Patented May 22, 1951 2,554,459

UNITED STATES PATENT OFFICE

Rudolph L. Heider, Dayton, Ohio, assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application March 20, 1948, Serial No. 16,140 3 Claims. (C. 260-348.5) 2 This invention relates to the manufacture of high activity requires the use of very low coni. ethylene oxide, and more particularly to the proc Centrations of ethylene in the gas mixture which ess of producing ethylene oxide by the cata is Subjected to these catalysts. Thus, while the lytic oxidation of ethylene in contact with the conversions obtained with these alumina catal. combination catalyst of silver deposited upon 5 lysts are good, the output of ethylene oxide is beryllium oxide. low. Another disadvantage of the alumina car An object of the invention is the production of riers is that the silver salts on the surface of ethylene oxide by catalytic oxidation of techni these materials must be reduced at a very low cal gas mixtures, particularly in processes in temperature, such as temperatures of approxi Which temperature Surges may occur. Another 0 mately 150° C. for the reductions which are nec object is the provision of a catalyst which obvi eSSary to maintain the activity of a catalyst. ates the necessity for long and careful aging, or The necessity for low temperature reduction is low temperature operation during reduction described in U. S. Patent No. 2,142,948. Here which has been characteristic of the catalysts of the reduction of silver upon an aluminous car. the prior art. Still another object of the in rier was carried out first at 250° C., and all sub vention is the provision of a silver bearing cata sequent reductions were carried out at 150° C., lytic material which includes a carrier composed whereas the ethylene oxide reaction itself was of beryllium oxide particles suitable for the cat carried out at 290° C. to 295° C. - alytic Oxidation of ethylene to ethylene oxide. It is recognized by those skilled in the art that Other objects will appear hereinafter. 20 lower reduction temperatures are necessary with The catalytic oxidation of ethylene for the the conventional alumina, based carriers if an aca. production of ethylene oxide has been widely tive silver catalyst is to be produced. In obtain. investigated and it has been found that while ing an active form, however, the resultant Silver silver or silver oxide is a catalyst for the reac crystallites are very small and display poor wet tion, the efficiency of this oxidation is determined 25 ting with resultant poor adherence to the alumina, largely by the nature of the catalyst carrier upon carrier. The beryllia carrier, in contrast to which the silver is supported or deposited. Cat alumina and silica carriers, appears to be more alyst carriers employed in the prior art include thoroughly wetted by the deposited silver film. pumice, carbon, silica, zeolite, kieselguhr, alun For this reason the silver is held more tenacious dum, corundum, etc. Some of these carriers, for 30 ly, so that it is not readily flaked or sloughed off example, zeolite give only very low conversions by erosion of the gas stream in the operation of per paSS. the ethylene oxide process. The Silica carriers are also Subject to various It has been found by microscopic examination disadvantages. For example, Silver on silica gel of catalyst Samples that the low temperature re. tends to develop hot spots during the reaction duced Silver formed upon such alumina carriers so that carriers employing this material are soon exists in a very finely divided state. When such deactivated and become WOrthleSS as a catalytic low temperature reduced Silver-alumina cata. support. The silver may also become catalytical lysts are used for ethylene oxide production at ly ineffective by reason of a reaction with the conventional temperatures, it has been found that Silica, to form silver silicates. Some forms of 40 the micro-crystallites of silver gradually increase silica, also exhibit a further disadvantage because in effective size during use, and that the crysa they promote a combustion reaction forming CO2, tallites eventually reach a large size. This which must be mitigated by means of surface growth of the silver crystallite is further ac blanketing materials or promoters, such as bari centuated when hot spots develop during nor um and calcium peroxides and other salts. 