SYSTEMS AND METHODS FOR PRODUCING FUEL FROM A RENEWABLE FEEDSTOCK

Abstract

Methods and systems are provided for producing a fuel from a renewable feedstock. The method includes deoxygenating the renewable feedstock with a hydrogenation catalyst in a deoxygenation reaction zone to produce normal paraffins. The normal paraffins are isomerized to form isomerized paraffins using an isomerization catalyst in an isomerization reaction zone. Aromatic compounds are formed from non-aromatic compounds with an aromatic catalyst in an aromatic production zone downstream from the deoxygenation reaction zone.

Description

TECHNICAL FIELD

The present disclosure generally relates to systems and methods for producing fuels from renewable feedstocks, and more particularly relates to systems and methods for converting renewable feedstocks into normal paraffins, isomerized paraffins and aromatic compounds useful for fuel.

BACKGROUND

The demand for diesel boiling range fuel is increasing, and there is increasing pressure to produce fuels with lower environmental impact. Diesel fuel produced from renewable feedstocks is more environmentally friendly because there are fewer green house gas emissions, and renewable feedstocks provide an alternate source for diesel fuel. Renewable sources include, but are not limited to, plant oils such as corn, rapeseed, canola, and soybean, animal fats such as tallow and fish oils, algal oils, and various waste streams such as yellow and grown greases and sewage sludge. The common feature of these sources is that they are composed of glycerides and free fatty acids (FFA). These classes of compounds contain aliphatic carbon chains having from about 8 to about 24 carbon atoms, where many oils have aliphatic carbon chains with a more narrow range of carbon atoms. The aliphatic carbon chains in the glycerides or FFAs can be saturated or mono-, di-, or poly-unsaturated.

One type of distillate boiling range fuel is jet fuel, which has a more narrow boiling range than diesel. The boiling range for jet fuel is within the diesel boiling range, but limited towards the lower end of the boiling range. Most jet fuels are made from compounds having about 9 to about 14 carbons, and most diesel fuels are made from compounds having about 9 to about 18 carbons. A higher number of carbon atoms in a molecule typically results in a higher boiling point, as long as the basic nature of the compounds are the same. Jet fuel produced from renewable sources is sometimes called green jet fuel, or just “green jet” for short. Other terms used to describe jet fuel produced from renewable sources include hydroprocessed renewable jet (HRJ), or hydroprocessed esters and fatty acids (HEFA). There are some specific requirements for green jet that may not apply to jet fuel from petroleum crude oil feedstocks. For example, current ASTM standards call for the blending of green jet with petroleum based jet in order to meet a minimum concentration of 8 volume percent aromatics in the blended fuel. The aromatic compounds may help swell gaskets in jet engines, which is thought to help prevent leaks. Current production processes for green jet produce straight chain or branched paraffins, with very low concentrations of aromatic compounds. Many specifications for jet fuel establish a maximum concentration for aromatic compounds, such as 25% by volume, so there is an upper limit to the amount of aromatics in green jet.

Accordingly, it is desirable to develop methods and systems for converting renewable feedstocks into a fuel with some aromatic compounds. In addition, it is desirable to develop methods and systems for converting renewable feedstocks into a green jet fuel with acceptable concentrations of aromatic compounds, where the aromatic compounds are produced from the renewable feedstock. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.

BRIEF SUMMARY

A system is provided for producing fuel from a renewable feedstock. The system includes a renewable feedstock feed system upstream from a deoxygenation reaction zone. The deoxygenation reaction zone has a hydrogenation catalyst. An aromatic production zone is downstream from the deoxygenation reaction zone, and includes an aromatic catalyst. An isomerization reaction zone is also downstream from the deoxygenation reaction zone, and includes an isomerization catalyst.

A method is also provided for producing a fuel from a renewable feedstock. The renewable feedstock is deoxygenated in a deoxygenation reaction zone to produce normal paraffins. The normal paraffins are isomerized to form isomerized paraffins in an isomerization reaction zone. Aromatic compounds are formed from non-aromatic compounds in an aromatic production zone downstream from the deoxygenation reaction zone.

In another embodiment, a method is provided for producing a fuel from a renewable feedstock. The renewable feedstock is deoxygenated in a deoxygenation reaction zone to produce normal paraffins. The cold flow properties of the normal paraffins are improved by forming aromatic compounds from the normal paraffins.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will hereinafter be described in conjunction with the following figures, wherein like numerals denote like elements.

FIG. 1 is a schematic diagram of an exemplary embodiment of a renewable feedstock feed system.

FIG. 2 is a schematic diagram illustrating an exemplary embodiment of a system and method for converting a renewable feedstock into paraffinic and aromatic compounds useful as a fuel. Heat exchangers are shown as circles in the process lines.

FIGS. 3-5 are schematic diagrams illustrating different exemplary embodiments for preparing different types of hydrocarbon products produced from a renewable feedstock. Heat exchangers are shown as circles in the process lines.

FIGS. 6-9 are schematic diagrams showing various exemplary embodiments of a system and method for converting a renewable feedstock into paraffinic and aromatic compounds useful as a fuel. Heat exchangers are shown as circles in the process lines.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the application or uses of the embodiment described. Furthermore, there is no intention to be bound by any theory presented in the preceding technical field, background, brief summary, or the following detailed description.

The various embodiments relate to systems and methods for producing a hydrocarbon stream useful as a diesel boiling range fuel, a jet fuel, or a fuel blending component. The hydrocarbon stream is produced from renewable feedstocks such as bio renewable feedstocks originating from plants or animals. The renewable feedstock is first deoxygenated to produce normal paraffins (n-paraffins). The n-paraffins are isomerized to form isomerized paraffins, which are branched paraffins, to improve the cold flow properties of the product. Some of the paraffins are converted to aromatic compounds, so the hydrocarbon stream can be used without blending, or with minimal blending. The systems and methods are configured such that the aromatic compounds are not sent through the isomerization process, because most aromatics are converted to non-aromatic compounds in the isomerization process.

