306
Ind. Eng. Chem. Prod. Res. Dev. 1985,2 4 , 306-313
Schlosberg, R . H.; Ashe, T. R.; Pancirov, R. J.; Donaklson, M. Fuel. 1981, 60, 155. Simmons, M. B.; Klein, M. T. I n d . Eng. Chern. Fundam. 1985, 2 4 , 55. Townsend, S. H.; Klein, M. T. fuel 1984, in press. Virk, P. S. Fuel 1979, 58, 149. Whttehead, J. C.; Williams, D. J. J. Inst. Fuel. 1975, 82, 182.
Received for review SeDtember 7. 1984 ’Accepted December 17; 1984 We gratefully note the support of the (NO.DE-FG-22-82PC50799).
US.Department of Energy
Synthesis of Graft Copolymers from Lignin and 2-Propenamide and Applications of the Products to Drilling Muds John J. Melster’ and Damodar R. Pat11 Department of Chemistry, Southern Methodlst Univers& Dallas, Texas 75275
Harvey Channel1 Messina, Inc., Dallas. Texas 75204
Poly(1ignin-g-( l-amidoethylene)), previously made by reacting Kraft, pine lignin, and 2-propenamide, in oxygenbubbled, irradiated dioxane, can be prepared by combining lignin, 2-propenamide, calcium chloride, cerium (IV), and 1,4dioxane autoxidation products in such solvents as l-methyl-2-pyrrolidlnone, dimethyl sulfoxide, dimethylacetamide, dlmethylformamide, and pyridine. The product, a highly water-soluble brown solid containing 4 to 7 wt % lignin and 70+ wt % l-amidoethylene repeat units, is purifiable by precipitation in 2-propanone and dialysis against water through a 3500 molecular weight permeable membrane. Poly(lign1n-g+amidoethylene)) and its hydrolyzed derivative, poly(lignin-g-((l-amidoethylene)-co-(sodium l-carboxylatoethylene))),lower yield point, lower gel strength, and lower API filtrate volume in a bentonite drilling mud. After hot rolling at 121 O C for 16 h, the graft copolymer outperformed an equal concentration of chrome lignosulfonate when the compounds were tested as thinners or as filtrate control agents.
Introduction Since over 15 million tons of lignin is produced as waste from Kraft pulp mills in the United states alone (Goheen and Hoyt, 1981), there is a significant economic incentive to find uses for this biomass. One particularly versatile method for derivatizing lignin is to attach a polymeric side chain to the lignin molecule that will produce engineering, interfacial, or solubility properties in the resulting two-part molecule, a graft copolymer, that are needed in commercial products or processes. One method used in research to make these polymers is the irradiation of lignin slurries with y-or X-rays followed by polymerization of a vinyl monomer on the “activated” lignin (Koshijima et al., 1964a,b; Simionescu et al., 1975). This method is hard to control and produces large amounh of side chain ungrafted to lignin. Several chemical reagents have been used to graft side (Mikhailov and chains of 2-0xy-3-0~0-4-methylpent-4-ene Livshits, 1969) or prop-2-enoic acid (Krause et al., 1975), to lignin. These methods are more flexible and syntheti d l y productive, but they fail to produce a graft copolymer of lignin and 2-propenamide (Kobayashi et al., 1971; Phillips et al., 1973). Grafting 2-propenamide to lignin is chemically important because the structure and reactions of this natural product are a major and growing area of current research. It is commercially important because the graft copolymer should have properties which will make it useful in water purification, mineral benefication, and energy recovery. To meet these needs, a method has now been developed to chemically initiate free-radical polym0196-432118511224-0306$01.50/0
erization of 2-propenamide on Kraft pine lignin.
Experimental Section Materials. Lignin, which makes up the backbone of the graft copolymers, is a cross-linked, oxy[3-methoxyphenylenelpropylene polymer which acts as a binder in woody plants. Lignin used in these studies is a commercial product. The material is a Kraft pine lignin prepared in “free acid” form with a number average molecular weight of 9600 and a weight-average molecular weight of 22000. The ash content of the product is 1w t % or less. Kraft pine lignin is essentially insoluble in water at pH 7 but dissolves readily in aqueous solutions at a pH above 9. 2-Propenamide (common name: acrylamide), used in all reactions, was reagent grade monomer which was recrystallized from trichloromethane after hot filtration and dried under vacuum (P< 1mmHg) at room temperature for 24 h. 1,4Dioxane was stabilized reagent grade material which was freshly distilled before use. Calcium chloride and other salts used were reagent grade materials and were used as supplied. Gases used in the syntheses were standard commercial grade cylinder gases. The lignin-acrylamide reaction products were tested for effectiveness in a water-base mud containing 28 lb/bbl (ppb) of Wyoming bentonite and 40 ppb of Revdust, a commercial clay mixture used to represent solids generated by drilling. Methods. Two methods are now available to graft 2propenamide onto lignin. In the first method, autopho0 1985 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24,
