Process for preparing diaryl carbonates from dialkyl carbonates
The present invention relates to a process for continuously preparing diaryl carbonates from dialkyl carbonates and at least one monohydroxyl compound in the presence of catalysts, and to the use thereof for preparation of polycarbonates. The alkylene glycol obtained in the preparation of the dialkyl carbonate used is recycled by oxidative carbonylation with carbon monoxide in the presence of a catalyst to give the cyclic alkylene carbonate which is in turn converted to the dialkyl carbonate. More particularly, the process utilizes the alkylene glycol obtained for the diphenyl carbonate preparation process (DPC process).
1. A process for preparing at least one diaryl carbonate from at least one dialkyl carbonate and at least one aromatic hydroxyl compound, comprising
(a) preparing alkylene carbonate by reaction of alkylene oxide with carbon dioxide,
(b) reacting the alkylene carbonate formed in step (a) with at least one alkyl alcohol in the presence of a catalyst, and optionally organic solvent, to form at least one dialkyl carbonate and alkylene glycol,
(c) removing and working up at least a portion of the at least one dialkyl carbonate formed in step (b),
(d) removing and optionally purifying at least a portion of the alkylene glycol formed in step (b),
(e) oxidatively carbonylating at least a portion of the alkylene glycol removed in step (d) with carbon monoxide to give the alkylene carbonate with formation of water,
(f) removing and optionally purifying at least a portion of the alkylene carbonate formed in step (e),
(g) recycling at least a portion of the alkylene carbonate prepared in step (f) into the preparation of dialkyl carbonate in step (b),
(h) reacting at least a portion of the dialkyl carbonate prepared in step (c) with a monophenol to give the alkyl aryl carbonate and/or diaryl carbonate and alkyl alcohol; optionally recycling at least a portion of the alkyl alcohol formed in step (h) into step (b),
(i) disproportionating at least a portion of the alkyl aryl carbonate prepared in step (h) to give the diaryl carbonate and dialkyl carbonate and optionally recycling at least a portion of the diaryl carbonate and/or dialkyl carbonate prepared in step (i) into step (b),
(j) transesterifying at least a portion of the diaryl carbonate prepared in step (i) with a bisphenol to give a oligo-/polycarbonate and a monophenol; optionally recycling at least a portion of the monophenol formed in step (j) into step (h).
2. The process according to claim 1 , wherein the oxidative carbonylation in step (e) uses a catalyst comprising at least one noble metal selected from palladium, rhodium, iridium and platinum in elemental form or as the ionic or nonionic compounds thereof and a cocatalyst comprising at least one compound selected from manganese compounds, cobalt compounds and copper compounds.
3. The process according to claim 2 , wherein the catalyst comprises salts or organometallic compounds of palladium in the II oxidation state, rhodium in the I or III oxidation state, iridium in the I or III oxidation state or platinum in the II oxidation state.
4. The process according to claim 2 , wherein the catalyst comprises palladium in elemental form or as an ionic or nonionic compound.
5. The process according to claim 2 , wherein the cocatalyst comprises at least one compound selected from the group consisting of manganese compounds, cobalt compounds and copper compounds, in a weight ratio of catalyst compound to cocatalyst of 1:1 to 1:100.
6. The process according to claim 5 , wherein the weight ratio of catalyst compound to cocatalyst is from 1:2 to 1:30.
7. The process according to any of claim 1 , wherein the cyclic alkylene carbonates are of the formula (I):
wherein, R 1 and R 2 , independently of one another, represent hydrogen, substituted or unsubstituted C 1 -C 4 -alkyl, substituted or unsubstituted C 2 -C 4 -alkenyl or substituted or unsubstituted C 6 -C 12 -aryl and R 1 and R 2 together with the two five-membered ring carbon atoms may be a saturated carbocyclic ring having 5-8 ring members.
8. The process according to claim 7 , wherein the cyclic alkylene carbonate is at least one compound selected from the group consisting of ethylene carbonate, propylene carbonate and butylene carbonate.
9. The process according to claim 1 , wherein the dialkyl carbonates are of the formula (II):
wherein R 3 and R 4 , independently of one another, represent a linear or branched, optionally substituted C 1 -C 34 -alkyl.
10. The process according to claim 9 , wherein the dialkyl carbonate is selected from the group consisting of dimethyl carbonate, diethyl carbonate, di(n-propyl)carbonate, di(isopropyl)carbonate, di(n-butyl)carbonate, di(sec-butyl)carbonate, di(tert-butyl)carbonate and dihexyl carbonate.
11. The process according to claim 1 , wherein the diaryl carbonates used are those of the formula (VII):
wherein R, R′ and R″, independently of one another, represent H, linear or branched, optionally substituted C 1 -C 34 -alkyl, C 1 -C 34 -alkoxy, C 5 -C 34 -cycloalkyl, C 7 -C 34 -alkylaryl, C 6 -C 34 -aryl or a halogen radical; wherein R, R′ and R″ on both sides of the formula (VII) may be the same or different; and wherein R may also represent —COO—R′″ where R′″ represents H, optionally branched C 1 -C 34 -alkyl, C 1 -C 34 -alkoxy, C 5 -C 34 -cycloalkyl, C 7 -C 34 -alkylaryl or C 6 -C 34 -aryl.
12. The process according to claim 11 , wherein the diaryl carbonate is selected from the group consisting of diphenyl carbonate, 4-tert-butylphenyl phenyl carbonate, di(4-tert-butylphenyl)carbonate, biphenyl-4-yl phenyl carbonate, di(biphenyl-4-yl)carbonate, 4-(1-methyl-1-phenyl ethyl)phenyl phenyl carbonate and di[4-(1-methyl-1-phenylethyl)phenyl]carbonate.
13. A polycarbonate obtained from the processes according to claim 1 .