US2367169A - Process for treatment of olefins - Google Patents

Description

Jan. 9, 1945. D. GARDNER PROCESS FOR :TREATMENT OF OLEFINES Filed Feb. ll, 1941 out oN: En No w1 Nu .0,5 .v1 NU lNvENToR z YY) ,K BY i `'l-TORNEYS, n

Patented Jan. 9, 1945 PROCESS FOR TREATIVIENT F OLEFINS Daniel Gardner, New York, N.- Y., assignor to Gardner Thermal Corporation, a corporation of Delaware Application February 11, 1941, Serial No. 378,438 claims. (c1. 26o-348) This-invention is a process for the treatment of the oleflns, or unsaturated hydrocarbons of the formula CnHa., whether in a pure or dilute state, for the production of the oxides thereof or the aqueous or other derivatives of such oxides; a typical instance being the oxidation of ethylene C2H4 into (CHzzO, adapted to further conversion, as to ordinary or ethylene glycol C21-i602. The principles are operable for the higher olefins as well, such as propylene Cal-ls, oxidizable and convertible to propylene glycol; and the yet higher ethylene homologs, 04H8 and 05H10 and 06H12 and 01H14 and 03H16 and C9H1a and C1oH2o, etc., With the indicated adaptations or proportions and treatment; but the first instance will be particularly described as illustrative of all.

Pure or concentrated ethylene can be obtained in quantities for the purpose, e. g., starting fromv ethyl alcohol; and the several olens are also otherwise obtainable, for instance from the modern oil cracking processes. In the latter case the olens are highlydiluted, representing but a fraction of the total gas mixture, the major part comprising methane or other saturated hydrocarbons, accompanied usually by small quantities of other gases, such .as free hydrogen or of sulphureted hydrogen. However, from practical considerations, the extraction and utilization of the olenic or ethylenlc compounds of the gases obtainable by cracking processes represents by far the more industrially promising scheme. It is clear that a process such as this invention which is adaptable for treating dilute gaseous ethylenic mixtures will so much the more easily provide economic industrial treatment of a more concentrated or pure ethylene gas.

Among the heretofore used methods of olen oxidation are those carried out by using chlorine. Such, however, are costly, and various attempts have been made to cheapen the product, in some cases by direct oxidation, using molecular oxygen of the air, by the reaction Various other objects and advantages wil1 be explained in the further description.

Practical examples will be stated to illustrate the factors which are involved and to be strictly observed, but rst certain general facts will be recited. Thus, it is known that ethylene 02H4, Whose heat of formation is 9.6 Cal., can under certain conditions be oxidized to ethylene oxide, 02H40, whose heat of formation is +17.6 Cal.

. Ethylene oxide is a liquid with the low boiling point of 12.5 C. and density of .894 (at 0). It readily mixes with water in all proportions, and it combines with water forming ethylene glycol of the formula C2H4(OH)2. When ethylene oxide is rapidlyheated up to about 400 C. it is lost by Ethylene glycol on the other hand upon heating can give polyglycols by direct combination of two or more molecules, followed by splitting off of water. Also, in presence of dilute sulfuric acid two molecules of water can be removed from two molecules of glycol, whereby cyclic compounds are formed, as shown by Favorsky, for instance in the formation of diethylenic ether.

It is to be remembered that ethylene is stable only up to about 350 C., and thereabove it is converted into a mixture of methane and acetylene, thus:

It is further to be remembered, as was shown by G. Wagner, that through action of a weak solution of potassium permanganate having an alkaline reaction, ethylene may be oxidized, and converted to glycol, as follows:

An important part of the present invention comprises the condition in which oxygen is supplied to the reaction, namely, as atomic oxygen, which it has been discovered acts spontaneously and greatly enhances the quickness and completeness of the combination, improving yield and economy, as will be hereinbelow elaborated.

Important factors that should be given definite consideration in laying out the reactions are first enumerated as follows, to be later fully discussed:

(a) The temperature of the reaction must never exceed certain limits, and, as a rule, must be kept as low as possible, within such limits, if the formationof undesirable compounds is to be avoided. This temperature for the oxidation of ethylene must be well under 350 C., and may run somewhat below 320, a desirable average being about 340.

