Patent Application
20160168486
Not applicable.
1. Field of the Invention
This invention relates to a system and method for treating hydrocarbon waxes; specifically it relates to a system and method for improving the color of waxes produced by a Fischer-Tropsch process.
2. Background of the Invention
The Fischer-Tropsch (or “Fischer Tropsch,” “F-T” or “FT”) process (or synthesis or conversion) involves a set of chemical reactions that convert a mixture of carbon monoxide and hydrogen (known as reformed gas, synthesis gas, or “syngas”) into liquid hydrocarbons (called “liquid FT hydrocarbons” herein). The process was first developed by German chemists Franz Fischer and Hans Tropsch in the 1920's. The FT conversion is a catalytic and exothermic process. The FT process is utilized to produce petroleum substitutes, typically from carbon-containing energy sources such as coal, natural gas, biomass, or carbonaceous waste streams (such as municipal solid waste) that are suitable for use as synthetic fuels, waxes and/or lubrication oils. The carbon-containing energy source is first converted into a reformed gas (or synthetic gas or syngas), using a syngas preparation unit in what may be called a syngas conversion. Once the syngas is created, the syngas is used as an input to an FT reactor having an FT catalyst to make the liquid FT hydrocarbons in a Fischer-Tropsch synthesis (or FT synthesis or FT conversion). Depending on the type of FT reactor, the FT conversion of the syngas to liquid FT hydrocarbons takes place under appropriate operating conditions.
Depending on the physical form of the carbon-containing energy source, syngas preparation may involve technologies such as steam methane reforming, gasification, carbon monoxide shift conversion, acid gas removal gas cleaning and conditioning. These steps convert the carbon-containing energy source to simple molecules, predominantly carbon monoxide and hydrogen, which are the active ingredients of synthesis gas. The synthesis gas will also inevitably contain carbon dioxide, water vapor, methane, nitrogen. Impurities deleterious to catalyst operation such as sulfur and nitrogen compounds are often present in trace amounts and are removed to very low concentrations as part of synthesis gas conditioning.
Turning to the syngas conversion step, to create the syngas from natural gas, for example, methane in the natural gas reacts with steam and oxygen in a syngas preparation unit to create syngas. The syngas comprises principally carbon monoxide, hydrogen, carbon dioxide, water vapor and unconverted methane. When partial oxidation is used to produce the synthesis gas, typically, the syngas contains more carbon monoxide and less hydrogen than is optimal and consequently, steam is added to the react with some of the carbon monoxide in a water-gas shift reaction. The water gas shift reaction can be described as:
CO+H2O⇄H2+CO2 (1)
Thermodynamically, there is an equilibrium between the forward and the backward reactions. That equilibrium is determined by the concentration of the gases present.
Once the syngas is created and conditioned, the syngas is used as an input to an FT reactor having an FT catalyst to make the liquid FT hydrocarbons in a Fischer-Tropsch synthesis (or FT synthesis or FT conversion). Depending on the type of FT reactor, the FT conversion of the syngas to liquid FT hydrocarbons takes place under appropriate operating conditions. The Fischer-Tropsch (FT) reactions for the FT conversion of the syngas to the liquid FT hydrocarbons may be simplistically expressed as:
(2n+1)H2+nCO→CnH2n+2+nH2O, (2)
where ‘n’ is a positive integer.
In addition to liquid FT hydrocarbons, the Fischer-Tropsch synthesis also commonly produces gases (called “FT tail gases” herein) and water (called “FT water” herein). The FT tail gases typically contain CO (carbon monoxide), CO2 (carbon dioxide), H2 (hydrogen), light hydrocarbon molecules, both saturated and unsaturated, typically having carbon values ranging from C1 to C4, and a small amount of light oxygenated hydrocarbon molecules such as methanol. Typically, FT tail gases are mixed in a facility's fuel gas system for use as fuel. The FT water will typically include dissolved oxygenated species, such as alcohols, and light hydrocarbons, which are typically removed prior to disposal of the FT water.
