Patent Application
20140005448
This invention relates to a process for producing aviation fuel boiling range hydrocarbons useful as aviation fuel from renewable feedstocks such as the glycerides and free fatty acids found in materials such as plant oils, animal oils, animal fats, and greases. The process involves reforming n-paraffin and isomerized reaction products to form a mixture of aromatics, and mixing the aromatics into a renewable aviation fuel product.
As the demand for fuels such as aviation fuel increases worldwide, there is increasing interest in sources other than petroleum crude oil for producing the fuel. One source is renewable feedstocks including, but not limited to, plant oils such as corn, jatropha, camelina, rapeseed, canola, soybean and algal oils, animal fats such as tallow, fish oils, and various waste streams such as yellow and brown greases and sewage sludge. The common feature of these feedstocks is that they are composed of mono- di- and tri-glycerides, and free fatty acids (FAA). Another class of compounds appropriate for these processes is fatty acid alkyl esters (FAAE), such as fatty acid methyl ester (FAME) or fatty acid ethyl ester (FAEE). These types of compounds contain aliphatic carbon chains generally having from about 8 to about 24 carbon atoms. The aliphatic carbon chains in the glycerides, FFAs, or FAAEs can be saturated or mono-, di- or poly-unsaturated. Most of the glycerides in the renewable feed stocks will be triglycerides, but some may be monoglycerides or diglycerides. The monoglycerides and diglycerides can be processed along with the triglycerides.
There are references disclosing the production of hydrocarbons from oils. For example, U.S. Pat. No. 4,300,009 discloses the use of crystalline aluminosilicate zeolites to convert plant oils (e.g., corn oil) to hydrocarbons (e.g., gasoline), and chemicals (e.g., para-xylene). U.S. Pat. No. 4,992,605 discloses the production of hydrocarbon products in the diesel boiling range by hydroprocessing vegetable oils such as canola or sunflower oil. Finally, US 2004/0230085 A1 discloses a process for treating a hydrocarbon component of biological origin by hydrodeoxygenation followed by isomerization.
One aspect of the present invention relates to a method of making highly renewable aviation fuel component. In one embodiment, the method includes reacting a renewable feedstock in a reaction zone to form a mixture of n-paraffins and isomerized paraffins. The mixture of n-paraffins and isomerized paraffins is separated into at least a heavy SPK fraction, and a light SPK fraction. A portion of the light SPK fraction is reformed in a reforming zone under reforming conditions to form a mixture of renewable aromatics. A portion of the mixture of renewable aromatics is mixed into the light SPK fraction, the heavy SPK fraction, an aviation fuel made from a renewable feedstock, or combinations thereof to form the highly renewable aviation fuel component.
The Figure is a general flow schematic of one embodiment of a process.
Renewable aviation fuel is currently made by hydroprocessing renewable feedstocks to produce aviation range hydrocarbons. This product is known as synthetic paraffinic kerosene (SPK). The process also produces paraffinic green diesel, paraffinic green naphtha, and liquefied petroleum gas (LPG). In a second stage of the process, the n-paraffins are isomerized and mildly cracked to improve the cold properties of the resulting paraffins.
SPK typically cannot meet the commercial specifications for density for aviation fuel, so the SPK is blended with aviation range aromatics to obtain a blended fuel meeting the density specification. The aviation range aromatics are currently not derived from renewable sources, but are conventional fossil fuel derived aromatics. Because of the requirement for high quality aromatics in the aviation fuel boiling range, aviation fuel from 100% plant and animal oils is difficult to make.
