MXPA96000556A - Chemical depletion process to substantially remove waste mills in polymerization processes in emuls - Google Patents

Abstract

The present invention relates to a chemical depletion process for substantially removing residual monomers in an emulsion polymerization process by polymerizing a mixture of a vinyl monomer and / or conjugated dienes at a temperature ranging from 45 ° C to 60 ° C. , in a reactor to obtain a latex in emulsion having a residual monomer content within a range of 200 to 100,000 ppm, the depletion process is characterized by the steps of: a) contacting the latex obtained in a reactor with a reduction system consisting of: i) an oxidizing agent generating free radicals having high activity selected from the group comprised by diacyl peroxides, peroxydicarbonate, peroxyesters or hydroperoxides or in a mixture of any of them with a peroxyester of tertiary butyl 2-ethylhexanoate hydrogen peroxide and ii) a reducing agent selected from the group consisting of sulfoxylate of mol and zinc formulfoxylate of formalin and iron, reducing sugars or their derivatives and carboxylic acids, b) heating and stirring the resulting mixture at a stirring temperature of 50 ° C to 90 ° C during a depletion time of 0.5 to 5 hours to obtain a latex having a residual monomer content of at least 50 to 1000 p

Description

CHEMICAL DEPLETION PROCESS FOR SUBSTANTIALLY ELIMINATING WASTE MONOMERS IN POLYMERIZATION PROCESSES IN EMULSION ANTECEDF "TES DE LA INVENCIÓN A variety of processes for preparing emulsions of different monomers have been known in the art for several decades, whereby an infinity of polymeric compounds based on homopolymers, copolymers and terpolymers involving vinyl monomers and / or conjugated dienes have been produced. The components commonly used in emulsion polymerization are monomers to which they are dispersed in water by means of ulsifiers, which may be ionic, non-ionic or amphoteric, dispersants, transfer agents, pH regulators, electrolytes, inhibitors and the initiator . The initiator can be soluble in water or soluble in the phase or ganic. And to reduce the half-life of the initiator, reducing agents can be used.

The processes; They can be defined in several ways. The oldest were batch processes that were classified as cold or hot. Cold processes are carried out at low temperatures (around 5 ° C) and hot processes are considered when the reaction temperature is higher than 50 ° C. In some reactions it is required to stop the reaction at low conversions (from 50 to 75%) to obtain the appropriate characteristics in the rubbers. Batch processes are those in which all the ingredients are loaded at the beginning of the reaction. There are lots of processes, in which a portion of the ingredients is loaded at the beginning of the reaction and the rest are dosed by pre-established times.

The on-stream processes consist of an input current of the polymerization inputs and a product output current, and in the case of continuous processes, a cascade of reactors is generally required to achieve high conversions. .

In recent years, environmental regulations have paid more attention to the dispute over residual monomers and so-called organic volatiles, examples of which are styrene, acrylonitrile, vinyl chloride, etc.

Regardless of the reaction process, the total conversion to polymer is not achieved up to 100%, which implies that residual monomer occluded in the emulsion polymer particles.

Traditionally the removal of residual monomer is carried "Cape dragging said monomer by vacuum and / or steam.

Among the dev? Lanes that are presented when using trawling, they say that it is a highly consumer process, ". Energy (vacuum and steam). The equipment in which the dragging takes place is considerably dirty, which causes a reduction in productivity, due to the problem of contamination caused by the crusts adhering to the equipment.For the application of the vacuum foam is generated and antifoam is added to avoid it. these affect the functional characteristics of latex (film formation, solvent resistance, adhesiveness, gloss, etc.). There is also the problem of destabilization and degradation of the polymer due to the long r? E times required for the drag. The water removed during the drag contains residual monomer and latex, which forces to treat this wastewater to meet the ecological standards that are stricter every day.

For example, in US Pat. No. 4,130,527 it is indicated that, in general, volatile organic compounds are removed from the latex, using water vapor, gases or gas mixtures. In this technology it is established that the velocity of removal of volatiles is not controlled by the velocity of dif "" i; output of the particle, but by the speed at which < r > 1 gas can contact the polymeric particle to entrain the volatile material to the aqueous phase and subsequently to the gas phase. Some of the factors that affect the design of this type of equipment are: a) foam production during the process; b) the colloidal instability resulting from the temperature and mechanical stress, and c) the high viscosities caused by the concentration of the product. In US Pat. No. 4,529,753 it is pointed out that commercially there are devolatilizers of various types, from those operating in batches to continuous and having cascades of equipment with gas flows against the flow or with crossed fluids. Another piece of equipment that has been found is referred to as ^^ dragging columns that form a thin film of the latex, under reduced pressure conditions, to increase the contact surface with the entrainment gas (removal of the monomer of lát ', SM England publication, Dow Chemical Co. Midland, Mich 48640 USA). It is obvious to emphasize that these equipments are expensive and due to the process there is a great loss of p * tal by coagulation.

