Polymerized Rosin. A Continuous Method Bernard A. Parkin, Jr., and Walter H. Schuller* Naval Stores Laboratory, Southern Region-FloridalAntilles
Area, ARS, USDA, Olustee, Flu. 32072
The separation of a polymer-rich phase from a solution of rosin in acetic acid-aqueous sulfuric acid was investigated and the basis for a continuous process to produce polymerized rosin (mainly dimerized) was developed. Polymerized rosin containing 30-5070 polymer, depending on the abietic-type acid content of the starting rosin, was produced. Decarboxylation was low and the ratio of weights of rosin to 70% sulfuric acid was about 9:1. A rapid, convenient method of gas-liquid chromatographic analysis of the methyl esters of the monomeric and dimeric species was found using Dexsil 300 gc columns with temperature programing from 160 to 430".Softening points of the resins were 101-1 06". The softening point of the glyceryl ester was 1 1 1 ",
I n previous investigations in this laboratory (Parkin and Schuller, 1972) of catalyst-solvent systems for t'he dimerization of rosin acids, a polymer-rich phase separabed from a solution of abietic acid, acetic acid, and aqueous sulfuric acid. I n this system, the presence of limited amounts of water gave higher conversion to polymeric materials than 100% sulfuric acid catalyst. Using pure abietic acid (the polymerizing component of rosin), opt'imum conversion to polymer occurred o when sufficient water was present to dilute the 1 0 0 ~ HzS04 catalyst to about 86%. ProducC phase separation was first observed when the water was sufficient to dilut'e the catalyst to
80% HzS04. The factors affecting this phase Separation were investigated with the objective of developing a basis for a continuous process for the production of polymerized rosin. When suitable conditions were established, a cont,inuous laboratory reactor was constructed. Inconsistent analytical results with the gas-liquid chromatographic (glc) method previously described prompted development of a method which gave excellent results. Experimental Section
Apparatus. T h e react'or was constructed from a 2-1. flask as shown in Figure 1. T h e addition rate of the 6-%mesh granular rosin was controlled b y the vibrator (B) and percentage times (C) . T h e capacitive-type controller ( H ) was of the type having a separate sensing head (G). The clips on the sensor were extended to give a greater sensing area and thus greater sensit'ivity. T h e circulation rate through t h e side a r m was determined by t h e speed of the stirrer which acted as a pump. The entire apparatus was blanket'ed with COn to reduce air contact. Procedure. Initially, t'he reactor was charged with 2 1. of solvent, prepared b y mixing 5 1. of glacial acetic acid and 250 ml of aqueous &So4 (70% b y weight), and about 200 g of rosin. T h e reaction mixture was heated and stirred slowly until product phase began t o appear. T h e stirring rate was increased uiitil circulation through the side a r m throughly mixed the reactor contents and then was reduced to give circulation through t h e side a r m a t a rate
* To whom correspondence should be addressed at the Agricultural Research Service, U. S. Department of Agriculture, ARC-W, Beltsville, RId. 20705. 238 Ind. Eng.
Chem. Prod. Res. Develop., Vol. 12, No. 3, 1 9 7 3
which permitted the product phase to separate. Product phase was allowed to collect until the interface reached the set point and the solvent addition system was activated to maintain that level. If sufficient product phase did not collect, rosin addition was started. When sufficient product phase to give outflow was produced from the initial rosin charged, rosin addition was started after the solvent-addition system was activated. After all systems mere operating, the product phase collected in the side arm uiitil it overflowed to a receiver. The product was isolated by one of two procedures. For a completely continuous process the product phase was collected, the small amount of dissolved strong acid (mainly sulfuric) was neutralized with sodium hydroxide (3-6 Y) or sodium acetate in acetic acid, and the acetic acid was fractionally distilled and returned to the process. The resinous product remaining was dissolved in a limited amount of isooctane and filtered to remore sodium sulfate. The filtered solution could, at this point, be evaporated to recover a crude polymerized rosin containing polymerized rosin and unreacted rosin acids and the less isooctane-soluble materials. Alternatively, and more conveniently, in the laboratory, the product phase from the reactor was diluted with a limited amount of isooctane or other water-immiscible solvent and the sulfuric and acetic acids were washed out with water until the wash water reached pH 5 . The solvent then was distilled to yield a crude product with essentially the same composition as that from the distillation procedure. With either procedure, the product was refined by diluting the isooctane solution to 10% resin with isooctane and filtering to remove the insoluble materials which are probably