CA1278305C - Reactor configuration for alkylene oxide production process - Google Patents
Reactor configuration for alkylene oxide production processInfo
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- CA1278305C CA1278305C CA000483718A CA483718A CA1278305C CA 1278305 C CA1278305 C CA 1278305C CA 000483718 A CA000483718 A CA 000483718A CA 483718 A CA483718 A CA 483718A CA 1278305 C CA1278305 C CA 1278305C
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- alkylene oxide
- hydroperoxide
- molybdenum
- reactors
- propylene
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Abstract
REACTOR CONFIGURATION FOR
ALKYLENE OXIDE PRODUCTION PROCESS
ABSTRACT OF THE DISCLOSURE
The invention relates to a method of preparing an alkylene oxide compound comprising reacting an olefinically unsaturated compound in the presence of a molybdenum catalyst with an organic hydroperoxide in a series of continuous stirred tank reactors in more than one stage in which the mole of olefin to hydroperoxide at no point in any of said reactors exceeds 3.0:1 and maintaining more than 60 wt. % of polar components in the reaction medium in each of said reactors. Extremely low productions of olefin oligomers, the most troublesome by-products, can be achieved with this technique. Surprisingly, high alkylene oxide concentrations, selectivities and yields may also be achieved together with high hydroperoxide conversions and high molybdenum catalyst recoveries, all simultaneously.
ALKYLENE OXIDE PRODUCTION PROCESS
ABSTRACT OF THE DISCLOSURE
The invention relates to a method of preparing an alkylene oxide compound comprising reacting an olefinically unsaturated compound in the presence of a molybdenum catalyst with an organic hydroperoxide in a series of continuous stirred tank reactors in more than one stage in which the mole of olefin to hydroperoxide at no point in any of said reactors exceeds 3.0:1 and maintaining more than 60 wt. % of polar components in the reaction medium in each of said reactors. Extremely low productions of olefin oligomers, the most troublesome by-products, can be achieved with this technique. Surprisingly, high alkylene oxide concentrations, selectivities and yields may also be achieved together with high hydroperoxide conversions and high molybdenum catalyst recoveries, all simultaneously.
Description
3~
REACTOR CONFIGURATION FOR
ALKYLENE O~IDE PROD~CTION PROCESS
(D#80,361-F) CROSS-REFERENCES TO RELATED APPLICATIONS
This application is related to Canadian patent application Serial No. 483,414, filed June 7, 1985, which is concerned with an improved,method for making alkylene oxides from alkenes using a non-acidic molybdenum catalyst, and Canadian patent application Serial No. 484,477, filed June 19, 1~ 1985, which is concerned with unusually high molybdenum recovery in methods for making alkylene oxides, both filed of even date. This application is also related to Canadian patent application Serial No. 483,290, filed June 19, 1985, which is concerned with a method for making alkylene oxides with an unusually low alkylene oligomer by-product production.
BACKGROU~D OF THE_INVE~TION
1. Field of the Invention The invention relates to the catalytic production of alk~lene oxides from olefinically unsaturated organic compounds 2~ and more particularly relates to the productions of alkylene oxides using particular reactor configurations.
2. Other Related Method in the Field .. . . . . . ...
It is well known that the epoxidation of olefins to give various oxide compounds has long been an area of study by those skilled in the art. It is equally well known that the reactivities of the various olefins differs with the number of substituents on the carbon atoms involved in the double bond.
Ethylene itself has the lowest relative rate of epoxidation, with propylene and other alpha olefins being the next slowest.
Compounds of the formula R2C-CR2 ~here R simply represents alkyl or other substituents may be epoxidjzed fastest.
Of course, the production of ethylene oxide from ethylene has long been known to be accomplished by reaction with molecular oxygen over a silver catalyst. Numerous patents have issued on various silver-catalyzed processes or the production of ethylene oxide.
Unfortunately, the silver catalyst route is poor for olefins other than ethylene. For a long time the com-mercial production of propylene oxide could only be accom-- plished via the cumbersome chlorohydrin process.
Another commercial process for the manufacture of substituted oxides from alpha olefins such as propylene was not discovered until U. S. Patent 3,351,635 taught that an organic oxide compound could be made by reacting an olefini-cally unsaturated compound with an organic h droperoxide in the presence of a molybdenum, tungsten, titanium, columbium, tantalum, rhenium, selenium, chromium, zirconium, tellurium or uranium catalyst. U. S. Patent 3,350,422 teaches a simi-lar process using a soluble vanadium catalyst. Molybdenum is the preferred catalyst. A substantial excess of olefin relative to the hydroperoxide is taught as the normal pro cedure for -the .reaction. See also U. S. Patent 3,525,645 which teaches the 510w addition of organic hydroperoxide to an excess of olefin as preferred.
However, even though this work was recognized as extremely important in the development of a commercial propylene oxide process that did not depend on the chloro~
hydrin route, it has been recognized that the molybdenum process has a number of problems. For example, large 3~
quantities of the alcohol corresponding -to the peroxide used were formed; if t-butyl hydroperoxide was used as a co-react-ant, then a use or market for _-butyl alcohol had to be found.
Other troublesome by-products were the olefin oligomers.
If propylene was used, various propylene dimers, sometimes called hexenes, would result. Besides being undesirable in that the best use of propylene was not made, prcblems would -also be caused in separating the desired propylene oxid~
from the product mix. In addition, the molybdenum catal~st may not be stable or the recovery of the catalyst for recycle may be poor.
A number of other methods for the production of alkylene oxides from epoxidizin~ olefins (particularly propylene) have been proposed. U. S. Patent 3,655,777 to Sargenti reveals a process for epoxidizing propylene using a molybdenum-containing epoxidation catalyst solution prepared by heating molybdenum powder with a stream cont~ining unre-acted tertiary butyl hydroperoxide used in the epoxidation process as the oxidizing agent and polyhydric compounds.
~0 The polyhydric compounds are to have a molecular weight from 200 to 300 and are to be formed as a by-product in the epoxi-dation process. A process for preparing propylene oxide by direct oxidation of propylene with an organic hydroperoxide in the presence of a catalyst ( such as molybdenum or vanad-ium) is described in British Pa-tent 1,338,015 to Atlantic-Richfield. The improvement therein resides in the inclusion of a free radical inhibitor in the reaction mixture to help eliminate the formation of Cs to C~ hydrocarbon by products which must be removed by extractive distillation. Proposed _3_ 3~;
free radical inhibitors are tertiary butyl catechol and 2,6-di-t-butyl-4-methyl phenol.
Stein, et al. in U. S. Patent 3,~49,451 have im~
proved upon the Kollar process of U. S. Paterts 3,350,422 and 3,351,635 by requiring a close control of the reaction temperature, between 90-200C and autogeneous pressures, among other parameters. The primary benefits seem -to be im-proved yields and reduced side reactions. The molybdenum-catalyzed epoxidation of alpha olefins and alpha substituted olefins with relatively less stable hydroperoxides may be accomplished according to IJ. S. PatPnt 3,862,961 to Sheng, et al. by employing a critical amount of a stabilizing agent consisting of a C3 to Cg secondary or tertiary mcnohydric alcohol. The preferred alcohol seems to be terti2ry butyl alcohol. Citric acid is used to minimize the iron-catalyzed decomposition of the organic hydroperoxide withou-t adversely affecting the reaction between the hydroperoxidé and the ole-fin in a similar oxirane producing process taught by Herzog in U. S. Patent 3,928,393. The inventors in U. S. Patent 4,217,287 discovered that if barium oxide is present iIl the reaction mixture, the catalytic epoxida-tion of olefins wi~h organic hydroperoxides can be successfully carried out with good selectivity to the epoxide based on hydroperoxide con-verted when a relatively low olefin to hydroperoY~ide mole ratio is used. The alpha-olefinically unsaturated compound must be added incrementally to the organic hydroperoxlde to provide an excess of hydroperoxide that is effective.
Selective epoxidation of olefins with cumene hydro-peroxide (CHP) can be accomplished at high CHP to olefin _~_ ratios if barium oxide is present ~7ith the molybdenum cat-alyst as reported by Wu and Swift in "Selective Olefin Epoxi-dation at High Hydroperoxide to Olefin Ratios," Journal of Catalysis, Vol. 43, 380-383 (1976).
Catalysts other than molybdenum have been tried.
Copper polyphthalocyanine which has been acti~-ated by contact with an aromatic heterocyclic amine is an effective catal~st for the oxidation of certain aliphatic and allcyclic compounds (propylene, for instance) as discovered by ~rownstein, et al.
described in U. S. Patent 4,028,423.
Various methods for preparing molybdenum catalysts useful in these olefin epoxidation methods are described in the following patents: U. S. 3,362,972 to Kollar; U. S.
