April 15, 1931
INDUSTRIAL AND ENGINEERING CHEMIXTRY
is 9 cm. long and 3 mm. in diameter. The dimensions of the assembly are shown on the diagram. The surface of the mercury at E may be cleaned readily by pouring in a suitable solvent and then expelling it through D by plugging up A and C and blowing a t B. If the surface of the mercury is oxidized or corroded, a small portion of the mercury itself may be expelled in the same way. Thus it is only occasionally necessary to refill the divider. This device has proved to be satisfactory at pressures as low as 1 mm. The adjustment is sensitive, and the screw turns easily. If the tube A-C is of small bore, say less than 15 mm., the reading of the thermometer may be affected by the proximity of the cold reflux returning from B. We may modify the construction of the stillhead itself so as to return the reflux a t a lower point, as shown in Figure 2. This con-
139
struction gives rigidly accurate temperature readings, but is fragile. A simpler, although not quite as effective method of eliminating thermometer error is to flare out the joint at F into a bulge of 2 to 3 cm. in diameter. The returning stream is then far enough away from the thermometer bulb not to affect the reading, A simpler valve, one which may be used where there is not a large amount of fractionation to be continuously done, can be made from the same stillhead. At E, instead of sealing on the valve, a piece of rubber tubing is slipped over the stem. This is closed tightly at the far end, and is filled with mercury. The level of the mercury in the elbow is controlled by an ordinary pinchcock around the rubber tubing. This device is quite as efficacious as the more complicated one. Its disadvantage is that it is difficult to keep the tube from leaking over long periods of time.
Glass Temperature and Float Regulators' D. F. Othmerz EASTMAN KODAKCOMPANY, ROCHESTER, N. Y.
The development of industrial processes on a labothe cock with the free end unratory and pilot-plant scale is frequently hindered der the liquid surface of a dish ects are usually deby the lack of controlling apparatus of such simplicity containing both the volatile veloped as a result of and smallness as will fit in with the minute process liquid and mercury. The des t u d i e s m a d e with small equipment employed. Several types of temperature sired amount of volatile liquid units, and in the operation and float controllers representative of those which is drawn in first, then merof such pilot eqJipment i t have been successfully employed are described as being cury is allowed to fill the rest is f r e q u e n t l y desirable to suitable not only for use with ordinary chemical laboof the tube. have apparatus to regulate ratory apparatus, but adaptable to the regulation of The flow controller, Figure the processes similar to the pilot-plant distillation and related operations. 3, is mounted above the conautomatic controllers of indensers and its bottom outdustrial usage. The electrical thermostat circuit described (3) in a previous paper has been let connected to the inlet tube of the Sensitive bulb. The used as a pressure regulator for glass and pilot-plant stills and, connecting tube is filled with mercury and the system by means of its use with a n inclined manometer and a n in- heated to the desired operating temperature, as shown by ternal electric heater, a very constant rate of distillation may an auxiliary thermometer. The level of the flow controller be maintained, A similar manometer circuit with the bulb is adjusted so that the vapor pressure of the liquid in the of a vapor-pressure or liquid-expansion thermometer as the sensitive bulb a t the set temperature forces the mercury sensitive element may be used for controlling temperature, high enough to submerge the inverted V-weir of the central but it has the disadvantage of a simple on-and-off regulator tube. Cooling water flows into the tube at the upper left of the with no intermediate steps automatically controlled. A self-contained temperature controller using a vapor flow controller and, when the mercury is below the level of pressure bulb as the sensitive element and requiring no auxili- the weir, down the annular space, up through the inner ary power is shown in the accompanying figures.* Its use tube, and out through the discharge tube on the left to waste. as applied to control of stillhead temperature by regulation As the mercury rises and throttles the flow through the weir, of the amount of wash liquid returned to a fractionating the water rises in the central tube and overflows the tube column is indicated in Figure 1. The sensitive bulb of Figure on the right side. Both outflow tubes have insealed tips 2 is inserted above the depblegmator condenser of a double to enable visual inspection of the comparative amounts condenser unit (2) and maintains the temperature of the flowing in each, and are vented to prevent siphoning. The vapor stream between the two condensers at a constant pre- right, and higher outlet discharges through a rubber determined value. It is previously charged with a liquid tube to the base of the dephlegmator coils and furnishes of suitable volatility, preferably one with a vapor pressure cooling water for condensing the liquid to be refluxed as of about 90 to 125 cm. of mercury, at the temperature to be wash. As the temperature in the head of the dephlegmator maintained. Only enough of the volatile liquid is required rises, the flow of water through the weir and to waste is to give always a liquid phase. A bubble of air is allowed to throttled and a larger amount overflows the right tube and remain to insure a gas and vapor phase, and the rest of the thus passes through the dephlegmator condenser. This tube is filled with mercury. The bulb is readily charged by additional cooling water produces more condensate, which, Connecting with a straight glass cock, evacuating with a by its washing action in the rectifying column, reduces the water pump, disconnecting the vacuum hose, and opening amount of high boilers in the vapor and therefore the temperature Because of the lag caused by the small time in1 Received November 3, 1930. * Present address, 356 Clay Ave., Rochester, N. Y. terval in the change of the distillation with a change of reflux 8 All the glass apparatus described and pictured herein has been conratio, the amount of cooling water required is never exactly structed of Pyrex glass by the Technical Glass Co., 42 Galusha St., obtained as a steady stream, and the temperature varies which is also prepared to supply additional equipment of Rochester, N. Y., slightly with accompanying changes in flow of cooling water name type.