Exemplary embodiments of systems and methods for producing a jet fuel from a renewable feedstock 10 are described, beginning with reference to FIG. 1. The renewable feedstocks 10 are stored and delivered to the system and process described below from a renewable feedstock feed system 6. In some embodiments, the renewable feedstock feed system 6 includes a renewable feedstock storage tank 12, a renewable feedstock pump 14 for pumping the feedstock to the system, and associated piping. Other embodiments of the renewable feedstock feed system 6 exist, such as a pipeline from a different source, and a pressurized renewable feedstock feed tank 12 without a renewable feedstock pump 14. The renewable feedstock 10 is passed to the system and process described below in a renewable feedstock feed stream 8.

The term renewable feedstock 10 is meant to include feedstocks other than those derived from petroleum crude oil. The renewable feedstocks as contemplated herein are any of those which include glycerides or free fatty acids (FFA). Most of the glycerides will be triglycerides, but monoglycerides and diglycerides may be present and processed as well. Examples of these renewable feedstocks include, but are not limited to, canola oil, corn oil, 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, camelina oil, pennycress oil, tallow, yellow and brown greases, lard, train oil, jatropha oil, fats in milk, fish oil, algal oil, sewage sludge, and the like. Additional examples of renewable feedstocks 10 include non-edible vegetable oils, such as oils from Madhuca indica (mahua), Pongamia pinnata, and Azadirachta indica (neem).

The glycerides and FFAs of the typical vegetable or animal fat contain aliphatic hydrocarbon chains in their structure which have about 8 to about 24 carbon atoms. The majority of the fats and oils contain high concentrations of fatty acids with 16 to 18 carbon atoms, and many types of oils contain aliphatic hydrocarbon chains within a limited range, such as 14 to 18. Only a limited number of oil types include aliphatic hydrocarbon chains with about 8 carbon atoms or 24 carbon atoms, so the 8 to 24 carbon atoms range is meant to encompass mixtures of all types of oils. Co-feeds, or mixtures of renewable feedstocks 10 and petroleum derived hydrocarbons, may also be used as the feedstock. Other feedstock components that may be used, especially as a co-feed component in combination with the above listed feedstocks, include spent motor oils and industrial lubricants; used paraffin waxes; liquid derived from the gasification of coal, biomass, or natural gas followed by a downstream liquefaction step such as Fischer-Tropsch technology; liquids derived from depolymerization (thermal or chemical) of waste plastics such as polypropylene, high density polyethylene, and low density polyethylene; and other synthetic oils generated as byproducts from petrochemical and chemical processes. Mixtures of the above feedstocks may also be used as co-feed components. One advantage of using a co-feed component is the transformation of what may have been a waste product into a valuable co-feed component to the current process.

In some embodiments, a sulfiding agent 24 can be added to the renewable feedstock 10. Several reactors described more fully below use catalysts of various types, and these catalysts are used in a sulfide state. Sulfur is added to the process to maintain the catalysts in the sulfided state. In some embodiments, the sulfur is added using a sulfiding agent feed system 23 configured to add a sulfiding agent 24 to the renewable feedstock feed stream 8, which is upstream from the reaction zones described below. In some embodiments, the sulfiding agent feed system includes a sulfiding agent tank 26 and a sulfiding agent pump 28, but other embodiments are also possible. The sulfur is measured as elemental sulfur, regardless of the compound containing the sulfur. Sulfur can be added in many forms. For example, suitable sulfiding agents 24 include, but are not limited to, dimethyl disulfide, dibutyl disulfide, and hydrogen sulfide. The sulfur may be obtained from various sources, such as part of a hydrogen stream from a hydrocracking unit or hydro treating unit, or sulfur compounds removed from kerosene or diesel, and disulfide oils removed from sweetening units such as Merox® units. A hydrogenation catalyst is described more fully below, and sulfur concentrations of less than 2,000 ppm are typically sufficient to maintain the hydrogenation catalyst and the other catalysts described below in a sulfide state. FIG. 1 illustrates adding the sulfiding agent 24 to the renewable feedstock feed stream 8, but other embodiments are possible. For example, some renewable feedstocks 10 contain sufficient sulfur to maintain the catalysts in a sulfided state. Sulfur can also be added to the renewable feedstock storage tank 12, the reactors containing the catalysts, or a wide variety of other locations.

Referring to FIG. 2, in an exemplary embodiment, the renewable feedstock feed stream 8 passes to a pretreatment zone 16. Many renewable feedstocks 10 that can be used herein contain a variety of impurities. For example, tall oil is a byproduct of the wood processing industry, and includes esters and rosin acids in addition to FFAs. Rosin acids are cyclic carboxylic acids. The renewable feedstocks 10 may also contain contaminants such as alkali metals, (e.g. sodium and potassium), phosphorous, various solids, water, and detergents. The renewable feedstock 10 may be pre-cleaned (not shown) prior to introduction into the processes illustrated in FIG. 2, where several different types of pre-cleaning are possible. For example, the renewable feedstock 10 can be subjected to a mild acid wash by contact with dilute sulfuric, nitric, or hydrochloric acid in a reactor. The acid wash can be a continuous process or a batch process, and the dilute acid contact can be at ambient temperature and atmospheric pressure. Other possible pre-cleaning steps include, but are not limited to, contacting the renewable feedstock 10 with an ion exchange resin such as Amberlyst®-15, subjecting the renewable feedstock 10 to a caustic treatment, bleaching the renewable feedstock 10 with an adsorbent, filtration, solvent extraction, hydro processing, or combinations of the above.