tolysis products are formed in oxygen-bubbled l14-dioxane, and the reaction is then run in the irradiated dioxane. In the second method, oxidized 1,4-dioxane is vacuum distilled to separate 1,4-dioxaneand its autoxidation products. Autooxidation products are then used to initiate the grafting reaction in another solvent. Before preparing the graft-copolymer in 1,4-dioxane,the time required to product a maximum concentration of oxidizing agents in 1,Cdioxane must be determined by irradiating samples of dioxane with a 1000-W xenon lamp. A 20-mL aliquot of freshly distilled 1,4-dioxaneis placed in a 125-mL Pyrex Erlenmeyer flask and bubbled for 5 min. The sealed samples is mounted 2 to 4 cm from the lens face of a 1000-W xenon lamp and is stirred and photolyzed for a fixed time. The sample is then titrated by the iodine-thiosulfate method (Mair and Graupner, 1964), to determine the number of oxidizing equivalents produced by the irradiation. The duration of photolysis which produces the largest number of oxidizing equivalents in 1,Cdioxane is the optimum photolysis time. This is usually 2.5 to 3.5 h. 1,4-Dioxane is photolyzed for this length of time to produce solvent for one method of graft copolymer production. This method is as follows. Synthesis Method 1. An aliquot of 20 mL of distilled 1,4-dioxane is placed in a 125-mL conical flask, bubbled with oxygen for 5 min, and exposed to the output of a 1000-W xenon lamp for the optimum photolysis time. Samples undergoing photolysis are mounted 2 to 4 cm from the lens face of the lamp housing and are stirred continuously during irradiation. Lignin and finely ground anhydrous calcium chloride are added to the irradiated dioxane solvent and the mixture is stirred for 20 min. 2Propenamide is added while nitrogen gas is bubbled into the mixture. After 10 min, a volume of 0.05 M ceric sulfate in 1.0 M aqueous sulfuric acid is added, the flask is sealed under nitrogen, and the slurry is stirred for an additional 10 min. Thickening will start immediately. The flask contents will first clarify into a brown, homogeneous solution and then quickly solidfy into a precipitate-laden, viscous slurry. The reaction flask is placed in a 30 "C bath and allowed to sit for 2 days. The reaction is then terminated with 0.5 mL of 1% by weight hydroquinone in water. The reaction mixture is diluted with 100 mL of water and stirred until uniform. Reaction product is precipitated by adding the dilute reaction mixture drorwise to 1 L of 2-Propanone. The solid is recovered from l-propanone by filtration and dried under vacuum at 40 "C. Yield is calculated from the formula wt % yield = (g of polymer recovered)/(g of lignin added + g of 2-propenamide added) X 100 (1) Graft copolymer can also be produced by using the isolated autoxidation product of 1,4-dioxane as an initiator in another solvent. Autoxidation product is prepared (Gierer and Pettersson, 1968) by refluxing 250 mL of freshly distilled dioxane while bubbling the contents of the reflux vessel with air at a rate of 4.3 mL/s. Again, an optimum duration for this treatment must be determined by titrating aliquots refluxed and bubbled for different times to determine oxidizing agent concentration as a function of time. Optimum time is usually 12 to 14 h. After refluxing and aerating 1,4-dioxanefor the optimum time, unreacted dioxane is removed at 0.27 KPa nitrogen pressure and 23 "C temperature. The isolated white solid is stored at 4 OC in a refrigerator. Synthesis Method 2. The grafting reaction is run by adding lignin and calcium chloride to a nitrogen-flushed 125-mL flask containing 20 mL of solvent. The mixture
No. 2, 1985 307
is bubbled with nitrogen for 3 min, oxidation products of dioxane are added, and the flask contents are bubbled with nitrogen for an additional 2 min. Flask contents are stirred for 20 min and bubbled with nitrogen for 4 min. The 2-propenamide is then added, flask contents are bubbled with nitrogen for 10 min while being stirred, 0.15 mL of 0.05 M cerium(1V) sulfate in 1M aqueous H2S04is added, the sample is stirred and bubbled for an additional 10 min, and it is then capped with a septum stopper. After 2 days of storage in a 30 "C constant-temperature bath, the reaction is terminated and product recovered as previously described. Centrifugation was used to recover precipitates or remove incompletely dissolved material from polymer solutions. Samples were centrifuged in test tubes that had been dried to constant weight. Tubes were then dried under vacuum and the solids recovered from the centrifuged sample were determined by difference. Treatment of poly(1-amidoethylene) with aqueous sodium hydroxide produces a salt, poly(sodium 1carboxylatoethylene) [sodium polyacrylate] (-CHzCH-),
I
t nNa'
+
nOH-
-
/C=O NHz (-CHzCH),..-((CHzCH-),
I
c=o
I c=o
+
nNH3
(2)