oxygenated and sulfonated rosin derivatives. This procedure generally improved color and changed acid number and reduced the softening point slightly. Further improvement in color was obtained by passing the 10% solutions slowly through Fuller's earth (2 g of 200-mesh Fuller's earth to 1 g of resin) and washing through with a n equal volume of isooctane. Analytical Method. Previously, dimer content of the polymerized rosin samples was determined by the method of Sinclair, et al. (1970). We found t h a t , under some conditions, t h e glc samples of the products were not completely volatile and t o obtain meaningful quantitative d a t a a n internal standard was necessary. T o obtain t h e polymer response factor, it was necessary to isolate a material t h a t
Figure 1. Continuous reactor for rosin polymerization: A, rosin hopper; B, vibrator; C, percentage times; D, temperature controller; E, temperature controller sensing head; F, head lamp; G, solvent level sensing head; H, solvent level controller; I, solenoid valve; J, solvent reservior
was representative of t h e dimer or polymerized rosin observed in t h e glc analyses. Pure materials could not be collected from the SE 52 column previously used. -1 new column, Dexsil 300 gc 10% on Chromosorb IT K h n ' , was selected. -4 460-mm x 3.0-mm i.d. columii separated tlie monomer and dimer methyl esters so that dotriacontane could be used as a n internal standard. Polymer materials collected from the Dexsil column gave a response factor of 1.48 relative to dotriacontane, \T hile abietic, dehydroabietic, and pimaric acid esters gave values close to and averaging 1.10 as defined by eq 1. TT', is the weight of ester of interest in the sample, A,
is the area of the curve attributed to the ester of interest, TT-, is the weight of the internal standard in the sample, A , is the area attributed to the standard, and K is tlie relative response factor of the ester of interest. The Dessil column described separated the groups of materials in about 20 min when operated with ai1 injection port temperature of 320-330", 175-200 mlimiii of helium with temperature programing from 160 to 430" at' 25":'min. A thermal conductivity detector operating a t 330" and 160 mX was used. -4s shown in Figure 2 , the curves resembled that of Sinelair, et al. (197O), with the dotriacoiitaiie eluting between the monomer and dimer regions. Acid numbers (-1s) were determined as described by Parkin, et al. (1969). Ball a i d shouldered ring softening points were run in glycerol (ASTM, 1958). Color grades were determined by comparison of standard 7/8-i~1. blocks with LXD.1 rosin color standards. Results and Discussion
Since rosin is the starting material in this study, conditions were adjusted to accommodate its properties. Tall oil rosin, with a n abietic-type acid content lower than that of either gum or wood rosin, produces less polymer. With tall oil rosin as the starting material, phase separation was achieved
Figure 2. Gas-liquid chromatogram of polymerized rosin with dotriacontane internal standard: A, monomeric materials; B, dotriacontane; C, dimeric materials
Y
a
Figure 3. Per cent of available abietic-type acids converted to polymer at various feed rates using gum rosin
readily using iOYOaqueous sulfuric acid catalyst. To avoid esceptionally long reaction periods using 70% sulfuric acid, the reaction temperature was increased from 28" (room temperature) to 70-80". Sulfur dioxide evolution iiidicated some reduction of the sulfuric acid a t 80"; most run.;, t,herefore, were made a t 70". Rosin was added to the reaction as a solid atid acetic acid70% sulfuric acid was added as a solution of fixed ratio (1 m l of iOYOsulfuric to 20 ml of acetic acid). Product phase was collected as it formed and solvent' phase was removed as required to maintain the reaction. The product was isolated from the product phase and the acetic acid returned to the reaction. The behavior of this multicomponent system arid the reactor are the basis of the continuous method. The ultimate polymer content of the product depends upon the abietic-type acid content of the starting rosin. At a given temperature, in the continuous process, the degree of reaction also will depend upon t,he contact time which, in turn, depends upon the rosin feed rate. This latter dependence results from the high degree of solubility of the starting rosin in the product phase. The relationship of rosin feed rate to product Ind. Eng. Chem. Prod. Res. Develop., Vol. 1 2 , No. 3, 1973
239
Table 1. Properties of Products Obtained from Continuous Process Utilizing Tall Oil Rosin Sample no.
Total wtf g
% solidsb
W t of net solids, g
70dimerC
AN
SPR~B
% gIc volatile
1 1236 49.5 611.8 42.2 152.0 105 2 2008 48.6 975.9 34.9 158.9 101 I 8 3 1454 50.5 734.3 34.6 156.0 102.4 4 1284 50.2 644.6 32.6 153.4 102,o 5 1251 51.0 637.5 31.3 l58,4 101.3 a Total weight of product phase collected. * Determined by isolation of product from aliquot of sample. c Per cent of total determined by glc analysis, i.e., both volatile and nonvolatile material.
