INDUSTRIAL AND ENGINEERING CHEMISTRY
1456
LITERATURE CITED (1)
Vol. 43, No. 6
Fenske, M. R., Ibid., 24, 482 (1932) Griswold, 35i 247 (1943). Podbielniak, W. J., Ibid., 34, 126 (1942). Podbielniak, W. J., private communication. (10) Struck, R. T., and Kinney, C. R.,IND. ENG.C H m f . , 42, 77 (6) (7) (8) (9)
Berg, L., and Popovac, D. O., Chem. Eng. Progress, 45, 683 (1949).
(2) Bragg, L. B., IND.ENG.CHENI., ANAL. ED.,11, 283 (1939). (3) Ibid., 15, 290 (1943). (4) Byron, E. S., Bowman, J. R., and Coull, J., IND.ENG.CHEM., 43, 1006 (1951). (5) Feldman, J., Myles, M., Wender, I., and Orchin, M., Ibid., 41, 1032 (1949).
J.3
(1950). RECEIVED October 4, 1950. Presented before the Division of Petroleum Chemistry a t the 116th Meeting of the AMBRICANCHEMICALSOCIETY, Atlantic City, N . J.
for Adsorption
Enggiring ROWSS
t Streams
development I
R. L. HOPKINS U. S. BUREAU OF MINES, BARTLESVILLE, OKLA.
of oil fractions of any desired size and of providing for direct observation of the oil to solvent ratio a t all times. This simplifies determination of the “break point” between the paraffincycloparaffin and aromatic portions by observation of the sudden increase in oil to solvent ratio and by the appearance of ma-
T h e continuous stripper described was developed to facilitate large scale Iaboratory adsorption operations in which pentane, benzene, and isopropyl alcohol are used and must subsequently be removed from the sample. Solvent removal is accomplished with this device as the effluent emerges from the column. This results in great saving of time and laboratory space over that rea quired for batch stripping, and the sample is less subject to damage through prolonged heating and oxidation.
r24-40 15-35
f
% A-7
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HE Diesel fuel studies a t the Bureau of Mines required separation of severa1 hundred samples by adsorption in the course of a year. Most of these were approximately 1200 ml. in volume and ranged in boiling point from 150’ t o 400 C. The direct displacement technique ( 1 ) previously used in this laboratory proved inadequate for a program of this scope because of interference in the adsorption pattern by the highly viscous naphthenes, whichresulted inpoorseparation, and because of the desorbent costs. It was therefore necessary to resort t o a technique involving dilution of the sample with pentane (9). It was realized t h a t removal of solvent by batch distillation of each separate cut from such a large number of samples would be very costly in time, labor, and working space. I n addition, the samples would be subjected t o comparatively high temperatures for long periods, which might result in thermal changes in the samples. To adapt the dilution technique t o this program, it became advisable to devise an apparatus for continuous and complete removal of the solvent from the sample as it emerged from the adsorption column. This process of continuous stripping also has theadvantage of permitting collection
5
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Figure 1.
MILLIMETERS 1
2
3 4 INCNES
5
6
Vapor Heated Solvent Stripper
--
INDUSTRIAL AND ENGINEERING CHEMISTRY
lune 1951 --,-I
. Sampfe
Inlet A
Steam l n l e f (Oufer Jacket)
I
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No. 14 Copper W i r e Helix IO m m p i t c h
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Figure 2.
