Abstract:
A process is presented for the removal of oxygen from a hydrocarbon stream. The oxygen can react and cause polymerization of the hydrocarbons when the hydrocarbon stream is heated. Controlling the removal of the oxygen from the hydrocarbon stream produces a hydrocarbon stream that is substantially free of oxygen and has a reduced activity for generating undesired compounds.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/358,427 filed Jun. 25, 2010. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the processes of treating fluids. In particular, the invention relates to the treatment of fuels to remove oxygen contaminated materials. 
     BACKGROUND OF THE INVENTION 
     Chemicals, and in particular, hydrocarbon mixtures, that are stored for extended periods of time can become contaminated, or in the presence of contaminants accumulate deposits that are detrimental to the equipment through which the chemicals flow. In particular, fuels can often sit in storage containment units, such as storage tanks or shipping vessels. The fuels are usually hydrocarbon mixtures, and contaminants in the fuels can bring about some polymerization or the creation of gums. These molecules can impair the performance of engines which run on the fuel. The gums or other materials can create deposits that impair flow, or heat transfer characteristics in an engine, which in turn can impair engine performance. 
     An important contaminant is oxygen. Oxygen contaminants lead to undesirable chemical products by a variety of reaction processes. These reactions include autocatalytic mechanisms that include free radical chain reactions. Olefins and other reactive chemical compounds, in the presence of oxygenate contaminants can lead to polymerization products and potentially also to deposits on metal surfaces. Fouling causes increased maintenance of equipment, and reduces operation times, and a loss of production. 
     The removal of oxygen and residual oxygen contaminants from hydrocarbon feedstocks can reduce the down times and protect equipment from excessive fouling due to deposits created from reactions by the presence of oxygen in the hydrocarbon feedstocks. 
     SUMMARY OF THE INVENTION 
     Oxygen contamination in a jet fuel, or in kerosene is an important problem. The present invention provides a method of removing residual dissolved oxygen to prevent the problems associated with the presence of oxygen in either a jet fuel or kerosene. 
     The process is for stripping oxygen from a hydrocarbon feedstream, and in particular a kerosene feedstock. The process includes passing the hydrocarbon feedstream through a preheater, where the feedstream is heated to a temperature of up to 140° C. The preheated feedstream is passed to an oxygen stripper, where a stripping gas, having substantially zero oxygen, is passed to the stripper to remove the dissolved oxygen from the hydrocarbon feedstream. The dissolved oxygen is passed out of the stripper in the overhead vapor stream comprising the stripping gas. The stripped hydrocarbon stream is passed out of the bottom of the stripper, and is heated to remove dissolved stripping gas. The removed stripping gas is vented or passed to other units for possible usage. 
     In one embodiment, a portion of the heated stripped hydrocarbon stream is cycled back to the bottom of the stripper to heat the bottom section of the oxygen stripper. 
     Additional objects, embodiments and details of this invention can be obtained from the following drawing and detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       FIGURE is a flow diagram of the process. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Oxygen contamination can reduce the quality of many organic streams. Oxygen or oxygenate contamination in kerosene, and jet-fuel which is derived from kerosene, can have deleterious effects on the specifications. The contamination can come about in numerous ways. One example is by contacts with atmospheric oxygen in an unblanketed storage container or shipping vessel. During the transit time and storage time oxygen is dissolved into the kerosene and jet-fuel. Another example is through mercaptan sweetening in the making of jet fuel. The production of jet fuel from kerosene requires several processing steps such as hydroprocessing or mercaptan sweetening. During the mercaptan sweetening process, oxygen is contacted with the kerosene, and some of the oxygen is residual in the jet fuel after the processing. 
     In some jet turbine engines on aircraft, the jet fuel is circulated between the fuel tanks and the engines to control the engine temperatures. Using jet fuel as a thermal sink for the engine temperatures heats up the jet fuel. During these normal processes, the jet fuel is heated and residual oxygen and oxygenates that are in the jet fuel can react and polymerize to form gums and deposits in the jet fuel circulation system, and in the jet fuel lines to the engines. These deposits change the heat transfer characteristics of the engine, and can affect the flow through the fuel lines resulting in a reduction in the engine performance. In addition, jet fuel and kerosene can be used as a feedstock for the production of normal paraffins in the C10 to C16 range. These normal paraffins are used in the production of linear alkylbenzenes (LAB). LABs are used in the production of biodegradable detergents. During the process of normal paraffin extraction, the kerosene is heated. The heating of the kerosene in the presence of oxygen dissolved in the kerosene can cause polymerization reactions that in turn can result in gums and deposit formation. These gums and deposits result in the fouling of equipment and in increased down time of the processes, and subsequent loss of production. 
