Abstract:
Methods and apparatus are provided for exploiting coated paper products such as coated paper cups. End products include biofuels that have a high energy density. The biofuels may be mixed with coal or other fuels and have good binding characteristics. In some embodiments, useful chemicals such as HMF are produced. The methods involve heat treatment at relatively mild temperatures and pressures under acidic conditions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. application No. 61/174466 filed on 30 Apr. 2009 and entitled PROCESS AND APPARATUS FOR RECYCLING COATED PAPER PRODUCTS which is hereby incorporated herein by reference. For purposes of the United States of America, this application claims the benefit under 35 U.S.C. §119 of U.S. application No. 61/174466 filed on 30 Apr. 2009 and entitled PROCESS AND APPARATUS FOR RECYCLING COATED PAPER PRODUCTS which is hereby incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to paper recycling, and more specifically, to methods and apparatus for recycling coated paper products. 
       BACKGROUND 
       [0003]    Paper products are used in a wide variety of applications. For example, plastic coatings are used in packaging, paper cups, containers for food or beverages, and the like. The plastic coatings in these products can impart water resistance and improve wet-strength. Plastic coated paper products (such as hot beverage cups and food wrappers) are often excluded from recycling programs, because the coating is incompatible with current recycling technology. This adds to the accumulation of waste in landfills. 
       SUMMARY 
       [0004]    There is a need for a method of recycling coated paper products into useable products. Aspects of this invention provide methods and apparatus that address this need. 
         [0005]    One aspect of the invention provides a method of recycling coated paper products. The method involves breaking-up coated paper products to make a pulp. The pulp is heated in a basic solution, and is cooled and de-watered to yield a mixture comprising de-coated pulp and coating fines. The mixture is then heated under acidic conditions to produce residual solids and useable chemicals. The residual solids and useable chemicals may be separated. 
         [0006]    The residual solids have an excellent energy density and can be burned as a green replacement for coal or other fuels. The energy density of the residual solids can be on the order of 27 to 30 GJ/Tonne. The residual solids may be pelletized for use as a fuel, used as a binder in pelletizing coal or other fuels, and/or mixed with coal or other fuels to provide blended fuels. 
         [0007]    In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]    The accompanying drawings illustrate non-limiting example embodiments of the invention. 
           [0009]      FIG. 1  is a block process diagram according to an example embodiment of the invention. 
           [0010]      FIG. 2  is a block process diagram illustrating one possible arrangement for the breaking-up step of  FIG. 1 . 
           [0011]      FIG. 3  is a block process diagram illustrating one possible arrangement for the separation step of  FIG. 1 . 
           [0012]      FIG. 4  is a block process diagram illustrating one possible arrangement for the conversion step of  FIG. 1 . 
           [0013]      FIG. 5  is a block process diagram illustrating one possible arrangement for the product separation step of  FIG. 1 . 
           [0014]      FIG. 6  is a schematic diagram of a batch mode apparatus according to an example embodiment. 
           [0015]      FIG. 7  is a schematic diagram of a continuous mode apparatus according to an example embodiment. 
       
    
    
     DESCRIPTION 
       [0016]    Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense. 
         [0017]    This invention provides a method and apparatus for recycling coated paper products into useable products, such as useable chemicals and residual solids. The invention also provides a method of producing useable chemicals and residual solids. The coated paper products may comprise plastic coated paper products such as: beverage cups, fast food wrappers, paper plates, paper bags for take-out food, coated cardboard, baby diapers, mixtures thereof, and the like. 
         [0018]    Polyethylene, also referred to as polycoat, is a commonly-used plastic coating in coated paper products. Polycoat can impart water resistance and improve wet-strength. However, the methods of the present invention are not restricted to polyethylene-coated paper or even plastic-coated paper and may be used with any number of coatings, for example, waxes, lacquers, varnishes, adhesives and hot melts. The methods may be used with most coated paper products wherein the individual fibers are not embedded in a plastic or hydrophobic matrix. 
         [0019]      FIG. 1  shows a block diagram of a method  10  according to an embodiment of the invention. Coated paper products are subjected to a breaking-up step  20  to form a pulp. The pulp is then subjected to a separation step  40  to form a mixture comprising de-coated pulp and coating fines. This mixture is subjected to a conversion step  60 , wherein the de-coated pulp and coating fines are converted into useable products. In a product separation step  80 , the useable products may be separated and optionally purified to provide useful end products. 
