CN110357825B

CN110357825B - Improved co-production of pentahydroxy and hexamethylol melamine

Info

Publication number: CN110357825B
Application number: CN201810320624.XA
Authority: CN
Inventors: 周建平; 李平; 胡劲松; 陈铁能
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: 2023-01-24
Anticipated expiration: 2038-04-11
Also published as: CN110357825A

Abstract

The coproduction of pentahydroxyl melamine and hexamethylol melamine is improved. According to the method, the pentahydroxyl melamine and the hexamethylol melamine are co-produced, the high-concentration formaldehyde with the concentration of more than 60% is prepared and used on site through an improved process, and the pentahydroxyl mother liquor and the hexahydroxy mother liquor are completely recycled for producing the hexamethylol melamine. The invention solves the problem of high cost of producing the pentamethyl melamine independently and realizes zero pollution emission at the same time.

Description

Improved co-production of pentahydroxy and hexamethylol melamine

Technical Field

The invention relates to a production process of pentamethyl melamine.

Background

The pentamethyl melamine is a raw material for producing melamine resin with various characteristics. At present, the production of pentamethyl melamine 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 prior patent application CN107245057A of the applicant basically solves the problems by co-producing pentamethyl melamine and hexamethylol melamine, but still has the problems of incomplete recycling of mother liquor, high production cost and the like.

Disclosure of Invention

The invention aims to provide a combined production process of pentahydroxyl melamine and hexamethylol melamine with low cost and zero pollution emission.

The co-production process of the pentamethyl melamine and the hexamethylol melamine comprises the following steps:

1) Adding formaldehyde and melamine into a five-hydroxyl reaction kettle to ensure that the molar ratio of the melamine to the formaldehyde is 1: about 5;

2) Adjusting the pH value of the reaction solution in the five-hydroxyl reaction kettle to about 8;

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 pentamethoxyl melamine product and a pentamethoxyl mother solution;

5) Returning all the five-hydroxyl mother liquor to the six-hydroxyl 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 about 9;

9) Controlling the temperature of the reaction solution to 65-75 ℃, and keeping the temperature for about 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;

11 ) repeating steps 1) to 4) to continuously produce a pentamethyl melamine product;

12 All the five-hydroxyl mother liquor and the six-hydroxyl mother liquor in the steps 5) and 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 polysilicon particles, and mixing the polysilicon particles with silver nitrate and copper nitrate solution;

heating to about 90 ℃ under stirring regulation to evaporate water, and 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 methanol can be added into the silver nitrate solution, for example, the volume ratio of the silver nitrate and copper nitrate solution to the methanol can be about 2:1.

According to the present invention, in the prepared silver catalyst, the supported amount of silver may be about 15% (mass ratio) and the supported amount of copper may be about 10% (mass ratio) with respect to the polycrystalline silicon carrier.

According to the invention, a catalyst activation process can 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, the silver catalyst with excellent performance is used, so that high-concentration formaldehyde can be prepared on site at low cost, and then the zero-pollution emission co-production of the pentamethyl melamine and the hexamethylol melamine can be realized, so that the pentamethyl melamine product can be produced at remarkably low cost.

Detailed Description

The co-production process of the present invention generally includes the production of pentamethylolmelamine and the production of 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 process details described above can also be found in the applicant's prior related application CN107245057a, the entire contents of which are incorporated herein by reference.

Relevant parameters in the context of the present invention with respect to the production of pentamethylmelamine are: the molar ratio of melamine to formaldehyde is 1: about 5; the pH value of the reaction solution is about 8; 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 6-15; the pH value of the reaction solution is about 9; the reaction temperature is 65-75 ℃, and the reaction time is about 3 hours.

The mother liquor (the five-hydroxyl mother liquor) separated in the process of producing the five-hydroxyl methyl melamine is not easy to control, so that the mother liquor is not suitable for recycling to produce the five-hydroxyl methyl melamine generally, and the problems of high production cost and pollution discharge are caused. If the production of the pentamethyl melamine is combined with the production of the hexamethylol melamine, namely, the pentamethyl mother liquor is involved in the production of the hexamethylol melamine, the condition that the formaldehyde is in an excessive amount is only required to be controlled (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 pentahydroxy 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, precipitate during storage, and thus, in order to realize an industrial production process, it is necessary to prepare high concentrations of formaldehyde on site to realize rapid production and reduce costs. The above application CN107245057a also discloses a step of preparing high concentration formaldehyde by silver catalyzed methanol oxidation reaction.

In the actual production process of formaldehyde in high concentration 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 present 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 it in the above process.

The preparation example of the composite silver catalyst of the invention is as follows:

the cauliflower material polysilicon (silicon content 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 polysilicon particles with silver nitrate and copper nitrate (the silver loading is controlled to be about 15 percent, the copper is controlled to be about 10 percent), and adding a proper amount of methanol and water (based on immersing the polysilicon particles), wherein the volume ratio of the methanol to the water is about 1:2. Heating to about 90 ℃ under stirring regulation to evaporate water, and drying at about 130 ℃ to form the composite particles. The composite 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 composite silver catalyst of the present invention with the previously used pumice-type catalyst.

TABLE 1

Catalyst type	Silver loading	Copper loading	Conversion rate	Replacement cycle
					The invention	15％	10	95％	For 5 months
Pumice stone type	38％	0	85％	2 months old

The use of polycrystalline silicon particles in the above-mentioned size range as a carrier has the following advantages: due to the characteristics of high melting point, high hardness and the like of polycrystalline silicon, the 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 catalyst, the addition of the methanol can enhance the adhesive force of silver on the polysilicon particles after thermal decomposition of the silver nitrate. The participation of copper enhances the adhesion of silver on the one hand and further improves the catalytic activity in a combined manner on the other hand.

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

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

The formaldehyde solution with the concentration of over 60 percent can be efficiently produced with low cost by using the high-efficiency compound silver catalyst, so that the co-production of the pentamethyl melamine can be industrially realized with low cost, and the zero-pollution emission can be realized at the same time.

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 co-production process of pentamethyl melamine and hexamethyl melamine comprises the following steps:

1) Adding formaldehyde and melamine into a five-hydroxyl reaction kettle to ensure that the molar ratio of the melamine to the formaldehyde is 1:5;

2) Adjusting the pH value of the reaction solution in the five-hydroxyl reaction kettle to be 8;

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 pentamethyl melamine product and a pentamethyl mother solution;

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

8) Adjusting the pH value of the reaction solution in the hexahydroxy reaction kettle to 9;

9) Controlling the temperature of the reaction solution to be 65-75 ℃, and preserving the heat for 3 hours;

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

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 a 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 prepared silver catalyst has a silver loading of 15% and a copper loading of 10%.