Abstract:
A green process and system are disclosed for utilizing a biomass filter aid in the filtration of a bio-oil. The process comprises filtering a bio-oil containing residual solids from a conversion reaction in the presence of the biomass filter aid to produce a filtered bio-oil. The biomass filter aid facilitates efficient removal of residual solids from the bio-oil. The spent biomass filter aid containing the residual solids may be recycled as a conversion feedstock or used as a combustion heat source in the biomass conversion system.

Description:
RELATED APPLICATION 
       [0001]    This application is a divisonal of co-pending U.S. patent application Ser. No. 12/835,499, filed Jul. 13, 2010, entitled “SOLIDS REMOVAL FROM BIO-OIL USING BIOMASS FILTER AID,” the entire disclosures of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to the treatment of bio-oil. More specifically, the invention concerns processes and apparatuses for removing undesirable solid components from bio-oil. 
         [0004]    2. Description of the Related Art 
         [0005]    With its low cost and wide availability, biomass has increasingly been emphasized as an ideal feedstock in alternative fuel research. Consequently, many different conversion processes have been developed that use biomass as a feedstock to produce useful biofuels and/or specialty chemicals. Existing biomass conversion processes include, for example, combustion, gasification, slow pyrolysis, fast pyrolysis, liquefaction, and enzymatic conversion. 
         [0006]    Many of the existing biomass conversion processes produce bio-oils containing small residual solid particles. Such bio-oils may require filtration in order to remove these residual solid particles. Since the residual solids often contain fine particles of less than 30 microns in size, fine-scale filters are required. Most filters capable of removing residual solids from bio-oil are rapidly clogged by gelatinous-type solids found in bio-oil. This rapid clogging can cause residual solids filtration methods to be expensive and challenging to scale up. 
         [0007]    Accordingly, there is a need for an improved and “green” process and system for removing residual solids from bio-oil. 
       SUMMARY OF THE INVENTION 
       [0008]    In one embodiment, the present invention is directed to a bio-oil treatment process comprising the steps of (a) coating a porous filter element with particles of a biomass filter aid to thereby provide a coated filter element and (b) passing an initial bio-oil having a liquid phase and residual solids through the coated filter element. During step (b), a substantial portion of the residual solids are retained by the coated filter element, while substantially all of the liquid phase passes through the coated filter element to provide a filtered bio-oil. 
         [0009]    In another embodiment, the present invention is directed to a bio-oil treatment process comprising the steps of (a) combining particles of a biomass filter aid with an initial bio-oil having a liquid phase and residual solids to thereby provide a pre-filter mixture and (b) passing the pre-filter mixture through a filter element so that a substantial portion of the residual solids and biomass filter aid are retained by the filter element, while substantially all of the liquid phase passes through the filter element to provide a filtered bio-oil. 
         [0010]    In a further embodiment, the present invention is directed to a biomass conversion system comprising a biomass feedstock source for providing solid particulate biomass, a splitter coupled to the biomass feedstock source that is operable to split the solid particulate biomass into a biomass feedstock fraction and a biomass filter aid fraction, a conversion reactor for thermally converting the biomass feedstock fraction into an initial conversion product, a residual solids separator for removing residual solids from at least a portion of the initial conversion product, a biomass feed system for transporting the biomass feedstock fraction from the splitter to the conversion reactor, and a biomass filter aid transport mechanism for transporting the biomass filter aid from the splitter to the residual solids separator. 
         [0011]    Using biomass as a green filter aid makes it feasible to recycle the spent biomass filter aid for bio-oil production and/or as a combustion heat resource instead of waste disposal as with a conventional filter aid. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0012]    Embodiments of the present invention are described herein with reference to the following drawing figures, wherein: 
           [0013]      FIG. 1  is a schematic diagram of a biomass conversion system according to one embodiment of the present invention; 
           [0014]      FIG. 2  depicts a horizontal plate filter suitable for use in conjunction with the present invention; 
           [0015]      FIG. 3  depicts a bag filter suitable for use in conjunction with the present invention; 
           [0016]      FIG. 4  depicts a centrifuge suitable for use in conjunction with the present invention; 
           [0017]      FIG. 5  depicts a rotary filter suitable for use in conjunction with the present invention; 
           [0018]      FIG. 6  is a picture of an unfiltered bio-oil under 100× magnification; and 
           [0019]      FIG. 7  is a picture of a filtered bio-oil under 100× magnification. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  depicts a biomass conversion system  10  that employs a residual solids separator  12  to remove residual solids from bio-oil. It should be understood that the biomass conversion system shown in  FIG. 1  is just one example of a system within which the present invention can be embodied. The present invention may find application in a wide variety of other systems where it is desirable to efficiently and effectively remove residual solids from bio-oil. The exemplary biomass conversion system illustrated in  FIG. 1  will now be described in detail. 