When this reaction occurs on poly(1-amidoethylene) side chains of a graft copolymer, the copolymer is derivatized to a polyanionic terpolymer. The extent to which this hydrolysis reaction goes to completion is called percent hydrolysis and is calculated from 90 hydrolysis = av no. of neutralized acid groups on molecule/av no. of amide groups originally on molecule (3) Hydrolyzed samples are prepared as described in Meister et al. (1984). Poly(1-amidoethylene) homopolymer can be separated from graft copolymer by dissolving in aqueous base and dialyzing. This separation process also partially hydrolyzes the (l-amidoethylene). Homopolymer is separated from copolymer by preparing a 2.5 g/dL solution of reaction product in 0.5 M sodium hydroxide. The solution is stirred for 7 days, dialyzed using Spectrapor no. 2 tubing against water for 3 days, and dialyzed against 0.01 M hydrochloric acid for 3 days. Upon dialysis against 0.01 M hydrochloric acid, a precipitate forms inside the dialysis bag. This precipitate contains virtually all of the graft copolymer while the solution in the dialysis bag contains homopolymer from the reaction mixture. For additives tested for dri!ling mud applications, the concentration of reaction product in the base mud is fixed at 0.5 ppb. Reaction product is added to base mud that has been aged 24 h at room temperature to hydrate the clays. Sample viscosity at 4 shear rates, apparent viscosity, plastic viscosity, yield point, gel strength after 10 s and after 10 min of setting, and American Petroleum Institute (API) filtrate volume are then determined on the sample. The sample is hot-rolled in a pressurized bomb for 16 h at 1 2 1 "C to simulate exposure to well-bore conditions, after which the same series of tests are run on the hotrolled samples. Drilling mud tests were performed ac-
308
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 2, 1985
Table I. Yield and Limiting Viscosity Number for Lignin-(2-propenamide) Reactions" wt
g 3.36 3.64 2.88 2.57 2.22 1.80
wt %
4 5 6
anhyd CaCl, in reaction mixture, wt % 4.0 2.0 0.8 0.2 0.04 0.02
7'
2.2
1.5
sample no. 1 2 3
90.8 98.4 77.8 69.5 60.0 48.6
limitingb viscos no., dL/g 0.59 0.46 0.49 0.49 0.51 0.38
lignin 7.5 6.95 8.68 10.0 11.2 17.7
polymerized 2-propenamide 67.6 73.4 71.6 79.5 77.7 82.0
100.0
0.21
12.4
48.3
70
Ca before ashing 2.8 0.8 0.5
Ca after ashing 4.91 2.25 1.90 0.48 0 0 6.94
"All reaction mixtures contain 20.0 mL of oxygen-bubbled, irradiated dioxane, 0.5 g of lignin, and 0.15 mL of ceric sulfate solution. Reactions run in a Pyrex flask and contained l,4-dioxane irradiated for 3 h and 0.045 mol (3.2 g) of 2-propenamide. bDetermined in distilled water at 30 "C. 'Reaction run with 0.014 mol (1.0 g) of 2-propenamide.
cording to specifications with viscosity and gel strength performed according to section 2 and filtration tests performed according to section 3 of API Recommended Practice (1982). Analytical procedures used to characterize the reaction product and prove grafting are summarized in Meister et al. (1984). Calcium content of the reaction product is determined by atomic absorption spectroscopy. Between 0.3 and 0.5 g of reaction product, analytically weighed, is placed in a 125-mL Erlenmeyer and is heated to 400 "C for 24 h. Ash in the cooled sample is then dissolved by adding 100 mL of 1 M hydrochloric acid and boiling for 1 h. The resulting solution is diluted to 250 mL and its absorbance is measured a t 422.7 nm. Concentrations are measured from a calibration curve. Several reactions were used to test the distribution of products and reactants in the final reaction mixture. Components of the reaction mixture were quantified as follows. The reaction was run by use of method 1. After the reaction was terminated, the reaction mixture was diluted with 75 mL of water and added dropwise to 1.0 L of 2propanone. The precipitate from this step was recovered by centrifugation and dried under vacuum as fraction A. Supernate from the centrifugation was dried under vacuum and the recovered solids, B, were weighed. A sample of B in a Soxhlet thimble was extracted with water for 16 h. The solids in the extraction water were recovered by freeze-drying as sample C and the residue in the extraction thimble was dried to form sample D. Lignin content of a fraction was determined by quantitative ultraviolet spectroscopy, 2-propenamide content was determined by Kjeldahl assay, and calcium content was determined by atomic absorption spectroscopy. Equipment. The photolysis device used is a 200-V Oriel Model 8540 power supply driving a no. 6269,lOOO-W xenon lamp held in a Model 6410 lamp housing. Viscosities were measured with a No. 75 Cannon-Fenske capillary viscometer. Atomic absorption assays were run on a Perkin-Elmer Model 4000 double-beam atomic absorption spectrophotometer. Drilling muds were prepared with a Model 9B multimixer. Mud properties were tested with a Fan Model 35A motor-driven viscometer. Samples were hot-rolled in Model 760-12 stainless steel aging cells contained in a Baroid Model 701 roller oven. Results and Discussion Reaction product is an amorphous, brown solid which can be crushed into a fine tan powder with a mortar and pestle. The product is insoluble in most organic solvents but does dissolve in water or dimethyl sulfoxide. Proof that lignin and poly(1-amidoethylene) are grafted together has been obtained from size exclusion chromatography,