In the North American patent 4,301,264 describes an "emulsion polymerization process" in which the oxidizing system consists of hydroperoxides and the reducing system consists of amines. In this patent the oxidant is charged to the emulsion from the polymerization process.

There is also reported a method of "chemical and steam entrainment" in which reduced pressure conditions are used. The oxidizing system is a hydrogen peroxide, a diazo or azo compound and the reducing agent is a sulfur compound.

SUMMARY OF THE INVENTION A process for substantially aggregating the residual monomer from the reaction of homo, copolymerization or terpolimerizat * in emulsion resulting from conversions less than 0%. Characterized in that the tex is subjected to a post-polymerization by means of a treatment of oxide-reduction. This treatment consists in the addition of the oxide-reduction system; the ratio used being 0.01-0.5 / 0.01-0.5 percent by weight based on 100 parts of polymer. The process is carried out at a temperature of 50-90 ° C and at atmospheric pressure. The depletion time in which the maximum residual monomer reduction is achieved is 0.5 to 5.0 hours, in the reactor. The process is also characterized in that the oxide-reduction system continues its action of accumulation in the latex during the storage time prior to use.

The process described here is applied in emulsions involving vinyl monomers and conjugated dienes containing from 2000 to 100000 ppm of residual monomer, and reduction of these contents up to 50 to 1000 ppm is achieved.

The object of the present invention preferably provides a process that instead of trying to remove the residual monomer by conventional techniques allows to polymerize it < _ - the same emulsion, without affecting the functional characteristics of the latex and at a temperature such that the latex trttado does not degrade or coagulate, thus avoiding the entrainment steps with steam or gases, latex concentration of known processes and then its treatment " wastewater and emissions to the environment resulting from these processes.

One of the objects of the invention is to provide a more productive and less expensive process that by using a system of oxidizing and reducing components achieves a more efficient process by considerably reducing its manufacturing time, since the exhaustion can be carried out in the same reactor where the polymerization was carried out either separately in a stirred tank at room temperature and under pressure conditions where the residual monomer is reduced to levels accepted by international environmental standards.

DESCRIPTION * 'DETAILED OF THE INVENTION Traditional Processes Steam distillation. - In the conventional technologies to remove the volatile monomers that did not react during the polymerization, a vapor dragging process is carried out in order to desorb the monomer that is still free.

The low solubility in water of the monomers for example (Butadiene, styrene, vinyl chloride, etc.) causes that most of the residuals of these are in 1- colloidal particles of the polymer. A controlled equilibrium is established between the continuous phase (water) and the particles. Water and part of the dissolved organics are distilled by vacuum and high temperatures.

It literally requires distilling several times the original volume of water d > , emulsion to reduce the amount of volatiles. It should be noted that this part of the process is very long (from 8 hours onwards), extensive in the use of energy (steam and < - - ticity), and contributes notably to the emanation of volatiles to the atmosphere; that the latex is diluted and tends to degrade and causes fouling in the equipment when performing the operation.

On the other hand, during the distillation small latex ts (some ge '* s would be sufficient) towards the distillates produces effluent contamination very difficult to eliminate (white water), since the average particle size is 200 nano e ros , which can be eliminated by very sophisticated and economically inaccessible methods.

Concentration. - Due to the fact that in the distillation stage the solids content of the latex Jis inuye (part of the steam condenses to heat the latex), it is necessary to concentrate for two main reasons: a) The freight cost is affected by the unnecessary transport of water, b) During the application of the adhesives and coatings, the formulations of the customers do not support high amounts of water, mainly due to the long drying times (high energy consumption) that are required.

Therefore, once the distillation stage is finished, an additional stage of concentration of the latex is required. Vacuum is applied and the latex is heated at higher temperatures to evaporate water.

Also during this process, appreciable amounts of "white water" are generated that need to be treated to comply with the effluent disposal requirements, in addition to the equipment being considerably incrusted by the coagulated lax, resulting in downtime due to equipment cleaning. .

It is worth mentioning that by drastically lengthening the reaction cycles and adding more initiator, conversions close to 100% could be achieved, but the process is not profitable (very low productivid. J) and the functionality of the product is affected by secondary reactions, for example, crosslinking .

