EP0386436B1 - Rational process for the deacidification of books and other paper products without pollution - Google Patents

Abstract

In a process and equipment for the bulk deacidification of books and other printing and paper products without pollution, with predrying of these products by high-frequency radiation in vacuo, subsequent application of a neutralisation treatment with solutions for deacidification, followed by drying-off of the solvents used, likewise by high-frequency radiation in vacuo, preferably a single treatment chamber (1) is used for predrying, neutralisation and drying-off, the interior of the treatment chamber can be exposed to the HF microwave radiation of a generator (2), and devices (4, 8, 9; 10 to 19 and 5) for introducing and discharging the solutions, for evacuation and for non-polluting precipitation of the vapours from the waste air arising in drying-off are connected, in a closed movable installation, to the chamber (1). The process and the equipment allow rapid and efficient and nevertheless non-polluting bulk deacidification with recovery of the solvents. <IMAGE>

Description

The present invention relates to a method for environmentally friendly mass deacidification of books and other printed and paper products of all kinds such as magazines, files, etc., and an apparatus for performing this method.

The aging that occurs in all printed and paper products and especially in the case of books during storage leads to progressive damage to the paper substance, above all due to traces of acids released in the paper. If no countermeasures are taken, this damage leads to a complete decay of the paper after a few decades.

To preserve archives and library holdings from a few hundred million books worldwide, it is therefore necessary to neutralize the acids in the paper and at the same time to anchor in the paper the sufficient amount of a substance that will also neutralize future acid release in the paper.

In view of the very large volumes of books, only methods are suitable for this which allow treatment of the entire books, ie methods in which it is not necessary to open the book binding and to treat the pages individually. The same also applies to archival holdings of all kinds to be preserved, which also deal with bound or otherwise summarized paper pages require.

A known method is to treat books with vapors of metal alkyls, especially vapors of diethyl zinc. Due to the moisture in the paper, the metal alkyls are converted into the oxides of the metals, e.g. converted to zinc oxide, which remains in the paper and is a good neutralizing agent for free acids. However, the metal alkyls suitable for this application are self-igniting substances in air, which represent a constant fire and explosion hazard during handling and therefore require an extremely high level of care and appropriate qualifications.

According to a further known method, the books are treated with a solution of an organomagnesium compound, such as, for example, methyl magnesium carbonate, in a suitable solvent after a previous drying. Here too, the magnesium compound is converted into magnesium oxide and magnesium carbonate by moisture in the paper, both of which are able to neutralize acids. Particularly suitable solvents are fluorocarbons, e.g. Trichlorotrifluoroethane mixed with alcohols such as e.g. Methanol.

In addition to the advantage of non-flammability and non-toxicity, fluorocarbons and chlorofluorocarbons also offer good compatibility with most book materials such as paper, cardboard, printing inks, glue and other adhesives and are therefore particularly suitable for the present purpose.

In addition to the high price, it is particularly disadvantageous that the substances mentioned, if they escape into the atmosphere, pose a considerable burden and endanger the environment. Write the relevant laws therefore for the handling of these substances their extensive recovery and a very extensive purification of the exhaust air, which is derived from the treatment plants.

Also in the case of the treatment of books and other printed products, this means that after their treatment they have to be dried so carefully that they practically no longer contain any solvents, and that the solvent-containing waste air from the drying process is reduced to very low residual levels of solvents used is clean.

While drying of solvent-based bulk goods is generally not a problem, drying compact, bound paper has previously required very long drying times. It is known that the drying of books can be effectively supported by lowering the ambient pressure, but the reduced pressure at the same time makes it difficult to supply the heat required for solvent evaporation.

It is also known that when drying under reduced pressure, i.e. vacuum drying, to bring the heat of vaporization into the material to be dried by means of heat radiation. In the case of books, however, this method can only be used with very low heating outputs, since otherwise the books and in particular the book sizing will be damaged.

