Field of the Invention

The present invention lies within the field of catalytic cracking processes, in particular those that take place in the presence of steam. In particular, the invention relates to a method for the production of, for example, ethene and synthetic gas in a reactor, which may have a circulating fluid bed. The invention teaches that charges such as hydrocarbon charges with at least 11 carbon atoms, or charges consisting of raw materials with a high oxygen content, undergo pre-cracking upon coming into contact with a catalyst in the presence of steam and in the absence of oxygen. The burning of the carbonaceous material such as coke deposited on the catalyst in another reaction bed enables the generation of the energy required for the endothermic reactions.

BACKGROUND OF THE INVENTION

Hydrogen is widely used in refineries - particularly in the hydrogenation of streams of diesel oil and gasoline, or in the hydrocracking of residual streams - for the removal of sulfur or nitrogen compounds (DeSOx and DeNOx) and for the manufacture of more noble and higher-quality derivative products.

Catalytic reforming makes it possible to produce hydrogen via the cracking of molecules with steam in the presence of catalysts. First the so-called "synthesis gas" (1 ) is produced:

C _n H _m + nH ₂ O ^■ » nCO + (n+m/2) H ₂ (-1 )

In the presence of an excess of steam, CO ₂ is produced, as well as hydrogen (2):

CO + H ₂ O ^■ » CO ₂ + H ₂ (2)

The reactor that is employed is a standard reforming converter that consists of a multi-tube furnace fed by a charge mixed with steam, . into which a structured catalyst, based on NiO-K ₂ O, is inserted. During the reforming, at a temperature of approximately 800 C, endothermic reactions occur that consume a large amount of energy. The heat necessary for the reactions is supplied via lateral blowpipes and is obtained through the burning of combustible gas.

The deposition of coke on the catalyst takes place more rapidly during the processing of heavier charges. Consequently, early deactivation of the catalytic bed causes a drastic reduction in the production of synthesis gas. The charges that are suitable for use in this process are limited to streams of light hydrocarbons. The most typical ones are natural gas, fuel gas or liquefied gas (LPG) [liquefied petroleum gas], and naphtha.

When the catalytic reforming process uses charges with a high oxygen content (such as, for example, vegetable oils), the coking speed is correspondingly greater. Furthermore, relatively light raw materials, such as ethanol, are economically unfeasible. The literature on the continuous deposition of coke on the catalyst is fairly broad.

The publication by R.K.S. Santos entitled "Caracterizaςao e aplicaςao de catalisadores de cobalto suportados em gama AI ₂ O ₃ e SiO ₂ para produςao de hidrogenio a partir da reforma a vapor e oxidative de etanof ["Characterization and implementation of supported catalysts in the AI ₂ O ₃ and SiO ₂ range for the production of hydrogen via the steam-based and oxidative reformation of ethanol"] (Instituto de Quimica de Sao Carlos [St. Charles Chemistry Institute] (IQSC) ₁ master's thesis, Sao Carlos, 2006) indicates that the use of ethanol as a charge leads to coke deposition ranging from 2.7 mg/h to 12.7 mg/h per gram of catalyst.

The publication by Haryanto et al. entitled "Current Status of Hydrogen Production Techniques by Steam Reforming of Ethanol: A Review" (Energy & Fuels, Vol. 19 (2005), pp. 1098-2106) indicates, among other pertinent results, that nickel-based AI ₂ O ₃ -supported catalysts are deactivated after a few minutes.

The publication by Cavallaro et al. entitled "Performance of RhZAI ₂ O ₃ Catalyst in the Steam Reforming of Ethanol: H ₂ Production for MC" (Applied Catalysis, Vol. 249, No. 1 (2003), pp. 119-128) describes the formation of 0.27 mg/h per gram of catalyst in AI ₂ O ₃ -supported rhodium catalysts.

U.S. patent No. 6,207,078 teaches that autothermic reforming is an alternative (albeit a weak one) for reducing the coking effect and reducing the total amount of energy consumed by the process.

