CA1048501A - Airstream flash drying of trichloro-s-triazine trione - Google Patents
Airstream flash drying of trichloro-s-triazine trioneInfo
- Publication number
- CA1048501A CA1048501A CA76265409A CA265409A CA1048501A CA 1048501 A CA1048501 A CA 1048501A CA 76265409 A CA76265409 A CA 76265409A CA 265409 A CA265409 A CA 265409A CA 1048501 A CA1048501 A CA 1048501A
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- CA
- Canada
- Prior art keywords
- trichloro
- drying
- triazine trione
- dryer
- airstream
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D251/00—Heterocyclic compounds containing 1,3,5-triazine rings
- C07D251/02—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings
- C07D251/12—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members
- C07D251/26—Heterocyclic compounds containing 1,3,5-triazine rings not condensed with other rings having three double bonds between ring members or between ring members and non-ring members with only hetero atoms directly attached to ring carbon atoms
- C07D251/30—Only oxygen atoms
- C07D251/36—Only oxygen atoms having halogen atoms directly attached to ring nitrogen atoms
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Drying Of Solid Materials (AREA)
- Catalysts (AREA)
- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
Abstract
TITLE: AIRSTREAM FLASH DRYING OF TRICHLORO-S-TRIAZINE TRIONE
INVENTORS: GEORGE D. NELSON
KENNETH J. NISSING
WILLIAM F. SYMES
ABSTRACT OF THE DISCLOSURE
A method for drying wet trichloro-s-triazine trione particles which comprises introducing the particles to an airstream flash dryer and controlling the particle temperature between about 80°C. and about 120°C.
INVENTORS: GEORGE D. NELSON
KENNETH J. NISSING
WILLIAM F. SYMES
ABSTRACT OF THE DISCLOSURE
A method for drying wet trichloro-s-triazine trione particles which comprises introducing the particles to an airstream flash dryer and controlling the particle temperature between about 80°C. and about 120°C.
Description
~048~()1 TITLE: AIRSTREAM FLASH DRYING OF TRICHLORO-S-TRIAZINE TRIONE
INVENTORS: GEORGE D. NELSON
RENNETH J. NISSING
WILLIAM F. SYMES
BACKGROUND OF THE INVENTION
Field of the Invention This invention relates to an improved method for drying trichloro-s-triazine trione. More specifically, this invention pertains to airstream or gas stream flash drying of trichloro-s-triazine trione'wherein superior process con-trol is achieved together with reduction of undesirable moisture in the finished product.
',' Description of the Prior Art Trichloro-s-triazine trione, sometimes termed tri-chloroisocyanuric acid or trichlorocyanuric acid, is a well known material which is widely employed as a source of avail-able chlorine in sanitizing and bleaching applications. It is used, for example, in various cleaning and bleaching formu-lations and is also a well known substitute for elementalchlorine in swimming pools.
It is known to prepare trichloro-s-triazine trione by several different methods. One typical method is described in U.S. Patent No. 2,969,360, issued January 24, 1~61. In this process, cyanuric acid is fed along with aqueous alkali -(in molar ratio of about one mole of caustic per atom of chlor-ine to be added) and chlorine to an aqueous reaction zone which
INVENTORS: GEORGE D. NELSON
RENNETH J. NISSING
WILLIAM F. SYMES
BACKGROUND OF THE INVENTION
Field of the Invention This invention relates to an improved method for drying trichloro-s-triazine trione. More specifically, this invention pertains to airstream or gas stream flash drying of trichloro-s-triazine trione'wherein superior process con-trol is achieved together with reduction of undesirable moisture in the finished product.
',' Description of the Prior Art Trichloro-s-triazine trione, sometimes termed tri-chloroisocyanuric acid or trichlorocyanuric acid, is a well known material which is widely employed as a source of avail-able chlorine in sanitizing and bleaching applications. It is used, for example, in various cleaning and bleaching formu-lations and is also a well known substitute for elementalchlorine in swimming pools.
It is known to prepare trichloro-s-triazine trione by several different methods. One typical method is described in U.S. Patent No. 2,969,360, issued January 24, 1~61. In this process, cyanuric acid is fed along with aqueous alkali -(in molar ratio of about one mole of caustic per atom of chlor-ine to be added) and chlorine to an aqueous reaction zone which
- 2 -.
1~48SOl ;
is maintained at a pH in the vicinity of 3.5. The crude trichloro-s-triazine trione precipitates from the solution as a solid slurry. The slurry product is continually or periodically filtered to separate the crystalline products from the mother liquor whereupon the crystalline product is dried.
