Industrial process for production of high-quality aromatic polycarbonate

An industrial process for the production of a high-quality aromatic polycarbonate in which an aromatic polycarbonate is continuously produced from a dialkyl carbonate and an aromatic dihydroxy compound, the process comprising the steps of:

• (I) continuously producing a diaryl carbonate by taking the dialkyl carbonate and the aromatic monohydroxy compound as a starting material, continuously feeding the starting material into a first continuous multi-stage distillation column in which a catalyst is present, carrying out reaction and distillation simultaneously in said first column, continuously withdrawing a first column low boiling point reaction mixture containing a produced alcohol from an upper portion of said first column in a gaseous form, continuously withdrawing a first column high boiling point reaction mixture containing a produced alkyl aryl carbonate from a lower portion of said first column in a liquid form, continuously feeding said first column high boiling point reaction mixture into a second continuous multi-stage distillation column in which a catalyst is present, carrying out reaction and distillation simultaneously in said second column, continuously withdrawing a second column low boiling point reaction mixture containing a produced dialkyl carbonate from an upper portion of said second column in a gaseous form, continuously withdrawing a second column high boiling point reaction mixture containing a produced diaryl carbonate from a lower portion of said second column in a liquid form, and continuously feeding the second column low boiling point reaction mixture containing the dialkyl carbonate into the first continuous multi-stage distillation column;
• (II) purifying said diaryl carbonate so as to obtain a high-purity diaryl carbonate;
• (III) reacting said aromatic dihydroxy compound and said high-purity diaryl carbonate together so as to produce an aromatic polycarbonate molten prepolymer, and producing an aromatic polycarbonate using a guide-contacting downflow type polymerization apparatus in which said molten prepolymer is made to flow down along surfaces of guides, and said molten prepolymer is polymerized while flowing down;
• and
• (IV) circulating the aromatic monohydroxy compound by-produced in step (III) back into the diaryl carbonate production step (I) so as to recycle the aromatic monohydroxy compound;
• wherein:
• (a) said first continuous multi-stage distillation column comprises a structure having a cylindrical trunk portion having a length L1 (cm) and an inside diameter D, (cm), and having an internal with number of stages n1 thereinside, and has a gas outlet having an inside diameter d11 (cm) at a top of the column or in an upper portion of the column near to the top, a liquid outlet having an inside diameter d12 (cm) at a bottom of the column or in a lower portion of the column near to the bottom, at least one first inlet provided in the upper portion and/or a middle portion of the column below said gas outlet, and at least one second inlet provided in the middle portion and/or the lower portion of the column above said liquid outlet, wherein L1, D1, L1/D1, n1, D1/d11, and D1/d12 respectively satisfy the following formulae (1) to (6):
• 1500≦L1≦8000 (1),
• 100≦D1≦2000 (2),
• 2≦L1/D1≦40 (3),
• 20≦n1≦120 (4),
• 5≦D1/d11≦30 (5),
• 3≦D1/d12≦20 (6);
• and
• (b) said second continuous multi-stage distillation column comprises a structure having a cylindrical trunk portion having a length L2 (cm) and an inside diameter D2 (cm), and having an internal with number of stages n2 thereinside, and has a gas outlet having an inside diameter d21 (cm) at a top of the column or in an upper portion of the column near to the top, a liquid outlet having an inside diameter d22 (cm) at a bottom of the column or in an lower portion of the column near to the bottom, at least one third inlet provided in the upper portion and/or a middle portion of the column below said gas outlet, and at least one fourth inlet provided in the middle portion and/or the lower portion of the column above the liquid outlet, wherein L2, D2, L2/D2, n2, D2/d21, and D2/d22 respectively satisfy the following formulae (7) to (12):
• 1500≦L2≦8000 (7),
• 100≦D2≦2000 (8),
• 2≦L2/D2≦40 (9),
• 10≦n2≦80 (10),
• 2≦D2/d21≦15 (11),
• 5≦D2/d22≦30 (12);
• and
• (c) said guide-contacting downflow type polymerization apparatus comprises:
• (1) an apparatus having a molten prepolymer receiving port, a perforated plate, a polymerization reaction zone having a plurality of guides that extend downward from said perforated plate provided in a space surrounded by said perforated plate, a side casing and a tapered bottom casing, a molten prepolymer feeding zone for feeding a molten prepolymer via said perforated plate onto the guides in the polymerization reaction zone, a vacuum vent provided in said polymerization reaction zone, an aromatic polycarbonate discharge port provided in a lowermost portion of the tapered bottom casing, and an aromatic polycarbonate discharge pump connected to said discharge port, wherein:
• (2) an internal sectional area A (m2) taken through a horizontal plane of the side casing in said polymerization reaction zone satisfies the following formula (13),
• 0.7≦A≦300 (13),
• (3) a ratio between said A (m2) and an internal sectional area B (m2) taken through a horizontal plane of the aromatic polycarbonate discharge port satisfies the following formula (14),
• 20≦A/B≦1000 (14),
• (4) the tapered bottom casing in said polymerization reaction zone is connected at an internal angle C (°) to the side casing thereabove, wherein said angle C (°) satisfies the following formula (15),
• 120≦C≦165 (15),
• (5) a length h (cm) of said guides satisfies the following formula (16),
• 150≦h≦5000 (16), and
• (6) a total external surface area S (m2) of said guides satisfies the following formula (17),
• 2≦S≦50000 (17).