The FT reaction is performed in the presence of a catalyst, called a Fischer-Tropsch catalyst (“FT catalyst”). Unlike reagents, a catalyst does not participate in the chemical reaction and is not consumed by the reaction itself. In addition, a catalyst may participate in multiple chemical transformations. Catalytic reactions have a lower rate-limiting free energy of activation than the corresponding un-catalyzed reaction, resulting in higher reaction rate at the same temperature. However, the mechanistic explanation of catalysis is complex. Catalysts may affect the reaction environment favorably, or bind to the reagents to polarize bonds, e.g. acid catalysts for reactions of carbonyl compounds, or form specific intermediates that are not produced naturally, such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause lysis of reagents to reactive forms, such as atomic hydrogen in catalytic hydrogenation. In addition to FT catalysts, other catalysts may also be used in other steps of an FT process.
The FT process results in longer-chain hydrocarbons than the feedstock, mainly n-paraffins, but with small amounts of impurities, such as branched chain material (for example, 2-methyl and 3-methyl derivatives), alpha olefins and oxygenates. The n-paraffins have a full range of carbon numbers from C1 to well above C100. Lighter materials C1 through C4 are typically not condensed in the process and remain in a gaseous phase. The lighter materials contain substantial amounts of alpha olefins (i.e. ethylene, propylene and 1-butene. Products of a typical FT process may include FT naphtha (which may have carbon numbers C5− to C12), FT diesel (which may have carbon numbers C9 to C25) and FT wax (mostly C20+ material). It is possible to cut narrower distillation range products such as kerosene (C8-C16), drilling fluid, distillate and the various single carbon number materials (such as heptane).
The production of olefins and oxygenates decline relative to the paraffins as the molecular weight increases. Nevertheless, there may be sufficient impurities in FT wax, including olefins and oxygenates, that may cause problems with the FT wax product. An olefin is an unsaturated hydrocarbon with a carbon-carbon double bond. Oxygenates, as used herein, mean compounds such as alcohols, aldehydes, ketones and carboxylic acids that have an oxygen-containing group as a termination group (in the case of alcohols, carboxylic acids and aldehydes), or contained within (in the case of ketones) a predominantly paraffinic carbon/hydrogen chain. The olefins may react with oxygen via a process that leads to the production of aldehydes and ketones associated with an undesirable odor. Pure paraffin hydrocarbons are transparent and colorless as a liquid and colorless to white (Saybolt 30) as a solid. Untreated FT wax tends to be colorless to light yellow (liquid), white to off-white (solid) and the color tends to deteriorate in storage.
Olefins in FT waxes are unstable with respect to oxygen. If an olefin becomes an oxygenated compound, it may become rancid and may cause problems with color or odor in the FT wax.
If a fixed bed FT reactor is used with a synthetic gas (“syngas”) made from a feedstock, the amount of impurities, such as olefins and oxygenates, contained in the untreated FT wax may depend on the catalyst used. For example, use of an iron-based catalyst with a syngas in a fixed bed FT reactor may result in the an FT wax having up to about 20% olefins and oxygenates, while use of the same elements, except with a typical cobalt-based catalyst, may result in the FT wax having up to only about less than 3% olefins and about less than 0.1% oxygenates. Hydrogenation can be used to remove impurities such as olefins and oxygenates from FT wax.
Typically, trickle bed reactors, packed with catalyst, have been used for FT wax hydrogenation. Hydrogen and wax are generally added as inputs at the top of the reactor and products are collected at or near the bottom of the reactor. These systems work with a constant flow of FT wax and they work well when the FT wax is heavily contaminated, such as in the case of when a fixed bed FT reactor is used with iron-based catalysts to produce FT products. The trickle bed reactors operate at high temperatures and high pressures and are, accordingly, expensive. The size of the catalyst particles used in beds with trickle bed hydrogenation reactors is generally larger than one millimeter in diameter, to avoid a high pressure drop through the reactor. The trickle bed reactors often require between 20 and 50 molecules of hydrogen for every one molecule of hydrogen consumed during the process. Hydrogen is generally collected, compressed and recycled.
