CA2188721C - Process for metathesis - Google Patents
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Abstract
A slurry of sodium acid sulfate crystals generally from a chlorine dioxide generating process, is metathesized on no more than one drum filter. The crystals are fed to a first filtration zone on the filter wherein the crystals are separated from the slurry. The crystals are contacted with an aqueous metathesizing medium to effect solid phase conversion of the sodium acid sulfate crystals to neutral sodium sulfate crystals.
The resulting slurry is fed to a second filtration zone on the drum filter element separate from the first filtration zone, wherein the neutral sodium sulfate crystals are separated from the acidic medium formed in the metathesis step. The employment of a single dual service drum filter provides a simplification and cost reduction compared to conventional procedures and to also a minimization or elimination of the impact imposed by the additional evaporative load on the chlorine dioxide generator.
The resulting slurry is fed to a second filtration zone on the drum filter element separate from the first filtration zone, wherein the neutral sodium sulfate crystals are separated from the acidic medium formed in the metathesis step. The employment of a single dual service drum filter provides a simplification and cost reduction compared to conventional procedures and to also a minimization or elimination of the impact imposed by the additional evaporative load on the chlorine dioxide generator.
Description
TITLE OF INVENTION
IMPROVED PROCESS FOR METATHESIS
FIELD OF INVENTION
The present invention relates to the metathesis of acidic by-products from the production of chlorine dioxide.
BACKGROUND TO THE INVENTION
In U.S. Patent No. 5,205,995, assigned to the assignee hereof, there is described the metathesis of by-product sodium sesquisulfate from a chlorine dioxide generation process to recover acid values therefrom while not significantly increasing the evaporative load on the chlorine dioxide generator when the recovered acid values are recycled to the chlorine dioxide generator.
One of the metathesizing agents described as being employed in the process is water but, in order to minimize water usage and resulting evaporative load on the generator, it is necessary to employ, as seen in Figure 3 of that patent, two filters, which may be rotary drum filters, a mixing tank and to recycle part of the resulting acidic solution to the first filter.
In the recently issued U.S. Patent no. 5,399,332, assigned to the assignee hereof, a simplification of the metathesis procedure of USP 5,205,995 is described in which a dynamic leaching apparatus is employed. The leaching process preferably is carried out by conveying a bed of solid crystalline sodium sesquisulfate on a horizontal vacuum filter belt and spraying water onto the bed at a plurality of longitudinally-adjacent locations along the length of the conveyor.
Since the dynamic leaching procedure of USP
5,399,332 requires quite different equipment than that utilized in the process described in USP 5,205,995, it 2 ? ~ 8~7~1 cannot be easily retrofitted into the existing installations, without incurring substantial capital expenditures. There is a need, therefore, for a simplified metathesizing procedure which can be readily employed in existing operations without the necessity of effecting significant and costly modifications.
SUMMARY OF INVENTION
In the present invention, the prior metathesis procedure, as described in USP 5,205,995, is much simplified and a single filter unit of specific design is employed in place of the equipment described in USP
5,205,995. This simplification of equipment results in a lower installation cost for the metathesis process, improved operating cost and lower maintenance requirements. In addition, this improvement to the prior art processes offers an opportunity to further minimize or eliminate the impact imposed by the additional evaporative load.
In accordance with the broadest aspect of the present invention, there is provided a metathesis process for converting sodium sesquisulfate to neutral sodium sulphate using an aqueous metathesizing medium with the recovery of acid values from the sodium sesquisulfate using no more than one filtration device, preferably a single filter. The ability to effect the metathesis process employing no more than a single filtration device distinguishes the present invention from prior art processes, which utilize at least two filtration devices.
In one aspect of the present invention, there is provided a process for the conversion of sodium sesquisulfate, particularly produced in a chlorine dioxide generation operation, to neutral anhydrous sodium sulfate which employs a single dual service drum filter.
In accordance with this aspect of the present invention, there is provided a method of metathesizing a slurry of sodium acid sulfate crystals in an aqueous medium, which comprises:
IMPROVED PROCESS FOR METATHESIS
FIELD OF INVENTION
The present invention relates to the metathesis of acidic by-products from the production of chlorine dioxide.
BACKGROUND TO THE INVENTION
In U.S. Patent No. 5,205,995, assigned to the assignee hereof, there is described the metathesis of by-product sodium sesquisulfate from a chlorine dioxide generation process to recover acid values therefrom while not significantly increasing the evaporative load on the chlorine dioxide generator when the recovered acid values are recycled to the chlorine dioxide generator.
One of the metathesizing agents described as being employed in the process is water but, in order to minimize water usage and resulting evaporative load on the generator, it is necessary to employ, as seen in Figure 3 of that patent, two filters, which may be rotary drum filters, a mixing tank and to recycle part of the resulting acidic solution to the first filter.
In the recently issued U.S. Patent no. 5,399,332, assigned to the assignee hereof, a simplification of the metathesis procedure of USP 5,205,995 is described in which a dynamic leaching apparatus is employed. The leaching process preferably is carried out by conveying a bed of solid crystalline sodium sesquisulfate on a horizontal vacuum filter belt and spraying water onto the bed at a plurality of longitudinally-adjacent locations along the length of the conveyor.
Since the dynamic leaching procedure of USP
5,399,332 requires quite different equipment than that utilized in the process described in USP 5,205,995, it 2 ? ~ 8~7~1 cannot be easily retrofitted into the existing installations, without incurring substantial capital expenditures. There is a need, therefore, for a simplified metathesizing procedure which can be readily employed in existing operations without the necessity of effecting significant and costly modifications.
SUMMARY OF INVENTION
In the present invention, the prior metathesis procedure, as described in USP 5,205,995, is much simplified and a single filter unit of specific design is employed in place of the equipment described in USP
5,205,995. This simplification of equipment results in a lower installation cost for the metathesis process, improved operating cost and lower maintenance requirements. In addition, this improvement to the prior art processes offers an opportunity to further minimize or eliminate the impact imposed by the additional evaporative load.
In accordance with the broadest aspect of the present invention, there is provided a metathesis process for converting sodium sesquisulfate to neutral sodium sulphate using an aqueous metathesizing medium with the recovery of acid values from the sodium sesquisulfate using no more than one filtration device, preferably a single filter. The ability to effect the metathesis process employing no more than a single filtration device distinguishes the present invention from prior art processes, which utilize at least two filtration devices.
In one aspect of the present invention, there is provided a process for the conversion of sodium sesquisulfate, particularly produced in a chlorine dioxide generation operation, to neutral anhydrous sodium sulfate which employs a single dual service drum filter.
