Ind. Eng. Chem. Res. 1989, 28, 500-504
500
Borgwardt, R. H.; Bruce, K. R. Effect of Specific Surface Area on the Reactivity of CaO with SOz. AZChE J . 1986, 32, 239. Borgwardt, R. H.; Bruce, K. R.; Blake, J. An Investigation of Product-Layer Diffusivity for CaO Sulfation. Ind. Eng. Chem. Res. 1987, 26, 1993. Borgwardt, R. H.; Roache, N. F.; Bruce, K. R. Method for Variation of Grain Size in Studies of Gas-Solid Reactions Involving CaO. lnd. Eng. Chem. Fundam. 1986,25, 165. Coble, R. L. Sintering in Crystalline Solids, 11. Experimental test of diffusion models. J . Appl. Phys. 1961, 32, 793. Coutant, R. W.; Simon, R.; Campbell, B.; Barrett, R. E. Investigation of the Reactivity of Limestone and Dolomite for Capturing SO2 from Flue Gas. EPA Report APTD 0802 (NTIS P B 204385), Oct 1971. German, R. M.; Munir, Z. A. Surface Area Reduction During Iso1976, 59, 379. thermal Sintering. J . Am. Ceram. SOC. Gjostein, N. A. Diffusion. American Society of Metals, Metals Park, OH, 1973. Johnson, D. L. Ultra Rapid Sintering. In Sintering in Heterogeneous Catalysis; Kuczynski, G. C., Miller, A. E., Sargent, G. A., Eds.; Plenum: New York, 1984. Mai, M. C. Analysis of Simultaneous Calcination, Sintering, and Sulfation of Calcium Hydroxide Under Furnace Sorbent Injection
Conditions. Ph.D. Thesis Department of Chemical Engineering, University of Texas a t Austin, Austin, TX, 1987. Nelson, G. 0. Controlled Test Atmospheres; Ann Arbor Science: Ann Arbor, MI, 1971. Nicholson, D. Variation of Surface Area During the Thermal Decomposition of Solids. Trans. Faraday SOC.1965, 61, 990. O'Neill, E. P.; Keairns, D. L.; Kittle, W. F. A Thermogravimetric Study of the Sulfation of Limestone and Dolomite-the Effect of Calcination Conditions. Thermochim. Acta 1976, 14, 209. Pigford, R. L.; Sliger, G. Rate of Diffusion-Controlled Reaction Between a Gas and a Porous Solid Sphere. Ind. Eng. Chem. Process Des. Deu. 1973, 12, 85. Schlaffer, W. G.; Adams, C. R.; Wilson, J. N. Aging of Silica and Alumina Gels. J . Phys. Chem. 1965, 69, 1530. Sotirchos, S.V.; Yu, H. C. Mathematical Modelling of Gas-Solid Reactions with Solid Product. Chem. Eng. Sci. 1985, 40, 2035. Ulerich, N. H.; O'Neill, E. P.; Keairns, D. L. A Thermogravimetric Study of the Effect of Pore Volume-Pore Size Distribution on the Sulfation of Calcined Limestone. Thermochim. Acta 1978,26, 269.
Received for review June 1, 1988 Accepted December 27, 1988
Recovery of Solids from Melamine Waste Effluents and Their Conversion to Useful Productst Shawqui M. Lahalih* and Mamun Absi-Halabi Petroleum, Petrochemicals and Materials Division, Kuwait Institute for Scientific Research, P.O. Box 24885, 13109 Safat, Kuwait
Melamine waste effluent stream solids were recovered, which contained melamine, oxytriazines, and polycondensates. T h e recovered solids were reacted with formaldehyde followed by sulfonation. A four-step process was followed to convert the recovered solids into sulfonated resins. The reaction conditions were similar but higher than those used for pure melamine. The sulfonated resins were found to be very effective dispersants. They improved the compressive strength of concrete by 70% and the compressive strength of sandy soil by a factor of 3. They were found to be useful as thinners to control the rheological properties of drilling muds. In addition to the recovery and conversion of waste solids into useful products, the problem of pollution is minimized.
