Process to upgrade oil using metal oxides
Described herein are compositions and methods for using metal oxides to upgrade oil. Metal oxides may be used as catalysts to reduce the TAN of the oil by converting carboxylic acids such as naphthenic acids into non-corrosive products. In some cases, the conversion occurs by a decarboxylation of the carboxylic acid to produce CO2. A second process promoted by metal oxides is hydrocarbon cracking. Cracking decreases the viscosity and increases the API, and produces lower molecular-weight hydrocarbons that are useful for many fuels and lubricants. Reductions in TAN and the increases in API improve the quality of increase the value of oil.
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This application claims the benefit of priority from U.S. Provisional Application Ser. No. 60/586,026, filed Jul. 7, 2004.
GOVERNMENT RIGHTSThe United States Government has certain rights in this invention pursuant to Grant No. DE-FC26-02NT15383; S-105,724 awarded by the U.S. Department of Energy.
FIELD OF THE INVENTIONThe invention relates to methods useful for upgrading, or improving the quality of oil.
BACKGROUND OF THE INVENTIONCrude oil, or petroleum, is a complex mixture of hydrocarbons that is the basis for the world's energy economy. Crude oil, which is usually highly viscous, often contains contaminants, including water, suspended solids, water-soluble salts, and organic acids. These contaminants corrode pipes and oil processing equipment, leading to reduced oil quality.
Naphthenic acids, a collection of unfunctionalized aliphatic, alicylic, and aromatic carboxylic acids, are found to varying degrees in crude oil, and are especially prevalent in heavy or biodegraded oils. Naphthenic acids have a high degree of chemical reactivity, and in addition to being recognized as a major source of corrosion in transportation pipelines and distillation units in refineries, they often react with other materials to form sludge and gum that plug pipelines and operating machinery. As a result, oil products with high concentrations of naphthenic acid are identified as being of poor quality and result in a lower price in the market.
Due to its complex compositional heterogeneity, it is presently very difficult to predict the severity of the corrosion of an individual or a small group of NA compounds by any analytic measurements. A Total Acidity Number (TAN) or the neutralization number (Neut Number), defined by the number of milligrams of KOH required to neutralize the acidity in one gram of oil, is therefore the commonly adopted criterion for predicting the corrosive potential of a crude oil. With this standard, high TAN oils (>0.5 mg KOH/g) are less desirable than lower TAN oils, resulting in a much lower price. Crude oils from California, Venezuela, North Sea, Western Africa, India, China and Russia have typically higher naphthenic acid contents. The development of a naphthenic acid removal process will significantly help the petroleum industry in improving refinery processing of heavy crude oils possessing high contents of naphthenic acid.
Another important component in the process of refining crude oil is the process of converting crude oil into smaller hydrocarbon components that are useful for lighter fuels and lubricants. This process is known as “cracking,” and involves the cleavage of carbon-carbon bonds, resulting in hydrocarbons with lower boiling points. There is an ongoing need in the art for lower-temperature methods that lead to the reduction in oil viscosity.
The conventional method to remove naphthenic acid is based on a caustic wash to neutralize the organic acids present in crude oil. However, this treatment results in the formation of an emulsion that, once formed, is difficult to break down or remove. Furthermore, the salts of many larger naphthenic acids remain in the oil after neutralization. An alternative approach is to mix oil containing high levels of naphthenic acid with oil(s) having a low level of naphthenic acid, thereby diluting the naphthenic acid. While this approach does ultimately reduce the concentration of carboxylic acid in the oil sample, it does not effectively remove naphthenic acids.
Several U.S. patents relate to the process of upgrading oil. For example, U.S. Pat. No. 5,985,137 describes the use of alkaline earth metal oxides as catalysts to reduce the TAN of oil. U.S. Pat. No. 6,547,957 describes a method for decreasing the TAN and increasing the API gravity using non-metal oxide catalysts. U.S. Pat. Nos. 6,096,196 and 5,961,821 describe methods for removing naphthenic acids using alkoxylated amines. However, the techniques described in the aforementioned references, each of which is incorporated by reference herein, are limited in their commercial application or leave room for significant improvement.
Based on the ongoing demand for refined petroleum, there is a significant need in the art for improved techniques to both reduce the viscosity of oil, as well as reduce the amount of naphthenic acids in oil.
SUMMARY OF THE INVENTIONThe invention described herein provides compositions and methods for upgrading oil using metal oxides. One embodiment of the invention comprises a method for upgrading oil, in which a quantity of an oil is contacted with an amount of a metal oxide agent sufficient to upgrade the quantity of oil.
Further embodiments include methods wherein the metal oxide agent is selected from the group consisting of alkaline earth metal oxides, oxidative transition metal oxides, rare earth metal oxides, and combinations thereof.
Additional embodiments include methods wherein the alkaline earth metal oxide is selected from the group consisting of calcium oxide (CaO), magnesium oxide (MgO), as well as oxides of beryllium (Be), oxides of magnesium (Mg), oxides of calcium (Ca), oxides of strontium (Sr), oxides of barium (Ba) oxides of silver (Ag), oxides of copper (Cu), oxides of manganese (Mn), oxides of lead (Pb), oxides of nickel (Ni), oxides of cerium (Ce), oxides of lanthanum (La), oxides of yttrium (Y), oxides of zirconium (Zr), and combinations thereof.
Still further embodiments include methods wherein the oxidative transition metal oxide is selected from the group consisting of AgO, Ag2O, and combinations thereof.
Other embodiments of the invention relate to the temperature of the reaction, wherein the above-described contacting step is performed within a temperature range selected from the group consisting of from about 200° C. to about 450° C., from about 250° C. to about 450° C., from about 300° C. to about 450° C., from about 350° C. to about 450° C., and from about 400° C. to about 450° C., as well as from about 300° C. to about 370° C.
Other embodiments include oil upgrading systems wherein the above-described contacting is carried out in a reaction system selected from the group consisting of a sealed glass tube, an autoclave, a flow reactor, a batch reactor, a slurry reactor, and combinations thereof.