In accordance with this aspect of the present invention, there is provided a method of metathesizing a slurry of sodium acid sulfate crystals in an aqueous medium, which comprises:
3 2T~~1~~
feeding the slurry of sodium acid sulfate crystals to a first filtration zone on a drum filter element, separating sodium acid sulfate crystals from the slurry in the first filtration zone, removing the separated sodium acid sulfate crystals from the first filtration zone, contacting the removed sodium acid sulfate crystals with a metathesizing medium to effect a solid phase conversion of the sodium acid sulfate crystals to neutral sodium sulfate crystals and to form a second slurry of the neutral sodium sulfate crystals in an acidic medium, feeding the second slurry to a second filtration zone on the drum filter element separate from the first filtration zone, separating neutral sodium sulfate crystals from the acidic medium in the second filtration zone, recovering the separated acidic medium, and removing the neutral sodium sulfate crystals from the second filtration zone.
The slurry of sodium acid sulfate may comprise a slurry of sodium sesquisulfate formed in a chlorine dioxide generating process wherein the aqueous medium is entrained chlorine dioxide generator liquor. Aqueous medium separated from the sodium sesquisulfate crystals in the first filtration zone is returned to the chlorine dioxide generator, and the recovered acidic medium is recycled to the chlorine dioxide generator.
In another aspect of the invention, there is provided a process for the conversion of sodium sesquisulfate, particularly produced in a chlorine dioxide generation operation, to neutral anhydrous sodium sulfate which employes a drum filter having a contacting device integral therewith wherein at least partial metathesis is effected.
In this aspect of the invention, the metathesis operation is effected by:
contacting said slurry in said integral contacting device with a metathesizing medium to effect solid phase conversion of said sodium acid sulfate crystals at least partially to neutral sodium sulfate crystals and to form a second slurry contacting said neutral sodium sulfate crystals and in an acidic medium, feeding said second slurry to a filtration zone on said single filtration drum, separating neutral sodium sulfate crystals from said acidic medium in said second filtration zone, recovering said separated acidic medium, and removing said neutral sodium sulfate crystals from said second filtration zone.
GENERAL DESCRIPTION OF INVENTION
In one embodiment of the metathesizing procedure of the present invention, the slurry containing sodium sesquisulfate crystals from the chlorine dioxide generator is first fed to a dual service rotary drum filter through a top feed arrangement, whereby the slurry containing sodium sesquisulfate crystals is deposited onto an acidic cake sector of the rotary drum filter to effect filtration thereof substantially free from entrained generator liquor while the filtrate is recycled to the chlorine dioxide generator.
After being removed from the acidic cake sector of the rotary drum filter, the sodium sesquisulfate crystals are mixed with the metathesizing medium of the type described in USP 5,205,995, such as, for example, water, to effect metathesis of the sodium sesquisulfate crystals to neutral sodium sulfate in crystalline form and formation of an acidic slurry. The resulting acidic slurry containing neutral sodium sulfate crystals, is fed through a bottom feed arrangement to the dual service rotary drum filter whereupon neutral cake is deposited in the neutral cake sector of the filter.
In another embodiment of the invention, the slurry from the chlorine dioxide generator containing sodium sesquisulfate crystals is fed through a bottom feed arrangement while the acidic slurry containing neutral ?~~~7~1 saltcake is introduced through the top feed arrangement to a single dual service rotary drum filter.
In yet another embodiment of the invention, the slurry from the chlorine dioxide generator is fed through 5 a bottom feed arrangement depositing the sodium sesquisulfate on the filter cloth. On partial or full liquor displacement and washing completion, the cake continues upward on the drum passing into an integral contacting chamber where metathesis occurs by a dynamic leaching action similar to that described in the previously cited USP 5,399,332. This contacting chamber can employ water sprays and/or steam jet to complete the metathesis reaction. As the cake continues on the rotating drum and exits this integral contacting chamber it then continues to a removal device where it is mechanically and/or hydraulically separated from the drum surf ace .
The only modification required to be made to existing equipment to effect the improved operation of the present invention is the installation of the second (bottom) feed assembly, which may act fully or partially as the metathesizing zone, onto the existing conventional drum filter employed to separate the sodium sesquisulfate crystals from entrained reaction medium.
The modification effected herein is not only simple and inexpensive but permits a previously unused area of the rotary drum filter to be used to perform the secondary service of separating the neutral saltcake. In this way, the whole available area of the rotary drum filter surface is usefully employed. The bottom feed assembly promotes the displacement of the filtrate at the filter cloth and allows the saltcake to be carried upward on the filter cloth for doctor blade removal.
In another embodiment of the present invention, both acid and neutral saltcake filtration is performed in parallel on substantially laterally contiguous regions of a single rotary drum filter. In this embodiment, the filter is designed to accept separate streams, which may ~~~~1~~
be pre-concentrated in solids by a peripheral pre-concentration device, then through separate feed assemblies. The filter also is designed to segregate the filtered cakes after liquor displacement and washing. A
physical separation of the cakes may be employed, although this is not necessary. If physical separation during filter cake formation is not employed, the segregation of the cakes using a cake splitting device can be designed or controlled to accept a small portion of neutral saltcake to reduce the importance of a complex physical separation design.
In addition to the simplification of the filtration unit, the present invention provides an optional, novel procedure for reduction or elimination of the additional evaporative load on the chlorine dioxide generator resulting from recycle of the recovered acid liquor to the generator. This improvement can be achieved by treating the filtrate or lean liquors returned from preconcentration steps, to induce evaporation or water vapour removal from these streams. The heat source may be hot water, steam or any other suitable heating medium.
One approach to such procedure utilizes a heated jacketed flash/separator tank to induce the extraction of water vapour. Another approach to such procedure utilizes a heat exchange device, of a simple design, which may be a concentric pipe or any other suitable heat exchanger configuration to effect the required heat exchange.
An alternative approach to water vapour removal is to provide a separate evaporation zone maintained under partial vacuum, within the metathesis reactor, to induce the extraction of water vapour. The evaporation zone may comprise a separate chamber, if desired. This evaporation zone can also serve to effect a preconcentration step for the acid liquor, prior to filtration to remove neutral sodium sulfate, if necessary.
In another embodiment of the present invention, the slurry from the chlorine dioxide generator is pre-1 ~~~~~
concentrated in solids by a peripheral preconcentration device then passes into a contacting chamber, integral with a single rotary drum filter, wherein metathesis occurs by a dynamic leaching action similar to that described in 5,399,332, assigned to the assignee hereof, or through a co-current or countercurrent mixing with metathesis agents, as described in USP 5,116,595, assigned to the assignee hereof, or other suitable procedure.
The contacting chamber can employ water sprays and/or steam jets to complete the metathesis. The contacting chamber may be a specific device which may cause liquor displacement through hydraulic action imparted by mechanical means and/or by the force of gravity, should the device present an inclined path to the feeding region of the rotary drum filter.