solubility, dialysis, and fractionation studies (Meister et al., 1984). Yield, limiting viscosity number, and product assay for a series of samples synthesized in 1,4-dioxanethat had been photolyzed for 3 h are given in Table I. These results show that calcium chloride content of the reaction mixture is a coritrolling variable of yield and that products synthesized in reaction mixtures containing more than 0.2 wt % calcium chloride are contaminated with that salt. The grafting reaction is extremely rapid and may be over in times as short as 1 h. However, no test of the effects of duration of reaction on product properties has been made. This reaction is critically dependent on the autoxidation products produced in oxygen-bubbled dioxane by photolysis. These autoxidation products should be 2-hydroperoxide-1,4-dioxacyclohexane or 2,3-bis(hydroperoxide)-l,4-dioxacyclohexane(Varfolomeeva and Zolotova, 1959). Autoxidation products recovered from l,4-dioxane, air-bubbled and refluxed for 14 h, had a melting point of 48 "C.The product infrared spectra in Nujol had a broad OH absorption at 3350 cm-'. Peaks at 1135 and 1085 cm-', possibly from C-0 asymmetric stretching, and at 880 cm-', possibly due to -0-0- vibration, were sharp in the chloroform solution spectrum but broad in the spectrum from the product in Nujol. Iodine-thiosulfate titration of the recovered autoxidation equiv/g and to be product showed it to contain 7.4 X 88.7 wt % active based on all equivalents being 2-hydroperoxy- 1,4-dioxcyclohexane. A 90-MHz proton spectrum of a 10 wt % solution of autoxidation product in D20gave the peak pattern shown in Table IIa. There is a close match for all proton resonances with those found by Gierer and Pettersson (1968) save for that attributed to the peroxide proton. Since hydroxyl protons change chemical shift as a function of solvent more than do aliphatic protons, this difference in chemical shift may be due to solvent effects; 200-MHz carbon-13 NMR of the sample gave the peaks listed in Table IIb. These peaks show the expected deshielding and splitting pattern for 2-hydroperoxy-1,4-dioxacyclohexane. These data provide very strong support for the hypothesis that the autoxidation product of 1,4-dioxane necessary for the initiation of graft copolymerization is 2-hydroperoxy-1,4-dioxacyclohexane. A set of reactions was run to test the role of cerium(1V) ion and hydroperoxides in the reaction. These reactions were run in distilled dioxane using tert-butyl hydroperoxide in place of the autophotolysis products of dioxane. Results from these tests are given in Table 111. They show that tert-butyl hydroperoxide initiates the polymerization when used in place of 2-hydroperoxy-l,4-dioxacyclohexane. Further, the yield of the reaction does not correlate with cerium(1V) concentration in the reaction mixture nor with hydroperoxide to cerium(IV)mole ratio. This suggests that
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 2, 1985 300 Table 11. Absorbance Peaks in Nuclear Magnetic Resonance Spectra of a 10 wt % Solution of l,4-Dioxane Autoxidation Products i n Deuterium Oxide
o,
b'
a
CH2
CHOd
CH2 '0'
CH2
I
I b
a. Proton Spectra
peak set 1 2 3 4 5 6 6'
label leading multiplet pentuplet multiplet triplet singlet doublet broad singlet
peak no.
1 2 3 4 pure dioxane
decoupled spectra 58.47 64.05 64.52 96.67 65.69
1,4-dioxaneb autox product peaks, ppm 3.58 3.76 4.12 5.00 5.12 8.13
2-hydroperoxyo 1,4-dioxane peaks, ppm 3.59 3.75 4.20 5.05 5.13 9.78 b. Carbon-13 Spectrac peak location: ppm coupled spectra assigned peak center C 58.43 b' 64.03 b 64.48 a 96.66
pattern triplet triplet triplet doublet
" With respect to tetramethylsilane in trichloromethane at ambient temperature. With respect to DHO (g = 4.67) in D20at 22 "C. cRun a t 24 "C, 22' pulse, 400 scans. With respect to methanol in D20at 22 "C. Table 111. Graft Copolymerization Reactions Run Using tert-Butyl Hydroperoxide (TBHP) as Initiator TBHP" Ce(1V) compn, wt % yield product mol X mol X 1-amido x 103 105 g wt% lignin ethylene no. g 103 1 0.254 2.82 1.05 0.75 2.37 64.1 13.9 70.9 2 0.508 5.64 1.05 0.75 2.70 73.0 9.26 70.8 3 0.135 1.50 1.05 0.75 2.70 73.0 9.54 68.6 4 0.254 2.82 3.15 2.25 2.71 73.2 8.29 71.0 5 0.254 2.82 5.25 3.75 2.16 58.4 9.76 68.9 6 0.254 2.82 0.21 0.15 2.36 63.8 7.88 68.1 7 0.508 5.64 3.15 2.25 2.3 62.2 8 0 0 1.05 0.75 0 0 "All reactions save no. 8 contained 0.5 g of lignin, 3.2 g of 2-propenamide, and 0.5 g of calcium chloride in 20 mL of distilled dioxane. Reaction 8 was similar to the other reactions but contained only 0.2 g of calcium chloride. Table IV. Results of Fractionation of Lignin i n Reaction Mixtures fraction A: 2-propanone solids anal, wt sample w t recov w t % of total solids % lignin 1 0.17 4.05 64.7 2 2.20" 52.4 7.60
sample 1 2
fraction C and D Soxhlet extr of solute solids extract (C) residue (D) g wt%ofB g w t % of B 0.9158 40.5 0.5605 24.8 0.6467 46.2 0.4408 31.5
sample 1 2
lignin 61.8 65.4
anal, wt % 1-amidoethylene 64.7
fraction B, 2-propanone solute solids recovd, g wt % of total solids 2.26 53.8 1.40 33.3
assays: lignin content, w t %
extract (C) 0.0 0.0
residue (D) 35.6 36.3
total amount of material recovered, wt % 2-propenamide 19.4 57.6
1-amidoethylene repeat units, w t % extract ( C ) Ca, extract (C) 67.8 13.6 64.5 9.3
Ca 34.6 16.6
"Yield of reaction 2 is 59.5 w t %.
