Ind. Eng. Chem. Prod. Res. Dev. 1986,
25,103-108
103
Isolation of Vanillin from Alkaline Oxidized Spent Sulfite Liquor Kaj G. Forss,' Esko 1.Taika, and Kaj-Erik Fremer The Finnish Pulp and Paper Research Institute, P.O. Box 136, SF-00 10 I Helsinki, Finland
A method is presented for isolating low-molar-mass aromatic compounds such as vanillin, acetovanillone, guaiacol, and p-hydroxybenzaldehyde,which are formed from lignin by alkaline air oxidation of spent sulfite liquor. The compounds are adsorbed on a strong cation-exchange resin in sodium form and then separated from other compounds of the oxidized spent sulfite liquor by elution with either water or a sodium carbonate solution.
Introduction Vanillin is produced mainly by oxidation of spent sulfite liquor, which is a byproduct of the sulfite wood pulping process. The dry solids content of spent sulfite liquor is usually 12-15%. Of the solutes 55-60% consists of lignosulfonates, 20-30% of monosaccharides, and the rest of salts of organic and inorganic acids. For oxidation, the liquor, which is often concentrated by evaporation, is made about 2 M in sodium hydroxide and oxidized by heating under air or oxygen pressure. In the oxidation process, other reaction products in addition to vanillin are formed such as oxidized lignin, acetovanillone, dehydrodivanillin, guaiacol, p hydroxybenzaldehyde, and aromatic acids. The isolation of vanillin from the oxidized solution is an important stage in vanillin production. One problem is that vanillin constitutes only about 5% of the solutes, and because of the high solids content the concentration of vanillin in solution cannot be significantly increased by evaporation. The vanillin is present as sodium vanillate, which is difficult to extract. Vanillin can be isolated from such a solution after acidification of the liquor and subsequent extraction with suitable solvents such as benzene or toluene (Hibbert and Tomlinson, 1937). However, owing to the high alkalinity, neutralization requires large amounts of acid, and precipitated lignin further complicates the extraction and causes loss of vanillin. In another process, lignin precipitation is avoided by extraction of sodium vanillate from the alkaline solution, for instance with n-butyl alcohol or isopropyl alcohol (Sandborn et al., 1936; Bryan, 1956). A drawback of this process is the limited solubility of sodium vanillate in organic solvents. Craig and Logan (1971) used weak cation-exchange resins in acid form for vanillin isolation. If the alkaline solution is eluted through a column filled with such a resin, sodium vanillate and other phenolates are converted into the phenolic form. The weak cation-exchange resin is regenerated with acid sodium bisulfite sohtion. Ultrafiltration is used in one of the more recent vanillin production processes (Evju, 1979),whereby lignosulfonates are isolated from spent sulfite liquor. Vanillin is then produced from the lignosulfonate solution by the usual oxidation process. The disadvantages of the current processes are the requirement for large amounts of acids for neutralization prior to the extraction of vanillin and the ineffective extraction of sodium vanillate. In both cases the extraction takes place from large volumes of solution with low vanillin content but high dry-matter content. Furthermore, neutralization of the liquor causes precipitation of lignin ac0196-4321/86/1225-0103$01.50/0
companied by extraction difficulties and loss of vanillin. The process described here avoids these problems by adsorbing the sodium vanillate on a cation-exchange resin in sodium form. The elution of sodium vanillate from the column is performed after each adsorption phase by using either water or a sodium carbonate solution. The column maintains its sodium form and is thus immediately ready for a new adsorption phase without regeneration (Forss et al., 1981, 1984). Experimental Section Oxidation of Spent Sulfite Liquor. Spent sulfite liquor from the pulping of spruce wood (Piceu abies) yielding 52% unbleached pulp was used for preparation of vanillin. The spent liquor was neutralized to pH 7 with 2 M sodium hydroxide solution, whereupon the solution was evaporated to a volume with a dry solids content of 10%. One mole (40 g) of sodium hydroxide was added to 500 mL of this solution in a 1000-mL autoclave equipped with a magnetic stirrer and pressure valves for inlet and outlet of air. Copper sulfate, (CuS0,.5H20), 1.5 g, was added as a catalyst. The autoclave was heated for 3.5 h a t 160 "C. During the oxidation, air was added to the solution a t a rate of 0.5 L/min. After the oxidation, the solution was transferred to a flask and distilled water added to bring the solution volume to 500 mL. Determination of Vanillin and Other Oxidation Products. Vanillin and other oxidation products