Abstract:
A method and plant for treating laminated glass having at least two glass sheets between which is arranged at least on intermediate sheet of non-glass material. The glass is attacked in a basic solution of fragmented laminated glass, so as to obtain an attack medium, wherein the fragments are disintegrated into non-laminated glass fragments and non-glass material, separating in a) the basic solution, b) the disintegrated non-laminated fragments and c) the disintegrated fragments of the non-glass material, and neutralizing the disintegrated fragments “b) and c)” before their subsequent recycling or upgrading.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Belgium Application No. 9700581, filed Jul. 7, 1997 and PCT Application No. PCT/BE98/00103, filed Jul. 7, 1998, both of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     This invention concerns a process for the processing of inter-leaved glass and a plant to implement the process. 
     Interleaved glass is to be understood as a product consisting of two or more sheets of drawn glass, plate glass or cast glass, joined over all their surface by one or a number of intermediate layers not made of glass. These may for example act as wiring that holds together the fragments of glass in case of breakage and ensures residual strength to the whole. Interleaved glass is used in particular in manufacturing the windscreens of vehicles such as motor-cars, aeroplanes, passenger ships, etc., or for safety glass, in particular for bank counters. 
     Up to now interleaved glass scrap material has been of little or no reuse value. At present, in fact, scrap windscreens are crushed by passing them between two pressure rollers. It might thus be possible to recover certain glass fragments that have separated from the inter-medisate layers and to recycle them, but in general everything is simply dispatched to a dump. The risk, for example, of presence of plastic residues containing fragments of glass makes it inappropriate in current glass recycling operations to recover interleaved glass and recycle it. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to provide a solution to the problem by simultaneously allowing recovery and perhaps recycling of the material of which the intermediate layers of interleaved glass are made. Advantageously the process and plant set up for this purpose should not lead to another significant environmental problem. 
     Under the invention the problem posed is resolved by a process of treatment of interleaved glass comprising at least two sheets of glass between which at least one intermediate layer made of a non-glass material is inserted, the said process comprising 
     fragmentation of the interleaved glass to be processed, 
     attack of the fragmented interleaved glass with a basic solution, 
     separation of basic solution, glass and c) non-glass material, this process being characterized by the fact that the attack includes an attack on all the interleaved glass in fragments originating from the fragmentation, in such a way as to obtain an attack medium in which a disassociation takes place, in all the said fragments originating from fragmentation, of non-interleaved fragments of glass and fragments of said non-glass material, that the separation comprises separation between a) the basic solution, b) the fragments of non-interleaved glass that have undergone attack by the basic solution and c) the fragments of non-glass material that have undergone attack by the basic solution, and that the process also includes neutralization of the disassociated fragments b) and c), before any recycling or reuse thereof. 
     Thus with the process under the invention the glass and the material constituting the intermediate layers are disassociated. The glass and the non-glass material are perfectly clean on leaving the process. They emerge in the form of small fragments immediately reusable in glass processes on one hand, and non-glass materials on the other. This chemical process has the particular feature that it does not involve any chemical reaction between the basic solution and the fragments and that the basic solution remains virtually unaltered after the process, so that it can be reused a number of times for subsequent operations. 
     The basic attack solution may be water-solution of an OH ion generating agent soluble in water, specifically an alkaline base or earth-alkaline base. preferably NaOH or KOH. Advantageously the basic attack solution is a water-solution of 5 to 15 molar, preferably about 10 molar, NaOH. 
     Glass may according to the invention be any type of non-composite glass, whether drawn, cast, tinted, transparent, translucent, opaque cut, or treated in another way. 
     Non-glass material may according to the invention be any material of which the intermediate sheets used in manufacture of interleaved glass are made. Polyvinylbutyral may be mentioned as an example. 
     According to one mode of implementation of the process according to the invention, the said separation includes sedimentation of a mix of disassociated fragments b) and c), previously separated from the basic solution, in a sedimentation liquid in which the disassociated fragments of the non-interleaved glass having undergone attack by the basic solution b) are deposited, and the disassociated fragments of non-glass material having undergone attack by the basic solution c) float, and a separate collection of the disassociated fragments b) and disassociated fragments c). This mode of implementation advantageously profits from the difference in density between the glass and the non-glass material of the intermediate layers having undergone attack by the basic solution so that they can easily be separated by a simple sedimentation process. The liquid used may advantageously be simply water. Preferably the said liquid does not react in any way either with the fragments of the glass or with the fragments of the non-glass material, and its long use and/or recycling may easily be envisaged. 
     According to another mode of implementation under the invention, the process comprises the said neutralisation of a mix of the disassociated fragments b) and c), previously separated from the basic solution, by means of an acid not aggressive for glass or the non-glass transparent material. The non-aggressive acid may be a weak acid, in particular phosphoric acid. This acid may also be used on occasion, when the basic attack solution becomes overloaded, to neutralise the basic solution used and thus form a water-solution of sodium phosphate which may itself be reusable, for example in the area of fertiliser manufacture. 
