Patent Application
20220009774
This disclosure relates to reforming of hydrocarbons, and in particular, dry reforming of hydrocarbons.
Synthesis gas, also referred to as syngas, is a fuel gas mixture that includes hydrogen, carbon monoxide, and sometimes carbon dioxide. Syngas is combustible and can be used as a fuel of internal combustion engines. In some cases, syngas can be used as an intermediate for producing synthetic petroleum for use as a fuel or lubricant. Syngas can also be used to produce methanol or as a hydrogen source for various processes. Hydrocarbon reforming is one example of a process for producing syngas.
This disclosure describes technologies relating to hydrocarbon reforming.
Certain aspects of the subject matter can be implemented as a dry reforming process for producing a synthesis gas from a hydrocarbon fuel. A feed stream is preheated. The feed stream includes the hydrocarbon fuel and carbon dioxide. The feed stream is flowed to a reactor. The reactor includes a catalyst. Flowing the feed stream to the reactor brings the feed stream into contact with the catalyst in the absence of oxygen and causes a dry reforming reaction within the reactor for a period of time sufficient to reform the hydrocarbon fuel to produce the synthesis gas. The catalyst includes nickel (Ni), lanthanum oxide (La2O3), cerium oxide (Ce2O3), and platinum (Pt).
This, and other aspects, can include one or more of the following features.
In some implementations, the feed stream is preheated to a temperature in a range of from about 750 degrees Celsius (° C.) to about 950° C.
In some implementations, an operating pressure within the reactor during the dry reforming reaction is in a range of from about 7 bar to about 28 bar.
In some implementations, the feed stream has a carbon dioxide to hydrocarbon ratio in a range of from about 1:1 to about 4:1.
In some implementations, the carbon dioxide to hydrocarbon ratio of the feed stream is in a range of from about 1:1 to about 2:1.
In some implementations, the feed stream includes water.
In some implementations, the feed stream has a water to carbon ratio in a range of from about 1:10 to about 3:1.
In some implementations, the water to carbon ratio of the feed stream is in a range of from about 1:10 to about 1:1.
In some implementations, the catalyst includes zirconium oxide (ZrO2), rhodium (Rh), rhenium (Re), and an aluminate support.
In some implementations, the catalyst includes about 0.5 weight percent (wt. %) to about 15 wt. % of Ni, about 0.5 wt. % to about 10 wt. % of Ce2O3, about 0.5 wt. % to about 5 wt. % of La2O3, about 0.1 wt. % to about 2 wt. % of Pt, up to about 1 wt. % of ZrO2, up to about 2 wt. % of Rh, and up to about 2 wt. % of Re.
In some implementations, potassium (K) is incorporated into the aluminate support.
In some implementations, the catalyst includes about 0.5 wt. % to about 5.0 wt. % of K.
The details of one or more implementations of the subject matter of this disclosure are set forth in the accompanying drawings and the description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.
This disclosure describes reforming of hydrocarbons. The conversion of hydrocarbon fuels to hydrogen can be carried out by several processes, including hydrocarbon steam reforming, partial oxidation reforming, auto thermal reforming, and dry reforming. Hydrocarbon dry reforming involves the reaction of carbon dioxide (CO2) with the fuel (for example, methane, CH4) in the presence of a catalyst and the absence of oxygen to produce hydrogen (H2) and carbon monoxide (CO) as given in Equation (1). A mixture of hydrogen and carbon monoxide can be referred to as synthesis gas (syngas). In some cases, syngas also includes carbon dioxide.
CH4+CO2→2CO+2H2(ΔH298K=+247 kJ·mol−1) (1)
The subject matter described in this disclosure can be implemented in particular implementations, so as to realize one or more of the following advantages. Dry reforming produces hydrogen and carbon monoxide in a 1:1 molar ratio, which is suitable for a diverse array of hydroformylation applications. About half of the carbon atoms in the resulting syngas from the dry reforming process originates from the carbon dioxide instead of the methane. This reduces the dependency of the dry reforming process on methane feedstock in comparison to other reforming processes (for example, steam reforming in which all of the carbon atoms originate from the methane). Further, carbon dioxide, which is a known greenhouse gas, is feedstock for the dry reforming process to form a useful product instead of, for example, being expelled into the atmosphere. The catalyst described herein exhibits resistance to coke formation and sintering, even under elevated temperature and pressure conditions. The processes and catalysts described can allow for economical ways to reduce greenhouse gas emissions. The processes described can integrate renewable hydrogen in existing industrial processes and can mitigate carbon footprint chemicals and fuels.
