?@
INDUSTRIAL A N D E,VGINEERISG C H E X I S T R Y
various times. The results are all in close enough agreement to warrant the followine conclusions : v
1-On the basis of the 1922-23 results, the volume of marc in 26 grams of cossettes is very close to 0.6 ml., so that, if the COSsette flask is graduated to take account of marc alone, its capacity should be 200.6 ml., the volume now usually employed. If the flask is graduated to take account of the combined marc and lead precipitate, and there seems to be no good reason why this is not a better basis than the marc alone, the volume should be 200.9 ml. 2-The 1922-23 beets are abnormally low in marc as well as sugar. A range of 4.00 to 4.25 per cent would probably not underestimate the average marc content of Colorado and Nebraska beets, With a marc content of 4.00 to 4.25 Der cent. the volume allowance for the combined marc and lead precipitate
Vol. 15, No. 8
would be about 1.0 ml., and the cossette flask should accordingly be graduated a t 201.0 ml. 3-The employment of a volume of 201.0 ml. for the cossette flask in place of 200.6 ml. would lower the polarization of a 16 per cent beet to the extent of 0.03. The error under the present volume allowance is therefore almost negligible, but there is no reason why the cossette flask should not be regraduated to conform with the best available data.
ACKNOWLEDGMENT The writer's thanks are hereby expressed to C. C. Crawford, Geo. Goldfain, G. E. Stevens, and J. H. Zisch for the data and ideas in the of the investigation.
Conversion of Methyl Chloride to Methanol-11' By Ralph H. McKee and Stephen P. Burke COLUMBIA UNIVERSITY, NEWY O R X , ii.
N ORDER to interpret
I
the results obtained in the experimental work described in Part I, it was found. necessary to investigate in some degree the simultaneous reactions occurring in the reaction chamber. Ca(0H)z = CaO
+ HzO
(1)
In Part I the authors have shown, both experimentally and theoretically, that it is impossible to effect the direct hydrolysis of methyl chloride to yield methanol by means of steam alone. An experimental investigation of the use of metallic hydroxides to &ct this conversion was described, and it was shown that calcium hydroxide is the most advantageous. B y passing methyl chloride mixed with steam over calcium hydroxide at elevated temperatures, 95 per cent of the methyl chloride is converted into methanol and methyl ether, the remainder undergoing decomposition. A theoretical study of the reacting system was made and by means of an approximate calculation' of the free energy relationships (Nernst's heat theorem) the equilibrium points of the reactions inuolued were determined. The experimental results have been found to be in very good agreement with the theoretical values. In this article the simultaneous or side reactions encountered are studied, and detailed analyses of the factors and conditions influencing the conversion of methyl chloride to methanol are made. A catalytic process for the conoersion to methanol of the methyl ether obtained as a by-product is presented. I n conclusion, a brief rationale of the process is given and estimated production costs of methanol by this process are shown.
In order to determine whether, under the conditions obtaining during the runs discussed in Part I, any decomposition of the calcium hydroxide took place, the calcium hydroxide and chloride residues were examined for the presence of calcium oxide in many cases where anhydrous methyl chloride was used in the experiment. Its presence was detected only in very small amounts a t 400" and 450' C. This was to be expected, however, for at 350" C. the partial pressure of water due to this decomposition does not exceed 14 mm.2 It may be pointed out here that under these conditions magnesium hydroxide would be very unstable, for the partial pressure of water from magnesium hydroxide becomes equal to one atniosphere a t a temperature slightly above 200" C. For this reason it is far less desirable than calcium hydroxide in effecting the conversion of methyl chloride. CaClz
+ HzO = Ca(0H)Z + 2HC1
(2)
No quantitative data on the extent of this reaction could be found in the literature. Therefore, a number of experiments were performed a t 350' C., with partial pressures of water in excess of 600 mm. These experiments were cawied out using part of the apparatus shown in Fig. 1 of Part I. The reaction tube was charged with C. P. anhydrous calcium chbride (containing approximately 10 per cent moisture) of 12-mesh size. Air was passed slowly through the humidifier heated to 93' C. (vapor pressure of water = 590 mm.), and thence through the reaction chamber, and on through the 1 2
Y.
Received December 4, 1922. Part I, THISJOURNAL, 18, 682 (1923). Dragert, Inaugural Dissertation, University of Berlin, 1914.
