I
LEON B. GORDON,' PAUL D. MAY, and ROBERT J. LEE American Oil Co. (Texas), Texas City, Tex.
Converting Aromatics to Useful Resins Concentrated formic acid catalyzes clean-cut reactions of aromatic hydrocarbons with paraformaldehyde at 105" C. Methylnaphthalenes yield resins of about 500 molecular weight; rn-xylene is converted mainly to dixylylmethane
CATALYTIC
reforming processes in the petroleum industry have made available large quantities of low cost aromatic hydrocarbons of both monocyclic and dicyclic structures. The availability of these aromatics, particularly those of the naphthalene series, has led to a renewal of interest in the formolite reaction for converting such aromatics to useful resins. This reaction involves the condensation of aromatics with formaldehyde (6, 7, 70),as illustrated by the following equation :
Table 1.
Higher Yields of Higher Molecular Weight Resin Are Obtained with 90 and 99% Formic Acid as Catalyst" Formic Acid Quantity, Resin Properties Acid grams/100 Resin Charge concn.. grams Yield. Softenine Gardner Stoci2 wt. % aromatic Wt. point, OF. color MOL wt.
A A A A C
A A B
0
+ HC-H CH8
CH3
56 74 85
120 135 140
8 10 12
291 310 310
90 90
90
107 350 400
88 90 90
144 198 165
8 8 11
314 391 375
99 99
350d 350
98 98
223" 235'
14 13
493 533
comparatively good color of the resinous products are also noteworthy. A variety of catalysts have been used by previous investigators (2-4, 9). Zinc chloride in glacial acetic acid (4) gives good yields of light colored resins, but catalyst cost is high. Other catalysts, such as sulfuric acid or aluminum chloride, generally produce serious emulsion problems and darker colored resins.
CH3
Formic acid catalyzes this reaction, and high yields of light colored resins result from reaction of paraformaldehyde with methylnaphthalene concentrates produced as a by-product in catalytic reforming. Formic acid has several advantages as a catalyst in the formolite reaction (6),an important one being abjence of emulsion problems. No solvents are needed, as formic acid functions both as the reaction medium and catalyst. Another advantage is the fact that the formic acid can be recovered readily by distillation and recycled. Absence of side reactions and 1
107 400 600
Reaction temp., 105' C.; reaction time, 6 hr.; reactants: 100 grams of methylnaphthalenes, 20 grams of paraformaldehyde. A = 235-290O C. mono-, di-, and trimethylnaphthalene concentrate from hydroformer bottoms; B = 235-270' C. mono- and dimethylnaphthalene concentrate; C = purified 2-methylnaphthalene. Based on hydrocarbon charge. 4-hr. run. e Powers' cloud point (8),45' C.
-+
CHI
77.5 77.5 77.5
Experimental Materials. Flake paraformaldehyde (Cellanese Corp.) was used in all runs. Aqueous formalin (37%), evaluated in preliminary work, was much less satisfactory because of the large quantity of water it contains.
Present address, Pan American Petro-
leum Corp., Tulsa, Okla.
*
Formic acid (85 to 90%) and anhydrous formic acid (Victor Chemical Co.) were used as received. An aromatic concentrate, rich in mono-, di-, and trimethylnaphthalenes, with a boiling range of 235' to 290' C. was obtained by fractionating a high boiling aromatic oil known as "hydroformer bottoms." This material was produced as a by-product in catalytic reforming of petroleum naphthas in the fixed bed hydroforming unit of the American Oil Co. Analysis showed about 40% monomethylnaphthalenes, 30% dimethylnaphthalenes, 20% trimethylnaphthalenes, and 10% Tetralins and other hydrocarbons. This fraction was freshly distilled and then acid treated before use. A 50% pentane solution of methylnaphthalenes VOL. 51, NO. 10
OCTOBER 1959
1275