3,480,563 to Bonetti, et al.i U. S. 3,578,690 to Becker;
U. S. 3,953,362 and U. S. 4,009,122 both to Lines, et al.
More pertinent to the subject discovery are those patents which address schemes for separating propylene oxide from the other by-products produced. These patents demon-strate a high concern for separating out the useful propylene oxide from the close boiling hexene oligomers. It would be a great progression in the art if a method could be devised where the oligomer by-products would be produced not at all or in such low proportions that a separate separation step would not be necessary as in these patents.
U. S. Patent 3,464,897 addresses the separation of propylene oxide from other hydrocarbons having boiling points close to propylene oxide by distilling the mixture in the presence of an open chain or cyclic paraffin containing from 8 to 12 carbon atoms. Similarly, propylene oxide can be sep-arated from water using idenkical entrainers as disclosed in ~5--~%'7~33~3~
6~878-28 U.S. Patent 3,607,669. Propylene oxide is purified from lts by-products by fractiona~ion in the presen~e of a hydrocarbon having from 8 to 20 carbon atoms according ~o U.S. Patent 3,843,~88. Additionally, U.S. Patent 3,90g,366 ~eaches that propylene oxide may be purified with respeck to contamina~iny para~finic and olefinic hydrocarbons by extractive distillation in the presence of an aroma~ic hydrocarbon having from 6 to 12 carbon atoms.
SUM~ARY OF THE lNVENTION
lQ According to one aspec~ of the present invention there is provided a method of preparlng an alkylene oxide compound comprlsing reacting an olePinically unsatura~ed compound in the presence of a molybdenum catalyst with an organic hydroperoxide in a series of continuous s~irred tank reactors in more than one stage in which the mole of ole~in to hydroperoxide at no poln~ in any of said reactors exceeds 3.0~1 and maintaining more than 60 wt.~ of polar components in the reaction medium in each of said reactors.
According to a further aspect of the present invention there is provided a method of preparing an alkylene oxide compound comprising a) reacting an olefinically unsaturated compound wlth an organic hydroperoxide in the presence of a molybdenum catalyst~ in a series o~ continuous stirred tank reactors in more than one stage to give an intermediate reaction mixture, and b) further reactlng the intermediate reaction mixture from the series of continuous stirred tank reactors in a second reactor to give an alkylene oxide reaction product, and maintaining more than 60 wt.~ of polar components in the reaction medium in each of said reactors.
~%~
6~7g-~8 According to ano~her aspect of ~he present invention there is provided a method for preparing an alkylene oxide compound comprising a) reacting an olefinically unsaturated compound wi~h and organic hydroperoxide in the presence of a non-acid molybdenum catalys~, in a series of continuous stirred tank reactors in more than one stage to give an intermediate reaction mixture, and b) subsequently reac~ing the intermediate reaction mixture from the series of continuous stirred tank reactors in a plug flow reactor at a higher temperature than that used in the continuous stirred tank reactor to give an alkylene oxide reaction product containing 5 ppm or less olefin oligomer by-product, and maintaining more than 60 wt.% of polar components in the reaction medium in each of said reactors.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has been discovered that the process of producing alkylene oxide compounds, especially propylene oxide, from olefinically unsaturated compounds, such as propylene, together with organic hydroperoxides over a molybdenum ca~alyst can be improved by reducing the mole ratio of olefinic substrate to organic peroxide. Extremely low productions of olefin oligomers, the most troublesome by-products, can be achleved with this technique. Surprisingly, high alkylene oxide concentrations, selectivities and yields may also be achieved together with high hydroperoxide conversions and high molybdenum catalyst recoveries, all simultaneously It has also been discovered that a series of continuous stirred tank reactors (abbreviated CSTR) may be employed to implement a system whereby the mole ratio of olefin 6a .. 2~
to hydropero~ide is maintained low. Since the contents of 2 CSTR are continuously stirred, the organic hydroperoxide only "sees" a very small proportion of olefinically unsat-urated compound at any one time. Maintenance of a low molar ratio of olefin to hydroperoxide is furt~er aided by option-al s-taged addition of olefin to a staged series of reactors.
By staged addition is meant the injection of olefin into the reaction mixture contained in the staged series of reactors at more than one point along the staged series of reactors.
By this technique, buildup of olefin at any one point in the staged series of reactors, rela-tive to the hydroperoxide, is mini mized.
Normally, the ratio of olefinic substrate to or~
ganic peroxide is thought to be variable over the range of from about 2 1 to 20:1, expressed as a mole ratio. A mole ratio of olefin to hydroperoxide of less than 2:1 has been thought to be unsuitable. In this invention, the mole ratio of olefin to hydroperoxide should never exceed 3.0:1. The broad range, expressed in terms of the overall contents of the reactor, for ~he mole ratio of olefinic substrate to organic peroxide of this invention is from 0.9:1 to 3.0:1, and preferably from 1.8:1 to 0.9:1. Most preferably, the mole ratio of olefin to hydroperoxide is 1.05:~ to 1.35:1.
of course, the local, instantaneous ratios at any place in the staged series of CST~s will be appreciably lower than these ratios.
One of the particularly preferred embodiments of this invention involves the use of a staged series of CSTRs in series with a tubular or plug flow reactor (abbreviated PFR). In one preferred version, the CSTR ls placed in fron-t ~7B~
of the PFR in the scheme of reac-tant flow; i.e., the reac-tants encounter the CSTR first and are subsequently transfer-red to the PFR. This reactor con~iguration provides good temperature control of a highly exothermic reactlon during the initial stage of the epoxidation reaction ar.d good hydro-peroxide conversions in the latter stage. In addition to the above mentioned benefits, the formation of olefin dimers, which are particularly undesirable by-products because they are difficult to remove, is minimized.
Another of the preferred embodiments include oper-ating conditions which allow for a relatively cool reaction to take place in a CSTR followed by a PFR operating at rel-atively severe temperatures, and preferably, a feed ratio of olefin to hydroperoxide that is low, with high catalyst con-centrations. The CSTR may be operated at a temperature in the range of about 70 to 115C, 90 to 115C being preferred, with 100-110C as the most preferred reaction temperature range. The PFR should be operated at a higher temperature, from over 115C to 150C, with 120`-140C as the most pre-ferred range. The effluent from the CSTR may be termed anintermediate reaction mixture since there is more reacting still to occur. The residence time of the reactants in each reactor is left to the operator although it is preferred that the reactants stay in each reactor approximately the same length of timeO T~pically, the residence times may be 0.5 to 4.0 hours, preferably l.0 to 2.0 hours per reactor.
Surprisingly, the same temperatures, 120-i40C, which normally produce large amounts of alkylene dimer, par-ticularly propylene dimer, yield only small amounts of alkyl-ene dimer when employed with a PFR, in series after a CSTR.
3~5 However, it is also con~emplat~d that somewhatdifferent reactor configurations may also be particularly effective. For example, the PFR might be placed before the CSTR in sequence. Or a series of continuous s~irxed tank reactors may prove advantageous. Staged introduction of -the olefinically unsaturated reactant may be inco~porated in any of these con~igurations.
Addi-tionally, it is contemplated that the temper-ature se~uence may be changed from that recom~"ended above with positive results. For example, the higher reaction temperature may occur first followed by a relatively cooler reactor region. Or a series of hotter regions inierspersed ~ith cooler ones may be effective.
Continuous stirred tank and tubular plug flow re-actors are well known in the art. It is expected that theinventive method would work well with any of -the two tyoes available.
The other advantages to the preferred embodiments of this invention include much higher oxidè concentrations (29-32~), higher oxide selectivities (96-99~%) and hydro-peroxide conversions ~96-99%) and oxide yields (94-98%) than are described as possible in the current literature or patent art. Further, olefin oligomer by-product contents in the crude alkylene oxide reaction product stream as low as 5 ppm and lower can be achieved. Molybdenum catalyst contents in the product stream, also called recoverable molybdenum, may be 85% or higher relative to -the charged catalyst proportion.
Further, a molybdenum alcohol catalyst which COIl-tains no free or excess carboxylic acid is employed whereas 3~
the catalyst cited in commercial process descrip-tions is derived from an acid reactant and contains excess acid.
For example, the preferred catalysts are molybdenum 2-ethyl-hexanol, molybdenum ethylene glycol or molybderum propylene glycol complexes whereas the commercial catalyst is a mo-lybdenum naphthenate or molybdenum octoate derived from naphthenic acid or 2-e.thyl hexanoic acid. These catalysts inherently contain a substantial amoun-t of lre-e (excess) acid (up to 50-70 wt.% acid).