The use of zeolites in the pentasyl family (such as ZSM-5) or of the faujasite type enables the burning of the charge molecules beforehand, thus facilitating the later reactions and slowing the deposition of coke. The reforming reactions take place in the presence of supported metals, such as nickel, copper, iron, zinc, cobalt, cerium, manganese, and magnesium, or metal oxides or supported metal oxides, such as oxides of zinc and cobalt supported on alumina, rhodium oxide supported on alumina, and nickel oxide supported on gamma- or alpha-alumina or on silica.

It is desirable to provide a method and apparatus for steam cracking in which deactivation of the catalyst is reduced or avoided.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided a method of steam cracking comprising the steps of: regenerating a catalyst in a first section of an apparatus for steam cracking by a first reaction; and conveying the regenerated catalyst from the first section to a second section of the apparatus; wherein a second reaction between a charge and steam takes place in the presence of the catalyst in the second section.

Functioning in the same way as in cracking units, according to the present invention, the catalysts promote the burning of long chains and the formation of desirable products such as gasoline and light olefins. The reforming catalyst is continuously regenerated, in order to avoid deactivation. These converters have two different reaction environments that are preferably isolated by catalytic seals located between the reaction environments. Steam-based catalytic cracking takes place preferably via endothermic reactions in one of the environments and preferably in the absence of oxygen, while, preferably simultaneously in the second environment, the catalyst is continuously regenerated preferably through the combustion of the coke with air.

Preferably, the first section and the second section are independent sections, wherein the catalyst is conveyed from the first section to the second section through an interconnection interconnecting the sections.

Preferably, the second reaction results in carbonaceous material being deposited on a surface of the catalyst, and the catalyst is conveyed from the second section to the first section.

According to the present invention, the reforming catalyst is continuously regenerated, in order to avoid deactivation due to the deposition of carbonaceous material (e.g. coking) of the catalytic bed.

Preferably, the first reaction is a combustion of carbonaceous material deposited on a surface of the catalyst.

Preferably, heat produced by the first reaction is transferred from the first section to the second section.

In this way, less heat needs to be provided from external sources in order to promote the second reaction (i.e. the steam cracking). This improves the thermal efficiency of the steam cracking and reduces the cost of producing, for example, ethene and synthesis gas.

Preferably, the second reaction takes place substantially in the absence of oxygen.

The present invention allows the catalyst to be regenerated and accordingly avoid deactivation without needing to add any oxygen to the second reaction. Hence it is only necessary to provide the direct reactants for the second reaction, along with the catalyst, to the second section.

Preferably, the second reaction is endothermic. In the case that the steam cracking reaction is endothermic, the present invention has the further advantage of keeping the unit in heat balance by continuously removing heat from the regenerator and providing heat to the endothermic reactions that take place inside the reactor.

Preferably, substantially all of the heat used by the second reaction is produced by the first reaction.

Thus, the burning of the coke heats the catalyst in an independent section and, thanks to the circulation of this heated catalyst, allows an amount of energy suitable for the endothermic reactions to be conveyed from the second section to the first section. Accordingly, no external heat needs to be provided to the second section to promote the steam cracking reaction. -In this way, the two sections of the apparatus can be in thermal equilibrium.

Preferably, the first reaction and the second reaction take place simultaneously.

Accordingly, the catalyst is continuously regenerated. Hence, it is not necessary to periodically stop the reactions in order to replace the used catalyst. This improves the overall reaction efficiency and throughput rate.

Preferably, the charge comprises hydrocarbons including molecules with at least 11 carbon atoms, or a raw material with a high oxygen content.

The present invention teaches a method for the production of ethene and synthesis gas from raw materials that contain heavy hydrocarbons or from raw materials with a high oxygen content.

Preferably, the second reaction takes place at a temperature between 77O ⁰ C and 850 ⁰ C.

Accordingly, the steam cracking reaction for the production of, for example, ethene and synthesis gas takes place at high temperature.

Preferably, the first section comprises a first fluidized bed and the second section comprises a second fluidized bed.

Accordingly, the reforming catalyst is continuously regenerated, via the use of interconnected circulating fluidized beds (CFBs), in order to avoid deactivation due to coking of the catalytic bed.

Preferably, the circulating fluidized beds include a percentage, ranging from 5% to 40%, of particles having a diameter of less than 40μm and a density within the range of 150 kg/m ³ and 1800 kg/m ³ .

