EP1915404A1

EP1915404A1 - Anionic spray polymerization of styrene

Info

Publication number: EP1915404A1
Application number: EP06764287A
Authority: EP
Inventors: Wolfgang Loth; Volker Seidl; Stefan Bruhns; Klaus-Dieter Hungenberg; Jürgen Koch; Christian Schade; Claudius Schwittay
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2005-08-09
Filing date: 2006-08-01
Publication date: 2008-04-30
Also published as: US20100168348A1; DE102005038037A1; WO2007017420A1

Abstract

The invention concerns a process for continuous production of styrene polymers by anionic spray polymerization characterized in that i) styrene and the initiator solution are mixed in a dynamic or static mixer and subsequently spray dispensed, ii) the droplets formed transition from the liquid monomeric state into the molten polymeric state during their free fall in the spray tower, iii) the melt droplets are collected as a melt at the foot of the tower, the melt having a monomer content of below 1%, preferably below 0.1% (< 1000 ppm), and being discharged by means of a suitable apparatus.

Description

Process for the anionic spray polymerization of styrene

description

The invention relates to a process for the continuous preparation of Styrolpolyme- ren by anionic spray polymerization, characterized in that

i) Styrene and the initiator solution are mixed in a dynamic or static mixer and then sprayed,

ii) during the free fall in the spray tower the formed droplets change from the liquid monomer to the molten polymer state,

iii) collecting the melt droplets at the base of the tower as a melt, wherein the melt has a monomer content of less than 1%, preferably below 0.1% (<1000 ppm), and is discharged by means of a suitable device.

The anionic polymerization of styrene proceeds with great positive heat of reaction and is therefore usually carried out in solution of a low boiler, which absorbs the heat of polymerization by the evaporative cooling. In most anionic processes for styrene (co) polymers, the polymers accumulate as a solution in a solvent (USP 4,442,273, USP 4,883,846, USP 5,902,865) and must be freed of solvent and optionally low molecular weight impurities such as monomers and oligomers via suitable degassing agents and be converted into a solid.

In the case of the polymerization of pure styrene at low temperature - as described in DE 1 139 975 - fall the polymers as a solid. Another method starting from monomer, initiator and optional solvent, which also ends in the solid, is described in USP 5,269,980.

Anionic spray polymerizations of 1, 3-butadiene are described in the literature, in which the polymer formed in a countercurrent hydrocarbon (US 3,350,377) and in a styrene solution (DE 199 04 058) collected while a dispersion or solution is generated and the polymerization is stopped.

Anionic polymerization of styrene in bulk, ie without solvent, is described in US 5,587,438. The temperatures in the spray tower are regulated by an inert gas countercurrent, so that the polymerization takes place in the 0.5 to 3 mm large droplets at temperatures below 100 ⁰ C. The polystyrene formed thus accumulates as a solid. US 2003/0073792 describes a batch process for the anionic polymerization of styrene. The reaction is carried out adiabatically. To trap the large heat of reaction, solid polystyrene is added to the reaction process.

As previously stated, the prior art discloses the anionic polymerization of styrene in the case of an isothermal reaction under 100 ^° C. This procedure leads to a solid polystyrene with relatively high residual monomer content. Before assembly, the polystyrene usually has to be melted and degassed. Alternatively, it is polymerized in solution, which leads to considerable expense in the subsequent solvent removal and work-up. The low reaction temperatures also lead in both cases to low space-time yields and high residence times, which make the process economically unattractive.

On the other hand, in order to realize an adiabatic procedure as in US 2003/0073792, the reaction mixture must be diluted with previously formed polystyrene, which in turn leads to low space-time yields and thus is uneconomical.

Object of the present invention was therefore to find a method that the o.g. Disadvantages not. In particular, a process should be found which, with high space / time yields, provides a high purity polystyrene melt which is directly, i. can be further processed without a complex degassing.