         [0020]    The breaking-up step  20  acts to break-up and at least partially pulp the paper in coated paper products. The resulting pulp may comprise intact cellulose fibers bonded with some coating, broken cellulose fibers bonded with some coating, de-coated cellulose fibers, particles of coated paper, or a combination of these. Separation stage  40  acts to at least partially break bonds between the cellulose fibers or the paper and the coating, resulting in a mixture comprising de-coated pulp and coating fines. The de-coated pulp may comprise cellulose fibers bonded with some coating, de-coated cellulose, or a combination thereof. 
         [0021]    The paper of coated paper products may predominantly comprise cellulose fibers. However, other types of fibers, such as hemicellulose fibers, may be present. In an embodiment of the invention, the coated paper products are made from wood fiber. Alternatively, the invention may be practiced with paper made from other types of fibers. For example, the coated paper products may be made from cotton, linen, hemp, bamboo, jute, bagasse, straw, esparto, or combinations of these. 
         [0022]      FIG. 2  is a block diagram showing a possible breaking-up step  20 . Coated paper products  102  may be broken-up in water in a breaking-up stage  24  to produce a pulp-water slurry  104  comprising pulp  106 . Breaking-up stage  24  may comprise disintegrating or pulping coated paper products  102  in water. Additionally or alternatively, breaking-up stage may comprise breaking-up coated paper products  102  using other mechanical processes, such as shredding, tearing, cutting, grinding, milling, chopping, beating, subjecting to waterjets, or a combination of these. Optionally, pulp-water slurry  104  can be de-watered in a de-watering stage  26  to yield pulp  106 . 
         [0023]    In breaking-up stage  24 , a disintegrator may be used to break-up coated paper products  102 . In one embodiment, a pulper is used to agitate coated paper products  102  in water, thereby disintegrating and dispersing the coating-bonded cellulose fibers, the de-coated cellulose fibers, particles of coated paper or combination thereof. The pulper may comprise a water jet pulper, a hydropulper, or another type of pulper. In other embodiments, other types of disintegrators are used, for example choppers, comminutors, grinders, mills, shredders and water jets. 
         [0024]    Pulp  106  may comprise intact cellulose fibers bonded with some coating, broken cellulose fibers bonded with some coating, de-coated cellulose fibers, particles of coated paper, or a combination of these. In an example embodiment, coated paper products are agitated in breaking-up stage  24  for a period of time that is sufficient to convert the coated paper products into small, water-soaked particles of coated paper. In an example embodiment, breaking-up stage  24  is carried out at ambient temperature and pressure. 
         [0025]    The properties of pulp  106  may depend on a number of factors, such as the fiber source and the pulp refining methods that were used in making the paper of the coated paper product. The properties of pulp  106  may also depend on the equipment and parameters used in breaking-up stage  24 . The method may be used with coated paper products comprised of cellulose fibers having a variety of average fiber lengths. 
         [0026]    In optional de-watering stage  26 , pulp-water slurry  104  is thickened or de-watered. In an example embodiment, pulp-water slurry  104  has a consistency that is dilute, for example, 1% to 5% AD. In this embodiment, pulp-water slurry  104  is de-watered to yield pulp  106  having a consistency in the range of 30% to 50% AD. Any of a number of different types of de-watering assemblies may be used to de-water pulp-water slurry  104  in optional de-watering stage  26 . For example, de-watering assemblies may comprise gravity thickeners or deckers, slushers, extractors, filters or a combination of these. 
         [0027]      FIG. 3  is a block process diagram showing a possible separation step  40 . In a heating stage  42 , pulp  106  is heated in basic (i.e. alkaline) conditions for a period of time that is sufficient to produce a slurry  112  of de-coated pulp and coating fines. Optionally, after heating, slurry  112  is allowed to cool in a cooling stage  44 . Slurry  112  is then de-watered in a de-watering stage  46 , to remove a basic solution  110 ′, leaving de-coated pulp and coating fines  116 . Basic solution  110 ′ may be recycled to heating stage  42  to process more slurry  112  of de-coated pulp and coating fines. Optionally, after de-watering stage  46 , de-coated pulp and coating fines  116  may be washed in a washing stage  48 . 
