IXDUSTRIAL -4ND ENGINEERING CHEMISTRY
684
VOL. 32. NO. 5
as much as is precipitated. Unless there was a considerable circulation of sludge downward through the port, the mixing zone would soon lose most of its sludge. Since the mixingzone sludge does not decrease in strength, this recirculation of sludge must take place.
tor design is applicable for this purpose in such cases, but instead of lime or soda ash, such coagulants as alum, copperas, or Ferrisul are employed.
Distribution of Mixed Water into Sludge Filter Zone
Behrman, A. S., and Green, W. H., ISD. ENG.C H E M .31, , 128-33
Another feature of the precipitator design is the uniformity of distribution of the mixed water into the sludge filter zone. I n all of the precipitator designs described, sludge filter bottom port opening is of relatively small area, usually about one twelfth of the area of the top of the tank. Whether this port consists of the apex of a single funnel or the annular shaped port in Figure 1, it effects a uniform distribution of the mixed water into the sludge filter zone, with the aid of the agitator. Thus, channeling and short-circuiting through the sludge filter are avoided. Most of the precipitator installations have been made for lime-soda water softening. Some plants, however, have been installed for the removal of turbidity and color from surface supplies where softening is not needed. The same precipita-
Literature Cited (1939).
Hoover, C. P., “Water Supply and Treatment”, pp. 82-86, Washington, D. C., Natl. Lime Assoc., 1936. Jensen, J. A., J . Am. Water W o r k s h s o c . , 30, 1847 (1938). Klassen, C. TI’., and Spafford, H. A , , Ibid., 31, 1734 (1939). Sheen, R. T . , Beta, W. H., and Betz, L. D., Maryland-Delaware Water Works and Sewerage .4ssoc., Cumberland, Md., May, 1939.
Spaulding, C. H . , J . Am. Water W o r k s Assoc., 29, 1697 (1937). Spaulding, C. H., Ohio Conf. Water Purification, Ann. Rept. 18, 52 (1938).
Spaulding, C. H., 8 0 . Dak. Water & Sewerage Conf., Watertown, S. Dak., Sept., 1938. Spaulding, C. H., 27th Ann. Meeting, S. W. Section, Am. Water Works Assoc., Oct., 1938. Spaulding, C. H., Water W o r k s & Sewerage, 85, 153 (1938). Spauldinp, C. H., and Timanus, C. S., J. Am. Water W o r k s Assoc., 27, 326 (1935).
PRESENTED before the Division of Water, Sewage, and Sanitation
Chemistry
at the 98th Meeting of the American Chemical Society. Boston. Mass
COAL BY-PRODUCTS Yellowing of indene-coumarone is attributed to the development of a highly unsaturated molecular structure, representative of a class of compounds known as fulvenes. Hydrogenation prevents the formation of these highly colored bodies in the resinous mass by preventing a series of reactions beginning with entry of oxygen and its expulsion later as water. Bleaching with hydrogen destroys the fulvene originally present, which results from process operation. Influence of pressure, temperature, catalyst concentration, time, completeness of reaction, distribution of hydrogen have been determined. Water-white resin is now produced on a small scale with operating conditions of 1000 pounds per square inch pressure, 200” C. (392’ F.), 70 per cent resin concentration, and a cycle of 20 hours. F T H E most recent advances in the chemistry of synthetic resins, the theoretical studies applied to indenecoumarone polymers have been highly successful in originating new and modified polyindene resins. This paper is concerned entirely with practical developments, specifically with the influence of the factors involved in the introduction of hydrogen by metallic catalyst into the resin polymers a t a multitude of points in the molecule. Commercial resin of today can be produced in standard grades with very pale color. This initial color is intriguing, but despite the apparent visual perfection, these resins are
0
1 The
fint paper in this aeries appeared in April (f).
The Hydrogenation of Indene-Coumarone Resins’ WILLIAM H. CARMODY, HAROLD E. KELLY, AND WILLIAM SHEEHAN Carmody Research Laboratories, Inc., Springfield, Ohio
undependable as to color stability. The development of dark color is attributed to the formation of a fulvene structure throughout the mass ( I ) . This color behavior and other minor characteristics have been noted in these resins, but there was no coordinating theory until recent study revealed the simple interrelations. The foregoing explanation deals with the role of the double bond and the methylene group in the indene polymers. The remaining portion of these resin molecules is apparently immaterial to the development of fulvene structure and takes part in secondary roles during hydrogenation. Owing t o the number of aromatic rings in the structure of these resins and to the certainty of their saturation, other aspects enter into the problem besides that of mere hydrogenation of the solitary alkene linkage in the terminal indene unit of the polymer. The numerous possible points of hydrogen entry bring about a complexity of reactions. Based on the number of indene units (each having an aromatic nucleus) in one mole weight of the commercial grade of resin, it is possible to introduce, on an average, 42 atoms of hydrogen. Study of the situation has permitted the distribution of the hydrogen to be determined, and it is definitely known t o react in the manner described in the following paragraphs.