Prior art processes for producing trichloro-s-tri-azine trione have been beset with numerous difficulties. For example, considerable manufacturing downtime and rate variances have been experienced in the manufacture of trichloro-s-triazine trione because of difficulties in dewatering which result in a slu$hy feed to the dryer. When very wet or slushy product material reaches a conventional dryer such as a vibrating heated pan dryer, it frequently becomes necessary to reduce the pro-duction rate or shut down the unit to avoid packaging wet trichloro-s-triazine trione. Those skilled in the art recognize the undesirability of packaging wet trichloro-s-triazine trione because of the evolution or gassing of chlorine and NC13 within the packaging drum. The latter condition is potentially hazard- -ous and undesirable for other reasons.
It is known to employ fluid bed drying for trichloro-s-triazine trione although certain disadvantages can be encoun-tered with this method. For example, dust generation presents a problem; the fluid bed can collapse when overheated; wet cake mixing with hot, drying material in the bed can produce hazardous NC13 and the large mass of material within the fluid bed dryer can cause difficulties under certain operating conditions.
A phenomenon associated with the drying cycle of trichloro-s-triazine trione is the effect of maximum drying temperature on the eventual density of the dried particles. It 1~485~1 has been observed, for example, that a less dense particle is obtained when the particle temperature during drying exceeds about 130C., as compared to the density of dried particles exposed to lower drying temperatures.
An abrupt absorption of heat into the particle is usually observed when the particle temperature during the dry-ing step is allowed to exceed about 130C.
The phenomenon associated with particle drying temperatures in excess of about 130C. is sometimes referred to as a phase change. The reduced density of the particle obtained after cooling is characterized by expansion of the -lattice in the crystalline structure of the particle.
Although the reduction in physical density is not in itself undesirable, there are certain characteristics of the "phase change" crystals which make those crystals less desirable than the normal crystals for many applications.
For example, there is evidence that the phase change crystals or particles are more difficult to compact into tablets or other solid shapes. Particles which have gone through the phase change are found to exhibit poorer stability in some bleaching formulations. Such particles often exhibit unusual electrostatic properties which contributes to blending problems in subsequent granulation steps. In manufacturing practice, the particle density of trichloro-s-triazine trione is used to determine which phase particle is present, i.e., the normal phase or the high temperature phase.
Two key objectives in the drying of trichloro-s-triazine trione, therefore, are to maintain the particle tem-perature during the drying step at such a level as to avoid the high temperature phase change and to avoid excessive mois-ture in the dried product to obviate the tendency toward storage 1C)48501 drum gassing. Less than about 0.25% by weight moisture in the dried product is usually acceptable for trichloro-s-triazine trione.
Trichloro-s-triazine trione, with its absorption of heat during phase change coupled with latent expansion of ; the crystal lattice ~tructure, is clearly seen to behave dif-ferently from the alkali metal dichloro-s-triazine triones which also are used in sanitizing, bleaching and chlorine-supplying applications. It is well known that the alkali metal dichloro-s-triazine triones, when exposed to a high temperature source, can begin to burn and continue burning after the initial heat source has been removed until all of the material is consumed. Heat i8 naturally given off during ~;~ thiS occurrence. This phenomenon is referred to as self-sustoining and self-propagating decomposition. Because of this ~ ~ diverse behavior between the acid and the salts, provisions for drying the respective materials are subs~antially different and essentially unrelated. Prior art teachings applicable to the handling and drying of alkali metal dichloro-s-triazine triones ;20 are therefore not necessarily valuable in finding improved dry-~; ing methods for trichloro-s-triazine trione The principal object of the present invention, therefore, is to provide a superior method for drying trichloro-s-triazine trione. Another object of this invention is to pro-vide a drying method for trichloro-s-triazine trione which ~-minimizes the tendency to encounter the phase change because of overheating in the particles themselves which eventually alters the crystalline lattice structure. Yet another objeat is to provide a drying process for trichloro-s-triazine trione which permits the feeding of product wet cake (filter cake or centri-fuge cake) directly to the dryer without having previously _ 5 _ '. . : . . . " , . :~`
~6~48501 divided or beaten the wet cake into discrete particles such as in the method disclosed in U. S. Patent No. 3,289,312 is-sued December 6, 1966. Still another object of this invention is to provide an improved method for drying trichloro-s-triazine trione wherein process control characteristics are enhanced and the ability to handle upsets in the process is maximized. Yet another object is to minimize the production of potentially harmful and hazardous wet trichloro-s-triazine trione product.