The modification effected herein is not only simple and inexpensive but may also permit the combination of previously two unit operations into one device integral with a rotary drum filter.
The metathesis process of the present invention enables there to be effected a very efficient conversion of sodium sesquisulfate to a neutral sodium sulfate whereby the co-produced aqueous acid-containing medium reaches the total acid normality of up to about 6.5 normal.
The metathesis process generally is carried out using water at a temperature of about 40oC to about 100oC, preferably about 65oC to about 95oG. At these metathesis temperatures, the neutral sodium sulfate is recovered in an anhydrous form. Alternatively to water, other aqueous metathesizing media, such as those disclosed in U.S. Patent No. 5,205,995, namely aqueous sodium chlorate solution, aqueous sodium chloride solution, aqueous methanol and chlorine dioxide generator condensate, can be employed in the process.
8 ~ ~ ~~~21 BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic representation of a metathesis operation employing a dual service drum filter in accordance with one embodiment of the invention;
Figure 2 is a schematic perspective representation of a dual service drum filter equipped with both top feed box and a lower feed box assembly for use in the procedure of Figure 1;
Figure 3 is a schematic representation of a metathesis operation employing a divided drum filter in accordance with another embodiment of the invention;
Figure 4 is a schematic perspective representation of a portion of a divided drum filter for use in the procedure of Figure 3, and Figure 5 is a schematic representation of a metathesis operation in employing a drum filter in accordance with a further embodiment of the invention.
DESCRIPTION OF THE PREFERRED EN~ODINIENTS
Referring first to Figures 1 and 2, there is illustrated therein an embodiment of a chlorine dioxide generating unit 1 in accordance with the invention. The chlorine dioxide generating unit may be one in which chlorine dioxide is produced from an aqueous acid reaction medium having a total acid normality of about 4N
and higher, in which sodium chlorate, sulfuric acid and a reducing agent, such as methanol or hydrogen peroxide, react together while the reaction medium is maintained at its boiling point under a subatmospheric pressure applied to the chlorine dioxide generating unit 1.
Chlorine dioxide and steam are removed from the chlorine dioxide generating unit 1 and a by-product sodium acid sulfate is precipitated therein, which may be sodium sesquisulfate or sodium bisulfate, depending on the total acid normality of the reaction medium. Since the most common form of the sodium acid sulfate encountered in commercial operations is sodium sesquisulfate, the illustrated embodiments will be described further with respect thereto.
?1~~~?i Crystalline sodium sesquisulfate precipitated from the reaction medium is removed in slurry form by line 2 to a rotary drum filter 20. In the illustrated embodiment, a preconcentration device 4, which can be a cyclone type or any other suitable device, is employed to enrich the solids volume of the slurry and removing a portion of the entrained chlorine dioxide generating reaction medium, before directing the preconcentrated stream to a top feed box assembly 5 located adjacent an upper region of the rotary drum 22. When a preconcentration device 4 is used, the resulting liquid stream 3, lean in solids, generally is returned to the chlorine dioxide generating unit 1.
The crystalline sodium sesquisulfate is removed from the preconcentrated slurry by deposition on sector or filtration zone 6 and draining of entrained reaction medium through the filter cloth. The crystalline sodium sesquisulfate is conducted over a solid material removal device (not shown), which can be a blade type or hydraulically assisted arrangement, to remove the crystalline sodium sesquisulfate from the filter cloth.
Wash water or steam can be used to assist in separation of the crystalline material from entrained reaction medium on the filter cloth in sector 6.
The recovered sodium sesquisulfate is then channelled through a conveying duct 14 and introduced into a sealed inlet arrangement 16 of the metathesis device 17 or devices, wherein metathesis of the crystalline sodium sesquisulfate is performed using water as the metathesizing sodium converting solid phase sodium sesquisulfate into solid phase neutral sodium sulfate and forming an acid medium, which may have an acid normality of up to about 6.5N. In general, the weight ratio of water to sodium sesquisulfate in the metathesis step is less than about 0.6:1, preferably about 0.4:1 to about 0.6:1. The slurry resulting from the metathesis step is forwarded by line 15 to a second filter feed assembly 9 located adjacent a lower region of the rotary drum 22 of ~i~87~
the filter. A preconcentration step may be provided prior to feed to the feed assembly 9. The second filter feed assembly 9 allows displacement of the acid medium from the neutral sodium sulfate, deposition of the crystalline neutral sodium sulfate on the drum sector or filtration zone 7. It may be desirable to collect the liquid which is lean in solids within the feed assembly 9 or the optional preconcentration device and conduct such liquid through line 13 to the metathesis devices) 17 or to chlorine dioxide generating unit 1.
Alternatively, feed assembly 9 can be designed to effect partially or fully the metathesis reaction, thereby further simplifying the process. Optionally, an integral feed device which effects fully or partially the metathesis process can be employed for this purpose.
Such device may be of the type of, for example, an agitated chamber, paddle type mixer or any other integral solid/liquid contacting device.
The solid neutral sodium sulfate conveyed on the surface of the filter cloth in section 7 is conducted over a solid material removal device 24, which can be a doctor blade type or hydraulically assisted arrangement.
Wash water or steam can be used to assist in separation of the crystalline material from the entrained acid medium. The crystalline neutral sodium sulfate material is then channelled through a conveying duct 10 and introduced into the dissolving device 11 to prepare a solution product in stream 12. Such solution then may be further processed or disposed of. Alternatively, device 11 may be a solids conveying device in the event that wet solid material is required.
The solids separation on drum sectors 6 and 7 may be assisted by vacuum conditions within the filtrate side of the drum 22 and the common filtrates are collected and may be returned to the chlorine dioxide generating unit 1 through line 8.
Referring now to Figures 3 and 4, there is illustrated thereon a second embodiment of a chlorine 11 ~ ~ ~ ~ ~2 dioxide generating unit 1 in accordance with the invention. Elements of the arrangements which are in common with Figures 1 and 2 have been designated by the same numerals. As seen therein, crystalline sodium sesquisulfate is precipitated from the reaction medium and is removed in slurry form by line 2 and passed to the filter 20. A preconcentration device 4, which may be a cyclone type or any other suitable device, may be provided to enrich the solids before directing this stream to one side of a divided feed box assembly 5.
When a preconcentration device is used, stream 3 lean in solids generally is returned to the chlorine dioxide generating unit 1.
The crystalline sodium sesquisulfate is removed from the preconcentrated slurry, thereby extracting the spent reaction liquid filtrate, by deposition to one side of the drum in sector or filtration zone 6. The crystalline sodium sesquisulfate is conducted over a solid material removal device (not shown), which can be a blade type of hydraulically assisted arrangement, to remove the crystalline sodium sesquisulfate from the filter cloth.
wash water or steam can be used to assist in separation of the crystalline material from entrained reaction medium on the filter section 6.
