Formic Acid rates through a platinum tube N RECEST A study was made of the dehydration of h e a t e d t o 1160" C. T h e y years the in€ormic acid vapor over the following cataconcluded that the carbon monvestigation lysts : activated alumina, silica gel, thoriaoxide in the gaseous products of high-pressure synthetic reacsilica gel. phosphorus pentoxide-silica gel, resulted from a secondary reactions involving carbon monoxide, aluminum phosphate, and titania-silica tion, such as the formation of methyl gel. Over the temperature range and and higher alcohols, has occuH:: -t co2 = co -I- HzO ( 5 ) pied a prominent part in the space velocities employed, the thoria-silica instead of from the primayy research program of many ingel catalyst proved to be the most efficient decomposition of formic acid stitutional and industrial laborain the yield and purity of carbon monoxide rapor according t o reaction 2. tories. While the c a t a l y t i c obtained. Hinshelwood, Hartley, and synthesis of methyl alcohol is Topley (2), on the other hand, The results from this investigation indinow on an i n d u s t r i a l scale, claim that the effect of react h e r e s t i l l r e m a i n s a large cate that, for small-scale production of 5 is negligible a t 350" C, tion amount of work to be clone on carbon monoxide, the catalytic dehydration They also show ( I ) that the exthe efficient production of higher of formic acid vapor may advantageously tent of reaction 2 is dependent alcohols. One of the difficulreplace the usual liquid-phase dehydration. upon the products formed. ties attending the small-scale Kelson and Engelder (6)using l a b o r a t o r y r e s e a r c h is the different t y p e s of r e a c t i o n simple, cheap, and efficient proE. G. GRAEBER AND D. S. CKYDER t u b e s f o u n d t h a t reaction 1 duction of carbon monoxide. normally takes place in addition The usual method consists in Pennsylvania State College, State College, Pa. to a small percentage of reacthe dehydration of formic acid tion 3. Thev state further that bv means of sulfuric or phosp6oric acids, the acids being contained in either glass or the carbon monoxide formed comes either from the decomacid-resistant containers. The disadvantages to this method position of the acid or from the decomposition of the formalinclude the breakage or leakage of containers, the handehyde. dling of strong acids, the construction of cumbersonie equipment for relatively small amounts of carbon monoxide, and Rlaterials the difficulty in the control of the reaction. The catalytic The formic acid used in this investigation was prepared dehydration of formic acid in the vapor phase eliminates Irom 86 per cent acid by dehydration with either phosphoric the use of sulfuric or phosphoric acid and offers an easily anhydride according t o Jones (5') or anhydrous copper bulcontrolled method for the production of carbon monoxide. fate. The resulting mixture xyas distilled through a small The thermal decomposition of formic acid may proceed in rectifying column which had the equivalent of eight theoretiseveral ways as illustrated by the following equations ; cal plates. The purity of the acid prepared by t)he Jones method was 98.3 per cent, while the acid prepared by dehyHCOOH = COe f Hz HCOOH = CO f H20 dration with anhydrous copper sulfate mas 98.0 per cent pure. SHCOOH = COz HzO HCHO Catalysts The formaldehyde produced by reaction 3 may reduce formic SILICAGEL. The silica gel (6 to 10 mesh) was first washed acid further according to the equation : with dilute hydrochloric acid to remove nietallic impurities HCOOH HCHO == GO, CHZOIE and then tempered by heating carefully in an open dish over a (4) Bunsen burner. Previous investigators have studied the course of the dePHOSPHORVS PENTOXLDE ON SILICAGEL. Sufficient 86 per cent solution of phosphoric acid was added to cover the composition reactions over various catalysts but not with the silica gel, and the mixture was heated to dryness over a Bunparticular object of producing carbon monoxide according sen burner. to reaction 2. THORIAON SILIC-4GEL. Twenty cubic centimeters of Sabatier and Maihle (7) studied the decomposition of thorium nitrate were added to 30 cc. of silica gel. Kitric formic acid vapor over various dehydrogenating and dehyacid was added to form a thick paste and the mass slowly drating catalysts. Those catalysts of the latter type which favor the formation of carbon monoxide according to reaction heated until all the nitrogen oxides mere driven off. TITANIA ON SILICAGEL. A 15 per cent solution of ti2 include titanium oxide, blue oxide of tungsten, and alumitanium chloride was added to the silica gel to form a paste. num oxide. No comprehensive comparative data are given. The mixture was then heated slowly over a flame until a pure Wescstt and Engelder (8) passed formic acid vapor tlpough an unglazed clay combustion tube containing alumiwhite color developed. ALUMINA. Activated alumina (10 to 20 mesh) obtained num oxide, titanium oxide, and reduced nickel as catalysts. from the Alcoa Ore Company was used. The aluminum oxide catalyst a t 287" C. gave a carbon monALUMINUM PHOSPEATE. Three hundred grams of alumioxide gas of the highest purity (92 ger cent). num nitrate mere dissolved in 2 liters of water. The alumiMuller and Peytral(5) passed formic acid vapor at different
-+
+
+
+
828
JULY, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
was washed by decantat:on until free from nitrates.” then filtered, washed, dried, and weighed. The exact amount of phosphoric acid to form aluminum phosphate was added, arid the mixture was dried and screened to 10 t o 20 mesh.