absorption bulbs containing distilled water with R few drops of phenolphthalein. The hydrogen chloride produced by thereaction was collected in the absorption train, and a t equal time intervals it was titrated with standard 0.1 N sodium hydroxide, The results obtained show that under these conditions, even at vapor pressures exceeding 600 mm., over a period of time greatly in excess of that required for the conversion of methyl chloride, the hydrolysis of calcium chloride would not exceed 2.5 per cent by weight. Thus, it can be concluded that the hydrolysis of the calcium chloride
formed in the reaction Ca(0H)n
4- 2CH3C1 =
CaClz 3- 2CHaOH
(3)
by the presence of steam is practically inappreciable, and hence, that the displacement of the equilibrium of this reaction is negligible. Any displacement of the equilibrium to the right due to the hydrolysis of calcium chloride would probably be neutralized by the immediate reaction of hydrochloric acid with methanol. STUDYOF REACTION: CaClz 2CH30H = Ca(OH)z 2CH3Cl-This reaction, which is the reverse of that used to effect the conversion of methyl chloride to methanol, was investigated to determine the extent to which it could be carried out. The experimental method used here was very similar to that employed in the investigation of the hydrolysis of calcium chloride. The reaction tube was filled with C. P. anhydrous calcium chloride, and air was sent slowly through the humidifier and on through the reaction tube. In this case, however, the humidifier contained absolute methanol. The partial pressure of'the methanol was maintained as near to one atmosphere as possible. The absorption train was replaced by a 4-liter gas collection bottle, and the gases produced were collected directly. Several experiments were run with the same result. The methanol used (50 grams) was
+
+
IhTD USTRIAL AiTD EKGINEERISG CHEXISII'RY
August, 1923
789
The commercial methyl chloride was passed through the apparatus shown in Fig. 1, Part I, the reaction tube being filled vith pure silica sand. Trials were made a t temperatures of 200°, 300", 400°, and 500' C., using rates about the same as those employed in the conversion runs. It was found that while decomposition was observable by the formation of traces of carbon and hydrogen chloride a t 300" C., it did not become appreciable until 400' C. The results obtained are shown graphically by Curve 12A. T h e , analysis of the gas received showed that methane was formed, but that hydrogen and ethylene were absent. Carbon and hydrogen chloride were ' also formed. Hence, under these conditions the reaction probably is 2CHsCI +C $- 2HC1 CHa (7) It has been observed that barium chloride acts catalytically in the decomposition of ethyl chloride under similar condit i o m 8 Hence, the foregoing experiments were repeated , using calcium chloride instead of silica in the reaction tube, to determine whether the former had any catalytic effect. The decomposition was not increased, however. STUDYOF REACTION:CH30H HC1 = CHsC1 H20 (8)-This reaction, which is the reverse of the direct hydrolysis of methyl chloride by steam, has already been fully discussed, and it has been shown that the equilibrium point is CHsOH ---f CO CH4 Hz (4) far over to the right. Hence, this reaction will occur in This result has been confirmed by other in~estigators.~the reaction chamber when high partial pressures of steam are However, in the presence of catalytic agents it has been shown used, because the resulting slight hydrolysis of calcium that methanol decomposes a t 300" C., according to the chloride will give rise to the formation of some hydrogen equations5 chloride. But since the amount of hydrogen chloride so 2CHsOH = CHs.O.CH3 HzO (5) produced is extremely small, the re-conversion to methyl CHsOH = HCHO Hz = CO 2Hz (6) chloride effected by this reaction must be very slight. STUDYOF REACTION: CH30H CH3C1 = (CH3)z0 Which of these reactions predominates depends upon the HC1 (9)-Since the formation of methyl ether was not due nature of the catalyst present. Apparently, no appreciable simultaneous decomposition to the dehydration of methanol (Reaction 5), this reaction of the methanol formed takes place under the conditions of suggested itself as its source. However, considering the our experiments except above 400" C. The low temperature equilibrium from a theoretical point of view in the light of employed and the absence of carbon monoxide exclude Nernst's theorem, it was shown above that Reaction 4. The small amounts of methane and hydrogen obtained are probably principally the result of the decomposition of methyl ether and methyl chloride, as shown below. That is, equilibrium is far over to the left, and hence, if our Likewise, the absence of formaldehyde (except in traces) assumptions are correct, this reaction could not possibly proves the absence of Reaction 6. While a considerable give rise to the amounts of methyl ether obtained. quantity of methyl ether was formed, it cannot be attributed I n order to verify this conclusion, an experimental to Reaction 5, for when methanol vapor was passed over determination of the extent of this reaction was made under calcium hydroxide and chloride in the experimental work the conditions prevailing during the conversion runs. The described above, methyl ether was formed in very small apparatus shown in Fig. 1, Part I, was used. The methyl amounts, although the conditions here were much more chloride, after leaving the meter, .passed through the drying favorable for its formation according to Reaction 5 . More- train and then through the humidifier and on through the over, from the results of Sabatier's work we would not expect entire apparatus. The reaction tube was iilled with glass any of the substances present in the reaction chamber to beads. The humidifier contained absolute methanol, and catalyze this reaction. The formation of the methyl ether methyl chloride was passed through the reaction chamber, obtained is caused by a different reaction to be explained which was filled with glass beads (temperature, 350" (3.). later. A small amount of distilled water was placed in one of the PYROGENETIC DECOXPOSITION OF METHYL CHLORIDE- absorption bulbs to absorb the hydrogen chloride formed. Different observers working under various conditions have The temperature of the humidifier was maintained a t 48" C., obtained various combinations of decomposition products so that an equimolecular mixture of methyl chloride and of methyl chloride. At high temperatures one observer6 methanol was sent through the reaction tube. reports, The results obtained were in excellent accord with the CH3C1C CloHs C2H4 CHI (HCl?) theoretical conclusion. The methyl chloride was almost On passing methyl chloride over reduced nickel a t 220" C., quantitatively recovered (a small amount dissolved in the water of the absorption train). The amount of hydrogen carbon, hydrogen, and hydrogen chloride are obtained.' However, no previous work was found on this decomposition chloride obtained was determined by analyzing the water under the conditions obtaining in our reaction chamber, and of the absorption bulbs for chloride; and from the amount of so a brief experimental investigation was carried out. hydrogen chloride so determined the extent of the reaction 8 Igatjew, Ber., 35, 10.56 (1902). was computed on the assumption that equilibrium conditions Bone and Davis, J. Chem. Soc. (London), 105, 1691 (1914). had been obtained. The result obtained was Kp(38O0C.)= 6 Ssbatier and Maihle, Ann. chzm. phys , 2 0 , 289 (1910). 0.000008. This result is seen to be much smaller than the 6 Ptrrot, Ann., 101, 375 (1857). almost quantitatively recovered. A very small amount of gas (less than 100 cc.) was obtained, which proved to be partly methyl ether. Methyl chloride, if produced, was too small in amount to be positively identified. Since there was a possibility that Ca(OH)Cl, or some similar compound other than CaC12, was the principal end product Obtained during the conversion of methyl chloride to methanol, these experiments were repeated, using the residue remaining in the reaction chamber after one of the conversion runs. The results in this case were practically the same as those obtained when using calcium chloride. It is evident, of course, that these results are quite in accord with the calculations based on Nernst's theorem, given in Part I. According to the calculated equilibrium point, even if equilibrium were attained here, the methyl chloride formed would be less than 2 per cent of the methanol used (= 400 cc. methyl chloride). The formation of the small amount of ether was probably due to a secondary reaction (Reaction 10). PYROGENETIC DECOMPOSITION O F METHANOL-The decomposition of methanol under the action of heat has been investigated, and it has been s h o r n that this alcohol is the most stable of the primary alcohols toward heat.3 On passing the vapor of methanol through glass tubes, decomposition begins only above 700" C., according to the reaction:
+
+
+
7
+
Compt. rend, 138, 407 (1904).