Preferably, the method further comprises the step of promoting contact between the charge and the catalyst.

Preferably, the second reaction results in the production of ethene and synthesis gas.

The total ethene yield of the process according to the present invention is approximately 20% by weight in relation to the charge.

Preferably, the method further comprises the step of separating products resulting from the second reaction.

Preferably, the catalyst is continuously regenerated in the first section, through the burning, with air, of the coke deposited on the catalyst.

Preferably, the charge includes an oil. Preferably, the oil is selected from a group consisting of an oil of renewable origin, a vegetable oil, castor oil, soy oil, cashew oil, cotton oil and peanut oil.

Preferably, the charge includes an alcohol. Preferably, the alcohol is selected from a group consisting of ethanol, fusel oil and glycerol.

Preferably, the charge includes a ligneous-cellulose material. Preferably, the ligneous-cellulose material is selected from a group consisting of sugar-cane straw, sugar-cane bagasse, wood shavings and wood sawdust. Accordingly, desirable products such as ethene and synthesis gas can be produced from materials that are obtained from renewable raw materials.

Preferably, the charge includes at least one of kerosene, gas-oil, heavy vacuum gas- oil and fuel oil.

Preferably, the charge has an initial boiling point above 21O ⁰ C.

Preferably, the catalyst includes from 0% to 60% by weight of solid acid, 0% to 50% by weight of alumina, and 0% to 40% by weight of silica, with the remainder consisting of kaolin.

Preferably, the solid acid includes at least one zeolite. Preferably, the zeolite is a zeolite in the pentasyl family or a zeolite of the faujasite type.

Preferably, the catalyst includes at least one metal oxide. Preferably, the metal oxide includes at least one of the following metals: nickel, copper, iron, zinc, cobalt, cerium, rhodium, manganese, and magnesium. Preferably, the metal oxide is supported by an aluminum, silica, or magnesium substrate.

Preferably, the catalyst includes microspheroidal particles having an average particle size that is between 50μm and 90μm.

Preferably, the method further comprises the step of providing the charge to the second section of the apparatus.

Preferably, the steam cracking reactions take place at a pressure between 0.10MPa and 0.45MPa

Preferably, the steam cracking reactions take place with a charge/steam mass ratio between 2:1 and 10:1.

Preferably, the steam is at a temperature between 300 ⁰ C and 1000°C.

According to a further aspect of the present invention, there is provided an apparatus for steam cracking comprising: a first section configured to contain a first reaction for regenerating a catalyst takes place; a second section configured to contain a second reaction between a charge and steam in the presence of the catalyst; and means for conveying the catalyst between the first section and the second section.

Preferably, the first section comprises a first fluidized bed and the second section comprises a second fluidized bed, wherein the first fluidized bed and the second fluidized bed are interconnected, independent sections.

Preferably, a catalytic seal isolates the first section from the second section. Preferably, the means for conveying the catalyst between the first section and the second section comprises a standpipe. Preferably, catalyst circulation between the first section and the second section is driven by unit pressure balance.

Thus, the present invention relates to a method for the production of ethene, CO, and hydrogen in interconnected circulating fluidized beds, from charges that contain hydrocarbons with at least 11 carbon atoms or from charges with a high oxygen content, using a catalyst preferably in particulate form.

In an embodiment, the invention relates to the generation of ethene and synthesis gas in reactors with interconnected circulating fluidized beds, in which raw materials that include hydrocarbons with at least 11 carbon atoms or raw materials with a high oxygen content are placed in contact with a catalyst, in the presence of steam and in the absence of oxygen.

DETAILED DESCRIPTION OF THE INVENTION

In an embodiment of the present invention, there is continuous catalyst circulation between the two sections of an apparatus for steam cracking. For ease of understanding, these two sections may be termed the reactor (second section) and the regenerator (first section). The two sections may be interconnected catalyst fluidized beds. The reactor may be positioned to one side of the regenerator. A vertical riser through which the catalyst moves vertically upwards may connect the reactor to the regenerator. The catalyst is transported through the vertical riser up to a dense fluidized bed reactor, where the desired reactions take place.