Still another object is to reduce the dust problems which have been experienced with prior art drying systems for trichloro-s- -triazine trione. Yet another object is to avoid generation of nitrogen trichloride as can occur in a fluid bed dryer or in any drying system wherein trichloro-s-triazine trione wet cake ~;~
is caused to mix with hot dried material. Other objects of the present invention will become apparent from the following description and claims.
SUMMARY OF THE INVENTION
The objects of the present invention are achieved by introducing wet trichloro-s-triazine trione to an airstream or gas stream flash dryer and controlling the temperature of ;~
the trichloro-s-triazine trione particles to avoid high tqmpera- -ture phase change. This is usually accomplished by controlling the particle temperature between about 80C. and about 120C., preferably about 95C. to about 105C. It has been unexpectedly found that the use of airstream flash drying (sometimes called pneumatic conveying-type drying) has overcome many of the dif-ficulties previously experienced in the drying of trichloro-s-triazine triQne.
. , . ., ... , .: : :
1~1148501 DESCRIPTION OF PREFERRED EMBODIMENTS
In practicing the present invention, trichloro-s-triazine trione wet cake or centrifuge cake may be prepared by any of several conventional methods such as hereinbefore described. The wet, solid product is usually separated from the reactiorl medium or slurry and may thereupon be directly - ~ -used in the drying process of this invention. Surprisingly, it has been found unnecessary to employ recycled dried product in cooperation with the wet material for providing a feed to the airstream flash dryer. Thus, wet trichloro-s-triazine trione may be fed directly to the dryer without recycle of dried material, thereby avoiding the prior art hazard of NC13 development.
Control of particle temperature is important to the drying process disclosed herein. Particle temperature in the dryer should be controlled in a manner which minimizes or avoids the occurrence of high temperature phase change. Satisfactory results are generally achieved when the particle temperature in the airstream flash dryer is controlled between about 80C. and about 120C. Superior results have been achieved with particle temperature control between about 95C. and about 105C. which , results in moisture content in the final product between about ~;
0.2~ and 0.25~ by weight. Such moisture levels have been found to be acceptable for most applications of trichloro-s-triazine trione. Excessive drum gassing is usually not encountered with tri-chloro-s-triazine trione product containing moisture levels within that range.
~he time duration for airstream flash drying in the process of this invention varies according to the desired parti-cle temperature which in turn is dependent upon hot air or hot gas temperature in the dryer stream. In pneumatic conveying --. .
16~4850~ :
dryers such as those which are useful for airstream flash dry-ing according to the present process, the heat transfer is by convection from the conveying gas. Moisture is almost instan-taneously removed from wet solid particles by dispersing and conveying them in direct intimate contact with the hot air or hot gas. The characterizing feature of airstream flash drying is the extremely short retention time which can be in the order of
1~48SOl ;
is maintained at a pH in the vicinity of 3.5. The crude trichloro-s-triazine trione precipitates from the solution as a solid slurry. The slurry product is continually or periodically filtered to separate the crystalline products from the mother liquor whereupon the crystalline product is dried.
Prior art processes for producing trichloro-s-tri-azine trione have been beset with numerous difficulties. For example, considerable manufacturing downtime and rate variances have been experienced in the manufacture of trichloro-s-triazine trione because of difficulties in dewatering which result in a slu$hy feed to the dryer. When very wet or slushy product material reaches a conventional dryer such as a vibrating heated pan dryer, it frequently becomes necessary to reduce the pro-duction rate or shut down the unit to avoid packaging wet trichloro-s-triazine trione. Those skilled in the art recognize the undesirability of packaging wet trichloro-s-triazine trione because of the evolution or gassing of chlorine and NC13 within the packaging drum. The latter condition is potentially hazard- -ous and undesirable for other reasons.
It is known to employ fluid bed drying for trichloro-s-triazine trione although certain disadvantages can be encoun-tered with this method. For example, dust generation presents a problem; the fluid bed can collapse when overheated; wet cake mixing with hot, drying material in the bed can produce hazardous NC13 and the large mass of material within the fluid bed dryer can cause difficulties under certain operating conditions.
A phenomenon associated with the drying cycle of trichloro-s-triazine trione is the effect of maximum drying temperature on the eventual density of the dried particles. It 1~485~1 has been observed, for example, that a less dense particle is obtained when the particle temperature during drying exceeds about 130C., as compared to the density of dried particles exposed to lower drying temperatures.