(b) There must be an optimum duration for the stay of the mixed gases in the hot reaction zone, while the heat should be uniformly distributed throughout the zone.

(c) It is of great importance to control the speed of the gases passing through the hot zone; the speed of course being related to the length of the heated zone and the duration of the treatment.

(d) In regard to pressure, it is necessary to determine whether there is an advantage in work.- ing under pressure or in vacuo, rather than operating at normal atmospheric pressure.

(e) A repeated passage or recirculation of the reaction gases through the hot zone or a duplicate zone may in some circumstances be favorable.

(f) It may sometimes be useful to bring the supplied gases, ethylene and oxidizing gas, by separate paths to the reaction zone, so that they do not mix prematurely.

(g) It may be advisable to introduce into the reaction zone solid substances which are porous or can adsorb the reaction gases, thus permitting a better and longer contact.

(h) It is of importance to make a proper selection of the refractory materials composing or lining the hot zone w^lls; for, as is known, an advantageous refracnry can assist in promoting the desired reaction.

(i) Of highest importance is the ,selection of the catalyst or oxidation-promoting agent to be used.

(9') In some cases it may be advisable to add to the gas stream a suitable amount of steam to pass through the heated zone.

(lc) The process for economic reasons should be arranged to be operated as a continuous process.

This invention is intended to be performed on the lines indicated so as to afford the advantage and results noted, and each of the above points (a) to (k) will next be dealt with in successive discussions designated A to K.

A. Reaction temperatura- A furnace should be used which comprises means for automatic temperature control with the temperature uniformly distributed throughout the cross section and effective length of the reaction zone. It is preferable to have a long furnace or tubular i'lue of small diameter; preferably a tube of a suitable material, and its interior being occupied by a contact or catalytic substance, or by highly heat conductive metallic or other tubes or rods; or by a system of metallic strips or threads, to be highly heated. thus permitting the reacting gases to come in touch with these glowing metallic threads. In any case the temperature must not be so high as to impair the gases, bearing in mind that ethylene breaks up at a temperature slightly above 350 C., and that at a temperature of about 400 ethylene oxide has a tendency to isomerization; and the best determination of furnace details depends upon the catalyst or oxidizer used in the process.

B. Duration of reaction-It is of no advantage to keep the heated gases in the uniformly heated reaction zone longer than necessary; it is not advisable to keep any portion of the gases, once the reaction has actually taken place, in the hot zone. However, it is advisable to preheat the constituentI gases before they enter the reaction zone, for example to a temperature which is about 50,

or between 40 and 60, under the reaction temperature in the furnace, or at least approaching the same. The gases should be introduced in proportions consistent with the equation, permitting however a reasonable oversupply of the oxygen-containing constituent. It is important to arrange controls of all factors of the process, the same to be strictly automatic and in correspondence with the analysis of the gases supplied and the reactions expected. The gases should be well dried, since moisture in no way favors but may impair the reactions, especially at the initial stage.

C. Gas travel speed.-Control of velocity in the hot zone of the furnace is o f great practical importance; and i1; can readily be empirically established for each special gas mixture. Obviously, the speed is a function of the working temperature among other factors. But it is advisable to keel) the speed down rather than to push the temperature up. For if, for instance, a gas mixture is used which contains a predominant proportion of saturated hydrocarbons, these may, under ce1'- tain conditions, become liable undesirably to enter into reaction if the temperature becomes too high. Once a definite gas speed has been found to be the optimum speed under prevailing conditions, no alteration of speed should be permitted, since the reaction of oxidation of olens, while simple in theory, is a most capricious process, in which even slight errors may extensively interfere with the desired reactions and yields.

D. Pressure conditions.-As a rule, it is preferable to work at atmospheric pressure, since the whole system is simpler and more easily controlled. However, if so desired, and particularly when the process of oxidation is combined with modern cracking procedure, then working under some particular pressure becomes useful, provided measures are taken to avoid any trouble brought about through possible excessive temperature, which could seriously affect the yield.

