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Separation of Formic Acid/Dioxane and Formic Acid/3-Methyl-2-Butanone By Separation of formic acid/dioxane and formic acid/3-methyl-2-butanone by extractive distillation by Richard Randolph Rall A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Chemical Engineering Montana State University © Copyright by Richard Randolph Rall (1989) Abstract: Extractive distillation of the formic acid/dioxane and formic acid/3-methyl-2-butanone azeotropes was investigated using dimethylformamide or dimethylacetamide admixed with other oxygenated or nitrogen-containing organic compounds. Initial screening of extractive agents at two concentrations was carried out in an Othmer vapor-liquid equilibrium still. Over eighty extractive agents were evaluated in all. Subsequent testing of selected agents was carried out in a perforated-plate rectification column which was found to have the equivalent of 5.3 theoretical plates. Relative volatilities for extractive distillation runs made in the plate column were calculated using the Fenske equation. Both azeotropes investigated were successfully negated using some of the extractive agents. In all cases formic acid was recovered as a bottoms product. The use of polarity diagrams was investigated as a means of screening potential extractive agents. Polarity diagrams were found to be a simple and effective technique for determining system behavior in the plate column. SEPARATION OF FORMIC ACID/DIOXANE AND FORMIC ACID/3-METHYL-2-BUTANONE BY EXTRACTIVE DISTILLATION by Richard Randolph Rail A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Chemical Engineering MONTANA STATE UNIVERSITY Bozeman, Montana March 1989 APPROVAL of a thesis submitted by- Richard Randolph Rail This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citations, bibliographic style, and consistency, and is ready for submission to the College of Graduate Studies. t oaeChairperson, Graduatfeate CoDate Committee Approved for the Major Department 3-7 , / W Date4— ^ ^ad, Major Department Approved for the College of Graduate Studies “ 7" z Date iii STATEMENT OF PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a master's degree at Montana State University, I agree that the Library shall make it available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission provided that accurate acknowledgement of source is made. Permission for extensive quotation from or reproduction of this thesis may be granted by my major professor, or in his absence, by the Dean of Libraries when, in the opinion of either, the proposed use of the material is for scholarly purposes. Any copying or use of the material in this thesis for financial gain shall not be allowed without my written permission. Signature Date iv TABLE OF CONTENTS page APPROVAL............................................... ... • ii STATEMENT OF PERMISSION TO USE ......................... iii TABLE OF CONTENTS........................................ iv LIST OF TABLES........................................... vi LIST OF FIGURES.......................................... vii ABSTRACT.................................................. viii INTRODUCTION.............................................. I Distillation In General.......... '................ I Extractive and Azeotropic Distillation......... 3 Extractive Agent Selection........................ 7 THEORETICAL ASPECTS OF DISTILLATION................... 9 Thermodynamics of Vapor-Liquid Equilibrium...... 9 Relative Volatility................................ 12 The Fenske Total-Reflux Equation................. 13 THEORETICAL ASPECTS OF EXTRACTIVE DISTILLATION...... 16 Altering Relative Volatility..................... 16 Extractive Agent Selectivity................ 17 Factors Affecting Selectivity.................... 17 Prediction of Attractive Interactions........... 19 RESEARCH OBJECTIVES...................................... 21 AZEOTROPIC SYSTEMS TO BE SEPARATED..................... 22 Formic Acid/Dioxane................................ 22 Formic Acid/3-Methyl-2-Butanone.................. 23 V TABLE OF CONTENTS-Continued page EXPERIMENTAL AND ANALYTICAL EQUIPMENT................. 25 Othmer Vapor-Liquid Equilibrium Still........... 25 Perforated-Plate Column........................... 27 Extractive Agent Recovery....................... 30 Gas Chromatograph for Sample Analysis........... 31 EXPERIMENTAL PROCEDURE.................................. 3 3 Operation of the Othmer Still.................... 3 3 Calibration of the Perforated-Plate Column...... 33 Extractive Distillation Using the Plate Column.. 35 RESULTS...... 37 The Formic Acid/Dioxane System................... 37 The Formic Acid/3-Methyl-2-butanone System...... 