Traditionally, the polivvization in aqueous emulsion of vinyl monomers and / or conjugated dienes is effected by polymerizing the monomers in the presence of emulsifiers, molecular weight modifiers, electrolytes, master water carriers, antioxidants and initiators. Examples of water-soluble initiators that can be used are ammonium, potassium or sodium persulfates C, as well as perborates, peracetates, peroxides, metal percarbonate alkali (eg, sodium or potassium), hydrogen peroxide; which can act alone or activated by a water-soluble reducing agent, among the * '*' * * '* * n *': water-soluble azo initiators, such t &g or the 2, 2 'azo bis (2 amidine propane), dihydrochloride, 4,4 'azo bis 4 cyanopentanoic acid, etc. Examples of initiators which are soluble in the organic phase are organic peroxides or hydroperoxides, such as diterbutyl peroxide, benzoyl peroxide, lauryl peroxide, etc. azo initiators such as 2, 2'-azo bis isobutyronitrile, 2,2'-azo bis- (2-methylbutyronitrile), etc., peroxyesters, such as t-butyl-peroxine-deocene, t-butyl peroxypivalate, t-butyl peroxy-2-ethyl hexanoate, etc. The initiators mentioned above, when used as initiators of the main polymerization, are aggregated in amounts ranging from 0.05 to 0.5% by weight with respect to the total monomer mixture. oxide-reduction is used in amounts comprised in the range of 0.01 to 0.5% by weight based on 100 parts of polymer, for the oxidizing agent and the reducer. It being understood that when we mention oxidizing agent it may comprise an agent or the mixture of two or more of these aditives. It also applies in the case of the reducer. In the oxide-reduction system, an initiator of the peroxy ester type soluble in the organic phase must always be present in the oxidizing part.

Suitable reducing agents include complex carboxylic acids of iron, cobalt, zinc, copper or nickel or reducing adducts or their derivatives, such as, imnitol or gluconates. P? ^ '-p also be sulfur-containing compounds, such as sulfates or alkali bisulphites or sulfates of alkaline earths. Examples of these agents are sodium sulfoxylate and formalin, dextrose, fructose, sodium bisulfite, metabisulfite • sodium, ascorbic acid, erythorbic acid, etc.

NEW PROCESS The following describes the process object of the present invention: Chemical exhaustion. - To reduce practically all the monomers that did not react in the emulsion polymerization processes, an alternate system is used that produces more active free radicals through reactions of reduction. The new radicals must produce more polymer chains without affecting the functionality of the product. This is achieved with the systems described above, which have the ability to preferentially activate the residual monomer and not the emulsion polymer.

In general, redox systems produce reactive radicals and reactive towards the previously formed polymer, which leads to crosslinking reactions (network formation) that decrease the flexibility of the material adversely affecting its functionality. The novel feature of the described innovation is to selectively control transfer reactions to the polymer to achieve conversions close to 100% by using the aforementioned oxide-reduction system.

The process of "Chemical Exhaustion" object of the invention has the advantage that, on the one hand it eliminates contaminating substreams, which instead of contaminating become part of the product, which increases the yield of the reaction and therefore the productivity of process. The achievements reached in terms of productivity are reflected in a significant reduction in the total manufacturing times of the product in emulsion, the result of the elimination of the stages of "-racking with steam and concentration. the net depletion time was reduced by more than 65%, and the distillation and concentration time (from 1 hrs to 0 hrs) was 100%, as a result of the above, the consumption of services (steam, electricity, cooling water ) was reduced in the same proportion.

The invention is described below in the following examples, in order to better clarify the same, but certainly without restricting its scope.

EXAMPLE 1. A mixture of styrene-butadiene monomers is charged to a stirred reactor and subjected to a polymerization at temperatures of 45 ° to 60 ° C, obtaining an emulsion (latex) with a residual monomer content from 10,000 to 30,000. ppm; then additives are added such as pH stabilizers, an aqueous vehicle in minimum concentrations of 0.1 to 0.3% by weight, after which the temperature of the polymer mixture is increased from 60 ° to 80 ° C; and a system of oxidizing agents in d of the oxidizing agent is added is selected from di acyl peroxides, peroxydicarbonates, peroxyesters or hydroperoxides or in a mixture of any of them with a peroxy ester of tert-butyl peroxy 2 ethyl hexanoate or with hydrogen peroxide 7; and a reducing agent selected from metal complexes of sulfoxylates, such as formalin and zinc sulfoxylate or formol sulfoxylate and iron or in admixture with carboxylic acids such as ascorbic acid, erythorbic acid, citric acid, tartaric acid, etc .; pn a concentration of 0.01 to 0.5 parts by weight per 100 parts by weight of latex, during a reaction time of 1 to 3 hours. Subsequently, the residual monomer content is determined to be 50-500 ppm.

