Abstract:
A bio-oil reactor leverages chemically recalcitrant lignocellulosic biomass using a moderate temperature molten-salt based process to unlock hydrocarbon content having the potential to substantially supplement demand for petroleum based fuels and chemicals. Bio-oil is a precursor to production of other chemicals and hydrocarbons, and can be refined as an effective replacement to conventional petroleum products and fossil fuels. A disclosed approach employs Molten-Salt Pyrolysis (MSP), for the efficient and economical production of such precursor chemicals directly from whole biomass under moderate conditions (˜400° C., 1 atm.). Lignocellulosic biomass, freely available in renewable wood and plant products, undergoes a moderate temperature heating process in a eutectic molten salt mixture to generate a condensable vapor of the precursor or platform chemicals.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 62/188,841, filed Jul. 6, 2015, entitled “MOLTEN-SALT CATALYTIC PYROLYSIS: A SINGLE-POT PROCESS FOR FUELS AND CHEMICALS FROM BIOMASS,” incorporated herein by reference in entirety. 
     
    
     BACKGROUND 
       [0002]    Fossil fuels, such as crude oil, natural gas and coal were formed in a process spanning millions of years, yet are being consumed at a rate that guarantees their depletion in decades. Further, their rapid usage is causing a “green house effect” and climate change. Hydrocarbons based in prehistoric plants and animals formed the reserves that are continually sought for combustible fuels. Vast supplies of renewable hydrocarbons still exist in abundant forests in the form of lignocellulose, yet can be difficult to access due to the recalcitrance of its molecular structure. 
         [0003]    Lignocellulosic biomass, in the form of agricultural waste, trees, grasses, and other plant based mediums, is the most abundant, potentially carbon neutral, renewable resource available in the world, with more than one billion tons/y potentially available in the U.S. This could yield ˜85 billion gallons of fuels/chemicals, enough to supplant 30% of U.S. petroleum consumption. Developing new technologies that can utilize this huge renewable resource effectively and economically could have dramatic implications in the wake of expiring fossil fuels. 
       SUMMARY 
       [0004]    A method of producing bio-oil and platform chemicals leverages chemically recalcitrant lignocellulosic biomass using a moderate temperature molten-salt based process to unlock hydrocarbon content having the potential to substantially supplement demand for petroleum based fuels and chemicals. Bio-oil hence produced is a precursor to production of other chemicals and hydrocarbons, and can be refined as an effective replacement to conventional petroleum products and fossil fuels. A disclosed approach employs Molten-Salt Pyrolysis (MSP), for the efficient and economical production of such precursor chemicals directly from whole biomass under moderate conditions (˜400° C., 1 atm.). Lignocellulosic biomass, freely available in renewable wood and plant products, undergoes a moderate temperature heating process in a eutectic molten salt mixture with or without a catalyst to generate a condensable vapor of the bio-oil precursor or platform chemicals. Condensation of the vapor results in a high yield bio-oil having either a broad distribution of products or relatively pure precursor chemicals such as furfural and acetic acid, depending on the molten-salt and catalysts employed and other reaction conditions. Moderate temperatures avoid excessive gasification into non-condensable gases associated with partial combustion or gasification, and avoid non-selective introduction of extraneous chemicals, as in the higher temperature conventional pyrolysis process, that require extensive upgrading or refinement to generate useable yields. 
         [0005]    Configurations herein are based, in part, on the observation that current fossil fuel reserves are finite, and subject to inevitable depletion as demand continues. Unfortunately, conventional approaches to petroleum resource management suffers from the shortcoming that alternatives to fossil fuel production are too slow for largescale application or require high temperatures that increase combustion and/or venting of harmful gases. Accordingly, configurations herein substantially overcome the shortcomings of conventional petroleum chemical production by leveraging extensive hydrocarbon resources remaining locked up in renewable vegetation resources. A bio-oil generation process employs common wood and plant feedstock for lignocellulosic biomass input to a moderate temperature MSP for generating high yield and high purity bio-oil that is more easily refineable as a replacement to conventional petroleum based chemicals. 
