Ethylene Concentration Control in Rubber Synthesis

Synthetic rubber is a man-made elastomer produced by petroleum byproducts. It’s often used for applications like automotive sectors -- tyres, doors and windows. Raw monomer extraction involves refining these oil fractions—through processes like naphtha cracking and distillation—to purify the target monomers, as contaminants would disrupt the subsequent polymerization reaction. The resulting purified monomers typically have a purity of 99.5% or higher, laying the foundation for rubber synthesis.

The core production step is polymerization: purified monomers are mixed with initiators and either dispersed in water or dissolved in organic solvents. This process converts small monomer molecules into long polymer chains, yielding crude rubber with a rubber hydrocarbon content of 80–90%. A critical follow-up step is vulcanization, where sulfur or peroxides are added and heated to form cross-links between polymer chains—unvulcanized rubber is too soft and sticky to be useful. The vulcanized rubber initially has a polymer purity of 95–98%, but for high-performance applications, further purification is required.

Difficulty in Concentration Measurement of Ethylene Concentration

In rubber synthesis, particularly for ethylene-propylene-diene monomer (EPDM) or ethylene-propylene rubber (EPR/EPM), precise measurement of ethylene concentration is critical for controlling polymerization kinetics, ensuring consistent polymer properties and minimizing waste.

Overview of the Rubber Synthesis Process

Rubber synthesis for EPDM/EPR typically involves:

Feedstock Delivery: Ethylene and propylene (and diene for EPDM) are fed as gases into a reactor, often dissolved in a solvent or maintained in gas/liquid phases.

Polymerization Reactor: A CSTR or loop reactor where monomers react with catalysts at 30-90°C and 10-30 bar, forming polymer chains.

Solvent/Monomer Recovery: Unreacted monomers are stripped, recycled, or purged, often via devolatilization or flash drums.

Finishing: Polymer is separated, washed, and extruded, with quality checks for density and Mooney viscosity.

Ethylene serves as a critical monomer in rubber synthesis, a key raw material in the petrochemical industry. The concentration of this monomer within the reaction vessel directly dictates the kinetics of polymerization and, consequently, the physical and chemical properties of the final polymer, such as molecular weight and melting temperature. When the ethylene concentration is not precisely controlled, the resulting polymer can exhibit an uncontrolled polydispersity, leading to a wider distribution of molecular weights and inconsistent final product quality. For instance, a linear relationship exists between increasing ethylene pressure and the ethylene content in the produced copolymers, which in turn affects their melting temperature.

This variability in product quality has a direct and tangible financial impact. To ensure that every manufactured batch meets minimum quality specifications, operators often practice a method known as "quality giveaway". This involves intentionally producing a product with quality characteristics that exceed the required specifications, in effect over-engineering the process to compensate for measurement and control variability. This practice, while ensuring product acceptance, leads directly to increased raw material consumption, higher energy usage, and extended cycle times, all of which translate into significant operational costs and diminished profit margins. The core of this problem is not a flaw in the chemical process itself, but a deficit in the real-time measurement and control loop that governs it, leading to a reactive rather than proactive mode of operation.

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Continuous Lonnmeter Concentration Measurement Solution

Traditional offline lab-based analysis is ill-suited for the dynamic, continuous demands of a modern production line. They often cause analysis lag and repeated labor-intensive measuring. In other words, data that operators receives is a snapshot of the process from minutes or even hours. Information deficit causes quality deviations after they have already occurred and potentially after an entire batch has been compromised, leading to costly waste and rework.

Lonnmeter has engineered ethylene sensor concentration to realize precise concentration measurement in real time in a continuous chemical process. It works well even in a rapid-changing environment; Online ethylene concentration meter is an industrial-grade instrument designed to address the precise measurement requirements of chemical processes. It utilizes advanced sensing technologies -- an acoustic signal source to excite a metal tuning fork, causing the fork to vibrate at its natural resonant frequency. Notably, this resonant frequency exhibits a direct correlation with the density of the liquid that the tuning fork contacts. Subsequently, the density of the liquid can be determined through frequency analysis—with temperature compensation implemented to counteract temperature drift within the system, ensuring measurement accuracy.

Ethylene Concentration Meter

For continuous concentration measurement in pipelines or tanks

Tuning Fork Structure

Installation Placements in Rubber Synthesis Process

Monomer Feed Line: Place sensor in the ethylene feed pipeline post-compressor to ensure purity and adjust dosing.
Reactor Inlet: Install at the monomer-solvent mixing point with hexane/propylene to control dissolved ethylene.
In-Reactor: Position inside the CSTR near the agitator for real-time polymerization control.
Recycle Line: Locate at the flash drum outlet to optimize unreacted ethylene recovery.
Vent Line: Mount in the purge/vent line to monitor emissions and ensure safety.