         [0021]    The biomass conversion system  10  of  FIG. 1  includes a biomass source  14  for supplying a biomass feedstock to be converted to bio-oil. The biomass source  14  can be, for example, a hopper, storage bin, railcar, over-the-road trailer, or any other device that may hold or store biomass. The biomass supplied by the biomass source  14  is preferably in the form of solid particles having a mean particle size of 0.01 to 1,000 microns, 1 to 750 microns, or 50 to 500 microns. The biomass particles can be fibrous biomass materials comprising cellulose. Examples of suitable cellulose-containing materials include algae, paper waste, and/or cotton linters. In one embodiment, the biomass particles can comprise a lignocellulosic material. Examples of suitable lignocellulosic materials include forestry waste, such as wood chips, saw dust, pulping waste, and tree branches; agricultural waste such as corn stover, wheat straw, and bagasse; and/or energy crops such as eucalyptus, switch grass, and coppice. 
         [0022]    As depicted in  FIG. 1 , the solid biomass particles from the biomass source  14  can optionally be fed to a splitter  16  that splits the biomass into a feedstock fraction and a filter aid fraction. The biomass filter aid fraction can then be supplied directly or indirectly to the residual solids separator  12 , while the feedstock fraction can be supplied to a biomass feed system  18 . The splitter  16  can be any conventional device capable of dividing solid particulates into separate fractions. When the splitter  16  is employed, the biomass used as a filter aid in the residual solids separator  12  has the same composition as the biomass provided to the biomass feed system  18 . 
         [0023]    When the splitter  16  is not employed, the biomass filter aid supplied to the residual solids separator can be provided by a separate biomass filter aid source  20 . When all or part of the biomass filter aid is supplied by the separate biomass filter aid source  20 , the composition of the biomass filter aid employed in the residual solids separator  12  can be different than the composition of the biomass that is supplied to the biomass feed system  18 . 
         [0024]    As used herein, “biomass filter aid” means a biomass-containing medium that promotes the efficiency or effectiveness of a filtration process for removing solids from a fluid. The biomass filter aid described herein can be formed of at least 50 weight percent biomass, at least 75 weight percent biomass, or at least 90 weight percent biomass. As alluded to above, in one embodiment, the biomass filter aid can have the same composition, properties, and particle size as the biomass converted to bio-oil. 
         [0025]    Referring again to  FIG. 1 , the biomass feed system  18  can be any system capable of feeding solid particulate biomass to a biomass conversion reactor  22 . As described in further detail below, in one embodiment, the biomass feed system  18  combines the fresh biomass received from the biomass source  14  with spent biomass filter aid recovered from the residual solids separator  12 . Also, it may be desirable to combine the biomass with a catalyst in the biomass feed system  18  in order to promote conversion of the biomass to the desired bio-oil product. Suitable catalytic materials that can be combined with the biomass prior to introduction into the conversion reactor  22  include, for example, zeolites, hydrotalcites, hydrotalcite-like materials, clays, and/or refractory oxides such as alumina. 
         [0026]    In one embodiment of the present invention, the biomass feed to the conversion reactor is unprocessed. As used herein, “unprocessed biomass” means biomass that has not been subjected to any pretreatments that significantly change the chemical make-up of the biomass. An example of a pretreatment that would significantly change the chemical make-up of biomass would be delignification. Thus, unprocessed biomass excludes cellulose fibers extracted from lignocellulose. Examples of pretreatment methods that do not significantly change the chemical make-up of biomass include particulating, grinding, agitating, drying, and mixing with a catalyst. 
         [0027]    In the conversion reactor  22 , biomass is subjected to a conversion reaction that produces bio-oil. The conversion reactor  22  can facilitate different chemical conversion reactions such as fast pyrolysis, slow pyrolysis, liquefaction, gasification, or enzymatic conversion. The conversion reactor  22  can be, for example, a fluidized bed reactor, cyclone reactor, ablative reactor, or a riser reactor. 
         [0028]    In one embodiment, the conversion reactor  22  can be a riser reactor and the conversion reaction is fast pyrolysis. Fast pyrolysis is characterized by short residence times and rapid heating of the biomass feedstock. The residence times of the fast pyrolysis reaction can be, for example, less than 10 seconds, less than 5 seconds, or less than 2 seconds. Fast pyrolysis may occur at temperatures between 200 and 1,000° C., between 250 and 800° C., or between 300 and 600° C. 