ARGE distillation proj-
L
140
ANALYTICAL EDITION
to the dephlegmator. A much smaller variation is obtained owing to the taper of the weir, however, than would be possible with a simple on-and-off valve. During the progress of a discontinuous distillation, as the liquid in the still pot approaches exhaustion of the more volatile component, a larger amount of wash liauid is required, and the temperature and mercury level increase slightly to furnish additional water to the dephlegmator. If a sensitive liquid is chosen with a vapor pressure a little over 100 cm. at the temperature to be maintained, the rate of change of vapor pressure with temperature will be s u c h t h a t a few tenths of a degree rise of t,empera t u r e raises the mercury a centimeter or more to shut off the flow t h r o u g h the weir completely. I n the operation of continuous distillation processes, the use of this regulator has enabled the maintenance of a boiling point of d i s t i l l a t e never more than two-tenths of a degree high over a period of weeks of o p e r a t i o a , practically without attention and with large changes in rate and composition of feed and rate of distillation. The same regulation of larger pilot-plant distillaFlgure 1-Temperature Controller tion systems has been seInstalled on Stillhead cured with this flow divider by using it to control the reflux ratio directly instead of controlling the water supply to a dephlegmator condenser. I n this case, a single condenser is used for condensing all of the vapors and the sensitive bulb is mounted in the top of the rectifying column. The condensate flows through the flow divider directly, similar to the flow of cooling water in Figure 1, out through the left lower tube as product, and through the right connection as reflux to the column. The temperature a t the head of the column and the resulting vapor pressure in the sensitive bulb control the mercury level in the flow divider which in turn regulates the ratio of product to reflux. A much larger amount of condensate may be handled in this manner, with a somewhat larger controller than that shown in Figure 3, and the time interval is reduced because of the comparative closeness of cause and effect. This regulator has been adapted for numerous other uses in the regulation of pressure or temperature when a flowing liquid causes the change of conditions. It has proved an especially simple and efficient thermostat in water baths varying in size up to hundreds of liters. (For pressure regulation, the vessel with controlled pressure is connected to one arm of a U-tube filled with mercury, and the other arm is connected directly to the bottom outlet of the controller.) For holding temperatures between that of the room and that of tap water, at approximately 20" C., the regulator is used exactly as described above for controlling distillation processes. The sensitive liquid used is Eastman ethylene oxide, which has a boiling point of 14' C. and a suitable vapor
Vol. 3, No. 2
pressure at 20" C. The vapor-pressure bulb is immersed in the bath and cold water from the right outlet runs directly into the stirred water, that from the left outlet runs to waste. An overflow pipe or siphon maintains a constant water level in the bath by allowing an amount equal to the cold water introduced to be discharged. An efficient stirring, accomplished by bubbling several jets of air through the water, must be maintained, as with any constant-temperature bath. A control with reverse action to that described is made by simply interchanging connections on the left and right side arms. For temperatures above that of the room, any point below that of the hot water available may be m a i n t a i n e d with one so arranged. The t e m p e r a t u r e of a 100-liter water bath was maintained a t 40" C. within very narrow limits over a period of weeks with ethyl ether as a sensitive liquid, and hot water discharging through the left arm to supply the heat required. The hot water supply varied in temperature between 48" and 95" C. during different times of the day, but this variation merely changed the size of the stream necessary to supply the re- F!