AU2020101904A4

AU2020101904A4 - Unitary intumescent flame retardant and a process for the preparation and application thereof

Info

Publication number: AU2020101904A4
Application number: AU2020101904A
Authority: AU
Inventors: Jiyan Liu; Xueqing Liu; Zhihong Liu; Qingliang You; Liyong Zou
Original assignee: Jianghan University
Current assignee: Jianghan University
Priority date: 2020-08-20
Filing date: 2020-08-20
Publication date: 2020-09-24
Anticipated expiration: 2028-08-20

Abstract

The present invention provides a unitary intumescent flame retardant (IFRs) and a process for the preparation of IFRs, which comprises: a) Reacting methylcyclophosphonic anhydride with piperazine or piperazine derivative in a molten state or in a solvent to obtain a solid piperazine or piperazine derivative-contained phosphorus acid. b) Reacting the piperazine or piperazine derivative-contained phosphorus acid with alkali hydroxide to form solution of an alkali metal salt of piperazine or piperazine derivative-contained phosphorus acid. c) Reacting of solution of alkali metal salt of piperazine or piperazine derivative-contained phosphorus acid with metal sulfate to obtained unitary IFRs. The unitary IFRs are of high thermal stability with the initial thermal decomposition temperature of above 400°C. Besides, the IFRs show a good compatibility with organic polymer matrix. They have high flame retardancy and char forming capability in polymer because of the high phosphorus content and synergistic effect of P, N and metal element during combustion. The invention further related to their use as flame retardant in polyamide. 100 4,37.74'CG95.00% 80 0) 0 40 20 0 100 200 300 400 500 600 700 Temperature (OC) Universal V43A TA Instrumenits FIG 1.

Description

4,37.74'CG95.00%

80

0) 0

40

20 0 100 200 300 400 500 600 700 Temperature (OC) Universal V43A TA Instrumenits

FIG 1.

AUSTRALIA

PATENTS ACT 1990

PATENT SPECIFICATION FOR THE INVENTION ENTITLED: UNITARY INTUMESCENT FLAME RETARDANT AND A PROCESS FOR THE PREPARATION AND APPLICATION THEREOF

The invention is described in the following statement:-

UNITARY INTUMESCENT FLAME RETARDANT AND A PROCESS FOR THE PREPARATION AND APPLICATION THEREOF TECHNICAL FIELD

[0001] The present invention relates to unitary intumescent flame retardants, to their

preparation and to their use.

BACKGROUND

[0002] In the field of flame retardancy, the halogen-free intumescent flame retardants

(IFRs) are used widely in the various polymers. It is known that a typical IFR system is

usually composed of three sources: an acid source, a carbon source (or char forming agent)

and a gas source (or a blowing agent). These three sources can be combined by the method

of physical blending. IFR system also can act as the unitary compound in which the acid

source, carbon source and gas source are combined by chemical interaction. Compared

with IFRs prepared by the physical mixture of multi components, unitary IFRs showed a

better dispersibility and compatibility with the polymer matrix. However, either

multicomponent or unitary IFRs reported or current used have a low thermal stability with

the initial decomposition temperature below 300 °C.

[0003] Some of reported unitary intumescent flame retardants have showed good thermal

stability [CN108794746A, CN103333493, CN104231266A, CN104559204A,

CN107501493A, CN207652324A, and CN105924645A]. However, they have problems

such as poor compatibility with polymer matrix, high moisture absorption and low flame

retardant efficient due to low phosphorus content of the molecule.

SUMMARY

[0004] The object of the present invention is to provide a unitary IFRs with high thermal

stability, good compatibility with polymer matrix and excellent flame-retardant efficiency.

Besides, the invention is related to their synthesis and application thereof,

[0005] To achieve the above object, in a basic embodiment, the present invention provides

a unitary IFRs having a structural formula as follows:

H2 H2 C -C

H2 H2

H H2 t H 3C H3C

o A

0 P CH o 2H C H2CI H3 O Al O CH2 O AN CH CH 2

N CH 2 H 2C N H2 \CH2 H 2C IH 3 oP CH 2 H 2C H H C CH2 H2C' /

o C CH 2

[0006] A method for synthesis of IFRs as described above, which comprises:

[0007] Reacting methylcyclophosphonic anhydride with piperazine or piperazine

derivative in a molten state or in a solvent to obtain a solid piperazine or piperazine

derivative-contained phosphorus acid.