         [0029]    The product exiting the conversion reactor  22  generally comprises gas, vapors, and solids. In the case of fast pyrolysis, the solids in the product exiting the conversion reaction generally comprise particles of char, ash, and/or catalyst. As depicted in  FIG. 1 , the product from the conversion reactor  22  can be introduced into a primary solids separator  24 . The primary solids separator  24  can be any conventional device capable of separating solids from gas/vapors such as, for example, a cyclone separator or a gas filter. The primary solids separator  24  removes relatively larger solids (e.g., greater than  20  microns) from the reaction product, but small residual solids remain entrained in the gas/vapor phase. The relatively large particles recovered in the primary solids separator  24 , which can include any spent catalysts and char, are introduced into a regenerator  26  for regeneration, typically by combustion. 
         [0030]    The remaining gas/vapor phase conversion products from the primary solids separator  24  are introduced into a condenser  28 . The condenser  28  condenses at least a portion of the remaining conversion products into bio-oil, while the residual gas and uncondensed vapor are drawn off in a separate stream. The bio-oil recovered from the condenser  28  comprises a liquid phase and residual solids. The amount of residual solids in the bio-oil is generally about 0.05 to 5 weight percent, and the residual solids can have a mean particle size of about 0.1 to 200 microns or 1 to 100 microns. The condenser  28  may also function as a fractionator that separates and removes residual water from the conversion products and/or bio-oil. 
         [0031]    After exiting the condenser  28 , the bio-oil is introduced into a residual solids separator  12  for removal of the residual solids present in the bio-oil. The types of residual solids separators  12  that may be used can include, for example, centrifugal separators, gravitational separators, and/or pressure separators. Specific examples of the residual solids separator  12  include a horizontal plate filter, a centrifuge, a rotary filter, and a bag filter. Exemplary types of residual solid separators are depicted in  FIGS. 2-5  and are described in more detail in a later section of this document. 
         [0032]    Referring again to  FIG. 1 , the residual solids separator  12  comprises a porous filter element through which the bio-oil flows in order to remove the residual particles from the bio-oil. Any sufficiently-fine conventional filter known in the art may be used as the filter element. The filter element has an inlet side and outlet side relative to the residual solids separator  12 . The inlet side is capable of being supplied with and supporting a biomass filter aid. 
         [0033]    In one embodiment of the present invention, the filter element of the residual solids separator  12  is pre-coated with a biomass filter aid prior to passing the bio-oil through the filter element. Such pre-coating can be carried out by any method known in the art such as, for example, spraying the biomass filter aid onto the inlet side of the filter element. 
         [0034]    In another embodiment of the present invention, the biomass filter aid is combined with the bio-oil upstream of the residual solids separator  12  to create a pre-filter mixture. The pre-filter mixture is then passed through the filter element (optionally pre-coated with biomass filter aid), where both the biomass filter aid and the residual solids are retained by the filter element. 
         [0035]    As shown in  FIG. 1 , the biomass filter aid can be supplied to the residual solids separator  12  by a biomass filter aid transport mechanism  30 . The biomass filter aid transport mechanism can be any conventional device for transporting solids such as, for example, a pneumatic conveyor or simply a wheeled vehicle capable of carrying a container of the biomass filter aid. When pre-coating of the filter element is employed, the biomass filter aid transport mechanism  30  supplies the biomass filter aid directly to the residual solid separator  12 . When pre-mixing of the biomass filter aid and bio-oil is employed, the biomass filter aid transport mechanism  30  supplies the biomass filter aid to a mixing location upstream of the residual solids separator  12 . 
         [0036]    When the bio-oil (optionally pre-mixed with the biomass filter aid) is passed through the filter element (optionally pre-coated with the biomass filter aid), at least 50 weight percent, 75 weight percent, or 90 weight percent of the residual solids present in the bio-oil is retained by the filter element, while substantially all of the liquid phase of the bio-oil passes through the filter element. The resulting filtered bio-oil can then be used directly or further processed into a variety of end products. 
         [0037]    After filtering the bio-oil, the spent solids on the filter element (i.e., spent biomass filter aid and the residual solids retained thereon, therein, and/or therewith) can be removed from the residual solids separator  12 . In one embodiment, the spent solids removed from the residual solids separator  12  can be routed by a spent solids transport mechanism  32  to the conversion reactor  22  for use as a conversion feedstock. In another embodiment, the spent solids can be routed to a combustor  36  to provide heat that can be used in the biomass conversion system  10 . 