MAY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
685
A . Hydrogenation of the Existing Fulvene Structure in the Polymer
C. Saturation of Aromatic or Benzenoid
Figure 1 indicates that there is an unusual degree of unsaturation in the terminal unit. The three double bonds (indicated heavy) involved in the fulvene structure are essential to the existence of color. Saturation with hydrogen
Each of the aromatic rings can receive and absorb 6 atoms of hydrogen. Each carbon atom in the ring requires one additional hydrogen atom to bring it to a state of complete saturation. The amount of hydrogen entering into the benzenoid structure of indene resins is thus strictly proportional to the molecular weight of the resin treated. For obvious reasons the consumption of hydrogen toward this end should be limited unless there is justification for its use. It will be shown later that, up to a certain amount but not beyond, the use of this additional hydrogen does confer some useful properties. Considering the present immediate goal of hydrogenation to be the prevention of afteryellowing, it is definitely desired to limit the entry of hydrogen to that required in reaction B. Over and above this amount is a waste of hydrogen, since it is apart from color stability. It does, however, confer improved solubility upon the resin in petroleum solvents. Commercially reaction B is of the highest importance, but actually C is most easily accomplished and most difficult to restrict. The above simplified explanations bring out the points that these resins are modified in their properties in strict accordance with the extent to which reactions B and C are permitted to take place. The reactions are inseparable, but it has been found possible to choose working conditions which favor the one and retard the other. With the present state of knowledge the two reactions cannot be completely separated nor can reasonable selectivity be obtained. -4s carried out in the present commercial installation, operating conditions favor the two reactions in unequal degree. The most widely separated conditions available operate in such manner as to produce reaction C about 90 per cent complete and reaction B about 50 per cent complete. I n directing a limited distribution of hydrogen, it is necessary to resolve the treatment into two phases, one of which may be termed a “pretreatment”. The reaction mixture is first treated with a quantity of bentonite or recovered nickel from a previous operation and then given a second treatment with an amount of fresh nickel catalyst. The role of such material is not completely understood, but the effects are definite and of benefit to the resin. The following examples indicate the efficacy of the combined steps:
R
I
R-
‘GU-
t
FIGURE 1. FULVENATED RESIN, FULVENE STRUCTURE INDICATED BY THREEHEAVY DOUBLEBONDS
WITH THE
of either of the three is sufficient to destroy the colorresponsible structure. The initial amount of this color-bearing body in a recently produced resin is small. Relatively, a trace of hydrogen is sufficient to react with the highly colored fulvene and destroy its structural identity. This bleaching does not require severe experimental conditions and is easily accomplished by agitation with freshly prepared Raney nickel catalyst. Owing to the method of catalyst preparation, sufficient hydrogen remains on its surface in the active state to react readily with and bleach the resin without the necessity of an additional supply of hydrogen. The bleaching described in this section is of no permanent value in itself since, upon continued exposure to conditions favoring fulvene development, the color will reappear and even surpass that originally present.
B.
Saturation of Nonaromatic Double Bond
Earlier workers (6) presented evidence bearing on the existence of only one double bond in indene polymers, regardless of molecular magnitude. The present viewpoint supports their contention, places this double bond in a definite location, and ascribes undesirable characteristics to it. The introduction of 2 atoms of hydrogen into the resin molecule at this point is sufficient from a theoretical point to prevent the deterioration of the initial pale color of resins. As the molecular size becomes greater, the required amount of hydrogen becomes less. This is due to the double bond existing in the terminal unit only, and the ratio of this unit to the entire molecule becomes smaller. This fact indicates that, t o be of value, the process should deal with resins of high melting point and high molecular weight, and thus keep hydrogen consumption a t a low figure. I n practice, the desired goal is to employ one mole of hydrogen per mole of resin; that is, 2 pounds of hydrogen should be sufficient to saturate approximately 775-800 pounds of resin.
