Dec. 3, 1946. 2,412,014 T. K. sHi-:Rwoon MANUFACTURE Ior’ Fo:umLmmf'nla4 Filed Nov. 19, 1943> 2 Sheets-Sheet l y», mm \\\\\\\\\\\\\\\\\\ NN IlIllllll/ll/l O èÈ MN mSSgm. whi_m HNWSDB Bm _0 E HN zmkìnërm Suu.mm_ NNmuy f HN, NN .uN QN, .D4mQuì 0 NN Szbtr N my.._ a., Dec.> 3, 1946. 2,412,014 T. K. SHERWOOD MANUFACTURE oF FORMALDEHYDE Filed Nov. 19, 1943 2 Sheets-Sheet 2 91 \ Ã§ 95 /90 ~ WKK 95 l/ // /NVENTU/z @y „ j 2,412,014 Patented Dec. 3, 1946 UNITEDik 4's'rA'rlëis _PATENT OFFICE 2,412,014 MANUFAc'rURE or FORMALDEHYDE Thomas K. Sherwood, Wellesley, Mass.. anignor ' to Godfrey L. Cabot, Inc.,`Bolton, Maas., a cor poration of Massachusetts . `Application November 19, 1943, Serial No. 510,898 s claims. (q1. 26o-co4) l 2 This invention consists in improvements in processes of producing formaldehyde from edly higher temperature, for example at least natural gas. It has been known for many years As a result of the rich air-gas mixture I employ that methane may be converted into formalde hyde by mixing natural gas with nitrogen oxides as a gaseous catalyzer and heating, thus induc ing an oxidizing reaction in the mixture result ing in the formation of formaldehyde. Processes of this character as heretofore carried out have 1200° F. » and .the lincreased working temperature, I find that the process may be very appreciably speeded up. For'example, in processes heretofore prac ticed a contact time of about 8 seconds for re . acting the methane has been considered neces sary, whereas the contact time of my lnovel not been entirely satisfactory for large scale pro-A 10 process is in the order of 1A to 1/2 second. ' Another extremely important advantage of my duction and have been carried out only under improved process is that the amount of catalyzer , conditions of high pressure with poor efficiency employed may be very substantially reduced. For in respect both to time and materials used. The present invention consists in improvements by example', heretofore it has been considered-neces which .the output of formaldehyde maybe greatly 15 sary to employ NO2 in amounts between 4.5 and 9 lbs. per 1000 cu. ft. of methane. I have discovered increased as compared to the output of previous processes, the emciency of ¿the manufacturing ` -.that in practicing my process I require only about process greatly increased in respect -to lthe use .29 lb. of NO2 per 1000 cu, ft. of methane. I am of gas and catalyzers, and the time for com .thus able -to reduce by more than one-half the pleting the process substantially reduced as com 20 amount of the most expensive item required in carrying out my process. ' pared .to the time formerly required. Moreover, the process of my invention may be advanta A characteristic feature of the process of my geously carried out in apparatus of compact de invention comprises the step of cooling the -vapo rized formaldehyde as it leaves the reactor' by sign at atmospheric pressure and in a continuous manner of operation. 25 direct contact ' with a formaldehyde solution. Formaldehyde will decompose rapidly at the tem Heretofore it has been considered necessary to peratures at which the gasesmust leave the re employ an air-gas mixture containing a large ex actor station. Ii' the yield of formaldehyde is rto cess of air, for example, .to five parts Aof air one be appreciable, therefore, it is necessary to cool par-t of methane. In accordance with my novel process however, we require a much smaller pro 30 the gases very rapidly. The rate of heat transfer portion of air, and may employ about equal parts ‘ between a hot gas and a solid surface is rela tively slow, and it is well known in engineering of air and methane or 30 to 50 parts methane practice that .the rapid cooling of large quantities With 70 to 50 parts air. From this striking dif of hot gases by -the use of ordinary heat transfer ference in procedure flow several extremely im portant advantages. In the ilrst place, the less 35 apparatus involves `very large surfaces and cor respondingly expensive equipment. The 4formal air used lthe higher the yield of formaldehyde -per dehyde decomposes so rapidly at the elevated volume treated and per volume of methane. This .temperatures .that a cooler is not practical if a advantage results partly from the fact that when metal wall is interposed between the cooling me~ a larger proportion of air is used in the processl a very appreciable amount oi' methane is neces 40 dium and the gas. sarily burned up and wasted. In the second place, It is not uncommon to quench the` hot gases by the use of water sprays. Such >procedure has the -smaller volume of air used results in less two principal advantages: (1) the provision of a dilution of lthe product than heretofore, so that recovery is more complete and cheaper. In the large area of contact between the gas and the third place, the reaction rate is faster and the 45 cooling medium, and (2) .the maintenance of a -maximum temperature (the boiling point of the process therefore is more emcient in -respect .to time than heretofore. Finally, since‘the dilution Water) 'of the cooling medium. However, if the of the gas is less, I come out with a more com gas contains a constituent soluble in water and bustible waste gas mixture and this may be if this constituent is present in small amounts utilized as an efficient fuel for heating the re relative to the total heat carried by the gas, then actors. ' lthe amount of water needed will be large and the resulting solution objectionably di1ute`.