Abstract:
Disclosed is a process for manufacturing bleach (or sodium hypochlorite) and caustic potash (or KOH) without the need for shipping or storing chlorine gas. Specifically, the present invention relates to the manufacture of potassium hydroxide and chlorine gas, through several process options, for the manufacture of sodium hypochlorite (or bleach), hydrochloric acid (HCl) and/or other chlorinated compounds. The disclosed process allows operating flexibility based on chlorine demand, reduces capital costs and eliminates the need for the transportation and storage of chlorine gas.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to provisional application Ser. No. 60/493,435 filed on Aug. 8, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a means for producing bleach (sodium hypochlorite) and potassium hydroxide (KOH) using chlorine gas produced on-site from electrolysis of potassium chloride. More specifically, the invention relates to a process that will allow the manufactured chlorine gas to be sold directly to an adjacent plant, or to be used onsite for the manufacture of hydrochloric acid and/or bleach. The flexibility of this process provides unique operating alternatives based on current market demand and never requires the transportation of or the onsite storage of the extremely hazardous chlorine gas.  
       BACKGROUND OF THE INVENTION  
       [0003]     Currently, all potassium hydroxide plants in the United States sell liquid chlorine and potassium hydroxide. Chlorine and potassium hydroxide are transported by rail to customers. At present, five plants produce chlorine and potassium hydroxide. Potassium chloride and water are electrolyzed to produce chlorine, potassium hydroxide and hydrogen according to the following reaction: 
 
2KCl+2H 2 O--&gt;Cl 2 +2KOH+H 2 
 
 Between 2,400 and 3,200 kiloWatt hours per ton of chlorine produced are needed for this reaction depending on the electrolysis technology. 
 
         [0005]     Chlorine, potassium hydroxide and hydrogen are produced from an aqueous potassium chloride solution by mercury, asbestos diaphragm or membrane cell electrolysis. With some variations, the usual process involves brine purification and de-ionization, electrolysis, chlorine processing, potassium hydroxide processing, and hydrogen processing.  
         [0006]     Processes for potassium hydroxide (KOH) production are well known in prior art. One such process is depicted in  FIG. 1 . Solid potassium chloride (KCl) salt  1  arrives at a processing plant via rail car  4 . Potassium chloride  1  is transferred to a salt dissolver  2 , wherein the solid, impure potassium chloride  1  is dissolved in water to form brine  3 . At some plants, sodium chloride (NaCl) is substituted for potassium chloride to ultimately produce sodium hydroxide (NaOH) instead of potassium hydroxide (KOH). Next, appropriate chemicals are added to the brine  3  to precipitate impurities. The resulting mixture is fed to a thickener  5 , from which precipitates and clarified raw brine  3  are separately withdrawn. The clarified brine  3  is then filtered by brine filter  6 . Solid precipitates are sent to a landfill, or disposed of by any suitable method. The filtered brine  3  is then pumped to a filtered brine tank  7 . Next, secondary brine purification is performed on brine  3  via an ion exchange unit  8 . Secondary brine purification ensures high efficiency and long lasting membrane electrolyzer operation. Deionized brine  3  is stored in tank  9  before being sent to electrolyzer  10 .  
         [0007]     In electrolyzer  10 , electric power is provided via an AC-DC rectifier  11 . Deionized brine  3  and purified water  12  are pumped into electrolyzer  10 . Application of electricity causes anions, i.e. chloride ions, to collect at the anode side of the electrolyzer  10  and cations, i.e. potassium and hydrogen ions, to collect at the cathode side of the electrolyzer  10 . The chlorine produced from the weak solution of brine  3 , is either drawn from the anode side of the cell in a vacuum or the solution is pumped to a dechlorination process.  
         [0008]     To process the wet chlorine, the gas is cooled and the brine  3  condensate is removed in a dechlorinator  14 . The weak solution of brine  3  is then returned to the brine treatment area, specifically the salt dissolver  2 . Next, the chlorine gas is dried with a sulfuric acid dryer  15 . The dry gas is then compressed and chilled for storage in rail cars  17 . The chlorine gas may also be stored in cylinders or bulk plant storage.  
         [0009]     However, drying, compressing storing the chlorine gas are major drawbacks to plant operation. Drying and compressing the chlorine is expensive and increases the capital costs for plant operation by as much as 10-20%. Additionally, storage of chlorine gas on-site is undesirable because it is potentially very hazardous and may be a terrorist target.  
         [0010]     Potassium hydroxide and hydrogen, collected at the cathode side of electrolyzer  10 , are drawn from the membrane cell electrolyzer  10 . Potassium hydroxides leave the electrolyzer  10  at approximately 30-35% by weight in an aqueous solution at a temperature between approximately 190 and 200° F. This low strength potassium hydroxide solution is split. One stream is cooled and stored for use in the brine treatment tank  5 . The other, major, stream is sent to the evaporator  18  for removing the water. In the evaporator  18 , the hot potassium hydroxide solution is concentrated to the commercial grade specification, i.e., approximately 45%. Next, the product is cooled to about 170° F. and sent to product storage  20 .  
         [0011]     Hydrogen gas, also produced on the cathode side of the electrolyzer  10 , may be sent to vent  21  for pressure control. The majority of the produced hydrogen, however, is cooled to remove water vapor before it is pumped to hydrogen compressor. After the hydrogen is compressed, it is sent to the boiler  22  where it is burned as fuel.  
         [0012]     Currently, there are many chemical plants in the United States that produce sodium hypochlorite by the chemically reactive combination of chlorine and sodium hydroxide. However, current facilities require the delivery of hazardous chlorine gas by truck or rail to the production site. Integration of potassium hydroxide production with bleach manufacture is a logical combination that can both reduce transportation costs and eliminate the need to store hazardous chlorine gas on-site. Presently, however, there are no known plants in the United States that produce potassium hydroxide and sodium hypochlorite by the processes according to the present invention.  
         [0013]     It is anticipated that there will be a new demand for these dedicated chlorine plants, since the Department of Homeland Security wants the public transportation of hazardous chlorine and chlorine storage eliminated as possible terrorist targets.  
       SUMMARY OF THE INVENTION  
       [0014]     This invention described herein relates to the process for the integrated manufacture of potassium hydroxide and bleach. Specifically the process allows several process options which can provide economic flexibility based on the varying demands of chlorine products. The chlorine gas that is produced via electrolysis of KCl may be sold directly to a customer via pipeline. Alternatively, the plant operator can divert the chlorine production from chlorine pipeline deliveries to either NaOCl (bleach) or HCl (hydrochloric acid) production.  
         [0015]     The chemical reactions of the new process combination can be summarized as follows: 
 