         [0038]      FIGS. 2-5  illustrate examples of residual solids separators suitable for use in conjunction with the present invention. It should be understood that these examples are included merely for the purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated. 
         [0039]    In one embodiment of the invention, the biomass filter aid may be used in a horizontal plate filter  100 , as depicted in  FIG. 2 . In this embodiment, a plurality of plate-type filter elements  102  are contained within a filter housing  104 . An unfiltered bio-oil (optionally pre-mixed with a biomass filter aid  106 ) is introduced at the top of the horizontal plate filter  100  and passes by gravitational force through the filter elements  102  (optionally pre-coated with a biomass filter aid  106 ). Upon passing the bio-oil through the filter elements  102 , the residual solids  108  are retained on the filter element  102 , along with the biomass filter aid  106 . The resulting filtered bio-oil exits the bottom of the plate filter  100 . 
         [0040]    In another embodiment of the invention, the biomass filter aid may be used in a bag filter  200  as depicted in  FIG. 3 . In this embodiment, a bag-type filter element  202  is contained within a filter housing  204 . An unfiltered bio-oil (optionally pre-mixed with a biomass filter aid  206 ) is introduced at the top of the bag filter  200  and passes by gravitational force through the filter element  202  (optionally pre-coated with a biomass filter aid  206 ). Upon passing the bio-oil through the filter element  202 , the residual solids  208  are retained on the filter element  202 , along with the biomass filter aid  206 . The resulting filtered bio-oil exits the bottom of the bag filter  200 . 
         [0041]    In a further embodiment of the invention, the biomass filter aid may be used in a centrifuge separator  300  as depicted in  FIG. 4 . In this embodiment, a rapidly-rotating filter element  302  is contained within a filter housing  304 . The filter element  302  (optionally pre-coated with a biomass filter aid  306 ) surrounds an inner cavity where an unfiltered bio-oil (optionally pre-mixed with a biomass filter aid  306 ) is introduced. The liquid phase of the bio-oil passes by centrifugal force through the filter element  302 , while the residual solids  308  and biomass filter aid  306  are retained on the filter element  302 . The centrifuge separator  300  includes a motor  310  for rotating the filter element  302 , thereby providing the centrifugal force required for separation. The resulting filtered bio-oil exits the bottom of the centrifuge  300 . 
         [0042]    In yet another embodiment of the invention, the biomass filter aid may be used in a rotary filter  400  as depicted in  FIG. 5 . In this embodiment, a cylindrical filter element  402  forming the outside surface of rotating drum is contained within a filter housing  404 . An unfiltered bio-oil (optionally pre-mixed with a biomass filter aid  406 ) is introduced into the rotary filter  400 . Upon passing the bio-oil through the filter element  402  (optionally pre-coated with a biomass filter aid  406 ) the residual solids  408  and biomass filter aid  406  are retained on the filter element  402 . The unfiltered bio-oil may be drawn through the filter element  402  by pressurizing the outer chamber  410  and creating a pressure differential across the filter element. Alternatively, a vacuum may be created in the inner chamber  412 , which draws the unfiltered bio-oil through the filter element  402 . The spent biomass filter aid  406  and residual solids retained  408  thereon may be removed from the filter element  402  by a knife  414  present in the outer chamber  410 . The filtered bio-oil exits the rotary filter after passing through the inner chamber  412 . 
       EXAMPLE 
       [0043]    Biomass (2 g; 32.3 weight percent of biomass particles ranging in sizes from 0-150 micron and 67.7 weight percent of biomass particles with sizes greater than 150 micron) was evenly applied onto circular filter paper with a 7 cm diameter. A fresh bio-oil sample (47 g) was filtered through the coated filter medium under vacuum conditions to obtain a filtered bio-oil (41 g). Pictures of the fresh/unfiltered bio-oil ( FIG. 6 ) and the filtered bio-oil ( FIG. 7 ) were taken under a 100× microscope. As shown in  FIGS. 6 and 7 , the filtered bio-oil was visually particle free and significantly clearer than the fresh/unfiltered bio-oil. 
         [0044]    The preferred forms of the invention described above are to be used as illustration only, and should not be used in a limiting sense to interpret the scope of the present invention. Modifications to the exemplary embodiments, set forth above, could be readily made by those skilled in the art without departing from the spirit of the present invention.