Apparatus and Procedure The essential features of the apparatus employed are shown diagrammatically in Figure 1 :
FIGURES 2 AND 3. EFFECTOF TEMPERATURE AND SPACE VELOCITY ON PERFORNANCE OF THORIA-SILICA GEL CATALYST Per cent carbon monoxide in gaseous product u s . apace velocity Figure 3 (below). Per cent decomposition of formic acid vs. apace velocity Figure 2 (above).
A
I,
The constant feed device consisted of a &foot (0.9meter) section of 48-mm. Pyrex tubing, B, connected by 5-mm. capillary tubing t o the graduated tube, F. Mercury was placed in the large tube until it rose above the rubber stopper. Formic acid was then introduced through the side arm, G, to a convenient level. By allowing a controlled flow of water t o enter the large tube from the constant-head device, A , the formic acid was forced into the heated section, H , where it was vaporized before entering the reaction chamber, C. By means of this feed device, rates as low as 4 cc. of formic acid per hour could be accurately measured. The reaction chamber ronsisted of 21 inches (53.3 cm.) of 18-mm. Pyrex tubing wound with 1/18 .inch (1.6 mm.) nichrome ribbon. This was covered with a 1.5-inch (3.8-cm.) layer of magnesia lagging. From the reaction chamber the exit gsses passed to the first of the two collecting bottles, E, containing a saturated sodium chloride solution. With the catalyst tube at the desired temperature, water was admitted to the large tube, B , from the constant-head bottle to give the desired rat,e of flow of formic acid. After the residual air had been flushed from the system, the gaseous products were collected in the first receiver, the pressure on the system being maintained constant by siphoning the liquid from the second container. In the initial experiments the exit gases were collected by bubbling up through the retaining solution, the pressure on t’he system being regulated by the rate of siphoning the liquid from the container. By this method the retaining solution was saturabed with the gas to be analyzed, and no errors due to absorption were introduced into the gas analysis. It was found, however, to be exceedingly difficult to maintain a constant rate of flow of vapors over the catalyst. In addition, pulsations caused by the
a29
CATAL YTIc D E ~ U RATION O
Lutz (4)has investigated the errors introduced in gas analysis by the solubility of carbon dioxide in retaining solutions, and his results encouraged the belief that the method of direct aspiration over the solution was feasible. The retaining solution was prepared as follows: To a saturated sodium chloride solution was added a small amount of sodium carbonate, and then hydrochloric acid until the solution was barely acid. The solution was then stirred in contact with air until all excess carbon dioxide was released. Using this solution, Lutz found that a total of 0.7 cc. of carbon dioxide was dissolved from 100 cc. of a gas mixture containing 17.6 per cent carbon dioxide under the conditions of use in gas analysis. Lutz also found that the absorption of carbon dioxide occurred mainly in the liquid draining the walls of the buret. The data covered a wide range of gas mixtures and showed the solubility to be much less for smaller partial pressures of carbon dioxide. Since, in the most significant data of the present investigation, the carbon dioxide content of the exit gases was less than 10 per cent, and since the area of the liquid draining the sides of the container is small compared to the volume of the contained gahes, the error introduced into the gas analysis by absorption of carbon dioxide should be much less than the figure quoted above. Preliminary experiments using this method of gas collection were made. The gas was sampled directly from the exit line during the course of a run and from the receiver after the gas had been collected. For gas mixtures containing the maximum carbon dioxide (about 20 per cent) the difference between the two analyses was less than 1.0 per cent carbon dioxide. For the majority of runs where the carbon dioxide content was 5.0 per cent or less, the difference could not be detected. Accordingly, two containers were connected by a liquid bridge as shown in Figure 1, and the solution was siphoned from the second container. Precise control of vapor flow was possible with this arrangement. Preceding each run, the salt solution was “standardized” by recarbonizing as above and agitating in contact with air. Occasionally gas samples were withdrawn from the gas line to serve as a check on the accuracy of the gas analysis. The condensate in trap D was divided into two parts; one part was titrated for undecomposed acid, the other part ex-
1SDUSTR IAL AND ENGINEERING CHEJIZSTKY
538
aniined for formaldeligde by means of Schiff 'a reagent. The formation of formaldehyde was negligible in all cases except n-ith activated alumina. Carbon dioxide was absorbed in 40 per cent potassium hydroxide solution, oxygen in 25 per cent pyrogallol solution, and carbon monoxide in a solution of ammoniacal cuprous chloride, and hydrogen m s determined by conibu t'ion over copper oxide a t 300" C.
