DE19815737A1 - Process for the hydrogenation of aromatic polymers in the presence of branched hydrocarbons - Google Patents

Abstract

The invention relates to a method for hydrogenating polymers, optionally in the presence of catalysts, whereby branched hydrocarbons are used as solvents, possessing no more than one hydrogen atom at the branch point and having a boiling temperature above 45 DEG C and an ignition temperature (DIN 51794) of above 280 DEG C, or a mixture of such hydrocarbons with solvents that are suitable for hydrogenating reactions.

Description

The present invention relates to a method for aroma hydrogenation tischer polymers, which is characterized in that ver branched saturated hydrocarbons are used at the branching point have a maximum of one hydrogen atom, a boiling temperature greater than 45 ° C and have an ignition temperature (DIN 51794) greater than or equal to 280 ° C and so forth made polymers, or a mixture of solvents containing these carbons Hydrogen and the usual solvents for hydrogenation reactions.

The hydrogenation of aromatic polymers is already known. DE-AS 11 31 885 be writes the hydrogenation of polystyrene in the presence of catalysts and solutions medium. Aliphatic and cycloaliphatic hydrocarbons are used as solvents substances, ethers, alcohols and aromatic hydrocarbons generally mentioned. As a mixture of cyclohexane and tetrahydrofuran is preferred.

WO 96/34 896 (= US-A-5 612 422) describes, for example, a method for Hydrogenation of aromatic polymers, in the presence of a silica supported metal as a hydrogenation catalyst with certain pore size ver Division of the silicon dioxide is hydrogenated. Aliphatic or Cycloaliphatic hydrocarbons mentioned as branched saturated coal water isopentane (2-methylbutane) is called. Diethylene glycol is used as ether called dimethyl ether and tetrahydrofuran.

EP-A-322 731 describes the production of predominantly syndiotactic polymers ren based on vinylcyclohexane, a styrene-based polymer in counter Was hydrogenated by hydrogenation catalysts and solvents. As a solution medium cycloaliphatic and aromatic hydrocarbons are mentioned.

The specific solvents of the present invention are not mentioned.  

The hydrocarbons described in the above-mentioned documents, apart from iso Pentan have ignition temperatures of less than or equal to 260 ° C and are for one techni The process is not an easy-to-use solvent. The solvents have to sufficiently high ignition temperatures (DIN 51 794) for a technical process have, since during the polymer processing a contact to hot metal surfaces in possible presence of air and processing temperatures Polymer solution from e.g. B. hydrogenated polystyrene in the presence of the solvent Can reach or exceed 240 ° C. There is the possibility of Ignition and explosion if not a sufficient temperature difference between Processing temperature and ignition temperature is maintained.

Solvent exchange before the processing step for the production of granules is included considerable costs and technical effort.

Inertification measures of the entire polymer processing step, which prevent that a solvent / air contact is made are expensive and in practice for a large-scale process can hardly be realized because z. B. the entire apparatus would have to be encapsulated under inert gas.

Without such or other complex and expensive arrangements, those in the known documents known solvents other than isopentane (WO96 / 34 896; US 5 612 422) ignite and present a considerable safety risk. Isopentane is however no solvent for e.g. B. polystyrene, this solvent is therefore for the Hydrogenation of this polymer is unsuitable. Isopentane as a solvent also has the Disadvantage to boil at 28 ° C, which on the one hand the handling of the solutions difficult, on the other hand due to the necessary cooling in the refurbishment step expensive and complex cooling and condensing equipment leads.

The object is that the solvent used dissolves the starting polymer, the hydrogenation to a virtually complete hydrogenation of the aromatic one leads, the reaction product is dissolved and this system directly to the  Processing step is supplied, with a temperature difference of (min. 15% based on the Celsius temperature scale) between processing temperature and Ignition temperature of the solvent is maintained.

It has now been found that certain branched hydrocarbons ge have required properties and thereby an industrial process for Hydrogenation of aromatic polymers and their polymer processing clearly is simplified. The process is characterized in that the hydrogenated Polymer solution can be fed directly to the workup step and none complex technical measures to exclude a solvent / air contact on a surface greater than or equal to the ignition temperature are necessary. Another advantage of using this particular branched hydrocarbon substances is that the solvent at higher temperatures from the polymer can be separated, resulting in lower solvent residues and higher ones Polymer throughput leads.

