Patent Publication Number: US-2006016727-A1

Title: Gel assisted separation method and dewatering/desalting hydrocarbon oils

Description:
FIELD OF THE INVENTION  
      This application claims the benefit of U.S. Provisional Application 60/590,891 filed Jul. 23, 2004. 
    
    
      The invention relates to separating polar hydrocarbons from hydrocarbon oils. The invention also relates to desalting and/or dewatering hydrocarbon oils.  
     BACKGROUND  
      Hydrocarbon oils, particularly heavy crude oils, contain polar hydrocarbon compounds such as naphthenic acids, nitrogen and sulfur containing hydrocarbon compounds and pose problems in refining. There is a need to upgrade such hydrocrabon oils. Separation of polar hydrocarbon compounds such as naphthenic acids, nitrogen and sulfur containing hydrocarbon compounds from crude oils results in upgrading. The present invention addresses this need.  
      Hydrocarbon oils, particularly crude oils when produced comprise varying amounts of water and inorganic salts like halogens, sulfates and carbonates of Group I and Group II elements of The Periodic Table of Elements. (The Periodic Table of Elements is the common long form of the periodic table; Advanced Inorganic Chemistry by F. A Cotton and G. Wilkinson Interscience Publishers, 1962) Removal of water from produced crude oils is termed dewatering and salt removal is termed desalting. Often, the process of dewatering also desalts the crude oil since water-soluble salts are removed with the water.  
      Dewatering the produced crude oil is desired at crude oil production facilities as it impacts the value of crude oil and its economic transportation. The presence of salts, especially chlorides of Group I and Group II elements of The Periodic Table of Elements, corrode oil processing equipment. In order to mitigate the effects of corrosion, it is advantageous to reduce the salt concentration to the range of 1 to 5 ppm or less and water content to about 0.25 to 1 wt % by weight of the crude oil prior to transportation and processing of the oil.  
      Among the crude oil dewatering and/or desalting methods in use today, electrostatic separation methods are commonly used. Heavy crude oils containing high concentrations of asphaltenes, resins, waxes, and napthenic acids are difficult to dewater and desalt and usually require longer processing times, higher process operation temperatures and higher concentrations of demulsifier chemicals to effect the desired dewatering and desalting. As a result of these processing requirements for heavy crude oils the process throughput is lowered and costs for dewatering and desalting increased. Consequently, there is a need for improved crude oil dewatering and/or desalting methods that improve the efficiency of dewatering and/or desalting especially with heavy crude oils containing asphaltenes and naphthenic acids. The present invention also addresses this need.  
     SUMMARY OF THE INVENTION  
      In one embodiment is a method for separating polar hydrocarbon compounds from a hydrocarbon oil containing polar hydrocarbon compounds comprising the steps of: 
          a) forming a gel in the hydrocarbon oil, and thereafter     b) separating the gel from the hydrocarbon oil to produce a separated gel and a separated hydrocarbon oil.        

      In another embodiment is a method for dewatering and/or desalting a hydrocarbon oil containing water and salt comprising the steps of: 
          a) forming a gel in the hydrocarbon oil,     b) separating the gel from the hydrocarbon oil to produce a separated gel and a separated hydrocarbon oil, and thereafter     c) separating water and salt from the separated hydrocarbon oil to provide a dewatered and desalted hydrocarbon oil.       

    
    
     DETAILED DESCRIPTION OF THE PRFERRED EMBODIMENTS  
      The gel separation method of the instant invention is useful for hydrocarbon oils comprising polar hydrocarbon compounds. It is particularly useful for crude oils that contain polar hydrocarbon compounds such as naphthenic acids, asphaltenes and metalloprophyrins. Separation of the polar hydrocarbon compounds from the crude oil results in a upgraded crude oil. Preferred hydrocarbon oils are hydrocarbon oils selected from the group consisting of crude oil, crude oil distillate, crude oil residuum or mixtures thereof.  