In the present process, the SPK is subjected to a reforming process to produce aviation range aromatics. The aviation range aromatics can then be blended with another portion of SPK or a separate SPK stream to make an aviation fuel component meeting the necessary specifications. The aviation range aromatics are generally about 5 wt % to about 25 wt % of the aviation fuel component, or about 8 wt % to about 25 wt %. Because the aviation range aromatics are derived from a renewable feedstock, the resulting aviation fuel component is highly renewable. By aviation fuel component, we mean any component that can be blended to produce aviation fuel, up to and including the resulting aviation fuel itself (e.g., when blended with a petroleum based aviation fuel). By highly renewable, we mean that at least about 25 wt % of the total aromatics used in an aviation fuel component are derived from a renewable feedstock, or at least about 50 wt %, or at least about 75 wt %, or at least about 80 wt %, or at least about 90 wt %, or at least about 95 wt %.
The naphtha product from the process described above is very paraffinic and low octane. Optionally, a portion of the green naphtha can be also be subjected to the reforming process to make naphtha range aromatics, which can then be blended with the green naphtha to make high-octane green naphtha.
One embodiment of the process is illustrated in the Figure. The renewable feedstock 5 enters the reaction zone 10. The reaction zone 10 includes one or more zones for one or more of hydrotreating, isomerization, and hydrocracking. The effluent 15 from the reaction zone 10 includes a mixture of n-paraffins and isoparaffins. The effluent 15 is sent to a stripping column 20. The overheads 25 from the stripping column 20 is exported from the unit as LPG or fuel gas. The bottoms 30 from the stripping column 20 is sent to a fractionator 35 where it is separated into different streams which can include at least one or more of a green naphtha fraction 40, a light SPK fraction 45, a heavy SPK fraction 50, and a green diesel faction 55.
In some embodiments, the light SPK fraction 45 is split into two portions 45A and 45B. Light SPK fraction 45A is sent to reformer 60. In other embodiments, the entire light SPK fraction 45 is sent to the reformer. In some embodiments, all or a portion 40A of the green naphtha fraction 40 is also sent to reformer 60.
The light SPK fraction 45A and green naphtha fraction 40A (if present) are reformed in reformer 60. The reformer conditions typically include a temperature in the range of about 300° C. to about 520° C., or about 410° C. to about 500° C., or about 380° C. to about 470° C., a pressure in the range of about 345 kPa (about 50 psig) to about 2758 kPa (about 400 psig), or about 1034 kPa (about 150 psig) to about 2068 kPa (about 300 psig), and a ratio of H2:HC of about 0.5 to about 10, or about 2 to about 8.
The effluent 65 from the reformer 60 includes aviation range aromatics, and naphtha range aromatics if a green naphtha fraction was reformed, as well as hydrogen. The effluent 65 is separated in a separator 70 into a hydrogen stream 75 and a liquid stream 80 including the aviation range aromatics and the naphtha range aromatics. The hydrogen stream 75 can be recycled back to the reaction section 10 and/or reformer 60, if desired. The liquid stream 80 is sent to fractionator 85 where the aviation range aromatics 90 are separated from the naphtha range aromatics 95.
The aviation range aromatics 95 can be combined with one or more of the light SPK fraction 45B, the heavy SPK fraction 50, and a stream of renewable aviation fuel made in a separate process to form a highly renewable aviation fuel.
In some embodiments, the naphtha range aromatics 95 can be combined with the naphtha fraction 40 to make high octane green gasoline.
In some embodiments, the green diesel fraction 55 can be recovered.