     This invention also concerns a plant for implementation of the interleaved treatment process. The said plant comprises: 
     an interleaved glass fragmentation device, 
     a reactor into which the interleaved glass fragments issuing from the fragmentation device are fed together with a basic solution so as to form an attack medium in which disassociation of all the fragments coming from the fragmentation device into fragments of non-interleaved glass and fragments of the said non-glass material takes place, 
     a separating device allowing a) the basic solution. b) the disassociated fragments of non-interleaved glass having undergone attack by the basic solution and c) the disassociated fragments of the said non-glass material having undergone attack by the basic solution to be separated, and 
     a source of neutralising agent enabling neutralisation of the disassociated fragments b) and c) prior to any recycling or reuse. 
     This relatively simple plant has an entirely justifiable cost as it allows each of the constituent elements of interleaved glass to be reused. A plant of this kind can even be envisaged on one or two semi-trailer platforms in order to provide a mobile plant transportable from dump to dump. 
     The fragmentation device may be any kind of mill, for example of blade, hammer or ball type, or any crushing device, possibly a mincroniser. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other details and particular features of the invention will emerge from the description given below, devoid of limiting effect, with reference to the single annexed figure. 
     The said single figure diagrammatically represents a plant according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The basic solution, of caustic soda for example, is prepared in any of the ways known to experts. In this connection reference may for example be made to International Patent WO-97/00099. 
     In the example illustrated, caustic soda flakes or pellets are put and stored in a bin  1 . By means of a batcher  2  the caustic soda is transferred to a pressure vessel  3  into which water is injected through the connecting pipe  4 , shut off by a valve  5 . The water is only injected into the vessel  3  for the first preparation of basic attack solution. For subsequent preparations the water may be wholly or partly replaced by previously prepared basic solution. The basic solution is then transferred through pipe  6  to a preparation tank  7 . This is filled gradually in order to avoid the thermal and exothermal shocks of the reaction between soda and water, which lead to a temperature in the region of 80° C. A static mixer  8 , through a set of pipes  9  and  10  and valves  11 ,  12 ,  13  and  14 , allows constant movement of the basic solution contained in the preparation tank  7 . A heating element  15  allows a basic solution having a temperature of about 200° C. to be gradually achieved. 
     The glass scrap is put into a mill  16  through a hopper  17  which channels the interleaved glass between two crushing rollers  18 . These grind the interleaved glass into small fragments which are removed by a conveyor belt  19 . 
     The reactor  20  is mounted on a tipping platform  24  on a pivot  21 . 
     The tipping motion is generated in a known way, for example by the action of a hydraulic or pneumatic jack and connecting rods, designated as a whole by reference  22 . 
     The reactor is enveloped at least in part by a heating system  23  and is mounted on the platform  24  so that it can rotate around its lengthwise axis under the action of a driving motor  25 . 
     The end of the reactor  20  is connected to the preparation tank  7  by the pipe  9 , a pump  60 , the valve  12 , a valve  26 , the feed pipe  27 , a valve  28 , a flexible tube  29  and a valve  30 . Inside the reactor, in front of the orifice through which the flexible tube  29  emerges into the reactor  20 , there is a filter  31  represented diagrammatically by a dashed line. The reactor head has a door  32  movable between open position and closed position. The reactor walls may be furnished with pyramidal points and/or a beating chain in order to improve the grinding effect. 
     Through the valve  30  and flexible tube  29 , and also valves  33  and  34  and the recycling pipe  35 , the end of the reactor  20 , is also in communication with a buffer tank  36  fitted with a heating element  37 . This is itself in communication with the preparation tank  7  through the pipe  38  and the valve  39 . The buffer tank allows recycling of the basic attack solution, while adjustment of the refed basic solution&#39;s molarity in the feed circuit is carried out through the preparation tank  7 . 
     A neutralisation tank  40  full of a dilute water-solution of phosphoric acid is linked to the end of the reactor by the pipe  41 , pump  42 , static mixer  43 , feed pipe  44 , valve  45 , valve  33 , flexible tube  29  and valve  30 . Fresh phosphoric acid is fed into the neutralisation tank through the pipe  46 . The buffer tank  36  and the neutralisation tank  40  can communicate with each other through a transfer pipe  61 . 
     Above the reactor  20  there is a sedimentation tank  46 . which is fed with sedimentation liquid, specifically water, through a water pipe  47  coming from a water tank  48 . The fragments of plastic material from the intermediate layers float, while the glass is deposited on the bottom of the tank. 
