H . W . Fr e v e b t a n d E . H . Fr a n c i s, H o llan d T unnel Offices, N ew Y ork, N . Y.
A
CONTINUOUS carbon monoxide recorder for small concentrations in air has been described by Fieldner, K atz, and M eiter (7), and by K atz and others (8).In this apparatus the oxidation of the carbon monoxide as it comes in contact with a granular catalyst results in a tem perature rise in th e air stream within the catalyst cell, which is transm itted to a recording potentiom eter through a series of differential thermocouples. The cell potential is directly proportional to the carbon monoxide concentration in the absence of readily oxidizable or inhibiting impurities which affect the catalyst.
To remove moisture and other condensable constituents the air sample is passed through a train of concentrated sulfuric acid, soda-lime and charcoal, and calcium chloride, previous to passing through the hopcalite catalyst. Fourteen instrum ents of this type were installed a t the Holland Tunnel (2) where they record carbon monoxide in the seven exhaust air ducts leading from each of the two tubes for vehicular traffic between New Jersey and M anhattan. In practice the use of sulfuric acid as an air drier is objectionable because of its corrosive nature and the difficulties of frequent re
newal and disposal. This led to the development of a modified form of the analyzer, which is here described. The acid train whose chief function is the removal of moisture has been replaced by duplicate adsorbers using either silica gel or activated alumina. Alumina of 1.2 to 2.4 mm. size was used in tests on this apparatus and in the preliminary tests re
ported in this paper.
De s c r i p t i o n o f Ap p a r a t u s
Continuous drying is obtained b y alternating the adsorbers and activating th e adsorbent between periods of use by means of a heater inside each cylinder. Interchange o f c y l in d e r s is effected by syn
chronized four-way cocks which determ ine the direction of air flow in each cylinder. The other parts of the original K atz analyzer have been rearranged and modified for suction flow supplied by a rotary blower, whereby the air sample enters the apparatus directly in
stead of first passing through the blower and then to th e apparatus.
This arrangem ent eliminates the possibility of contamination of the adsorbent or the catalyst by oil spray from the blower.
The adsorbers A and B in Figures 1 and 2 have an inner a d s o r b e n t cylinder of 8.9-cm. (3.5-inch) brass tubing, 40 cm. long, filled w ith 1.2- mm. to 2.4-mm. (S- to 14-mesh) alum ina to w ithin 10 cm. of the top.
This tube is surrounded by a 2.5-cm.
jacket through which cooling w ater flows during the cooling p e r i o d
following activation of the adsorbent and throughout the suc
ceeding 8-hour period in which th e adsorbent is drying air.
T his is surrounded by a 2.5-cm. jacket of loose asbestos to im
prove the conservation and distribution of h eat in the adsorbent during the activation, when the jacket is em pty and contributing to the insulation of the adsorbent. T he u n it a, Figure 2, for supplying the activating h eat to th e passing air stream is a 200-watt element from a reflector heater- suspended from a cover plate through which two spark plugs, b, are screwed for term inal connections. The heater circuits are connected to limit, switches, W , shown in Figure 1, which control the sequence of heating through contact with fingers on th e cooling w ater cocks, c and d.
The analyzer is connected to the 110-volt alternating current electrical supply through th e 2-pole fused switch, t, Figure 1, to which the three-heat immersion heater inside boiler C is connected directly. The supply to th e m otor and activating heaters passes through an overload relay magnetic switch, u, which cuts off the supply to the heaters when the m otor stops. A push b u tto n , v, sta rts and stops the m otor and heaters independent of the boiler supply.
Below the adsorbers are w ater tube air coolers, c, Figure 2, surrounded by w ater in th e cooling reservoir D, which cool th e moisture-laden air from each adsorber when it is being activated by the downward passage of hot air. T he coolers comm unicate w ith catch bulbs below and w ith the four-way cock, / . This cock tu rn s sim ultaneously through a vertical connecting bar w ith the upper four-way cock, g, comm unicating w ith the top of the adsorbers.
The three-way cock, h, is connected to the inlet side of cock g and is th e means of providing additional air while activating to insure a more even heat distribution in the adsorbent. Following activation this air, since it contains moisture, is not allowed to enter th e cooling adsorbent b u t is diverted through by-pass i to the blower, r, by a tu rn of th e cock. The q u a n tity of a ir passing into this three-w ay cock is regulated by plug cocks j to give a tem perature not greater th an 340° C. a t the top of th e alum ina and not less than 150° C. a t the bottom .
