Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-07-20
2002-12-31
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S534000, C549S536000, C549S541000
Reexamination Certificate
active
06500970
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to a process of recovering and purifying 3,4-epoxy-1-butene (epoxybutene) from a reaction product gas, obtained by the vapor phase catalytic partial oxidation of 1,3-butadiene with oxygen over a silver catalyst. More specifically, the present invention pertains to a process of recovering epoxybutene from an epoxybutene-laden reaction product gas by absorption into a high-boiling solvent. This invention also pertains to a method of separating epoxybutene from the solvent and other reaction by-products by a novel combination of distillation and decantation steps.
BACKGROUND OF THE INVENTION
Ethylene oxide (EO) and epoxybutene both may be produced in large scale plants by similar catalytic partial oxidations of the corresponding olefin with oxygen over a silver catalyst. See for example, U.S. Pat. Nos. 2,773,844 and 3,962,136, and 4,356,312 for EO and U.S. Pat. Nos. 4,897,498, 4,950,773, and 5,081,096 for epoxybutene. Considerable effort has been devoted to the development of efficient methods of recovering these epoxides, particularly EO, from the reaction product gas and subsequent purification of the epoxide.
According to U.S. Pat. Nos. 3,745,092 and 3,964,980 and Dever et al.
Ethylene Oxide,
in
Kirk
-
Othmer Encyclopedia of Chemical Technology,
4th Ed., 1994, pp. 929-930, EO is recovered and purified according to the following procedure. A reaction product gas containing typically 0.5 to 5% EO, obtained by the vapor phase catalytic oxidation of ethylene with oxygen over a silver catalyst, is introduced to an EO absorption tower where it is contacted counter-currently with an absorbent comprised mostly of water, within which the EO is absorbed. The absorber is typically maintained at a temperature of 5 to 40° C. and 10 to 30 bars absolute (bara).
The EO-laden absorbent is then sent to a stripping column where vaporous EO is recovered from the top of the tower at a temperature of 85 to 140° C. by steam stripping at reduced pressure. The water remaining after the distillation of EO is recycled to the absorption tower for reuse. EO reacts readily with water under absorption and distillation conditions to form ethylene glycol, which can react further to form diethylene glycol, triethylene glycol, and higher oligomers. Although ethylene glycol is a valuable and marketable chemical, diethylene glycol and higher oligomers have much less commercial demand and are thus generally undesirable by-products. Formation of ethylene glycol oligomers can be controlled to some extent by limiting ethylene glycol concentration in the recycled water to the absorber. Typical levels are less than 10 weight per cent ethylene glycol in the recycled absorber water.
The crude EO vapor recovered in the stripper overhead comprises EO as the main component, as well as impurities such as water, argon, nitrogen, carbon dioxide, methane, ethane and ethylene, formaldehyde, and acetaldehyde. The light or low-boiling components, e.g., nitrogen, carbon dioxide, argon, methane, ethane, and ethylene are removed overhead in a second stripping column. The partially purified EO is removed from the lower section of base of the second stripping column and is transferred to the mid-section of a refining column for final purification. U.S. Pat. Nos. 5,529,667 and 3,418,338 disclose the use of extractive distillation with water as a solvent in either the second stripping column or the refining column to reduce the level of aldehyde impurities in the final purified EO product.
By employing the above-described procedure, EO purities of greater than 99.5 mole per cent are possible. Although these water-based processing steps function effectively for EO recovery and purification, they cannot be employed equally efficaciously for the recovery and purification of epoxybutene. Firstly, whereas EO is completely and infinitely miscible with water, epoxybutene is only sparingly miscible with water. At 25° C., the solubility of epoxybutene in water is only about 5 to 6 weight percent. As a result, water is a very poor absorbent for epoxybutene. High water to epoxybutene ratios, e.g., upward of 50/1 to 150/1, are required to ensure complete absorption of epoxybutene from the reaction off gas. Such ratios are prohibitive from equipment cost and energy usage standpoints.
Secondly, EO is a relatively low-boiling component compared to water, i.e., normal boiling point of 10.4° C. versus 100° C., respectively, and does not form an azeotrope with water. Thus, EO can be distilled readily from water by simple fractional distillation techniques as described above for the conventional EO recovery scheme. However, epoxybutene is much more hydrophobic than EO and forms a minimum-boiling azeotrope with water. High purity epoxybutene cannot be obtained by the simple fractional distillation techniques employed for EO recovery.
Other methods proposed for recovery of EO from ethylene oxidation effluents likewise are not effective or are uneconomical for epoxybutene recovery and purification. For example, U.S. Pat. No. 3,948,621 discloses a method of separating EO and carbon dioxide simultaneously from a mixed gas obtained from catalytic oxidation of ethylene by oxygen using methanol as an absorbent. As with water, epoxybutene forms a minimum-boiling azeotrope with methanol and, thus, epoxybutene and methanol cannot be separated readily by simple fractional distillation.
U.S. Pat. Nos. 4,437,938 and 4,437,939 disclose methods using supercritical or near supercritical carbon dioxide and water at the same time as absorbents. EO is first absorbed into water as in conventional recovery methods. The EO-rich aqueous absorbent contacted with (near) supercritical carbon dioxide, and EO is extracted to the carbon dioxide solvent. The carbon dioxide is separated from EO by distillation under reduced pressure. The carbon dioxide is recompressed before recycling as the extraction solvent. This method, however, has many drawbacks. First, the required amount of (near) supercritical carbon dioxide is approximately 35 times the amount of EO to be absorbed therein, resulting in large equipment. The extraction is carried out at high pressures, e.g., 86 bara, while the distillation step is carried out at lower pressure, i.e., about 0.1 to 2 bara. The wide pressure swings results in high compression costs and thus does not provide an economical solution.
U.S. Pat. Nos. 4,221,727 and 4,233,221 discloses an EO recovery method that uses ethylene carbonate as an absorbent for EO. Ethylene carbonate has many advantages as an absorbent. The absorption affinity of ethylene carbonate for EO is higher than that of water. The vapor pressure of ethylene carbonate is quite low, i.e., normal boiling point of 239° C., so losses into the recycle gas are minimal. Moreover, ethylene carbonate is stable and does not directly react with EO. The process disclosed in U.S. Pat. No. 4,233,221, however, has the following drawbacks for EO and epoxybutene recovery. The most preferred temperature range for operation of conventional water absorption of EO is 5 to 40° C. The melting point of ethylene carbonate is 39° C., so ethylene carbonate would be a solid over almost all of the preferred temperature range. In order to avoid solidification it is necessary to operate the absorber and other processing equipment substantially above, i.e., at least 10 to 20° C., above the melting point of ethylene carbonate. This is much higher temperature than an operation using water. The absorbing power of the ethylene carbonate correspondingly decreases so that the amount of circulating absorbent must be increased, reducing the economic utility of the process.
U.S. Pat. No. 5,559,255 describes the use of propylene carbonate as an absorbent for EO. The EO-laden propylene carbonate is stripped with an inert gas to recover EO and the water by-product from the epoxidation reactor as a vapor. Purified EO is produced from the mixed water-EO vapors as in conventional methods described in U.S. Pat. Nos. 3,745,092 and 3,964,980. Unlike ethylene carbonate, propylene
Barnicki Scott Donald
Hamilton Jackie Lee
Kline Robert Sterling
Stavinoha, Jr. Jerome Leonard
Blake Michael J.
Eastman Chemical Company
Graves, Jr. Bernard J.
Trinh Ba K.
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