#E;&g$Fquired amount of heat. Baths with temperatures between 15" and 25" C. require provisions for both heating and cooling if the temperature of the room fluctuates widely from day to night or month to month. Such regulation may be accomplished with mercury or other metallic expansion systems, relays operating electrical heaters, and solenoid valves controlling cooling water circulated through coils of tubing. Besides the involved mechanism, and the simple on-and-off features in both heating and cooling devices instead of gradual increments of heat added or removed, these devices have the a d d i t i o n a l disadvantages of large expense and considerable space requirements in a bath. The utiliz a t i o n of two liquid flow controllers, one diverting a stream of cold water and the other reversed in action and diverting a stream of hot water, accomplishes the same purpose with a single sensitive bulb in the bath connected to the two flow controllers. Figure 4 pictures such a system ready for mounting in the bath but with the bulb indicated as if heated to force the mercury into the divider. The flow controller on the left is "direct acting" for cold water, that U on the right is "reverse actFigure 3-Flow Diverters ing" for hot water. The extra length of the sensitive bulb is a precaution to prevent the very volatile liquid from blowing out the mercury in case it is allowed to come to room temperature. The vapor pressure of ethylene oxide a t room temperature is less than the height of meroury in the inner tube when the mercury is forced down and practically out of the annular space by the vapor pres-
} (
April 15, 1931
INDUXTRIAL AND ENGINEERING CHEMISTRY
141
The same type of vapor-pressure bulb that actuates all of the above-mentioned flow diverters has been used to open and close valves or cocks where a closed system under vacuum or pressure must be regulated. Figure 6 shows a typical member of this series. It is simply an ordinary cock having a short glass tube for a handle through which is placed a beam terminating in two mercury reservoirs. The left arm is connected to a sensitive bulb which, on increase of temperature, forces mercury into the reservoir. This counterbalances the mercury placed as a weight in the right reservoir, gradually overbalances it, and rotates the plug within the seat to open or close the valve, depending on the relative position of the bore in the plug and barrel. The desired leverage and travel is adjusted by varying the position of the cock along the beam and adding mercury to the reservoir on the right. Such a force or weight, variable with changes of temperature or pressure, may be applied to other uses, such as raising a piston, globe, or gate of a small metal valve, or pinching a light-walled rubber tubing to constrict or stop the flow. I n any case the vertical motion downward is usually comparatively rapid, since .the lowering of the upper mercury level causes a rapid flow of mercurx to balance the vapor pressure, and the cause and effect are cumulative until the movement is mechanically checked or until the system as a whole comes to the equilibrium or steady state desired. A mechanical advantage by fluid balance, similar to that which has been utilized for sensitive manometers ( I ) , gives a great increase of power to such mechanisms.
Figure4-Combined Hot- and ColdFlow Controllers for Heating and Cooling
Figure 5-Double-Flow Controller for Heating and Cooling
sure. The feed connections are as before, the left to cold, the right to hot water. The two inner outflow connections go to waste and the two outer connections go to the bath. The two weirs are at the same height and the increase of vapor pressure in the bulb raises the mercury level to throttle both simultaneously. This increases the cold-water flow and decreases the hot-water flow to the bath, the respective flows to waste changing to compensate. A combination of two of these regulators with mercury, waste, and bath connections joined is shown in Figure 5. The comparative compactness and simplicity of the connections is apparent and this type may be set up very readily. A small adjustment of relative heights of weirs to change the flow of the hot and cold water with respect to each other may be made if desirable by tilting the apparatus to throw either side slightly higher. Thus it is possible to stop the flow of cold water to the bath at one temperature and start the flow of hot water a t another temperature, lower by 0.05" C., say. Usually, however, the weirs are at exactly the same height and the streams of both hot and cold water are throttled so that a mixture of the two streams is discharged to the bath at just the average temperature required to equalize the amount of heat flowing into or out of the bath due to other causes. The same arrangement would obviously serve to supply a stream of liquid of any desired temperature by mixing a hot and a cold stream. A large gas-heated feeding tank has been maintained at a temperature constant within 0 2' C. by controlling the gas fed to the burner with a regulator such as shown in Figure 3. Gas is introduced through the upper left side arm and discharged through the lower left side arm, all other openings save the bottom being plugged. Mercury, actuated by a vapor pressure bulb, is used to throttle the flow of gas. A pilot light is, of course, necessary to relight an extinguished flame.