~ This is Heretofore a. minimum .temperature of about 1000° F. has been employed for inducing the de the problem to be solved in the present instance for. since the desired product is a relatively c_on sired oxidizing reaction, whereas I find that im proved results are attained by employing decid 55 centrated solution, the use of water would lead to .9.... » 3 2,412,014 considerable added expense for concentration. Actually the gas contains both water and form aldehyde, and the condensate naturally formed :ticularly favorable since contact of the mixture with S102 of the silica tube tends to retard oxi dation of the formaldehyde which is formed in on a cold surface would be a .fairly strong solu the reaction. tion, for example, as high as 19%. Consequently, the use of a solution approximating the concen tration of the condensible portion of .the gas re ’ The gaseousproducts of the reaction are de livered from .the silica tubes I3 of the reactors `through a manifold, not shown, into an outlet sults in a, product which requires no greater ex duct 24 in Vwhich they are Y_immediately cooled pense for concentration .than if the condensate by a spray of cool formaldehyde solution of ap were formed directly on a cold surface. In prac l0 proximately 19.2% concentration supplied by a tice, a slightly more dilute solution may be em ì spray head 28. The prompt occurrence of this ployed since the cold gas carries more water step after ythe formation of the formaldehyde vapor than the hot gases leaving the reactor. vapor eliminates any substantial decomposition By the spray-cooling step of my‘novel process of the' formaldehyde which would otherwise .- the solution picks up the heat and -this heat must 15 rapidly occur at .the .temperatures at which the be removed in the liquid~ cooler. Heat exchangers vapor must leave the reactor. ’I'he spray head for this purpose are standard equipment items ' is connected through a pipe 21 and a vertical pipe and relatively cheap. Therefore, the advantage 28 to a pump 29, which draws the cool formalde of the spray-cooling step of my process is that it. hyde solution from a storage tank 40, .the pump makes possible the substitution of .a simple and 20 having an inlet connection 30 with the tank 40.. ` .cheap spray coolerlplus a standard-design liquid 'I‘he spray head 26 has' return connections 32, cooler inv place of an expensive gas cooler which 33, 34 to a second pump 35 by which the form is impractical for formaldehyde treatment. The aldehyde solution, heated by contact with the use of .the ~formaldehyde solution corresponding vaporized product in its spraying operation, is to the condensate concentration makes it possible 25 delivered to a hot solutionI cooler 36 and then '-to do this without adding to the process the cost forced from the cooler through a .ver-tical pipe of concentrating an .aqueous solution. 31 and the horizontal pipe 38 to the storage tank 40. ’ ' 'I'he process of my invention will be best under stood and appreciated by ñrst considering the The outlet duct 24 leads from the reactor mani accompanying diagrammatic flow sheet of ap 30 fold Ito the bottom of a packed cooler condenser paratus which may be advantageously employed -tower 25. That portion of the vaporized product in carrying out my novel process, although it will not condensed by the formaldehyde spray from the spray head 26 now passes upwardly through be understood that the process is not restricted to this or to any speciñc type of apparatus; In the accompanying drawings: Fig. 1 is a diagrammatic flow sheet, and Fig. 2 is a diagrammatic view in Vertical sec .tion and in some `detail of a furnace having -tubes the condenser 25. Formaldehyde solution con densed in its progress through the condenser 25 is drawn off through pipe connections 4I-»42 and delivered to the storage .tank 40. That part of the vaporized product not condensed in the con arranged in vertical position rather than hori denser 25 passes into an outlet duct 43 which zontal as in the conventional showing in Fig. 1. 