In US-A-3,676,182 it is mentioned that numerous methods for drying the solvents in a vacuum can be used, whereby in addition to conventional external heating in a vacuum, the possibility of heat induced by high-frequency radiation is indicated. Instructions for carrying out such a heat induction can be found by the person skilled in the art in CA-A-911 110, which names the same priority document as US Pat. No. 3,676,182. It will be a dielectric Heating by means of electrodes lying on the books or arranged very close to them in a vacuum is proposed, voltage values for the RF voltage to be applied being recommended and the necessity of avoiding discharge effects in the event of excessive potential differences being pointed out. With regard to the rational deacidification of large volumes of books, the placement of individual books between electrode plates does not seem to be very advantageous, especially since there is no specific information about the drying times required with such a system.

The invention has for its object to provide a method according to the preamble of claim 1, which allows quick and therefore rational treatment for mass deacidification of books and other paper products in an environmentally friendly manner. Furthermore, an apparatus for performing the method according to the invention is to be specified. This object is solved by the subject matter of claims 1 and 6. Advantageous further developments are characterized in the subclaims.

Surprisingly, it was found that the solvents suitable for the treatment of books, such as fluorocarbons and chlorofluorocarbons, are accessible to effective microwave heating. So far, only the possibility of dewatering by heating the water-containing material to be dried was considered. As is known, water is extremely well suited for heating by high-frequency radiation or microwave radiation on account of its physical and chemical substance data, and can be evaporated in this way.

However, the fact of successfully applying microwave treatment with standard microwave frequencies to the above and other suitable solvents is not only new and surprising, but also brings decisive advantages. In comparative experiments, the time required for predrying was reduced by more than a factor of fifty compared to using a slight warming in a vacuum that was not harmful to the books. A considerable amount of time was also saved when drying the solvents, which, in contrast to conventional long-term storage under normal pressure or reduced pressure, could be removed almost completely in just 15 minutes.

The speed of the process sequence according to the invention is extremely important. It is not only advantageous, but ultimately enables the handling of large volumes of books, which will be required to a large extent in the future. Effective drying is extremely gentle due to the low heating of the treated print and paper products. As a result of the practically complete solvent removal that can be achieved in practical times, the solvents mentioned, which are suitable but are environmentally harmful, can also be used.

The speed of the process also offers the advantage that predrying, neutralization treatment and drying can be carried out in a single chamber, since time-consuming drying processes in special dryers are eliminated. Such a chamber in turn offers the advantage of a closed system with the optimal possibility of complete recording and controlled processing of the exhaust air quantities. The expensive solvents can also be recovered by environmentally friendly separation, whereby all of the airborne amounts of solvent in the process are recorded.

By combining the actual treatment system with the exhaust air purification system and the storage containers for the treatment solution, it is possible to implement a compact, transportable device which can be brought to the respective libraries and archives, for example. Since completely closed systems are possible, operation by the library staff is possible with appropriate automatic control of the process steps. The exposure to microwave radiation does not require a great deal of technical effort. The same microwave radiation can be used for pre-drying and the final drying. Thus, a two-chamber system with a separately provided predrying chamber can also be easily realized with the advantage of a simultaneous predrying and treatment of book quantities and a higher throughput.

• Fig.1 ein erstes Ausführungsbeispiel der erfindungsgemäßen Vorrichtung und
• Fig.2 ein zweites, modifiziertes Ausführungsbeispiel der erfindungsgemäßen Vorrichtung.

The method according to the invention and the device for carrying it out are explained in more detail below. Show it

• 1 shows a first embodiment of the device according to the invention and
• 2 shows a second, modified exemplary embodiment of the device according to the invention.

The device in FIG. 1 has as its main component a single chamber 1 both for predrying and for treatment with solutions and subsequent post-drying. For this purpose, the treatment chamber 1 is provided with a microwave generator 2, with which the interior of the chamber e.g. can be exposed to microwave radiation of 2450 MHz, as indicated schematically. The possibilities of generating microwave radiation in such e.g. As in the case shown, cylindrical cavities are well known from other technical fields. In the exemplary embodiment, a microwave chamber with a radiation frequency of 2450 MHz was used.