Further embodiments include methods wherein the quantity of oil is located in a subsurface reservoir.
Further embodiments include methods wherein the oil is a fat-based oil.
Further embodiments include methods wherein water is added to dissolve water-soluble impurities.
Further embodiments include methods wherein pyridine, nickel (Ni), copper (Cu), and/or Al2O3 are added to promote acid conversion.
Further embodiments include methods in which the quantity of oil is contacted with an amount of an adsorbent material sufficient to reduce the total acidity of the quantity of oil.
Still further embodiments include methods wherein the adsorbent material is a clay mineral or a mixture of clay minerals. These minerals may be selected from the group consisting of kaolinite, illite, illite-smectite, palygorskite, montmorillonite, Ca-montmorillonite, sepiolite, hectorite, Na-montmorillonite, and combinations thereof. Contacting the quantity of oil with the adsorbent material and with the metal oxide agent may occur in parallel, in series, or simultaneously. Other embodiments include methods wherein the adsorbent material catalyzes acid conversion.
Another embodiment involves a method for reducing the total acidity of a quantity of oil, comprising contacting the quantity of oil with an amount of a metal oxide agent sufficient to reduce the total acidity and/or the total acid number of the quantity of oil.
An additional embodiment includes a method wherein reducing the total acidity comprises reducing a quantity of naphthenic acids in the quantity of oil.
Further embodiments include methods for reducing the viscosity of a quantity of oil, comprising contacting the quantity of oil with an amount of a metal oxide agent sufficient to reduce the viscosity of the quantity of oil. Additional embodiments include methods wherein reducing the viscosity of the quantity of oil comprises increasing the API gravity of the quantity of oil.
Further embodiments include compositions comprising a quantity of an upgraded oil, produced by a process, comprising: providing a quantity of an oil; and contacting the quantity of oil with an amount of a metal oxide agent sufficient to upgrade the quantity of oil.
Still further embodiments include compositions of upgraded oil wherein the metal oxide agent used in its production is selected from the group consisting of alkaline earth metal oxides, oxidative transition metal oxides, rare earth metal oxides, and combinations thereof.
Additional embodiments also include compositions of upgraded oil wherein the process further comprises contacting the quantity of oil or the quantity of upgraded oil with an amount of an adsorbent material sufficient to reduce the total acidity of the quantity of oil or the quantity of upgraded oil.
BRIEF DESCRIPTION OF THE DRAWINGS
The aims of the instant application are to provide cost-effective methods for upgrading and/or improving the quality of oil using metal oxides. In accordance with alternate embodiments of the present invention, two methods that may be implemented separately or together to achieve this are: (1) to reduce the amount of carboxylic acids, such as naphthenic acids, present in the oil, and (2) to decrease the viscosity of the oil. The present invention is based on surprising studies that demonstrated that metal oxides can be used to upgrade oil. Other features may be added to the process, as described in greater detail in the ensuing discussion. Treatment of oil with the metal oxides disclosed herein may improve the quality of oil by both decreasing carboxylic acid levels and by decreasing the viscosity of the oil.
Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. One skilled in the art will recognize many methods and materials similar or equivalent to those described herein, which could be used in the practice of the present invention. Indeed, the present invention is in no way limited to the methods and materials described.
As used herein, the term “oil” refers to a liquid, hydrocarbon or fat-based substance that is derived from animals, plants, mineral deposits, or is manufactured artificially. Oils are generally not miscible with water. The term “oil” also encompasses petroleum and petroleum derivatives.
As used herein, the term “petroleum,” or crude oil, refers to a naturally occurring mixture composed predominantly of hydrocarbons in the gaseous, liquid or solid phase. Petroleum can be processed (refined) into a number of useful products including asphalt, diesel fuel, fuel oil, gasoline, jet fuel, lubricating oil, and plastics.
Two mechanisms to reduce the levels of carboxylic acids in oil include: (1) acid conversion, a process by which carboxylic acids are converted into non-corrosive components, and (2) the use of a solid adsorbent to remove carboxylic acids from the system. A goal of both of these processes is to reduce the Total Acid Number (TAN) of the sample. In connection with various embodiments of the present invention, these techniques may be implemented together or separately.
The TAN, or neutralization number, is defined by the number of milligrams of KOH required to neutralize the acidity in one gram of oil. The TAN and the neutralization number are the commonly adopted criterion for predicting the corrosive potential of crude oil. High TAN oils (>0.5 mg KOH/g) are less desirable than lower TAN oils, resulting in a much lower price when such oils are sold in the market. Crude oils from California, Venezuela, North Sea, Western Africa, India, China and Russia typically have a higher TAN than crude oil obtained from other sources.
Another technique for improving the quality of oil is to decrease the viscosity of oil by converting large hydrocarbons into smaller ones. This process is also known as “cracking.” Viscosity is a measure of the resistance of a fluid to deformation under shear stress. It is commonly perceived as “thickness,” or resistance to pouring. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. A useful unit for quantitating viscosity is the “centipoise,” or cP. An alternate unit for viscosity that is often used is “API gravity.”
The term “API gravity” refers to the commonly accepted scale adopted by the American Petroleum Institute (API) for expressing the density of liquid petroleum products. The API gravity is related to the specific gravity, which is the ratio of mass of any material to the mass of the same volume of pure water at 4° C. Units of API gravity are expressed as degrees, and in general, the higher the API gravity, the lighter the oil and the lower the viscosity. Crude oil is often classified as light, medium or heavy, according to its measured API gravity. Generally speaking, higher API gravity degree oil values have a greater commercial value and lower degree values have lower commercial value.
As used herein, the term “cracking” refers to a process by which complex substances, such as the high molecular weight hydrocarbons in petroleum, are broken down into smaller molecules (that tend to have lower boiling points). Cracking generally involves breaking carbon-carbon bonds. Cracking may occur as a result of a number of processes including heat (thermal cracking) and catalysis (catalytic cracking). Treatment of oil with metal oxides may increase the quality of the oil by promoting the cracking process. Contacting oil with one or more metal oxides may allow the cracking process to occur at lower temperatures.
