Product Spotlight pH Control

Product Spotlight — pH Control

Ethylene, LCC is a leading manufacturer of high performance, seamless fluoropolymer lined components designed to protect and restore equipment used in chemical, petrochemical and pharmaceutical industries. We offer a broad range of both standard and customized corrosion resistant products lined with seamless PTFE, PFA andn Tefzel® fluoropolymers.

Automated pH Control Boosts Reactor Efficiency

Product:	pHampler® In-line sampling systems
Service:	Batch antibiotic production
Benefit:	Elimination of manual sampling saves time, increases accuracy and reduces emissions.
History:	Thanks to an automatic sampler, batch times for antibiotic production at a Midwest pharmaceutical plant have been reduced more than 20%. During the crystallization stage of the reaction, pH is reduced from 12 to 2.5 at a controlled rate by addition of concentrated HC1. The time saving is a result of eliminating opening the reactor manway, dipping out a sample, taking the pH, and then adjusting the acid feed rate to maintain the correct pH reduction schedule. Time is also saved by the controlled and continuous reduction without excursions from the desired path. Completely lined with PTFE, the sampler resists corrosion by any of the chemicals involved in the reaction. Yield and product quality have also improved with more accurate pH measurement and control, and by closer adherence to the planned pH reduction schedule. By the previous method if the pH fell at an erratic rate due to the manual adjustments in acid feed, the yield would suffer. On occasion, it was off by as much as 40%. There have been five successful multi-batch runs of the antibiotic since the sampler was installed early in 1990. Yields and product quality have been excellent for all runs. The supplier designed and built the sampler in consultation with the pharmaceutical manufacturer, whose engineers specified brands and types of all important components and approved the design. The sampler was shipped in three parts and was assembled and installed in one day with minimal disruption of the reactor operating schedule. The sampling system uses a two-wire pH transmitter in conjunction with a combination measurement/reference electrode. The transmitter provides digital pH read- out and sends an electronic signal to an Electro-pneumatic transducer, which converts it to a 3-15 psi air signal, which regulates the position of a stainless steel automatic acid valve. The transducer is engineered for harsh environments with vibration resistance, easy maintenance, and minimum spare parts requirement. The stainless steel acid valve has an encapsulated PFA core and a tantalum valve plug. With 1000:1 rangeability, the valve is especially suitable for pH control. The acid is delivered through the valve from a nitrogen pressurized storage tank. In the second antibiotic run with the pH controller, operators experienced pH drift. It was determined that the problem was due to pH electrode deterioration during non-antibiotic runs. To avoid this, the practice of removing the electrode between antibiotic runs was established. The electrode is stored in a manufacturer specified liquid when not in use. No further electrode problems have been experienced. An air-operated double-diaphragm pump withdraws liquid from the reactor at a rate of approximately 10 gpm and circulates it through the sampler and back into the reactor. The pump is made of Hastelloy C alloy with PFA diaphragms, balls and seats. Max operating temperature for the pump is 220'F; max suction inlet pressure is 10 psig. With the previous method, when the manway was opened to take a sample, an exhaust sweep would remove any vapors released. The vapors consisted of a mixture of HC1 and ethanol. The fumes were sent through a scrubber before discharge to the atmosphere. With the automatic system, the manway is never opened during the run, so no vapors escape. The justification for installation of the J automatic system was pH control, but another benefit has been ease of sampling for crystal structure during the run. Samples are tapped off the automatic sampler, tested, and returned to the reaction without opening the reactor. With the previous method both the pH and crystal structure samples had to be disposed of by an environmentally approved procedure, because by the time the tests had been run, the reactor was already closed. The pHampler sampling pH measurement system was designed and assembled to the pharmaceutical manufacturer's process, dimension and individual component specifications by Sermatech-Ethylene, Murray Hill, NJ. Reprinted from October 1991 CHEMICAL PROCESSING pH is measured continuously during reaction, but sampler also allows batch sampling for other analyses without manway opening.