      The desalting and/or dewatering method of the instant invention is useful for hydrocarbon oils comprising salts, water and mixtures thereof. It is particularly useful for heavy and waxy crude oils that are generally difficult to dewater and/or desalt. The salts present in the hydrocarbon oil are inorganic salts including halogens, sulfates and carbonates of Group I and Group II elements of The Periodic Table of Elements. The concentration of the salts can vary from about 0.001 to 10 wt % based on the weight of the hydrocarbon oil. The process is effective for both water-soluble and water insoluble salts that are suspended in the hydrocarbon oil. The water content of the hydrocarbon oil-water mixture can vary in the range of 0.5 wt % to 20 wt % based on the weight of the hydrocarbon-water mixture. The hydrocarbon oil required to be dewatered and/or desalted can be a crude oil, crude oil distillate, and crude oil residuum obtained from distillation or mixtures thereof. Generally the water of the hydrocarbon oil is in a form wherein the water is dispersed as droplets in the hydrocarbon oil. In this form of occurrence the hydrocarbon oil-water mixture is generally a water-in oil emulsion.  
      The gel of the invention is a complex fluid comprising hydrocarbon oil, water, water soluble salts such as sodium, potassium and calcium chlorides, water insoluble salts such as calcium carbonate and calcium sulfate, organic carbonaceous solids like coal and coke, crude oil derived compounds such as asphaltenes, naphthenic acids, naphthenic acids salts such as sodium and calcium naphthenates, organo sulfur compounds, organo nitrogen containing compounds and metalloporphyrins. The crude oil derived compounds in the gel are polar hydrocarbon compounds, preferably surface active polar hydrocarbon compounds, and more preferably surface active polar hydrocarbon compounds that are surface active at a hydrocarbon-water interface. Surface activity of the polar hydrocarbon compounds can be determined using known tensiometric techniques such as hydrocarbon/water interfacial tension by one of ordinary skill in the art of interfacial science.  
      The gel has physical properties suitable for separation from the hydrocarbon oil from which it is formed. Preferably the density of the gel is greater than that of the hydrocarbon oil at the temperature the method is conducted. More preferably the density is greater than that of the hydrocarbon oil and less than that of water at the temperature the method is conducted. The density of the gel being greater than that of the hydrocarbon oil and less than that of water allows easy separation of the gel from the hydrocarbon oil. The gel is preferably viscoleastic. Viscoelastic properties of materials is known to one of ordinary skill in the art of rheology. By virtue of its viscoelastic nature the gel has an elastic modulus and a viscous modulus. The elastic modulus and viscous modulus of the viscoelastic gel can be measured by one of ordinary skill in the art of fluid rheology using oscillatory visometry techniques. Preferably the viscous modulus of the gel is at least two times that of the hydrocarbon oil from which it is formed at a given temperature. Preferably the elastic modulus of the gel is at least two times that of the hydrocarbon oil from which it is formed at a given temperature.  
      The first step of the method is to form a gel in a hydrocarbon oil. To form the gel, a variety of methods can be employed. One non-limiting example includes adding gel forming agents including but not limited to lignin, cellulose, coke fines, coal fines, synthetic cross linked polymers, cholesteryl and cholestanyl derived gellation compounds and oxidized alkyl aromatic hydrocarbons and water. Water is a preferred gel-forming agent. The amount of gel forming agent to be added can vary in the range of 0.01 to 20 wt % based on the weight of the hydrocarbon oil. When water is the gel forming agent it is preferred to add water also the range of 0.01 to 20 wt % based on the weight of the hydrocarbon oil. More preferrably water is in the range of 0.01 to 10 wt % based on the weight of the hydrocarbon oil. Water addition can be in one lot or in aliquots. After addition of the gel forming agent the hydrocarbon oil is mixed and allowed to stand for a period of time and at a temperature sufficient to promote gel formation. Mixing can be conducted during or after addition of the gel forming agent. The preferred temperature of addition and mixing is in the range of about 15° C. to about 85° C. and preferred period of time of addition and mixing is in the range of 5 minutes to 10 days.  
