VARNISH AND LACQUER DILUENTS FROM CALIFORNIA PETROLEUM
L
Above) MIXEM O F COMMERCIAL EDELEBIVI: LANT IN WHICH EXTRACTIOPI' OF CALIFORMA DISTILLATES WITH LIQUIDSULFUR DIOXIDE Is CARRIED OUT Capacity, 3000 barrele a day
(Right) EXPERIMEXTAL EDBLEANU PLANTIX WHICHTHE DEVELOPMENT WORKON SOLVSOLS W.4s CONDUCTED
658
T
HE use of synthetic resins in oleoresinous
and nitrocellulose varnishes has created within the protective coating industry a growing demand for naphthas of higher solvency power and greater compatibility than ordinary petroleum mineral spirits. The petroleum industry has met this demand by the development of new petroleum diluents of the aromatic type.
Source Petroleum which contains aromatic hydrocarbons in appreciable quantity is available in several countries, the most outstanding being the Dutch East Indies and the United States. Gasoline, kerosene, and naphthas from selected crudes in Borneo contain up to 40 per cent aromatic hydrocarbons, and during the World War distillates from this source were actually used for the recovery of toluene and for the manufacture of trinitrotoluene. Mineral spirits made from Borneo crude, on account of their special properties, are in demand by the paint, varnish, and lacquer industries in Europe. Those fields producing petroleum of appreciable aromatic content in the United States are located in Arkansas, Texas, Oklahoma, and California.
Manufacture With such an abundant source of raw material for the manufacture of diluents suitable for the paint, varnish, and lacquer industries, it seems desirable to devote a small part of this paper to a brief discussion of the methods used for recovering these products. There exist two fundamentally different approaches to the problem. In cases where aromatic constituents occur naturally, their isolation can be accomplished by extracting direct the proper fractions of petroleum with a selective solvent. The most suitable selective solvent method for this purpose is the Edeleanu process. Liquid sulfur dioxide is the extracting medium for the separation of the aromatic from the other groups of hydrocarbons present in petroleum fractions. As another alternative, petroleum can be subjected to various processes to bring about molecular rearrangement resulting in the formation of aromatic hydrocarbons. Such conversion processes need not be limited to any one fraction of petroleum but may be applied to all gaseous and liquid fractions available to the petroleum industry. All of these processes fall under the classification of pyrolytic reactions, because heat is the common factor in all of them; but, depending on the nature of the raw material and the type of product desired, there may be great variations in pressure conditions and in the use of catalysts, In a special type of pyrolytic conversion process called “catalytic high-pressure hydrogenation,” the introduction of hydrogen as another variable has enabled the production of aromatic diluents from refractory raw materials such as sulfur dioxide extracts and gas oil obtained from cracking operations (3).
FRACTIONATING TOWERS FROM WHICHTHE RAWMATERIAL FOR
SOLVSOLS Is OBTAINED
Capacity, 40,000 barrels of crude oil a dag
0
Products and Properties To fit the present requirements of the protective coating industry, four principal grades of aromatic diluents are a t present commercially manufactured and distributed; their properties are shown in Table I. The evaporation ratios of those four products have been selected in such manner as to make possible their substitution for the various grades of commercially used coal-tar diluents: 19-27 Solvsoll is equivalent in evaporation rate to commercial toluene, 24-34 Solvsol to 5” xylene, 3 0 4 0 Solvsol to industrial xylene, 40-50 Solvsol to heavy solvent naphtha, as illustrated by Figure 1. The slightly overlapping boiling ranges of the individual Solvsols enable the consumer to obtain a great number of intermediate grades of aromatic petroleum diluents by blending any pair of adjacent products in varying proportions. Thus evaporation characteristics can be adjusted to suit a particular purpose without distorting the slope and smoothness of the evaporation curve. The following properties of the aromatic petroleum diluents are of particular importance for their function in protective coatings:
Refinement In the isolation of naturally occurring aromatic hydrocarbons by extraction, certain impurities are also included which are objectionable to the paint, varnish, and lacquer industry. When using California petroleum as raw material, these impurities may include nitrogen bases, sulfur compounds, organic acids, and small amounts of unstable unsaturated hydrocarbons of olefinic or terpene character. With the proper chemical treatment and fractionation, aromatic diluents of suibstantially water-white color, mild and agreeable odor, and excellent stability on aging can be manufactured.