Struot ure
Hz Pressure,
%
G r a m s G r a m s Time Lb./Sq. Ye!low- Solubility. Expt. Grams Cc. NO.^ Resins Solvent Nlokel Clays Hours 1ng C. In. 1 2 2a 3
3s 6
4500 4500
4000
135
4500
4000
135 135
. . . . 4000 . ... ....
....
...
135 All experiments a t 200° C.
0 450
... .... ..
12 6 8
900
51
900
38
...
..
6
,
8
900
.. .. 9
27 .... -48 .... -65
Experiment 1 indicates that when 3 per cent of nickel catalyst is employed, only moderate hydrogenation takes place. In 2 and 2a, when a combined pretreatment and hydrogenation is given in consecutive steps, there is a more definite entry of hydrogen into both the double bond and the aromatic rings. In 3 and 3a, when nickel is used in both steps, there is further increased entry of hydrogen into the polymers. In practice quite a range is permitted in the preparation of the various grades of hydrogenated polymers; conditions are chosen which are a composite of 1 and 3a, and which result in hydrogenation to the extent of roughly 50 per cent of reaction B and 90 per cent of reaction C. An increased amount of catalyst is called for in 3 and 3a, and hence such a product is more expensive but does have a reduced tendency to yellow. The present account briefly describes the effect of the main variables on the composite hydrogenation reactions and indi-
IYDUSTRIAL AND ENGINEERING CHERIISTRY
686
:i. 0
COLUMN
NAPHTHA
I,
I
WASHER
VOL. 32,
so. 5
I STORAGE
L
pq I
J
METER
noun
FIGURE 2. FLOWSHEET OF A COMBINED POLYMERIZlTION A N I HYDROGENATION PL.4KT
FORMULA
C
R
FORMULA
f
R
cates their relations in the broadest manner. Briefly, the process is carried out as an added series of steps following the regular production of coumarone-indene resin. Figure 2 is a simplified layout of B combined polymerization-hydrogenation plant. The compactness or adjacency suggested in the drawing is not carried out in practice; the operations are spread over a considerable acreage.
The Polymerization-HydrogenationProcess U
2
I
u2 FORMULA
0
FIGURE 3. SATURATION OF DOUBLE BONDONLY,AS IN REACTION B Reaotion C illustrates aromatic ring saturation; reactions B and C take place concurrently with Raney nickel
Crude solvent naphtha, obtained from the fractionation of coke-oven light oil containing approximately 60 per cent of indene and coumarone constituents is diluted with lowboiling petroleum benzine to a polymerizable content of 12 to 15 per cent. The reaction mixture is chilled, and t o it is added in a controlled stream, with efficient agitation, several per cent by weight of concentrated sulfuric acid. The temperature rises immediately and is accompanied by increase in viscosity and formation of polymers. I t is during this temperature surge that some oxidation always takes place, which unfortunately supplies one of the reactants for the fulvene-forming reaction. The evolution of sulfur dioxide and the presence of aldehydes have been noted in the polymerizer sludge for a number of years. The intensity of surge is also related to the final color of the resin produced in any given batch. The acid sludge is settled and drained; several water and alkaline washes are given to reduce the
M A Y . 1944
687
INDUSTRIAL .4ND EYGINEERING CHEMISTRY
B
FI(.I'HE 4 EXPERIMENT A L HYDROGENATORS ( A ) 1-quart, ( B ) Zquart, ( f ' ) 3.5-gallon capacity
content of mineral matter. After settling, the resin solution is drawn to storage and later to stills for solvent removal. Combined steam and vacuum remove all diluent and inert material as well as high-boiling polymer oils. Distillation is continued until the desired melting point is reached, when the still charge, in molten condition, is drained into drums, pans, or a flaking machine, depending on the final disposition of the resin. It is commonplace for a batch of resin solution of pale color, from which a light resin was expected, to emerge from the final distillation in the stills with a very dark color. The explanation was often assumed to be contamination from equipment, etc.; but in this new light of fulvene formation it is believed more likely that the resin polymers had been "inoculated" with aldehydes during the polymerization process. Subsequent heating in the still caused the formation of the characteristic fulvene body. For hydrogenation work, resin of high melting point is in demand and 150" C. (302' F.) is an arbitrary minimum. Resin of such characteristic is redissolved in warm petroleum benzine to produce a 70 per cent by weight solution or a 50
per cent by volume solution. ,4 measured amount of this resin solution is pumped into a semiworks hydrogenation vessel of about 120 gallons capacity. The proper weight of Raney nickel catalyst (usually 5 per cent of the resin weight) is added, and the ressel is closed and flushed with hydrogen to exclude air. Steam is supplied to the jacket to heat the contents to 200" C. (392" F.). Compressed hydrogen is introduced into the vessel a t a working pressure of 1000 pounds per square inch for a cycle approximating 20-24 hours. The reactions will then average from 50-95 per cent complete. The distribution of hydrogen between reactions B and C is influenced entirely by the working conditions imposed on the system. At the end of the hydrogenation period the pressure is reduced to atmospheric, the bomb is drained, the mixture is filtered to remove spent catalyst, and the colorless resin solution is distilled. The resin obtained is of the original melting point, within 1" or 2" C. (1.8' or 3.6' F.), but is more soluble in petroleum solvent and has a reduced yellowing tendency proportional to the completeness of reaction B.