were determined by gas chromatography. The oxidized solution (25 mL) was neutralized with 2 M sulfuric acid and extracted with toluene for 24 h in a liquid-liquid extractor. The toluene extract was dried over sodium sulfate and then evaporated to dryness under reduced pressure. The residue was dissolved in 25 mL of methylene chloride containing 10 pg/mL of n-docosane as internal standard. Authentic compounds were used to determine the response factors of vanillin and the other compounds. The analyses were conducted with a Carlo Erba 2300 gas chromatograph equipped with a Carbowax-20M glass capillary column (13 m X 0.35 mm i.d.). Spectrophotometric Determination of Oxidation Products. Ultraviolet absorption spectra of vanillin, acetovanillone, and dehydrodivanillin dissolved in 0.1 M sodium hydroxide solution were run on a Beckman DK-2 spectrophotometer and the absorptivities uZfim and u348m (L-g-km-') were calculated. Fractionation on a Column Containing a CationExchange Resin. Reaction products in the oxidized spent sulfite liquor were separated from lignin and excess alkali by elution through a column with a diameter of 2 cm and a length of 40 cm filled with the strong cation-exchange 0 1986 American Chemical Society
104
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 1, 1986
Table I. Phenolic Compounds in the Oxidized Spent Sulfite Liauor ( d L ) vanillin 9.9 acetovanillone 0.6 guaiacol 0.1 0.1 p-hydroxybenzaldehyde Table 11. Absorptivities in 0.1 M Sodium Hydroxide Solution (L g-' cm-') absorptivity UV maxima ______ %snmI ~
oxidized lignin vanillin acetovanillone dehydrodivanillin
XI, nm
X P , nm
a348nm
a2mnm
a2mnm
248 247 258
348 343 359
175.2 125.5 130.8
12.0 15.8 31.9
0.7 - 1 14.6 7.9 4.1
resin Dowex-50 W, X-2, 200-400 mesh, in its sodium form. The eluent was distilled water, and the flow rate was adjusted by a peristaltic pump to 6.7 mL-h-1.cm-2. The volumes of the samples were 2,4,8,16,32 and 64 mL. The effluent was collected as 4-mL fractions. In the effluent range of the oxidized products the fractions were taken at 2 mL intervals. The size of the fractions was determined by weighing. The absorbances A280nmand A348nmof the fractions were determined with a Zeiss PMQ I1 spectrophotometer and the sodium content with a Perkin-Elmer 303 atomic absorption spectrophotometer. A preparative experiment was conducted using a column with a diameter of 4 cm and a length of 190 cm. The column was filled with the cation-exchange resin Dowex-50 W, X-8, 200-400 mesh, in its sodium form. The sample was 800 mL of oxidized solution. The eluent was distilled water with a flow rate of 4.8 mL.h-1.cm-2. The size of the fractions collected was 40 mL. The following analyses of the fractions were carried out: A280nm,ASdanm,sodium content, density, dry-matter content, consumption of sulfuric acid on neutralization to pH 7 , and amounts of vanillin, acetovanillone, guaiacol, and p-hydroxybenzaldehyde. Fractionation experiments using 0.25,1, and 2 M sodium carbonate solutions as eluents were also performed. The length of the column was 25 cm; other properties were the same as in water elution. The flow rate of the eluent was 6.4 mL.h-1,cm-2. The ultraviolet absorbances &on,,, and A348nmand the sodium contents were measured. Results and Discussion Analysis of Oxidation Products in the Oxidized Spent Sulfite Liquor. The amounts of vanillin, acetovanillone, guaiacol, and p-hydroxybenzaldehyde in the oxidized alkaline spent sulfite liquor were analyzed by gas chromatography (Table I). Table I1 shows that in 0.1 M sodium hydroxide solution the absorptivity of vanillin is 14.6 times greater at wavelength 348 nm than at wavelength 280 nm. For the oxidized lignin, the ratio AW,/Azaonm is only 0.7-1. By measuring the absorbances a t both wavelengths, it is thus possible to estimate the amount of vanillin even in the presence of small amounts of oxidized lignin and the other oxidation products. Separation of Vanillin and Other Oxidation Products from Oxidized Lignin. It was found that eluting the strongly alkaline-oxidized spent sulfite liquor with water through a cation-exchange column filled with resin in sodium form gave good separation of vanillin and other oxidation products from the oxidized lignin. In order to evaluate the influence of the sample volume on the separation, 2-64 mL of the oxidized solution containing 9.9 g/L of vanillin (Table I) was eluted with distilled water through a cation-exchange column with resin
Table 111. Distribution of Oxidized Lignin and Sodium Salts between Fractions A and B in Figures 1 and 4 (Percent of Total) lignin AzSonm sodium sample, mL A B A B 2 96.2 3.8 68.5 31.5 4 89.3 10.7 62.1 37.9 8 82.8 17.2 60.5 39.5 16 77.8 22.2 60.2 39.8 32 78.5 21.5 64" (64.1) (35.9) (57.8) (42.2) 800 74.6 25.4 66.8 33.2 'Overloaded column; see Figure 2.
