RECOVERY OF ACRYLIC ACID FROM PROCESS OR WASTE WATER STREAMS

Abstract: Disclosed is a method for recovering acrylic acid from process or waste water streams in which the stream is vaporized and contacted with a liquid high boiling solvent for acrylic acid, thereby absorbing acrylic acid into the solvent. Mixed trialkylphosphine oxides are a preferred solvent. Acrylic acid is stripped from the solvent with heat and, optionally, stripping gas. It may be separated from any accompanying materials to produce acrylic acid of high purity.

Description: RECOVERY OF ACRYLIC ACID FROM PROCESS OR WASTE WATER STREAMS TECHNICAL FIELD OF THE INVENTION This invention is related to a novel absorption process for recovering acrylic acid from an acrylic acid-containing process or waste water stream. DISCLOSURE OF THE INVENTION In this process, a high boiling liquid solvent is used to contact a vapor feed stream containing acrylic acid , in a counter-current or co-current fashion in a column. The column normally contains trays or packings to facilitate the necessary vapor and liquid contact, allowing acrylic acid to be absorbed by the solvent. For example, the lean (liquid) solvent can be fed near the top the column, while the vapor feed stream can enter the column near the bottom of the column. As the lean solvent flows down through the column, it contacts the upcoming vapor stream and preferentially absorbs acrylic acid from the vapor stream. The rich (acrylic acid-laden) solvent exits the column at the bottom, while the acrylic acid-removed vapor stream exits at the top the column. The rich solvent is then fed to the middle portion of a solvent stripper where acrylic acid is stripped from the solvent by heat alone, or heat in combination with stripping nitrogen. Acrylic acid is withdrawn from the top of the stripper as the product or as the subject for further purification. The lean solvent from the bottom of the stripper is recycled back to the absorption column for reuse. 1 In accordance with a preferred embodiment of the invention, the high boiling liquid solvent is a phosphine oxide solvent, such as CYANEX 923 manufactured by Cytec Corporation, and is used as the absorption solvent in the invention. It is a mixture of four trialkylphosphine oxides, and has a reported composition as follows: R 3 P(O) R 2 R'P(O) RR 2 'P(O) R 3 'P(O) Where R = [CH 3 (CH 2 ) 7 ] - normal octyl R' = [CH 3 (CH 2 ) 5 ] - normal hexyl Average Molecular Weight = 348 (approximately) Typical properties of this solvent are reported as follows: Trialkylphosphine oxides 93% Appearance Colorless mobile liquid Specific Gravity 0.88 at 23° C. Freezing Point -5 to 0° C. Viscosity 40.0 centipoise at 25° C. 13.7 centipoise at 30° C. Flashpoint 182° C. (Closed Cup Setaflash) Autoignition Temperature 218° C. Vapor Pressure 0.09 mm Hg at 31 o C. Boiling Point 310° C at 50 mm Hg Solubility in Water lO mg/l Solubility of Water in 8 wt % CYANEX 923 extractant When in this specification and in the accompanying claims the term 'solvent consisting essentially of mixed trialkylphosphine oxides' is used, the material referred to is that just described and characterized above, and its equivalents. The non-limiting solvents for this invention also include dialkyl alkyl phosphinates, alkyl dialkyl phosphinates, trialkyl phosphine oxides, dialkyl alicyclic amidophosphates, dialkyl sulfoxides, tetra-alkyl ureas, sulfones (including sulfolane), 2 glycols (including tetraethylene glycol), pyrrolidones (including N-methyl pyrrolidone and 2-pyrrolidone), morpholines (including N-formyl morpholine), acetamides (including dimethyl acetamide), formamides (including dimethyl formamide), tertiary amines, etc. BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a schematic diagram of a sample absoφtion column. Figure 2 is a schematic process flow diagram of a process scheme for commercial applications. SUMMARY OF THE INVENTION The advantages of the present invention are more clearly described in the following examples but they do not limit it in any way. EXAMPLE 1 Test runs were conducted in a stainless steel absoφtion column 2-inches in diameter and 14 feet high packed with 8 feet of structured packings. A schematic diagram of this absoφtion column is shown in Figure 1. A vapor feed stream withdrawn from a commercial acrylonitrile