Table 111.
Sample No. 7104 :7175 7378 8145 8435 8844 9880 9892 9899 16564 0
Analyses of MEG Production Materials
%DEG id&, % by GLC Periodate H200 3.2, 3.1 96.5 0.4 3.1, 3.3 96.5 0.3 0.3 3.0,3.3,3.196.5 0.04 0.35, 0.33 99.3 3.3, 3.5 96.3 0.4 3.0, 2.9 96.3 0.4 0.30, 0.28 99.3 0.04 0.65, 0.58 99.0 0.06 0.06 0.60, 0 . 5 7 9 9 . 0 3.1, 3.1 96.4 0.4
Karl Fischer titration.
GLC only. The data indicate that GLC results are somewhat more accurate when the M E G contents are higher. The D E G contents of several of the samples shown in Table I1 were also determined by the difference between periodate and dichromate titrations (1) and the results indicate that the dichromate method is not usable for determining D E G in this range.
The results of GLC and periodate determination of production samples of regular grade and antifreeze grade M E G are shown in Table 111. In the case of commercial grade M E G the sum of per cent D E G by GLC and per cent M E G by periodate differed from 100% by the amount of water found b y Karl Fischer titration. With regular grade M E G (less than 1% DEG) this difference is as much as 0.4%. Probably this is due to the fact that for samples of high M E G content GLC gives a direct determination of the minor constituent while the periodate method is indirect.
include most of the commercially produced grades of glycol. The GLC determination of glycols is comparable in accuracy to conventional methods for the determination of D E G and TEG. In addition, GLC has a considerable advantage with regard to analytical time and convenience compared to conventional methods. ACKNOWLEDGMENT
The help and advice of J. G. Hanna as well as the technical assistance of W. M. Campbell are gratefully acknowledged.
CONCLUSIONS
LITERATURE CITED
M E G and T E G present in amounts up to 2% each in D E G can be satisfactorily determined by the recommended GLC procedure. Up to 8% D E G can be satisfactorily determined in M E G b y the same technique. Using the procedure described, linear calibrations are obtained and the accuracy is generally well within =kO.l% absolute. The concentration ranges examined in this work
(1) Allen, N . , et al., IND.ENG.CHEM. ANAL.ED.12, 384 (1940). (2) American Society for Testing Ma-
terials,
Philadelphia, Pa., Method art 5, p. 253, 1952. ogare, S., Safranski, L. W., ANAL.CHEM.30,894 (1958). (4) Ogilvie, J. L., Simmons, SI. C., Hinds, G. P., Ibid., 30,25 (19%3). D1078 (3) Dal
'8
RECEIVEDfor review April 2, 1959. Accepted August 4, 1959.
Determination of Solvent Impurities in Waxes and Lubricating Oil Stocks by Gas-Liquid Chromatography LARRY RANDALL DURRETT Houston Refinery laboratory,
Shell Oil Co., Houston, rex.
A method employing gas-liquid chromatographic techniques has been developed specifically for the determination of methyl ethyl ketone and toluene in waxes and lubricating oil stocks. This method could be applied with equal success to the determination of other solvents dissolved as impurities in waxes and lube stocks. The sample is weighed, heated, and stripped with the carrier gas, helium, until all the solvents have been removed. The solvents, thus stripped from the sample, are retained in a trap held a t -50" C. The trap i s then heated to flash the solvents into the GLC resolvlng column. Solvent concentrations of 0.00 1 to 0.05% weight are currently being determined by this method, but lower or higher concentrations could b e determined as well.
