CARLIN PAOLO (IT)
CARLIN FRANCESCO (IT)
CARLIN PAOLO (IT)
DE2521780C2 | 1982-10-21 | |||
DE2759097C2 | 1987-03-05 | |||
DE2832972A1 | 1980-02-07 |
set free duπng the polymenzing itself The reaction occurs under constant pressure At the end of the reaction, a gradual drop in pressure is observed that indicates that the loaded VCM has changed into solid Poiyvinylchloride (PVCS) in aqueous suspension in one part, wherefore the aqueous suspension still contains the un-reacted vinyl chlonde monomer (VCM) The percentage of vinyl chloride monomer (VCM) that remains embodied in the aqueous suspension can vary between 8% and 20% in weight of the total amount initially loaded, depending on technologies and load formulations adopted The entire suspension is then submitted to a degasing, by opening a gas exit system from the reactor This operation completely sets free the aqueous suspension of the vinyl chloride monomer (VCM), because at this temperature (solution still hot), the whole monomer is in the gaseous state The aqueous suspension therefore without monomer and with the Poiyvinylchloride (PVCS) in suspension in the form of solid particles, is then discharged by the reactor and submitted to filtration or centπfugation to remove the greatest possible amount of water (60- 107c in weight of the entire suspension) from the polymer The polymer is then sent to a desiccation plant where it is completely dned for marketing The drawbacks that result are - the necessity to liquify the gaseous monomer coming from the reactor for its complete recovery and reloading in the subsequent reactions with high costs and above all with serious danger of immission into the external atmosphere with highly toxic and
polluting effects. - the reflux water resulting from the separation of Poiyvinylchloride (PVCS), still contains Poiyvinylchloride wastes (PVCS) that are also highly pollutant. If one considers that in order to produce 1 ton of PVCS, approximately 3 tons of water are normally used, one understands the large amount of such environmental pollution, considering that on average about 1000 p. p.m. of PVCS remain in the reflux waters, in micropolymer form not easily separable from the water itself, precisely because the particles in solution are minute in size.
The most obvious thought would be that of re-using the reflux water in a subsequent reaction, but this is not possible because the micropol ymers contai ned i n i t would generate centers of polymerization that would irreparably damage the quality of the finished product . Therefore these reflux waters are regularly sent to very expensi ve industrial depuration plants with further environmental pollution problems for the elimination of separate products. Even though the waters have been purified, they cannot be re- used in new reloads because even after the depuration processes the necessary degree of purity is not reached. For the gas one is obliged to use expensive liquefaction and recovery plants for the subsequent re-use. Furthermore it is known that one can have difficult moments during reactions, necessity of immediate pressure discharge and/or risk and/or danger of explosion. The aim of the present invention is to eliminate the above-
mentioned drawbacks In particular, attention is drawn on the possibility of recovery of reflux waters directly in the reactor and surprisingly it was found that, if the reflux waters are added after the reaction has started and after the microparticles of PVCS have begun their formation (therefore, already structured genetically), there is no damage to the reaction and no qualitative damaging of the product, probably because the microparticles of the reflux waters are no longer the genetic basis of the reaction but particles that will unite with the previous ones already codified and therefore without introducing substantial alterations in them In this way the problem of recovery of reflux waters is completely solved, because they are re-used in the continuous process, without ever having discharged on the outside As claimed the problem is solved therefore, by the use of a plant for Poiyvinylchloride production that has at least one reactor to transform the vinyl chloride monomer into Poiyvinylchloride in aqueous suspension and vinyl chloride monomer wastes to the gaseous state, and to separate at least one part of the water from the aqueous Poiyvinylchloride suspension, as reflux water, characterized by the fact that the said reflux water is loaded in polymerization reactors, dunng the polymenzation process This technique of adding reflux waters does not damage the polymerization process inasmuch as the main chemo-physical and morphologic characteristics of formation of PVCS particles have already been formed in the presence of water and pure VCM monomer Advantageously the plant has at least two reactors interconnected with each other to operate in a continuous wa\