The term renewable feedstock is meant to include feedstocks other than those obtained directly from petroleum crude oil. Another term that has been used to describe this class of feedstocks is renewable fats and oils. The renewable feedstocks that can be used in the present invention include any of those which comprise glycerides and free fatty acids (FFA). Examples of these feedstocks include, but are not limited to, canola oil, corn oil, soy oils, rapeseed oil, soybean oil, colza oil, tall oil, sunflower oil, hempseed oil, olive oil, linseed oil, coconut oil, castor oil, peanut oil, palm oil, mustard oil, cottonseed oil, tallow, yellow and brown greases, lard, train oil, fats in milk, fish oil, algal oil, sewage sludge, cuphea oil, camelina oil, jatropha oil, curcas oil, babassu oil, palm kernel oil, crambe oil, and the like. Biorenewable is another term used to describe these feedstocks. The glycerides, FFAs, and fatty acid alkyl esters, of the typical vegetable oil or animal fat contain aliphatic hydrocarbon chains in their structure which have about 8 to about 24 carbon atoms with a majority of the oils containing high concentrations of fatty acids with 16 and 18 carbon atoms. Mixtures or co-feeds of renewable feedstocks and fossil fuel derived hydrocarbons may also be used as the feedstock. Other feedstock components may be used if the carbon chain length is well-defined before mixing with renewable oils to allow meeting desired yields and specifications for diesel and aviation range paraffins.
Various additives may be combined with the aviation fuel composition generated in order to meet required specifications for different specific fuels. The specifications could include physical characteristics, chemical characteristics, or both. The specifications could be industry standard, government, and/or military fuel standard specifications. In particular, the hydrocarbon product stream in the aviation fuel range generated herein complies with, is a blending component for, or may be combined with one or more additives to meet at least one of: ASTM D 7566 Specification for Aviation Turbine Fuel Containing Synthesized Hydrocarbons, ASTM D 1655 Specification for Aviation Turbine Fuels Defense Stan 91-91 Turbine Fuel, Aviation Kerosene Type, Jet A-1 NATO code F-35, F-34, F-37 Aviation Fuel Quality Requirements for Jointly Operated Systems (Joint Checklist) A combination of ASTM and Def Stan requirements GOST 10227 Jet Fuel Specifications (Russia) Canadian CAN/CGSB-3.22 Aviation Turbine Fuel, Wide Cut Type Canadian CAN/CGSB-3.23 Aviation Turbine Fuel, Kerosene Type MIL-DTL-83133, JP-8, MW-DTL-5624, JP-4, JP-5 QAV-1 (Brazil) Especifcacao de Querosene de Aviacao No. 3 Jet Fuel (Chinese) according to GB6537 DCSEA 134A (France) Carbureacteur Pour Turbomachines D'Aviation, Type Kerosene Aviation Turbine Fuels of other countries, meeting the general grade requirements for Jet A, Jet A-1, Jet B, and TS-1 fuels as described in the IATA Guidance Material for Aviation Turbine Fuel Specifications. Additives may be added to the jet fuel in order to meet particular specifications. One particular type of jet fuel is JP-8, defined by Military Specification ML-DTL-83133, which is a military grade type of highly refined kerosene based jet propellant specified by the United States Government.
Renewable feedstocks that can be used in the present invention may contain a variety of impurities. For example, tall oil is a byproduct of the wood processing industry, and it contains esters and rosin acids in addition to FFAs. Rosin acids are cyclic carboxylic acids. The renewable feedstocks may also contain contaminants such as alkali metals, e.g. sodium and potassium, phosphorous, as well as solids, water and detergents. An optional first step is to remove as much of these contaminants as possible. Any known pretreatment steps can be used including, but not limited to, contacting the renewable feedstock with an ion-exchange resin in a pretreatment zone at pretreatment conditions, contacting the renewable feedstock with a bleaching earth, such as bentonite clay, in a pretreatment zone, mild acid washing, the use of guard beds, filtration and solvent extraction techniques, hydroprocessing, such as that described in U.S. application Ser. No. 11/770,826, hydrolysis may be used to convert triglycerides to a contaminant mixture of free fatty acids, and hydrothermolysis may be used to convert triglycerides to oxygenated cycloparaffins, or combinations thereof.