reactor was fed to a point near the bottom of the absoφtion column. The vapor feed composition is given in Table 1. TABLE 1 Component Weight percent CO 0.96 CO 2 2.47 N 2 62.20 NH 3 0.40 o 2 1.49 Propane 0.04 Propylene 0.30 HCN 1.89 Acrolein 0.15 Acrylonitrile 11.57 Acetonitrile 0.53 H 2 O 17.64 Acetic acid 0.02 Acrylic acid 0.26 The vapor feed stream was contacted counter-currently with mixed trialkylphosphine oxides liquid solvent (CYANEX 923 ), which was fed to a point near the top of the column. The product vapor stream was withdrawn from the top of the column. The acrylic acid content in the feed and the product vapor streams were analyzed simultaneously during the operation. The column was operated according to the following conditions: Solvent / feed ratio: 15-50 gallons / 1000 CFM Absoφtion temperature: 200 - 210°C; 170 - 180°C; 130 - 140°C Gas velocity in column: 5 ft/sec (about 7 CFM vapor feed rate) Pressure: 0.6 Kg/cm 2 (gage) The results are summarized in Table 2. TABLE 2 Acrylic acid in Acrylic acid in vapor vapor feed stream product streams % of Acrylic Temperature (°C) kg/hr) (kg/hr) Acid Absorbed 200-210 307 19 93.7 200-210 290 19 93.4 200-210 201 8 96.1 200-210 266 16 94.2 200-210 269 23 91.4 170-180 286 10 96.6 170-180 228 6 97.4 170-180 286 6 98.0 130-140 276 4 98.6 130-140 267 4 98.5 130-140 205 4 98.1 As shown in Table 2, the percent of absoφtion figures at various temperatures are very high, even at temperatures as high as 200 to 210° C. EXAMPLE 2 Based on the experimental results demonstrated in Example 1, in accordance with the invention, a process scheme was developed for commercial applications. The schematic process flow diagram is presented in Figure 2. According to Figure 2, the effluent from an acrylonitrile reactor (207, 118 lbs hr), containing 0.26 wt% acrylic acid is fed to Absorber C-101 through Line 1. The stream is contacted with 22,742 lbs/hr of CYANEX 923 solvent counter-currently in Absorber C-101. Approximately 80% of the acrylic acid is absorbed by the solvent exiting at the bottom of the C-101 via Line 3, while the vapor stream with acrylic acid largely removed exits at the top of the column for further processing in the acrylonitrile plant. The bottoms stream is fed through to Solvent Stripper C-102 where the absorbed acrylic acid is stripped from the solvent by heat or heat plus stripping gas such as nitrogen. The lean solvent (22,742 lbs/hr) is recycled through Line 5 to Absorber C-101 for reuse. The stripped stream (2,596 lbs/hr) containing 16.7 wt% acrylic acid is withdrawn from C-102 via Line 4 and cooled by Cooler E-103 before entering a liquid settler T-102 to remove the heavies (50 lbs/hr). The vapor stream leaving T-102 through Line 6 is further cooled by Cooler E-104 before entering liquid accumulator T-103 which is operated under vacuum to remove lights (1,378 lbs/hr) containing mainly nitrogen and acrylonitrile, to be recycled to the acrylonitrile plant. The liquid stream from T-103 (1,168 lbs hr) with 36.4 wt% acrylic acid, 56.4 wt% water, 3 wt% acetic acid and minor amount of lights is sent to the acrylic acid column to distill off water, acetic acid and lights. The product acrylic acid (428 lbs/hr) at 95 wt% purity is withdrawn at the bottom of Column C-103 through Line 12. The detailed material balance figures for all process streams shown in Figure 2 are presented in Table 3. TABLE 3 1 2 3 4 lbs/hr wt% lbs/hr wt% lbs hr wt% lbs hr wt% CO 1989 0.96 1979 0.97 10 0.38 10 0.38 co 2 5128 2.48 5102 2.49 26 0.99 26 0.99 N 2 128834 62.20 128190 62.68 644 24.82 644 24.82 NH 3 820 0.40 812 0.40 8 0.32 8 0.32 o 2 3078 1.49 3063 1.50 15 0.59 15 0.59 Propane 75 0.04 74 0.04 1 0.03 1 0.03 Propylene 611 0.30 605 0.30 6 0.24 6 0.24 HCN 3911 1.89 3872 1.89 39 1.51 39 1.51 Acrolein 315 0.15 312 0.15 3 0.12 3 0.12 Acrylonitrile 23966 11.57 23487 11.48 479 18.47 479 18.47 Acetonitrile 1096 0.53 1074 0.53 22 0.84 22 0.84 Methacrylonitrile 130 0.06 33 0.02 98 3.76 98 3.76 H 2 0 36526 17.64 35795 17.50 731 28.14 731 28.14 Acetic Acid 44 0.02 9 0.00 35 1.36 35 1.36 Acrylic Acid 542 0.26 108 0.05 434 16.71 434 16.71 Nicotinonitrile 53 0.03 8 0.00 45 1.74 45 1.74 Solvent Total lbs/hr 207118 100.00 204522 100.00 2596 100.00 2596 100.00 Moles, Ibmols 7581 7496 85 85 TABLE 3 Continued 5 6 7 8 lbs/hr wt% lbs/hr wt% lbs/hr