         [0006]    Configurations below, for example, depict a biomass processing platform that involves catalytic pyrolysis of whole biomass in a molten-salt (e.g., KCl—LiCl—ZnCl 2 ) at moderate temperatures (˜400° C.) that directly provides a high yield (&gt;20%) and selectivity (&gt;90%) of platform chemicals, including furfural and acetic acid. Lignocellulosic biomass has the potential to supplant up to a third of petroleum feedstock, a tenth of which is used for chemicals, often commanding a 50% higher market value than fuels, which have been the focus of conventional biomass conversion processes. These include: 1) the low-temperature (&lt;150° C.) solution-phase routes that are selective, but require extensive pretreatment, are sluggish, and produce significant waste; and 2) high-temperature (&gt;500° C.) pyrolysis routes, that are fast but not selective, requiring many upgrading steps to improve purity due to the varied selectivity of the yield. The disclosed approach is an intermediate temperature (350-450° C.) molten-salt pyrolysis (MSP) route that combines these two approaches by using a molten-salt as a solvent phase for efficiently and selectively producing fuels and commodity chemicals directly from whole biomass. The inexpensive molten-salts provide a highly reactive and nonvolatile ionic medium with excellent heat transfer characteristics that allows biomass: 1) dissolution, 2) deconstruction, 3) catalytic dehydration &amp; reconstruction into chemicals, and 4) overhead recovery of product vapors, all in a single containment. 
         [0007]    Pyrolysis is generally defined as a thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen. It typically refers to an irreversible change of chemical composition and physical phase, producing a complex and corrosive conventional bio-oil that can be difficult to refine further, along with significant gases such as carbon monoxide, carbon dioxide, and hydrogen. Configurations herein therefore depict use of MSP for a lower temperature pyrolysis reaction for generating a condensable vapor from which the novel bio-oil is extracted such that gasification of non-condensable products has not yet occurred to a significant extent, as is the case with higher temperate pyrolysis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The foregoing and other objects, features and advantages of the invention will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
           [0009]      FIG. 1  is a diagram of a bio-oil or chemicals generation apparatus as disclosed herein; 
           [0010]      FIG. 2  is a transition diagram of some of the compounds formed in an example configuration in the apparatus of  FIG. 1 ; 
           [0011]      FIG. 3  is an apparatus of a particular configuration for condensation of furfural and acetic acid from the molten-salt pyrolysis process; and 
           [0012]      FIG. 4  shows the effect on liquid yield from vapor condensation of varying the eutectic salt composition, temperature of operation, and biomass feed particle size in various arrangements of the apparatus of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Depicted below is an example of operation of a configuration including a containment and condensers for evaporating and collecting the bio-oil. The containment, such as a closed vessel, couples to a cooled condenser or other vessel to undergo cooling for causing the collected vapors to condense. A variety of suitable containment, condensing, and related couplings and/or interconnections may be envisioned in alternate configurations. 