Although dry reforming has been known, currently known catalysts, for example, nickel-alumina based catalysts, can suffer from deactivation due to excessive coke deposition and agglomeration (that is, sintering) of metal particles at the elevated temperatures required for dry reforming, which can cause reduction of usable surface area of the catalyst. Sintering involves agglomeration of small metal particles to form larger metal particles and results in the reduction of active sites of the catalyst. Coking involves a carbon-containing compound cracking on the surface of the catalyst, which gives selectivity to undesirable side reaction products and also results in the reduction of active sites of the catalyst. Catalysts based on Group VIII noble metals may be less sensitive to coking in comparison to nickel based catalysts, but they can also be more expensive to form and can also be more prone to sintering. Certain precious metals, such as platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), and ruthenium (Ru) can exhibit favorable dry reforming activity while resisting deactivation via coking and sintering.
Referring to
The feed stream 101 flows to the preheater 103. The preheater 103 is configured to preheat the feed stream 101. In some implementations, the preheater 103 is configured to preheat the feed stream 101 to a temperature in a range of from about 700 degrees Celsius (° C.) to about 950° C. In some implementations, the preheater 103 is configured to preheat the feed stream 101 to a temperature in a range of from about 700° C. to about 850° C. In some implementations, the preheater 103 is configured to preheat the feed stream 101 to a temperature in a range of from about 750° C. to about 950° C. Referring to Equation (1), the dry reforming reaction is endothermic. In some implementations, preheating the feed stream 101 to a temperature that is greater than 750° C. can improve selectivity towards the generation of hydrogen and carbon monoxide (which are the preferred products) and away from forming other carbon-containing compounds. Preheating the feed stream 101 (for example, to a temperature greater than 750° C. or greater than 800° C.) can mitigate methane cracking both during the preheating process and in the dry operating mode (that is, without addition of steam) of the dry reforming process.
The preheated feed stream 104 exits the preheater 103 and flows to the reactor 105. In some implementations, the reactor 105 is a packed bed reactor. In some implementations, the reactor 105 is a fluidized bed reactor. Within the reactor, the methane reacts with the carbon dioxide to produce syngas 106 (carbon monoxide and hydrogen). In other words, the dry reforming reaction represented by Equation (1) occurs within the reactor 105.
The reactor 105 includes a catalyst. Flowing the preheated feed stream 104 to the reactor 105 brings the preheated feed stream 104 in contact with the catalyst. In the absence of oxygen, the catalyst speeds up and causes the dry reforming reaction within the reactor for a period of time sufficient to reform the hydrocarbon fuel (for example, methane) to produce the syngas 106. Because oxygen gas is not introduced to the reactor 105, combustion does not take place within the reactor 105. In some implementations, an operating pressure within the reactor 105 during the dry reforming reaction is in a range of from about 7 bar to about 28 bar. On one hand, as the dry reforming reaction forms a volume of products that is larger than the volume of reactants, so in some cases lower operating pressure within the reactor 105 may be preferred during the dry reforming reaction. On the other hand, a higher operating pressure allows for increased throughput of reactants being processed within the reactor 105, so in some cases higher operating pressure within the reactor 105 may be preferred during the dry reforming reaction. In some implementations, the operating pressure within the reactor 105 depends on the operating pressures of downstream operations (for example, syngas application or purification). For example, in applications using syngas to produce dimethyl ether (DME), the operating pressure of such applications tend to be higher, so the syngas produced from the reactor 105 can be compressed, and the operating pressure within the reactor 105 can be optimized for improved conversion at pressures greater than 10 bar. In some implementations, coking becomes more dominant at higher pressures, especially in cases where the dry reforming reaction is completely dry (that is, there is no addition of water in the form of steam), so in such conditions, an operating pressure within the reactor 105 during the dry reforming reaction is in a range of from about 10 bar to about 15 bar. The range of operating pressure can be expanded through the addition of water in the form of steam with the feed to the reactor 105. The operating pressure within the reactor 105 during the dry reforming reaction can be determined based on one or more of the aforementioned factors and economics of the process.
In some implementations, the catalyst within the reactor 105 is pre-treated. For example, the catalyst is preheated within the reactor 105, such that the catalyst is at a desired temperature before the feed stream 104 is flowed to the reactor 105. In some implementations, the inner volume of the reactor 105 is preheated, such that the operating temperature within the reactor 105 is at a desired temperature before the feed stream 104 is flowed to the reactor 105. In some implementations, the desired temperature of the catalyst, operating temperature within the reactor 105, or both are the same as or within a deviation of 10% from the temperature to which the feed stream 104 is preheated in the preheater 103.