         [0028]    In heating stage  42 , pulp  106  is heated in basic conditions. As an example, basic conditions may be achieved by adding basic solution  110  to a vessel prior to, during or after adding pulp  106 . Basic solution  110  may comprise an aqueous base, such as a hydroxide (for example, sodium hydroxide or potassium hydroxide). In an example embodiment, basic solution  110  comprises sodium hydroxide. The slurry of pulp  106  in basic solution may have a pH above 10. In an example embodiment, the slurry of pulp  106  in basic solution has a pH in the range of 13 to 14. 
         [0029]    Heating stage  42  in separation stage  40  acts to at least partially break bonds between the cellulose fibers and the coating in any coated fibers or particles of coated paper in pulp  106 . In an example embodiment using polycoated paper products, heating pulp  106  in basic conditions causes the cellulose fibers to swell and the bond between the polycoat and fibers to break, yielding de-coated pulp and coating fines. The coating fines produced from polycoated paper products may have an average length in the range of 1 to 5 mm and an average diameter of approximately 1 mm. Preferably, the slurry of pulp  106  in basic solution is heated at a temperature, pressure and for a duration of time that is sufficient to break most of the bonds between the cellulose fibers and the coating. The endpoint may be detected by the formation of small particles of coating fines in the slurry. 
         [0030]    In one example embodiment, the slurry of pulp in basic solution is heated to a temperature above 125° C. at a pressure in the range of 2 atm to 5 atm and is held at this temperature and pressure for an appropriate time, for example, 30 minutes. The slurry of pulp  106  in basic solution may be heated in a pressure vessel. 
         [0031]    Optionally, the resulting slurry  112  of de-coated pulp and coating fines may be allowed to cool or may be cooled before subjecting it to de-watering stage  46  and optionally, washing stage  48 . For example, slurry  112  may be allowed to cool to below 50° C. 
         [0032]    In de-watering stage  46 , slurry  112  is thickened or de-watered. In an example embodiment, slurry  112  has a consistency in the range of 1% to 10% AD. In this embodiment, slurry  112  is de-watered to yield de-coated pulp and coating fines  116  having a consistency in the range of 30% to 50% AD. A number of different types of de-watering assemblies may be used to de-water slurry  112  in de-watering stage  46 . For example, de-watering assemblies may comprise gravity thickeners or deckers, slushers, extractors, filters, or a combination of these. 
         [0033]    Washing stage  48  may comprise any of various suitable washing or rinsing processes. In one embodiment, in washing stage  48 , the pulp is rinsed and filtered. In some embodiments, washing assemblies such as rotary vacuum washers, pressure washers and/or dilution/extraction equipment may be used. Optionally, washing stage  48  may be a multi-staged process. 
         [0034]      FIG. 4  is a block process diagram of a possible conversion step  60 . De-coated pulp and coating fines  116  may be combined with water in a re-wetting stage  62  before being submitted to a conversion stage  70 . Alternatively, de-coated pulp and coating fines  116  are re-wet in conversion stage  70 . In conversion stage  70 , a slurry of the de-coated pulp and coating fines  116  is heated in acidic conditions for a period of time that is sufficient to produce a mixture of residual solids and useable chemicals. Optionally, this mixture may be cooled or allowed to cool in a cooling stage  72 . 
         [0035]    Optionally, prior to conversion stage  70 , the slurry of de-coated pulp and coating fines  116  may be submitted to a neutralization stage  64 . In one example of neutralization stage  64 , bubbles of a weak acid gas  120 , such as carbon dioxide are released or sparged through the slurry of de-coated pulp and coating fines to neutralize at least some of any base remaining from separation step  40 . In another example of neutralization stage  64 , the slurry is mixed with a solution of weak acid. Optionally, neutralization stage  64  may be followed by a de-watering stage  66 , a washing stage  67  and a re-wetting stage  68 , prior to conversion stage  70 . 