The recovered solid material is then channelled through one side 14 of a divided conveying duct and introduced into the seal inlet arrangement 16 of the metathesis device 17 or devices wherein metathesis of the crystalline sodium sesquisulfate is performed, as described above for Figures 1 and 2. The resulting slurry resulting from the metathesis step is forwarded by line 15 to other side of the divided feed box assembly 5 from the feed of slurry of sodium sesquisulfate. When a preconcentration device 18 is used in conjunction with the slurry of neutral sodium sulfate, stream 13, lean in solids, generally is returned to the metathesis device 17 or the chlorine dioxide generating unit 1.
The crystalline neutral sodium sulfate is separated from the slurry thereof, thereby extracting the acid medium, through parallel deposition on the other side of the drum sector, or filtration zone 7, and the solid neutral sodium sulfate is conducted over a solid material removal device (not shown) to remove the crystalline sodium sesquisulfate from the filter cloth. Wash water or steam can be used to assist in separation of the crystalline material from the acid medium. The solid material is then channelled through the other side 10 of a divided conveying duct and introduced into dissolving device 11 to prepare a solution product in stream 12.
Alternatively, device 11 can be a solids conveying device in the event wet solids are required. The solids separation on drum sectors 6 and 7 may be assisted by vacuum conditions within the filtrate side of the drum 22 and the filtration step be returned to the chlorine dioxide generation unit 1 through line 8.
Referring now to Figure 5, there is illustrated therein a third embodiment of a chlorine dioxide generating unit 1 in accordance with the invention.
Elements of the arrangements which are in common with Figures 1 and 2 have been designated by the same numerals. As seen therein, crystalline sodium sesquisulfate is precipitated from the reaction medium and is removed in slurry form by line 2 and passed to a preconcentration device 4, which may be a cyclone type or any other suitable device, to enrich the solids before directing stream 25 to the contacting device 9. Stream 3, lean in solids, generally is returned to the chlorine dioxide generating unit 1.
In this embodiment of the present invention, an integral contacting device which effects fully or partially the metathesis process can be employed. Such device may be, for example, an agitated chamber, screw/extruder, paddle type mixer or any other integral solid/liquid contacting device.
13 ?~~~7?_1 The metathesized crystalline solid phase, which may be enriched by the action of device 9, is conveyed out through stream 27 to enter into feed arrangement 5.
Metathesis agents can be introduced at various suitable points on device 9 (not shown).
The present embodiment allows various flow regimes to be employed solely, or in combination, to cause efficient metathesis reaction. Depending on the direction of crystalline solid phase flow through device 9, the metathesizing agents can be arranged in a co-current or counter-current method, or suitable combination thereof.
As an alternative arrangement, device 9 may provide a similar solids enriching action to that of the preconcentrating device 4. In this particular case, stream 26, which is lean in solid phase, is returned to the chlorine dioxide generating unit 1.
The crystalline sodium sulfate, or mixtures with sodium sesquisulfate, is removed from the preconcentrated slurry, thereby extracting the spent reaction liquid filtrate, by deposition on the drum 22. Residual sodium sesquisulfate may be converted to sodium sulfate by metathesis on the drum, as described in the other illustrated embodiments. The crystalline solids are conducted over a solid material removal device (not shown), which can be a blade type or hydraulically assisted arrangement, to remove the crystalline sodium sesquisulfate from the filter cloth. Wash water or steam can be used to assist in separation of the crystalline material from entrained reaction medium on the filter drum 22.
The crystalline neutral sodium sulfate is separated from the slurry thereof, thereby extracting the residual acid medium. The solid material is then channelled through the other side 10 of a conveying duct and introduced into dissolving device 11 to prepare a solution product in stream 12. Alternatively, device 11 can be a solids conveying device in the event wet solids 14 ~ ~ X8721 are required. The solids separation on drum 22 may be assisted by vacuum conditions within the filtrate side of the drum 22 and the filtration step be returned to the chlorine dioxide generation unit 1 through line 8.
Alternatively, for particular cases, stream 27 may be of sufficient quality and composition whereby further treatment is not required. In these cases, rotary drum filter separation is not required and filtration can be eliminated completely.
EXAMPLES
Example I
This Example illustrates the opportunity to reduce the complexity and size of the metathesis reactor, so as to allow one to design the device to be small and integral with the rotary drum filter equipment, if desired, thereby eliminating the need for extensive piping; pumps and associated control systems.
These experiments illustrate that the reaction period for metathesis required to produce a crystalline product which is readily filterable by conventional means, is relatively short.
A series of experiments was carried out wherein various amounts of sodium sesquisulfate were mixed in a continuously stirred small 3L reactor as set forth in Table I below. Once the reaction period was complete, the solid phase was separated and analyzed to determine metathesis reaction efficiency.
The results are set forth in the following Table I:
TABLE I
Test (min) Na3H(S04)Z Water Added Metathesis Reaction Added (g/g Na3H(S04)~Reaction Period (g) EfEciency ( % ) 1 3 1395 0.45 98.95 2 3 1402 0.42 99.14 3 5 1404 0.42 98.25 4 10 1392 0.42 99.09 Example II
This Example illustrates the potential effect of counter-current stages wherein the initial bulk acidity, that the solid phase experiences, is greater than with the addition of water.
A synthetic filtrate with several initial acidities was prepared to react with the solid sesquisulfate to compare to the other results. These results are shown in the following Table II:
TABLE II
Test (min) Na3H(S04)2)Filtrate FiltrateMetathesis Reaction Added Added Acidity Reaction Period (g) (ml) (N) Efficiency (%) 5 5 870 650 3.0 98.93 6 2 876 650 3.0 97.63 7 10 325 1152 5.65 99.18 SUNll~IARY OF THE DISCLOSURE
In summary of this disclosure, the present invention provides an effective yet simple and inexpensive 5 procedure for effecting metathesis of by-product sodium sesquisulfate from a chlorine dioxide generator and other sources of sodium acid sulfate to solid phase neutral anhydrous sodium sulfate. Modifications may be made within the scope of the invention.
feeding the slurry of sodium acid sulfate crystals to a first filtration zone on a drum filter element, separating sodium acid sulfate crystals from the slurry in the first filtration zone, removing the separated sodium acid sulfate crystals from the first filtration zone, contacting the removed sodium acid sulfate crystals with a metathesizing medium to effect a solid phase conversion of the sodium acid sulfate crystals to neutral sodium sulfate crystals and to form a second slurry of the neutral sodium sulfate crystals in an acidic medium, feeding the second slurry to a second filtration zone on the drum filter element separate from the first filtration zone, separating neutral sodium sulfate crystals from the acidic medium in the second filtration zone, recovering the separated acidic medium, and removing the neutral sodium sulfate crystals from the second filtration zone.