An abrupt absorption of heat into the particle is usually observed when the particle temperature during the dry-ing step is allowed to exceed about 130C.
The phenomenon associated with particle drying temperatures in excess of about 130C. is sometimes referred to as a phase change. The reduced density of the particle obtained after cooling is characterized by expansion of the -lattice in the crystalline structure of the particle.
Although the reduction in physical density is not in itself undesirable, there are certain characteristics of the "phase change" crystals which make those crystals less desirable than the normal crystals for many applications.
For example, there is evidence that the phase change crystals or particles are more difficult to compact into tablets or other solid shapes. Particles which have gone through the phase change are found to exhibit poorer stability in some bleaching formulations. Such particles often exhibit unusual electrostatic properties which contributes to blending problems in subsequent granulation steps. In manufacturing practice, the particle density of trichloro-s-triazine trione is used to determine which phase particle is present, i.e., the normal phase or the high temperature phase.
Two key objectives in the drying of trichloro-s-triazine trione, therefore, are to maintain the particle tem-perature during the drying step at such a level as to avoid the high temperature phase change and to avoid excessive mois-ture in the dried product to obviate the tendency toward storage 1C)48501 drum gassing. Less than about 0.25% by weight moisture in the dried product is usually acceptable for trichloro-s-triazine trione.
Trichloro-s-triazine trione, with its absorption of heat during phase change coupled with latent expansion of ; the crystal lattice ~tructure, is clearly seen to behave dif-ferently from the alkali metal dichloro-s-triazine triones which also are used in sanitizing, bleaching and chlorine-supplying applications. It is well known that the alkali metal dichloro-s-triazine triones, when exposed to a high temperature source, can begin to burn and continue burning after the initial heat source has been removed until all of the material is consumed. Heat i8 naturally given off during ~;~ thiS occurrence. This phenomenon is referred to as self-sustoining and self-propagating decomposition. Because of this ~ ~ diverse behavior between the acid and the salts, provisions for drying the respective materials are subs~antially different and essentially unrelated. Prior art teachings applicable to the handling and drying of alkali metal dichloro-s-triazine triones ;20 are therefore not necessarily valuable in finding improved dry-~; ing methods for trichloro-s-triazine trione The principal object of the present invention, therefore, is to provide a superior method for drying trichloro-s-triazine trione. Another object of this invention is to pro-vide a drying method for trichloro-s-triazine trione which ~-minimizes the tendency to encounter the phase change because of overheating in the particles themselves which eventually alters the crystalline lattice structure. Yet another objeat is to provide a drying process for trichloro-s-triazine trione which permits the feeding of product wet cake (filter cake or centri-fuge cake) directly to the dryer without having previously _ 5 _ '. . : . . . " , . :~`
~6~48501 divided or beaten the wet cake into discrete particles such as in the method disclosed in U. S. Patent No. 3,289,312 is-sued December 6, 1966. Still another object of this invention is to provide an improved method for drying trichloro-s-triazine trione wherein process control characteristics are enhanced and the ability to handle upsets in the process is maximized. Yet another object is to minimize the production of potentially harmful and hazardous wet trichloro-s-triazine trione product.
Still another object is to reduce the dust problems which have been experienced with prior art drying systems for trichloro-s- -triazine trione. Yet another object is to avoid generation of nitrogen trichloride as can occur in a fluid bed dryer or in any drying system wherein trichloro-s-triazine trione wet cake ~;~
is caused to mix with hot dried material. Other objects of the present invention will become apparent from the following description and claims.
SUMMARY OF THE INVENTION
The objects of the present invention are achieved by introducing wet trichloro-s-triazine trione to an airstream or gas stream flash dryer and controlling the temperature of ;~
the trichloro-s-triazine trione particles to avoid high tqmpera- -ture phase change. This is usually accomplished by controlling the particle temperature between about 80C. and about 120C., preferably about 95C. to about 105C. It has been unexpectedly found that the use of airstream flash drying (sometimes called pneumatic conveying-type drying) has overcome many of the dif-ficulties previously experienced in the drying of trichloro-s-triazine triQne.
. , . ., ... , .: : :
1~1148501 DESCRIPTION OF PREFERRED EMBODIMENTS
In practicing the present invention, trichloro-s-triazine trione wet cake or centrifuge cake may be prepared by any of several conventional methods such as hereinbefore described. The wet, solid product is usually separated from the reactiorl medium or slurry and may thereupon be directly - ~ -used in the drying process of this invention. Surprisingly, it has been found unnecessary to employ recycled dried product in cooperation with the wet material for providing a feed to the airstream flash dryer. Thus, wet trichloro-s-triazine trione may be fed directly to the dryer without recycle of dried material, thereby avoiding the prior art hazard of NC13 development.