E. Repetition of reaction- While often in gaseous reactions it is not sufficient to pass a gas mixture only once through the hot reaction zone, and it has been practiced to repass the gas several times, this has distinct drawbacks, since the mixing of the old and raw supplies upsets the proportions of the reacting gases. Besides, the

.ethylenic oxides are very sensitive compounds, as l ferred to pass the two gases by separate paths or currents to the reaction place, whereby the ethylenic compound and the oxidizing gas do not meet prematurely, but only encounter each other as they arrive at the hot zone. Ethylene is three times more explosive lin contact with oxygen than is methane, the reaction having a tendency rst to go according to the following equations:

02H4+3o2- 2Co2+2H2o+335`.2 cai.

whereupon further amounts of ethylene can react with the carbon'dioxide so formed, with production of carbon monoxide and methane, thus: C2H4+CO2- 2CO+CH439.3 Cal.

The explosive reactions can be avoided, if the reacting gases approach differently to the reaction, since then only the direct oxidation of the gases can occur. However, this is a matter of secondary importance in certain cases, as will be seen further below.

G. Solids promoting gas contact-The employment in the heated zone o f gas adscrbing substances is of advantage. Several types of materials can be used. as powdered pumice, porcelain, sand, silica, mica or many other substances which have similar effect, in that they do notv cause special reactions between the adsorbing solids and the gases, but only increase the contact surface and efficiency of the gaseous reactions.

0n the other hand certain materials can be used which can physically adsorb the gases at lower than the normal reaction temperatures. Now, if an oxidizing gas is employed which also is adsorbed by the solid material, then more intimate gas contact and reaction take place and the oxidation is achieved at a lower temperature. As an example of such a material can be indicated an active carbon, of which there are several known, the selection of which is, however, limited to such cases as those wherein the active carbon does not include any matter which could be detrimental to the reaction. The reaction gases become occluded in the porous carbon body. Instead of active carbon powdered silica gel can also be used. A

H. Refractory passage walls-Not all refractories operate to promote a reaction in the same direction. Certain refractories, such as aliunina. silica, their mixtures, boric acid, lime, barium oxide and others, disadvantageously promote the breakdown of oxygen-containing organic compounds; for instance Ipatief found that ethylene can -be obtained from ethyl alcohol by passing its vapors through a hot tube in contact with anhydrous alumina,'which acts Aas a catalyst.

0n the other hand, certain other refractories act in the opposite way and distinctly favor the oxidation of ethylenic hydrocarbons. Amongst such refractories magnesia, beryllia, lithia, titania. zirconia, thoria, ferrie oxide, chromium oxide, tin oxide, tungsten oxide and others specially favor the reaction of oxidation. It has been found that a tube made of lithium tungstate Li2W04, with a melting point of 742 C., or of tungsten oxide W03, melting point 1473 C., are particularly suitable for the above reaction. Good results have also been obtained by using flues or tubes of Austrian or other magnesite. A point to be considered is that the refractory used must not be subject to chemical attack by the hot; air or gases used, while the refractory should favor the reaction by acting catalytically.

I, Catalyzing agent-The choice of the catalyst or oxidation promoter is of great importance. For' description purposes references will here be made to the aforementioned spontaneous acton of atomic oxygen, which, when generated, has but an exceedingly short span of life. Two particular examples/ will next be referred to illustratively. A i

First: Atomic oxygen is producible by passing a current of dry air over glowing strips or filaments of certain metals, such as platinum, iridium, osmium, tantalum, tungsten, gold or silver. or their alloys. The atomic oxygen thus generated and supplied reacts immediately with the ethylene gas by the following reaction, differing from the prior known equation:

Csi

The splitting of Oz into 2O is preferably per-- formedwithin the reaction zone, and the metallic threads may be suspended in parallel inside the refractory tube, and heated to a glow, as by electric current.

The temperature in the reaction space should be upkept at a mean of about 340 C., which ternperature is easily produced and can be steadilyA maintained; it should never exceed about 350 nor fall below a low limit of about 320. It should be stated that saturated hydrocarbons do not oxidize under these temperature conditions; therefore their presence in the gas mixture does not interfere with the reaction, which therefore may be performed in conjunction with gas crackingr operations. Very satisfactory yields of ethylene oxide are obtained as the eiilciency of oxidation is high; and this is true also of propylene and the other higher oxides.