41 DISCUSSION................................................ 45 Data From the Othmer Still....................... 45 Data From the Perforated-Plate Column........... 4 6 Solubility Parameters and Polarity Diagrams.... 49 SUMMARY AND CONCLUSIONS................................. 54 RECOMMENDATIONS FOR FUTURE RESEARCH................... 55 LITERATURE CITED.................................. ...... 56 vi LIST OF TABLES Table Page 1 Favorable characteristics of an extractive agent.. I 2 Relative volatility vs. theoretical plates........ 15 3 Agents for formic acid/dioxane...................... 37 4 Column results: formic acid/dioxane................ 40 5 Agents for formic acid/3-methyl-2-butanone........ 41 6 Column results: formic acid/3-methyl-2-butanone... 43 7 Agents which decomposed formic acid................ 44 8 Solubility parameters and volumetric data at 25 0C. 49 \ vii LIST OF FIGURES Figure page 1 Fractional distillation column................ 2 2 Extractive distillation column................... 6 3 Structures and physical data for key components. 24 4 Othmer vapor-liquid equilibrium still,............ 26 5 Batch-wise extractive distillation column.... 28 6 Agent recovery by simple distillation............. 32 7 Polarity diagram for formic acid/dioxane system. 51 8 Polarity diagram for formic acid/3-methyl- 2-butanone system............... 52 viii ABSTRACT Extractive distillation of the formic acid/dioxane and formic acid/3-methyl-2-butanone azeotropes was investigated using dimethylformamide or dimethylacetamide admixed with other oxygenated or nitrogen-containing organic compounds. Initial screening of extractive agents at two concentrations was carried out in an Othmer vapor-liquid equilibrium still. Over eighty extractive agents were evaluated in all. Subsequent testing of selected agents was carried out in a perforated-plate rectification column which was found to have the equivalent of 5.3 theoretical plates. Relative volatilities for extractive distillation runs made in the plate column were calculated using the Fenske equation. Both azeotropes investigated were successfully negated using some of the extractive agents. In all cases formic acid was recovered as a bottoms product. The use of polarity diagrams was investigated as a means of screening potential extractive agents. Polarity diagrams were found to be a simple and effective technique for determining system behavior in the plate column. I INTRODUCTION Distillation In General Fractional distillation is the process of separating a mixture of two dr more volatile substances into its components by a series of vaporizations and condensations [I]. This process takes advantage of component concentration differences in the liquid and vapor phases at equilibrium. This concentration difference is generally quantified in a term known as the relative volatility of the components. The distillation process is the oldest and most widely used of all liquid separation techniques [2]. Because it is a simple and effective separation technique that is well understood and easily scaled up from the laboratory bench to commercial design, it is of extreme commercial value to the chemical industry [3]. In 1976, 2.25 trillion pounds of materials were separated by distillation [4]. One of the few drawbacks to the distillation process is its energy intensiveness. Three percent of our nation's energy used in 1976 was consumed by distillation, a total of 2 quads of energy [4]. Figure I on page 2 illustrates a typical fractional distillation column [5]. Feed enters the column at or near a stage which has approximately the same liquid composition 2 Condenser Overhead Product -H c -P o Feed Plate -H o -H U -P Ui Reboiler Bottoms Product Figure I. Fractional distillation column 3 as the feed. The "plate" where the feed enters the column is referred to as the feed plate. All plates below and including the feed plate constitute the stripping section of the column. Plates above the feed plate constitute the rectification section. Liquid from the feed plate travels downward through the column and is intimately contacted by rising vapor at each plate. By trading latent heat of vaporization between the high and low boiling components, the vapor deposits its high boiling component in the liquid phase and removes low boiling component from the liquid as vapor to be carried to the overhead condenser. There it is either completely or totally condensed, part is taken off as product, and the rest returned to travel down the column as liquid. Without this liquid returned to the column no rectification would occur in the rectification section. This liquid serves to wash the high boiling
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