40 leads from the top of the condenser'and is carried through a refrigerated condenser 44. Formalde The flow sheet of Fis. 1 illustrates one suitable form of apparatus arranged compactly for carry hyde solution condensed from this vapor passes ing out the process of my invention in a con down through the vertical pipe 45 and back to tinuous manner. A furnace I0 is shown on the the storage tank 4I), while gases still uncondensed left hand side of .the assembly and this contains are discharged -through the waste gas stack 23 or a series of horizontal .two-pass reactors, only one are drawn from this stack through .the connection appearing in Fig. 1. Each reactor may comprise 22 for fuel. . a lower tube I I of alloy steel connected outside A portion of the formaldehyde solution pumped the furnace wall by a metal U-bend I2 to .an upwardly through the pipe 28 on its way to the upper horizontal tube I3 of silica. Natural gas 50 vspray head 26 is .deflected lby a connection“ and and air mixed in the proper proportions are de conducted through a series of tubular coolers~48 livered to the apparatus Ithrough a horizontal passing from these through the outlet pipe-48 supply pipe I4, the mixture being led down- ' which leads back to the top of the condenser wardly through a vertical pipe I5 to a blower tower 25. The cooled formaldehyde solution I6 and forced by the blower through a vertical 65 passes downwardly through .the condenser 25 in pipe I1 .to the right hand end of the tube II.v counter-flow relation to the ascending vaporized product. ~ Oxides of nitrogen are introduced into the vertical pipe I5 from a catalytic ammonia combustion An ammonia refrigeration unit 50 is provided _ unit I9 through a horizontal pipe I8. The vapor for the purpose of supplying a refrigerating me of nitrogen oxides is thus drawn into the blower, 60 dium to the condenser 44. Liquiiied ammonia forced by it into the air-gas mixture and then in gas passes upwardly from the vertical pipe 5I a turbulent current lthrough the tubes of the re and the‘horizontal pipe 52 to the condenser 44, actor. and expanding into .the condenser, is returned In -the apparatus herein shown the furnace is .through .the vertical pipe 53 to the compressor heated by natural gas fuel and the supply pipe I4 5.4. It is drawn from .the compressor 54 .throug is shown as‘connected to a fuel inlet pipeA -2| the horizontal pipe 55, to the unit 50. „ l through a connection 20. To this gaseous fuel Cooling water for .the refrigeration unit is may be added waste gas, uncondensed in its drawn from a cooling tower 58 through an outlet progress through the apparatus, taken from the pipe 51 and forced by a circulating pump 58 waste gas stack 23 through the horizontal pipe 70 upwardly through the vertical pipe 59, horizontal 22 which leads directly to the fuel inlet pipe 2i. _ pipe 60 and the vertical pipe 6I, to the main The furnace is regulated preferably so that the solution coolers 46. It is discharged from these steel tube ofthe reactor is heated to approxi coolers through the pipes 82, 63, 64, and de ` mately 900° F. and the silica tube I3 to about livered to the hot solution cooler 36. It leaves 1200° F. ‘I'hese conditions have been found par 75 the hot solution cooler through the vertical pipe 2,412,014 5 high operating pressure and the presence of solid catalysts. water is also taken _from the horizontal pipe 60 through the vertical pipe 61 toa condenser 68 connected .to the top of a rectifyingcolumn10, while the spent cooling water is discharged from the cooler 68 by the connection 82. Formaldehyde which has been collected from 6 tofore attempted which have invariably required i5 and is returned through the horizontal -pipe 68 through the top of the cooling tower. Cooling The silica tubes and their employment in .the process disclosed are not herein claimed but con stitute the subject-matter of the co-pending ap 5 plication of Raymond P. Rossman, Ser. No. 509,733, flled November 10, 1943. Having thus disclosed my invention and de scribed an illustrative example thereof, I claim the quenching station at the furnace and the two condensers 25 and 44 in .the storage tank 40 at a concentration of about 19.2% by weight is now as new and desire .to secure by Letters Patent: l. The ,process of making formaldehyde from to beconcentrated to the 38% formalin solution required in commerce. The solution withdrawnv . from the storage tank 40 contains upl to 1.5% formic acid and a small amount of acetaldehyde. The former should be removed or neutralized before concentration in order to reduce corro-4 sion in .the concentration _equipment and to pro mixture of methane and air with NO2 to a tern natural gas which includes the steps of heating a 4perature above 1100° F., and then immediately and before any substantial decomposition can take place, cooling the vaporized product by direct contact with a cool formaldehyde solution-_ 2. The process of making formaldehyde from duce an acceptable formalin product. Accord- _ ingly the 19.2% solution withdrawn from the 20 natural gas which includes the steps _of mixing methane, air and NO2, heating the mixture above 1100° F., then immediately and before any sub stantial decomposition