2KCl+2H 2 +electricity--&gt;Cl 2 +2KOH+H 2 
 
         [0016]     (Electrolysis of potassium chloride salt with demineralized and deionized water yields chlorine, potassium hydroxide and hydrogen.) 
 
 Cl   2 +2NaOH--&gt;NaOCl+H 2 O+NaCl
 
         [0017]     (Chlorine reacts with purchased sodium hydroxide to yield sodium hypochlorite, water and sodium chloride.) 
 
 H   2 +Cl 2 --&gt;2HCl
 
         [0018]     (The reaction of hydrogen and chlorine produces hydrochloric acid.)  
         [0019]     The present invention is the first process of its kind to integrate the processes of KOH and bleach manufacture. This new process design provides for easy economical balance and allows the plant operator to shift production based on the varying demands of the chlorine products. Further, the disclosed process eliminates the need for onsite storage of potentially hazardous chlorine gas.  
         [0020]     It is therefore an object of the invention to eliminate the need for the transportation and onsite storage of highly dangerous chlorine gas.  
         [0021]     It is another object of the invention to provide greater production flexibility than existing caustic potash plants.  
         [0022]     It is still another object of the invention to offer greater profitability than existing caustic potash plants or electrolysis bleach plants.  
         [0023]     It is still a further object of the invention to provide a process in which production of chlorine gas can be easily diverted from direct sale to production of bleach and/or hydrochloric acid.  
         [0024]     It is yet a further object of the invention to provide a process with better economics than existing caustic potash plants and electrolysis bleach plants.  
         [0025]     Other objects, features, and characteristics of the present invention, as well as the methods of operation and functions of the related elements of the structure, and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following detailed description with reference to the accompanying drawings, all of which form a part of this specification.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     A further understanding of the present invention can be obtained by reference to a preferred embodiment set forth in the illustrations of the accompanying drawings. Although the illustrated embodiment is merely exemplary of systems for carrying out the present invention, both the organization and method of operation of the invention, in general, together with further objectives and advantages thereof, may be more easily understood by reference to the drawings and the following description. The drawings are not intended to limit the scope of this invention, which is set forth with particularity in the claims as appended or as subsequently amended, but merely to clarify and exemplify the invention.  
         [0027]     For a more complete understanding of the present invention, reference is now made to the following drawings in which:  
         [0028]      FIG. 1  shows a schematic of the process of producing potassium hydroxide and chlorine gas.  
         [0029]      FIG. 2  depicts a schematic of the manufacturing process in accordance with the preferred embodiment of the present invention.  
         [0030]      FIG. 3  shows an expanded view of the manufacturing process in accordance with the preferred embodiment of the present invention.  
         [0031]      FIG. 4  is a schematic representation of a cell gas bleach reactor according to the preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     As required, a detailed illustrative embodiment of the present invention is disclosed herein. However, techniques, systems and operating structures in accordance with the present invention may be embodied in a wide variety of forms and modes, some of which may be quite different from those in the disclosed embodiment. Consequently, the specific structural and functional details disclosed herein are merely representative, yet in that regard, they are deemed to afford the best embodiment for purposes of disclosure and to provide a basis for the claims herein which define the scope of the present invention. The following presents a detailed description of the preferred embodiment (as well as some alternative embodiments) of the present invention.  
         [0033]     This invention is applicable for a standalone plant or a plant dedicated for gaseous chlorine delivery to an adjacent plant for production of hydrochloric acid, bleach, or various chemicals which require chlorine gas as a reactant.  
         [0034]     The present invention involves the integrated process for the manufacture of potassium hydroxide, KOH, also called caustic potash, and sodium hypochlorite. Chlorine gas that is produced by the electrolysis of a potassium chloride solution in an electrolysis cell is used directly in sodium hypochlorite (bleach) manufacture by chemically combining the chlorine with purchased sodium hydroxide. Alternatively, hydrochloric acid, HCl, may be produced by the burning of chlorine in the presence of co-product hydrogen. Direct use of chlorine from KOH manufacture eliminates the need for transporting or storing the hazardous chlorine gas. Further, co-product hydrogen may be collected independently, dried and sold to customers.  
         [0035]     According to the preferred embodiment of the present invention, shown in  FIG. 2 , solid potassium chloride (KCl) salt  41  arrives at a processing plant via rail car  44 . Potassium chloride  41  is transferred to a salt dissolver  42 , wherein the solid, impure potassium chloride  41  is dissolved in water to form brine  43 . In an alternative embodiment, sodium chloride (NaCl) may be substituted for potassium chloride to ultimately produce sodium hydroxide (NaOH) instead of potassium hydroxide (KOH).  
         [0036]     Next, appropriate chemicals are added to the brine  43  to precipitate impurities that may be potentially damaging to the membrane in the electrolyzer. Among the most common adulterants found in impure brine are sulfate ions, which may be removed by precipitation with barium or calcium. The resulting mixture is fed to a thickener  45 , from which precipitates and clarified raw brine  43  are separately withdrawn. The clarified brine  43  is then filtered by brine filter  46 . Solid precipitates are sent to a landfill, or disposed of by any suitable method. The filtered brine  43  is then pumped to a filtered brine tank  47 . Next, secondary brine purification is performed on brine  43  via an ion exchange unit  48 . Secondary brine purification ensures high efficiency and long lasting membrane electrolyzer operation. Deionized brine  43  is stored in tank  49  before being sent to electrolyzer  50 .  
         [0037]     Electrolyzer  50  is preferably a single or multiple membrane electrolyzer cell, as it is known to be safe, asbestos and mercury free and effective. However, in alternative embodiments, other electrolyzers may be used. Such commonly known electrolyzers are mercury and asbestos diaphragm electrolyzers, and membrane electrolyzers—monopolar and bipolar.  
         [0038]     In electrolyzer  50 , electric power is provided via an AC-DC rectifier  51 . Deionized brine  53  and purified water  52  are pumped into electrolyzer  50 . Application of electricity causes anions, i.e. chloride ions, to collect at the anode side of the electrolyzer  50  and cations, i.e. potassium and hydrogen ions, to collect at the cathode side of the electrolyzer  50 . The chemical equations below describe the reactions that take places upon electrolysis of the brine. 
 
2Cl − --&gt;Cl 2 +2 e   −  (Anode)
 
2H 2 O+2 e   − --&gt;H 2 +2OH −  (Cathode)
 
 The chlorine gas will form at the anode while the water will be electrolyzed to form hydrogen gas. The remaining ions, K+ and OH −  will combine to form an aqueous solution of the desired caustic potash product. 
 
