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(6) Emerson, Ralph, and Allen, P. J., unpublished maiiuaciipt. (7) Hauser, E. A., and leBeau, D. S.,I n d i a Rubber World, 106, 447-49 (1942). ( 8 ) Ibid., 107, 568-70 (1943). (9) Houwink, R., Rubber Chem. Technol., 16, 571-590 (1943); reprinted from I n d i a Rubber W o r l d , 107, 369-77 (1943). (10) Lloyd, F. E., P l a n t Physiol., 7, 131-8 (1932). (11) Miehe, Hugo, "Die Selbsteihitsung des Heus. Eine biologische Studie," Jena, Gustav Fischer, 1907. (12) Nishimura, M. S., Hirosawa, F. N., and Emerson, Robert, IND. ENG.CHEX.,39, 1477-85 (1947). (13) Spence, D., Ibid., 22, 384-7 (1930). (14) Spence, D., U. S. Patent 1,918,671(July 18, 1933). (15) Spence, D., and Boone, C. E., Natl. Bur. Standards, Tech. P a p e r 353 (1927). (16) Spence, D., and Caldwell, M. L., IND. ENG.CHEM., ANAL.ED., 5, 371-5 (1933).
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(17) Spence, D., and van Niel, C. B., IND.ENG.CHEM.,28, 847-50 (1936). (1s) Stoller, B. B., Smith, F. B., and Brown, P. E., J . Am. SOC. Agron., 29, 717-23 (1937). (19) Takamine, Jokiohi, IND.ENG.CHEM., 6,824-8 (1914). (20) Vavilov, N. I., T r u d y , Priklad. Botan., Genetike i SelektsiI, 26, 201-67 (1931). (21) Walter, E. D., J.Am. Chem. SOC., 66,419-21 (1944). (22) Whitby, G. S.,"Monographs on Industrial Chemistry. Planta. tion Rubber and Testing of Rubber," London and New York, Longmans, Green & Co., 1920 (23) White, J. W., Naghski, J., Allen, P. J., Hoover, S. R., and Willaman, J. J., I n d i a Rubber W o r l d , 111, 570-3 (1945). (24) Willits, C. O., Swain, M. L., and Ogg, C. L., IND. EXG.CHEM., Aii.41,. ED.,18, 439-42 (1946). R&EIVEDOctober 22, 1947.
hase Oxidation of Furfural ERIK R. NIELSEN' The Quaker Oats Compuny, Chicago, I l l .
HE catalytic vapor It has been shown that maleic acid can be produced to recover uncow from furfural in yields above 75%, based on the furfural verted furfural with the above phase oxidation of furan scrubbing system, the runs compounds has attracted conconverted. A method of depositing a catalyst on a carrier were made under such condisiderable attention since the in emulsion form is described. The importance of not cooling down the catalyst,between experiments has been tions that 95% Or better of advent of COmmercial furfural. In 1928, Sessions ( 6 ) demonstrated and i t has been shown that a catalyst can be the was reported that he had obdeveloped by subjecting it to air and heat alone. It has except for experiments of been shown also that nickel is a superior catalyst tube Short duration. The only tained, a t best, a 12.2% yield runs of the latter type are of theory of maleic acid from material for this oxidation process. those shown in Figure 7. The furfural. Zumstein (7), in position of the thermometer 1929, stated that maleic acid could be produced by the vapor phase oxidation of furfural in bulb was chosen on the basis of the color development noted duryields of 30 to 359& of theory and in 1934 (8),reported a 90% ing the continued use of a vanadium pentoxide-molybdenum trioxide catalyst, modified by phosphoric acid and iron molybdate. yield of theory. Milas and Walsh (4), in 1935, reported that the vapor phase oxidation of furfuryl alcohol, furfural, furoic acid, and The color of the first quarter of the catalyst bed varied from a furan produced yields, in the above order, of from 22.5 to 65y0 rust-brown at the point of entrance of the furfural-air mixture to green a t the other end of the section. This lower part of the bed of maleic acid of theory. They further stated that no more than 25% of maleic acid could be expected from furfural, because of the served primarily to preheat the gas mixture and little oxidation took place here, except a t the end where the color had changed latter's tendency t o polymerize. The present paper is a report to green. The center of the bed (about half of the catalyst mass) of later work in the field and prefients studies in catalyst preparation and aging and choice of batalyst tube materials. was black and was believed to be the zone of niaximum activity because it showed the greatest change in color. This section CATALYST FURNACES extended to about 10 em. below the toD tee-that is, the thermometer bulb (13 em. below the top tee) registered the temMost of the work was carried out in the type of equipment perature at a point of maximum activity. shown in Figure 1. Metered filtered a h (0.7 kg. per square The choice of nickel and aluminum as tube materials was made em.) was passed into the center tube of the furfural carburetor after an extensive study. I n 1926, Downs ( 1 ) reported on a steel and the furfural feed was regulated by varying the temperature tube furnace and stated that such a tube was without catalytic of the furfural and the flow rate of the air. Metered secondary effect when used in the study of the vapor phase oxidation of air was added to the furfural vapor-air mixture before i t entered organic compounds. Marek and Hahn (3) state in their monothe catalyst tube. To prevent condensation, the tee was heated graph that iron, silica, and aluminum are noncatalgtic materials by means of resistance wire. with respect to the vapor phase oxidation of benzene and derivaThe catalyst tube was a 2.54-cm. nickel or aluminum pipe tives. The earlier experiments therefore were carried out in with a tee a t each end and wound evenly with resistance wire for steel tubes. Later it was found that nickel, aluminum, and heating. The capacity of the heater was 270 watts at 110 volts. stainless steel all were superior to steel as a tube material. Thus, It was hooked up in series with a slide-wire resistance for variain one series of experiments, nickel, aluminum, and steel were tion of the input and the current was drawn through a constant compared. Three tubes were charged mith 192 cc. of catalyst voltage transformer to ensure uniformity at a given setting of the each (catalyst 1, the preparation of which will be described below). resistance. The bulb of a thermometer or the end of a thermoThe tubes were kept hot and fed furfural continuously during the couple was positioned 13 cm. below the lower edge of the upper investigation. Performance was checked in 16- t o 18-hour runs: tee. The capacity was about 192 cc. and the length of the catalyst 0.25 to 0.35 gram of furfural per hour and 8 liters of air per minute bed was 38 em. The scrubber consisted of five Erlenmeyer flasks a t a temperature of 270" C. Figure 2 shows that nickel and (500 cc.) connected in series (only one shown). Since i t was aluminum both are better than steel, but that nickel is outstanding. 1 Present address The Armour Research Foundation, Chicago 16, Ill.
