I
T.
H. BAIZE
Jefferson Chemical Co., Inc., Houston, Tex.
Polymerization of Ethylene Oxide Autopolymerization products Bead to production difficulties and have adverse effects on qualities of condensates used in industrial and household detergents
ESTIMATED
PRODUCTION of ethylene oxide derived surface active agents will approach approximately 285 million pounds per year by 1965 (7, 2). With the increasing demand by the industrial and household detergent markets, quality of raw materials such as ethylene oxide and formulated surfactants is playing a greater role in consumer selection. This emphasis has prompted greater product quality research by detergent and detergent intermediate suppliers. This article is a series of studies on the quality of ethylene oxide as related to the development and identification of autopolymerization impurities in ethylene oxide. Attention is given to the impurities’ effect upon the clarity of ethoxylated condensates. Suggestions are made on minimizing operational difficulties encountered when polymerization occurs.
Polymer Identification To determine the chemical and physical structure of ethylene oxide polymer, referred to as nonvolatile residue (NVR), a microscopic examination was made of a sample of this impurity drawn from an ethylene oxide transfer line. Microscopically this NVR appeared transparent and anisotropic in its thin portions, but was opaque in the thicker areas due to the abundant presence of a second phase of scattered particles. After evaporation of a hot water extract of the NVR sample, the residue appeared microscopically similar to the original fibrous material except for small areas which had crystallized, The average refractive index of the extract residue and of the original fibrous material measured about 1.52-the same as commercial ethylene oxide polymers, polyethylene glycol 4000 and 6000, respectively. T h e solubility of the residue in ether, acetone, and ethyl alcohol was about the same as that of polyethylene glycol 4000. An abundant ash was left after ignition of the sample. This
There are clearly defined factors which influence ethylene oxide polymerization. Any o r a combination of these will result in an excessive increase of the impurity.
b Elevated temperature conditions b High surface-to-volume ratio b Type of surface of the containing vessel o r system
was shown to be high in iron and silicon by qualitative spectrochemical analysis. The hot water insoluble fraction of the original sample was examined microscopically and found to consist principally of oxides of iron with small amounts of quartz and a few metallic machine turnings. This fraction consisted largely of three iron oxides: magnetite, F e 3 0 4 ; limonite, Fez03.nHz0; and goethite, H F e 0 2 . There was a minor amount of quartz and several rare constituents. Magnetite was the most abundant constituent. The uneven magnetism of the original sample was undoubtedly due to the magnetite particles entrained in the fibrous polymer. Under the microscope the magnetite was usually in flat scales or flakes, but some of the finest particles were granular. The scaly shape suggests that it had been produced in the mill as “black iron” or rollscale on sheet iron or steel. Limonite and goethite are common phases of iron rust, which form readily under atmospheric conditions. Most of the limonite and goethite were associated with magnetite as coating and crust and had developed a t the expense of magnetite. Some of the limonite and goethite was free and unattached. Problems Caused b y Autopolymerization There are two distinct problems attending autopolymerization of ethylene
oxide. Of concern to all companies, who store and use ethylene oxide, is the product’s inherent characteristic of forming NVR in handling equipment. Excessive build-up results in the malfunction of safety release mechanisms, the plugging and general fouling of floats and meter orifices and other transfer system appurtenances. Generally, since NVR is water soluble, it may be removed through use of hot water of about 180 to 200’ F. Steam is not recommended as certain types of NVR will tend to become hard. Sand blasting the surface is an efficient means of removing heavy deposits of both NVR and iron rust. This to a degree is objectionable, however, since the cleaned surface is more porous and a greater surface area is exposed to the fresh oxide. Solvents or inhibited acids may be used for cleaning; however, care must be exercised from a safety standpoint as ethylene oxide reacts exothermically with certain acids and bases ( 3 , 5 ) . A liberation of about 20 kcal. per gram mole of ethylene oxide reacted may be involved. T h e second and more critical problem is NVR and its effect upon production of ethylene oxide condensates. T h e NVR content of ethylene oxide causes turbidity in finished adducts. T h e extent of the haze or turbidity is directly related to the NVR content of the ethylene oxide. This haze, attributable to NVR, seems to consist of sort, crystal-like particles which may be uniformly dispersed through0 the ethoxylated condensate or found as a residue at the bottom of the container, depending on the relative density of the liquid and solid polymer. Sometimes the solids exist in the form of large flocks suspended in the liquid. Frequently the solids are colored, perhaps due to some form of surface attraction for colored bodies. Haze attributable to NVR precipitates slowly in the condensate at room temperature, often requiring weeks for full development. T h e adduct sometimes, therefore, is found to be of good VOL. 53, NO. 1 1
.’ NOVEMBER
1961
903
~
Table 1. A Rapid Autopolymerization Occurs a t Elevated Temperatures N V R , G./100 M1.