The slurry of sodium acid sulfate may comprise a slurry of sodium sesquisulfate formed in a chlorine dioxide generating process wherein the aqueous medium is entrained chlorine dioxide generator liquor. Aqueous medium separated from the sodium sesquisulfate crystals in the first filtration zone is returned to the chlorine dioxide generator, and the recovered acidic medium is recycled to the chlorine dioxide generator.
In another aspect of the invention, there is provided a process for the conversion of sodium sesquisulfate, particularly produced in a chlorine dioxide generation operation, to neutral anhydrous sodium sulfate which employes a drum filter having a contacting device integral therewith wherein at least partial metathesis is effected.
In this aspect of the invention, the metathesis operation is effected by:
contacting said slurry in said integral contacting device with a metathesizing medium to effect solid phase conversion of said sodium acid sulfate crystals at least partially to neutral sodium sulfate crystals and to form a second slurry contacting said neutral sodium sulfate crystals and in an acidic medium, feeding said second slurry to a filtration zone on said single filtration drum, separating neutral sodium sulfate crystals from said acidic medium in said second filtration zone, recovering said separated acidic medium, and removing said neutral sodium sulfate crystals from said second filtration zone.
GENERAL DESCRIPTION OF INVENTION
In one embodiment of the metathesizing procedure of the present invention, the slurry containing sodium sesquisulfate crystals from the chlorine dioxide generator is first fed to a dual service rotary drum filter through a top feed arrangement, whereby the slurry containing sodium sesquisulfate crystals is deposited onto an acidic cake sector of the rotary drum filter to effect filtration thereof substantially free from entrained generator liquor while the filtrate is recycled to the chlorine dioxide generator.
After being removed from the acidic cake sector of the rotary drum filter, the sodium sesquisulfate crystals are mixed with the metathesizing medium of the type described in USP 5,205,995, such as, for example, water, to effect metathesis of the sodium sesquisulfate crystals to neutral sodium sulfate in crystalline form and formation of an acidic slurry. The resulting acidic slurry containing neutral sodium sulfate crystals, is fed through a bottom feed arrangement to the dual service rotary drum filter whereupon neutral cake is deposited in the neutral cake sector of the filter.
In another embodiment of the invention, the slurry from the chlorine dioxide generator containing sodium sesquisulfate crystals is fed through a bottom feed arrangement while the acidic slurry containing neutral ?~~~7~1 saltcake is introduced through the top feed arrangement to a single dual service rotary drum filter.
In yet another embodiment of the invention, the slurry from the chlorine dioxide generator is fed through 5 a bottom feed arrangement depositing the sodium sesquisulfate on the filter cloth. On partial or full liquor displacement and washing completion, the cake continues upward on the drum passing into an integral contacting chamber where metathesis occurs by a dynamic leaching action similar to that described in the previously cited USP 5,399,332. This contacting chamber can employ water sprays and/or steam jet to complete the metathesis reaction. As the cake continues on the rotating drum and exits this integral contacting chamber it then continues to a removal device where it is mechanically and/or hydraulically separated from the drum surf ace .
The only modification required to be made to existing equipment to effect the improved operation of the present invention is the installation of the second (bottom) feed assembly, which may act fully or partially as the metathesizing zone, onto the existing conventional drum filter employed to separate the sodium sesquisulfate crystals from entrained reaction medium.
The modification effected herein is not only simple and inexpensive but permits a previously unused area of the rotary drum filter to be used to perform the secondary service of separating the neutral saltcake. In this way, the whole available area of the rotary drum filter surface is usefully employed. The bottom feed assembly promotes the displacement of the filtrate at the filter cloth and allows the saltcake to be carried upward on the filter cloth for doctor blade removal.
In another embodiment of the present invention, both acid and neutral saltcake filtration is performed in parallel on substantially laterally contiguous regions of a single rotary drum filter. In this embodiment, the filter is designed to accept separate streams, which may ~~~~1~~
be pre-concentrated in solids by a peripheral pre-concentration device, then through separate feed assemblies. The filter also is designed to segregate the filtered cakes after liquor displacement and washing. A
physical separation of the cakes may be employed, although this is not necessary. If physical separation during filter cake formation is not employed, the segregation of the cakes using a cake splitting device can be designed or controlled to accept a small portion of neutral saltcake to reduce the importance of a complex physical separation design.
In addition to the simplification of the filtration unit, the present invention provides an optional, novel procedure for reduction or elimination of the additional evaporative load on the chlorine dioxide generator resulting from recycle of the recovered acid liquor to the generator. This improvement can be achieved by treating the filtrate or lean liquors returned from preconcentration steps, to induce evaporation or water vapour removal from these streams. The heat source may be hot water, steam or any other suitable heating medium.
One approach to such procedure utilizes a heated jacketed flash/separator tank to induce the extraction of water vapour. Another approach to such procedure utilizes a heat exchange device, of a simple design, which may be a concentric pipe or any other suitable heat exchanger configuration to effect the required heat exchange.
An alternative approach to water vapour removal is to provide a separate evaporation zone maintained under partial vacuum, within the metathesis reactor, to induce the extraction of water vapour. The evaporation zone may comprise a separate chamber, if desired. This evaporation zone can also serve to effect a preconcentration step for the acid liquor, prior to filtration to remove neutral sodium sulfate, if necessary.
In another embodiment of the present invention, the slurry from the chlorine dioxide generator is pre-1 ~~~~~
concentrated in solids by a peripheral preconcentration device then passes into a contacting chamber, integral with a single rotary drum filter, wherein metathesis occurs by a dynamic leaching action similar to that described in 5,399,332, assigned to the assignee hereof, or through a co-current or countercurrent mixing with metathesis agents, as described in USP 5,116,595, assigned to the assignee hereof, or other suitable procedure.
The contacting chamber can employ water sprays and/or steam jets to complete the metathesis. The contacting chamber may be a specific device which may cause liquor displacement through hydraulic action imparted by mechanical means and/or by the force of gravity, should the device present an inclined path to the feeding region of the rotary drum filter.
The modification effected herein is not only simple and inexpensive but may also permit the combination of previously two unit operations into one device integral with a rotary drum filter.
The metathesis process of the present invention enables there to be effected a very efficient conversion of sodium sesquisulfate to a neutral sodium sulfate whereby the co-produced aqueous acid-containing medium reaches the total acid normality of up to about 6.5 normal.