In the embodiment shown in FIG. 2, a recycle hydrogen stream 95 (described more fully below) is added to the renewable feedstock feed stream 8 and flows downstream to the pretreatment zone 16. In this description, the terms “upstream” and “downstream” means two process units or components are fluidly coupled together, and at least a portion of the fluid from one of the process units or components flows to the other process unit or component. In some embodiments, a portion of a hot separator bottoms stream 34 (described more fully below) is also added to the renewable feedstock feed stream 8 before entry into the pretreatment zone 16. One possible pretreatment step in the pretreatment zone 16 involves metals removal by contacting the renewable feedstock feed stream 8 with a guard bed catalyst in the pretreatment zone 16 at pretreatment conditions. In some embodiments, the guard bed catalyst is alumina, either with or without demetallation catalysts such as nickel or cobalt. The conditions at which the reactor containing the guard bed catalyst is operated are well known in the art, and include a temperature from about 40° C. to about 400° C., for example from about 150° C. to about 300° C. Operating pressures for the guard bed catalyst are from about 690 kilopascals (kPa) absolute (100 pounds per square inch absolute (psia)) to about 13,800 kPa absolute (2,000 psia), for example from about 1,380 kPa absolute (200 psia) to about 6,900 kPa absolute (1,000 psia). A portion of the hot separator bottoms stream 34 may be added at various locations in the pretreatment zone to aid in temperature control, hydrogen solubility, or other purposes, but in other embodiments different streams are added or no streams are added at side locations in the pretreatment zone 16.

After the optional pretreatment zone 16, a pretreatment effluent 18 flows downstream to a deoxygenation reaction zone 20 including one or more catalyst beds in one or more reactors. In an exemplary embodiment, the guard bed catalyst in the pretreatment zone 16 initiates the deoxygenation of the renewable feedstock feed stream 8 to some degree. In the deoxygenation reaction zone 20, the pretreatment effluent 18 is contacted with a hydrogenation catalyst 22 (sometimes referred to as a hydrotreating catalyst) in the presence of hydrogen at hydrogenation conditions. The hydrogen for this reaction is provided from the recycle hydrogen stream 95 added to the renewable feedstock feed stream 8. Under these conditions, the olefinic or unsaturated portions of n-paraffinic chains are hydrogenated. In some embodiments, a portion of the hot separator bottoms stream 34 is added at various locations in the deoxygenation reaction zone 20 to aid in temperature control, hydrogen solubility, and other purposes. In other embodiments, streams other than the hot separator bottoms stream 34 (or even no streams) are added at side locations in the deoxygenation reaction zone 20.

Hydrogenation catalysts 22 are any of those well known in the art such as nickel or nickel/molybdenum dispersed on a high surface area support. Other hydrogenation catalysts 22 include one or more noble metal catalytic elements dispersed on a high surface area support. Non-limiting examples of noble metals include Pt and/or Pd. Hydrogenation conditions include a temperature of about 40° centigrade (C) to about 400° C., and a pressure of about 690 kilopascals (kPa) absolute (100 psia) to about 13,800 kPa absolute (2,000 psia). In another embodiment the hydrogenation conditions include a temperature of about 200° C. to about 300° C., and a pressure of about 1,380 kPa absolute (200 psia) to about 6,900 kPa absolute (1,000 psia). Other operating conditions for the deoxygenation reaction zone 20 can also be used. A sulfiding agent 24, such as from the sulfiding agent feed system or from the renewable feedstock 10, maintains the hydrogenation catalyst in a sulfided state.

The hydrogenation catalysts 22 discussed above are also capable of catalyzing decarboxylation, decarbonylation and/or hydrodeoxygenation of the renewable feedstock 10 to remove oxygen. Decarboxylation, decarbonylation, and hydrodeoxygenation are herein collectively referred to as “deoxygenation reactions”, and the deoxygenation reactions and the olefin hydrogenation reactions simultaneously occur in the deoxygenation reaction zone 20. Decarboxylation conditions include a relatively low pressure of about 3,450 kPa (500 psia) to about 6,900 kPa (1,000 psia), a temperature of about 200° C. to about 400° C., and a liquid hourly space velocity of about 0.5 to about 10 hr⁻¹. In another embodiment the decarboxylation conditions include the same relatively low pressure of about 3,450 kPa (500 psia) to about 6,900 kPa (1,000 psia), a temperature of about 288° C. to about 345° C., and a liquid hourly space velocity of about 1 to about 4 hr⁻¹.

Hydrogenation is an exothermic reaction, so the temperature in the deoxygenation reaction zone 20 increases as the renewable feedstock feed stream 8 passes through. Decarboxylation and hydrodeoxygenation reactions begin to occur as the temperature increases. The rate of the deoxygenation reactions increases from the front of the bed to the back of the bed as the temperature increases. The deoxygenation reaction zone 20 can include one or more reactors in series, and can also include parallel reactors or sets of reactors.

The hydrodeoxygenation reaction consumes hydrogen and produces water as a byproduct, while the decarbonylation and decarboxylation reactions produce carbon monoxide (CO) or carbon dioxide (CO₂) without consuming hydrogen. However, hydrogen is present for all the reactions in the deoxygenation reaction zone, regardless of whether the reaction consumes hydrogen or not. The product from the deoxygenation reactions includes a liquid portion and a gaseous portion. The liquid portion includes a hydrocarbon fraction that is largely n-paraffin compounds having a high cetane number. The gaseous portion includes hydrogen, carbon dioxide (CO₂), carbon monoxide (CO), water vapor, propane, and perhaps sulfur components such as hydrogen sulfide. It is possible to separate and collect the liquid (n-paraffin compound) portion as a diesel fuel product without further reactions. However, in most climates, at least a portion of the liquid n-paraffins can be isomerized to produce isomerized paraffins, which improves the cold flow properties of the fuel. The cold flow properties can also be improved by adding aromatic compounds with an average boiling point lower than the n-paraffin average boiling point. The isomerized paraffins are branched, and both n-paraffins and branched paraffins are non-aromatic compounds.

