DEVELOPMENT OF
DAKOTA LIGNITE XI. Influence of Catalysts
in Reaction between
Lignite Tar Distillate and Formaldehyde' WILLIAM FRANTA AND IRVIN LAVINE University of North Dakota, Grand Forks, N. Dak.
QT
HE commercial utilization of the tar distillate obtained in the low-temperature carbonization of Dakota lignite is a problem of considerable interest in connection with the development of this fuel. The School of Mines of the University of n'orth Dakota has been interested for a number of years in many phases of this development program. The present paper reports certain results of an investigation begun in June, 1933, and dealing with the tar distillate obtained in the carbonization of lignite by the Lurgi process. Future publications from this laboratory will deal with other phases of the present research. The conversion of phenols in primary coal tar by interaction with formaldehyde has engaged the attention of several investigators. In 1919 Gluud and Breuer (6) published an account of a number of experiments they performed with the object of testing the possibility of preparing resins of the Novolak, Bakelite A, and Bakelite C types from brown-coal low-temperature tar and formaldehyde. Several different condensing agents were tried with various fractions of the tar. Alcoholic solutions of several of the soluble resins produced in this work were found to possess satisfactory varnish qualities. More recent reports by Morgan (8), Morgan and Megson (9), and Holmes and Megson (6) give results of additional researches that offer valuable contributions in this field. The exact nature of the chemical reactions that can take place between phenols and formaldehyde is not known, nor can the chemical formulas of the resinous products of the various reactions be easily determined. However, detailed studies have led to the recognition of certain definite reactions and the identity of certain reaction products. For a review of the many theories that have been advanced for these reactions, the reader is referred to Baekeland ( I ) , Baekeland and Bender ( d ) , Raschig (II), Sheiber and Sandig (IS), Redman, Weith, and Brock (I,%'), and Ellis (4).
The distillate obtained for this work represents the fraction of the primary tar boiling between 210" and approximately 355" C. according to readings of a thermometer in the ceiling of the still proper (not the still head) a t the plant of the company. The carbonizing plant of the company has a daily capacity of 200 tons of lignite from which are obtained about 4.8 tons of primary tar. From this amount about 600 gallons of distillate (specific gravity a t 20" C., approximately 1.016) are obtained. Table I gives data on the fractionation of a 250-gram asreceived sample a t this laboratory. The phenolic content of the distillate as received a t the laboratory varies somewhat from time to time. Samples of the crude distillate extracted with 10 per cent sodium hydroxide solution showed 50 per cent by volume of caustic soluble material. Table I1 gives the results of extraction
Tar Distillate The lignite tar distillate used in this investigation is a representative sample of low-temperature lignite distillate obtained from the Lehigh Briquetting Company. This company operates a plant near Dickinson, N. Dak., for carbonizing and briquetting lignite mined in that vicinity. Carbonization is effected by the Lurgi process (7). 1 Previous articles in this series appeared i n INDUSTRIAL AND ENQINE~RING CHEMISTRY in 1930, 1931, 1932, and 1933.
119
Low-temperature tar distillate from North Dakota lignite can be made to react with formaldehyde to produce a resin of the Bakelite type. Although this reaction is catalyzed by certain substances inherent in the distillate, it has been found that the time required to produce a "plastic solid" resin at 93" C. can be materially altered by the addition of foreign catalysts. It has been found that, in general, the organic acids and the alcohols tend to retard the normal reaction time; neutral organic compounds and nearly neutral inorganic salts have but little influence; and strong acids, bases, acid and basic salts, and strong oxidizing and reducing agents have marked accelerating effects. Thus, it was found that the normal reaction time of 330 minutes can be varied from 2 to 847 minutes by choice of foreign catalyst
.
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TABLE I. FRACTIONATIONS OF LEHIGHTARDISTILLATE Boiling Range, O
c.
Under 170 170-200 200-210 210-225 225-240 240-265 265-285 285-315 3157345 Residue
Weight of Fraction,
I Grams I1 8.69 2.85 2.93 12.52 43.93 58.64 34.87 38.37 24.77 20.80
Per Cent of Total
I
12.4 3.3 4.4 25.3 22.0 54.0 33.2 26.3 33.6 28.4
3.49 1.15 1.18 5.03 17.66 23.75 14.02 15.42 9.95 8.35
I1
5.1 1.4 1.8 10.4 9.1 22.2 13.6 10.9 13,s 11.7
Cumulative Per Cent, Distd.