Cooling w ater enters a t both ends of reservoir D through valves k, and passes through the tubes of the coolers to the center. Three-w ay cocks c and d ad m it w ater from the reservoir to the cooling jackets of th e adsorbers or em pty them as re
quired.
Precautions were taken to insure a proper operating sequence by the use of the blocking cross bars, s, Figure 1, attached to the vertical connecting bar, which synchronize the move
m ent of w ater cocks c and d w ith th e position of the four-way air cocks.
The w ater when flowing through the jackets passes through the o u tlet tubes, I, whose ends are water-sealed in adjoining overflow com partm ents in trap m, from which the w ater passes to th e steam b ath condenser of th e cell assembly, C. T he w ater tr a p com partm ents are joined by a small hole which allows w ater to pass from either side to seal both tubes against entrance of air when one adsorber jacket has been em ptied. A ja c k e t is drained previous to activating th e adsorbent through th e t h r e e - w a y cocks c or d by which process a ir enters to displace the w ater through the overflow com partm ent in t h e w ater trap, to.
A cylinder of 330 cc. of charcoal, n, removes quantities of hydrocarbon vapors from th e air sample which
Fi g u r e 1 . Co n t i n u o u s An a l y z e r f o r Ca r b o n Mo n o x i d e i n Ai r
226
Ma y 15, 1934 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 227
m ight affect the accuracy of the analyzing cell. This has a screw cap a t one end for periodical replacement of the activated charcoal.
Ope r a tio n
The air sample is continuously drawn into the apparatus a t o. T h a t in excess of 12 liters per minute to the flowmeter, Pi by-passes through th e regulating valve, q, and through the flow compensator, E , directly to th e blower, r.
At th e point of sequence illustrated in Figure 2, the regu
lated flow from th e flowmeter passes into cock / and upward through adsorber A , through charcoal cylinder n, and into the preheating coil inside the steam bath a t C, from which it passes through the catalyst chamber also enclosed by the steam bath. The return air from the catalyst chamber reenters th e four-way cock, g, together with additional air from the room for activating purposes through three-way cock h. T he increased flow of about 30 liters per minute enters adsorber B and passes downward over the heater and through the adsorbent which a t the end of 4 to 6 hours^ac- quires a tem perature of about 320° C. a t the top and 180 C.
a t the bottom . The air leaves the adsorber through the after-cooler, e, from which it reenters the four-way cock, /, and joins the previously by-passed air to the blower, r.
A t th e end of th e 4- to 6-hour activating period the water cock, d, is turned 90° to fill the w ater jacket of the activated adsorber, and th e auxiliary air entering cock h is diverted to th e blower by a 90° tu rn of th e cock. A finger on the w ater cock has contacted a lim it switch which shuts off the activating heater. Adsorber A continues to dry the air sample and adsorber B receives the dry return air from the cell until th e end of th e 8-hour period.
A t th e end of th e 8-hour period the four-way cocks, the w ater cock below adsorber A , and th e three-way air cock, h, are turned 90°, whereby th e path of the air sample is trans
ferred from A to B, w ater is drained from the cooling jacket of A , the lim it switch is actuated to sta rt the heater, and room air is diverted into A for activation of the adsorbent.
T he operations m entioned before are repeated in succeeding cycles, commencing w ith the turning of cocks c and h a t the end of 4 to 6 hours to cool the activated adsorbent in A .
A drying period of 8 hours per adsorber was selected be- cause it allows a convenient tim e for reactivating and cooling and because it coincides with the working hours of operators who would operate th e analyzer when in service. The rate of flow of 1 2 liters per m inute produced the best sensitivity
in th e c a t a l y s t cell with a minimum of variation for small changes in air velocity.
Air-Dr y in g Test s
Preliminary tests a t a flow rate of 15 liters per m inute, using adsorbers roughly similar in form to these described, were used as a basis for determ in
ing the cylinder size required for th e 8-hour period.
These adsorbers were con
structed of 2 2-gage sheet iron, were 51 cm. long, and con
tained an i n n e r a d s o r b e n t cylinder 1 0 . 2 cm. in diam eter which was surrounded by a concentric 2.5-cm. air jacket.
One of the cylinders was further jacketed with a 2.5-cm. layer of asbestos over the air jacket.
T he 8- to 14-mesh alumina, obtained in 1931, was reac
tivated downward w ith heaters suspended above th e ad sorbent as in the analyzer described. Thermocouples placed in th e top and bottom of the adsorbent beds indicated tem peratures of activation and adsorption.
