Ind. Eng. Chem. Res. 1992,31, 1971-1981
1971
Analysis of Organic Extractant Systems for Acetic Acid Removal for Calcium Magnesium Acetate Production James W. Althousef and Lawrence L. Tavlarides* Department of Chemical Engineering and Materials Science, Syracuse University, Syracuse, New York 13244-1190
A process for the production of the deicing salt, calcium magnesium acetate, is described. A crucial step for technical and economic feasibility is the organic extraction of acetic acid from dilute aqueous streams. This work focuses on selection of two organic systems chosen for pilot studies: a phosphine oxide (50%) and a tertiary amine (20%) in an aliphatic hydrocarbon (30%);a tertiary amine (40%) in cyclohexanone. Almost 50 candidate systems were screened, the equilibrium behavior of each system was determined experimentally or from the literature, and the extraction capabilities of several classes of candidate systems were characterized. An equilibrium model was used to compare the relative efficiency of the systems. Their relative efficiency, economy, physical interphase behavior, tendency toward side reactions, and toxicity were employed to select the above two candidates.
Introduction The use of sodium chloride to deice road surfaces has raised numerous objections from government agencies and the public at large (Wise and Augenstein, 1988). The lifetimes of civil works and motor vehicles are dramatidy reducd by repeated wintertime exposure to salt brine. The environment also suffers from the runoff of chloride-laden water. Alternatives have been proposed but none has been shown to be as cost-effective as the use of naturally occurring salt. Road salt now costa about $20.00 per US ton (2.15cnt/kg). The cost of any practical substitute must be of the same order of magnitude. Calcium magnesium acetate has excellent properties as a deicing salt (Wise and Augenstein, 1988). It is not corrosive to metal or concrete and is not as harmful to the environment as chloride salta. However, the commodity chemical is 2 orders of magnitude more expensive than sodium chloride. An explanation for ita high cost is the use of glacial acetic acid as an intermediate in the manufacture of the acetate. The production of glacial acetic acid requires at least one costly distillation operation to concentrate the product. The goal of this project is to develop a means of producing calcium magnesium acetate without the use of unnecessary thermal operations or expensive intermediates. A potentially viable process for the economical production of calcium magnesium acetate is illustrated in Figure 1 and consists of the following steps. A dilute aqueous stream of acetic acid is produced by biofermentation of woody biomass. Acid is extracted from this stream by a suitable organic extractant, and the raffiiate is recycled to the fermenter. The organic extractant is then stripped of acid with a aqueous slurry of a basic calcium magnesium salt to yield an almost saturated solution of calcium magneaium acetate. Water is evaporated from the saturated solution to produce the salt. This last step is the only thermally driven operation in the process. To minimize the size of the equipment and the coat of production, the concentration of acetic acid should be as high aa possible at each step of the process. The concentration in the aqwrous stream is limited by the autotoxicity of the acid to acetogenic fermentation bacteria. It may be aa high aa 3.5% by weight, but higher values are not currently femible. The concentration of acid in the organic
extractant can be higher than that in the feed. There are a number of organic extractanta whose distribution coefficients are greater than 1. The higher the distribution coefficient of the extractant, the lower the material inventory and size of the equipment required. Finally, the concentration of acetate in the stripping solution should be as high as possible in order to minimize the heat load on the evaporator. This article addresses the selection of the optimum extractant for a dilute aqueous stream of the acetic acid and conditions for ita me. Economic considerations are restricted to the relative cost per pound of the extractant to the acetic acid recovered. A subsequent article will address the selection and use of suitable basic calcium salt for stripping the acid from the organic extractant. Almost 50 potentially viable extractant systems are examined. Their properties are described and various standard criteria are established in order to rate their suitability for use in the process described above. The conclusions are process specific, but the data and analysis presented here are of general interest. For example, they could be applied to the extraction of acetic acid from aqueous industrial waste streams. Prior Work. There are two bodies of literature on the subject of the extraction of acetic acid from aqueous streams. The first of these is concerned with various industrial processes aimed at the economical production of glacial acetic acid as a bulk commodity (Treybal, 1973; Robbins, 1979;King, 1983). Distillation is a central step in all of these processes. This literature compares extractive systems based on vapor/liquid equilibrium