ANALYTICAL CHEMISTRY
470
who made the precision studies, many of the interference studies, and helped in the differential polarographic end-point studies; E. bl. Kinderman, who helped with the pretreatment and interference studies and the early automatic titrations; W. W. Mills, who furnished the standards for the investigation; and Roy KO and G. Rleyer, viho established the need for iron in the generation system.
s., Jr., k A L . CHEM., 25, 226
(1950). (4) Reilley, C. (1931).
K.,Cooke, W. D., and Furman, N. H., Ibid.,
23, 1223
(5) Shsw, J. A,, ISD.ENG.CHEM., ANAL.ED.,6,479 (1934). (6) Shipley, E. D., Atomic Energy Commission, AECD-2804 (Nov. 2, 1949). (7) Sill, C. W., private communication.
(8) Sill, C. W,, and Peterson, H. E., ANAL.CHEM., 24, 1173 (1952).
LITERATURE CITED
(1) Carson, TI-,
(2) Carson, W.S., Jr., and KO, R., Ibid., 23, 1019 (1951). (3) Cooke, W,D., Hazel, F., and hlcNabb, W. M., Ibid., 22, 654
(1953).
RECEIVED for review June 21,
1952.
Accepted January 8. 1953.
Direct Semimicrodetermination of Oxygen in Organic Substances Improved Apparatus and Procedure f o r Use with Carbon Reduction-Titrimetric Carbon Dioxide Method ROBERT D. HINKEL AND RAPHAEL RAYIIOKD Synthetic Fuels Research Branch, Bureau of Mines, Bruceton, Pa.
A n improved apparatus and procedure have been developed to overcome interference due to hydrogen in the Unterzaucher method, to permit accurate analyses of substances of both low and high oxygen content, and to reduce the time required for analysis. Carbon monoxide formed in the pyrolysis is oxidized with iodine pentoxide, the resulting carbon dioxide is absorbed in a measured excess of 0.05 N alkali, and the excess is back-titrated with 0.025 N acid after precipitation of the carbonate formed with barium chloride. Numerous data on pure oxygenated compounds, hydrocarbons, and miscellaneous substances indicate that accurate results are obtained over the range of 0.05 to 50% oxygen, utilizing sample weights of 15 to 350 mg. and a total analysis time of 35 to 45 minutes. The apparatus required is simple and serviceable and includes a unique style of reaction tube which permits easy and accurate handling of volatile and nonvolatile samples. Blanks caused by variation in furnace construction are discussed, and experiences with different reaction tube materials are described.
S
TUDIES related to the research and development activities of the synthetic liquid fuels program have been concerned with the development of a direct method of oxygen determination for use in identifying synthesis products. Such a method is preferred to the customary by-difference analysis, because the results are not affected by a summation of the errors made in analyzing other constituents. These errors are particularly important when carbon, hydrogen, oxygen, nitrogen, sulfur, and/or halogen are present simultaneously and when the quantity of oxygen present is small. The direct method proposed by Schutze in 1939 (21)has aroused considerable interest among those concerned with this problem. This was evident, first, in the work of Zimmerman (24) and, later, in the well-known modification of the method described by Unterzaucher (%). Asubsequent review by Elving and Ligett (11) pointed out the advantages of the Schutze-Unterzaucher technique over other methods of analysis and stimulated further interest in its use.
Briefly, the method involves pyrolyzing the sample in a closed system and sweeping the products of pyrolysis through a carbonpacked reaction tube a t 1120’ C. with a stream of oxygen-free nitrogen. I n passing through the reaction tube, the oxygencontaining pyrolytic fragments are converted quantitatively into carbon monoxide, which is determined subsequently by oxidation with iodine pentoxide and measurement of the by-product iodine evolved in the reaction. To increase the sensitivity of the method, the iodine is absorbed in alkali, oxidized to the iodate form, and, finally, reduced with potassium iodide and titrated with standard thiosulfate solution. Among the first to investigate the method in this country were Aluise and coworkers ( 8 ) and Dinerstein and Klipp (9), who reported on the use of American-made equipment and reagents for this purpose. Walton, McCulloch, and Smith ( I S ) expressed . dissatisfaction with the use of iodine pentoxide, because it yielded variable blanks, and devised a modification in which the carbon monoxide is determined colorimetrically, using a specially prepared, impregnated gel. Later, Maylott and Lewis (18) described a comparison of the ter Muelen and Unterzaucher methods wherein the latter was found t o be preferable, provided that a liquid nitrogen-cooled trap was used to eliminate interfering constituents from the gases entering the iodine pentoxide tube. Recent investigations indicate rather general dissatisfaction with the Tjnterzaucher procedure, particularly when applied to the ahalysis of materials of low oxygen content, because of the reducing action of pyrolysis hydrogen on iodine pentoxide and the resultant production of iodine, which causes high results. Moreover, this action is not quantitative and, apparently, is very erratic, depending on the sensitivity of the iodine pentoxide, thus making the application of a correction factor impossible. To circumvent this difficulty, various investigators have resorted to measurement of the carbon dioside produced by oxidation of the carbon monoxide. Thus, Holowchak and K e a r (14) have adopted a manometric method, while Dundy and Stehr (10) have employed a gravimetric method similar to that initially used by Schutze (91). Other investigators have also used the gravimetric method, though not specifically for avoiding hydrogen interference (6,1b, 17). An entirely different line of approach has been followed by Campanile and coworkers (6),who retained Unterzaucher’s iodometric determination, but eliminated hydrogen interference by allowing the bulk of the gas to diffuse from the reaction tube gases through a palladium thimble similar to that described by Harris, Smith, and Mitchell (IS).
47 1
V O L U M E 25, NO. 3, M A R C H 1 9 5 3 The experience gained in this laboratory with hydrogen interference in the Unterzaucher method parallels that described above. At the start of this work, hydrogen interference mas anticipated because of the earlier results of Berger and Schrenk ( 4 ) , although neither Unterzaucher ( 2 2 ) nor -4luise et al. ( 2 ) had reported any such difficulty. It appeared, therefore, that the much higher iodine pentoxide temperature (150" C.) used by Berger andSchrenkmightaccount for this difference, and whennoevidence of reaction was detected by passing inert gas-hydrogen mixtures through iodine pentoxide a t 120' to 122" C., both the reagent and temperature conditions were regarded as suitable for use. However, as data were accumulated from analyses of a variety of pure organic compounds (Table 111),hydrogen mas suspected again of causing interference, and I epeated tests with inert gas-hydrogen mixtures confirmed this belief. As the first set of tests was performed with relatively new and unused iodine pentoxide, the anomaly of these observations appears to be due to the increased surface reactivity developed by continued use and exposure to reducing gases (3). Supporting evidence is found in Table I, which shows how the efficiency of carbon monoxide oxidation v,a3 improved in this same batch of reagent hy successive exposure. to acetylene, a gas with Li-hich i t reacts very intensively.
were analyzed. hccordingly, a replica of the Pieters apparatus was constructed and several reference analyses with acetanilide (11.84y0oxygen) were performed using 0.02 N and 0.04 S baryta and 0.04 iY sodium hydroxide solutions as absorbing media, and 0.02 S hydrochloric acid for back-titration. The results obtained with both baryta solutions were low, whereas sodium hydroxide gave nearly theoretical values. However, when analyses of benzoic acid (26.20Yo oxygen) were made with this same absorbent, the result. were low again (Table 111. To permit back-titration with the more dilute acid without eyceeding the volume of a 50-nil buret, the analyses with the 0.04 S solutions were made using smaller quantities of absorbent than required by the Pieters and Deinum and Schouten procedures. IVhile this reduced volume of absorbent was adequate for filling the spiral absorbing section of the apparatus and for absorbing all of the carbon d i o d e generated in the analysis, i t is evident that the capacity of the apparatus was being exceeded slightly in the benzoic acid analyses. An improved absorber (Figure 4 ) was constructed, therefore, which can be operated satisfactorily with this small quantity (25 ml.) of absorbent. Compared with Pieters' apparatus, it provides greater residence time for gas bubbles in the spiral, increased wetted surface area for alisorption, and shorter diffusion paths to wetted surfaces.