The metathesis process generally is carried out using water at a temperature of about 40oC to about 100oC, preferably about 65oC to about 95oG. At these metathesis temperatures, the neutral sodium sulfate is recovered in an anhydrous form. Alternatively to water, other aqueous metathesizing media, such as those disclosed in U.S. Patent No. 5,205,995, namely aqueous sodium chlorate solution, aqueous sodium chloride solution, aqueous methanol and chlorine dioxide generator condensate, can be employed in the process.
8 ~ ~ ~~~21 BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic representation of a metathesis operation employing a dual service drum filter in accordance with one embodiment of the invention;
Figure 2 is a schematic perspective representation of a dual service drum filter equipped with both top feed box and a lower feed box assembly for use in the procedure of Figure 1;
Figure 3 is a schematic representation of a metathesis operation employing a divided drum filter in accordance with another embodiment of the invention;
Figure 4 is a schematic perspective representation of a portion of a divided drum filter for use in the procedure of Figure 3, and Figure 5 is a schematic representation of a metathesis operation in employing a drum filter in accordance with a further embodiment of the invention.
DESCRIPTION OF THE PREFERRED EN~ODINIENTS
Referring first to Figures 1 and 2, there is illustrated therein an embodiment of a chlorine dioxide generating unit 1 in accordance with the invention. The chlorine dioxide generating unit may be one in which chlorine dioxide is produced from an aqueous acid reaction medium having a total acid normality of about 4N
and higher, in which sodium chlorate, sulfuric acid and a reducing agent, such as methanol or hydrogen peroxide, react together while the reaction medium is maintained at its boiling point under a subatmospheric pressure applied to the chlorine dioxide generating unit 1.
Chlorine dioxide and steam are removed from the chlorine dioxide generating unit 1 and a by-product sodium acid sulfate is precipitated therein, which may be sodium sesquisulfate or sodium bisulfate, depending on the total acid normality of the reaction medium. Since the most common form of the sodium acid sulfate encountered in commercial operations is sodium sesquisulfate, the illustrated embodiments will be described further with respect thereto.
?1~~~?i Crystalline sodium sesquisulfate precipitated from the reaction medium is removed in slurry form by line 2 to a rotary drum filter 20. In the illustrated embodiment, a preconcentration device 4, which can be a cyclone type or any other suitable device, is employed to enrich the solids volume of the slurry and removing a portion of the entrained chlorine dioxide generating reaction medium, before directing the preconcentrated stream to a top feed box assembly 5 located adjacent an upper region of the rotary drum 22. When a preconcentration device 4 is used, the resulting liquid stream 3, lean in solids, generally is returned to the chlorine dioxide generating unit 1.
The crystalline sodium sesquisulfate is removed from the preconcentrated slurry by deposition on sector or filtration zone 6 and draining of entrained reaction medium through the filter cloth. The crystalline sodium sesquisulfate is conducted over a solid material removal device (not shown), which can be a blade type or hydraulically assisted arrangement, to remove the crystalline sodium sesquisulfate from the filter cloth.
Wash water or steam can be used to assist in separation of the crystalline material from entrained reaction medium on the filter cloth in sector 6.
The recovered sodium sesquisulfate is then channelled through a conveying duct 14 and introduced into a sealed inlet arrangement 16 of the metathesis device 17 or devices, wherein metathesis of the crystalline sodium sesquisulfate is performed using water as the metathesizing sodium converting solid phase sodium sesquisulfate into solid phase neutral sodium sulfate and forming an acid medium, which may have an acid normality of up to about 6.5N. In general, the weight ratio of water to sodium sesquisulfate in the metathesis step is less than about 0.6:1, preferably about 0.4:1 to about 0.6:1. The slurry resulting from the metathesis step is forwarded by line 15 to a second filter feed assembly 9 located adjacent a lower region of the rotary drum 22 of ~i~87~
the filter. A preconcentration step may be provided prior to feed to the feed assembly 9. The second filter feed assembly 9 allows displacement of the acid medium from the neutral sodium sulfate, deposition of the crystalline neutral sodium sulfate on the drum sector or filtration zone 7. It may be desirable to collect the liquid which is lean in solids within the feed assembly 9 or the optional preconcentration device and conduct such liquid through line 13 to the metathesis devices) 17 or to chlorine dioxide generating unit 1.
Alternatively, feed assembly 9 can be designed to effect partially or fully the metathesis reaction, thereby further simplifying the process. Optionally, an integral feed device which effects fully or partially the metathesis process can be employed for this purpose.
Such device may be of the type of, for example, an agitated chamber, paddle type mixer or any other integral solid/liquid contacting device.
The solid neutral sodium sulfate conveyed on the surface of the filter cloth in section 7 is conducted over a solid material removal device 24, which can be a doctor blade type or hydraulically assisted arrangement.
Wash water or steam can be used to assist in separation of the crystalline material from the entrained acid medium. The crystalline neutral sodium sulfate material is then channelled through a conveying duct 10 and introduced into the dissolving device 11 to prepare a solution product in stream 12. Such solution then may be further processed or disposed of. Alternatively, device 11 may be a solids conveying device in the event that wet solid material is required.
The solids separation on drum sectors 6 and 7 may be assisted by vacuum conditions within the filtrate side of the drum 22 and the common filtrates are collected and may be returned to the chlorine dioxide generating unit 1 through line 8.
Referring now to Figures 3 and 4, there is illustrated thereon a second embodiment of a chlorine 11 ~ ~ ~ ~ ~2 dioxide generating unit 1 in accordance with the invention. Elements of the arrangements which are in common with Figures 1 and 2 have been designated by the same numerals. As seen therein, crystalline sodium sesquisulfate is precipitated from the reaction medium and is removed in slurry form by line 2 and passed to the filter 20. A preconcentration device 4, which may be a cyclone type or any other suitable device, may be provided to enrich the solids before directing this stream to one side of a divided feed box assembly 5.
When a preconcentration device is used, stream 3 lean in solids generally is returned to the chlorine dioxide generating unit 1.
The crystalline sodium sesquisulfate is removed from the preconcentrated slurry, thereby extracting the spent reaction liquid filtrate, by deposition to one side of the drum in sector or filtration zone 6. The crystalline sodium sesquisulfate is conducted over a solid material removal device (not shown), which can be a blade type of hydraulically assisted arrangement, to remove the crystalline sodium sesquisulfate from the filter cloth.
wash water or steam can be used to assist in separation of the crystalline material from entrained reaction medium on the filter section 6.
The recovered solid material is then channelled through one side 14 of a divided conveying duct and introduced into the seal inlet arrangement 16 of the metathesis device 17 or devices wherein metathesis of the crystalline sodium sesquisulfate is performed, as described above for Figures 1 and 2. The resulting slurry resulting from the metathesis step is forwarded by line 15 to other side of the divided feed box assembly 5 from the feed of slurry of sodium sesquisulfate. When a preconcentration device 18 is used in conjunction with the slurry of neutral sodium sulfate, stream 13, lean in solids, generally is returned to the metathesis device 17 or the chlorine dioxide generating unit 1.