         [0040]     The chlorine produced from the weak solution of brine  43 , is either drawn from the anode side of the cell in a vacuum or the solution is pumped to a dechlorination process. To process the wet chlorine, the gas is cooled and the brine  43  condensate is removed in a dechlorinator  54 . The weak solution of brine  43  is then returned to the brine treatment area, specifically the salt dissolver  42 . According to the present invention, the costly steps of drying and liquefying chlorine gas are eliminated. Instead, the chlorine is pumped to the hypo tower  64 .  
         [0041]     The sodium hypochlorite, or hypo, system consists of two plate exchange scrubbing towers  64  and  66 , with associated pumps, tanks, coolers and fans. Operation of the hypo system is continuous. For safety reasons, the critical equipment is provided with a secure electric power supply to ensure continued operation during power failures and to avoid catastrophic consequences.  
         [0042]     In order to manufacture sodium hypochlorite, chlorine gas from the dechlorinator  54 , as well as vent gases from miscellaneous sources in the plant, are drawn by a vacuum or pumped through the primary hypo tower  64 . Sodium hydroxide  65  from the secondary hypo tower  66 , as well as recirculated sodium hydroxide and sodium hypochlorite from the primary hypo tower pump, are fed to the top of the primary hypo tower  64 . The sodium hydroxide and chlorine react to form bleach according to the following equation: 
 