Details of Reac~ants and Catalysts The method of this invention could be used to ep-oxidize any olefinically unsaturated compound such as sub-stituted and unsubstituted aliphatic and alicyclic olefins which may be hydrocarbons, esters, alcohols, ketones, ethers and the like. It is expected that the process would be par-ticularly useful in epoxidizing compounds having 2 to 30 carbon atoms and at least one double bond situated in the alpha position of a chain or internally. Representative compounds include ethylene, propylene, normal butylene, isobutylene, pentenes, methyl pentenes, hexenes, octenes, dodecenes, cyclohexene, substituted cyclohexenes, butadiene, styrene, substituted styrenes, vinyl toluene, vinyl cyclo-hexene, phenyl cyclohexenes and the like. Olefins having substituents containing halogens, oxygen, sulfur and the like may be used. In general, all olefinic materials epoxi-dized by previous methods could be used in connection with this process including olefinically unsaturated polymers.
The invention will probably find its greatest utility in the epoxidation of primary or alpha olefins. How-ever, it is propylene that may be epoxidized particularly -lQ-7~
advantageously by the inventive technique, and it is this olefin that is par-ticularly preferred.
Any of the hydroperoxldes used in the previously described prior epoxidation methods may be used effectively in this invention. Suitable organic hydroperoxide reactants may have the formula ROOH where R is an organic radical.
Preferably, R is a substituted or unsubstituted alkyl, cyclo~
alkyl, aralkyl, aralkenyl, hydroxy aralkyl, cycloalkenyl, hydroxy cycloalkyl and the like having about 3 to 20 carbon atoms. R may also be a heterocyclic radical.
However, it has been discovered that t-butyl hydro-peroxide ~TB~P~ gives better resulks to propylere oxide than do other hydroperoxides, such as cumene hydroperoxides (CHP) even though both show improvements when a two-stage reaction scheme is used. Thus, the most preferred hydroperoxide for the method of this invention is TB~P in a solution of t-butyl alcohol (TBA). The weight ratio of the mixture should be 40-80% TBHP with the balance being TBA and other minor species.
A TBHP ~oncentration of 68-~0% is particularly preferred~
Catalysts suitable for the epoxidation method of this invention include any molybdenum complexes with no free or excess carboxylic acid present. If an acidic catalyst is used, as in complexes of molybdenum with 2-ethyl hexanoic acid, the excess acid should be removed, such as by distil-lation with a higher boiling paraffin such as a Cl~ (hexa-decane, for example). A "non-acidic" catalys-t i5 defined as one having an acid number no higher than 5Q due to free or excess carboxylic acid.
It is especially preferred that the catalyst be molybdenum complexes of 2-ethyl-1-hexanol or molybdenum ~%~33~5 complexes of glycols. A detailed account of the pre-Eerred preparation of these complexes may be found in co-pending Canadian patent applications Serial Nos. 483,719, filed June 12, 1985 and ~83,634, filed June 11, 1985. E~or the purposes of the instant applica~ion, the complexes are generally made by reacting a molybdenum compound, such as M003 with ~-ethyl-l-hexanol in the presence of NH40H and heat over a period of time. The mole ratios of 2-ethyl-1-hexanol to gram atoms of molybdenum should range from 10:1 to 55:1. The ratio of moles of ~H40H to gram atoms of molybdenum should range from 1:1 to 5:1. These ratios of reactants and reaction temperatures of 150 to 185C accompanied by removal of water will afford a surprisingly high molybdenum content (2 to 7 wt.~) catalyst complex which is stable upon standing.
Alternatively, the molybdenum 2-ethyl-1-hexanol catalyst can also be made by reaction of ammonia heptamolybdate (AHM) with 2-ethyl-1-hexanol and water in the right proportions. The mole ratios of 2-ethyl-1-hexanol to gram atoms molybdenum in AHM
should range from 7-13:1. The amount of water used initially should be in the range of 1-3:1 moles water/molybdenum~ The three reactant mixture should be heated at 125-185C for 5-8 hours, affording a molybdenum catalyst with 5-10% molybdenum content. The molybdenum glycol complexes are made by digesting ammonium heptamolybdate or ammonium dimolybdate with ethylene or propylene glycol (mole ratio of glycol to gram atoms of molybdenum 8:1 to 16:1) for approximately one to two hours at about 90-130C and then pulling a vacuum and stripping off water and glycol to leave a clear catalyst bottoms product amounting to 75 to 95~ of the total charge to the catalyst ~7~
preparation. The molybdenum contents of these glycol catalysts range from about 10 to 16~. Canadian patent application Serial No. 483,634, filed ~une 11, 1985 provides more details on the synthesis of these catalysts.
Other Reaction Conditions The reaction should be carried out in liquid phase under autogenous pressure which should not exceed about 800 psig. The pressure is preferably kept in the range of 200 to 800 psig.
The catalyst concentrations in the method of this invention should be in the range of 100 to 1000 ppm (0.01 to 0.10 wt.~) based on the total reactant charge. A preferred range is 200 to 600 ppm. Generally, about 250 to 500 ppm is the most preferred level. These catalyst levels are higher than those presently used in prior methods, which tend to run from 50 to 200 ppm.
The epoxidation reaction of this invention can be carried out in the presence of a solvent and it is preferred that one be used. Ideally, the solvent should be inert in the reaction and have the same carbon s~eleton as the hydroperoxide used to minimize solvent separation problems. For example, if TBHP is used as the hydroperoxide, TBA is preferably the solvent. Of course, the TBA in the TB~P solution may be enough to serve as the solvent in the reaction.
It is preferred that the reaction mixture contain very little water, between zero and 0.5 wt.~.
Preferably, the reaction should be carried out to achieve as high a hydroperoxide conversion as possible, typically 96 to 99~, consistent with reasonable oxide se-3~)5i lectivities, ~ypically also 96 to 99% for the method of this invention. For both of these values to be simultaneously so high is very unusual. While prior me~hods concerning propyl-ene epoxidation have accomplished hydroperoxide conversions o 98 to 99%, the propylene oxide selectivity b2sis TsHp con-sumed runs only about 90 to 91%. As a result, the yield or utilization to the oxide for the inventive process runs about 94 to 98% as compare`d with 8~ to 90% for prior ?rocesses~
Although such differences seem small, they may provide the distinction between a profitable process and a 'otally un-acceptable, wasteful one. When the plant size is several hundred million pounds of product, the 4-8% differences in yields are very significant.
For a batch mode, the reaction procedure generally lS begins by charging the olefin to the CSTR, if the CSTR is first in the configuration. Next, the hydroperoxide, sol-vent and catalyst may be added and the contents heated to the desired reaction temperature. Alternatively, the olefin reactant may be heated to at or near the preferred reaction temperature. Further heat may be provided by the exotherm of the reaction. The reaction is then allowed to proceed for the desired amount of time before transfer to the PFR
for the desired time. The mixture finally is cooled do~m and the oxide recovered. In a continuous mode, the re-actants are run through the chosen reaction configurationcontinuously, with the residence times for each reactor ad-justed as desired.
Generally, for the method of this invention, the oxide concentration runs from abou-t 29-32% which is quite a bit higher than the oxide concentrations possible in prior ~7~
methods, usually in the neighborhood of 12-16%.
A significant advantage of this invention is that there is very little propylene dirner (hexenes) content in the reactor effluent (when propylene is reactea). It typi-cally runs less than 5 ppm in the total reactor productstream. This level of dimer would very likely eliminate the high capital cost for the typical three tower e~tractive dis-tillation module typically used to remove propylene dimer from commercial product streams, as well as save money on operating costs for this unit. Further, no hydrocarbon en-trainer is needed as suggested by the prior ar_. Instead, the low dimer level of this invention (e~uiv21ent to less than 20 ppm on a "pure" oxide basis; that is, after the UIl-reacted products are removed) allows an operator to leave the dimer in the oxide where it is virtually trouble ~ree at these low levels.
The process of -this invention may be preferably used in a continuous mode.
At olefin/hydroperoxide ratios of 1.2:1 to 1.8:1, the preferred temperature in the one or more CSTRs in series is 70-115 for 1.0-2.0 hours and the preferred temperature is 120-130C for 1.0-2.0 hours at catalyst Ievels of 200-600 ppm, preferably 300 to 500 ppm. If the olefin/hydro-peroxide level is relatively low, about 1:1 to 1.2:1, the preferred -temperature in the one or more CSTRs in series is 90-120C for 1.0-2.0 hours and the preferred PFR temperature is 125-140C for 1.0-2.0 hours at 300 to 500 ppm catalyst levels without any appreciab1e effects on selectivity, etc.
The method of this invention is illustrated, but not limited, by the following examples.
~2~
FXAMPLE
To a 300 ml Hastelloy C agitated au~oclave followed by a 200 ml 316 stainless steel tubular reac~or was fed 56.9 g/hr of propylene and 126.7 g/hr of a T~EP/TBA/ca-talyst mixture (which analyzed as 71.0 ~t.% TBHP, 28.8 wt.% TBA, 0.2 wt.% H2O, 695 ppm molybdenum complex of 2-e hyl-l-hexanol catalyst). The CSTR was operated at llOC, the EFR at 120C.