The catalyst includes a rare earth group metal oxide, such as lanthanum oxide (La2O3), cerium oxide (Ce2O3), or a mixture of both. In some implementations, the catalyst includes an oxide of a Group IV metal, such as zirconium oxide (ZrO2). In some implementations, the catalyst includes nickel (Ni), a reducible compound of Ni (for example, nickel oxide (NiO)), or a mixture of both. In some implementations, the catalyst includes a platinum group metal, such as platinum (Pt), Rh, or a mixture of both. The platinum group metal can be included in pure elemental form or as a part of a chemical compound that includes the platinum group metal. In some implementations, the catalyst includes a Group VIIB metal, such as rhenium (Re). The Group VIIB metal can function as a promoter to enhance the efficiency of the dry reforming activity of the catalyst.
In some implementations, the catalyst includes about 0.5 weight percent (wt. %) to about 15 wt. % of Ni. In some implementations, the catalyst includes about 0.5 wt. % to about 10 wt. % of Ce2O3. In some implementations, the catalyst includes about 0.5 wt. % to about 5 wt. % of La2O3. In some implementations, the catalyst includes about 0.1 wt. % to about 2 wt. % of Pt. In some implementations, the catalyst includes up to about 1 wt. % ZrO2. In some implementations, the catalyst includes up to about 2 wt. % Rh. In some implementations, the catalyst includes up to about 2 wt. % Re.
In some implementations, the catalyst is supported on an aluminate support. In such implementations, the aluminate support can be considered a portion of the catalyst. The aluminate support can include magnesium aluminate, calcium aluminate, or a mixture of both. In some implementations, an alkaline metal, such as potassium (K), is incorporated into the aluminate support. Including alkaline metal in the aluminate support can mitigate coke formation on the catalyst and can therefore mitigate catalyst deactivation. In implementations where the catalyst is supported on an aluminate support incorporated with K, the catalyst can include about 0.5 wt. % to about 5.0 wt. % of K.
In some implementations, catalyst includes a refractory support that includes alumina (for example, theta-alumina), magnesium aluminate, or a mixture of both. In some implementations, a refractory cement that is based on calcium aluminate is incorporated into the catalyst to improve the mechanical strength of the catalyst. In some implementations, the catalyst has a specific surface area in a range of from about 15 square meters per gram (m2/g) to about 125 m2/g.
The refractory support can be provided in different shapes, such as spheres, extrudates, or rings. For production of hydrogen-rich gas for use in fuel cells, it can be beneficial to use refractory supports in the form of spheres, for example, having diameters within a range of from about 1 millimeter to about 4 millimeters; complex extrudates, for example, trilobe, quadralobe, or raschig rings; or honeycomb structure. For large-scale production of hydrogen-rich gas (for example, greater than 100,000 normal cubic meters per day), it can be beneficial to use refractory supports in the form of rings with multiple holes.
In some implementations, the catalyst is prepared by a multiple step sequence of impregnation, calcination, and reduction of the components on the support. The catalyst impregnation can be carried out using an aqueous solution of a soluble salt, such as a nitrate salt. In some implementations, the rhodium and rhenium metal salts are impregnated after which they decompose upon subsequent heat treatment to form corresponding oxides. After impregnation, the composite material is dried (calcined) at a slow heating rate, for example, of about 0.5° C. increase per minute until reaching about 120° C., and then the temperature is maintained at about 120° C. for about one hour. The temperature is then increased to about 250° C. at a slow heating rate, for example, of about 0.5° C. increase per minute, and then the temperature is maintained at about 250° C. for about 1.5 hours. The aforementioned heating (calcination) steps can be carried out in the presence of air or another oxygen containing gas. In some implementations, after impregnation and before heating, the catalyst can be treated at about 60° C. for about 10 to about 30 minutes with an ammonia containing gas. The catalyst can then be reduced with a hydrogen containing gas at a temperature in a range of from about 400° C. to about 450° C. for about 2 hours. The aforementioned impregnation, calcination, and reduction steps can be repeated with salts of Pt and Zr. The aforementioned impregnation, calcination, and reduction steps can be repeated with salts of Ni, Ce, and La. The reduction step for the salts of Ni, Ce, and La can be conducted at a temperature in a range of from about 400° C. to about 1,100° C., from about 600° C. to about 800° C., or from about 700° C. to about 750° C.
