Phosphorus Chemistry - ACS Publications - American Chemical Society

Chapter 19 Crystalline Chloro-Trisodium Orthophosphate C. Y. Shen and David R. Gard

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Chemistry of the crystalline chloro-trisodium orthophosphate is elucidated. This widely used cleaning and sanitation ingredient can be produced by a melt crystallization approach. A hot phosphatesolution with a Na/P mole ratio of about 2.8 is mixed with a hypochlorite solution. The resulting solution is vacuum cooled to produce crystalline product with a size distribution of about -20+200 mesh, suitable for formulating into automatic dish washing compounds. Crystalline chloro-trisodium orthophosphate (hence after, this name is abbreviated as Cl-TSP, commonly used in the trade) has versatile properties in saponification, emulsification, peptization, dispersion, and sanitation (1). It is widely used in formulations, such as hard surface cleaners, scouring cleansers, industrial and institutional cleaners, and automatic dish washing compounds. In the seventies, its growth rate is about 4 to 5 percent per year and in 1978 its annual consumption rate reached about 200 million pounds per year (2). Cl-TSP with a high level of water hydration is easy to cake. Storage and transport of C l TSP is difficult, especially in hot summer days. For this reason, the use of Cl-TSP in commercial formulation is being replaced by chlorinated cyanuric salts. If a simple preparation procedure of producing Cl-TSP can be developed to produce Cl-TSP at the site of formulators, the use of Cl-TSP may be revived because of low costs, safety, and simple equipment requirement.

0097-6156/92/0486-0240$06.00/0 © 1992 American Chemical Society Walsh et al.; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

19.

Crystalline Chloro-Trisodium Orthophosphate

SHEN AND GARD

241

According t o B e l l ( 3 ) , Cl-TSP has the e m p i r i c a l formula 4 (Na P0 · XH 0 ) ·NaY, where X=ll-12 and Y i s OC1. T h i s e m p i r i c a l formula, however, i s not i n agreement with the composition g i v e n by Mathias (4) and A l d e r ( 5 ) . The e a r l i e r i n v e n t o r s showed t h a t Cl-TSP has a Na/P mole r a t i o t o be l e s s than t h r e e . The B e l l proposed formula has been w e l l accepted and a term, c h l o r i n a t e d t r i s o d i u m phosphate has o f t e n been used, as d e p i c t e d by r e a c t i o n 1 below. U n f o r t u n a t e l y , the i m p l i e d chemical r e a c t i o n , c h l o r i n a t i o n of c r y s t a l l i n e t r i s o d i u m orthophosphate, does not produce the d e s i r e d product, Cl-TSP. Some c l a r i f i c a t i o n of t h i s p r e p a r a t i o n i s needed. 3

4

2

2 [ 4 ( Na P0 · 12H 0 ) · NaOH ] + C l Downloaded by UNIV OF ARIZONA on May 6, 2017 | http://pubs.acs.org Publication Date: April 7, 1992 | doi: 10.1021/bk-1992-0486.ch019

3

4

2

2

(1)

4(Na P0 *12H 0) •NaOCl + 4(Na P0 - 12H 0)*NaCl + 3

4

2

3

4

2

H0 2

CHEMISTRY OF Cl-TSP There are probably more than 50 US patents r e l a t e d t o Cl-TSP. A d d i t i v e s , from s u r f a c t a n t s t o s i l i c a t e s , were used t o produce c r y s t a l s with more s t a b l e a c t i v e c h l o r i n e . Examples of these patents are r e f e r e n c e s (6-13) which a p p a r e n t l y followed B e l l ' s proposed formula. Analyses of c a r e f u l l y c r y s t a l l i z e d Cl-TSP c r y s t a l s from a l i q u o r prepared from a phosphate l i q u o r with a Na/P r a t i o between 2.7-3.0 and s u f f i c i e n t amounts of a v a i l a b l e c h l o r i n e from a b l e a c h s o l u t i o n (Sunny S o l 150, Jones Chemicals, Inc., Calendonia, New York, 14423) show the composition of Cl-TSP c r y s t a l s t o be as follows: Weight %

E q u i v a l e n t Composition of Cl-TSP Na P0 Na HP0 Cl Na 0 combined w i t h C l Water Total 3