The task is solved as follows. The cooled monomer solution including Initiatorlö- solution is optionally heated to 30 to 50 ⁰ C and sprayed or dripped so that small droplets of preferably 0.05 mm to 1 more preferably 0.1 to 0.4 mm are formed. During free fall through the spray tower, the monomers in the droplets are polymerized. Preferably, neither a solvent is added nor cooled in countercurrent. The droplets thus heat up above the melting temperature of polystyrene. In other words, the droplets are in liquid or molten form throughout the duration of the fall. The droplets are caught in a melt lake. At temperatures at the foot of the tower of over 200 ⁰ C, the monomers can be implemented almost quantitatively. The result is a melt of less than 1%, and preferably below 0.1 (1000 ppm) residual monomer content. Due to the high purity of the melt is usually unnecessary a degassing or other purification step and the polymer melt can directly the further processing, eg granulation, are supplied, or the optional degassing can be easily and inexpensively (for example, as strand degassing). Suitable styrene monomers are all anionically polymerizable vinyl polymers, such as, for example, styrene itself, α-methylstyrene, t-butylstyrene, vinyltoluene and divinylbenzene and mixtures thereof.

If the styrene polymer is a copolymer, the amount of the comonomers is usually 1 to 99, preferably 5 to 70 and more preferably 5 to 50 wt .-% based on styrene.

Preferably, the process according to the invention produces rubber-free polystyrene (GPPS, general purpose polystyrene). In addition, styrene-α-methylstyrene copolymers (PSaMS) having an α-methylstyrene content of e.g. 1 to 50 wt .-% with the inventive method produce.

The weight-average molecular weight M w of the polymer produced according to the invention is generally from 10,000 to 1,000,000, preferably from 50 to 500,000 and in particular from 100,000 to 400,000 g / mol.

Suitable initiators are alkali metal compounds selected from hydrides, amides, carboxyls, aryls, arylalkylenes and alkyls of the alkali metals, or mixtures thereof. It is understood that various alkali metal compounds can also be used. The preparation of the alkali metal compounds is known or the compounds are commercially available.

In particular, alkali metal organyls are suitable. These include alkali metal aryls and alkyls. Alkali metal alkyls are compounds of alkanes, alkenes and alkynes having 1 to 10 C atoms, for example ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, hexamethylenedio, butadienyl, isoprenyl Lithium, sodium or potassium, or multifunctional compounds such as 1, 4-dilithiobutane or 1, 4-dilithio-2-butene. Alkali metal alkyls are particularly well suited for the preparation of the styrene matrix. for the polymerization of polystyrene preferably sec-butyllithium use.

Suitable alkali metal aryls are, for example, phenyl lithium and phenyl potassium, and the multifunctional compound 1, 4-dilithiobenzene. Alkali metal arylalkyl compounds which are suitable in particular are alkali metal compounds of vinyl-substituted aromatics, in particular styrylpotassium and styrylsodium M-CH =CH-C ₆ H ₅ where M is K or Na. They are obtainable, for example, by reacting the corresponding alkali metal hydride with styrene and the presence of an aluminum compound such as TIBA. Also suitable are oligomeric or polymeric compounds, such as polystyryl lithium or sodium, which can be obtained, for example, by mixing sec-butyllithium and styrene, and then adding TIBA. Furthermore, it is also possible to use diphenylhexyl lithium or potassium. Such adducts of the initiator to the monomer are also referred to as pre-activation. The pre-activation causes a faster and better controlled start of the reaction after spraying.

Suitable alkali metal hydrides are, in particular, lithium hydride, sodium hydride or potassium hydride.

As initiators, it is also possible to use reaction products, so-called macroinitiators, of the alkali metal or alkaline earth metal compounds with butadiene (for example polybutadienyllithium) or styrene-butadiene block structure-based macroinitiators.

Furthermore, alkali alkoxides can be used to modify the reactivity and stability of the anions.

One can also mixtures of different alkali metal compounds and Aluminiumbzw. Use magnesium organyls to stabilize the reactive anionic species for polymerization at high temperatures. As regards the amounts of alkali metal compound and aluminum organyl, the following is to be said:

The required amount of alkali metal compound depends i.a. according to the desired molecular weight (molecular weight) of the polymer to be produced, the type and amount of the aluminum or magnesium organyl used - if it is also used - and the polymerization temperature. In general, 0.00001 to 1, preferably 0.0001 to 0.1 and particularly preferably 0.0001 to 0.01 mol% of alkali metal compound, based on the total amount of the monomers used.

Organylaluminum in particular those of the formula R3-AI can be used to advertising, where the radicals R are independently hydrogen, halogen, Ci _-2 o-alkyl, C6-2o-aryl or _C7-2-o arylalkyl. As aluminum organyl, aluminum trialkyls are preferably used.