688
IXDUSTRIAL AND ENGINEERING CHEMISTRY I
VOL. 32, NO.5
In theory the reactions are well defined; they might be expected to begin with formula C, and by a hydrogen selectivity pass a t will to formula D and then to formula E. Alternatively, nonselectivity should result in the direct production of formula E. In actual practice, D and E are simultaneously produced. Nickel is an aggressive catalyst and does not permit of such fine distinctions as the problem requires. Preponderance of points of entry in the rings over the points of entry into the double bond always leads to the formation of some of E type, even though all attempts are centered on the production of the dihydroresin, type D.
Experimental Equipment Figure 4 illustrates a rotating I-quart and 2-quart, and a tumbling 3.5-gallon hydrogenator vessel. Figure 5 is a sketch of a 5-gallon vessel. Relatively simple equi ment may be used for such work. The smaier vessels may be gasFIGURE 5. DIAGRAM O F 8-GALLON HYDROGENATOR heated, and temperature can be contrdled within narrow limits. The larger vessels were heated electrically and could be held at any temperature between about 125" and 300" C. (257' and 572" Percentage of Hydrogen Involved in the F.). The semiworks vessel was jacketed, and temperature was Reactions maintained by pro er balance between steam, water, and reaction rate. The gomb was constructed of seamless tubing, The relative desirability of reactions B and C makes it with thick flat end plates welded in place. Opposite ends carried desirable to have some degree of control. Nickel as a catalyst a thermometer well and connections for gas inlet. G shows the is more efficient in the saturation of aromatic rings than in the commutator and rheostat. The drive was through the combined motor-reducer, H . Hydrogen was supplied from a standsaturation of the alkene linkage. It follows that with this ard 192-cubic foot cylinder held in place by screw Z and several catalyst the desired selectivity can never be realized, owing encircling bands. Regulation gage B controlled and reduced to the fundamental nature of the Raney catalyst. the hydrogen pressure. By such a design it was possible to carry Calculation shows the following interesting possibilities sufficient hydrogen to treat 20 pounds of indene-coumarone resin with no interruption. At intervals readings were taken of concerning the theoretical goals on paper, which have recently temperature and of working and supply pressures. Samples been reached in the laboratory and are being tested on a semiwere removed through D; filling and draining was accomplished works scale. The molecular weights of the resins studied average about 775, and they are mixtures of tetramers and m i octamers mainly, with a smaller residual amount of dimer zoo 90 oil. The number of indene (or coumarone) units will average 6.67. Two atoms of hydrogen required by reaction B increase the molecular weight by about 0.26 per cent. Forty 70 160 atoms are required in reaction C with a final weight of 815 and a weight increase of 5.1 per cent. Specilic direction of so I20 hydrogen entry becomes of importance since these resins have high capacity to absorb hydrogen in the aromatic rings. This concurrency of reactions is indicated in Figure 3. 30 80 Group R represents the remaining portion of the resin and has an average value of 5.67 units, each containing the aroIO 40 matic ring and requiring 6 atoms of hydrogen. On this theoretical basis all of the forty-odd hydrogen atoms have HOURS been allocated a position into which they can be directed. Briefly, formula C is an unhydrogenated indene polymer. FIGURE6. CHANGESIN YELLOWING AND Formula D is the structure after 2 atoms of hydrogen have SOLUBILITY IN AN INDENE RESIN been directed into the double bond in the terminal unit of I. Yellowing tendency retained by resin, yo the polymer. This structure does not admit of afteryellow11. Solubility of resin, C. 111. Reaction temperature, C . ing on the basis of the fulvene structure development. Its IV. Hydrogen supply pressure, Ib./sq. in. solubility in petroleum cuts is still poor and practically the same as before treatment. This retention of the original at this point. On this vessel was obtained most of the data solubility is due to the fact that the 2 atoms of hydrogen are shown in the charts. The small units were used for trial runs, relatively a small weight of the mass of resin polymer and and a large amount of fundamental work was carried out on the are practically without influence in conferring improvement. measurement of gas absorption under various conditions. To obtain a nonyellowing resin, it is sufficient to complete Hydrogenation Data reaction B and stop at formula D. Formula E represents a polymer which has been hyOver one hundred runs were made in the 3.5-gallon unit. drogenated to the fullest extent. The double bond is satuBased on the data found, the larger unit was constructed rated, and each of the aromatic rings has received its quota of with reasonable assurance that most of the difficulties had hydrogen. The resin is nonyellowing and extremely soluble, been met and overcome on a small scale. lacks molecular association, and produces solutions of low Figure 6 shows the important changes in yellowing and viscosity. solubility which occur in an indene resin when carried through O