direct reaction of cerium(1V) and hydroperoxide is not the mechanism for the production of radicals leading to graft copolymerization. Mass Balance Study. Two experiments were performed to monitor the distribution of reactants and
products in the final reaction mixture. For each experiment, a reaction which duplicated sample 2 of Table I was run. In the first reaction, the 1,bdioxane was not irradiated and no reaction occurred. For the second reaction, the solvent was irradiated for 3 h. Results from the sep-
310
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 2, 1985
Table V. Results of Reactions Run in the Presence of Propanamide meciaitation test vield
I---
sample'
g
wt%
1 2 3
3.7 3.7 3.7
100.0 100.0 100.0
4 5
2.24 2.20
60.5 59.5
- limiting viscos no. mL/g correl coeff Plus Propanamide 49.2 0.998 56.0 0.999 62.8 0.998
wt of react.
w t of solids
prod. used, g
recovd, g
0.2003 0.50032 0.50010
0.0022 0.0063 0.01145
0.50065 0.5003
0.0566 0.0467
w t. %. react. prod. that is insol
1.1
1.26 2.29
No Propanamide 68.0 61.5
0.996 0.999
11.3 9.3
'All samples contained 0.5 g of lignin, 3.20 g of 2-propanamide, 0.15 mL of ceric sulfate solution, and 0.50 g of calcium chloride in 20 mL of 1,4-dioxane that had been bubbled with O2for 5 min and irradiated with a 103-WXe lamp for 3 h. distilled water at 30 OC.
Table VI. Results of Synthesesa Run in Different Solvents ureciuitation test
sample solvent 1 l-methyl-2pyrrolidinone 2 dimethyl sulfoxide 3 dimethylacetamide 4 dimethylformamide 5 dimethyl sulfoxide, dioxane (5050, v/v) 6 dimethyl sulfoxide, water (50:50, v/v) 7 pyridine
wt of react. prod. used, g 0.20075
wtof solids recovd, g 0.002
wt% insol in 1.0
phases in reacted mixt. precipitate
32.2 27.6 32 53
0.20065 0.20065 0.20015 0.2005
0.001 0.0018 0.0023 0.00175
0.5 0.9 1.1 0.9
gelled solution precipitate precipitate precipitate 2 fluid-phase sample, gelled bottom layer precipitate
limiting react prod. compm, wt % l-amidoviscos yield, g lignin ethylene Ca C1 no., dL/g 4.4 4.74 75.36 3.11 2.85 14.2 2.79 2.07 2.77 1.85 2.82 1.90
H20
4.71 4.13 4.25 4.19
6.5 5.61 7.18 5.13
76.73 57.43 73.75 72.14
4.28
6.27
71.52
66
0.2005
0.00585
2.9
4.00
5.42
71.67
47
0.2001
0.001
0.5
'Each reaction contained 0.50 g of lignin, 3.2 g of 2-propenamide, 0.4 of 1,4-dioxane autoxidation product, 0.15 mL ceric sulfate solution, and 20.0 mL of solvent.
aration for these two reaction mixtures are given in Table IV. These reactions were run to obtain a mass balance on reactants and products, to confirm that the products and reactants were being separated, and to ensure that the process of conducting the reaction was not changing the lignin backbone. Of the 3 reactants, 2-propenamide is the most difficult material to recover because it sublimes. Large portions of 2-propenamide are lost in this fractionation process when the samples are vacuum-dried or freeze-dried. Significant fractions of 2-propenamide were only recovered when the compound was successfully polymerized into side chain or homopolymer. The fractionation results show that 22 wt % of the lignin in the reaction pot is recovered as water-insoluble solids from the precipitation step. Further, the lignin soluble in 2-propanone is also water-insoluble, as shown by the Soxhlet extraction. From these data, it was concluded that the reaction process did not alter lignin and that graft copolymerization was responsible for the water solubility of fraction A, sample 2, Table IV. This test also shows that the polymer is effectively separated from unreacted lignin, 2-propenamide, and calcium chloride. Small amounts of calcium chloride are retained by the separated polymer precipitated in 2propanone, but most calcium chloride is removed from the product. Solvent Effects. Both the sequence of events in the synthesis and the characteristics of the product support the idea that dioxane is a poor solvent in which to run this reaction. Dioxane samples containing 2.4 wt % lignin (a common reaction concentration) are 2-phase slurries rather than being solutions. During the initial stages of the reaction, the lignin slurry becomes a homogeneous solution
but then rapidly thickens, clouds up, and becomes a slurry again. A hypothesis that will explain this solution behavior is that the growth of a poly(1-amidoethylene) side chain on lignin makes a soluble intermediate which precipitates as its molecular weight increases. Previous separation studies (Meister et al., 1984) have shown that the reaction product is not completely soluble in distilled water. Parts of the reaction product which dissolve only in basic aqueous solution would be produced if the lignin particles in the reaction mixture did not completely dissolved during the reaction and were precipitated as a lignin core enveloped in a grafted, poly(1-amidoethylene) sheath. Further, if these explanations are correct, using a more effective lignin solvent for the reaction would produce more uniform grafting of lignin and less insoluble material in the product. The first test on solvent improvement was run by adding 3.29 g (0.045 mol) of propanamide to reactions run in irradiated dioxane (method 1). Prepanamide was added to the reaction because of its chemical similarity to the monomer, 2-propenamide, which appeared to act as a solubilizing agent for lignin in 1,4-dioxane. Results of these and comparison reactions are contained in Table V. These data show that reactions run in mixtures containing propanamide have a 40 wt % higher yield and contain less than 1/7 of the water-insoluble product found in samples prepared without propanamide in the reaction mixture. Thus, a solvent which swells or dissolves the lignin molecule is critical to the formation of a high yield of molecularly dispersed graft copolymer. Using synthesis method 2 , 7 solvents or solvent mixtures were tested as media in which to conduct the graft copolymerization. The results of these solvent tests are given in Table VI. More than 3.7 g of material, the total mass
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 2, 1985 311
Table VI1 batch no. 1 1 3 reaction mixture composition 1,4-dioxane, mL lignin, g 2-propenamide, g 0.05 M Ce (SO,), solution, mL CaCh, g irradiation time after oxygen purge, h yield grams weight percent limiting viscosity number in water a t 30 "C, dL/g product composition wt % lignin 1-amidoethylene repeat units % hydrolysis
20.0 0.50 3.20 0.15 0.50 3.0
20.0 0.50 1.00 0.15 0.50 3.0
20.0 0.50 3.20 0.15 0.50 3.0
3.64 1.50 3.68' 98.4 100 99.4a 0.46 0.21 0.52' 6.92 73.4 0
12.44 7.27 48.3 73.8 0 0
aThese values are averages for four repetitions of the reaction.