[0008] Reacting the piperazine or piperazine derivative-contained phosphorus acid with

alkali hydroxide to form solution of an alkali metal salt of piperazine- or piperazine

derivative-contained phosphorus acid.

[0009] Reacting of solution of alkali metal salt of piperazine- or piperazine derivative

contained phosphorus acid with metal sulfate to obtained unitary IFRs.

[0010] According to the method of the present invention, in a preferred embodiment, the

reaction in the step a) in the melting state was carried out in the temperature range from

100 °C to 140 °C for I to 5 hours. Especially preferred reaction temperature is 120 °C. The

preferred reaction time is 2 hours.

[0011] According to the method of the present invention, in a preferred embodiment, the

reaction in the step a) in a solvent was carried out in the temperature range from 90 °C to

130 °C for 1-5 hours; the reaction temperature is preferably 120°C and the reaction time is

preferably 3 hours.

[0012] According to the process of the present invention, the examples of the piperazine

and its derivative used in accordance with this invention are the following: N

methylpiperazine, N-methylpiperazine, 2-methylPiperazine, j-hydroxyethylpiperazine

and p-aminoethylpiperazine, or the mixture of two or more above compounds.

[0013] According to the process of the invention, in a preferred embodiment, the molar

ratio of methylcyclophosphonic anhydride to piperazine or piperazine derivative is 1.8: 1

to 2.2: 1, preferably 1.9: 1: 2: 1.

[0014] The preferred alkali hydroxides used in the step b) are sodium hydroxide, potassium

hydroxide or the mixture of them in any molar ratio. Preferably choosing sodium

hydroxide.

[0015] According to the process of the present invention in a preferred embodiment, the

neutralization reaction in the step b) comprises the following step: 1 M alkali hydroxide

solution was added dropwise at 50-100°C until the pH value of the reaction mixture reaches

7.0.

[0016] According to the process of the present invention, in a preferred embodiment, the

metal sulfates used in the step c) are following: aluminum sulfate, magnesium sulfate, zinc

sulfate. The aluminium sulfate is precedence.

[0017] In reaction in the step c), the metal sulfate is added dropwise at a temperature of

50-100°C within 1-3 hours, preferably at 90°C. During this procedure, the product

precipitates from the solution, so that the time of from about 1-3 hours during which the

dropwise addition continues corresponds to the reaction time. It is also necessary to

continue stirring.

[0018] The metal salts maybe isolated by simple filtration and washing 3 times with water

to remove any sulfate which may still be adhering to the product.

[0019] The amount of the aluminium sulfate which to be used is a stoichiometric amount

of 1/6 to 1/4 equivalent on the alkali salt of methylcyclophosphonic acid obtained from the

step b.

[0020] The substantial advantageous of the invention are as follows:

[0021] The piperazine based metal salt of phosphinate is a unitary IFR, which integrates

the "acid source," "carbon source" and "gas source" in to a single molecule (the phosphinic

acid part acts as the acid source; the part from piperazine or its derivative acts as the carbon

source and the gas source). This unitary IFR can be used alone in the polymer with no extra

additives. Especially, the phosphorus content---which plays the key role in the performance

of flame retardancy, is high in the unitary IFR, so the flame retardancy of high efficientcy

can be achieved at a low loading of the IFR.

[0022] The obtained unitary IFR is good thermal stability and excellent carbon-forming

performance with initial thermal decomposition temperature (the temperature for 5% mass

loss) above 400 °C and the residual high to 50% at 700 °C. They may be applied for the

flame retardancy of polymer which has a high processing temperature such as high

temperature polyamide and non-charable polymer such as olefin-based polymer. In

addition, the molecule of the unitary IFR contains a huge organic group, which makes it

more hydrophobic and shows a good compatibility with organic polymer material.

Simultaneously, the metal ions can make the intumescent layer becoming more compact

and firmer to prevent the heat spreading and melt-material dripping during the combustion

of the polymer.

[0023] In addition, the process for preparing the products is simple and water is used as a

solvent. The process is environment friendly.

BRIEF DESCRIPTION OF THE FIGURES

[0024] FIG. 1 TG curves of the IFRI.

[0025] FIG.2 Digital photo of the IFRI. (a): IFRI; (b) IFRI after heating at 500 °C for 10

minutes.

