Abstract:
A process for producing a diesel fuel of biological origin. The process includes a biological component to be trans-esterified into a fatty acid alkyl ester. A fraction of the fatty acid alkyl ester is hydrodeoxygenated and hydroisomerized to produce an iso-paraffinic hydrocarbon. The fatty acid alkyl ester and the iso-paraffin components are combined into a middle distillate product suitable for direct use as diesel or jet fuel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application Ser. No. 60/883,529, filed Jan. 5, 2007, which is hereby expressly incorporated by reference herein in its entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates generally to a process for the production of diesel fuel from renewable resources, and more particularly, not by way of limitation, to an improved process for the production of diesel fuel from renewable resources for use as alternatives or additives to petroleum-based or gas-to-liquid produced products. 
         [0005]    2. Brief Description of the Related Art 
         [0006]    Processes useful for producing fatty acid alkyl esters from renewable sources such as animal fats and vegetable oils have been in use for many years. Examples of such processes are found in U.S. Pat. Nos. 5,424,467; 5,389,113; 5,525,126; 6,642,399; 6,712,867; 6,768,015; 6,855,838; 6,878,837; 6,884,900; and 6,982,155, the disclosures all of which are incorporated herein by reference. The products of these processes are generally referred to as “biodiesel”. 
         [0007]    Biodiesel is produced commercially by the transesterification reaction of triglycerides (the molecular building block of vegetable oils and fats) with methanol. Among the advantages of biodiesel is its role as a lubricity improver when blended with ultra-low sulfur conventional diesels. 
         [0008]    However, several factors limit the choice of feedstock for biodiesel production. If the triglyceride molecule is made up of mostly saturated fatty acids, the resulting biodiesel will have poor low temperature properties (e.g. high cloud point and pour point). The more abundant and less expensive vegetable oils such as palm oil (mostly saturated fatty acids) are not used for biodiesel except when highly diluted with conventional diesel fuel and in tropical climates. 
         [0009]    Another factor affecting feedstock choice is the level of free-fatty acid (FFA). Since fatty acids convert to soaps under typical base-catalyzed transesterification conditions, high levels of FFA result in operating problems and catalyst consumption inefficiencies. 
         [0010]    To this end, although processes of the existing art utilize renewable sources to produce diesel fuel, a need exists for a process for producing hydrocarbon products, particularly high quality paraffinic middle distillates in high yields, from renewable sources. It is to such a process that the present invention is directed. 
       SUMMARY OF THE INVENTION 
       [0011]    The process of the present invention produces a diesel fuel of biological origin. A biological component, such as a vegetable oil, an animal fat and any combination thereof, is provided to be trans-esterified into fatty acid alkyl ester. An alcohol, such as methanol, is used for trans-esterification of the biological component. The trans-esterification catalyst is potassium hydroxide, sodium hydroxide, or sodium methoxide. Trans-esterification is carried out at a temperature of about 80° F. to about 200° F. 
         [0012]    A fraction of the fatty acid alkyl ester is subjected to hydro-deoxygenation and hydro-isomerization to produce an iso-paraffinic hydrocarbon. The fraction of the fatty acid alkyl ester subjected to hydro-deoxygenation and hydro-isomerization is recovered by distillation or crystallization. The hydrodeoxygenation pressure is about 500 psig to about 2,500 psig and the temperature is about 400° F. to about 800° F. The hydrodeoxygenation catalyst is a supported NiMo, NiW, or CoMo catalyst. The support is alumina, or alumina with phosphorous or silicon oxides. The hydroisomerization pressure is about 500 psig to about 2,000 psig and the temperature is about 500° F. to about 800° F. The hydroisomerization catalyst contains one or more of Pt, Pd, Ni, on amorphous or crystalline supports containing one or more of alumina, fluorided alumina, silica, ferrierite, ZSM-12, ZSM-21, ZSM-22, ZSM-23, SAPO-11, SAPO-31, and SAPO-41. 
         [0013]    The fatty acid alkyl ester and the iso-paraffin components are combined into a middle distillate composition suitable for direct use as diesel or jet fuel. 
