Patent Publication Number: US-2023139489-A1

Title: Solvent-extract filter apparatuses and methods

Description:
TECHNICAL FIELD OF THE INVENTION 
     The invention relates to filtering fluids and particularly solvent-extract mixtures produced by an extraction process. Filtering apparatuses may be employed for removing, for example, tars, tannins, fats, (plant-derived) waxes, chlorophyll, water, and/or other components from a solvent-extract mixture. 
     BACKGROUND OF THE INVENTION 
     The processes and apparatuses utilized for solute extraction from some starting material typically place the starting material in contact with a suitable solvent, and then collect the resulting solvent-extract mixture. Such solvent-based extraction may be applied, for example, to extract an oil from animal or plant-derived material and/or other substances (e.g., synthetic substances, pharmaceutically active substances derived from fermentation and/or biosynthesis). 
     Biomass extraction may include the extraction of terpenoids, flavors, fragrances and/or (possibly other) pharmaceutically active ingredients from materials of natural origin. Examples of biomass materials include but are not limited to flavorsome or aromatic substances such as hops, coriander, cloves, star anise, coffee, citrus peels, fennel seeds, cumin, ginger and other kinds of bark, leaves, flowers, fruit, roots, rhizomes and seeds. Biomass may also be extracted in the form of biologically active substances such as pesticides and pharmaceutically active substances or precursors thereto, obtainable from plant material, a cell culture or a fermentation broth, for example. 
     Biomass also may include, but are not limited to terpenoids (e.g., cannabinoids and terpenes), flavonoids, and/or other components from (1) cannabis, hemp, and/or derivatives thereof (e.g., hash, sift, kief, and rosin, among other examples) and (2) other botanical substances such as terpenoid-bearing plants and/or fruits and/or extracting psilocin, baeocystin, and/or norbaeocystin from psilocibe mushrooms and/or derivatives thereof. 
     Example solvents include carbon dioxide, hydrocarbon(s), ethanol and mixture thereof. For example, a hydrocarbon solvent may include at least one of Isobutane, N-Butane, and/or propane. Other possible solvents may include the family of solvents based on organic hydrofluorocarbons. Solvents may be a liquid, gas, and/or subcritical or supercritical fluid within an extraction system component. Solvents may change phases within an extraction cycle, such as being in gas phase during a solvent removal step and a liquid phase during an extraction step. 
     There are known techniques for “post-processing” a “raw” solvent-extract mixture including processes for removing solvent(s), lipids, waxes, and/or fats and thereby producing a filtered solvent-extract mixture (sometimes referred to as “polishing” a mixture). Known techniques include employing cooled in-line de-waxers and various types of filter apparatuses for removing certain components from a solvent-extract mixture. Filter apparatuses include devices that include some type of filter medium which is capable of capturing the components to be removed from the solvent-extract mixture as the solvent-extract mixture passes through the filter medium. The resulting effluent or filtrate from the filter apparatus includes at least a reduced content of the components to be removed. 
     The above systems, methods, and techniques may be improved upon and examples of new and useful systems and methods that are relevant to the needs in the field are discussed below. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide filter apparatuses and methods for filtering particularly solvent-extract mixtures in a space-efficient and otherwise desirable manner. It is also an object of the invention to provide an extraction system employing such filter apparatuses and methods. 
     A filter apparatus according to a first aspect of the present invention includes an elongated housing with a filter input port to the housing and a filter output port to the housing. A mixture flow path is defined within the housing, that is, within a volume defined by the housing, and extends from the filter input port to the filter output port such that the filter input port is in fluid communication with the output port through the mixture flow path. Two or more filter medium receiving volumes are defined within the housing along the mixture flow path, each filter medium receiving volume configured to receive a filter medium and contain the filter medium in the respective filter medium receiving volume. The filter medium receiving volumes are arranged within the housing such that a total length of the filter medium receiving volumes along a housing longitudinal axis is longer than the length of the housing along the housing longitudinal axis defined by the housing. This arrangement of flow path and filter medium receiving volumes within the housing according to this first aspect of the invention has allows a desired filtering of an input fluid to be performed in a very space-efficient manner. This space-efficient filtering in turn allows a desirable layout of a given system in which the filtering apparatus is used, such as a solvent-based extraction system, for example. 
     Implementations according to this first aspect of the invention may configure the filter medium receiving volumes so as to define a number of longitudinal path sections of the mixture flow path. In these implementations a first such longitudinal path section defines a first flow direction along the housing longitudinal axis from the filter input port and a second longitudinal path section defines a second flow direction along the housing longitudinal axis that is opposite to the first flow direction. The mixture flow path here also includes at least one transverse path section that is oriented transversely to the housing longitudinal axis. In particular, a transverse path flow section connects the first and second longitudinal path sections. The first and second longitudinal flow path sections, and other longitudinal flow path sections may extend parallel to the housing longitudinal axis. Such as series of parallel longitudinal flow path sections may be formed within the housing using a hollow cylinder which may be concentrically positioned within the housing so as to extend parallel to the housing longitudinal axis. In this arrangement of a hollow cylinder mounted in the housing, one longitudinal path section is formed along the external surface of the hollow cylinder while another longitudinal path section is defined along the internal surface of the hollow cylinder. A number of such cylinders of different diameters may be similarly included in the housing to define additional longitudinal path sections. 
