BACKGROUND

[0001] Emulsion polymerization is a type of radical polymerization and has been used to produce of a variety of polymers, including for example acrylonitrile-butadiene styrene (ABS), styrene-butadiene styrene (SBS), methyl methacryl ate-butadiene styrene (MBS), acrylonitrile styrene acrylate (ASA), polytetrafluoroethylene-styrene-acrylonitrile (TSAN) and styrene acrylonitrile (SAN). In such emulsion polymerization processes, a reaction mixture, and optionally additives for initiation and control of the reaction and emulsifying agent(s) may be combined with a liquid medium, thereby forming an emulsion, which is subjected to conditions for polymerization. During the polymerization, a polymer latex is formed. Such polymer latex may be understood to be a colloidal distribution of polymeric particles in the liquid medium.

[0002] In order to obtain the desired polymer as a particulate product from the process, the polymeric particles that are present in the polymer latex need to be isolated. This can be achieved by the addition of a coagulant to break the polymer latex. During this coagulation process, the original particles in the latex are agglomerated to form bigger particles. While various coagulation processes are known in the art, foam and chunk formation can be observed in the coagulation system in addition to not achieving the targeted particle size distribution. Accordingly, there is a continuing need for an improved process and system for manufacturing particulate polymers.

[0003] JPS5763332 relates to a preparing apparatus of a coagulated latex having a means for preventing the adhesion of reactants in the top of a coagulating cylinder and a latex sprayer.

[0004] US4110491 A relates to a method and apparatus for encapsulating and coagulating an elastomeric latex wherein the latex is introduced as drops into an encapsulating-coagulating liquid via a draft tube through which the encapsulatingcoagulating liquid is impelled downwardly in generally linear flow.

[0005] CN110252237A relates to a kind of process equipment for the deamination of colloidal liquid recycling and reusing that natural emulsion generates

[0006] US2561256A relates to the separation of solid polymers in substantially dry condition from slurries in liquids. [0007] US4890929A relates to a method of manufacturing coagulated grains from polymer latex and apparatus for exercising this method.

[0008] BE880827A relates to a latex coagulation method and apparatus.

SUMMARY

[0009] A method of manufacturing a particulate polymer comprises: introducing a polymer latex into a vessel; distributing the polymer latex in the vessel to a coagulator via a distribution member and a redistribution member, wherein the coagulator is equipped with an agitator having an agitator shaft; the distribution member is mounted on the agitator shaft and extending upwardly into the vessel through a bottom wall of the vessel, the distribution member having an open top in the vessel and an opposite open bottom facing the coagulator; and the redistribution member is mounted on the agitator shaft, the redistribution member having an open top facing the open bottom of the distribution member; and wherein the polymer latex in the vessel enters the open top and exits the open bottom of the distribution member and flows into the redistribution member, and the polymer latex in the redistribution member overflows into the coagulator; introducing a coagulant and steam into the coagulator; mixing the polymer latex, the coagulant, and the steam to break the polymer latex forming the particulate polymer; and separating the particulate polymer from a liquid in the coagulator.

[0010] A system for manufacturing a particulate polymer comprises: a coagulator equipped with an agitator having an agitator shaft; a distribution member mounted on the agitator shaft and extending upwardly into a vessel through a bottom wall of the vessel, the distribution member having an open top in the vessel and an opposite open bottom facing the coagulator; a redistribution member mounted on the agitator shaft, the redistribution member having an open top facing the distribution member; and a coagulant dispensing means for introducing a coagulant into the coagulator, wherein the distribution member and the redistribution member are configured such that a polymer latex in the vessel is flowed into the redistribution member via the open bottom of the distribution member, and the polymer latex in the redistribution member overflows into the coagulator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A description of the figures, which are meant to be exemplary and not limiting, is provided in which:

[0012] FIG. 1 illustrates a system for manufacturing a particulate polymer;

[0013] FIG. 2 illustrates the introduction of a polymer latex from a vessel to a coagulator via a distribution member and a redistribution member;

[0014] FIG. 3 illustrates a coagulant spray ring;

[0015] FIG. 4 illustrates the injection of steam jets into a coagulator;

[0016] FIG. 5 is a graph of weight percent versus particle size showing the particle size distributions of ABS made in the inventive process and the comparative process;

[0017] FIG. 6 is a boxplot showing the moisture percent of the wet ABS (cake) made in the inventive process and the comparative process;

[0018] FIG. 7 is a boxplot showing the residual acid contents in the ABS made in the inventive process and the comparative process.

