| Claims [Claim 1] A method for Improving purity, crystallization, and granulation of hexamethylenetetramine (hexamine) product wherein, hexamine product characterized by a purity of 100 ± 0.5 was manufactured by some actions such as improving the formaldehyde feed through the purification of silver catalyst, monitoring and controlling the use of ammonia during the process, accurate control of the process temperature upon adding a chiller system, controlling the conditions of nucleation and improving crystallization by designing the system and determining the percentage of solids in the reactor along with using vacuum evaporator, preventing the damage of the formed hexamine crystals by using a screw pump to transfer the suspension and maintaining the physical properties of the product by determining the amount of stabilizer with uniform dispersion under vacuum cor dition and according to the following exothermic reaction. 6CH2O + 4NH3 (CH2)6N4+6H2O + 745/29kj/mol [Claim 2] The method for Improving hexamethylenetetramine product according to claim 1 , to produce 1 -ton hexamine, 3.5 tons of 37% formaldehyde, and 530-550 kg of ammonia are required, and to increase the reaction progress, some extra ammonia in the system is required. [Claim 3] The method for Improving hexamethylenetetramine product according to claim 1 , the addition of a chiller system next to the vacuum evaporator controls and maintains the reactor temperature stability and keeps the mother liquid in the supersaturated range, which results in the improvement of nucleation and the formation of high-purity hexamine crystals. [Claim 4] The method for Improving hexamethylenetetramine product according to claim 1 , improvement of the formaldehyde feed through purification, dissolving, electrolysis, and regeneration of high-purity silver catalyst leads to the production of formaldehyde with special properties such as acidity less than 0.012% and residual methanol less than 0.45%, which improved the purity of the final product of hexamine by preventing side reactions. [Claim 5] The method for Improving hexamethylenetetramine product according to claim 1 , the addition of the EC control parameter at the same time as moving the pH monitoring device to the vicinity of the reactor for continuous monitoring and controlling and reducing the amount of ammonia used improved the crystallization process and increased the purity of hexamine. [Claim 6] The method for Improving hexamethylenetetramine product according to claim 1 , the purity of the product is improved by controlling the rate of nucleation by determining and monitoring the solid content in the reactor at less than 20% by dissolving the solid particles in the returned mother liquid before entering the reactor. [Claim 7] The method for Improving hexamethylenetetramine product according to claim 1 , using a screw pump in the transfer of hexamine suspension prevents the destruction of hexamine crystals, preserves their crystalline form, and improves granulation. [Claim 8] The method for Improving hexamethylenetetramine product according to claim 1 , the prevention of agglomeration of high-purity hexamine during its storage and supply to the market is determined by the addition of stabilizers so that while conserving the physical properties, the purity of the product is also maintained and a ribbon mixer was used for mixing and dispersion stabilizers. [Claim 9] The method for Improving hexamethylenetetramine product according to claim 8, even using stabilizers, the purity of hexamine remains above 99.5%, the amount of ash is 0.001% and the humidity is in the range of 0.08-0.15%. [Claim 10] The method for Improving hexamethylenetetramine product, for environmental control and to prevent wastage of raw materials, an ammonia stripping tower was added to the system, and the amount of ammonia recovery was controlled by installing a temperature gauge and flowmeter and continuously monitoring the low temperature of the tower. |
Title of Invention : method for Improving purity, crystallization, and granulation of hexamethylenetetramine (hexamine) product
Technical Field
[0001] The technical field of this invention relates to the hexamine as a white crystalline heterocyclic organic compound that is used in the synthesis of other chemical compounds and is applied in the pharmaceutical, military industries, etc.
Background Art
[0002] The hexamine production process was first disclosed in the number
GB156136 in 1922 under the title Process for the Manufacture of Hexamethylenetetramine and Formaldehyde. Subsequently, several disclosures were made to improve the process and purification of hexamine as follows:
Patent
Title Date number
US1566820 Production and purification of Hexamine 22. Des.1925
US1635707A Manufacture of Hexamethylenetetramine 12.Jul.1927
US1774929 Method of Making Hexamethylenetetramine 2.Sept.1930
US2293619 Art of making Hexamethylenetetramine 18.Agu.1942
US2449040 Manufacture of Hexamethylenetetramine 7.Sept.1948
US2542315A Method for production of Hexamethylenetetramine 20.Feb.1951
US2640826 Production of Hexamine 2.Jun.1953
US2762799 Manufacturing of Hexamethylenetetramine 3.JUI.1953
BE509296A Method for manufacturing of Hexamethylenetetramine 31.Jul.1953
US2865919 Production of Hexamethylenetetramine 12. May.1954
CA 510326D Production of Hexamine 22. Feb.1955
FR1 167435A Manufacturing process of Hexamethylenetetramine 1 1.Agu.1958
US3061608 Preparation of Hexamethylenetetramine 30.Oct.1962
DE1271119 Verfahren zur herstellung von Hexamethylenetetramine 4.Mar.1963
DE977337 Verfahren zur herstellung von reinstem, kristallinem und wasserfreiem 30.Des.1965 Hexamethylenetetramine
[0003] The hexamine production process with a purity of 99.9% was disclosed in patent number DE977337. In the present invention, the purity of hexamine was increased to 100±5%, the crystal structure was improved, and upon using suitable stabilizers, as well as maintaining the purity, the physical properties were also improved.