In some implementations, the catalyst is prepared by a single step sequence of impregnation, calcination, and reduction at a temperature in a range of from about 400° C. to about 1,100° C., from about 600° C. to about 800° C., or to about 700° C. to about 750° C. The refractory support can be impregnated with an aqueous solution of a soluble salt, such as a nitrate salt of Ni, Ce, La, and Pt. After impregnation, the composite material is dried (calcined) at a slow heating rate, for example, of about 0.5° C. increase per minute until reaching about 120° C., and then the temperature is maintained at about 120° C. for about one hour. The temperature is then increased to about 250° C. at a slow heating rate, for example, of about 0.5° C. increase per minute, and then the temperature is maintained at about 250° C. for about 1.5 hours. The temperature is then increased to about 400° C. to about 450° C. The aforementioned heating (calcination) steps can be carried out in the presence of air or another oxygen containing gas. The catalyst can then be reduced with a hydrogen containing gas at a temperature in a range of from about 400° C. to about 1,100° C., from about 600° C. to about 800° C., or from about 700° C. to about 750° C. In some implementations, depending on the volume of pores in the support, the impregnation, drying, and calcination can be repeated one or more times to obtain desired contents of each component in the catalyst.
In some implementations, the feed stream 101 also includes water (H2O) in the form of steam. In some implementations, the feed stream 101 has a water to carbon (that is, carbon atoms from any carbon-containing species, such as the carbon dioxide and the hydrocarbon fuel) ratio in a range of from about 1:10 to about 3:1. In some implementations, the feed stream 101 has a water to carbon ratio in a range of from about 1:10 to about 1:1. Including steam in the feed stream 101 can reduce the severity of the carbon-carbon reaction at the operating conditions of the dry reforming reaction within the reactor 105. Including steam in the feed stream 101 can mitigate coke formation on the catalyst and can therefore mitigate catalyst deactivation. Including steam in the feed stream 101 can increase the hydrogen to carbon monoxide ratio in the syngas 106 that is produced by the reactor 105. Including steam in the feed stream 101 can improve selectivity of the catalyst in producing syngas 106 as opposed to other carbon-containing compounds.
At step 204, the preheated feed stream (such as the preheated feed stream 104) is flowed to a reactor including a catalyst (such as the reactor 105). The catalyst can be the catalyst that was described previously. Flowing the preheated feed stream 104 to the reactor 105 at step 204 brings the preheated feed stream 104 into contact with the catalyst. In the absence of oxygen, the catalyst causes a dry reforming reaction (for example, the reaction represented by Equation (1)) within the reactor 105 for a period of time sufficient to reform the hydrocarbon fuel to produce the syngas (such as the syngas 106). In some implementations, the feed stream is brought into contact with the catalyst in the absence of oxygen at a gas hourly space velocity in a range of from about 1,000 h−1 to about 3,000 h−1 at step 204. In some implementations, an operating pressure within the reactor during the dry reforming reaction at step 204 is in a range of from about 7 bar to about 28 bar.
The syngas 106 can be discharged from the reactor 105. In some implementations, additional hydrogen can be mixed with the syngas 106 discharged from the reactor 105 to increase the hydrogen to carbon monoxide ratio. For example, the hydrogen stream 107 can be mixed with the syngas 106.
For each of the experimental runs whose results are shown in the plots of
Although some of the aforementioned examples included inert gas (for example, nitrogen (N2), helium (He), or both) in the feed stream, the inert gas was included in order to verify quality of the experiments through mass balance checks, and the inert gas is not necessarily included in industrial applications of the dry reforming processes described here.
While this specification contains many specific implementation details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular implementations. Certain features that are described in this specification in the context of separate implementations can also be implemented, in combination, in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations, separately, or in any suitable sub-combination. Moreover, although previously described features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.
As used in this disclosure, the terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. The statement “at least one of A and B” has the same meaning as “A, B, or A and B.” In addition, it is to be understood that the phraseology or terminology employed in this disclosure, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.
As used in this disclosure, the term “about” or “approximately” can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.
As used in this disclosure, the term “substantially” refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more.
Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of “0.1% to about 5%” or “0.1% to 5%” should be interpreted to include about 0.1% to about 5%, as well as the individual values (for example, 1%, 2%, 3%, and 4%) and the sub-ranges (for example, 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement “X to Y” has the same meaning as “about X to about Y,” unless indicated otherwise. Likewise, the statement “X, Y, or Z” has the same meaning as “about X, about Y, or about Z,” unless indicated otherwise.
Particular implementations of the subject matter have been described. Other implementations, alterations, and permutations of the described implementations are within the scope of the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations may be considered optional), to achieve desirable results. In certain circumstances, multitasking or parallel processing (or a combination of multitasking and parallel processing) may be advantageous and performed as deemed appropriate.
Moreover, the separation or integration of various system modules and components in the previously described implementations should not be understood as requiring such separation or integration in all implementations, and it should be understood that the described components and systems can generally be integrated together or packaged into multiple products.
Accordingly, the previously described example implementations do not define or constrain the present disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of the present disclosure.