[0019] The above described and other features are exemplified by the following detailed description and Examples.

DETAILED DESCRIPTION

[0020] Process and system for producing particulate polymers having controlled particle size distribution and minimized chuck/foam formation are disclosed. Referring to FIGS. 1-4, the system comprises a coagulator (60) equipped with an agitator having an agitator shaft (20); a distribution member (40) mounted on the agitator shaft (20) and extending upwardly into a vessel (30) through a bottom wall (31) of the vessel (30), the distribution member (40) having an open top (42) in the vessel (30) and an opposite open bottom (41) facing the coagulator (60); a redistribution member (10) mounted on the agitator shaft (20), the redistribution member (10) having an open top (11) facing the distribution member (40); and a coagulant dispensing means (70) for introducing a coagulant into the coagulator (60). The vessel (30) and the distribution member (40) together are also referred to as weir box (100). The weir box can be at the center of the coagulator (60) around agitator shaft (20).

[0021] The coagulator (60) is where the coagulation takes place. The coagulator (60) is equipped with an agitator, which can have, in addition to the agitator shaft (20), a motor (25) and a blade (26). The agitator can be at the center of the coagulator (60). The coagulator (60) has a jacket (65) to control a temperature of the polymer latex and the coagulant in the coagulator. Optionally the coagulator (60) has a cover (66).

[0022] The vessel (30) holds the polymer latex which is to be distributed to coagulator (60). The polymer latex can be introduced into the vessel (30) through a tubular member (50) via an inlet disposed on the bottom wall (31) of the vessel (30). The polymer latex can also be added to the vessel (30) from the open top of the vessel (30) or through the side walls of the vessel (30).

[0023] The latex in the vessel (30) is distributed into the coagulator (60) via the distribution member (40) and the redistribution member (10). The distribution member (40) has a frustoconical wall (43) defining an open top (42) in the vessel (30) and an opposite open bottom (41) facing the coagulator (60). The open top (42) of the distribution member can have a larger surface area than the open bottom (41) of the distribution member.

[0024] The redistribution member (10) is also mounted on the agitator shaft (20). The redistribution member (10) has a frustoconical wall (12) defining an open top (11) facing the open bottom (41) of the distribution member (40), and a second bottom wall (15) secured to the frustoconical wall (12) and the agitator shaft (20). The redistribution member (10) can rotate with the agitator shaft (20).

[0025] The coagulant dispending means (70) can be a coagulant spray ring having an inlet (71) for introducing a coagulant into the spray ring means and at least two evenly spaced nozzles (72) for adding the coagulant directly into the coagulator (60). The coagulant spray ring is a larger size ring outside of weir box (100) and close to the coagulator wall. The weir box is smaller size, which is at the center of coagulator (60) around agitator shaft (20). Both the coagulant spray ring and weir box (100) can be at the similar vertical level.

[0026] The system further comprises a steam jet injector configured to inject a steam jet (86) into the coagulator (60). Preferably the steam jet injector is configured to inject at least two steam jets (86) into the coagulator (60) via separate lines (80).

[0027] A method of manufacturing a particulate polymer comprises: introducing a polymer latex into a vessel; distributing the polymer latex in the vessel to a coagulator via a distribution member and a redistribution member; introducing a coagulant, steam, and optionally water into the coagulator; mixing the polymer latex, the coagulant, the steam, and the optional water to break the polymer latex forming the particulate polymer; and separating the particulate polymer from a liquid in the coagulator.