(a) Freedom Erom detrimental sulfur compounds, indicated by nonreactivity with lead resinate at the initial boiling point of the particular diluent. (b) Light color. All except the heaviest grade are waterwhite in color. (c) Excellent color stability even on extended aging. ~~
1 “Solvsol” is the trade name for aromatia diluents made by the Edeleanu process.
659
INDUSTRIAL AND ENGINEERING CHEMISTRY
660
TABLEI. PROPERTIES OF AROMATIC DILUENTS FROM CALIFORNIA PETROLEUM Solvsol No. Evapn. rate, m i x a Sp. gr. at 15O C. A. P. I. gr., 60' F. (15.6' C.) Initial b. p., ' F. (" C.) End point, O F. (" C.) Color Color after 6 mo. Lead resinate test Sulfur, % Aniline point, ' F. ~
19-27 70 0.792
24-34 138 0.806
30-40 240 0.844
40-50 540 ( 2 0 % ) 0,891
47.2
44.0
36.1
27.3
190 (87.8)
240 (115.6) 300 (148.9) 400 (204.4)
270 (132.2) Water-white Unchanged Negative Trace
340 (171.1) Water-white Unchanged Negative 0.02
400 (204.4) 4-27 Saybolt Unchanged Negative 0.06
500 (260) +20 Saybolt +18 Negative 0.14
c.,
C43 (+6.1) +36 (+2.2) +20 (-6.7) +10 (-12.2) (" 66.0 68.0 74.0 Kauri butanol value 64.0 Dilution ratio6 1.87 1.89 1.93 2.00 Copper strip cor. Negative Negative Negative Negative Neutralization No mg./KOH/gra$ Neutral Neutral Neutral Neutral a Determined by the Hart evaporation balance: see also Figure 1. b Determined with solutions of 1/2-second nitrocellulose in n-butyl acetate. Initial concentrations were so adjusted that the final concentrations of nitrocellulose in all cases fell within the range of 8-10 per cent.
( d ) Good solvency power and compatibility with solutions of the conventional film-forming ingredients, indicated by aniline point and Kauri butanol value.
Solvency power and compatibility increase in proportion to boiling range. The significance of this feature for the drying characteristics of protective coatings will be discussed later. Table I1 gives comparative compatibility data for commercial toluene, aromatic petroleum spirits, and ordinary mineral spirits of similar evaporation characteristics. To broaden the basis of comparison, dilution ratios were determined for nitrocellulose solutions made up with a number of commonly used active solvents. These dilution ratio determinations were carried out in accordance with the procedure described by Gardner (3) which gives the dilution ratios for final concentration of nitrocellulose, approaching that in a finished lacquer. Table I11 lists a number of examples to demonstrate that the aromatic petroleum diluents can be used in many compositions where ordinary mineral spirits are generally unsuitable, such as bituminous paints, pipe line coatings, roofing materials, antifouling coatings, priming paints for woodwork, and rubber solutions. The various ingredients covered in Table 111 are selected from the three principal classes of products used in protective coatings-namely, active solvents, plasticizers, and film-forming solids. Commercial alcohol (95 per
TABLE11. DILUTION RATIOS OF DILUENTS WITH NITROCELLULOSE SOLUTIONS MADE WITH DIFFERENT ACTIVE SOLVENTS Final Concn. of Nitrocellulose 8.7 8.3 8.0
Active Solvent Ethyl aoetate
Diluent Petroleum spiritsa Aromatic petroleum diluentb Coal-tar diluent
Dilution Ratio 1.01 2.01 3.2
%-Butylacetate
Petroleum spirits Aromatic petroleum diluent Coal-tar diluent
1.27 1.87 2.41
8.4 8.2 8.0
Cellosolve
Petroleum spirits Aromatic petroleum diluent Coal-tar diluent
0.90
8.0
2.3 2.7
8.0
Butyl Cellasolve
Petroleum spirits Aromatic petroleum diluent Coal-tar diluent
2.08 2.55
8.1
Petroleum spirits Aromatic petroleum diluent Coal-tar diluent Ordinary California petroleum thinner. Solvsol. Toluene.
