Gum Deposits in Gas Distribution Systems I. Liquid-Phase Gum (Continued) A. L. WARD,C. W. JORDAK,
AND
W. H. FULWEILER
The United Gas Improvement Company, Philadelphia, Pa.
N THE first part of this paper
I
(14) the quantities of the f o u r c o n d e n s a b l e unsaturated hydrocarbons occurring in different types of manufactured gas were shown. From a consideration of the relative q u a n t i t i e s of these hydrocarbons present and a comparison of the quantity of gum formed by sulfuric acid with the degree of unsaturation determined by bromine t i t r a t i o n s a n d t h e known properties of the hydrocarbon in question, it was est a b l i s h e d that butadiene and cyclopentadiene a r e a s m u c h potential sources of gum as are styrene and indene. I n view of this fact it became n e c e s s a r y definitely to establish the identity of the parent s u b s t a n c e s of natural gums. The o b v i o u s line of attack was to attempt to isolate and identify pure c o m p o u n d s in the gums, If this were successful, and e s p e c i a l l y if it could be followed by the synthesis of
acetone, c h l o r o f o r m , cyclohexane, e t h y l a c e t a t e , amyl acetate, carbon disulfide,,petroleum ether, ether, p y r i d i n e , nitrobenzene, benzene, carbon tetrachloride, kerosene, turpentine, x y l e n e , a n i l i n e , tetrahydronaphthalene, and methyl salicylate. It is practically insoluble in ethyl or methyl alcohols.
Styrene and indene are demonstrated to be the parent substances of 70 to 80 per cent of the liquid-phase gum formed in gas distribution systems. The gums are principally polymerized and oxidized styrene and indene. The nitrogen and ash contents of this type of gum are not essential constituents, and, aside from impurities, the gums are neither the products of oxides of nitrogen nor the salts of organic acids. The formation of liquid-phase gum is catalyzed by mercaptans and retarded by phenols. Systems distributing coal gas or coke-ooen gas under a thermal standard are immune to this type of gum because such gas contains an insuficient quantity of condensable hydrocarbons to produce the oily condensate that is a prerequisite to its formation. The absence of liquid-phase gum in certain systems distributing mixed gas may probably be explained by the fact that the gas contains a su8cient quantity of phenols to ottercome the catalytic efect of the mercaptans present.
depending on the condition of the system and the place where the sample was taken. I n general, it is contaminated with a greater or lesser amount of liquid condensate. Removed
M ~ t B roum
soluble in
Acetone
REFRACTIVITY An a t t e m p t was m a d e to d e t e r m i n e the specific refractivity of fractions of the gum separated by differences in solubilities in organic solvents. Although no confidence was placed in the absolute values, it was felt t h a t t h e r e l a t i v e values would be sufficiently acc u r a t e to p e r m i t the use of this easily determined constant as a means of f o l l o w i n g the s e p a r a t i o n s obtained. The values for R were c a l c u l a t e d bv the Gladstone-Dale formula.
Soluble
Aloohol
xylDl Insoluble, R
i.
0.558
Insoluble, R
0.487
INDUSTRIAL AND ENGINEERING CHEMISTRY
n'ovember, 1932
They have recently been misconstrued by Berkhoff (2) who cited the nitrogen contents of 0.34 to 3.47 as proof that the gums are nitrogen compounds. In view of the importance of keeping clear the distinction between liquid-phase and vapor-phase gums, the authors are republishing some of their analyses in Tables VIII to XI. TABLEVIII. GUMSPREPARED FROM IXDESE
--
hloL.
PREPAR.ATIOX WEIGHT C %
:.~AMPLE
-
ULTIMATE ANALYSIS H N S Ash
0
%
%
%
%
%
554 9 1 . 9 0 6 . 8 2 0 . 0 2 0 . 4 7 0 . 6 5 0 . 1 4 528 9 2 . 0 4 6 . 7 1 0.11 .. 1.14
1 2 3
Sulfur,ic acid Standine Standing in presence of copper 3-a Refluxed with copper
..
461 9 1 . 6 9 531 .
..
6.74 0.08
..
0.16
..
..
... .