Control of particle temperature is important to the drying process disclosed herein. Particle temperature in the dryer should be controlled in a manner which minimizes or avoids the occurrence of high temperature phase change. Satisfactory results are generally achieved when the particle temperature in the airstream flash dryer is controlled between about 80C. and about 120C. Superior results have been achieved with particle temperature control between about 95C. and about 105C. which , results in moisture content in the final product between about ~;
0.2~ and 0.25~ by weight. Such moisture levels have been found to be acceptable for most applications of trichloro-s-triazine trione. Excessive drum gassing is usually not encountered with tri-chloro-s-triazine trione product containing moisture levels within that range.
~he time duration for airstream flash drying in the process of this invention varies according to the desired parti-cle temperature which in turn is dependent upon hot air or hot gas temperature in the dryer stream. In pneumatic conveying --. .
16~4850~ :
dryers such as those which are useful for airstream flash dry-ing according to the present process, the heat transfer is by convection from the conveying gas. Moisture is almost instan-taneously removed from wet solid particles by dispersing and conveying them in direct intimate contact with the hot air or hot gas. The characterizing feature of airstream flash drying is the extremely short retention time which can be in the order of
3 to 10 seconds, sometimes even a fraction of 1 second.
With a free-flowing material and primarily surface moisture only, the dryer frequently assumes the form of an air-conveying system using heate~ gas the conveying medium.
There are four fundamental factors which govern evaporation in a short retention time convection dryer (air-stream flash dryer) where the heat is supplied and the moisture transported by air or gases. These factors are moisture dis-persion, temperature differential, particle size and agitation.
Such factors are described in detail and typical airstream flash dryers are illustrated on pages 242 through 251 of the ENCYCLOPEDIA OF CHEMICAL PROCESS EQUIPMENT, by William J. Mead, Reinhold Publishing Corporation, New York, New York (1964).
In carrying out the method whereby wet trichloro-s-triazine trione is flash dried, air is the preferred contacting medium although other drying gases may also be utilized to achieve the same result. In this regard, the contact of gas and solid may be carried out using any of the drying apparatus known to those skilled in the art which permits intimate con-tact of the product particles with the gas for the required time duration.
The typical particle temperature range r~cited herein for airstream flash drying of wet trichloro-s-triazine trione was established because at particle temperatures in the vicinity ~ 43-4262A
, ~048501 of 130C., phase change coupled with crystalline lattice ex-pansion upon cooling can occur which results in a reduction in particle density. Similarly, at particle temperatures below about 80C., an undesirable increase Ln product moisture . .
is usually encountered which, as described above, can lead to evolution of chlorine and NC13 (gassing) within the storage drums.
further understanding of the drying method of the present invention will be derived from the following Exam-ples which are intended to illustrate the invention but notto limit the scope thereof, parts and percentages being by weight unless otherwise specified.
ExA~LE 1 '.', ..
This Example illustrates a convenient method for r ~, ~; preparing trichloro-s-triazine trione. Although conducted on a laboratory scale, this process scheme is adaptable to con-; tinuous manufacturing operations. A feed solution was prepared by mixing a cyanuric acid slurry with sodium hydroxide to pro-~; duce a solution containing 7.6~ cyanuric acid with a mole ratio of sodium hydroxide to cyanuric acid of 3.2:1. The chlorina-tion reaction was provided for by a jacketed 1.4 liter glass reactor equipped with a stirrer, side arm for product overflow, subsurface feed tube and a fritted glass sparger. Starting with water in the reactor, feed solution is introduced through the feed tube at about 40 ml./min. and chlorine is introduced through the sparger at about 5.5 grams/min. ~he pH was con-trolled in the range of 3.5 to 3.8 by adjusting the chlorin~
feed rate and reaction temperature was controlled between 22C.
and 27C. by circulating ice water through the reactor jacket.
_ g _ :- . .
. ' . , ~ .
., . ' ' ~
'' , 1~485~
The product slurry, which overflows the side arm, i8 filtered to separate the wet crystalline product from the mother liquor. ;
Preliminary drying of the crystals to be flash dried was achieved by filtering on a fritted glass filter on a suction ;
flask. The wet cake of trichloro-s-triazine trione thus pre-pared contained 8 percent moisture and when airdried had an air pycnometer density of 2.08 grams/ml. as measured by an air pycnometer.