wt% lbs/hr ■ wt% CO 0 0.00 10 0.39 0 0.00 10 0.73 co 2 0 0.00 26 1.02 0 0.00 26 1.89 N 2 0 0.00 644 25.30 0 0.00 644 46.72 NH, 0 0.00 8 0.31 0 0.00 8 0.58 o 2 0 0.00 15 0.59 0 0.00 15 1.09 Propane 0 0.00 1 0.04 0 0.00 1 0.07 Propylene 0 0.00 6 0.24 0 0.00 6 0.44 HCN 0 0.00 39 1.53 0 0.00 39 2.83 Acrolein 0 0.00 3 0.12 0 0.00 3 0.22 Acrylonitrile 0 0.00 479 18.81 0 0.00 455 33.01 Acetonitrile 0 0.00 22 0.86 0 0.00 20 1.44 Methacrylonitrile 0 0.00 98 3.85 0 0.00 78 5.69 H j O 0 0.00 731 28.71 0 0.00 73 5.30 Acetic Acid 0 0.00 34 1.35 1 1.41 0 0.00 Acrylic Acid 0 0.00 425 16.69 9 17.37 0 0.00 Nicotinonitrile 0 0.00 5 0.18 41 81.22 0 0.00 Solvent 22742 100.00 Total lbs hr 22742 100.00 2546 100.00 50 100.00 1378 100.00 Moles, Ibmols 65 84 1 41 TABLE 3 (Continued) 9 10 11 12 lbs hr wt% lbs hr wt% lbs/hr wt% lbs/hr wt% CO 0 0.00 0 0.00 0 0.00 0 0.00 co 2 0 0.00 0 0.00 0 0.00 0 0.00 N 2 0 0.00 0 0.00 0 0.00 0 0.00 NH 3 0 0.00 0 0.00 0 0.00 0 0.00 o 2 0 0.00 0 0.00 0 0.00 0 0.00 Propane 0 0.00 0 0.00 0 0.00 0 0.00 Propylene 0 0.00 0 0.00 0 0.00 0 0.00 HCN 0 0.00 0 0.00 0 0.00 0 0.00 Acrolein 0 0.00 0 0.00 0 0.00 0 0.00 Acrylonitrile 24 2.05 24 9.55 0 0.00 0 0.00 Acetonitrile 2 0.19 2 0.88 0 0.00 0 0.00 Methacrylonitrile 20 1.68 20 7.81 0 0.00 0 0.00 H 2 0 658 56.35 197 78.69 451 92.34 9 2.15 Acetic Acid 34 2.95 3 1.38 25 5.08 6 1.45 Acrylic Acid 425 36.39 4 1.69 13 2.58 408 95.34 Nicotinonitrile 5 0.39 0 0.00 0 0.00 5 1.05 Solvent Total lbs hr 1168 100.00 251 100.00 489 100.00 428 100.00 Moles, Ibmols 44 12 26 6

Claims: What is claimed is: 1. A method for recovering acrylic acid from an acrylic acid-containing process or waste water stream comprising: vaporizing said acrylic acid-containing process or waste water stream if it is a liquid form to form a vapor stream containing acrylic acid; contacting said vapor stream with a liquid high boiling solvent for acrylic acid, thereby absorbing acrylic acid into said solvent to form a rich solvent; and stripping acrylic acid from said rich solvent to thereby recover it. 2. A method in accordance with claim 1 in which said vapor stream and said liquid solvent are contacted in counter-current flow. 3. A method in accordance with claim 1 in which said liquid high boiling solvent consists essentially of mixed trialkylphosphine oxides. 4. A method in accordance with claim 1 in which said liquid high boiling solvent is selected from the class consisting of dialkyl alkyl phosphinates, alkyl dialkyl phosphinates, trialkyl phosphine oxides, dialkyl alicyclic amidophosphates, dialkyl sulfoxides, tetra-alkyl ureas, sulfones, sulfolane, glycols, tetraethylene glycol, pyrrolidones, N-methyl pyrrolidone, 2-pyrrolidone, moφholines, N-formyl moφholine, acetamides, dimethyl acetamide, formamides, dimethyl formamide, and tertiary amines. 5. A method in accordance with claim 1 in which said stripping of acrylic acid from said rich solvent is performed by heating said solvent. 6. A method in accordance with claim 5 and further in which a stripping gas is passed through said rich solvent to aid in stripping acrylic acid therefrom. 7. A method in accordance with claim 1 in which lean solvent resulting from said stripping of said rich solvent is recycled to contact additional vapor containing acrylic acid. 8. A method in accordance with claim 1 in which acrylic acid stripped from said rich solvent is separated from water and organic materials accompanying it to produce high purity acrylic acid. 9. A method in accordance with claim 8 in which said acrylic acid stripped from said rich solvent is separated from any materials accompanying it by forming a second vapor stream of acrylic acid and accompanying materials, cooling said second vapor stream to condense and thereby separate from it relatively heavy accompanying materials, further cooling said second vapor stream to condense from it acrylic acid, water, acetic acid, and other accompanying materials, leaving a vapor stream containing nitrogen and acrylonitrile, and distilling the condensed acrylic acid, water, acetic acid and other accompanying materials to thereby recover acrylic acid of high purity. 10

Inventors: GUALY RONALD G, LEE FU-MING, GUALY, RONALD, G., LEE, FU-MING
Applicants: HFM INT INC, HFM INTERNATIONAL, INC.
Application year: 1999
Main classification: C07C51
IPC codes: C07C51