of lignin and 2-propenamide, was recovered from these syntheses. The mass excess and the calcium and chlorine analysis results show that product from other solvents is not purified by the precipitation procedure used for the dioxane-based syntheses. The amount of polymeric solid recovered in sample V-2 was determined by dissolving 0.5052 g of product in 20 mL of distilled water and dialyzing the solution against distilled water with a 3500 molecular weight (maximum) permeable dialysis membrane. After three days, dialyzed solution was freeze-dried, and 0.3003 g of product was recovered. A total of 59.4 wt % of the solids recovered from the reaction did not pass through a membrane with a 3500 molecular weight permeability limit. The yield of polymeric product from the dimethyl sulfoxide reaction is thus 75.7 w t %. The amount of water-insoluble material contained in the reaction products formed in alternate solvents
is less than l/lo of that usually found in products formed in dioxane. Further, the dimethyl sulfoxide reaction contains a single phase, viscous fluid at the end of the reaction. A uniform, fluid reaction mixture is a desirable state for the final reaction product because precipitate, formed in three of the solvent mixtures, usually does not entrap living polymers and thus promotes termination of the polymer. A precipitation reaction, run by method 1, thus controls product properties by solubility of the product in the reaction mixture. Reaction in solvent, however, allows the product properties to be controlled by mole ratios of reagents in the solution and by monomer reactivity. Specific benefits of solution polymerization will be the opportunity (1)to produce high-molecular-weight polymer since polymerization is not terminated by precipitation and (2) to take adavantage of the gel effect which might occur in dimethyl sulfoxide. Studies of the reaction in dimethyl sulfoxide are continuing. Applications to Drilling Muds. Data for the samples prepared for drilling mud tests are given in Table VII. Each batch of material was made up from repeated reactions, each of which produced several grams of product. All reaction product samples forming a given batch were combined into one sample, thoroughly blended, and then broken into equal mass samples for hydrolysis. Batch 1 was the result of five duplications of the reaction composition given in Table I, no. 2. Batch 2 was the result of 14 repetitions of the composition given in Table I, no. 7. Batch 3 was the result of 5+ repetitions of composition no. 2, Table I. Batches 1and 2 were broken into parts and hydrolyzed with sodium hydroxide to make samples of differing degrees of hydrolysis. Since the presence of charged sites on a polymer is a controlled variable of its effectiveness as a deflocculant or thinner, the degree of hydrolysis was expected to control the properties of the copolymer in drilling muds. Batch 1 was broken into three parts with
Table VIII. Elemental Assay, Percent Hydrolysis, a n d Limiting Viscosity Number for Partially Hydrolyzed Copolymer Used in Mud Tests deg of elemental assay, wt % hydro1 from SamDle C H N S 0 Na assav" lim viscos no.. d L l e Batch 1 a 50.19 7.30 16.19 0.24 29.02 0.095 0 0.32 b 43.73 5.97 10.45 0.14 34.13 7.40 24.8 15.2 C 41.52 5.03 6.37 0.18 38.74 12.49 51.4 15.1 e f g h
48.49 45.69 43.17 46.05
7.51 6.07 5.60 5.94
12.76 8.63 7.14 5.69
Batch 2 0.43 28.40 0.57 33.04 0.67 33.33 0.28 31.47
0.02 7.85 9.72 10.13
0 26.6 38.0 50.4
0.13 1.31 4.09 3.84
Based on nitrogen loss from samples 2 or 9. Table IX. ProDerties of Test Muds Before a n d After Hot Rolling. SamDle: Batch 1. Table VI11 reaction product base mud a b property before after std dev before after before after viscosity in CPat a shear rate of 1020 s-1 78 80 0.71 94 102 86.5 98 58 50 0.0 70 75 59 74 510 s-l 340 s-l 49 38 0.71 60 64 48 64 170 s-l 39 24 0.0 48 51 34 52 gel strength in lb/100 ft2 after mud has set for 32 28 10 41 10 s 29 4.0 7.8 10 min 54 5.5 11.3 58 68 41 78 apparent viscosity, CP 39 40 0.71 47 51 43 49 24 27 28 24 20 30 0.71 plastic viscosity, CP 50 yield point, lb/100 ft2 36 20 0.71 46 48 32 API filtrate volume, mL 11 8.0 0.99 11 12.3 7.4 13
C
before
after
94 62 50 34
68 41 31 20
6.5 31 47 32 31 6.8
3.0 4.0 34 27 14 7.2
312
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 2, 1985
Table X. Properties of Test Muds Before and After Hot Rolling. Sample: Batch 2, Table VI11 reaction product base mud e f g before after before after before after before property viscosity in CPat a shear rate of 1020 s-1 79 80 76 103 78 75 67 58 50 510 52 46 57 77 44 50 38.5 48 66 42 35 35 340 s-l 39 24.5 170 s-l 38 51 29 22 23 gel strength in lb/100 ft2 after mud has set for 18 4 9 20 7 4 5 10 s 10 min 38 6 44 70 35 5 25 apparent viscosity, CP 40 40 38 52 39 38 34 21 30 19 36 29 23 plastic viscosity, CP 26 yield point, lb/100 ft2 37 20 38 41 26 17 21 12.4 8.0 12.8 12.6 10.0 10.4 10.0 API filtrate volume, mL
h after
before
after
68 41 32 19
67 43 33 22
63 38 28 18
3 4 34 27 14 10.0
3 12 34 24 19 9.2
3 4 32 25 13 9.7