As used herein, the term “upgrade” refers to a process in which the quality of an oil is improved. Upgraded oil may be defined as oil that has undergone a process resulting in a substantial decrease in its total acidity, a substantial increase in its viscosity, or a combination thereof. A “substantial” decrease in the total acidity, as that term is used herein to modify total acidity, may be defined as a decrease in the TAN that is greater than one TAN unit. A “substantial” decrease in the viscosity, as that term is used herein to modify viscosity, may be defined as an increase in the API gravity that is greater than one API degree, or a decrease in the cP number by greater than one cP.
A process of upgrading oil is illustrated in
Acid conversion is a process by which organic carboxylic acids such as naphthenic acid are decarboxylated, often resulting in a decrease in the TAN. One possible product of acid conversion is carbon dioxide (CO2). However, acid conversion may also occur in the absence of CO2 production. Other possible products of acid conversion include the formation of carboxylic acid salts through traditional acid-base reaction and/or the formation of alkaline earth metal carbonates through the adsorption of CO2 by metal oxides. Examples of reactions that may occur during a metal oxide-mediated acid conversion are illustrated in
An alternative method to acid conversion for decreasing the TAN involves the binding of carboxylic acids by an adsorbent solid material. An adsorbent is a material that is capable of the binding or collecting substances or particles on its surface. As will be readily recognized by those of skill in the art, a number of adsorbent materials may be used to remove acids from oil and/or reduce the TAN, including, by way of example, a number of different clays. In one embodiment of the present invention, adsorption and catalytic acid conversion may be performed individually, or in series, as shown in
In a further embodiment of the present invention, the acid conversion and the adsorption may be carried out in parallel, as shown in
In yet another embodiment of the present invention, adsorption and acid conversion occur simultaneously with a quantity of oil. Indeed, as will be readily recognized by those of skill in the art, a single material may be used to perform both adsorption and acid conversion simultaneously. For instance, a number of different metal-oxide containing clay minerals may be able to catalyze both the acid conversion and the adsorption.
Metal oxides are defined as compounds comprising one or more metal atoms combined with one or more oxygen molecules. Different classes of metal oxides include alkaline earth metal oxides, oxidative transition metal oxides, and rare earth metal oxides. Examples of alkaline earth metal oxides include, but are not limited to, oxides of calcium (Ca), strontium (Sr), magnesium (Mg), and barium (Ba). Examples of oxidative transition metal oxides include, but are not limited to, oxides of silver (Ag), copper (Cu), manganese (Mn), lead (Pb), nickel (Ni), cobalt (Co), and iron (Fe). Examples of rare earth metal oxides include, but are not limited to, oxides of the lanthanide series, as well as cerium (Ce), lanthanum (La), yttrium (Y), and zirconium (Zr), and scandium (Sc). As will be readily recognized by those of skill in the art, there are many metal oxides suitable for use in connection with alternate embodiments of the present invention.
The term “metal oxide agent,” as used herein, refers to a metal oxide or mixture of metal oxides. A metal oxide agent may also comprise other additional inert ingredients.
The term “contacting,” as used herein, refers to a process by which two or more reaction components are placed in sufficiently close proximity to one another such that they are able to chemically react with one other.
The term “naphthenic acids,” as used herein, refers to a group of unfunctionalized aliphatic, alicylic, and aromatic carboxylic acids that are often found in petroleum and petroleum products. Naphthoic acid is a type of naphthenic acid that generally has the formula CnH2n.
One of skill in the art will recognize that there are a variety of different types of reactors that would be suitable for the process of upgrading oil in connection with alternate embodiments of the instant invention. Several examples are provided here, but the application of the instant invention is not in any way limited to the use of these particular reactors. One system for carrying out an acid conversion reaction is a sealed glass tube batch reactor. An acid sample, catalyst, and/or other additive (if any), in milligram quantities, may be sealed in a glass tube under a vacuum. The sealed glass tubes may then be placed in oven to start a desired reaction under controlled reaction conditions. The reactions may be carried out at the temperature range of from about 200° C. to about 450° C. for about 4 hours, although temperatures outside this range as well as longer or shorter incubation times may also be suitable; particularly depending upon the configuration of the system and its scale. The reaction gas may be collected and quantified in a vacuum line using a standard gas transfer method.
For crude oil test experiments, larger sample volumes are often needed, and an alternative experimental procedure that uses an autoclave reactor has been established. For example, an autoclave reactor with the volume of approximately 40 mL may used. A sample operation procedure is as follows: (i) a quantity of an oil and a metal oxide agent (2˜5 wt % of oil) are added to the reactor; (ii) the components are mixed by shaking the reactor for one hour; (iii) the reaction is incubated at a temperature range of 250-300° C. for 4 hours while keeping the reactor moving to maintain contact between the reactants and catalysts; (iv) the reactor is cooled at the end of the reaction and the treated oil is recovered by solvent extraction using dichloromethane or another suitable solvent. The solvent extraction may be carried out, for example, by vacuum filtration and followed by evaporation of the solvent.
As illustratively depicted in
In a flow reactor setup, a pump 400 is used to pump decane, or another suitable solvent, into a transfer vessel 402 at a constant flow rate. Pressure gauges 1 and 2 (401 and 403, respectively) indicate system pressure changes upstream and downstream of the transfer vessel. Crude oil is added to the other side of the transfer vessel and is pressed out by the decane through a transfer piston. An N2 (or other suitable gas) purge line 404 may be used to purge the oil from the system after the reaction. The catalysis takes place in a furnace 405, which is regulated by a temperature control unit 406. The resulting oil may be collected in a vessel 407 at the end of the reaction. The reaction may have stop valves (408 and 409, respectively). The transfer tubing lines and valves may be wrapped with heating tape and maintained at or about 80° C. to keep the oil at a temperature where it flows easily; although this temperature can be varied in connection with alternate embodiments of the present invention. Optional components of a flow reactor system include, but are not limited to, flow control units, heat supply sources, oil recycling loops, oil cooling units, and the like, which will be readily recognized by those of skill in the art. A fixed-bed flow reactor system may be scaled up to accommodate reaction volumes required for industrial applications.