DEVELOPMEh-T OF TlTRIWETRIC CARBON DIOXIDE 3IETHOD
The use of a method based on the determination of carbon dioxide obviates the possibility of interference due to the reduction of oxide pentoxide by hydrogen, and provides a direct measure of the carbon monoxide formed in the pyrolysis. Such a method was reported recently by Deinuni and Schouten ( 8 ) ,who usrd a elightly modified form of the titrimetric procedure described by Pieters ( 2 0 ) : Carbon dioxide is absorbed in a measured ewess volume of 0.05 1V baryta solution contained in a special glass absorber, and the excess baryta is back-titrated with 0.05 S acid to a p H of about 8.5, using a suitable indicator. A study of this method showed that improvements in accuracy and precision might result through the use of more dilute solutions, if this modification could be made without exceeding the capacity of the absorber when substances of high oxygen content
Table I. Effect of Activation by Acetylene on Efficiency of Carbon Monoxide Oxidation by Iodine Pentoxide" at 120" c. Approx. Space Av. R a t e of Gas Flow Av. Concn. CO (Sz
+ CO)
through 1205, .\II./IIin. 1206
18 16
Velocity, Min. -1
of CO in Gas,
5
Oxidized,
relatively new and unused 0.52 6.7 0.47 4 s
% 52.7 93.1
I I O s exposed t o 225 ml. of 97% nitrogen-3% acetylene mixture, a t rate of 15 ml./min.
16 18
0.47 0.52
9 8 S i
92.1 96.0
9 2
98 2
1 2 0 s exuosed as before 17 a
0 49
APP4RATUS
The apparatus used in this study is shown schematically in Figure 1. The flow of nitrogen from the tank source to the reaction tube is metered through a needle valve and rotameter, and purified by passage over hot copper and through an absorber filled with Anhydrone and Sscarite. Pyrolysis gases from the reaction tube pass successively through a liquid nitrogen-cooled trap, iodine pentoxide oxidation tube, and iodine absorber into the carbon dioxide absorption and titration unit. The auxiliary nitrogen metering system controls the flow of nitrogen through the latter unit during titration. The nitrogen-purification furnace. F , consists of three concentric glass tubes, the inner tivo of n hich are silica, while the outer one is of borosilicate glass. The innermost tube (17 mm. in outside diameter) is packed x i t h a 30-cni. length of wire-form metallic copper held between plugs of glass no01 and is provided with a 7 19/38 silica joint at one end and a 7 10/30 joint a t the other. The intermediate silica tube (25 mni. i n outside diameter) is wrapped n i t h 45 turns of S o . 24 B. B: S. gage Nichrome mire spaced 7 mm. apart. The outside borosilicate glass tube (70 mm. in outside diameter) encloses an insulating air jacket around the furnace. Spacers made from coiled asbestos tape are used a t each end to align the tubes concentrically. The operating temperature ofthe furnace is measured with a potentionvter and a No. 24 B. & S. gage Chromel-Alumel thermocouple, the hot junction being placed a t the center of the furnace in the air space between the tn o silica tube.. The carbon dioxide and mater (U-tube) absorber. G, is constructed from borosilicate glass tubing 25 mm. in outside diameter and provides the equivalent of a 66-em. straight length of chemical filling, the first and last thirds of xi-hich ale .lnhydrone, and the middle third is Ascarite. II-a\-sealed, ground-glass caps a t the top of each arm of the U-tube permit easy filling and cleaning. Details of the silica reaction tube,
Merck's iodic anhydride, see description of reagents.
Table 11. Determination of Oxygen by Titrimetric Carbon Dioxide Method Using Apparatus of Pieters Compound Analyzed .4cetaniliden (11.84% 0 2
)
Weight, Ilg. Sample Abqorbent 30.7 0 . 0 2 .L'Ba(OH)2 34.2 0.04.VBa(OH)z 33 0 0 04NNaOH 33 .5 0 . 0 4 3- 3-aOH
Volume of , Absorbentb, 311. 50.0 25.0 25.0 25.0
Oxygen Found, qr, ," 8.22 8.82 11.75
Deviation from Theoretical,
11.68
Benzoic acid 16.1 0 04 S X a O H 24.0 25.61 ( 2 6 . 2 0 % 02) 19.1 0 04 S h-aOH 24 0 25.48 a Iiicrochemical standards from National Bureau of Standards b Procedures of Pieters and Deinum and Schouten require use oi 50 ml. of absorbent.
V " ,-
-3.62 -3.02 -0.09 -0.16
-0 59 -0.72
M ,are shown 111 Figure 2.
Its three unique features are the largebore borosilicate glass stopcock attar&d to it by a graded seal, the purging lock, and the V-shaped indentation in the top of the tube which acts as a stop for the sample boat when the latter is pushed into the tube. The tube is heated to 1120' f 5" C. by a furnace, S (Model HDT-1712, Hevi-Duty Electric Co.), which is 39.5 cm. long and is provided with a helical h-ichrome-wire heating element and a multiple-tap transformer. Control is accomplished by manual adjustment of a 220-volt Variac connected in series x i t h the primary circuit of the transformer. Reaction-tube tempern-
ANALYTICAL CHEMISTRY
472
Figure 1. A.
Sitrogen tank source B. Hydrogen tank source C. Keedle valve D. Overpressure blowoff E . Rotameter F . Nitrogen purification furnace 0. COP and Hz0 absorber H . Pusher rod
Schematic Drawing of Apparatus J.
K. L. M, h.. 0. P.
Q. R.
Guide block Pusher-rod guide tube Purging lock Reaction tube Reaction tube furnace Liquid nitrogen-cooled trap IzOa oxidation tube Oxidation tube heater Iodine absorber
tures are measured with a potentiometer and a calibrated S o . 14 B. & S. gage Chromel-Alumel thermocouple, the hot junction of which is placed close to the tube in the center of the furnace. The sample introductory mechanism is detailed in Figure 3.