DESCRIPTION OF THE INVENTION

[0026] All the chemicals or raw materials used in the invention are commercial grade and

can be obtained from company.

[0027] The X-ray fluorescent spectroscopy (XRF) analysis of the sample was done on

pressed powder pellet of 4 cm in diameter. The operation was performed on a ZSX Primus

II (Rigaku, Japan) XRF spectrometer.

[0028] Thermogravimetric (TG) measurement was performed with TSDT Q600 (TA,

USA) under N2 atmosphere at heating rate of 20 °C min-1, using alumina crucible and

sample mass of about 9-10 mg.

[0029] Limiting oxygen index (LOI) test was conducted with a HC-2 instrument

(Jiangning, China) according to ASTM D2863-77. The sheet sample was cut into 130 mm

in length, 6.5 mm in wide and 3.3 mm in thickness.

[0030] The size of sample bars for the vertical combustion (UL 94) test is 130x13x3.0

mm3. The measurements were carried out with a CZF3 instrument (Jiangning, China). A

Bunsen burner with propane flux of 35 kW m -2 was applied. The distance from the end of

the bar to the burner nozzle was 25 cm. The UL 94 classification was obtained according

to the standard STM D3801.

[0031] The invention is illustrated below by means of example:

Example 1

[0032] Adding 1 mol of methylcyclophosphonic anhydride and 0.5 mol of anhydrous

piperazine to a 1000 ml of flask, the mixture was melted at 120°C and stirred for 2 hours.

After the reaction completed, the flask cooled down to the ambient temperature to obtain a

white solid bis-methyl (piperazindipropionamido) phosphinic acid. Then, adding distilled

water of the same volume as the aforesaid product under stirring until the mixture dissolved

a homogeneous solution. IM NaOH aqueous solution was added dropwise. It indicated the

neutronization completed when the pH of the solution reached 7.0. The solution was then

heated to 90°C and 0.17 mol of A2(SO4)3 aqueous solution was added dropwise under

stirring at 90°C within 3 hours. After the reaction completed, the flask cooled down to the

ambient temperature. The white precipitate was filtered and washed with distilled water

three times to obtain aluminium salt of bis-methyl (piperazine dipropionamido)

phosphinate (IFR). The product was dried with vacuum oven at 100 oC for 24 hours to

remove the moisture (Yield = 96.7 %).

[0033] The chemical reaction of IFRI in the example 1 is shown in the as below:

0 0 0 /HHFI N H, N-- C - - -OH H 2 C- H2C ' CH3 + H2 H2 / c-C\ H 2 /\CH2 H3/ H2 ! HN \ NH 1 H2 H2 H3C0 120 H2H. H2 H2 H2 H2 C-C -C -P-OH

\ H3/

2 H 2 N--C -C -P 7/? eH e7 OH 90'C H2C CH 2 H3C + NaOH + Al(SO 4 )3 H2\ / -H' H2 H2 e/ N-C -C- -P OH

H3C H2 H2

N" N

N C H 2C O C H2 C

H 2C H 2C H3C.NI H3C I

0 O

N H 2C 0 O 0A C_'CH c5CH C 2 | H2C CH3 l CH2 N

N cH2 H2 P CH3 C N

H2C CHCH CH 2 H 2C IH NC H2 / H2 C N C, ,CH2 6o N

[0034]

[0035] The TG curve of aluminon salt of IRFI is presented in the FIG.2. The temperature

of 5 % mass loss (T5%) is 437.7 °C.

[0036] FIG 3a and 3b are the digital photo of IFRI ( FIG 2a ) and IFRI after heating at

450 °C for 10 min (FIG 2b ).The phosphorus and nitrogen of the IFRI are 17% and 8%

correspondingly, according to the result from X-ray fluorescence spectrometer.

[0037] IRF Iis applied as a flame retardant for polyamide 6 (PA6): 20 parts by weight of

the granulated IRFl mixed with 80 parts by weight of PA6 and processed in a SHJ-20 twin

screw extruder at 230 °C, and the pellets were compression molded and cut into standard

testing bars. The composite passes UL 94 VO rating with LOI value of 31.5%.

Example 2

[0038] To a solution of 0.5 mol of 2-methylpiperazine in 500 ml of 1,4-dioxane in a 1000

mL of round bottom three-neck flask, 1 mol methylcyclophosphonic anhydride was added.