     In embodiments where a hollow cylinder is included within the housing for defining or cooperating to define portions of the flow path through the housing, a suitable aperture may extend through the cylinder wall to provide at least a portion of one of the transverse path sections connecting two longitudinal path sections. Such an aperture may be included at or near a longitudinal end of the hollow cylinder within the filter apparatus housing. 
     A filter apparatus in accordance with this first aspect of the invention may include a removeable end cover configured to be placed in an operating position at one end of the housing. Such a removable end cover may be used to define a surface along the flow path through the housing. In particular, such an end cover may define an end surface of one or more of the longitudinal path sections. In some cases, such an end cover may define at least a portion of one of the transverse path sections. In any case, the removable end cover may be removed as desired to provide access to the volume defined by the housing. Such access may be desirable for the placement of one or more hollow cylinders within the housing for defining the longitudinal path sections and for placing filter medium in the filter medium receiving volumes or removing spent filter medium. 
     A filter apparatus in accordance with the first aspect of the invention may include at least one thermal element that is thermally coupled to at least one of the filter medium receiving volumes. As used in this disclosure and the accompanying claims a “thermal element” may comprise any device or arrangement of devices operable to heat or cool any material included in a respective filter medium receiving volume, including a filter medium received in the filter medium receiving volume and solvent-extract mixture as it passes through the filter medium and filter medium receiving volume. Examples of such thermal elements will be described below in connection with the example embodiments shown in the drawings. 
     Embodiments of a filter apparatus in accordance with the first aspect of the invention may also include filter medium received in the various filter medium receiving volumes defined along the flow path from the housing inlet port to housing outlet port. Each one of the different filter medium receiving volumes may receive a dissimilar filter medium or each may include the same filter medium. Any combination of filter media may be used along the flow path within the various filter medium receiving volumes. As used in this disclosure and the accompanying claims a “filter medium” may comprise any material that is adapted to allow certain components of a fluid to pass therethrough while blocking or trapping other components from the fluid. Example filter media may include one or more of zeolites, porous glass, active carbon, clays, silicon dioxide, and mesoporous silica. Another possible advantage is selecting different filter media that resides along the same or different fluid path sections. Dissimilarities can include differences in the filtering media materials, average particle size, and/or average pore size. Filter media may include media that is commonly referred to as a molecular sieve, which may function at a molecular level to capture molecules of a certain size or shape. Molecular sieves may be used as desiccants (e.g., activated charcoal or silica gel absorbent media) among other applications. 
     A second aspect of the invention, comprises an extraction system that includes a filter apparatus in accordance with the first aspect of the invention. Such an extraction system includes an extraction arrangement operable for placing a solvent in contact with a starting substance to produce a solvent-extract mixture. The filter input port as described above is operably connected to the extraction system for receiving the solvent-extract mixture, and a filtrate receiving system is operably coupled to the filter output port for receiving the solvent-extract mixture from the filter apparatus for further processing. 
     Another aspect of the invention encompasses methods for removing at least one component from a solvent-extract mixture. A method in accordance with this third aspect of the invention may include receiving the solvent-extract mixture at an input port of an elongated housing and causing the solvent-extract mixture to flow from the filter input port through a first filter medium contained in a first filter medium volume defined along a mixture flow path within the elongated housing. The method may also include causing the solvent-extract mixture to flow from the first filter medium volume to a second filter medium volume defined along the mixture flow path and through a second filter medium contained in the second filter medium volume. The combined lengths of the first filter medium volume along a housing longitudinal axis and the length of the second filter medium volume along the housing longitudinal axis is greater that the length of the housing along the housing longitudinal axis. A method in accordance with this third aspect of the invention may finally include causing the solvent-extract mixture to flow from the second filter medium volume to an output port of the housing. 
     As used in this disclosure and the accompanying claims a step of “causing” a particular flow of material may be accomplished in any fashion suitable for the given material. Any technique of applying a motive force to induce the described flow may be used. Such techniques may include pumping, applying a vacuum, thermal processes, displacement with a displacing fluid, gravity flow, or any other technique. 
     Regardless how the flow is induced, the solvent-extract mixture may flow through the first filter medium in a first direction with respect to the housing longitudinal axis and then through the second filter medium in a second direction with respect to the housing longitudinal axis opposite to the first direction. Causing the solvent-extract mixture to flow from the first filter medium volume to the second filter medium volume may include causing the solvent-extract mixture to flow along a first transverse path section in a direction transverse to the housing longitudinal axis. This first transverse path section may include an aperture in a hollow cylinder mounted concentrically within the housing and separating at least some of the first filter medium volume from the second filter medium volume. The first transverse path section may also or alternatively include a volume defined within an end cover of the housing. 