The renewable feedstocks are flowed to a reaction zone or stage comprising one or more catalyst beds in one or more reactor vessels. Within the reaction zone or stage, multiple beds or vessels may be employed, and where multiple beds or vessels are employed, interstage product separation may or may not be performed between the beds or vessels. The term feedstock is meant to include feedstocks that have not been treated to remove contaminants, as well as those feedstocks purified in a pretreatment zone or an oil processing facility. The renewable feedstocks, with or without additional liquid recycled from one or more product streams, may be mixed in a feed tank upstream of the reaction zone, mixed in the feed line to the reactor, or mixed in the reactor itself. In the reaction zone, the renewable feedstocks are contacted with a multifunctional catalyst or set of catalysts comprising deoxygenation, hydrogenation, and isomerization functions in the presence of hydrogen.
A number of reactions occur concurrently within the reaction zone. The order of the reactions is not critical to the invention, and the reactions may occur in various orders. One reaction occurring in the reaction zone is hydrogenation to saturate olefinic compounds in the reaction mixture. Another type of reaction occurring in the reaction zone is deoxygenation. The deoxygenation of the mixture may proceed through different routes such as decarboxylation, where the feedstock oxygen is removed as carbon dioxide, decarbonylation, where the feedstock oxygen is removed as carbon monoxide, and/or hydrodeoxygenation, where the feedstock oxygen is removed as water. Decarboxylation, decarbonylation, and hydrodeoxygenation are herein collectively referred to as deoxygenation reactions.
Sufficient isomerization to prevent poor cold flow properties is needed. Aviation fuel and aviation blending components must have better cold flow properties than is achievable with essentially all n-paraffins, and another reaction occurring in the reaction zone is isomerization to isomerize at least a portion of the n-paraffins to branched paraffins. The yield of isomerization needed is dependent on the specifications required for the final fuel product. Some fuels require a lower cloud or freeze point, and thus need a greater yield from the isomerization reaction to produce a larger concentration of branched-paraffins. Alternatively, depending on the product properties targeted, and the blend of feedstocks used, the isomerization step may not be absolutely necessary.
As mentioned above, the multifunctional catalyst or set of catalysts comprise deoxygenation, hydrogenation, and isomerization functions. The catalyst function for deoxygenation and hydrogenation will be similar to those already known for hydrogenation or hydrotreating. The deoxygenation and hydrogenation functions, which may be the same or separate active sites, may be noble metals such as a platinum group metals including but not limited to ruthenium, rhodium, palladium, platinum, and mixtures thereof, supported on a high surface area carrier material such as alumina, silica, silica-alumina, magnesium oxide, titania, zirconia, activated carbon and others known in the art, at levels ranging from about 0.05 to about 10 weight-% of the catalytic composite. Examples of other active sites that may be employed to provide the deoxygenation and hydrogenation functions are sulfided base metals such as sulfided NiMo or sulfided NiW. A base metal is a metal which oxidizes when heated in air, and other base metals, in addition to nickel, molybdenum and tungsten, which may be a catalyst component herein include iron, lead, zinc, copper, tin, germanium, chromium, titanium, cobalt, rhenium, indium, gallium, uranium, dysprosium, thallium and mixtures and compounds thereof. Sulfided base metal catalysts may optionally be supported on carrier material such as alumina, silica, silica-alumina, magnesium oxide, activated carbon and others known in the art, or may alternately be used without additional support components,
Catalyst functions and conditions for isomerization are well known in the art. See for example US 2004/0230085 A1 which is incorporated by reference in its entirety. Due to the presence of hydrogen, these reactions may also be called hydroisomerization.
