CN1180699A

CN1180699A - Technology for producing ammonium carbonate with combined production of melamine

Info

Publication number: CN1180699A
Application number: CN 97117275
Authority: CN
Inventors: 姬东宝; 阎常河
Original assignee: GUANGPING COUNTY FERTILIZER FACTORY HEBEI PROV
Current assignee: GUANGPING COUNTY FERTILIZER FACTORY HEBEI PROV
Priority date: 1997-09-19
Filing date: 1997-09-19
Publication date: 1998-05-06

Abstract

A process for preparing both melamine and ammonium carbonate includes such technological steps as feading urea and ammonia gas, heating, catalyzing and polymerizing; one path cooling and carbonating to obtain ammonium carbonate; the other path dissolving, filtering crystallzing centrifugal separation and baking to obtain melamine. Its advantages include short process as purifying and compression steps are omitted, low cost, and high productivity.

Description

Novel process for co-production of melamine from ammonium carbonate

The invention relates to a new process for producing melamine, in particular to a new process for producing ammonium bicarbonate and co-producing melamine.

At present, the melamine is produced, for example, the existing melamine production plant which produces 1000 tons of melamine every year in China is taken as an example, the production process is complex, and the purification process and the compression process are adopted, so the process flow is long, the production efficiency is low, and by-products can not be reasonably utilized, which is the defect of the existing melamine production process.

The invention aims to provide a new process for co-producing melamine by using ammonium carbonate, which is used for directly sending tail gas and carrier gas ammonia which are discharged from a catcher to a carbonization procedure of an ammonium carbonate device after cleaning and cooling, is used for producing ammonium carbonate as a byproduct, and simultaneously omits a purification procedure and a compression procedure so as to overcome the defects of the existing process for producing melamine.

The object of the present invention can be achieved by the following embodiments:

the production process flow of the invention is as follows: a. the urea enters a fluidized bed reactor together with gas ammonia which is sent by a feeder and an ammonium bicarbonate device and is used as a carrier, under the action of a catalyst, melamine and dioxide, ammonia and polymer generated by side reaction are generated through polymerization reaction after being heated, and the melamine and the polymer are separated by a catcher to be a melamine crude product; cooling the dioxygen dicarbon, ammonia and carrier gas ammonia, and then sending the mixture to a carbonization procedure of an ammonium carbonate device to obtain ammonium carbonate as a byproduct; dissolving, filtering, crystallizing, separating and drying the melamine crude product to produce a melamine product;

b. the reaction equation is as follows:

the whole process is divided into a rough working section and a refining working section:

a. the polymerization, trapping and cooling process is a rough working section; the high-purity ammonia gas of 0.16-0.18mpa sent from the synthesis procedure of an ammonium bicarbonate device is heated to 260-280 ℃ by molten salt, enters an interlayer at the upper part of a fluidized bed reactor and an annular space of a heat-preservation cyclone separator to exchange heat with reaction gas, enters the bottom of the fluidized bed reactor when the temperature reaches 300-320 ℃ to keep a catalyst in the bed in a good fluidized state, granular raw material urea is pressed into a feeder by air andis sent into the fluidized bed by the ammonia gas, and is decomposed at the high temperature of 385-395 ℃ under the action of the catalyst to be polymerized into melamine, and carbon dioxide, ammonia and a small amount of high polymer generated by side reaction are simultaneously produced.

The polymerization reaction is endothermic and the heat of reaction required is provided by dissolved salts circulating in heated tubes in the fluidized bed reactor. The melamine gas is naturally cooled and crystallized into solid powder which is settled down after the catalyst carried by the ammonia is separated by a cyclone separator in the fluidized bed and then the catalyst powder and part of high polymer are separated by a heat-preservation cyclone separator and the gas-ammonia heat exchange is carried out, and the solid powder enters a catcher. The carbon dioxide, ammonia and gas ammonia as carrier are cooled in the cleaning tower and fed into the ammonium bicarbonate producing apparatus for carbonizing. The carrier gas ammonia is not recycled.

b. Dissolving, filtering, crystallizing, centrifugal separating and drying to obtain the refined product. Feeding the crude melamine into a dissolving tank, dissolving the crude melamine by using mother liquor, heating steam from a boiler working section of an ammonium bicarbonate device, and simultaneously adding a small amount of acetic acid and activated carbon to adjust the pH value and decolor; the dissolved melamine solution is removed of impurities insoluble in water through a filter press, the solution enters a crystallization kettle and is cooled by cooling water, the cooling water comes from a water supply working section of an ammonium bicarbonate device, the solution is cooled by a cooling tower and is recycled, the melamine crystals are folded, wet melamine is separated by a centrifugal machine, mother liquor returns to a mother liquor tank and is recycled by a mother liquor pump. Wetmelamine is sent into an air flow dryer and dried by hot air sent by an air blower, finished melamine is separated by a separator, then the finished melamine is crushed, weighed and packaged to be used as a product to be put in storage, and the dry air is discharged after melamine dust is recovered by a bag filter.