In some embodiments, aromatic compounds are desired in the fuel product. There is often an upper specification on aromatics, such as 25% by volume for Jet A, so only a partial conversion of paraffins to aromatics is desired. Paraffins, including normal and/or isomerized paraffins, are partially converted to aromatic compounds in an aromatics reaction zone 60, which can be placed in a variety of locations in the process flow. The embodiment shown in FIG. 2 depicts the aromatics reaction zone 60 as a catalyst bed in the same reactor as the deoxygenation reaction zone 20, where the aromatics reaction zone 60 is downstream from the deoxygenation reaction zone 20. The aromatics reaction zone 60 could also be in a separate reactor directly downstream from the deoxygenation reaction zone 20, and many other locations are possible in various embodiments. Some of the different possible embodiments are described more fully below.

The aromatics reaction zone 60 includes an aromatic catalyst 62 that converts paraffins, which are non-aromatic compounds, into aromatic compounds. The aromatic catalyst 62 will form aromatic compounds from either n-paraffins or branched paraffins, so the aromatic production zone 60 can be either upstream or downstream from the isomerization reaction zone 40 (described below) in various embodiments. However, the aromatic production zone 60 should be downstream from the deoxygenation reaction zone 20, so the feed to the aromatic production zone 60 is paraffinic hydrocarbons. In some embodiments, a portion of the hot separator bottoms stream 34 is added at various locations to the aromatics reaction zone 60, but different side feeds or no side feed are added in other embodiments. The hot separator bottoms stream 34 can aid in temperature control and hydrogen solubility, among other purposes.

Aromatic production zone conditions include a temperature of about 300° C. to about 450° C. and a pressure of about 100 kPa absolute (15 psia) to about 4,140 kPa absolute (600 psia). However, other aromatic reaction conditions are also possible, as known in the art. Several different types of aromatic catalysts 62 can be used. For example, nickel and tungsten deposited on a silica alumina substrate is effective, but other metals and other substrates can also be used. Some examples of other possible catalysts include aluminum chloride, platinum, platinum and tin, platinum and rhenium, and others. A wide variety of catalyst substrates can also be used, including but not limited to zeolites, silica alumina, amorphous alumina, etc. In some embodiments, excess sulfur from the deoxygenation reaction zone 20 maintains the aromatic catalyst 62 is a sulfided state. In other embodiments, the aromatic catalyst 62 is not sulfided.

In some embodiments, the aromatic production zone effluent 64 passes to an optional hot separator 30, so the hot separator 30 is downstream from the aromatic production zone 60. The hot separator 30 is also downstream from the deoxygenation reaction zone 20 in many embodiments. One purpose of the hot separator 30 is to separate at least some of the gaseous portion from the deoxygenation reaction zone 20 from the liquid portion. The entire gaseous portion from the deoxygenation reaction zone 20 is fed to the aromatic production zone 60 in the embodiment shown in FIG. 2. Much of the gaseous portion exits the hot separator 30 in a hot separator overhead stream 32, and the liquid portion exits the hot separator in the hot separator bottom stream 34. The separated hydrogen is recycled back to the deoxygenation reaction zone 20 in some embodiments, as described more fully below.

In some embodiments, water, CO, CO₂, and any ammonia or hydrogen sulfide are selectively stripped in the hot separator 30 using hydrogen. In some embodiments (not shown), additional hydrogen is used as the stripping gas, but other gases could also be used. The temperature is controlled to achieve the desired separation, and the pressure can be maintained at approximately the same pressure as the deoxygenation reaction zone 20 and the isomerization reaction zone 40 to minimize both investment and operation costs. The hot separator 30 may be operated at conditions ranging from a pressure of about 690 kPa absolute (100 psia) to about 13,800 kPa absolute (2,000 psia), and a temperature of about 40° C. to about 350° C. In another embodiment, the hot separator 30 may be operated at conditions ranging from a pressure of about 1,380 kPa absolute (200 psia) to about 6,900 kPa absolute (1,000 psia), or about 2,410 kPa absolute (350 psia) to about 4,880 kPa absolute (650 psia), and a temperature of about 50° C. to about 350° C.

The paraffinic components of the hot separator bottoms stream 34 are primarily n-paraffins which range from about 8 to about 24 carbon atoms depending on the type of renewable feedstock 10 used, and the aromatic components (if present) are either comparable in size or smaller. Different renewable feedstocks 10 will result in different distributions of paraffins. The hot separator bottoms stream 34 is divided and transferred to various locations in different embodiments. A portion of the hot separator bottoms stream 34 may be recycled and added to the pretreatment zone 16, the deoxygenation reaction zone 20, and the aromatic production zone 60, at various locations, as described above. The recycled hot separator bottoms stream 34 can help control the temperature and/or the hydrogen solubility in the various reaction zones.

In the embodiment shown in FIG. 2, the hot separator bottoms stream 34 primarily includes n-paraffins (from the deoxygenation reaction zone 20) and aromatic compounds (from the aromatic production zone 60). The aromatic compounds are separated from the n-paraffins and diverted around the isomerization reaction zone 40 described below, as the isomerization reaction zone converts aromatic compounds into non-aromatic compounds. In some embodiments, the aromatic compounds have a lower boiling point than the n-paraffins, so distillation can be used for the separation. In other embodiments, the molecular weight of the aromatic compounds and the non-aromatic compounds are approximately the same, and thus the boiling points are approximately the same. If the aromatic compounds have comparable boiling points with the non-aromatic compounds, other types of separators can be used to separate the aromatics from the non-aromatics. For example, liquid/liquid extraction systems with an extraction solvent, such as sulfolane, can be used.