In order to ascertain whether the total content of ethylenic hydrocarbons is thus oxidized, the gases, or samples thereof, at the final outlet of the furnace may be tested by being introduced, after cooling, into a solution of potassium permanganate. If no precipitation of a brownish deposit of manganous peroxide occurs, the oxidation of the oleflns is to be considered as complete. Before passing the cooled gases into the potassium permanganate solution, it is advisable first to wash them with water thereby to dissolve out all ethylene oxide which may be entrained and carried away with the other gases, by which step the ethylene oxide slowly changes over to ethylene glycol.

Second: Atomic oxygen can also be produced by passing nitrous oxide N20 through the flue or other duct in contact with glowing metallic filaments. The reaction goes as follows:

From this equation it is noted that an exothermic reaction results, notwithstanding the fact that the heat of formation of ethylene (-9.6 Cal.) and that of nitrous oxide (-20.0 Cal.) are negative.

It is known, that N20 is a good oxidizer, but it needs a push, as by a catalyst or by heat or both. In this particular case it is impossible to rely upon the heat decomposition of nitrous oxide, since up to 700 C. or even at 1000 the decomposition is not always complete. Besides, at high temperatures N20, like all endothermlc compounds, is apt to become more stable, and the reaction may reverse and go from rightto left, thus:

mized or eliminated. It is known that hydrogen reduces N20 on the one hand; and on the other hand that sulfur (like phosphorus, carbon, boron,

copper, iron, cadmium, lead, cobalt, nickel and vmany others) is by it oxidized to sulfurous oxide.

Also that N20 is stable toward HzS; in fact should some N0 be present, then H25 will transform it to N20. 0n the other hand, N20 well resists oxidizing agents. Therefore, for the present invention N20 can advantageously be decomposed before it otherwise reacts'. It has been found during a series of tests that N20, in presence of glowing metallic threads, immediately decomposes by discharging the desired atomic oxygen. In itself N10 is a stable gas and begins to dissociate only above 520 C.

N20 can readily be obtained by any oi the well known methods, for instance by the heating, up to 170 C., of ammonium nitrate, NH4.NO3. However, at 240 C. this reaction becomes very energetic and even dangerous, and a better method is to heat a mixture of sodium nitrate and arnmonium sulfate to 230 C. in a cast iron retort. It is found that 100 parts of ammonium nitrate give about 40 parts of N20, that is to say 90% of the theoretical value. When produced, the N20 may be collected in a gas-holder over mercury, or hot water, or a saturated salt solution.

When operating as thus described, the N20 in contact with the glowing metal threads immediately discharges atomic oxygen, which on the spot oxidizes the olens present.

N20 can quantitatively be also produced according to Quartacoli (1911), by heating formic acid with various nitrates as NaNOa, whereby the CO2 formed is absorbed by the sodium hydrate obtained.

One volume of water at dissolves 1.3 volumes 0f N20.

It is also found that a mixture of air and nitrous oxide can be utilized with good success to generate as described a supply of spontaneously combinable atomic oxygen, and this is true for the oxidation of all known ethylenic hydrocarbons.

It ought to be also said, that once the ethylenic oxide is obtained, it can easily be reacted with ammonia gas, whereby derivative products are obtainable belonging to the mixed type of amino alcohols, as for instance, `ethylene oxide and ammonia, reacting as follows:

ICH OH During this reaction no free N20 should be present, since it tends to react with NH3 in the following undesirable manner:

J. Addition of steam.-In some cases, for instance when pure ethylene gas is being treated, it is advantageous to introduce into the gas stream traversing the reaction zone small amounts of steam, but only in minor quantities. Since the process is carried out at a comparatively low temperature, no dissociation of water vapor takes place.

K. Continuous operation-From an industrial aspect the process of this invention is of denite value since it is adapted to be worked as a continuous process. proportions of the gases introduced into the system, the temperature and the pressure, should be rigorously maintained and controlled by automatic measuring and correcting apparatus. The ethylene oxide is finally collected as such, or can be first converted to a derivative, as for example, directly transformed into ethylene glycol by introduction into water. A11 of the other ethylenic oxides or their respective derivatives or glycols can be produced in similar manner.