properties of the acid, water, extractant, and solvent mixtures at fairly high concentrations of acid in the aqueous streams. Concentrations in this range cannot be achieved by biofermentation. A second body of literature examines the extraction of acetic acid from water at very low concentrations ( 20) reported in the literature are only applicable to the very dilute aqueous solutions. They are a consequence of the strong convexity of typical equilibrium curves for Adogen 283 based systems. However, this steep portion of the equilibrium curve cannot by utilized in a practical design scheme. It is technically unnecessary and very costly to attempt to reduce the concentration of acetic acid in the aqueous raffinate to a very low value. Consequently,the fact that the screening procedure described above automatically eliminated all of these systems is acceptable. Systems Containing a Phosphine Oxide. These systems are plotted on Figures 12-15 and follow the standard format described above with the following exceptions. The curve or l i e shown on the plots represents linear behavior. The degree to which a point lies above this line indicates any synergistic effect of the diluent in each system. There is diluent synergism with the phosphine oxides, but the data are sparse. The contribution of a diluent becomes more significant as the concentration of acetic acid in the aqueous phase goes up. This effect is the opposite of that observed for amine-based systems. It is also evident that the polarity of the diluent cannot be simply related to its effectiveness. Ricker (1978)made the same observation with respect to trioctylphosphine oxide based systems which have a familial resemblance to those containing Cyanex 923. Cyanex 923 is relatively expensive, so cost arguments pertain strongly to the optimum system. Neat Cyanex is
1980 Ind. Eng. Chem. Res., Vol. 31, No. 8,1992
relative cost model needs refinement through pilot studies. Our work here narrows the scope of future investigations by eliminating extractive systems which are clearly not viable and characterizing those which now appear to be most promising.
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Figure 15. Standard slope vs extractant concentration: phosphine oxide.
not as cost effective as some of the more dilute systems examined. In addition, neat Cyanex is rather viscous at 37 "C and is difficult to disperse into the aqueous phase.
Conclusion A thorough Bcreening evaluation was conducted for some 50 potential systems for the extraction of acetic acid from dilute aqueous streams. Factors considered included the relative cost of the systems as well as toxicity, side reactions, and dispersive properties. On the basis of these criteria, a short list of candidates for further screening was selected. The list of candidates can be further reduced to the following. Adogen 381 40% in Cyclohexanone. This system surpasses tributyl phosphate 33% in 2-heptanone (cyclohexanone) system because it is superior with respect to relative cost and efficiency. It does not emulsify. It does have potential toxicity. Adogen 381 Xy-Mix. Among the systems with no known process problem, this one appears to be the best. The relative costa of all of these systems are about the same, but the slope and distribution coefficients for the tertiary amine based Xy-mixes make them clearly the best candidates. Of the two candidates in this class, it is difficult to distinguish a real difference in performance. The Adogen 381 baaed system is better in mechanical behavior for the forward extraction step but may suffer emulsification problems in the back extraction step leading to calcium magneaium acetate. Thie system forms a milk-like dispersion with the dilute acetic acid aqueous phase which quickly d e s c e a into two transparent p k on standing. Only systems diluted with kerosene behave in this way, and this particular system appears to be the best of these. However, recent experiments in our laboratory show that severe emulsification can be a problem in the stripping step. This problem needs further study. Either of these systems could be used as the basis for the extraction step shown in Figure 1. The extraction of acetic acid from the outflow of a biofermenter is both technically and economicallyfeasible. However,the second step of the process, recovery of the acid as calcium magneaium acetate, needs further inveatigation. The question of how to recycle the extractant, particularly with respect to toxicity and emulsification downstream from the first extractive step, remain to be resolved. The simplified
KD = distribution coefficient N, N = normality X = mass fraction Y = molar concentration Subscripts
e = pertains to the extract f = pertains to the aqueous feed i = pertains to mass fraction of active component in the organic phase r = pertains to the raffinate s = pertains to the recycled extractant system after stripping 0 = initial state of extract system before contact with feed Ragistry No,TBP,126-73-8;Adogen 381,25549-16-0;Adogen 283,57157-80-9;Cyanex 923,100786-00.3;cyclohexanone, 10894-1; cyclohexanol, 108-93-0; acetic acid, 64-19-7;diisobutylcarbinol, 108-82-7;calcium magnesium acetate, 76123-46-1;water, ice, 7732-18-5.