MOL. 7 SEPAR%TION WEIGHT C
8.411PLE
% G U N RECOVERED
5
6 7 8 9
Insol. petroleum ether, sol. ether, pptd. b y alcohol Insol. petroleum ether, sol. ether not pptd. by aicohdl Sol. petroleum ether Sol. petroleum ether sol. ether, pptd. b; alcohol Sol. petroleum ether, sol. ether not pptd. b y alcohol
ULTIMATE .~N~LYSISH N S Ash % % % %
..
..
89.21
7.68
1.03 2.25
393 443
89.30 8 . 0 2 0.10 0.69
...
..
..
620
89.80
7.61
0.04
375
90.18
8 . 0 0 0.03 0.56
,
.
0.60
0.91
..
0
%
.. 0.98
..
1.65 0.30 0.87
0.36
1.38 19.40 0.30
8.72
GUX FORMED BY E X P O S U R E TO AIR
10
...
T h o l e product
64.22
5.98
TABLE X. NATURAL GUMS ~AXPLE
20 21 22 23
MOL. --ULTIMATE SOURCE WEIGHT C H N % % %
Main Governor Meter valve Meter
. ..
447 4%
-
ANALPEIE 9 Ash
%
%
0 %
58.11 5 . 4 1 2 . 9 8 2 1 . 2 0 2 . b 8 11.-22 53.72 4 . 7 3 1 . 4 8 0 . 6 0 16.26 23.21 2 6 . 0 2 3 . 6 0 Nil 9.36 50.25 9.62 75.42 6.68 0.44 1.76 3 . 5 9 12.11
TABLEXI. FRACTIONS SEPARATED FROM NATURAL METERGnu METHOD OF MOL. -ULTIMATE SAMPLE SEPARATION WEIGHT C H N 24 ?5
Insol. in acetone, sol. in chloroform Insol. in acetone, insol. i n chloroform
26
Sol. in
27 28
acetone, pptd. byalcohol Sol. in acetone, not pptd.byalcoho1 Sol. in acetone, not pptd. b y alcohol, pptd. b y hot xylene
519
%
%
%
72.76
7.17
0.46
Too insol. 14.05
ANALYSISS Ash
%
%
0
%
1.79 4.43 13.39
2.23
1 . 6 1 0 . 9 2 7 0 . 2 0 10.99
975
79.84
7.39
0.34
1.35 2.22
852
81.46 7.08
0.55
1.78 0.90 8 . 2 3
Too insol. 6 7 . 3 1 Sol in acetone, not pptd b y alcohol, not pptd. b y hot xylene, pptd. on cooling ;tl500 8 1 . 6 5 30 Sol. in acetone. not pptd. by alcohol, not pptd. by xylene, pptd,byalcohol 1275 8 3 . 8 4 31 Sol. in acetone, not pptd. b y alcohol not pptd. ~. b> xvleiie not pptd-. b y 463 82.95 alcohol 32 Insol. Detroleum ether" 68.73 a From different original sample. 29
..
ISTERPRETATION OF hf.0LECULAR WEIGHTS AND
ASALYSES
O N DISTILL4TION
789
Kjeldahl and Eschka methods, respectively. The ash was determined by weighing the residue from the ultimate analysis. The oxygen was determined by difference. The ash as Tveighed was largely (up to 90 per cent) iron oxide. Since it was probably not completely oxidized in the original sample, the oxygen as reported is low by the difference between the weight of the partially and completely oxidized metals. Except in the case of samples with high ash content, the error is not of importance. The indene used in preparing the gums in Table VI1 (14) was isolated from drip oil by fractionation, preparation of the picrate, and decomposition of the latter with steam.