Other types of reaction systems that may be suitable for the acid conversion process include a batch reactor system and a slurry reactor system. A batch reactor is a system in which the reaction components are added to a tank or other suitable container. In general, all reaction components are added at the beginning of the reaction, and products remain in the tank until the reaction has progressed for the desired amount of time. Following the reaction, the products are removed for analysis or further processing. A slurry reactor is similar to a batch reactor, except that the catalyst is continuously mixed with the reactants to maintain the reaction mixture as a slurry, which is defined as a liquid containing suspended solids. Both batch and slurry reactor systems may be readily scaled up to accommodate the needs of an industrial setting by persons having ordinary skill in the art.
Decarboxylization is significant in the acid conversion process. Theoretical studies of the decarboxylation mechanism suggest that the radical pathway will be predominant when transition metals such as Cu(II) and Mn(III) are involved. These cation species are able to generate an internal electron-transfer due to the closed-shell (from Cu(II), −3d9 to Cu(I), −3d10 electronic configurations) and half closed-shell (from Mn(III) −3d4 to Mn(II) −3d5 electronic configurations). These studies also suggest that the concerted pathways may be a mechanism when involving base metals. In a concerted pathway, a nucleophilic attack on the β-carbon is the initiative step. These studies still further suggest that the hydroxyl group on the metal surface may assist the breaking of the carbon-carbon bond. While not wishing to be bound by any particular theory, it is believed possible that basic conditions promote the initial base-acid reaction, while acidic conditions promote the subsequent decarboxylation reaction.
In addition to acid conversion, adsorption is an effective method for removing carboxylic acids, such as naphthenic acid, from oil. The “adsorbent material” refers to a material that has a capacity or tendency to adsorb another substance. Clay minerals have been used as solid absorbents to remove naphthenic acid. The major components of clay minerals are silica, alumina, and water, frequently with appreciable quantities of iron, alkali, and alkaline earth cations. Natural clays usually have high cation-exchange capacity (CEC) and surface areas. In addition, they are inexpensive and environmentally friendly. Clay minerals may interact with many organic compounds to form complexes of varying stabilities and properties. Clay organic interactions are multivariable reactions involving the silicate layers, the inorganic cations, water and the organic molecules. The chemical affinity between the acid compound and the solid surface depends on structure (molecular weight, chain length, etc.) of the acid molecule, functional groups present in the acid molecule such as hydrophobic groups (—C—C—C—C—), electronegative groups (—C═O, —C—O—C—, —OH), π bonds (—C═C—, aromatic rings), and configuration of the acid molecule (Kowalska, M. et al., The Sci. of the Total Environ., (1994) 141, 223-240). Examples of clays that may be useful for adsorbing metal oxides include but are not limited to kaolinite, illite, illite-smectite, palygorskite, montmorillonite, Ca-montmorillonite, sepiolite, hectorite, and Na-montmorillonite.
Zeolites may also be used to partially upgrade oil. Zeolites are synthetic or naturally-occurring minerals that have a porous structure. In general, they are hydrated alumino-silicate minerals with an open structure that can accommodate a variety of positive ions as well as other compounds. Some of the more common naturally-occurring mineral zeolites are: analcime, chabazite, heulandite, natrolite, phillipsite, and stilbite. An example mineral formula is: Na2Al2Si3O10-2H2O, the formula for natrolite. Natural zeolites form where volcanic rocks and ash layers react with alkaline groundwater. There are several types of synthetic zeolites that form by a process of slow crystallization of a silica-alumina gel in the presence of alkalis and organic templates. Zeolites in the ZSM and HZSM families may be coated with substances that may be useful for upgrading oil. ZSM-5 is already well known for its utility in cracking oil.
The methods described above are useful for removing corrosive materials such as carboxylic acids from petroleum. However, this process is also suitable for other fat-based oils, such as plant and animal-derived oils, as will be readily recognized by those in this, and related fields of art, and the application of the inventive technology to such related fields is considered to be within the ambit of the present invention. These other types of oil often contain naphthenic acids that lead to unwanted chemical reactions that negatively affect their stability. Therefore, methods of removing acids in these types of oils is a useful goal and lies within the scope of this invention.
Methods for upgrading the quality of oil are applicable both above the surface of the earth, as well as below the surface, such as in an underground oil reservoir. The reactors used in connection with alternate embodiments of the present invention may thus be configured for use in above-ground or underground settings. Either or both of these configurations may be desirable depending upon the particular industrial application of the inventive technology.
In an alternate embodiment of the present invention, a range of different substances may be added to one or more of the oil upgrade reactions described herein that aid in the reaction process or promote or enhance the upgrade. Some such additives are water and pyridine, copper, nickel, Al2O3 and other metallic or organic substances.
An individual of ordinary skill in the art will recognize that the processes described herein may be carried out at a variety of different temperatures, for varying lengths of time, depending on the type of reactor, sample size and a number of other conditions. Examples of temperature ranges that may be suitable for contacting a sample of oil with a metal oxide in connection with alternate embodiments of the present invention are as follows, although are in no way limited to: from about 200° C. to about 450° C., from about 250° C. to about 450° C., from about 300° C. to about 450° C., from about 350° C. to about 450° C., from about 400° C. to about 450° C., and from about 300° C. to about 370° C. These ranges are given by way of illustration and not by way of limitation.
The following examples are offered by way of illustration, and not by way of limitation.
EXAMPLE 1Total Acid Number Measurement
An in-house Total Acid Number (TAN) measurement method was developed following the procedure of ASTM standard method D664. The principle of this measurement is based on non-aqueous acid base potentiometric titration determined by a PH/mv meter (Oakton PH510 Series).
Procedures
Preparation of Alcoholic Potassium Hydroxide Solution
6 g of KOH were added to approximately 1 L of anhydrous isopropanol. The solution was then gently boiled for 30 min to increase the solubility of KOH in the solution. The solution was stored overnight and then standardized with potassium acid phthalate (KHC8H4O4 or KHP).