[0028] The methods of introducing the polymer latex into the vessel (30) are not particularly limited. Preferably at least a portion of the polymer latex is introduced into the vessel (30) via an inlet at the bottom wall (31) of the vessel (30). Once the polymer latex in the vessel (30) reaches a level that is higher than the top surface of the distribution member (40), the polymer latex in the vessel enters the open top (42) of the distribution member (40) and exits its open bottom (41) and flows into the redistribution member (10). The polymer latex in the redistribution member (10) can then overflow into the coagulator (60). Because the redistribution member (10) is mounted on the shaft (20), and the overflow of the polymer latex is along all the directions of the circular edge of the frustoconical wall (12) that defines the open top (11), the polymer latex can be fed evenly and directly into the high shear region in the coagulator (area near agitator blade) to achieve the best coagulation effect, and to improve the control on coagulation.

[0029] The coagulant feeding as described herein also contributes to the controlled agglomeration. Preferably, the coagulant is introduced directly into the coagulator (60) via the at least two evenly spaced nozzles (72). Because the coagulant spray ring is a larger size ring close to the coagulator wall, the coagulant can be evenly added to the low shear region in the coagulator (area away from the agitator blade). As disclosed herein, the polymer latex can be fed evenly and directly into the high shear region in the coagulator (area near agitator blade). Thus the method avoids the early contact of the polymer latex with the coagulant, which may lead to foam and chunk. By using the system as described herein, the method also allows for the uniform mixing of the coagulant and the polymer latex in the vortex zone created by the steam jets.

[0030] A pressured steam injection into the coagulator (60) can facilitate the mixing of various components in the coagulator. Steam jets can also help to achieve the desired mixing temperature. There can be at least two steam jets (86) in the coagulator (60) which are symmetrically positioned. The steam jets are below a liquid surface in the coagulator and are in the direction of vortex flow (81) to ensure vortex in the coagulator (60) is circular and to enhance high shear mixing. In addition to steam, water can be introduced into the coagulator (60) via nozzles (90). [0031] The polymer latex, the coagulant, the steam, and the optional water introduced into the coagulator (60) can be mixed to break the polymer latex forming the particulate polymer. A Rushton turbine agitator can be used in the coagulator to achieve the high shear mixing. The mixing can be conducted at a temperature of 80 to 100°C, 85 to 95°C or 88 to 94°C. Using the system and the method described herein, the polymer latex, the coagulant, water, and the steam can be homogeneously mixed in the coagulator.

[0032] As a result of the coagulation process, polymeric particles agglomerate and settle at the top or at the bottom of the coagulation unit. The polymeric particles may subsequently be separated from the aqueous phase. The isolation of the coagulated product may be conducted using conventional means for separating solid/liquid systems such as filtration and centrifugation. The isolated product can be dried if desired.

[0033] The process can be a continuous process. The flowrates can be metered and ratioed based on the latex feed rate. Coagulant to latex flow ratio can be 0.05 to 0.065, or 0.057 to 0.061. The residence time of various components in the coagulator can be 1 to 20 minutes.

[0034] The particulate polymer prepared in accordance with the process described herein can have a narrower particle size distribution and/or a higher percentage of particles within the desired particle size range. In particular, 35 to 50 wt% of the particulate polymer can have a size that is less than 850 microns but greater than 150 microns. In addition, less than 27 wt%, less than 26 wt%, or 10 to 26 wt%, 15 to 26 wt%, or 18 to 25 wt% of the particulate polymer prepared in accordance with the process described herein has a particle size of greater than 850 microns. As used herein, the particle size distribution is determined by sieve analysis.

[0035] The particulate polymer prepared in accordance with the process described herein also has reduced %cake moisture content and reduced residual acid as compared with particulate polymer prepared in accordance with a comparative process using a coagulation system that does not include a weir box as described herein.