Table IV. Separation of Sodium Vanillate from Alkaline Oxidized Spent Sulfite Liquor on Cation-Exchange Resins in Sodium Form vanillin separation resin type capacity" Dowex-50 W, X-2 strong 30 Dowex-50 W; X-8 strong 31 Dowex-50 W, X-12 strong 13 n Dowex-50 W, X-16 strong Amberlite-200 strong, macroreticular 13 Bio-Rad AG-MP-50 strong, macroreticular 11 Amberlite CG-50 weak 11 Maximum sample volume, percent of resin bed.
in sodium form (length 40 cm, diameter 2 cm), Figure 1. In Figure 1,most of the oxidized lignin was eluted within elution range A, whereas the oxidation products (vanillin, acetovanillone, etc.) were eluted within solution range B. The overlapping increased with increasing sample volume. Distribution of Oxidized Lignin between Fractions A and B. Figure 2 shows that the area under the AZmnm curve in fraction B increases linearly up to a sample volume of about 30% of the resin bed, i.e., 40 mL. With a sample volume of 51% of the resin bed (Figure 1, bottom right) the column was overloaded, and fraction B contained much lignin. According to Table I11 (based on Figure 1 and considering the ratios A3&,m/A28(,nmin Table 111, about 78% of the lignin was found in fraction A and 22% in fraction B at a sample volume of 32 mL. The neutralization of fraction B did not cause any precipitation of lignin. Table IV shows that the resins Dowex-50 W X2 and X8 had the largest vanillin separation capacity of the seven resins studied. Separation of Sodium Salts. As mentioned earlier, neutralization of the oxidized liquor before extraction requires large amounts of acid. As can be seen from the sodium curves in Figure 1 and from the distribution of sodium between fractions A and B in Table 111, more than 60% of the sodium contained in the original sample was eluted together with the oxidized lignin and could easily be returned without any neutralization for recovery of chemicals. Dilution Caused by the Column Operation. The dilution of the original sample in the column during elution is shown in Table V. On elution of large samples, owing to fractionation of the polydisperse lignin, the volume of lignin fraction (A) was 1.6 times the sample volume but the oxidized products (B) were eluted without significant dilution. Influence of Sample Volume on Vanillin Yield. Table VI shows the yield of vanillin on elution with water. With small samples, about 75% of the vanillin in the original sample was detected in the effluent. On eluting large samples, about 95% of the vanillin was recovered.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 1, 1986
I
ABSORBANCE
ABSORBANCE 1000-
-
105
Na(gll)
Azsonm
.A
34anm
500-
0 25
'Oo0
A - 50
+0 ELUTION 4 7 5
VOLUME
2000 -
t
1000 -
- 30 20
- 10 0 E L U T I O N V O L U M E (ml)
8 -
(ml I
VOLUME
Figure 1. Fractionation of oxidized spent sulfite liquor. Column Dowex-50W, X-2,200-400 mesh, Na+, (40 cm X 2 cm); eluent water: (top left) 2-mL sample; (top right) 4-mL sample; (middle left) 8-mL sample; (middle right) 16-mL sample; (bottom left) 32-mL sample; (bottom right) 64-mL sample. Table V. Influence of Sample Volume on Elution Volume of Lignin and Oxidation Products" sample, mL sample, % of resin bed lignin fraction (A), mL A/sample oxidation products (B), mL 8 30 15.0 2 1.6 13 4 3.2 32 8.0 16 8 6.4 39 4.9 21 16 12.7 46 2.9 38 32 25.5 61 1.9 800 33.5 1250 1.6 800
B/sample 4.0 3.3 2.0 1.3 1.2 1.0
"Figures 1 and 4.