2

35.6 5.5 4.2 3.7 51.0 100.0

4

4

2

2

2

Excluding Na 0 combined with C l , the Na 0 t o P 0 mole r a t i o of Cl-TSP was found t o be 2.85. This s u b s t a n t i a t e d the f a c t t h a t Cl-TSP cannot be produced by r e a c t i n g c r y s t a l l i n e TSP with c h l o r i n e as d e p i c t e d by equation 1. 2

2

2

2

5

The Cl-TSP c r y s t a l s were s t u d i e d u s i n g the x-ray d i f f r a c t i o n equipment. The l a t t i c e constants and space group were determined u s i n g the Syntex P A u t o d i f f r a c t o m e t e r . R e s u l t s are i n agreement w i t h 2

Walsh et al.; Phosphorus Chemistry ACS Symposium Series; American Chemical Society: Washington, DC, 1992.

PHOSPHORUS CHEMISTRY

242

e a r l i e r p u b l i c a t i o n s ( 6 ) . The x-ray p a t t e r n s of commercial products w i t h a wide range of moisture and a v a i l a b l e c h l o r i n e l e v e l s a r e n e a r l y a l l the same as the c r y s t a l l i n e TSP. I t i s o f i n t e r e s t t o note when c r y s t a l l i n e TSP w i t h a t h e o r e t i c a l amount o f water o f about 56% w i l l l o s e i t s c h a r a c t e r i s t i c x-ray p a t t e r n when i t i s dehydrated t o c o n t a i n about 54% water. The Cl-TSP c r y s t a l s can t o l e r a t e a wide l e v e l o f water. The x-ray p a t t e r n was unchanged when a Cl-TSP with 52% water was d r i e d a t 25 C and 50% RH t o about 49%. T h i s property appears t o f a c i l i t a t e the production o f Cl-TSP. For r e f e r e n c e s , the c h a r a c t e r i s t i c s o f Cl-TSP l a t t i c e constants are given below:


e e

a = b c α /

= = « =

11.908 (4) A 12.660 (4) A β = 90.00° 120.00° 4

C r y s t a l c l a s s = T r i g o n a l , Space Groups = P Cl""(D ) C a l c u l a t e d d e n s i t y = 1.589 3

29

i / L

8.7 15.0 16.5 20.6

75 75 50 45

2Θ 22.3 22.9 24.0 26.0

3d

IZL 20 20 20 80

PROCESS DEVELOPMENT One of the purposes of t h i s work i s t o f i n d a simple way f o r producing Cl-TSP i n an o p e r a t i o n which c o u l d be e a s i l y s e t up i n t h e u s e r s ' p l a n t s . Three approaches were considered and e v a l u a t e d . Dry N i x Approach. In t h i s approach, s o l i d NajHP0 o r i t s hydrates are mixed w i t h an a p p r o p r i a t e amount of s o l u t i o n s c o n t a i n i n g NaOH and C l a t temperatures below 60 C t o avoid l o s s e s o f a v a i l a b l e c h l o r i n e . The product i s not s u f f i c i e n t l y c r y s t a l l i n e thus showing high tendencies t o cake and t o l o s e a v a i l a b l e c h l o r i n e . 4

2

e

C r y s t a l l i z a t i o n from S o l u t i o n . Although Cl-TSP c r y s t a l s c o u l d be produced from a s o l u t i o n as mentioned b e f o r e , t h i s approach i s not commercially v i a b l e . Some h y p o c h l o r i t e converts t o c h l o r a t e which causes a d i s p o s a l problem. The c r y s t a l l i n e s i z e s are l a r g e and not s u i t a b l e f o r commercial f o r m u l a t i o n s . C r y s t a l l i z a t i o n from a M e l t . I t i s known t h a t Cl-TSP can be melted i n i t s water of h y d r a t i o n . Laboratory


19. SHEN AND GARD


243

t e s t s show t h a t when 103.68 weight u n i t o f a s o l u t i o n o f sodium phosphate with Na/P = 2.8 a t 90°C i s mixed with 33.05 weight u n i t o f h y p o c h l o r i t e s o l u t i o n c o n t a i n i n g 14.5% a v a i l a b l e c h l o r i n e and 3% excess Na 0, i t w i l l form a Cl-TSP melt which can be vacuum c o o l e d t o produce about 100.68 p a r t s c r y s t a l s w i t h a s i z e d i s t r i b u t i o n e s s e n t i a l l y -20+200 meshes meeting u s e r s ' s p e c i f i c a t i o n s . T h i s product can be f u r t h e r c o o l e d i n 25°C dry a i r t o g i v e the d e s i r e d water content and flow p r o p e r t i e s . Since the process produces no waste and t h e product does show the d e s i r e d p r o p e r t i e s , i t i s considered t o be t h e c h o i c e approach (14).