1.33
TABLEIX. FRACTIONS SEPARATED FROM DRIP-OIL GUMS METHOD OF
1239
8.86
5.54 3.47
0 . 8 2 13.77
6.15
0.69
1.65
1.09 8.77
6.85 0.47
1.53
0.40 6.91
9.19
The analysis of the gums prepared from indene indicated that little oxidation had taken place, the products having been formed by the condensation (polymerization) of an average of 6 molecules of indene. Subsequent attempts to prepare indene (or styrene) resins of high oxygen contents were unsuccessful. Even when prepared by heating in pure oxygen, the gums were largely formed by polymerization reactions. The drip-oil gum, from which samples 5 to 9 in Table IX were separated, was obtained by distilling off the liquid portion of the drip oil. The treatment by solvents indicated that precipitation from an ether or petroleum ether-ether solution with alcohol had the effect of separating an insoluble fraction having a higher molecular weight, higher ash content, and lower ratio of carbon to hydrogen than the fraction remaining soluble in the mixture of solvents. Sample 10 of this series was prepared by exposing thin films of a sample of drip oil in air. The product had an oxygen content of somewhat the same order of magnitude as natural gums, but its sulfur content was so high that it obviously was a different type of product from natural gums. Considering the four samples of natural gums taken from different sources given in Table X, the sample taken from a main was heavily contaminated with free sulfur, and the samples taken from the governor and meter valve having ash contents of 16 and 50 per cent, respectively, were obviously contaminated with a large percentage of metals and oxides. The analysis (with the possible exception of the carbon-hydrogen ratios) of samples as they were removed from the distribution system offered little light on the materials and reactions involved in their formation. The analysis of the meter resin, which was typical of other anaIyses of different samples, indicated far less contamination. In view of this and of the fact that the deposition of gums in the meters had given more trouble than in other parts of the system, i t was decided to concentrate on gums removed from meters. I n Table XI the results of an attempt to resolve a typical meter gum into its constituents are given. Considering first the m e t h o d of s e p a r a t i o n SOLU6LE r2SH040 and the ash and nitrogen contents, we have the f;ollowing diagram: llsu ASH030 %Lu6LE
1
-
7.54
0.43
1.17
0.30 7.61
6.27
0.32
0 . 2 6 7 . 4 0 17.02
The molecular weights were determined by the boiling point method, using benzene or chloroform in the Menzies apparatus. The carbon and hydrogen determinations were made by the usual methods. Nitrogen and sulfur were determined by the
SOLUS.!
I
e
Nr
5 > i u T i O N CCQLED
SOL~JEL~ Hor XYLENE
'INSOLUBLE. res ASH t os
WASH 0 90
Nu VPJ ASH I 3 7 7 3.44
Ne
009
045
I N D U S T R I A L A N D E S G I iY E E R I N G C H E M I S T R Y
1240
Each precipitation gave an insoluble product with high ash and nitrogen contents, and a soluble fraction with much lower ash and nitrogen contents, until the last precipitation with alcohol gave two samples, both of which had nitrogen and ash contents of less than 0.5 per cent. The question naturally arises as to whether the insoluble fractions with their high nitrogen and ash contents represent impure, but nevertheless definite, chemical compounds such as salts of organic acids or nitrogen-oxygen compounds. The question is important because Berkhoff ( 2 ) quoted these analyses as previously published by Brown to prove that these gums were the same as those with which he is now working; but Brown (6) stated that samples 25 and 29 (his numbers 9 and 10) were “mostly leather and iron oxide.” This statement was correct. Leather contains about 17 per cent nitrogen, so that the nitrogen contents of the insoluble fractions are readily explained. On the other hand, Brown (6) placed great stress on the fact that some of the gums are acid, and states: “This explains the inevitable and frequently considerable ash content of a resin even when the latter had been freed from foreign material by dissolution in and reprecipitation from organic solvents.” The heterogeneous character of samples like 25 and 28 could be seen by examination under a microscope. The ability of fine shreds of leather and of iron oxide to remain with the gum through alternate solution, filtration, and precipitation with organic solvents was truly remarkable. The fact, however, that, if this type of treatment was continued long enough, the material could be so nearly freed of ash and nitrogen, offered proof that these substances were not essential constituents of the gums. A small portion of the ash in the original gum may have represented small quantities of salts of organic acids originally present as such, just as a portion of the nitrogen may have represented small quantities of nitrogen-oxygen compounds originally formed in the vapor phase and brought down and mixed with t.he liquid-phase gum. The point is that neither class of compounds was essential, and the liquid-phase gum would have been present even if nitrogen and ash had been absent. A closer study of the analyses of the most completely purified samples (30 and 31) confirms this. MOL.
SAMPLE WEIGHT 1275 463
30 31
83.84 82.95
N
0
H
C
S
ASHQ
AFALYIIS, PER CEKT
-ULTIMATE
6.85 7.54
6.91 7.61
0.47 0.43
1.53 1.17
0.40 0.30
0.0478 0.0366
0.00502 0.00377
ATOMIC R A T I O
30 1275 6.99 31 463 6.91 Assumed all FezOz.