The crystalline neutral sodium sulfate is separated from the slurry thereof, thereby extracting the acid medium, through parallel deposition on the other side of the drum sector, or filtration zone 7, and the solid neutral sodium sulfate is conducted over a solid material removal device (not shown) to remove the crystalline sodium sesquisulfate from the filter cloth. Wash water or steam can be used to assist in separation of the crystalline material from the acid medium. The solid material is then channelled through the other side 10 of a divided conveying duct and introduced into dissolving device 11 to prepare a solution product in stream 12.
Alternatively, device 11 can be a solids conveying device in the event wet solids are required. The solids separation on drum sectors 6 and 7 may be assisted by vacuum conditions within the filtrate side of the drum 22 and the filtration step be returned to the chlorine dioxide generation unit 1 through line 8.
Referring now to Figure 5, there is illustrated therein a third embodiment of a chlorine dioxide generating unit 1 in accordance with the invention.
Elements of the arrangements which are in common with Figures 1 and 2 have been designated by the same numerals. As seen therein, crystalline sodium sesquisulfate is precipitated from the reaction medium and is removed in slurry form by line 2 and passed to a preconcentration device 4, which may be a cyclone type or any other suitable device, to enrich the solids before directing stream 25 to the contacting device 9. Stream 3, lean in solids, generally is returned to the chlorine dioxide generating unit 1.
In this embodiment of the present invention, an integral contacting device which effects fully or partially the metathesis process can be employed. Such device may be, for example, an agitated chamber, screw/extruder, paddle type mixer or any other integral solid/liquid contacting device.
13 ?~~~7?_1 The metathesized crystalline solid phase, which may be enriched by the action of device 9, is conveyed out through stream 27 to enter into feed arrangement 5.
Metathesis agents can be introduced at various suitable points on device 9 (not shown).
The present embodiment allows various flow regimes to be employed solely, or in combination, to cause efficient metathesis reaction. Depending on the direction of crystalline solid phase flow through device 9, the metathesizing agents can be arranged in a co-current or counter-current method, or suitable combination thereof.
As an alternative arrangement, device 9 may provide a similar solids enriching action to that of the preconcentrating device 4. In this particular case, stream 26, which is lean in solid phase, is returned to the chlorine dioxide generating unit 1.
The crystalline sodium sulfate, or mixtures with sodium sesquisulfate, is removed from the preconcentrated slurry, thereby extracting the spent reaction liquid filtrate, by deposition on the drum 22. Residual sodium sesquisulfate may be converted to sodium sulfate by metathesis on the drum, as described in the other illustrated embodiments. The crystalline solids are conducted over a solid material removal device (not shown), which can be a blade type or hydraulically assisted arrangement, to remove the crystalline sodium sesquisulfate from the filter cloth. Wash water or steam can be used to assist in separation of the crystalline material from entrained reaction medium on the filter drum 22.
The crystalline neutral sodium sulfate is separated from the slurry thereof, thereby extracting the residual acid medium. The solid material is then channelled through the other side 10 of a conveying duct and introduced into dissolving device 11 to prepare a solution product in stream 12. Alternatively, device 11 can be a solids conveying device in the event wet solids 14 ~ ~ X8721 are required. The solids separation on drum 22 may be assisted by vacuum conditions within the filtrate side of the drum 22 and the filtration step be returned to the chlorine dioxide generation unit 1 through line 8.
Alternatively, for particular cases, stream 27 may be of sufficient quality and composition whereby further treatment is not required. In these cases, rotary drum filter separation is not required and filtration can be eliminated completely.
EXAMPLES
Example I
This Example illustrates the opportunity to reduce the complexity and size of the metathesis reactor, so as to allow one to design the device to be small and integral with the rotary drum filter equipment, if desired, thereby eliminating the need for extensive piping; pumps and associated control systems.
These experiments illustrate that the reaction period for metathesis required to produce a crystalline product which is readily filterable by conventional means, is relatively short.
A series of experiments was carried out wherein various amounts of sodium sesquisulfate were mixed in a continuously stirred small 3L reactor as set forth in Table I below. Once the reaction period was complete, the solid phase was separated and analyzed to determine metathesis reaction efficiency.
The results are set forth in the following Table I:
TABLE I
Test (min) Na3H(S04)Z Water Added Metathesis Reaction Added (g/g Na3H(S04)~Reaction Period (g) EfEciency ( % ) 1 3 1395 0.45 98.95 2 3 1402 0.42 99.14 3 5 1404 0.42 98.25 4 10 1392 0.42 99.09 Example II
This Example illustrates the potential effect of counter-current stages wherein the initial bulk acidity, that the solid phase experiences, is greater than with the addition of water.
A synthetic filtrate with several initial acidities was prepared to react with the solid sesquisulfate to compare to the other results. These results are shown in the following Table II:
TABLE II
Test (min) Na3H(S04)2)Filtrate FiltrateMetathesis Reaction Added Added Acidity Reaction Period (g) (ml) (N) Efficiency (%) 5 5 870 650 3.0 98.93 6 2 876 650 3.0 97.63 7 10 325 1152 5.65 99.18 SUNll~IARY OF THE DISCLOSURE
In summary of this disclosure, the present invention provides an effective yet simple and inexpensive 5 procedure for effecting metathesis of by-product sodium sesquisulfate from a chlorine dioxide generator and other sources of sodium acid sulfate to solid phase neutral anhydrous sodium sulfate. Modifications may be made within the scope of the invention.
Claims (24)
1. A method of metathesizing a slurry of sodium acid sulfate crystals in an aqueous medium, which comprises effecting metathesis of said sodium acid sulfate crystals to neutral sodium sulfate crystals and an aqueous acid medium employing a single filtration device, said single filtration device being a dual service drum filter and wherein said metathesis operation is effected by:
feeding said slurry of sodium acid sulfate crystals to a first filtration zone on said dual service drum filter, separating sodium acid sulfate crystals from said slurry in said first filtration zone, removing said sodium acid sulfate crystals from said first filtration zone, contacting said removed sodium acid sulfate crystals with an aqueous metathesizing medium to effect a solid phase conversion of said sodium acid sulfate crystals to neutral sodium sulfate crystals and to form a second slurry of said neutral sodium sulfate crystals in an acidic medium, feeding the second slurry to a second filtration zone on the dual service drum filter separate from said first filtration zone, separating neutral sodium sulfate crystals from said acidic medium in said second filtration zone, recovering said separated acidic medium, and removing said neutral sodium sulfate crystals from said second filtration zone.
feeding said slurry of sodium acid sulfate crystals to a first filtration zone on said dual service drum filter, separating sodium acid sulfate crystals from said slurry in said first filtration zone, removing said sodium acid sulfate crystals from said first filtration zone, contacting said removed sodium acid sulfate crystals with an aqueous metathesizing medium to effect a solid phase conversion of said sodium acid sulfate crystals to neutral sodium sulfate crystals and to form a second slurry of said neutral sodium sulfate crystals in an acidic medium, feeding the second slurry to a second filtration zone on the dual service drum filter separate from said first filtration zone, separating neutral sodium sulfate crystals from said acidic medium in said second filtration zone, recovering said separated acidic medium, and removing said neutral sodium sulfate crystals from said second filtration zone.
