Calcium carbide for acetylene production

Calcium Carbide is best known as a source of acetylene gas for metal fabrication and construction and is a precursor to many specialty chemicals; it is the premier desulfurizing reagent for iron and steel, and is crucial in cleaning pollutants from our environment.

Calcium Carbide Description

Physical and Chemical Properties:

• Appearance: This material is a solid, with color variations ranging from grey to brown or black. Notably, higher-purity samples exhibit a purple coloration.
• Specific Gravity: The specific gravity of the substance is 2.22 at 18°C.
• Melting Point: The material possesses a high melting point of 2300°C.
• Hygroscopic: It can absorb water vapour from the surrounding atmosphere.
• Electrical Conductivity: The material exhibits electrical conductivity, with conductivity increasing proportionally to its level of purity.
• Chemical Reactivity: It reacts with water (H2O) to undergo a hydrolysis reaction, producing acetylene (C2H2) and calcium hydroxide (Ca(OH)2) while releasing heat (exothermic reaction).

Acetylene (C₂H₂):

• Classification: Acetylene is a colourless gas with a characteristic odour that is classified as combustible.
• Applications: This versatile gas is a crucial raw material in producing various organic chemicals. Additionally, it finds application as a fuel component in metal cutting and oxy-acetylene welding processes. Notably, its use has expanded to include producing several types of plastics.
• Production Methods: Acetylene can be generated through a variety of methods. The following section will explore two commonly employed techniques (details about the production methods will follow here).

Introduction to Acetylene Generation Process Using Calcium Carbide

Calcium Carbide Feedstock and Reaction:

• Generators: These reaction vessels come in various capacities, ranging from 8 cubic meters (m³) to 200 m³ per hour of acetylene production.
• Controlled Introduction: Calcium carbide is fed into the generator’s top portion, interacting with the contained water. This controlled introduction allows for precise management of the reaction rate and subsequent gas generation.
• Chemical Reaction: The reaction between calcium carbide and water adheres to the following chemical formula: CaC2 + 2H2O → C2H2 + Ca(OH)2. This exothermic reaction produces the desired product, acetylene gas (C2H2), along with calcium hydroxide (Ca(OH)2), also known as slaked lime, as a byproduct.

Process Safety Measures:

• Sensor and Valve Systems: The processing unit is outfitted with pressure and temperature sensors to monitor the reaction and prevent continuously exceeding safe pressure limits. Additionally, non-return valves are incorporated to hinder the backflow of gas, enhancing overall safety.

Acetylene Gas Treatment:

• Cooling: A condenser effectively cools the hot acetylene gas produced during the reaction, making it easier to handle in subsequent stages.
• Ammonia Scrubbing: The ammonia scrubber selectively removes ammonia (NH3) from the acetylene stream before purification. Because ammonia is corrosive, removal is necessary for a high-quality final product.
• Moisture Removal: The medium-pressure drier employs anhydrous calcium chloride (CaCl2) to eliminate moisture from the acetylene gas stream. Excess humidity can negatively impact the quality and stability of the produced acetylene.
• Purification: The purifier contains a designated material that selectively removes impurities like phosphine (PH3) and hydrogen sulfide (H2S) formed during the reaction. These impurities pose safety hazards and can hinder the intended use of the acetylene.
• Purifier Scrubber: This component safeguards the compressor by preventing any purifying material from entering its system, protecting it from potential damage or clogging.

Compression:

• Flammable Gas: Acetylene is classified as a highly flammable gas.
• Water-Cooled Compressor: A specialized compressor designed for acetylene is employed. This compressor is surrounded by a water jacket, which cools the gas following each compression stage. This cooling step is crucial because compressing the gas elevates its temperature, and excessive heat poses a safety risk.

Considerations:

• The calcium carbide process offers a relatively simple and cost-effective method for small-scale acetylene production.
• However, a significant drawback of this method is the generation of calcium hydroxide as a waste product, necessitating proper disposal procedures.
• Due to safety concerns and environmental considerations associated with calcium carbide waste, modern industrial facilities often favour alternative methods for producing large amounts of acetylene.

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