Steel in Oxide
Hours
110' F.
14OOF.
Polished Oxidized
144
144
0.0082 0.0061
0.051 0.056
Table II. Polymers Are Formed with Excessive Temperatures and High Surface Area-to-Product Volume Ratios Temp., F.
Room 110 140
quality during and shortly after production, but fails specification requirements on clarity after a storage period.
Effect of NVR on Condensate Quality
A series of four runs of production of a 9.5 mole ethylene oxide to 1 mole nonyl phenol adduct was made in which only the NVR quantity varied. Varying concentrations of NVR were added to the ethylene oxide used for the ethoxylations of the alkyl phenol (below), A correlation is observed between NVR contents and adduct haze. This investigation stresses the need for supressing NVR content in handling and storage of theoxide. I t is common practice in the industry to store ethylene oxide without refrigeration and/or insulation. The following work correlating temperature increase with NVR increase of ethylene oxide suggests higher quality ethoxylated adducts may be achieved using oxide which has been chilled during storage.
KVR, G . j l 0 0 A l l . 0.166 3.89 Oxide converted to a gummy, viscous mass, which when dried yielded three separate phases : a rubber-wax solid ; a soft wax; a heavy, oily liquid
year period. T h e temperature of the material fluctuated only to the extent of ambient conditions (see p. 907). During the periods of high ambient temperatures-normally the start of the third quarter of each year-the NVR levels were a t peaks. This suggests that storage tanks and other vessels containing ethylene oxide should be insulated and/or refrigerated,
Table 111.
Av. Test Temp., ' F.
76 76
Surface-to-Volume Ratio of Container T h a t ethylene oxide NVR increase is, a t least in part, a function of the ratio of the surface area of the containing vessel to the volume of the product is also suggested. Two ethylene oxide samples of the same original quality were held a t a constant temperature of 76' F. in vessels with different surface areas to volume ratios. A significant increase in NVR content occurs where the ratio of surface area to container volume is greater (Table 111). It has also been observed that NVK build-up is kept to a minimum where high storage throughput of product is involved. Laboratory apparatus was fabricated to simulate actual storage conditions. T h e equipment consisted of a 5inch steel pipe, 16-inches long and sealed a t both ends. 4 coil of 3/4-inch pipe on the inside of the pipe gave the desired surface area. Ethylene oxide was charged to the bottom of this vessel and drawn from the top through a heat exchanger and subsequently received in a n ice-
Increasing Carbon Steel Surface Area-to-Product Volume Ratios Result in Greater Nonvolatile Residue Formation Cylinder Surface Area, Sq. In.
Ethylene Oxide T'ol., 311
Surf. hrea/Vol. Ratio, 8s. In./XIl.
Initial
10 Days
2 2 Day
5 2 Days
201 503
3,000 13,000
0.067 0.039
Nil Nil
0.0063 0.0022
0.0444 0.0030
0.1565 0.0123
SYR,G./100 131. ~~
Influence of Temperature on NVR Formation
A series of tests were undertaken to determine the effect of varying temperature upon the quality of ethylene oxide. T h e oxide was subjected to different temperature levels and then analyzed for NVR. T h e sample was stored in clear glass bottles, to each of which was added polished and oxidized wire. Approximately one half of the wire was submerged beneath the liquid surface (Table I). There is a rather rapid increase in NVR a t a temperature of 140°F. A refrigerated sample @ O F . ) , as control, when held for 144 hours did not increase appreciably in NVR content. A sample taken from ethylene oxide storage was held for 96 hours and the results (Table 11) confirm previous data that a significant increase is noted a t approximately 140° F. The effect of temperature on NVR formation is greatly accentuated in comparison to the above work due to the greater ratio of steel surface area to the contained quantity of oxide stored in the latter test. Daily temperature recordings and NVR analysis were obtained over a 4-
904
Increasing concentrations of nonvolatile residue in ethylene oxide result in increasing turbidities of ethylene oxide-nonyl phenol condensates
INDUSTRIAL AND ENGINEERING CHEMISTRY
ETHYLENE OXIDE Apparently, it takes a holding time of between 15 to 30 minutes under the test conditions to appreciably increase the NVR of the oxide. Beyond this time a sharp increase occurs.