     The oxygen in kerosene is a precursor to hydroperoxides. The hydroperoxide species react using a free radical mechanism to form polymers. The present invention uses a specific set of conditions to strip oxygen from kerosene, and from jet fuel in a controlled fashion resulting in a kerosene and jet fuel product stream with a reduced tendency to form gums and deposits. 
     The present invention is a process for stripping oxygen from a hydrocarbon feedstream. The process, as illustrated in the FIGURE, comprises passing a hydrocarbon feedstream  10  through a preheater  20 , creating a preheated feedstream  22 . The preheated feedstream  22  is passed to an oxygen stripper  30 . The oxygen stripper  30  strips the hydrocarbon stream of oxygen to create an overhead stream  32  and an intermediate stripped stream  34 . The stripper  30  is operated with a stripping gas  36  passed to the stripper  30  to remove oxygen from the hydrocarbon feedstream. The overhead stream  32  created during the stripping process comprises the stripping gas and oxygen. The intermediate stripped stream  34  is passed through a bottoms heater  40  to remove additional stripping gas and additional oxygen from the intermediate stripped stream  34 , thereby creating a liquid bottoms stream  42 . The liquid bottoms stream  42  is heated to a higher temperature to drive oxygen from solution. The additional stripping gas removed from the liquid bottoms stream is returned to the oxygen stripper  30 . 
     The process can, optionally, include returning a portion  44  of the bottoms liquid stream to the oxygen stripper  30  to maintain a desired heat level in the bottom of the oxygen stripper  30 . The stripping gas  36  used to strip oxygen from the hydrocarbon feedstream is a substantially oxygen free gas stream. Examples of suitable stripping gas streams for this application are fuel gas or a hydrogen stream. Other gases that are possible include nitrogen, steam, and carbon dioxide, or other gases that are substantially oxygen free. 
     This process is preferred for use with hydrocarbon streams in the kerosene boiling range, or in the jet fuel boiling range. The sources of heat for the preheater  20  and the bottoms heater  40  can be supplied by hot streams available elsewhere in the refining facility, thereby minimizing the energy impact of the stripping process. 
     The preheater  20  heats the feedstream  10  to a temperature below 220° C. for facilitating the removal of oxygen from the feedstream as it is processed in the stripper  30 . Preferably the temperature is below 140° C. The control of the temperature is important for maintaining the hydrocarbon stream below a temperature wherein the polymerization reactions substantially occur. Although stripping is generally favored at higher temperatures, the present invention is aimed at controlling the stripping at a temperature below the fouling temperatures, or below temperature where substantial polymerization can take effect due to the presence of oxygen in the hydrocarbon stream. 
     The bottom heater  40  heats the intermediate stripped stream  34  to a higher temperature to remove dissolved stripping gas. The intermediate stripped stream  34  is heated to a temperature of at least 140° C. The process can further include the addition of anti-foulants  38  to the intermediate stripped stream  34 . 
     The invention can further include a fractionation unit  50  for separating out a light liquid stream  52 . The fractionation unit  50  produces a vapor overhead stream  54 , a light liquid stream  52  and a heavy bottoms stream  56 . The light liquid stream  52  is a light kerosene stream, comprising C10 and lighter hydrocarbons, that can be used for further processing. 
     The heavy bottoms stream  56  can be further processed by passing the stream to a rerun column  60 . The rerun column  60  separates the heavy bottoms stream  56  into an overhead kerosene cut  62 , where the kerosene can be further processed. The rerun column  60  further generates a heavy kerosene stream  64  and a heavy bottoms stream  66 . Further processing includes using the heavy kerosene stream  64  for the recovery of normal paraffins in the C10 to C14 range for use in linear alkylbenzenes. The heavy bottoms stream  66  comprises C14 and heavier hydrocarbons. 
     In one embodiment, the process is for the stripping of oxygen from a kerosene feedstream. The process comprises passing the kerosene through a preheater to heat the kerosene to a temperature of approximately 140° C. The preheated kerosene is passed to an oxygen stripper, where a stripping gas removes the dissolved oxygen form the kerosene. The dissolved oxygen is passed out in the overhead stream with the stripping gas, and the stripped kerosene is passed out of the bottom of the stripper. The kerosene exiting at the bottom of the stripper is heated with a bottoms heater to remove any dissolved stripping gas, and a portion of the heated kerosene may be cycled back to the bottom of the stripper to heat the bottom section of the oxygen stripper. 
     While the invention has been described with what are presently considered the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.