Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-04-28
2003-04-29
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S857000, C568S865000, C568S868000
Reexamination Certificate
active
06555720
ABSTRACT:
BACKGROUND OF THE INVENTION
Butanediols, and in particular 1,4-butanediol (1,4-BG), find wide use in the chemical industry. 1,4-BG is used for a variety of purposes, and notable examples of its utility include use as a raw material for the production of a number of chemicals such as for the production of polyester. A number of processes are conventionally utilized to produce 1,4-butanediol. Conventional methods generally employ a hydrolysis reaction to produce 1,4-butanediol. For example, butadiene is reacted in an acetoxylation reaction with acetic acid (AcOH) and Oxygen then further hydrogenated to form 1,4-diacetoxybutane (1,4-DAB). 1,4-DAB is then further reacted with water (H
2
O) in liquid phase to produce 1,4-BG, 1,4-hydroxyacetoxybutane (1,4-HAB) and AcOH. Therefore, the product stream generally includes 1,4-HAB, AcOH, unreacted 1,4-DAB and various by-products. Purified 1,4-BG is typically recovered by multiple distillation steps. Typically, the 1,4-HAB and unreacted 1,4-DAB may be further reacted with H
2
O at different reaction conditions to form tetrahydrofuran (THF).
These conventional methods of producing 1,4-BG and additionally THF, are very energy intensive. Very large amounts of H
2
O are consumed in the hydrolysis reaction. One conventional method of reducing the amount of H
2
O used in the reaction is to employ more than one reaction/separation stage. An example of one illustrative embodiment of a prior art reaction system
10
is shown in
FIG. 1
a
. Typically, multiple hydrolysis reactions are carried out in one or more reactors, and in
FIG. 1
a
three reactor stages in series
12
a
-
12
c
are shown, each having an associated separation stage
14
a
-
14
c
. Large amounts of H
2
O, along with AcOH are separated in the separation stages and then conveyed to a waste water treatment plant (not shown) where the waste is treated which usually includes the recovery of AcOH in an acetic acid purification section (not shown). The boiling point of H
2
O and AcOH are lower than our desirable product(s), and thus they are typically removed as the distillate from the distillation tower. Although a very large relative volatility exists (i.e. the separation is relatively easy), it is necessary to boil off all of the H
2
O and AcOH. Hence, a large amount of energy is consumed.
To reduce the total amount of fresh H
2
O consumption, an alternative embodiment of the system
10
may be used; where typically, fresh H
2
O will only be added to the last stage of the reactors (i.e.
12
c
) in series, as shown in
FIG. 1
b
. Then, the H
2
O together with AcOH formed in this separator of the last stage reactor, is recycled back to the previous reactor, or alternatively a recycled back to both of the previous reactors, and further, H
2
O and AcOH formed in the separator of the middle stage reactor may also be recycled to the first reactor as shown in
FIG. 1
b
. This typical recycling system increases the total amount of H
2
O consumption slightly, however we can reduce the amount of total fresh H
2
O consumption significantly, consequently we will lower the energy consumption at the AcOH purification section and reduce the loading on the waste water treatment plant. However, regarding the total energy consumption for the overall system
10
, it is still dominated by the total amount of H
2
O usage in the reactors, as a large amount of energy is needed to vaporized the H
2
O and AcOH from the mixture in the separators.
To understand the relationship of H
2
O usage (and therefore energy consumption) to the amount of 1,4-BG and 1,4-HAB production, lets start with the simple case of a system having one reactor stage with no recycle stream or system.
FIG. 2
a
shows the performance of such a prior art reaction system. The x-axis shows the amount of H
2
O usage in the reactor, while the y-axis shows the amount of 1,4-BG production (curve A) and the corresponding production of 1,4-HAB (curve B) for a fixed feed amount of 1,4-DAB (in this example 12,800 kg/hr of 1,4-DAB as feed). It clearly shown that to achieve a typical desirable yield of 1,4-BG to 1,4-HAB (i.e., 1,4-BG/1,4-HAB mix) of a ratio of say 6:1 (5929 kg/hr-1,4-BG and 988 kg/hr-1,4-HAB), a large amount of H
2
O is used, in this case 145,000-kg/hr H
2
O. To determine the H
2
O efficiency of such as system, the amount of product, in this case 5929 kg/hr of 1,4-BG is divided by the total amount of H
2
O used (145,000 kg/hr) to arrive at a water efficiency of only 4.09%. This is illustrated in
FIG. 2
b
where Curve I shows the production of 1,4-BG and Curve II is the water efficiency.
To reduce this amount of total H
2
O usage and/or energy consumption, one method used is to introduce an additional number of reactors to the system
10
, as mentioned above. Moreover, since the system is employing multiple reactor stages, it is possible to reduce the total amount of fresh H
2
O by recycling the H
2
O from the separators to one or more of the previous reactors. However, in doing so, there is a very small penalty on the total amount of H
2
O usage.
There is another element that needs to be considered when determining the best overall performance of the system
10
. This additional element is the capital cost of the system
10
. For this hydrolysis reaction system, since it is an equilibrium reaction and the reaction conditions are close to equilibrium. Further, the amount of H
2
O flow in the system is almost equal to the total flowrate at the system due to the small value of equilibrium constant. Therefore, the amount of total H
2
O usage can be used as the measurement of the capital cost. This is because as the system uses more H
2
O, the reactor size is greater, and consequently the capital cost of the system is higher.
While the amount of H
2
O usage, and thus the energy consumption or costs, associated with producing 1,4-BG and additionally THF are reduced by employing more reactor stages (i.e. reactors/separators) and H
2
O recycle streams, the capital costs increase with the addition of these units. The prior art system configuration employing three reactors/separators and two H
2
O/AcOH recycle streams is desirable from both an energy and capital cost point of view. For the capital cost, although this prior art configuration uses two additional reactors as compared to the single reactor case, the total flow rate for the reactor system is significantly smaller than that for the single reactor case. Consequently, the size of the equipment is much smaller and this offsets the cost of the additional equipment necessary for the three-reactor configuration. Hence, in this instance the total capital cost for the three reactors with two H
2
O/AcOH recycle streams is lower than that for the one reactor with no H
2
O/AcOH recycle. However, there are many variables, constraints and tradeoffs between the energy costs and capital costs that must be considered.
Another technique that has been employed in the prior art is to recycle 1,4-HAB produced in the reaction back to the reactor. For example, Japanese Patent No. 55-16489 discloses recycling AcOH, diols and/or 1,4-HAB to a reactor. Japanese Patent No. 11-169435 describes recycling an effluent stream including 1,4-HAB to one or more reactors and focuses on reducing the amount of 1,4-HAB recycle. While these methods have provided an improved process, further improvement is desirable. Moreover, in these prior art patents it is believed that the desirable product is only 1,4-BG. Consequently, 1,4-HAB is considered as a waste and thus recycling it will be desirable. Accordingly, it would be highly desirable to provide a method and system for producing 1,4-BG, and optionally additionally THF, which promotes the more efficient usage of H
2
O and is capable of minimizing both the operating or energy costs of production and the capital expense of the system.
SUMMARY OF THE INVENTION
Accordingly, in summary, it is an object of the present invention to provide a method and system for producing 1,4-BG, and optionally additionally THF, in a hydrolysis reaction of 1,4-DAB.
It is another object of t
Iwasaka Hiroshi
O'Young Lionel
Ookubo Kazuyuki
Toratani Nobuo
Dorsey & Whtiney LLP
Mitsubishi Chemical Corporation
Price Elvis O.
Richter Johann
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