Batch hydrogenation is extensively applied in fine chemicals and pharmaceutical industries. Other industries have used also batch processes for hydrogenation, for example, for perfume oils and edible products like margarine. Hydrogenation reactors used with such processes operate at relatively low temperatures and pressures. For example, use of a low pressure, low temperature hydrogenation reactor having an eductor was pioneered by Buss ChemTech, based in Switzerland, in the 1950's. See, for example, the Buss ChemTech web sites:
However, oils of plant or animal origin differ considerably from FT waxes. Hydrogenation is sometimes used for plant or animal oils to address other issues not presented with FT waxes, such as adding a desired texture. Moreover, the concerns in the edible oil industry are different from concerns with respect to an FT wax. As an example, in edible oils, trans-olefins can be a concern. Trans-olefins are not present in FT waxes. In FT waxes, the concerns focus on alpha olefins.
Another difference between edible oil hydrogenation requirements and FT wax hydrogenation requirements concerns the difference in the starting hydrogen demands for each. A starting hydrogen demand is a ratio of the double bonds present to the total carbon present in an oil. For example, typically, edible oils are triglycerides of C10 to C20 fatty acids, each fatty acid having between zero and four double bonds. Therefore, a typical chemical hydrogen demand for an edible oil would likely be between 0.002 and 0.006 kg-mols/kg. By contrast, an FT wax might have a carbon number of 20 (C20) or above and three percent of such molecules on average have a single double-bond, yielding a typical chemical hydrogen demand of 0.0001 kg-mols/kg. In edible oil hydrogenation, consequently, the chemical hydrogen demand is substantially higher than is the case for a Fischer Tropsch wax.
Furthermore, in edible oil process, it is typically not desirable to hydrogenate the edible oil completely; a certain amount of residual olefin can be desirable in these applications. By contrast, one wishes to hydrogenate an FT wax as completely as possible. In the edible oil industry, it is a typical practice to measure an Iodine number, which is linearly related to the hydrogen demand, rather to directly measure the hydrogen demand itself. For example, in a typical edible oil application, one may need to reduce the Iodine number from 70-110 down to 20-40. By contrast, for an FT wax, the starting Iodine number would be much lower (less than 10, more typically less than 2) and the objective would be to get the Iodine number as close to zero as practical. Accordingly, given these differences, such low pressure, low temperature reactors and processes have not been previously considered for use with FT wax hydrogenation.
Accordingly, there are needs in the art for novel systems and methods for treatment of FT wax having light contamination with impurities. Desirably, such systems and methods yield a high quality product at lower cost.
Methods in one of more embodiments of the present disclosure for hydrogenating a Fischer-Tropsch (“FT”) wax include placing the FT wax at a low temperature up to a pre-determined level within a low-temperature hydrogenation reactor having a mixing sub-system and a vent at the top and containing hydrogenating catalyst particles, leaving a vapor space above the predetermined level. The method also includes adding a hydrogen gas under pressure into the low-temperature hydrogenation reactor, bringing the low-temperature hydrogenation reactor up to a pre-determined operating pressure. The method further includes mixing the input FT wax, the hydrogen gas and the hydrogenation catalyst particles together using the mixing subsystem under operating conditions including a low temperature and the pre-determined operating pressure to create a mixture, thus permitting the FT wax to become hydrogenated, and stopping the mixing to allow the hydrogenation catalyst particles to settle for a period of time, and removing the hydrogenated FT wax with residual hydrogenating catalyst particles from the low-temperature hydrogenation reactor.
