New Powder Coating Curing Agent, Triglycidyl Isocyanurate (TGIC)

TGIC, chemically known as Triglycidyl Isocyanurate, is primarily used as a crosslinking curing agent for polyethersulfone (PES) powder coatings. It can also serve as a curing modifier for amine-based curing agents to form tightly bonded insoluble structures. TGIC is utilized in the production of high-performance insulating materials for electrical applications. It is employed as an additive in self-extinguishing polymers, modified epoxy resins, and in the formulation of high-efficiency adhesives and stabilizers for polyvinyl chloride (PVC), among other applications.

This article introduces the domestic production process of TGIC using epichlorohydrin as a raw material. This production process is characterized by mild operating conditions, low energy consumption, easy control, process stability, stable product quality, minimal pollutant emissions, and minimal environmental impact. It is considered an advanced process route both domestically and internationally.

 Triglycidyl Isocyanurate TGIC manufacturer of

Triglycidyl Isocyanurate Production Process

Ring-Opening Reaction

Epichlorohydrin is metered using a metering pump and pumped into the synthesis reactor. Measured cyanuric acid and a predetermined amount of catalyst, tetramethylammonium chloride, are added to the reactor. The feeding port is sealed, and then steam is introduced into the coil inside the reactor for heating. The temperature is controlled at 90°C (the optimal temperature for the ring-opening reaction) for 1 hour. To ensure a more complete ring-opening reaction, the reaction mixture is gradually heated to 105°C and maintained for an additional 2 hours to complete the ring-closure reaction. A secondary chilled brine condenser is installed on the upper part of the reactor to condense and reflux any escaping materials back into the reactor. The temperature of the brine is controlled between -2°C and -15°C. The excess amount of epichlorohydrin added during the reaction serves both as a reactant and as a solvent, ensuring maximum reaction completion without the need for additional solvents.

Ring-Closure Reaction

The ring-opening reaction mixture is cooled down to 60-70°C using ice-cold brine. Caustic soda is slowly added continuously, while the ring-closure reaction takes place. This reaction is exothermic, so cooling water is circulated through the jacket of the reactor to control the reaction temperature between 50°C and 60°C. The addition of caustic soda is stopped after approximately 40 minutes, and the ice-cold brine is removed. The reaction mixture is then maintained at a temperature of 30 minutes for insulation, and the ring-closure reaction is completed. Ice-cold brine is introduced to cool the reaction mixture to 30°C, and vacuum filtration is carried out.

 for the synthesis of (Triglycidyl isocyanurate)
The synthesis of (Triglycidyl isocyanurate)

Vacuum Filtration

The composition of the ring-closure reaction mixture includes the product, Triglycidyl Isocyanurate (TGIC), excess epichlorohydrin, sodium chloride, and water formed during the reaction. Vacuum filtration is employed to separate the salt layer from the oil layer. The oil layer consists of a mixture of epichlorohydrin and TGIC. A small amount of water generated during the reaction enters the salt layer and is removed along with the salt layer during the drying process in a double-cone dryer, resulting in a by-product of sodium chloride. The oil layer is sent to the distillation process to recover epichlorohydrin. The exhaust gas from the filtration process mainly contains epichlorohydrin and is introduced into a water-ring vacuum pump for circulation. Some of the epichlorohydrin is retained in the circulating water and settles, while the remaining non-condensable gas is collected through pipelines and directed to an activated carbon adsorption tower for purification treatment.

Vacuum Distillation

The mixture containing epichlorohydrin and the product is pumped into the distillation kettle and operated under negative pressure. Steam is used for heating, and the vacuum pressure is controlled at -0.009 MPa. As the temperature increases, the epichlorohydrin in the mixture gradually vaporizes in the distillation kettle. When the temperature reaches around 60°C, the vapor of epichlorohydrin enters the condenser from the top of the distillation kettle. Through a secondary condensation process, the vapor of epichlorohydrin is recovered and directly connected to a receiving drum through the liquid outlet pipe of the condenser. The recovered epichlorohydrin is returned to the synthesis process for reuse. The distillation kettle operates under negative pressure, and a water-ring vacuum pump is used to evacuate the system. The gas outlet pipe of the condenser on the top of the distillation kettle is connected to the water-ring vacuum pump. An appropriate amount of water is introduced into the pump as the working fluid. By continuously suctioning, compressing, and discharging the non-condensable gas, a continuous vacuum is maintained in the connected distillation kettle with a vacuum pressure of -0.009 MPa. To reduce the emissions of non-condensable gas, a buffer tank is installed in front of the water-ring vacuum pump, along with a condenser for further recovery. After the secondary condensation, a minimal amount of exhaust gas enters the circulating water of the water-ring vacuum pump. The remaining non-condensable gas is collected through pipelines and directed to an activated carbon adsorption tower for purification treatment. The residue at the bottom of the distillation kettle after the recovery of epichlorohydrin is crude TGIC, which is a viscous paste. It is further refined and purified by adding methanol.