It consists of a boat pusher rod, a pusher-rod guide tube, and a guide block. The guide block IS tubular ( 3 / 4 inch in outside diameter, 17/64 inch in inside diameter, and 3 inches long) and is mounted rigidly t o the apparatus framework by an adjustable clamp, in approximate coaxial alignment with the reaction tube. The usher-rod guide tube is supported by the guide block through whici it extends; a 28/15 glass socket joint sealed t o one end of it permits connection to the reaction tube and serves as a closure for the purging lock. Lateral, coaxial motion of the tube is controlled by the guide block when the lock is opened and closed. The pusher rod is of conventional design, except for the serrations cut in the leading face of the bent end; it extends through the entire assembly into the purging lock. The liquid nitrogen-cooled trap, 0, has been dcsigned to provide adequate cooling of the pyrolysis gases; the details of its
construction are shown in Figure 6. Its total immersed volume is approximately 35 ml., two thirds of which is contained in two helical glass coils wound one within the other; the remaining third is in a bulb a t the bottom of the trap to serve as a sump for any condensable components. The iodine pentoside oxidation tube, P , is larger than that described by Aluise and coworkers ( g ) .
It consists of a 20-cm. length of borosilicate glass tubing 16 mm. in outside diameter having a T 19/38 inner joint a t one end and a 5-cm. length of capillary tubing 2 mm. in inside diameter terminated by a 6 10/30 inner joint a t the other. It is heated by means of a double-walled glass vessel, Q, equipped with an internal electric heater and a water-cooled condenser (22). A constant temperature of 122' to 123" C. is maintained with boiling methyl Cellosolve. The iodine liberated in the oxidation tube is absorbed in a Utube, R, constructed of borosilicate glass tubing 18 mm. in outside diameter. This tube provides the equivalent of a 28-cm. straight length of chemical filling and is filled with approximately 60 ml. of 14- to 60-mesh anhydrous sodium thiosulfate.
Shield rolled from 24
Figure 2.
Stovcocks
Silica Reaction Tube
A11 dimeneionb in centimeters
V O L U M E 25, NO. 3, M A R C H 1 9 5 3
473 celain boats, size No. 2, which are slotted a t the end, as shown in Figure 5 . Volatile liquid samples are handled in borosilicate glass ampoules such as that shown in Figure 5 . The rotameters are borosilicate glass Flowrator tubes (Fischer & Porter Co.), size 08-150, and are provided uith l/ls-inch glass-ball floats. Graduations permit direct reading of flow rates of 4 to 58 ml. per minute, measured at 70" F. and 760 mm. of mercury. RE i G ENTS
Nitrogen. High-purity, dry, 0.0017 0 oxygen (Linde Air Products CO.). Hydrogen. Electrolytic commercinl grade (Linde Air Products CO.).
Coors No. 2 porcelain combustion boot
Sample Introductory >Iechauism
I
.
I I
' f
'
1
\I
Seal-off after filling point
Figure 3.
Slot for pusher-rod (approximately 3 x6 mm.)
I
Boat PuLher-rOd detail
Pusher-rod putdl lube dc'ml
f
pyrex tubing
i
,, (, k;;
'Ploce file scratch inside bend
5-6 mm. O.D.
; Approximately
6 m~m .l ~ m m I mm. . 0 I.D. . D . x
1-
/
I
rl 6 m m .rad b
Outside coil 50 mm. I.D. 5 turns
Inside coil 22 mm. I.D. DI m r l i p to
Figure 4.
2 mm 0 0 ,thin
II 1111. a n d Center
h turns
Carbon Dioxide Absorber
The carbon dioxide produced is absorbed in the specially designed absorber, T , shown in detail in Figure 4. The absorber is closed a t the top by means of a No. 7 rubber stopper through which extend the tips of the two titrating burets and a short, tubular, reagent-addition funnel which is closed with a S o . 00 rubber stopper. The inlet and oldlet are connected to the system and guard tube, respectively, n-ith short, rubber tubing connections (Figure 1) to facilitate removal for emptying and cleaning a t the end of an analysis. A manually propelled Meker burner is used for pyrolyzing the sample. When high temperatures are required, a hood is laid over the reaction tube and burner. The hood is constructed from a 15 X 15 cm. piece of 10-mesh nickel gauze bent in the form of a 1' and covered with Sauereisen Insalute adhesive cement No. 1. The large-bore sto cock is protected from heat radiation by a circular shield of 'j-inch Transite having a diameter of 22 cm. Solid and nonvolatile liquid samples are handled in Coors por-
25 mm. O.D. bulb
Figure 6. Liquid Nitrogen-Cooled Trap
Copper. Kire-form, prepared from ACE4 grade cupric oxide (Eimer and ilmend) by reduction with hydrogen in situ. Ascarite. Sodium hydrate asbestos absorbent, 8- to 20-mesh (Arthur H. Thomas Co.). Anhydrone. Anhydrous magnesium perchlorate (G. Frederick Smith Chemical Co.). Carbon. Wyex Compact Black, pelleted, amorphous, ash (Arthur H. Thomas Co ). The 20- to 42-mesh fraction (0.35to 0.85 mm.) was used in this work.
ANALYTICAL CHEMISTRY
474
Iodine Pentoxide. Reagent-grade iodic anhydride (JIerck and
Co., Inc.). This material was sized through a 100-meqh screen
and the coarser fraction was used. Sodium Thiosulfate. -4 14- t o 60-mesh fraction of anhydrous material was prepared from ACS grade pentahydrate crystals (Industrial Distributors, Inc.) by repeated drying in vacuo a t 40" C. followed by crushing and screening. Sodium Hydroxide. A 0.05 A- solution of ACS grade pellets (Hema Drug Co.) in distilled water, standardized against the 0.025 S hydrochloric acid used. The sodium hydroxide pellets used must contain a t least 2.5y0 by weight of sodium carbonate. If this quantity is not present, an appropriate amount should be
against pure sodium carbonate using methyl red indicator. and the end point adjusted after removal of carbon dioxide by boiling. Barium Chloride. A 10% solution of -4CS grade crystals (Baker and Adamson) in distilled water. Thymol Blue. A 0.04% solution (Fisher Scientific Co.), standardized and adjusted to the mid-point of the pH range 8.0 to 9.6. Acetone. ACS grade, Rimer and Amend (Fisher Scientific CO.). Silica Chips. ; i 14- to 28-mesh fraction was prepared by carefully sizing crushed scraps of clear, fused quartz tubing. Before using, the chips were treated with boiling 1 to 1 hydrochloric acid for 10 minutes, washed well with distilled water, dried, and finally heated in a muffle furnace at 800' to 900" C. for 5 hours. Glass Wool. Pyrex brand glass S o . i22 (Corning Catalog S o .
