CN110357826B

CN110357826B - Process for coproducing tetrahydroxymethyl melamine

Info

Publication number: CN110357826B
Application number: CN201810321989.4A
Authority: CN
Inventors: 胡劲松; 王文武; 王庆华; 唐学军
Original assignee: Chongqing Jianfeng Haokang Chemicals Co ltd
Current assignee: Chongqing Jianfeng Haokang Chemicals Co ltd
Priority date: 2018-04-11
Filing date: 2018-04-11
Publication date: 2023-01-31
Anticipated expiration: 2038-04-11
Also published as: CN110357826A

Abstract

A new process for coproducing tetrahydroxymethyl melamine. The invention co-produces the tetramethylol melamine and the hexamethylol melamine, and completely recycles the tetramethylol mother liquor and the hexahydroxy mother liquor for producing the hexamethylol melamine by on-site preparation and using more than 60 percent of high-concentration formaldehyde. The invention solves the problem of high cost of producing the tetramethylolmelamine independently and realizes zero pollution emission at the same time.

Description

Process for coproducing tetrahydroxymethyl melamine

Technical Field

The invention relates to a production process of tetramethylolmelamine.

Background

Tetramethylolmelamine is a main raw material for producing high imino group, high etherified melamine resin and the like. The existing production of tetramethylolmelamine generally adopts melamine and formaldehyde aqueous solution or paraformaldehyde as raw materials to carry out hydroxymethylation reaction under the alkaline condition according to a certain stoichiometric ratio, and the product is obtained after dehydration and drying. The problems in the technology are that the aldehyde-containing waste water is much, the pollution is large, and the separate production cost is high. The applicant's prior patent application CN103724286A basically solves the above problems by co-producing tetramethylolmelamine and hexamethylolmelamine, but still has the problems of incomplete recycling of mother liquor, high production cost, etc.

Disclosure of Invention

The invention aims to provide a production process of tetramethylolmelamine with low cost and zero pollution emission.

The coproduction process of the tetramethylolmelamine comprises the following steps:

1) Adding formaldehyde and melamine into a four-hydroxyl reaction kettle, wherein the molar ratio of the melamine to the formaldehyde is 1:4 or so;

2) Adjusting the pH value of the reaction solution in the tetrahydroxy reaction kettle to be between 7 and 9;

3) Controlling the temperature of the reaction solution to be 50-60 ℃, and preserving the heat for about 3 hours;

4) After the reaction solution is cooled, introducing the reaction solution into a centrifugal machine for centrifugal separation to obtain a tetramethylol melamine product and a tetramethylol mother solution;

5) Returning all the tetrahydroxy mother liquor to the hexahydroxy reaction kettle;

6) Adding high-concentration formaldehyde into a hexahydroxy reaction kettle to keep the formaldehyde content at about 20%;

7) And adding melamine into the hexahydroxy reaction kettle to ensure that the molar ratio of the melamine to the formaldehyde is 1:6 to 15;

8) Adjusting the pH value of the reaction solution in the hexahydroxy reaction kettle to be between 8 and 10;

9) Controlling the temperature of the reaction solution to be 55-75 ℃, and keeping the temperature for about 3 hours;

10 Cooling the reaction solution, and introducing the cooled reaction solution into a centrifugal machine for centrifugal separation to obtain a hexamethylol melamine product and a hexahydroxy mother solution;

11 Repeating steps 1) to 4) to continuously produce a tetramethylolmelamine product;

12 All the four-hydroxyl mother liquor and the six-hydroxyl mother liquor in the step 5) and the step 10) are returned to the six-hydroxyl reaction kettle; and

13 ) repeating steps 6) to 10) to continuously produce a hexamethylolmelamine product.

The co-production process of the invention, wherein the formaldehyde used in the step 1) can be a formaldehyde aqueous solution with the concentration of less than 40% (mass percent); the high-concentration formaldehyde used in the step 6) is a formaldehyde aqueous solution which is prepared on site and has a concentration of more than 60%.

The high-concentration formaldehyde used in the present invention is preferably prepared by catalytic oxidation of methanol using a silver catalyst. This silver catalyst was prepared by the following method:

crushing the polysilicon into polysilicon particles with the particle size of 20-60 meshes;

cleaning the polycrystalline silicon particles, and mixing the polycrystalline silicon particles with a silver nitrate solution;

heating to about 90 ℃ under stirring regulation to evaporate water, and then drying at about 130 ℃ to form composite particles;

roasting at 1200 deg.c for 6 hr to obtain the silver catalyst.