EXAMPLE 2. Following the same technique of. Example 1, the temperature of the mixture is increased to 70 ° C and then a system of benzene peroxide and pe * -lulfat '*' is added. potassium as oxidants with a mixture of sugars such as dextrose, fructose, glucose or galactose, in a concentration of 0.01 to 0.1 parts by weight per 100 part by weight of latex, during a depletion time of 1 to 3 horéis, obtaining a monomeric residue d «50 to 200 ppm.

EXAMPLE 3. Following the same technique as in Example 1, the temperature is increased to 70 ° C, and the oxide-reduction system based on terbutil hydroperoxide ammonium persulfate and erythorbic acid in a ratio of 0.07 parts per 100 is added slowly. 1"polymer, during a depletion time of 1 to 2 hours, obtaining a residual monomer content of 100 to 200 ppm.

EXAMPLE 4. Following the same technique of Example 1, an oxide-reduction system based on formalin and zinc sulphoxylate, t-butyl peroxy 2 ethyl hexanoate and t-butyl peroxy benzoate is added in a ratio of 0.15 parts per 100. of polymer, after r13 4 to 5 hours the residual monomer content is determined obtaining from 50 to 120 ppm.

Claims (7)

Having described the invention is considered a novelty and therefore the content is claimed in the following: R E I V I N D I P A C I O N S

1. - A chemical exhaustion process for substantially eliminating residual monomers in emulsion polymerization processes, wherein a mixture of vinyl monomers and / or preferably conjugated dienes, styrene-butadiene, is polymerized at temperatures of 45 ° C to 60 ° C, a reactor to obtain an emulsion (latex) with a residual monomer content from 2000 to 100,000 ppm. the process being characterized by the steps of: contacting said latex in the same reactor with an oxide-reduction system that < rende a) an oxidizing agent generating free radicals of higher activity selected from diacyl peroxides, peroxydicarbonates, peroxyesters and hydroperoxides; and b) a reducing agent selected from sulfexylated compounds, reducing sugars or their acid and carboxylic derivatives of C5-C40 in a ratio of 0.01 to 0.5 / 0.01 ~ 0.5 oxidant-reducing% by weight per 100 parts of polymer; heating the resulting mixture to a stirring temperature of from> 50 ° C to 90 ° C for a depletion time of 0.3 to 5 hours to obtain a latex with a residual monomer content of at least 50 to 1000 ppm.

2. - A chemical exhaustion process for substantially eliminating residual monoes in emulsion polymerization processes according to clause 1, characterized in that the reductive action of the oxide-reducing system continues to be active even during storage of the latex reducing the content of free monomer from 10 to 50% of that obtained in the exhaustion stage.

3. - A chemical exhaustion process for substantially eliminating residual substances in polymerization processes in emulsion in accordance with clause 1, characterized in "the reducing agent of the oxide-reduction system sulfoxylated compounds are used and preferably" plfr * Formalin and zinc lato.

4. - A chemical depletion process for substantially eliminating residual monomers in polymerization processes in accordance with clause 3, characterized in that the reducing agent is a mixture of sulphonylated compounds and carboxylic acids, preferably erythorbic acid, ex J .ico or itaconico.

5. - A chemical exhaustion process for eliminating substantially residual monomers in emulsion polymerization processes according to clause 1, characterized in that the reducing sugars can be dextrose, fructose, glucose or galactose.

6. - A chemical depletion process for substantially eliminating residual monomers in polymerization processes t > n emulsion according to clause 1, characterized in eg the oxidizing agent of the oxide-reduction system can be selected preferably from the "peroxyster of t-1" such as tertbutyl peroxy neodecanoate, tertiary butyl p - ^ - oxy valate, terbutyl peroxy 2 -ethyl hexanoate or terbutyl peroii benzoate.

7. - A chemical depletion process for substantially eliminating residual monomers in emulsion polymerization processes according to clause 6, characterized in that mixtures of peroxyesters are preferably used with potassium persulfate, ammonium persulfate, terbutyl peroxide or tert-butyl hydroperoxide . ABSTRACT A process for substantially reducing the residual monomer resulting at the end of the n-emulsion polymerization reaction has been de-aerated. The process consists of subjecting the latex to a reduction process after the polymerization reaction. The recommended environment consists of a homo or copolymer of vinyl monomers and / or conjugated dienes having a residual monomer content not exceeding 100,000 -i at the end of the reaction. After chemical exhaustion, residual monomer contents of 50 to 1000 rr "i are achieved in a process that lasts 0.5 to 5 hours maximum.