Standardization of Alcoholic KOH Solution
The solution was standardized with potentiometric titration of weighed quantities of KHP dissolved in CO2-free water.
Preparation of Oil Sample
One 5 g oil sample was dissolved in 125 mL titration solvent (500 mL toluene/495 mL anhydrous isopropanol/5 mL water). The resulting solution was then filtered and transferred to a 250 mL beaker, which is used as the titration vessel.
Titration of KOH to Oil Sample
A suitable amount of KOH alcoholic solution was added. Once a constant potential has been observed, the meter readings were recorded. When the sample has been titrated close to the inflection point, fewer drops of KOH were added. For each set of samples, a parallel blank titration was performed as a control.
Calculation
The volumes of KOH solution added versus the corresponding electrode potential (mv) were plotted. The inflection points A and B for oil sample and solvent only were marked, which are believed to reflect the largest potential changes for a unit KOH. The TAN was calculated using the following equation: Acid number (mg KOH/g)=(A−B)×M×56.1/W, in which M is the concentration of alcoholic KOH solution (mol/L) and W is the sample mass (g).
Results
Two typical titration curves for KOH to KHP and KOH to oil are shown in
This Example outlines a process useful for the catalytic decarboxylation of naphthenic acids in crude oil. MgO was shown to have decarboxylation activity with both saturated and aromatic model naphthenic acid compounds in a 4 hour reaction carried out at a temperature range of 150° C. to 250° C. In the presence of Ag2O, the amount of CO2 produced matched the amount of the other decarboxylation product, naphthalene, resulting in a “direct” catalytic decarboxylation. These findings provide a low-temperature, cost-effective catalytic decarboxylation process to remove naphthenic acids from oil. Furthermore, this Example demonstrates that catalytic decarboxylation reactions of naphthenic acids in the presence of various solid catalysts have been investigated. Among catalysts tested, MgO exhibits the high reactivity toward the decarboxylation of model saturated and aromatic naphthenic acid compounds. Ag2O not only promotes acid conversion, but also “directly” converts naphthoic acid to naphthalene.
Experimental Methods
Selected Model Compounds and Oil Samples
A pair of carboxylic acids, naphthoic acid (C10H7COOH) and cyclohexane carboxylic acid (CHCA) were selected as the model compounds to represent the aromatic and saturated naphthenic acids.
Five organic acids (cyclopentane carboxylic acid (CPCA), cyclohexane carboxylic acid (CHCA), benzoic acid (BA), C5H11—CHCA and C7H15-BA) were dissolved in dodecane resulting in weight concentrations in a range of 0.871%˜2.471%.
Texaco crude oil, donated by ChevronTexaco with Total Acid Number (TAN) of 4.38 was used in the study.
Experimental Setups
NA sample, catalyst, and other additive, in orders of milligram, were sealed in a glass tube under a reduced atmosphere. The sealed glass tubes were placed in oven to undergo reaction under with a controlled temperature. The gas produced by the reaction was collected and quantified in a vacuum line via a standard gas transfer method.
For crude oil test experiments, a different experimental procedure was established that used a 40 mL autoclave reactor to carry out the reaction instead a glass tube. Detailed description of the procedure is as follows: (i) 12 g oil and 0.24-0.60 g catalyst (2˜5 wt % of oil) were loaded into the reactor; (ii) the two components were pre-mixed by shaking the reactor for one hour; (iii) the reaction was allowed to run at temperature of 250˜300° C. for 4 hours with the continuous shaking of the reactor to achieve a good contact between the oil and the catalyst; (iv) after the desired reaction time had elapsed, the reactor was cooled, and the treated oil was separated from the catalyst by vacuum filtration.
Analysis Methods
The reaction gas was collected and quantified in a vacuum line via a standard gas transfer method. The resulting gas was then analyzed with GC to quantify the amount of CO2 and other gases produced in the reaction. The solid residue, which presumably contained the unreacted acids, was extracted using dichloromethane and subjected to GC analysis. These numbers were used to calculate the amount of acid conversion that occurred.
For crude oil tests, the Total Acid Numbers (TAN) of the naphthenic samples, before and after reactions, were measured by Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration, ASTM-D 664. This work was performed at The Oil Analysis Lab.
Theoretical Methods
The gas phase geometries of reactants, products, intermediates and transition states (TS) have been optimized using the B3LYP flavor of density functional theory. The 6-31G(d) basis set for all of computations were used. All stationary points have positively identified for local minima (zero imaginary frequencies) and for TS (one imaginary frequency). Vibration frequencies were also calculated at all stationary points to obtain zero point energies (ZPE) and thermodynamic parameters.
Results
Catalytic Decarboxylation of Model Compounds
Table 2 lists the CO2 generation of catalytic reactions. Among the various solid catalysts that were tested, the amounts of the CO2 generated from MgO for both saturated and aromatics (30.38 and 33.20 ml/g, corresponding to the 17.4% and 25.5% mol conversion) were much higher than that from other solid catalysts. A lack of CO2 formation does not necessarily mean that acid conversion did not occur, as it is likely that some of the CO2 was adsorbed by the metal oxides to form carbonates. However, detection of CO2 clearly indicates the conversion of acid compounds. MgO exhibited the highest reactivity towards the decarboxylation of the naphthenic compounds. Addition of the organic bases, such as pyridine, can slightly promoted the catalytic reactivity. In the presence of pyridine, MgO catalyzed decarboxylation occured at temperatures as low as 100° C.
Reaction temperature and time are 200° C. and 4 hrs, expect for b reaction temperature and time for 100° C. and 4 hrs.
Catalytic Decarboxylation of the Acid Mixture
To test effectiveness of the developed MgO series catalyst on decarboxylation of organic acids, a mixture of five acid compounds was prepared to partly simulate an oil composition with an elevated acid content. As listed in Table 3, higher acid conversions were obtained from MgO, in the case of a single acid test. The acid conversions were further improved when small amounts of Ni and Cu were loaded on MgO and the conversions reached >90%.