Acetone a
b
8.0 8.0
3.3
8.0
0.66 1.33
8.0 8.0 8.0
2.16
VOL. 28, NO. 6
cent CZH5OH) is given as a representative of the solvent class; technical castor oil as the most common of the plasticizer group; rubber, rosins, and pitches are given as representatives of the film-forming solids.
Special Features As diluents for oleoresinous, synthetic resinous, and cellulose ester varnishes, these new products are far superior to mineral spirits and approach in solvency power and compatibility the coal-tar diluents. Their special features and their evaluation for practical application in the protective coating industry are discussed here. The average evaporation rates of the petroleum diluents have been chosen to match those of the more commonly used commercial grades of coal-tar products comprising toluene, xylene, and solvent naphthas. On account of the more complex chemical structure of petroleum fractions it is neither economical nor practical to attempt to duplicate the narrow boiling ranges of the coal-tar diluents. Commercial grades of aromatic petroleum diluents are marketed with individual boiling ranges of approximately 100O F. Practical experience with the new aromatic petroleum diluents has shown that, as long as the evaporation characteristics are maintained, the comparatively wide boiling range is of definite advantage in their use in protective coatings. This statement may be further substantiated by the following argumentation. The ideal diluent for a protective coating is the one that will evaporate from the film a t the same rate as the active solvent or solvent mixture employed, thus keeping the solventdiluent ratio during the drying period constant and preventing deficiencies in the finished surface. Since it is practically impossible to predetermine by calculation the evaporation characteristics of a lacquer composition from the evaporation
1
FIGURE
EVAPOIPATIOH C H A R A c T C 4 \ 5 1 1 C S
450
w
AROMATIC PETSOLCUM DILUCMS AND COAL-TAR DILUCNT3
-- 19-27 SLVSOL OLUENE -- T24-34 S'XYLLNZ 5 - 30-40SOLVSOL XYLENE 7 - 40-59 50LV.VML 8 - WAVY
400
I
2
5 350 z 300
3 d
w
Q
F
Z50
d
\NDUS?RIAL
6
5oLVC
z
1g
JOLVSOL
5 *0°
4 3
150
100 I 2
50
IO
20
30
40
SO
00
70
80
90
characteristics of the individual ingredients (I), experimentation is necessary for proper adjustment of the proportions of solvent and diluent in order to prevent disturbance of the solvent-diluent balance during the drying process. With aromatic petroleum diluents such disturbances can be avoided more easily than with coal-tar diluents. The more complex composition of the aromatic petroleum diluents is probably responsible for this very desirable feature, since the solvency power and compatibility with film-forming ingredients increase with the boiling range. Therefore it is reasonable to assume that during the drying of the film there would be a steady increase of solvency power in the unevaporated portion of the diluent, resulting in an improvement of its compatibility with the film-forming ingredients, Table I confirms the
INDUSTRIAL AND ENGINEERING CHEMISTRY
JUNE, 1936
661
a favorable picture in regard to their affinity to pigments, as follows. Various types of hydrocarbons are present in the aromatic petroleum diluents : Group 1, monocyclic aromatics (benzene homologs) ; group 2, monocyclic hydroaromatics (naphthenes); group 3, bicyclic hydroaromatics (hydronaphthalenes) ; group 4,substituted bicyclic aromatics. Of the first group there have been isolated in pure form and identified : toluene, ethylbenzene, 0-, m-, and p-xylene, pseudocumene, mesitylene, and hemimellitene. As yet no reliable analytical method has been developed to determine the exact percentage of each of these groups in the mixture, and no quantitative data are given here. However, approximately 70 per cent of the hydrocarbons in aromatic petroleum diluents are represented by groups 1, 3, and 4. COMPATIBILITY AND SOLVENCY POWER OF MINERAL TABLE 111. These three groups, because of the presence of double bonds SPIRITS AND AROMSTIC PETROLEUM DILUENTS and free valences in their molecules, possess peculiar surface Aromatic petroleum tension characteristics which are responsible for their ability Ingredient Mineral‘spiritsa diluentb to penetrate