In tests m ade w ith these adsorbers and w ith the analyzer later constructed, air saturated by bubbling through a bottle of w ater a t room tem perature and precooling a t 1 2.8° to
2 1.7° C. was passed through the activated alum ina and the effluent air was tested a t intervals for m oisture with a weighed tube of phosphorus pentoxide. T he air dryness determ ina
tions for these tests appear in Figure 3, which shows the relation between grams of m oisture per cubic m eter of air and the tim e from
s t a r t of t h e r u n w h e n t h e dryness tests were made.
Other d ata in con
n e c tio n w ith t h e tests are g iv e n in Table I. The quan
tity of moisture ad
sorbed is calculated fro m the moisture e n t e r i n g in th e saturated air a t the tem perature stated, corrected for mois
ture which passed through the adsorb
ent.
The object of tests
1 and 2 was to de
term ine the effective drying period of th e activated alum ina adsorbent w ith and w ithout water-cooling. In te st 1, 2.2 kg. of th e alumina were activated and tested for adsorp
tion in check runs la and lb in the asbestos-insulated air- jacketed cylinder. In test 2 an equal q u an tity of alum ina was similarly tested in a cylinder of the same size w ith w ater passing through the jacket during adsorption. T he relative efficiencies of the adsorbent under these two conditions are indicated in Figure 3.
A laboratory te st on adsorbers A and B of the assembled analyzer is reported in test 3 of Table I. The ap paratus was run as for the continuous analysis of air, with one ad
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Al u m i n a Ad s o r b e n t
228 A N A L Y T I C A L E D I T I O N Vol. 6, No. 3
• T e st discontinued before break in a d so rb en t efficiency.
Following these tests th e experimental analyzer was con
nected to an air-sampling line in parallel with the analyzer
factory and the hopcalite cell sensitivity remained normal throughout th e period.
Di s c u s s i o n
T he curve of te st 1 in Figure 3 indicates a break point in adsorption in the insulated adsorber a t 6 hours from the sta rt of the test, a t which point moisture in the effluent increased rapidly. Before this break in drying efficiency the effluent contained less than 0.14 gram of moisture per adsorbed a t the top of the bed before the test began and again a t 7.5 hours from th e sta rt of the te st when the ru n was stopped overnight. The adsorptive capacity of the alumina was multiplied three times by th e 2 1° to 29° C. of cooling effected by the water. T he dry alum ina had adsorbed 3 . 9 per cent of its weight of moisture in te st 1 and 11.4 per cent in test 2 when moisture broke through.
No gain of moisture in the effluent air from adsorbers A and B was found for the periods of test. T he average moisture content of the air coming from adsorber A was 0.07 gram per cubic meter of air and from adsorber B, 0.04 gram.
T he effective adsorptive capacities remaining in adsorbers A and B when the runs were stopped are estim ated a t 60
and 30 per cent, respectively, based on th e 11.4 per cent capacity of activated alum ina shown in test 2. The probable effective drying period of th e 1.4 kg. of alum ina in each of drier was developed which consists of duplicate cylinders containing granular adsorbent. T his is reactivated in place- as the analyzer continues to operate b y a heater inside the- cylinder, assisted in p a rt b y the recirculation of th e d ry return air from th e analyzing u n it of th e recorder.
Since prelim inary tests indicated the desirability of cooling the adsorbent during use to increase drying capacity, the adsorbers are jacketed for cooling w ith w ater. T he w ater is drained from the jacket during th e activating period, b u t the activating air stream passes through a cooler as it leaves th e adsorbent.
T he m aintenance required for the operation of th e analyzer consists of valve m anipulation twice in every 8 hours or other drying period selected, and removal of w ater from th e condensation tra p below the adsorbers as required. Al
though the possibility of simplification of valve arrange
m ent and other parts of th e apparatus has become apparent its operation was satisfactorily carried on b y th e operators in charge of ventilating equipm ent in the building.
accuracy in our article “Extraction of Triethanolamine Oleate from Aqueous Solution,” appearing in I n d . E n g . C h e m ., Anal.
Ed., <5, 7S (1934). The statement was made, referring to extrac
tion of fatty acid from triethanolamine soaps, “ Normally, soaps other than those of abietic acid are not decomposed by extraction of an aqueous solution with ethyl ether.” We should have added
“by recognized methods,” since small amounts of fatty acid are extracted from aqueous solutions of neutral soap by ethyl ether.
This is adequately provided for in the usual methods.
This in no way invalidates our conclusions, since the extraction of oleic acid was high in experiments 2 and 5, in which 0.05 M triethanolamine, the alkali of the soap under discussion, w as.
present in’excess. F r a n k M. B i f f e n a n d F o s t e r D e e S n e l l