion to dimethyl ether and methanol.

9. The process of claim 1,wherein the process is carried outin multiple microchannel reactors to produce from about 80%CO conversion to about 88% CO conversion to dimethyl etherand methanol. 3010.The process of claim 1,wherein the process is carried

out at a temperature of from about 2400 C. to about 2900 C.with a contact time of less than about SOO milliseconds.

11. The process of claim 1,wherein the source ofsyngas isbiomass. 3512.A method of making DME, comprising: passing syngas

in c~ntact with a hybrid catalyst comprising a methanol syn­thesis catalyst and a dehydration catalyst in a micro channelreactor at a temperature of from about 2400 C. to about 2900C. with a contact time of less than about 1 second and at a 40pressure in the range of about O.S MPa to about 8 MPa; and

producing greater than about 70% CO conversion to DMEand methanol.

13. The process of claim 12,wherein the methanol synthe­sis and dehydration catalyst comprises a methanol synthesis 45catalyst and a zeolite catalyst that have been mixed together.14.The process of claim 12,wherein the methanol synthe­

sis and dehydration catalyst comprises a copper or palladiumbased methanol synthesis catalyst and a zeolite catalyst hav­ing a SilAl ratio of about 30. 5015.The process of claim 12,wherein the methanol synthe-

sis and dehydration catalyst are present in a weight ratio ofabout 1:1 to about 2: 1.

US 8,957,259 B213