Abstract:
Embodiments of methods for co-production of linear alkylbenzene and biofuel from a natural oil are provided. A method comprises the step of deoxygenating the natural oils to form paraffins. A first portion of the paraffins is hydrocracked to form a first stream of normal and lightly branched paraffins in the C 9  to C 14  range and a second stream of isoparaffins. The first stream is dehydrogenated to provide mono-olefins. Then, benzene is alkylated with the mono-olefins under alkylation conditions to provide an alkylation effluent comprising alkylbenzenes and benzene. Thereafter, the alkylbenzenes are isolated to provide the alkylbenzene product. A second portion of the paraffins and the isoparaffins are processed to form biofuel.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to methods for co-production of alkylbenzene and biofuel using hydrocracking, and more particularly relates to methods for producing renewable alkylbenzene and biofuel from natural oils. 
     BACKGROUND OF THE INVENTION 
     Linear alkylbenzenes are organic compounds with the formula C 6 H 5 C n H 2n+1 . While n can have any practical value, current commercial use of alkylbenzenes requires that n lie between 10 and 16, or more specifically between 10 and 13, between 12 and 15, or between 12 and 13. These specific ranges are often required when the alkylbenzenes are used as intermediates in the production of surfactants for detergents. Because the surfactants created from alkylbenzenes are biodegradable, the production of alkylbenzenes has grown rapidly since their initial uses in detergent production in the 1960s. 
     While detergents made utilizing alkylbenzene-based surfactants are biodegradable, processes for creating alkylbenzenes are not based on renewable sources. Specifically, alkylbenzenes are currently produced from kerosene derived from fossil fuels. Due to the growing environmental concerns over fossil fuel extraction and economic concerns over exhausting fossil fuel deposits, there may be support for using an alternate source for biodegradable surfactants in detergents and in other industries. 
     There is also an increasing demand for the use of biofuels in order to reduce the demand for and use of fossil fuels. This is especially true for transportation needs wherein other renewable energy sources are difficult to utilize. For instance, biodiesel or green diesel and biojet or green jet fuels may provide for a significant reduction in the need and use of petroleum based fuels. 
     Accordingly, it is desirable to provide methods and systems for co-production of alkylbenzene and biofuel from natural oils, i.e., oils that are not extracted from the earth. Further, it is desirable to provide methods and systems that provide renewable alkylbenzenes and biofuels from easily processed triglycerides and fatty acids from vegetable, nut, and/or seed oils. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawing and this background of the invention. 
     SUMMARY OF THE INVENTION 
     Methods for the co-production of an alkylbenzene product and biofuel from a natural oil are provided herein. In accordance with an exemplary embodiment, the method deoxygenates the natural oil to form paraffins. A first portion of the paraffins is hydrocracked to form a first stream of normal and lightly branched paraffins in the C 9  to C 14  range and a second stream of isoparaffins. The first stream is dehydrogenated to provide mono-olefins. Then, benzene is alkylated with the mono-olefins under alkylation conditions to provide an alkylation effluent comprising alkylbenzenes and benzene. Thereafter, the alkylbenzenes are isolated to provide the alkylbenzene product. A second portion of the paraffins and the isoparaffins are processed to form biofuel. 
     In another exemplary embodiment, a method is provided for the co-production of an alkylbenzene product and a biofuel from natural oil source triglycerides. In this embodiment, the triglycerides are deoxygenated to form a deoxygenated product comprising water, carbon dioxide, propane, a first portion of paraffins, and a second portion of paraffins. This stream is fractionated to separate first and second streams of paraffins. Then, the first stream of paraffins is hydrocracked to form a normal paraffin stream and an isoparaffins stream. The normal paraffin stream is dehydrogenated to provide mono-olefins. The mono-olefins are used to alkylate benzene under alkylation conditions to provide an alkylation effluent comprising alkylbenzenes and benzene. Thereafter, alkylbenzenes are isolated to provide the alkylbenzene product. The second stream of paraffins and the isoparaffins stream are processed to form biofuel. 
     In accordance with another embodiment, a method for co-production of an alkylbenzene product and biofuel from a natural oil is provided. In the method, the natural oil is deoxygenated with hydrogen to form a stream comprising paraffins. The paraffins are hydrocracked to form a normal paraffin stream and an isoparaffin stream. The normal paraffin stream is dehydrogenated to provide mono-olefins and hydrogen. According to the exemplary embodiment, the hydrogen provided by dehydrogenation is recycled to deoxygenate the natural oils. The mono-olefins are used to alkylate benzene under alkylation conditions to provide an alkylation effluent comprising alkylbenzenes and benzene. Then, the alkylbenzenes are isolated from the effluent to provide the alkylbenzene product. The isoparaffins stream is processed to form biofuel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Embodiments of the present invention will hereinafter be described in conjunction with the following drawing FIGURE wherein: 
         FIG. 1  schematically illustrates a system for co-production of alkylbenzene and biofuel in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following Detailed Description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding Background or the following Detailed Description. 
     Various embodiments contemplated herein relate to methods and systems for co-production of an alkylbenzene product and biofuel from natural oils. In  FIG. 1 , an exemplary apparatus  10  for producing an alkylbenzene product  12  and biofuel  13  from a natural oil feed  14  is illustrated. As used herein, natural oils are those derived from plant or algae matter, and are often referred to as renewable oils. Natural oils are not based on kerosene or other fossil fuels. In certain embodiments, the natural oils include one or more of coconut oil, babassu oil, castor oil, canola oil, cooking oil, and other vegetable, nut or seed oils. The natural oils typically comprise triglycerides, free fatty acids, or a combination of triglycerides and free fatty acids. 
     In the illustrated embodiment, the natural oil feed  14  is delivered to a deoxygenation unit  16  which also receives a hydrogen feed  18 . In the deoxygenation unit  16 , the triglycerides and fatty acids in the feed  14  are deoxygenated. Structurally, triglycerides are formed by three, typically different, fatty acid molecules that are bonded together with a glycerol bridge. The glycerol molecule includes three hydroxyl groups (HO—) and each fatty acid molecule has a carboxyl group (COOH). In triglycerides, the hydroxyl groups of the glycerol join the carboxyl groups of the fatty acids to form ester bonds. Therefore, during deoxygenation, the fatty acids are freed from the triglyceride structure and are converted into normal paraffins. The glycerol is converted into propane, and the oxygen in the hydroxyl and carboxyl groups is converted into either water or carbon dioxide. The deoxygenation reaction for fatty acids and triglycerides are respectively illustrated as: 
                                