In one or more embodiments of the present disclosure, a method for hydrogenating a Fischer-Tropsch (“FT”) wax includes the steps of (1) placing an input FT wax, at a low temperature of below about 200° C., up to a predetermined level within a low-temperature, low-pressure hydrogenation reactor, having a mixing sub-system comprising a hollow shaft gas impeller system, having a vent at the top and containing hydrogenation catalyst particles, leaving a vapor space above the predetermined level; (2) adding hydrogen gas under pressure to the low-temperature low-pressure hydrogenation reactor, bringing the low-temperature low-pressure hydrogenation reactor up to a pre-determined low operating pressure of below about 100 psig; (3) mixing the input FT wax, the hydrogen gas and the hydrogenation catalyst particles together using the mixing subsystem under operating conditions including a low temperature and the pre-determined operating pressure to create a mixture, thus permitting the FT wax to become hydrogenated; (4) depressurizing the low-temperature low-pressure hydrogenation reactor; (5) flushing the hydrogen gas from the vapor space of the low-temperature low-pressure hydrogenation reactor using nitrogen at a low pressure; (6) stopping the mixing and allowing the hydrogenation catalyst particles to settle for a period of time, leaving at least one residual hydrogenation catalyst particle suspended in the hydrogenated FT wax; (7) removing the hydrogenated FT wax and the at least one residual hydrogenation catalyst particle from the low-temperature, low-pressure hydrogenation reactor through a dip tube by adding nitrogen under a low pressure to the low-temperature, low-pressure hydrogenation reactor; (8) sending the removed hydrogenated FT wax and the at least one residual hydrogenation catalyst particle through a catalyst filter to remove at least one residual hydrogenation catalyst particle and to create a filtered hydrogenated FT wax; (9) degassing the filtered hydrogenated FT wax; (10) subjecting the degassed, filtered hydrogenated FT wax to a vacuum distillation process in a short path distillation system to produce at least a first FT wax product having a congealing point between about 50° C. and about 70° C. and a second FT wax product having a congealing point between about 85° C. and about 100° C.; and (11) sending the second FT wax product to the low-temperature, low-pressure hydrogenation reactor, for supplemental hydrogenation.
In one of more embodiments of the present disclosure, a system for hydrogenating an FT wax includes hydrogenation reactor for FT wax, designed for low temperature conditions and a pre-determined operating pressure. The hydrogenation reactor for FT wax has a mixing sub-system, a vent at the top for excess hydrogen, a first inlet to allow input of hydrogen gas under pressure, and a second inlet to allow input of the FT wax. The mixing subsystem is suitable for mixing the FT wax at a low temperature and the pre-determined operating pressure with a plurality of hydrogenation catalyst particle and hydrogen gas to produce a mixture. The hydrogenation reactor for FT wax also includes an outlet to allow egress of a fluid comprising the hydrogenated FT wax, after the mixing has stopped and the hydrogenation catalyst particles have been permitted to settle for a period of time. In one of more embodiments of the present disclosure, an apparatus for hydrogenating FT wax includes a hydrogenation reactor shell designed for low temperature and low pressure operating conditions and having a vent at the top for excess hydrogen, a first inlet in the hydrogenation reactor shell to allow hydrogen gas to enter the hydrogenation reactor shell under a low pressure, a second inlet suitable for an FT wax, a third inlet to allow input of hydrogen gas and an outlet to allow egress of a fluid including hydrogenated FT wax. The apparatus further includes a mixing mechanism inside the hydrogenation reactor shell, suitable for mixing a mixture comprised of hydrogenation catalyst particles with the FT wax and the hydrogen gas to facilitate hydrogenating the FT wax.
Other embodiments are also disclosed herein.
These and other embodiments, features and advantages will be apparent in the following detailed description and drawings.
For a more detailed description of the present invention, reference will now be made to the accompanying drawings, wherein:
None of the Figures are drawn to scale.
As used herein, the term “low-pressure” with respect to a hydrogenation reactor means below about 350 psig. While pressures above this level are still in the scope of this disclosure, the pressure is typically limited to be below a pressure at which (given the anticipated temperatures and selected metallurgy) the flange rating jumps from ANSI Class 300 to ANSI Class 600, in order to keep costs low.
As used herein, the term “low-temperature” with respect to a hydrogenation reactor means under about 280° C. Ideally, in a “low temperature” hydrogenation reactor, the temperature of the FT wax within the hydrogenation reactor would be high enough so that the wax is liquid, but low enough that hydrocracking of the FT wax is not significant.
