Distillation: processes – separatory – With measuring – testing or inspecting – Of concentration
Reexamination Certificate
2001-07-09
2003-09-02
Manoharan, Virginia (Department: 1764)
Distillation: processes, separatory
With measuring, testing or inspecting
Of concentration
C203S008000, C203S049000, C203S098000, C203SDIG007, C203SDIG002, C562S600000
Reexamination Certificate
active
06613196
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for stopping a purifying column which handles an easily polymerizing compound-containing solution and more particularly to a method for stopping a purifying column which, by the supply of an inert gas, lowers the oxygen concentration in the interior thereof below the limit and consequently avoids a flammable range.
2. Description of the Related Art
Such easily polymerizing compounds as acrylic acid and methacrylic acid are raw materials for commercial production and are chemical substances which are produced in a large amount at a plant of a large scale. In the case of (meth)acrylic acid, for example, the easily polymerizing compound is produced by the reaction of catalytic gas phase oxidation of propylene, isobutylene, t-butanol, methyl-t-butyl ether, or acrolein. The reaction gas obtained by this reaction of catalytic gas phase oxidation contains (meth)acrylic acid, the target product, as mixed with other by-products. For example, this reaction generates mainly non-condensable gases, namely unreacted propylene and, isobutylene, low-boiling compounds having lower boiling points than acrylic acid, namely steam and unreacted acrolein, formaldehyde produced by a side reaction, and impurities such as acetic acid, and high-boiling compounds having higher boiling points than acrylic acid, namelymaleic anhydride, furfural, benzaldehyde, benzoic acid, and acrylic acid dimer. For the purpose of purifying this reaction gas thereby producing the target product, therefore, the reaction gas is washed and extracted with a counter flow water or a heavy solvent , and then the extraction is supplied to a purifying column and purifying it therein generally. Further, since the purifying column for an easily polymerizing compound is liable to give birth to a polymer of the compound owing to the properties of the compound itself, the practice of supplying a molecular oxygen-containing gas for the purpose of preventing the generation of the polymer is popularly employed.
The supply of the molecular oxygen-containing gas, however, results in enlarging the possibility of inducing explosion. When the concentration of the molecular oxygen-containing gas in the column falls within a specific range, this gas forms an explosive mixed gas and sets off explosion on exposure to a spark emitted by the static electricity. The operation of the purifying column of this nature has a high possibility of entailing combustion, explosion, and damage to equipment because the target product, solvent, generated gas, etc. are shut up in a mixed state in the purifying column. Particularly, the purifying column handling an easily polymerizing compound enlarges this possibility further because the interior of the column forms a multicomponent system and, during a start or a stop of the column, the composition in the column changes every moment unlike the operation proceeding in a stationary state.
The expression “stop of the purifying column” as used herein means an operation of stopping the supply of the raw material and the operation of accessorial devices and, at the same time, causing the interior of the purifying column to revert to the atmospheric pressure. This operation has heretofore followed more often than not the procedure of stopping the heat source and the cooling source, stopping the supply of the raw material, extracting the bottom liquid of the column, and cooling or heating the purifying column sequentially in the order mentioned, and finally causing the internal pressure of the purifying column to revert to the atmospheric pressure. There are times when the procedure of supplying a circulating liquid and a cleaning liquid in place of the raw material after the stop of the supply of the raw material to the purifying column, heating these liquids to a prescribed temperature, circulating the hot mixture of such liquids to the column thereby cleansing the interior thereof, and thereafter stopping the purifying column is performed for the purpose of expelling the residue, scale, rust, etc. from the interior of the column.
In the purifying column which particularly handles an easily polymerizing compound-containing substance, however, there are times when the easily polymerizing compound in the gaseous state condenses and induces adhesion of a polymer to the inner wall of the column, the pipes, and other accessorial devices during the course of the operation for stopping the column. Thus, the supply of the molecular oxygen-containing gas to the interior of the column is continued and the possibility of the purifying column incurring combustion and explosion persists. Particularly, the air which is supplied for allowing the inner pressure of the column to revert to the atmospheric pressure has the possibility of changing the gas composition in the column and setting off combustion and explosion on exposure to a slight impulse such as static electricity.
For the purpose of precluding such combustion and explosion, the method which comprises supplying steam to the interior of the column and causing the inner pressure of the column to revert to the atmospheric pressure has been heretofore adopted after the internal liquid of the column has been extracted from the column. In this case, the interior of the column is left cooling naturally. The natural cooling, however, requires an unduly long time till the inner temperature of the column falls to an expected level and suffers the easily polymerizing compound-containing gas to condense and form a polymer in the column. Such a polymer, in the purifying column handling such an easily polymerizing compound as (meth)acrylic acid, occurs copiously in a reboiler, a condenser, the wall of the purifying column, and in the bottom part of the column particularly after the stop of the heat source. When the polymer happens to adhere to the interior of the strainer of the extraction pump attached to the bottom of the column, however, the pump develops cavitation and ceases to operate and entails new work of removing the polymer from the interior thereof and possibly impairs the procedure for safe stop of the purifying column. Further, the adhesion of the polymer to the strainer and the consequent clogging of the strainer necessitate a cleansing operation. The chemical irritations from the raw material for reaction, the reaction product, and the by-products and the physical hindrances due to the adhesion of the polymer inflict spiritual displeasure on workers and bring an alarming influence on the workers' health. Further, the organic solvent used for distillation has the problem of jeopardizing the safety of the operation of the column by ignition. It is generally difficult to remove and discard the adhering polymer with human power, because of the huge purifying column and devices to be cleaned.
The work of cleansing the purifying column and other devices attached thereto for the removal of the polymerizing substance generated therein or adhered thereto necessitates a large volume of a detergent solvent. When the used detergent is discarded or disposed of as by combustion, however, the treatment entails generation of carbon dioxide and inevitable release of the organic solvent into rivers and coasts, it causes the result that the spirit of environmental protection will be spoiled. Moreover, the waste liquid resulting from the use of the detergent also requires a treatment for disposal, which forms the matter for improvement in the viewpoint of not merely economy but also environmental preservation.
Further, when a polymerization inhibitor is used for the purpose of precluding polymerization and clogging due to the easily polymerizing compound, the polymerization inhibitor has a high boiling point and, therefore, is incapable of preventing the easily polymerizing substance left in the gas from yielding to polymerization. If it is used actually at all, it will fail to produce a sufficient effect of preventing the polymerization because the easily polymerizing compound is liable to conden
Hamamoto Kei
Inada Misao
Matsumoto Yukihiro
Nakahara Sei
Manoharan Virginia
Mathews, Collins Shepherd & McKay, P.A.
Nippon Shokubai Co. , Ltd.
LandOfFree
Method for stopping purifying column does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for stopping purifying column, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for stopping purifying column will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3075173