6.85
7.54
0.432 0.476
0.0336 0.0307
These would give the following formulas: SAMPLE 30 31
FORNULA Ci38zH1d3ssN:SioFe
Ci6~~HaoooO:rsNssioFe
MOLECULAR WEIGHT Smallest aalcd. Determined 1275 19,919 433 26,500
If we omit the iron and sulfur, we have the following: 30 31
3022 3215
1275 433
Both the determined molecular weights and the difficultv of conceiving of a formula with 200 carbon atoms and only 1 nitrogen show the impossibility of considering the nitrogen to be an essential constituent. The nitrogen must, of course, be combined with something. It may have been originally present in meter leather or it may represent cyanogen compounds, ammonia compounds, or any of a large number of possible organic nitrogen compounds. As stated above, there is also a possibility that it represents some vapor-phase gum carried down by the condensation of liquid hydrocarbons and occluded by the gum formed as a
Vol. 24, No. 11
result of their polymerization and oxidation in the liquid phase. The nitrogen content of vapor-phase gums as received is 5 per cent or more. These partially purified liquid-phase gums could thus contain as a maximum not more than 8.6 t o 9.2 per cent of the nitrogen-oxygen compounds which make up vapor-phase gum. I n any case, the nitrogen represents an impurity foreign to the essential constituents of liquid-phase gum. If we consider the iron, sulfur, and nitrogen to be impurities and neglect whatever carbon, hydrogen, and oxygen (other than as iron oxide) may have been combined with them, we begin to arrive a t something like reasonable formulas: hfOLECEL4R mEIGHT
SlMPLE
Smallest calcd Determined
FORMULA
If we consider butadiene, cyclopentadiene, styrene, and indene, me could have, among others, the following combinations: AIOLEfi 4TOh19 O F
PAREFT SUBETANCE Butadiene Butadiene Cyclopentadiene DicvcloDentadiene Cyriope‘ntadiene Dicyclopentadiene Styrene Styrene Indene Indene
CON- OXYGEN DENISED
24 8 18 9 6 3 12
MOL.
COMBINED FORMULA WEIGHT 6 CisHziO(C~eHi4~0~) 1392 2
6 2 6 2
4 10
3
Ci&~0(CnH4~0~)
464
428 1344 448 1256 380
It is obviously impossible to draw conclusions as t o the parent substances of the gum from these results. Butadiene is probably eliminated, but cyclopentadiene, styrene, and indene are all possible, n-ith the results of analysis 30 favoring styrene and those of 31 favoring cyclopentadiene or dicyclopentadiene. Brown used these and a few analyses made by the Bureau of Mines to support the theory that styrene and indene are the parent substances. He considered only the carbon and hydrogen ratios and showed that, taking the values for a large number of samples, the carbon ranged from 90.5 to 92.5. The evidence appears to be strong until one considers that none of the samples for which he reported analyses was pure. Considering his Table 4 (6) the first two analyses were made on gum without purification. The others were made on the products from the attempted re-solution with organic solvents described here. Sone of these samples was sufficiently pure to draw definite conclusions. Those which came nearest to being pure were 30 and 31 (Brox-n’s samples 6 and 8). The ratio of carbon t o hydrogen for these two samples and for styrene, indene, and cyclopentadiene are as follows: Cyclopentadiene Sample 31 Styrene
C L R B O XHYDROGEP CARBOFHIDBOGEN 90 91 9.09 Sample 30 92 43 7.57 91 66 34 Indene 93.10 G 90 92 31 ,.69
8
The values for styrene are closest to both samples. Those for indene are close to sample 30, whereas those for cyclopentadierie are close to 31. In any case, the ultimate analysis cannot be cited as proof that styrene and indene are the sole causes of meter gums, since, as far as the analyses are concerned, the samples could easily have been formed from a mixture of cyclopentadiene and indene either with or without styrene. Having failed in the attempt to isolate and identify pure compounds from the natural gums, the second most obvious line of attack was to attempt to prepare synthetic gums from pure hydrocarbons and to compare the properties of the synthetic gums with those of natural gums.