stock was agitated with 5 NY. r; of concentrated sulfuric acid for 30 minutes a t 30" to 35" C. After separating the sludge, the hydrocarbon mixture \cas percolated through a column of Attapulgus clay (10 parts of hydrocarbon per part of clay). Finally the pentane diluent was removed by distillation. This pretreatment resulted in a resin product of considerably lighter color. Both m-xylene (Oronite Chemical Co.) and p-xylene (A. D. hfackay, Inc.) of 95+70 purity icere used as received. T h e 2-methylnaphthalene (Reilly T a r and Chemical Corp.) \cas acid- and claytreated, as described above, before use. Procedure. The condensation rractions \cere carried out in a three-necked flask, equipped Lcith a thermometer, reflux condenser, and stirrer. Formic acid (usually 17 parts bl- lveighr) and paraformaldehyde (1 part) \cere added to the reactor and heated until the paraformaldehyde dissolved. Aromatic hydrocarbon (usually 5 parts) \vas then added rapidly. T h e reaction mixture \cas stirred a t 100' to 110" C. for 2 to 6 hours and cooled. and the formic acid layer \vas decanted from the solid resinous product which had separated upon cooling. Some additional formic acid was recovered from the hydrocarbon phase by distillation a n d was added to the decanted formic acid for recycle or concentration. Solid resin was combined with the hydrocarbon phase: and any liquid condensation products were separated by vacuum distillation a t 10 mm. of mercury. Resin products \vere recovered as distillation bottoms after removal of
I
z
y
600
a
k
t
5501
I-
I
0
500
3
5
450
J
3
0
400 0 5
350
I-
300
I
I 70
I
volatile products by distillation and stripping to 200" C . pot temperaiurr a t 5 to 10 mm. of mercury. Resins f r o m M e t h y l n a p h t h a l e n e s
and F o r m a l d e h y d e Condensation of either the 235" to 290" C . methylnaphthalene fraction of hydroformer bottoms or 2-merh>-lnaphthalene \cith formaldehyde produces a
FORMIC ACID C E NTR AT I 0N
i 200 U
B
52 4 -
I80 160
I-
s:
therinoplastic. 11) di.ocdrlxJn i ~ t ~ s i ~11111l~lc ii in common organic s o l \ ~ ~ n t s . l'lii, wsin contains no olefinic. unsaitiration and only a sinall ainount ~f os\~cii-c~c~iitaiiiing groups. For I l l o i l dpl)lic.atiotis, usrfulness o f thesc wsins is pat,riall> dvfined by color. softrnint: poinr. ancl molrcular weight. \.ariatioils in > icld and rcsin properties ~ i r r c.iruclicd a s a function of temperature. tiiiir. l'oi.iiiic acid concrntration, and ratio o f iorinic acid to aromatic chary? stock. I n addition, ttir r l f e c t of a promorri. ;ic.c.[ic. anhydridr, as dctet~inin~cl. .4ll y-irlds arc. rxpressed as \\(.iqlir pt.r cent based on total h).drocai.bon c.h;irqd r o the rraction. .imounts of I'orlnic~acid arc- expressed as thc equi\.alcnt quanti[>. o f anhydrous acid. ~ I ' h cmolr ratici of rnethylnaphrhaleiies t o paraI'(ii~inalt1chyde \\-asapproximarel\- 1 t i > 1 i t i all cases.
z w
LL
)O
Figure 2. Resin structure varies from a 2 to 1 to a 3 to 2 condensation ratio of methylnaphthalenes with formaldehyde, depending on formic acid concentration
yrn 99% CON
, 220
I
I 90 FORMIC ACID CONCENTRATION, W T . '/a
240
P
I 80
140
/.'
7 7 o/'
-@-e,
I20
/I
I
2
3
4
5
6
WT. RATIO FORMIC A C I D / A R O M A T I C Figure 1. Reaction of methylnaphthalenes and paraformaldehyde (1 to 1 mole ratio) produces resins of high softening point with an excess of 90 to 99% formic acid as catalyst and reaction medium 6 hours, 105' C., 235-290'
1 276
C. methylnaphthalenes
INDUSTRIAL AND ENGINEERING CHEMISTRY
fraction of hydroformer bottoms
Effect of Formic Acid Concentration and Ratio, Thc most iirilx)i~tani ('sperimrnral factors \ w r c tirriiic acid concenrrarion and quantit\. o r riiiio oU formic acid t o other rractants. 'l'livir effrct on d q r e e of condcnsaiioti. a s measured ti>- softening p o i n t ot' thc resin product, is shown in Figure 1. Reaction conditions, yields. and other resin pr(iperties are summarized in Tablc I . For a given acid concentration. resin yield and molecular weight. softening point. and color increased with increasing amounts of formic acid- -e+.. thc first three runs M.ith 77.55; formic acid. Molecular weights in these runs rangrd from 291 to 310 which corresponds t o the dinaphthylmethane structure ( I . Fiqure 2). .A product of this lo\c softcniiig point and molecular bveiqhr is not of
METHYLNAPHTHALENE A N D XYLENE CONDENSATION Table 11. Typical Properties of a Methylnaphthalene- Form a Id e hyd e Resin Produced with 99% Formic Acid Softening point (ASTM E 28-51T) 223-235' F. Gardner color ( 1 to 1 in toluene) 11-12 3 Cumar color Power's cloud point ( 8 ) O 113' F.-(4S0 C.) Iodine number (Wijs) Nil Acid number Nil Molecular weight (MenziesWright) 493-533 C-H analysis 90.70 c, % 7.88 H,% Remainder (assumed to be 0) 1.42 Molecular formula CasHssOo,4max.) a
70% resin in Nujol.