2

The sodium phosphate s o l u t i o n with a Na/P mole r a t i o of 2.7-2.8 can be produced by many p o s s i b l e ways such as: a. Reacting 50% NaOH and 77-85% H P0 i n a simple s t e e l mixing tank. The heat o f r e a c t i o n c o u l d be used t o evaporate the excess water. F i g u r e 1 shows t h e s o l u b i l i t y c h a r a c t e r i s t i c o f a s o l u t i o n with Na/P=2.8. 3

4

b. M e l t i n g commercially a v a i l a b l e c r y s t a l l i n e TSP 4[Na P0 «12H 0] and disodium phosphate, Na HP0 . Bags o f c r y s t a l l i n e TSP and DSP are more e a s i l y a v a i l a b l e . 3

4

2

2

4

c. Reacting monosodium phosphate NaH P0 *2H 0 with c a u s t i c solutions. 2

4

2

OPTIMIZATION OF MELT-CRYSTALLIZATION T e s t Procedure. The h y p o c h l o r i t e s o l u t i o n was prepared by absorbing a known weight o f c h l o r i n e i n known weight of hydroxide s o l u t i o n a t a temperature o f l e s s than 20°C by c o o l i n g i n an i c e bath. For example, per 100g o f h y p o c h l o r i t e s o l u t i o n , t h e f o l l o w i n g composition was used: Combined Na 0 Free Na 0 H0 Cl 2

2

2

2

Na 0/H 0 composition i s e q u i v a l e n t t o 38.83 p a r t s o f 50% NaOH i n 46.62 p a r t s o f water.

= 12.72g = 2 . 30g = 70.40g = 14.55g

2

2

The amount o f a v a i l a b l e c h l o r i n e was determined by t i t r a t i o n with standard sodium s u l f i t e s o l u t i o n . There was no l o s s o f any a v a i l a b l e c h l o r i n e i n t h i s preparation. The phosphate s o l u t i o n was prepared from r e a c t i n g a n a l y t i c a l grade 85% H P0 and 50% NaOH i n a heavy duty mixer. A f t e r the temperature o f t h e phosphate s o l u t i o n was c o o l e d t o the d e s i r e d l e v e l , t h e s p e c i f i c amounts o f h y p o c h l o r i t e s o l u t i o n a t a temperature o f 20°C were added. The mixture was mixed f o r a predetermined time 3

4



244

PHOSPHORUS CHEMISTRY

% Max. Na20 in Solution with Na/P - 2.8

5h

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95 100

Temperature, °C F i g u r e 1. S o l u t i o n P o i n t s of Sodium Phosphate with a Na/P Mole R a t i o of 2 . 8 .


19. SHEN AND GARD


245

i n t e r v a l before vacuum c o o l i n g was a p p l i e d . The mixture was cooled i n about 5 minutes t o 45°C and e s s e n t i a l l y f r e e - f l o w i n g damp c r y s t a l s with an aimed water content of 56.0% were o b t a i n e d . These c r y s t a l s were aged under 25°C and 50% RH a i r f o r a p e r i o d o f 27 and 47 hours and analyzed. T e s t V a r i a b l e s . Examining the melt c r y s t a l l i z a t i o n process, t h e r e a r e t h r e e v a r i a b l e s t h a t should be optimized. The v a r i a b l e s and the ranges used f o r t h i s study a r e : A v a i l a b l e C l i n NaOCl s o l u t i o n : Let h = 14.5% C l with 3.0% excess Na 0 A = 13.5% C l with 0.8% excess Na 0


2

x

2

2

2

2

2

Temperature o f phosphate s o l u t i o n when h y p o c h l o r i t e s o l u t i o n i s added: Let B = High Temperature = 90]C B = Low Temperature = 80°C x

2

Time p e r i o d o f mixing b e f o r e vacuum i s a p p l i e d : Let C = 5 minutes. C = 1 minute. t