The product from the said reactor system analyzed as follows:
Propylene, wt.% 9.83 Propylene oxide, wt.% 29.81 TBA, wt.% 56.18 TBHP, wt.% 2.64 Recoverable molybdenum catalyst, ppm 445 Propylene dimer, ppm ~pure PO basis) 10 Propylene dimer, ppm (crude product basis) <5 NOTE: Propylene/TBHP molar ratio was 1.355/1.
3~5 To the same reactor systern as above was fed 50.0 g/hr propylene and 128.2 g/hr of TB~P/~A/catalyst (72.4 wt.% TBHP, 27.4 wt.% TBA, 0.2 wt.% H~, 51~ ppm molybdenum complex of 2-ethyl-1-hexanol catalysi). The CSTR was operated at 110C, the PFR at 130C. The product analyzed as follows:
Propylene, wt.% 5.22 Propylene oxide, wt.~ 31.40 TBA, wt.% 58.61 TBHP, wt.% 2.63 Recoverable molybdenum catalyst, ppm 445 Propylene dimer, ppm (pure PO basis) 10 Propylene dimer, ppm (crude product b~sis) ~S
NOTE: Propylene/TBHP molar ratio was 1.154/1.
In contrast to the above results, Ex2mple 3, con-ducted at 120C for two hour reaction time in a s-tirred auto-clave in the batch mode, resulted in a substantial make of the undesired by-product, propylene dimer (94 ppm pure PO
basis), which co-distills with propylene oxide upon sep-aration/pur~fication.
3~i To a 300 ml 316 stainless steel autoclave were charged 48.lg propylene (1.145 moles) followed by a solution containing 129.21g of a t-~utyl hydroperoxide solution (con~
taining 61.50% TBHP, 38.30% _~butyl alcohol, ~d 0.2% H2O) and 1.29g of molybdenum 2-ethyl hexanol (6.50% molybdenum).
The clave was stirred and heated to 120C for 2.0 hours, cooled and sampled under pressure to GLC. ~;~e recovered total product was 177.2g. Total liquid product after flashing propylene was 150.4g. The liquid product con-tained 1.03% TBHP unreacted (T~P conversion = 98.0%) and 594 ppm molybdenum (essentially quantitative molybdenum re~
covery). GLC indication was that 6.86% propylene was un-reacted with PO make at 26.56% (selectivity moles PO/moles TBHP reacted = 93.7%). Yield moles PO/moles TBHP fed =
91.9%. Propylene dimer (basis pure PO) was analyzed for and found to be 94 ppm.
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When reseaLch into this area was first be~1n, it was discovered ~hat results irnproved dramatically when dry TBHP (less than 0.4 wt.% H20) was used instead of the com-mercially available TsHp~ ~here~ore, it is preferred that the mixture of reactants contains very little water, 0.5% or less.
The high olefin/hydroperoxide mole ra'io was chosen initially because of -the repeated mention in pat~nts and the literature that selectivities are lower when propylene/TsHp mole ratios are too low. ~owever, when low propylene/TBHP
mole ratios were used, it was surprisingly disco~ered that propylene oxide selectivities were actually his:~er rather than lower, as expected. In addition, it was also surpris-ingly discovered that the molybdenum recoveries increased upon reduction of the propylene/TBHP mole ratio.
Using this new technique, different catalysts were screened. Generally, the various dilute ethylene and propy-lene glycol molybdenum complexes and those similarly dilute catalysts derived from ethylene or propylene carbonate were less active or selective than the several low acidity molyb-den~um octoate catalysts made by distilling out the excess acid from standard molybdenum octoate preparations. This involved heating 2-ethyl hexanoic acid with molybdenum tri-oxide or ammonium heptamolybdate. However, the molybdenum 2-ethyl-1-hexanol catalysts and concentrated (10-16% molyb-denum content) molybdenum ethylene or propylene glycol ca-t-alysts are the most preferred. The former preferred cat~
alysts are made from MoO3, 2-ethyl-1-hexanol and ammonium hydroxide or from ammonium heptamolybdate and 2-ethyl-1-hexanol. These latter preferred catalysts are made ~rom 7B3~353 ammonium heptamolybdate or ammonium dimolybdate and propyl-ene or ethylene glycol Propylène dimer, as noted, is an objectionable by-product because it co-distills with propylene oxide and is best separated from propylene oxide by a costly extractive distilla-tion. The cost of the extractive towers as well as the utilities cost to operate such a purification unit is very high. The reactor configuration, low reaction temper~
atures and low propylene/TBHP mole ratios are the major ~actors in the low propylene dimer proportions. The ex-` amples of Table I where the conventional propylene oxide process is used reveals that the propylene dime- levels seen in Table II are surprisingly low. The low propylene dimer content of the resultant propylene oxide product may be left in the propylene oxide product without adverse effect or costly distillation.
The examples of Table II demonstrate the two-step reactor scheme which permits extremely low propylene to TBHP
ratios (0.88:1) and yet produces little or no propylene dimer.
These examples further point out the unusual characteristics of the instant invention.
The inventive process provides much higher concen-trations of propylene oxide in the reac-tor effluent (29-32%) than current commercial processes (13-15%) and u-tilizes much less propylene due to the lower propylene/TBHP mole ratio.
Thus the reactors and other equipment (distillation towers) are much reduced in size as well. In this process, 4 to 16%
of the propylene is unreac-ted in the reactor effluent as com-pared with a~out 35 to 55% unreacted propylene in prior art processes. Cur yields (moles of propylene oxide formed per ~æ~
mole of TB~P consumed) do not drop as we lower the propyl-ene/TBHP mole ratio as expected or projected from the liter-ature. Surprisingly, increased selectivities a~d conversions were observed. Perhaps this is because the media is more polar rendering the molybdenum catalyst more active, soluble and stable than in a largely propylene media. The latter situation would prevail if the epoxidation is conducted at higher propylene to TBHP mole ratios. However, the inven-tion should not be limited by any such theory.
It is surprising that selectivities ~o propylene oxide are at least 96%, concentrations of prop-lene oxide in the crude product stream can be at least 29%, ~ields to pro-pylene oxide are at least 94%, hydroperoxide conversions are at least 96% and propylene dimer contents are 5 ppm or less, lS all simultaneously, using the method of this invention.
Examples 27 through 36 of Table III show that propylene oxide may be formed with a different organic hydro-peroxide, cumene hydroperoxide (C~). Although the previous examples using TBHP give better results than the experiments using CHP, the advantage of a two-step reaction scheme is demonstrated. Compare Examples 27 and 37 where the CHP con-version is only 66% for a one-stage scheme as compared with 97.7% for a two-step scheme.
Although cumene hydroperoxide has been shown to be undesirable as the hydroperoxide in the inventive process, hydroperoxides haviny a structure closer to that of t-bu-tyl hydroperoxide, such as t-amyl hydroperoxide, is expected to be useful in this method.
Many modifications could be made by one skilled in ~7~3~
the art in the invention without changing its spirit or scope which are defined only by the appended claims. For example, ;` within the parameters of the claims, a particular combination of reactants, catalysts, mode of addition or sequence procedure may prove to be particularly advantageous.
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REACTOR CONFIGURATION FOR
ALKYLENE O~IDE PROD~CTION PROCESS
(D#80,361-F) CROSS-REFERENCES TO RELATED APPLICATIONS
This application is related to Canadian patent application Serial No. 483,414, filed June 7, 1985, which is concerned with an improved,method for making alkylene oxides from alkenes using a non-acidic molybdenum catalyst, and Canadian patent application Serial No. 484,477, filed June 19, 1~ 1985, which is concerned with unusually high molybdenum recovery in methods for making alkylene oxides, both filed of even date. This application is also related to Canadian patent application Serial No. 483,290, filed June 19, 1985, which is concerned with a method for making alkylene oxides with an unusually low alkylene oligomer by-product production.
BACKGROU~D OF THE_INVE~TION
1. Field of the Invention The invention relates to the catalytic production of alk~lene oxides from olefinically unsaturated organic compounds 2~ and more particularly relates to the productions of alkylene oxides using particular reactor configurations.
2. Other Related Method in the Field .. . . . . . ...
It is well known that the epoxidation of olefins to give various oxide compounds has long been an area of study by those skilled in the art. It is equally well known that the reactivities of the various olefins differs with the number of substituents on the carbon atoms involved in the double bond.
Ethylene itself has the lowest relative rate of epoxidation, with propylene and other alpha olefins being the next slowest.
Compounds of the formula R2C-CR2 ~here R simply represents alkyl or other substituents may be epoxidjzed fastest.