The mixture was heated to 120°C and maintained for 3 hours under stirring. Then the flask

cooled to ambient temperature, a white solid bis-methyl (2

methylpiperazindipropionamido) phosphinic acid was precipitated from the solution and

filtered.

[0039] Then, adding distilled water of the same volume as the aforesaid product under

stirring until the mixture dissolved into a homogeneous solution. IM NaOH aqueous

solution was added dropwise. It indicated the neutronization completed when the pH of the

solution reached 7.0. The solution was then heated to 90 °C and 0.17 mol of A2(SO4)3

aqueous solution was added dropwise under stirring at 90 °C within 3 hours. After the

reaction completed, the flask cooled down to the ambient temperature. The white

precipitate was filtered and washed with distilled water three times to obtain aluminium

salt of bis-methyl (2-methylpiperazinedipropionamido) phosphinate (IFR2). The product

was dried with vacuum oven at 100 °C for 24 hours to remove the moisture (Yield = 97.7

%). The initial decomposition temperature of IFR2 is 428.3 °C. The phosphorus and

nitrogen of the IFR2 are 16% and 8% correspondingly, according to the result from X-ray

fluorescence spectrometer.

[0040] The composite which contains 20 parts by weight of the granulated IRF2 and 80

parts by weight of PA6, was prepared following the process described in the example 1.

The composite passes UL 94 VO rating with LOI 30.2%.

Example 3

[0041] To a solution of 0.53 mol of N-methylpiperazine in 500 ml of toluene in a 1000 mL

of round bottom three-neck flask, 1 mol methylcyclophosphonic anhydride was added. The

mixture was heated to 120°C and maintained for 3 hours under stirring. Then the flask

cooled to ambient temperature, a white solid bis-methyl (N

filtered.

[0042] Then, adding distilled water of the same volume as the aforesaid product under

stiring until the mixture dissolved into a homogeneous solution. IM NaOH aqueous

reaction completed, the flask cooled down to the ambient temperature. The white

salt of bis-methyl (N-methylpiperazinedipropionamido) phosphinate (IFR3). The product

was dried with vacuum oven at 100 °C for 24 hours to remove the moisture (Yield = 97.2

%). The initial decomposition temperature of IFR3 is 432.6°C, The phosphorus and

nitrogen of the IFR 3 are 16% and 7% correspondingly, according to the data from X-ray

fluorescence spectrometer.

[0043] The composite which contains 20 parts by weight of the granulated IRF3 and 80

The composite passes UL 94 VO rating with LOI 29.1 %.

Example 4

[0044] To a solution of 0.5 mol of 2-methylpiperazine in 500 ml of 1,4-dioxane in a 1000

cooled to ambient temperature, a white solid bis-methyl (2

filtered.

[0045] Then, adding distilled water of the same volume as the aforesaid product under

solution reached 7.0. The solution was then heated to 90°C and 0.25mol of MgSO4 aqueous

solution was added dropwise under stirring at 90°C within 3 hours. After the reaction

completed, the flask cooled down to the ambient temperature. The white precipitate was

filtered and washed with distilled water three times to obtain magnesium salt of bis-methyl

(2-methylpiperazinedipropionamido) phosphinate (IFR4). Drying the product with vacuum

oven at 100 °C for 24 hours to remove the moisture (Yield = 95.7 %). The initial

decomposition temperature of IFR4 is 427.3 °C, The phosphorus and nitrogen of the IFR

4 are 17% and 8% correspondingly, according to the results from X-ray fluorescence

spectrometer.

[0046] The composite containing 20 parts by weight of the granulated IRF4 and 80 parts

by weight of PA6 was prepared following the process described in the example 1. the

composite passes UL 94 VI rating with LOI 27.5%.

Example 5

[0047] To a solution of 0.5 mol of piperazine in 500 ml of dimethylbenzene in a 1000 mL

cooled to ambient temperature, a white solid bis-methyl (piperazindipropionamido)

phosphinic acid was precipitated from the solution and filtered.