     Methods according to this third aspect of the invention may also include causing the solvent-extract to flow through at least one additional filter medium volume containing additional filter medium. For example, causing the solvent-extract mixture to flow from the second filter medium volume to the output port of the housing may include causing the solvent-extract mixture to flow through a third filter medium contained in a third filter medium volume defined along the mixture flow path. This flow through the third filter medium may be in the same direction relative to the housing longitudinal axis as a flow direction through the first filter medium and opposite to a flow direction through the second filter medium. Similarly to the flow from the first filter medium volume to the second filter medium volume, the solvent-extract mixture flow from the second filter medium volume to the third filter medium volume may occur at least in part through a second transverse path section in the direction transverse to the housing longitudinal axis. 
     Methods in accordance with this third aspect of the invention may thermally drive solvent or mixtures thereof to flow through a filter medium and/or through extraction system components. Methods in accordance with this third aspect of the invention may also thermally regulate solvent or mixtures thereof in addition to any thermal driving. In some example embodiment implementations of this aspect, the entire extraction cycle may be thermally driven via temperature differentials between extraction system components and avoid using a pump for causing or assisting a solvent or mixture thereof to flow. 
    
    
     
       These and other advantages and features of the invention will be apparent from the following description of representative embodiments, considered along with the accompanying drawings. 
         FIG.  1    is schematic view of a closed-loop extraction system. 
         FIG.  2    is a schematic view of an extraction sub-system. 
         FIG.  3    is a somewhat schematic representation of a filter apparatus which may implement one or more aspects of the present invention. 
         FIG.  4    is a somewhat schematic side view of the filter apparatus shown in  FIG.  3    and showing internal elements of the apparatus in hidden lines. 
         FIG.  5    is a somewhat schematic section view taken along line 5-5 in  FIG.  4   . 
         FIG.  6    is an enlarged plan view of a mixture flow path arrangement which may be employed between filter medium areas in the embodiment shown in  FIG.  4   . 
         FIG.  7    is a somewhat schematic side view similar to  FIG.  4    but showing an alternate arrangement of internal elements for the filter apparatus. 
         FIG.  8    is a somewhat schematic section view taken along line 8-8 in  FIG.  7     
         FIG.  9    is section view along ling 9-9 in  FIG.  8   . 
         FIG.  10    is a somewhat schematic side view similar to  FIG.  4    but showing an alternate arrangement of internal elements for the filter apparatus. 
         FIG.  11    shows a method that includes filtering a solvent-extract mixture. 
     
    
    
     DESCRIPTION OF REPRESENTATIVE EMBODIMENTS 
     In the following description  FIGS.  1 ,  2 , and  11    will be referenced to describe an extraction system in which solvent-extract filter apparatuses and methods in accordance with one or more aspects of the invention may be used.  FIGS.  3 - 10    will then be referenced to describe the solvent-extract filter apparatuses and methods and various features of such apparatuses and methods. 
     Referring to  FIG.  1   , an example extraction system  101  includes a first tank  110  associated with a thermal element  111 , an extraction system component  140  associated with a thermal element  141 , an extraction column  100 , a filter  150  associated with thermal element  151 , and a collector  120  associated with thermal element  121 . Filter  150  in this example system comprises a filter defining a mixture flow path in accordance with the above-described first aspect of the present invention. Solvent conduit  112   a  and valve  102  are arranged between first tank  110  and extraction column  100 . Liquid mixture conduit  112   b  and valve  104  are arranged between extraction column  100  and extraction system component  140 , before the mixture is directed to filter  150  via filter input conduit  112   c  through valve  108 . Filtered solvent-extract mixture, that is a filtrate solvent-extract mixture, is directed to collector  120  through filter output conduit  112   e  and valve  106 . 
     Component  140  may apply a suitable process to the solvent-extract mixture received from extraction column  100 , including heating or cooling the mixture, via thermal element  141 . The heating that may be performed at component  140  may cause a portion of solvent to evaporate from the solvent-extraction mixture, and this evaporated solvent may then be re-captured and re-directed to a solvent tank such as tank  110  after any further processing that may be necessary or desirable. Alternatively or additionally, the heating or cooling at component  140   may include thermally regulating the solvent-extract mixture to a pre-defined value for optimizing the downstream filtering processes and apparatus described herein. For example, component  140  may function to thermally regulate the solvent-extract mixture for ensuring a minimum or maximum viscosity of the solvent-extract mixture, among other possible optimizations for downstream filtering. 
     Additionally or alternatively, component  140  may mix further solvents (e.g., ethanol) for optimizing (or enabling) downstream filtering. The further solvents may alternatively be mixed upstream of or within extraction column  100 . 
     The example extraction system shows a device  152  (for example, a displacement fluid tank, pump, or compressor) to induce the desired flow of solvent-extract mixture through filter  150  and a thermal element  151  for cooling or heating solvent-extract mixture within filter  150 . Device  152  may alternatively or additionally be operable for moving or assisting in moving materials components residing within filter  150  before and/or after the solvent-extract mixture filtering process. Regardless of whether device  152  and/or thermal element  151  is included in the system or otherwise and regardless of how the solvent-extract mixture is cause to flow through filter  150 , the filter can remove one or more of tars, tannins, waxes, chlorophyll, water, or some other component from the solvent-extract mixture. As noted above, and as described further below in connection with the example filter embodiments, filter  150  may employ any suitable filter medium or combination of such media and may, for example, minimize solvent loss (such as residual solvent that retained by filter  150 ). In one example, the average pore size of the filter material may decrease, in stages, as the solvent-extract mixture flows through filter  150 . 