CPCA, cyclopentane carboxylic acid;
CHCA, cyclohexane carboxylic acid,
BA, benzoic acid, 200° C., 4 hr.
MgO-Catalyzed Decarboxylation Reactions
The temperature dependence and MgO loading effect of naphthenic acid decomposition during the reaction was investigated. The reactions were run separately by changing reaction temperatures in the range of 100 to 300° C. at a fixed MgO loading, 20 wt %, and changing the MgO loading from 0 to 40 wt % at 250° C. Gaseous and the remaining solid products were analyzed to obtain the data for the CO2 yield as well as the acid conversion.
The results as shown in
Mechanistic Studies of the MgO-Catalyzed Decarboxylation Reaction
A plausible concerted oxidative decarboxylation pathway in the presence of MgO has been theoretically studied in gas-phase with the energy diagram of all of stable, intermediated and transition states computed. The reaction path is summarized as a three-step mechanism that converts benzoic acid to phenol, as shown in
-
- Step 1: Nucleophilic attack at the C atom of the carboxyl group, from (A) to (B);
- Step 2: Transfer of the hydroxy group via a 4-member ring transition state, from (B) to (D) through TS-1 (C);
- Step 3: Proton transfer accomplishing by decarboxylation, from (D) to (F) through TS-2 (E).
The computed transition barrier for TS-1, featuring attacking of the hydroxy group on the ortho-position of the aromatic ring (˜30 kcal/mol) is consistent with experimental conditions (200° C., 4 hrs) disclosed herein. The barrier for TS-2, featuring proton transferring from ortho- to ipso- (49 kcal/mol), however, is higher than expected. This could be partially due to the fact that only gas-phase, single-molecule calculations were performed. Further calculations with larger metal oxide clusters, and/or water assisting are expected to lower this barrier.
The CO2 Yield vs. the Acid Conversion
While most of the metal oxides tested did result in CO2 production, acid conversion may still have occurred. In fact, by comparing the CO2 yield and the acid conversion in the presence of several metal oxides, as shown in Table 4, is becomes clear that the acid conversion is in general much higher than the CO2 yield in most cases. This large difference could be either due to the formation of carboxylic acid salts through a traditional acid-base reaction, or the formation of alkaline earth metal carbonates through the adsorption of CO2 by metal oxides. These formations are, however, known to lead to series emulation problems that make them less appealing. In this sense, the case of Ag2O is certainly a good choice of “clean” catalyst, because the acid conversion agrees with the CO2 yield. Furthermore, the decarboxylated product, naphthalene, was also detected. This clearly indicates that a “direct” catalytic decarboxylation reaction did occur.
250° C.; cat ˜10 mg
Test Runs with Crude Oil
The results of initial test runs of a group of metal oxide catalysts as reagents towards the decarboxylation reaction of crude oils are illustrated in
Several rare earth metal oxides, including CeO2, La2O3, Y2O3 and ZrO2 were tested with model acid, naphthoic acid (C10H7COOH) and the result was shown in Table 2. The low CO2 yields, defined as the carbon conversion to CO2 as shown in Table 5, suggest that they were inactive towards catalytic decarboxylation. The metal oxide ZrO2 exhibited acid-base dual functionalities.
NA, C10H7COOH, 2-naphthoic acid
More oxidative metal oxides were investigated in the catalytic decarboxylation of model compounds, naphthoic acid and cyclohexane pentanoic acid. The latter is considered to be more representative as the component of naphthenic acid in crude oil. The tested metal oxides include Ag2O, AgO, MnO2, Mn2O3, PbO2, CuO, Cu2O, Fe2O3 and CO2O3. All of these metal oxides have variable oxidative states.
The data in Table 6 show that the CO2 formation, which is an indication of the catalytic decarboxylation, was detected in each case except for Fe2O3. At the temperature of 250° C., the CO2 yields were all lower than 10% although the acid conversion could reach higher. Increasing the reaction temperature to 300° C. resulted in the higher CO2 yields, as well as higher acid conversions, suggesting that the catalytic activities of these metal oxides are temperature sensitive. Importantly, the CO2 yield from Ag2O reached as high as 96.93%, indicating the naphthoic acid has been almost completely converted to CO2. The high acid conversion of 93.3% is consistent with these data. In addition, naphthalene, as another important decarboxylated product, was also detected. The yield of naphthalene, defined as the carbon conversion to naphthalene, reached 66.2%. Moreover, The GC-MS analysis also identified the formation of 1,2′-binaphthalene and 2,2′-binaphthalene (C20H14). These byproducts might be the result of dimerization of naphthalene. This result strongly suggested that the reaction occurred through a radical mechanism.
Comparison of the same metal atoms at different oxidative states does not show a general trend on their decarboxylation efficiency. For instance, Ag(I) is much more active than Ag(II), but Mn(IV) yields more CO2 than Mn(III), while Cu(I) and Cu(II) gave almost equal CO2 yields at the temperature of 300° C.
When applying Ag2O, MnO2 and PbO2 to a new acid substrate, cyclohexane pentanoic acid (CHPA), CO2 was also detected although the yields were not as high due to the lower reaction temperature. These results show promise for the application of oxidative metal oxide catalysts to react with diverse acid substrate structures.
Regarding the mechanism of catalytic decarboxylation on oxidative metal oxides, oxidative decarboxylation via radical intermediate would be the most plausible reaction path. Accordingly, the oxidative abilities of these compounds will be essential to the activities.
NA, C10H7COOH, 2-naphthoic acid
CHPA, C6H11C4H8COOH, Cyclohexane pentanoic acid
The TAN, oil viscosity and IR adsorption of the treated oil were measured at different reaction stages using multiple cold traps. Two catalysts, MgO and MnO2, were investigated. MgO and MnO2 have been shown to be effective to the decarboxylation of model compounds and the removal of naphthenic acid from crude oil in batch reaction tests.