I
I1
3.49 4.64 5.82 10.85 28.51 52.26 66.28 81.70 91.65 100,00
5.1 6.5 8.3 18.7 27.8 50.0 63.6 74.5 88.3 100,o
VOL. 28, NO. I
TABLE 111. EFFECTOF VARIOUS COMPOUNDS ON REACTION AT 93“ C. BETWEEN 50 GRAMSOF LIGNITETARDISTILLATE AND 27 GRAMS OF 40 PERCENTFORMALDEHYDE Catalyst
Amount Used
Aniline 7.00 cc. Citric acid 5.08 grams Tartaric acid 5 . 4 4 grams Rosin 5 . 0 0 grams Methyl alcohol 7.00 cc. _ _ _ _ _ _ _ _ Ethyl alcohol 10.00 cc. 248.37 242.9 100.00 100.0 Succinic acid 4 . 2 8 grama Methyl acetate 7.00 cc. Glycerol 4 . 5 0 CC. Sucrose 5 00 grams Starch 5.00 grams TABLE 11. TARACIDCONTENT OF LEHIGH LOW-TEMPERATUREAcetone’ 2.6 9 0 00. cc. TARDISTILLATE Chloroform Toluene 7.00 cc. Fraction of Fraction of Carbon tetrachloride 3.50 cc. Tar Dist. Per Cent Per Cent Tar Dist. Per Cent Per Cent Magnesium nitrate hexahydrate 9 , 2 7 grams Boiling. of Crude Tar Acid Boiling of Crude Tar Acid Cobalt nitrate hexahydrate 10.65 nrams between: Dist. Content between: Dist. Content No catalyst added (av. of 7 tests) Magnesium chloride hexahydrate ?:35 grams Aluminum sulfate trihexahydrate 12.07 grams Potassium chloride 5 , 4 0 grams Potassium nitrate 7 . 3 2 grams Sodium bromide 7.46 grams 10.00 cc. Kerosene Sodium oxalate 4.85 6.30 grams Potassium sulfate Nickel sulfate hexahydrate 9 . 5 3 grams Strontium chloride hexahydrate 9 67 grams Pyridine 2 . 9 0 cc. Potassium bisulfate 4.92 grams tests of various fractions of the distillate with 10 per cent Aluminum chloride (anhydrous) 3 21 grams Aluminum chloride hexahydrate 8.73 grams sodium hydroxide solution. Ammonium hydroxide 4.85 cc. The work of Caplan, Ross, Sevag, and Switz (3) and Morgan Ammonium carbonate 4.13 grams Aluminum sulfate (anhydrous) 4.14 grams and Soule (IO)may be of interest in this connection. Zinc nitrate (anhydrous) 6.84 grams Zinc sulfate (anhydrous) 5 . 8 3 grams Ammonium sulfide 2.50 00. Influence Catalysts Zinc chloride 4.92 gram8 Pyrogallic acid 3.05 grams Ferric sulfate 4.82 grams A series of tests was first made to determine the catalytic Oxalic acid dihydrate 4.57 grams effect of various substances on the reaction between formaldeCalcium carbonate 3.62 grams Ferrous sulfate heptahydrate 10.10 grams hyde and the tar distillate as received a t the laboratory: Phosphoric acid 4.17 cc. Nitric acid 4.59 0 0 . The work consisted of adding a predetermined quantity of the 8 . 0 8 grams 12.00 grams catalyst to a mixture of 50 grams of distillate and 27 rams of 7.10 grams 40 per cent formaldehyde. These mixtures, in porcefain cas3.52 grams seroles, were then placed on a steam bath. The mixtures were 1 2 . 9 8 grams stirred frequently and the process of resinification was carefully Sodium-hydroxide 2.90 grams Potassium hydroxide 4.06 grams observed and timed. Resinification was in each case permitted 2 . 0 3 grams Calcium oxide to proceed to a stage of “plastic solidity” at a steam bath tem2.02 cc. Sulfuric acid perature of approximately 97’ C. “Plastic solidity” is defined Potassium cyanide 2 . 