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Figure 1. Test Apparatus
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air per minute; temperature, 270" C. ; furfural convcrsioIi, 957, or better. The data are shown in Figure 3. The curves shom that i t is desirable to let the promoter form in place as the catalyst develops a t a faster rate. In time, both catalysts probably m ould have given substantially the same yields as indicated by the slopes of the curves. This methad of distributing a small amount of a n insoluble promoter over the bulk of the catalyst should have general application (6). At the time this investigation was made, it was intended to study only a catalyst in which the promoter had been formed in place and t o compare the data with those obtained previously with the regular catalyst 1 (Figure 2 ) . However, because new lots of raw materials had to be used, it was decided also to prepare and study a fresh batch of the regular catalyst 1 (promoted with iron molybdate, &s such) to be sure of making a fair comparison. A comparison of the data obtained on the latter catalyst with those obtained previously on the regular catalyst 1 (aluminum tube data, Figure 2 ) show that one batch (Figure 3) cured a t a faster rate than the other (Figure 2 ) . This is a n illustration of the difficulty, if not impossibility, of duplicating exactly a catalyst from time to time and is a point which must be carefully considered when making comparative studies. The conventional method of cvaporating an agitated catalyst suspension to dryness, in the presence of the carrier, is subject to the objection that the catalyst becomes contaminated because of the erosive action of the carrier on the vessel used in the preparation of the catalyst. This difficulty was overcome by converting the suspension into an emulsion by adding furfural under agitation. After the liquid phase has been saturated with furfural, an emulsion starts to form. The viscosity of the cmulsion mag hr varied within wide limits, but a viscosity about likc that
I n a similar investigation, aluminum was compared Tyith steel which had been sprayed with 18-S stainless steel. The latter was found t o be as good a tube material as aluminum but not any better. It might be assumed a t f i s t that the possibility of rust formation was t'he explanation of the inferiority of steel as iron oxide is known to promote complete combustion. However, this docs not explain why nickel was found to be superior to aluminurn and stainless steel. It may be a fair assumption that nickel is a good catalyst for one of the steps in t,he oxidation process. CATALYSTS AND CARRIER
Grained aluminum w a selected as the standard carrier and most of the work mas carried out with one catalyst-that is, catalyst I-which was one of the catalysts disclosed in a private communication by Zumstein (9). Zumstein claimed 70 to 75a/, yields for this catalyst; the method of preparation ( 9 ) was as folloTm : Twenty grams of ammonium m-vanadate, 5 grams of a,rnmo~ ~ , 2.5 grams of iron nium molybdate, ( K H I ) & ~ O & . ~ H and molybdate are suspended in water contained in a porcelain waporat,ing dish. Next, 25 cc. of concentrated ammonia is added, followed by 6 grams of ,85% phosphoric acid which has in advance been neutralized with ammonia. Finally, the carrier is added (250 cc.) and the whole evaporated to dryness Rhile stirring. Care must be taken not to decompose the ammonium salts by overheating. Since it was found to be difficult to prepare iron niolybdate of uniform catalytic activity, it was decided later not to use iron molybdate as such, but t o add instead an equivalent mixture of iron nitrate and ammonium molybdate. A sample of the best iron molybdate therefore was analyzed. Next, two catalysts were prepared. One was prepared with the iron molybdate and according to the method described. For the other catalyst, separate solutions of Iron nit'rate and ammonium molybdate m-ere prepared in amounts equivalent to the iron molybdate of the first catalyst and mixed to produce a suspension of iron molybdate. The remaining ingredients of catalyst 1 then were added, in the manner already described. The performance of the two cat,alysts was checked in 16- to 18-hour runs: 0.25 t.0 0.35 gram of furfural per hour; 4 liters of
Calalyst A g e , Weeks
Figure 2. Camparison of Nickel, Aluminum, and Iron as Tube Materials Using Catalyst 1 (Iron Molybdate, Lot 1)
0 e
-.U
s
Catalyst Age, Weeks
Figure 3. Comparison of Iron RIolybdute (Lot 1) with Iron Nitrate and Ammonium \Iolybdate as Promoters Catalyst 1, aluminum tub
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I
I
Catalyst Age, Weeks
Figure 4.
Effect on Yield of Cooling Down a Catalyst Cntalymt 2, a l u m i n u m tubes
of mayonnaise is preferred. The carrier is folded into the emulsion and the coated carrier spread out to dry. The emulsion does not break down visibly while drying onto the carrier (6). EXPERIMENTAL AND ANALYTICAL METHODS
A fresh catalyst first was treated with air a t 300" C. for 24 hours to decompose the ammonium salts. Next, the catalyst was cured for several days at 250' C. before making analytical runs t o establish the optimum temperature for B the catalyst. Further U curing was then con80 ducted a t the optimum *z or higher temperature. At no time was the cat