Literature Cited Althouse, J. W. Design of an Organic Extractant for the Production of Calcium Magnesium Acetate. M.S. Thesis, Syracuse University, 1990. American Cyanamid Co., "Cyanex 923 Extractant". Information sheet 86-2408,September 1986. Data, R. Acidogenic Fermentation of Corn Stover. BiotechnoL Bioeng. 1981,23,61. Grinstead, R. R. (Dow Chemical). Extraction of Carboxylic Acids from Dilute Aqueous Solutions. US. Patent 3,816,524,1974. King, C. J. Removal and Recovery of Carboxylic Acids and Phenols from Dilute Aqueous Streams. h o c . Znt. Solvent Ertr. Conf.
1980,2,"6. King, C. J. Acetic Acid Extraction. In Handbook of Solvent Ertraction; Wiley: New York, 1983. Playne, M. J.; Smith,B.R. Toxicity of Organic Extraction Reagents. BiotechnoL Bioeng. 1983,25,1251. Ricker, N. L. Recovery of Carboxylic Acids and Related Organic Chemicals from Wastewaters by Solvent Extraction. Ph.D. Dissertation, University, of California a t Berkeley, 1978. Ricker, N. L.; King, C. J. "Solvent Extraction of Wastewaters from Acetic-Acid Manufacture":- ReDort No. EPA600/2-80-064, U.S. EPA, April 1980. Ricker, N. L.; Michaels, J. N.; King, C. J. Solvent Properties of Organic Bases for Extraction of Acetic Acid from Water. J. S e n Pr&ess Technol. 1979,l (l),36. Ricker, N. L.; Pittman, E. F.; King, C. J. Solvent Extraction with Aminea for Racovery of Acetic Acid from Dilute Aqueous Industrial Streams. J . Sep. Process Technol. 1980,1 (21, 23. Robbins, L. A. Liquid-Liquid Extraction. In Handbook of Separation Techniques for Chemical Engineers; McGraw-Hill: New York, 1979;pp 1-255. Tamada, J. A.; King, C. J. Extraction of Carboxylic Acids with Amine Extractanta. 2. Chemical Interactions and Interpretation of Data. Ind. Eng. Chern. Res. 1990a,29,1327-1333. Tamada, J. A.; King, C. J. Extraction of Carboxylic Acids with Amine Extractaata. 3. Effect of Temperature, Water Coextraction and Proceee Considerations. I d . Eng. Chern. Res. 199Ob,29,
1333-1338. Tamada, J. A.; K e d , A. S.; King,C. J. Extraction Carboxylic Acids with Amine Extractanta. 1. Equilibria and Law of Mass Action Modeling. znd. Eng. Chern. Res. 1990,429,1319-1326.
Znd. Eng. Chem. Res. 1992,31, 1981-1984 Treybal, R. E. Liquid Extraction. In Chemical Engineer's Handbook, 5th ed.; Perry, R. H.,Chilton, C. H.,Eds.; McGraw-Hill: New York, 1973; Section 15. Wardell, J. M. Gas Chromatographic Analyses of Acetic Acid Production Wastewaters and Selection of Solvents for Extraction of the Carboxylic Acids. M.S.Thesis, University of California at Berkeley, 1976. Wardell, J. M.; King, C. J. Solvent Equilibria for Extraction of Carbxylic Acids from Water. J. Chem. Eng. Data 1978,23,144. Watson, E. K.; Rickelton, W. A.; Robertson, A. J.; Brown, T. J. A Liquid Phosphine Oxide: Solvent Extraction of Phenol, Acetic Acid and Ethanol. Solvent Eztr. Zon Ezch. 1988,6 (2), 207. Wise, D. L.; Augenstein, D. An Evaluation of the Bioconversion of Woody Biomass to Calcium Acetate Deicing Salt. Solar Energy 1988,41 (51, 453.