689
INDUSTRIAL AND ENGIKEERING CHEMISTRl
h I A I , 1940
40
00
120
160
200
212
140
284
356
DEGREES f
DEGREES C
OF INDENE DIMER ( A ) AND OCTAMER ( B ) FIGURE 7. HYDROGENATION
on the basis of 10 pounds resin, 0.5 pound Raney nickel, 4000 cc. of petroleum benzine, initial hydrogen supply pressure 2000 pounds and working pressure 1000 pounds per square inch. Samples were withdrawn at intervals, and the recovered resin was examined and evaluated. The values found gave an exact knowledge of the extent of the solubilizing reaction (C) and the color-stabilizing reaction (B). Hydrogen was admitted to the vessel, and the reaction was started a t 200" C. which was reached 6 hours after heat mas applied. Curve I, Figure 6, shows the rate a t which the elimination of yellowing takes place. The data by which the curve was established were found by exposure of films of the resin to a mercury vapor lamp. The color change was evaluated in a colorimeter and expressed in percentage of the untreated resin coloration. Curve 11, Figure 6, shows the solubility value found in the resin after hydrogenation has progressed for some time. The continued entry of hydrogen causes a drop in the cloud point of a standard solution of resin. Initially a 20 per cent resin solution will show cloud a t +60" C. (140" F.); a t the end of 11 hours of hydrogenation this value has been depressed to -55" C. (-67" FJ, The test was not intended for use a t such low temperatures, and results are not dependable below about -50" C. (-58" F.), although rough approximations may be made. Curve 111, Figure 6, illustrates the temperature surge at the beginning of the reaction. The exothermic reaction often caused a rise of 30" C. (54" F.) within the first 5 minutes in a vessel of about 400 pounds weight, with a high capacity t o absorb heat. Calculation shows that the heat liberated on the surface of the catalyst was in excess of that required to cause charring and darkening of the resin polymers. This charring is evidenced directly by the presence of dark resin on the surface of the catalyst a t the end of a run and by the fact that an excessively fast-starting reaction is less apt to progress to the same degree of completion that the use of a smaller amount of catalyst permits. Catalytic power is inhibited by the sudden and intense reaction on the active metallic surface. Curves I and 11, Figure 6, collectively show the distribution of hydrogen. The sudden change in the slope of curve I indicates the sluggishness with which hydrogen is entering into the color-stabilizing reaction. Curve I lags while I1 leads in the competitive race to absorb hydrogen. Curve IV shows the drop in hydrogen supply pressure in the system as the two reactions proceed. The group of curves is r e p
resentative of those encount,ered in laboratory batch processes. Resin polymers of all magnitudes react in the same manner. The dimer, tetramer, octamer, and a resin with a molecular weight of 2500 have been successfully treated, with no important deviation. Figure 7 shows the general similarity of the behavior of the octamer and dimer of indene under comparative conditions. The limited capacity of the small units necessitated several successive fillings with hydrogen in the course of each experiment. Curve 1, Figure 7-4, shows initial pressure of 1150, rising to 1450 pounds per square inch when heated to 155" C. (311" F.), a t which point absorption begins at a very rapid rate. The bomb was cooled and recharged several times to attain full saturation of the material. With each successive charge of hydrogen, higher pressures are reached before rapid absorption takes place. Slightly higher temperatures are necessary each time to cause a rapid drop in pressure. As the percentage of untreated resin in the system decreases, it is increasingly difficult for catalyst, hydrogen,
1600
3
e s
bJIZO0
%
5 800
e
600 400
86
19s 302 DEGREES 6
4M