The invention has the advantages that: 1. the tail gas and carrier gas ammonia from the trap are cleaned and cooled and then directly sent to the carbonization procedure of an ammonium bicarbonate device for producing the carbon amine as a by-product, thereby omitting the purification procedure, shortening the process flow, reasonably utilizing the by-product produced by the melamine, improving the recovery rate and reducing the environmental pollution. 2. The carrier gas ammonia comes from the synthesis process of the ammonium bicarbonate device and directly returns to the carbonization process after passing through the co-production device, thereby saving the compression process for pressurizing when the gas ammonia is recycled, greatly reducing the production power consumption, and saving 800 kilowatt-hours per ton of product power consumption in test production. 3. The product has high productivity, the carrier gas ammonia comes from the synthesis process, and the carrier gas ammonia does not contain impurities such as carbon dioxide, water and the like, and has high purity. Therefore, the high polymer generated during the polymerization reaction of the urea is less, the melamine productivity is high, and 0.20 ton of urea can be saved per ton of products after the trial production. 4. The new production process saves two working procedures of purification and compression, can save investment by 40 percent, and can reduce the occupied area of land.

The following description will be made with reference to the accompanying drawings.

FIG. 1 is a flow chart of the prior art

FIG. 2 is a process flow diagram of the present invention

Comparing fig. 1 and fig. 2, the present invention omits a purification process and a compression process, thereby greatly simplifying the process flow.

Claims

1. A new production process of ammonium bicarbonate and melamine is characterized in that:

a. the production process flow is as follows: the urea enters a fluidized bed reactor together with gas ammonia which is sent by a feeder and an ammonium bicarbonate device and is used as a carrier, under the action of a catalyst, melamine and dioxide, ammonia and polymer generated by side reaction are generated through polymerization reaction after being heated, and the melamine and the polymer are separated by a catcher to be a melamine crude product; cooling the dioxygen dicarbon, ammonia and carrier gas ammonia, and then sending the mixture to a carbonization procedure of an ammonium carbonate device to obtain ammonium carbonate as a byproduct; dissolving, filtering, crystallizing, separating and drying the melamine crude product to produce a melamine product;

b. the reaction equation is as follows:

2. the process as set forth in claim 1, characterized in that the whole process can be divided into a crude and a refined section:

a. the polymerization, trapping and cooling process is a rough working section; heating the high-purity gas ammonia with the purity of 0.16-0.18mpa sent from the synthesis process of an ammonium bicarbonate device to 260-280 ℃ through molten salt, entering an interlayer at the upper part of a fluidized bed reactor and an annular space of a heat-preservation cyclone separator to exchange heat with the gas, entering the bottom of the fluidized bed reactor when the temperature reaches 300-320 ℃ to keep the catalyst in a good fluidized state, pressing granular raw material urea into a feeder through air, sending the gas ammonia into the fluidized bed, decomposing the gas ammonia at the high temperature of 385-395 ℃ under the action of the catalyst, polymerizing the gas ammonia into melamine, and simultaneously producing carbon dioxide, ammonia and a small amount of high polymer;

the polymerization reaction is endothermic reaction, and the required reaction heat is provided by molten salt circularly flowing in a heating pipe in the fluidized bed reactor; separating the catalyst carried by the melamine, carbon dioxide and ammonia generated by the reaction by a cyclone separator in the fluidized bed, separating catalyst powder and part of high polymer by a heat-preservation cyclone separator, exchanging heat with the gas and ammonia, entering a catcher, naturally cooling and crystallizing the melamine gas into solid powder, and settling; the carbon dioxide, ammonia and gas ammonia as carrier are cooled by the cleaning tower and then enter the carbonization procedure of the ammonium bicarbonate device to produce ammonium bicarbonate; the carrier gas ammonia is not recycled;

b. a refining section is formed by dissolution, filtration, crystallization, centrifugal separation and drying; feeding the crude melamine into a dissolving tank, dissolving the crude melamine by using mother liquor, heating steam from a boiler working section of an ammonium bicarbonate device, and simultaneously adding a small amount of acetic acid and activated carbon to adjust the pH value and decolor; removing impurities insoluble in water from the dissolved melamine solution through a filter press, cooling the solution in a crystallization kettle by using cooling water, wherein the cooling water is from a water supply working section of an ammoniumbicarbonate device, cooling the solution by a cooling tower for recycling, so that melamine crystals are folded out, separating wet melamine by a centrifugal machine, returning mother liquor to a mother liquor tank, and recycling the mother liquor by using a mother liquor pump; wet melamine is sent into an air flow dryer and dried by hot air sent by an air blower, finished melamine is separated by a separator, then the finished melamine is crushed, weighed and packaged to be used as a product to be put in storage, and the dry air is discharged after melamine dust is recovered by a bag filter.