682
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 15, No. 7
T h e Conversion of Methyl Chloride to Methanol-I’ By Ralph H. McKee and Stephen P. Burke COLUMBIA UNIVERSITY, NEW YORK,hT. Y.
N NORMAL times the The electrolysis of brine In brief, the method proposed here is to treat natural gas (methane) United States produces produces caustic soda and with chlorine under conditions conducive to a maximum yield of about one-half of the chlorine in unchangeable methyl chloride, and then by the use of lime to convert the methyl world’s supply of methanol. proportions (100 lbs. sodium chloride to methanol. In the past, the endeavor in carrying out the Previous to the war this hydroxide to 90 lbs. chlochlorination of methane has been to chlorinate all the methane with amounted to over 10,000,rine). The ratio of the relathe primary object of obtaining the higher chlorinated products, 000 gal. a year,4 all of which tive demands for these two chloroform and carbon tetrachloride. From the work reported by was obtained by the deproducts is very different, the Bureau of Mines and others,Z there is every reason to believe, structive distillation of however, caustic soda being however, that by using an excess of methane a product can be obtained wood, for up to the present in greater demand than which, while diluted with methane, will be contaminated with cery time the so-called hardchlorine. It is the practical little of the higher chlorinated products. The presence of this excess woods have been the only impossibility of the disposal of methane will not interfere with the subsequent conversion of the industrial source of this of this chlorine, even as a methyl chloride to methanol. Where natural gas of suitable quality compound. During the waste material, that has is not available, the methane can be produced catalytically from war the urgent demand for prevented the increased prowater gas, as carried out by the Cedford p r o ~ e s s . ~At the present wood distillation products duction of electrolytic caustime methyl chloride made by the chlorination of natural gas is gave an impetus to this intic to meet this relatively acailable on the market. This investigation, therefore, is concerned dustry, which resulted in strong demand. By furnishentirely with the second stage of this synthesis-that is, with the a n increase in productive ing a market for chlorine problem of the conversion of the methyl chloride to the final product, capacity of over 25 per this methanol process would methanol. cent.5 At the present time assist in equalizing these the moductive capacity of demands and thus would be this &countryis approximately 17,000,000 gal. of methanol, economically beneficial. requiring the consumption of over 2,000,000 cords of wood A sufficiently cheap source of methanol will assist in filling per year. the increasing need of a new squrce of motor fuel. It has The yield of methanol obtained by destructive distillation been shown that methanol is satisfactory for this purpose amounts a t best to 8 gal. per cord of wood,2 which is less than from a technical standpoint,7 for it stands very high compres1.5 per cent by weight of the wood. I n addition, charcoal, sion without preignition, and causes no carbon formation. acetic acid, and acetone are produced. The war period, These factors, together with its high vapor pressure a t ordihowever, saw the development and establishment on a com- nary temperatures, make it an excellent component for a mercial scale of several competitive processes, of which blended motor fuel. acetic acid and acetone are the products. These processes RESUMB OF PREVIOUS WORK are: (I) the fermentation process for acetic acid, ( 2 ) the synthetic production of acetic acid from calcium carbide, and I n this investigation attention has been fixed on effecting the (3) the fermentation process for acetone. Thus, with the conversion of methyl chloride to methanol in the gaseous phase, exception of charcoal and methanol, these new processes offer because in this way certain advantages are gained when regarded an engineering aspect. By this method of treatment competition on all the products formerly produced by wood from greater continuity of operation is effected, the problem of the handistillation only. Moreover, developments in the metallurgy dling of materials is simplified, and the troubles attendant on the of iron and the improvements in the production of metal- use of high-pressure autoclaves, necessary if t h e liquid phase is lurgical coke have greatly reduced the demand for charcoal.2s6 present, are avoided. The reactions occurring between metallic hydroxides and Methanol remains, therefore, the only product for the pro- alkyl chlorides in the gaseous phase have been the subject of a duction of which the distillation of vast quantities of our most meager amount of investigations in the past. Dumas and useful hardwoods is indispensable. The desirability of a Stas,8 in an attempt to form methylene, passed methyl chloride synthetic method for the production of this product is accord- over heated potash lime and obtained potassium formate, hyingly evident. It is the purpose of this paper to describe such drogen, and potassium chloride. Methane was also obtained, owing, the authors state, to the decomposition of t h e formate. a synthetic process. It is also shown t h a t the presence of the formate was due to the oxidation by the potassium hydroxide of the methanol which MATERIALS REQUIRED was first formed. Sodium hydroxide was found t o exert the The raw materials for methanol prepared by this process same effect. Later Nefg obtained similar results on passing are natural gas, chlorine, and lime. Katural gas isacheap ethyl chloride over heated hydroxides. Using soda lime, 30 and plentiful raw material, which has not received the chem- per cent of the alkyl halide was converted t o ethyl alcohol and acetate. Methane and hydrogen were also obtained. ical exploitation it deserves. Certainly, it is a far more de- sodium I n a recent paper, Whistonlo proposed to synthesize methanol sirable source of methanol than our valuable hardwoods. from natural gas by the chlorination of the gas and the subsequent Chlorine is a raw material for which new demands are greatly conversion of the methyl chloride to methanol. He attempted hydrolysis of the methyl chloride by steam, b u t found t h a t needed, for the disposal of chlorine is one of the factors which the no more than traces of methanol could be obtained. He also has limited the growth of the electrolytic alkali industry. tried some experiments on calcium hydroxide as a means of effect;
I
Received December 4, 1922. Bur Mines, Tech. Paper 266 (1921), Curme, U.S Patent 1,422,838 (1922). 3 Rideal and Taylor, “Catalysls in Theory and Practice,” 1919, p. 182 4 Brown, “Forest Products,” 1919, p . 221; cf. Manufacturers’ Census for 1914. 6 Tariff Information Surveys, “The Wood Chemical Industry,” 1921. 5 Bunbury, Chem. A g e (London), 6 (1922), 162. 1
ing this conversion, and found after repeated, circulation at 300
2
7 8 g
Bur Mznes, Bulls 32 and 48; J . S o c Chem I n d , 27 (1908), 779. A n n , 35 (1840), 169 l b z d , SO9 (1899), 126, 318 (1901), 1 ; J . A m Chem. S O L ,26 (1904),
