Why is the purity of the distillation product not increasing? The problem might be with the packing material.
In chemical production, low separation efficiency is one of the most troublesome problems—high tower pressure drop, substandard product purity, soaring energy consumption, frequent shutdowns for maintenance… each problem erodes a company’s profits.
Today, we delve into a proven solution: PTFE Pall ring packing, and how it fundamentally solves the persistent problem of low separation efficiency in chemical processes.
Why is your separation efficiency always unsatisfactory?
Before addressing the problem, let’s diagnose the common causes of low chemical separation efficiency:
1. Packing blockage and uneven gas-liquid distribution: When processing media containing solid particles or easily polymerizable media, ordinary packing materials are prone to scaling and blockage, leading to gas deviation and liquid wall flow, significantly reducing the mass transfer area.
2. Corrosion causing packing failure: In highly corrosive environments such as hydrochloric acid, sulfuric acid, and other acids, metal packing materials corrode rapidly, ceramic packing materials are easily broken, and the packing layer collapses, causing a precipitous drop in separation efficiency.
3. Excessive pressure drop and alarming energy consumption: An unreasonable packing structure leads to high airflow resistance, high fan/compressor load, and persistently high electricity costs, even becoming a bottleneck for production capacity.
4. Frequent replacement and significant downtime losses: Ordinary packing materials have a short lifespan, requiring multiple shutdowns for replacement each year. The losses from production interruptions far exceed the value of the packing material itself.
The common root cause of these problems is the mismatch between the packing material and the operating conditions. PTFE Pall rings were developed precisely to solve these problems.
PTFE Pall rings: Four mechanisms for improving separation efficiency
1. Anti-clogging Design: Non-stick Surface
PTFE material has extremely low surface tension (18.5 dyn/cm), meaning almost nothing can adhere to it. The direct benefits of this “non-stickiness” are:
Polymers, tar, and crystals have difficulty adhering.
Solid particles are self-cleaned by being flushed away by the liquid.
Long-term operation without clogging; the gas-liquid passage remains unobstructed.
A chlor-alkali plant’s hydrochloric acid desorption tower originally used ceramic packing, which required monthly cleaning due to clogging. After replacing it with PTFE Pall rings, it operated continuously for 18 months without clogging, and the desorption efficiency remained stable at over 99%.
2. Corrosion Resistance: Unchanged for 10 Years
PTFE is resistant to almost all chemical media (except molten alkali metals and liquid fluorine), which means:
It remains unaffected in concentrated sulfuric acid, nitric acid, and mixed acids.
It maintains stable performance in high-temperature hydrochloric acid and wet chlorine gas.
No metal ion leaching occurs, making it suitable for the production of electronic-grade chemicals.
In sulfuric acid drying towers, the service life of PTFE Pall rings can reach 8-10 years, which is more than 5 times that of metal packing and more than 3 times that of ceramic packing.
3. Fluid Dynamics Optimization: High Throughput, Low Pressure Drop
The unique open structure of the Pall ring significantly optimizes the gas-liquid two-phase flow path:
Increased Opening Area: The open area of the ring wall accounts for more than 30%, allowing gas and liquid to freely pass through the windows.
Low Pressure Drop: For the same throughput, the pressure drop is 50%-70% lower than that of Raschig rings.
High Throughput: For the same column diameter, the throughput is increased by 50%-100%.
Data Comparison (Taking Φ50 specification as an example)
Parameters Ordinary Raschig Ring PTFE Pall Ring Improvement Amount
Pressure Drop (mmH₂O/m) 50-80 20-35 ↓50%-60%
Mass Transfer Unit Height (m) 0.8-1.2 0.5-0.8 ↑30%-40%
Flooding Gas Velocity (m/s) 1.5-2.0 2.2-3.0 ↑40%-50%
4. High and low temperature resistance: adaptable to various process conditions
From cryogenic separation at -180℃ to high-temperature distillation at 260℃, PTFE Pall rings maintain dimensional stability and consistent performance. They do not soften and deform at high temperatures like plastic packings, nor do they become brittle at low temperatures like metal packings.
Which operating conditions are suitable for using PTFE Pall rings?
Based on numerous application cases, PTFE Pall rings are the preferred choice for the following scenarios:
Operating Condition Characteristics | Recommendation Reason | Typical Application
Strong Acid Environment (pH<2) | Resistant to all acid corrosion | Sulfuric acid drying tower, hydrochloric acid stripping tower, nitric acid concentration tower
High Temperature (>120℃) | Resistant to 260℃ without deformation | High-temperature distillation, pyrolysis gas washing
Easily polymerizable and crystallizable media | Non-stick surface, self-cleaning | Styrene distillation, TDI production, caprolactam recovery
High Purity Requirements | No metal ion leaching | Electronic grade chemicals, pharmaceutical intermediates
Frequent Start-up and Shutdown Conditions | Good thermal shock resistance, no cracking | Intermittent production units