general utility as a resin, although it may have some value as a resinous plasticizer. However, useful resins of higher softening point and molecular weight were obtained by increasing formic acid concentration to 90% or higher. With formic acid of 90 or 99% concentration, an acid to hydrocarbon ratio of 3.5 to 1 or 4 to 1 gave resin yields of 90 to 98% and softening points above 200" F. I t is important that a large enough quantity of formic acid be used so that water produced in the reaction will not reduce formic acid concentration, and hence its catalytic activity, to the point that low yields of low molecular weight resin are obtained. For example, about 0.08 pound of water is formed in the reaction per pound of resin produced. This water is taken u p by formic acid, but it does not seriously affect the reaction at a 3.5 to 1 acid to hydrocarbon ratio. T h e resin produced from purified 2methylnaphthalene with 90% formic acid catalyst was similar to that produced from the mixed methylnaphthalenes from hydroformer bottoms. The 2-methylnaphthalene resin had somewhat better color and a higher softening point under equivalent reaction conditions, but yields were about the same. Resin Properties a n d Structure. Satisfactory resinous products of 223 " to 235 O F. softening point were obtained when 99% formic acid was used as catalyst (last two runs in Table I). A number of other properties of the f 2 2 0 O F. softening point resin are shown in Table 11, as a product of this type is in the range of commercial interest. Average molecular weight of this resin was 493 to 533, which indicates that the bulk of the material has a structure similar to formula 11, with lesser amounts of I11 (Figure 2). It was not possible to increase the softening point or
molecular weight of this resin to any appreciable extent by prolonged vacuum stripping at 5 to 10 mm. of mercury and 220' C. pot temperature. T h e resin thus contains little of the low molecular weight structure I product; hence, it must be predominantly the trimeric structure 11-type material. T h e naphthalene nuclei may have one, two, or three methyl groups attached, although the structures are shown with an average of two methyl groups. The nil iodine number and acid number values indicate the absence of unsaturation and complete removal of catalyst from the resin. Carbon-hydrogen analysis was in agreement with formula I1 and also showed a very low content of oxygen-containing groups in the resin. Average molecular formula was calculated to be CssH~eOo.4(max.). Oxygen was not determined directly, but the oxygen content cannot exceed 0.4 atom per molecule based on carbonhydrogen data for several different samples. The relatively high Powers' cloud point (8) is a desirable property not possessed by most of the common lowmolecular weight hydrocarbon resins. Cloud point was determined a t a 70% resin concentration in Nujol. This test gives some measure of the compatibility of resins with plasticizing oils used in asphalt floor tile manufacture. A laboratory evaluation of the resin in a n asphalt floor tile formulation showed generally good performance characteristics. Effect of Reaction Temperature. Condensation of methylnaphthalenes with formaldehyde does not occur in satisfactory yield at temperatures below
'T 60
about 50" C. when using 90% formic acid as catalyst. At 0" C. only a 5% yield of an oily product was obtained, whereas at 105" C. a 91 wt. % yield of a 368-molecular weight resin was produced. Results of these runs, using the 235' to 290' C. methylnaphthalene fraction of hydroformer bottoms as charge stock, are shown in Figure 3. As expected, both color and softening point of the resin increased at the higher reaction temperatures. Because the reaction proceeded satisfactorily at the reflux temperature of 105' C. and was easy to control under these conditions, this temperature was used in most of the runs involving changes of other variables. Higher temperatures may lead to a higher degree of condensation. However, formic acid begins to decompose a t an appreciable rate at about 125' C. and decomposes rapidly at 160' C. ( 7 7 ) . T h e higher temperature range was explored briefly in one run a t 120' to 130' C. in a Monel autoclave. This run resulted in a much darker resin product (18+ Cardner), and this deterred any further interest i s operation at temperatures above 110' c. Effect of Reaction Time at Different Formic Acid Concentrations. The formic acid-catalyzed reaction proceeds at a moderate rate at the preferred temperature of 105 ' C., generally requiring 2 hours or more to produce acceptable yields. Optimum reaction time is also a function of formic acid concentration (Table 111). With 77.5% formic acid (azeotropic composition with water) as catalyst, the reaction was very slow, giving only a 60% yield in G hours and 75% in 12 hours. T h e product obtained
4 HRS.
99% AC1D-r
'12
'2 HRS. ACID CATALYST
REACTION TEMP,,
OC.