A major problem with most processes in the petrochemical industry is the contamination of effluent streams with various chemicals, including unrecovered amounts of the primary product of the process. This is particularly important in the case of the melamine industry. Melamine is manufactured on a commercial scale by converting urea to melamine in several stages, including B crystallization stage which purifies the melamine to the required specifications. The mother liquor following the crystallization stage is normally stripped of ammonia and concentrated t u a solids content of about 1.5-5% by weight. This final effluent stream which is usually disposed of as wastewater, contains various proportions of melamine, oxyaminotriazines,cyanuric acid, melam, melan, melon, biuret, triuret, and other higher polycondensates of urea and melamine. These various components, the percentages of which vary depending on process conditions, are considered to be major contributors to the pollution problems of melamine manufacturing plants. In addition to the pollution problems created by these waste solids, the actual tonnage of melamine lost in these waste solids is rather substantial. Accordingly, it would be most desirable from both an economic and ecological standpoint to recover the waste melamine and byproducts in a commercially usable form. The problem of recovering these waste materials has __. -
__-___________
'Publication no. KISR 2645
been dealt with by various melamine manufacturers and research organizations during recent years. For example, it has been demonstrated that the solid content in the effluent stream can be reduced by such varying techniques as biological hydrolysis, thermal hydrolysis, absorption on activated carbon, the production of cyanuric acid from wasted melamine, and the recovery of the various waste products by means of ion exchangers. Partial recovery of melamine under suitable conditions of pH and temperature is possible. This approach may result in high-grade melamine, but substantial amounts of byproducts as well as some melamine will remain in the waste stream. On the other hand, melamine and other byproducts of the effluent stream could be decomposed under pressure and temperature to NH3 and COz (FMC Corporation, 1978; Carlik and Zagaranichi, 1971; Berkowitz and Juerke, 1977). Alternatively, the waste mother liquor could be treated with H,S04 and cyanuric acid. The resulting precipitate is then hydrolyzed to cyanuric acid (Matsushima and Shimamura, 1967; Meijer-Hoffman and De Jonge, 1979; Roginskaya et al., 1979). Similarly, ammelide, ammeline, and melamine could be utilized as feedstock for making melamine or cyanuric acid (Siele and Gilbert, 1975; Mitsui Toatsu Chemicals, Inc., 1981; Fujiyoshi, 1975). While all of the above techniques can somewhat reduce the solid content of the waste effluent stream from a melamine process, none has been utilized commercially.
0888-5885/89/2628-05Q0$01.50/0 C 1989 American Chemical Society
Ind. Eng. Chem. Res., Vol. 28, No. 4, 1989 501 Table I. Analysis of the Solids Content from a Mother Liquor Wastewater Stream effluent stream composition sample, % w t total solids 1.80 1.27 melamine oxytriazines" 0.42 polycondensatesb 0.012 a Oxytriazines include ammeline, ammelide, and cyanuric acid. Polycondensates include mainly melem, melam, and melon.
This is because they are either considered uneconomical or technically too complicated. Therefore, it is the objective of this paper to report on a method to recover the solids of the effluent stream and convert them into a commercially usable product, thereby improving the economics of the melamine synthesis plant while simultaneously reducing the plant's waste disposal problems.
Experimental Section Materials. Solid wastes from a melamine effluent stream was obtained from Kuwait Melamine Industries Company. Paraformaldehyde (94%) and sodium metabisulfite, both of laboratory pure grade, were acquired from BDH, Dorset, England. Commercial sulfonated melamine formaldehyde is manufactured by SKW, Trostberg, Germany, in powder form and bears the designation Melment F-10. The solid waste from melamine waste effluent stream was first recovered and chemically transferred into a sulfonated amino-formaldehyde resin according to a novel procedure adopted at the KISR laboratory (Lahalih and Absi-Halabi, 1987a,b). The solid waste had the following composition (N, 59.9%; C, 29.8%; H, 4.45%) and contained up to 30% oxyaminotriazines. Cement (type I) manufactured by the Kuwait Cement Company was used to study the effects of these products as superplasticizers. Tests were also conducted on the stabilization of sandy soil obtained from a quarry in the Sulaibiya area in Kuwait. This type of sand is referred to as "gatch". Tests on the effect of these products as drilling mud thinners were conducted on a standard mixture of brackish water, Wyoming bentonite, caustic soda, and (carboxymethyl)cellulose,all of which are commercially available. Procedure. Analysis of the Solids. Samples of the mother liquor wastewater stream were taken periodically and were stored at ambient temperature for several days before solids were separated. Typical solid contents of the stream and the compositions of the solids are shown in Table I. Separation of Solids from the Wastewater Stream. For most of the chemical studies conducted on waste solids, solids were separated from the wastewater by evaporating the water content at 100 "C. A number of experiments were also carried out to assess the feasibility of separating the solids by vacuum filtration using ordinary fine pore sintered glass funnels and by centrifugation using a continuous flow centrifuge into which the wastewater was fed by a diaphragm pump a t relatively low water flow rates. The centrifuge speed ranged between 5000 and 15000 rpm. Preparation of Sulfonated Resins. The procedure adopted to prepare the sulfonated resins was similar to that developed by us for preparing sulfonated melamine-formaldehyde condensates (Lahalih and Absi-Halabi, 1987a,b). Reaction conditions such as pH, temperature, and timing were, however, different. The procedure consisted of four consecutive steps in which hydroxymethylation, sulfonation, and condensation at low and high pH take place. The detailed description of a typical experiment is described
elsewhere (Lahalih and Absi-Halabi, 1987a,b). Physical Testing of Sulfonated Resins in Concrete, Sandy Soil, and Drilling Mud. Concrete Mix. The concrete mix design chosen for this study had ratios of various constituents as follows: cement, 385; water, 205; sand, 625; 10-mm aggregate, 395; 200-mm aggregate, 759. The available sand was zone 3 and the gravel was single and 20-mm maximum size. Water substituted for aggregate absorption was 1.7% sand weight, 1.6% 10-mm gravel weight, and 1.2% 20-mm gravel weight. Compressive Strength Test on Concrete. This test determines the compressive strength of concrete mixes using 15- x 15- x 15-cm cubes. The concrete cubes were cast and kept in high-humidity conditions for 24 h. They were then removed from the molds and kept in a freshwater tank until the test ages of 3, 7, and 28 days were reached. Compressive Strength Test on Sandy Soil. For control specimens, water (20 g) was mixed with 200 g of sandy soil (e1mm) until it was homogeneous. The wet sandy soil was compacted in a standard mold (5.0-cm diameter) on a universal testing machine under a compactive effort 100 kg/cm2. The specimen was taken out of the mold and dried in an oven at 70 "C (drying conditions and interval were variable). The dry samples were loaded until failure in a universal testing machine operated at a head rate of 0.05 cm/min. For stabilized soil, 20 g of the soil stabilizer resin solution (10% solid) was added instead of water and the same procedure was followed. Testing Sulfonated Resins in Drilling Fluids. Brackish water measuring 2283 g (total dissolved solids = 2600) was mixed with 165 g of 100% Wyoming bentonite and 30 g of 10% caustic soda solution in a high-speed mixer for 30 min. The suspension was left for 24 h to stabilize and for the bentonite to hydrate. A sample was taken and approximately 2 lb/barrel (ppb) of (carboxymethy1)cellulose of low viscosity (CMC-LV) was added. The mixture was blended in a high-speed blender for 5 min. Various doses of a commercially available thinner known as Spersene (lignosulfonate-based additive) were added. Similarly, various doses of sulfonated melamineurea-formaldehyde and sulfonated waste solids of melamine additives, prepared according to the above procedure and in accordance with U.S. Patent 4,677,159 (Lahalih and Absi-Halabi, 1987a,b), were also added instead of Spersene. To this mixture, 120 ppb of barite (barium sulfate) was then added, and the resulting mixture was blended for 5 more min at high speed. The sample was added and the resulting mixture blended for 5 more min at high speed. Its plastic viscosity (PV) and yield point (YP) were determined by using standard procedures. Equipment. Standard equipment were used. These included pH meters, Haake CV-100 rotational viscometer, Universal Mechanical Testing Machine Instron Model 1195, and standard mixers and blenders.
Results This study was carried out to evaluate various possibilities for separating maximum amounts of the solid contents of a melamine plant mother liquor and to assess the possibility of preparing useful products from this waste solid. It was recognized a t the onset of this study that useful materials such as adhesives, molding resins, and other well-known applications of amino resins could be synthesized from the effluent solids. However, the investigations concentrated on the development of a sulfonated product which can be used as dispersant for a number of applications such as concrete admixture, soil stabilizer, and drilling mud additive.