During the deoxygenation reaction, the length of a paraffin chain R n  created will vary by a value of one depending on the exact reaction pathway. For instance, if carbon dioxide is formed, then the chain will have one fewer carbon than the fatty acid source (R n ). If water is formed, then the chain will match the length of the R n  chain in the fatty acid source. Typically, water and carbon dioxide are formed in roughly equal amounts, such that equal amounts of C n , paraffins and C n−1  paraffins are formed.
 
     In  FIG. 1 , a deoxygenated stream  20  containing normal paraffins, water, carbon dioxide and propane exits the deoxygenation unit  16  and is fed to a separator  22 . The separator  22  may be a multi-stage fractionation unit, distillation system or similar known apparatus. In any event, the separator  22  removes the water, carbon dioxide, and propane from the deoxygenated stream  20 . Further, the separator  22  may provide a first portion of paraffins  23  and a second portion of paraffins  21 . In certain embodiments, the first portion of paraffins  23  has carbon chain lengths of C 10  to C 14 . In other embodiments, the first portion of paraffins  23  has carbon chain lengths having a lower limit of C L , where L is an integer from four (4) to thirty-one (31), and an upper limit of C U , where U is an integer from five (5) to thirty-two (32). The second portion of paraffins  21  may have carbon chains shorter than, longer than, or a combination of shorter and longer than, the chains of the first portion of paraffins  23 . In a preferred embodiment, the first portion of paraffins  23  comprises paraffins with C 10  to C 13  chains and the second portion of paraffins  21  comprises paraffins with C 17  to C 18  chains. 
     As shown in  FIG. 1 , the first portion of paraffins  23  is introduced to a hydrocracking unit  24 . The hydrocracking unit  24  preferably holds a mild hydrocracking catalyst, such that results in lower isoparaffin production. Hydrocracking of the paraffins  23  results in a stream of normal and lightly branched paraffins  25  and an isoparaffin stream  26 . Preferably, the normal and lightly branched paraffins  25  are in the C 9  to C 14  range. As shown, the normal and lightly branched paraffin stream  25  is fed to an alkylbenzene production zone  28 . Specifically, the normal and lightly branched paraffin stream  25  is fed into a dehydrogenation unit  30  in the alkylbenzene production unit  28 . In the dehydrogenation unit  30 , the normal and lightly branched paraffin stream  25  is dehydrogenated into mono-olefins of the same carbon numbers as the paraffin stream  25 . Typically, dehydrogenation occurs through known catalytic processes, such as the commercially popular Pacol process. Di-olefins (i.e., dienes) and aromatics are also produced as an undesired result of the dehydrogenation reactions as expressed in the following equations:
 