         [0036]    In conversion stage  70 , a slurry of the de-coated pulp and coating fines  116  is heated in acidic conditions. As an example, acidic conditions may be achieved by adding one or more acids  122  to a vessel prior to, during or after adding the slurry of the de-coated pulp and coating fines  116 . One or more acids  122  may comprise an aqueous acid, such as sulfuric acid or hydrochloric acid. However, depending on the desired products, other acids may be used, for example, weak organic acids, such as maleic acid, malonic acid and/or oxalic acid. The slurry of de-coated pulp and coating fines  116  may have a pH below 5 and below 2 in some embodiments. In an example embodiment, the slurry of de-coated pulp and coating fines  116  has a pH in the range of 0 to 2. Other acids that may be used to achieve acidic conditions include other strong acids such as phosphoric, sulphuric, hydrochloric, or hydrobromic acid; or other weak acids such as carbonic (H 2 CO 3 ), formic, acetic, oxalic, maleic, malic, malonic etc. In some embodiments carbonic acid is provided by contacting CO 2  with the slurry, for example by sparging CO 2  gas through the slurry. 
         [0037]    Conversion stage  70  acts to break glycosidic bonds between sugar molecules in the cellulose fibers of the de-coated pulp, yielding sugars  124   d.  In some embodiments of conversion stage  70 , some or all of sugars  124   d  are degraded to yield other useable chemicals, for example, levulinic acid, formic acid and/or 5-hydroxymethyl furfural. Conversion stage  70  also acts to degrade the coating fines to yield residual solids  124   b  comprising humins. 
         [0038]    Preferably, the slurry of the de-coated pulp and coating fines  116  is heated under acidic conditions at a temperature, pressure and for a duration of time that is sufficient to break substantially all of the glycosidic bonds in the cellulose. In one embodiment, the slurry is acidified to a pH below 1, is heated to a temperature above 175° C. and a pressure in the range of 5 atm to 30 atm and is held at this temperature and pressure for an appropriate time, for example 30 minutes to 4 hours. In conversion stage  70 , the slurry of de-coated pulp and coating fines  116  may be heated in a pressure vessel. 
         [0039]    Optionally, the resulting mixture  124  of useable chemicals and residual solids may be cooled or allowed to cool in cooling stage  72  before further processing. In one example, mixture  124  is allowed to cool to below 50° C. before product separation step  80 . 
         [0040]      FIG. 5  is a block process diagram for an example product separation step  80 . Mixture  124  of useable chemicals and residual solids in acid is filtered in the filtering stage to remove residual solids  124   b.  Residual solids  124   b  may comprise humins and/or other polymeric carbon compounds. Humins are polycarbon solids made up of carbon, hydrogen and oxygen. Humins and similar polycarbon materials make excellent high energy fuels. The presence of oxygen helps such fuels to burn cleanly. In one embodiment, residual solids  124   b  are dried and pelletized to produce a solid fuel. Alternatively, residual solids  124   b  can be dried and pelletized with coal to produce a coal-like fuel. 
         [0041]    The resulting solution of useable chemicals in acid may be subjected to a product separation stage  84  to separate sugars  124   d,  organic compounds  124   c  and acid  120 ′. In one embodiment, sugars  124   d  comprise glucose. The glucose may be taken off for use/sale. Alternatively, the glucose may be fermented to produce ethanol, which may be taken off for use/sale. Organic compounds  124   c  may comprise one or more organic compounds, such as levulinic acid, formic acid, and/or 5-hydroxymethyl furfural. These organic compounds may be separated and taken off for use/sale, for example as industrial chemicals. Optionally, one or more of the useable products may be purified. Acid  120 ′ may be separated and recycled to conversion stage  70  to produce more useable chemicals and residual solids. 
         [0042]    Useable chemicals may be separated by any of a number of different separation techniques, such as column chromatography, solvent extraction, or high performance liquid chromatography. 
         [0043]    As an example embodiment of the invention, 50 g of coated paper products are combined with 1 L of water in a hydropulper to produce a pulp-water slurry having a consistency of 5% AD. The pulp-water slurry is then de-watered to produce pulp. 
         [0044]    The pulp is then combined with 0.25 molar sodium hydroxide solution in a pressure vessel at a ratio of 10 to 20 parts sodium hydroxide solution to 1 part pulp. The quantity of sodium hydroxide solution is sufficient to ensure that all of the pulp is immersed. The container is sealed to prevent the solution from boiling off during heating. 