given in Table X. These data show that the reaction product produces the desirable effect of lowering yield point, lowering gel strength, and lowering API filtrate volume as degree of hydrolysis of the reaction product increases. This is true for both batches of reaction product. After hot-rolling, the reductions in the above three variables are only significant for the two reaction products that are 50% hydrolyzed, samples ICand 2h of Table VIII. Though the data are limited, batch 2 samples, which probably have lower molecular weights, appear to give greater yield point lowering and lower gel strength than do samples synthesized with more 2-propenamide in the reaction mixture (batch 1, Table VIII). The data from these first two batch tests indicated that poly(1ignin-g-(1-amideothylene))has properties which make it a potentially effective drilling mud additive. There is, however, a problem in interpreting the results of these tests because the reaction product (Meister et al., (1984) is a mixture of graft copolymer and poly(1-amidoethylene) homopolymer. After hydrolysis, the homopolymer in the reaction product would be converted to poly( l-amidoethylene-co-[sodium 1-carboxylatoethylene]) (partially hydrolyzed polyacrylamide), a common drilling mud additive (Clark et al., 1976). The beneficial effects of the additive could thus be coming from a contaminant of the reaction product rather than from the graft copolymer. To test this hypothesis and determine if the graft copolymer produced beneficial effects in benetonite muds, a third batch of reaction product was made. This material, batch 3, was base-dialyzed to produce separate fractions of graft copolymer and homopolymer. Data for the separated products are contained in Table XI. Data from tests on mud samples formulated with the separated products are given in Table XI1 along with data from tests of base mud
Table XI. Separated Products from Lignin-(2-propenamide) Reactions Crude Reaction Product 18.0 weight, g content, wt % lignin 7.27 1-amidoethylene units 73.8 [VI, water, 30 O C 0.51 After Separation; 3.h Graft Copolymer Fraction weight, g 9.09 wt % of original sample 50.5 content, wt 70 lignin 9.52 1-amidoethylene units 36.43 degree of hydrolysis 49.4 6.77 [TI. in water, 30 O C 3.j Homopolymer Fraction weight, g 3.20 wt % of original sample 17.8 content, wt % lignin 1.53 1-amidoethylene units 36.94 degree of hydrolysis 50.1 [TI, in 0.50 M NaOH, 30 " C 0.83
one part left unhydrolyzed, one part 25% hydrolyzed (b), and one part 51% hydrolyzed (c). Batch 2 was broken into four parts with one part left unhydrolyzed (e) and the other three parts converted to 27% hydrolyzed (0, 38% hydrolyzed (g), and 50% hydrolyzed (h) samples, respectively. Data on these batch fractions are given in Table VIII. Drilling mud test data for the three samples of batch 1, Table VI11 are given in Table IX. Standard deviation is calculated from duplicate measurements on the base mud. Similar mud test data for mud samples containing the lower molecular size samples of batch 2, Table VIII, are
Table XII. ProDerties of Test Muds Before and After Hot-Rolling
property viscosity in CPat a shear rate of 1020 s-1 510 s-' 340 s-l 170 s-l gel strength in lb/100 ft2 after mud has set for 10 5 10 min apparent viscosity, cP plastic viscosity, CP yield point, lb/100 ft2 API filtrate, volume, mL PH high-pressure, high-temperature filtrate, mL (I
Table XI, 3.h. *Table XI, 3.j.
base mud before after
graft copolymer fraction" before after
52 36 30 21
69 47 39 28
74 49 40 27
42 24
6 25 26 16 20 12.0 9.1
12 35 35 22 25 13.8 8.6 62.8
5 20 37 25 24 7.8 9.0
3 3 21 18 6 8.0 8.0 52.4
17 10
homopolymer fraction* before after
chrome lignosulfonate before after
74 49 40 27
43 24 17
29 16
10
7
5 20 37 25 24 7.8 9.0
2 3 22 19 5 8.4 8.0 46.0
12
2 9 15 13
3 11.6 9.5
50 33 26 18 11
24 25 17 16 14.0 8.2 64.0
Ind. Eng. Chem. Prod. Res. Dev., Vol. 24, No. 2, 1985 313
and base mud formulated with 0.5 ppb of chrome lignosulfonate. The mud tests show that chrome lignosulfonate is a better low-temperature thinner than either of the reaction product fractions. the lignosulfonate also lowers low-temperature gel strength and yield point, indicating that it is acting as a deflocculant and dispersant. The poorer performance of the reaction product fractions before hotrolling may have been caused by incomplete solutions of the separated solids. The lumpy lab products were not ground before being added to the mud. The two reaction products thicken the base mud at low temperature, possibly indicating that the products have too high a molecular weight to act as a low-temperature thinner. After hot-rolling, both synthesis samples outperform lignosulfonate as viscosity reduction agents. The synthetic additives also reduce gel strength. The synthetic additives raise yield point and apparent and plastic viscosity in the cold mud but they decrease all three variables and out-perform the lignosulfonate after hot-rolling. The synthetic compounds decrease API filtrate before and after hot rolling and also lower high-temperature-high-pressure filtrate. Chrome lignosulfonate does not control filtrate loss. The tests show that poly(1ignin-g-(1-amidoethylene)) acts as a high temperature thinner and as a filtrate control agent. The tests also show (batch 2, Table X) that reaction products prepared from reactions containing less 2propenamide act as thinners for the base mud. products from low 2-propenamide content reactions have smaller molecular size, as shown by their smaller limiting viscosity number (Table I), and should have lower molecular weights than the products in batches 1 or 3.