Figure 6-Mercury-Weighted
Cock
Float Controls
For maintaining a constant liquid level in various small vessels, baths, feeding bottles or siphons, and still pots, several types of float valves constructed of glass have been used. The first of these, Figure 7, allows liquid to flow through the upper inlet tube into the container until the ball float rises
ANALYTIC,4L EDITION
142
and the rubber valve seat throttles or closes the mouth of the inlet tube. The neck of a 200-cc. Pyrex spherical flask is removed and a stem of 8-mm. glass tubing sealed on in its place. The top closed end of this stem is capped with a piece cut from a rubber stopper of suitable size. This rubber cap and valve seat is notched on the lower side to allow liquid to
Figure 7-Inflow Float Valve with Rubber Seat
Figure &Outflow Float Valve, Intermittent Type
flow around it and down to the container beneath. The outer tube is of suitable size to act as a bearing for the vertical motion of the stem, and is enlarged at the top to accommodate a rubber stopper holding the inlet tube. The device as illustrated is for use in Pyrex 22-liter flasks, may be inserted through the 75-mm. neck, and is firmly supported in a hole in the rubber stopper. The level desired is regulated either by changing the length of the stem or by sliding the whole unit to the desired position in the rubber stopper. Such a level regulator has been used over a period of weeks at a time to control the level of acetone boiling in a flask, and it allowed gcetone from an overhead storage tank to flow into the still pot to replace that distilled out through a system of rectifying columns. The level of the boiling liquid did not change perceptibly - while the float was in operation, and when it was desired to shut down overnight or for other reasons, no attention was required, as this valve closed tightly. In the operation of continuous distillation operations, it is usually desirable to allow the slops, higher boiling residue, or product to flow out from the base heater. A type of float control which may be used for this overflow service as well as the inflow service of the one described above, is p i c t u r e d Figure 9-Outflow Float Valve, Constant-Level Type in Fimre 8. I n this v a l v e .. the s g m is separate from the float and is enlarged to form a hollow plug pierced by several holes as shown. A tube is sealed through the float of a size suitable to act as a bearing for the stem and is enlarged to form the sleeve for the plug. The sleeve and plug are ground to a good joint, and a small hole to equalize the pressure above
Vol. 3, No. 2
and below the ground joint is blown between it and the float bulb. When used to drain a vessel to a minimum level, this regulator is set in the position illustrated, and the lower end of the stem is sealed off or stoppered. The upper end is supported rigidly and connected to a suitable siphon which draws liquid between the ground surfaces, through the holes in the hollow plug, and up through the stem when the float is raised. As the liquid level lowers, the sleeve of the ground joint seats itself on the plug to close the perforations, and the liquid stops flowing. This vaIve works intermittently and dumps the liquid between a high level necessary to cause the ground joint to unseat, and a low level a t which a tight joint is again made. It is useful as a feeder for glass-packed columns for distillation or gas-absorption systems where an intermittent-flooding feed is desirable. I n such service it has worked unattended for hundreds of consecutive hours. The float control of Figure 8 is also used for regulating the inflow of liquid to maintain a constant level when the rubber seat of the one in Figure 7 is undesirable. It is then inverted from the pictured position and the end of the stem opposite the ground plug is sealed off. Liquid flows through the stem and the perforations in the plug when the float is down, and the stream is cut off as the float rises. I n this position this valve throttles and the liquid level is maintained within very narrow limits. Still another type which is all glass and is able to work against a higher pressure difference than the one of Figure 8 is shown in Figure 9. The liquid flows up through Figure the annular space past the ground seat and Steam or Vapor Trap of Float out the exit tube. A very short, blunt tip T~~~ on the inner tube is ground into the seat and because of the very small amount of friction and the minimized chance of seizing owing to the bluntness of the ground joint, this valve maintains a constant level against a discharging flow. It will maintain a level practically constant within a flask boiling with an internal pressure up to several pounds per square inch by discharging accumulated residue to atmospheric pressure. It is equally useful for maintaining a constant level in feeding tanks and other similar vessels, or when inverted it acts as a throttling inflow valve. Its small ground surface, compared with that of the one in Figure 8, makes i t a more sensitive and powerful valve. The glass float of Figure 10 serves in the pictured position as a steam or vapor trap. It has served several purposes where a separator for liquids and vapors was desired, and is particularly "useful for discharging liquid from a glass still pot. The liquid flows through the upper cock and fills the float chamber until the buoyancy on the float causes it to rise, unseat the ground glass joint a t the bottom, and discharge, without breaking the seal, a part of the accumulated liquid. The side arm near the bottom serves to drain the float or by-pass the liquid, and the glass points on the float keep it free from the inner walls of the chamber. A pressure differential up to five pounds per square inch across the trap shown has been used but, for higher pressure differences, a bulb with a larger volume and buoyancy or smaller ground exit would be required. I n an inverted position this device when connected to a source of supply of liquid may be used to maintain a constant head on the cock, and hence a constant flow. Rise of liquid in the chamber above the buoyant level raises the plug and stops the flow, and the opposite condition brings
April 15, 1931
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
about the omosite effect. I n this service. unless onlv verv small differences of pressure of the liquid'supply are" to ge smoothed out, the control is no better than that of a Marriott bottle.