[0036] As used herein, a polymer latex may be understood to be an aqueous system comprising polymeric particles in dispersion. For example, a polymer latex may comprise 20.0 - 60.0 wt% of polymeric particles with regard to the total weight of the polymer latex. Preferably, the polymer latex comprises 25.0 - 55.0 wt% of polymeric particles with regard to the total weight of the polymer latex. More preferably, the polymer latex comprises 30.0 - 50.0 wt% of polymeric particles with regard to the total weight of the polymer latex. [0037] Such polymeric particles may for example have an average particle size of 60 to 500 nanometers (nm). Preferably, the polymeric particles have an average particle size of 150 to 500 nm. The average particle size may for example be determined according to ASTM D1417 (2010).

[0038] The polymer latex comprises a polymer of one or more monomers of a vinyl aromatic monomer, an acrylate, an unsaturated cyanide, or a diene.

[0039] Suitable vinyl aromatic monomers include for example styrene, a-m ethyl styrene, halostyrenes such as dibromostyrene, vinyltoluene, vinylxylene, butylstyrene, p- hydroxystyrene, methoxystyrene, or combinations thereof. Particularly suitable vinyl aromatic monomers are for example styrene and a-methyl styrene. It is preferred that the vinyl aromatic monomer is styrene.

[0040] Suitable unsaturated cyanides include for example acrylonitrile, methacrylonitrile, ethacrylonitrile, a-chloroacrylonitrile, a-bromoacrylonitrile, or combinations thereof. It is preferred that the vinyl cyanide is acrylonitrile.

[0041] Suitable dienes include for example butadiene, isoprene, chloroprene, 2- methyl-l,3-butadiene, 2,3-dimethyl-l,3-butadiene, 1,2-propadiene, 1,4-pentadiene, 1,2- pentadiene, 1,5-hexadiene, or combinations thereof. It is preferred that the diene is butadiene.

[0042] Examples of acrylates include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, benzyl acrylate, isopropyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isopropyl methacrylate, cyclohexyl methacrylate, vinyl acetate, dimethyl maleate, diethyl maleate, or combinations thereof. The preferred acrylate is methyl acrylate or methyl methacrylate or a combination thereof.

[0043] The polymer in the latex can be at least one of acrylonitrile-butadiene styrene (ABS), styrene-butadiene styrene (SBS), methyl methacryl ate-butadiene styrene (MBS), acrylonitrile styrene acrylate (ASA), polytetrafluoroethylene-styrene-acrylonitrile (TSAN), or styrene acrylonitrile (SAN). In one example the polymer latex can be an acrylonitrilebutadiene styrene latex, particularly with 30 to 80% butadiene rubber based on total weight of the ABS in the latex.

[0044] As used herein, the coagulant is understood to contribute to the destabilization of the aqueous dispersion of the polymeric particles in the latex. The coagulant may for example be at least one of an acid, such as sulfuric acid, hydrochloric acid, acetic acid, nitric acid, and phosphoric acid; an alkali metal salt; an alkaline earth metal salt; or an ammonium salt. The alkali and alkaline earth metal salts can be alkali metal halides, alkali metal halides, alkali metal sulphates, or alkaline earth metal sulphates. Examples of alkali and alkaline earth metal salts include sodium chloride, sodium sulfate, and calcium chloride. Examples of ammonium salt include ammonium acetate and alum. Combinations of two or more of the coagulant can be used. The coagulant may for example be added to the polymer latex in such quantity as to ensure a pH of the polymeric latex of < 5.0.

[0045] The methods of manufacturing polymers having the controlled particle size distribution are further illustrated by the following non-limiting examples.

