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Paraformaldehyde plant , Paraformaldehyde equipment , Paraformaldehyde Technology

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Jiangsu Kaimao Chemical Technology Co., Ltd

Paraformaldehyde plant , Paraformaldehyde equipment , Paraformaldehyde Technology

City & Province Wuxi Jiangsu
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Paraformaldehyde plant , Paraformaldehyde equipment , Paraformaldehyde Technology

 

After many years development, formaldehyde industry in China has made big progress in production scale, output, quality and technology, and has approached or reached the international advanced level in many aspects, however, the formaldehyde down stream products ——Paraformaldehyde has more development spaces.

 

Section A. Paraformaldehyde Properties

 

Paraformaldehyde, short form PF is a white powder form or particle form solid. It is an important linear polymer, molecular formula (CH2O)n,; molecular weight (30)n; density 1.39 (water=1.0), melting point: 120-170℃; flash point: 71℃; ignition temperature: 300-410℃; heat of combustion :510 KJ/mol,heat of formation:177 KJ/mol,vapor pressure:0.19Kpa/25℃,low explosion limit of powder dust: 40g/m3 .Paraformaldehyde will be slowly decomposed into gas form formaldehyde at ambient temperature and will form formaldehyde water solution. Therefore, it has general formaldehyde properties. Paraformaldehyde is a mixture of formaldehyde molecule and HO(CH2O)nH etc. Paraformaldehyde can be divided into tow types which is low polymerization degree paraformaldehyde, and solid form paraformaldehyde. Mainly use polymerization degree ——n( the molecules number in the chain) for distinguishing, paraformaldehyde with low polymerization degree, in which, n<100, is easy dissolved in water; depolymerization thoroughly. The product is loose form with uniform grains, which is the ideal raw material for formaldehyde, and is excellent replacement for industrial formaldehyde. Therefore it has big development value and potentials.

 

Section B. Paraformaldehyde Application

 

Paraformaldehyde is mainly used in
⑴ Pesticides: synthesis of acetochlor, butachlor, and glyphosate.
⑵ Medicine and pharmaceutics: produce vitamin A.
⑶ Coatings: synthesis of high grade automobile paint.
⑷ Resins: applied in resin production such as ion exchanging resin and melamine resin etc. Among them, 70-80% of paraformaldehyde are used to produce synthetic glyphosate herbicide; in resin industry, use paraformaldehyde to replace 37% of industrial formaldehyde to produce phenolic resin; not only can produce high quality thermoplastic and thermosetting phenolic resin, also can greatly reduce waste water discharge and lower materials consumption more than 10%.

 

Section C. Paraformaldehyde Production Process

 

So far, there are two paraformaldehyde production processes. One is vacuum Rake type drying process, another is spray drying process.

 

1.Rake type drying process
Raw material formaldehyde is firstly concentrated and dehydrated until the formaldehyde concentration is increased from 37% to 65%,then, it is sent to the vacuum Rake type dryer for further dehydration and drying to make powders. The whole drying process is operated under vacuum condition. The evaporation condensates contain 10-15% of diluted formaldehyde, which returned to formaldehyde shop to form 37% formaldehyde for sale or produce methylal or hexamine. It is batch form operation. Each batch feed for Rake type dryer is around 4-5m3,drying time: 4-6 hours. This process has long production period, low capacity and the products are powder or block form.

 

2.Spray Drying Production Process
Formaldehyde concentration, through two stages of vacuum concentration, reaches 85%, then, is pumped to spray dryer. The concentrated formaldehyde is sprayed out to form particles of paraformaldehyde. This is a continuous process, in which, concentrated formaldehyde becomes to be solids within short time. It is able to form short linear formaldehyde molecule chain; as a result, product has good water solubility.