In the reaction, 0.5 g of catalyst (particle size 28-65) and crude oil from Texaco with 2% CHPA added were added to a reactor at a flow rate of 3-4 g/hr. During the reaction, infrared spectroscopy (IR) was used to monitor the effectiveness of the catalyst. The catalyst was considered to be deactivated if the RCOOH absorption (as indicated by a peak at around 1,700 nm) significantly recovered. When this occurred, the reaction was complete. The oils were collected at different reaction intervals and were subjected to TAN analysis and viscosity measurement.
The thermal treatment results at different temperatures are shown in
For MgO catalyst, the reaction was continuously run for 29.25 hr in total (80° C. for 2 hr, 150° C. for 2 hr, 250° C. for 21.33 hr, and 300° C. for 4 hr) with the result shown in
The inventors further increased the reaction temperature to 300° C. and the oil was treated with MgO catalyst for a longer time, as illustrated in
On the role of MgO to acid removal, it is considered have multiple mechanisms. The results with model acid compound identified its decarboxylation activity, due to the CO2 formation. Meanwhile, because of its inherent strong basicity, MgO will also tend to react with acid through acid-base neutralizsation. At higher temperature, MgO is reported to be active to promote C—C cracking of hydrocarbons.
The inventors ran a flow test on MnO2, as illustrated in
MgO, 0.5 mg
MgO 0.5 g, 300° C., 350° C.
Feed, Oil + 2% CHPA
Flow rate: 4.57˜2.08 ml/hr
Model naphthenic acid (NA) solutions were prepared by using four commercial NAs (i.e., cyclohexanepropionic acid (NA1), benzoic acid (NA2), cyclohexanepentanoic acid (NA3), and 4-heptylbenzoic acid (NA4)) with tetradecane dissolved in dodecane (C12). Their concentrations were about 0.5% each in weight percent. Several clay samples (from the Source Clay Repository of Clay Mineral Society at Purdue University, West Lafayette, Ind.), ie., kaolin (KGa-2), illite (IMt-1), illite-smectite mixed layer 60/40 (ISMt-2), illite-smectite mixed layer 70/30 (ISCz-1), palygorskite (PF1-1), montmorillonite (SAz-1), Ca-montmorillonite (SAz-2), montmorillonite, CA (SCa-3), sepiolite (SepSp-1), hectorite (SHCa-1), and Na-montmorillonite, WY (SWy-2), were chosen as model absorbents for this study. The chemical compositions of clay minerals used are shown in Table 11.
The adsorption experiments were carried out using the batch equilibration technique. Desired amounts of a NAs solution were added to different glass centrifuge tubes, which contained known amounts of clay minerals. The tubes were shaken at 25° C. and 66° C. for 24 hours, followed by centrifugation for 10 min. Supernatants were sampled and subject to analysis to determine the NA concentration using a Hewlett Packard Gas Chromatography-Mass Spectroscopy (GC-MS). No changes in solute concentrations without clays were detected in the tubes within the experimental period. Therefore, solute mass lost in the supernatant from clay slurries was assumed to be adsorbed by clay. The amount of NAs adsorbed was calculated from the difference between the initial and equilibrium solute concentration in dodecane solution.
Table 12 summarizes the results of NAs adsorbed onto the selected clay absorbents. The order of the affinity of various clays as adsorbents to NAs is: SepSp-1>SWy-2>SAz-1>PF1-1>SHCa-1≧SCa-3>SAz-2>IMt-1>IScz-1>KGa-2>ISMt-2. In addition, in each test no significant adsorption was observed for tetradecane. This result shows that these clay adsorbents are selective toward NAs but not hydrocarbon. This demonstrates that sepiolite (SepSp-1) and Na-montmorillonite (SWy-2) are potential efficient adsorbents for removing NAs from crude oil. The capacity of the adsorption of NAs reached 68 and 53 mg-acid/g-clay for SepSp-1 and SWy-2, respectively. In contrast, ISCz-1 was found to be inactive towards the acid adsorption. In most of clays used, the order of the affinity of four NAs adsorbed onto clays is: NA2>NA3>NA1>NA4, except onto KGa-2. The adsorption of benzoic acid onto the clays was more effective in comparison with the adsorption of other NAs. Benzoic acid with an aromatic ring showed strong effect on physical-chemical adsorption.
The analysis of the minerals is reported as percentages of oxide, rather than as percentages of metals as shown in Table 11. The NA adsorption was correlated with the concentrations of MgO, CaO, and Na2O, individually or together. The amount of NAs adsorbed was found to roughly increase with the amount of MgO (
NA1 = Cyclohexanepropionic acid, FW = 156.23
NA2 = Benzoic acid, FW = 122.1
NA3 = Cyclohexanepentanoic acid, FW = 184.28
NA4 = 4-Heptylbenzoic acid, FW = 220.31
1 g MgO with a particle size of 20-60 mesh was added to a sample of crude oil in a flow reactor. Reactions were carried out at 300° C. and 350° C. The reaction run at 300° C. was run for 54 hr, and during the reaction, the flow rate of the oil changed from 15.35 to 1.76 mL/hr, mostly in the range of 2-5 mL/hr. The total oil collected during the reaction was 206.23 g. The TAN changes at the different reaction stages are plotted in
MgO 1.0 g, 20-60 mesh
For the reaction sample that was tested at 350° C. for 7.7 hr, the TAN decreased from 4.72 to 1.75, and the viscosity decreased from 6,300 cP to 174 cP at 40° C. The estimated API for the treated oil was 18 degrees, and the original feed (crude oil) was around 13 degrees.
A similar reaction was carried out at 325° C. for 8 hr. In this case, the TAN decreased from 4.72 to 2.91, and the viscosity at the end was roughly half of what it was at the beginning.
EXAMPLE 8 Reaction of Mixed Acid in the Presence of Catalysts Acid conversion analyses were performed using MgO in the presence of nickel and Al2O3. A mixed acid solution comprising the following acids was used: CPCA (cyclopentane carboxylic acid) 2.47%; CHCA (cyclohexane carboxylic acid) 1.93%; BA (benzoic acid) 0.87%; C5H11-CHCA 1010%; C7H15-BA 1.11%. The solvent used for the reaction was decane. The reaction was carried out at 200° C. for 4 hours. The results are shown below in Table 14.