Steam Heated Solvent Stripper
terial fluorescent in ultraviolet light at the outlet of the stripper. The latter indication would be much less sensitive with the highly diluted sample. Continuous stripping has been in use in this laboratory for 3 years and has been of great value in the adsorption program. Several forms of strippers were constructed and tested. Figure 2 shows the design originally constructed and used in this laboratory. The diluted sample from the column flows through the sample inlet ( A )onto a wire helix ( B )which closely fits the outer wall of the vaporization space. The tube enclosing the vaporization space is surrounded by a steam jacket. Inside the helix is another steam heated tube ( C ) which fits closely the inside of the helix over the lower two thirds of its length. The upper third of the inside tube is of smaller diameter to provide space for flashing solvent without flooding. Most of the solvent flashes off in this
1452
space, allowing the nearly stripped sample t o flow down the helix countercurrent to a stream of nitrogen which assists in removing the remaining solvent. The U-trap (D)at the bottom provides a liquid seal, forcing all the vapor out of the top of the stripper. The vapor outlet tube is packed with several inches of glass helices and fitted with a small dephlegmator ( E ) . This steam heated stripper is satisfactory for removing pentane or isopropyl alcohol. However, when benzene is used as the solvent its complete removal from the aromatic portion of a sample is a much more difficult operation, requiring the maximum flow of nitrogen which the stripper will tolerate without prohibitive sample loss and a much lower rate of sample flow than is possible with pentane. It is possible to increase the efficiency of benzene stripping somewhat by feeding an auxiliary solvent such as acetone or methanol into the stripper below the point a t which the bulk of the benzene was flashed. The lower boiling solvent acts as an entraining agent to carry off the remaining benzene. Although this improves the effectiveness of the apparatus, it leaves much t o be desired. Consequently the apparatus was redesigned to utilize vapors other than steam for heating in order that increased operating temperatures could be utilized. This design is illustrated in Figure 1. The flashing and stripping surface is similar to that of Figure 2, except that the helix ( A ) is constructed of 3mm. glass rod and the inner tube ( B )is open throughout its length and joined to the tube surrounding the helix by a Dewar seal. An outlet through this seal conducts the stripped sample through an expansion helix ( C ) and out through the wall of the vapor jacket. A condenser (D)for the heating vapor is provided a t the top of the inner tube. A series of four small holes ( E ) through the wall of this tube just below the ring seal allows vapor to ascend both inside and outside the helix. The position of the packing and dephlegmator ( F ) is the same as in the preceding design, except that in this case both vapor tube ( G ) and sample inlet tube ( H )must pass through the wall of the vapor jacket. The immersion heater ( I ) , which is a modified 250-W Pyrex immersion heater, extends down through the condenser and inner tube and is suspended just above the bottom of the jacket. It is completely immersed in a liquid having a boiling point to correspond with the desired operating temperature. Much wider flexibility of operating temperature is possible by selection of suitable heating liquids for use in the revised strippers. For example, an operating temperature of about 130" C., desired for stripping benzene was obtained by using sec-butylcarbinol (active amyl alcohol), boiling point, 128" C. Stripping of benzene is greatly improved by this apparatus, permitting a sample throughput a t least double that possible with a steam heated unit of comparable size. This has been found by experience to be about 150 ml. of stripped sample per hour. The maximum benaeneflashing capacity has not been determined as the benzene to sample ratios usually employed are about 1: 1 under which conditione the throughput of the sample portion of the mixture is the determining factor. The vapor heated stripper also has been useful for routine solvent recovery operations. Pentane contaminated with residual oil has been conveniently reclaimed, using acetone as the heating medium. Mixed pentenes, which had formed considerable polymer and peroxide, were similarly recovered without the necessity of handling large amounts of liquid a t one time or accumulating large quantities of peroxides at high end temperatures, as may occur in batch distillation. Construction of a unit with a glass helix presented considerable difficulty because of the necessity of fitting the helix closely to both inside and outside of the pieces of tubing between which it is placed. It may, therefore, be appropriate to comment on the method of fabrication used. Individual lengths of 3-mm. glass rod were wound separately on a mandrel, which consisted of the piece of tube t o be used on the inside. The mandrel was h s t lubricated with a paste of powdered graphite and Carbowax 1500, after which the end of the rod was temporarily fused to the end of
INDUSTRIAL AND ENGINEERING CHEMISTRY
1458
the mandrel and wound. KO difficulty was experienced in removing the windings. rlfter the end portions of each piece of coil were discarded, the sections were joined and slipped over the tubing, using the graphite-Carbon-ax mixture for lubrication. The principal difficulty arose in placing this within the outer tube without breakage. This was accomplished by cementing the coil to the inner tube with asphalt. The outer edge of the helix was easily brought to proper diameter by rubbing with emery cloth, after which it could readily be slipped into place. The asphalt was removed by heating with an infrared lanip, followed by washing with a solvent. A third design, which is easier to construct but less efficient,
Erigineering F,%:*development
Vol. 43, No. 6
utilizes a closely pitched coil of 8-mm. glass tubing exposed directly to the vapor in place of the loiwr section of the helix. Rccause of the smaller holdup this stripper is especially suitable for smaller scale work with samples of about 100 to 200 ml. LITERATURE CITED
Gooding, R. M., and Hopkins, R. L., papers presented before the Division of Petroleum Chemistry, 110th Meeting, AMERIC4~ CwafIcAr. SOCIETY, Chicago, 111. ( 2 ) Lipkin, &I. R.,Hoffecker. W. A . , Martin, C. C., and Ledley, R. E., Jr., Anal. Chetn., 20.130 (19483. (1)
RECEIVED .July 22, 1950.