The alkyl radicals may be the same, e.g. Trimethylaluminum (TMA), triethylaluminum (TEA), triisobutylaluminum (TIBA), tri-n-butylaluminum, tri-iso-propylaluminum, tri-n-hexylaluminum, or various, e.g. Ethyl-di-iso-butyl-aluminum. It is also possible to use aluminum dialkyls such as di-isobutylaluminum hydride (DiBAH).

Aluminum organyls which can also be used are those which are formed by partial or complete reaction of alkyl, arylalkyl or arylaluminum compounds with water (hydrolysis), alcohols (alcoholysis), amines (aminolysis) or oxygen (oxidation), or the alkoxide , Thiolate, amide, imide or phosphite Bear groups. Hydrolysis gives aluminoxanes. Suitable aluminoxanes are, for example, methylaluminoxane, isobutylated methylaluminoxane, isobutylaluminoxane and tetraisobutyldialuminoxane.

As the reaction accelerator for the anionic polymerization, inert, polar substances such as ethers, preferably cyclic ethers, e.g. Tetrahydrofuran or Crown 16-ether can be used. They cause a stronger dissociation of the aggregated anionic species. This causes a dramatic increase in the reaction rate over the proportion of active ("awake" as opposed to "dormant") molecules both at the start and during the polymerization.

Preferably, the polymerization is carried out without a solvent. However, it may be advisable to add the initiator dissolved in a solvent. The choice of solvent also depends on the alkali metal compound used. Preference is given to choosing alkali metal compound and solvent such that the alkali metal compound dissolves at least partially in the solvent. Furthermore, solvents are used which preferably have a lower boiling point than the monomer and provide by evaporation for targeted heat removal in the droplet. The solvents used are typically C3 to Ce alkanes or cycloalkanes such as cyclohexane, methylcyclohexane or hexane or tedrahydrofuran. Also, mineral oils such as white oil can be used, which have a low vapor pressure and preferably remain in the polymer.

Conventional additives, such as stabilizers, flow aids, flame retardants, blowing agents, fillers, etc., can be added to the finished polystyrene melt between tower discharge and granulation. Additives which do not or only insignificantly influence the anionic polymerization can be added to the mixture before spraying. An example of an adjuvant that can be added before spraying is white oil.

The mixture of monomer and initiator takes place by means of dynamic or preferably static mixing devices.

Compared with the dynamic mixers listed in WO 03/103818, the static mixers have the advantage that they are less expensive and less susceptible. Preferably, the two components styrene and initiator at temperatures <10 ⁰ C, preferably <0 ⁰ C, in a static mixer with a minimum flow rate expressed as Reynolds number (Re> 50) at a shear rate> 100 1 / s and a maximum residence time of < 1 s mixed in the mixing section. At lower flow velocities, the shear stress on the pipe wall caused by the flow is not great enough and deposits are formed which grow out and consequently change to a closure / breakthrough and thus to an unsteady one Conduct behavior. At too high a temperature and a long residence time, an initiation of the polymer formation can be initiated in the mixing section, as a result of which the viscosity of the mixture increases uncontrollably and the drop formation on spraying or dripping is negatively influenced.

The design of the static mixer must be capable of sufficiently homogenizing streams of widely differing volumes in the correspondingly short time, since after the spraying no concentration balance between the compartments (droplets) is possible and small differences in concentration lead to dramatic differences in the resulting polymer molecular weight. As for the claims of the application not limiting but suitable embodiments have for larger volume flows or throughputs so-called. Split and Recombine mixer, the expert as "Kenics or Sulzer mixer type" known and both for large and for small throughputs suitable, eg in the laboratory, so-called interdigital or interlaminator mixers (see: Hessel et al., AIChE J. 49 (2003) 3, pp. 566-577; Lob et al., Preprints of 11th Europ. Conf. on Mixing, Bamberg, 14-17-Oct. 2003, pp. 253-260).

The supply of the mixture to the spray tower is done to avoid premature polymerization start and consequent tendency to clog the Sprühbzw. Drop unit in cooled pipe. Preferably, the mixture is cooled to temperatures below 10 ⁰ C and more preferably below 0 ⁰ C.

Further possibilities mentioned in the patent literature for avoiding clogging during spraying are the introduction of an initiator component or a (co) catalyst via the gas phase (eg JP 2003-002905), the use of externally mixing nozzles, in which monomer and initiator pass through separate nozzle openings are sprayed and mix only after leaving the nozzle (eg EP 1424346).