         [0014]    The configurations below disclose a method of producing bio-oil from biomass by combining a plurality of salts to form a eutectic salt mixture having a melting point lower than any of the salts individually, and adding a particulated biomass to form a mixture with the eutectic salt. A heat source or furnace heats the mixture in a containment sealed from ambient oxygen above the melting point to generate a molten salt mixture including the particulated biomass and resulting in a vapor. An exhaust conduit, pipe or outflow collects the vapor including bio-oil components, and condenses the vapor for recovering the bio-oil components to generate bio-oil suitable for chemicals or for refining into fuels. In the disclosed configurations, the liquid yield of bio-oil is between 40-60% of the added biomass, substantially higher than conventional pyrolysis approaches. Further, temperatures below 450° C., and typically between 300°-400° C., produce the bio-oil rich vapor, well below that of conventional pyrolysis and refining techniques. The reactor or containment also recovers and reuses the molten salt, since the molten salt remains unconsumed by the evaporative process. This is permitted because pyrolysis of the bio-mass occurs in MSP at a temperature between the low-temperature solvent based processes that are slow and high temperature pyrolysis processes resulting in gasification of non-condensable gases including H 2  and CO 2 . 
         [0015]    It should be emphasized that the term “Bio-oil” is a generally accepted industry term for products resulting from pyrolysis. Bio-oil is therefore a term often used for the liquids resulting from conventional pyrolysis, which is a mixture of dozens if not hundreds of organic chemicals, hence the name that reminds one of crude oil Like crude oil, substantial processing is often employed to refine it into fuels and chemicals. The liquid products resulting from MSP often include much fewer chemicals, e.g., the example cited frequently has only a couple—furfural and acetic acid, and are easier to separate. Such MSP-produced bio-oil as disclosed herein defines the liquid fuels and chemicals resulting from this MSP proves. The claimed MSP bio-oil is distinguishable from conventional pyrolysis oil in that the yield is higher and the number of chemicals in it is much smaller, so that it is easier to process as well. 
         [0016]      FIG. 1  is a diagram of a bio-oil or chemical generation apparatus as disclosed herein. Referring to  FIG. 1 , the apparatus  100  for performing molten salt pyrolysis (MSP) as disclosed herein includes a single containment vessel  110  receptive to the biomass  120  delivered via a feed auger  122  or other suitable introduction mechanism. Also in the containment vessel  110  is the molten salt mixture  130  and an optional catalyst  124 , discussed further below. A furnace  140  or other heat source heats the molten salt mixture (mixture)  130  to result in a vapor  150  drawn into one or more condensers  152 - 1  . . .  152 - 2  ( 152  generally). The condensers  152  cool the vapor  150  to cause condensation of the bio-oil  160 - 1  . . .  160 - 2  ( 160  generally). Depending on the conditions in the MSP process and temperature of each condenser  152 , the extracted condensate may comprise a high purity of condensed substances, such as furfural  160 - 1  and acetic acid  160 - 2 . Varying the temperature, composition of the molten-salt and catalysts, and arrangement of the bio-oil condensers  154  allows collection of varying substances and purity, also discussed further below. Uncondensed gases  166  are exhausted or reused to heat the containment  110 , however the exhausted gases such as recycled CO 2  are expected to result in a net reduction in gaseous by-products and certainly less harmful than corresponding fossil fuel production. 
         [0017]      FIG. 2  is a transition diagram of some of the compounds in an example configuration in the apparatus of  FIG. 1 . Referring to  FIGS. 1 and 2 , in the disclosed approach, leveraging the lignocellulose encapsulated in woody plants  200  for harvesting and deconstruction includes some of the chemical transformations shown in  FIG. 2 . A particular difficulty in exploiting the vast lignocellulosic resource is that it is structurally and chemically recalcitrant, comprising of a matrix of cross-linked polysaccharide network of: 1) cellulose  202  (C 6  sugars) and 2) hemicellulose  204  (C 5  sugars), with 3) lignin  206  (aromatic). This recalcitrance is a result of: a) cellulose crystallinity, because of the hydrogen bonding between OH groups on the glucose with O atoms on the same or a neighboring chain, b) presence of biologically and chemically resistant lignin, and c) the cross-linking between polysaccharides (cellulose and hemicellulose) and lignin. To access the carbohydrates for production of bio-based fuels and chemicals, one must first deconstruct this matrix and disrupt the hydrogen-bonding network, either via rapid heating as in pyrolysis, or by the use of a strong derivatizing or non-derivatizing solvent as in solution-phase routes. For instance, in a conventional Kraft process, an NaOH and Na 2 S solution (white liquor) is used to separate cellulose from lignin. 