Initial testing indicated that hexadecane or soybean oil was partially converted to aromatic compounds with a nickel tungsten catalyst on a silicon aluminum substrate at temperatures ranging from about 375° C. to about 400° C., and pressures ranging from about 2,070 kPa absolute (300 psia) to about 3,450 (500 psia). The hydrocarbon liquid hourly space velocity tested was 0.75 hr-1, the hydrogen feed rate was 369 standard cubic centimeters per minute, and the aromatic catalyst 62 was sulfided. The conversion to aromatic compounds was favored by higher temperatures. Hexadecane is a C16 compound, and the majority of the aromatics produced had an average molecular weight significantly lower than that of hexadecane. However, the aromatics produced from the soybean oil were approximately the same molecular weight as the feedstock. The aromatic production zone 60 operating conditions can be modified to produce smaller aromatic compounds from soybean oil or other renewable feedstocks 10, such as higher temperatures, more active catalysts, removal of water, CO, and CO₂ before the aromatic catalyst, etc.

As a general rule, the lower the molecular weight for either paraffins or aromatic compounds, the lower the boiling point. Smaller aromatic compounds help improve cold flow properties of the fuel, and can be separated from the higher molecular weight paraffins by a relatively simple distillation step. The aromatics reaction zone 60 can be positioned upstream from the isomerization reaction zone 40, so the aromatic compounds in the aromatic production zone effluent 64 flow to the aromatic distillation column 70 by way of the hot separator bottoms stream 34.

The aromatics distillation column 70 has an aromatics distillation column bottoms stream 71 with heavy components. Many of the n-paraffins from the deoxygenation reaction zone 20 are not converted to smaller aromatic compounds, and these are transferred to the isomerization reaction zone 40 from the aromatics distillation column bottoms stream 71. Any large aromatic compounds with approximately the same number of carbon atoms as the paraffinic compounds will also be in the aromatics distillation column bottoms stream 71. In some embodiments, the aromatics distillation column 70 is upstream from the isomerization reaction zone 40, and the aromatic distillation column bottoms stream 71 is fed to the isomerization reaction zone 40. The aromatic distillation column bottoms stream 71 is combined with a hydrogen feed line 36 in some embodiments, where the hydrogen feed line 36 introduces fresh hydrogen for the isomerization reaction. A fresh hydrogen compressor 98 helps urges the fresh hydrogen into the process.

Smaller, lighter aromatic compounds are removed in an aromatics distillation column side stream 73, and these aromatic compounds are diverted around the isomerization reaction zone 40. In some embodiments, the aromatics distillation column side stream 73 serves as an aromatic compounds stream, but in other embodiments the aromatic compounds are removed in an aromatic distillation column overhead 75 with other light compounds. Therefore, the aromatic distillation column overhead 75 is the aromatic compounds stream in some embodiments. In some embodiments, the aromatic compounds stream is directed to the aromatics storage tank 72, but the aromatic compounds can be diverted around the isomerization reaction zone 40 in other manners, such as direct piping. Light compounds such as hydrogen, water vapor, CO, CO₂, and propane exit in an aromatics distillation column overhead stream 75, and are combined with the hot separator overhead stream 32 in some embodiments. To avoid converting the aromatic compounds to non-aromatic compounds, the aromatic compounds in the aromatic storage tank 72 are added to the hydrocarbons downstream from the isomerization reaction zone 40, as shown more fully below.

The aromatic distillation column bottoms stream 71 primarily contains n-paraffins, and may contain some large aromatic compounds in some embodiments, and could be used as a diesel boiling range fuel. However, the cold flow properties can be improved by isomerizing at least some of the n-paraffins in the isomerization reaction zone 40. The isomerization reaction zone 40 contains an isomerization catalyst 42, and the aromatic distillation column bottoms stream 71 are contacted with the isomerization catalyst 42 under isomerization conditions to at least partially isomerize the n-paraffins to branched paraffins. The isomerization reaction zone 40 is downstream from the hot separator 30, and in some embodiments the isomerization reaction zone 40 is also downstream from the aromatic distillation column 70. A jet fractionator bottoms stream 90, described below, can also be added to the aromatic distillation column bottoms stream 71 upstream from the isomerization reaction zone 40. The jet fractionator bottoms stream 90 includes hydrocarbons that are too heavy, with too high a boiling point, to be useful as a jet fuel. These larger molecules may be cracked into smaller molecules in the isomerization reaction zone 40 to improve the jet fuel yield. The larger molecules can also aid the isomerization reaction zone 40 in other ways, such as temperature control and hydrogen solubility.

The isomerization reaction zone effluent 41 is a branched-paraffin-rich stream. By the term “rich” it is meant that the isomerization reaction zone effluent 41 has a greater concentration of branched paraffins than the stream entering the isomerization reaction zone 40, which is the aromatics distillation column bottoms stream 71 in the embodiment shown in FIG. 2, and preferably includes greater than 50 mass percent branched paraffins. It is envisioned that the isomerization reaction zone effluent 41 may contain 70, 80, or 90 mass percent branched paraffins. The isomerization reaction zone 40 also converts most aromatic compounds to non-aromatic compounds, so if aromatic compounds are desired in the final product they should not be processed in the isomerization reaction zone 40.

Isomerization can be carried out in a separate bed of the same reactor used in the deoxygenation reaction zone 20, or the isomerization can be carried out in a separate reactor. For ease of description, the following will address the embodiments where a second reactor is employed for the isomerization reaction zone 40. The aromatic column distillation bottoms stream 71 is contacted with the isomerization catalyst 42 in the presence of hydrogen at isomerization conditions to isomerize the n-paraffins to branched paraffins. Only minimal branching is required to overcome the poor cold-flow characteristics of the n-paraffins. In some embodiments, the predominant isomerized paraffin product is a mono-branched hydrocarbon, because process conditions that produce significant branching also increase the risk of undesired cracking. Undesired cracking produces smaller compounds that are not useful as a jet fuel or a diesel fuel, and therefore reduce the overall yield.

