Patent Publication Number: US-2015068954-A1

Title: Alkaline solution contact process and apparatus relating thereto

Description:
FIELD OF THE INVENTION 
     This invention generally relates to a process for contacting an alkaline solution with kerosene or diesel. 
     DESCRIPTION OF THE RELATED ART 
     Generally, a hydrocarbon feed, such as kerosene or diesel, is treated, and accompanying acidic components removed or reduced, in a prewash zone which is upstream of a mercaptan oxidation reactor vessel, a water wash column, a salt filter vessel, and a clay filter vessel for sweetening the hydrocarbon feed. Such vessels can be disclosed in, e.g., U.S. Pat. No. 7,223,332. 
     As the quality of crude oil decreases and refiners move to processing lower quality hydrocarbon feedstocks, the concentrations of naphthenic and other acids in kerosene, diesel and other hydrocarbon cuts may increase. This increased acidic concentration can express itself, with a kerosene feed for example, as Total Acid Numbers (hereinafter may be referred to as “TAN”) of above 0.15 mg caustic consumed/gram kerosene. In some instances, refining operations have observed TAN numbers of up to 0.45 in the field, which can result in greater corrosion within the crude refinery. 
     Furthermore, the presence of acid in a hydrocarbon feed, such as kerosene or diesel, can deactivate downstream catalysts, such as, e.g., the downstream catalyst used to sweeten kerosene to jet fuel. Such catalysts often have an activated carbon base that may be susceptible to deactivation by plugging of the carbon pores by an acid salt formed by the reaction of the acid with strong caustic. Although the plugging is reversible, it would clearly be desirable not to have such acid salts present in downstream processes. These acid salts such as sodium naphthenate can lead to increased water and caustic in the product, which can increase salt and clay consumption and potentially lead to product failing to meet specifications. 
     A dilute caustic solution can be used to remove naphthenic acids from a kerosene or diesel feed by adding the caustic solution to the feed, mixing the two phases, and passing the mixture through an electrostatic coalescer or electrostatic coalescer precipitator, which may also be referred to as “ECP”. Typically, the caustic coalesces and separates from the hydrocarbon, resulting in a very thick emulsion, sometimes referred to as a “rag layer” by operators, at an interface of the caustic and kerosene in the electrostatic coalescer. In the case of a feed with a high TAN with limited equipment or flexibility, such as insufficient control of the valves or caustic strength, the formed rag layer may grow in thickness and shorting of the ECP grids and potentially pass in the effluent from the ECP. Emulsion formation after caustic treatment can be of concern because emulsion formation and accumulation can impede sweetening of the mercaptan in the downstream reactor by deactivating the catalyst in the reactor, increasing consumption of salt for drying and clay treatments, and possibly causing product to not meet specification. To avoid this situation, the emulsion layer is manually drained and sent to a water treatment plant. Typically, water treatment plants have difficulty processing this heavy emulsion layer, resulting in a reduction in the processing capabilities that can ultimately cause complications with the entire refinery operation. 
     Generally, a dilute caustic is used to minimize emulsion formation after treatment of the kerosene or diesel feed. A dilute ammonia solution may also be used to remove the naphthenic acids in an electrostatic coalescer. Although ammonia is generally a weaker base, emulsion concerns can still persist. 
     Accordingly, there is a need in the art for a method and apparatus providing a single stage for naphthenic acid and similar acid removal while controlling or treating emulsions independent of the strength of the solutions, such as caustic, involved. 
     SUMMARY OF THE INVENTION 
     One exemplary embodiment can be a process for contacting an alkaline solution with kerosene or diesel. The process can include providing a stream of kerosene or diesel and at least one of a naphthenic acid and a salt thereof, with an additional alkaline solution to a prewash vessel, forming an emulsion interface between a kerosene or diesel phase and an alkaline phase in the prewash vessel, controlling an amount of the emulsion interface by withdrawing at least a portion of the emulsion interface between the two phases, and adding an acid to a withdrawn emulsion. 
     Another exemplary embodiment can be a process for contacting an alkaline solution with kerosene or diesel. The process can include providing a stream including the kerosene or diesel and at least one of a naphthenic acid and a salt thereof and the alkaline solution to a prewash vessel, forming an emulsion interface between a kerosene or diesel phase and an alkaline phase in the prewash vessel, detecting the emulsion interface, and withdrawing at least a portion of the emulsion interface. 
     A further exemplary embodiment can be a process for contacting an alkaline solution with kerosene or diesel. The process can include providing a stream of kerosene or diesel and at least one of a naphthenic acid and a salt thereof and the alkaline solution to a prewash vessel. An emulsion interface can form between a kerosene or diesel phase and an alkaline phase in the prewash vessel. The process may further include detecting the emulsion interface, measuring the emulsion interface prior to withdrawal, comparing the measured emulsion interface with a setpoint, sending a first signal to a first control valve for withdrawing at least a portion of the emulsion interface, sending a second signal to a second control valve for releasing an acid for contacting the portion of the withdrawn emulsion interface to form a hydrocarbon phase and an alkaline phase, and withdrawing at least a portion of at least one of the hydrocarbon phase and the alkaline phase. 