The invention relates to a process for the hydrogenation of aromatic polymers, optionally in the presence of catalysts, with branched solvents Hydrocarbons are used at the branching point at most Have a hydrogen atom, a boiling temperature greater than 45 ° C and an ignition temperature tur (DIN 51794) above 280 ° C, or a mixture of such hydrocarbons with solvents suitable for hydrogenation reactions.

The reaction is generally branched at volume concentrations saturated hydrocarbons to the total solvent of 0.1% -100% preferably 1% -80% carried out very particularly preferably 5-70%.

The process according to the invention generally leads to a practically full constant hydrogenation of the aromatic units. As a rule, the degree of hydrogenation ≧ 80%, preferably ≧ 90%, very particularly preferably ≧ 99%, in particular 99.5 until 100%. The degree of hydrogenation can be determined, for example, by NMR or UV spectroscopy determine copy.  

Aromatic polymers are used as starting materials, for example are selected from optionally in the phenyl ring or on the vinyl group substi tuiert polystyrene or copolymers thereof with monomers selected from the Group of olefins, (meth) acrylates or mixtures thereof. Other suitable poly mers are aromatic polyethers, especially polyphenylene oxide, aromatic Polycarbonates, aromatic polyesters, aromatic polyamides, polyphenylenes, poly xylylene, polyphenylene vinylene, polyphenylene ethylene, polyphenylene sulfide, polyaryl etherketones, aromatic polysulfones, aromatic polyether sulfones, aromatic Polyimides and their mixtures, copolymers, optionally copolymers with aliphatic compounds.

As the substituents in the phenyl ring are C ₁ -C ₄ alkyl such as methyl, ethyl, C ₁ -C4- alkoxy, such as methoxy, ethoxy, fused aromatic compounds, the atom via a carbon or two carbon atoms are bonded to the phenyl ring, with phenyl, Biphenyl, naphthyl in question.

Possible substituents on the vinyl group are C ₁ -C ₄ -alkyl, such as methyl, ethyl, n- or isopropyl, in particular methyl in the α-position.

Suitable olefinic comonomers are ethylene, propylene, isoprene, isobutylene butadiene, cyclohexadiene, cyclohexene, cyclopentadiene, optionally substituted norbornene, optionally substituted dicyclopentadiene, optionally substituted tetracyclododecenes, optionally substituted dihydrocyclopentadienes,
C ₁ -C ₈ -, preferably C ₁ -C ₄ alkyl esters of (meth) acrylic acid, preferably methyl and ethyl esters
C ₁ -C ₈ , preferably C ₁ -C ₄ alkyl ether of vinyl alcohol, preferably methyl and ethyl ether,
C ₁ -C ₈ -, preferably C ₁ -C ₄ -alkyl esters of vinyl alcohol, preferably of ethanoic acid,
Derivatives of maleic acid, preferably maleic anhydride, derivatives of acrylonitrile, preferably acrylonitrile and methacrylonitrile.

The aromatic polymers generally have molecular weights Mw of 1000 to 10,000,000, preferably from 60,000 to 1,000,000, particularly preferably from 70,000 to 600,000, determined by light scattering.

The polymers can have a linear chain structure as well as through Co-Ein have branching points (e.g. graft copolymers). The branching centers include e.g. B. star-shaped polymers or other geometric shapes primary, secondary, tertiary, possibly quaternary polymer structure.

The copolymers can be either random, alternating or as block copolymers available.

Block copolymers include di-blocks, tri-blocks, multi-blocks and star-shaped Block copolymers.

The starting polymers are generally known (e.g. WO 94/02 720).

Preferred solvents are branched hydrocarbons of the formula (I) which have boiling temperatures greater than 45 ° C. and ignition temperatures (DIN 51 794) greater than or equal to 280 ° C.

in which
the radicals R ¹ , R ² , R ³ and R ⁴ stand for straight-chain or branched C ₁ -C ₁₀ alkyl and at most one of the radicals R ¹ , R ² , R ³ and R ^{4 can} also stand for hydrogen.