m i - _n _
Liquid Nitrogen. Methyl Cellosolve. Ethylene glycol monomethyl ether, purified (Fisher Scientific Co.). PREPARATION OF 4PPARATUS
Assemble the apparatus as shown in Figure 1, omitting the reaction tube, M , and the iodine pentoxide oxidation tube, P; use n-ax-sealed, ground-glass joints and glass tubing for connections. With nitrogen flowing through the purification furnace, F , and venting through stopcock SI,heat the furnace to 500" C. 411ow alternating streams of hydrogen and air to flow slowly (10 to 20 ml. per minute) through the copper to develop its surface activity. Conduct the activation slowly and cautiously to prevent sintering, and purge each gas stream completely from the furnace and lines with nitrogen before introduction of the other. -4t least three oxidation-reduction cycles are recommended, the copper being left, finally, in the reduced state under nitrogen. While a slow purge stream of nitrogen is flowing through the purification furnace, F , and absorber, G, fill the reaction tube, JI. with glass wool, carbon, and silica chips, as shonn in Figure 2. Then mount it vertically, exit end down, and pass dry nitrogen upward through it a t a rate of 30 to 50 ml. per minute. Heat the tube strongly with a gas-oxygen flame to dispel the bulk of the moisture and adsorbed oxygen-containing gases. Tap periodically, while heating, to promote maximum settling of the filling, and finally allow it to cool while nitrogen is flowing through it. Place a i.5-cm. length of rolled nickel sheet (So. 24 gage) around the tube as shown in Figure 2, quickly insert the tube through furnace N , and connect the tube to the system. Adjust stopcocks SI to Si, as required, to purge the reaction-tube bypass line, and finally to permit a flow of nitrogen through the carbon filling. Heat the tube and filling slowly to 1120' zk 5" C., and maintain a flow of nitrogen of 20 ml. per minute through the tube for 24 to 36 hours to condition the carbon. Meanwhile, fill the oxidation tube, P , with iodine pentoiide, using plugs of glass wool at both ends of the tube to retain i t in place. Condition it by passing a slow stream of dry nitrogen through the tube while heating for 4 hours a t 230' to 240' C. and thereafter for 24 hours a t 150" to 160" C. Finally, insert the oxidation tube through its heater, connect it to the system, and adjust stopcocks 8 6 ) 1$7, and SSso that nitrogen from the reaction tube passes through it and the flow-indicating bubbler, 2. Add methyl Cellosolve to the heater, and heat it to boiling. After all apparatus components have been connected and, except for the liquid nitrogen-cooled trap, brought to operating temperature, close stopcock 8 9 , and pressure-test the system with nitrogen. PROCEDURE
Determination of Operating Blank. ilt the start of a day's operations, adjust the nitrogen flow rate to 20 ml. per minute, and increase the furnace temperature from the stand-by level (800"to 900" C.) to 1120' C. Xeanwhile, a d d liquid nitrogen to the
Dewar flaek surrounding t,he trap, and control the rate of addition by observation of the flow-indicating bubbler, t.o prevent suckback of liquid from the lat,ter. Preferably, the nitrogen-flow rate should be increased to about 50 nil. per minute during this operation. .4s soon as the tube reaches operating temperature, flame the pyrolysis sect,ion strongly for 3 minutes. using the hIeker burner and hood, and then purge the system with nitrogen for 10 minutes using a flow rate of 50 nil. per minute. Flame an eniptg sample boat thoroughly at 800' to 1000" C., cool it in a desiccator, and transfer it to the purging lock. Close the lock by sliding the pusher-rod guide tube into place and securing the ball and socket joint, with a clamp; no lubricant should be used on this joint. Increase the nit'rogen flow rate to 50 nil. per minute, and then open stopcock S a slightly to permit the Iiuik of the nitrogen to flow through the lock and escape to the atmosphere through the annular space in the guide tube. While air is being purged from the lock for 5 minutes, purge the carbon dioxide absorber, T , n-ith a flow of nitrogen of 50 ml. per minute admitted through stopcock Ss from. t'he auxiliary supply line. Allow approximately 4 minutes for this purging, filling the buwt,s in the meanwhile, then add exactly 25 nil. of 0.05 A' sodium hydroxide to the absorber from the buret and 5 drops of thymol blue indicator through the reagent-addition funnel. Adjust stopcocks Sg and Sgt.o connect the absorber to the reaction system, open stopcock S3 fully, and push the boat into the reaction tube as far as the V-notch will permit. JVithdran- the pusher rod, close stopcock St, and reduce the flow of nitrogen t.o 20 ml. per minute. Adjust the Meker burner to provide a soft, low, nonluminous flame about 3.5 to 4 cni. long; t,hen place the burner under the tube at a point 16 cni. from the furnace TT-all. and move it stepn-ise toward the furnace, about 1 em. per minute, so that it will have reached the furnace wall in 15 minut.es. Quickly return the burner to its initial position, and readjust it t.o produce a hard, nonluininous flame about 6 to 8 em. long. Cover the tube with the nickel gauze shield, and advance the burner toa-ad the furnace, stepwise, at a rate of approximately 1.5 cm. per minute, so that the heating period is complete in 10 minutes. Remove the burner and hood and allow the reaction tube to cool for 10 minut,es while maintaining the nitrogen f l o ~to sweep the pyrolysis ent the tail end of the reaction system to the atmosphere through stopcock SI and the flow-indicating bubbler, and simultaneous1~-pass nitrogen at the rate of 50 ml. per minute t,hrough the carbon dioside absorber from stopcock Sy and the ausiliary nitrogen supply line. Remove the st,opper from the reagent-addition funnel in the top of the,absorber, and quickly add 5 nil. of acetone and 10 ml. of 10% barium chloride to the absorber solution. Replace the stopper, and allow 1 to 2 minutes for thorough mixing of the reagents and,complet'e precipitation of the barium carbonate. Finally, titrate sloyly with ,standardized 0.025 -T hyrochloric acid to the rnd point. Sample Analysis. Keigh accurately ( 1 0 . 0 5 mg.) a 15- to 350-mg. sample, depending upon its osygeu content; choose the sample weight so that the carbon dioxide formed will not coiisunie more than i 5 5 of the alkali used. JVeigh any nonvolatile solid or liquid material direct,ly into a previously flamed and cooled boat, and place the boat and sample in the purging lock. Open stopcock Sa slightly, increase the nitrogen flow rate to 50 nil. per minute, and purge the lock for 5 minutes. Then open st'opcock SI fully, push t,he boat into the reaction tube. and proceed as described above for the blank determination. To analyze a volatile liquid, construct a borosilicat,e g h s aiiipoule as shown by the dotted outline in Figure 5, and scratch it &h a file a t the point designat,ed. Heat the ampoule to 500" bo 600" C. over a radiant electric heater t o destroy any orgauic matter on its surface, and then cool it in a desiccator. Tare and fill the ampoule Lvith an appropriate quantity of liquid by alternately cooling and x-arming the bulb d i i l e the open end is dipping below t,he surface of the sample. Attach a short section of rubber tubing, closed in the middle with a pinch clamp, to the open end of the ampoule, and immerse the ampoule carefully in liquid nitrogen to freeze the sample slowly. Connect the open end of the rubber tubing to a high-vacuum pump; after the connecting line is evacuated and the sample is frozen, open the pinch clamp t.o permit evacuation of the ampoule. Pump for about 2 to 3 minutes, and seal the ampoule under vacuum with a small, soft, nonluminous flame. Cool and reweigh bolh sections of the ampoule toget,her to obtain the weight of the sample by difference, applying suitable corrections for the buoyant effect of air. Lay the sealed ampoule in a previously flamed and cooled boat, with the bent capillary tip near the slotted end of the boat and extending upward, and place the boat in the lock. Purge the lock as described previously, and push the boat into the tube as far as the V-notch will permit. Disengage the hook of the pusher rod quickly from the slotted end of the boat, and rotate the rod EO
415
V O L U M E 25, NO. 3, M A R C H 1 9 5 3 that it can be pushed for\\-ard over the top of the boat against the protruding capillary tip. ilpply pressure against the tip to break it o f f at the file scratch, withdraw the pusher rod quickly, and close stopcock 83. Carry out the remainder of the procedure as deqcribed previously, except for modifying the rate of heating, if necesary, de ending on the volatility of the liquid. Calculate tEe percentage of oxygen as follon-s:
The copper is reduced every 4 to 6 months, when newly filled cylinders of nitrogen are put into use. Similarly, the capacity o$ the iodine pentoxide oxidation tube is adequate for 4 to 6 months operation without requiring additional filling; occasional retamping of the bed is advisable to minimize channeling. The filling in absorber G ia adequate for a t least 2 years of regular use. RESULTS