     The embodiments herein can treat a hydrocarbon stream, such as diesel or kerosene that has one or more naphthenic or similar acids and at least one salt thereof, by treating the stream with an alkaline solution, thereby neutralizing the acidic components. These embodiments may provide a practical method for purifying and substantially separating the hydrocarbon stream from other less desirable acidic components, improving the quality of the hydrocarbon product with greater efficiency and cost savings. Furthermore, a greater variety of hydrocarbon feeds, particularly those with higher acid numbers, e.g., above about 0.3 mg KOH/g, can be processed, and higher strength caustics, such as NaOH, can be used thereby reducing volume used and corresponding waste. 
     DEFINITIONS 
     As used herein, the term “stream” can include various hydrocarbon molecules, such as straight-chain, branched, or cyclic alkanes, alkenes, alkadienes, and alkynes, and optionally other substances such as impurities, including heavy metals, and sulfur and nitrogen compounds. The stream can also include aromatic and non-aromatic hydrocarbons. Moreover, the hydrocarbon molecules may be abbreviated C1, C2, C3 . . . Cn where “n” represents the number of carbon atoms in the one or more hydrocarbon molecules. Furthermore, a superscript “+” or “−” may be used with an abbreviated one or more hydrocarbons notation, e.g., C8 +  or C8 − , which is inclusive of the abbreviated one or more hydrocarbons. As an example, the abbreviation “C8 + ” means one or more hydrocarbon molecules of eight carbon atoms and/or more. In addition, the term “stream” may be applicable to other fluids optionally without having one or more hydrocarbons, such as aqueous and non-aqueous solutions of alkali, such as sodium hydroxide, and at least one acid in an aqueous solution. 
     As used herein, the term “zone” can refer to an area including one or more equipment items and/or one or more sub-zones. Equipment items can include one or more reactors or reactor vessels, heaters, exchangers, pipes, pumps, compressors, and controllers. Additionally, an equipment item, such as a reactor, dryer, or vessel, can further include one or more zones or sub-zones. 
     As used herein, the term “rich” can mean an amount of generally at least about 50%, and preferably about 70%, by mole, of a compound or class of compounds in a stream. If referring to a solute in solution, e.g., one or more naphthenic acids and salts thereof in an alkaline solution, the term “rich” may be referenced to the equilibrium concentration of the solute. As an example, about 5%, by mole, of a solute in a solvent may be considered rich if the concentration of solute at equilibrium is 10%, by mole. 
     As used herein, the term “substantially” can mean an amount of at least generally about 80%, preferably about 90%, and optimally about 99%, by weight, of a compound or class of compounds in a stream. 
     As used herein, the term “parts per million” may be abbreviated herein as “ppm” and “weight ppm” may be abbreviated herein as “wppm”. Generally, parts per million is based on weight unless otherwise indicated. 
     As used herein, the terms “mercaptan” and “thiol” may be used interchangeably. 
     As used herein, the terms “acid value” or “total acid number (TAN)” can be a mass of potassium hydroxide in milligrams required to neutralize one gram of a hydrocarbon, e.g., kerosene or diesel containing, e.g., one or more naphthenic acid compounds. Generally, the mass of acid value can be abbreviated “mg KOH/g” and may be measured by UOP Method 565-05, Procedure C, ASTM D3242-11 for acid numbers no greater than 0.1 and ASTM D664-11a, Test Method A for acid numbers of at least 0.1. 
     As used herein, the term “alkali” can mean any substance that in solution, typically a water solution, has a pH value greater than about 7.0, and exemplary alkali can include sodium hydroxide, potassium hydroxide, or ammonia. Such an alkali in solution may be referred to as an alkaline solution or an alkaline. 
     As used herein, the term “caustic” can mean an alkaline solution, such as, e.g., a solution of sodium hydroxide. 
     As used herein, the term “kerosene” can mean a fluid having one or more C8-C15 hydrocarbons and boiling at about 160-about 275° C. at atmospheric pressure. 
     As used herein, the term “diesel” can mean a fluid having one or more C8-C21 hydrocarbons and boiling at about 250-about 340° C. at atmospheric pressure. 
     As used herein, the term “naphthenic acid” can mean a cycloalkyl, typically cyclopentyl, moiety having at least one bridging group, typically an alkyl group having 5 to 20 carbon atoms, terminating in a carboxyl substituent. A salt of a naphthenic acid can have one or more cations, such as sodium or potassium, replacing the hydrogen of at least one carboxyl group. 
