Abstract:
A process for producing a cellulose based sorbent material for the removal of water soluble contaminants from water and other aqueous solutions comprising reacting one or more biomass based cellulose containing raw materials with dilute phosphoric acid where the reaction mixture containing said cellulose containing materials is heated to a reaction temperature and after completion of the reaction time, separation of the dilute phosphoric acid solution from the remaining insoluble raw material, neutralization of the solution by means of a suitable neutralizing agent resulting in precipitation of the modified cellulose, and then separating, washing and removing excess water from the resultant precipitate.

Description:
This application is the U.S. national phase of International Application No. PCT/AU2012/000083 filed 1 Feb. 2012 which designated the U.S. and claims priority to AU 2011900307 filed 1 Feb. 2011, the entire contents of each of which are hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     This invention relates to a chemical process for synthesising a modified cellulose phosphate powder from biomass sources of cellulose including, but not limited to, algae, bagasse, and waste paper. 
     This invention further relates to the application of the cellulose phosphate powder for use in removal of venous contaminants or chemical species from water, including but not limited to Mercury, Cadmium, Chromium, Copper, Zinc, Iron, Bismuth, Selenium, Tin, Cobalt, Nickel, Vanadium, Manganese, Uranium, Thorium, Arsenic, Lead and Ammonia. 
     BACKGROUND OF THE INVENTION 
     This invention has particular application in near neutral pH aqueous solutions that are contaminated with various water soluble species. Typical species include those containing transition metals, and also other contaminants containing ammonia, arsenic, and selenium. At low concentrations these contaminants are soluble in water and often have toxicological, clinical or environmental impacts. At low concentrations, many contaminants are difficult to separate from water. The existing solutions for removal of trace level contaminants, particularly those utilized in industrial applications, include the use of on exchange resins, activated carbon or alumina, or titanium dioxide, reverse osmosis, chemical precipitation, or biological filtration. Each of these works with only specific contaminants. However none of these options is satisfactory for all contaminants. Further, other limitations of these processes include insufficient removal of particular contaminants, impractical application for large volumes, and high expense. Often a combination of two or more techniques is necessary, and creates process engineering difficulties. 
     SUMMARY OF THE INVENTION 
     The present invention involves creating a modified cellulose based powder by reacting a biomass based cellulosic raw material with dilute phosphoric acid at elevated temperature. The cellulosic raw material is partially dissolved and then the remaining insoluble raw material is separated from the dilute phosphoric add solution. The clear phosphoric acid solution is then neutralized with subsequent precipitation of the modified cellulose, followed by, separating, washing and removal of excess water prior to use. The resulting product is a sorbent powder. (Wherever the term “sorbent” is used in this specification, this shall be interpreted to mean adsorbent. However, it is to be understood that the product may also have absorbent properties.) The sorbent product, which may be in the form of a powder or a slurry, is particularly useful for removal of low levels of contaminants from water and aqueous solutions. The solid residue resulting from extraction is then inert and non flammable, and the remaining filtrate is discarded, or may be processed for recovery of unreacted phosphoric acid. 
     As a sorbent for trace contaminants, the method of application includes but is not limited to contacting the sorbent product with the contaminated water or aqueous solution by musing and then separating either by allowing the product to settle and decanting the supernatant treated water or solution, or by filtering, or some other method of solid liquid separation. 
     Additionally the sorbent product can be used as an active component in a filter or permeable reactive barrier 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The synthesis of the sorbent powder is performed by utilizing a cellulosic feedstock. This may include but is not limited to algae, bagasse, and favourably, waste paper. The cellulosic feedstock is then mixed with dilute phosphoric acid (typically in the concentration range from approximately 2 g/l up to 40 g/l but may also be in the range 1 g/l up to 80 g/l), and heated to reaction temperature for at least 2 minutes, but more preferably at least 5 minutes, up to 4 hours. The heating may be performed by conventional means, but may also include alternative heating technologies for water including microwave heating. The ratio of cellulosic feedstock to dilute phosphoric add may typically be between a ratio of 1 part feedstock to 5 parts dilute phosphoric acid, up to 1 part feedstock to 40 parts of dilute phosphoric acid. However, this ratio may also foreseeably be in the range of 1 part feedstock to 2 parts dilute phosphoric acid, up to 1 part feedstock to 80 parts of dilute phosphoric add. This is more of a practical issue rather than a technical limit. The yield of sorbent from feedstock ranges from 4% by weight up to 40% by weight depending upon the feedstock used, the dilute acid concentration and volume, and the temperature and heating time of the synthesis. 
     Following reaction of the feedstock with dilute phosphoric acid, the remaining solids and the solution are separated by any suitable means. Simple filtering has been shown to be effective. The solid residue consists of insoluble and unreactive cellulosic feedstock. This residue is non flammable and, based upon this characteristic, may be useful as a fire retardant and in insulation products. Subsequent to the initial solid liquid separation, the filtrate or supernatant is neutralized to pH 7 with any suitable neutralizing agent but preferably caustic soda. As the neutralization is performed, a fine precipitate develops in solution which settles easily and filters easily. This precipitate is the object of the process and is recovered by filtering or other suitable solid liquid separation technique. The precipitate is then washed with water to remove any remaining salts, and excess water removed. Accordingly, the product may be a dried powder or may be in the form of a slurry. 
     The application of the sorbent product for treatment of low level water contaminants is performed by simple mixing of the sorbent product with water. Contact and mixing time may typically be between approximately 5 minutes and 2 hours. However, this range may be greater and foreseeably may be between approximately 2 minutes and 24 hours, with dose rate determined by total load of contaminants and capacity of the sorbent for a given contaminant. Following mixing of the sorbent and the water to be treated, solid liquid separation is performed by any suitable means including but not limited to filtering, centrifugation, and decanting. Additionally the sorbent can be utilized as a filter bed with the contaminated water passed through the filter bed with removal of various contaminants taking place within the filter bed. 
     The use of cellulose phosphate derivatives has been described in prior art patents DE19850286 (A1); DE19753196 (A1); DE19869746 (A1); U.S. Pat. No. 6,579,977 (B1); U.S. Pat. No. 6,761,272 (B1); U.S. 2007093664 (A1); GB1001603 (A). In these patents all cellulose feedstocks described are prepared via several steps which include caustic pulping, further pulp preparation, and derivatisation with complex and expensive phosphate reagents. In the above prior art documents, derivatisation is performed in organic solvents which increase the safety risks and expense of producing a cellulose phosphate derivative. Further, additional derivatisation is needed to achieve satisfactory performance for trace contaminant removal and this usually includes but is not limited to addition of amine or nitrogen species to effect an improved functionality of the cellulose derivative. 
     The present invention provides an alternative and more cost effective solution for the removal of the abovementioned contaminants from water. The cellulose phosphate product has different physical characteristics and improved performance as water treatment product, particularly for trace contaminants. In addition, the cellulose phosphate of the present invention has a Fourier Transformation Infrared spectrum that shows significant differences from conventional cellulose phosphate esters and ethers. The process described in the present invention utilizes a different method of synthesis to previously taught approaches and offers a number of advantages including greater simplicity, lower risk and production costs. This results in a product with affinity for a range of contaminants (the affinity of which may vary according to the contaminant) without the need for further functionalization. 
     The following examples are provided in order to illustrate the process: 
     Example 1 
     3.128 g of waste paper was reacted with 120 mls of 8% w/v phosphoric acid at 104 degrees C. for 2 hours 43 minutes. The resultant mixture was cooled, separated by filtering and the residue washed and dried. 2.206 g of residue was recovered. The filtrate and washings were neutralized with 40 g/l caustic soda to a pH of 7.0, the resultant precipitated powder was filtered and washed and dried to give a final weight of 0.845 g of sorbent powder. 0.5 g of this powder was added to a 1 liter water sample with 24 hours mixing and the resultant change in composition was: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Untreated 
                 Treated 
               