3 6 grams here as that degree of hardness at which the resin will just supSodium bicarbonate 3.05 grams Potassiumferrocyanide trihydrate 15.30 grams port a weight of 23 grams. This testing weight consisted of a Lead peroxide 4 . 3 3 grams glass rod 4 mm. in diameter and 3 grams in weight, to which Potassium ferricyanide 11 90 grams was attached a weight of 20 grams. No difficulty was encoun3 . 8 4 grams Sodium carbonate Potassium carbonate (av. 10 tests) 5 . 0 0 grams tered in determining this standard end point within an accuracy Acetic acid 4.17 cc. of 5 per cent. The time required for each mixture to reach the Potassium ermanganate 5 . 7 2 grams state of plastic solidity was recorded in minutes. The resins 11.40 grams Barium hyfroxide octahydrate taken a t this stage were all brittle, friable solids at room tem6 . 0 0 cc. Hydrochloric acid 5.87 grams Molybdic acid perature. Potassium dichromate 10.65 grams After the resin had attained the arbitrarily established end Sodium aluminate 2.97 grams point on the steam bath, the mixture was allowed to cool at Potassium chromate 7.03 grams room temperature. The supernatant water and oils were then Stannous chloride 6.86 grams Stannic chloride pentahydrate 12.68 grams poured off and the resin was weighed. The resins were then
of
carefully observed as to gloss, hardness, and friability. Judgment of these qualities could be made on a c o m p a r a t i v e basis only, comparison being limited to TAR DISTILLATE o t h e r resins in the series. A standard r e a c tion mixture consisting of 5 g r a m s o f potassium carbonate, 5 0 g r a m s of distillate, and 27 grams of 40 per cent formaldehyde was adopted in t h i s work for purposes of control and standardization 0 of operating condi-
Time t o Reach Plastic Fria- HardSolidity Gloss bility ness Min. 847 10 t b 742 9 t a 658 9 t a 643 .. . , 639 9 t b 606 6 c b 605 8 t a 426 9 t a 424 10 b b 423 8 t b 421 8 t b 386 t b 360 b b 348 b b 343 t 332 t 331 b t 330 9 t b 330 8 b a 316 7 t b 310 7 t b 303 9 t a 298 8 t b 298 10 t a 298 292 2 t b 9 b b 286 8 b b 283 9 t b 283 8 b b 267 8 t a 258 8 t b 257 8 t b 228 6 b b 211 2 b c 205 8 t a 203 10 t b 199 9 t a 199 3 t b 197 10 t b 191 9 t a 9 t b 187 186 7 b b 185 4 t b 173 8 t b 142 ., 140 5 6‘ ‘L
b”
49 48 44 37 36 32 31 26 25 25 24 22 20 17 14 10 9 7 6 6 2
l 2
.. 9 2 2 3 6
l 2 5 8 3
..
7 4
c c
f d
b b c
.b. e e
.
;
:
c c b t c
.. t c
d f c a e
.a.. f
: : ;
O 3 4
c c o
e e e
tions. Chemically equivalent (and in some cases also equimolal), quantities of the other compounds were added to the same quantities of distillat,e and formalin. Table I11 lists the results of this series of experiments. It should be kept in mind that the end point established. for this work determines the effect of the compound not only as a condensing agent but also as a polymerizing agent, because the resin at this end-point stage is in a rather highly polymerized condition. A gloss scale of 0 to 10 was arbitrarily chosen for making, comparisons. A gloss rating of 10 indicates a very high lustrous gloss, and a gloss rating of 0 indicates probably t h e least gloss possible for a resin. Intermediate degrees of gloss were rated numerically between 0 and 10.