Elution with Sodium Carbonate Solutions. In order to study the influence of eluent composition on the separation of lignin and the reaction products, experiments were conducted in which sodium carbonate solutions were used as eluents. The result presented in Figure 3 (top left), obtained when 4 mL of the oxidized solution was eluted with 0.25 M sodium carbonate solution through a column 25 cm long, is little different from the result obtained on elution with water (Figure 1,top right). The volumes of fractions A are approximately equal in these figures, al-
Table VI. vanillin Yield" sample, vanillin % of sample, mL resin bed out, mg in, mg 2 1.6 14.5 19.8 39.6 30.3 4 3.2 67.9 79.2 6.4 8 16 12.7 158.4 151.1 32 25.5 316.8 300.8 16.7 x 103 800 33.5 17.6 x 103 "Figures l and 4.
yield, % 73.2 76.5 85.7 95.4 95.0 94.9
106
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 1, 1986 LIGNIN IN FRACTION 8'
50k
LO-
Figure 2. Determination of the vanillin separation capacity of the cation-exchange resins Dowex-50 W X-2 and X-8 Na+, 200-400 mesh. *Lignin = the area under the AZmnmcurve in fraction B (A280nm.L), corrected for the contribution of vanillin with the aid of the A348nm/A280nm ratio, Table 11.
though the column was shorter in the latter case. Because of the influence of the sodium carbonate, the peak of the oxidized products moved to a later elution volume and the volume of fraction B was larger than on elution with water. An increase of the sodium carbonate concentration in the eluent from 0.25 to 1 M had no effect on the elution volume of lignin in fraction A (Figure 3, top right). The oxidation products, in contrast, moved slowly in the column, and the elution was therefore continued with distilled water. The elution resulted in a 40-mL separation between the lignin fraction A and the oxidation products B. The latter were partially separated from each other. When 40 mL of the oxidized spent sulfite liquor was eluted with 1 M sodium carbonate solution the oxidation products (B) did not separate from the lignin fraction (A)
completely (Figure 3, bottom left), but separation was at least as good as on elution with water (Figure 1, bottom left) in spite of the shorter column. Some of the oxidation products were separated from the main part and could be eluted with water. The dilution of the sample was greater than when eluted with water. Thus the volume of both the A and B fractions was double that of the original sample. On elution of 40 mL of the oxidized spent sulfite liquor with a 2 M sodium carbonate solution (Figure 3, bottom right), no significant changes were detected in the elution of the lignin fraction (A) compared with Figure 3 (bottom left), but the oxidation products were very slowly eluted and the volume of fraction B increased considerably. The column became clean only after the water elution subsequent to the carbonate elution. From Figure 3 it can be concluded that sodium carbonate only slightly influences the elution of lignin, but it increases the adsorption of the oxidation products. Fractionation by Water Elution through a Preparative Column. In addition to the fractionations by water elution through the 40-cm column, 800 mL of oxidized spent sulfite liquor was eluted through a column 190 cm long and 4 cm in diameter. The sample volume was thus 33.5% of the resin bed. The solids content of the sample used in this experiment was 452 g/L, its pH was 13.8, and its sodium content was 110.8 g/L. According to a gas chromatographic analysis, the sample contained 22.0 g/L of vanillin, 0.5 g/L of acetovanillone, 0.3 g/L of guaiacol, and 0.2 g/L of p-hydroxybenzaldehyde. Figure 4 shows that the oxidation products as determined by gas chromatography were eluted as well-defined peaks within 800 mL (fraction B), i.e., the same volume as that of the original sample. Integration of the areas under the elution curves showed that they corresponded to 95% of the vanillin, 100% of the acetovanillone, 100% I
I
ABSORBANCE
~
600
1-
I
---=
-
A280nm A348nm
400 -
OXIDATION PRODUCTS
I \
LIGNIN WATER
200
0-
1
I
125 1 ELCTION VOLUME'(m1)
-
ABSORBANCE
ABSORBANCE ~
I
3000r
PRODUCTS
WATER
4
A,..
I \
ELUTION VOLUME
(mil
100 1
200
300
I
42
Figure 3. Fractionation of oxidized spent sulfite liquor. Column Dowex-BO W, X-2, 200-400 mesh, Na+, (25 cm X 2 cm): (top left) 4-mL sample, eluent 0.25 M sodium carbonate solution; (top right) 4-mL sample, eluent 1 M sodium carbonate solution; (bottom left) 40-mL sample, eluent 1 M sodium carbonate solution; (bottom right) 40-mL sample, eluent 2 M sodium carbonate solution.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 25, No. 1, 1986 107
1.
