A H Marks Monitors Phenol-Refining Process

A H Marks and Company Limited, located at Wyke in West Yorkshire, is the UK's largest privately-owned, independent chemical manufacturing company. It produces a wide range of specialty chemicals for customers in the agricultural, petrochemical, and personal care markets. The Wyke plant employs more than 350 people and has been in operation since 1877 when the company began production of dyes for the textile industry. Today, the company produces chemicals in large batches (up to thousands of tonnes), involving one to three stage syntheses. Products include styrenic and non-stryenicinhibitors, biocides, chlorophenols, and various intermediates.

Key aspects of the refining process are acidification and washing to purify the phenols. Pure phenolic products have high melting points; therefore, the refining processes are carried out at temperatures of about 100° C (212° F), and all the transfer pipework is steam-jacketed with temperatures reaching up to 140° C (284° F). In the process tanks, agitators mix the material with the acid or water before allowing the mixture to settle. In the settling process, the phenolic material and the waste (acid, water, and other impurities) split into two very separate layers due to their different specific gravity. At this point, the phenolic product is allowed to drain from the reactor. Monitoring the draw-off of phenols used to be done manually by observing through a sight glass. The company wanted to automate this process to enhance accuracy and free operators from this time-consuming task.

Acids and water are highly conductive materials, while the phenols are non-conductive. This difference is a good way to detect the end product from the waste material. In the settling tanks, the company installed a Siemens SITRANS LC 500 capacitance transmitter to measure the interface of waste and end product. Another LC 500 transmitter is mounted directly in the steam-jacketed line to monitor the draw-off process. Unlike conventional capacitance devices that measure voltage drop or current flow, LC 500 employs a unique frequency based technology that consistently outperforms other devices. Even small level changes create large changes in frequency, resulting in better resolution and accuracy, along with repeatable level detection. The LC 500 is designed for extreme and critical process conditions. For this application, the probe is coated with enamel to handle the hot process and corrosive materials (PFA coating is also available). Patented Active- Shield technology protects the measurement from the effects of moisture, vapor, foam, temperature or pressure variations, and material build-up. Advanced electronics provide one-step, push-button calibration and local display for easy, on-site installation and set-up. The smart 2-wire transmitter has HART® communications for remote commissioning and inspection.

"The SITRANS LC 500 provides a continuous 4-20 mA signal to our central DCS," said Steve Hodges, Control and Instrumentation Engineer with A H Marks. "It gives us constant, reliable monitoring of this harsh process with consistent
results. We have now made this instrument the standard for this application."

Return on Investment

A H Marks can now detect and control the product-to-effluent interface without human intervention. Accurate, reliable measurement helps ensure product quality and enhance plant safety. It frees a technician from the sight-monitoring task, representing a saving in staff time as well.