The following are particularly preferred:
2,2,3-trimethylbutane; 2,2-dimethylbutane; 2,3-dimethylbutane; Methylcyclopentane; 2-methylpentane; 3-methylpentane; 3,3-diethylpentane; 2,4-dimethylpentane; 2,2-dimethylpentane 2,3-dimethylpentane; 2,4-dimethyl-3-ethylpentane; 2,2,3-trimethyl pentane; 2,3,3-trimethylpentane; 2,2,4-trimethylpentane (isooctane); 2,2,3,3-tetra methyl pentane; 2,2,3,4-tetramethylpentane; 2,3,3,4-tetramethylpentane; 2-methylhexane; 3-methylhexane; 2-methyl-4-ethylhexane; tert-butylcyclohexane; 2-methylheptane; 2,5,5-trimethylheptane; 3,3-dimethylheptane; 2,2,5-trimethylheptane.

Is very particularly preferred for the hydrogenation of polystyrene and its derivatives Methylcyclopentane, which compared to those in the hydrogenation of the above ge known hydrocarbon is a good solvent, has a boiling temperature of 72 ° C and an ignition temperature of 315 ° C.

The amount of catalyst to be used is, for example, in WO 96/34896 wrote.

The amount of catalyst used depends on the process being carried out, this can be carried out continuously, semi-continuously or discontinuously become.

In the continuous system, the response time is much shorter; it is from the Dimensions of the reaction vessel affected. In the continuous way of working are the trickle system and the sump system, both with fixed catalytic converters gates, just as possible as a system with suspended and z. B. guided in a circle Catalyst. The fixed catalysts can be in tablet form or as Extrudates are present.  

The polymer concentrations, based on the total weight of solvent and Polymer are generally 80 to 1, preferably 50 to 10, in particular 40 up to 15% by weight.

The hydrogenation of the starting polymers is carried out according to generally known methods (e.g. WO 94/02 720, WO 96/34 895, EP-A-322 731). A large number of known hydrogenation catalysts can be used as catalysts. Preferred metal catalysts are mentioned for example in WO 94/21 694 or WO 96/34 896. Any catalyst known for the hydrogenation reaction can be used as the catalyst. Both catalysts with a large surface area (for example 100-600 m ² / g) and small medium pore sizes (for example 20-500 Å) as well as with a small surface area (for example ≧ 10 m ² / g) are suitable ) and large average pore size, which is characterized by the fact that 98% of the pore volume is defined to be larger than 600 Å (e.g. approx. 1000-4000 Å) (cf. e.g. US-A 5,654,253, US-A 5,612,422, JP-A 03076706). In particular, Raney nickel, nickel on silicon dioxide, aluminum oxide or silicon dioxide / aluminum oxide, nickel on carbon as a support and / or noble metal catalysts, for. B. Pt, Ru, Rh, Pd used.

The reaction is generally carried out at temperatures between 0 and 500 ° C preferably between 20 and 250 ° C, especially between 60 and 200 ° C leads.

The solvents which are customary for hydrogenation reactions are solvents described for example in DE-AS 11 31 885 (see above).

The reaction is generally preferred at pressures from 1 bar to 1000 bar 20 to 300 bar, in particular 40 to 200 bar, carried out.

Examples Examples 1-2

A 1 liter autoclave is flushed with inert gas. The polymer solution and the catalyst are added (table). After sealing, use protective gas several times then charged with hydrogen. After relaxing, the respective water adjusted fabric pressure and the mixture with stirring to the corresponding reaction heated temperature. The reaction pressure is after the onset of hydrogen recording kept constant.

The response time is the time from heating the batch to complete Hydrogenation of the polystyrene or, if the hydrogenation is incomplete, the time until Hydrogen uptake strives towards its saturation value.

When the reaction has ended, the polymer solution is filtered. The product is precipitated in methanol and dried. The isolated product shows the physical properties listed in the table.

The platinum catalyst (table) hydrogenates polystyrene in cyclohexane at 140 ° C (Comparative Example 1). Cyclohexane has an ignition temperature of 260 ° C and leads problems during product refurbishment because of a solvent / air contact Metal surfaces near the ignition temperature must be excluded. The The inventive method (Example 2) shows comparative example 1 complete However, hydrogenation all involved solvents have higher ignition temperatures 310 ° C.

Claims (1)

Process for the hydrogenation of aromatic polymers, optionally in the presence of Catalysts, using branched hydrocarbons as solvents that have at most one hydrogen atom at the branching point, one Boiling temperature greater than 45 ° C and an ignition temperature (DIN 51794) above 280 ° C have, or a mixture of such hydrocarbons with for hydrogenation reactions suitable solvents.