Iiei e T', and Vb are, respectively, the volumes (in milliliters) of baqe and acid used in titrating the sample, S, and blank, B, F is a tliniensionless ratio expressing the volumetric equivalence of acid to base, S is the normality of the acid, and W is the weight oi sample (in milligrams). If identical volumes of alkali are used ioi the blank and sample determinations, then
To deterniine the value of F used in the above equation, attach the carbon dioxide absorber to the syst,eni, and pass nitrogen tliTough it from t,he auxiliary system at the rate of 50 ml. per minute. Purge the absorber for 4 minutes, and then add exactly 25 nil. of 0.05 N sodium hydroxide to it from the buret. Remove the stopper from the reagent-addition funnel and add 5 drops of thymol blue solution, 5 nil. of acetone, and 10 ml. of 10% barium chloride solution to t,he absorber. Replace the stopper, allow 1 to 2 minutes ior complete mixing of the reagents, and then titrate slon-1)- with 0.025 A- h>-drochloricacid to the end point. Calculate F as the volumetric ratio of acid to base used. ired if the purging and filling of the carbon dioside alrsorber a t the beginning of an analysis are timed to coincide, as described, n i t h the purging of the boat in the lock. Similarly, a t the end oi an anal>-sis,the titration can be completed, escept for final end-point adjustment, 17-hile the lock is being purged before removal of the boat. Stopcork SI need be opened only slightly, a3 directed, to purge the lock. Because of the large diameter of its bore and the resistance t o foiv of the carhon bed and other fillings, all of the nitrogen can be diverted easily through the lock in this manner. The end point obtained with thymol blue is sharp and distinct; the brilliance of the colors appears to be improved by the addition of acetone ( 7 ) as described. h mixed indicator consisting of cresol red :ind thymol blue, which s h o w a sharp color change within the p H range of 8.2 to 8.4, has been described by Kolthoff anti Stenger (16). I t is useful in the analysis of substances of low oxygen content where the amount of barium carbonate formed is snia11.
During the titration, the tip of the acid buret must estend well below the surface of the solution, and the titration must be conducted slowly t o prevent loss of carbon dioside from the solution. The reproducibility is improved by locating the t,ip of the reagentaddition funnel above that of the sodium hydroxide buret, so t'hat t.he subsequent additions of acetone and barium chloride can n.ash any remaining droplets of alkali off the buret tip. Daily maintenance of the apparatus consists primarily of the removal of pyrolysis carbon from the reaction tube and of condensate from the cold trap, both operations being performed, preferably, a t the end of a day. The former is accomplished by inserting a silica tube 4 to 5 mm. in outside diameter, carrying a slow stream of air, through stopcock S , and burning out the carbon xhile nitrogen is fed through the tube in the reverse direction vin stopcncks Sz and Sa (9). Condensable substances are removed from the cold trap by allowing it' to warm up and vent to the atmosphere through stopcock S, and an Anhydrone-filled guard tube. Xliphatic substances of low oxygen content do not undergo active decomposition until their vapors approach the vicinity of the silica chips ahead of the carbon packing. Deposit,ion of carI Ion. therefore, is highly localized, and when successive samples whose cumulative weights approach 350 to 400 mg. have been pyrolyzed, flow through the tube becomes highly restricted, and the carbon deposit must be burned out. By placing an auxiliary burner under the tube and nickel shield adjacent to the furnace, a verJ- high temperature zone is created ahead of the silica chips and some of the deposition can be made to take place on the walls of the tube, instead. This technique has been useful with all types of samples for delaying the development of excessive pressure drops through the reaction tube. During overnight and other stand-by periods, the temperature of the reaction tube is reduced to about 800" to 900" C., and a continuous flon- of nitrogen of 4 to 5 nil. per minute is maintained through the system.
Comparative analj-ses of known compounds were made with both the iodometric and titrimetric methods (Table 111). The results show that the latter method gives lower and more nearly correct results, as interference due to the reducing action of hydrogen on iodine pentoxide is eliminated. The advantages are particulaily evident in the range of 0 to 13% oxygen; above 20% oxygen, the methods appear to be equally reliable in precision and accuracy. The results reported have not been selected, but, rather, represent data accumulated over a 2-year period under comparable and valid, but not identical, operating conditions. The occasional wide deviations among the data for anisic acid and sucrose are believed to be due, mainly, to errors in sample weights The consistently high values obtained for 5-ethyl-2-nonanol ( 9 . 2 9 5 oyygen) led to the belief that this substance hadnot been completely dried prior to analysis, even though it had been standing over Drierite for several weeks. Subsequent analysis by the Karl Fischer method revealed the presence of 0.228% water; the corrected, theoretical oxygen content of this compound ( 9 . 4 7 5 ) listed in Table I11 was computed from this analysis. I n order to obtain the iodometric results listed in Table 111, it was necessary to modify the procedure described by Aluise et al. ( 2 ) and Unterzaucher ( 2 2 ) for determination of the iodine liberated by the iodine pentoxide. Testa performed with known quantities of elemental iodine revealed that a reagent contact time of 5 to 10 minutes was required before destruction of the excess bromine with formic acid, in order to ensure complete oxidation of the 5- to 10-fold larger amounts of iodine evolved from the larger samples used. In addition, a doubled quantity of mineral acid was used for the titration reaction to overcome the sluggishness caused by acetate buffering. The wide applicability of the titrimetric method to the analysis of miscellaneous substances is shown by the data in Table IT-. Included here are data for materials with low and sharp boiling points as \?-ell as for materials boiling over wide ranges. ACCURACY AhD PRECISIOh
The results listed for the pure oxygen-containing compounds in Table I11 indicate that the accuracy and precision of the titrimetric data are both well within +lT of the actual oxygen contentofthe substances analyzed, except in the case of cinnamalacetophenone and cystine. The causes of the discrepancies here appear to be related to a lack of purity in the former and to the interference caused by sulfur in the latter (see also Table VI). The analyses of the miscellaneous substances represented by samples 5 to 17, inclusive, of Table IS- show a similar order of precision, with few exceptions. However, the results shown for the cetane-octyl alcohol mixtures, samples 1 to 4, exhibit a much wider range of deviation and present certain anomalies when compared with the titrimetric data for cetane in Table 111. For example, the average apparent oxygen content of cetane (0.018~0) is nearly the same as that for mixture 1 (0.021%); the method thus is not sensitive to the small amount of oxygen in this sample (0.011%). I n the case of the second mixture, the average value (0.041%) is higher than the estimated value (0.0277,) by an amount (0.01470) that is very close to the average value for cetane, indicating that a correction for the apparent oxygen content of cetane may be in order. On the contrary, if such a correction were applied to the third and fourth mixtures, the good agreement between the experimental and estimated values would be lost. It appears, therefore, that the method in its present form
ANALYTICAL CHEMISTRY
416 Nuua*---Y
0-a=--00
O-QNhCNQd
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477
V O L U M E 25, NO. 3, M A R C H 1 9 5 3
thereby permitting a twofold increase in the volume of titrant measured under equivalent conditions of sample weight and oxygen content. This modification has been extended to further analyses of the cetane-octyl alcohol mixtures referred to above with some improvement in precision as shown by the data in Table V (Titrimetric Method B). In considering these data, it should be noted that the deviations do not vary with the sample weights in any uniform pattern, such as might be anticipated if they were caused by the presence of dissolved air or water in the sample. This suggests the possibility that they might result from Table IV. Determination of Oxygen in llfiscellaneous Substances by the erratic reducing effects of small Titrimetric Carbon Dioxide Rlethod amounts of -~vrolvsis - - hydrogen on the Per Cent Oxygen tube walls, as the water-formed thereby Deviation Substance Sample Keight, Sample Estimated Found from average would in turn be converted into carbon ZIg. SO. monoxide and, thus, be indistinguishable -0 003 152.7 1 Cetane-octyl alcohol mixture 1 -0 002 152.7 from oxygen in the sample. For example, -0 002 156.2 + O 003 351.0 a simple calculation will show that the + O 005 354.0 reaction of as little as 0.03 ml. of hydrogen (NTP) in this fashion could produce +o 008 0.027" 0.049 255.1 Cetane-octyl alcohol mixture 2 2 0.045 +O 004 257.2 enough apparent oxygen to cause an -0 005 0.036 301.6 -0 008 0.033 305.9 error of 0.01 % in the analysis of a 200-mg. Av. 0.041 sample.
