Recovery of acrylic acid from process or waste water streams

Details Recovery of acrylic acid from process or waste water streams Recovery of acrylic acid from process or waste water streams

1999-01-14

2001-01-30

Killos, Paul J. (Department: 1623)

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acids and salts thereof

C562S513000

Reexamination Certificate

active

06180827

ABSTRACT:

SUMMARY 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. 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 Acrylic acid is withdrawn from the top of the stripper as the product or as the subject for farther purification. The lean solvent from the bottom of the stripper is recycled back to the absorption column for reuse.
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° C.
Boiling Point
310° C. at 50 mm Hg
Solubility in Water
10 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), glycols (including tetraethylene glycol), pyrrolidones (including N-methyl pyrrolidone and 2-pyrrolidone), morpholines (including N-formyl morpholine), acetarnides (including dimethyl acetamide), formamides (including dimethyl formamide), tertiary amines, etc.


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