Process for the production of polycarbonate of constant viscosity

• US 5,412,060 A
• Filed: 01/31/1994
• Issued: 05/02/1995
• Est. Priority Date: 08/20/1991
• Status: Expired due to Fees

• Current Assignee: Bayer AG
• Original Assignee: Bayer AG
• Inventors: Weymans, Gunther, Bachmann, Rolf, Hucks, Uwe, Kadelka, Jurgen, Wulff, Claus, Herrig, Wolfgang
• Primary Examiner(s): Kight, III, John
• Assistant Examiner(s): BOYKIN, TERRESSA M
• Application Number:
  US08/189,382
• Time in Patent Office: 456 Days
• Field of Search: 528/196, 528/198, 528/199, 528/204, 528/125, 528/126, 528/171, 528/174, 526/59, 526/60
• US Class Current: 528/196
• CPC Class Codes: C08G 64/24 and phenols

Abstract

The invention relates to a process for the production of polycarbonates by the two-phase interfacial method in which deviations between measured and estimated variables are continuously minimized by means of a suitably selected observer or filter system on the basis of a process model with an empirical Mark-Houwink relation adapted to the process. The variables estimated by the observer/filter are converted into control variables which are used to set input streams of the production process. Product quality is kept constant, changes in load or set values are quickly intercepted and even disturbances not readily accessible to measurement are taken into account by the process control.

Claims

1. A process for the production of polycarbonates by the two-phase interfacial method in at least two reaction steps, in which a phosgene-containing organic phase and a bisphenol-containing water phase with or without alkali hydroxide or chain terminator are mixed in a first step to form a first input stream and in a second step polycarbonate producing catalyst with or without chain terminator is added as a second input stream, said first input stream and said second input stream being controlled by the value of the relative viscosity Of the polycarbonate, wherein the relative viscosity of the resulting polycarbonate is measured at the end of the reaction, a viscosity number (VZ*) defined as V-number=100×

(relative viscosity -1) is calculated from the measured concentration and quantity of phosgene, bisphenol, catalyst and alkali hydroxide and applying an empirical relation conforming to

space="preserve" listing-type="equation">V-number=a+b.n+c.n.sup.2

in which n denotes the average number of bisphenol units in the polymer chain which is calculated from the measured concentrations and quantities in which a, b, c . . . are empirical constants and the variation in time of the V number is calculated from the measured variations in time of the input streams and concentrations;

a V number VZ** is then formed by adding a correction term Δ

VZ to VZ* resulting in a minimization of the deviation between VZ** and the measured V number;

the correction term Δ

VZ.sup.(new) =Δ

VZ.sup.(old) +f (VZ measured-VZ**) is recalculated every time a new measured V number is available, and the calculated VZ** together with the concentrations of the input streams are converted into control variables which set the input streams of the running reaction and with or without converting correspondingly the concentration of the alkali hydroxide or of the alkali carbonate or of both at the end of the reaction into controlled variables to set the input streams of the running reaction.

2. A process as claimed in claim 1, wherein the deviation between the calculated V-number VZ** and the measured V-number VZ is minimized comprising the following steps each time a new measured V number is available:

VZ**=VZ*+Δ

VZ with

Δ

VZ.sup.(new) =Δ

VZ.sup.(old) +RVZ(VZ_measured -VZ**), wherein Δ

VZ.sup.(new) denotes the corrected calculated deviation of the V-number, Δ

VZ.sup.(old) the last corrected deviation of the calculated V-number, RVZ an empirical constant, VZ* the firstly calculated V-number and VZ the measured V-number.

3. A process as claimed in claim 1, characterized in that the concentration of the alkali hydroxide or of the alkali carbonate or of both at the end of the reaction additionally control the input streams of the running reaction.

4. A process as claimed in claim 1, characterized in that a controller selected from the group of proportional, proportional-plus-integral, proportional-plus-integral-plus-derivative state controller or cascade controllers, self-adjusting controllers, frequency-dependent controllers, nonlinear controllers, model predictive controllers, multivariable or decoupling controllers converts the variables calculated into control variables.

5. A process as claimed in claim 2, wherein the constant RVZ denotes 0.25.

6. Process according to claim 1, characterized in that the two-phase interfacial process comprises the following process steps:

a) mixing the organic and aqueous reaction phases in a tank reactor with a circulation loop,

b) forming an emulsion in the tank reactor with the circulation loop, adjusting a temperature of less than 60°

C. in the circulation loop with the aid of a heat exchanger, maintaining the tank reactor with the circulation loop an average dwell time of at least 2 minutes and the emulsion being continuously removed from the tank reactor,

c) introducing this emulsion into a tube reactor which is equipped with mixing and dwell zones and for a total dwell time of at least 2 minutes,

wherein the organic phase is a solvent for the polycarbonate and contains phosgene, and the aqueous phase consists of water and a mixture of an alkali metal hydroxide and phenolic components.

7. Process according to claim 1, characterized in that the two-phase interfacial process comprises the following sequential process steps:

a) preheating a 10 to 30% by weight alkali bisphenolate solution to at least 45°

C., the percentages by weight being based on the weight of alkali bisphenolate in the aqueous solution, and the solution having a minimum content of free alkali hydroxide,

b) introducing gaseous phosgene in methylene chloride or chlorobenzene or a mixture of methylene chloride/chlorobenzene in such quantities that, based on the quantity of alkali bisphenolate employed in step a), a molar excess of phosgene of from 5 to 80 mol % is present,

c) mixing the solutions of steps a) and b) in a mixer which delivers the mixed emulsion into a tube at least partially in a counter-gravitational direction,

d) with or without introducing an additional amount of alkali bisphenolate into this tube after a dwell time of at least 10 seconds without dissipation of the heat of reaction,

e) subsequently adding chain terminators and alkali hydroxide solution to establish a pH value of 11 to 14,

f) subsequently dissipating the heat of reaction in a stirred vessel and building up the polymer chain by adding alkali hydroxide solution and a catalyst, an oil-in-water emulsion being present in the stirred vessel.

8. Process according to claim 6, characterized in that the V number is measured directly at the end of the reaction.

9. A process as claimed in claim 1, wherein calculated input streams of phosgene, chain terminator, solvents, catalyst or alkali hydroxide are the control variables.