Silica (silicon dioxide), an important inorganic chemical product, is primarily produced by two methods: the fumed and precipitation methods. These two methods differ significantly in their principles, processes, product characteristics, and economics. The following provides a detailed comparative analysis from multiple perspectives.

I. Comparison of Production Process Principles
1. Vapor Phase Production Process Principle
The vapor phase method, also known as chemical vapor deposition (CAV), produces silica through a high-temperature vapor phase reaction:

Raw materials: Silicon tetrachloride (SiCl₄), hydrogen (H₂), and oxygen (O₂)
Reaction equation: SiCl₄ + 2H₂ + O₂ → SiO₂ + 4HCl
Reaction conditions: Vapor phase hydrolysis at a high temperature of approximately 1800°C
Reaction process: Silicon tetrachloride vaporizes at high temperatures and then reacts with a mixture of hydrogen and oxygen to produce extremely fine silica particles.

2. Precipitation Production Process Principle
The precipitation method precipitates silica through a liquid phase reaction:
Raw materials: Sodium silicate (water glass) and sulfuric acid/hydrochloric acid
Reaction equation: Na₂SiO₃ + 2H⁺ → SiO₂·nH₂O + 2Na⁺ + H₂O
Reaction Conditions: Moderate temperature, room temperature to 100°C
Reaction Process: Sodium silicate solution reacts with acid to form silica precipitate

II. Production Process Comparison
1. Vapor-Phase Process
Raw Material Processing: Silicon tetrachloride distillation and purification, hydrogen/oxygen drying and filtration
High-Temperature Hydrolysis: Vapor-phase hydrolysis at 1800°C
Particle Aggregation: Fine particles aggregate into larger particles in an aggregator
Separation and Collection: Product collection via cyclone separator
Deacidification: Purging with nitrogen-containing air to a pH of 4-6
Product Packaging: High-purity fumed silica is obtained

2. Precipitation Process
Sodium Silicate Preparation: Quartz sand and soda ash are melted at high temperature to produce water glass
Dilution Preparation: Prepare water glass into a solution of a certain concentration
Acid Precipitation Reaction: Add sulfuric acid or hydrochloric acid to precipitate silica
Aging and Filtration: The reaction solution is aged and then filtered and separated
Washing and Drying: Wash to remove impurities, then dry and pulverize
Packaging: The precipitated silica product is obtained

III. Product Property Comparison
Characteristics: Fumed Silica, Precipitated Silica
Chemical Composition: Anhydrous Silica (SiO₂), Hydrated Silica (SiO₂·nH₂O)
Purity: ≥99.8% 87-95%
Average Particle Size: 8-19nm 11-100nm
Specific Surface Area: Large (100-400m²/g), Small (50-200m²/g)
Density: 200g/cm³ 1.93-2.05 g/cm³
pH 3.9-4.0 5.7-9.5
Reinforcement Properties Excellent Fair
Transparency Good Poor
Processing Properties Poor (slow powder absorption, poor flowability) Good

IV. Performance and Application Differences
1. Fumed Silica Characteristics
Advantages:
Excellent reinforcement properties, high tensile and tear strength
Good abrasion resistance, fast hardening rate
Good transparency, suitable for high-end applications
Disadvantages:
Expensive (3-5 times more expensive than precipitation silica)
Poor processing properties, prone to flyaways
Excessive heat generation, requiring special handling

Main Applications:
High-end rubber products (such as high-performance tires)
Electronic packaging materials
High-end coatings and cosmetics
Pharmaceutical and food additives

2. Characteristics of Precipitated Silica
Advantages:
Low price, high cost-effectiveness
Good processing properties, easy dispersion
Slightly better compression set
Low heat generation
Disadvantages:
Poor reinforcement
Poor transparency
Contains water of crystallization, which affects some applications
Main Applications:
Common rubber products (shoes, ordinary tires)
Plastic filler
Papermaking industry
Agricultural chemicals

V. Economic and Environmental Comparison
Comparison Items: Vapor Phase Method
Precipitation Method
Equipment Investment: High (requires high-temperature equipment)
Relatively low
Technical Requirements: Complex
Relatively simple
Production Cost: High (expensive raw materials, high energy consumption)
Low
Production Scale: Small
Large
Byproduct Disposal: HCl can be recycled
Generates large amounts of wastewater
Environmental Performance: Good (byproduct can be recycled)
Poor (wastewater treatment is difficult)
Product Price: Expensive (30,000-50,000 RMB/ton) Low Cost (5,000-10,000 RMB/ton)

VI. Summary and Selection Recommendations
Technology Selection:

Gas phase method is suitable for applications with high performance requirements and a high cost tolerance.
Precipitation method is suitable for cost-sensitive applications with lower performance requirements.
Development Trends:

Gas phase method is moving towards higher purity and smaller particle size.
Precipitation method is improving performance and reducing pollution through modification technology.
Selection Recommendations:

Consider the product's end use and performance requirements.
Evaluate production costs and environmental requirements.
Balance performance and cost.
Both processes have their advantages and disadvantages. Companies should choose the appropriate technology based on their product positioning and market strategy. With increasing environmental requirements, precipitation method needs to strengthen pollution control, while gas phase method needs to reduce costs to expand its application.