This Example illustrates the direct conversion;by airstream flash drying of wet trichloro-s-triazine trione to -~
a final product form containing less than 0.25% moisture. A
full scale flash dryer of a design similar to that described in the ENCYCLOPED~A OF CHEMICAL PROCESS EQUIPMENT was utilized in conjunction with a continuous manufacturing process adapted from the exemplary product preparation set forth in Example 1.
The flash dryer was started up maintaining a vent temperature of 145C. Centrifuged cake comprising wet trichloro-s-triazine trione from the continuous manufacturing process was fed directly to the dryer with no recycle of dried material. After startup - -of the airstream flash dryer the particle temperature and vent air (exit air) temperature of the dryer were gradually lowered until a maximum product density was reached with a product moisture of less than 0.25~. Density measurements were ob-tained with a conventional air pycnometer. Samples were taken from the discharge of the airstream flash dryer cyclone for moisture and density measurement after each change in dryer temperatures. This provided data relating product temperature, product moisture and stability. The product temperature was allowed to drop slightly below the optimum to determine the i -- 10 --~0485¢1 ~ -necessary control ranges and the moisture loss through the airveying and compaction system. Several natural upsets oc-curred during this process which demonstrated the system's ability to handle surges in feed flow rate and moisture con-tent. Samples also were taken from the mill discharge and finished product at each dryer temperature to determine any effect of dryer conditions and product stability on the product cut obtained through compaction and screening efficiencies.
Particle temperature was conveniently controlled in the airstream flash dryer by adjusting the burner tempera-ture. Particle temperature was measured in the dump gate at the discharge of the dryer cyclone. A direct relation-ship was found between particle temperature and product mois-ture in the final trichloro-s-triazine trione product. In a preferred embodiment of the present invention, a control range of about 100C. to 105C. in particle temperature afforded a desirable moisture level in the final product between 0.2 and 0.25%. It was surprisingly found that such careful control of particle temperature will preclude the production of "wet"
material. If the specified particle drying temperatures are maintained, the trichloro-s-triazine trione product will be dried regardless of upset in the feed. In at least one instance the wet cake feed to the flash dryer became so wet that a por-tion was not airveyed but instead collected at the bottom of the dryer which resulted in a plugging condition that had to be washed out. Notwithstanding the occurrence of this process-ing upset, no wet material was produced from the flash dryer during that time. No difficulties were encountered in feeding the centrifuged cake from the manufacturing process directly to the dryer. This condition prevailed even ~hough previously : ' .
. , ~'~ 43-4262A
1~48SOl `~
dried material was not recycled to the dryex intake. This unexpected advantage was surprising in view of prior art difficulties encountered with attempts to process centrifuged cake or filtered cake directly to a drying apparatus. The dryer exhaust temperature necessary to maintained the particle temperature necessary to maintain the particle temperature in the range of 100C. to 105C. was 135C. to 140C. Inlet temperature~ to the dryer were normally 220C. to 240C. de-pending on rate and feed moisture content. Depending upon the process equipment upstream of the dryer, significant variations can be expected in the inlet temperature control ranges.
A relationship was found which relates particle density values readable by air pycnometer at the airstream dryer discharge to phase change. Thus, it was observed that ;
those particles having a pycnometer reading of about 2.02 grams per milliliter or higher as they exit from the dryer, will exhibit on aging (eg., for 24 hours) the same density as parti- -cles which were air dried at room temperature. Such particles have obviously not undergone phase change, In contrast, however, ~ . -particles which undergo phase change because of excessive drying temperatures usually exhibit pycnometer values of about 1.9 s grams/ml. at the dryer discharge and, upon aging, never exceed about 2.00 grams/ml. pycnometer density values. -While this invention has been described with respect to cpecific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.
With a free-flowing material and primarily surface moisture only, the dryer frequently assumes the form of an air-conveying system using heate~ gas the conveying medium.
There are four fundamental factors which govern evaporation in a short retention time convection dryer (air-stream flash dryer) where the heat is supplied and the moisture transported by air or gases. These factors are moisture dis-persion, temperature differential, particle size and agitation.
Such factors are described in detail and typical airstream flash dryers are illustrated on pages 242 through 251 of the ENCYCLOPEDIA OF CHEMICAL PROCESS EQUIPMENT, by William J. Mead, Reinhold Publishing Corporation, New York, New York (1964).
In carrying out the method whereby wet trichloro-s-triazine trione is flash dried, air is the preferred contacting medium although other drying gases may also be utilized to achieve the same result. In this regard, the contact of gas and solid may be carried out using any of the drying apparatus known to those skilled in the art which permits intimate con-tact of the product particles with the gas for the required time duration.