         [0018]    In the disclosed approach, the bio-oil is defined by organic compounds resulting from a lignocellulose solution and deconstruction of the biomass. The bio-mass is easily obtainable from renewable forestry and vegetation sources, and may be in the form of wood chips, shavings, or sawdust, or any suitable plant material. The expected biomass, therefore, is a lignocellulosic biomass defined by a matrix of cross-linked polysaccharide network of the cellulose  202  (C 6  sugars), a hemicellulose  204  (C 5  sugars) and lignin  206 . 
         [0019]    The MSP process as disclosed herein facilitates deconstruction of the lignocellulosic matrix plus cellulose dissolution via a molten-salt medium, teeming with ions, that is readily able to disrupt the hydrogen-bonding network with its strong intermolecular forces. Further, via a choice of molten salt anions (e.g. Cl − ) and cations (e.g. Zn 2+ ), multi-step catalysis can be accomplished in situ. In fact, additional catalysts such as acids, bases, metals, and oxides may be readily dispersed within the molten salt for further enhancing selectivity and yield. Furthermore, by using significantly higher temperatures (−400° C.) than allowed by conventional solvents or even ionic liquids (ILs) (&lt;200° C.), the MSP process is able to effectively combine the solvation and the lower temperature pyrolysis to accrue the advantages of both routes. The vapor therefore includes non-volatile components resulting from heating below a temperature defining conventional pyrolysis, which would result in significant gasification of non-condensable substances as well as in a complex bio-oil. The MSP is, thus, is a transformative improvement over competing biomass routes. A particular configuration, shown in  FIGS. 1 and 2 , results in a high yield and purity of furfural and acetic acid. Potential reaction pathways for the wood and woody plants  200  to furfural  210 , acetic acid  212 , char  214 , and other gases are depicted in  FIG. 2 . 
         [0020]      FIG. 3  is an apparatus of a particular configuration for condensation of furfural and acetic acid from the bio-oil. Referring to  FIGS. 1 and 3 , in a production scale, the apparatus  100  defines a continuously operating arrangement  100 ′ for reusing the molten salt  130  and handling particulate accumulations such as char. The arrangement  100 ′ includes a reactor  300  containing the molten salt  130 , and a carrier gas  311  to provide a continuous flow and inert environment  312  in the reactor devoid of oxygen and other gases that hinder purity and yield. A carrier gas flow  314  at a regulator  316  controlled pressure ensures a continuous flow  340  of low pressure vapor at the reactor  300  (i.e. containment) outflow  325 . A cyclone  330  removes particulate matter from the vapor flow  340  before passing to the collection condensers  154  where the vapor  150  is condensed by a cooling medium  170  surrounding the respective condensers. It should be noted that any suitable condensing device for containing and routing the vapor  150  to a region of lower temperature where the bio-oil components in the vapor are permitted to condense may be employed. 
         [0021]    In the example of  FIG. 3 , the arrangement  100 ′ introduces an inert gas  311  into the sealed containment or reactor  300  for displacing the vapor  150  to a lower temperature containment (condenser  154 ) for condensing and to ensure an inert atmosphere. The vaporization of the bio-mass occurs at a temperature between solvent based processes and high temperature pyrolysis that would result in gasification of non-condensable gases including H 2  and CO 2 . This further results in condensing furfural in a purity of at least 75% and a yield of at least 21% at a temperature substantially around 120° C. (condenser  154 - 1 ), and in condensing acetic acid in a purity of at least 75% and a yield of at least 25% at a temperature substantially around 105° C. (condenser  154 - 2 ). 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 Operating Condition 
                 Value 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 P (MPa) 
                 0.1 
               