     After filtering through filter  150 , a filtered solvent-extract mixture flows through a solvent-extract mixture outlet conduit  112   e  to extract collector  120 . Extract collector  120  may be heated via thermal element  121  to, for example, evaporate a portion or practically all remaining solvent included in the filtered solvent-extract mixture. The evaporated solvent may be directed via solvent return line  112   f  and valve  109  and to tank  110  where it may be condensed if not condensed before entering tank  110 . 
     Thermal elements  111 ,  121 ,  141 , and  151  may be removably coupled and/or directly mechanically coupled to the exterior of its respective extraction system component. In one example, thermal elements  111 ,  121 ,  141 , and  151  are fluid jackets that may be respectively welded or otherwise connected to the respective tank or component. 
     Thermal elements  111 ,  141 ,  121 , and  151  may respectively heat and/or cool the fluid contents of their respective extraction system component in any suitable fashion. In some cases, thermal elements  111 ,  141 ,  121 , and  151  may thermally drive a fluid from one extraction system component to another. In some embodiments, solvent and solvent-laden mixtures may be thermally driven through the entire fluid path of extraction system  101 , including thermally driving a solvent-extract mixture through filter  150 . 
     Additionally or alternatively, thermal elements  111 ,  141 ,  121 , and  151  may thermally condition a fluid for optimizing a process of an extraction system component upon a fluid. For example, thermal elements  141 ,  121 , and  151  may thermally condition a solvent-extract mixture before, while, and/or after the solvent-extract mixture flows through filter  150 . According to such examples, one goal of thermally conditioning a solvent-extract mixture is to modify a characteristic of said mixture such as distillation during solvent recovery, to facilitate more efficient filtering, and/or to manipulate pressure differentials for thermally driving solvent or mixtures thereof within extraction system  101 . 
     In  FIG.  2   , extraction sub-system  201  includes fluid source  252 , thermally coupled to thermal element  251 , filter  250 , and filtered material collector  220 . Similarly to filter  150  shown in  FIG.  1   , filter  250  comprises a filter in accordance with the above-described first aspect of the present invention. Fluid connectors such as valves are omitted in  FIG.  2   , but it will be appreciated by those skilled in the art that various valves and other flow control devices may be included in the sub-system for controlling the flow of materials from one component to the next. 
     Fluid source  252  may provide a fluid for purging, for example, residual solvent from the filter material within filter  250 . Fluid source may provide a thermally regulated fluid, via fluid conduit  212   a , that is either directly applied to the filter material of filter  250  (for example, a nitrogen gas or steam purge) or feeds thermal element  251  in fluid jacket embodiment example. That is, fluid source  252  may provide a thermally regulated fluid for a fluid jacket that is thermally coupled to filter  250  for heating, in some cases, the filter material to a solvent boiling point. Alternatively, thermal element  251  may be an electric thermal element such as an electric thermal jacket. 
     Regardless of the manner in which the filtered fluid is removed from the filter medium, a residual fluid flows via residual conduit  212   b  to filter residual collector  220 , which may be thermally coupled to thermal element  221 . The residual fluid flow may be thermally driven via temperature differentials between filter  250  and collector  220 . Additionally or alternatively, pressure provided from source  202  and/or a fluidly-coupled pump may assist via positive or negative pressure in inducing or otherwise facilitating the flow of residual fluid from filter  250  and towards collector  220 . 
       FIG.  3    shows a filter apparatus which may be used as the filter  150  shown in  FIG.  1    and filter  250  shown in  FIG.  2   . In the embodiment shown in  FIG.  3   , the filter apparatus includes an elongated housing  300  extending along housing longitudinal axis H and defined by a housing cylinder  301  closed at each end with a respective end component  304  and  305 . The upper end component  304  shown in  FIG.  3    comprises a disk-shaped cover  308  connected in an operating position on a flange  307  on housing cylinder  301 . Similarly, lower end component  305  comprises a second disk-shaped cover  310  connected to a flange  309  on housing cylinder  301 . The schematic view of  FIG.  3    (and the side view in  FIG.  4   ) does not include any illustration of means for connecting the respective flange  307 ,  309  and cover  308 ,  310 . It will be appreciated that any suitable connecting structure may be employed to place the respective cover in its operating position on housing cylinder  301 . 
     For example, each flange  307 ,  309  may be provided with corresponding bolt holes spaced apart about its circumference in position to align with corresponding bolt holes formed around the periphery of the respective cover  308 ,  310 . In this arrangement, a suitable bolt may be installed across each corresponding set of bolt holes to secure the cover  308 ,  310  to the respective flange  307 ,  309 . Alternatively, a clamp such as a circumferential clamp or a series of clamps spaced apart about the periphery of the respective flange  307 ,  309  and cover  308 ,  310  could be used to connect the two elements of the respective component,  304  and  305 . Also, it will be appreciated that one or more sealing elements such as O-rings or other sealing features may be used to provide a suitable peripheral seal between the flange  307 ,  309  and respective cover  308 ,  310  regardless of how the two components are connected to form the respective end component  304 ,  305 . 