143
Literature Cited
A.
(1) Hickman, J . Oplical sot. A m , , 18, 305 (1929). (2) Othmer. IND. ENG. CHEM., a2. 322 (3) Othmer; Ibid., Anal. Ed., 1, 97 (lQ29).
Comparative Efficiencies of Gas-Washing Bottles' F. H. Rhodes and D. R. Rakestraw CORNELLUNIVERSITY, ITAACA. N. Y. 2
HE investigation described in this article was under-
T
taken for the purpose of obtaining information as to the comparative efficiencies of some of the typesof gas-washing bottles commonly used in chemical laboratories. Each test was made by passing a known mixture of air and carbon dioxide through a solution of sodium hydroxide contained in the bottle, and determining the percentage of carbon dioxide in the exit gas at various rates of flow. The apparatus used is shown in Figure 1. Carbon dioxide from a cylinder of the liquefied gas was passed through a capillary orifice meter, A , and mixed with air which was admitted through a second orifice meter, B. By maintaining a constant reading on each of the two manometers, A1 and B1, mixed gas of constant composition was obtained. A
the system. If no precipitate appeared in the U-tube within 3 minutes, the rate of flow of the gas was increased slightly and an observation was taken as before. Repeated tests were made at increasing rates of flow until a point was found a t which the carbon dioxide in the ihlet air was no longer completely absorbed by the alkaline solution in the wash bottle. After the point a t which complete absorption can be obtained was determined, the stopcocks in the dischargeTline were set so that all of the gas passed directly to the orifice meter, E, and tests were made a t higher rates of flow. At each rate, observations were taken to determine the rate of flow of the exit gas, the percentage of carbon dioxide in the exit gas, and the drop in pressure through the washing bottle. The gas-washing bottles tested were as follows: HEIGHT OF
BOTTLE
TYPE
SOLN.DURING NOFLVAL OPERATION Cm.
1 2 3 4 5 6
Figure 1-Diagram
of Apparatus Used
7 8
Constant pressure on the discharge side of the orifice meters was maintained by keeping the rate of flow of gas high enough to maintain constant flow of gas through the water-sealed discharge tube, C. The mixed gas was passed through a solution of sodium hydroxide in the bottle to be tested, D,and then through a calibrated orifice meter, E , which measured the rate of flow of the exit gas. A manometer, F,was connected across the line so as to measure the drop in pressure through the bottle. The rate of flow of gas through the train was regulated by the stopcock G. Samples of the inlet gas were Collected a t H ; the outlet gas was sampled at I . A by-pass was placed in the exit-gas line so that the washed gas could be passed through a U-tube, J,containing a solution of barium hydroxide. Samples of gas for analysis were collected in a Hempel buret over mercury and were analyzed by absorbing the carbon dioxide in a solution of caustic soda contained in a Hempel pipet. The bottle to be tested was filled to the normal working height with a solution of sodium hydroxide (32.7 grams per liter) and was inserted in the train. Air was passed through &hesystem to sweep out any carbon dioxide that might be present. A clear solution of barium hydroxide was placed in the U-tube, J, and stopcocks JI,Jz,K1,and KZwere set so that all of the exit gas passed through this solution. If no precipitate appeared within 3 minutes, the current of air was discontinued and a mixture of air with a known amount of carbon dioxide was passed very slowly through 1 Received
December 10, 1930.
Muencke Friedrichs spiral Habermann Habermann Schott and Gen. (Jena), with sintered-glass distributing plate, inlet tube at center of plate Schott and Gen., with sintered-glass distributing plate, inlet tube at side of plate, pattern No. 83 Schott and Gen., sintered-glass distributing plate, pattern No. 101 Muencke with space between inlet tube and wall of bottle filled with glass beads approx. 3 mm. in diameter
"0
2
4 6 8 IO 12 RATE OF FLOW- CC./SEC.
Figure 2-Determination
10.5 11 11 14.5
12 12 15.5
10.6
I4
with 13.4 Per Cent COz in Inlet Gas
Two series of determinations were made, one with an inlet gas containing 13.4 per cent of carbon dioxide, and the other with a n inlet gas containing 5.1 per cent of carbon dioxide. The results are shown in Figures 2 and 3. The tests made with the inlet gas of high concentration show that the Friedrichs spiral gas-washing bottle was the most efficient of all the forms tested by us. No carbon dioxide could be detected in the exit gas until the rate of flow exceeded 4.3 cc. per second, and even at higher rates the percentage of unabsorbed carbon dioxide in the outlet gas was