 

Section D. Low polymerization Degree Paraformaldehyde Production Technology

 

Low polymerization degree paraformaldehyde reaction is as following:
nCH2(OH)2 → (CH2O)n + (n-1)H2O
To produce low polymerization degree paraformaldehyde must take care of the following issues:
⑴Formaldehyde dehydration, polymerization, depolymerization must be performed at the same time in the formaldehyde concentration process. If process condition is not well controlled, it is easy to cause large amount of formaldehyde loss or formaldehyde polymerized to clog the system.
⑵In the concentrating and drying process, if the formaldehyde concentration is not high enough, with relatively high water content; the product will be sticky and easy to be agglomerated.
⑶Because the raw material formaldehyde contains small amount of methanol and formic acid polar molecules, in the concentration process, these materials will lead to further paraformaldehyde polymerization and form insoluble polymers.

 

1.Formaldehyde Concentration
Formaldehyde water solution is a co-polymerization mixing solution; mainly contains methylene glycol CH2(OH)2; HO(CH2O)nH and methylal HO(CH2O)n-1H. No more than 0.1%(wt)formaldehyde monomers exist, even in the concentrated formaldehyde solution. There are free water composition and hydration water composition two types of formaldehyde water solution to be existed. Hydration water is namely the water concentration in formaldehyde hydration molecules, which is related to polymerization degree and formaldehyde concentration. (see the following table)

Hydration water and polymerization degree relationship table Unit: wt%

 

polymerization degree

1

2

3

4

5

6

7

8

9

10

100

300

water concentration in hydration composition

37.5

23.1

16.7

13.0

10.7

9.1

7.9

7.0

6.2

5.7

0.6

0.2

Formaldehyde concentration in hydration composition

62.5

76.9

83.3

87.0

89.3

90.9

92.1

93.0

93.8

94.3

99.4

99.8

 

In the formaldehyde solution concentration process, along with the vaporization of free water, methylene glycol condensation polymerization reaction also takes place at the same time to form a series of different polymerization degree paraformaldehyde HO(CH2O)nH, but, besides free water vaporization, in the concentration process, methylene glycol itself also will occur polymerization to form high polymerization paraformaldehyde. The concentration of formaldehyde is related to the temperature, at which ,the polymer crystallized from the solution. So, it is important to control the temperature for preventing formaldehyde from polymerization. Formaldehyde will have Cannizzaro reaction at over high temperature, therefore, formaldehyde concentration usually use vacuum dehydration.

 

2.Concentrated formaldehyde solidification
The relationship between formaldehyde solution cooling solidification temperature and formaldehyde concentration indicates that over high temperature will cause formaldehyde and water evaporation at the same time, big formaldehyde loss will occur. Temperature too low also will cause formaldehyde dehydration process too slow and cause formaldehyde deep polymerization. The product will have poor water solubility, so, it is crucial to control polymerization and drying temperature.

 

3.Equipment Structure
When design the dryer, spraying pressure, spray angle, and the diameter, height of sprayer chamber, material retaining time in the tower, and cooling medium temperature, flow etc. all have big impact to the product quality. For example, the concentrated formaldehyde solidification temperature will affect the height of dryer; if spraying temperature too high it will cause the grain soft and sticky, easy scaling and affect continuous operation. Therefore, spray drying design is a systematic engineering work; copy normal dryer is not practical.

 

 

 

Section E. Main Consumption

No.

Name

Unit

Rake  Type Dryer

Spry Dryer

1

Formaldehyde(50%)

kg/t

2738-2812

2620-2720

2

Steam

kg/t

2800-3200

1750-2200

3

Power

KWH/t

80-120

235-300

4

Diluted Formaldehyde

kg/t

3000-3380

2500

5

Cooling Water

M3/t

300-350

330

This is a continuous process, in which, concentrated formaldehyde becomes to be solids within short time. It is able to form short linear formaldehyde molecule chain; as a result, product has good water solubility; and the single plant capacity can reach to 30000tons/year. Kai Mao technology has been included in the national environmental friendly directory; at present, it is the sole supplier of paraformaldehyde technology in domestic China, who owns one-stop independent intellectual property rights including 1 invention patent.

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