Technical Problem
[0004] Given the sensitivities in various industries, such as the defense and pharmaceutical industries, producing high-purity hexamine is a main objective. To achieve this objective, the formaldehyde feed was improved by optimizing the silver catalyst regeneration process which resulted in the production of formaldehyde characterized by very low acidity and methanol. Additionally, controlling the reaction temperature of hexamine production at less than 100 C, determining the percentage of solids in the reactor, and measuring pH should be performed continuously.
[0005] The crystals of hexamine produced in the phase of transfer to the centrifuge are susceptible to damage, and the hexamine generated in the storage phase undergoes physical changes (agglomeration), which this issue in this invention is solved using different materials and equipment.
Solution to Problem
[0006] Hexamine is the solid by-product resulting from the reaction of formaldehyde with ammonia gas under vacuum conditions. Given that in critical industries, the lowest amount of impurities can affect the function of materials, producing hexamine with the highest possible purity and improving and maintaining the crystal structure, optimizing the consumption of ammonia, and conserving the physical properties of the manufactured product through the following measures were taken:
[0007] Formaldehyde gas, as one of the ingredients in the production of hexamine, is produced by passing methanol through the silver catalyst bed. The formaldehyde feed was improved through optimization of the silver catalyst regeneration process by making corrections in various parameters of this process, including performing pre-treatment, determination of the concentration of the electrolyte solution, adjustment of the temperature, and specification of the flow density and filtration, which resulted in formaldehyde with special nature. [0008] Then, the formaldehyde gas emitted from the formalin unit passes through the filter and enters the hexamine reactor. On the other hand, liquid ammonia is converted into gas and enters the reactor after twice filtration, reducing the amount of impurities. In the hexamine reactor, for the initial start-up, there is some hexamine as the initial nucleus of crystal formation, and in the subsequent stages, the available mother liquid is used.
[0009] Formaldehyde and ammonia react together in the reactor in the presence of the mother liquid. For a proper nuclear reaction, it is necessary to maintain the temperature of the reactor in the range of 080, and by adding a chiller system the reactor cooling system was upgraded. By using the evaporator under vacuum, the mother liquid was kept in the relative supersaturation range and the nucleation was improved, in turn, helps to keep the reactor temperature low.
[0010] Determining the appropriate concentration of ammonia to form the suitable structure of hexamine crystals on the one hand and trying to use the minimum amount of ammonia due to environmental and economic considerations requires continuous monitoring of the pH of the process. As a result, the EC control parameter was added to the process as well as moving the installation location of the pH meter to the tank adjacent to the reactor.
[0011] Two outlets are embedded in the hexamine reactor, one of which is the suspension containing the hexamine crystal, which exits from the lower part of the reactor and enters the stirred tank and in order to prevent damage to the formed nuclei, they are pumped to the head tank using a screw pump instead of a centrifugal pump. The head tank like a funnel, transfers the suspension to the centrifuge, and the excess liquid is poured into the circulator tank of the mother liquid, and then it enters the reactor by passing through the twin filter and participates in the process again.
[0012] At this stage, the solid particles of hexamine in the returned mother liquid are completely dissolved and the clear mother liquid enters the reactor because the presence of solid particles will increase the crystal nucleus in the reactor, and as a result, the size of the hexamine crystals will be reduced. A mesh is embedded inside the centrifuge and the size of the crystal particles is formed within it. The material exiting from the centrifuge enters the funnel, and from the lower part of it, the crystals enter the spiral conveyor to reach the pneumatic dryer. The drying operation is performed by blowing air through a blower in the dryer. The hexamine product coming out of the dryer enters the silicone separator and is packed.
[0013] The second material exiting from the reactor consisted of formalin and ammonia, which did not participate in the reaction. This mixture is emitted as steam from the top of the reactor and injected into the lower part of the regeneration tower. The regenerated ammonia is collected as diluted ammonia water and discharged into the stripping tower. In the stripping tower, ammonia is disposed of by steam injection and returned to the hexamine reactor. By adjusting the conditions of the stripping tower, the amount of ammonia in the resultant liquid at the bottom of the tower will be suitable for use in the cooling system. The exhaust gases from the vacuum pump are washed in the final absorption tower to remove the ammonia and then transferred to the off-gas furnace for burning.