Figure 3. Temperatures of 100" to 110' C. give highest yields of resin from methylnaphthalenes and paraformaldehyde VOL. W , NO. 10
OCTOBER 1959
1277
with the 37.595 acid was a soft, low molecular weight material (I, Figure 2). Molecular weight and other properties were not changed by prolonging the reaction for 6 or 12 hours from 2 hours. IVith 90% formic acid, a 6-hour reaction time yielded %yoresin. -411additional 6 hours of reaction time gave only a 370 increase in yield and did not appreciably increase the molecular ireight or softening point. Ho\ve\rer. with 99yG ortnic acid as catalyst. a 98Yc yield was obtained in 4 hours' reaction time. Moreover: the product obtained with this concentrated acid had a much higher softening point (223" F.) and molecular weight. Thus, properties and molecular Lveight of the resin product are primarily determined by strength of the formic acid catalyst, whereas resin yield is a function of reaction time and temperature. as well as formic acid concentration. The relation of resin structure and molecular weight as a function of formic acid concentration, at 3.5 to 1 acid to hydrocarbon ratio. is summarized in Figure 2. .Addition of acetic anhydride to 90% formic acid catalyst. in a mole ratio of about 1 to 9, reduced the required reaction time by about one half for a given yield and produced a resin of higher softening point. An example of this is shown in Table I11 (a 3-hour run) for comparison with the 6-hour run \vith straight 9070 acid. T h e rpaction of acctic anhydride with water formed or present in the reaction mixture. probably accounts for its effectivencss. Formic Acid Recycle a n d Recovery.
As shown, the reaction of aromatic hydrocarbons with formaldehyde is dependent on both formic acid concrntration and ratio of formic acid to aromatic ernployed. Because \vater is a by-producr of the condensation reacrion and formic acid is diluted as the reaction proceeds. bvater must be removed from formic acid to maintain its effectiveness if i t is to be recycled. The number of acid recycles depends on initial ratio of formic acid to aromatic, initial concentration of formic acid, and properties desired in the reaction product. To demonstrate the feasibility of catalyst recycle, reaction of the 235' to 290" C. boiling range methylnaphthalene concentrz-te and formaldehyde \vas satisfactorily carried through five recyclrs of acid, using a n initial ratio of 907, formic acid to aromatic of 4 to 1. Yields of resin in excess of 9056 (Lvt.) \ v e x obtained in all runs. but the softening point gradually declined to a level of 150' F. in the last run. \t'hen high softening point resins (i,e.>200' F.) arc required acid concentration is more critical, and it is necessary to start rvith 9970 formic acid and reconcentrate the acid when water content reaches a level of about 5 to 67,. Pure formic acid boils a t 100.8" C.
1 278
Table 111.
99% Formic Acid Gives Nearly Quantitative Yields of Resin in 4-Hour Reaction Time"
l h i n Prouertk ~~
Reaction Time, Hr.
Formic Acid rotirii., %
l h i n Yield, Yt. %
2
77.5 77.5 77.5
45
6 12 2 12 3
90 90 90 90
4
99
* Reaction
trinli.. I E J ~C'.
6
~~~~~~~~
iofteiiiiig ~loillt,
Gardtier eolor
~
Xf Airirricsn Chemical Society, \Vashington D. C . , .4d/.once~ in Chem. Ser. So. 6 , 6 (1952). 2 ) Badertscher, D. 1:. (to Socony-\-aciium Oil C:o.):U. S. Patent 2,397,398 (Ifarch 26. 1946). 3 1 Fidton. S . C:. (to Standard Oil I k \clrpmrnt C'o. I , Ihid.. 2,035,123 [ l f a r c l i 24. 1936). A . H. ( t o Standard O i l Ikvclopment C'o.1. Ihid., 2,216,941( O c t . 8: 1940H: IND. LNG. C m b t . 52, N 6
1 4 ) Glrasun.
(19.101. 1 5 I Kirk, I