502 Ind. Eng. Chem. Res., Vol. 28, No. 4, 1989
Solids Recovery. Various procedures were used to separate the colloidal matter from the waste stream. The various procedures included evaporation, filtration, and flocculation and coagulation. Evaporation. The total solid content of the samples obtained from the waste stream was determined by total evaporation of water and other volatile materials found in the stream such as residual ammonia a t 110 "C. The percentage solids in the stream as determined by total water evaporation was found to vary slightly on different sampling dates. Typical values obtained were 16.3, 15.7, and 21.5 g of solids/L of effluent. Filtration. A sintered glass funnel of fine porosity equipped with vacuum suction was used to obtain an approximation of the percentage of colloidal matter in the waste stream. Typical values for the percentages of solids recovered by single and double filtrations were 7.8 and 10.8 g/L of waste water. These values represented 48% and 67% of the total solid found in the stream. Flocculation and Coagulation. The particles of organic matter found in the waste stream were very fine, especially when the sample was freshly obtained. This accounts for the difficulty in separating the solids from fresh sample water by filtration or centrifugation. Therefore, the water was treated with various common reagents to effect rapid coagulation. The reagents used included carbon dioxide, sodium hydroxide, and sulfuric acid. In each case, the solid was separated by filtration. The experiments and the results are summarized as follows: Carbon dioxide bubbling at a rate of approximately 120 mL/min for 10 min was sufficient to lower the pH from 10.5 to 6.46 for a 2-L sample of the wastewater. The percentage of solid recovered by a single filtration (72%) was significantly better than the result obtained without the C 0 2 treatment (48%). The addition of sodium hydroxide in the form of concentrated solution or pellets to samples of the waste stream resulted in a slight increase of the original pH value (10-11) to approximately 12.5. The solid collected by a single filtration following this treatment was observed to increase to around 70% if a sufficient amount of NaOH was added to raise the pH to 12.5. Waste stream treatment with sulfuric acid was studied more extensively than the previous two treatments. The acid was added as a concentrated solution of 14-16 N in amounts ranging between 0.1% and 0.6% by weight. It was observed that, as the pH of the water decreased when acid was added, the weight of the solid collected from equal samples of the wastewater increased proportionally with the pH value (Figure 1). In general, the solids from wastewater treated with H,SO, were more easily and more effectively separated, whether by filtration or by centrifugation than solids from the untreated water. This indicates that H2S04is an effective flocculating agent. As indicated in Figure 1, the percentage of solids obtained a t a very low pH (i.e., pH 1.07) is higher than the total solids present in the wastewater. Chemical analysis of the solid obtained at pH 1.07 indicates that it contains 3.4% sulfur, which corresponds to 10.2% sulfate group. Thus, sulfuric acid probably forms sulfate salts with some of the components of the waste stream. The above results indicate that the separation techniques potentially suitable for recovering the solids are sedimentation, filtration, and continuous flow centrifugation after the proper treatment of the effluent stream with a suitable flocculating agent such as H2S04.
0
2.0
4.0
6.0
8.0
10.0
PH
Figure 1. Variation of amounts of solids recovered from 100 g of mother liquor effluent stream with different pH values. The pH was adjusted by adding H2S04.
Sulfonated Resin Preparation. Experiments have shown that, under certain reaction conditions, it is possible to synthesize a sulfonated product from the waste effluent solid with similar properties as pure melamine-based products. The reaction procedure was the same for both pure melamine and waste effluent solids except that the reaction conditions of pH, time, and temperature were different. Table I gives the reaction conditions for the sulfonation of the waste solids of the effluent stream compared to the sulfonation of pure melamine. The table shows that, in order to have the same viscosity as that of pure melamine, the reaction conditions of the third step, where polymerization takes place at low pH values, had to be doubled in case of waste effluent solids reactions. Similar observation was also made for the sulfonation time of the second step where it was also doubled for waste solids sulfonation compared to pure melamine sulfonation. Stability. Stability tests were also conducted on the resins of the waste solids (sample 8001) and Melment L-10. Figures 2 and 3 show the variations of viscosity and pH after the samples were aged at 60 "C for different lengths of time. It can be seen that the stability of sample 8001, prepared from the waste effluent stream, was far superior to that of the commercial sample which is prepared from pure melamine. After 2 weeks (336 h) of aging a t 60 "C, the drop in the viscosity of the commercial sample was 40%, but a slight increase was observed for sample 8001. Stability of sulfonated products in the solution form is extremely important, especially in hot climates such as that in the Arabian Gulf region. Physical Testing of Some Sulfonated Resins. Several laboratory-prepared samples were tested on concrete mixes to determine their performance as concrete superplasticizers. Tests on water reduction and compressive strength were conducted. Similarly, these sulfonated resins were also tested on sandy soil to see if they can be used as soil stabilizers. Finally, some of these resins were also tested as thinners in drilling muds to check their effectiveness as thinning agents to control the rheological properties of the drilling mud. The results are summarized below. Compressive Strength of Concrete. A concrete mix was designed by a computer program to have compressive
Ind. Eng. Chem. Res., Vol. 28, No. 4, 1989 503
4.5
4.0
k
0
3.5
e
2 3.0
.-
h
8
x
5 2.5
Figure 4. Compressive strength of plain concrete (0) and concrete treated with commercial Melment L-10 (m), waste solids based sample 8001 (01, and pure melamine-based sample 2062 (A).