FIGURE8. SPLITTING OUTOF HYDROGEN AT HIGH AS INDICATED B Y EXCESS PRESSURE TEMPERATURE and polymer to contact one another. Curve 3, Figure 7A, shows that when a temperature of 200" C. (392" F.) is maintained, there is a sharp drop in pressure. To avoid overlapping, the curve is terminated a t 1700 pounds, but the
INDUSTRIAL AND ENGINEERING CHEMISTRY
690
actual value was 600 pounds per square inch a t the end of the reaction. I n Figure 7B indene octamer was used, and the only notable differences are the relatively lower temperatures a t which absorption begins and the slower rate of reaction. I n an octamer there are numerous points for hydrogen entry, and the overlapping of each separate reaction curve gives B complicated appearance. All commercial resins, regardlesb of molecular magnitude, give results entirely within the limits shown in Figure 7 . The observation that the resins offer resistance to complete hydrogenation indicated the possibility that such a reaction could be demonstrated to be reversible. This is distinctly brought out in Figure 8 which indicates the result of a n experiment where heating was continued over and above that usually employed for such work. In the early part of the run the reaction proceeded in the normal manner. Continued heating caused a rise in pressure up to about 1350 pounds per square inch, which is in excess of the initial pressure, Readings taken during the cooling of the bomb indicated a greater volume of hydrogen in the bomb after the superheating than had been present a t 200 " C. earlier in the run. The arrows indicate the course of the pressure-temperature relation. Approximately 450 pounds of hydrogen pressure were split out of the resin due to the excessive heating. When unhydrogenated indene resin is subjected to similar heating, depolymerization results but no fixed gas is liberated. Definite working limits are indicated. The threshold temperature is near 85" C. (185' F.), and near
VOL. 32, NO. 3
resin hydrogenation to be advanced toward completion. In Figure 9 that portion of the curve marked A was carried out a t a pressure of 400 pounds per square inch, and the drop in the supply pressure indicated the rate and extent of the reaction. After 5 hours it was necessary to elevate the pressure to 650 pounds to resume the reaction, and after 9
1900
I800
s
1700
iu
3
1600
/400 I300 875
1200
\ I 3
6
/5
I2
9
I8
21
HOURS
FIGURE10. RATE A N D EXTENT OF DROPIS SUPPLYPRESSURE WHEN OPERATINGUXDER DIFFERENT WORKINGPRESSURES IN THE HYDROCENATOR V E S S E L
hours to 1000 pounds. This preliminary information revealed that the reaction would apparently stop in the vicinity of 42, 55, and 68 per cent completion when pressures were used of 400, 650, and 1000 pounds, respectively. Later i t was discovered that in the range 950-1000 pounds the reaction could be driven to 90-93 per cent of that expected. The pressure influence is further demonstrated in Figure 10 which records three runs. Higher pressures (2000 pounds) are much more favorable to the reaction and carry the products to a state of saturation
I600
s
'
k
1700
3
1600
ksoo
' 3
NO0
I
l
l
I
2
4
6
8
IO
I2
I4
HOURS
FIGURE 9. APPARENTEQUILIBRIU~I STATES AT VARIOUS PRESSURES, AND RESUMPTIOXOF REACTION FOLLOWING A N INCREASE IN P R E S S ~ R E
285" C. (545" F.) unfavorableresults areobtained. Staudinger (6)reported the hydrogenation of indene polymers of high molecular weight a t temperatures near 270" C. (518" F.) and stated that the results were erratic and difficult to interpret. It now appears that he encountered simultaneous depolymerization, reversal of reaction, and actual thermal cracking which clouded the situation and did not permit a clear understanding of results. Full credit must be given to Staudinger for being the first to hydrogenate indene polymers. His work pertained at the time to viscosity and association aspects of the problem, and the commercial angles such as color instability, yellowing, and solubility escaped his observing eye.
Effect of Pressure on the Reaction It was necessary to determine the minimum pressure to give a reasonable reaction rate, which would accomplish a given degree of completeness. The yellowing factor of such resins should be reduced to below 10 per cent of that possessed by the original indene-coumarone resin. Elevated pressures follow the well-known principles and permit the
I
3
5
7
9
I1
I3
HOUR5
FIGURE 11. RELATION BETWEEN PRESSURE AND PERCENTCATALYST 900 pounds per square inch hydrogen pressure used in upper group, 650 pounds in lower group
MA\-, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
in a short time. The rate, completeness, distribution of hydrogen, and final resin color are all influenced more or less by the initial rate of reaction and the intensity with which the reaction is permitted to continue.