Overall, the isomerization of the paraffinic product can be accomplished in any manner known in the art or by using any suitable catalyst known in the art. In general, catalysts or catalytic components having an acid function and mild hydrogenation function are favorable for catalyzing the isomerization reaction. For a single multi-component catalyst, the same active site employed for deoxygenation can also serve as the mild hydrogenation function for the isomerization reactions. In general, suitable isomerization catalysts comprise a metal of Group VIII (IUPAC 8-10) of the Periodic Table and a support material. Suitable Group VIII metals include platinum and palladium, each of which may be used alone or in combination. The support material may be amorphous or crystalline, or a combination of the two. Suitable support materials include, aluminas, amorphous aluminas, amorphous silica-aluminas, ferrierite, ALPO-31, SAPO-11, SAPO-31, SAPO-37, SAPO-41, SM-3, MgAPSO-31, FU-9, NU-10, NU-23, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, ZSM-50, ZSM-57, MeAPO-11, MeAPO-31, MeAPO-41, MgAPSO-11, MgAPSO-31, MgAPSO-41, MgAPSO-46, ELAPO-11, ELAPO-31, ELAPO-41, ELAPSO-11, ELAPSO-31, ELAPSO-41, laumontite, cancrinite, offretite, hydrogen form of stillbite, magnesium or calcium form of mordenite, and magnesium or calcium form of partheite, each of which may be used alone or in combination. ALPO-31 is described in U.S. Pat. No. 4,310,440. SAPO-11, SAPO-31, SAPO-37, and SAPO-41 are described in U.S. Pat. No. 4,440,871. SM-3 is described in U.S. Pat. Nos. 4,943,424; 5,087,347; 5,158,665; and U.S. Pat. No. 5,208,005. MgAPSO is a MeAPSO, which is an acronym for a metal aluminumsilicophosphate molecular sieve, where the metal Me is magnesium (Mg). Suitable MgAPSO-31 catalysts include MgAPSO-31. MeAPSOs are described in U.S. Pat. No. 4,793,984, and MgAPSOs are described in U.S. Pat. No. 4,758,419. MgAPSO-31 is a preferred MgAPSO, where 31 means a MgAPSO having structure type 31. Many natural zeolites, such as ferrierite, that have an initially reduced pore size can be converted to forms suitable for isomerization by removing associated alkali metal or alkaline earth metal by ammonium ion exchange and calcination to produce the substantially hydrogen form, as taught in U.S. Pat. No. 4,795,623 and U.S. Pat. No. 4,924,027. Further catalysts and conditions for skeletal isomerization are disclosed in U.S. Pat. Nos. 5,510,306, 5,082,956, and U.S. Pat. No. 5,741,759.
The isomerization catalyst function may also comprise a modifier selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, phosphorus, samarium, gadolinium, terbium, and mixtures thereof, as described in U.S. Pat. No. 5,716,897 and U.S. Pat. No. 5,851,949. Other suitable support materials include ZSM-22, ZSM-23, and ZSM-35, which are described for use in dewaxing in U.S. Pat. No. 5,246,566 and in the article entitled “New molecular sieve process for lube dewaxing by wax isomerization,” written by S. J. Miller, in Microporous Materials 2 (1994) 439-449. The teachings of U.S. Pat. Nos. 4,310,440; 4,440,871; 4,793,984; 4,758,419; 4,943,424; 5,087,347; 5,158,665; 5,208,005; 5,246,566; 5,716,897; and U.S. Pat. No. 5,851,949 are hereby incorporated by reference.
U.S. Pat. No. 5,444,032 and U.S. Pat. No. 5,608,968 teach a suitable bifunctional catalyst which is constituted by an amorphous silica-alumina gel and one or more metals belonging to Group VIIIA, and is effective in the hydroisomerization of long-chain normal paraffins containing more than 15 carbon atoms. U.S. Pat. Nos. 5,981,419 and 5,908,134 teach a suitable bifunctional catalyst which comprises: (a) a porous crystalline material isostructural with beta-zeolite selected from boro-silicate (BOR-B) and boro-alumino-silicate (Al-BOR-B) in which the molar SiO2:Al2O3 ratio is higher than 300:1; (b) one or more metal(s) belonging to Group VIIIA, selected from platinum and palladium, in an amount comprised within the range of from 0.05 to 5% by weight. Article V. Calemma et al., App. Catal. A: Gen., 190 (2000), 207 teaches yet another suitable catalyst.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.