               
                   
                 T (° C.) 
                 400 
               
               
                   
                 N 2  sweep rate (L min −1 ) 
                  2-10 
               
               
                   
                 Salt mass (kg) 
                 0.10 
               
               
                   
                 Biomass feed rate* (hr −1 ) 
                 0.5-2.0 
               
               
                   
                 Salt composition 
               
               
                   
                 ZnCl 2  (mol %) 
                 50 
               
               
                   
                 LiCl (mol %) 
                 25 
               
               
                   
                 KCl (mol %) 
                 25 
               
               
                   
                 Condenser Temperatures 
               
               
                   
                 Furfural condenser (° C.) 
                 120 
               
               
                   
                 Acetic Acid condenser (° C.) 
                 105 
               
               
                   
                 Water condenser (° C.) 
                 0 
               
               
                   
                   
               
               
                   
                 *Normalized by total salt mass 
               
             
          
         
       
     
         [0022]    In further detail, an example reactor operating according to the parameters in TABLE I is a  316  stainless steel, bolted enclosure, equipped with a high-sheer impeller, electric heating blanket  318 , and sapphire window  319  for visual access of the process. The less corrosive nature of the bio-oil from MSP permits the use of more conventional vessels and containments. A further advantage to the moderate temperature, eutectic salt mixture is the conventional containment materials utilized. An auger type biomass feeder  322  delivers ground biomass  320  (1-5 mm diameter) to the reactor  300  and feed rate varied to determine an optimum for stable operation. The inert carrier gas  311  is (N 2 ) and may be used to strip away volatiles and particulate char. Downstream of the reactor  300 , the cyclone  330  removes particular matter larger than 2.5 um, and three temperature-controlled condensers at appropriate temperatures for fractional collection of furfural (B.P.=162° C.), acetic acid (118° C.), and water, respectively. An electrostatic precipitator or HEPA filter  342  may be used for removal of finer particles. An exhaust valve or filter  346  may be used to segregate liquid and gaseous exhaust. 
         [0023]    Product gas will be continuously analyzed using a dedicated on-line mass spectrometer  344  (1-100 amu). 
         [0024]    As indicated above, eutectic salt mixtures have a melting point lower than any of the individual salts. The most favorable results were generated using chloride based molten salts. The selection criterion of molten salts was based on their melting point, pyrolysis performance, and cost. It should be apparent that low melting point, high performance in bio-oil production and lower costs are preferable. Conventional single chloride salts usually have very high melting points; for example potassium chloride melts at 770° C., sodium chloride at 801° C., and lithium chloride at 605° C. In contrast to a single salt, the melting point of mixed salts is usually much lower, especially at some compositions corresponding to eutectic points. Phase diagrams may assist in finding a suitable composition of a eutectic that will melt at a given temperature. TABLE II lists example types of molten salts and eutectic characteristics employed in various configurations. A large variety of other eutectic salt mixtures may be employed. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 CHLORIDE SALTS USED IN PYROLYSIS OF BIOMASS. 
               
             
          
           
               
                 Molten Salts 
                 Molar Ratio 
                 Melting Point (° C.) 
               
               
                   
               
               
                 ZnCl 2 —KCl—LiCl 
                 40:20:40  a   
                 240 
               
               
                 AlCl 3 —KCl 
                 67:33 
                 128 
               
               
                 AlCl 3 —NaCl 
                 55:45 
                 133 
               
               
                 CuCl—KCl 
                 65:35 
                 150 
               
               
                 ZnCl 2 —KCl—NaCl 
                 52.9:33.7:13.4 
                 204 
               
               
                 ZnCl 2 —KCl—NaCl 
                 60:20:20 
                 203 
               
               
                 KCl—LiCl—NaCl 
                 36:55:9 
                 346 
               
               
                 KCl—LiCl—NaCl 
                 24:43:33 
                 357 
               
               
                 KCl—MgCl 2 —NaCl 
                 28.75:43.75:27.5 
                 383 
               
               
                 ZnCl 2   
                 — 
                 283 
               
               
                 ZnCl 2 —KCl 
                 70:30 
                 262 
               
               
                 ZnCl 2 —NaCl 
                 70:30 
                 255 
               
               
                 ZnCl 2 —SnCl 2   
                 70:30 
                 / 
               
               
                   
               
               
                   a  These mole percentages are based on the molecular weight of the metal cation. 
               
             
          
         
       
     
         [0025]    TABLE III depicts the effect of molten salts on the bio-oil composition both qualitatively and quantitatively. Referring to TABLE III and  FIG. 3 , various bio-oil  160  samples are depicted. Gas chromatography-mass spectrometry (GC-MS) is an effective analytical method to determine the composition of the samples that were produced. Three samples of vapor  150  collected without molten salts comprising the reactor contents yield scattered results of multiple components in the extracted vapor. In contrast, a yield from a MSP generated vapor  150  depicts highly selective and pure furfural and acetic acid. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE III 
               
             
             
               
                   
               
               
                 GC/MS results (area %) with (MSP) 
               
               
                 and without (No. 1-3) molten salts. 
               