Supplemental remarks.-The present invention in its preferred embodiment may be described as the continuous process for the treatment of ethylene or other olefins ilowing in gaseous phase through a ue, comprising the step of directly oxidizing successive portions of the olefin All factors, such as the right stream at an elevated temperature in the presence of'a catalyst within the reaction zone of the due; such process being characterized by supplying to the reaction a due proportion of oxygen, consistent with the combining equation, namely, about 1 atom per molecule, or at least one gram atomic weight of oxygen for each gram molecular weight of olefin, inthe form of atomic oxygen which is adapted to combine spontaneously with the' oleiin, and in said zone maintaining the reaction temperature at a point between about 350 C. and about 320, such as about 340, causing the reaction to terminate after a limited duration when the oxidation of the olen has become substantially complete, and thereafter collecting from the product gases the olefin oxide as such or with further conversion to some derivative thereof. The mode of supplying to the reaction freshly split er atomic oxygen is preferably one of the modes hereinabove described in detail; and various other considerations or reaction i factors, such as dimensions of flue and reaction zone, gas pressure and speed conditions are preferably as already above pointed out and recommended.

The accompanying drawing shows in a single gure a diagram indicative of the structure and mode of operation pertaining to a preferred example of the present invention; it being assumed for the purpose of the diagram that ethylene is the olefin to be oxidized and that the oxidizing gas initially comprises molecular oxygen as in air.

At the center of the diagram is shown the reaction zone 0, which may be a chamber or length of ilue through which the mixture of gases flows. Suitable heating means is to be understood for maintaining a reaction temperature such as about '340 C., evenly distributed throughout the section and volume of the zone; while the presence therein of a suitable catalyst is conventionally indicated at 8, and the presence of powdered or other contact-increasing substances is indicated at I0. The reaction zone is shown enclosed by refractory walls II, to be of the character already described, and the diagram is shown broken away at the center to indicate that the reaction zone may be of greatly extended length, as is preferable, thereby to allow a duration suihcient for completion of the reaction at the moderate temperature stated.

The ethylene C2H4, usually with dilution by other gases, is shown as being supplied to the hot zone by a duct l2, which is connected with the delivery of a gas pump or blower I3, the intake duct I4 of which constitutes the supply pipe for the gases comprising C2H4. As already explained it is preferable to conduct the oxygencontaining gases to the reaction place by a separate passage, and for this purpose a duct I 6 is shown, supplied by blower I5, and joining the duct I2 and therewith entering the heated zone 9. In order that the air or gases supplied through duct I6 may be caused to furnish atomic oxygen to the reaction a means for this purpose is indicated in the form of glowing filaments I1 which, in the case of air, can split the molecular into atomic oxygen.

At the other end of the zone is shown a duct I9 leading therefrom to a chamber 29 or place for collection of the olen oxide, such as 02H40. The chamber 29 is shown as a tower provided with a water spray device 30, fed by a valved water pipe 3|, whereby the C2H4O may be dissolved in the water. In such case this material is converted into the derivative glycol, which remains dissolved and, with the excess water is received 'in the trough bottom 32 of the chambena liquid pipe 33 leading therefrom to a suitable receptacle. The undissolved gases may pass out from the tower by an exit duct or flue 35, conducting them away as may be desired.

As a specific typical example, assuming atmospheric pressure and temperature about 340 the hot reaction zone may have the following dimensions: Its (circular) diameter between 6 and 12 inches. Its length between 10 and 20 feet. The duration of reaction for each portion of gas mixture, depending on the catalyst and other factors described, may vary widely, as between 30 and 180 seconds. Assuming a duration of 100 seconds and length of feet the velocity will be about V5 feet per second. Whatever factors are determined for a particular process they should be maintained steadily.

The volume of gases per minute traversing the zone will equal the velocity times the eiective sectional area. Once the total quantity or weight of gases per minute is known, the composition of the two constituent gases, and the proportion between them as determined from the expected equation, determine the actual supply rate for each of the two gases, to be so forced through ducts I2 and I6, under complete control, for mixing and entry into the reaction zone.