The isomerization of the n-paraffins can be accomplished by using a variety of suitable catalysts. The isomerization reaction zone 40 includes one or more beds of isomerization catalyst 42, and the catalyst beds can be in series and/or parallel. A single reactor may include one or more catalyst beds, so the isomerization reaction zone 40 can also include one or more reactors. In some embodiments, the isomerization reaction zone is operated in a co-current mode of operation. Fixed bed trickle down flow or fixed bed liquid upward flow modes are both suitable. Remaining sulfur compounds maintain the isomerization catalyst 42 is a sulfided state.

Suitable isomerization catalysts 42 include 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, and many different support materials can be used. Suitable support materials include, but are not limited to, amorphous alumina, amorphous silica-alumina, ferrierite, metal aluminumsilicophosphates, laumontite, cancrinite, offretite, the hydrogen form of stillbite, the magnesium or calcium form of mordenite, and the magnesium or calcium form of partheite, each of which may be used alone or in combination. Many natural zeolites, such as ferrierite, that have an initially reduced pore size can be converted to forms suitable for olefin skeletal isomerization by removing associated alkali metals or alkaline earth metals by ammonium ion exchange and calcination to produce a substantially hydrogen form. The isomerization catalyst 42 may also include one or more modifiers, such as those selected from the group of lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, terbium, and mixtures thereof.

The isomerization reaction occurs when hydrocarbons pass through the isomerization catalyst 42 at isomerization conditions. Isomerization conditions include a temperature of about 150° C. to about 360° C. and a pressure of about 1,720 kPa absolute (250 psia) to about 4,720 kPa absolute (700 psia). In another embodiment, the isomerization conditions include a temperature of about 300° C. to about 360° C. and a pressure of about 3,100 kPa absolute (450 psia) to about 3,800 kPa absolute (550 psia). Other operating conditions for the isomerization reaction zone 40 can also be used.

The isomerization reaction zone effluent 41 is processed through one or more separation steps to obtain a hydrocarbon stream useful as a fuel, such as jet fuel or diesel fuel. The isomerization reaction zone effluent 41 includes both a liquid component and a gaseous component, various portions of which can be recycled, so multiple separation steps may be employed. For example, in some embodiments the isomerization reaction zone effluent 41 is separated in an isomerization effluent separator 44 positioned downstream from the isomerization reaction zone 40. In the embodiment shown in FIG. 2, the isomerization effluent separator 44 is optional. Hydrogen exits the isomerization effluent separator 44 in the isomerization effluent separator overhead stream 46, and the liquid portion exits in the isomerization effluent separator bottoms stream 48. The isomerization effluent separator overhead stream 46 is fed to the aromatics distillation column 70 in some embodiments, and the gaseous portions flow into the aromatics distillation column overhead stream 75.

Suitable operating conditions of the isomerization effluent separator 44 include, for example, a temperature of about 230° C. and a pressure of about 4,100 kPa absolute (600 psia), but other operating conditions are also possible. If there is a low concentration of carbon oxides, or the carbon oxides are removed, the hydrogen may be directly recycled and re-used in the process. The hydrogen is a reactant in the oxygenation reaction zone 20 and the isomerization reaction zone 40, and different renewable feedstocks 10 will consume different amounts of hydrogen. The isomerization effluent separator 44 allows flexibility for the process to operate even when larger amounts of hydrogen are consumed in the deoxygenation reaction zone 20. Furthermore, at least a portion of the isomerization effluent separator bottoms stream 48 can be recycled to the isomerization reaction zone 40 (not shown) to increase the degree of isomerization, to aid in temperature control, or for other purposes.

The remainder of the isomerization effluent separator bottoms stream 48 still has liquid and gaseous components and can be cooled by various techniques, such as air cooling or water cooling. After cooling, the isomerization effluent separator bottoms stream 48 is passed to a cold separator 50 where the liquid component is separated from the gaseous component. The hot separator overhead stream 32 and the aromatic distillation column overhead stream 75 can be combined with the isomerization effluent separator bottoms stream 48 upstream from the cold separator 50. Suitable operating conditions of the cold separator 50 include, for example, a temperature of about 20° C. to about 60° C. and a pressure of about 3,850 kPa absolute (560 psia). A water byproduct stream is also separated in the cold separator 50 (not shown).

A cold separator overhead stream 52, or the gaseous component separated in the cold separator 50, is mostly hydrogen and the carbon dioxide from the decarboxylation reaction. Other components such as CO, propane, and hydrogen sulfide or other sulfur containing components may be present as well. Water, CO, and CO₂ can negatively impact the catalyst performance in the isomerization reaction zone 40. It is desirable to recycle the hydrogen, but if the CO₂ and other components are not removed, their concentrations can build up and effect the operation of the isomerization reaction zone 40. A recovery gas cleaner 74 can be used to increase the purity of the cold separator overhead stream 52. The carbon dioxide can be removed from the hydrogen by several different processes, including but not limited to absorption with an amine, reaction with a hot carbonate solution, pressure swing absorption, etc. If desired, essentially pure carbon dioxide can be recovered by regenerating the spent absorption media. A sulfur containing component, such as hydrogen sulfide, may also be present. The sulfur containing component is used to help control the relative amounts of the decarboxylation reaction and the hydrogenation reaction in the deoxygenation reaction zone 20. The amount of sulfur is generally controlled, so the sulfur is also removed before the hydrogen is recycled. Various methods can be used, such as absorption with an amine or a caustic wash, and the carbon dioxide and sulfur containing components (as well as other components) are removed in a single separation step in some embodiments.

The recycle hydrogen stream 95 exits the recovery gas cleaner 74 after the impurities have been removed. A recycle hydrogen compressor 96 urges the hydrogen back into the process. As discussed above, the recycle hydrogen stream 95 is combined with the renewable feedstock feed stream 8 and feeds the pretreatment zone 16.