Advantageous Effects of Invention
[0014] The improvement of formaldehyde as a feed of hexamine production unit using regenerated silver catalyst resulted in producing hexamine with a purity of 100±5%. Also, some actions such as the use of a chiller and evaporator system under vacuum to control the process temperature and improve the crystallization and the use of a screw pump to prevent the damage of the formed crystals led to the generation of hexamine products with appropriate granulation.
[0015] The hexamine product of this complex has favorable physical stability, which is possible by using the lowest amount of stabilizer while maintaining the purity of the product. Ultimately, the produced hexamine is of high purity, suitable granulation, and in the form of powder, which makes it possible to use it in critical industries.
Brief Description of Drawings
[0016] Fig 1 : map process
Description of Embodiments [0017] The equipment applied in the hexamine production including the reactor, ammonia evaporator, head tank, centrifuge, screw pump, vacuum pumps, drying system, ammonia stripping tower, and other equipment is shown in process map number.
1. Ammonia
2. Evaporator
3. Coke Filter
4. Filter
5. Formaldehyde
6. FM Filter
7. Aminate Reactor
8. HL Seal Trough
9. Screw Pump
10. HL Recirculating Tank
11 . Pump
12. HL Filter
13. Vacuum Evaporator
14. Vacuum Cooling Tower
15. Vacuum Tank
16. Vacuum Pump
17. AM Recover Tower
18. AIR Cooler
19. Vacuum Tank
20. Vacuum Pump
21 .AM Absorber
22. Pump 23. OFF GAS
24. Head Tank
25. Centrifuge
26. Hoper
27. Blower
28. Drier
29. Cyclone
30. Hexamine
31 .Tail Gas Washer
32. Pump
33. Blower
34. AW Pre-Heater
35. AM Stipper
36. Pump
37. AW Collecting Tank
38. SW Collecting Tank
39. Steam Dispenser
40. Steam
Examples
[0018] Following adjusting the reactor pressure to less than -20 kpa by the vacuum pump, formaldehyde gas enters the hexamine reactor by passing through the filter with a temperature of 110 C° from the formalin unit. The ammonia feed after entering the evaporator, turns into gas and enters the reactor by passing through the filter. By controlling the temperature of the reactor at 80 C through the chiller system and also by adjusting the pressure of -20 kpa, formaldehyde, and ammonia gases begin to nucleate in the presence of the mother liquid. The pH of the reactor is continuously monitored, and in case the pH is lower than 9.5, the amount of ammonia entering the system is increased.
[0019] After sufficient growth and condensation, the formed crystals are removed from the end of the reactor in the form of a suspension and transferred to the head tank using a screw pump. In the head tank, the solid particles of hexamine are settled, and after the solid particles are dissolved, the overflow enters the reactor as a clear liquid, so that the solid content of the reactor is controlled at about 20%. After dewatering, the settled solid is dried in a centrifuge by blowing air at a temperature of 110 C and transferred to the packaging unit.
[0020] To prevent the formed hexamine from agglomeration, a suitable amount of stabilizers is added to the final product using a ribbon mixer. Ammonia in the unreacted gases exiting from the top of the reactor is recovered in different stages and collected in the form of diluted ammonia liquid. The ammonia in liquids is finally removed by steam injection in the stripping tower. The resulting gas is returned to the reactor and the water at the bottom of the stripping tower with the permitted amount of ammonia is used in the cooling system.
Industrial Applicability
[0021] The prepared hexamine is utilized in the following industries:
[0022] Military and defense industries: as a raw material for the production of RDX (hexagon), HMX (octagon), and HMTA (hexamethylene triperoxide amine).
[0023] Fertilizer industry: anti-agglomeration agent in urea fertilizer, production of agricultural pesticides, fungicide in the citrus production industry.
[0024] Metal industry: corrosion inhibitor against acid and H2S.
[0025] Fuel industry: HMT fuel pellets, production of smokeless fuel pellets or smokeless pellets.
[0026] Pharmaceutical industry: Urinary tract disinfectant.
[0027] Resin industry: stabilizing agent for liquid resin UF, MF, PM, curing agent for UF, MF, PM molding powders, carbohydrate resins, hardener for Novalac (PF) resins, vulcanizing agent for vinyl resins and copolymers. [0028] Organic synthesis industry: as an additive in deodorizing powder, absorption of phosgene gas, and preservation of fresh products.
[0029] Leather industry: protection of fur and skin.
[0030] Cellulose and paper industry: surface improvement during the production of waterproof papers and boards.
[0031] Lubricants industry: stabilizer in greases and oils.