     As will be described further below in connection with the side view of  FIG.  4   , an inner surface of each end cover  308  and  310  in this embodiment together an inner surface of housing cylinder  310  define a housing volume through which the mixture flow path and filter medium receiving volumes described above in the summary section are formed. Material to be filtered may be directed to the housing volume through an inlet conduit  312  and exit the housing volume through an outlet conduit  314 . As shown in  FIG.  4    inlet conduit  312  connects to an inlet port  313  of the filter apparatus while outlet conduit  314  is connected to an outlet port  315  of the filter apparatus. 
     The side view of  FIG.  4    and the transverse section view of  FIG.  5    show that the example filter apparatus includes a number of inner cylinders in addition to housing cylinder  301 . These inner cylinders function to help define the mixture flow path through housing  300  and a number of flow path sections which make up the flow path. The example of  FIGS.  4  and  5    include in addition to housing cylinder  301  a first cylinder  321 , a second cylinder  322 , and a third inner cylinder  323 . Housing cylinder  310  together with the inner cylinders  321 ,  322 , and  323  produce a number of annular volumes within the housing volume,  321   a ,  322   a , and  323   a , respectively, with each annular volume defining filter medium receiving volume and a portion of the overall mixture flow path through housing  300 . The innermost cylinder  323  forms a cylindrical volume  235  that is also part of the mixture flow path in this embodiment. The crosshatching in both  FIGS.  4  and  5    (aside from the crosshatching through flange  307  in  FIG.  5   ) indicate a respective filter medium received in a respective filter medium receiving volume included along the flow path. 
       FIG.  4    shows the directions of flow through housing  300  along the mixture flow path defined from inlet port  313  to outlet port  315 . A fluid under a suitable motive force flows from inlet port  313  upwardly in the orientation of this figure along a first longitudinal path section through the first annular filter medium volume  321   a  defined between an inner surface of housing cylinder  301  and an outer surface of cylinder  321  as indicated by arrows L1. The fluid then flows through a transverse path section indicated by arrows T1 to the next annular filter medium receiving volume defined between an inner surface of cylinder  321  and an outer surface of cylinder  232 , and then in the direction of arrows L2 downwardly in the orientation of figure along a second longitudinal path section through the annular filter medium receiving volume  322   a . 
     The fluid being filtered next flows along a transverse path section indicated by arrows T2 to the next annular filter medium volume defined between an outside surface of cylinder  322  and an inside surface of cylinder  323 . The fluid then flows in the direction indicated by arrows L3 along a third longitudinal path section of the overall mixture flow path. At the end of this flow path through filter medium receiving volume  323   a , the fluid flows along a third transverse path section indicated by arrows T3 to reach the innermost filter medium receiving volume  325  in this example. The fluid flows along a fourth longitudinal path section through this volume  325  in the direction indicated by arrow L4 to reach outlet port  315  and outlet conduit  314 . 
     It will be appreciated from  FIG.  4    that a portion of each flow path in this particular embodiment is defined by a surface of the end covers  308 ,  310 . Using the outermost annular filter medium receiving volumes  321   a  as an example, an annular surface  308   a  of end cover  308  forms an end surface of that respective annular filter medium receiving volume. Similarly, at the opposite end of filter medium receiving volume  321   a  an annular surface  310   a  of end cover  310  forms an end surface of the volume  321   a . 
     Each of the inner cylinders in the embodiment shown in  FIG.  4    includes an arrangement for allowing fluid to flow from one annular filter medium receiving volume along one of the transverse path sections T1, T2, and T3 to the next along the mixture flow path through the filter apparatus. Such an arrangement may include a number of apertures spaced apart suitably along the circumference of the wall of the respective cylinder  321 ,  322 , and  323  at the end thereof at which the transverse flow is desired.  FIG.  6    shows an example of suitable apertures in the wall of cylinder  321 . These example apertures comprise a series of elongated slot-shaped openings  330  in the wall defining cylinder  321 . 
     It will be appreciated that any suitable apertures may be used to allow fluid communication between the annular volumes, preferably around the entire circumference of the respective separating cylindrical wall. Other suitable apertures may comprise circular openings arranged in any suitable pattern. Also, although the example elongated slot-shaped openings  330  are shown in  FIG.  6    as terminating before the end of the cylinder wall  321 , other embodiments may include slots or other openings that extend to the end of the cylinder wall  321 . More broadly, embodiments of a filter apparatus according to the present invention may include any apertures or any other arrangement to allow the desired transverse flow from one longitudinal flow path section to the next longitudinal flow path section along the mixture flow path. 