Reference is now made to FIG. 3, with continuing reference to FIGS. 1 and 2. The cold separator bottoms stream 54, or the liquid component separated in the cold separator 50, contains the hydrocarbons useful as jet fuel or diesel boiling range fuel, as well as smaller amounts of naphtha 100 and liquid propane gas (LPG) 102. The cold separator bottoms stream 54 may be recovered as diesel boiling range fuel or it may be further purified in a product stripper 76 which separates lower boiling components and dissolved gases from the diesel boiling range hydrocarbons. The product stripper 76 can be operated, for example, with a vapor temperature of from about 20° C. to about 200° C. and a pressure from about 0 kPa (0 psia) to about 1,380 kPa absolute (200 psia) at the overhead of the product stripper 76.

The product stripper 76 produces a product stripper overhead stream 78 and a product stripper bottoms stream 80. The product stripper overhead stream 78 includes the LPG 102, naphtha 100, and light hydrocarbons present in a lean gas 104. The lean gas 104 is separated from the LPG 102 and naphtha 100 in a light gas separator 106 as a gas in a light gas separator overheads stream 108. A light gas separator bottoms stream 110 from the light gas separator 106 includes the liquid LPG 102 and naphtha 100. The LPG 102 and naphtha 100 may be further separated in a debutanizer 82 (also called a depropanizer) that produces the LPG 102 as an overhead stream and the naphtha 100 as a bottoms stream. The debutanizer 82 can be operated, for example, at a vapor temperature of about 20° C. to about 200° C. and a pressure from about 0 to about 2,760 kPa absolute (0 to 400 psia) at the debutanizer overhead, but other conditions are also possible. The LPG 102 may be sold as a valuable product, used as a fuel gas, or used in other processes such as the feed to a hydrogen production facility, a co-feed to a reforming process, or used as a fuel blending component.

In an exemplary embodiment, the product stripper bottoms stream 80 is fed to a jet fractionator 84 to separate jet fuel from higher boiling range diesel fuel compounds. The jet fractionator 84 is an optional component used when jet fuel 92 is desired. The jet fractionator 84 produces a jet fractionator overhead stream 86, a jet fractionator side stream 88, and a jet fractionator bottoms stream 90. The jet fractionator overhead stream 86 include some light naphtha compounds that are combined with the debutanizer bottoms stream 114 in some embodiments. The jet fractionator side stream 88 contains the jet fuel 92, and heavier compounds exit in the jet fractionator bottoms stream 90. In some embodiments, kerosene is stripped from the jet fuel 92 after separation (not shown). The jet fractionator bottoms stream 90 has too high a boiling point to use as a jet fuel. However, the jet fractionator bottoms stream 90 can be used in alternative ways, such as recycling into the isomerization reaction zone 40, direct use or blending for diesel fuel, or combined with the feed to the isomerization reaction zone 40.

The aromatic compounds from the aromatic storage tank 72 can be added back to the fuel at several different locations downstream from the isomerization reaction zone 40. The embodiment shown in FIG. 3 illustrates the aromatic compounds added to the jet fractionator side stream 88. In an alternative or additional embodiment, referring to FIG. 4, the aromatic compounds are added to the product stripper bottoms stream 80. In another alternative or additional embodiment, referring to FIG. 5, the aromatic compounds are added back to the cold separator bottoms stream 54. In other embodiments, the aromatic compounds are added to other locations downstream from the isomerization reaction zone 40. In some embodiments, the aromatic compounds are added to the hydrocarbons downstream from the isomerization reaction zone 40 without the use of an aromatic storage tank 72.

The aromatics reaction zone 60 can be located in many different locations in various embodiments, and other modifications to the process illustrated in FIG. 2 are also possible. For example, FIG. 6 illustrates another embodiment where the aromatics reaction zone 60 is directly downstream from the deoxygenation reaction zone 20, so a deoxygenation reaction zone effluent 21 serves as the feed to the aromatics reaction zone 60. FIG. 6 shows separate reactors for the aromatics reaction zone 60 and the deoxygenation reaction 20, but one reactor could also be used as illustrated in FIG. 2. The embodiment illustrated in FIG. 6 also shows the hot separator bottoms stream 34 feeding only the aromatics distillation column 70. The hydrogen feed line 36 and the jet fractionator bottoms stream 90 are added to the aromatic distillation column bottoms stream 71, and then fed as side streams into the pretreatment zone 16, the deoxygenation reaction zone 20, and the aromatics reaction zone 60. The aromatic distillation column bottoms stream 71 is also combined with the renewable feedstock feed stream 8 and fed into the inlet for the deoxygenation reaction zone 20. Other portions of the aromatic distillation column bottoms stream 71 serve as the feed for the isomerization reaction zone 40.

FIG. 7 illustrates another embodiment, where the aromatic production zone 60 and the aromatic distillation column 70 are positioned downstream from the hot separator 30 and upstream from the isomerization reaction zone 40. In this embodiment, the deoxygenation reaction zone effluent 21 feeds the hot separator 30 because the aromatics reaction zone 60 is downstream from the hot separator 30. This embodiment also includes an enhanced hot separator 38 downstream from the hot separator 30, where the isomerization effluent separator overhead stream 46 is fed into the enhanced hot separator 38. An enhanced hot separator overhead stream 37 is combined with the hot separator overhead stream 32, and then flows to the cold separator 50 to recover the gases. An enhanced hot separator bottoms stream 39 flows from the enhanced hot separator 38 downstream to a pre-aromatics hydrogen separator 94, and the hydrogen feed line 36 and the jet fractionator bottoms stream 90 are added to the enhanced hot separator bottoms stream 39 before the pre-aromatics hydrogen separator 94. Excess hydrogen is separated in the pre-aromatics hydrogen separator 94 and fed to the isomerization reaction zone 40 from a pre-aromatics separator overhead stream 91. The pre-aromatics separator overhead stream 91 by-passes the aromatics reaction zone 60, so the isomerization reaction zone 40 is the first reaction zone for most of the fresh hydrogen from the hydrogen feed line 36. A pre-aromatics separator bottoms stream 93 feeds the liquid components to the aromatics reaction zone 60.