1549. 10
tion
J
Chem SOC (London), 117 (1920), 183, and a private communlca-
INDUXTRIAL A N D ENGINEERING CHEMISTRY
July, 1923
C. t h a t the methyl chloride disappeared almost quantitatively. He determined qualitatively the presence of methanol and methyl ether.in the reaction products. No experimental details or data are given. This is the first suggestion of the hydrolysis in the gaseous phase of methyl chloride t o give methanol. It was, however, carried out in the absence of steam. EXPERIMENTAL
HYDROLYSIS OF METHYL CHLORIDE BY MEANS OF STEAM The direct hydrolysis of methyl chloride by means of steam would obviously be the simplest and most desirable method, from a commercial viewpoint, of effecting the conx-ersion of methyl chloride to methanol. For this reason, in spite of the negative results obtained in earlier attempts,lO a thorough experimental investigation was made of the reaction CH3C1
+ HzO = CHIOH + HC1
The methyl chloride used came in iron cylinders, each containing 10 lbs. of the liquefied gas. Its compositionas determined by the methods of analysis described in a previous article1' was found to be 99 per cent methyl chloride, the remaining 1 per cent consisting of methane and inert gas, with possibly some methylene chloride and ethylene. The method of hydrolysis employed was to pass the methyl chloride through an apparatus very similar to that shown in Fig. 1and described below. The gas, after leaving the meter, was mixed to the desired extent with water vapor in the humidifier, and then passed over pure silica sand in the reaction tube in the furnace. Any methanol formed was recovered by the absorption train. From the thermal analysis of the reaction given below, it is evident that the production of methanol should be favored by high temperatures. I n these experiments temperatures u p to 350" C . were employed, and the ratio of water t o methyl chloride was varied from 1:l to ratios in excess of 3 : l . I n every case, however, the volume and analysis of the methyl chloride were practically unchanged after passing through the reaction chamber. (Absorption of methyl chloride did not exceed 1 per cent.) Traces of methanol and hydrogen chloride were produced, for their presence could be detected i n the water of the absorption train. Since these very low yields of alcohol might be attributed to a very low reaction velocity, the attempt was made t o discover a catalyst to accelerate this reaction. The rare earth oxides offered hope of success in this direction, in view of their high catalytic activity in reactions involving primary alcohols.12 Of these oxides, zirconium oxide was found by some inve~tigatorsl~ to give the best results in the esterification of methanol. Since this reaction may also be regarded as an esterification reaction using a mineral acid, zirconium dioxide was tried, but it was found to have no discernible effect on the extent of the reaction. Several other substances were investigated (anhydrous calcium chloride, anhydrous aluminium chloride and silica), but none displayed any catalytic effect. At this point the search for a catalyst was abandoned, for, in view of these results and those of previous investigators, it was concluded that in all probability the equilibrium point was far over to the left side of the reaction, and that any attempt to bring about the conversion of methyl chloride to inethanol in this manner must be futile. This conclusion is fully substantiated (see below) by the application of Kernst's theorem to this reaction. It may be conclusively accepted, therefore, that the direct hydrolysis of methyl chloride by means of steam cannot be employed for the commercial production of methanol. l1
l2 13
THISJOURNAL, 15 (1923), 578. Sabatier and Maihle, Compt. vend , 162 (1911), 494, 669, 1044. Maihle and Godon, Bull soc chim , 29 (1921), 101.
683
USE OF HYDROXIDES FOR PRODUCTION OF METHANOL FROM M.ETHYLCHLORIDE The possibility of -effecting this conversion by means of metallic hydroxides was next investigated. A consideration of all the metallic hydroxides from a standpoint of cost, availability, and physical and chemical properties restricted those meriting investigation to a very few. The hydroxides of the metals below aluminium in the electromotive series were excluded from consideration on account of their instability a t the temperatures required and their objectionable catalytic behavior in the presence of methanol, resulting in the decomposition of the latter.I4 Likewise, sodium and potassium hydroxides were ruled out, for it has been shown8 that a t temperatures above 200" C. they oxidize methanol to formic acid, which in turn is decomposed a t higher temperatures. Thus, there remained as the most promising hydroxides those of aluminium, calcium, and magnesium. Of these, aluminium hydroxide had a n especial merit, provided i t proved sufficiently stable, since aluminium chloride, formed by the reaction in view, boils a t 183" C. This seemed to promise that it might be possible to accomplish the conversion of methyl chloride very effectively using this hydroxide a t a temperature above 200" C., since the aluminium chloride might sublime off in the current of the excess gas as fast as i t formed, thus constantly exposing a fresh surface of the hydroxide. Magnesium hydroxide, on the other hand, was least promising, for compared with calcium hydroxide it was less available and more expensive, and considerably less ~tab1e.I~
EXPERIMENTS WITH ALUMINIUM HYDROXIDE A series of runs was carried out to investigate the possibility of using aluminium hydroxide. The hydroxide was prepared by precipitation from a solution of aluminium nitrate by ammonium hydroxide. The precipitate was then carefully washed and dried a t 110" C. The apparatus employed was similar to that shown in Fig. 1. The hydroxide was placed in the reaction tube in the central unit of the furnace, which was carefully maintained a t a uniform and constant temperature. Experiments were made using the hydroxide both en masse and precipitated on pumice. The methyl chloride was sent through the reaction tube, and collected in the gasometer after passing through t,he absorption train. It was found possible to convert a small amount of the methyl chloride to methanol during the first few minutes of the run, but the reaction immediately ceased owing to the dissociation of the hydroxide, forming the oxide and water. Attempts were made to prevent this decomposition by using high concentrations of water vapor in the gas, but at temperatures as low as 200" C. and partial pressure of water in excess of 600 mm. i t proved impossible. Hence, the use of aluminium hydroxide was abandoned. CSEOF CALCIUM HYDROXIDE Since i t possessed certain advantages over magnesium hydroxide, as pointed out above, the use of calcium hydroxide as a conversion agent was next investigated. The calcium hydroxide employed in these experiments gave the following average analysis :
+
Calcium hydroxide trace of magnesium hydroxide, . , . , , , , Calcium carbonate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Moisture. . . . . . . . . . . . . . . . . . . . . Impurities (SiOt, e t c . ) , b y differe ......