Refinement of the Product

The temperature of the crude TGIC paste is maintained at 60-70°C. Ice-cold methanol, which has been cooled using ice-cold brine (-0~5°C), is added to the crude product while stirring to lower the temperature and form a dispersed solution. The temperature of the dispersed solution is around 30°C. It is then transferred to a crystallization kettle. Ice-cold brine is circulated through the jacket of the kettle to lower the temperature of the material to 10°C, promoting crystallization and separation into two layers. The upper layer consists of methanol, while the lower layer contains crystallized TGIC, which is the desired product. The crystallization mother liquor is separated using a centrifuge, and the methanol mother liquor is collected in a storage tank for methanol recovery. The wet TGIC product proceeds to the drying and granulation process.

Drying of the Crude Product

The drying process utilizes a glass-lined double-cone rotary vacuum dryer. During operation, hot water (steam) is circulated through the jacket of the dryer to indirectly heat the material inside the vessel. At the same time, a vacuum is applied to the dryer to maintain a certain level of vacuum. This combination of negative pressure and low temperature enables fast drying of the material. Due to the continuous rotation of the double-cone vessel that contains the material, the material is constantly lifted and tumbled, creating a semi-suspended state and a diamond-shaped trajectory. This enhances the heating surface area and achieves efficient, low-energy, and uniform drying. After drying, the material is separated using a centrifugal separator to obtain dried TGIC product. Methanol present in the material is vaporized during the drying process and then condensed and recovered for reuse. A small amount of exhaust gas enters the circulating water of the vacuum pump, and some of the methanol dissolves in the circulating water. The remaining non-condensable gas, which is not dissolved in water, is collected through a pipeline and purified using an activated carbon adsorption tower.

Granulation

Dry compaction granulation is used in this process. The dry powder is transferred through a screw conveyor, belt conveyor, or manual handling into the raw material bin of a bucket elevator. The bucket elevator then delivers the powdered material to a vibratory transition hopper. The material is uniformly fed into a variable-frequency vertical spiral feeder through a metering device. The material undergoes deaeration and pre-compression. The pre-compressed material is then compacted between two rotating rolls. The compacted ribbon-shaped material automatically detaches from the rolls and enters a crusher, where it is crushed into uneven-sized particles. The crushed particles then enter a sizing machine for refinement. The refined particles are extruded through a perforated screen plate and enter a screening machine. The finished granules are directly packaged or transferred to a finished product bin via a bucket elevator for storage. The fine powder separated during screening is returned to the raw material hopper of the bucket elevator using a recycling device, and the process continues in a closed-loop fashion. Since the entire process is operated in a closed system, there is minimal dust emission during the compaction granulation process.

Methanol Recovery

The centrifuged methanol mother liquor is transferred to the methanol distillation kettle, and steam is introduced for heating. Methanol gradually vaporizes inside the distillation kettle as the temperature increases. A large-area condenser is installed above the distillation kettle, and the gaseous methanol is condensed and recovered using ice-salt water. The condensed methanol is then cooled through a methanol cooler and directed into an intermediate methanol tank. Methanol that meets the quality standards is transferred to the methanol storage tank for future use. Methanol that does not meet the quality standards is returned to the original raw material measuring tank for further purification in the next cycle. Methanol non-condensable gas is treated in a water spray packed tower, and the exhaust gas is discharged through a 15m exhaust pipe. A small amount of residual liquid from the distillation tower bottom is sent to a hazardous waste disposal facility for treatment.

Drying of By-product Sodium Chloride

The drying process for by-product sodium chloride is the same as that for crude product drying. It utilizes a double-cone rotary vacuum dryer. After drying, the material is separated using a centrifugal separator, resulting in the by-product sodium chloride. During the drying process, any remaining epoxy chloropropane in the material is vaporized and then condensed and recovered for reuse. A small amount of exhaust gas enters the vacuum pump circulating water system, where some epoxy chloropropane is retained and dissolved in the water. The remaining non-condensable gas, which is not dissolved in water, is collected through a pipeline and directed into an activated carbon adsorption tower for purification.

Reaction Equations for the Synthesis of Triglycidyl isocyanurate

(1)The open-loop reaction equation for the synthesis of (Triglycidyl isocyanurate) TGIC can be represented as follows:

Epichlorohydrin + Cyanuric acid + Tetramethylammonium chloride → Triglycidyl isocyanurate + Ammonium chloride

(2) Closed-loop reaction equation

2.3 Process Flowchart

2.4 Main Production Equipment

5000 L Synthesis Reactor

2000 L Distillation Column

250 m Condenser

51800 Filtration Bucket

500 L Receiving Tank

440,000 kcal Freezer

1000 Model Centrifuge

ISK-5131 Water Ring Vacuum Pump

1500 L Double Cone Rotary Vacuum Dryer

GZL Dry Granulator

Additionally, the company pays special attention to environmental protection and has added activated carbon adsorption towers and environmentally friendly natural gas boilers.

Conclusion:

The two-step synthesis of TGIC has the following advantages: a simple and convenient process, easy control of temperature and pressure. This process is classified as a batch production process, requiring low investment and yielding high profits. It is also easily scalable and can be widely adopted. However, it is important to note that the primary raw materials involved in this process are hazardous chemicals. Therefore, strict safety measures must be implemented during production to ensure safe operations.

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