2

The r e s u l t s a r e summarized i n Table I . The i n i t i a l products were aimed t o have the same composition i n weight percent Na 0 = 24.46, P 0 = 16.04, ave. C l = 4.50, and H 0 = 56.0%. The l a r g e v a r i a t i o n o f water i n the f r e s h product was unexpected. These experiments c o u l d lead t o the f o l l o w i n g t e n t a t i v e c o n c l u s i o n s . I t i s d e s i r a b l e t o use the more concentrated h y p o c h l o r i t e s o l u t i o n with an excess o f c a u s t i c . The temperature o f the phosphate s o l u t i o n when the h y p o c h l o r i t e was added, and the length o f mixing time b e f o r e the vacuum was a p p l i e d are r e l a t i v e l y not s i g n i f i c a n t , thus g i v i n g t h e o p e r a t i o n more leeway t o prepare the d e s i r e d product. 2

2

5

2

2

SUMMARY A r e l a t i v e l y simple process t o produce the v e r s a t i l e C l TSP from melt c r y s t a l l i z a t i o n approach was demonstrated. The melt composition can be obtained by mixing a sodium phosphate s o l u t i o n w i t h a Na/P mole r a t i o o f about 2.72.8 and a h y p o c h l o r i t e s o l u t i o n c o n t a i n i n g 14.5% a v a i l a b l e c h l o r i n e and 3.0% excess Na 0. The mixture i s vacuum cooled t o r e s u l t i n e s s e n t i a l l y -20 +200 mesh c r y s t a l s which can be used i n v a r i o u s c l e a n i n g products such as automatic d i s h washing compounds t o avoid t r a n s p o r t a t i o n and storage of t h e troublesome Cl-TSP crystals. 2



1 2 1

C

1

2

ABC

2

2

2

2

2

2

ABC

C

2 1 1

B

2

Α Β^

A

2

AiB C

B

C

A

B

1 1 1

A

NO.

Sample

4.09

4.33

56.97

55.24

57.82

57.32

4.11

54.77

4.11

53.73

4.24

4.11

54.13

53.65

2

H0

4.10

2

4.27

Ave. C l

Samole. Wt.%

Initial

3.33

3.58

3.64

3.31

3.94

4.14

4.19

4.10

Ave. C l 2

53.37

52.68

53.20

53.28

52.61

52.48

52.67

53.00

2

H0

18.58

17.32

11.43

19.46

4.14

2.36

1.87

0

Loss

Acreina / Drvincr. Wt.%

A f t e r 27 Hrs

3.31

3.57

3.56

3.28

3.83

4.14

4.17

4.03

Ave. C l 2

52.28

52.40

51.54

52.34

52.54

52.42

52.61

52.92

2

H0

19.07

17.55

13.38

20.20

6.81

2.36

2.34

1.71

LOSS

Aaeina / Drvina. Wt.%

A f t e r 47 Hrs

T a b l e I . E f f e c t s o f P r e p a r a t i o n C o n d i t i o n s on A v a i l a b l e Chlorine S t a b i l i t i e s o f Cl-TSP


19. SHEN AND GARD

247 Crystalline Chloro-Trisodium Orthophosphate


ACKNOWLEDGMENTS We are in debt to S. H. Ramsey for his help in various tests and determinations, and to B. R. Stults for the X-ray diffraction studies of crystalline TSP and C l TSP. LITERATURE CITED 1. Dibello, P.M., et al., Soap/Cosmetics/Chem. Spec. Aug. 1974, 46. 2. Ayers, J.H., CEH Marketing Research Report, SRI Menlo Park, CA., April 1978. 3. Bell, R.N., Ind. Eng. Chem. 1945, 41, 2901. 4. Mathias, L.D., U.S. Pat. No. 1,555,474, Sept. 29, 1925. 5. Alder, H., U.S. Pat. No. 1,965,304, July 3, 1934. 6. Clark, G.L. and Gross, S.T., Z. Krist. 1937, 98, 107. 7. Hull, H.H., U.S. Pat. No. 2,324,302, July 13, 1943. 8. Miller, D.E., U.S. Pat. No. 2,536,453, Jan. 2, 1951. 9. Shere, L . ; Carrera, R.T., U.S. Pat. No. 3,281,364 Oct. 25, 1966. 10. Stamm, J.K., U.S. Pat. No. 3,364,147, Jan. 16, 1968. 11. Taylor, J.A., U.S. Pat. No. 3,342,737, Sept. 19, 1967. 12. Toy, A.D.F.; Bell, R.N., U.S. Pat. No. 3,656,890, April 18, 1972. 13. Vickers, R.H., U.S. Pat. No. 3,525,583, Aug. 25, 1975. 14. Shen, C.Y., U.S. Pat. No. 4,402,926, Sept. 6, 1983. RECEIVED November

12, 1991


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