is not suitable for determining oxygen contents below 0.05%, although in the range of 0.05 to 0.1% oxygen differences of 0.02 to 0.03% can be distinguished. It has been found possible to improve the method further, particularly for the analysie of substances containing less than 5% oxygen, by using more dilute absorbing and titrating solutions. Preliminary experimental results have indicated that the scrubber will perform satisfactorily with 0.025 N sodium hydroxide,
3
Cetane-octyl alcohol mixture 3
4
Cetane-octyl alcohol mixture 4
56
n-Heptane-isopropyl alcohol azeotrope (b.p. = 76.3' C . )
152.0 200.4 203.6 206.6
0.060a
0.054 0.062 0.069 0.070 Av. 0.064
-0
010
-0 002 + O 007 + O 006
-0 018 + O 005 +O 026 +O 006 -0 017
151.6 152.7 152.8 153.1 207.8 13.5P
n-Pentane-isopropyl alcohol azeotrope (b.p. = 35 5' C.)
62.6 77.7 86.5
1 62O
ic
Fischer-Tropsch reflux oil (boiling range '= 60' t o 250' C.)
95.4 99.9 110.2
4.426
5
Fischer-Tropsch heavy oil (wax) No. 146 (boiling range = 300' to 1450' C.)
104.5 116.2
9
Fisoher-Tropsch heavy oil (wax) No. 149 (boiling range = 300' t o +450° C.)
100.9 106.9
1.30b
1.11 1.15 Av. 1.13
-0 02 +o 02
IOC
Coal-hydrogenation vaporphace gasoline (200' C. end point
80.6 88.0 96.6
0.441,
-eo
115
Coal-hydrogenation light oil (Kentucky coal) (boiling range = O o to 250e C.
102.7 106.6
3.44b
0.40 0.36 0.38 4 r . 0.38 4.20 4.00 Ar. 4.10
Coal-hydrogenation light oil (Wyoming coal) (boiling range = Oo t o 250° C.) Coal-hydrogenation heavy oil (Kentucky coal)
101.2 106.8
3.46b
Coal-hydrogenation heavy oil (Kyoming coal)
56.5 83.5
High-temperature coal carbonization t a r (boiling range = 230' C. a n d up)
64.4 69.8
Topped crude oil
55.1 58.6 63.7 66.7 68.7
6C
12c
13 14 -15
16
17
a
b e
Clarified used oil
63.5 68.1
78.4 78.7 81.8 98.4
Based on gravimetric preparation of mixturea. Value obtained from ultimate analysis, b y difference. Samples weighed a n d handled in sealed ampoules.
13.64 13.65 13.61 Av. 13.63 1 68 1 64
to 01
44.8 47.9 48.4
1 69
Av. 1 6 7 5.14 5.05 5.06 Av. 5.08 1,06b 0 40 0 85 Av. 0.88
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3.66 3.60 1.91 1.97
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Av. 1 . 94
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0.90 0.95 1.00 0.96 0.98 Av. 0.96 0.60 0.57 0.61 0.63 4 r . 0.60
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DISCUSSION
Blanks. Operating blanks are determined once daily, as previous experience revealed that blanks determined at the beginning and end of a day were constant within 0.03 ml. of 0.025 N hydrochloric acid (0.006 mg. of oxygen). When a newly packed carbon bed has been conditioned as described previously, the operating blank usually mounts to 0.2 mi. of acid (0.04 mg. of oxygen). Continued purging with nitrogen for 2 to 4 days will reduce it further to a stable value of 0.10 to 0.13 ml. (0.02 to 0.026 mg. of oxygen). However, if one or two 100-mg. samples of naphthalene or phenanthrene are pyrolyzed through the bed after the initial conditioning with nitrogen, it has been found possible to stabilize the blank a t the lower value within a few hours. This procedure has now been adopted as standard practice. In the early phases of this investigation, large and erratic increases in operating blank were noted after the pyrolysis of acetanilide. These so-called "afterblanks" were 100 to 300% higher than the value determined before an analysis, and were eliminated only after purging for more than 3 hours with nitrogen. Holdup of oxygen in the tube-i.e., "straggling"-was discounted as a source of trouble, as oxygen values very close to the theoretical (but slightly high) were determined and both benzene and p toluidine likewise produced the afterblank effect. Afterblanks were also noted after runs with diphenyl and phenanthrene, although with these substances their magnitude was greatly reduced. This led to the belief that reactive pyrolysis fragments, deposited in a low temperature zone ahead of the carbon packing, were reducing the tube wall slowly and causing the blanks. Because such a zone couldexist only along that
478
ANALYTICAL CHEMISTRY
section enclosed by the thick, forward inTable V. Determination of Oxygen i n Cetane-Octyl Alcohol Mixtures by sulating wall of the furnace, the nickel Titrimetric Carbon Dioxide Methods shield shown in Figure 2 was installed to Titrimetric Method A= Titrimetric Method B" raise its temperature by conduction of Oxygen heat outward from the hot, inner portion Content, Sample weight, Oxygen Content, % Sample weight, .OxYgen Content, % Sample of the furnace. This produced an imme% mg. Found Dev. mg. Found Dev. Mixture 1 diate elimination of the afterblank and 0.011 152.7 0.018 +0.007 202.1 0.021 fO.010 152.7 0.019 +0.008 208.5 0.021 f0.010 its related effects, and no further trouble +0.008 215.9 0.022 +0.011 156.2 0.019 351.0 0.024 +0.013 260,O 0 . 0 2 0 +0.009 was encountered thereaftqr, despite the 354.0 0.026 +0.015 numerous analyses made and the variety A r . 0 , 0 2 1 +0.010 0.021 +0.010 3 I i ~ t u r e 2 0.027 2 5 5 . 1 0.049 +0.022 200. 5 0.045 f0.018 of substances tested. 