CN1175579A - Process for catching pyromellitic acid dianhydride using water - Google Patents

Abstract

A process for capturing pyromellitic acid dianhydride (PMDA) with water features use of only one water washing absorption tower instead of conventional five apparatuses, and includes filler absorption and spray washing. Its advantages are high content of PMDA in raw product (more than 90%), qualified rate of product and capturing rate, no process block and good working condition of workers.

Description

The method of water catching pyromellitic acid dianhydride

Present method belongs to the chemical technique technical field.

Pyromellitic acid anhydride (hereinafter to be referred as PMDA) is a kind of important chemical material, it is to be dewatered by Pyromellitic Acid, its main application is a synthesis of polyimides, is widely used in the interpolation auxiliary agent of industries such as space flight, aviation, electromechanics, electronics as H level high-temperature insulation material.

At present, the product trapping technology that adopted of domestic PMDA manufacturer all is the isolating method of trapping of sublimating of promoting the circulation of qi solid phase of being gone forward side by side by the direct crystallisation by cooling of air.Its operational path is reactant gases (the PMDA-air gas mixture of being come out by interchanger, hereinafter to be referred as gas mixture) enter first trap and carry out the constant temperature capture of sublimating, obtain the portioned product of purity 〉=95%, enter second, third trap again and carry out the cold conditions capture of sublimating entirely, obtain containing PMDA and reach 30～85% product, enter tail gas absorber at last, wash tail gas with water, to remove remaining acidic substance.Its capture is operating as semi continuous operation, therefore needs two row totally six trap blocked operations.Discharge method is artificial clear material, and generally speaking, per tour will be expected once clearly.

Adopt two row six to capture and switch the problem that technology exists several respects.The one, product percent of pass is low, and underproof product will just can be delivered to the distillation operation through secondary water washing and recrystallization operation, and water consumption is big, and loss is big, and quantity of wastewater effluent is big; The 2nd, the product trapping rate is low, because it three is caught material and be difficult to handle, the unit consumption cost is increased, and increases the quantity discharged of solid slag simultaneously; The 3rd, there is the technology blockage problem, in case stop up, all necessary cleanings of stopping of device have a strong impact on production; The 4th, operational condition is very abominable, owing to adopt artificial clear material mode discharging, the PMDA dust has a strong impact on health of operators.Simultaneously, because the repeatedly refinement treatment of usual manner causes the energy consumption of its aftertreatment also to be doubled and redoubled.

At the problem that above capture technology exists, we grind the method for having developed the water catching pyromellitic acid dianhydride.The major equipment that present method is used shown in Figure of description 1, is column washing absorption tower, a garden.The washing absorption tower by up and down two absorb washing sections and form, on absorb washing section by evacuated tube [1], scum dredger [2], go up spray equipment [3], go up distribution apparatus [4], upward dry load layer [5], catch tray [6] and upflow tube [7] are formed; Under absorb washing section by following spray equipment [8], down distribution apparatus [9], dry load layer [10], anti-fall screen [11], make up water inlet tube [12], gas mixture inlet tube [13], tower still [14], absorption liquid vent pipe [15] and skirt [16] are formed down.Install position shown in each integral part by specification accompanying drawing 1 on columnar water absorption tower, garden.The miscellaneous equipment relevant with present method also has a water cooler and two recycle pumps.