         [0014]    The fraction of fatty acid alkyl ester is combined with a biological component rich in free fatty acids before being subjected to hydro-deoxygenation. The biological component rich in free fatty acids is rendered fat, restaurant grease, waste industrial frying oil, tall oil fatty acid, and combinations thereof. 
         [0015]    A glycerol byproduct of trans-esterification is used to wash the biological component rich in free fatty acid before this biological component is subjected to hydro-deoxygenation. The glycerol byproduct of trans-esterification may be subjected to hydro-deoxygenation. 
         [0016]    An object of certain embodiments of the invention is converting triglycerides with varying levels of saturation and free-fatty acid to diesel blends having both iso-paraffinic and methyl ester components. The iso-paraffin component improves low temperature properties while the methyl ester improves lubricity. 
         [0017]    Another object of certain embodiments of the invention is to produce a high quality middle distillate with improved yields and properties that meet the generally accepted specifications for conventional fuels. 
         [0018]    Another object of certain embodiments of the invention is to produce kerosene, jet fuel, or diesel from renewable feedstock. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a schematic diagram illustrating one embodiment of the process for converting a renewable feedstock to a diesel fuel blend having improved low temperature properties. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The process of the present invention relates to converting a renewable feedstock to a diesel fuel blend having improved low temperature properties. The process of the present invention produces high yields of an improved middle distillate product. 
         [0021]    The term “renewable feedstock” refers to animal fats, vegetable oils, plant fats and oils, rendered fats, restaurant grease and waste industrial frying oils, tall oil fatty acids and combinations thereof. 
         [0022]    The term “middle distillate product(s)” and “middle distillate” refer to hydrocarbon mixtures with a boiling point range that corresponds substantially with that of kerosene and gas oil fractions obtained in a conventional atmospheric distillation of crude oil material. The middle distillate boiling point range may include temperatures between about 150° C. and about 600° C., with a fraction boiling point between about 200° C. and about 360° C. 
         [0023]    The term “middle distillate fuel” refers to jet fuel, kerosene, diesel fuel, gasoline and combinations thereof. 
         [0024]    The term “FAME” refers to fatty acids methyl esters. 
         [0025]    Referring now to the  FIG. 1 , shown therein is a schematic of the operation of the process in accordance with the present invention as described herein. A renewable feedstock  10 , containing glycerides, is introduced into a transesterification unit  12 . The renewable feedstock  10  may be pretreated before being introduced into the process. It should be understood that any method known to one of ordinary skill in the art for pretreating the feedstock may be utilized. In one embodiment, the fatty acids are mostly saturated fatty acids, such as found in palm oil. However, it should be understood that any fatty acid containing varying levels of saturation known to one of ordinary skill in the art may be used. Stream  14  containing an alcohol and stream  16  containing a catalyst are added to the transesterification unit  12  and reacted with the fatty acid. In one embodiment, methanol and a potassium hydroxide catalyst are used. However, it should be understood that although methanol is utilized in one embodiment of the present invention that any alcohol known by one of ordinary skill in the art and used in accordance with the present invention may be utilized. Further, although potassium hydroxide is used in one embodiment as the transesterification catalyst, it should be understood that any variety of catalyst such as, but not limited to, sodium hydroxide, sodium methoxide or the like may be utilized in accordance with the present invention. 
         [0026]    In the transesterification unit  12 , the fatty acid reacts with the alcohol using the catalyst to produce an effluent  18  containing biodiesel. An effluent  20  containing crude glycerol byproduct is also produced from the reaction in the transesterification unit  12 . 
         [0027]    When palm oil, for example, is utilized in the process, the saturated fatty acids are of C 16  carbon length and the unsaturated fatty acids are C 18 . The C 16  fatty acids methyl esters (FAME) are stripped from the biodiesel to improve the cold flow properties of the biodiesel. Effluent  18  containing biodiesel is introduced into a vacuum distillation unit  22  so that the C 16  FAME is stripped from the biodiesel to produce effluent  24  containing C 16  FAME and effluent  26  containing C 18  FAME. It should be understood that although the C 16  FAME is shown being stripped from the biodiesel by vacuum distillation, the stripping of the C 16  FAME may be accomplished by distillation under pressure, stream stripping, thin film evaporators, wiped film evaporators or the like. 