      Another example of forming a gel from a hydrocarbon oil is to subject the hydrocarbon oil to temperature cycles i.e., increase and decrease the temperature of the hydrocarbon oil in a temperature range several times. Preferrably the temperature cycling is in the temperature range of 10° C. to 90° C. at atmospheric pressure and the number of cycles is at least 2 and the total time period of cycling is from 5 minutes to 10 days. In another example a hydrocarbon oil is subject to pressure cycles in a suitable pressure range. A pressure in the range of 14 psia (96.46 kPa) to 150 psia (1033.5 kPa) is preferred. The hydrocarbon oil can be subject to both temperature and pressure cycles at the same time. In yet another example the hydrocarbon oil can be subject to electrostatic fields. Preferably the electrostatic field is at potentials ranging from about 10,000 volts to about 40,000 volts, A.C. or D.C. Voltage gradients in the electrostatic field range from about 500 volts per inch to about 5,000 volts per inch, preferably ranging from about 500 to about 1,000 volts per inch. Residence times in the electrostatic fields range from about 0.5 to about 120 minutes, preferably from about 0.5 to about 15 minutes. In yet another example the hydrocarbon oil can be subject to shear cycling i.e., subject the hydrocarbon oil to shearing forces of varying intensities. This can be accomplished for example by subjecting the hydrocarbon oil to turbulent force field followed by a quiescent force field. The hydrocarbon oil can also be subject to sonic treatment cycles. In this embodiment the hydrocarbon oil is subject to cycles of ultrasonic waves by turning on and turning off the ultrasonicator alternately for a period of time sufficient to form the gel. The temperature, pressure, electrostatic, sonic and shear treatments can be conducted on the hydrocarbon oil or on the hydrocarbon oil treated with gel forming agents. For example, one can treat the hydrocarbon oil with water and then subject it to the temperature, pressure, electrostatic, sonic or shear treatments to promote gel formation.  
      The amount of gel formed in the hydrocarbon oil is an amount sufficient to extract at least 1 weight percent of polar hydrocarbon compounds in the starting hydrocarbon oil, preferably at least 1 weight percent surface active polar hydrocarbon compounds, and more preferably at least 1 weight percent surface active polar hydrocarbon compounds that are surface active at a hydrocarbon-water interface. Preferably the surface active polar hydrocarbon compounds are nitrogen, oxygen, sulfur and metals containing surface active compounds of the hydrocarbon oil. The total amount of polar hydrocarbon compounds of the hydrocarbon oil can be measured by one of ordinary skill in the art of organic compound analyses. Preferably, the amount of gel that is formed is in the range of 0.5 to 20 wt % based on the initial weight of the hydrocarbon oil. More preferrably the the amount of gel that is formed is in the range of 0.5 to 10 wt % based on the initial weight of the hydrocarbon oil.  
      The second step of the method comprises separating the gel from the hydrocarbon oil to produce a separated gel and a separated hydrocarbon oil. This separation can be accomplished by methods known to one of ordinary skill in the art of separations. The system for separation can be considered as a liquid-viscoelastic gel system. Because of the favorable density and viscoelastic properties of the formed gel the preferred separation method is gravity settling followed by removal of the top oil phase. Centrifugation or hydrocyclone techniques can also be employed to increase the rate of separation of the gel from the treated oil. Suitable centrifugal force fields can be applied for the separation. Suitable filtration methods can also be employed. For example, for gels formed from crude oils one can use a mineral or rock bed such as a gravel bed as a filtration medium to filter off or separate the gel from the oil. Other filtration media such as membrane filters can also be used. After gel formation and separation, the separated hydrocarbon oil contains polar hydrocarbon compounds that are at least 1 wt % less than the starting hydrocarbon.  