             
          
           
               
                 Content 
                 No. 1 
                 No. 2 
                 No. 3 
                 MSP 
               
               
                   
               
             
          
           
               
                 Water 
                 28.63 
                 24.51 
                 14.28 
                 49.89 
               
               
                 Acetic acid 
                 25.06 
                 25.81 
                 19.82 
                 25.86 
               
               
                 Furfural 
                 11.63 
                 14.11 
                 6.90 
                 21.62 
               
               
                 2-propanone,1-hydroxy- 
                 11.20 
                 11.50 
                 10.36 
                 — 
               
               
                 Acetic acid, methyl ester 
                 2.98 
                 2.73 
                 1.96 
                 — 
               
               
                 Propanic acid 
                 2.02 
                 2.28 
                 1.15 
                 — 
               
               
                 1-hydroxy-2-butanone 
                 0.97 
                 1.81 
                 1.87 
                 — 
               
               
                 2-cyclopenten-1-one,2-hydroxy- 
                 — 
                 1.46 
                 2.6 
                 — 
               
               
                 Phenol,2-methoxy-4-methyl 
                 2.50 
                 1.23 
                 3.66 
                 — 
               
               
                 Ethanone,1-(2-furanyl)- 
                 1.47 
                 1.18 
                 2.34 
                 — 
               
               
                 Undefined organic products 
                 10.88 
                 9.78 
                 66.68 
                 — 
               
               
                   
               
             
          
         
       
     
         [0026]    Another contributing factor is the particle size of the shredded and/or particularized biomass fed through the auger. Four groups of sawdust biomass, each having a different particle size range, were processed through the reactor  310 . The mass of sawdust in each run was 5 g and the reaction was conducted at carrier gas flow rate of 165 CC/min and at a temperature of 350° C. TABLE IV shows the effect of particle size of biomass on bio-oil yield without molten salts. Theoretically, the finer the particle size that biomass has, the higher the bio-oil yield should be. Since the woody composition exhibits low thermal conductivity, fine particle size biomass has the ability of transferring heat to its inner core faster than the larger particle size biomass, which favors the formation of bio-oil. Moreover, smaller particles show better mass transfer. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE IV 
               
             
             
               
                   
               
               
                 Effect of particle size on yield of bio-oil without molten salt. 
               
             
          
           
               
                   
                 Particle size (μm) 
                 Yield (%) 
               
               
                   
                   
               
             
          
           
               
                   
                 &lt;106 
                 18.6 
               
               
                   
                 106-212 
                 19.1 
               
               
                   
                 300-450 
                 14 
               
               
                   
                 600-850 
                 13.8 
               
               
                   
                   
               
             
          
         
       