2.0
1.5
1.o
I
0.0
60
120
180 Aging time (h)
240
,
300
,
2
I
Figure 2. Variation of viscosity with aging time for a commercial superplasticizer solution: Melment L-10 (A)and laboratory-prepared sample 8001 (0).Samples were aged a t 60 "C; viscosities were measured a t 20 "C.
Table 11. Effect of Various Additives on t h e Compressive S t r e n g t h of Sandy Soil compressive strength, samDle ke/cm2 control (no additive) 4.74 sulfonated melamine-formaldehyde 13.38 (sample 2062) sulfonated "waste solids"-formaldehyde 13.01 (sample 8006) urea-formaldehyde 3.50 Table 111. Effect of Sulfonated Amino-Aldehyde Resins on Drilling Mud Properties
additiven none (control) Spersene (commercial)* sulfonated pure melamine-formaldehyde sulfonated "waste solids"-formaldehyde (sample 8006) A dose of 3 ppb was used. based on lignosulfonate.
8 . 0 1 ' ' 0 60
"
120
"
'
180 Aging time (h)
'
240
"
300
3
Figure 3. Variation of pH with aging time for a commercial superplasticizer solution: Melment L-10 (A)and laboratory prepared sample 8001 (0).The samples were aged at 60 "C; pH was measured at room temperature.
strength (28 days) of 300 kg/cm2 and slump of 60-120 mm. When the mixes were treated with 3% Melment L-10, a commercial sulfonated melamine-based product, and 3% 8001, a sulfonated waste solid product, they became very flowable, having collapse slumps. Water was then reduced until the slump of neat concrete (51 mm) was reached.
PV, CPat
lb/(100 YP,
25 "C 16.0 15.0 14.5 15.0
ft2 year) 18.0 9.0 11.0 12.0
* Spersene is a commercial thinner
Water reduction was 28% in the case of 8001 sample compared to 30% for the commercial Melment L-10 and 31% for pure melamine-based sulfonated resins prepared at the KISR laboratory. The compressive strength of the mixes was determined at 1, 3, 7, and 28 days (Figure 4). The compressive strength of concrete treated with the sulfonated waste solids after 28 days of aging was higher than that treated with commercial Melment L-10. This shows the effectiveness of the sulfonated waste solids as possible concrete admixtures. Compressive Strength of Sandy Soil. The effect of sulfonated waste solids was also tested as possible soil stabilizers. Their effect on the compressive strength of sandy soil is shown in Table 11. The results show that these sulfonated solids improve the compressive strength of sand significantly and are effective dispersants similar to pure melamine-based resins. Rheology of Drilling Muds. The sulfonated resins were also tested as thinners on drilling mud. Pure melamine-based sulfonated resins were discovered to be effective thinners when they were added to normal drilling mud mixtures (Lahalih and Daranieh, 1988). Similarly, when the sulfonated "waste solids" of the effluent stream were added to a normal mix of drilling mud, the rheological properties changed favorably, similar in their effect to the other additives (Table 111).