     It will be appreciated from  FIG.  4    that each cylinder within housing  300  includes an end at which transverse flow in not desired. For example, the points at which cylinder  321  meets the inner surface of end cover  310  should allow substantially no flow from volume  321   a  to volume  322   a . Blocking flow at these points may be accomplished in any suitable fashion. For example, a sealing element such as an O-ring or gasket (not shown due to the scale of the  FIG.  4   ) may be positioned in a suitable manner between the end of wall  321  and the inner surface of end cover  310 . In some embodiments the inner surface of end cover  310  may have machined therein a groove for receiving a sealing element such as an O-ring to provide a seal against the end of cylinder  321  and also provide a positioning feature for cylinder  321  (as will be described further below). Such a sealing arrangement or other sealing/positioning arrangement may be provided also in end cover  310  for the end of cylinder  323  and in end cover  308  for cylinder  322 . 
     The embodiment shown in  FIG.  7    may have an outward appearance similar to that shown in  FIG.  3   . In particular, the device shown the side view of  FIG.  7    includes a housing  400  including a housing cylinder  401  and end components  404  and  405 . End component  404  in this alternative embodiment includes a flange  407  and an end cover  408 , while end component  405  includes a flange  409  and an end cover  410 . Similarly to the embodiment shown in  FIGS.  3 - 5   , the embodiment shown in  FIG.  7    includes three inner cylinders  421 ,  422 , and  423  concentrically mounted within the volume defined by housing cylinder  401 . Unlike the embodiment shown in  FIGS.  3 - 5   , end covers  408  and 4010 are formed to define a portion of the housing volume and portions of the overall mixture flow path through the housing. Thus in the example of  FIG.  7   , the transverse flow paths from one longitudinal flow path section to the next is through a volume defined within the respective end cover. In particular, the transverse flow path section indicated by arrows T4 in  FIG.  7    is through a volume  441  defined within the upper end cover  408  between a surface  441   a  and ridge  441   b  machined or otherwise formed in the material comprising end cover  408 . The transverse flow path section indicted by arrows T5 is through a volume  442  defined within a volume within the lower end cover  410  defined between an inner surface of ridge  447   b  and outer surface of ridge  450   a . Similarly, the transverse flow path section indicated by arrows T6 is through a volume  443  defined within upper end cover  408  by the inner surface of ridge  441   b . 
     It will be noted in  FIG.  7    that the portions of the flow path in defined within the end covers  404  and  405  are shown as not including any filter medium or other material. Leaving these volumes as essentially open voids may be accomplished by positioning annular shaped screens at the end of each annular flow path section (or a disk-shaped screen at the upper end of cylinder  422  and at the lower end of cylinder  423 ). The example of  FIG.  7    shows an annular screen  445  in the area between housing cylinder  401  and cylinder wall  422  at the upper end of the device. Annular screen  445  extends over the top of cylinder  421  to cover the entire annular area between housing cylinder wall  401  and cylinder  422  and thus separates the volume  441  from two adjacent filter medium receiving volumes  421   a  and  422   a . A similar, but narrower in the horizontal direction, annular screen  446  at the lower end of the device separates filter medium receiving volume  421   a  from an annular volume  447  adjacent to inlet port  413  and defined between surface  447   a  and an inner surface of ridge  447   b . 
     Annular screen  446  covers the area at the lower end of the filter medium receiving volume between housing cylinder  401  and cylinder  421 . At the top of housing  400  a disk-shaped screen  448  extends across the area defined by the top of cylinder  422  in position to separate filter medium receiving areas  423   a  and  425  from volume  443  defined in end plate  408 . At the bottom of housing  400  in the orientation of  FIG.  7   , and annular screen  449  extends between cylinder  421  and cylinder  423  to separate volume  442  from filter medium receiving volumes  422   a  and  423   a , and a disk-shaped screen  450  is located over the area defined by the lower end of cylinder  423 . The screen material in each case is highly permeable to the fluid to be filtered so as to allow the fluid to pass but to ensure filter medium is retained in the desired volumes within housing cylinder leaving the volumes defined in the end covers  408  and  410  unoccupied by filter medium. It should also be appreciated that the various screens shown in  FIG.  7    are shown in a somewhat exaggerated scale vertically in the orientation of the drawing in order to call the screens out in the figure. The screens may in fact be very thin in the vertical direction on the order of a millimeter or less. 
     It should be noted here that the flow in the desired transverse path sections as indicated by arrows T4, T5, and T6 may be ensured by providing an appropriate seal at locations between the respective end cover and the longitudinal flow path section defining cylinders. In particular, the example of  FIG.  7    has a substantial seal (under the desired operating parameters and considering the fluid to be filtered) between the end of ridge  441   b  and the upper end of cylinder  422 . A substantial seal is also employed between the end of ridge  447   b  in end cover  410  and the lower end of cylinder  421  and between the end of ridge  450   a  and the lower end of cylinder  423 . These seals may be provided in any suitable manner as discussed above in connect with  FIG.  4   . 
     As an alternative to the screens shown in  FIG.  7   , and suitable unreactive (to the fluid to be filtered) and highly permeable material may be positioned in the various volumes defined in the end covers  408  and  410 . A suitable stainless steel wool material or fibrous or perhaps sintered metal or plastic material, or a highly permeable ceramic material may be used to fill the volumes formed in end covers  408  and  410  either with or without the illustrated annular and disk-shaped screens, all for the purpose of leaving those volumes essentially unfilled with filter medium. 