Discussion of Results Material balances on carbon were made for each run and gave satisfactory checks. The greatest deviation was 5.0 per cent. To eliminate errors due t o the decrease in catalyst activity from prolonged usage. all catalysts were renewed eyery ten runs, the last run duplicating an earlier run to serve I
V O L . 27, TUO. I
poor, resulting in a gas of lower carbon monoxide content and higher carbon dioxide and hydrogen. As the space velocity is increased, the carbon monoxide reaches a maximum value which i s independent of further increase in space yelocity. However, Figure 3 shows that a t these higher space velocities the catalyst i s less efficient in decomposing the forniic acid. At 300" C., for example, and a space velocity of 2.8 there remains undecornposed about, 16,O per cent 06 the original formic acid, Figures 2 and 3 also show that the capacity for decomposing formic acid increases with increase of temperature, but a t the same time the purity of gas is decreased. I n other words, to secure the maximum amount of a gas rich in carbon monoxide from a given quantity of formic acid it is necessary to use a low temperature and an intermediate rate of feed. Higher rates of production of the same gas require additional formic acid per unit of carbon monoxide produced. These curves are, in general, characteristic of the performance of the other catalysts investigated. The gaseous products are carbon monoxidepcarbon dioxide, and hydrogen (the latter two in approximately equal amounts). By absorbing the carbon dioxide in alkaline solutions, the percentage of carbon monoxide is increased and hydrogen is left as the only impurity. By reference to Figure 2, a simple calculation will show that a t 280" C, it is thus possible to secure a gas mixture containing 99.0 per cent carbon monoxide and 1.0 per cent hydrogen. The presence of hydrogen will not interfere with the use of the carbon monoxide in the high.-pressure synthesis of alcohols. TABLE
r,
~ o m m s o No r ~AriaLvfirs
---Max. Catalyst
Deoompn. &--a Formic Acid t o 60 Temp.$ Space % CO ' C. velocity in gas 280 94.8 0.45 3.35 90.4 330 0.21 87.6 300 92.8 0.46 300 280
300
0.71.
0.49
98.1.
90.4
CO in.-------, Gaseous Product5 Space % deoompn. velocity to CO 0.71 23.8 2.83 (7.8 1.05 32.3 0.46 90.3 1.06 94.4 2.08 66.8
,------- Max.
'$emp.,
C.
280 300 240 300 280 300
~
FIGURE$ 4 AND 5. EFFECT OF TEMPERATURE ON
OPTIMUM
PERFORMANCE
OF
VABIOUS
CATALYSTS
(above). Maximum decompositioii of formic acid AS. temperature Figure 5 (below). Maximum carbon monoxide i n gaseous products b s . temperature
Figure 4
as a check on the activity of the catalyst. Each catalyst was tested over a temperature range from 280" to 380" C. and a range of space velocities (cc. per minute of formic acid vapor a t normal temperature and pressure per cc. of catalyst) from 1.0 to 3.0. The efficiency of a catalyst for the production of carbon monoxide from formic acid must be judged not only by its selective action but also by its activity. d gas rich in carbon monoxide is desired, and in addition a high percentage of formic acid must enter into the reaction even a t the higher space velocities. On this basis the thoria-silica gel catalyst proved to be the most efficient of those investigated. The data for its performance are plotted in Figures 2 and 3. Figure 2 shoivs that a t low space velocities the selective action of the catalyst is
The most significant data on the comparative perEormsiice 01 the various catalysts investigated is shown in Figures 4 and 5 and in Table 1, For each temperature B series of runs was made at varying space velocities, The maximum dscompobition of formic acid and carbon monoxide content of the gas were noted for each series, Figures 4 and 6 are plots of fhcse riiaximurn points. %nTable I are listed supplementary data corresponding to the maximum decomposition of formic acid and highest carbon monoxide content of the gas obtainable with each catalyst for the range of temperature employed. From an examination of the data it n~oulclappear that the phosphoric pentoxide-silica gel catalyst is the most efficient an the dehydration of formic acid at low temperature.. Nilmerous tests have shown, however, that the life of this catalyst i s comparatively short. Its action appears to be one of straight chemical combination rather than catalytic dehydration. In one run a t 280" C. and a space velocity of 0.96, during which this catalyst was subjected to 32 hours of con tinual use, the percentage decomposition of formic acid to carbon monoxide decreased from 96.0 to 65.0 per sent, The life of the titanium oxide-silica gel catalyst i s alqo comparatively short, A supplementary series of runs was condueted wing a larger reaction tube and higher rates of ked. The results froni this apparatus of higher mpa city cbecked closely with the results from the smaller apparatus. Thus, with a 2-inch (S-cm,) reaction tube containing 130 cc, of tho thoria Gatalyqt a t 360" C., and using a sate of feed corresponding to a space
INDUSTRIAL AND ENGINEERING CHEMISTRY
JULY, 1935
velocity of 3.0, it is possible to obtain 5.25 liters per hour of a gas containing 90.4 per cent of carbon monoxide. Upon the removal of carbon dioxide this figure would be raised to 95.0 per cent. As shown by the graphs, higher rates of production of the same gas are possible with no increased consumption of formic acid. Insufficient data are presented in this investigation to warrant any conclusions as to the probable course of reactions occurring. It appears, that the main reaction is one of the direct dehydration of the formic acid, with the secondary formation of carbon dioxide and hydrogen either by direct dehydrogenation of formic acid according to reaction 1 or by the interaction of carbon monoxide and water vapor according to reaction 5. No evidence of formaldehyde or methyl alcohol in the condensable products of dehydration was found except with the alumina catalyst. In this case formal-
834
dehyde was indicated by Schiff’s reagent but the amount was small enough to be neglected in the calculations.