2NaOH+Cl 2 --&gt;NaOCl+NaCl+H 2 O+ heat
 
         [0043]     The exothermic nature of the above reaction causes the temperature to rise in the primary hypo tower  64 , and therefore to maintain product stability the hypo is cooled before storage in storage tank  68 . The primary hypo tower  64  is a plate exchanger with cooling water used to cool the liquor. The primary hypo chiller further reduces the hypo solution temperature to 60° F. using chilled water to slow down the chemical disintegration of the hypo product.  
         [0044]     A portion of the cooled hypo product is transferred to storage tank  68  by primary hypo pump through the hypo filter. The filter ensures a clear product solution for storage. Product in various strengths, up to 20% by weight, can be produced by controlling the balance between chlorine, sodium hydroxide and water.  
         [0045]     Vent gases leaving primary hypo tower  64  are piped to the secondary hypo tower  66 . The gas flows upward through tower  66  under suction from hypo fan  67 . Sodium hydroxide solution is circulated around tower  66  by the secondary hypo tower pump and absorbs any residual chlorine from primary hypo tower  64 . Any unexpected large chlorine vents from primary hypo tower  64  will be absorbed and the chlorine emissions kept to a minimum with a two-tower scrubbing system.  
         [0046]     The secondary hypo cooler  69  is used to remove the heat resulting from the reaction of chlorine in the secondary hypo tower  66 , and the dilution of sodium hydroxide.  
         [0047]     In the process that uses hypo fan  67 , suction throughout the hypo system is provided by a centrifugal fan connected to the outlet of the secondary hypo tower  66 . Effluent is scrubbed with caustic soda and discharged to the atmosphere. The suction provided by hypo fan  67  introduces an additional safety feature. In the case of a leak in the chlorine line in the hypo system, the pressure differential created by hypo fan  67  will cause air to be sucked into the line and not permit chlorine gas to escape. An installed spare fan is also provided. Both fans are connected to the standby power supply.  
         [0048]     An alternative embodiment for the manufacture of sodium hypochlorite is shown in  FIG. 4 . As discussed with respect to the preferred embodiment, the costly steps of drying and liquefying chlorine are also eliminated in this alternative embodiment. Chlorine from electrolyzer  50 , vent gases and “off spec” product are mixed with purchased sodium hydroxide  80  solution to form sodium hypochlorite, i.e. hypo, solution. The system  85  consists of an eductor  72 , bleach reactor  74 , refrigerated cooler  76 , static mixer  78  and various pumps and control valves. Purchased sodium hydroxide  80  from storage is pumped into the system.  
         [0049]     Chlorine, saturated with water, leaves the electrolyzer  50  at a temperature of approximately 190-200° F. and is pumped through an eductor  72 . Eductor  72  mixes the chlorine in solution with recycled hypo. The hypo solution enters the bleach reactor  74  where recycled, chilled hypo is pumped into reactor  74  for mixing. Then, bleach from reactor  74  is pumped through a refrigerated cooler  76  where specification product is drawn off and sent to storage. Other bleach is recycled onto the static mixer after controlled quantities of water and sodium hydroxide are added to the bleach. Through controls and analyzers for the amount of chlorine, water, sodium hydroxide and temperature in the system permit the production of bleach up to 20% by weight.  
         [0050]     Additionally, the process may be modified to manufacture hydrochloric acid, as shown in  FIG. 3 . The hydrogen gas generated at the cathode of electolyzer  50  is sent to acid burner  88 . Chlorine gas that comes out of the dechlorinator  54  may also be sent to acid burner  88 . The chlorine is then burned in the presence of hydrogen and demineralized water provided by stream  90  to form hydrochloric acid, which is then sent to tank  92 . The concentration of the acid may be controlled by the amount of water used in the process.  