The chamber 1 is connected via a valve to an air dryer 3, via which dried purging air can be supplied to the chamber. Furthermore, the chamber 1 is connected to a storage container 4 for treatment solutions via valves and cleaning filters, which are each provided in the inflow and outflow lines. A feed pump is provided in the feed line upstream of the filter.

In addition, the chamber 1 is connected to a vacuum pump 5, the chamber pressure being measurable and controllable by means of a pressure sensor PC (dashed line to the purge air valve). The temperature in the chamber can also be controlled, a temperature sensor TC with corresponding feedback to the generator 2 being provided for this purpose. The temperature of the outer wall of the chamber can be adjusted by means of an electrical, direct or indirect jacket heating indicated at 6 so that water vapor condensation on the chamber wall is avoided and microwave drying is accelerated.

A compressor 7 connected to the vacuum pump 5 via a valve is connected to the chamber 1 and represents the connection to the preparation and recovery devices for the solvents. A solvent tank 8 is also connected to these devices via a corresponding recovery line. This and a storage tank 9 for the active compound to be used - in the present case methyl magnesium carbonate - have supply lines to the storage container 4.

The solvent tank 8 is supplied by a device 10 for solvent preparation by drying and neutralization, which in turn is connected to a solvent collecting container 11. This solvent collecting container 11 is connected, on the one hand, to a condenser 13 connected to a refrigeration machine 12, to which the exhaust air resulting from the after-drying is fed via the compressor 7. The condenser 13 is connected via a valve to a device 14 for adsorptive exhaust air purification. This valve is also connected to a blower 15, which forms an adsorption treatment circuit with the device 14 and an air cooler 16 connected thereto and to the blower. The device 14 for adsorptive exhaust air purification are supplied with desorption steam and, depending on the position of the valve to the condenser 13 and blower 15, either the exhaust air from the compressor or for dilution of the exhaust air additional air via the blower. For dilution, a valve for feeding in additional air is connected between air cooler 16 and blower 15. In addition, an exhaust air valve for cleaned exhaust air is provided in front of the air cooler.

The device 14 for adsorptive exhaust air purification also supplies regenerated solvent to the solvent collecting container 11 via a further condenser 17 and a device 18 for water / desorbate phase separation, which is connected to a device 19 for water treatment.

The single-chamber process carried out with the device according to FIG. 1 for environmentally friendly mass deacidification of books proceeds as follows. The books are used for back-to-back treatment in baskets made of a suitable material, such as polyethylene or polypropylene. By inserting spacers, the books can be fanned out and floating can be avoided.

The pre-drying is then carried out in the vacuum and pressure-resistant chamber 1. For this purpose, the chamber is evacuated to a pressure of approximately 100 mbar using the vacuum pump 5. At the same time, the books are heated to a maximum of 60 ° C in the microwave field, using the pressure and temperature control mentioned. A small air flow from the air dryer 3 conducted through the chamber and simultaneous jacket heating (6) of the chamber avoid water vapor condensation on the chamber wall and accelerate the drying. In this pre-drying phase, the vacuum exhaust air is passed outside via pump 5.

As soon as the drying has reached the predetermined residual moisture value, the vacuum pump 5 is switched off and the treatment chamber 1 is flooded with neutralization solution. In order to improve the impregnation with the feed pump in the supply line from the reservoir 4 in the chamber, an excess pressure is generated. If necessary, pressure pulsation and / or sonication with suitable frequencies can be used for an even better impregnation.

After the required exposure time has expired, the solution is conveyed back into the storage container 4, the fine filter provided retaining dirt particles and rinsed-off magnesium oxide. Then the microwave generator 2 is switched on again and the drying of the Solvent is introduced.

The solvent vapors generated when the books are heated are first sucked off with the refrigeration compressor 7 and towards the end of the drying phase with the pump 5 switched on via the valve, and compressed and cooled in the condenser 13. A considerable part of the solvent vapors thus extracted condenses and is passed into the solvent collecting container 11.

The further separation of the solvent vapors to the legally prescribed limit values takes place in the adsorptive exhaust air purification in the circuit consisting of the devices 14, 15 and 16. By introducing additional air via the fan 15 into this circuit, the solvent emission in the exhaust air discharged is further reduced.