JANUARY, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
121
The hardness ratings are mere comparisons of the ease with which the point of a pen knife penetrated lumps of the various resins. Varying degrees of friability tended, of course, to cause errors in judgment, but some useful comparison was made. The hardest resins made in this series were rated a. These were harder than talc and softer than gypsum (actual standard rating about 1.5). Softer resins were graded b, c, d, e, and f , respectively, in corresponding order of decreasing hardness. All of the resins obtained in this work were very brittle a t room temperature. FIGURE 2. COXCENTRATION A rating of t (tough) in Table EFFECT OF CATALYSTS I11 indicates only that such a resin is less friable than one marked b (brittle). A resin which crumbled under stress rather than breaking into a few small pieces was marked c (crumbly). The data of Table I11show that, in general, the organic bonate exerts--a acids and alcohols retard the marked influence reaction; neutralorganic comon the rate of pounds and nearly neutral inr e a c t i o n . The organic salts have little catacatalytic effect of this agent lytic effect; s t r o n g a c i d s , b e c o m e s practically conbases, acid and basic salts, and stant after a definite constrong oxidizing and reducing centration of catalyst has agents have very pronounced been reached. accelerating effects. It was The first additions of stannous chloride apfound also that organic repear to have no catalytic effect on the retarders and the neutral comaction. This may be due, perhaps, to chemical reaction bepounds of little or no catalytic effect produced the glossier, tween the stannous chloride and some of the constituents of tougher, and harder resins, The dull, crumbly resins were all formed with the comparatively violent catalysts. the tar. The further additions of stannous chloride, however, introduce pronounced catalytic effects. Color The hydrochloric acid curve might indicate that the catalytic effect of the substances inherent in the distillate is deAll of the resins produced in the work were dark brown to stroyed by addition of a small quantity of hydrochloric acid. black in color. This dark color made it practically impossible This would be due, no doubt, to chemical reaction between to grade the resins into various color classes or to determine the acid and the inherent catalyst of the distillate. Further the influence of catalysts on color. addition of the acid causes a definite increase in reaction rate. The curves for sulfuric acid and potassium bisulfate take a Effect of Catalyst Concentration form well in accord with that for hydrochloric acid. The three curves a t the bottom of Figure 2 are so plotted that Several tests were made to determine the effect of catalyst equal abscissas indicate equimolal amounts of the three comconcentration on the time required for the resinification pounds represented. Thus, potassium bisulfate appears to process. The work consisted of varying the amounts of exert a catalytic effect similar to but less active than that of potassium carbonate, potassium hydroxide, stannous chloride, sulfuric acid, Only a slight catalysis, however, was obtained hydrochloric acid, sulfuric acid, and potassium sulfate as with potassium sulfate, even with large additions of this catalysts in the resinification of the standard tar distillatecompound. The influence of hydrogen ions in the catalysis formaldehyde mixture. Each of the reactions was carried out under the standardized procedure described. The data of this reaction seems definite from these data. obtained in these tests are plotted graphically in Figure 2. Literature Cited The potassium hydroxide curve of Figure 2 indicates that (1) Baekeland, J. IND. ENQ.CBEM.,1 , 545 (1909); 4, 737 (1912); the first small additions of this base introduce marked cata5, 506 (1913). lytic effects. With increased additions of potassium hydroxide the time of reaction drops to a minimum and then ( 2 ) Baekeland and Bender, Ibid.7 17,225 (1925). (3) Caplan, Ross, Sevag and Switz, IND.ENQ.CHEM.,Anal. Ed., increases. It is significant that, in determining the tar acid 6, 11 (1934). (4) Ellis, “Synthetic Resins and Their Plastics,” New York, content of the tar distillate, between 3.5 and 5.0 grams of Chemical Catalog Co., 1923. potassium hydroxide were required to form phenolate with ( 5 ) Gluud and Breuer, Ges. Abhandl. Kenntnis Kohle, 4, 221 (1919). Of the phenols present in 50 Of the Un(6) Holmes and Megson, J. sot. Chem, I n d , , 52, 415T (1933). doubtedly potassium phenolate is formed when potassium (7) Kersohbaum, Proc. 2nd Intern. Conf. Bituminous Coals, 1, 283 hydroxide is added to the distillate-formaldehyde mixture. (1920). (8) Morgan, J. Soc Chem. Ind., 49, 2491‘ (1930). It appears, then, since the curve is a t its lowest level between (9) Morgan and Megson, Ibid., 50* 191T ( l g 3 1 ) . points representing the quantities required to form phenolate (10) Morgan and Soule. Chem. & Met. Eng., 26, 927 (1922). in 50 cc. of the distillate, that the potassium phenolates and (11) Raschig, z, Chem., 25, 1945 (1912), formaldehyde react readily in the presence of the catalyst (12) Redman, Weith, and Brock, IND. ENQ.CHEM.,6, 4 (1914). (13) Sheiber and Sandio, “Artificial Resins,” London, Sir Isaac present in the distillate which may be excess phenol, organic Pitman & Sons, 1931. bases, or slight excess of caustic. The addition of even small quantities of potassium carR E O E I V ~AD ~ 22,~ 1935. ~ I