..................... TOTAL
.................
Per cent 93.0 3.0 2.5
1.5 100.0
Sabatier and Maihle, A n n . chim. phys., 20 (1910), 289. Johnston, Z. Phys. Chem., 62 (19081, 347; Dragert, Inaugural Dissertation, Berlin, 1914. 14
15
A**\& p
684
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
FIG.I
The calcium hydroxide was obtained by slaking fat highcalcium lime. Five pounds of the oxide, carefully slaked, were made into a paste by adding a small excess of water, and this material was then dried in a vacuum shelf drier a t 125" C. The product obtained was very uniform and fairly porous. The hydroxide was then ground and screened to sizes varying froin 5 to 50 mesh. The sieving operation reduced the porosity somewhat by filling up the pores, so that the final product consisted of smooth, white, nearly spherical granules. During these experiments the analysis was checked up several times, and it was found that the composition of the hydroxide did not change. APPARATUS-The apparatus used in carrying out this experimental work is shown in Fig. 1. The gas issuing from the cylinder, 1, passes from the wet meter, 2, through the humidifier, 3, to the reaction tube, 6, in the furnace, 5, and thence through the absorption train, 7 , which removes the methanol. The excess methyl chloride and any gases formed during the reaction pass on to the gasometer, where they are collected and measured. I n certain experiments where dry gas was desired, a calcium chloride drying train was substituted for the humidifier. The meter was calibrated against a standard cubic foot bottle. The water in the meter was always kept saturated with methyl chloride. The humidifier consisted of a tower about 15 in. high by 2 in. in diameter, filled, as shown, with glass beads to within 2 in. of the top. The level of the water coincided with the height of the beads. The gas entering through a tube down the center, drawn out to a capillary opening, passed up through the beads and became saturated with vapor on its way. Any subsequent condensation of the water vapor was prevented by having the temperature of the path from the humidifier t o the reaction chamber well above 100" C. This was accomplished by means of the electrically heated resistance wire, 4. The entire humidifier was immersed in a large water bath. The temperature of the humidifier did not in general vary more than * 2' C. during a run. The effectiveness of the humidifier was determined experimentally, and i t was found t h a t under the most extreme conditions encountered in this investigation the relative humidity of the gases after passing through the humidifier was 100 per cent. A calcium chloride drying train (not shown in figure) was used in some of the runs t o dehydrate the gas issuing from the meter. The effectiveness of this drying train was also determined and it was found t h a t the partial pressure of water vapor
in the gases issuing therefrom was approximately 2 mm. of mercury. The reaction tube was a Pyrex glass tube of 2.5 cm. internal diameter. A heavy copper sheath surrounded t h a t portion of t h e tube in the interior of the furnace. The purpose of this sheath was to equalize t h e temperature over t h e length of t h e tube, for without it a very considerable temperature gradient existed between the mid-point and the ends of t h e different units. By means of this sheath and the first and third units it was possible t o maintain a temperature uniform t o within 5 O C. over a length of 25 cm. in the middle unit. This section of uniform temperature contained the charge of hydroxide (50 g.) during the runs. The first unit-which also served as a preheater-and the third unit were filled with glass beads o r pure silica sand. A slit about 5 mm. wide cut lengthwise in the sheath permitted observation of the interior of the reaction tube. The furnace was placed in an almost vertical position in order to prevent the gases from channeling across the surface of the hydroxide, and, in addition, t o facilitate the collection of the liquid products of reaction. A narrow-bore Pyrex tube ( 2 mm. diameter) extended up t h e center of the reaction tube as shown, and contained a noblemetal thermocouple, by means of which the temperature was determined. The absorption train consisted of two Meyer sulfur bulbs in series, each containing about 150 cc. of water saturated with methyl chloride. This was found by trial to be the most satisfactory type of absorption train for this purpose. Two bulbs were found t o be sufficient, for the amount of methanol which was collected in a third bulb was less than the error of the subsequent analysis for methanol. Besides, i t was desirable to keep the amount of water in the absorption train as small as possible in order t o reduce the error due t o the solution of gases therein. The gasometer has a capacity of 20 liters, and was designed and built especially for this work. The rise of the gas holder was about 2 mm. for 50 cc. of gas, and hence volumes could be determined readily to *10 cc. The gas holder worked in a very narrow annulus, so the amount of liquid exposed t o the gas was as small as possible. The containing fluid used was a saturated solution of calcium chloride, for it was found by trial t h a t methyl chloride had a lower solubility in this solution than in any other available liquid. The gasometer was carefully calibrated over the entire range of its capacity, and this calibration was then checked against the gas meter. Since the gas meter could be read t o * 10 cc. and the gasometer to * 10 cc., the determinations of the absorption of gas taking place in the apparatus were good t o * 2 0 cc.
