Fractional Distillation Columns and Siemens CVD Reactor Dynamics

01Fluidized Bed Hydrochlorination Tool Architecture

The initial chemical conversion of crude solid Metallurgical-Grade Silicon ($\text{MG-Si}$) into volatile trichlorosilane (${\text{HSiCl}}_3$, TCS) occurs in a high-pressure Fluidized Bed Reactor (FBR).

Fluidization Kinematics

1. Gas Distribution Grid: Anhydrous $\text{HCl}$ gas is pumped upward through a perforated bottom grid plate at velocities exceeding the minimum fluidization velocity ($v_{\text{mf}}$).
2. Bed Behavior: Solid $\text{MG-Si}$ particles ($100-300\mu \text{m}$) become suspended in the upward gas stream, behaving like a bubbling liquid. This maximizes gas-solid contact area and maintains uniform thermal distribution ($300^{\circ }\text{C}-350^{\circ }\text{C}$ at $20-30\text{ bar}$).
3. Exothermic Heat Extraction: The hydrochlorination reaction ($\text{Si}+3\text{HCl}\to {\text{HSiCl}}_3+{\text{H}}_2$) is strongly exothermic ($\Delta H=-218\text{ kJ/mol}$). Internal cooling coils circulate heat-transfer fluids to prevent thermal runaway above $400^{\circ }\text{C}$, which favors unwanted silicon tetrachloride (${\text{SiCl}}_4$, STC) formation.

02Multi-Stage Distillation Train Hardware

To achieve the parts-per-trillion purity needed for 11N EGS, crude TCS liquid passes through a distillation train consisting of high-efficiency tray or packed columns operating under closed-loop nitrogen pressure:

Column Component Engineering

• High-Theoretical-Plate Columns: Distillation towers utilize structured stainless steel packing (providing 50-100 theoretical plates per column) to separate chlorosilane species with close boiling points (${\text{HSiCl}}_3$ at $31.8^{\circ }\text{C}$ vs ${\text{SiCl}}_4$ at $57.6^{\circ }\text{C}$).
• Complexation Additives: To remove boron impurities (${\text{BCl}}_3$, boiling point $12.6^{\circ }\text{C}$) whose volatility overlaps with TCS, Lewis base complexing agents (such as benzaldehyde or triphenylchloromethane) are injected. These agents bind selectively to ${\text{BCl}}_3$, forming non-volatile adducts that drop to the column reboiler.

03Siemens CVD Bell Jar Reactor Mechanics

The heart of EGS production is the Siemens Bell Jar CVD Reactor, a high-current, water-cooled pressure vessel.

Key Mechanical Subsystems

1. Double-Walled Silver/Steel Bell Jar: A water-cooled outer dome keeps wall temperatures below $150^{\circ }\text{C}$, preventing gas-phase nucleation and undesirable silicon deposition on wall surfaces.
2. Filament Power Control: Thin silicon seed filaments ($7-8\text{ mm}$ diameter, $1.5-2\text{ meters}$ high) are arranged in inverted U-configurations. Direct AC Joule heating drives filament temperatures to $1050^{\circ }\text{C}-1100^{\circ }\text{C}$.
3. Power Scaling Electronics: As rod diameters expand from $8\text{ mm}$ to $200\text{ mm}$, electrical resistance drops dramatically. High-power transformer arrays automatically adjust voltage (downward) and current (upward, reaching several thousand amperes per bridge) to maintain a constant $1100^{\circ }\text{C}$ surface temperature.

04Equipment Parameter Comparison Matrix

→Prerequisites & continue reading

Prerequisites: Understanding of TCS synthesis and Siemens process fundamentals

Also in Topic 1.2, Chemical Purification & the Siemens Process:

Tier 1 · Achieving 11N Purity: Trichlorosilane and the Siemen…Tier 3 · CVD Deposition Kinetics and Mass-Transfer Dynamics i…