I
quantities of methyl ethyl ketone (MEK) and toluene dissolved in both waxes and lube stocks. If a suitable means of removing the solvent from the wax or lube stock could be devised, it could be accomplished very easily by gas-liquid chromatography (QLC). An effective solvent-stripping manifold system was designed and installed on an existing gas-liquid chromatography unit. This manifold system consists of a small stainless steel cylinder in which the sample is heated and stripped with the carrier gas, and a freeze-out trap in which the solvent is retained prior to its introduction to the gas-liquid chromatography column. Another technique for determining light components in a heavy base material has been described by Porter and Johnson (1) for the determination of fuel. dilution in lubricating oil. APPARATUS
N
THE
SOLVENT
EXTRACTION
ANALYTICAL CHEMISTRY
ANALYTICAL PROCEDURE
Of
paraffin waxes from lubricating oil stocks, it is necessary t o determine small
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which screws into the manifold arrangement, and a 1-foot solvent trap constructed from 1I4-inch copper tubing and packed with 20- to 30-mesh firebrick. A conventional gas-liquid chromatograph is used to resolve the solvents after they have been stripped from the sample and trapped. A schematic gas flow diagram of the principal components of the apparatus-Le., the thermal conductivity cell, stripping cylinder, solvent trap, and resolving column-is shown in Figure 1. Polar Resolving Column. T h e resolving column consists of a coiled 10-foot length of 1/4-inch copper tubing packed with Carbowax "22" on 30- t o 60-mesh Johns-Manville C-22 firebrick (40 grams of Carbowax per 100 grams of firebrick). T h e column is held a t 100" C. and a helium flow rate of 40 ml. per minute, measured at atmospheric pressure at the column exit, is employed.
The solvent-stripping manifold system consists of a stainless steel cylinder
Ten grams of the sample are weighed and placed in the stainless steel stripping
FROM SOURCE-----
I I
1
I
I/l-nck
,HOKE
VALVES
_____
I\
I
I
5-75
ItI/
STRIPPIN
Figure 1. Schematic g a s flow diagram of modified GLC unit used in solvent impurities determination cylinder which is then screwed into position on the solvent-stripping manifold. A Dewar flask containing dry ice and isopropyl alcohol at -50' C. is then placed around the U-tube solvent trap. The hrlium carrier gas flow is dirrcted through the stripping manifold by opening toggle valvcs Nos. 1 , 4, 5, and 7 and closing toggle valves Nos. 2, 3, and 6 (Figure 1). An electric heating mantle a t 220' C. is placed around thc cylinder. The solvent is removed from the sample by stripping with helium for 20 minutes at the above temperature. When the solvent has been removed from the sample, the stripping cylinder and the solvent trap are isolated from the flow of the carrier gas by opening valves Nos. 2, 3, and 6 and closing valves Kos. 1, 4, 5, and 7. It is important to open valve No. 3 first, as this releases the pressure from thc stripping system, othcrwisc the manifold may become clogged (in the case of a wax sample) and nrcessitatc dismantling and cleaning. The dry ice-isopropyl alcohol bath is removed from the trap, excess alcohol is wiped away, and an' electric heating jacket is placed around the U-tube trap. This heating jacket is held at 125' C. After the trap has been heated for 2 to 3 minutes, the vaporized solvent is swept into the resolving column by opening valves Nos. 5 and 7 and closing valve No. 6. The retention times measured from this point for methyl ethyl ketone and toluene are approximately 12.3 and 21.3 minutes, respectively. Any water present in the sample or condensed from the air originally present in the cylinder emerges in approximately 40 minutes. This relatively long retention time for water, however, does not delay a second analysis as the solvent can be stripped from the second sample as soon as toluene from the first sample has emerged from the column. Water associated with the first sample passes through the column while the solvent is being stripped from the second sample. The time required for each analysis is a p proximately 1 hour. Calibration. T h e method of internal normalization is used for purposes of calibration in this determination. Known amounts of solvents a r e dissolved in a solvent-free lube