     As used herein, the term “kilopascal” may be abbreviated herein as “KPa”. 
     As depicted, process flow lines in the figures can be referred to interchangeably as, e.g., lines, pipes, liquids, solutions, alkalines, alkaline solutions, caustic, acid solutions, feeds, products, or streams. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The FIGURE is a schematic, partial cross-sectional depiction of an exemplary apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the FIGURE, an exemplary alkaline solution contact apparatus  100  is shown. The apparatus  100  can include a pre-wash vessel  110 , a piping network  150 , and a vessel  200  for separating emulsion products after treatment. 
     In one preferred embodiment, a stream  10  comprised substantially of kerosene, diesel or both, and impurities typically of at least one of a naphthenic acid and a salt thereof, is provided. Usually, the stream  10  includes the naphthenic acid with the salt of the naphthenic acid only present at equilibrium levels. Often, the salt of the naphthenic acid is a sodium and/or potassium salt thereof, although additional or different acids or salts may be present. Preferably, the naphthenic acid and salt thereof includes a cyclopentyl moiety having an alkyl group of 5 to 20 carbon atoms, and preferably the naphthenic acid and salt thereof are present at a concentration of about 0.015-about 1.2 mg KOH/g of kerosene also known as diesel acid value. Alternatively, the naphthenic acid and salt may be present at a concentration of at least 50-about 1,000 wppm. In an effort to simplify the discussion, the stream  10  and its downstream derivatives, such as a phase or product stream, can be referred to as a “kerosene stream” or including kerosene, but it should be understood that the stream  10  and its downstream derivatives can include or be substituted with any suitable hydrocarbon, including diesel. 
     Generally, the kerosene stream  10  combines with an alkaline stream  20  to form a combined stream  30 . The alkaline stream  20  can be comprised of a caustic, and in preferred embodiments, is comprised of sodium hydroxide, an ammonia, a potassium hydroxide, or a combination thereof. Preferably, the alkaline stream  20  has a concentration of alkali of at least about 1-about 10%, by weight, based on the weight of the solution. 
     When the kerosene stream  10  and alkaline stream  20  combine, the alkaline stream  20  may neutralize and separate the acidic components from the hydrocarbon portion of the stream. Although not wanting to be bound by theory, the acidic impurities such as naphthenic acid typically convert to a salt or salts after contacting the alkaline stream  20 . Optionally, some of the acid or salt may be present before or after contacting. 
     Generally, the combined stream  30  enters a pre-wash vessel  110 , in which the components of the combined stream separate, generally, into a kerosene phase  114  at the upper end of the pre-wash vessel  110 , and an alkaline phase  122  at the lower end of the pre-wash vessel  110 . In a preferred embodiment, the prewash vessel  110  is an electrostatic coalescer precipitator. 
     Sometimes a rag or an emulsion layer or emulsion interface  118  may form between the separated kerosene phase  114  and alkaline phase  122 . Usually, the rag layer  118  has a thick consistency, roughly that of mayonnaise, and is comprised of materials that do not separate out into either the kerosene phase  114  or alkaline phase  122 . The rag layer  118  typically has a pH greater than about  10  and can include water, hydrocarbons such as kerosene, an acid such as naphthenic acid, a sodium naphthanate, a sodium phenylate, and a sodium hydroxide. 
     After separation, a kerosene product stream  140  can exit a top and a spent alkali stream  144 , which may include one or more naphthenic salts, can exit a bottom of the prewash vessel  110 . The kerosene product stream  140  is typically obtained with a lowered content of the naphthenic or other acids and/or at least one salt thereof, of less than about 100 ppm, by weight. The kerosene product stream  140  can optionally be sent downstream for further processing. Generally, the kerosene product stream  140  can have an acid value of no more than about 0.015 mg KOH/g of kerosene. The spent alkali stream  144  can be comprised of caustic salts, such as a potassium or sodium naphthenic salt, and be sent for waste water treatment for processing or to spent alkali disposal. 
     The piping network  150  can include several lines  160 ,  164 ,  168 ,  172 , and  176  that may form branches that can be combined into a main or combined line  182 . In this embodiment, the set of lines  160 ,  164 ,  168 ,  172 , and  176  is comprised of five lines. Each line  160 ,  164 ,  168 ,  172 , and  176  may have a corresponding control valve  162 ,  166 ,  170 ,  174 , and  178  and be at a different elevation on the prewash vessel  110 . Each control valve  162 ,  166 ,  170 ,  174  and  178  can be considered, independently, a first control valve. In an alternative embodiment, the lines  164 ,  168 , and  172  can have respective control valves, and the lines  160  and  176  may have manual valves. In a further embodiment, the line  168  may have a control valve, the other lines  160 ,  164 ,  172 , and  178  can have manual valves. In yet another embodiment, the lines  160 ,  164 ,  168 ,  172 , and  176  can all have manual valves. However, it should be understood that any suitable number of lines and valves are optional with no or one or more control valves. 