4
ELUTION
Figure 4. Fractionation of oxidized spent liquor. Column Dowex-50 W, X-8, Na+, 200-400 mesh, (190 cm mL. V = vanillin, AV = acetovanillone, G = guaiacol, p-HB = p-hydroxybenzaldehyde. Table VII. Comparison between Oxidized Spent Liquor and Fraction C oxidized spent sulfite fraction C liquor volume, mL 800 540 137 452 dry-matter content, g/L 100 20.5 dry matter, % of total 22.0 29.2 vanillin, g/L 21.3 4.9 vanillin, % of dry matter 16.4 100 lignin, % of total 29.4 110.8 sodium, g/L 17.9 100 sodium, % of total 87.2 16.8 neutralization, g of H2S04 5.0 1.1 neutralization, kg of H2S0,/kg of vanillin
of the guaiacol, and 60% of the p-hydroxybenzaldehyde in the original sample. In Figure 4, effluent fraction C contains 95% of the eluted vanillin. At the elution volume of 2350 mL the vanillin concentration was 50 g/L, i.e., more than twice the vanillin concentration of the sample. Consequently, the vanillin concentration of the combined effluent fraction C is one third larger than the original concentration, as revealed by Table VII. It can be seen that fraction C contained only 20.5% of the dry matter in the sample. Thus the proportion of vanillin in the dry matter was increased by a factor of 4.3 to 21.3%. In the top fractions near the elution volume of 2350 mL, this proportion is about 40%. The dry-matter content of fraction C (137 g/L) was only 30.3% of the original. Provided that column fractionation is followed by extraction of vanillin and that this operation can be successfully carried out at a dry-matter content of 450 g/L, this means that fraction C can be evaporated to 160 mL or one fifth of the original volume before the extraction. Vanillin is much easier to extract from a neutral solution than from an alkaline solution. The neutralization of
X 4
VOLUME
cm); eluent water; sample 800
fraction C required only 22% of the sulfuric acid required for neutralization of the original liquor. The amount of sulfuric acid needed was 1.1kg/kg of vanillin in solution.
Conclusions The observations described show that a strong cationexchange resin in sodium form adsorbs vanillin, acetovanillone, guaiacol, and p-hydroxybenzaldehyde from an oxidized, strongly alkaline spent sulfite liquor. On elution these oxidation products are well separated from lignin and excess alkali. The adsorbed compounds can be eluted from the columns with either water or a sodium carbonate solution. These experiments describe the principle of the separation. Optimization would naturally have to be performed on a large scale with the oxidized spent sulfite liquors actually used in vanillin production. When carried out between the oxidation and extraction phases in the production process of vanillin, the method described offers the following advantages: (1)About 80% of the lignin, sodium, and dry matter can be separated from the vanillin-containing fraction, the dry-matter content of which is thus enriched with respect to vanillin. (2) The volume of the vanillin fraction to be extracted is less than that of the original solution, and because of its low dry-matter content it can be reduced further by evaporation, thus facilitating the subsequent extraction of vanillin. (3) The quantity of acid needed to neutralize the vanillin fraction is small compared with the quantity needed for the oxidized spent sulfite liquor. (4) There is no precipitation of lignin during the neutralization to cause extraction difficulties and loss of vanillin. (5) Equipment costs are low, and no equipment working under pressure is needed. (6) The ion-exchange resin does not need to be regenerated.
Ind. Eng. Chem. Prod. Res. Dev. 1986, 25, 108-111
108
Dowex-50W x12, 9056-03-5;Dowex-50w ~16,9057-28-7; Amberlite-200, 12626-25-+ Bio .Rad AG-MP-50,55576-80-2;Amberlite CG-50, 9042-11-9; sodium carbonate, 497-19-8. Literature Cited
(7) Only water is needed to elute the sodium vanillate from the column. (8) About 80% of the lignin and alkali can be returned without neutralization into the chemical recovery of the pulp mill. Acknowledgment
Bryan, C. C. Can. Patent 528837, 1956. Craig, D.; Logan, C. D. Pulp Pap. 1971, 4 5 , 137. Evju, H. U.S. Patent 4 151 207, 1979. Forss. K. G.; Talka, E. T.; Fremer, K.-E. US. Patent 4277626, 1981. Forss, K. G.; Talka, E. T.; Fremer, K.-E. Can. Patent 1169093, 1984. Hibbert, H.;Tomlinson. G., Jr. U.S. Patent 2069 185, 1937. Sandborn, L. R.; Salvesen, J. R.; Howard, G. C. U.S.Patent 2057 117, 1936.