EXAMPLES

[0046] In the inventive example, the system as illustrated in FIG. 1 was used. The coagulator was equipped with an agitator, two steam jets, a coagulant spray ring, a weir box, and a redistribution member, where the weir box includes a vessel and a distribution member. An ABS latex in the vessel flowed into the redistribution member via the distribution member. The polymer latex in the redistribution member overflowed evenly into the high shear zone (vortex zone) of the coagulator. The coagulant spray ring had multiple nozzles, and distributed a coagulant (sulfuric acid) evenly into the coagulator. The flow of the latex and coagulant were controlled, and the coagulant to latex flow ratio was kept at 0.055. Two steam jets were introduced to the coagulator at the opposite wall of the coagulator, both at the agitation direction.

[0047] During the coagulation, the agitator was run to promote the mixing in the coagulator tank, and all the components in the coagulator were mixed at 90°C. The steam jets provided velocity to improve the mixing, heating, and forming a vortex in the tank. In the continuous process, the residence time of the components in the coagulator was about 5 minutes. The generated ABS particles was separated from the liquid phase through centrifugation.

[0048] In a comparative example, the coagulator was equipped with an agitator, two steam jets and a coagulant spray ring only. The coagulation process is similar to the process of the inventive example, except that the latex feed was directly added to the vortex zone without using a weir box. Without wishing to be bound by theory, it is believed that under this situation, the latex feed is highly concentrated in a very small area and then mixed with the coagulant, and therefore, the coagulation is not well controlled. RESULTS

ABS RESIN PARTICLE SIZE DISTRIBUTION

[0049] A 20-cm diameter test sieve set, consisting of 4, 8, 20, 40, 60, 100 and 200- mesh sieves, a cover and a pan was used to determine the particle size distribution of the ABS products. In the sieve analysis, a weighed sample was blended with an antistatic agent and sifted through a set of standard tared sieves. The sieves were reweighed to determine the percentage of sample retained on each sieve. The results are summarized in Table 1 and graphically illustrated in FIG. 5.

Table 1.

[0050] Too fine particles are not desired as they may be lost in the downstream recovering process or may lead to troubles in resin powders followability. Too large particles are not desired either because it may lead to chunk formation and asset reliability (i.e. pump/pipe plugging). As shown in Table 1 and FIG. 5, the ABS prepared with the inventive process has a narrower particle size distribution as there are fewer large particles with a size of > 4.75 mm and similar percentage of fine particles with a size of < 75 pm as compared to the ABS made from the comparative process. In addition, the ABS prepared with the inventive process have higher percentage of particles in the 250-425 pm range as compared to the ABS made with the comparative process.

PERCENT CAKE MOISTURE

[0051] %Cake moisture refers to the water content in the wet resin (cake) that comes out of the centrifuge process. The % cake moisture was measured using moisture analyzer equipment (i.e. Mettler Toledo HX204 halogen moisture analyzer). A halogen bulb inside the equipment chamber heated the sample to a pre-determined temperature and drove off all volatiles in the sample. The weight loss of the sample was used to calculate moisture content, and the results are summarized in Table 2 and graphically illustrated in FIG. 6.

[0052] Table 2.

[0053] The data shows that the mean of %Cake Moisture has significantly reduced when the ABS is prepared according to the inventive process as compared to the ABS made in the comparative process using a comparative system. The results indicate that dewatering efficiency has improved as result of controlling the particle size distribution.

RESIDUAL ACID

[0054] Resin residual acid was measured through a non-aqueous dynamic titration, in which a weighed amount of the ABS was dispersed in an acetone/isopropanol/water solution, and an auto-titrator was used to dispense a standardized KOH/methanol solution into the ABS sample. The pH of the solution was monitored until an equivalence point was reached. The instrument was programmed to automatically select the equivalence point, or “steepest jump” in the titration curve, and the concentration of acid was output to the instrument’s display panel in terms of mass percent. The results are summarized in Table 3 and graphically represented in FIG. 7.

Table 3.

[0055] The data shows that the mean of %Residual Acid has significantly reduced when the ABS is prepared in accordance with the inventive process as compared to ABS made in the comparative process using the comparative coagulation system.

[0056] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. The endpoints of all ranges directed to the same component or property are inclusive and independently combinable. “Optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not. Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs. As used herein, a “combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.