      The last step of the method for dewatering and desalting is separating water and salt from the separated hydrocarbon oil. Methods known for separating water and salt from the hydrocarbons oils can be employed. These include methods such as electrostatic separation, centrifugation and hydrocyclone treatment. Electrostatic separation is the preferred method to separate the water and salts from the separated hydrocarbon oil. Preferably demulsifier chemicals known to one of ordinary skill in the art of dewatering and desalting hydrocarbon oils are added to the separated hydrocarbon oil and subject to electrostatic treatment to provide the dewatered desalted oil.  
      The following non-limiting examples illustrate one embodiment of the invention.  
      Step-1: Gel Formation  
      100 grams of a crude oil from Canada was used. To the crude oil was added 1 wt % water based on the weight of the crude oil. The crude oil was subject to temperature cycling by heating the crude oil to 60° C. and holding the temperature at 60° C. for 30 minutes. The sample was then cooled to 25° C. The heating and cooling was conducted five times. The sample was then allowed to gravity settle for 5 days.  
      After 5 days a gel layer was observed to settle at the bottom of the jar containing the temperature cycled oil. The amount of gel formed was 5 wt % based on the initial weight of the crude oil. A bright light source held in front or behind the jar containing the oil was sufficient to detect the gel layer.  
      Step-2: Separation of Oil and Gel  
      The oil residing on top of the gel was carefully siphoned off to provide the separated oil (denoted, sample-1). The gel was at the bottom of the jar and is the separated gel (denoted, gel sample-G). Step-3: Separation of water and salts from the separated oil (electrostatic treatment)  
      Two samples were examined. Sample-1 was the separated oil (obtained from step 2) and Sample-2 untreated Canadian crude oil. Water (5 wt %) was added to samples 1 and 2 and both samples shaken for 5 minutes on a wrist shaker. A phenol formaldehyde ethoxylated alcohol demulsifier formulation sold by BASF Corporation as Pluradyne DB7946 was added to both samples at a treat rate of 100 ppm based on the weight of crude oil and the mixture shaken on a wrist shaker for an additional 10 minutes. Both samples were subject to electrostatic demulsification by applying 830 volts/square inch AC current to the samples at 60C for 1 hour. After completion of the procedure the samples were examined and amount of water separating out recorded. The samples were also analyzed for sodium content by Inductively Coupled Plasma (ICP) analyses. Sample-2 did not demulsify under the conditions of the experiment and no water was observed to split out at the bottom of the demulsifier vessel. In Sample-1, 97% dewatering and 80% reduction in salt content was observed. Thus, formation and separation of the gel results in effective dewatering and desalting whereas the untreated crude oil does not demulsify under the same conditions.  
      Analyses of the Separated Gel  
      The separated gel (gel sample-G) from step 2 was subject to Theological analyses using oscillatory viscometry. A Haake viscometer in the oscillating mode was used and analyses conducted at 25° C. The separated gel (gel sample-G) had a viscous modulus of 32.5 Pascal and an elastic modulus of 4.4 Pascal. In contrast, the separated oil (sample-2) had a viscous modulus of 7.7 Pascal an elastic modulus of 0.7 Pascal. Thus the formed gel has a significantly higher elastic and viscous modulus compared to the crude oil.  
      Next, the gel phase was subject to component analysis. The gel was found to contain 95% oil and 5% water. The oil and water from the separated gel was analyzed. The oil of the gel (Gel Oil) was itself observed to have a micro-concarbon residue (MCCR), naphthenic acid (TAN), basic nitrogen and sulfur level higher than the separated oil (sample-2) obtained from step-2. Additionally, the surface activity of the oil from the gel was an order of magnitude higher than the surface activity of the separated oil. This is evident in the oil/water interfacial tension {IFT (o/w)} values. Thus, in the method of the invention the gel extracts the most surface active sulfur, nitrogen and naphthenic acid compounds. Results of the analyses are shown in Table-1.  
                                       TABLE 1                               Total N   Basic N           IFT (o/w)       Oil   S (%)   (ppm)   (ppm)   TAN   MCCR   dynes/cm                                                            Separated Oil   3.0   3800   960   0.99   6   20       Gel Oil   4.0   4700   1200   1.82   13   2