The dispersion in the tower and generating the droplets is usually done with

Single or multi-fluid nozzles, for example by means of coaxial nozzles. In the

EP-A-1 424 346 and in particular EP-A 05 / 010325.8 describe spray nozzles with which droplets having the desired size distribution can be realized. Alternatively, the reactive mixing can be done by dripping, whereby both the "vibrating nozzle" and a liquid-defined oscillation of defined frequency in the kHz range can be used for drop formation A preferred but non-limiting method of dripping is described in US-A 5,269,980.

The droplets formed have an average drop size of preferably 0.05 to 1 mm and particularly preferably 0.1 to 0.4 mm. The dripping has the advantage over the spray that it leads to a homogeneous and narrow droplet size distribution. The narrow droplet size distribution in turn facilitates the controlled polymerization in the spray tower. In particular, with the dripping can be an efficient and process-capable polymerization process for polystyrene realize.

The droplets formed, which initially have low temperatures (about 0 to 10 ⁰ C), meet when entering the tower on inert gas, which has a temperature of 80 to 180, preferably 100 to 140 ⁰ C. Due to the large surface / volume ratio and the small diameter, the drops reach a temperature near the gas temperature almost instantaneously. The inert gas can be passed to the falling drops in cocurrent or countercurrent. The DC principle is advantageous for the swarm behavior of the droplets and thus for avoiding collisions, uncontrolled aggregation and deposit formation in the tower. The temperature increase is limited by the evaporation of monomers and auxiliaries. The countercurrent principle leads to a longer mean residence time of the droplets in the tower and can absorb more heat at the end of the drop distance / reaction, but is known for its difficulties of deposit formation from spray drying. Preferably, the process is operated in cocurrent of droplets and inert gas.

Subsequently, the polymerization after starting within a few seconds (usually less than 20, preferably less than 10 seconds) with release tion of the heat of polymerization and evaporation of monomer and optionally solvent to the end point from. The endpoint is determined by depletion of monomer and eventual death of the active anions at high temperatures. To stabilize the product, a special break-off agent can be metered into the melt in the outlet of the tower. The termination of the living anions takes place by elimination reaction or by protonation upon discharge and shaping / granulation by traces of protic substances, e.g. Water, alcohols or carbon dioxide.

The temperature profile of the gas phase and the drop on the way through the tower is determined by the feed temperature of the mixture (feed), the temperature of the gas phase at entry, the oil jacket temperature (little influence, rather "active insulation"), the mass flows, the pressure level in the tower , the drop size, the evaporation of monomer and optional solvent and the tower geometry due to the high heat of polymerization allows the temperature of the drops increase rapidly.In the lower half of the tower, the drops already have temperatures greater than 110, preferably greater than 150 ⁰ C. At the foot of the tower, the highest temperatures occur: the drops on the feet, which are finally caught in a melt lake. As a rule, they have a maximum temperature of 300 ^° C., preferably 250 ^° C., and more preferably 220 ^° C. If the temperatures are too high, discoloration occurs and premature chain termination occurs. The consequence of the latter is the undesirable increase in the residual monomer content.

The temperature in the drops can preferably be controlled by the droplet size. Small droplets can better dissipate the heat of reaction over the relatively large surface area by evaporation. In large drops local overheating takes place. Bursting and deformation of the polymer droplet formed are the result. The mean droplet size is therefore preferably in the o.g. Area.

The circulating gas withdrawn from the tower, which typically contains 5-30%, preferably 10 to 15%, of the constituents which can be evaporated via the evaporative cooling, is usually conducted via a particle separator (eg cyclone) and a scrubber. In the particle separator entrained by the gas flow droplets are trapped before the condensation takes place in the scrubber. There, the recycle gas is preferably cooled to below 70 ⁰ C and more preferably below 50 ⁰ C via a quench circuit and condensed out in order to "discharge" the gas stream and unwanted (side) reactions, such as polymerization of the condensed monomer to avoid - the.

Further, in order to avoid spontaneous anionic polymerization in the aforementioned scrubber, the quench liquid, which consists essentially of the condensed monomer, is added with small amounts of a protic, high boiling substance such as stearyl alcohol.

The recycled polymer which has been freed of reactive polymer and depleted of monomer is recompressed and fed again to the tower at room temperature.

