In existing facilities, the desired end point of the resin product may be exceeded because of the time lag between taking the sample and receiving the analytical results.
The conventional method for monitoring the product viscosity and the acid/hydroxy number during the manufacture of synthetic resins is to draw samples from the reactor at regular intervals during the production process. These samples are then analyzed in the laboratory. After reaching the desired analytical end point, the reaction is stopped and the product is sent to the next processing step. Usually the test results from the laboratory are available approximately 15 – 30 minutes after sampling. Because the reaction proceeds while the sample is being analyzed, the specified end point values may be exceeded before the analyses are completed. This is especially true for the product viscosity, as the resin viscosity changes dramatically near the end of the reaction.
The patented continuous viscosity and acid/hydroxy number measurement system offered by AMCEC Inc. has several advantages over the conventional monitoring methods described above including:
- 1) The precise determination of the end point of the production process allowing the manufacturer to:
- – avoid the manufacture of off-spec material
- – optimize batch production times resulting in better overall plant productivity
- – reduce utility consumption rates
- 2) The signals supplied by the measurement system can be processed by a computer or equivalent control system.
- 3) The measurement system generates the documentation for quality control according to ISO 9001
The measurement system was developed primarily as a reliable analytical system for use in the manufacture of synthetic resins such as alkyds and polyesters. The measurement system is designed for product viscosities between 50 and approximately 5 x 103 centipoises at temperatures between 40 and 200°C (104 – 392°F). The products may display true viscous, intrinsic viscous, visco-elastic or thixotropic properties. For the determination of the acid/hydroxy number the product must be transparent.
The measurement system includes a sample circulation pump, tempering device, viscometer, and NIR spectrophotometer with transmission probe, all installed on a prefabricated skid. The measurement system provides signals to the customer’s control scheme (PLC, DCS, or PC). However, AMCEC Inc. can also provide a PC for controlling the measurement system.
From the lower part of the reactor a continuous sample stream is pumped to the viscometer through a jacketed pipe. In order to measure the product viscosity at a preset temperature, the feed stream flows through a tempering device, which is heated or cooled by thermal oil.
The viscosity is measured by a rotary type viscometer. This instrument is largely insensitive to solid particles, incrustations and solidifications, making it especially suitable for use with synthetic resins.
For measuring the acid/hydroxy number, a transmission probe is inserted into the sample stream through a special adapter. The probe is connected to the spectrophotometer by a special optical fiber. From the spectrophotometer, the data is passed to the customer’s control scheme for processing.
After the measurements, the sample is returned to the reactor.
For accurate temperature control a secondary heating circuit connected to the customer’s primary heating circuit, is provided. The thermal oil in the secondary circuit is pumped through the pipe jackets and the tempering device. The measuring temperature control software is included in a PLC, which is installed in a switch cabinet on the skid.
If required by the customer, AMCEC Inc. can supply a PC with communication interface for control of the measurement system. On the monitor of the PC the data for viscosity, acid/hydroxy number, and measuring temperature are displayed digitally in a simplified flow diagram of the measurement system.
AMCEC Inc. personnel will calibrate the viscosity measurement equipment during an onsite commissioning visit.
AMCEC Inc. personnel will check the acid/hydroxy number equipment for mechanical function and provide calibration instructions during an onsite visit.
The acid/hydroxy measurement calibration requires that the operator correlate the laboratory values with the measurement system values for each resin formulation over several batches. Because of the time involved, AMCEC Inc. recommends using the continuous acid/hydroxy measurement equipment in manufacturing facilities that make standard products from a limited number of different recipes.