               
                   
                 Sample Analyte 
                 Sample 
                 Sample 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 ARSENIC (mg/L) 
                 0.130 
                 0.078 
               
               
                   
                 COPPER (mg/L) 
                 0.023 
                 0.007 
               
               
                   
                 IRON (mg/L) 
                 3.388 
                 1.357 
               
               
                   
                 LEAD (mg/L) 
                 0.159 
                 0.001 
               
               
                   
                 SELENIUM 
                 1.698 
                 1.181 
               
               
                   
                 (mg/L) 
               
               
                   
                 ZINC (mg/L) 
                 0.042 
                 0.023 
               
               
                   
                 MERCURY 
                 0.009 
                 &lt;0.001 
               
               
                   
                 (mg/L) 
               
               
                   
                 THALLIUM 
                 0.0019 
                 0.0011 
               
               
                   
                 (mg/L) 
               
               
                   
                   
               
             
          
         
       
     
     Example 2 
     2.003 g of bagasse was reacted with 100 mls of 8% w/v phosphoric acid at 100 degrees C. for 3 hours and 15 minutes. The resultant mixture was cooled separated by filtering and the residue washed and dried. 1.782 g of residue was recovered. The filtrate and washings were neutralized with 40 g/l caustic soda to a pH of 7.0, the resultant precipitated powder was filtered and washed and dried to give a final weight of 0.241 g of sorbent powder. 
     Example 3 
     1.030 g of dried filamentous algae was reacted with 100 mls of 8% w/v phosphoric acid at 100 degrees C. for 3 hours and 15 minutes. The resultant mixture was Cooled separated by filtering and the residue washed and dried. 0.982 g of residue was recovered. The filtrate and washings were neutralized with 40 g/l caustic soda to a pH of 7.0, the resultant precipitated powder was filtered and washed and dried to give a final weight of 0.073 g of sorbent powder. 
     Example 4 
     1170 g of waste paper was boiled with 23.3 liters of 4.4% w/v phosphoric acid for 2 hours. The resultant mixture was cooled separated by decanting end then filtering and the residue washed and dried. The filtrate and washings were neutralized with 80 g/l caustic soda to a pH of 6.5, the resultant precipitated powder was filtered and washed and dried to give a final weight of 221 g of sorbent powder. 339 mg of this powder was prepared as a column filter and 100 ml of contaminated water was passed through the filter. The resultant change in water composition was: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Untreated 
                 Treated 
               
               
                   
                 Sample Analyte 
                 Sample 
                 Sample 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 IRON (ug/L) 
                 1620 
                 5 
               
               
                   
                 COPPER (ug/L) 
                 440 
                 035 
               
               
                   
                 MANGANESE 
                 3360 
                 1480 
               
               
                   
                 (ug/L) 
               
               
                   
                 LEAD (ug/L) 
                 9 
                 &lt;0.5 
               
               
                   
                   
               
             
          
         
       
     
     The invention enables the reduction of a range of trace contaminants from contaminated water sources with near neutral pH, without any toxic or aesthetic reduction in water quality. This invention has particular application in dilute waste water treatment, or environmental water treatment. 
     Accordingly the invention has both commercial and environmental advantages. It will of course be realised that while the foregoing has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is herein set forth.