According to the invention, a proper amount of ethanol can be added into the silver nitrate solution, for example, the volume ratio of the silver nitrate solution to the ethanol can be about 2.

According to the present invention, in the prepared silver catalyst, the supported amount of silver may be about 20% (mass ratio) with respect to the polycrystalline silicon carrier.

According to the invention, a catalyst activation process may also be included: dissolving the used silver catalyst in nitric acid to obtain polycrystalline silicon carrier particles; and reusing the obtained polycrystalline silicon carrier particles to prepare the silver catalyst.

According to a preferred embodiment of the invention, a cauliflower or carbon head material polysilicon containing impurities phosphorus, boron, carbon, with a silicon content not exceeding 99%, e.g. 90% to 95%, may be used.

According to the invention, due to the use of the silver catalyst with excellent performance, high-concentration formaldehyde can be prepared on site at low cost, and then zero-pollution emission co-production of the tetramethylolmelamine and the hexamethylolmelamine can be realized, so that the tetramethylolmelamine product can be produced at remarkably low cost.

Detailed Description

The coproduction process of the tetramethylolmelamine generally comprises the production of the tetramethylolmelamine and the production of the hexamethylolmelamine. The respective production processes of the two are similar, namely, formaldehyde and melamine with given proportion are added into a corresponding reaction kettle, then the pH value is adjusted to be alkalescent, the reaction temperature and the reaction time are controlled, and then the corresponding product and the mother liquor are obtained by centrifugal separation. The details of the above process can also be found in the applicant's prior related application CN103724286A and in the application CN 10724057A for the co-production of penta-and hexa-hydroxy, which are each incorporated herein by reference in their entirety.

Relevant parameters in the context of the present invention with respect to the production of tetramethylolmelamine are: the molar ratio of melamine to formaldehyde is 1: about 4; the pH value of the reaction solution is between 7 and 9; the reaction temperature is 50-60 ℃, and the reaction time is about 3 hours. Relevant parameters for the production of hexamethylol melamine are: the molar ratio of melamine to formaldehyde is 1: about 6 to 15; the pH value of the reaction solution is between 8 and 10; the reaction temperature is 55-75 ℃, and the reaction time is about 3 hours.

The mother liquor (tetrahydroxy mother liquor) separated in the production process of the tetramethylolmelamine is not easy to control in composition, so that the mother liquor is not suitable for recycling to produce the tetramethylolmelamine, and the problems of high production cost and pollution discharge are caused. If the production of the tetramethylolmelamine is combined with the production of the hexamethylolmelamine, namely, the mother liquor of the tetramethylolmelamine is involved in the production of the hexamethylolmelamine, the formaldehyde is only required to be controlled to be in an excessive condition (namely, the mol of the formaldehyde and the melamine is not less than 6). In practice, more than two hexahydroxy reaction kettles and more than two tetrahydroxy reaction kettles can be used for co-production during production.

However, in order to reduce the cost, the formaldehyde content in the mother liquor is lower because the formaldehyde is usually produced by using the formaldehyde with the conventional concentration (not more than 40%), and if the formaldehyde is used for producing the hexamethylol melamine, the high concentration (more than 60%) of the formaldehyde is needed to be used for completely recycling the mother liquor and controlling the total content of the formaldehyde to meet the production requirement (between 15% and 25%).

High concentrations of formaldehyde, for example 50% or more, can precipitate during storage, and therefore, in order to achieve an industrial production process, it is necessary to prepare high concentrations of formaldehyde on site to achieve rapid production and reduce costs. The above application CN 10724577A also discloses a process for preparing high concentration formaldehyde by silver catalyzed methanol oxidation.

In the actual production process of high concentration of formaldehyde by the silver method as described above, the applicant found that there is a disadvantage of poor conversion of methanol, resulting in excessively high production cost, due to the low catalytic efficiency of the silver catalyst used therein and the easy deactivation (e.g., sintering, etc.). Therefore, the invention realizes high methanol conversion rate and thus low-cost production of high-concentration formaldehyde (more than 60%) by independently developing and preparing a silver catalyst and using the silver catalyst in the process.

