Process for preparing diaryl carbonates from dialkyl carbonates

A process for preparing a diaryl carbonate from a dialkyl carbonate and an aromatic hydroxyl compound comprising the steps of:

• (a) reacting a dialkyl carbonate with an aromatic hydroxyl compound in the presence of a transesterification catalyst in a first reaction column, wherein said first reaction column comprises a rectifying section in the upper part of said first reaction column column and a reaction zone below said rectifying section, wherein said reaction zone comprises at least two sectors;
• (h) feeding bottom product produced in said first reaction column in step (a) to a further reaction column, wherein said further reaction column comprises a rectifying section in the upper part of said further reaction column and a reaction zone below said rectifying section, and further reacting said bottom product in said reaction zone;
• (c) separating at least a portion of unconverted dialkyl carbonate formed during the reaction in the reaction columns of steps (a) and/or (b) from alkyl alcohol formed during the reaction in at least one distillation column;
• (d) feeding at least a portion of vapor comprising said aromatic hydroxyl compound withdrawn from the top of said further reaction column in step (b), optionally after condensing said vapor in a condenser, to a distillation column to remove one or more compounds having a boiling point between that of said dialkyl carbonate and that of alkyl aryl carbonate formed during the preparation of said diaryl carbonate;
• and
• (e) feeding bottom product produced in said further reaction column in step (b), wherein said bottom product comprises diaryl carbonate, to a distillation column for purification, wherein said distillation column comprises a rectifying section in the upper part of said distillation column and a stripping section in the lower part of said distillation column;
• wherein at least one of said first reaction column and said further reaction column is equipped with a condenser and the heat of condensation obtained by condensation in said condenser is directly or indirectly recycled back into said process;
• wherein the evaporation temperature in the bottom of the at least one distillation column used in step (c) is below the condensation temperature in the condenser, and wherein the at least one distillation column used in step (c) can be operated fully or partly with the heat of condensation in the condenser;
• wherein the diaryl carbonate-is a diaryl carbonate of formula (I)
• wherein R, R′ and R″ represent, independent of one another, H, linear or branched, optionally substituted C1-C34-alkyl, C1-C34-alkoxy, C5-C34-cycloalkyl, C7-C34-alkylaryl, C6-C34-aryl or a halogen radical, R may also represent —COO—R′″ where R′″ represents H, branched or unbranched C1-C34-alkyl, C1-C34-alkoxy, C5-C34-cycloalkyl, C7-C34-alkylaryl or C6-C34-aryl;
• wherein the dialkyl carbonate is a dialkyl carbonate of formula (II)
• wherein R1 and R2 represent, independently of one another, a linear or branched, optionally substituted C1-C34-alkyl;
• wherein the aromatic hydroxyl compound is an aromatic hydroxyl compound of formula (III)
• wherein R, R′ and R″ represent, independent of one another, H, linear or branched, optionally substituted C1-C34-alkyl, C1-C34-alkoxy, C5-C34-cycloalkyl, C7-C34-alkylaryl, C6-C34-aryl or a halogen radical, R may also represent —COO—R′″ where R′″ represents H, branched or unbranched C1-C34-alkyl, C1-C34-alkoxy, C5-C34-cycloalkyl, C7-C34-alkylaryl or C6-C34-aryl.