readily into capillary structures. In ordinary Commercial alcohol Miscibility limited. at Miscible over a wide C. only 15% by range. At 20’ C. mineral spirits the average content of these types of hydro(”% CsHsoH) volume can be added more than 3 volumes carbons is only between 20 and 25 per cent. Hence it is evito form homogeneous of diluent can be added solution. to form homoaeneous dent that the aromatic petroleum diluents must have a greatly solution. superior wetting ability for solid surfaces in general and pigCastor oil (technical) Very slightly miscible at Miscible in a11 proportions at room temp. room temp. ments in particular, whereby their great importance in diffiRubber (Para) Swells up but does not Swells up first, then disdissolve. solves completely. cult grinding problems is established. Nard rosin (0010Partly sol. at room temp. Completely sol. at room phony) temp. Such notoriously obstinate pigments as Prussian blue and Completely sol. at room Partly sol. at room temp. Dammar resin carbon black, according to numerous field reports, can easily temp. Petroleum pitch Dissolyes first; asphaltic Dissolves completely; be handled when aromatic petroleum diluents are added to DreciDitate found on soln. remains clear on handing. standing. the grinding medium. Even small percentages have a marked Coal-tar pitch Dissolves only oily eon- Dissolves all except careffect on grinding speed and efficiency. stituents. bonaceous constituents. The petroleum industry is looking forward to a steadily ina Boiling range, 300-400’ F. (148.9-204.4’ (2.). 6 30-40 S o l v ~ o l . creasing demand for aromatic petroleum diluents, as the manufacturers of protective coatings become more acquainted with these new products. The supply of raw material is sufficiently abundant, and An important factor in the preparation, application, and the methods for their production commercially developed so h a 1 quality of a protective coating is the surface tension that they can be marketed a t a price level well below that characteristics. Reliable methods for measuring interfacial existing for coal-tar derivatives. The petroleum industry tension between a liquid and air or its own vapor, as well as invites the cooperation and constructive criticism of the between two immiscible liquids, have been developed. Such manufacturers of protective coatings in the development of mepsurements, although of great theoretical interest, have no the more widespread use of aromatic petroleum diluents. practical value for the paint and varnish manufacturer, and for this reason are not included in this paper. From the Literature Cited practical point of view of the protective coating industry, (1) Brown and Bogin, IND.ENG.CREY.,19, 968 (1927). data about interfacial tension between liquids and solids (2) Gardner, “Physical and Chemical Examination of Paints, Varwould be helpful. Unfoitunately no definite methods are nishes, Lacquers, and Colors,” 6th ed., pp. 963-5, Washington, known to measure directly the interfacial tension between Inst. of Paint & Varnish Research, 1933. (3) Sweeney and Tilton, IND.ENG.CHEM.,26, 693 (1934). liquids and solids which would allow us to predict such an important characteristic as the wetting ability of a liquid for RECEIVEn August 10, 1935. Presented before the Division of Paint and a certain pigment. However, based on our knowledge of the Varnish Chemistry at the 90th Meeting of the American Chemical Society, chemical structure of aromatic petroleum diluents, we obtain San Francisco, Calif., August 19 to 23, 1935.
statement that solvency power and compatibility, indicated by aniline points, Kauri butanol value, and dilution ratio, increase with the boiling range of the aromatic petroleum diluents. Coal-tar diluents, because of their less complex composition, do not show this feature; on the contrary, they have a tendency t o the opposite effect, as shown by Sweeney and Tilton (S),in their comparison between coal-tar naphthas and hydrogenated naphthas. Thus, during evaporation of a coal-tar diluent, solvency power and compatibility of the unevaporated portion must remain constant for straight toluene or xylene, and may even decrease for mixtures of the two or for high-flash naphtha.
ZOO