Pressure-Catalyst Relation Hydrogen entry is iduenced not only by the pressures involved but also by the amount of catalyst in use. It is often possible to increase one and reduce the other, and at the same time obtain identical end products. Figure 11 shows a group of experimental results. With pressures of 600 pounds per square inch the results appear to fall in the same band or average channel. Results differ with the higher pressure; the rates and slope of curves and the end pressures are different. At 900 pounds pressure with 4, 5, and 6 per cent catalyst, the reaction is about 60, 75, and 90 per cent completed in 12 hours.
691
cent. If the first amount could be selectively introduced as shown along curve 1, the reduction in yellowing would be strictly proportional to its entry and should be zero. The actual yellowing path is shown in curve 2. Actually when 0.26 per cent hydrogen has been introduced, the yellowing is still 97 per cent of its original value. The competitive rate, as nearly as can be estimated, is that the rings are absorbing
Re-use of Catalyst Figure 12 indicates the results obtained when spent catalyst is washed and re-used. It diminishes in value after a few cycles. Curve 1 shows the reaction t o be stopped in about 100 minutes with a pressure loss of 400 pounds per square inch. Curve 2, second cycle for catalyst, indicates a drop of 300 pounds in 55 minutes; curve 3 required 160 minutes to cause a pressure drop of 225 pounds.
J
2
3
4
5
PERCENT HYDROGFN
FIGUBE13. THEORETICAL AND ACTUALDISTRIBUTION
OF
HYDROGEN
I f 00
IO00
u
3
2
3 900
$ B
800
700 PO
40
60
80
IW
K O
140
160
MINU T E 5
FIGURE 12. Loss OF ACTIVITY OF RANEY NICKEL AFTER THREE CYCLES
Examination of the catalyst from many runs reveals an absorbed layer of very dark resin of low melting point. This soft resin results from thermal depolymerization and is retained on the catalyst; thus its efficiency is lowered in any later cycle. Hydrogenation is carried out in petroleum benzine as resin solvent, and the spent catalyst may be washed with it in the filter press, with no passage of this dark resin into the main mass of water-white filtrate. Release of this dark resin may be accomplished by a final wash with any aromatic solvent which removes i t from t8hecatalyst surface. This recovered catalyst is still of impaired efficiency.
Theoretical vs. Actual Distribution of Hydrogen The theoretical distribution was discussed earlier in this paper. Actual results show interesting relations and enable us properly to estimate the difficulty involved in directing hydrogen to enter where it is most needed. Figure 13 indicates that, when the full amount of hydrogen has been introduced, the weight is increased by approximately 5 per cent. Theoretically this division should be 0.26 and 5.1 per
thirty-three times faster than the alkene linkage a t the beginning of the reaction. To reduce the yellowing to 50 per cent, it is necessary to introduce more than 75 per cent of the total possible hydrogen. At times these values may rise to 50 and 93 per cent, respectively, in actual practice. The optimum condition is that curves 1 and 2 should be nearly coincident. Curve 3 is the expected path the resin solubility should follow as hydrogen is introduced, and curve 4 shows that the deviation is not too great. The rings consume the entering hydrogen and shift curve 2 from its expected position. These curves indicate the present status of indeae-coumarone resin hydrogenation, and reveal the tremendous volume of gas and catalyst required to accomplish a purpose, which from a theoretical point of view could be satisfied with a mere trace of hydrogen and catalyst. Work in progress offers promise that these conditions will he improved in time. 4
Commercial Production of Hydroindene Resins The above resins have been in commercial production for the past several years under the name “Nevillite” and are replacing some of the more expensive water-white resins. I n a number of uses, but not all, they are equally as adaptable as the styrene polymers and the colorless naphthalene resins. Increased production is contemplated as demand arises, and their uses become better known. Reduction in catalyst and hydrogen costs indicates further use by industry in large volumes. Production of a thousand pounds of resin per day gives rise to a hydrogen problem of no small magnitude. Regardless of molecular size, each pound of polymer consumes approximately 10 cubic feet of hydrogen. I n pilot-plant stage bottled hydrogen is one of the minor expenses. A small unit with a capacity of 300 pounds per day involves the use of thirty cylinders of hydrogen, with half the gas used and half remaining in the cylinders. Location of a fullsize plant is largely a matter of locating near low-cost highpressure hydrogen, where transportation is through highpressure pipe rather than cylinders.