257.2 0.045 +0.018 202. A 0.033 +O.OOG I t is believed that the blank corrections 301.6 0.036 +0.009 249. , 0.035 +0.008 305.9 0.033 +0.006 250 6 0 040 +0.013 and errors reported by Deinum and 252.1 0.041 f0.014 252.4 0.038 +0.011 Schouten (8) and Kirsten (15) as being 264.2 0.042 +0.015 hv. 0.041 +0.014 due to the deposition of pyrolysis carbon 0.039 +0.012 Mixture 3 0.060 152 0 0.064 -0.006 153.4 0.069 f0.009 in the tube are actually related to the 200 4 0.062 +0.002 153.8 0.069 +0.009 203 6 +0.007 afterblank noted in this work, and that 0,069 155.2 0.072 +0.012 206 6 155.7 +0.010 0.070 0.070 +0.010 they were caused by the existence of a Av. 0.064 4-0.004 0.070 +0.010 Mixtwe 4 0.107 1.51 6 0.092 -0.015 100.1 low temperature region ahead of the car0 094 -0 013 152 7 0.115 103,(J +0.008 0.116 +0.009 bon packing. Moreover, it appears likely 152 8 +0.029 104,s 0.136 0 10.5 -0 002 153 1 107.4 +0.009 0.116 0 100 -0 007 that these various blank effects are not -0.014 207 8 152.5 0.093 0.107 0.000 Ar. 0.110 + O , 003 0 104 -0.003 produced by pyrolysic carbon per se, but. Cetane 0 155 8 0 019 240.9 0.013 . .... rather, by a hydrogen-containing car169.2 0.027 244.3 0.016 ... 207.2 0.018 244,9 0.012 ... bonaceous residue (soot, tar, etc.) which 355 4 0 019 . . attacks and reduces the tube wall by slorv 3.58 4 n 01.5 3 6 i ,3 0 oio dehydrogenation. In view of the wide ilr. 0 018 .. ... . 0.014 . variety of reaction tube furnaces availa Methods are identical except t h a t method A uses 0.05 N alkaliand0.023 S acid, whereas solutions used in method B are only one half as strong. Data for method A are reproduced from Tables I11 able for use in this work and their variand IV. ation in constructional characteristics, devices such as the nickel shield (Figure 2), or the suecial burner described bv Aluise (1.1,should be used if low temperature zones are to be avoided. Keither Vxcor or silica is suitable for ampoule construction, The existence of such zones can produce anomalous results (low because significant losses in weight occur during the sealing-off process. Pyrev brand glass ( S o . 774) is free from this objection, or high, depending upon the nature of the sample), variable operand ampoules ( 5 to 6 mm. in outside diameter) constructed from ating blanks, and extended analysis times. Time Required for Analysis. Most of the analyses reported in this glass can be used successfully a t the high pyrolysis temperaTable 111 were conducted according to the procedure described tures encountered without danger of collapse. If the conand required 45 minutes of analysis time, exclusive only of that stricted capillary section is not drawn too thin, the sealed bent needed for weighing and sample preparation. Recently, calibratip will break off without fragmenting, fall into the boat, and be tion runs with pure compounds indicat,ed that the analysis time removed subsequently from the reaction tube. However, if the could be reduced to 35 minutes without loss of accuracy or pretip shatters, fragments may fall into the tube where fusion or cision. This faster procedure was used for the analyses reported in sintering to the surface may cause the tube to fracture. Actually, Tables I\' and V and now is standard practice in this laboratory. this difficulty has not been encountered, although shattering of A tinie breakdown of the two procedures by operations is as follows: the tip has occurred on a few occasions; presumably, the partially Time Required, Minutes devitrified inner surface of the tube prevented such fracture. Procedure New The possibility of breakage might be obviated entirely by inserting Analytical Operation described procedure a thin semicylindrical platinum liner under the boat to catch any Initial lock purging and absorber preparationn 5 5 Sample pyrolysis, low heat 1.5 15 glass fragments. 10 2 Sample pyrolysis,, high heat Advantages. The proposed method offers the following disCooling and purging 1 ? Final lock purging and titrationn -. tinct advantages: The apparatus required is simple and serviceTotal 45 35 able; larger samples can be used, thereby reducing errors due to a Operations performed simultaneously. b Sitrogen %ow rate increased t o 40 ml. per minute. sampling; no unusual balance facilities are required; the ampoule technique permits storage of weighed, volatile samples inKhen extremely volatile or large samples (250 to 350 mg.) are analyzed, longer pyrolysis periods may be required. However, definitely without change in elemental composition and lends considerable flexibility to a work program; the reaction tube det,he total analysis t,ime has rarely exceeded 45 minutes. Sample Manipulation. The special react.ion tube, purging sign permits purging of the sample boat in a cool restricted zone lock, sample introductory mechanism, and sample containers and reduces the time required for an analysis; the determination of carbon dioxide by acidimetry is easy to perform, and is standwere developed because existing equipment and met,hods were reard and accurate; and the efficient carbon dioxide absorber will garded as inadequate for handling the wide variety of samples permit the use of dilute solutions for the analysis of substances of encountered in synthetic fuels work, particularly those of moderlow oxygen content. ate to high volatility. K i t h the present apparatus and procedure, all types of samples can be handled quickly, accurately, and EFFECT O F OTHER ELEMEiVTS easily. External cooling of the tube is necessarj- only when liquids Nitrogen and Halogens. X o interference hm been noted in the of very high volatility-for example, the pent,anes-are analyzed, analysis of pure compounds containing nitrogen, chlorine, or in order to lower t.he pressure in the ampoule and prevent possible iodine. Presumably, those containing bromine could be analyzed spraying of liquid into the tube and, perhaps, on the pusher rod successfully also, though fluorine would certainly cause trouble. when the ampoule tip is broken. Such cooling can be accomThe presumption that iodine exerts a beneficial effect on the plished, however, with absolute freedom from errors, due to conanalysis is hard to justify theoretically, although i t is implied in densation of atmoepheric moisture inside the tube.