45 mal Operation as by variations in process condit. These, however, are only partly effective in re tions. As a direct result of such crystal growth ducing the activity of these silica, carriers and it the extensive surface area necessary to utilize the is found that the Silica, maintains its directive silver as a catalyst is lost. Consequently, an influence towards complete combustion without alumina, base catalyst which has once been over the formation of high yields of ethylene oxide 50 heated is worthless for future catalytic opera which are desirable. tions, because of its greatly lowered activity. The The alumina class of materials, such as car alumina, carriers for silver catalysts are, there. riers based upon alundum or corundum, when fore, characterized by poor stability With regard employed in combination with silver give good to variable temperature, since such catalysts conversions to ethylene oxide, but their initial must be reduced at a low temperature and must 2,554,459 rr re." - - - - always be maintained at a relatively low tempera the objective of the production of ethylene Oxide ture which is free from thermal fluctuation. from such cheap and readily available gas mix It has now been found that the combination tures may be realized. of silver upon fused beryllium oxide provides an The beryllium oxide may be employed in any extremely rugged catalyst which obviates the desired form or condition. Granules of the OX prior art requirements of low temperature reduc ide are convenient for disposal in catalytic Con tion, and which can withstand high temperature verters. A preferred embodiment is the use of SurgeS. beryllium oxide in fused form. This state of the The new catalyst may also be employed in an OXide is very stable and resistant against deg ethylene oxide process operating at considerably O radation by the gas stream. Which is passed higher catalyst temperatures than Was possible through the catalyst bed at a high velocity dur in the past. Since this catalyst is less Subject to ing the catalytic reaction. The fused beryllium crystallite growth of the deposited silver, it is oxide may be utilized in the form of fine particles far Safer as a commercial catalyst, since it can or as a relatively coarse aggregate, dependent Withstand temperature fluctuations and local 5 upon the particular types of reactors which may Overheating such as may occur, for example, in be used and upon the allowable pressure drop. the burning of carbon particles resulting from It is an advantage of the beryllium oxide that the presence of traces of acetylene in the feed the ruggedness of this material prevents the gaSeS. breakdown or powdering of the particles so that It has been conventional in the prior art op 20 the initial particle size is substantially main erations utilizing silica, or alumina based carriers tained throughout the life of the material in the to employ inhibitors or repressants in ethylene catalytic converter. Consequently, the pressure oxide production. For example, as shown in drop does not change greatly during the life of Patent No. 2,279,470 control of the complete com the catalyst, Since the initial particles are them bustion to carbon dioxide has been attempted by 25 Selves maintained intact without degradation, the addition of various compounds to mitigate and the deposited silver is also held with extreme Such undesired reactions. However, the pres tenacity Without the production of silver glob ent Silver-beryllium oxide catalyst, because of ules upon the Surface. The beryllium oxide is greater heat-stability, is not as prone to require preferably employed as the sole carrier of the inhibitorS or repressants, since this catalyst is 30 Silver catalytic material, but mixtures of beryl not Subject to the deleterious effects caused by lium oxide with other carriers may be employed. Sudden temperature Surges. However, the percentage of beryllium oxide as Because of the temperature stability of the an eSSential constituent in the carrier must be fused beryllium oxide carrier in combination maintained sufficiently high so that the char with Silver, it is possible to employ not only pure acteristic qualities such as high temperature ethylene for ethylene oxide production, but to stability, adherence of silver and high initial utilize commercial gas mixtures as well, includ ethylene feed concentration remain substantially ing. leaner ethylene concentrations than were unaffected. heretofore possible, for example, 90% or lower The combination of the fused beryllium oxide purity in the hydrocarbon feed stream. Thus, 40 With Silver may be accomplished by impregnating in addition to the possible contaminants, such or admixing with any convenient silver salt. as acetylene, which may result from the use of The beryllium oxide particles may be slurried by-product ethylene obtained in acetylene pro With the Silver Salt or may be impregnated there duction by high temperature combustion, gases in. Alternatively a slurry of finely divided obtained in petroleum cracking operations