[0048] Then, adding distilled water of the same volume as the aforesaid product under

solution reached 7.0. The solution was then heated to 90 °C and 0.25 mol of ZnSO4

aqueous solution was added dropwise under stirring at 85°C within 3 hours. After the

reaction completed, the flask cooled down to the ambient temperature. The white

precipitate was filtered and washed with distilled water three times to obtain zinc salt of

bis-methyl (piperazinedipropionamido) phosphinate (IFR5). Drying the product with

vacuum oven at 100 °C for 24 hours to remove the moisture (Yield = 92.7 %). The initial

decomposition temperature of IFR5 is 434.8 °C. The phosphorus and nitrogen of the IFR

2 are 17% and 8% correspondingly, according to the result from X-ray fluorescence

spectrometer.

[0049] The composite containing 20 parts by weight of the granulated IRF5 and 80 parts

composite passes UL 94 VI rating with LOI 26.8%.

Example 6

[0050] Adding 1 mol of methylcyclophosphonic anhydride and 0.45 mole offp

hydroxyethylpiperazine to a 1000 ml of flask, the mixture was melted at 100°C and stirred

for 5 hours. After the reaction completed, the flask cooled down to the ambient temperature

to obtain a white solid bis-methyl (p-hydroxyethylpiperazine dipropionamido) phosphinic

acid.

[0051] Then, adding distilled water of the same volume as the aforesaid product under

stirring until the mixture dissolved into a homogeneous solution. IM KOH aqueous

solution reached 7.0. The solution was then heated to 100°C and 0.25 mol of MgSO4

aqueous solution was added dropwise under stirring at 100°C within 3 hours. After the

reaction completed, the flask cooled down to the ambient temperature. The white

precipitate was filtered and washed with distilled water three times to obtain magnesium

salt of bis-methyl (p-hydroxyethylpiperazine dipropionamido) phosphinate (IFR6). The

product was dried with vacuum oven at 100 °C for 24 hours to remove the moisture (Yield

= 94.7 %). The initial decomposition temperature of IFR5 is 428.3 °C. The phosphorus and

nitrogen of the IFR 6 are 17.6% and 7.8% correspondingly, according to the results from

X-ray fluorescence spectrometer.

[0052] The composite containing 20 parts by weight of the granulated IRF6 and 80 parts

composite passes UL 94 VO rating with LOI 29.2 %.

Example 7

[0053] Adding 1 mol of methylcyclophosphonic anhydride and 0.48 mol offp

aminoethylpiperazine to a 1000 ml of flask, the mixture was melted and stirred at 140°C

for Ihour. After the reaction completed, the flask cooled down to the ambient temperature

to obtain a white solid bis-methyl (p-aminoethylpiperazine dipropionamido) phosphinic

acid.

[0054] Then, adding distilled water of the same volume as the aforesaid product under

solution reached 7.0. The solution was then heated to 80°C and 0.25 mol of ZnSO4 aqueous

solution was added dropwise under stirring at 100°C within 3 hours. After the reaction

filtered and washed with distilled water three times to obtained zinc salt of bis-methyl (p

hydroxyethylpiperazine dipropionamido) phosphinate (IFR7). Drying the product with

vacuum oven at 100 °C for 24 hours to remove the moisture (Yield = 94.7 %). The initial

decomposition temperature of IFR7 is 437.3 °C. The phosphorus and nitrogen of the IFR

7 are 15.8% and 8.1% correspondingly, according to the results from X-ray fluorescence

spectrometer.

[0055] The composite containing 20 parts by weight of the granulated IRF7 and 80 parts

composite passes UL 94 VO rating with LOI 28.6 %.

Example 8

[0056] To a solution of 0.56 mol of anhydrous piperazine in 500 ml of dimethylbenzene in

a 1000 mL of round bottom three-neck flask, 1 mol methylcyclophosphonic anhydride was

added. The mixture was heated to 130°C and maintained for 3 hours under stirring. Then

the flask cooled to ambient temperature, a white solid bis-methyl

(piperazindipropionamido) phosphinic acid was precipitated from the solution and filtered.

[0057] Then, adding distilled water of the same volume as the aforesaid product under

solution was added dropwise. The neutronization completed when the pH of the solution

reached 7.0. The solution was then heated to 60°C and 0.25 mol of ZnSO4 aqueous solution

was added dropwise under stirring at 60°C within 4 hours. After the reaction completed,

the flask cooled down to the ambient temperature. The white precipitate was filtered and

washed with distilled water three times to obtained Zinc salt of bis-methyl

(piperazinedipropionamido) phosphinate (IFR8). Drying the product with vacuum oven at

100 °C for 24 hours to remove the moisture (Yield = 90.7 %). The initial decomposition

temperature of IFR8 is 434.8 °C, The phosphorus and nitrogen of the IFR 8 are 16.7% and

8.2% correspondingly, according to the results from X-ray fluorescence spectrometer.

