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Solvent recovery from pentachlorophenol-treated wood
VACUUM Classified A b s t r a c t s
III - -
Vacuum Processing
Techniques
--
III
Contd.
Reactive Sputtering and Associated Plant Design See A b s t r a c t No. : 198/1
155/III
Electrically Heated Glass for Airplane Cabins See A b s t r a c t No. : 1 6 1 / I I
156/III
33 --
0
Abstract h'o. and References
IMPREGNATION
--
33
Solvent Recovery f r o m Pentachlorophenol-Treated W o o d United States. A new m e t h o d of preserving wood has recently been introduced which provides for the i m p r e g n a t i o n of the t i m b e r w i t h pentachlorophenol. The use of this material w i t h o u t a n y solvent is n o t practical as the material would n o t p e n e t r a t e the t i m b e r to a n y appreciable depth. The choice of a suitable solvent has p r o v e d difficult. Some tend to produce a ' b l o o m i n g ' effect on the surface of the wood, w h e n the solvent has evaporated, and others cause ' bleeding' to the surface. I t was decided, therefore, to investigate m e a n s of modifying the i m p r e g n a t i o n process w h e r e b y the solvent used is completely r e m o v e d after completion of the t r e a t m e n t . I n the n o r m a l ' v a p o u r - d r y i n g ' process green wood is loaded into the pressure-treating cylinder and exposed to v a p o u r s from an organic solvent boiling in an evaporator. The v a p o u r s condense on tile wood, h e a t the wood at the same time and cause the m o i s t u r e to e v a p o r a t e from the wood. The r e s u l t a n t v a p o u r m i x t u r e of w a t e r and solvent is conducted to a separator where the w a t e r is discharged and the solvent r e t u r n e d to the evaporator. The recovery of the solvent (xylene in this particular case) is effected as follows : After completion of the i m p r e g n a t i o n process xylene only is boiled in the e v a p o r a t o r at 280°F and the v a p o u r s produced are passed over the wood in the cylinder. After a b o u t 1 h o u r the wood h a s reached t h e t e m p e r a t u r e of the vapour. D u r i n g t h a t period some of the xylene condenses on the wood, drips off the wood and is collected in a condensate tank. At the end of the first h o u r the e v a p o r a t o r is s h u t off and a v a c u u m of a b o u t 25 inch. is applied which causes the xylene, which had entered the wood during impregnation, to evaporate. Repeating this cycle of 1 h o u r h e a t i n g and 1 h o u r v a c u u m results eventually in the complete r e m o v a l of the xylene from the wood. A p a r t from xylene, high-flash coal t a r n a p h t h a , perchloroethylene and trichloroethylene have been found to be solvents suitable for this form of t r e a t m e n t . The a u t h o r gives details of e x p e r i m e n t s carried o u t w i t h xylene as the solvent u n d e r varying conditions. Detailed results axe s h o w n in a table. I n e x p e r i m e n t s w i t h 5°//o p e n t a c h l o r o p h e n o l solution i m p r e g n a t i o n was carried out initially at a pressure of 125 l b / s q u , inch, m a i n t a i n i n g this pressure for an hour, following which the cylinder was evacuated and k e p t at reduced pressure for a n o t h e r hour. After additional t r e a t m e n t for solvent recovery in the m a n n e r described the solvent c o n t e n t in the wood was reduced to 0.1 lb./cu, ft. of dry pentachlorophenol. As this figure was below 0.25 lb./cu, ft., which w a s the residual solvent c o n t e n t aimed at, a second e x p e r i m e n t was conducted using a v a c u u m of 22.5 inch. during the i m p r e g n a t i o n process. I n t h a t case the a m o u n t retained was found to be excessive. Satisfactory results were finally obtained using a pressure of 25 l b . / s q u , inch during i m p r e g n a t i o n after increasing the p e n t a c h l o r o p h e n o l concentration to 10%. Sommaire : UII bois impregn6 de pentachlorophenol m o n t r e des taches dues a u x solvants volatiles employ6s. Un m6thode ~vitant cette difficult6 est d6crite.
157/III
Article by M. S. Hudson Industr. Eng~g. Chem. 45, July 1953 1576-1583
0 34 ~
FUMIGATION
--
34
Descriptive Terms for V a c u u m F u m i g a t i o n See A b s t r a c t No. : 188/I
158/III
36 - -
DRYING
- - 36
Evaporation United Kingdom. The a u t h o r s u r v e y s recent development in the field of evaporation processes and e v a p o r a t o r design. Reference is made to recent descriptions of the p r o d u c t i o n of a m m o n i u m n i t r a t e b y three different methods. .~_ table reproduced below gives the comparison of these methods. The prilling process consists essentially in s p r a y i n g h o t concentrated a m m o n i u m nitrate liquor from the top of a tower t h r o u g h which a s t r e a m of air at a lower t e m p e r a t u r e is rising. E v a p o r a t i o n is carried o u t in a stainless steel e v a p o r a t o r of the long-tube single-effect reeirculation t y p e r e m o v i n g a p p r o x i m a t e l y 2,000 l b . / h r , of w a t e r from a charge of 140 ton at a v a c u u m of 17 inch. Hg, achieving a concentration of 95%. Similar details are given of the v a c u u m crystallisation process (see also 2~bstract 2 1 4 / I I I , Vol. II). E v a p o r a t o r s , operating at 26 inch. Hg, are used in the production of chemicals from milk. Milk heated at 90°]7 is passed t h r o u g h solid bowl separators facilitating
October. 195.3 Vol.