*
July, 1923
IhTD USTRIAL AND ENGINEERING CHEMISTRY
PROCEDURE-After the charge of hydroxide had been placed in the reaction tube, a blank was run to see if the apparatus was in proper working order. A few cubic centimeters of methyl chloride were permitted to flow through the apparat,us in order t o establish the proper pressure drop throughout the train. Readings were taken of the dial, the temperature, the meter, the gasometer, and the barometer height. The use of proper counterweights kept the pressure in the gasometer always equal to atmospheric pressure. Four or five liters of methyl chloride were then sent through the apparatus a t the rate used in making the run. The meter a n d gasometer were then read again, and the volume of the gas sent through the meter was compared with that collected i n the gasometer. A blank was not considered satisfactory unless these two volumes agreed to within 40 cc., the limit of precision of the readings. I n this way any errors due to leaks or incoinplete saturation of the water could be detected. I n some cases blanks were also made after the runs to determine whether any such errors had arisen in the course of the run. After a satisfactory blank had been obtained, the furnace (all three units) was brought up to the proper temperature, t h e gasometer emptied, and methyl chloride permitted to flow through the apparatus a t the desired rate. Readings of temperatures, pressures, and volumes shown by the meter and gasometer mere taken every 15 or 20 min. When i t was evident t h a t the absorption of the methyl chloride-i. e., conversion to methanol-had practically stopped, the run was discontinued and final readings were taken. (Actually, the absorption of methyl chloride did not completely stop, but reached a small constant value. See curves for Runs 1to 9.) T h e duration of the runs varied from 4 to 6 hrs., and hence readings of the barometer were taken several times during the interval. From the data thus obtained and the analysis of the initial and final products, the conversion of methyl chloride to methanol and by-products could be computed. B y plotting the percentage decrease in the volume of the gas passing through the reaction tube in each 20-min. period, the course of the reaction could be followed. DISCWSSIOK OF EmoRs-The precision with which the absorption of the gas could be determined was * 2 0 cc. Since the total gas absorbed during a run exceeded 10 liters in almost all cases, this error amounted t o less than 0.5 per cent in the final calculations of yields. However, in determining the amount of gas absorbed during the 20-min. periods, it caused a very noticeable variation i n the readings, whir, -esulted in a staggering of the points on the curves. This . especially evident a t the ends of the runs where the actual absorption is small. Here an error of 40 cc. amounted in some cases to approximately 30 per cent of the actual volume absorbed. Pressure and temperature variations occurring during the run gave rise to additional errors. While the effect due to atmospheric variations was never significant, the variation in pressure of the gas in the meter, owing to pressure variatioas in the train of apparatus, occasionally amounted to k 2 . 5 mm. of mercury. This was taken care of to a great extent by using the average pressure in calculations. Fortunately, the prezisure on the water of the absorption train was not subject to this change of pressure, for the pressure in the gasometer was always maintained equal to that of the atmosphere. I n this way any error due to an increase or decrease in this amount of gas dissolved in the water was avoided. Variations in the temperature of the room gave rise to a more significant error, for occasionally these amounted to 2" C. The average temperature was used in making calculations. On the whole, however, the error of the determination of the total volumes of gas delivered and collected probably did not exceed 1 per cent.
685
RESULTSAND CALCULATIONS-The results obtained under varying conditions are shown by Curves 1 t o 9, and by Table I. The data obtained in one of the runs made at 400" C . , using anhydrous methyl chloride, are shown in Table 11. The following example will make clear the method of obtaining these curves : Column J is obtained by converting the readings in Column A (volume of gas admitted in cubic feet a t room temperature and pressure) t o gas volumes in cubic centimeters a t standard conditions. (20.95 -I- 0.90 - 0.61) 273 J = A X 28,320 X X 291 = A X 26,880 30.00 since the vapor pressure of water a t 18" C. = 0.61 in. of mercury. Column I, is obtained similarly from Column H : 29.96 - 0.61 273 X iyl = H X 0.9176 L =H X 30,00 The solid line Curve 8 was then plotted, using Column N as ordinates'and Column T as abscissas. The analysis of the final products in this case was as follows: GASSOUS: Methyl e t h e r . . . . . . . . . . . . . . . . . . . . . . . . . . . Methvl chloride., . . . . . . . . . . . . . . . . . . . . . . . Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . h-itrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~~~~~~
TOTAL ...............................
Per cent 31.2 52.9 1.8 2.0 4.8 7.5 100.0
--
Methanol = 9.83 g . Calcium chloride = 70.0 per cent = 65.4 per cent of the calcium hydroxide c h a r g e d i n t o t h e furnace 0.700 X (74.1/111) 100 0.93 = 65'4aper cent 1 - (0.700 X 37/111) Total methyl chloride delivered = 0.9358 X 26,800 X 0.99 = 24850 cc. Total methyl chloride recovered = 14,260 X 0.9175 X 0.529 = 7000 cc. Hence, total methyl chloride converted. . . . . . . . ? . . . . . . . . . . . . ..17,850 C C . Now, 17,830 cc.