The typical particle temperature range r~cited herein for airstream flash drying of wet trichloro-s-triazine trione was established because at particle temperatures in the vicinity ~ 43-4262A
, ~048501 of 130C., phase change coupled with crystalline lattice ex-pansion upon cooling can occur which results in a reduction in particle density. Similarly, at particle temperatures below about 80C., an undesirable increase Ln product moisture . .
is usually encountered which, as described above, can lead to evolution of chlorine and NC13 (gassing) within the storage drums.
further understanding of the drying method of the present invention will be derived from the following Exam-ples which are intended to illustrate the invention but notto limit the scope thereof, parts and percentages being by weight unless otherwise specified.
ExA~LE 1 '.', ..
This Example illustrates a convenient method for r ~, ~; preparing trichloro-s-triazine trione. Although conducted on a laboratory scale, this process scheme is adaptable to con-; tinuous manufacturing operations. A feed solution was prepared by mixing a cyanuric acid slurry with sodium hydroxide to pro-~; duce a solution containing 7.6~ cyanuric acid with a mole ratio of sodium hydroxide to cyanuric acid of 3.2:1. The chlorina-tion reaction was provided for by a jacketed 1.4 liter glass reactor equipped with a stirrer, side arm for product overflow, subsurface feed tube and a fritted glass sparger. Starting with water in the reactor, feed solution is introduced through the feed tube at about 40 ml./min. and chlorine is introduced through the sparger at about 5.5 grams/min. ~he pH was con-trolled in the range of 3.5 to 3.8 by adjusting the chlorin~
feed rate and reaction temperature was controlled between 22C.
and 27C. by circulating ice water through the reactor jacket.
_ g _ :- . .
. ' . , ~ .
., . ' ' ~
'' , 1~485~
The product slurry, which overflows the side arm, i8 filtered to separate the wet crystalline product from the mother liquor. ;
Preliminary drying of the crystals to be flash dried was achieved by filtering on a fritted glass filter on a suction ;
flask. The wet cake of trichloro-s-triazine trione thus pre-pared contained 8 percent moisture and when airdried had an air pycnometer density of 2.08 grams/ml. as measured by an air pycnometer.
This Example illustrates the direct conversion;by airstream flash drying of wet trichloro-s-triazine trione to -~
a final product form containing less than 0.25% moisture. A
full scale flash dryer of a design similar to that described in the ENCYCLOPED~A OF CHEMICAL PROCESS EQUIPMENT was utilized in conjunction with a continuous manufacturing process adapted from the exemplary product preparation set forth in Example 1.
The flash dryer was started up maintaining a vent temperature of 145C. Centrifuged cake comprising wet trichloro-s-triazine trione from the continuous manufacturing process was fed directly to the dryer with no recycle of dried material. After startup - -of the airstream flash dryer the particle temperature and vent air (exit air) temperature of the dryer were gradually lowered until a maximum product density was reached with a product moisture of less than 0.25~. Density measurements were ob-tained with a conventional air pycnometer. Samples were taken from the discharge of the airstream flash dryer cyclone for moisture and density measurement after each change in dryer temperatures. This provided data relating product temperature, product moisture and stability. The product temperature was allowed to drop slightly below the optimum to determine the i -- 10 --~0485¢1 ~ -necessary control ranges and the moisture loss through the airveying and compaction system. Several natural upsets oc-curred during this process which demonstrated the system's ability to handle surges in feed flow rate and moisture con-tent. Samples also were taken from the mill discharge and finished product at each dryer temperature to determine any effect of dryer conditions and product stability on the product cut obtained through compaction and screening efficiencies.
Particle temperature was conveniently controlled in the airstream flash dryer by adjusting the burner tempera-ture. Particle temperature was measured in the dump gate at the discharge of the dryer cyclone. A direct relation-ship was found between particle temperature and product mois-ture in the final trichloro-s-triazine trione product. In a preferred embodiment of the present invention, a control range of about 100C. to 105C. in particle temperature afforded a desirable moisture level in the final product between 0.2 and 0.25%. It was surprisingly found that such careful control of particle temperature will preclude the production of "wet"
material. If the specified particle drying temperatures are maintained, the trichloro-s-triazine trione product will be dried regardless of upset in the feed. In at least one instance the wet cake feed to the flash dryer became so wet that a por-tion was not airveyed but instead collected at the bottom of the dryer which resulted in a plugging condition that had to be washed out. Notwithstanding the occurrence of this process-ing upset, no wet material was produced from the flash dryer during that time. No difficulties were encountered in feeding the centrifuged cake from the manufacturing process directly to the dryer. This condition prevailed even ~hough previously : ' .