         [0028]    Effluent  24  containing the C 16  FAME is introduced into a hydrotreater unit  30 . The C 16  FAME may be combined with a free-fatty acid rich stream  32  and a hydrogen stream  34 . The high melt point C 16  FAME fraction from the transesterification unit  12  is converted to n-paraffins (for example, n-hexadecane (cetane)) (effluent stream  36 ) and water (effluent stream  38 ) in the hydrotreater unit  30 , according to the following example equation (1): 
         [0000]      C 15 H 31 —COO—CH 3 +3H 2 →C 16 H 34 +2H 2 O+CH 4   (1) 
         [0029]    In one embodiment, the hydrotreating process in the hydrotreater unit  30  employs a heterogenous supported bifunctional catalyst. The bifunctional catalyst is bimetallic. However, it should be understood that any variety of catalyst may be utilized in the hydrotreating process in accordance with the present invention. Examples of hydrotreating catalysts suitable for hydrodeoxygenation and olefin saturation include sulfided Ni—W (nickel-tungsten), Ni—Mo (nickel-molybdenum) and Co—Mo (cobalt-molybdenum) on an alumina, or alumina with phosphorus oxide or silicon oxide support. The catalysts may be sulfided during startup, or pre-sulfided and active when loaded into the hydrotreater unit  30 . The hydrotreater unit  30  deoxygenates fatty acids and saturates double bonds. In the case of fatty acid esters or glycerides the ester linkages are broken and free-fatty acids are deoxygenated and their double bonds saturated. The hydrotreater unit  30  operates at typical refining pressure and temperature conditions: LHSV (0.1-10 hr −1 ), temperature (300-850° F.), pressure (250-3000 Psig) and gas/oil ratio (1000 SCF/bbl-20,000 SCF/bbl). However, it should be understood by one of ordinary skill in the art that there may be times when the hydro-treater unit  30  may operate outside of typical refining pressure and temperature conditions in accordance with the present invention. 
         [0030]    The n-paraffin product from the hydro-treater unit  30  is introduced in a hydro-isomerizer unit  40  where the n-hexadecane product is converted to lower melting point branched isomers. A hydro-isomerization catalyst contains one or more of Pt, Pd, Ni, on amorphous or crystalline supports containing one or more of alumina, fluorided alumina, silica, ferrierite, ZSM-12, ZSM-21, ZSM-22, ZSM-23, SAPO-11, SAPO-31, and SAPO-41. Hydrogen  41  may also be added to the hydro-isomerizer unit  40  as needed. The hydro-isomerizer unit  40  operates at typical refining pressure and temperature conditions: LHSV (0.1-10 hr −1 ), temperature (300-850° F.), pressure (250-3000 Psig) and gas/oil (1000 SCF/bbl-20,000 SCF/bbl). However, it should be understood by one of ordinary skill in the art that there may be times when the hydroisomerizer unit  40  may operate outside of typical refining pressure and temperature conditions in accordance with the present invention. 
         [0031]    An effluent stream  42  containing isomers from the hydro-isomerizer unit  40  are introduced in a fuel blending unit  44  and blended with the C 18  FAME product of the trans-esterification unit  12  or vacuum distillation unit  18 . An effluent  46  containing a final diesel fuel product is produced from the fuel blending unit  44 . Since the hydro-treater unit  30  desulfurizes the renewable feedstock under the hydro-deoxygenation conditions of, for example, Equation (1), the alkyl ester component of the blended final diesel fuel product acts to improve lubricity. 
         [0032]    There are a number of ways that the transesterification process units can be integrated with hydroprocessing units to achieve additional operational synergies. For example, the glycerol byproduct of the transesterification unit  12  can be used to wash salt contaminants from the high free-fatty acid feeds  32  to the hydrotreater unit  30  before the biological component rich in free-fatty acid is subjected to hydro-deoxygenation. Alternatively, the glycerol byproduct may be co-fed to the hydrotreater unit  30  and subjected to hydro-deoxygenation to yield propane diols and other value-added co-products. 
         [0033]    From the above description, it is clear that the present invention is well adapted to carry out the objects and to attain the advantages mentioned herein as well as those inherent in the invention. While presently preferred embodiments of the invention have been described for purposes of this disclosure, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are accomplished within the spirit of the invention disclosed and claimed.