Hexamine (Liquid Phase Process) Plant

Hexamethylenetetramine (HMTA), produced via the mature liquid-phase method, leverages its cage-like molecular structure, high thermal stability (decomposition at 263°C), and pH-responsive decomposition to serve diverse applications. In the chemical industry, its controlled formaldehyde release enables efficient phenolic resin curing and uniform dispersion in rubber vulcanization. Pharmaceutical applications capitalize on high-purity HMTA crystals (ensured by liquid-phase recrystallization) for antibacterial agents and vaccine preservatives, where alkaline-triggered formaldehyde release in acidic environments ensures sterilization efficacy. Defense and energy sectors utilize its thermal stability as a combustion additive in solid propellants and nitrogen-rich component in explosives. Environmentally, HMTA acts as a reversible formaldehyde scavenger and corrosion inhibitor, benefiting from liquid-phase synthesis’s low impurity levels. Additionally, its water solubility and decomposition kinetics support textile flame retardancy and heavy metal chelation in water treatment, highlighting the synergy between HMTA’s physicochemical properties and the cost-effective, scalable liquid-phase process.

Applications of HMTA

Chemical Industry
- Phenolic Resin Curing Agent: High-purity HMTA from liquid-phase method ensures uniform formaldehyde release, enhancing resin cross-linking efficiency.
- Rubber Vulcanization Accelerator: Water-soluble HMTA disperses evenly in rubber matrices, improving vulcanization speed and mechanical properties.
Pharmaceuticals
- Antibacterial Agent (e.g., UTI Drugs): Alkaline HMTA releases formaldehyde in acidic urine for sterilization; liquid-phase process minimizes solvent residues, meeting pharmacopeia standards.
- Vaccine Preservative: High-purity crystals (via liquid-phase method) ensure vaccine stability without impurities.
Defense & Energy
- Solid Fuel Combustion Additive: HMTA’s thermal stability (decomposition at 263°C) enables controlled energy release in propellants, with cost-effective liquid-phase mass production.
- Explosive Component (e.g., RDX blends): High nitrogen content (40%) enhances detonation performance; liquid-phase purity control reduces side reactions.
Environment & Materials
- Formaldehyde Scavenger: Reversible binding with formaldehyde, enhanced by active surfaces from liquid-phase synthesis, used in air purification.
- Metal Corrosion Inhibitor: Weak alkalinity facilitates protective film formation on metal surfaces in liquid-phase applications.
Other Industrial Uses
- Textile Flame Retardant: HMTA decomposition releases inert gases, with liquid-phase ensuring uniform coating.
- Water Treatment Agent: Chelates heavy metal ions via its coordination capacity.

Introduction

Formalin reacts with ammonia in Reactor to yield hexamine solution. Meanwhile heat is released, to continuously remove which and control the reaction temperature lower than 70℃, cooling water is employed, otherwise, oil like polymers will be generated. To shift the equilibrium position towards the formation of hexamine, the pH of reaction solution shall be controlled in the range of 8.5-9 and ammonia shall be excessive by 1.0-1.5%. The obtained hexamine solution is first concentrated by Film Evaporator, and then further dehydrated by Evaporation Pot to produce saturated hexamine crystalline liquor. Finaly the crystals are separated with mother liquor, and then charged for drying to give hexamine product in powder.

Key Features

Industrial Maturity:
- A well-established process using simple equipment (e.g., enamel reactors, crystallization tanks), suitable for large-scale batch or continuous production.
Mild Reaction Conditions:
- Operates at 60–80°C under ambient pressure, avoiding the need for high-temperature or high-pressure equipment, with relatively low energy consumption.
Readily Available Raw Materials:
- Direct use of industrial formaldehyde solution (37–40%) and ammonia water (25–28%), ensuring low production costs.
High Process Controllability:
- Flexible adjustment of reaction progress by regulating pH (8–9), temperature, and ammonia dosage.
Simple Crystallization and Purification:
- Efficient purification (>99% purity) via evaporation, cooling crystallization, and recrystallization.

Core Advantages

Advantage	Description
1. High Product Purity	Mature crystallization achieves >99.5% purity (pharmaceutical-grade) with minimal impurities (e.g., methanol, formic acid).
2. Production Stability	Easy control of parameters (temperature, pH) ensures consistent batch quality.
3. Low Capital Investment	Requires only conventional equipment (e.g., enamel reactors, centrifuges).
4. Scalability	Adaptable to both large-scale (10,000-ton capacity) and small-batch custom production (e.g., pharmaceutical-grade).
5. Process Compatibility	Partial reuse of mother liquor reduces raw material consumption; mature wastewater treatment (e.g., biological methods).

III. Limitations

Wastewater Challenges:
- Mother liquor contains unreacted formaldehyde, ammonia, and organics, requiring advanced treatment (e.g., Fenton oxidation).
Energy-Intensive Steps:
- Vacuum evaporation in the concentration stage accounts for >60% of total energy consumption.
Long Production Cycle:
- Batch processes take 8–12 hours from reaction to drying; continuous production remains underdeveloped.
Particle Size Constraints:
- Crystallization limits nano-scale HMTA production; additional milling is required for ultrafine powders.

Application Scenarios

Pharmaceuticals: High-purity HMTA for antibacterial agents and vaccine preservatives.
Chemical Industry: Curing agent for phenolic resins, vulcanization accelerator for rubber.
Traditional Industries: Metal corrosion inhibitors, textile flame retardants.

The liquid-phase method remains the dominant HMTA production process due to its maturity, high-purity output, and cost-effectiveness, particularly in pharmaceuticals and fine chemicals. Despite challenges like wastewater management and energy demands, its reliability and economic viability ensure its irreplaceability in the short term. Innovations in continuous production and energy-efficient evaporation could further enhance its sustainability.

Technical Features

In production, in order to shift the equilibrium position towards the formation of hexamine, and at the same time to avoid side reactions which may affect product quality and consumption, it is important to well control the reaction temperature and ensure the excess of ammonia. That is to say, it is necessary to ensure the presence of free ammonia so that counter reactions and the formation of TMA(Trimethylamine) can be inhibited.

owing to the use of Evaporation Pot, the crystals are formed in a relatively long time, thereby hexamine product of bigger size can be obtained, which is popular with the end users.

Hexamine specification

Item	Superior	First grade	Acceptable grade
Appearance	White or lighted colored crystals without visible impurities
Purity, % ≥	99.3	99.0	98.0
Moisture, % ≤	0.50		1.0
Ashes, % ≤	0.03	0.05	0.08
Appearance of aqueous solution	Qualified		/
Heavy metal as per Pb²⁺, % ≤	0.001		/
Chloride as per Cl^-, % ≤	0.015		/
Sulphate as per SO₄^2-, % ≤	0.02		/
Ammonium as per NH₄⁺, % ≤	0.001		/