Of course, the production of ethylene oxide from ethylene has long been known to be accomplished by reaction with molecular oxygen over a silver catalyst. Numerous patents have issued on various silver-catalyzed processes or the production of ethylene oxide.
Unfortunately, the silver catalyst route is poor for olefins other than ethylene. For a long time the com-mercial production of propylene oxide could only be accom-- plished via the cumbersome chlorohydrin process.
Another commercial process for the manufacture of substituted oxides from alpha olefins such as propylene was not discovered until U. S. Patent 3,351,635 taught that an organic oxide compound could be made by reacting an olefini-cally unsaturated compound with an organic h droperoxide in the presence of a molybdenum, tungsten, titanium, columbium, tantalum, rhenium, selenium, chromium, zirconium, tellurium or uranium catalyst. U. S. Patent 3,350,422 teaches a simi-lar process using a soluble vanadium catalyst. Molybdenum is the preferred catalyst. A substantial excess of olefin relative to the hydroperoxide is taught as the normal pro cedure for -the .reaction. See also U. S. Patent 3,525,645 which teaches the 510w addition of organic hydroperoxide to an excess of olefin as preferred.
However, even though this work was recognized as extremely important in the development of a commercial propylene oxide process that did not depend on the chloro~
hydrin route, it has been recognized that the molybdenum process has a number of problems. For example, large 3~
quantities of the alcohol corresponding -to the peroxide used were formed; if t-butyl hydroperoxide was used as a co-react-ant, then a use or market for _-butyl alcohol had to be found.
Other troublesome by-products were the olefin oligomers.
If propylene was used, various propylene dimers, sometimes called hexenes, would result. Besides being undesirable in that the best use of propylene was not made, prcblems would -also be caused in separating the desired propylene oxid~
from the product mix. In addition, the molybdenum catal~st may not be stable or the recovery of the catalyst for recycle may be poor.
A number of other methods for the production of alkylene oxides from epoxidizin~ olefins (particularly propylene) have been proposed. U. S. Patent 3,655,777 to Sargenti reveals a process for epoxidizing propylene using a molybdenum-containing epoxidation catalyst solution prepared by heating molybdenum powder with a stream cont~ining unre-acted tertiary butyl hydroperoxide used in the epoxidation process as the oxidizing agent and polyhydric compounds.
~0 The polyhydric compounds are to have a molecular weight from 200 to 300 and are to be formed as a by-product in the epoxi-dation process. A process for preparing propylene oxide by direct oxidation of propylene with an organic hydroperoxide in the presence of a catalyst ( such as molybdenum or vanad-ium) is described in British Pa-tent 1,338,015 to Atlantic-Richfield. The improvement therein resides in the inclusion of a free radical inhibitor in the reaction mixture to help eliminate the formation of Cs to C~ hydrocarbon by products which must be removed by extractive distillation. Proposed _3_ 3~;
free radical inhibitors are tertiary butyl catechol and 2,6-di-t-butyl-4-methyl phenol.
Stein, et al. in U. S. Patent 3,~49,451 have im~
proved upon the Kollar process of U. S. Paterts 3,350,422 and 3,351,635 by requiring a close control of the reaction temperature, between 90-200C and autogeneous pressures, among other parameters. The primary benefits seem -to be im-proved yields and reduced side reactions. The molybdenum-catalyzed epoxidation of alpha olefins and alpha substituted olefins with relatively less stable hydroperoxides may be accomplished according to IJ. S. PatPnt 3,862,961 to Sheng, et al. by employing a critical amount of a stabilizing agent consisting of a C3 to Cg secondary or tertiary mcnohydric alcohol. The preferred alcohol seems to be terti2ry butyl alcohol. Citric acid is used to minimize the iron-catalyzed decomposition of the organic hydroperoxide withou-t adversely affecting the reaction between the hydroperoxidé and the ole-fin in a similar oxirane producing process taught by Herzog in U. S. Patent 3,928,393. The inventors in U. S. Patent 4,217,287 discovered that if barium oxide is present iIl the reaction mixture, the catalytic epoxida-tion of olefins wi~h organic hydroperoxides can be successfully carried out with good selectivity to the epoxide based on hydroperoxide con-verted when a relatively low olefin to hydroperoY~ide mole ratio is used. The alpha-olefinically unsaturated compound must be added incrementally to the organic hydroperoxlde to provide an excess of hydroperoxide that is effective.
Selective epoxidation of olefins with cumene hydro-peroxide (CHP) can be accomplished at high CHP to olefin _~_ ratios if barium oxide is present ~7ith the molybdenum cat-alyst as reported by Wu and Swift in "Selective Olefin Epoxi-dation at High Hydroperoxide to Olefin Ratios," Journal of Catalysis, Vol. 43, 380-383 (1976).
Catalysts other than molybdenum have been tried.
Copper polyphthalocyanine which has been acti~-ated by contact with an aromatic heterocyclic amine is an effective catal~st for the oxidation of certain aliphatic and allcyclic compounds (propylene, for instance) as discovered by ~rownstein, et al.
described in U. S. Patent 4,028,423.
Various methods for preparing molybdenum catalysts useful in these olefin epoxidation methods are described in the following patents: U. S. 3,362,972 to Kollar; U. S.
3,480,563 to Bonetti, et al.i U. S. 3,578,690 to Becker;
U. S. 3,953,362 and U. S. 4,009,122 both to Lines, et al.
More pertinent to the subject discovery are those patents which address schemes for separating propylene oxide from the other by-products produced. These patents demon-strate a high concern for separating out the useful propylene oxide from the close boiling hexene oligomers. It would be a great progression in the art if a method could be devised where the oligomer by-products would be produced not at all or in such low proportions that a separate separation step would not be necessary as in these patents.
U. S. Patent 3,464,897 addresses the separation of propylene oxide from other hydrocarbons having boiling points close to propylene oxide by distilling the mixture in the presence of an open chain or cyclic paraffin containing from 8 to 12 carbon atoms. Similarly, propylene oxide can be sep-arated from water using idenkical entrainers as disclosed in ~5--~%'7~33~3~
6~878-28 U.S. Patent 3,607,669. Propylene oxide is purified from lts by-products by fractiona~ion in the presen~e of a hydrocarbon having from 8 to 20 carbon atoms according ~o U.S. Patent 3,843,~88. Additionally, U.S. Patent 3,90g,366 ~eaches that propylene oxide may be purified with respeck to contamina~iny para~finic and olefinic hydrocarbons by extractive distillation in the presence of an aroma~ic hydrocarbon having from 6 to 12 carbon atoms.
SUM~ARY OF THE lNVENTION
lQ According to one aspec~ of the present invention there is provided a method of preparlng an alkylene oxide compound comprlsing reacting an olePinically unsatura~ed compound in the presence of a molybdenum catalyst with an organic hydroperoxide in a series of continuous s~irred tank reactors in more than one stage in which the mole of ole~in to hydroperoxide at no poln~ in any of said reactors exceeds 3.0~1 and maintaining more than 60 wt.~ of polar components in the reaction medium in each of said reactors.
According to a further aspect of the present invention there is provided a method of preparing an alkylene oxide compound comprising a) reacting an olefinically unsaturated compound wlth an organic hydroperoxide in the presence of a molybdenum catalyst~ in a series o~ continuous stirred tank reactors in more than one stage to give an intermediate reaction mixture, and b) further reactlng the intermediate reaction mixture from the series of continuous stirred tank reactors in a second reactor to give an alkylene oxide reaction product, and maintaining more than 60 wt.~ of polar components in the reaction medium in each of said reactors.
~%~
6~7g-~8 According to ano~her aspect of ~he present invention there is provided a method for preparing an alkylene oxide compound comprising a) reacting an olefinically unsaturated compound wi~h and organic hydroperoxide in the presence of a non-acid molybdenum catalys~, in a series of continuous stirred tank reactors in more than one stage to give an intermediate reaction mixture, and b) subsequently reac~ing the intermediate reaction mixture from the series of continuous stirred tank reactors in a plug flow reactor at a higher temperature than that used in the continuous stirred tank reactor to give an alkylene oxide reaction product containing 5 ppm or less olefin oligomer by-product, and maintaining more than 60 wt.% of polar components in the reaction medium in each of said reactors.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
It has been discovered that the process of producing alkylene oxide compounds, especially propylene oxide, from olefinically unsaturated compounds, such as propylene, together with organic hydroperoxides over a molybdenum ca~alyst can be improved by reducing the mole ratio of olefinic substrate to organic peroxide. Extremely low productions of olefin oligomers, the most troublesome by-products, can be achleved with this technique. Surprisingly, high alkylene oxide concentrations, selectivities and yields may also be achieved together with high hydroperoxide conversions and high molybdenum catalyst recoveries, all simultaneously It has also been discovered that a series of continuous stirred tank reactors (abbreviated CSTR) may be employed to implement a system whereby the mole ratio of olefin 6a .. 2~
to hydropero~ide is maintained low. Since the contents of 2 CSTR are continuously stirred, the organic hydroperoxide only "sees" a very small proportion of olefinically unsat-urated compound at any one time. Maintenance of a low molar ratio of olefin to hydroperoxide is furt~er aided by option-al s-taged addition of olefin to a staged series of reactors.