         [0051]     Potassium hydroxide and hydrogen, collected at the cathode side of electrolyzer  50 , are drawn from the membrane cell electrolyzer  50 . Potassium hydroxides leave the electrolyzer  50  at approximately 30-35% by weight in an aqueous solution at a temperature between approximately 190 and 200° F. This low strength potassium hydroxide solution is split. One stream is cooled and stored for use in the brine treatment tank  45 . The other, major, stream is sent to evaporator  58  for removing the water. In evaporator  58 , the hot potassium hydroxide solution is concentrated to the commercial grade specification, i.e., approximately 45%. Next, the product is cooled to about 170° F. and sent to product storage  60 .  
         [0052]     Hydrogen gas, also produced on the cathode side of the electrolyzer  50 , may be sent to vent  61  ( FIG. 3 ) for pressure control. The majority of the produced hydrogen, however, is cooled to remove water vapor before it is pumped to hydrogen compressor. After the hydrogen is compressed, it is sent to the boiler  62  for use as fuel. Alternatively, as discussed before, the collected hydrogen gas may be collected, stored and sold to customers, or send to acid burner  88  for use in hydrochloric acid production.  
         [0053]     At a standalone plant, the present invention offers greater operating flexibility, profitability and safety than existing plants. A standalone plant would produce KOH and bleach and/or HCl since the transportation of gaseous chlorine is difficult and dangerous. Currently, there are no known plants with this processing option.  
         [0054]     At a dedicated plant, for the situation where a customer wants to buy gaseous chlorine, this combination of processes enables the economic balancing of product production with chlorine demand. When gaseous chlorine demand is lowered, the plant operator can divert the chlorine production from chlorine pipeline deliveries to either bleach or HCl production. This permits the plant to continue to operate at full capacity. The liquid products, KOH, bleach, and HCl are all readily stored in rail cars or storage tanks and provide the capability of balancing supply and demand with alternate product sales or storage.  
         [0055]     According to the process of the present invention, bulk chlorine is never stored under pressure in storage drums or rail cars. This eliminates the hazard of a chlorine cloud being released unintentionally. Small quantities of elemental chlorine exist only in the process just prior to being combined with sodium hydroxide, hydrogen or in the customer pipeline. In the case of a dedicated plant, chlorine is delivered to nearby customers and eliminates the use of rail cars and onsite chlorine storage.  
         [0056]     Further, the invention is the combination of known processes that provide for greater revenue and profit than existing processes. There is no existing plant that combines the electrolysis of KCl with bleach and hydrochloric acid manufacture and has pipeline delivery of chlorine.  
         [0057]     In addition, the hydrochloric acid and bleach manufacture of the present invention adds flexibility to consume the chlorine production when other chlorine derivative requirements are low.  
         [0058]     According to another aspect of the present invention, the process, compared to existing potassium hydroxide-chlorine plants, eliminates the need for expensive chlorine drying and liquefaction. Two hypo towers, bulk sodium hydroxide storage, pumps and lines are added to the process. It is estimated that the net capital cost is reduced significantly with the invented process.  
         [0059]     While the present invention has been described with reference to one or more preferred embodiments, such embodiments are merely exemplary and are not intended to be limiting or represent an exhaustive enumeration of all aspects of the invention. The scope of the invention, therefore, shall be defined solely by the following claims. Further, it will be apparent to those of skill in the art that numerous changes may be made in such details without departing from the spirit and principles of the invention. It should be appreciated that the present invention is capable of being embodied in other forms without departing from its essential characteristics.