GB1441679A - Continuous process for the production of ethylene terephthalate polyesters - Google Patents

Abstract

1441679 Automatic control of viscosity KANEBO Ltd 14 Feb 1974 [22 Feb 1973] 6855/74 Heading G3R In a continuous process for producing polyesters, a polymer-forming melt is passed through a series of polymerization vessels. The melt viscosity at the inlet and outlet of each vessel, except for a first vessel, is measured, and a control signal for adjusting the conditions in a vessel is formed in dependence upon differences between the viscosities at the inlet and outlet of the vessel and command values for the viscosity. If the calculated setting for the adjustment lies outside a predetermined range, the command value for the viscosity of melt material leaving the preceding vessel is automatically varied accordingly. As shown, a melt of bis-2-hydroxyethyl terephthalate is pumped through low-pressure polymerization vessels 1, 2, 3 to form ethylene terephthalate polyesters for spinning into filaments 24, 25. The polymerization rate is determined by the pressure (near vacuum) in the vessels 1, 2, 3 which is controlled by regulators 14, 15, 16 setting valves 11, 12, 13 in ethylene glycol extraction circuits. The regulators 14, 15, 16 are controlled by a computer 26 periodically receiving inputs from viscosity measuring devices 21, 22, 23 connected to the outputs of the vessels 1, 2, 3. In the case of vessel 3, the signal from viscosity meter 23 is compared with a predetermined value and the difference is used to form a control signal in a PID circuit. This signal is added to a further signal representing a viscosity error at the meter 22 at an earlier time determined by the computer 26 from flow data. The resulting signal is used as a set value for the pressure regulator, but is also compared with a predetermined range of values, and if the signal falls outside this range, the computer 26 calculates a further signal to modify the desired value setting for the viscosity of the melt material leaving the vessel 2. In the case of vessel 1, the input viscosity is not measured, and if the calculated set point for the pressure regulator 14 lies outside a given range, an audible or visual alarm is actuated. The computer 26 may be of analog, digital or hybrid type.