         [0045]    The pressure vessel is heated to a temperature in the range of about 125° C. to 175° C. and is held at this temperature for an appropriate time (for example, 125° C. for 30 minutes). The vessel is then allowed to cool to below 50° C. The vessel is opened and the solution is removed via vacuum filtration. Optionally, the solution is re-constituted and recycled to process more pulp. The de-coated pulp is then rinsed with water. 
         [0046]    The washed, de-coated pulp and coating fines is then combined with 0.5 to 1 L water in a pressure vessel. The slurry of washed, de-coated pulp and coating fines in water is then sparged with carbon dioxide to neutralize any remaining hydroxide. Then, a solution of strong aqueous acid, such as hydrochloric or sulfuric acid is added to bring the pH to below 4 or 5 (below 2 in some embodiments). In some embodiments the pH is brought to an acceptably low value by contact with carbon dioxide (which yields carbonic acid). This facilitates performing the complete process within one vessel (a ‘one pot’ process). 
         [0047]    The pressure vessel is then sealed and heated to a temperature above 175° C., for example, 200° C. for an appropriate retention time, for example 30 minutes to 4 hours. The endpoint can be detected by witnessing the disappearance of the fibrous clumps of cellulose and the formation of humins as a fine precipitate. The pressure vessel is then is allowed to cool to below 50° C. 
         [0048]    The residual solids are separated from the useable chemicals by vacuum filtration. The residual solids may comprise humins or polymeric carbon compounds. The residual solids can be dried and pelletized as a solid fuel. Alternatively, they may be dried and pelletized with coal to produce a coal-like fuel. The coal like fuel may comprise a polycarbon polymer comprising HMF and glucose derivatives. Such fuel can have an excellent energy density of 27 to 30 JG/tonne and good combustion properties. 
         [0049]    Where the desired end product is a solid fuel heating step  42  is optional since small particles of plastic may not be objectionable as components of the solid fuel in at least some applications. In an example alternative embodiment, pulped feedstock is placed in a reactor and either CO 2  is bubbled through the pulped feedstock or an acid is added to the pulped feedstock or both. The reactor is then heated to a suitable temperature (e.g. a temperature of at least about 180° C. and typically in the range of 180° C. to 250° C. or 300° C.). The desired temperature will depend on factors such as the pH of the pulped feedstock prior to heating and the time permitted for the treatment to be completed. The stronger the acid (i.e. the lower the pH) the lower the temperature required. The higher the temperature the shorter the treatment time. 
         [0050]    For example CO 2  may be bubbled through a pulp slurry to produce a pH of ˜3-4. The reactor may then be sealed and heated to 220° C. for 1 hour to produce a solid biofuel material in which small plastic coating particles (e.g. 1-2 mm pieces) are present. The biofuel (including any plastic) may be separated by suitable filtration, dried and pressed into pellets, briquettes or the like. 
         [0051]    The useable chemicals are processed to separate the glucose, organic compounds and acid. The organic compounds produced may comprise levulinic acid, formic acid and/or 5-hydroxymethyl furfural. These compounds are separated and purified and then may be sold or used. The glucose may be purified and sold or used or may be fermented to ethanol using, for example,  Saccharomyces cerevisiae.    
         [0052]      FIG. 6  is a schematic diagram of a batch mode apparatus according to an example embodiment. Coated paper products  102  are placed into a pulper in breaking-up stage  24 ′ and are agitated for a duration of time that is sufficient to break coated paper products  102  into a pulp predominantly free of particles of coated paper. The pulp is piped into a pressure vessel in heating stage  42 ′. Controller  90  monitors the pH of the pulp slurry and triggers the addition of base  110  when the pH is below 10. Controller  90  also maintains the temperature and pressure of the pulp slurry in the ranges of 125-175° C. and 1.5 atm to 5 atm respectively. The pulp is in the vessel of heating stage  42 ′ for a duration of time that is sufficient to break a substantial number of the bonds between cellulose fibers and the coating. 