may 4: metallic Silver or Silver oxide particles may also be employed. Such still release gases, for ex be applied to the beryllium oxide carrier. ample, as those containing ethylene, other gase After the Silver has been deposited or impreg Ous olefins, and paraffins, as well as acetylenes nated upon the carrier as metal or salt, the cata may be utilized for the production of ethylene lytic material is dried and may be reduced be oxide by the catalytic oxidation of the ethylene 50 fore charging to the reactor, or may be reduced contained in Such gas mixture by my present in situ in the reactor. invention. While Leniher in U. S. Patent No. The reduced silver material, which in asso 1,995,991 Suggests that he may oxidize a mix ciation with the beryllium oxide carrier is the ture of hydrocarbons or a gas containing an active constituent in the ethylene oxide process, olefin hydrocarbon (page 3, col. 2, lines 61-63), 55 is probably metallic. silver, but may be silver the process employed by him is non-catalytic Oxide, and may also include variable proportions and results in the production of more aldehyde of silver oxide. The total silver content may than ethylene oxide. I have found that when vary from 5% to 25% referred to the carrier. a mixture of air with paraffinic hydrocarbons The reduction process employing beryllium ox Containing ethylene is passed over conventional 60 ide as a base may be carried out at far higher Silica or alumina based catalysts which were temperatures than has been possible with prior known to give conversions of pure ethylene to art materials. Thus, Silver nitrate impregnated ethylene oxide, there occurs so rapid an oxidiza upon beryllium oxide may be reduced at about tion of the parafiinic constituents of the mix 275 C. to 300° C. Without the danger of fusion of ture that overheating of the catalysts, resulting 65 the silver on the catalyst surface. With silverni in deterioration of the same, always takes place. trate deposited upon alumina in the same man The use of gaseous hydrocarbon mixtures con ner, it is found that the temperature must be taining paraffinic hydrocarbons, as well as the held about 100° C. lower than in the case of acetylenic hydrocarbons such as may occur in beryllium oxide. high temperature hydrocarbon processing, is, of 70 The catalytic operation employing the silver course, preferable from an economic standpoint beryllium oxide catalyst either in the presence or to the use of pure ethylene. The new catalyst absence of other gaseous hydrocarbons may be and the process employing the same herein pro carried out at temperatures of from 225° C. to vided obviates the necessity for purifying the 350° C. and preferably at temperatures of about ethylene previous to the oxidation step so that 75 250 C. to 300 C. A preferred embodiment is the

2,554,459 5 6 Óperation of ethylene oxidation utilizing beryl reach the dangerous condition of a runaway re lium oxide at about 275° C. The oxidizing me action. Which might propagate a flame and fuse dium may be air or a mixture of oxygen and an the catalyst. inert gas, such as may result from oxygen en I have found, moreover, that aside from the richment. Oxidation may be economically car 5 economic consideration of high throughput the ried out by a single pass operation, although, if space velocity can be considerably varied, de desired, recycling of the exit gases (from which pending upon other factors entering into the op the ethylene oxide has been removed by absorp eration, i. e., reaction temperature concentration tion) may be used by constant addition of ethyl of ethylene and air in the gas mixture proportion ene and air to the feed gases. By employing the 10 of beryllia used in the catalyst, etc. Generally present catalyst, from 70% to 80% of the ethyl the space velocity required for good conversions cene originally present in the feed gas is consumed sto ethylene oxide varies from 500 to 3,000 R. H. in one pass, from 40% to .45% and higher being While ordinarily a space Velocity in the range of converted to ethylene oxide and the remainder to 1,000 to 1,500 R. H. will be employed, this value other oxidation products, chiefly carbon dioxide. li5 may be varied, particularly if a recycle System is Thus, after absorption of the ethylene oxide the contemplated. iresulting gas mixture generally contains less than The operations in the present proceSS Were 1% of ethylene, the major proportion of this gas carried out utilizing a recycle ratio of 4:1. How stream being carbon dioxide, oxygen and nitro sever, this recycle ratio may be varied consider gen. In a specific instance, for example, em 20 ably, depending upon the type of product which ploying an initial gas mixture