November, 1932
I N D U S T R I A L A.ND E N G I N E E R I N G C H E M I S T R Y
The principal difficulties arise from the fact that a large number of different gums can be formed from the same unsaturated hydrocarbons. Superficially the different gums which can be formed from one parent substance vary from viscous oils to hard brittle resins. Fundamentally their character is determined by the number of molecules of the original hydrocarbon which polymerize to form one molecule of the gum, and by the presence or absence of oxygen, sulfur, nitrogen, or other elements in addition to carbon and hydrogen in the gum molecule. Furthermore, the softer gums tend to absorb oxygen after their initial formation, and thus their ultimate analyses become a function of their age as well as of the method of their formation. Kotwithstanding the recognized difficulties, the importance of the results, should they be successful. justify the fairly thorough study. d :
= m Y 0
15
20 9
$2
a
25
17
2 5 o u l
2-
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Yb
,5
15
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2-L"
I3
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lil
os
2 -
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$2
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0 0
i
Rs-0
NDEhlE -0 S'YRENL
3
4
-
5
OF 9AkENT SUBSTAUCES OF G U I
FIGURE 4. DECOMPOSITION OF MIXED INDENE A ~ D STYRENE GUMS
Instead of working with pure hydrocarbons, it was decided to do the preliminary work with fractions of condensate. Gums were prepared from the fractions boiling below 80" C. by allowing the material, both before and after polymerization, to stand in a n atmosphere rich in oxygen. I n addition to the gums for which analyses have been given, gums were prepared from styrene and indene fractions by several methods. One property which distinguished the gums prepared from the low-boiling hydrocarbons from those prepared from styrene and indene was their reaction to heat. The styrene and indene gums decompose quietly on heating, giving a relatively large quantity of oil containing styrene and indene. The decomposition of the others proceeds with almost esplosire violence. The only way in which the decomposition could be controlled was to heat gently a small quantity in a flask, removing the flame just as the decomposition started. The heat of the reaction was sufficient to complete the decompoqition and to distil the products. In this way small quantities of oil were obtained, but no individual (compounds in the decomposed material could be identified. The results obtained with the styrene and indene fractions were so interesting that an attempt was made to determine if there was any quantitative relationship between the quantity of gum decomposed and the quantity of styrene and indene formed. The results of this n-ork on both natural and synthetic gunis are given below. PPROGEXETIC DECOJIPOSITIOS OF GUJIH PREPARED GL-JIS. Thirteen samples of gums prepared by different methods nere decomposed. The gum was heated under a high vacuum to remove any unpolyinerized and unoxidized liquid compounds present. The residue TT as destructively distilled, the distillate was fractionated, the different fractions were titrated with bromine to determine the degree of unsaturation, and the unsaturated hydrocarbons present mere identified by their bromine compounds. The results are summarized in Tables XI1 and XIII.
2 Standing
3 Heat
4 Oxidation
93:9
66:7
89:5
0.7 72.3
0.9
34:4 9.6 3.6 1.0 14.4
3i:o 10.7
15.8
12.1
4.6 20.4
5.0 17.1
..
..
..
5 Oxidation Solder
..
2,2
c. 25.0 4i:3 6712 160-200° C. 10.6 15.7 8.1 200-2500 c. 5.0 2.1 1.9 250--300° C. 3.4 1.4 0.4 300-350' C. 30.0 13.9 9.8 Styrene by Br2: I n 120-160' C. fraction 20.3 23.2 44.4 I n 160-200° C . fraction 10.3 11.4 5.4 Total styrene 30.6 34.6 49.9 a Corrected for unpolymerized oil and water.
..
.. .. ..
TABLEXIII. PYROGEXETIC DECOMPOSITION OF INDESE GUMS
Catalyst
y:
1 Acid
~ ~ O - E O O
Eg
gn
E:
Sample Prepared by Catalyst Recovered in % of original gum:" Water Total oil Fractions of oil: Below 120' C.
Sample Prepared b y
kc2
51
TABLEXII. PYROGENETIC DECOMPOSITION OF STYRENE GUMS
$2 d?
w 3
1241
1 2 Acid Standing
..
3 Heat
..
..