The quenched monomer is freed from the trace of the protic, high-boiling substance by distillation or adsorption to the monomer feed of the tower. Alternatively, the remaining amount of the protic, high-boiling substance can be compensated ("run over") by a higher initiator dosage.

Examples:

The following compounds were used, where "purified" means that it was purified over alumina and dried All reactions were carried out with exclusion of moisture. Styrene, purified from BASF sec-butyllithium (s-BuLi) as a 12 wt .-% solution in mineral oil, finished solution from. Chemetall

Mineral oil Winog® 70, a medical white oil from Wintershall

example 1

Continuous production of polystyrene

From templates, 570 g / hr (5.5 moles / hr) of styrene and 1.6 g / hr (3.0 mmol / hr) of s-butyllithium in mineral oil (12 wt%) were added to a static mixer. From this temperature-controlled to 0 ° C mixing unit, the reaction solution was transferred via a 40 ⁰ C tempered heat exchanger on the shortest path in a vibrating Vertropfereinheit. In this unit, drops of about 0.15 mm were formed from the reaction mixture and placed on a tempered drop tower at atmospheric pressure. The drop tower had a jacket tube with a diameter of 80 mm and height of 2500 mm, which temperature had Ölmantel- 120 ⁰ C. In the downpipe, a weak nitrogen DC was set at 100 ⁰ C tempered. At the bottom of the tower, the melt droplets were collected in a melt stream of 220 ⁰ C.

According to GPC, the melt had polystyrene having a weight-average molecular weight of 220,000 g / mol. The HPLC analysis gave a residual styrene content of 300 ppm.

With the aid of the spray polymerization according to the invention, it was possible to obtain polystyrene with a high molecular weight and reduced residual monomer content compared with comparable technical products.

Claims

claims

1. A process for the continuous production of styrene polymers by anionic spray polymerization, characterized in that

i) styrene and the initiator solution are mixed in a dynamic or static mixer and then sprayed or dripped into an inert and tempered gas space,

iii) collecting the molten droplets at the base of the tower as a melt, the melt having a monomer content of less than 1% and being discharged by means of a suitable device.

2. The method according to claim 1, characterized in that the droplets in the lower half of the tower have a temperature of 110 to 250 ⁰ C.

3. The method according to claim 1, characterized in that the melt at the foot of the tower has a temperature of 200 to 250 ⁰ C.

4. The method according to claim 1, characterized in that the initiator is an alkali metal or an alkaline earth metal organyl or an alkali metal or an alkaline earth metal hydride is used.

5. The method according to claim 4, characterized in that is used as an initiator s-butyllithium.

6. The method according to claim 4, characterized in that in addition to the initiator as the reaction accelerator, an ether is used.

7. The method according to claim 6, characterized in that the reaction accelerator is tetrahydrofuran (THF).

8. The method according to claims 6 and 7, characterized in that the reaction accelerator is not sprayed or dropped with monomer and initiator, but the drop is supplied via the gas phase.

9. The method according to claims 4 to 8, characterized in that in addition to the initiator an anions stabilizing substance is used.

10. The method according to claim 9, characterized in that is used as the anions stabilizing substance an organoaluminum compound.

11. The method according to claims 1 to 10, characterized in that the droplets formed by spray polymerization have an average diameter of 0.1 to 0.4 mm.

12. The method according to claims 1 to 11, characterized in that initiator and styrene are mixed in a static mixer.

13. The method according to claim 12, characterized in that initiator and styrene are mixed in a static mixer of the split Recombine type.

14. The method according to claim 12, characterized in that initiator and styrene are mixed in a static mixer of Interlamellierungstyp.

15. The method according to claims 1 to 14, characterized in that the initiator is dissolved in a solvent having a lower boiling point than styrene.

16. The method according to claims 1 to 14, characterized in that the initiator is dissolved in a solvent having a higher boiling point than styrene and is largely discharged with the polymer formed.

17. The method according to claims 1 to 16, characterized in that gas and droplets are passed in cocurrent through the reaction space.

18. Process according to claims 1 to 17, characterized in that the droplets are produced by spraying with one or more nozzles.

19. The method according to claims 1 to 17, characterized in that the droplets are generated by dripping.

20. The method according to claims 1 to 19, characterized in that the collected in a melt droplets at the bottom of the tower have a monomer content of less than 0.1%.