y
419
V O L U M E 25, NO, 3, M A R C H 1 9 5 3
extensive use, a trial tube revealed no visible evidence of deterioration, but the difficulty encountered i n s t a b i l i z i n g TheoTheooperating blanks made its use appear retical retical Su!fur impractical. Other commercially availOxygen Sulfur Sample in Oxygen in Mg. Deviation Content, Content, Weight, Sample, Th,eoDeviaas able ceramic materials including zirconia, ‘6 7c RIg. Ilg. retical Found tion 3Ig.O/Ilg.S Sample zirconium silicate, thoria, silica, and $0.011 5 . 7 5 +0.06 5.71 5.69 21.4” 26.68 26 63 Cystine -0,002 5.72 -0.01 5.73 5.74 21.56 alumina were evaluated subsequently as $ 0 . 0 1 4 5.88 $0.08 5.80 5.82 21.W +0.018 6.23 + O . l l possible materials of construction b v 6.12 6.14 23.0 +O.Oil 6.23 6.30 +0.07 6,25 23,4b measuring qualitatively their coinpal a+0.010 6.40 +0.06 6.34 6.36 23.86 +0.010 6 . 5 2 6.60 +0.08 6.54 24.5b tive reactivities toward Wyex carbon at $0.012 6 . 8 7 4-0.08 6.81 6.79 25.5 1120’ C. These tests revealed that the 0 . 1 1 4-0.11 +0.016 6.52 0.00 Thioacetainidec 0 42.67 15.3 various grades of zirconia and zirconium 0.11 + O . l l $0.016 7.17 0.00 16.8 4 c a t e examined were as reactive :$s 0.09 +0.09 +0.014 5.6 0.00 Sulfurd 0 100.00 L 6 0.07 $0.07 $0 012 6.5 0.00 6.5 mullite, whereas thoria and silica were Bottom of liquid nitrogen-cooled trap filled with 5- t o 7-mm. lengths of S o . 27 B. &- S. gage silver less so, and alumina was least reactive. wire. Subsequent testing of a sample alumina 6 Ascarite-filled C - t u b e placed ahead of liquid nitrogen-cooled trap. c Recrystallized a n d dried in vacuo a t 90° C. fox 5 hours before use. tube indicated that this material could d Dried in vacuo for 2 hours a t 90° C. before me. not be used, because the thick-walled r o n s t r u c t io n required to mininiize porosity together with the high coefficient of cspansion of alumina would not permit rapid heating and the excellent results obtained for 2-iodobenzoic acid by the iodocooling, as required, v-ithout breakage. metric method (Table 111). It appears more likely that a preI n vievi of these observations, silica appears to be the most dominance of low values, such as is characteristic also of benzoic suitable material for react’ion t’ube construction. By lowering the acid, 2-chlorobenzoic acid, and anisic acid (p-niethosybenzoic operating temperature to 800’ to 900” C. for overnight and other acid), may be conipensating the otherwise high results due to standby periods, tuhes have been kept in continuous service as hydrogen interference. long as 5 months without causing any increase in operating Sulfur. According to RIaylott and Lewis (18) and others blank. (6, IO), hydrogen sulfide, carbon disulfide, and carbonyl sulfide ACKNOWLEDGMEST are formed in varying amounts, depending upon the parent substance, when sulfur- and oxygen-containing eonlpounds are The services of Irma Fincke, Elaine G. Aiken, and the staff of analyzed. As these sulfides react with iodine pentoxide, their the Coal Hydrogenation Inspection and Control Laboratory are presence in the reaction tube gases can cause high results, and the gratefully acknov-ledged for assistance in supplying analywq I , + use of a liquid nitrogen-cooled trap has been recommended (18) lated to this work. for their removal. I n this laboratory, consistently high results have been deterLITERATURE CITED mined for cystine (Table 111) by both the iodometric and titri(1) Xluise, 1.. -I., .ha. CHEM., 21, 746 (1949). metric methods, in spite of the use of a liquid nitrogen-cooled (2) Aluise, I-. -I.. Hall, R. T., Staats, F. C., and Becker, IT. IV., trap that permits a residence time of 4 to 7 minutes for cooling the I h i d . , 19, 3 4 i (1947). (3) Astapenya, Tapnik, and Zelkin, J . G o ? .C‘hem. (U.S.S.R.), 3 , 8 3 9 reaction tube gases. Moreover, the results could not be improved (1933). by inserting an Ascarite-filled U-tube ahead of the trap, or by fill(4) Berger, L. B., and Schrenk, H. H., U. S. Bur. Mines, Tech, Paper ing the bottom portion of the trap with short lengths of silver wire 582,ll (1938). ( 5 ) Berret, R., and Poirier, P., BiiZZ. S O C . chim. France, 16,539 (1949). (6). JThile these tests virtually precluded the possibility of inter(6) Campanile, V. -I., Badley, J. H., Peters, E. D., Agazzi, E. J.,and ference from the above named substances, further checks were Brooks, F. R., i l s . 4 ~ .CHEM.,23, 1421 (1951). made and the absence of sulfur in the gases leaving the iodine (7) Christensen, B. E., TVong, R., and Facer, J. F., Ixn. Esc,. prntoxide oxidation tube was confirmed. CHEY.,-4s.4~.ED.,12,364 (1940). In view of these observations, it is believed that the piesence of (8) Deinum, H. K., and Schouten, A., -4nal. Chinb. Acta, 4, 2% (1950). sulfur in the pyrolysis gases causes the release of some oxygen CHEM.,21, 545 (9) Dinerstein, R. -I.,and Klipp, R . I V ~ ,.IXAL. from the silica tube mall (IO), and that this oxygen is converted (1949). subsequently to carbon monoxide, thus causing high results. I n (10) Dundy, Jf., and Stehr, E.. Ibid., 23, 1408 ~ 1 9 5 1 ) . Table I?, the titrimetric data for cystine (Table 111) have been i l l ) Elving, P. J., and Ligett, W.B., Chein. Rers., 34, 129 (1944). (12) Gourerneur, P:, Schreuders, 31. -I., and Degens, P. S . , Jr., recalculated to show the ratio between the excess osygen deterAnal. Chim. Acta, 5,293 (1951). mined and the amount of sulfur in the sample. It appears evident (13) Harris, C. C., Smith, D. XI., and .\litchell, J., Jr., AKAL.CHEM., that this ratio is a nearly constant quantity which is affected 22, 1297 (1950). only slightly, if a t all, by a lack of oxygen in the sample, as in the (14) Holovehak, J., and JVear, G. E. C., I h i d . , 23,1404 (1951). %ilzrochemie per. Mikrochirn. Acta, 34, 151 (1949). (15) Kirsten, W., case of thioacetamide, or by a lack of carbon and hydrogen, as in (16) Kolthoff, I. AI., and Stenger, V. A., “Volumetric .halysis,” Vol. the case of sulfur. No attempts were made to see if this action on 11, p. 59, Sew York, Interscience Publishers, 1947. the tube wall will disappear when samples containing smaller (17) Korshun, .\I. C., Zarodskaya Lab.. 10, 241 (1941). amounts of sulfur are analyzed. (18) Maylott, -4.O., and Lewis, J XLL, CHEM., 22, 1051 (1950). (19) Mellor, J. IT., “Comprehe Treatise on Inorganic and Theoretical Chemistry,” Vol. VI, p. 985, London, Longman, STUDY OF VARIOUS REACTION TUBE MATERIALS
TableVI.
Effect of Sulfur in Determination of Oxygen b y Titrimetric Carbon Dioxide Method
Q
.It the start of this investigation it appeared desirable to eyplore the possibility of using materials other than silica for the reaction tube, because silica was known to devitrify and spa11 badly under the extreme conditions of usage required in the analysis. Mullite appeared to be a logical choice for this purpose, since it is used in high temperature work, is available in suitable tube form, and has a high density (low porosity) and low coefficient of thermal expansion. After more than 4 months of
Greens & Co., 1947. (20) Pieters, H. A. J., A n a l . Chim. Acta, 2, 263 (1948). (21) Schutze, M.,2. anal. Chem., 118, 241 (1939). (22) Unterraucher, J., Bor., 73B, 391 (1940). and Smith, W. H., J . Re(23) Walton, W.W., McCulloch, F. W., search S a t l . Bur. Standards, 40, 443 (1948). (24) Zimmerman, W.,2.anal. Chrm., 118, 258 (1939).
R E C E I V E D for review J u n e 17, 1952. Accepted November 24, 1952. Presented before t h e Division of Refining, American Petroleum Institute, San Francisco, Calif.. May 12, 1952.