=
Yield of methanol
=
17,&50+21,900 = 0.815 mol 9.83 9.83 = = 0.307 mol = 37.8 per cent yield 32
-
0'312 = 0.377 mol = 46.3 per cent yield 22,000 Yield of methyl ether = 13'300 Yield of methane Products recovered
13'300 o'020 = 0.019 mol = 1.5 per cent yield 22,400 0.703 mol = 85.6 per cent yield = =
-
-
The remainder, equal to 0.112 mol (equivalent t o 1.23 liters of methyl ether), was present as methyl ether dissolved in the water of the absorption train. This was readily determined by passing a stream of methyl chloride through the train for several hours until all the ether had been swept out, and .then analyzing the resulting gas mixture. The amount of methyl ether obtained was equivalent to the remainder to within 1 per cent. The 0.815 mol. of methyl chloride used would require 0.815 x 74.1/2 = 30.2 g. of calcium hydroxide = 65.8 per cent [30.2/ {60 x 0.95) = 65.81 of t h e calcium hydroxide charged into the reaction chamber. The divergence between this and the result found by analysis is less than the error of sampling.
It is obvious that' the curve drawn with the actual percentages of gas absorption as the ordinat,es does not give a true indication of t,he conversion of methyl chloride, since considerable amounts of methyl ether and some hydrogen and methane were produced, which great,ly reduce t'he apparent absorption. This difficulty can be lessened to some extent by using the act,ual conversion of methyl chloride as ordinates, on the assumption t h a t the composition of the gas received, as shown by the final analysis, was the same throughout the run. This was done and t'he dot'ted curves were obtained. This gives a closer approximation to the true conversion curves, but they are still somewhat distorted since most of the methyl ether gas generated during the run is certainly produced during the first, two-thirds of the run. The actual conversion of methyl chloride t o methanol and methyl ether, therefore, probably follows the course shown by the dot-dash curve. The labor and time involved in carrying out a run from start to finish, including the necessary blanks and the analyses of all the products, were too great to' permit duplicate runs
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
688
to be made in every case. However, a number of duplicates were run in the preliminary investigation to determine whether the apparatus as a whole and the method followed would give reliable data. The results obtained were very satisfactory.
Vol. 15, No. 7
tively converted into methanol and methyl ether. Traces of formaldehyde were also formed, but they never amounted to as much as 0.1 per cent of the methyl chloride. THEORETICAL
/20
The following calculated results of the theoretical relations of the reactions encountered in this investigation served as a guide in pursuing this research and as an aid in interpreting the experimental results. THERM.4L ANALYSIS O F THE PRINCIPAL REACTIONS HYDROLYSIS OF METHYL CHLORIDEIN THE GASEOUS
IO0 BO
60 40
10
0
PHASECHICI HzO = HC1 CHIOH X,* Cal. X, Heats of formation -29.0 -58.3 = -22 0 -53.3 Therefore, X , ( ~ Sc.) O ( a ) = -12.0 Cal. From the reaction isochor of van't Hoff,
+
'00
i
! : +
don KP) dT
20
u8 o
/oo 80 60
40 20 8
0
6 / O / 5 1 0 2 5 30 35 40 45 5 0 5 5 60 65
Duration of Ruq Hours
One instance of this is shown in Runs 1 and 2 (Table I). The analytical data for these runs are given in Table I, and it is seen that the agreenient is very good. Moreover, the concordance of the results among themselves is an additional argument for the precision of the work. As an additional check a run was made using methyl chloride prepared by Groves' method.l6 About 50 liters of the gas were collected after having been purified by passage through concentrated sulfuric acid, sodium hydroxide, and water. This gas was then displaced from the container, and passed through the meter and on through the apparatus in place of the commercial gas. The result is shown as Run 5. The conditions of this run duplicated those of Run 4, except that the humidity was slightly higher. Here again the excellent agreement between duplicate runs is seen, and since this run was made with pure methyl chloride, it serves as a check on the entire work. Run 7 was carried out as a continuation of Run 6, in order to investigate the small constant absorption of methyl chloride in evidence a t the end of all the runs. This run was preceded and followed by a blank, and was carried out exactly as the other runs, except that the charge of calcium hydroxide was the residue from Run 6, which had not been removed from the reaction chamber. The curve obtained shows that this small constant absorption of methyl chloride continues for a considerable time. I n all these experiments a slight deposition of carbon was obtained, caused by the thermal decomposition of the methyl chloride and the products of reaction. This deposit began a t the point where the entering gas first met the charge of calcium hydroxide, and during the course of the run it slowly progressed down through the hydroxide. At 350" C . it was very slight, causing the hydroxide t o become gray in color. At 450' C. it caused the charge to become black. Increasing concentrations of water vapor caused a noticeable decrease in this carbon formation. The other products obtained in these runs are shown in Table I. With the exception of a small amount of methane and hydrogen the methyl chloride was practically quantita10
A n n . , 174 (1874),377.