By staged addition is meant the injection of olefin into the reaction mixture contained in the staged series of reactors at more than one point along the staged series of reactors.
By this technique, buildup of olefin at any one point in the staged series of reactors, rela-tive to the hydroperoxide, is mini mized.
Normally, the ratio of olefinic substrate to or~
ganic peroxide is thought to be variable over the range of from about 2 1 to 20:1, expressed as a mole ratio. A mole ratio of olefin to hydroperoxide of less than 2:1 has been thought to be unsuitable. In this invention, the mole ratio of olefin to hydroperoxide should never exceed 3.0:1. The broad range, expressed in terms of the overall contents of the reactor, for ~he mole ratio of olefinic substrate to organic peroxide of this invention is from 0.9:1 to 3.0:1, and preferably from 1.8:1 to 0.9:1. Most preferably, the mole ratio of olefin to hydroperoxide is 1.05:~ to 1.35:1.
of course, the local, instantaneous ratios at any place in the staged series of CST~s will be appreciably lower than these ratios.
One of the particularly preferred embodiments of this invention involves the use of a staged series of CSTRs in series with a tubular or plug flow reactor (abbreviated PFR). In one preferred version, the CSTR ls placed in fron-t ~7B~
of the PFR in the scheme of reac-tant flow; i.e., the reac-tants encounter the CSTR first and are subsequently transfer-red to the PFR. This reactor con~iguration provides good temperature control of a highly exothermic reactlon during the initial stage of the epoxidation reaction ar.d good hydro-peroxide conversions in the latter stage. In addition to the above mentioned benefits, the formation of olefin dimers, which are particularly undesirable by-products because they are difficult to remove, is minimized.
Another of the preferred embodiments include oper-ating conditions which allow for a relatively cool reaction to take place in a CSTR followed by a PFR operating at rel-atively severe temperatures, and preferably, a feed ratio of olefin to hydroperoxide that is low, with high catalyst con-centrations. The CSTR may be operated at a temperature in the range of about 70 to 115C, 90 to 115C being preferred, with 100-110C as the most preferred reaction temperature range. The PFR should be operated at a higher temperature, from over 115C to 150C, with 120`-140C as the most pre-ferred range. The effluent from the CSTR may be termed anintermediate reaction mixture since there is more reacting still to occur. The residence time of the reactants in each reactor is left to the operator although it is preferred that the reactants stay in each reactor approximately the same length of timeO T~pically, the residence times may be 0.5 to 4.0 hours, preferably l.0 to 2.0 hours per reactor.
Surprisingly, the same temperatures, 120-i40C, which normally produce large amounts of alkylene dimer, par-ticularly propylene dimer, yield only small amounts of alkyl-ene dimer when employed with a PFR, in series after a CSTR.
3~5 However, it is also con~emplat~d that somewhatdifferent reactor configurations may also be particularly effective. For example, the PFR might be placed before the CSTR in sequence. Or a series of continuous s~irxed tank reactors may prove advantageous. Staged introduction of -the olefinically unsaturated reactant may be inco~porated in any of these con~igurations.
Addi-tionally, it is contemplated that the temper-ature se~uence may be changed from that recom~"ended above with positive results. For example, the higher reaction temperature may occur first followed by a relatively cooler reactor region. Or a series of hotter regions inierspersed ~ith cooler ones may be effective.
Continuous stirred tank and tubular plug flow re-actors are well known in the art. It is expected that theinventive method would work well with any of -the two tyoes available.
The other advantages to the preferred embodiments of this invention include much higher oxidè concentrations (29-32~), higher oxide selectivities (96-99~%) and hydro-peroxide conversions ~96-99%) and oxide yields (94-98%) than are described as possible in the current literature or patent art. Further, olefin oligomer by-product contents in the crude alkylene oxide reaction product stream as low as 5 ppm and lower can be achieved. Molybdenum catalyst contents in the product stream, also called recoverable molybdenum, may be 85% or higher relative to -the charged catalyst proportion.
Further, a molybdenum alcohol catalyst which COIl-tains no free or excess carboxylic acid is employed whereas 3~
the catalyst cited in commercial process descrip-tions is derived from an acid reactant and contains excess acid.
For example, the preferred catalysts are molybdenum 2-ethyl-hexanol, molybdenum ethylene glycol or molybderum propylene glycol complexes whereas the commercial catalyst is a mo-lybdenum naphthenate or molybdenum octoate derived from naphthenic acid or 2-e.thyl hexanoic acid. These catalysts inherently contain a substantial amoun-t of lre-e (excess) acid (up to 50-70 wt.% acid).
Details of Reac~ants and Catalysts The method of this invention could be used to ep-oxidize any olefinically unsaturated compound such as sub-stituted and unsubstituted aliphatic and alicyclic olefins which may be hydrocarbons, esters, alcohols, ketones, ethers and the like. It is expected that the process would be par-ticularly useful in epoxidizing compounds having 2 to 30 carbon atoms and at least one double bond situated in the alpha position of a chain or internally. Representative compounds include ethylene, propylene, normal butylene, isobutylene, pentenes, methyl pentenes, hexenes, octenes, dodecenes, cyclohexene, substituted cyclohexenes, butadiene, styrene, substituted styrenes, vinyl toluene, vinyl cyclo-hexene, phenyl cyclohexenes and the like. Olefins having substituents containing halogens, oxygen, sulfur and the like may be used. In general, all olefinic materials epoxi-dized by previous methods could be used in connection with this process including olefinically unsaturated polymers.
The invention will probably find its greatest utility in the epoxidation of primary or alpha olefins. How-ever, it is propylene that may be epoxidized particularly -lQ-7~
advantageously by the inventive technique, and it is this olefin that is par-ticularly preferred.
Any of the hydroperoxldes used in the previously described prior epoxidation methods may be used effectively in this invention. Suitable organic hydroperoxide reactants may have the formula ROOH where R is an organic radical.
Preferably, R is a substituted or unsubstituted alkyl, cyclo~
alkyl, aralkyl, aralkenyl, hydroxy aralkyl, cycloalkenyl, hydroxy cycloalkyl and the like having about 3 to 20 carbon atoms. R may also be a heterocyclic radical.
However, it has been discovered that t-butyl hydro-peroxide ~TB~P~ gives better resulks to propylere oxide than do other hydroperoxides, such as cumene hydroperoxides (CHP) even though both show improvements when a two-stage reaction scheme is used. Thus, the most preferred hydroperoxide for the method of this invention is TB~P in a solution of t-butyl alcohol (TBA). The weight ratio of the mixture should be 40-80% TBHP with the balance being TBA and other minor species.
A TBHP ~oncentration of 68-~0% is particularly preferred~
Catalysts suitable for the epoxidation method of this invention include any molybdenum complexes with no free or excess carboxylic acid present. If an acidic catalyst is used, as in complexes of molybdenum with 2-ethyl hexanoic acid, the excess acid should be removed, such as by distil-lation with a higher boiling paraffin such as a Cl~ (hexa-decane, for example). A "non-acidic" catalys-t i5 defined as one having an acid number no higher than 5Q due to free or excess carboxylic acid.
It is especially preferred that the catalyst be molybdenum complexes of 2-ethyl-1-hexanol or molybdenum ~%~33~5 complexes of glycols. A detailed account of the pre-Eerred preparation of these complexes may be found in co-pending Canadian patent applications Serial Nos. 483,719, filed June 12, 1985 and ~83,634, filed June 11, 1985. E~or the purposes of the instant applica~ion, the complexes are generally made by reacting a molybdenum compound, such as M003 with ~-ethyl-l-hexanol in the presence of NH40H and heat over a period of time. The mole ratios of 2-ethyl-1-hexanol to gram atoms of molybdenum should range from 10:1 to 55:1. The ratio of moles of ~H40H to gram atoms of molybdenum should range from 1:1 to 5:1. These ratios of reactants and reaction temperatures of 150 to 185C accompanied by removal of water will afford a surprisingly high molybdenum content (2 to 7 wt.~) catalyst complex which is stable upon standing.