IKDUSTRIAL AND ENGINEERING CHEMISTRY
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Acknowledgment During the early stages of development, cooperation of a number of firms was essential before a smooth functioning process was in operation. The authors acknowledge and appreciate the assistance rendered by George Pool of Compressed Industrial Gases, Inc., in the design of the compressed hydrogen handling system, and for many suggestions. The Keville Company generously assisted in working out the problem by supporting the project over a number of years when it seemed more a theory than a definite commercial goal. Numerous members of the organization con-
LACTIC ESTERS
VOL. 32,
so. 3.
tributed and assisted with their personal skill. The authors deeply appreciate the interest shown in their work.
Bibliography (1) Caimody, W. H., ISD. ENQ.CHEW, 32, 525 ( 1 9 4 0 1 . (2) Carmody, W. H. (to Seville Co.), U. S. Patents 2,104,829, 2,108,250, 2,128,984-5, 2,139,722 (1938), 2,152,533 (1939). (3) Kelly, H. E., ISD. ENG.CHEY.,29, 576 (1937). (4) Gheehan. William. Ibid.. 30. 245 (1938). (5) Staudinger, H., Swiss Patent 121',817 (1926); H e h . Chirn. Acta, 12, 962 (1929). ( 6 ) Whitby and Kate, J . A m . Chem. SOC.,50, 1160 (1929;.
Preparation and Properties
LEE T. SMITH'AND H. V. CLABORK Bureau of Dairy Industry, U. S. Department of Agriculture, Washington, D. C.
A description of methods for the preparation of lactic esters is given. Inordertoobtain high yields of the pure lactic esters with alcohols containing less than four carbons, it is necessary to use a large excess of alcohol during esterification and then rapidly remove the excess alcohol and water from the ester at low temperatures, preferably in vacuo with the aid of an efficient fractionating column. Some of the physical properties of thirty esters are given. The methods of preparation described here have commercial possibilities.
I
N A STUDY of the utilization of lactic acid made from whey by the fermentation processes, described by Whittier and Rogers ( l a ) , Olive @), and Burton (4), this acid has been converted into various mono- and diesters that may have utility. The esters which are known already, as well as several new ones, have been made from crude calcium or crude sodium lactate obtained by the fermentation of whey Because the methods are in some respects novel, they are described in detail. Lactic acid possesses two active hydroxyl groups; t h e r e fore, three types of esters are possible: (a) The hydroxyl in the carboxyl group will react with an alcohol (IS) to form the corresponding lactic acid ester, CHsCHOHCOOR. (b) The secondary alcohol group in the alpha position of these esters reacts with acid chlorides (IO), acid anhydrides (S), and ketene (6) to form the correwonding alpha (R-C=O) oxypropionate; O-OCR
This compound may also be prepared by the partial saponioxypropionate. fication (I3) of ethyl alpha (R-C=O) The esterification of the hydroxyl in the carboxyl group is easily accomplished by the reaction of an alcohol with lactic acid, especially if a small amount of sulfuric acid is used as catalyst. The yield of the ester will vary from about 60 to nearly 100 per cent, depending largely upon the method used for removing the water as it is formed during the esterification reaction. It is more difficult to obtain a high yield of ester with methyl or isopropyl alcohol than it is with a longchain alcohol such as butyl, amyl, cetyl, lauryl, and stearyl, because the lower alcohols and the corresponding lactic esters are soluble in water and do not form azeotropic mixtures with benzene, toluene, ethyl acetate, etc. It is necessary, therefore, to resort to other methods of removing this water or reducing the ratio of water to alcohol in the reacting mixture by using a large excess of alcohol. The general methods used in the preparation of the esters are given in the following sections.
CHsAHCOOR
Low-Boiling Esters Soluble in Water
(c) Similarly, the secondary alcohol group in lactic acid re acts with acetic anhydride and acid chlorides ( 1 ) to form the alpha (R-C=O) oxypropionic acid,
Five moles (1090 grams) calcium lactate or 10 moles (1120 grams) sodiumlactate, dry basis, are dissolved or mixed with 50 moles methanol (1600 grams), ethanol (2300 grams), or isopropanol (3000 grams). An equivalent amount of sulfuric acid is added to liberate the lactic acid and precipitate the calcium or sodium sulfate. An additional 20 grams of sulfuric acid is also added as catalyst. The mole ratio of this mixture is 1 part lactic acid, 5 parts alcohol, 0.02 part sulfuric acid, and 1 part calcium sulfate or 2 parts sodium sulfate. This mixture is heated for 4 t o 8 hours at refluxing temperature to
W C R CHsbHCOOH 1 Present address, Eaatern Regional L a b o r a t o r y , B u r e a u of BgricuItural Chemistry and Engineering, Wyndmoor, Penna.