G%
+
(where Q,
+
+
(a)
heat evolved by the reacting system), it, follows, since Q p is negative, that the point of equilibrium will be shifted to the right as the temperature is raised, resulting in a greater yield of methanol. CONVERSION OF METHYLCHLORIDETO METHANOL BY MEANSOF CALCIUM HYDROXIDE2CHaC1 Ca(OH)%= CaCL 2CHiOH X, Cal. ( b ) Heats of formation** -2(29.0) -219.1 = -173.4-2(53.3) X, Therefore, Xp(150 c.) ( b ) = 4-2.9 Cal. Since Q, is positive, the yield of methanol will decrease with increasing temperatures. Fortunately, the magnitude of Q, is small so that the diplacement of the equilibrium with increasing temperature is not very great. It is possible, therefore, to obtain the advantage of the increased velocity of reaction occurring a t high temperatures without any considerable diminution in the extent of the reaction. Calculating the heat of reaction a t 390' C., we have from Kirchoff's law: =
+
+
'2
= Z C , ~(reactions)
+
+
- ZC,~' (resultants)
* X, = heat of reaction at constant pressure. ** The values given, except those for calcium chloride and calcium hydroxide, correspond to the heats of formation of the compounds in the gaseous state at 15O C from the elements
I N D U S T R I A L A N D ENGINEERING CHEMIXTR Y
July, 1923
TABLE I-EXPERIMENTAL RESULTS 1 2 3 4 5 350 350 350 350 350 50 50 55 50 45 425 180 350 20 20 67.0 50.8 66.9 40.0 ........... 42.0 34.8 46.3 41.5 50.0 49.5 Per cent C:aCIz in residue.. 15.28 18.12 13.85 13.70 16.99 7.22 11.15 4.78 7.34 7.06 78.1 79.1 97.32 11,5 . . . . . . . . . . . . . . . . 192.3" 95,O a 17.0 2.1 1.6 1 . 1 Per cent H a in gas received.. . . . . . 1.0 2.0 0.3 0.7 0.4 Per cent CHI in gas received.. . . . 6:OO 5:OO 5:OO 4:30 4:45 Duration of run hrs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 50 50 50 50 Amount Ca(OH\z charged into reaction tube, g r a m s . . . . . . . 9.40 9.41 Volume CHIC1 absorbed during run, l i t e r s . . . . . . . . . . . . . . . . 11.80b 11.83b 10.486 6.72 5,16b 3.37b 1 9Ob 5.87 Volume CHsCl recovered, liters. . . . .? . . . . .; . . . . . . . . . . . . . . 30 .... .... 30 50 Volume CHa obtained, CC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.6 0.6 Trace Trace 0.2 Per cent yield as decomposition products, Ha, CHI, etc. . , . . 32.4 49.P 32.5 . . . . . . . . . . . . . . 5 8 . 5a 6 0 . Oa Per cent yield as CHs.0.CHs.. Trace 1 .o 1.0 Trace 3.0 Per cent decomposition of unconverted CHaCl. . . . . . . . . . . . . 34.2 .... .... .... 34.2 Per cent Ca(0H)a converted calculated from CHIC1 used. :. 34.5 40.0 35.0 43.0 43.4 Per cent Ca(0H)z converted: calculated from CaClz found. . a Determined by absorption in glacial acetic acid [Allison and Meighan, THIS JOURNAL, 11 (19191,9431. RUN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
687 6
350 90 2 35.9
8
7 336 65 300 66.5
400 70 2 37.8 70.0 i9:i5 1430 25.10 12.21 12.71 13.31 66.5 95.0 52.8 19.6 3.0 31.2 Trace ... 4.8 Trace 2.0 , . . 6:lO 4305 4:OO 50 50 50 2.10 18.10 11.05 8.10 12.10 7.00 . . . . 270 .... .... 3.0 64.1 59.2 33.0 0.5 ... 7.0 7.6 40.3 65.8 ... 65.4 BesVmethod of analysis of
9 450 70 z 31.6 74.0 24.80 14.85 36.8 29.4 16.0
10 400 70 380
R 9
60.8
62.6 25.92 14.43 69.0
20.2 4.0 2.6
8:OO 5:30 50 50 19.30 15.92 5.50 10.00 14.70 375 4.6 15.2 35.0 53.3 4.2 35.0 58.0 70.2 70.5 57.0 methyl chloride
had not yet been perfected. b Calculated on basis of calcium chloride obtained.
Meter Meter Meter Incremenit Pressure Temp. Cu. F t . Cu. F t . In. Hg " C . (B) ('2) (A) +0.80 16.0 10:50 4,1005 0.0000 0.85 . . . . 4,1230 0,0225 11:05 0.85 . . . . 11:20 4.1570 0,0340 0.85 16.0 4,2060 0.0490 11:40 0.85 . . . . 12:00 4.2510 0,0480 0.85 16.5 4,2990 0.0480 12:20 0.85 16.5 12: 42 4.3530 0,0540 0.85 17.0 4,3970 0,0440 1:oo 0.85 . . , , 4.4500 0,0530 1:21 0.85 1 8 . 3 4.5150 0.0650 1:45 0.85 . , . . 2:00 4.5500 0,0350 0.85 . . . . 2:20 4.6050 0.0550 0.85 . . . . 2:40 4.6543 0,0493 0.95 19.0 3:OO 4.7073 0,0530 1.00 19.0 3:20 4.7627 0,0554 1.00 19.5 4.8140 0,0513 3:40 1.00 19.5 4:OO 4.8700 0.0560 4:20 1.00 . . . . 4.9230 n nmo 1.00 . . . . 4:40 4 9795 0 OS65 5 : 00 1.00 . . . . 5.0325 0 0530 1.00 20.3 5:03 5 0373 0 0048 6 h r x r m i n . 0.9368 0.9368 0.90 18.0 Time
-
TABLE 11-CONVERSIONRCN 8 (Drying Train Substituted for Humidifier) Furnace Gasometer Temp. Temp. Barometer Gasometer Increment o c . o c . In. Hg c c. c c. (D) (E) ( F) (G) (H) 400 16.0 30.09 240 0 400 .... ..... 830 590 .... ..... 1,300 470 400 16.6 ..... 1,600 300 400 400 16.5 1,800 200 29:ss 1,960 160 400 16.5 404 16.5 ..... 2,130 170 400 .... ..... 2,270 140 .... ..... 2,500 230 400 ., , , ..... 2,870 370 390 ..... 3,200 330 400 17.5 400 18.0 ..... 3,840 640 .... 29.93 4,630 790 400 ..... 5,850 1,220 400 18.5 .... ..... 7,300 1,450 400 ..... 8,600 1,300 405 i6.0 ..... 10,020 1,420 405 .. , . ..... 11,400 1,380 405 405 19.5 ..... 12,980 1,550 .... ..,.. 14,350 1,400 405 ..... 14,500 150 400 20.3 29,95 14,260 :14,260 400
- - __
+
whence Q p ( 3 b ~ : c.) = Q p ( 0 o c,) 350 (BCJ the mean specific heats are as follows: (At 0 to 360' C.) Calcium hydroxide Calcium chloride Methanol Methyl chloride
t
-
18.0'
-
ZC,r'), where
25.0cal.t21i 10.0 cal.17 18.0ca1.18 12.5cal.19
cal. = gram calories; Cal. = kilogram calories.