The financial support of the Foundation for Research into Natural Resources of Finland and of the Foundation of Finnish Inventions is gratefully acknowledged. Registry No. V, 121-33-5;AV, 498-02-2;G, 90-05-1;p-HB, 123-08-0;dehydrodivanillin, 2092-49-1; sodium vanillate, 2850848-7: 13owex-50W x2, 12612-37-2; Dowex-50W x8, 11119-67-8;
Received for review October 31, 1984 Revised manuscript received March 19, 1985 Accepted September 3, 1985
Polysaccharide Suspending Agents for Fertilizers Containing Paraquat George T. Colegrove Division of Merck & Co., Inc., San Diego, California 92123
Xanthan gum and polysaccharide 5-194 can be used in suspension fertilizers containing paraquat without inactivating the herbicide. Both field and laboratory data indicate no interaction at normal application rates in contrast to attapulgite clay, which inactivates the paraquat to a degree that depends on the clay concentration. Both gums can be used in suspensions based on ammonium polyphosphate or monoammonium phosphate within the limits of compatibility with these materials. A dispersible xanthan gum is particularly useful for this application.
According to a survey released early in 1984 by the Conservation Tillage Information Center, over 87 million acres of cropland were planted in some form of conservation tillage-over 31% of the total 1983 cropland, which represented a rise of 7 % over the 1982 planting figure. Slightly more than 10 million acres were no-till. These figures show the increasing importance of conservation tillage practices by US. farmers to whom the benefits are well-known for controlling soil erosion. In no-till farming particularly, there is a need to use a contact herbicide to burn down existing vegetation at planting time. Paraquat is one of the most commonly used herbicides for this purpose for several reasons: it is nonvolatile and water soluble for easy mixing and spraying; it does not leave a biologically active residue that could interfere with the crop; it is fast acting; it works over a wide range of temperatures; and it is quickly absorbed into plant tissue before rain can wash it off. One of the most attractive features is deactivation of paraquat by soil minerals to prevent any residual effects. A number of research papers can be found in the literature regarding the interaction with soils. All of them indicate that most of the adsorption occurs on clay minerals, although some organic substances are also able to tie up some paraquat. Deactivation of paraquat by clay minerals has been shown to be related to the cation-exchange capacity of the clay and what is sometimes called the strong adsorption capacity. For clays such as kaolinite, the adsorption is rather low, on the order of 2.5-3.0 mg/g, while on the montmorillonite type of clay the adsorption is more significant, Le., 75-85 mg/g. X-ray analysis has shown that paraquat is bound within the interlayer spacings of the montniorillonite by van der Waal forces and Coulombic 0196-4321/86/1225-0108$01.50/0
attraction, while for kaolinite adsorption occurs on the external faces and edges (Summers, 1980). This adsorption presents a problem in suspension fertilizers where attapulgite and bentonite clays are almost universally used as the suspending agent because any paraquat added to the tank mix will be at least partially deactivated by the clay and lose its effectiveness. This deactivation occurs despite the presence of high concentrations of soluble salts. Other studies have shown that in the presence of either ammonium or calcium cations, paraquat is still preferentially adsorbed by the clay. In order to prevent loss of paraquat it therefore becomes necessary to apply fertilizers and paraquat in separate operations or use a low analysis clear solution fertilizer with the paraquat. Time, energy, and labor costs are therefore increased when these procedures are used. There is an alternative process to circumvent this problem. Two polysaccharide suspending agents can be used to produce suspension fertilizers containing paraquat which is not inactivated in the process. These are xanthan gum and polysaccharide S-194, which will be described in this paper. Both polysaccharides, or gums as they are commonly called, are produced by bacterial fermentation of two different organisms. Xanthan gum is produced by Xanthomonas campestris and has been used in industrial suspensions for about 20 years. S-194 was first described at the ACS Convention in Las Vegas in 1982 and is produced by a species of Alcaligenes. The structure of xanthan gum is well-known, as shown in Figure 1, and comprises a repeating unit containing glucose, mannose, and glucuronic acid with acetyl and pyruvate substituents. The complete structure of S-194 has not been determined but C
1986 American Chemical Society