         [0053]    From heating stage  42 ′, a slurry of de-coated pulp and coating fines is piped into a de-watering assembly of de-watering stage  46 ′. Basic solution  110 ′ is removed from the de-coated pulp and coating fines and is re-constituted and recycled into heating stage  42 ′. Alternatively, the pulp may be de-watered prior to heating stage  42 ′, and basic solution  110 ′ may be recycled with little or no re-constitution. 
         [0054]    The de-coated pulp and coating fines are piped into a pressure vessel in conversion stage  70 ′. Acid  122  is piped into the pressure vessel to re-wet de-coated pulp and coating fines and to create acidic conditions. Controller  92  monitors the pH, temperature and pressure of the pressure vessel of conversion stage  70 ′. When the pH rises above 2, controller  92  triggers the addition of acid  122 . Controller  92  maintains the temperature and pressure of the slurry of de-coated pulp and coating fines in the ranges of 170° C. to 220° C. and 5 atm to 25 atm respectively. The de-coated pulp and coating fines are heated in conversion stage  70 ′ until substantially all of the cellulose is hydrolyzed into sugars and optionally, organic compounds and the coating fines are degraded into residual solids comprising humins. 
         [0055]    The residual solids and useable chemicals from conversion stage  70 ′ are piped into a filter in filtering stage  82 ′. The residual solids  124   b  are filtered out and taken off, optionally, for further processing into fuel or coal. The useable chemicals comprising of sugars and/or organic compounds are piped into a resin extraction column (or chromatographic column) of product separation stage  84 ′. The mixture of useable chemicals in acid is separated into acid solution  122 ′, sugars  124   d  and organic compounds  124   c.  Acid  122 ′ is recycled into conversion stage  70 ′. Sugars  124   d  and organic compounds  124   c  are taken off and may be further processed before sale and/or use. 
         [0056]      FIG. 7  is a schematic diagram of a continuous mode apparatus according to an example embodiment. Coated paper products  102  are fed into a pulper in breaking-up stage  24 ″ and are agitated. The resulting pulp is fed through a vessel in heating stage  42 ″. The pulp is in the vessel of heating stage  42 ″ for the duration of time that it takes to travel from one end of the vessel to the other. Controllers  90 ′ monitor the pH of the pulp slurry and trigger the addition of base  110  when the pH is below 10. Controllers  90 ′ also maintain the temperature and pressure of the pulp slurry in the ranges of 125-175° C. and 2 atm to 5 atm respectively.  FIG. 7  shows two controllers  90 ′. Alternatively, any other number of controllers  90 ′ may be used. 
         [0057]    The resulting slurry of de-coated pulp and coating fines is fed through a de-watering conveyer of de-watering stage  46 ″. Basic solution  110 ′ is removed from the de-coated pulp and coating fines and is re-constituted and recycled into separation stage  42 ″. 
         [0058]    The de-coated pulp and coating fines are fed through a vessel in conversion stage  70 ″. Acid  122  is piped into the vessel to re-wet de-coated pulp and coating fines and to create acidic conditions. The de-coated pulp and coating fines are heated in conversion stage  70 ″ for the duration of time it takes to travel from one end of the vessel to the other. Controllers  92 ′ monitor the pH, temperature and pressure of the vessel of conversion stage  70 ″. When the pH rises above 2, controllers  92 ′ trigger the addition of acid  122 . Controllers  92 ′ maintain the temperature and pressure of the slurry of de-coated pulp and coating fines in the ranges of 175° C. to 200° C. and 5 atm to 30 atm respectively.  FIG. 7  shows two controllers  92 ′. Alternatively, any other number of controllers  92 ′ may be used. 
         [0059]    The residual solids and useable chemicals from conversion stage  70 ″ are fed through a filter in filtering stage  82 ″. The residual solids  124   b  are filtered out and taken off, optionally, for further processing into solid fuel or coal-like fuel. The useable chemicals comprising sugars and/or organic compounds are piped into a resin extraction column (or chromatographic column) of product separation stage  84 ″. The mixture of useable chemicals in acid is separated into acid solution  122 ′, sugars  124   d  and/or organic compounds  124   c.  Acid  122 ′ is recycled into heating stage  70 ″. Sugars  124   d  and/or organic compounds  124   c  are taken off and may be further processed before sale and/or use. 
         [0060]    While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following aspects of the invention and any claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.