Conclusions Poly(1igning-g-(1-amidoethylene)),previously made by reacting Kraft, pine lignin, and 2-propenamide in oxygen-bubbled, irradiated dioxane, can be prepared by combining lignin, 2-propenamide,calcium chloride, cerium(IV), and 1,Cdioxane autoxidation products in such solvents as l-methyl-2-pyrrolidinone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, and pyridine. The product, a highly water-soluble, brown solid containing 4 to 7 wt % lignin and 70+ wt % 1-amideothyelenerepeat units, is purifiable by precipitation in 2-propanone and dialysis against water through a 3500 mol wt permeable membrane. Mass balance studies on blank and complete grafting reactions run in dioxane show that over 75 wt % of the unreacted lignin is removed from the reaction product during precipitation in 2-propanone. Reaction product can contain up to 5 wt % calcium chloride. Calcium content of product decreases as calcium chloride content of the reaction mixture decreases. Calcium chloride not retained
by the reaction product is solubilized by 2-propanone, as is unreacted 2-propenamide. Studies using tert-butyl hydroperoxide and cerium(IV+) as initiators indicate that direct cerium(1V)-hydroperoxide reaction is not the source of the free-radical reaction site on lignin. Poly(1ignin-g-(1-amidoethylene))and its hydrolyzed derivative, poly(1ignin-g-((1-amideothye1ene)-co-(sodium 1-carboxylatoethylene))), lower yield point, lower gel strength, and lower API filtrate volume in a bentonite drilling mud. After hot rolling at 121 "C for 16 h, the graft copolymer outperforms an equal concentration of chrome lignosulfonate when the compounds were tested as thinners or as filtrate control agents. Products synthesized in reaction mixtures containing 2 g of 2-propenamidelg of lignin acted as thinners in bentonite-based mud while products made in reactions with 6.4 g of 2-propenamidelg of lignin acted as filtrate control agents.
Acknowledgment Support of portions of this research by the Robert A. Welch Foundation is gratefully acknowledged. This work was partially supported by the National Science Foundation under award number CPE-8260766. Helpful discussions with many of the faculty of the Chemistry Department of Southern Methodist University are gratefully acknowledged. Registry No. Ce(S04)2, 13590-82-4; Ca(C1J2, 10043-52-4; (acry1amide)-(kraft lignin) (copolymer), 90385-95-8.
Literature Cited "API Recommended Practice, Standard Procedures for Testing Drilling Fluids", 10th ed.;American Petroleum Institute Production Department. Dallas, TX, June 1, 1984. Clark, R. K.; Scheuerman, R. F.; Rath, J.; van Laar, H. G. J. Pet. Techno/. June 1978, 31(5), 719-727. Gierer, J.; Pettersson, I.Acfa Chem.Scand. 1968 22(10), 3183-3190. Goheen, D. W.; Hoyt, C. H. "Lignin" in the "Kirk-Othmer Encyclopedia of Chemical Technology"; 3rd ed., Wliey-Interscience: New York, 1981; VOi. 14, pp 298-299. Kobayashi, A.; Phillips, R. B.; Brown, W.; Stannett, V. T. Tappi 1971, 54(2), 215-221. Koshljima, T.; Muraki, E. Nippon Mokuzaei Gakkaishi June 1984, 70, 110-113. Koshljlma, T.; Muraki, E. Zaiwo 1976, 76(169), 834-838. Krause, T.; Gahln, M.; Schurz, J. Papier (Darmstadt) 1975, 29 (lOA, special issue), 1-7. Mair, R. D.; Graupner, A. J. Anal Chem. 1984 36, 194-204. Meister, J. J.; Patll, D. R.; Field, L. R.; Nicholson, J. C. J. Polym. Sci. 1984 22, 1963-1980. Mikhallov, G. S.; Llvshits, R. M. Izv. Vyssh. Ucheb. Zaved. Les. Zh. 1989, 72(8), 99-102. Phillips, R. B.; Brown, W.; Stannett, V. T. J. Appl. Polym. Sci. 1973, 17, 443-451. Slmionescu, Cr.; Cernatescu-Asandei, A.; Stoieru, A. Cellul. Chem. Techno/. 1975, 9(4), 363-380. Varfolomeeva, E. K.; Zolotova, 2 . G. Ukr. Khim. Zh. 1959 25, 708-712.
Received for review July 27, 1984 Accepted January 14, 1985