Literature Cited (1) Hinshelwood, C. N., and Hartley, H., J . Chem. Sac., 123, 1333 (1923). (2) Hinshelwood, C. N., Hartley, H., and Topley, B., Proc. Roy. Soc. (London), 100, 575 (1922). (3) Jones, D. C., J. Soc. C h m . Znd., 38, 362 (1919). (4) Luta, W. A., Master’s Thesis, Pennsylvania State College, 1934. (5) Muller, J. A., and Peytral, E., Bull. soc. chim., 29, 34 (1921). (6) Nelson, W. L., and Engelder, C. J., J. Phys. Chem., 30, 470 (1926). (7) Sabatier, P , and Maihle, A., Compt. rend., 152, 1212 (1911). (8) Wescott, B. B., and Engelder, C. J., J. Phys. Chem., 30, 476 (1926).
R ~ C E I V EJanuary D 21, 1935. The data of this paper are presented by E. G. Graeber in partial fulfillmentof the requirement8 for the M. S. degree in
chemical engineering, Pennsylvania State College.
Semi-Commercial Drying of Pressboard by Measuring Its Electrical Resistance E. R. WHITTEMORE, C. B. OVERMAN, WINGFIELD
AND BAKER
National Bureau of Standards, Washington, D. C.
D
URING experimental work on the production of pressboard from cornstalks it be-
came necessary to find some satisfactory method for measuring approximately the maximum moisture content at which the board could be safely removed from the hot press. This information is essential for proper control in manufacture. The expansion of entrapped steam in underdried boards results in the formation of surface blisters, and to dry boards longer than necessary to prevent blistering is uneconomical with regard to steam consumption and press output. The following four methods were investigated as means for indicating the point of safe release of boards in the hot press: the determination of an actual drying curve by trial, of platen temperature, of board temperature, and of the electrical resistance of the board.
Experimental Procedure In the preparation of pressboards from cornstalkg, the prepared pulp was formed into a continuous mat on the board-forming machine. The mat was cut into sections about 30 inches square, and each section was pressed in a cold press until it contained approximately 60 per cent moisture. The small electrical press required mats about 9 X 12 inches, and the large steam-heated press could accommodate mats 30 x 30 inches. One or more mats, on one side of which was placed a polished steel plate and on the other side a No. 20 bronze screen (both plate and screen extending beyond the edges of the mat), were inserted between the platens of the preps. Pressure was applied slowly, to avoid crushing, up to about 200 pounds per square inch and maintained at this value
@
Experimental Study *
In the production of pressboards from cornstalks, it was necessary to develop a method for determining the maximum moisture content at which the boards can be safely removed from the hot press without danger of the development of steam blisters which result from underdrying. Further drying is uneconomical as regards both steam consumption and press output. Following the platen and board temperatures or making a time-moisture curve is unsatisfactory, but measurement of the electrical resistance is feasible for determining the safe minimum time for removal of the board from the hot press. during the drying process. Fifty pounds per square inch steam pressure was held in the platens of the steam press. PRELIMINARY METHODS. The trial drying or moisturetime method, which consisted in determining (Figure 3) the minimum time required to produce unruptured boards of equal area and increasing quantities of bone-dry pulp, showed that it was not possible to construct a curve correlating time and thickness with an accuracv satisfactosv for application in a commercial plant. The platen temperature method, which consisted in determining the temDerature of the platens during the drying process and releasing the