As used herein, the term “raw” with respect to a wax means a wax that has not been chemically treated.
As used herein, the term “sweet natural gas” means natural gas from which any excess sulfur or sulfur compounds such as H2S has been previously removed.
As used herein, the abbreviation “FT” stands for Fischer-Tropsch.
As used herein, the term “FT products” means hydrocarbon products produced from an FT reactor.
As used herein, the term “FT wax” means a wax made using a Fischer Tropsch process.
As used herein, the terms “reformed gas” or “syngas” means the effluent from a syngas conversion unit, such as (without limitation) a steam methane reformer, autothermal reformer, hybrid reformer, or partial oxidation reactor. Steam methane reformers do not use oxygen as part of the process; autothermal reformers do. Both use reformer catalysts. Hybrid reformers are a combination of steam methane reforming, as a first step, and an autothermal reforming with oxidation as a second step. Partial oxidation reactors are similar to autothermal reformers, but do not include the use of a reformer catalyst. Partial oxidation reactors operate in accordance with the following equation:
½O2+CH4═CO+2H2
(3)Steam reformers operate in accordance with the following equation:
H2O+CH4═CO+3H2 (4)
Autothermal reformers perform both reforming and partial oxidation and so operate in accordance with both Equation (3) and Equation (4). This explanation is a bit simplified as some carbon dioxide may be made by SMR reactors and additional reactions take place in autothermal reformers and partial oxidation reactors.
As used herein, the term “hydrogenation” means a reduction reaction that results in an addition of hydrogen (usually as H2). If an organic compound is hydrogenated, it becomes more “saturated.” Hydrogenation has many applications, but most people are familiar with the reaction as the one used to make liquid oils into semi-solid and solid fats. Hydrogenation is a form of hydrotreating, which also includes many other treatments. For example, hydrogenation may be done without hydrocracking, which is another form of hydrotreating, but hydrocracking includes hydrogenation.
The maximum size of the hydrogenation catalyst particles 22 used should generally be no greater than about 250 microns, so that the hydrogenation catalyst particles 22 may be suspended within the input wax 10 in the low-temperature, low-pressure hydrogenation reactor 20. If comparing the same volume of hydrogenation catalyst, hydrogenation catalyst particles with a smaller size will provide a greater surface area, meaning one can use less hydrogenation catalyst to treat a particular volume of wax. Examples of the hydrogenation catalyst particles 22 that may be used in accordance with one or more embodiments of the present disclosure include edible oil hydrogenation catalysts, such as skeletal nickel catalysts or palladium-containing catalysts. The hydrogenation catalyst particles 22 may comprise a single type of catalyst particles or may comprise a catalyst mixture of two or more types of catalyst particles. At least one of the types of catalyst particles in the catalyst mixture would be suitable for hydrogenation. In such an embodiment, one or more other types of catalyst particles making up the catalyst mixture could have other (non-hydrogenation) functions, such as oligomerization, isomerization, or cracking. For example, in an embodiment with a catalyst mixture having a hydrogenation catalyst and a oligomerization catalyst, a process might include a first step of oligomerization performed under a nitrogen-containing atmosphere with typical conditions of a low temp (about 150° C.) and moderate pressure (about 150 psig), followed by a second step of hydrogenation as previously described. In an embodiment with a catalyst mixture having a hydrogenation catalyst and an isomerization catalyst, a process might include simultaneously isomerizing and hydrogenating the FT wax at conditions as previously described for hydrogenation. In an embodiment with a catalyst mixture having a hydrogenation catalyst and a hydrocracking catalyst, a process might include a first step of hydrocracking (which includes hydrogenation) at temperatures above 300° C. (for example, 350° C.) with hydrogen at a pressure of 150-350 psig, followed by a second step of finishing hydrogenation at previously described hydrogenation conditions.