consisting of 3% is desired, since it is possible when producing by volume of ethylene and 97% by volume of air, ethylene glycol directly from the exit gas stream 45% of the ethylene is converted into ethylene to operate at considerably higher recycle ratios voxide, and 30% into carbon dioxide. Such as 8:1. In order to present the invention in greater de In the production of ethylene oxide as Such, I tail several examples are set out below, although prefer to employ low recycle ratios Such as 2:1, it is intended that the Subject matter of the said and may also use a once-through proceSS. examples shall be illustrative and not limitative of the present invention. Eacample 3 Eacample 1 30 A comparison was made of the present beryl lium oxide in combination. With Silver as a cata Fused beryllium oxide in the form of 4 x 8 lyst relative to the results obtained in another mesh particles Was dried in a vessel immersed in experiment made with the use of a silver on a nitrate bath at 300° C. for one hour. During silica. This catalyst consisted of 23% silver de this time the vessel was evacuated by applying 35 posited on 4 x 8 mesh silica particles. This cata full Water pump suction. After cooling the beryl lyst was employed with a gas mixture consisting illium oxide, a Water Solution containing 25% by of 3% of ethylene and 97% of air by Volume. Weight of Silver nitrate was added to the carrier in The temperature of the bath Surrounding the Such amount as to produce a carrier-Silver nitrate catalyst tube was maintained at about 244° C., containing 25% by weight of the latter salt based 40 which was as high as the temperature could on the Weight of the carrier. The mixture was safely be brought for continuous operation. Dur allowed to SOak overnight. The exceSS Water WaS ing the first 2.5 days the temperature of the removed under vacuum by heating the carrier in catalyst bed rose from 266° C. to 34.9° C. and the the same vessel. The dried silver nitrate in per cent conversion of introduced ethylene react pregnated catalyst Was then charged to a heated 45 ing to form ethylene oxide fell from 38.1% to reactor and reduced with hydrogen at 275° C. to 26.7%. The ethylene and air flows were 2.0 and .300 C. for 5 hours. 65.0 liters per hour, respectively, corresponding Eacample 2 to a space velocity of 650R. H. The utilization of the catalyst of Example 1 in 50 Eacample 4 an ethylene oxide process was carried out by In another test which was made to compare the scharging the impregnated catalyst to the same alumina, based silver catalyst, there was used a Stainless Steel tube in Which the reduction WaS tabular corundum catalyst containing 10% by carried out. The tube was surrounded with a weight of silver. A 3% ethylene-97% air mix constant temperature bath. 55 ture for a space velocity of 264 R. H. gave conver The reduced catalyst was operated in a recycle isions varying from 28.6% to 16.2% at tempera system. The make-up gas mixture of 7% ethyl tures as measured in the catalyst bed of from ene and 93% air, was mixed with 4 parts of the 208° C. to 360° C. The use of higher space veloc recycle gas from which the ethylene oxide had ities gave lower conversions; the conversion of previously been absorbed. The total mixture 60 introduced ethylene to ethylene oxide at a Space was then passed over the catalyst at a space ve velocity of 1100 R. H. and the catalyst bed tem locity of 1300 R.H. peratures of from 310° C. to 364° C. varied from It was found that space velocities could be 8.8% to 13.9%. utilized at a far higher range than was possible In the operation of the present process it was with prior art catalysts which generally oper 65 found that no preliminary aging of the catalyst is ated at about 500-700 reciprocal hours (R. H.). necessary, and that the operating temperature By the term "space velocity' expressed as re may be increased to a considerably higher tem ciprocal hours (R. H.) I mean the number of perature than was previously possible by reason volumes of gas measured at standard conditions of the greater thermal stability of the catalyst. (0° C./760 mm.) per hour passing over a unit 70 This thermal stability is attributable to the na volume of catalyst. The thermal stability of the ture of the combination of silver with beryllium beryllium oxide in avoiding hot spots, together Oxide, Since the present catalyst combination is with its quality of holding the deposited silver, considerably less susceptible to surface fusion of apparently allowed the use of far higher velocity the catalytic silver present on the beryllia. The gas streams Without permitting the hot spots to 75 present catalyst is consequently also uninfluenced 2,554,459 7 by accidental