An example of the preparation of the silver catalyst of the present invention is as follows:

the cauliflower material polysilicon (silicon content is 95%) is crushed into polysilicon particles with the particle size of 20-60 meshes, the polysilicon particles are placed in nitric acid (68%) for treatment for 1 hour, and then the polysilicon particles are cleaned by distilled water. And mixing the polycrystalline silicon particles with silver nitrate (the silver loading amount is controlled to be about 20%), and adding a proper amount of ethanol and water (based on the immersion of the polycrystalline silicon particles), wherein the volume ratio of the ethanol to the water is about 1. Heating to about 90 deg.C under stirring to remove water, and oven drying at about 130 deg.C to obtain composite granule. The silver catalyst of the invention is prepared by roasting the composite particles for about 6 hours at about 1200 ℃.

Table 1 shows the performance comparison of the silver catalyst of the present invention with the previously used pumice-type catalyst.

TABLE 1

Catalyst type	Silver loading	Conversion rate	Replacement cycle
				The invention	20％	93％	For 5 months
Pumice stone type	38％	85％	2 months old

The use of polycrystalline silicon particles in the above particle size range as silver carriers has the following advantages: due to the characteristics of high melting point, high hardness and the like of polycrystalline silicon, the silver catalyst is not easy to sinter together; the silver on the polysilicon during catalytic oxidation carries more positive charge than other silver catalysts such as silica/silver or electrolytic silver due to its crystalline properties and conductive properties, and this positively charged silver will form the active site for methanol dehydrogenation to formaldehyde.

In the process of preparing the silver catalyst, the addition of the ethanol can enhance the adhesive force of silver on the polysilicon particles after thermal decomposition of the silver nitrate.

In addition, the invention preferably uses a cauliflower material or carbon head material polysilicon containing impurities such as phosphorus, boron, carbon and the like, and the silicon content of the material is not more than 99%, and is preferably between 90% and 95%. The use of such impurity-containing polysilicon has the advantages that: a microporous structure is formed on the polysilicon particles through the acid washing process, and the specific surface area of the polysilicon is increased, thereby enhancing the activity of the catalyst. The price of the cauliflower material or the carbon head material polysilicon is very low, so that the silver catalyst of the invention can be prepared at low cost.

In addition, the silver catalyst used in the present invention can also be recycled: dissolving the used silver catalyst in nitric acid to obtain polycrystalline silicon carrier particles; and reusing the obtained polycrystalline silicon carrier particles to prepare the silver catalyst.

The invention uses the high-efficiency silver catalyst to efficiently produce the formaldehyde solution with the concentration of more than 60 percent at low cost, thereby realizing the co-production of the tetramethylolmelamine industrially at low cost and simultaneously realizing zero pollution emission.

It will be appreciated by persons skilled in the art that the foregoing description is only for the purpose of better understanding of the invention and is not intended to limit the invention in any way.

Claims

1. A coproduction process of tetramethylolmelamine comprises the following steps:

1) Adding formaldehyde and melamine into a four-hydroxyl reaction kettle to ensure that the molar ratio of the melamine to the formaldehyde is 1:4;

3) Controlling the temperature of the reaction solution to be 50-60 ℃, and preserving the heat for 3 hours;

4) After the reaction solution is cooled, introducing the reaction solution into a centrifugal machine for centrifugal separation to obtain a tetramethylol melamine product and a tetrahydroxy mother solution;

6) Adding high-concentration formaldehyde into a hexahydroxy reaction kettle to keep the formaldehyde content at 20%;

9) Controlling the temperature of the reaction solution to be 55-75 ℃, and preserving the heat for 3 hours;

10 Cooling the reaction solution, and introducing the reaction solution into a centrifugal machine for centrifugal separation to obtain a hexamethylol melamine product and a hexahydroxy mother solution;

13 ) repeating steps 6) to 10) to continuously produce a hexamethylolmelamine product,

wherein the formaldehyde used in the step 1) is a formaldehyde aqueous solution with the mass percentage concentration of below 40%; the high-concentration formaldehyde used in the step 6) is formaldehyde aqueous solution which is prepared on site and has the concentration of more than 60 percent,

wherein the high-concentration formaldehyde is prepared by adopting a silver catalyst to catalyze and oxidize methanol,

wherein the silver catalyst is prepared by the following method:

heating to 90 ℃ under stirring regulation to evaporate water, and drying at 130 ℃ to form composite particles;

roasting for 6 hours at 1200 ℃ to obtain the silver catalyst;

dissolving the used silver catalyst in nitric acid to obtain polycrystalline silicon carrier particles; and

and reusing the obtained polycrystalline silicon carrier particles to prepare the silver catalyst.

2. The co-production process of claim 1, wherein the silver loading in the prepared silver catalyst is 20%.