89 90 85 88 87 sample as
Table II. Properties of Products Obtained b y Various Isolation Procedures from Dimerized Rosin Reaction Mixtures Color
w*
Washed D Distilled DC Black Isooctane JV E refined D E Fuller's earth F refined D G a Based on total weight of sample. W indicates product ization of catalyst.
w
AN
Softening point, OC
% recovery
158.9 37.3 86.4 101.3 100 153.1 31.2 72.5 101,5 100 159.2 36.6 91.9 100.4 96.5 l61,8 42.1 93.8 98.1 94 160.1 30.4 92.3 101.3 88 158.0 41.0 100.9 103.0 74 isolated by washing. c D indicates product isolated by distilling after neutral-
dimer content' for gum rosin is shown in Figure 3. The polymer formation rate depends on the abietic-type acid coiicentration, and, therefore, the abietic-type acid content of the feed roaiii will determine the range of feed rates usable. Tall oil rosin, having an abietic-type acid content of 36% (excluding dehydroabietic acid) , has given phase separation with i8% conversion a t a feed rate of about 10 g/hr. High feed rates were difficult to handle, because of problems with plugging of the inlet system, but rates as high as 400 g i h r of gum rosin (abietic type 60%) have given phase separation in the reactor described. Table I gives data on a typical run utilizing a tall oil rosin having a n abietic-type acid (excluding dehydroabietic acid) content of 44.17c. During this run, 3806.4 g of 1-0:'.111 n-as added aiid 3942 g of product was collected. The product figure was obtained by isolation of the resin from representat'ive samples of the product solution and experimental error here may account for a large part of the weight differences. The total product also includes 338, remaining in the reactor, which is not included in the table. Solvent added to the process totaled 6580.9 g (6088.9 g of acetic acid and 492 g of 70% sulfuric acid) for a weight ratio of 9.2: 1 for rosin to HzSO4. No solvent phase was withdrawn during this run but product collection became slow. Samples were collected a t 24-hr intervals so some variation in rate was apparent'. A run utilizing gum rosin, from which the data for Figure 1 were collected, was cont,inued a t 80". An addition rate of i0 g/hr \vas used for about 8 hr per day until 2847.6 g of product resin was obtained. This intermittent run and the restarting of the tall oil run described indicate the flexibility of the procedure. Shutdowns cause no problems and if reaction ceases, i t is only necessary to reestablish active catalyst in the reactor to continue. Table I1 compares the products of different isolation procedures using a product' phase obtained from tall oil rosin. The products differed principally in color when isolated either by washing out or by distillation of the solvent. Small loss of material was noted with isooctane dissolution to 107, solids
240 Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 3, 1973
% glc volatile
% dimern
and filtering. Passing the loyo solutioii through a Fuller's earth column further improved color but considerable material was lost. Heat bleaching at' 2i5O for a few minutes reduced color by about two grades. Softening point,s also dropped 2-3". The product from the gum rosin run (2547.6 g) \yas isolated by the washing technique and then purified by dissolution in isooctane. The isooctane solution yielded 2322 g or resin: color grade, I-H; S P R ~ B106.6; , AX, 141. Chromatographic analysis indicated 45% u-as dimer and 95% was volatile material. Heating the product n-ith 10% molar excess of glycerol a t 275" for 4-5 hr gave the glyceryl ester: color, E(;S P R ~ B111.5; , AN, 10.2. The isooctane-insoluble material (225.3 g) was obtained as a tan powder that melted, with frothing, to a very dark resin a t l i 0 " : -11, 141; mol wt, 564. Conclusions
The work described is iiot inteiided as a process study but as a basis for a cont,inuous process. Distillation of the acetic
acid, after iieutralization of the sulfuric acid with sodium acetate in acetic acid, allows direct recycle of the solvent. Xcetic acid solutions of abietic acid have shown less deterioration of the abietic acid than hydrocarbon solutiolis stored for comparable periods. These factors, coupled with the low sulfuric acid requirement of this method, favor its consideration as a commercial process. The Dessil 300 gc column effectively separated t,he met'hyl esters of the monomeric and dimeric rosin acids. literature Cited
ASTM Report E28-68TJ American Society for Testing Materials, Philadelphia, Pa., 1968. Parkin, B. A,, Jr., Schuller, W.H., I n d . Eng. Chem., Prod. Res. Develop., 11, 166 (1972). Parkin. B. A.. Jr.. Schuller. W. H.. Lawrence, R. V., ibid.., 8,. 304 (1969). Sinclair, It. G., Berry, D. A., Schuller, W. H., Lawrence, R. V., ibid., 9, 60 (1970). I
,
RECEIVED for review March 19, 1973 ACCEPTED June 4, 1973