Process Control of Vinyl Ethers HIGH IMPEDANCE CONDUCTIVITY MEASUREMENTS I
HUGH R. DAVIDSON A N D JOSEPH M. LAMBERT G E N E R A L A N I L I N E AND F I L M CORP., E A S T O N , P A .
A
FAIRLY specialized instrumentation problem aiox-’ in connection with the manufacture of vinyl alkyl ethers. The method of s p t h e s i s and properties of these compounds have been described by Schildknecht, Zoss, and JlcIiinley ( 7 ) . \\'lien pilot plant production commenced it was desired to provide simple means for indicating continuously the purity of the product after distillation beforc it entered the storage tanks. Preliminary dielectric loss measurements, made with a conventional alternating current bridge method, showed that the low conductivity of pure vinyl ethers increased appreciably on addition of certain expected impurities such as alcohols or aldehydes. A comprehensive experimental and theoretical study of design principles of equipment for these measurements m-as made by Jones and Josephs ( 8 ) . However, such methods would not be practical for plant operation since either manual balaiicing or complicated servomechanisms would be required. The purpose of this paper is to describe the method that was finally developed for measuring and recording changes in the conductivity of methyl vinyl ether having a specific resistance of the order lola ohm-cm. Despite the inherent difficulties of low conductivity measurements, it was possible to design a suitable circuit that operated satisfactorily. Since the method might have broader applications, a general treatment of the problem is given preceding the presentation of typical data obtained for methyl vinyl ether. CONDUCTION OF ELECTRICITY IN LIQUIDS
Electrical conductivity measurements in aqueous systems have found many applications in plant operations, and a variety of comrnercial equipment has been available, suitable for testing steam condensates, boiler waters, and sugar solutions. These and other typical applications, recently reviewed by Rosenthal ( 6 ) , are based on the relationship betlveen electrolytic conductivity and the concentration of ionic materials dissolved in the aqueous phase. Since distilled water in contact with air has a specific resistance of the order 106 ohm-em., the conventional instruments are designed to measure relativeIy low specific resistance values from about lo2 to 106 ohm-em. In contrast to the manifold studies and applications of electrical
T h i s work was undertaken to provide a continuoiis and automatic indication of the purity of vinyl ethers, in order that some of the process variables might be adjusted to obtain the desired product. It was found that the electrical conductivity of methyl vinyl ethers was highly sensitive to impurities of the type normally encountered, and a method was developed for measuring this quantity. Because of the extremely high resistance of the pure ether and the need for simple, automatic recording of the results, conventional equipment could not be used. The methods described appear of potential value in many types of manufac turing processes where the product is a liquid having high specific resistance and the irnpurities to be controlled hale a lower specific resistance than the pure product.
conductivity in t,his low range of specific resistance, relatively fern investigations have been made on highly insulating liquids. Pao (4)reviewed much of the earlier work in this field giving
also a summary of the various theories that had been proposed to account for the observed phenomena, A number of investigators (among them P. Curie, G. Jaffe, L. s. Taylor, and A. Rogozinski) studied the effects of gamma or x-radiation on the conductivity of organic liquids. Some of these men attributed the residual conductivity of pure nonionizing liquids to cosmic radiation. However, more recently Plumley (6) applied the pot,ential diesociation theory originally proposed by Onsager ( 3 ) for very weak elect.rolytes t,o pure insulating liquids. The experimmtal data indicating a voltage dependence of conductivity can readily be explained by assuming an increase in the number of spontaneous dissociations caused by favorable orimtation of t,he molecules in the electric field or by prevention of recombination of the dissociated molecules. Various anomalies found in semiconducting organic liquids were described by Fuoss ( 1 ) dealing Tvith the influence of the solvent, medium on the conductivity of electrolytes.