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Ind. Eng. Chem. Res., Vol. 28, No. 4, 1989
Table IV. List of Experiments Conducted under Different Conditions Using Total Solids of Melamine Effluent Wastewater and Pure Melamine exDeriment code reaction step 2062 8000 8001 8003 8006 step 1 hydroxymethylation 12.0 12.0 12.0 11.35 12.0 PHI 55.0 45.0 45.0 45.0 45.00 TI, "C 15.0 15.0 15.0 15.0 15.00 t l , min step 2 sulfonation 12.0 12.0 12.0 11.35 12.0 80.0 80.0 80.0 80.00 80.0 120.0 120.0 120.0 60.00 60.0 f2, min step 3 low pH condensation 3.0 3.0 3.0 3.0 3.50 PH3 70.0 45.0 45.0 45.00 45.0 Ts,"C 150.0 60.0 60.0 90.00 30.0 t3, min step 4 high pH condensation t,, min final product viscosity for 20% solid content measd a t 20 "C
7.00 80.00 60.00 4.5
7.0 80.0 60.0 t.10
v materials
Discussion Survey of the literature on the treatment of melamine waste effluent streams reveals that serious efforts were exerted and resulted in treatments that were not economically feasible. Most of the efforts were directed either on the recovery of pure melamine from the waste solids, where melamine constituted about 70% of the total solids, or on the utilization of waste solids as feed material for manufacturing cyanuric acid or melamine. Because of strict pollution control measures taken by most industrial countries, the effluent stream solids of a melamine plant were, in some cases, treated biologically. In all of these efforts, the various treatments were either inefficient or economically not feasible. In this paper, a rather novel approach is offered where the total solids are converted into useful products. It has been shown that these sulfonated resins can be used as admixtures to concrete where concrete flowability and compressive strength have improved significantly (Figure 1). These materials can also be used as soil stabilizers where the compressive strength of treated sandy soil can be improved by at least a factor of 3 for very small doses (Table 11). Finally, these materials were used with drilling muds as thinners where the rheological properties have improved significantly (Table 111). The idea of using these materials as additives to concrete mixes, sandy soil, and drilling mud mixtures stems from the fact that these materials are sulfonated products and thus can be effective dispersants. When these materials are added to inorganic material such as cement, sand, or Wyoming bentonite, they tend to coat the particles of the inorganic matter. These particles become negatively charged and hence repel each other, forming a nicely dispersed matrix. In the case of concrete and sandy soil, the action of these materials ceases after the system is completely cured. Because of the dispersion and uniform structure, the compressive strength of the inorganic matrix improves. In the case of drilling muds, the addition of these sulfonated resins keeps the inorganic particles suspended and well dispersed in the mixture, thus minimizing settling and agglomeration of the inorganic particles, thereby improving the rheological properties of the drilling mud.
pure melamine
7.0 80.0 60.0 3.20
-
7.0 80.0 60.0 3.30
7.0 80.0 60.0
5.y
recovered waste effluent stream solids
Conclusions The solids of a melamine waste effluent stream can be recovered by sedimentation or simple addition of a flocculant such as sulfuric acid. Total recovery is possible. The recovered solids are then converted into sulfonated resins. The conversion is accomplished according to a four-step process developed by the authors for pure melamine resins (Lahalih and Absi-Halabi, 1987a,b). The sulfonated products are used successfully as effective dispersants on concrete, sand, and drilling muds. Significant improvements in compressive strength of concrete and sandy soil are obtained. The rheological properties of drilling fluids have also been improved with the addition of these dispersants. In addition to the utilization of these waste solids as useful products, the problem of pollution is also minimized. Acknowledgment The authors wish to acknowledge Kuwait Melamine Industries for introducing the problem to the authors. Registry No. Melamine, 108-78-1; formaldehyde, 50-00-0.
Literature Cited Berkowitz, S.; Juerke, C. V. US. Patent 4,013,757, 1977. Carlik, V. M.; Zagaranichi, V. I. Khim. Promst. (Moscow) 1971,47, 45-64. FMC Corpopration Belgium Patent 863,264, 1978. Fujiyoshi, K. Japanese Patent 50,26553, 1975. Lahalih, S. M.; Absi-Halabi, M. U S . Patent 4,663,387, 1987a. Lahalih, S. M.; Absi-Halabi, M. U.S. Patent 4,677,159, 1987b. Lahalih, S. M.; Daranieh, I. Development of Novel Polymeric Drilling Mud Dispersants. Eur. Polym. J . 1988, in press. Matsushima, A,; Shimamura, K.; Yoshida, S. U S . Patent 3,325,493, 1967. Meijer-Hoffman, L. R. M.; De Jonge, P. H. European Patent 1,4,397, 1979. Mitsui Toatsu Chemicals, Inc. Japan Kokai Tokkyo Koho 81,79,678, 1981. Roginskaya, Ts. N.; Finkelshtein, A. I.; Simkina, L. A. USSR Patent 681,001, 1979. Siele, V. I.; Gilbert, E. E. Utilization of Ammelide (by-product from Guanidine Nitrate Production. AD Report AD-A021343, 1975; U.S. NTIS.
Received for review May 9, 1988 Accepted November 16, 1988