temperature increases which are liasilver catalysts allow the higher ethylene feed inevitable in any technical process of this nature. gases to be used immediately after the reduction I have found that such accidental temperature Of the catalyst has been Completed. Because of increases which might raise the catalyst temper this gain in the ability to utilize high ethylene ature to values exceeding 350° C. do not influence Concentrations the present catalysts permit a the conversion, although such occurrences are proceSS to be carried out in which gradual and known to render an ordinary alumina catalyst constantly changing addition of ethylene need unfit for further use. not be controlled manually. The present process utilizing the catalyst of Since many widely different embodiments of beryllium oxide in combination with silver was O this invention may be made without departing found under the above conditions to give conver from the Spirit thereof, it is to be understood that Sions of 40% to 45% to ethylene oxide, and yields I do not limit myself to the specific embodiments of 55% to 50% based upon the ethylene con thereof except as defined in the appended claims. Sumed. What I claim as new and desire to secure by The above reaction was carried out at atmos 5 Letters Patent of the United States is: pheric pressure, although subsequent work has 1. The process for making ethylene oxide by shown that the reaction proceeds equally well at the direct chemical combination of ethylene and preSSures above or below atmospheric. OXygen. On a Silver catalyst which comprises pass Recovery of the ethylene oxide may be effected ing ethylene and gases containing molecular oxy by any of the methods known to the art, i. e., 20 gen at temperatures between 250° C. and 300° C. by absorption upon activated carbon or by solu Over a silver catalyst Surface supported upon a tion in water or other Solvents. Preferably, the Carrier comprising fused beryllium oxide. reaction gases are passed through a scrubbing 2. The process for making ethylene oxide by tower wherein the ethylene oxide-containing the direct chemical combination of ethylene and gases are thoroughly contacted with water or 25 OXygen. On a Silver catalyst which comprises pass other Solvents, and the ethylene oxide dissolved ing ethylene and gases containing molecular oxy therein for further processing. gen at temperatures between 225° C. and 350° C. The present combination catalyst of silver de Over a Silver catalyst Supported upon a carrier posited upon beryllium oxide is particularly ad comprising fused beryllium oxide. vantageous in large scale processes for the pro 30 3. The process for making ethylene oxide by duction of ethylene oxide. In a commercial unit the direct chemical combination of ethylene and it is highly advantageous to employ the same OXygen. On a Silver catalyst which comprises pass converter for the reduction of the catalyst and ing ethylene and gases containing molecular oxy for the oxidation step, particularly if both oper gen at temperatures between 225° C. and 350° C. ations are performed at the same converter tem 35 over a Surface which includes an active catalytic perature. material of the group consisting of silver oxide, The requirement of reducing alumina and Silica Silver, and mixtures thereof Supported upon a Supported Silver catalyst at low temperatures in carrier comprising fused beryllium oxide. Order to obtain the desired activity necessitates RUDOLPH L. HELDER. the added capital expenditure of another con 40 verter for the sole purpose of preparing catalyst. REFERENCES CTED The present silver-beryllium oxide catalyst avoids The following references are of record in the these difficulties Since it may be reduced at the file of this patent: normal Operating temperature without losing its UNITED STATES PATENTS activity. 45 It has been observed that the beryllia-silver Number Name - Date combination catalyst permits the use of higher 2,307,421 Overhoff ------Jan. 5, 1943 concentrations of ethylene such as 5% ethylene 2,354,892 Thacker ------Aug. 1, 1944 in air in the incoming gas. It has been a char 2,393,537 Huttman ------Jan. 22, 1946 acteristic of the prior art alumina-silver catalyst 2,424,083 Finch et al. ------July 15, 1947 that the ethylene concentration had to be kept 2,424,084 Finch et al. ------July 15, 1947 at a low value, particularly during the initial 2,430,443 Becker ------Nov. 11, 1947 break-in operations, and only slowly raised after OTHER REFERENCES many hours of operating time until the optimum ethylene concentration could be tolerated. 55 Bergman et al., Catalysis, page 697, 1940, Rein In contrast to this situation, the present beryl hold Publishing Corp., New York.