+
+
+
+
+
+
+
+
+
8Sabatier and Maihle, Compi. rend, 141, 238 (1905).
+
INDUSTRIAL AND ENGINEERING CHEMISTRY
790
I
Vol. 15, hTo. 8
equilibrium constant derived above on the basis of Kernst’s theorem [Kp(3500C.) = 0.00061. A discrepancy in this direction is to be expected, however, for undoubtedly equilibrium was not attained here. The experimental result obtained corresponds to an approach of 12 per cent to the equilibrium point calculated by Nernst’s formula. Further evidence for this conclusion is given by the observation of Kueneng that an irreversible reaction takes place slowly between methyl ether and hydrogen chloride a t 100’ C., with the formation of water and methyl chloride, and that the velocity of this reaction increases very rapidly with the temperature. This reaction is very probably the result of the two reactions
+ HCl = CH30H + CH3C1 + HCl = CHaCI + HzO
CH3.0.CHa CH30H
(9) (8)
both of which, according to the experimental and theoretical observations already made, have their equilibrium points
far to the right-that is, according to our calculations, methyl ether and hydrogen chloride should combine to give methyl chloride and water with methanol as an intermediate product. The presence of methanol as an intermediate product was probably overlooked. However, while Reaction 9 alone will not account for the formation of methyl ether, since a hydroxide is present in the reaction chamber during the conversion of methyl chloride, it is to be expected, by analogy to the reactions,
+ + + + that the reactions ZCH3C1 + 2CHaOH = CH3.0.CH3 + 2HC1 2HC1 + Ca(OH)2 = CaClz + 2Hz0 which may be regarded as 2CHaCl + 2CHgOH + Ca(0H)z = 2CHa.O.CHa + 2H20 + CaClz CHaC1 HzO = CH3OH HCl . 2CHaCl Ca(0H)Z = 2CH30H CaClz
(9) (3) (9)
(2)
(10)
This reaction, then, is the probable: source of the methyl ether obtained. THE CONVERSION CONDITIONSINFLUENCING I n the light of the fbregoing investigation of the nature and extent of the various simultaneous reactions taking place in the reaction chamber, it is possible to study and interpret the effect of certain variables on the conversion of the methyl chloride. Z. physik
Chem.. 37, 486 (1901).
ofdsoG
$
would result in the formation of considerable amounts of methyl ether. This conclusion is strongly confirmed by the application of Nernst’s theorem, which gives as the equilibrium point
9
Thermai decom~o?,tion C ? r w value. In other words, 18 ws the temperature in- ~ ~ ~ - 8 = c 2-CH ~ v e r Cl 5 , done 0nR~ns 1 Part Press H2°-350mm creases the effective $14 C-ConversionRuns porrpress n,o zomm volume of the calcium 8”hydroxide exposed to ‘8“ the gas is increased. /y,P VELOCITY OF GAS R~ --*-/ **.o A/’ FLow-While very lit-&/ &
tion of its effect can be obtained when Curve min.) 1 (rate=55 is compared cc. with per Curve 6 (rate = 90 cc. permin.). Thegeneral shape of the reaction
6’’
2
‘7 !.V+?
3gs0,
~
‘
OA
-
I
,bpLcjrL-*=A
:m
2s@
//.’