In flow reaction 20 (FR20), the reaction was run continuously for 164 hours with 1.0 g MgO at 325° C. with a flow rate of 2.05 to 6.56 mL/hr. In this reaction, glass beads were added to the catalyst to suppress movement of catalyst particles. In addition, the MgO used had a mesh size of 40-60. The TANs for the treated oil in this reaction were reduced by about 20-30%. The results of FR20 are shown in Table 15.
In an additional reaction, (FR21), the temperature was raised to 350° C., and the flow rate was set to 1.0 mL/hr, and the reaction was run for 40.9 hrs. In this case, the TAN decreased from 4.71 to 1.74, and the viscosity decreased from 6,300 to 282 cP (at 40° C.). The API of the resulting oil is estimated to be 17.7 degrees. The results of FR20 are shown in Table 16.
Claims
1. A method for upgrading oil, comprising contacting a quantity of an oil with an amount of a metal oxide agent sufficient to upgrade the quantity of oil.
2. The method of claim 1, wherein the metal oxide agent is selected from the group consisting of alkaline earth metal oxides, oxidative transition metal oxides, rare earth metal oxides, and combinations thereof.
3. The method of claim 2, wherein the alkaline earth metal oxide is selected from the group consisting of oxides of beryllium (Be), oxides of magnesium (Mg), oxides of calcium (Ca), oxides of strontium (Sr), oxides of barium (Ba), and combinations thereof.
4. The method of claim 3, wherein the alkaline earth metal oxide is selected from the group consisting of calcium oxide (CaO), magnesium oxide (MgO), and combinations thereof.
5. The method of claim 2, wherein the oxidative transition metal oxide is selected from the group consisting of oxides of silver (Ag), oxides of copper (Cu), oxides of manganese (Mn), oxides of lead (Pb), oxides of nickel (Ni), and combinations thereof.
6. The method of claim 5, wherein the oxidative transition metal oxide is selected from the group consisting of AgO, Ag2O, and combinations thereof.
7. The method of claim 2, wherein the rare earth metal oxide is selected from the group consisting of oxides of cerium (Ce), oxides of lanthanum (La), oxides of yttrium (Y), oxides of zirconium (Zr), and combinations thereof.
8. The method of claim 1, wherein contacting is performed within a temperature range selected from the group consisting of from about 200° C. to about 450° C., from about 250° C. to about 450° C., from about 300° C. to about 450° C., from about 350° C. to about 450° C., and from about 400° C. to about 450° C.
9. The method of claim 1, wherein contacting is performed within a temperature range of from about 300° C. to about 370° C.
10. The method of claim 1, wherein contacting is carried out in a reaction system selected from the group consisting of a sealed glass tube, an autoclave, a flow reactor, a batch reactor, a slurry reactor, and combinations thereof.
11. The method of claim 1, wherein the quantity of oil is located in a subsurface reservoir.
12. The method of claim 1, wherein the oil is a fat-based oil.
13. The method of claim 1, further comprising adding a quantity of water to dissolve water-soluble impurities.
14. The method of claim 1, further comprising adding a quantity of pyridine to promote acid conversion.
15. The method of claim 1, further comprising adding a quantity of nickel (Ni) to promote acid conversion.
16. The method of claim 1, further comprising adding a quantity of copper (Cu) to promote acid conversion.
17. The method of claim 1, further comprising adding a quantity of Al2O3 to promote acid conversion.
18. The method of claim 1, further comprising contacting the quantity of oil with an amount of an adsorbent material sufficient to reduce the total acidity of the quantity of oil.
19. The method of claim 18, wherein the adsorbent material is a clay mineral or a mixture of clay minerals.
20. The method of claim 18, wherein the clay mineral is selected from the group consisting of kaolinite, illite, illite-smectite, palygorskite, montmorillonite, Ca-montmorillonite, sepiolite, hectorite, Na-montmorillonite, and combinations thereof.
21. The method of claim 18, wherein contacting the quantity of oil with the amount of the metal oxide agent and contacting the quantity of oil with the adsorbent material occur in parallel, in series, or simultaneously.
22. The method of claim 18, wherein the adsorbent material catalyzes acid conversion.
23. A method for reducing the total acidity of a quantity of oil, comprising contacting the quantity of oil with an amount of a metal oxide agent sufficient to reduce the total acidity of the quantity of oil.
24. The method of claim 23, further comprising reducing the total acid number of the oil.
25. The method of claim 23, further comprising reducing a quantity of naphthenic acids in said quantity of oil.
26. A method of reducing the viscosity of a quantity of oil, comprising contacting the quantity of oil with an amount of a metal oxide agent sufficient to reduce the viscosity of the quantity of oil.
27. The method of claim 26, further comprising increasing the API gravity of the quantity of oil.
28. A composition comprising a quantity of an upgraded oil, produced by a process, comprising:
- providing a quantity of an oil; and
- contacting the quantity of oil with an amount of a metal oxide agent sufficient to upgrade the quantity of oil,
- whereby the quantity of upgraded oil is produced.
29. The composition of claim 28, wherein the metal oxide agent is selected from the group consisting of alkaline earth metal oxides, oxidative transition metal oxides, rare earth metal oxides, and combinations thereof.
30. The composition of claim 28, wherein the process further comprises contacting the quantity of oil or the quantity of upgraded oil with an amount of an adsorbent material sufficient to reduce the total acidity of the quantity of oil or the quantity of upgraded oil.
Type: Application
Filed: Jul 7, 2005
Publication Date: Jan 26, 2006
Applicant: California Institute of Technology (Pasadena, CA)
Inventors: Yongchun Tang (Walnut, CA), Aihua Zhang (Pasadena, CA)
Application Number: 11/176,716
International Classification: C10L 1/00 (20060101); C10G 29/16 (20060101); C10G 25/00 (20060101);