Recovered in % of original g u m ? Water Total oil 6 3 : s 70:6 Fractions of oil: 1 . 6 15.9 12O-16O0C. 37.5 31.8 160-200° C. 3.8 7.5 200-250O C. 2.2 3.9 250-300°C. 6.1 300-350°C. 8.7 Indene by Brz: I n 120-160° C . fraction 0.5 3.6 I n 160-200' C. fraction 1 0 . 0 10.0 Total indene 10.5 13.6 a Corrected for unpolymerized
4
5
6
7
8
. . . . . . . . .Moist oxygen., , . , . , .. .. . . Japan Solder drier
1.0 1 . 5 2.5 2 7 6 3 . 5 5 6 . 9 51.1 54 2
3.5 46.4
11.5 7.2 9.4 6 . 0 4.7 34.9 3 2 . 7 3 4 . 6 2 8 . 1 33.6 1 4 . 2 1 2 . 8 9 . 7 10.9 7.0 1.2 3 . 6 2 . 4 3 . 6 3 . 3 3.5 6.70.6 1.6 2.8
3.0 21.6 8.3 3.6 4.8
7i:6
3.6
1.8 1.26
1.28
1.04
0.58
1 6 . 8 11.2 7 . 6 7 9 . 3 3 1 0 . 8 3 2 0 . 4 1 3 . 0 8 . 9 3 10.60 12.00 oil and water.
7.32 7.90
Although the principal fraction of the oil obtained from the pyrogenetic decomposition corresponded in each case to the boiling range of the material from which the gum was originally made, a considerable quantity of oil boiling over a very wide range was also obt.ained. The interesting point was that from both styrene and indene gums the respective hydrocarbon was identified in the distillate over the whole boiling range, Thus, from indene gum 2 Table XIII, the results given in Table XIV v-ere obtained. TABLE XIV. DISTRIBUTIOS OF IXDESE IN OIL DECOMPOSED GUM Ex-
BOILINGYOLRANGE
UME
ISDENE
INDEJE
SATUIDENRA6TSa TIFIED
C. M1. Grnm/ml. 120- 140 Yes 1s Yes 24 140-150 Yes 160-160 39 Yes 59 160-170 52 Yes 170-180 34 Y e8 180-190 0 All calculated as indene.
FROM
ROILIxG R.ANGE
VOL-
C. 190-1700 200-230 230-250
X1. Grizm/rnl. 17.5 0 423 26 0.484 12 0.494 12 Too dark 31 Too dark
250-300 300-350
UXE
uSS.ATCRAXTJ"
IDESTIFIED
Yes Yes Yes Trace Trace
This distribution of a hydrocarbon boiling at 182" C. in fractions boiling all the way from 120" to 300" C. apparently means that the original decomposition gave some liquid, but only partly decomposed products, the decompositim of which continued gradually during the fractionation. It was obvious from these results that the styrene and indene obtained from breaking up a mixture of natural gums m-ould be contaminated with each other. Since this could not be preyented. it was decided t o base calculations on the assumption that all of the unsaturation in the 120" to 160" C. fractions was styrene, and that of the 160" to 200" C. fractions was indene, provided that these compounds were actually identified. It 7%-asdecided further to attempt to base the results on these two fractions only, neglecting for
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 ST R Y
1242
the moment the material boiling above 200" C. Table XI' gives results obtained from synthetic gums prepared from styrene and indene. T.4BLE
XLr. SUMMARY
O F STYRENE AND INDENE COVERED FROX SYSTHETIC Guvs
G u ~ PREPLRED s BY:
RE-
UKSATCRANTS RECOVERED CATALYST120-160° C. 160-200° C. Total --Per
cent of gum--
STTREKE G U M S
.Lad Standing Heat Heat and moist oxygen H e a t and moist oxygen Av. for oxygen gums
....
.... .... ....
Solder
....
20.3 23.2 44.4 15.8 12.1 14.0
10.3 11.4 5.48 4.62 5.01 4.82
30.6 34.6 49.9 20.4 17.1 18.8
10.0
10.5 13.6 20.4 13.0 8.93 10.6 12.0 7.90 10.5
I S D E K E GUMR
Acid Standing Heat Heat and moist oxvnen Heat and moist ox;$en H e a t a n d moist oxygen H e a t and moist oxygen H e a t and moist oxygen Av. for oxygen gums
.... .... .... .... .... ....
J a p a n drier Solder
....