e
L
-
IA'DUSTRIAL A N D ENGI NEERING CHEMISTRY
August, 1923
that the space-time yields can be considerably increased over those obtained in this work. Moreover, there is the added advantage that the thermal decomposition of the unconverted methyl chloride is decreased owing to the shorter time of contact with the hot reaction chamber. EFFECTOF TEMPERATURE-The temperature is the most significant variable governing the nature and relative amounts of the products obtained. Since the equilibrium points and the relative velocities of the two principal reactions resulting in the formation of the methyl ether and methanol do not change appreciably over the range of temperatures investigated, the general course of the methyl chloride conversion should not change. That this is the case is shown by the curves for Runs 1,8, and 9, all of which have the same general shape. For the same reason the ratio of the yield of alcohol to that of ether should be the same for similar conditions of humidity, which the data in Table I show to be true. The combined yield of alcohol and ether falis off as the temperature increases, on account of the pyrogerietic decomposition of the methyl chloride and methyl ether. CURVEl4 ' I
I
I
I
I
I
791
+
2CH3Cl+ 2CHaOH = 2(CH3)20 2HC1 2HC Ca(OH)2 = CaClz 2H20
+
+
(9) (2)
Now, since a t a temperature of 350" C. the thermal decomposition reactions are inappreciable, the two reactions Ca(OH)2
+
+
Ca(OH)2 2CH3C1 = 2CHaOH CaCIL (3) 2CHsC1 2CH30H = 2(CH&0 2H20 CaC12 (10)
+
+
+
+
occur alone in the reaction chamber, and it is possible to compare the experimental results obtained with those which this set of reactions should give. The application of Nernst's theorem gave as the points of equilibria of these equations:
If it is assumed that these values are correct, and if it is further assumed that equilibrium is established in the reaction .chamber, then the following reactions obtain: Let Then Let
y = partial pressure in atmosphere of H2O in initial H z O - C H ~ Cmixture ~ 1 - y = partial pressure in atmosphere of CHsCl in initial HzO-CHBCImixture x = partial pressure in atmosphere of (CH3)zO a t equilibrium y x = partial pressure in atmosphere of H20 a t equilibrium
+
dxw)
=
0
0.1
02
03
04
05
0.6
0.7
06
a9
LO
partial pressure in atmosphere of CHIC1 a t equilibrium
= partial pressure in atmosphere of CH30H a t
K8dx=)
equilibrium
Paftju/ Pressure o f H20, in Airnospheres
In the investigation of this thermal decomposition of methyl chloride previously described, it was found that the extent of decomposition increased with the temperature, as shown by Curve 12A. From the data obtained in the conversion runs (Table I, Part I), Curves 12B and 12C1"were plotted, showing the percentage decomposition of the methyl chloride passing through the reaction chamber, on the assumption that all the methane collected was formed bj7 this decomposition. A comparison of these curves shows that the decomposition occurring a t high temperatures is considerably in excess of that given by methyl chloride alone (Curve 14A). This must be attributed to a simultaneous decomposition of methyl ether, which, while present at 350" C., only becomes appreciable at 400" C. ilt 450" C., from the amounts of hydrogen and methane received, it is very significant. The most important effect of the temperature, however, is the variation it causes in the percentage of calcium hydroxide utilized, as shown by Curve 13. This phenomenon has already been discussed in a previous se'ction (Size of Calciuin Hydroxide Granules). EFFlCCT OF PARTIAL PRESSURE O F W A T E R VAPOR-The most significant result brought about by a variation of the partial pressure of water vapor in the reaction chamber was the effect it produced on the relative yields of ether and alcohol. Curve 14C shows graphically the results obtained. As previously explained, the formation of methyl ether must be attributed to the reaction Ca(0H)Z
+ 2CH3C1+ 2CH30H = 2(CH&0 + 2H20 + CaC12
(10)
which may be considered as occurring directly, or as the sum of 'OCurves 12B and 12C were plotted on the assumption t h a t all the methane. obtained was caused by the decomposition of methyl chloride according to the reaction found experimentally: 2CHsC1 = C CHI 2HC1
+
+
or 1 - 4x - 2y
+ 4x2 + 4xy + 4y2 = (1 +
K3)
(x
+ xy)
(b)
Now, from calculated values of K3 and K ~ o ,
Therefore,
1 - 4x
- 2y + 3 . 7 9 ~+~y z = 0
From this equation the partial pressure of methyl ether resulting from any initial partial pressure of water can be computed, assuming equilibrium is reached. Kow, evidently,
+
partial pressure of methyl chloride KBKIO used. Therefore, if x' = per cen: yield as methyl ether, it follows 2x x' = ('
- ')
-
22 ___ xy =
x2
(l
+ xy
(c)
- y, - & G G
where x is obtained from Equation b. Equation c is plotted as Curve 14A, while the results obtained experimentally are plotted as Curve 14C. Although the curves are obviously related, the agreement between the two is not good. When it is considered, however, that Reaction 10 is consecutive to Reaction 3, and, moreover, that the former is far more complex than the latter, requiring as it does the fortuitous juxtaposition of a molecule of methanol with one of methyl chloride and one of calcium hydroxide, it is hardly to be expected that under the conditions existing in the reaction chamber Reaction 10 will approach equilibrium as closely as will Reaction 3. On this assumption it follows :
INDCSTRIBL All-D ENGIXEERI-YG CHEMISTRY
792
If a = extent to which Reaction 3 approaches equilibrium, and e = extent t o which Reaction 10 approaches equilibrium, relative t o Reaction 3 , then the term
on the assumption that aK8 is large with respect to 1. This assumption is certainly true, because from the curve for Run 4 it is seen that although Reaction 10 was suppressed by water vapor, the conversion of methyl chloride is well above 90 per cent. Nernst’s formula indicates that it should be 98 per cent a t equilibrium; hence equilibrium is almost reached -that is, a very nearly equals 1. a Now if one assumes that the value of - = 8-that is, e that Reaction 10 approached equilibrium only one-eighth (1 K3)’ = -8K3 as closely as did Reaction 3, then Kli a’KsKio proximately. Hence, Equation 2 becomes
+
1 - 4~
- 2y + 4x2 + 4 %+~4y2 = 1.60(x2 + XY) - 4x - 2y + 2 . 4 0 ~ 2+ 2 . 4 0 + ~ ~y2 = 0
=1
(b’)
Hence, Equation c becomes c‘:
