Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
1998-12-23
2001-01-30
Walker, W. L. (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S651000, C210S652000, C210S805000, C134S010000, C134S012000
Reexamination Certificate
active
06180009
ABSTRACT:
The present invention relates to a process for fractionating organic circuit board manufacture process solutions as set forth in the preamble of claim
1
.
Many manufacturing and processing operations give rise to solutions which, on the one hand, cannot be directly discharged into the sewage system on account of their composition or toxicity and, on the other, comprise valuable materials whose recovery or recycling is of economic interest. For instance, the film processing industry is constantly producing chemical-comprising treatment and wash solutions which have to be worked up prior to any disposal or recycling.
For instance, DE-A-42 36 713 describes a separation process for constituents dissolved in a liquid to clean a minimally contaminated wastewater, i.e., a liquid comprising low proportions of dissolved constituents, so as to convert the dissolved chemicals and also the solvent into a recyclable form. This is accomplished by alternating two membrane filters in a removal or cleaning stage, the first membrane filter being capable of removing the dissolved constituents under conditions of high throughput and low concentration and the second membrane filter being designed for low throughput and high concentration. This process is used for removing and recovering photochemicals from wastewaters of a photochemical treatment bath.
Other sectors likewise employ filtration processes for separating, concentrating and/or cleaning mixtures.
For instance, the article “Baustein der Weisen” in: Oberfl{umlaut over (a)}che+JOT 1979, No. 7, pages 355-360, describes various applications for ultrafiltration ranging in the main from the separation of oil/water emulsions to the recirculation of degreasing baths for water and chemical recovery.
Furthermore, EP-A-0 521 369 describes apparatus and a process for recovering glycol-based antifreezes by reverse osmosis, for example to remove ethylene glycol from a concentrated antifreeze solution.
No such process is known to date in the sector of the circuit board manufacturing industry or the semiconductor industry, where aggressive organic solvents are frequently used, too. These industries, however, likewise produce considerable volumes of solutions—especially organic solutions—which have to be either disposed of or recycled.
Hitherto, such process media or solutions were separated by distillation at high temperatures under reduced pressure. However, this requires a great deal of energy and an extensive investment in terms of equipment and safety technology, especially explosion protection measures. In such a conventional process, the distillation residue is a mixture of resins and fillers, which has to be disposed of or incinerated.
U.S. Pat. No. 4,786,417 describes an alternative disposal process. It comprises subjecting a solution containing water-soluble photoresist materials to an ultrafiltration, recycling the permeate from the ultrafiltration and exposing the removed photoresist material to electromagnetic radiation to polymerize the photoresist material for simpler disposal.
This process likewise has the disadvantage that it only recycles the solvent, which is water in the present case, whereas the dissolved and partly valuable organic substances are disposed of at relatively large expense.
It is therefore an object of the present invention to provide, specifically for the circuit board manufacturing sector, a process for fractionating process solutions and recycling a plurality of their constituents.
This object is achieved by the features of claim
1
.
The process of the present invention provides for separation and reuse of individual constituents of organic circuit board manufacture process solutions into organic process solvent, water, dissolved substances and undissolved solids. In the process of the present invention, the separation of the solvent and of the substances dissolved therein is accomplished by very fine filtration.
The separation of the process of the present invention leads to at least two fractions, one fraction preferably comprising mainly solvent and a further fraction comprising mainly the substances dissolved therein. After separation, both the fractions can be at least partly reused.
The process of the present invention accordingly provides for at least partial recycling of the process solvent and of the substances dissolved therein.
In this connection, the process of the present invention has the advantage of requiring only relatively low capital costs and also of making it possible to achieve a high energy saving as compared with the earlier distillation process. This energy saving due to a reduction in the distillation requirement can be up to over 90%.
Furthermore, recycling of the solvent and of the substances dissolved therein provides for a distinct saving in the cost of material for circuit board manufacture.
Lastly, the process of the present invention makes it possible to reduce or even completely avoid circuit board manufacture waste, which likewise entails further possible cost savings for the otherwise necessary and also—owing to the aggressive solvents used in circuit board manufacture in some instances—costly disposal.
This last point is an important aspect, especially in the present day and age, where there is an increasing drive toward an ideally ecological and environmentally benign handling of chemicals.
The very fine filtration of the process of the present invention is advantageously a microfiltration, an ultrafiltration, a reverse osmosis or a pervaporation process. The choice among these processes will depend on the constituents of the particular process solution to be separated.
To increase the efficiency of the filtration, it can be sensible first to remove any solids or fillers present in the process solution. Such removal can be effected by filtration processes, sedimentation processes, the baffle plate method, centrifugation or other processes, especially those based on the difference in mass which is present.
Furthermore, as an additional step following the filtration, the concentrated retentate, comprising the dissolved substances and also solvent residues, can be distilled at low temperatures under reduced pressure to achieve further purification and more far-reaching recycling.
The distillation temperature should be below the temperature and time combination which is critical for curing, and temperatures of about 120° C. to about 160° C. are preferred. This also determines the level of the reduced pressure to be employed, which is preferably within the range from about 90,000 to about 50,000 Pa (about 900 to about 500 mbar).
Also, an additional step for removing water from the recovered solvent can be provided, and it can take the form of an ultrafiltration, a reverse osmosis or else a pervaporation process.
The additional removal of water has the advantage that the solvent can then be further used in the concentrated state or, in the case of a mixture, that it can be adjusted with greater accuracy.
In addition, the solvents used can be hygroscopic, which can then lead to a further accumulation of water. In such a case, the additional removal of water is particularly preferred.
The filtration is advantageously carried out using a membrane which is resistant to organic solvents. This is necessary especially in the case of aggressive organic solvents such as, for example, ethyldiglycol or methylpyrrolidone solutions. Furthermore, the membrane should have a suitable pore size, which depends on the process medium to be separated, in order that the separation of dissolved substances and solvent may be optimized as a result.
Such a membrane is preferably selected from the group consisting of organic, especially asymmetrical organic, polymer membranes, preferably those composed of polyvinylidene fluoride (PVDF), polypropylene (PP), polytetrafluoroethylene (PTFE) and/or polyethylene (PE), and inorganic membranes, especially ceramic or carbon membranes, and mineral-coated inorganic membranes.
The process of the present invention further provides for the advantageous possibility of
Crichton David R.
Kovaleski Michele A.
Vantico Inc.
Walker W. L.
Ward Richard W.
LandOfFree
Method of filtering the organic solutions arising in the... 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 of filtering the organic solutions arising in the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of filtering the organic solutions arising in the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2553879