Another embodiment is illustrated in FIG. 8. In this embodiment, the aromatics reaction zone 60 is downstream from the hot separator 30, so the deoxygenation reaction zone effluent 21 feeds the hot separator 30, and the hot separator bottoms stream 34 feeds the aromatics reaction zone 60. The aromatics distillation column 70 is fed by the aromatics reaction zone effluent 64, and the isomerization effluent separator overhead stream 46 is also fed to the aromatics distillation column 70. The aromatics distillation column bottoms stream 71 serves as the feed to the isomerization reaction zone 40, after the hydrogen feed line 36 and the jet fractionator bottoms stream 90 are added to it.

FIG. 9 illustrates yet another embodiment where the aromatics reaction zone 60 is downstream from the isomerization reaction zone 40. In this embodiment, the aromatic compounds are produced downstream from the isomerization reaction zone 40, so the aromatic compounds do not have to be separated to be diverted around the isomerization reaction zone 40. Therefore, the aromatics distillation column 70 is optional in this embodiment, but can be used to better control and measure the quantity of aromatics in the fuel product. Alternatively, the quantity of aromatics produced in the aromatic production zone 60 can be controlled by adjusting the operating conditions within the aromatic production zone 60, such as the amount of aromatic catalyst 62, flow rates, temperatures, etc. An enhanced hot separator 38 is illustrated in this embodiment, and the aromatic distillation column bottoms stream 71 feeds the isomerization effluent separator 44.

As can be seen, many different embodiments are possible, including some embodiments not illustrated, so it should be appreciated that a vast number of variations exist. It should also be appreciated that the embodiment or embodiments illustrated are only examples, and are not intended to limit the scope, applicability, or configuration of the application in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing one or more embodiments, it being understood that various changes may be made in the function and arrangement of elements described without departing from the scope as set forth in the appended claims.

Claims

1. A system for producing fuel from a renewable feedstock comprising:

a renewable feedstock feed system;

a deoxygenation reaction zone comprising a hydrogenation catalyst, wherein the deoxygenation reaction zone is downstream from the renewable feedstock feed system;

an aromatic production zone comprising an aromatic catalyst, wherein the aromatic production zone is downstream from the deoxygenation reaction zone; and

an isomerization reaction zone comprising an isomerization catalyst, wherein the isomerization reaction zone is downstream from the deoxygenation reaction zone.

2. The system of claim 1 further comprising:

an aromatics distillation column configured to produce an aromatics distillation column bottoms stream, wherein the aromatics distillation column is downstream from the aromatic production zone, and wherein the system is configured so that the aromatics distillation column bottoms stream flows to the isomerization reaction zone.

3. The system of claim 2 wherein the aromatics distillation column is configured to produce an aromatic compounds stream, and wherein the system is configured such that the aromatic compounds stream bypasses the isomerization reaction zone.

4. The system of claim 1 further comprising a hot liquid separator positioned downstream from the deoxygenation reaction zone.

5. The system of claim 1 wherein the aromatic production zone is downstream from the isomerization reaction zone.

6. The system of claim 5 further comprising an aromatics distillation column positioned downstream from the aromatic production zone.

7. The system of claim 1 further comprising a pretreatment zone downstream from the renewable feedstock feed system and upstream from the deoxygenation reaction zone.

8. The system of claim 1 further comprising a sulfiding agent feed system configured to add a sulfiding agent to the renewable feedstock prior to the deoxygenation reaction zone.

9. A method of producing fuel from a renewable feedstock, the method comprising the steps of:

deoxygenating the renewable feedstock in a deoxygenation reaction zone to produce normal paraffins;

isomerizing the normal paraffins in an isomerization reaction zone to produce isomerized paraffins;

forming aromatic compounds from non-aromatic compounds in an aromatic production zone, and wherein the aromatic production zone is downstream from the deoxygenation reaction zone.

10. The method of claim 9 further comprising:

separating the aromatic compounds from the non-aromatic compounds downstream from the aromatic production zone;

feeding the non-aromatic compounds from the aromatic production zone into the isomerization reaction zone; and

combining the aromatic compounds with the isomerized paraffins downstream from the isomerization reaction zone.

11. The method of claim 9 wherein the step of deoxygenating the renewable feedstock further comprises deoxygenating the renewable feedstock with a hydrogenation catalyst, the method further comprising sulfiding the hydrogenation catalyst.

12. The method of claim 9 wherein forming aromatic compounds from non-aromatic compounds further comprises forming aromatic compounds from non-aromatic compounds downstream from the isomerization reaction zone.

13. The method of claim 9 wherein forming aromatic compounds from non-aromatic compounds further comprises forming aromatic compounds from non-aromatic compounds upstream from the isomerization reaction zone.

14. The method of claim 9 further comprising:

removing gases from the non-aromatic compounds prior to forming the aromatic compounds.

15. The method of claim 9 further comprising:

removing contaminants from the renewable feedstock in a pretreatment zone prior to deoxygenating the renewable feedstock.

16. A method of producing fuel from a renewable feedstock, the method comprising the steps of:

deoxygenating the renewable feedstock in a deoxygenation reaction zone to produce normal paraffins;

improving a cold flow property of the normal paraffins by forming aromatic compounds from normal paraffins.

17. The method of claim 16 wherein improving cold flow properties further comprises forming isomerized paraffins from the normal paraffins in an isomerization reaction zone downstream from the deoxygenation reaction zone.

18. The method of claim 17 further comprising:

diverting the aromatic compounds around the isomerization reaction zone.

19. The method of claim 16 further comprising:

sulfiding the hydrogenation catalyst.

20. The method of claim 16 further comprising:

removing contaminants from the renewable feedstock in a pretreatment zone prior to deoxygenating the renewable feedstock.