By using Equation c‘ there is obtained a new set of values for d,which are plotted as Curve 14B. It is seen that this curve agrees quite well with the experimental curve. This theoretical confirmation of the experimental results obtained indicates that the explanation advanced of the entire mechanism of the conversion of methyl chloride is at least highly probable. Moreover, it gives an additional indication of the reliability of the application of Nernst’s approximation equation. An additional effect of the presence of steam is illustrated by Curves 11and 13. As the initial partial pressure of water vapor is increased, the extent of the conversion of calcium hydroxide to calcium chloride is decreased a t any given temperature. This effect cannot be attributed to the establishment of the equilibrium1’ CaClz
+
H20
= Ca(OH)*
+ HC1
(2)
by the water vapor, for it was previously shown that with far higher concentrations of water vapor this hydrolysis was almost negligible. The probable explanation is that the phenomenon is due to adsorption. Calcium hydroxide is hygroscopic a t ordinary temperatures, and the formation of hydrates has also been shown12to take place; therefore, it is to be expected that with this pronounced secondary valence for water it will be absorbed to some extent. The effect of this absorption would be to reduce the active surface13 of the hydroxide, which would be tantamount to a reduction of the effective volume of the latter. Since the absorption isotherm for a gas by a solid generally shows a decreasing rate of absorption as the partial pressure of the gas increases, the shape of the curve obtained is readily accounted for. On the basis of this explanation, however, since adsorption decreases with increase of temperature, Curve 13B should approach Curve 13A as the temperature increases. The experimental data are insufficient to determine whether or not this is true. 11 It is t o be noted t h a t experimentally i t was found t h a t one of the component reactions of Reaction 2 approached t o one-eighth of the equilibrium point predicted by Nernst’s formula. 12 Kosmann, Z. Elekfrochem., 86, 181 (1920). 1s Langmuir, Chem. News, November 4 , 1922.
Vol. 15, No. 8
EFFECT OF INERT GAS-A knowledge of the effect on the conversion of methyl chloride of the presence of an inert gas is desirable, since the methyl chloride made commercially by the chlorination of natural gas would probably contain considerable quantities of methane. While no experimental work was carried out to determine this effect directly, it is possible to make some pertinent deductions from the results obtained using high concentrations of water vapor. TheoreticalIy, since there is no change of volume in the course of the reaction, the diluting effect of an inert gas can cause no displacement of the equilibrium points. The extent of the reactions therefore will not be changed. It is more difficult to predict the effect of an inert gas on the velocity of the reactions, for this velocity depends on the rapidity of diffusion of the methyl chloride into, and of the products of reaction out of, the hydroxide granules. Under fixed conditions of temperature and pressure the coefficient of diffusion of a gas will depend on the nature of the gas mixture into which it must diffuse. If the inert gas added is such that the mean free path of the molecules is increased-which would probably be the case if the diluent gas were methanethen it is to be expected that the coefficient of diffusion of the original gases will increase very slightly,14 and hence the velocity of the reaction should increase very slightly. This is on the assumption that the adsorption of methane on the surface of the hydroxide is inappreciable. I n the reaction resulting in the formation of ether the situation is more complex, since the presence of an inert gas in considerable quantities will decrease the relative number of collisions or juxtapositions of the methanol and methyl chloride molecules. As a result, therefore, the probable effect of the presence of methane will be to increase the relative velocity of Reaction 3 with respect to that of Reaction 10, and thus to favor the formation of methanol over methyl ether. In addition, since methane is a product of the thermal decomposition of the reacting materials, its presence should inhibit the decomposition. The experimental results obtained using high partial pressures of water are in accord with these conclusions. A comparison of the curves for Runs 4 and 5 with Run 1 shows that in the presence of 0.5 atmosphere of water vapor, even though the velocity of the passage of methyl chloride through the reaction chamber is doubled thereby, the percentage absorption of methyl chloride shows no decrease. On the other hand, Curve 14C indicates by its deviation from 14B that the relative velocity of Reaction 10 has been decreased in the presence of increasing concentrations of water vapor. STRUCTURAL CHARACTER OF CALCIUM HYDROXIDE GRANums-Since the conversion of calcium hydroxide to calcium chloride depends upon the permeability of the hydroxide toward the gases, it is evident that the greater the porosity of the granule’s, the greater will be the utilization of hydroxide. Dense calcium hydroxide prepared by precipitation was found to give only one-third the yield of calcium chloride given by the hydroxide used in these experiments. No attempt was made to improve upon the character of the hydroxide used here, but undoubtedly it could be improved to a considerable extent before the porosity attained caused it to become too friable for industrial use. EFFECT O F MATERIAL ON REACTION CHAMBER-An experimental investigation was made to determine the most advantageous material in which this reaction could be carried out on an industrial scale. Steel was first tried as the cheapest and most available material. The apparatus used was essentially that shown in Fig. 1, Part I, except that a steel tube was substituted for the glass reaction tube. A number 14
iMeyer, “Kinetic Theory of Gases.”
I S D U S T R I S L A X D ENGINEERING CHEMISTRY
August, 1923
of runs were made, and it was found that at temperatures as low as 300" C. considerable decomposition of the alcohol took place, large quantities of hydrogen and methane and some carbon monoxide being obtained. As the temperature rose this decomposition rapidly increased. Copper was naturally excluded on account of its known catalytic effect on the decomposition of alcohol. Aluminium was next tried, experiments being made as i n the case of steel. The results showed that the decomposition taking place in the aluminium tube under given conditions did not exceed that occurring in the glass reaction chamber. These results agree very well with the known behavior of methanol. It has been shown3 that on passing methanol vapor through iron tubes, it is almost entirely decomposed a t 600" C. into carbon monoxide, hydrogen, and methane, while with a l u m i n i ~ mon , ~ the other hand, no decomposition takes place even a t 700" C. Aluminium, or probably its alloys, should therefore make a satisfactory material for an industrial reaction chamber.