. , ~'~ 43-4262A
1~48SOl `~
dried material was not recycled to the dryex intake. This unexpected advantage was surprising in view of prior art difficulties encountered with attempts to process centrifuged cake or filtered cake directly to a drying apparatus. The dryer exhaust temperature necessary to maintained the particle temperature necessary to maintain the particle temperature in the range of 100C. to 105C. was 135C. to 140C. Inlet temperature~ to the dryer were normally 220C. to 240C. de-pending on rate and feed moisture content. Depending upon the process equipment upstream of the dryer, significant variations can be expected in the inlet temperature control ranges.
A relationship was found which relates particle density values readable by air pycnometer at the airstream dryer discharge to phase change. Thus, it was observed that ;
those particles having a pycnometer reading of about 2.02 grams per milliliter or higher as they exit from the dryer, will exhibit on aging (eg., for 24 hours) the same density as parti- -cles which were air dried at room temperature. Such particles have obviously not undergone phase change, In contrast, however, ~ . -particles which undergo phase change because of excessive drying temperatures usually exhibit pycnometer values of about 1.9 s grams/ml. at the dryer discharge and, upon aging, never exceed about 2.00 grams/ml. pycnometer density values. -While this invention has been described with respect to cpecific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.
Claims (5)
1. A method for drying wet trichloro-s-triazine trione particles which comprises introducing said particles to a pneumatic conveying dryer and controlling the particle temperature between about 80°C and about 120°C.
2. A method of claim 1 wherein the particle temperature is controlled between about 95°C and about 105°C.
3. A method for drying trichloro-s-triazine trione wet cake which comprises introducing said wet cake directly to a pneumatic conveying dryer without mechanically dividing or beating said wet cake within the drying zone, and con-trolling the temperature of wet cake particles between about 80°C and about 120°C.
4. A method of claim 1 wherein the dried trichloro-s-triazine trione has a moisture content not greater than about 0.25 percent by weight.
5. A method of claim 1 wherein the density of the freshly dried product at the dryer discharge is about 2.02 grams/ml. or greater and the density after aging for at least 24 hours approaches about 2.08 grams/ml.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US62944875A | 1975-11-06 | 1975-11-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1048501A true CA1048501A (en) | 1979-02-13 |
Family
ID=24523038
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA76265409A Expired CA1048501A (en) | 1975-11-06 | 1976-11-05 | Airstream flash drying of trichloro-s-triazine trione |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5259177A (en) |
| BE (1) | BE848059A (en) |
| CA (1) | CA1048501A (en) |
| DE (1) | DE2650744A1 (en) |
| ES (1) | ES453028A1 (en) |
| FR (1) | FR2330684A1 (en) |
| GB (1) | GB1503869A (en) |
| IT (1) | IT1063648B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP7151778B2 (en) * | 2018-10-09 | 2022-10-12 | 三菱ケミカル株式会社 | Method for purifying (meth)acrylic acid |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3289312A (en) * | 1964-03-17 | 1966-12-06 | Fmc Corp | Drying of chlorinated isocyanurates and salts thereof |
-
1976
- 1976-11-05 FR FR7633528A patent/FR2330684A1/en active Granted
- 1976-11-05 ES ES453028A patent/ES453028A1/en not_active Expired
- 1976-11-05 IT IT2908976A patent/IT1063648B/en active
- 1976-11-05 BE BE172137A patent/BE848059A/en not_active IP Right Cessation
- 1976-11-05 GB GB4611076A patent/GB1503869A/en not_active Expired
- 1976-11-05 DE DE19762650744 patent/DE2650744A1/en not_active Ceased
- 1976-11-05 JP JP13251176A patent/JPS5259177A/en active Granted
- 1976-11-05 CA CA76265409A patent/CA1048501A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS616827B2 (en) | 1986-03-01 |
| FR2330684B1 (en) | 1979-08-17 |
| ES453028A1 (en) | 1977-11-01 |
| IT1063648B (en) | 1985-02-11 |
| GB1503869A (en) | 1978-03-15 |
| JPS5259177A (en) | 1977-05-16 |
| DE2650744A1 (en) | 1977-05-12 |
| FR2330684A1 (en) | 1977-06-03 |
| BE848059A (en) | 1977-05-05 |
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