Mono-olefin formation: C X H 2X+2 →C X H 2X +H 2  
 
Di-olefin formation: C X H 2X →C X H 2X−2 +H 2  
 
Aromatic formation: C X H 2X−2 →C X H 2X−6 +2H 2  
 
     In  FIG. 1 , a dehydrogenated stream  32  exits the dehydrogenation unit  30  comprising mono-olefins and hydrogen, as well as some di-olefins and aromatics. The dehydrogenated stream  32  is delivered to a phase separator  34  for removing the hydrogen from the dehydrogenated stream  32 . As shown, the hydrogen exits the phase separator  34  in a recycle stream of hydrogen  36  that can be added to the hydrogen feed  18  to support the deoxygenation process upstream. 
     At the phase separator  34 , a liquid stream  38  is formed and comprises the mono-olefins and any di-olefins and aromatics formed during dehydrogenation. The liquid stream  38  exits the phase separator  34  and enters a selective hydrogenation unit  40 , such as a DeFine reactor. The hydrogenation unit  40  selectively hydrogenates at least a portion of the di-olefins in the liquid stream  38  to form additional mono-olefins. As a result, an enhanced stream  42  is formed with an increased mono-olefin concentration. 
     As shown, the enhanced stream  42  passes from the hydrogenation unit  40  to a lights separator  44 , such as a stripper column, which removes a light end stream  46  containing any lights, such as butane, propane, ethane and methane, that resulted from cracking or other reactions during upstream processing. With the light ends  46  removed, stream  48  is formed and may be delivered to an aromatic removal apparatus  50 , such as a Pacol Enhancement Process (PEP) unit available from UOP. As indicated by its name, the aromatic removal apparatus  50  removes aromatics from the stream  48  and forms a stream of mono-olefins  52 . 
     In  FIG. 1 , the stream of mono-olefins  52  and a stream of benzene  54  are fed into an alkylation unit  56 . The alkylation unit  56  holds a catalyst  58 , such as a solid acid catalyst, that supports alkylation of the benzene  54  with the mono-olefins  52 . Hydrogen fluoride (HF) and aluminum chloride (AlCl 3 ) are two major catalysts in commercial use for the alkylation of benzene with linear mono-olefins and may be used in the alkylation unit  56 . As a result of alkylation, alkylbenzene, typically called linear alkylbenzene (LAB), is formed according to the reaction:
 
C 6 H 6 +C X H 2X →C 6 H 5 C X H 2X+1  
 
and is present in an alkylation effluent  60 .
 