793
the catalyst, which was maintained a t a uniform and constant temperature. The products of reaction passed out of the reaction tube, and were collected in the tubes A and B , each containing about 20 eo. of C. P. Concentrated sulfuric acid. The aluminium oxide used as catalyst was prepared and dried exactly as described by Sabatier and Maihle.lS The methanol used was freshly prepared, C . P. absolute methyl alcohol, 99.5 to 100 per cent.
1"
CONVERSION OF METHYLETHER TO METHAKOL
FIG.2n
c
In the foregoing discussion it has been shown that the yield of methanol can be increased at the expense of the methyl ether yield by the use of steam mixed with the entering methyl chloride (Curve 10). While possessing some advantages, this employment of steam is attended by the disadvantage that it appreciably reduces the percentage utilization of the calcium hydroxide (Curve 11). An endeavor was made to avoid this difficulty by effecting the conversion of methyl chloride under anhydrous conditions and subsequently converting the ether formed into methanol by the equilibrium: (CH3)20
+ HzO a 2CHaOH
The reaction has been extensively investigated in the reverse direction. It has been shown that this decomposition of methanol is catalyzed by certain metallic and a very extensive inquiry has revealed that a l u ~ n i u m oxidel6 is the most efficient catalyst for this decomposition. It has d s o been shown that water vapor will inhibit the reaction to some extent in the case of ethyl alcohol.17 HOMever, a search of the literature failed to reveal any data from which even an approximate indication of the point of equilibrium could he obtained. The application of Nernst's formula gave as the equilibrium point: (CHIOH)2 K = (CH&O X H10 = o'25
as shown in Part I. The existence of so efficient a catalyst and the almost complete absence of any side reactions, together with the fact that the velocity of this reaction is almost zero below 400" C. in the absence of a catalyst, greatly simplifies the task of determining the approximate equilibrium point experimentally. Hence, since the experimental determination would, in addition to giving the desired information, serve as an excellent check on the validity of the application of Kernat's approximation formula to these reactions, it was carried out. EXPERIMENTAL-The apparatus used is shown in Fig. 2. The me1,hanol passed directly from the buret D, through the capillary tube into the glass reaction tube in the furnace C, where it vaporized, and passing over the glass beads became heated Lo the proper temperature. It then passed through 15 Grigorieff, Bull. soc. chim., [3] 24, 612 (1902); Senderens, I b i d . , [41 5 , 480 (1909). Sabatier and Maihle, Compt. rend., 148, 1735 (1910); A n n . chzm phys., [8] 20, 343 (1910). 17 Engelder, J . Phys. Chem., 21, 676 (1917).
PROCEDURE-The furnace was brought to a constant temperature of 350' C . , and then methanol was permitted to flow slowly into the reaction tube, generating methyl ether, until the gases leaving the reaction tube were completely absorbed by concentrated sulfuric acid. I n this way all the air, moisture, etc., were displaced from the reaction tube. The buret was then shut off, and when equilibrium was established in t h e reaction chamber (shown by the complete cessation of the flow of gases from the reaction tube), the test tubes A and B containing concentrated sulfuric acid were put in place, as shown in the figure. The reading of the buret was recorded and the methanol was again permitted to flow very slowly into the reaction tube. The reaction proceeded very smoothly, the products of reaction being collected in tube A . A very small amount of gas, not exceeding 10 cc., bubbled through tube B in the course of a run, but the increase in weight of the latter never exceeded 2 mg. This small amount of gas was doubtless hydrogen, which, it has been shown, is formed in minute amount under these conditions. After approximately 12 to 15 cc. of alcohol had passed into the reaction tube, the bhret was shut off, and the reading recorded. When equilibrium had again been established in the reaction tube the test tubes A and B were removed. The sulfuric acid solution of ether in A (containing also the unchanged methanol and the water formed) was transferred to a small Erlenmeyer flask (150 cc.). Tube A was rinsed out several times with small amounts of concentrated sulfuric acid. The Erlenmeyer flask was fitted with a dropping funnel, a long delivery tube, and a third tube reaching to the bottom of the flask, and closed a t the other end with a pinch-clamp (Fig. 2a). The delivery tube of the flask was connected to a 4-liter gas collection bottle, using a concentrated solution of sodium silicate as the containing fluid. Sodium silicate solution was used on account of the small solubility of methyl ether therein. The silicate solution was saturated with methyl ether. Water was permitted to drop from the dropping funnel into the sulfuric acid solutioh of methyl ether in the flask, and the ether, given off a t a steady rate, was collected. When about 2.5 volumes of water had been added, i t was stopped, and the solution in the flask was slowly heated to gentle boiling. The delivery 1s
A n n . chim phys., [SI 20, 298 (1910).
794
INDUSTRIAL A N D ENGINEERING CHEMIXTR Y
tube served as a reflux condenser. When the evolution of ether had ceased, the system was put under a slight pressure ( l / ~ inch of mercury) by siphoning a small amount of silicate solution back into the gas collection bottle. The pinch-clamp of the flask was then opened (boiling being maintained continually), and all the liquid contents of the flask were driven out. When the flask had come t o room temperature, the volume of gas was read. In this way the re-solution of the liquid contents of the flask was prevented. The volume of the gas collected was corrected for pressure and temperature, and the volume of the original concentrated sulfuric acid solution of ether was added. It has been shown that over 98 per cent of the methyl ether can be recovered readily from a concentrated sulfuric acid solution by adding water and heating to b0i1ing.l~ With the precautions observed here, the recovery was probably improved.