In this way during a process that could advantageously proceed without continuity, firstly starting one reactor and then the other, staggered from the first,: - the toxic gases can be recovered, discharging them from one reactor to the other; - load at the right moment in one reactor and then the other, the reflux waters from the first on the second and vice versa from the second on the first. The interconnection can be carried out by a third reactor or interconnection container, that acts as a lung for a total continuity of plants. Advantageously the connection between the two reactors can be made by means of a container or even an intermediate reactor or third reactor that advantageously is smaller for the reasons that will be hereafter explained. In this way the third reactor or interconnection container, can act as a lung with the reflux gaseous and liquids of the other two, with transfer at the right moment in the process phases, or of possible emergency, from one to the other and this allows the continuity of the process without recovery units Advantageously the interconnection container or third reactor can act as a lung for the gaseous and liquid refluxes of one or the other of the two main reactors, with transfer at the right moment in the process phases, or of possible emergency, from one to the other and this allows the continuity of the process without recovery units The plant operates in a way that the vinyl chlorinated monomer not reacted in one of the two reactors, after liquefaction, is transferred to the second reactor, already in reaction phase
Said reflux water is loaded into the main polymerizing reactors, during the polymerizing process. This technique of reflux water addition does not damage the process of polymerizing inasmuch the main chemical-physical and morphologic characteristics of formation of the PVCS particles have already been formed in presence of pure water and monomer VCM. Advantageously the two reactors are started preferably staggered from 30 to 70% of the total reaction time. In this way the degasing phase of a reactor coincides with the central phase of polymerization of the second reactor. A further advantage results from the fact that in case of serious emergency the interconnection container or third reactor can collect the vinyl chloride monomer condensates, mix them with the inhibitor and supply the operator a precious elongation of handling and decision times before the opening of the safety valves for excess of internal pressure. Process: At the beginning of the loading the main reactor is loaded with a smaller amount of water when compared to the traditional formulations, in order to absolutely provide a necessity of further water addition during the process. Advantageously the lack of water in load will be lower than 40%-70% preferably 60% of the initial load for self sufficiency. Having reached the reaction time of 60 minutes (between 5% and 20% of the total reaction time) to the aqueous solution in violent reaction, the water taken away at the beginning of the loading is mising. and such is compensated for by the reflux waters of the PVCS separation.
In the meantime, in the first reactor the conclusive phase of discharge of VMC vapours is reached, that is discharged into the third reactor at the liquid state. After the addition of the reflux waters, and reaching the central part of polymerization phase, one proceeds to the addition of VCM coming from the other reactor. Advantageously therefore, after or during the addition of the reflux waters, one proceeds to the addition of the VCM coming from the other reactor, after its reaction has ended. These and other advantages will appear from the subsequent description of a preferential solution with the help of the included drawings the execution details of which of are not to be considered limitative but only given as an example. Figure 1 is a schematic view of the plant according to the present invention. Referring to the figures it is noticed that with 1 and 2 the reactors interconnected from tank 3 are i ndicated, that may preferably also be a third mini-reactor to polymerize or stop VCM monomer in case of emergency or necessity (for example imminent danger of opening of security valves of main reactors 1 and/or 2.) With 12-22 the VCM monomer is indicated at the gaseous state in main reactors 1,2. With 1 1 and 21 the PVCS aqueous suspension is indicated together with VMC liquid monomer in main reactors 1,2. With 4 and 5 the head capacitors of reactors 1 and 2 are indicated. With 6 the reflux water loading lines of PVCS separation are indicated.
With 7 the unloading of PVCS in aqueous suspension from the reactors is indicated. With 8 the filtration device for separation of PVCS from the water and the recircling of the water to reactors 1 and 2 is indicated, according to the described and claimed method, or after a certain period of time from the respective reaction starting phases. Obviously filtration system 8 will operate alternatively from one on to the other of the two reactors 1 ,2, in such a way that, in the continuous cycle, when a reactor has completed its polymerization, and the PVCS product + water has been unloaded and filtered, etc., the reflux water is loaded on the other that is already in an advanced reaction phase, and vice versa.