Optimizing pH Measurement in Styrene-Butadiene Crumb Slurry

How integrating advanced pH sensors with temperature compensation, chemical resistance, and a dynamic mounting system can prevent fouling and damage.
 

Introduction

Styrene-butadiene copolymers are produced via two main polymerization processes: emulsion and solution. This discussion focuses on the emulsion process, which creates products that can be marketed either as a granular solid (crumb) or in liquid form (latex). During production, fresh styrene and butadiene are fed into a continuous polymerization system where the reaction typically ceases at around 60% monomer conversion to maintain optimal product quality. Following polymerization, unreacted monomers are recovered through vacuum flashing and steam stripping, while the latex is later coagulated with a dilute acid and sodium chloride solution to release the copolymer as crumb slurry.

Fig. 1. Workflow at Styrene-Butadiene & Rubber (SB&R) Plant
 

 

Challenges

A significant challenge in this process is maintaining accurate pH control and ensuring reliable sensor performance in the harsh environment of crumb slurry processing.

Specific issues include:

• Fouling and Build-up: The rubbery nature of the crumb slurry tends to adhere to sensor holders, especially those with rigid mounting. This fouling can lead to inaccurate readings and increased maintenance downtime.
• Harsh Chemical Environment: The coagulation process involves acidic conditions (H₂SO₄ pH 4 to 4.5) and chemical exposure that can damage conventional sensors and their housings.
• Mechanical Strain: Static mounting methods may not accommodate the slurry’s dynamic flow, leading to physical damage or interference with sensor operation.

Fig. 2. pH Measurement for Crumb Slurry of SB&R Plant

Solution

To address these challenges, a two-pronged approach has been implemented involving an advanced sensor and a specially designed sensor holder:

1. SC25V Series Sensor:

• Integrated with a Pt1000 element within the pH compartment, ensuring highly accurate temperature compensation.
• Equipped with an external titanium Liquid Earth probe, this sensor is designed for precise and reliable pH measurements.
• Constructed with a large internal KCl volume to extend sensor lifespan and support CIP (Clean-In-Place) and steam cleaning procedures.
• The SC25V-ALP25 variant is available for applications that require resistance to harsh chemicals and high temperatures.

2. FD20 Immersion Sensor Holder with P37 Mounting:

• Features a hoisting cable made of SS316 stainless steel that allows the holder to hang freely in the vessel, enabling it to swing with the flow.
• This dynamic mounting minimizes the risk of damage from the abrasive and sticky crumb slurry.
• The design encourages easy removal for manual cleaning, preventing polymer build-up around the sensor.

Key Advantages

• Enhanced Accuracy: The integration of a Pt1000 element provides precise temperature compensation, ensuring consistent and reliable pH measurements.
• Durability in Harsh Environments: Both the sensor and its holder are engineered to withstand acidic conditions and chemically aggressive environments, reducing maintenance frequency.
• Improved Maintenance and Longevity: The design facilitates CIP and steam cleaning, while the large internal KCl volume extends the sensor’s operational life.
• Dynamic Adaptability: The swing-mounted sensor holder adapts to process flow, significantly reducing sensor fouling and mechanical damage.
• Cost Efficiency: By ensuring accurate measurements and minimizing downtime for cleaning and sensor replacement, the solution contributes to more economical operation of the polymerization process.