After the maximum solvent loading has been reached, the solvent adsorption in 14 is regenerated with water vapor supply and, if necessary, with vacuum support. After condensation and phase separation (17, 18), the solvent recovered from the collecting container 11, to which the solvent separated in the condenser 13 had also been fed, is neutralized and dried in the device 10 and then fed to the solvent tank 8.

After the methanol which has been used is separated off in the water treatment device 19, the water condensate is either used again for regeneration or passed into the waste water.

In order to strictly comply with the emission limit values, in addition to the solvent load from the dryer, all other exhaust air, i.e. the chamber exhaust air during filling and emptying, as well as the exhaust air from the storage containers and from the water treatment, are fed to the facility for exhaust air purification.

The device outlined in FIG. 2 corresponds to the device from FIG. 1 except for the formation of an additional predrying chamber 20. This chamber 20 is also connected to the air dryer 3 via a valve and is exposed to a microwave radiation with the generator 2. The method also corresponds to that explained above, with a higher throughput being possible since, while a batch of books is predried, an already predried batch can be neutralized at the same time. The process is also completely closed, since the exhaust air treatment in chamber 1 takes place, as in the example explained, without any emission of solvents into the environment. In addition to the outlined two-chamber process, it is also possible in principle, e.g. to use two treatment chambers and a predrying chamber, since the predrying can generally be carried out in shorter times than the post-drying.

The following test results were achieved using the method described. Books with a storage humidity of 8 to 10% were pre-dried to 2% residual moisture in just 30 minutes at a pressure of 50 mbar, a high-frequency output of 500 watts and a radiation frequency of 2450 MHz. In contrast, vacuum drying without this high-frequency heating requires 30 to 40 hours for a residual moisture of 1 to 2%.

Post-drying of books containing 100 to 120% of their dry weight of solvent trichlorotrifluoroethane after the neutralization treatment with the same high-frequency radiation and 280 watt high-frequency output gave solvent-free books after 15 minutes, the temperature of which was about 60 ° C. at the end of drying.

In the case of drying by storage in air at about 20 ° C., on the other hand, drying times of 24 to 30 hours are necessary, without complete removal of the solvent being possible in this way, the environmental impact having to be accepted. Vacuum drying with a final pressure of 1 mbar and a temperature of 50 ° C by conventional heating also took 2 to 5 hours.

Claims (7)

1. A method of environmentally friendly mass deacidification of books and other paper products, using a neutralising treatment with solutions for the deacidification and subsequent drying out of the solvent, characterized in that a pre-drying of the books or other paper products and the drying out after their deacidification are each carried out in a chamber under vacuum with heating by microwave radiation.
2. A method according to claim 1, characterized in that solutions known per se of a magnesium-organic compound in methanol, ethanol, a fluorocarbon, a chlorofluorocarbon, benzine or a mixture thereof are used and in that the pre-drying, deacidification and drying out are carried out in one treatment chamber.
3. A method according to claim 1 or 2, characterized in that the vapours of the solvent or solvents from the exhaust air occurring in the drying are separated out by means of condensation and/or adsorption and/or absorption.
4. A method according to any of claims 1 to 3, characterized in that the pre-drying is carried out in a separate chamber.
5. A method according to any of claims 1 to 4, characterized in that microwave radiation of a frequency of 2450 MHz is used for the heating.
6. Apparatus for carrying out the method according to any of claims 1 to 3 and 5, characterized in that there is provided a single treatment chamber (1) with a heating jacket (6), whose interior can be subjected to the radiation of a microwave radiation generator (2), and in that there are connected to the treatment chamber, forming a movable plant with the treatment chamber, devices (4, 8, 9; 10 to 19) for feeding solutions in and out, devices (5) for the evacuation, devices (3) for drying in-fed flushing air, devices (7) for taking off the vapours of the exhaust air occurring in the drying out and devices (13) for separating out these vapours.
7. Apparatus according to claim 6, characterized in that a separate chamber (20) for the vacuum pre-drying is provided in addition to the treatment chamber (1) and is subjected to the action of microwave radiation from the same generator as the treatment chamber.

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