Vol. 15, No. 8
Moreover, the reaction should be very readily carried out on a large scale, for the apparatus required is simple, the velocity of reaction is very rapid, and no side reactions occur. In addition, the products are readily separated in a pure state. If the heat of the steam employed can be used in processing, the cost of conversion should be very small.
RATIONALE OF PROCESS
From th'e foregoing investigation it appears that the most advantageous method of effecting the conversion of methyl chloride to methanol is to pass the methyl chloride mixed with steam over highly porous, granular calcium hydroxide. The optimum temperatyre is approximately The experimental results obtained are shown in the follow- 350" C. Rates of flow considerably higher than those used in this investigation may be employed, and under these ing table: conditions the thermal decomposition of the reacting gases TABLE 111-CONVERSION OF METHANOL TO METHYL ETHER will probably be inappreciable (under 2 per cent at this Temperature Duration (CHdaO per G. (CH!)10 CHsOH Delivered" Received of Catalyst ofRun CHaOH temperature). I n this way the methyl chloride can be cc. c. Hrs. c c. cc. almost quantitatively converted (98 per cent) to methanol 275 3300 350 1:20 15.07 272 2800 350 1: 00 12.85 and methyl ether. The relative amounts of the two products 276 2940 350 1:00 13.49 obtained will depend upon the relative partial pressures of Average 274 the methyl chloride and steam in the initial gas mixture. a All volumes are calculated t o 0 ' C. and 760 mm. Using equal partial pressures of methyl chloride and steam From the average of the results obtained, assuming that yields of methanol and methyl ether in the ratio 67 to 33 equilibrium was reached, the constant of equilibrium is per cent have been obtained. However, from Curve 10 it is evident that this ratio can be readily increased by using (CHa0H)2 - [(22400/32) - ( 2 X 274)]' = 0.308 larger proportion of steam. If, for example, the partial 2742 K = (CHdz0 X HzO pressure of water compared to that of methyl chloride in In order to verify the assumption that equilibrium was reached, the reaction was carried out in the opposite direction. To the initial mixture is 3 : 1, then the resulting ratio of the accomplish this, a known volume of pure methyl ether was dis- yield of alcohol to ether will be 80 to 20 per cent (based on placed from a gas bottle through a humidifier maintained a t extrapolation of Curve 10). Moreover, from Curve 13 84' C. (vapor pressure of water = 380 mm.), and thence through it is seen that increased concentrations of water vapor over a the reaction tube to the tubes A and 23. The humidifier was in 1 : 1 ratio will cause no further appreciable decreage in the principle the same as that shown in Fig. 1, but the design was percentage utilization of the calcium hydroxide. However, modified in order to require the use of a smaller volume of water. Here also an electrically heated resistance spiral prevented the the methyl ether can be readily converted to methanol condensation of the moisture from the gas. The water used in separately, as has been shown. the humidifier was previously saturated with methyl ether. If the methyl chloride employed is diluted with methane, The run was carried out exactly as in the case of the reverse reaction above, except that volumes of gas in the holder were the velocity of the reaction resulting in the production of read in place of volumes of alcohol in the buret. Tube A was methanol should be slightly increased, if it is affected at all. weighed before and after the run. The velocity of the reaction producing methyl ether, however, will probably be sensibly decreased. I n addition, the From the increase in weight due to the combined weight of methyl ether and water, and from the known weight of presence of methane should inhibit the thermal decomposition methyl ether used, the amount of water introduced was of the reacting gases. However, the presence of methane or computed. It was found to be 0.995 mol per mol of methyl any other diluent gas is objectionable because of the increased ether-i. e., the mixture of methyl ether and water was capacity of apparatus necessary to attain a given output of practically equimolecular. The results obtained are shown methanol. Moreover, the heat losses of the process will be increased, and the recovery of the products by absorption below: will be rendered slightly more difficult. TABLE IV-CONVERSION OF METHYLETHERTO METHANOL From an engineering aspect some considerations concerning CHaOH Temperature Duration of (CHdaO (CHahO this process may be noted. The problem of handling all Delivered Recovered. Catalyst Run Converted cc. c c. = c. Hrs. c c. materials, both reactants and resultants, should be relatively 3310 2580 360 1:lO 730 a simple one, for corrosion of pipes and containing vessels would be extremely slight. Moreover, the problem of the separaThe equilibrium constant, therefore, is tion and purification of the products should give no great difficulty. The necessity of careful temperature control is hardly a It is seen that this value agtees very well with that ob- serious disadvantage, although the coefficient of heat transfer tained by approaching the equilibrium from the opposite through the mass of porous granular hydroxide is quite low. direction. Moreover, these results confirm the validity Fortunately, the heat of reaction is small-only 0.45 and utility of. Nernst's approximation formula. Calories per mol of methyl chloride converted. This should Considered from the aspect of its industrial applicability, greatly simplify the problem of heat transfer. the result obtained for the equilibrium point shows that this While it is not possible to give a detailed cost analysis, reaction should serve very well as a method of converting one can, nevertheless, obtain a rough estimate of the cost of the methyl ether to methanol. In order to convert 50 production of methanol by this process. The largest single per cent of the ether to methanol, 8.5 volumes of steam per item in the raw materials cost is the price of chlorine. The volume of ether are required. However, if, as could very following table gives the estimated cost of production for readily be done, the conversion is carried out in successive various prices of gaseous chlorine. Lime is taken a t $10.00. stages, less steam is required. per ton and natural gas of 90 per cent methane content a t 10 cents per 1000 cubic feet. Steam is taken a t 70 cents a ton. Erlenmeyer and Kruchbaumer, B e y . , 7 , 699 (1874).