Type of Surface Ethylene oxide polymerizes in the presence of materials of construction normally considered for transfer and reactor systems. Table V indicates that steel, stainless steel, glass, lead, and zinc are all initiators of NVR to a greater or lesser degree. From these results stainless steel appears to be the preferred material of construction. The cadmium plated cylinder appeared to have consistently less NVR in its oxide than any of the others tested. Polymer of the wax type, which is normally formed in transfer systems, does not appear greatly affected by surface area. The formation of the dark rubberlike NVR does appear to be accelerated by certain materials of construction as well as by surface area. Activation of steel surfaces by pickling with phosphoric, sulfuric, or acetic acids was found to promote greatly the development of the rubber-type polymer. O n the basis of this work, there is question of the use of steel which previously has been pickled for ethylene oxide service. At p H 7 , NVR forms at a much slower rate than at either the higher or lower values.
-
Refrigeration of ethylene oxide in storage minimizes polymerization reactions
chilled container. The pipe was immersed in a constant temperature bath held at 140 to 145' F., and water from this bath was circulated through the internal coil a t about 2 gallons per minute. The oxide was forced through the system by nitrogen gas. In Table IV, the 4and 15-minute NVR increases are significant; however, this is due in part to initial pickup of iron oxide and other debris from the surface of the equipment.
Table IV. Nonvolatile Residue Development Is Minimized if a High Storage Throughput Is Possible Holding Time, Minutes
Feed
Effluent
Increase
4 15 30 60
0.1894 0.1894 0.1894 0.1894
0.1943 0.1936 0.2046 0.2608
0.0049 0.0042 0.0150 0.0714
NVR, G./100 11.11.
Table V.
Stainless Steel Appears to Be the Preferred Construction Material 10 Days
NVR,
NVR
22 Days
NVR, G./100 M1.
NVR
NVR
83 Days
NVR,
NVR
Descrip.
G./100 M1.
Descrip.
Waxy, straw color
0.0447
Waxy, straw color
0.1028
Waxy, Straw Color
0.0535
Yellow, oily wax
0.0916
Waxy, straw color
0.2489
Waxy with rust particles
G./100 M1.
Cadmium electroplate
Nil
0.0114
Waxy, straw color
0.0243
Tin electroplate
Nil
0.0501
Yellow, oily
Descrip.
52 Days
NVR, G./100 M1.
Initial
Test Cylinder
-
W&X
Descrip.
Nickel electroplate
Nil
0.0111
Waxy, yellow
0.0236
Waxy, yellow
0.0417
Waxy, yellow
0.1630
Waxy, little debris
Zinc electroplate
Nil
0.0168
Waxy, yellow
0.0362
Waxy, yellow
0.1438
Waxy, yellow
0.2676
Waxy with black particles
Chromium electroplate
Nil
0.0158
Waxy, yellow
0.0235
Waxy, yellow
0.0516
Waxy, yellow
0.2238
Waxy with debris
Lead electroplate
Nil
0.0356
Waxy, yellow
0.0779
Waxy, yellow
0.1647
Waxy with black particles
0.2616
Black, waxy, and rubbery
Glass bottle (citrate)
Nil
0.0135
Waxy, straw color
0.0520
Waxy, straw color
0.0954
Waxy with black particles
0.1723
Dark, waxy, and rubbery
Stainless steel
Nil
0.0103
Waxy, yellow
0.0273
Waxy with debris
0.0266
Waxy and black rubbery
...
...
Steel, 500-ml. container, pickled with phosphoric acid-oxide polymerized into whitish rubber polymer within 7 days. Steel, 500-ml. container. pickled with acetic acid-oxide polymerized into orange rubber polymer within 7 to 21 days. Steel, 500-ml. container, pickled with sulfuric acidNVR increased from 0.0205 to 0.4196 gram/100 ml.
VOL. 53, NO. 11
NOVEMBER 1961
905
Table VI.
Inert Gases as Well as Air Are Initiators of Polymerization NVR, G./100 hT1.
Initial Oxide and air Oxide and nitrogen Oxide and CO?
3 Days 0.0256 0.0217 0.1336
0.0103 0.0103 0.0103
Influence of Atmosphere Since the flammability range of ethylene oxide in air is 3 to loo%, it is normally stored under a n inert gas pad ( 4 ) . I n this investigation (Table VI), 500-ml. samples of oxide were stored in 1500-ml. steel bombs. T h e air was maintained a t atmospheric pressure, nitrogen under 170 p.s.i.g., and carbon dioxide at 500 p.s.i.g. T h e temperature in all instances was maintained in the
Table VII.