     In order to support the inner cylinders  421 ,  422 , and  423  in the desired longitudinal position within housing cylinder  401  shown in  FIG.  7   , the end covers  408  and  410  may include a number of supports spaced apart along a circumference in the respective end cover that corresponds with the circumference of the aligned cylinder. In the example of  FIG.  7   , such supports may be used in the upper end cover  408  to support the upper end of cylinder  421  and the innermost cylinder  423 . The lower end cover  410  may include supports for longitudinally supporting the lower end of cylinder  422 . The section view of  FIG.  8    shows an example configuration of such supports in end cover  408  in addition to and outer surface  460  of the end cover, the wall of housing cylinder  401 , and ridge  441   b  separating end cover volumes  441  and  443 . 
     In this example the longitudinal support for cylinder  421  twelve ridges  461  spaced apart along a circular shape corresponding to the circular shape of the upper end of cylinder  421  ( FIG.  7   ). Thus the ridges  461  are in position to substantially abut the end of cylinder  421  when the end cover  408  is in the operating position shown in  FIG.  7   , but the gaps between the ridges  461  allow fluid to flow in the direction of arrows T4 in  FIG.  7   . End cover  408  also includes a support made up of four ridges  462  spaced apart along a circular shape corresponding to the circular shape of the upper end of cylinder  423 . These four ridges  462  are thus positioned to abut the upper end of cylinder  423  when end cover  408  is in the operating position shown in  FIG.  7   , while still allowing the flow of fluid in the direction indicated by arrows T6 in  FIG.  7   . The section view of  FIG.  9    is taken along a line that shows how support ridges  461  in this example extend substantially to the level  464  of a lowermost edge of end cover  408  in position to abut the upper end of cylinder  421  when the end cover is connected in the operating position shown in  FIG.  7   . 
     It will be appreciated that although the example of  FIG.  8    shows a total of twelve spaced-apart support ridges  461 , other arrangements of support ridges may be used. As few as three support ridges  461  spaced apart equally along the circular shape may be employed to provide the desired longitudinal positioning support for the upper end of cylinder  421 . A similar supporting ridge arrangement may be used in the lower end cover to support the lower end of cylinder  422 . 
       FIG.  10    shows another example embodiment of a filter apparatus in accordance with aspects of the invention having an outward appearance similar to that shown in  FIG.  3   . The example of  FIG.  10    is similar to that shown in  FIG.  4    in that none of the mixture flow path through the housing  500  is defined within either of the device end covers  508  and  510 . Unlike the embodiment shown in  FIG.  4   , the filter medium receiving volumes defined along the mixture flow path do not extend the entire length of the housing cylinder  501 . In particular, the filter medium receiving volumes  521   a  and  522   a  leave an annular volume  570  at the top of the housing  500  and the filter medium receiving volume  521   a  leaves an annular volume  571  at the bottom of housing  500  adjacent to inlet port  513  from inlet conduit  512 . 
     Filter medium receiving volumes  522   a  and  525  leave a volume  573  at the top of housing  500 , while filter medium receiving volumes  522   a  and  523   a  leave an annular volume  574  at the bottom of housing  500 . In the example of  FIG.  10   , no open volume is provided adjacent to outlet port  515 , but a suitable volume could be formed here as well at the bottom of filter medium receiving volume  525 . Each of the volumes maintained in housing  500  such as volumes  570 ,  571 ,  573 , and  574  may be maintained free of filter medium in any suitable fashion such as with screens and/or suitable fill material that is suitably permeable and unreactive to the fluid to be filtered in the filter apparatus. 
     The volume of filter material included in each filter material receiving volume may be selected according to the filtering requirements expected for a given type and volume of fluid to be filtered. In some cases, it may be desirable to include the same volume of filter material in each of the different filter medium receiving volumes. In such cases, the size of the different cylinders (for example,  321 ,  322 , and  323  in  FIG.  4   ) may be selected and/or volumes such as  570 ,  571 ,  573 , and  574  may be selected to provide the same volume of filter material along each flow path section. The inner cylinders and open volumes may also be selected to provide different filter medium volumes along different flow path sections. Filter media of different characteristics or entirely different filter types of filter medium may be used in the different flow path sections within the filter housing (such as  300  in  FIG.  4   ). Dissimilarities in filter media may include different filter medium characteristics and/or different filter media used at different locations in the same filter medium receiving volume in a filter apparatus as described herein. In another example, the average pore size of the filter material may decrease, in stages that are defined by respective filter medium receiving volumes, as the solvent-extract mixture flows from inlet port  313  to outlet port  315 . 
     Regardless of what type or types of filter media are used in a given application of a filter apparatus in accordance with the present invention, the filter media may be placed in the various filter medium receiving volumes in any suitable manner. Where a given filter medium is in particulate form, for example, the housing cylinder may be positioned as shown in  FIG.  4    for example with the upper end cover  308  removed, and the particular matter filter medium may be poured into the desired annular volume. Filter medium may also be preformed into a desired annular or cylindrical shape and the preformed volume of filter medium slid into the desired location within the housing volume. Also, spent filter medium may be removed from the filter apparatus in any suitable fashion. For example, both end covers (such as  308  and  310  in  FIG.  4   ) may be removed and a suitable press may be used to longitudinally press out one or more of the inner cylinders and the filter medium located therebetween. 