INDUSTRIAL AiVD ENGINEERING CHEMISTRY
August, 1923
In these estimates, a yield of 70 per cent on the basis of the chlorine used is assumed for the chlorination of the methane. The hydrochloric acid produced is assumed to be recovered and is credited with its chlorine-content value. Labor and overhead are estimated at 18 cents per gallon of methanol. It may be noted that if the costs of methane, lime, and coal were all to double simultaneously, the resulting increase in the production cost of methanol would be only 7.5 cents per gallon. TABLEIV-COST Chlorine per Lb. 0 75 1 0 1 5 2 0 2 5
a
Materials Cost per Gal. 24 30 41 52 63
5 2
7
8 8
O F PRODVCTION O F
Overhead and Labor per Gal. 18 0 18 18 18 18
0 0 0 0
Gross Cost per Gal. 42 5 48 2 59 7 70 8 81 8
METHANOL~ Credit Net Cost for per Gal. HCI CHIOH 8 11 16 22 2s
4 3 9 6
2
34 36 42 48 53
1
9 8 2 6
795
A further consideration not to be overlooked is the fact that the product obtained by this process is free of acetone, which occurs as an impurity in the methanol as now manufactured. This impurity is extremely deleterious in the manufacture ol formaldehyde, which is the largest single use for methanol. The present low market price of methanol (November, 1922) is due to a temporary large oversupply. Bctually, a t prevailing costs of labor and wood it is very doubtful whether refined methanol can be produced a t a profit for less than 81.10 per gallon. Moreover, it isnot unlikely that in the near future, even with methanol a t $1.25 a gallon, the owner of wood will find it more profitable to sell to the paperpulp manufacturer, rather than to submit the wood to destructive distillation for methanol production.
Figures are given in cents.
The Freezing Point-Solubility Diagram of the System TNT-Picric Acidiaz By C. A. Taylor and W. H. Rinkenbach BUREAUOF
MINES,
PITTSBURGH, P A .
in sulfuric acid desiccators for a week before using. The product so obtained was a mass of very light, flaky crystals of a light been used for Some time in commercia1 detonators yellow color. The setting point was found to be 121.8' C., and in certain types of military explosives, yet a . and the melting point was found t o be constant at 121.9' C. search of the literature has failed to show any record that when an air-jacketed tube was used for making the determina-
A
LrHOUGH mixtures of TNT and picric acid have
the nature of the system of these two compounds has been determined. Accordingly, the binary system of T X T and picric acid has been studied with a view to obtaining data that would be a contribution t o the physical chemistry of explosive substances, and which might be of use in the analysis of compositions containing these bodies. The authors have previously published a study of the binary system 'TNT-tetryl,3 in which the methods used were discussed in detail. These methods were used without change in this work. The T N T used was a portion of the material used in the work with tetryl previously mentioned. It was a m a s s of very light, fluffy, white crystals, which had not colored in the least on being kept in a dark room for six months. The setting point, was 80.27' C. The picric acid used was purified as follows:
-
A very good grade of picric acid was thoroughly washed five times with distilled water. I t w a s then dissolved in hot distilled water, and the solution was filtered through paper in order t o remove any insoluble matter present. The solution, on cooling, deposited the greater part of the picric acid, a s very fine crystals. These were filtered off, washed several times with cold distilled water, dried on filter paper, and placed
--
1 8
Received February I O , 1923. by permission of the
THISJOURNAL,
15, 73 (1923).
u, s. Bureau
of Mines.
tlo&ch of these compounds was fused before using in order to minimize in weighing.
The results obtained follow, and are shown in the form of an equilibrium diagram. ThTT
%
0 19 39 49 59 66 69
00
97
Picric Acid
%
100 00
89.55
80 03 40 09 50 08 40 09 33 70 30 20 2 5 24 19.99 10.45
100.00
0.00
91
92 91 30 80 74 76
So.oi
Temperature of Extrapolated Point, OC (Average) 121 8 106 7
Eutectic Temperature, O C (At erage)
.. . . ..
89.5 78 85 66 3
...
68.4.
74.35 80.27
"
69 8
c9 4 n9 R. ~.
....
....
....
An inspection of the equilibrium diagram derived from these data shows this system to be a very simple one, no molecular compounds being formed. In order to corroborate this, melts containing different relative percentages were submitted for examination under the petrographic microscope. The materials were found to be in a very finely divided form which precluded measurement, but in each case only the two components appeared to be present. The data furnished in this paper may be utilized for the purpose of determining the relative percentages present in unknown mixtures of these two substances. For details. the reader is referred to the paper on TNT-tetryl previousli mentioned. As TNT-picric acid mixtures are not as common or important as those of T N T and tetryl, the use of this method for analytical purposes will probably not be as extensivein this case.
ACKNOWLEDGMENT The authors gratefully acknowledge the helpful*suggestions and criticisms of A. C. Fieldner, R. E. Hall, and the assistance of W. M. Myers, who examined the melts.
.