17 Days 0.1485 0.0692
10 Days 0.0954 0.0644 4.9204
...
range of 60 to 70" F. during the test. The residues found in the bombs with air and nitrogen were the usual yellowish, waxy materials. T h e nitrogen bomb was found to have a consistently lower NVR t h a n the others tested, and it a p p e a r e d to b e leveling out after 10 days of storage. T h e residue from the bomb of carbon dioxide was analyzed and appeared to be mostly polyethylene glycol. Since ethylene oxide will combine directly with
Inhibiting Ethylene Oxide against Polymerization Could Not Be Achieved with Water, Acids, and Other Compounds Test
Sample, Oxide with:
Container"
Temp., O
F.
NVR, G./100 M I . Initial 7 Days 21 Days
Total
Increase
Control, pure
Glass Steel
45-75 45-75
Nil Nil
0.0110 0.1013
0.0709 0.1883
0.0709 0.1883
Ethylene carbonate
Glass Steel Glass Steel Glass Steel
60-90 60-90
0.0318 0.0308
0.0556 0.3454
0.1378 2.0584
0.1060 2.0276
60-90 60-90
0.0186 0.0223
0.0544 0.2236
0.1309 0.5483
0.1123 0.5260
60-90 60-90
0.0004 0.0151
0.0257 0.9179
0.0832 1.5454
0.0828 1.5303
60-90 60-90
0.0026 0.0154
0.2131 2.0601
0.7581 3.0042
0.7555 2.9888
60-90 60-90
0.0201 0.0337
0.0432 0.0774
0.0820 0.3179
0.0619 0.2842
45-75 45-75
0.0184 0.0373
0.0241 0.0624
0.0552 0.4073
0.0368 0.3700
Cupric oleate Ethylene chlorohydrin Ferro-ferric cyanide Boric acid Cupric acetate
Glass Steel Glass Steel Glass Steel Glass Glass Steel
45-75
0.1153
0.1282
0.1426
0.0273
45-75 45-75
0.0038 0.0082
0.0337 0.1004
0.0391 0.1941
0.0353 0.1859
Water
Glass Steel
45-75 45-75
0.0079 0.0065
0.0496 0.1731
0.0417 0.1666
Gummy oxide polymer
Glass Steel Glass Steel
45-75 45-75
0.0113 0.0086
0.0257 0.1529 0.0377 0.0716
0.0486 0.0716
0.0373 0.0630
45-75 45-75
0.0045 0.0045
0.0124 0.2480
0.0480 0.2331
0.0435 0.2286
Waxy oxide polymer Acetic acid
Acetylene saturated a
Glass containers, 400 ml.; steel containers, 500 ml.
906
INDUSTRIAL AND ENGINEERING CHEMISTRY
carbon dioxide to yield the ester, ethylene carbonate, under certain conditions, the carbonate also was likely present. I t has been suggested that certain chemicals or impurities normally found in some ethylene oxide might inhibit the oxide against polymerization. Various classes of compounds did not offer any inhibiting effect against this reaction (Table VII). Seeding of ethylene oxide with either the waxy or rubber-type polymer did not appear to have an appreciable effect on the rate of polymerization. Analytical Procedure. Transfer, by means of a cooled, graduated cylinder, 100 ml. of sample to each of two. tared. clean platinum dishes. Cover the dishes with ribbed watch glasses and allow them to stand under a good hood in a warm place until the liquid evaporates. (An infrared lamp may be used to drive off volatile matter. I t is mounted above the dish, and the distance between the lamp and the dish must be greater than 12 inches.) Remove the watch glasses and place the dishes in an oven (105 to 110' C.) for exactly 30 minutes. Cool in a desiccator and weigh to determine the residue. CALCULATION Grams NVR per 100 ml. sample =
net weight of residue 70
NVR
5
Net weight of residue Sp. gr. of sample
The specific gravity is obtained at the same temperature a t Lvhich the sample is measured for analysis. Literature Cited (1) Chem. Eng. ,lrezcs 38, 52-3
1960).
(April 18:
(2) Chem. Week 86, 114, 116 (April 23,
1960).
(3) Gupta, A. K . , J. Sac. Chem. Ind. (London) 68, 179-3 (.June 1949) (4) Has, I. 6.:Tilton, V. V., IXD.ENG. CHEM.42, 1251-8 (1950). (5) Manufacturing Chemists' Association,
Inc., Washinston, D. C., Chemical Safety Data, Sheet SD-38 "Ethylene Oxide,'' 1951.
RECEIVED for review January 6, 1961 ACCEPTED April 17, 1961