Hence, X,
(3500
c.)(h)
= =
+
+2900 cal. 350(50-65) cal. 0.9 Cal. = 0.45 Cal. per mol methanol formed
This small heat of reaction is very advantageous in that it enables t,he temperature of the reaction chamber to be readily controlled. FORMATION OF
METHYL ETHER-
+
B(CHaC1 CH30H = CH3.O.CH3 -I- HCI) 2HC1 Ca(0H)Z = CaClz HzO
+
+
2CHaCl
+ 2CHsOH + Ca(OH), = CaC12
+ 2CHs.O.CH3-I- 2Hz0
(4
Estimated from specific heat tables in "Tabellen zur Berchnung des gesamten und freien Warmeinhalts fester Kdrper" by Miething (Halle, 1920),pp. 31 and 35. T h e specific heat of calcium chloride is not given, but i t is estimated fromsthe data given for lead chloride. Lead chloride and calcium chloride have the same molecular specific heat a t 0' C., and from the similarity of the compounds it is to be expected on the basis of Debye's theory t h a t their specific heat-temperature functions will be very nearly coinci+nt over this range. IR Estimated from specific heat data given in Landolt-Bornstein-Roth, "Tabellen." I9 Cp(i50 c,) = 11.95cal. (calculated from cp/cy ratio given inLandolt-Bornstein-Roth, 'Tabellen"). Using Nernst's empirical equation, C p = 3.5 f 1.5, f UT,or C, a t 350' C. = 13.0; hence, C, (mean) (0-350' C.) = 12.5. l7
(JJ
0 600
910
1315 1:205 1,285 1450
1:1so 1420 1:745 935 1,475 1,320 1,420 1,485 1,375 1,500 1,240 1,515 1,420 130 25,105
-
Gas Received c c. (L) 0 540 430 275 185 145 155 130 210 340 305 590 725 1,120 ' 1,330 1,195 1,300 1,265 1,420 1,285 135 13,310
Gas Absorbed Cc. (Mj 0 160 480 1,040 1,020
-
Gas Absorbed
630
0.0 26.7 52.7 79.1 84.70 88.7 89.3 89.0 85.2 80.5 67.4
885 595 300 155 180 200 155 95 135
45.1 21.1 10.4 13.1 13.3 9.2 6.3 9.5
1,140
1,295 1,050 1,210 1,405
_
...
_
11,800
60.0
I
-
....
....
The heat of reaction is readily computedas Q p ( 1 5 0 c , ) ( d ) = +9.1 Cal. The same observations made concerning Reaction b apply here. (It may be noted for future reference that the heat of Reaction c = X p ( , s oc ) = - 8.9 Cal.) CONVERSION O F METHYL ETHERTO METHANOL-The authors have demonstrated that the application of the following reaction, using aluminium oxide as a catalyst, permits the conversion of the methyl ether obtained t o methanol.
+
+
CH3.0.CH3 Hz0 = 2CH3OH X, Here Xp(150 c.) ( e ) = -3.1 Cal.
(e)
Evidently, increasing temperatures will favor this reaction. However, it has been shown20that when the reverse reaction is carried out above 350" C. side reactions occur.
(c)
For the purpose of this analysis we may consider them as equivalent to their sum:
.__.
Gas Delivered c c.
APPLICATIOX OF NERNST'S HEATTHEOREM I n a system such as obtained here, where several reactions are occurring simultaneously, it is very difficult to interpret correctly the experimental results or to control intelligently the final products without some quantitative knowledge of the existing equilibria. To determine these by experimental means is in general a very troublesome and often an impossible task. I n the present instance a knowledge of these equilibria was obtained to a surprisingly satisfactory degree by the use of Nernst's heat theorem.21 The application of Nernst's theorem has made it possible to calculate the free energy, and hence the point of equilibrium of any reaction occurring in a condensed system, Sabatier and Maihle, A n n . chzm phys., 20 (1910),343. Nernst, "Experimentalle und theoretische Grundlagen des neuen Warmesatzes" (Halle, 1918); cf. "Applications of Thermodynamics t o Thermochemistry," 1907. 20
21
INDUSTRIAL AhTD EhTGINEERING CHEMISTRY
688
provided the substances entering into the reaction are pure. By a further development he had extended this application to heterogenous reactions where one of the phases is gaseous. The equation for the equilibrium point which follows from his theorem is
where Q., = heat evolved a t constant pressure a t absolute zero CY’, b’, y’ = constants depending upon the specific heats of the substances reacting Z n i = summation of constants depending upon the nature of the reacting materials existing only in the gaseous phase
I n applying this theoretical equation to a specific case difficulties are immediately manifest, for it is necessary to know the specific heat as a function of temperature from absolute zero up to the temperature in question for each of the reacting materials, and in addition the same thing for the vapor pressure-temperature relations. I n the present state of knowledge these are known for very few substances. I n order to apply this equation, therefore, it is necessary to make many simplifying assumptions. This has been done by Kernst, among others.23 I n this work the assumptions made by him have been accepted because of the success already attained with them, and also because they have been found to give results in excellent agreement with this experimental work. On the basis of these assumptions Nernst arrives at his “approximation formula:”24 Log K =
- x ? 4 +T Zv 1.75 log T + 4m T + XnC Qo
where Zv = the change in the number of the molecules formed by the reaction Z:nC = the summation of the “chemical constants” of the reacting Substances existing only in t h e gaseous phase 0 = a term depending upon the specific heats of the reacting materials Moreover, Q, = Q, Zv 3.5T pT2, and ZC,r ZC,r’ - Zv 3.5 P = 2T
+
-
+
In order to determine the chemical constants, C, which are really the integration constants of the Clapeyron-Clausius vapor pressure equation, Nernst has used a number of devices. The results in all cases, however, are approximately the same, and are very nearly equal to the quite empirical value : C = 0.14 X/Te. P. whereX = heat of vaporization a t boiling point, and T lute temperature of boiling point.