oil. These standard samples are run in t h e same manner as are t h e samples of unknown solvent concentration. The peak areas produced by thv solvc nts are measured with a planimetrr ant1 calibration favtors for various concrntration ranges of each solvent are calculated as follows: K = %w x Sr P A X 100 where K is a calibration factor expressed in grams of solvent per square inch peak area, Tow is the weight per cent of the solvent, 81:is the sample size in grams, and P A is the peak area in square inches produced by the solvent. Therefore, after running the sample and knowing the calibration factors, unknown solvent concentrations can be calculated by solving for %w in the above formula. EXPERIMENTAL
The initial attempt was madc with a 10-foot column of triethylene glycol (TEG) on 30- to 60-mesh firebrick (40 grams per 100 grams) a t 100' C. and a helium flow rate of 40 ml. per minute with no solvent trap includcd. A sample size of 10 grams was choscn to produce full-scale recorder deflection at methyl ethyl ketone concentrations of 0.002 wt. yo and/or toluene concentrations of 0.01 wt. %. Sufficient resolution of methyl ethyl ketone and toluene was obtaincd but the peaks tailrd very badly. T o climinatc this tailing effect, it was neccssary to install a cold trap (-50' C.) between thc stripping cylinder and thc resolving column in order to flash the solvent into tho column. The time required for thc carricr gas to remove all the solvent from thc sample at 220' C. and 40 ml. per minute carrier flow rate was expcrimentally dctcrmincd to be 15 minutes. An additional 5 minutes was added to the stripping pcriod as a safety factor. A stripping pcriod of 20 minutes covrrs mrthyl ethyl ketone and/or tolucne conccntrations of 0.001 t o 0.05 w t . yo. The triethylene glycol columns were stable at 100' C. for 4 to 6 weeks only. After that period of time the resolution decreased rapidly until finally methyl ethyl ketone and tolucne were unrcsolved. The column tcmpcrature could have been lowcrcd to prolong the life of
Table I. Repeatability and Accuracy Duta for Solvent Impurities Determination Wt. yo,Toluene Wt. %, blEK DeterDeterAdded mined Added mined Lube Stock Standard No. 7" 0.0018 0 0016 0.0090 0.0089 0.0018 0,0090 0.0085 0.0018 0.0019 0.0090 0.0090 0.0018 0.0018 0.0018 0.0090 0.0083 0.0018 0.0017 0 . 0 9 0 0.0088 Av. 0.0017 0 0087 Lube Stock Standard No. loa 0 030 0.028 0.009 0.010 0.030 0 OS1 0.010 0.010 0.030 0 0:30 0.009 0,010 0,010 0.010
0.009 0.010 Av. 0 0094
0.030 0.030
0.026
0.03J
0.02!)0
Prepared by adding known amounts of solvent to solvent-free Iitbricating oil (1
base stocks.
the triethylene glycol columns, however, only a t the expense of analysis time. I n licu of lowering the column tcmperaturc, a different liquid substrate, Carbowax 22, was chosen. Carbowax 22 has been found to be much more stable at 100' C. than was triethylene glycol. The present column has been in use some nine months without signs of deterioration. I n order to determine the accuracy and repeatability of this method of analysis, known amounts of solvent were added to solvent-frcca lube oil and then analyzrd. These data are given in Table I. SUMMARY
This modified gas-liquid chromatog. raphy procedure offers a simple method for determining solvent impurities preseot in waxes and lubricating oil stocks, materials which are somewhat difficult t o handle using convrntional gasliquid chromatography tcchniqurs. The method is reproduciblr, accuratc, and relativcly fast. It has been used routinrly for approximately 1 year to provid(b guidance i n solvent rwovcry from waxvs antl lulmcating oil stocks in a mclthyl (thy1 kvtone solvcnt-dewaxing procc ss. ACKNOWLEDGMENT
The author is intlvhtcd to L. J. 1)uhv for helpful advice and criticisms concerning this determination antl to R. G. Evrld for his critical examination of thc manuscript. LITERATURE CITED
(1) F'ortw, It. S.. Johnson, J. F., ANAL. CHEM.31,806 (105!)).
RECFIVEUfor rc*virm A p r i l Acccspted July 22, 1959. VOL. 31, NO. 1 1 . NOVEMBER 1959
S,
1959.
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