     To optimize the alkylation process, surplus amounts of benzene  54  are supplied to the alkylation unit  56 . Therefore, the alkylation effluent  60  exiting the alkylation unit  56  contains alkylbenzene and unreacted benzene. Further the alkylation effluent  60  may also include some unreacted paraffins. In  FIG. 1 , the alkylation effluent  60  is passed to a benzene separation unit  62 , such as a fractionation column, for separating the unreacted benzene from the alkylation effluent  60 . This unreacted benzene exits the benzene separation unit  62  in a benzene recycle stream  64  that is delivered back into the alkylation unit  56  to reduce the volume of fresh benzene needed in stream  54 . 
     As shown, a benzene-stripped stream  66  exits the benzene separation unit  62  and enters a paraffinic separation unit  68 , such as a fractionation column. In the paraffinic separation unit  68 , unreacted paraffins are removed from the benzene-stripped stream  66  in a recycle paraffin stream  70 , and are routed to and mixed with the paraffin stream  25  before dehydrogenation as described above. 
     Further, an alkylbenzene stream  72  is separated by the paraffinic separation unit  68  and is fed to an alkylate separation unit  74 . The alkylate separation unit  74 , which may be, for example, a multi-column fractionation system, separates a heavy alkylate bottoms stream  76  from the alkylbenzene stream  72 . 
     As a result of the post-alkylation separation processes, the linear alkylbenzene product  12  is isolated and exits the apparatus  10 . It is noted that such separation processes are not necessary in all embodiments in order to isolate the alkylbenzene product  12 . For instance, the alkylbenzene product  12  may be desired to have a wide range of carbon chain lengths and not require any fractionation to eliminate carbon chains longer than desired, i.e., heavies or carbon chains shorter than desired, i.e., lights. Further, the feed  14  may be of sufficient quality that no fractionation is necessary despite the desired chain length range. 
     In certain embodiments, the feed  14  includes oils substantially having C 22  fatty acids. In other certain embodiments, the feed  14  is substantially homogeneous and comprises free fatty acids within a desired range. For instance, the feed may be palm fatty acid distillate (PFAD). Alternatively, the feed  14  may comprise triglycerides and free fatty acids that all have carbon chain lengths appropriate for a desired alkylbenzene product  12 . 
     In certain embodiments, the natural oil source is castor, and the feed  14  comprises castor oils. Castor oils consist essentially of C 18  fatty acids with an additional, internal hydroxyl groups at the carbon-12 position. For instance, the structure of a castor oil triglyceride is: 
                                
During deoxygenation of a feed  14  comprising castor oil, it has been found that some portion of the carbon chains are cleaved at the carbon-12 position. Thus, deoxygenation creates a group of lighter paraffins having C 10  to C 11  chains resulting from cleavage during deoxygenation, and a group of non-cleaved heavier paraffins having C 17  to C 18  chains. The lighter paraffins may form the first portion of paraffins  23  and the heavier paraffins may form the second portion of paraffins  21 . It should be noted that while castor oil is shown as an example of an oil with an additional internal hydroxyl group, others may exist. Also, it may be desirable to engineer genetically modified organisms to produce such oils by design. As such, any oil with an internal hydroxyl group may be a desirable feed oil.
 
     As shown in  FIG. 1 , the second portion of paraffins  21  and the isoparaffin stream  26  are co-fed to a system  80  for producing biofuel  13  such as diesel or jet fuel, such as synthetic paraffinic kerosene (SPK). Typically, no further deoxygenation is needed in the biofuel production system  80 . Rather, in the system  80 , the second portion of paraffins  21  are typically isomerized in an isomerization unit  82  or cracked in a cracking unit  84  to create the isoparaffins of equal or lighter molecular weight than the second portion of paraffins  21 . Hydrogen may be separated out from the resulting biofuel  13  to form a hydrogen stream  86  that is recycled to the deoxygenation unit  16 . While shown feeding the deoxygenation unit  16  directly, the hydrogen stream  86  could be fed to hydrogen feed  18 . In particular, in certain embodiments, the isoparaffin stream  26  is in the naphtha range, and system  80  includes a reformer that produces hydrogen  86  from the isoparaffin stream  26 . 
     In order to create biodiesel, the biofuel production system  80  primarily isomerizes the second portion of paraffins  21  with minimal cracking. For the production of biojet or green jet fuel, some cracking is performed in order to obtain smaller molecules (with reduced molecular weight) to the properties required by jet specifications. 
     While at least one exemplary embodiment has been presented in the foregoing Detailed Description, 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 and their legal equivalents.