     An overflow  49  is located at the side, in the upper part of the tank. The fragments of non-glass material are drawn through this overflow  49 , together with part of the sedimentation water, into a water/non-glass separator  50 . This consists of a perforated drum  51  provided with small hooks which carry along the fragments of for example plastic material. The water drains through the perforations into the water collection tank  52 . The plastic material is held by raking elements in a drainage gutter  53 . The water in the collection tank  52  can be recycled into the water tank  48  through the recycling pipe  54 . 
     At the bottom of the sedimentation tank there is a valve  55 , for example a slide valve, which can let the remaining water and the deposited glass pass from the sedimentation tanks  46  into a water—glass separator, for example a vibrating separator  56 . The water is drained from the bottom through a vibrating screen and can be recycled to the water tank  48  through a pipe  57  which comes out into the recycling pipe  54 . 
     The glass fragments are removed laterally by the vibrating screen to an outlet  58 . 
     The water tank  48  is provided with a bottom outlet pipe  59  for the stale water and a top pipe  62  for inlet of fresh water. 
     Operation of this plant will now be described on the basis of an example of implementation given solely for purposes of illustration. 
     Interleaved glass consisting of scrap from car windscreens and from safety glass coming from the demolition of bank branches is first broken down in the mill  16 . 
     A reactor  20  with a capacity for example of 2 m 3  is set with its head upwards (see representation with dashed lines). The door  32  can then be opened and the fragments of interleaved glass fed into the reactor  20  by the conveyor belt  19 . When about ⅔ of the volume of the reactor has been tilled, the door  32  is closed, and the reactor is swung back to its horizontal position. 
     NaOH basic solution at about a 10-molar concentration is sent from the preparation tank  7  to the reactor  20  through the feed pipe  27 . until the volume of the reactor is ¾ filled. 
     The reactor  20  is then set to turn around its axis at a speed for example of 25 revolutions per minute. The temperature inside the reactor is kept lower than the degradation temperature of the glass and the non-glass material of which the interleaved glass intermediate layers are made. The temperature is advantageously above 180° C., preferably about 200° C. 
     A vapour pressure of at least 8 bars, advantageously from 10 to 20 bars, preferably around 15 bars, is installed. 
     After 15 minutes of reaction, disassociation between the glass and the plastic material forming the intermediate layers has taken place. At this moment the valve  30  is opened and the basic attack solution is recycled through the pipe  35  to the buffer tank  13 , passing through the filter  31  located at the end of the reactor. The non-interleaved fragments of glass and plastic material are thus held in the reactor. The basic solution leaving the reactor is only slightly impoverished and the NaOH topping-up requirement is less than 2%. The NaOH has not therefore reacted with the layered glass components, but has allowed their disassociation through a thermochemical reaction. 
     Dilute phosphoric acid from the neutralisation tank  40  is then sent into the reactor  20 , which still contains disassociated fragments. The reactor is started up again for a few revolutions while the pressure is removed. The fragments of non-interleaved glass and plastic material are thus brought to a neutral pH in the range from 6 to 8. The reactor is then swung to the head downward position (see dashed line representation) and the door  32  is opened. The reactor contents consisting of neutralised fragments and a little sodium phosphate solution are poured into the sedimentation tank  9 , the valve  55  of which is closed. 
     The sedimentation tank  9  is then fed with water from the water tank  48  through the pipe  47 . The plastic fragments float on the water and are drawn through the overflow  49  into the separator  50 , while the non-interleaved glass fragments settle on the bottom of the tank  46 . 
     When the sedimentation water no longer contains floating fragments, the water feed is cut off and valve  55  opened. The water and the glass fragments are then separated in the separator  56 . 
     The fragments of plastic material, in the form of shriveled pellets, and the fragments of non-interleaved glass are fully ready to be sent to reusing or recycling industries. 
     The basic solution in the buffer tank  36  is transferred to the preparation tank  7  where it is equalised from the molar concentration standpoint, and a new process can start. A complete circuit takes about 30 minutes. With a 2 m 3  reactor a processing rate of 3 tons an hour can be expected. 
     After a number of treatments the overloaded basic solution must be neutralised. The solution in the tank  7  is cooled. It is transferred to the buffer tank  36  and then to the neutralisation tank  40 . The neutralised liquid is transferred to the water tank  48 . The water is immobilised for a time in order to allow decantation. Stale water mainly containing sodium phosphate is then removed through the bottom pipe  59 . 
     To summarise, the process and plant according to the invention allow the same basic attack solution to be used for a large number of cycles. The materials to be reused are separated and above all are not altered by this attack. It restores them clean and ready for recycling, in small fragments. There is no fear of any expulsion either into the atmosphere or into effluents, except from time to time for evacuation of a sodium phosphate solution. The process thus takes place in an almost closed circuit. Water consumption is very low. 
     It is to be understood that this invention is in no way limited to the form of implementation set out above and that many changes may be made without going outside the framework of the attached claims.