[0058] The composite containing 20 parts by weight of the granulated IRF8 and 80 parts

composite passes UL 94 VO rating with LOI 29.2%.

[0059] The preferred embodiment of the invention is described in detail above, but the

invention is not limited to this. Within the technical conception of the present invention, a variety variant can be applied to the present invention, including the combination or modification of technical features in any manner. Such variants shall also be regarded as the contents disclosed by the present invention and shall be covered by the present invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A unitary intumescent flame retardant (IFR) comprising:

H2 H2

N "C -CN

H 2C H 2C I H C I 2 H 2C H3 C,, I HC I o o

10,

0 H2C P 0 CH CH3 3

1 H 2C CH3 O Al CH2 O C -CH21

N 0CH2H2C N H2C CH2 H2C CH3 CH2 H2CCH HC C CH2 H2C N I C,CH2

2. A method for synthesis of IFRs according to claim 1 comprising the following

steps:

a) Reacting methylcyclophosphonic anhydride with piperazine or piperazine

derivative-contained phosphorus acid.

b) Reacting the piperazine or piperazine derivative-contained phosphorus acid with

alkali hydroxide to form solution of an alkali metal salt of piperazine or piperazine

derivative-containing phosphorus acid.

c) Reacting of solution of alkali metal salt of piperazine or piperazine derivative

contained phosphorus acid with metal sulfate to obtain unitary IFRs.

3. The method for synthesis of IFRs according to claim 2, wherein the reaction in the

step a) in the melting state was carried out in the temperature range from 100 °C to 140 °C

for 1 to 5 hour C, wherein the preferred reaction temperature is 120 °C and the preferred

reaction time is 2 hours.

4. The method for synthesis of IFRs according to claim 2, wherein the reaction in the

step a) in a solvent was carried out in the temperature range from 90 °C to 130 °C for 1-5

hours. The reaction temperature is preferably 120°C and the reaction time is preferably 3

hours.

5. The method for synthesis of IFRs according to claim 2, wherein the examples of

the piperazine and its derivative used in accordance with this invention are the following:

N-methylpiperazine, N-methylpiperazine, 2-methylPiperazine, -hydroxyethylpiperazine

and p-aminoethylpiperazine, or the mixture of two or more above compounds.

6. The method for synthesis of IFRs according to claim 2, wherein, the molar ratio of

methylcyclophosphonic anhydride to piperazine or piperazine derivative is 1.8: 1 to 2.2: 1,

preferably 1.9: 1: 2: 1.

7. The method for synthesis of IFRs according to claim 2, wherein the preferred alkali

hydroxides used in the step b) are sodium hydroxide, potassium hydroxide or the mixture

of them in any molar ratio, preferably sodium hydroxide.

8. The method for synthesis of IFRs according to claim 2, wherein the neutralization

reaction in the step b) comprises addition of 1 M alkali hydroxide aqueous solution to react at 50-100°C for 1-3 hours to obtain a colourless clear solution and adding alkali hydroxide dropwise until the pH value of solution reaches 7.0.

9. The method for synthesis of IFRs according to claim 2, wherein the metal sulfates

used in the step c) are following: aluminum sulfate, magnesium sulfate, zinc sulfate,

wherein the aluminium sulfate is precedence; wherein in reaction in the step c), the metal

sulfate is added dropwise at a temperature of 50-100°C within 1-3 hours, preferably at

90°C; during this procedure, the product precipitates from the solution immediately, so that

the time of from about 1-3 hours during which the dropwise addition continues

corresponding to the reaction time; it is also necessary to continue the stirring.

10. The method for synthesis of IFRs according to claim 2, wherein the metal salts can

be isolated by simple filtration and washing 3 times with water to remove any sulfate which

may still be adhering to the product; the amount of the aluminium sulfate which to be used

is a stoichiometric amount of 1/6 to 1/4 equivalent on the alkali salt of

methyleyclophosphonic acid from the step b.

-1/2-

FIG 1.