can-take place, condens ing a portion of the vaporized product by direct storage tank 40 and pumped Íthrough the vertical pipe 28 is drawn from this pipe by a horizontal pipe 1I and conducted through the vertical pipe 12 to a boiler 13 where the formaldehyde solu .tion may be boiled with caustic, for example, 100 contact with a cool formaldehyde solution, and solution, and then passed through a connecting subsequently cooling the uncondensed vapor and thereby securing a further condensation-of form pipe 14 to a condenser 15. From the condenser aldehyde. . - to 200 lbs. of caustic to 2000 gals'. of formalin 3._ The process ofvmaking formaldehyde from it is delivered by a pipe 16 .to approximately the center of the rectification column 10. The form 30 natural gas which includes the steps o_f mixing natural gas and air in approximately equal pro alin solution is collected from the bottom of the portions, adding a nitrogen oxide as a gaseous column and delivered by connecting pipes 11 and catalyzer, subjecting the mixture to a .tempera 1l to a formalin storage tank 19. From .there it may be pumped through a delivery pipe 80 as . ture of approximately 1200" F. for an interval required. Instead of wasting the spent water 35 not longer than one second; and then rapidly . cooling 4and ‘condensing the vaporized product. from the condenser 88 by the connection 8| this 4. The process of making formaldehyde from , water may be passed through the connection si natural gas which includes the steps of mixing to the condenser 1I and returned from there 3 to 5 parts natural gas with 7 to 5 parts air> and -through the vertical pipe '82 to the cooling tower 56. ` - . An alternative form of furnace of the vertical .type suitable for carrying out the process of >our invention is shown in Fig. 2. This comprises a circular refractory body 90 having an outlet stack ll for the products of combustion. Gaseous fuel is conducted to the bottom of the furnace through a duct 92 and delivered to its interior through burner openings 83. The entire interior of the furnace is ringed with a double bank of vertical tubes. The tubes 95 of the inner -series are of alloy steel and are connected outside the .top of the furnace b'y metal U-bends .to the tubes 91 of the outer series. These Aare preferably of silica as already explained in connection with the fur-‘ nace of Fig. 1. The air-gas-NO: mixture is sup plied to the tubes 85 through anannular gas inlet manifold 84 which is located outside and below the body of the furnace. The gases delivered from the manifold $4 pass upwardly through the tubes 8l where they may be heated to a tempera -ture approaching 900° F. for example, and then pass downwardly tothe tubes l1 where they are heated to a temperature of approximately 1200’ F. Reacted vaporized product is delivered to an 40 not over '2% NO2 by volume based on total natural gas, air, and NO2, passing the mixture through a reactor at an` emerging temperature of about 1200° F., and immediately condensing a portion of the yvaporized product by direct con 45 tact with aspray of cool formaldehyde solution thereby substantially eliminating decomposition of the formaldehyde which would otherwise _occur at the temperature at which .the vaporized prod 50 uct issues from the reactor. 5. The process of making formaldehyde from natural gas which 4includes the steps of mixing natural gas with air in substantially equaLpro-4 portions,~adding not over 2% NO2 by volume based on total natural gas, air, and NO2, pass-' 55 ing the mixture through a reactor at approxi mately 1200° F., immediately condensing the 4vaporized product .by direct contact with cool formaldehyde solution thereby eliminating de composition of the formaldehyde which would 60 otherwise occur -at the temperature at which the vaporized product issues from the reactor, and then concentrating the solution by vacuum recti flcation. 6. The process of making formaldehyde from annular outlet manifold Il and thence conducted 65 natural gas which includes thev steps of mixing methane, airand NO2, heating the gas mixture - to a station at which the quenching operation is` above 1100‘I F., and then condensing .the vapo effected by a spray of cool formaldehyde solution rized gas mixture by direct and immediate con as outlined in the explanation of the flow sheet of tact with a formaldehyde solution of substantially Pig. 1 or the quenching step may be carried outA 70 the same concentration'as that resulting from directly in the manifold Il. the condensation of the reacted gas mixture, and It will be noted that the apparatus above de thereby eliminating 'decomposition of the re 'scribed is designed to be operated at atmospheric pressure. This is a characteristic and very im portant feature of the process of my invention v acted mixture which would otherwise occur at andonethstdistinnuishesltfromproccsles'here 76 awroximßml 1100° F. THOMAS S» BmWOOD.