=
abso-
By the use of this formula Nernst has obtained his so-called “conventional chemical c ~ n s t a n t s . ” ~ ~ While these assumptions are based on a theoretical foundation, they are by no means in strict accord with the known facts concerning the specific heat-temperature relations a t low temperatures. The true chemical constants, for example, which have been calculated for a very few elements,26 are by no means in agreement with the conventional chemical constants. Nernst advocates these assumptions simply as a set of empirical relations, which in many cases are found to give very satisfactory approximations to the true equilibrium points. The results that have been obtained by their use fully confirm this contention, at least for the cases considered. Nernst, loc. cit., p. 104. Loc. cat , Cederberg, “Nie thermodynamische Berechnung chemischer Aftinitaten von homogenen und heterogenen Gas Reaktionen,” Berlin, 1916. 2 4 L O C . cit., p. 110. 25 L O C . cit., p. 111. 26 Egerton, Phil. Mag., 39 (1920), 1; Lindemann, I h z d . , 39 (1920), 21. 22
23
Vol. 15, No. 7
THERMAL DATA-The successful application of Kernst’s approximation formula to these reactions is possible because the substances entering into the reactions are not of great molecular complexity, so that the assumptions made by Nernst hold approximately. The thermal data employed in applying this formula are as follows: Ch(Oo C.)
Compound
Hz0 HC1 CHaOH CHaCl (CHa)aO Ca(0H)a CaClz
-.
T,-. - Z 8
X cal.
373
965028
8.032’ 7 129
14.0ao
...
340 250
gi(j(j2Q 487029 62408a.
11.958‘ 20.582 19.617
249
... ...
.... ....
1s. 2 2 9
C 3.628 3.028 3.64 2.73 2.95
,.. ...
APPLICATION-For convenience of reference the results obtained by the application of Nernst’s theorem to the reactions experimentally studied later are given here.
+ Hz0 = CH30H + HC1 = + 8.03) - (14.0 + 7.1) - 0 -- --1546 - 1 - -0.002
(1) To reaction: CHsCl 11.95
2 X 273 Cal. (Equation a), also Zv = 0, since there is no volume change 3.6 - 3.54 3.0 = -0.2 ZnC = 2.73 Hence, Q, = -12,000 - 0 0.002 (273)2 = -11.9 Cal. Substituting for log K in the equation of Nernst’s appraximation formula 0 f 0.002/4.571T - 0.2 log K, = 11,900/4.571T or log K, = 2600/T - 0.00044T 0.2, where K, = CHsC1 X HzO CH30H X HCI Therefore, a t 350” C., K, = 5.0 X 103 Evidently, if this result is correct, it will not be possible to obtain methanol by hydrolysis of methyl chloride with steam.
Q, = -12.0
Now,
+
-
+
+ -
+
+
(2) To reaction: 2CH3Cl Ca(0H)z = CaCln 2CH30H. By a similar calculation, we obtain the following formula for this equilibrium point : logK, = -715/T - 0.0011’I’ 1.62, where K, = (CH3Cl/CHaOH).2 Therefore, a t 350’ C., K, = 1.5 X 10-4,or l/,,/Fp = CHBOH/CHaCl = 54. That is, if equilibrium can be reached at 350” C., over 98 per cent of the methyl chloride can be converted to methanol.
-
+
+
(3) To reaction: CH3Cl CHaOH = (CH3)20 HCI. Here we have log K, = -1932/T 0.00019T - 0.3, where,
+
+
+
(4)To reaction: Ca(OH)% 2CHsC1 2CHaOH = 2CH3.0,CHs 2H20 f CaClz. This reaction, as previously stated, is really the sum of two reactions. Applying Nernst’s formula to this system, we have: -2110,”I’ - 0.0015T - 0.56. log K, Therefore. a t 350”:
+
Accordingly, this reaction will readily produce methyl ether.
+
( 5 ) To reaction: (CH3)20 HzO = 2CH3OH. It will be subsequently shown that this reaction furnishes a method for the conversion of methyl ether to methanol. In this case the value ZC,r - 2Cpr’ is so small that is taken as zero. Then, (CH30H)2 log K, = 678/T - 0.47, where K, = CH 0.CH3 H20 Therefore, a t 350’ C., 27
K,
=
0.25 (approx ) .
From cp = 0.0446 + 0 0000428 t (Holborn and Henning, 1905).
Same value given by Nernst, 206. c z t . , p. 112. Calculated from data in Landolt-Bbrnstein-Roth, “Tabellen,” p 840. Estimated from data in Landblt-BBrnstein-Roth, “Tabellen,” p. 774. 81 Calculated from c p / c v given in Landolt-Bbrnstein, “Tabellen,” p 774. a 2 Calculated from formula in Washburn, “Physical Chemistry,” p. 70: X/TB. P. = 9 5 logioTB 0 007T~. 23
29
30
-