Vacuum III No. d
159/III
467
III - -
Vacuum Processing
Techniques
--
III
Contd.
Reactive Sputtering and Associated Plant Design See A b s t r a c t No. : 198/1
155/III
Electrically Heated Glass for Airplane Cabins See A b s t r a c t No. : 1 6 1 / I I
156/III
33 --
0
Abstract h'o. and References
IMPREGNATION
--
33
Solvent Recovery f r o m Pentachlorophenol-Treated W o o d United States. A new m e t h o d of preserving wood has recently been introduced which provides for the i m p r e g n a t i o n of the t i m b e r w i t h pentachlorophenol. The use of this material w i t h o u t a n y solvent is n o t practical as the material would n o t p e n e t r a t e the t i m b e r to a n y appreciable depth. The choice of a suitable solvent has p r o v e d difficult. Some tend to produce a ' b l o o m i n g ' effect on the surface of the wood, w h e n the solvent has evaporated, and others cause ' bleeding' to the surface. I t was decided, therefore, to investigate m e a n s of modifying the i m p r e g n a t i o n process w h e r e b y the solvent used is completely r e m o v e d after completion of the t r e a t m e n t . I n the n o r m a l ' v a p o u r - d r y i n g ' process green wood is loaded into the pressure-treating cylinder and exposed to v a p o u r s from an organic solvent boiling in an evaporator. The v a p o u r s condense on tile wood, h e a t the wood at the same time and cause the m o i s t u r e to e v a p o r a t e from the wood. The r e s u l t a n t v a p o u r m i x t u r e of w a t e r and solvent is conducted to a separator where the w a t e r is discharged and the solvent r e t u r n e d to the evaporator. The recovery of the solvent (xylene in this particular case) is effected as follows : After completion of the i m p r e g n a t i o n process xylene only is boiled in the e v a p o r a t o r at 280°F and the v a p o u r s produced are passed over the wood in the cylinder. After a b o u t 1 h o u r the wood h a s reached t h e t e m p e r a t u r e of the vapour. D u r i n g t h a t period some of the xylene condenses on the wood, drips off the wood and is collected in a condensate tank. At the end of the first h o u r the e v a p o r a t o r is s h u t off and a v a c u u m of a b o u t 25 inch. is applied which causes the xylene, which had entered the wood during impregnation, to evaporate. Repeating this cycle of 1 h o u r h e a t i n g and 1 h o u r v a c u u m results eventually in the complete r e m o v a l of the xylene from the wood. A p a r t from xylene, high-flash coal t a r n a p h t h a , perchloroethylene and trichloroethylene have been found to be solvents suitable for this form of t r e a t m e n t . The a u t h o r gives details of e x p e r i m e n t s carried o u t w i t h xylene as the solvent u n d e r varying conditions. Detailed results axe s h o w n in a table. I n e x p e r i m e n t s w i t h 5°//o p e n t a c h l o r o p h e n o l solution i m p r e g n a t i o n was carried out initially at a pressure of 125 l b / s q u , inch, m a i n t a i n i n g this pressure for an hour, following which the cylinder was evacuated and k e p t at reduced pressure for a n o t h e r hour. After additional t r e a t m e n t for solvent recovery in the m a n n e r described the solvent c o n t e n t in the wood was reduced to 0.1 lb./cu, ft. of dry pentachlorophenol. As this figure was below 0.25 lb./cu, ft., which w a s the residual solvent c o n t e n t aimed at, a second e x p e r i m e n t was conducted using a v a c u u m of 22.5 inch. during the i m p r e g n a t i o n process. I n t h a t case the a m o u n t retained was found to be excessive. Satisfactory results were finally obtained using a pressure of 25 l b . / s q u , inch during i m p r e g n a t i o n after increasing the p e n t a c h l o r o p h e n o l concentration to 10%. Sommaire : UII bois impregn6 de pentachlorophenol m o n t r e des taches dues a u x solvants volatiles employ6s. Un m6thode ~vitant cette difficult6 est d6crite.
157/III
Article by M. S. Hudson Industr. Eng~g. Chem. 45, July 1953 1576-1583
0 34 ~
FUMIGATION
--
34
Descriptive Terms for V a c u u m F u m i g a t i o n See A b s t r a c t No. : 188/I
158/III
36 - -
DRYING
- - 36
Evaporation United Kingdom. The a u t h o r s u r v e y s recent development in the field of evaporation processes and e v a p o r a t o r design. Reference is made to recent descriptions of the p r o d u c t i o n of a m m o n i u m n i t r a t e b y three different methods. .~_ table reproduced below gives the comparison of these methods. The prilling process consists essentially in s p r a y i n g h o t concentrated a m m o n i u m nitrate liquor from the top of a tower t h r o u g h which a s t r e a m of air at a lower t e m p e r a t u r e is rising. E v a p o r a t i o n is carried o u t in a stainless steel e v a p o r a t o r of the long-tube single-effect reeirculation t y p e r e m o v i n g a p p r o x i m a t e l y 2,000 l b . / h r , of w a t e r from a charge of 140 ton at a v a c u u m of 17 inch. Hg, achieving a concentration of 95%. Similar details are given of the v a c u u m crystallisation process (see also 2~bstract 2 1 4 / I I I , Vol. II). E v a p o r a t o r s , operating at 26 inch. Hg, are used in the production of chemicals from milk. Milk heated at 90°]7 is passed t h r o u g h solid bowl separators facilitating
October. 195.3 Vol.
Vacuum III No. d
159/III
467