Accompanying drawing 2 is process flow sheets of present method, and technical process is mainly absorbed by two sections fillers and two kinds of technology types of spray washing are formed.As shown in Figure 2, the mixed gas that is come out by interchanger captures after the purity of separating that contains ultimate production 40%～60% is PMDA product more than 95% through the first trap constant temperature, still is mixed gas.This mixed gas enters water wash column from the gas mixture inlet [13] of water wash column bottom, and behind bubble cleaning of hypomere, temperature drops to below 100 ℃, the whole crystallizations of the coagulated component in the mixed gas.Remaining mixed gas, after the secondary spraying washing and filler absorption through epimere, noncondensable gas outside cat head evacuated tube [1] is discharged tower, and can coagulate be trapped in after the component crystallization in the absorption liquid with solution or form of suspension by tower at the bottom of absorption liquid vent pipe [15] be expelled to the crystallizer tank crystallization.In the absorption process of present method, entrained air is walked the minimizing that a large amount of water vapors cause the water yield in the tower, therefore, and make up water in the washing absorption tower constantly, make up water adds from the last spray equipment [3] of top of tower and the make up water inlet tube [12] two of tower bottom, and add-on depends on the needs.Absorb the standard value that will reach heat-obtaining in the operation at epimere, need regulate with outer pump of tower and cooler tube network.Simultaneously, for discharging the optimum proportion that liquid measure and liquid effluent are formed at the bottom of the maintenance tower, at absorption liquid vent pipe [15] peripheral hardware one pump circulation tube network, Control Circulation is to the amount of the interior absorption liquid of tower, to bring into play the maximum efficiency on washing absorption tower.

The washing absorption process captures technology and is used to replace two catching in the past, three to catch and tail gas absorption technology.Replace five equipment with equipment, the non-standard equipment investment reduces by 20%, simultaneously this processing method compatibility before one catch constant temperature and capture technology.One catch in the qualified product of 40%～60% output, former two, three PMDA that catch in the product are reclaimed, the rate of recovery is greater than 95%, and the PMDA content in the thick product is greater than 90%, this becomes simply postprocessing working procedures, and total acid loses less than 1.5%, and unit water consumption is less than 2.5T/T, total energy self balance need not outside heat supply.Continuous operation does not have technology and stops up, and the workman operates indirect contactant material, can be without face guard.The quantity discharged of three-waste pollution thing reduces 80%, and year increase benefit is more than 10%.

Most preferred embodiment:

Use the 30T/aPMDA production equipment, absorber portion total length 4.5m, the filler name is called ceramic raschig rings, filler specification ∮ 25 * 25 * 3, empty tower gas velocity 0.1～3m/s, specific liquid rate are 30～80m ³/ m ².h, spotting out rate 30%, uptake rate 3Kg/h, assimilated efficiency 95-98%, PMDA average content 91% in the thick acid anhydride of crystallization, the continuous operation situation reaches well, does not have and stops up.

Claims (4)

1, a kind of method of water catching pyromellitic acid dianhydride belongs to the chemical technique technical field.Mainly form by two sections fillers absorptions and two kinds of technology types of spray washing, it is characterized in that through constant temperature capture the gas mixture of operation back from first trap mixed gas that PMDA accounts for ultimate production 40%～60% containing of coming out from the water wash column bottom enter the mouth [13] enter water wash column, empty tower gas velocity is 0.1～3m/s, through behind bubble cleaning, temperature drops to below 100 ℃, the whole crystallizations of coagulated component in the mixed gas, the secondary spraying of passing through two sections again, specific liquid rate is 30～80m ³/ m ².h, absorb through filler simultaneously, assimilated efficiency is about 95%, noncondensable gas outside cat head evacuated tube [1] is discharged tower, and can coagulate be trapped in after the component crystallization in the absorption liquid with solution or form of suspension by tower at the bottom of absorption liquid vent pipe [15] be expelled to the crystallizer tank crystallization.

2, a kind of washing absorption tower device that is used for the described method of claim 1, comprise a garden column body of the tower, it is characterized in that this tower middle part is provided with dry load layer [5] and following dry load layer [10], goes up spray equipment [3] and following spray equipment [8], the tower bottom side is provided with gas mixture inlet tube [13], make up water inlet tube [12], bottom and absorption liquid vent pipe [15], top are set establish evacuated tube [1] and body of the tower skirt [16], tower still [14].

3, washing according to claim 2 absorption tower device is characterized in that epimere absorbs outer pump of tower and water cooler will be set in the operation.

4, washing according to claim 2 absorption tower device is characterized in that at absorption liquid vent pipe [15] peripheral hardware one pump circulation tube network.

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