0.53 3.61 3.55 l.i9 1.26 1.28 1.04 0.58 1.19
10.0
i6.s
11.2 7.67 9.33 10.93 7.32 9.29
Table XV s h o w that the recovery of styrene and indene from their gums varies with the method by which the gum was prepared. The result is in line with what was to be expected. Styrene gums, in general, gave about twice as much styrene as the indene gums gave indene. Gums prepared by heat alone gave the highest recoveries. Gums prepared with oxygen gave the lowest recoveries. I n general, the recovery decreased as the amount of water in the decomposed material increased. The amount of water is obviously a criterion of the degree of oxidation of the gum When the natural gums were decomposed, it was found that they resembled the synthetic oxygen gums more closely than any of the others prepared in the laboratory. For this reason it mas decided to base the comparison between the natural and synthetic gums entirely on the basis of those synthetic gums which had been prepared with oxygen. Using the average figures for the styrene and indene recovered from the synthetic oxygen gums, the curves in Figure 4 were constructed. For a given ratio of styrene and indene found in the oil obtained by decomposing a gum consisting of a mixture of polymerized and oxidized styrene and indene, curve A-A shows the ratio of indene to styrene which originally made up the gum,l and curve B-B shows the total quantity of these hydrocarbons which should be expected, expressed in percentage of the gum decomposed. From the latter i t is a simple matter to calculate the percentage of the gum for which styrene and indene can be definitely identified as the parent substances. NATURALGUMS. Many samples of gums taken from meters in cities distributing water gas or mixed gas were examined by the general method described above. Difficulties were encountered which rendered necessary some changes in the technic employed. As received from the meter shop, the gums are contaminated with unpoly,merized drip or condensate, and water, and sometimes with meter oil. A portion of these materials was recovered by pressing in cheesecloth Attempts made to remove the remaining volatile material by vacuum distillation ran into two 'difficulties, It was found that the natural gums had a tendency to swell to many times their natural size and to fill the flask, con'denser, and receiver. Even using a flask of ten times the original volume of gum did not eliminate the difficulty. Styrene and indene gums can be broken up by heating under a partial vacuum and some of the styrene gums will distil 1 Allowance waa made for the fact t h a t some indene in the styrene fraction would be reported as styrene, and vice versa.
Vol. 24, No. 11
unchanged if the vacuum is high enough. It was always difficult to know when to stop the vacuum distillation so that all the unpolymerized oil would be removed and yet none of the gum would be broken up. I n the case of the synthetic gums the end point of the vacuum distillation could be seen when the first signs of moisture appeared in the distillate. The natural gums contained mechanically held free water which was removable only with the greatest difficulty. It was, therefore, almost impossible to tell Then the water appearing in the distillate represented actual decomposition of the gum. Both difficulties were fairly well overcome by the following procedure: About 500 grams of the gum, after pressing in cheesecloth, were placed in a 3-liter tared flask surrounded by a sand bath, and 200 ml. of toluene were added. The toluene was gently distilled off, and more toluene was added and distilled off until no more water appeared with it. The apparatus was then evacuated, and the distillation continued until water again appeared in the distillate. The vacuum was released, the flask weighed, and the heating continued until no further oil R-as obtained. After the oil had been obtained and the unsaturation determined, further difficulties were encountered in identifying the styrene. The brominated material boiling below 160" C. consistently gave a black tar after the evaporation of whatever solvent was used. Attempts to extract styrene dibromide from this tar were unsuccessful. It was found that the trouble was caused by sulfur compounds which could not be removed by any ordinary methods. After considerWO
260 z1p
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210
c ul d
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$5
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21
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25
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sg
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ba
2 0
22
60
0 40
LO 4
I
t
1
4
5
5
7
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TIME
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lh DAYS
FIGURE 5 . EFFECTOF HYDROQUINONE AND PYROGALLOL ON ABSORPTIONOF OXYGEN BY MIXED INDENE AND STYRENE able work had been done on the subject, two methods were discovered which solved the trouble. If the material is shaken with normal mercurous nitrate, filtered: and washed with caustic soda, the styrene can be identified in the usual way. A better method is to wash out the sulfur compounds with sulfuric acid. To do this without resinifying the styrene requires care. I n practice, the best results were obtained by washing first with 10 per cent of 60 per cent sulfuric acid and then with 10 per cent of 70 per cent sulfuric acid. The results obtained with four samples of natural meter gums are summarized in Table XVI. INTERPRETATION OF RESULTS OBTAINED BY PYROGENETIC DECOMPOSITION OF KATURAL G u m . Styrene and indene were identified in the proper fractions of the distillate obtained from each of these natural gums. Styrene and indene were also identified in the unpolymerized oil distilled off under vacuum before breaking up the gums. Indene accounted for 1.8 to 4 times as much of the gum as did styrene. As mentioned elsewhere, this fact is explained by the greater ease with which indene condenses, since styrene reacts more
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E N G I X E E I1 1 N G C ME ,\I I S T I