Alternatively, the molybdenum 2-ethyl-1-hexanol catalyst can also be made by reaction of ammonia heptamolybdate (AHM) with 2-ethyl-1-hexanol and water in the right proportions. The mole ratios of 2-ethyl-1-hexanol to gram atoms molybdenum in AHM
should range from 7-13:1. The amount of water used initially should be in the range of 1-3:1 moles water/molybdenum~ The three reactant mixture should be heated at 125-185C for 5-8 hours, affording a molybdenum catalyst with 5-10% molybdenum content. The molybdenum glycol complexes are made by digesting ammonium heptamolybdate or ammonium dimolybdate with ethylene or propylene glycol (mole ratio of glycol to gram atoms of molybdenum 8:1 to 16:1) for approximately one to two hours at about 90-130C and then pulling a vacuum and stripping off water and glycol to leave a clear catalyst bottoms product amounting to 75 to 95~ of the total charge to the catalyst ~7~
preparation. The molybdenum contents of these glycol catalysts range from about 10 to 16~. Canadian patent application Serial No. 483,634, filed ~une 11, 1985 provides more details on the synthesis of these catalysts.
Other Reaction Conditions The reaction should be carried out in liquid phase under autogenous pressure which should not exceed about 800 psig. The pressure is preferably kept in the range of 200 to 800 psig.
The catalyst concentrations in the method of this invention should be in the range of 100 to 1000 ppm (0.01 to 0.10 wt.~) based on the total reactant charge. A preferred range is 200 to 600 ppm. Generally, about 250 to 500 ppm is the most preferred level. These catalyst levels are higher than those presently used in prior methods, which tend to run from 50 to 200 ppm.
The epoxidation reaction of this invention can be carried out in the presence of a solvent and it is preferred that one be used. Ideally, the solvent should be inert in the reaction and have the same carbon s~eleton as the hydroperoxide used to minimize solvent separation problems. For example, if TBHP is used as the hydroperoxide, TBA is preferably the solvent. Of course, the TBA in the TB~P solution may be enough to serve as the solvent in the reaction.
It is preferred that the reaction mixture contain very little water, between zero and 0.5 wt.~.
Preferably, the reaction should be carried out to achieve as high a hydroperoxide conversion as possible, typically 96 to 99~, consistent with reasonable oxide se-3~)5i lectivities, ~ypically also 96 to 99% for the method of this invention. For both of these values to be simultaneously so high is very unusual. While prior me~hods concerning propyl-ene epoxidation have accomplished hydroperoxide conversions o 98 to 99%, the propylene oxide selectivity b2sis TsHp con-sumed runs only about 90 to 91%. As a result, the yield or utilization to the oxide for the inventive process runs about 94 to 98% as compare`d with 8~ to 90% for prior ?rocesses~
Although such differences seem small, they may provide the distinction between a profitable process and a 'otally un-acceptable, wasteful one. When the plant size is several hundred million pounds of product, the 4-8% differences in yields are very significant.
For a batch mode, the reaction procedure generally lS begins by charging the olefin to the CSTR, if the CSTR is first in the configuration. Next, the hydroperoxide, sol-vent and catalyst may be added and the contents heated to the desired reaction temperature. Alternatively, the olefin reactant may be heated to at or near the preferred reaction temperature. Further heat may be provided by the exotherm of the reaction. The reaction is then allowed to proceed for the desired amount of time before transfer to the PFR
for the desired time. The mixture finally is cooled do~m and the oxide recovered. In a continuous mode, the re-actants are run through the chosen reaction configurationcontinuously, with the residence times for each reactor ad-justed as desired.
Generally, for the method of this invention, the oxide concentration runs from abou-t 29-32% which is quite a bit higher than the oxide concentrations possible in prior ~7~
methods, usually in the neighborhood of 12-16%.
A significant advantage of this invention is that there is very little propylene dirner (hexenes) content in the reactor effluent (when propylene is reactea). It typi-cally runs less than 5 ppm in the total reactor productstream. This level of dimer would very likely eliminate the high capital cost for the typical three tower e~tractive dis-tillation module typically used to remove propylene dimer from commercial product streams, as well as save money on operating costs for this unit. Further, no hydrocarbon en-trainer is needed as suggested by the prior ar_. Instead, the low dimer level of this invention (e~uiv21ent to less than 20 ppm on a "pure" oxide basis; that is, after the UIl-reacted products are removed) allows an operator to leave the dimer in the oxide where it is virtually trouble ~ree at these low levels.
The process of -this invention may be preferably used in a continuous mode.
At olefin/hydroperoxide ratios of 1.2:1 to 1.8:1, the preferred temperature in the one or more CSTRs in series is 70-115 for 1.0-2.0 hours and the preferred temperature is 120-130C for 1.0-2.0 hours at catalyst Ievels of 200-600 ppm, preferably 300 to 500 ppm. If the olefin/hydro-peroxide level is relatively low, about 1:1 to 1.2:1, the preferred -temperature in the one or more CSTRs in series is 90-120C for 1.0-2.0 hours and the preferred PFR temperature is 125-140C for 1.0-2.0 hours at 300 to 500 ppm catalyst levels without any appreciab1e effects on selectivity, etc.
The method of this invention is illustrated, but not limited, by the following examples.
~2~
FXAMPLE
To a 300 ml Hastelloy C agitated au~oclave followed by a 200 ml 316 stainless steel tubular reac~or was fed 56.9 g/hr of propylene and 126.7 g/hr of a T~EP/TBA/ca-talyst mixture (which analyzed as 71.0 ~t.% TBHP, 28.8 wt.% TBA, 0.2 wt.% H2O, 695 ppm molybdenum complex of 2-e hyl-l-hexanol catalyst). The CSTR was operated at llOC, the EFR at 120C.
The product from the said reactor system analyzed as follows:
Propylene, wt.% 9.83 Propylene oxide, wt.% 29.81 TBA, wt.% 56.18 TBHP, wt.% 2.64 Recoverable molybdenum catalyst, ppm 445 Propylene dimer, ppm ~pure PO basis) 10 Propylene dimer, ppm (crude product basis) <5 NOTE: Propylene/TBHP molar ratio was 1.355/1.
3~5 To the same reactor systern as above was fed 50.0 g/hr propylene and 128.2 g/hr of TB~P/~A/catalyst (72.4 wt.% TBHP, 27.4 wt.% TBA, 0.2 wt.% H~, 51~ ppm molybdenum complex of 2-ethyl-1-hexanol catalysi). The CSTR was operated at 110C, the PFR at 130C. The product analyzed as follows:
Propylene, wt.% 5.22 Propylene oxide, wt.~ 31.40 TBA, wt.% 58.61 TBHP, wt.% 2.63 Recoverable molybdenum catalyst, ppm 445 Propylene dimer, ppm (pure PO basis) 10 Propylene dimer, ppm (crude product b~sis) ~S
NOTE: Propylene/TBHP molar ratio was 1.154/1.
In contrast to the above results, Ex2mple 3, con-ducted at 120C for two hour reaction time in a s-tirred auto-clave in the batch mode, resulted in a substantial make of the undesired by-product, propylene dimer (94 ppm pure PO
basis), which co-distills with propylene oxide upon sep-aration/pur~fication.
3~i To a 300 ml 316 stainless steel autoclave were charged 48.lg propylene (1.145 moles) followed by a solution containing 129.21g of a t-~utyl hydroperoxide solution (con~
taining 61.50% TBHP, 38.30% _~butyl alcohol, ~d 0.2% H2O) and 1.29g of molybdenum 2-ethyl hexanol (6.50% molybdenum).
The clave was stirred and heated to 120C for 2.0 hours, cooled and sampled under pressure to GLC. ~;~e recovered total product was 177.2g. Total liquid product after flashing propylene was 150.4g. The liquid product con-tained 1.03% TBHP unreacted (T~P conversion = 98.0%) and 594 ppm molybdenum (essentially quantitative molybdenum re~
covery). GLC indication was that 6.86% propylene was un-reacted with PO make at 26.56% (selectivity moles PO/moles TBHP reacted = 93.7%). Yield moles PO/moles TBHP fed =
91.9%. Propylene dimer (basis pure PO) was analyzed for and found to be 94 ppm.
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When reseaLch into this area was first be~1n, it was discovered ~hat results irnproved dramatically when dry TBHP (less than 0.4 wt.% H20) was used instead of the com-mercially available TsHp~ ~here~ore, it is preferred that the mixture of reactants contains very little water, 0.5% or less.
The high olefin/hydroperoxide mole ra'io was chosen initially because of -the repeated mention in pat~nts and the literature that selectivities are lower when propylene/TsHp mole ratios are too low. ~owever, when low propylene/TBHP
mole ratios were used, it was surprisingly disco~ered that propylene oxide selectivities were actually his:~er rather than lower, as expected. In addition, it was also surpris-ingly discovered that the molybdenum recoveries increased upon reduction of the propylene/TBHP mole ratio.