     Implementations of a filter apparatus according to the present invention may include suitable features for maintaining the different inner cylinders in the desired parallel arrangement as the filter apparatus is filled with filter medium and during a filtering operation. For example, spacer elements may be included in each annular area at two spaced apart points along the length of a given cylinder and around the circumference of the given cylinder to ensure the desired spacing with the next larger cylinder. Alternatively or in addition to a spacer element arrangement, one or both end covers may include features for receiving an end of a given cylinder to maintain that cylinder end in a desired position relative to the other cylinders. 
     The various components of a filter apparatus according to the present invention may be formed from any suitable material or combination of materials. The materials should be selected for compatibility with the fluid to be filtered and with the expected operating parameters including temperature and pressure. For example, housing  300  shown in  FIG.  3    and the inner cylinders  321 ,  322 , and  323  shown in  FIG.  4    for example may be formed from a suitable stainless steel. In some cases, plastics such as PEEK may also be used for one or more of the components. 
       FIG.  11    shows a method that includes filtering a liquid solvent-extract mixture. Step 1102 includes thermally driving a solvent to contact a target substance that is contained within an extraction column and thereby create, typically in liquid-solvent extraction embodiments, a liquid solvent-extract mixture. Step 1104 includes thermally driving the liquid solvent-extract mixture towards the input port of a filter which may comprise a filter apparatus in accordance with the present invention as described above. The thermal driving step 1104 may drive the liquid solvent-extract mixture directly from the extraction column or directly from some intermediate processing element interposed between an output of the extraction column and the input port of the filter apparatus. 
     As indicated at step 1105 in  FIG.  11   , thermal conditioning and/or other processing steps may be included before, during, and/or after introducing the liquid solvent-extract mixture into the filter input port and thus mixture may be contained in one or more intermediary extraction system components before or after the filter apparatus. Such processing may include thermally conditioning the liquid solvent-extract mixture to reach and/or maintain a target temperature that optimizes a process (e.g., filtration) of a downstream extraction system component. 
     Step 1106 in  FIG.  11    includes thermally driving the liquid solvent-extract mixture through the filter. Step 1108 includes thermally driving the filtered solvent-extract mixture to a collector. A collector may further process the filtered, liquid solvent-extract mixture, including distilling most if not practically all solvent (below a certain threshold) out of the solvent-extract mixture, thereby providing a pure, safe extract. The collector may be fluidly coupled to a cooled solvent tank for recycling the distilled solvent. The method may move solvent and mixtures thereof entirely by “pump-less” techniques, including establishing thermal differentials between extraction system components. Of course, filter apparatuses and filtering processes in accordance with aspects of the present invention are not limited to any particular technique for driving a solvent-extract mixture through the filter. 
     As used herein, whether in the above description or the following claims, the terms “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” and the like are to be understood to be open-ended, that is, to mean including but not limited to. Also, it should be understood that the terms “about,” “substantially,” and like terms used herein when referring to a dimension or characteristic of a component indicate that the described dimension/characteristic is not a strict boundary or parameter and does not exclude variations therefrom that are functionally similar. At a minimum, such references that include a numerical parameter would include variations that, using mathematical and industrial principles accepted in the art (e.g., rounding, measurement or other systematic errors, manufacturing tolerances, etc.), would not vary the least significant digit. 
     Any use of ordinal terms such as “first,” “second,” “third,” etc., in the following claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another, or the temporal order in which acts of a method are performed. Rather, unless specifically stated otherwise, such ordinal terms are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term). 
     In the above descriptions and the following claims, terms such as top, bottom, upper, lower, and the like with reference to a given feature are intended only to identify a given feature and distinguish that feature from other features. Unless specifically stated otherwise, such terms are not intended to convey any spatial or temporal relationship for the feature relative to any other feature. 
     The term “each” may be used in the following claims for convenience in describing characteristics or features of multiple elements, and any such use of the term “each” is in the inclusive sense unless specifically stated otherwise. For example, if a claim defines two or more elements as “each” having a characteristic or feature, the use of the term “each” is not intended to exclude from the claim scope a situation having a third one of the elements which does not have the defined characteristic or feature. 
     The above-described preferred embodiments are intended to illustrate the principles of the invention, but not to limit the scope of the invention. Various other embodiments and modifications to these preferred embodiments may be made by those skilled in the art without departing from the scope of the present invention. For example, in some instances, one or more features disclosed in connection with one embodiment can be used alone or in combination with one or more features of one or more other embodiments. More generally, the various features described herein may be used in any working combination. 
     As a further example, the thermally driving steps of 1104, 1006, and 1108 are shown as discrete steps as both a possible embodiment and for didactic purposes. In fact, said thermal-driving steps may be accomplished by a single, continuous thermal differential that is established between two extraction system components (e.g., tanks) such that the liquid solvent-extract mixture in two or more steps of 1104, 1006, and 1108 is “flowing” from one step to another without a discrete demarcation such as stopping the flow of said mixture or modifying the thermal differential between steps.