1981
Won, K. W. Phase Equilibria for Extraction of Organic Solutes from Aqueous Waste Streams. Ph.D. Dissertation, University of California at Berkeley, 1974. Xu, J.-G.; Yu, W.; Tian, H.-S.; Su, Y.-F. Removal of Acids from Aqueous Solution of Glyoxal. International Solvent Extraction Conference, Moscow, Conference Papers; USSR Academy of Sciences:, Moscow, 1988; Vol. 3, p 298. Yang, S. T.; White, S. A.; Hsu, S.-T. Extraction of Carboxylic Acids with Tertiary and Quaternary Amines: Effect of pH. Znd. Eng.
Chem. Res. 1991,30,1335-1342.
Received for review April 16, 1992 Accepted May 11, 1992
GENERAL RESEARCH Finishing Additives in Treatments of Cotton Fabrics for Durable Press with Polycarboxylic Acids? B. A. Kottes Andrews* Southern Regional Research Center, Mid South Area, Agricultural Research Service, U. S. Department of Agriculture, New Orleans, Louisiana 70179
Billie J. Collier School of Human Ecology, Louisiana State University, Baton Rouge, Louisiana 70803
Recent activities by regulatory agencies that have limited the amount of formaldehyde that can be released by textiles have led to research on nonformaldehyde finishing for durable press. At the Southern Regional Research Center, we have discovered polycarboxylic acids as replacements for the currently-used methylol amide agents which give finishes that can release formaldehyde over the life of the textile. The ester finishes from these polycarboxylic acids, while as durable to home laundering as those from methylol amide agents, do not produce the same handle as the traditional ether finishes. Incorporation of certain finishing additives in the fiiish can improve the handle as well as enhance other textile properties. Optimization of pad baths and reaction conditions, and textile performance of the finished fabrics will be discussed.
Introduction At the Southern Regional Research Center (SRRC) we have found that certain polycarboxylic acids will esterify the cellulose hydroxyls of cotton to produce smooth drying textiles (Welch, 1988; Welch and Andrews, 1989a,b; Andrew et al., 1989). With the proper catalysis,ester f d e s from butanetetracarboxylic acid (BTCA) are as durable to home laundering as those from amidomethyl ether counterparts (Welch, 1990). Others have extended these findings to pilot scale processing (Brotherton et al., 1989; Brodmann, 1990). Also, with proper catalysis, citric acid can be used to produce cotton fabrics with acceptable durable press levels (Andrews, 1990). One failure of the polycarboxylic acid-finished fabrics, however, has been the noticeable lack of a smooth, crisp hand associated with fabrics finished with methylol amide-based agents. 'Presented, in part, at the 1990 Gulf Coast Textile Chemistry Conference of the Gulf Coast Section, American Association of Textile Chemists and Colorists, Dallas, T X , March 1-2, 1990.
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In this study, we have investigated the effect of inexpensive additives, both reactive and thermoplastic, that change fabric handle, on textile properties of fabrics finished with BTCA or citric acid (CA).
Experimental Section The fabric was an 80 X 80 cotton print cloth, desized, scoured, and bleached, weighing 3.2 oz/yd2. Butanetekacarboxylic acid and citric acid were obtained as reagent grade chemicals from Aldrich Chemical Co. [Names of companies or commercial products are given solely for the purpose of providing specific information; their mention does not imply endorsement by the U. S. Department of Agriculture over others not mentioned.] Sodium hypophoephite monohydrate catalyst was obtained from Baker Chemical Co.as a reagent grade chemical. The polycarboxylic acids and catalyst were used as 6% solids concentration of the aqueous padding solutions. The reactive additives, poly(oxyethy1eneglycols) (PEG) of molecular weight 400,600, and 1O00, glycerol (GLY), and diethylene glycol (DEG) were also reagent grade 1992 American Chemical Society