Referring again to
Another example of a stirrer in accordance with one or more embodiments of the present disclosure includes a separate device to circulate hydrogen 15 to a sparger, although this option may be more expensive than previously mentioned alternatives.
In a hydrogenation reaction process, as the hydrogen 15 is mixed as part of the slurry with the hydrogenation catalyst particles 22 and the input wax 10, the hydrogen 15 saturates carbon double bonds of the olefins and the carbon-oxygen bonds of the oxygenates within the input wax 10 to form paraffins and water. The hydrogenation reaction process of the present disclosure may be performed in a batch mode, in a semi-batch mode (having staged additions of ingredients and removal of product) or, in one or more embodiments, may be performed in a continuous mode. A typical operating temperature for the low-temperature, low-pressure hydrogenation reactor 20 may range from about 100° to about 280° C., preferably, from about 150° to about 250° C., and more preferably from about 200° to about 230° C. Ideally, the temperature range selected would be high enough that the input wax 10 is in a liquid form, but low enough that any hydrocracking that might incidentally take place is limited to a desired, very low level or avoided.
A typical operating pressure for the low-temperature, low-pressure hydrogenation reactor 20 may range from about 0 psig to about 350 psig, preferably from about 50 psig to about 350 psig, and more preferably from about 250 psig to about 350 psig. Although the low operating pressure may provide a significant cost advantage, higher pressures could be also used, with equipment designed to handle the high pressures.
Continuing to refer to
The filtered, hydrogenated wax 35 may be considered a product. However, the filtered, hydrogenated wax 35 might have too wide a distribution of carbon numbers to be appropriate for typical applications. Accordingly, it may be desirable to split the filtered, hydrogenated wax 35 into two or more products with properties conforming to market requirements. In the embodiment illustrated in
Referring back to
In one or more embodiments, the short path distillation system may comprise a plurality of wiped film evaporators and/or short path distillation units or a combination of both. For example, the short path distillation system may include a wiped film evaporator, followed by two short path distillation units in series.
Continuing to refer to
Referring again to
From the hydrogenated wax flowline 228, the hydrogenated wax (with the hydrogenated catalyst particles the hydrogenated wax may be carrying) passes through a fifth valve 231 and into the catalyst filter 230. In the embodiment of
While
Continuing to refer to
Referring again to
Looking again to
In the one or more embodiments of
The hydrogenated FT wax, which may include residual hydrogenation catalyst particles, is removed 540 from the low-temperature, low-pressure hydrogenation reactor. A heel of settled catalyst particles and some hydrogenated FT wax may be left within the low-temperature, low-pressure hydrogenation reactor. The hydrogenated FT wax and residual hydrogenation catalyst particles are passed 545 through a catalyst filter to remove the residual hydrogenation catalyst particles and to create a filtered hydrogenated FT wax. The filtered hydrogenated FT wax may be stored 550 if further processing is not immediately desired. When further processing is desired, the stored, filtered hydrogenated FT wax is released 555 from storage. If needed, the filtered hydrogenated FT wax may be heated 560 in order to help the filtered hydrogenated FT wax to flow. The filtered hydrogenated FT wax next passes to a degasser, where the heated, filtered hydrogenated FT wax is de-gassed 570. The gas removed from the filtered hydrogenated FT wax passes through a degasser vent to a vacuum system or other desired location. In one or more embodiments, gas leaving the degasser is cooled in a condenser or cold trap, which recovers some light liquids with the non-condensable material passing to a first stage of the vacuum system. The discharge from the first stage vacuum pump goes to flare or other suitable location.
Referring again to refer to
While some preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations. The use of the term “optionally” with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, and the like.
Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention. The inclusion or discussion of a reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent they provide background knowledge; or exemplary, procedural or other details supplementary to those set forth herein.
This application is the national phase entry of PCT Application No. PCT/US2014/052052, filed Aug. 21, 2014, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent App. No. 61/868,509, filed Aug. 21, 2013, the disclosure of each of which is hereby incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2014/052052 | 8/21/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61868509 | Aug 2013 | US |