Using this new technique, different catalysts were screened. Generally, the various dilute ethylene and propy-lene glycol molybdenum complexes and those similarly dilute catalysts derived from ethylene or propylene carbonate were less active or selective than the several low acidity molyb-den~um octoate catalysts made by distilling out the excess acid from standard molybdenum octoate preparations. This involved heating 2-ethyl hexanoic acid with molybdenum tri-oxide or ammonium heptamolybdate. However, the molybdenum 2-ethyl-1-hexanol catalysts and concentrated (10-16% molyb-denum content) molybdenum ethylene or propylene glycol ca-t-alysts are the most preferred. The former preferred cat~
alysts are made from MoO3, 2-ethyl-1-hexanol and ammonium hydroxide or from ammonium heptamolybdate and 2-ethyl-1-hexanol. These latter preferred catalysts are made ~rom 7B3~353 ammonium heptamolybdate or ammonium dimolybdate and propyl-ene or ethylene glycol Propylène dimer, as noted, is an objectionable by-product because it co-distills with propylene oxide and is best separated from propylene oxide by a costly extractive distilla-tion. The cost of the extractive towers as well as the utilities cost to operate such a purification unit is very high. The reactor configuration, low reaction temper~
atures and low propylene/TBHP mole ratios are the major ~actors in the low propylene dimer proportions. The ex-` amples of Table I where the conventional propylene oxide process is used reveals that the propylene dime- levels seen in Table II are surprisingly low. The low propylene dimer content of the resultant propylene oxide product may be left in the propylene oxide product without adverse effect or costly distillation.
The examples of Table II demonstrate the two-step reactor scheme which permits extremely low propylene to TBHP
ratios (0.88:1) and yet produces little or no propylene dimer.
These examples further point out the unusual characteristics of the instant invention.
The inventive process provides much higher concen-trations of propylene oxide in the reac-tor effluent (29-32%) than current commercial processes (13-15%) and u-tilizes much less propylene due to the lower propylene/TBHP mole ratio.
Thus the reactors and other equipment (distillation towers) are much reduced in size as well. In this process, 4 to 16%
of the propylene is unreac-ted in the reactor effluent as com-pared with a~out 35 to 55% unreacted propylene in prior art processes. Cur yields (moles of propylene oxide formed per ~æ~
mole of TB~P consumed) do not drop as we lower the propyl-ene/TBHP mole ratio as expected or projected from the liter-ature. Surprisingly, increased selectivities a~d conversions were observed. Perhaps this is because the media is more polar rendering the molybdenum catalyst more active, soluble and stable than in a largely propylene media. The latter situation would prevail if the epoxidation is conducted at higher propylene to TBHP mole ratios. However, the inven-tion should not be limited by any such theory.
It is surprising that selectivities ~o propylene oxide are at least 96%, concentrations of prop-lene oxide in the crude product stream can be at least 29%, ~ields to pro-pylene oxide are at least 94%, hydroperoxide conversions are at least 96% and propylene dimer contents are 5 ppm or less, lS all simultaneously, using the method of this invention.
Examples 27 through 36 of Table III show that propylene oxide may be formed with a different organic hydro-peroxide, cumene hydroperoxide (C~). Although the previous examples using TBHP give better results than the experiments using CHP, the advantage of a two-step reaction scheme is demonstrated. Compare Examples 27 and 37 where the CHP con-version is only 66% for a one-stage scheme as compared with 97.7% for a two-step scheme.
Although cumene hydroperoxide has been shown to be undesirable as the hydroperoxide in the inventive process, hydroperoxides haviny a structure closer to that of t-bu-tyl hydroperoxide, such as t-amyl hydroperoxide, is expected to be useful in this method.
Many modifications could be made by one skilled in ~7~3~
the art in the invention without changing its spirit or scope which are defined only by the appended claims. For example, ;` within the parameters of the claims, a particular combination of reactants, catalysts, mode of addition or sequence procedure may prove to be particularly advantageous.
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Claims (20)
1. A method of preparing an alkylene oxide compound comprising reacting an olefinically unsaturated compound in the presence of a molybdenum catalyst with an organic hydroperoxide in a series of continuous stirred tank reactors in more than one stage in which the mole of olefin to hydroperoxide at no point in any of said reactors exceeds 3.0:1 and maintaining more than 60 wt. % of polar components in the reaction medium in each of said reactors.
2. The method of claim 1 in which the mole ratio of olefinically unsaturated compound to hydroperoxide at any point in any continuous stirred tank reactor is in the range of approximately 1.35:1 to 1.05:1.
3. A method of preparing an alkylene oxide compound comprising a. reacting an olefinically unsaturated compound with an organic hydroperoxide in the presence of a molybdenum catalyst, in a series of continuous stirred tank reactors in more than one stage to give an intermediate reaction mixture, and b. further reacting the intermediate reaction mixture from the series of continuous stirred tank reactors in a second reactor to give an alkylene oxide reaction product, and maintaining more than 60 wt. % of polar components in the reaction medium in each of said reactors.
4. The method of claim 3 in which the mole ratio of olefinically unsaturated compound to organic hydroperoxide is in the range of 0.9:1 to 3.0:1.
5. The method of claim 3 in which the mole ratio of olefinically unsaturated compound to organic hydroperoxide is in the range of 0.35:1 to 1.05:1.
6. The method of any one of claims 3 to 5 in which the second reactor is operated at a higher temperature than the series of continuous stirred tank reactors.
7. The method of any one of claims 3 to 5 in which the series of continuous stirred tank reactors is operated at a temperature in the range of about 70 to 115°C and the second reactor is operated at a temperature in the range of above 115°C to about 150°C.
8. The method of any one of claims 3 to 5 in which the second reactor is a plug flow reactor.
9. The method of any one of claims 3 to 5 in which the olefinically unsaturated compound is propylene and the resulting alkylene oxide is propylene oxide.
10. The method of any one of claims 3 to 5 in which the organic hydroperoxide is t-butyl hydroperoxide and t-butyl alcohol is present as a solvent.
11. The method of any one of claims 3 to 5 in which the organic hydroperoxide is in a 40 to 80% solution with its corresponding alcohol.
12. The method of any one of claims 3 to 5 in which the molybdenum catalyst is a molybdenum complex of 2-ethyl-1-hexanol.
13. The method of any one of claims 3 to 5 in which the molybdenum catalyst is a molybdenum complex of ethylene glycol or propylene glycol.
14. The method of any one of claims 3 to 5 in which the molybdenum catalyst concentration is 200 to 600 ppm.
15. The method of any one of claims 3 to 5 in which the proportion of water in the reaction mixture is between 0 and 5.0%.
16. The method of any one of claims 3 to 5 in which the olefin oligomer content of the alkylene oxide reaction product is equal to of less than 5 ppm.
17. The method of any one of claims 3 to 5 in which a. the alkylene oxide compound concentration in the alkylene oxide reaction product is at least 29%, b. the selectivity to the alkylene oxide is at least 96%, c. the hydroperoxide conversion is at least 96%
d. the yield to alkylene oxide is at least 94%, and e. the molybdenum catalyst recovery from the alkylene oxide reaction product is at least 85%.
d. the yield to alkylene oxide is at least 94%, and e. the molybdenum catalyst recovery from the alkylene oxide reaction product is at least 85%.
18. A method for preparing an alkylene oxide compound comprising a. reacting an olefinically unsaturated compound with an organic hydroperoxide in the presence of a non-acid molybdenum catalyst, in a series of continuous stirred tank reactors in more than one stage to give an intermediate reaction mixture, and b. subsequently reacting the intermediate reaction mixture from the series of continuous stirred tank reactors in a plug flow reactor at a higher temperature than that used in the continuous stirred tank reactor to give an alkylene oxide reaction product containing 5 ppm or less olefin oligomer by-product, and maintaining more than 60 wt. % of polar components in the reaction medium in each of said reactors.
19. The method of claim 18 in which the mole ratio of olefinically unsaturated compound to organic hydroperoxide is in the range of 0.9:1 to 3.0:1 and the molybdenum catalyst recovery from the alkylene oxide reaction product is at least 85%.
20. The method of claim 19 in which the molybdenum catalyst concentration is in the range of 200 to 600 ppm and the alkylene oxide concentration in the alkylene oxide reaction product is at least 29% and the selectively to the alkylene oxide is at least 96%.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US68770284A | 1984-12-31 | 1984-12-31 | |
| US687,702 | 1984-12-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1278305C true CA1278305C (en) | 1990-12-27 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000483718A Expired - Fee Related CA1278305C (en) | 1984-12-31 | 1985-06-12 | Reactor configuration for alkylene oxide production process |
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| Country | Link |
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| CA (1) | CA1278305C (en) |
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1985
- 1985-06-12 CA CA000483718A patent/CA1278305C/en not_active Expired - Fee Related
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