     
         [0027]    In contrast,  FIG. 4  shows the improvement of addition of molten salts on the bio-oil yield. Compared with Table 3, 32.6% liquid yield was obtained with CuCl—KCl molten salts for the particle size between 106-212 μm, while only 19.1% was attained without molten salts at the same temperature. This improvement was even more significant for the particle size lower than 106 μm, i.e., 41% with molten salts and 18.6% without salts. In the presence of CuCl—KCl molten salts, biomass of particle size between 106-212 μm exhibited lower yield of bio-oil than that of particle size &lt;106 μm. This finding not only proved that fine particle should produce high yield of bio-oil, but also illustrated that the advantage of molten salts. Thus, biomass particles would be evenly distributed within a molten salt solvent which could suppress the possible agglomeration of fine particles in the absence of molten salts. The ternary molten salts, ZnCl 2 —KCL—LiCl also had the same function and gave higher yield below 450° C. 
         [0028]    Referring to  FIGS. 1 and 4 ,  FIG. 4  shows the effect of varying the eutectic salt composition and particle size in various arrangements of the apparatus of  FIG. 1 . Referring to  FIGS. 1 and 4 , various compositions and yields are as follows. An example biomass feed scenario includes a feed of 5 g sawdust at a flow rate of 165 CC/min. The mass ratio of feed to molten salt was 1:10. The % yield  410  plotted according to temperature  420  yields the following: 
         [0029]    Diamond  401 : CuCl (65% mol), KCl (35% mol), particle size: &lt;106 μm; 
         [0030]    Square  402 : CuCl (65% mol), KCl (35% mol), particle size: 106-212 μm; 
         [0031]    Triangle  402  : ZnCl2 (40% mol), KCl (20% mol), LiCl (20% mol), particle size: &lt;106 μm. 
         [0032]    Circle  402  : ZnCl 2  (40% mol), KCl (20% mol), LiCl (20% mol), particle size: 106-212 μm.) 
         [0033]    Mole percentages in ZnCl 2 —KCl—LiCl were based on the molecular weight of the metal cation. 
         [0034]    As discussed above, MSP product yield and selectivity can benefit from addition of additional catalysts  124 , such as Bronsted acids, Lewis acids, or Bronsted bases to the molten salt  130 . For example, phosphomolybdic acid generally improves liquid yield at all temperatures. It has been found that the stronger Lewis acids (e.g., AlCl 3  and CuCl 2 ) are less effective than ZnCl 2 , providing a lower yield, and a significantly wider product distribution. For Bronsted acids, we can use the Keggin-type heteropolyacids containing W, Mo, and Si, with a focus on silicotungsten and phosphotungstic acids, given their superior thermal stability.  100 These represent a clear trend in BrØnsted acidity (W&gt;Mo&gt;Si for the polyatom, and P&gt;Si=Ge for the central atom) permitting trends in acid strength to be examined. A tandem Lewis acid (e.g., ZnCl 2 ) and Bronsted acid functionality can also have beneficial effects. For Bronsted bases, KOH, NaOH, and LiOH may be employed. Again, these follow a clear trend in strength (LiOH&gt;NaOH&gt;KOH). 
         [0035]    Table V shows the effect of addition of a catalyst on the bio-oil yield with different molten salts. In Table V, yield  1  representbio-oil yields obtained without catalyst, while yield  2  represented bio-oil yields obtained with phosphomolybdic acid catalyst, just as an example of a catalyst that might be employed. In most cases shown, ternary molten salt provided higher bio-oil yield than binary molten salt. The groups containing ZnCl 2  gave higher yield than those without ZnCl 2 . In ZnCl 2  containing salts, the one with LiCl showed higher yield than the ones with Na. 
         [0000]                                      TABLE V                   Effect of combination of different molten salts (yield       1) and addition of catalyst (yield 2) on bio-oil yield.                Molten salt   Yield 1   Yield 2                       Cu—K   36.80%     48%           Zn—K—Li   51.50%   60.40%           Zn—Na—K   47.80%   51.60%           Zn—Na—K 1     46.70%   54.60%           K—Li—Na   36.20%   43.00%           K—Li—Na 1     39.50%   46.00%                       (Condition: Feed: 5 g sawdust; Flow rate: 165 CC/min; Mass ratio of feed to molten salt: 1:10; Particle size: 106-212 μm; Temperature: 400° C. Cu—K: CuCl (65% mol), KCl (35% mol); 2 g phosphomolybdic acid was used as catalyst; Zn—K—Li: ZnCl 2  (40% mol), KCl (20% mol), LiCl (20% mol), molar ratio based on the molecular weight of the metal cation; 1 g phosphomolybdic acid; Zn—Na—K: ZnCl 2  (52.9% mol), NaCl (13.4% mol), KCl (33.7% mol); 1 g phosphomolybdic acid; Zn—Na—K 1 : ZnCl 2  (60% mol), NaCl (20% mol), KCl (20% mol); 1 g phosphomolybdic acid; K—Li—Na: KCl (36% mol), LiCl (55% mol), NaCl (9% mol); 1 g phosphomolybdic acid; K—Li—Na 1 : KCl (24% mol), LiCl (43% mol), NaCl (33% mol); 1 g phosphomolybdic acid.)            
In summary, the composition of bio-oil derived from pyrolysis of sawdust can be very complicated which could contain hundreds of substances. Moreover, as the pyrolysis temperature increases, the composition of bio-oil became more complicated. Introduction of molten salt to the pyrolysis system narrows the product distribution significantly.
 
         [0036]    While the system and methods defined herein have been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.