A process for treatment of oleiins has thus been described which embodies the principles and attains the objects of the present invention; since many matters of operation, order of steps, speciiic reactions and character of compositions used may be variously modified Without departing from the principles of the invention, it is not intended to limit the patent to such matters except to the extent set forth in the appended claims.

What is claimed is:

l. The continuous process for the industrial treatment of oleiins, during flow in dry gaseous form through a flue or passage, comprising the step of directly oxidizing the successive portions of the flowing olefin gas at an elevated temperature and in the presence of catalytic means in thc reaction zone of the flue; characterized by maintaining in said zone a reaction temperature below about 350 C. but not substantially below about 320, and supplying to the hot reaction zone a dry gas containing oxygen in the form of atomic oxygen in about the amount of one gram atomic weight for each gram molecular weight of the olefin, to combine spontaneously with the olefin to produce the oxide thereof.

2. The process as in claim 1 and wherein following the stated reaction the olefin oxide is separated from the product gases and collectedas such.

3. The process as in claim 1 and wherein following the stated reaction the olefin oxide is reacted with water for conversion to a glycol.

4. The continuous processfor the industrial treatment of olens, during flow in dry gaseous form through a flue or passage in dilution in mixture with saturated hydrocarbon products of cracking processes, comprising the step of directly oxidizing the successive portions of the dilute flowing olefin gas at an elevated tempera'- ture and in the presence of catalytic means in the reaction zone of the flue; characterized by maintaining in said zone a hot reaction temperature below about 350 C. thereby avoiding decomposition of the saturated hydrocarbons, supplying to the hot reaction zone a dry gas containing proportion of the atomic weight of oxygen to the molecular weight of the oleiin, to combine spontaneously with the olefin to produce the oxide freshly generated atomic oxygen in about the thereof.

5. The process of oxidizing an olefin gas comprising subjecting it to an elevated oxidizing temperature below 350 in the presence of an oxidation-promoting catalyst while supplying to it a substantial proportion of atomic oxygen freshly generated for spontaneous combination with the oleiin to form directly the oxide of the olen.

6. The process as in claim 1 and wherein the initial oxygen-supplying gas is conducted separately to the reaction zone for mixing there with the olefin-containing gas, and each gas is preheated to within about 40 to 60 below the reaction temperature, and the oxygen-supplying gas is treated near its point of entry into the zone by glowing hot filaments of metal adapted to produce atomic oxygen for immediate combination of one atom of such oxygen with one molecule of the olefin' during the brief life of such oxygen.

7. The process as in claim 4 and wherein the atomic oxygen is supplied relatively in excess over the olefin, atom for molecule, and the hot reaction is continued for between about 30 and 180 seconds until at least a large part of the olen has been oxidized to the olefin oxide.

8. The process as in claim 1 and wherein the oxygen is supplied in the initial form of molecular oxygen which is split by the heat of glowing laments into atomic oxygen `fed to thel reaction 10. The process as in claim 1 and wherein the atomic oxygen is provided by splitting molecules containing oxygen by the use of glowing hot laments containing a metal of the group consisting of platinum, iridium, osmium, tantalum, tungsten, gold and silver.

11. The process as in claim 1 and wherein the reaction zone wall is composed-of a refractory composition adapted to withstand the heat of reaction and resist attack by the hot gases and as well to favor or assist the oxidation of the olefin. such composition containing one or more substances selected from the group consisting of lithium tungstate, tungsten oxide, magnesia, beryllla, lithia, titania, zirconia, thoria, ferric oxide, chromium oxide and tin oxide.

12. The process as in claim 1 and wherein the zone wall surface contains lithium tungstate.

13. The process as in claim '1 and wherein the zone wall surface contains tungsten oxide.

14. The process as in claim 1 and wherein, within the reaction zone, is maintained a quantity of a solid composition in powdery condition adapted to increase gas contact and thereby promote reaction.

15. The process as in claim 1 and wherein, within the reaction zone, is maintained a quantity of a solid composition in powdery condition adapted to increase gas contact and thereby promote reaction, said composition consisting of an active substance capable of absorbing or occluding the gases`at low temperatures and selected from the group consisting of: silica gel, and an active carbon, free of any constituent tending substantially to impair the aforesaid reactions.

DANIEL GARDNER.

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