2. The method of claim 1 wherein said slurry of sodium acid sulfate crystals comprises a slurry of sodium sesquisulfate formed in a chlorine dioxide generating process, said aqueous medium is entrained chlorine dioxide generator liquor, aqueous medium separated from the sodium sesquisulfate crystals in the first filtration zone is returned to the chlorine dioxide generating process, and the recovered acidic medium is recycled to the chlorine dioxide generating process.
3. The method of claim 2 wherein said first filtration zone is provided at an upper region of said drum filter element and said second filtration zone is provided at a lower region of said drum filter element.
4. The method of claim 2 wherein said first filtration zone is provided at a lower region of said drum filter element and said second filtration zone is provided at an upper region of the said drum filter element.
5. The method of claim 2 wherein said first filtration zone and said second filtration zone are provided by substantially laterally contiguous regions of said drum filter element.
6. The method of any one of claims 2 to 5 wherein said aqueous metathesizing medium is provided solely by water.
7. The method of any one of claims 2 to 6 wherein said acidic medium produced in the metathesis step is reduced in volume prior to said recycle to the chlorine dioxide generating process.
8. The method of claim 7 wherein said acidic medium reduced in volume by evaporating the same following separation of said neutral sodium sulfate crystals therefrom.
9. The method of any one of claims 2 to 8 wherein said first slurry is concentrated prior to feeding to the first filtration zone.
10. The method of claim 9 wherein said second slurry is concentrated prior to feeding to the second filtration zone.
11. The method of claim 10 wherein each said preconcentration step produces a lean liquor which is recycled to the chlorine dioxide generating process.
12. The method of any one of claims 2 to 11 wherein said recovered acidic medium has an acid normality of up to about 6.5.
13. The method of claim 12 wherein said contacting of said removed sodium sesquisulfate crystals with aqueous metathesizing medium is effected at a temperature of about 40° to about 100°C, whereby said neutral sodium sulfate is recovered in the form of neutral anhydrous sodium sulfate.
14. The method of claim 13 wherein said temperature is from about 65°
to about 95°C.
to about 95°C.
15. The method of any one of claims 2 to 14 including decreasing the volume of total liquor recycled to the chlorine dioxide generator.
16. A method of metathesizing a slurry of sodium acid sulfate crystals in an aqueous medium, which comprises effecting metathesis of said sodium acid sulfate to neutral sodium sulfate crystals and an aqueous acid medium employing a single filtration device, said single filtration device being a dual service drum filter, wherein said single filtration drum has integrally provided therewith a contacting device wherein metathesis is partially or fully effected and wherein said metathesis operation is effected by:
contacting said slurry in said integral contacting device with a metathesizing medium to effect solid phase conversion of said sodium acid sulfate crystals at least partially to neutral sodium sulfate crystals and to form a second slurry contacting said neutral sodium sulfate crystals in an acidic medium, feeding said second slurry to a filtration zone on said single filtration drum, separating neutral sodium sulfate crystals from said acidic medium in said second filtration zone, recovering said separated acidic medium, and removing said neutral sodium sulfate crystals from said second filtration zone.
contacting said slurry in said integral contacting device with a metathesizing medium to effect solid phase conversion of said sodium acid sulfate crystals at least partially to neutral sodium sulfate crystals and to form a second slurry contacting said neutral sodium sulfate crystals in an acidic medium, feeding said second slurry to a filtration zone on said single filtration drum, separating neutral sodium sulfate crystals from said acidic medium in said second filtration zone, recovering said separated acidic medium, and removing said neutral sodium sulfate crystals from said second filtration zone.
17. The method of claim 16 wherein substantially complete conversion of sodium acid sulfate crystals to neutral sodium sulfate crystals is effected in the integral contacting device.
18. The method of claim 17 wherein said slurry of sodium acid sulfate crystals comprises a slurry of sodium sesquisulfate formed in a chlorine dioxide generating process, said aqueous medium is entrained chlorine dioxide generation liquor and the recovered acidic medium is recycled to the chlorine dioxide generating process.
19. The method of claim 18 wherein said aqueous metathesizing medium is provided solely by water.
20 20. The method of claim 18 or 19 wherein said first slurry is concentrated prior to feeding to said contacting device and said concentration step produces a lean liquor which is recycled to the chlorine dioxide generating process.
21. The method of any one of claims 18 to 20 wherein said recovered acidic medium has an acid normality of up to about 6.5.
22. The method of any one of claims 18 to 21 wherein said contacting of said removed sodium sesquisulfate crystals with aqueous metathesizing medium is effected at a temperature of about 40° to about 100°C, whereby said neutral sodium sulfate is recovered in the form of neutral anhydrous sodium sulfate.
23. The method of claim 22 wherein said temperature is from about 65°
to about 95°C.
to about 95°C.
24. The method of any one of claims 18 to 23 including decreasing the volume of total liquor recycled to the chlorine dioxide generator.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US615795P | 1995-11-02 | 1995-11-02 | |
| US60/006,157 | 1995-11-02 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2188721A1 CA2188721A1 (en) | 1997-05-03 |
| CA2188721C true CA2188721C (en) | 2005-04-26 |
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ID=21719576
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2188721 Expired - Lifetime CA2188721C (en) | 1995-11-02 | 1996-10-24 | Process for metathesis |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102001689A (en) * | 2010-10-29 | 2011-04-06 | 广西博世科环保科技股份有限公司 | Method for recycling side product of sodium hydrogen sulfate generated by production of chlorine dioxide |
-
1996
- 1996-10-24 CA CA 2188721 patent/CA2188721C/en not_active Expired - Lifetime
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102001689A (en) * | 2010-10-29 | 2011-04-06 | 广西博世科环保科技股份有限公司 | Method for recycling side product of sodium hydrogen sulfate generated by production of chlorine dioxide |
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| Publication number | Publication date |
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| CA2188721A1 (en) | 1997-05-03 |
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