     The depth, location and width of the rag layer  118  can vary somewhat within the pre-wash vessel  110 , based upon factors such as the relative amounts of the kerosene phase  114  and alkaline phase  122  within the pre-wash vessel  110  at any given time. Accordingly, at least a portion of the rag layer  118  is drawn off by one or more of the lines  160 ,  164 ,  168 ,  172 , and  176  positioned at various heights along the pre-wash vessel  110 . The lines can be of any number and be suitable for drawing off the rag layer  118  within the pre-wash vessel  110 . 
     The flow of each stream through each of the lines  160 ,  164 ,  168 ,  172 , and  176  can be controlled by the control valves  162 ,  166 ,  170 ,  174 , and  178 . Each of the first set of control valves  162 ,  166 ,  170 ,  174 , and  178  can be opened, closed, or left in some suitable intermediate position based upon applicable factors, such as the location and thickness of the rag layer  118 . The control valves  162 ,  166 ,  170 ,  174 , and  178  can be regulated by a level controller  130 , which upon detecting the rag layer  118  can send a signal  132 . The signal  132  may pass to point “A” and be received at point “A” at the control valves  162 ,  166 ,  170 ,  174 ,  178 , and  184 . Point “A” is provided in the FIGURE to illustrate communicating the level controller  130  with the control valves  162 ,  166 ,  170 ,  174 ,  178 , and  184  and to not unduly clutter the FIGURE with excessive lines. In a preferred embodiment, the level controller  130  measures the level and thickness of the rag layer  118 , compares the measured rag layer  118  with a setpoint, and sends the signal to one or more control valves  162 ,  166 ,  170 ,  174 , and  178 , which can be independently opened. Any suitable level controller  130  can be utilized. One level controller is sold under the trade designation ID-201 Interface Detector by Agar Corporation Inc. of Houston, Tex. Another level controller may use an ultrasonic level measurement. 
     As an example, if there is a relatively small amount of the upper kerosene phase  114  relative to the alkaline phase  122 , then the emulsion interface  118  would be found to be relatively high within the pre-wash vessel  110 . Upon a signal  132 , the level controller  130  can open the uppermost first control valve  162  and the lower valves  166 ,  170 ,  174 , and  178  can remain closed, such that the rag layer  118  would be drawn off only by the line  160 . Alternatively, if the rag layer  118  is centered in the pre-wash vessel  110 , the control valve  170  may be opened to drain the rag layer  118  through the line  168 , as depicted in the FIGURE. 
     The stream or streams from the lines  160 ,  164 ,  168 ,  172 , and  176  can be joined into the main line  182 . Generally, the stream in the combined line  182  has a high pH, and to treat the main stream  182  and break down the emulsion into a hydrocarbon phase and an alkaline phase, an acid stream  180  can be added. The acid stream  180  can be comprised of any suitable acid, preferably an organic and/or a mineral acid, such as acetic acid, carboxylic acid, hydrochloric acid, or sulfuric acid; and in one preferred embodiment, is comprised of a carboxylic acid, acetic acid or both. 
     The acid stream flow to the combined stream  182  can be regulated by a control valve  184 , which may be considered a second control valve. The control valve  184  can be, in turn, actuated by the signal  132 , as previously discussed. Namely, once the level controller  130  detects the rag layer  118 , the signal  132  may be sent to the control valve  184  to release the acid stream  180 . 
     The components of the combined stream  182  can be added to the acid stream  180  to form a merged stream  188 . The fluids of the merged stream  188  may proceed through an inline static mixer  190 , which more thoroughly mixes the merged stream  188 . The alkaline components of the combined stream  182  are broken down by the added acid stream  180 , which can result in a stream having a pH of less than about 7, or even no more than about 2. Usually, the inline static mixer  190  has a pressure drop of less than about 21 KPa. As a result, the merged stream  188  can become much less viscous and liquefy. 
     The resulting mixed stream  192  enters a vessel  200 . The addition of the acid stream  180  can result in two phases, an aqueous or alkaline phase and a hydrocarbon phase, which may separate within the vessel  200 . The hydrocarbon phase, which can be comprised of hydrocarbons such as naphthenic acids, phenols, and residual kerosene, may be withdrawn from the upper portion of the vessel  200  as a hydrocarbon stream  202  and may proceed for further processing, such as, e.g., slops, and typically sent on to a main crude tower. Often, the aqueous or alkaline phase, which may contain acid salts such as sodium chloride, is withdrawn from the lower portion of the vessel  200  as an aqueous stream  210  and proceeds to a water treatment system. 
     Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. 
     In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated. 
     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.