The regenerator and the reactor may be contained in a single vessel. In this case, the reactor is positioned above the regenerator.

The charge, which may consist of long-chain hydrocarbon molecules, is diluted with steam. The resulting mixture is provided to the apparatus for steam cracking. This may be done by injecting the mixture into the reactor.

The present invention enables the production of ethene and synthesis gas from long chain hydrocarbons or materials with a high oxygen content. Long chain hydrocarbons and materials with a high oxygen content may be used because the deactivation of the catalyst due to coking, which is a particular problem when long chain hydrocarbons or charges with a high oxygen content are used, is prevented by regeneration of the catalyst in the regenerator. The provision of steam to the flow of the charge allows for steam cracking reactions to take place in the reactor. This promotes the production of small molecules such as ethene, carbon monoxide, carbon dioxide and hydrogen from the charges.

In particular, the composition of the hydrocarbon charge may include molecules with at least 11 carbon atoms. The charge may include a renewable raw material preferably has a high oxygen content.

In an embodiment, the charge includes an oil. Preferably, the oil is selected from a group consisting of an oil of renewable origin, a vegetable oil, castor oil, soy oil, cashew oil, cotton oil and peanut oil.

In an embodiment, the charge includes an alcohol. Preferably, the alcohol is selected from a group consisting of ethanol, fusel oil and glycerol.

In an embodiment, the charge includes a ligneous-cellulose material. Preferably, the ligneous-cellulose material is selected from a group consisting of sugar-cane straw, sugar-cane bagasse, wood shavings and wood sawdust.

Preferably, the steam cracking reactions take place with a charge/steam ratio between 2:1 and 10:1. More preferably, the reactions take place with a charge/steam ratio between 2:1 and 8:1, more preferably between 4:1 and 8:1 , more preferably between 5:1 and 7:1 , and more preferably between 6:1 and 7:1.

The catalyst, which has been heated in the regenerator and is preferably in powdered from, is transferred from the regenerator to the reactor. The catalyst preferably consists of microspheroidal particles whose average particle size is between 50 microns and 90 microns.

Preferably, the composition of the catalyst includes 0% to 60% by weight of solid acid, 0% to 50% by weight of alumina, and 0% to 40% by weight of silica, with the remainder consisting of kaolin.

Preferably, the solid acid includes at least one zeolite, which may be a member of the pentasyl family, such as ZSM-5, or may be of the faujasite type. The catalyst also preferably includes at least one supported metal, such as nickel, copper, iron, zinc, cobalt, cerium, manganese, and magnesium, or at least one metal oxide or supported metal oxide, such as oxides of zinc and cobalt supported on alumina, rhodium oxide supported on alumina, and nickel oxide supported on gamma- or alpha-alumina or on silica.

In a preferred embodiment of the invention, the catalyst preferably consists of microspheroidal particles. Preferably, the size of the particles is between 65 microns and 75 microns. Preferably, the composition of the catalyst includes from 0% to 20% by weight of solid acid, from 5% to 40% by weight of alumina, and from 5% to 25% by weight of silica ^' , with the remainder consisting of kaolin.

In the reactor, the charge is vaporised and cracked into smaller molecules of vapour by contact and mixing with the catalyst and steam. Substantially all of the steam cracking reactions take place in the reactor. The reactions may take place very briefly. The length of time allowed for the reactions to occur may be altered to control the products of the reaction and the overall yield. Preferably, the reactions are endothermic. Preferably, the reactions take place in the absence of oxygen.

Preferably, the reactions take place at temperatures between 500 ⁰ C and 850 ⁰ C. More preferably, the reactions take place at temperatures between 600 ⁰ C and 850 ⁰ C more preferably between 700 ⁰ C and 850 ⁰ C, and more preferably between 770 ⁰ C and 850 ⁰ C.

Preferably, the reactions take place at pressures between 0.10 MPa and 0.45 Mpa. More preferably, the reactions take place at pressures between 0.10 MPa and 0.35 Mpa, and more preferably between 0.10 MPa and 0.25 Mpa.

Preferably, both the regenerator and the reactor comprise circulating fluidised beds. The steam-based catalytic cracking of the charges involves high concentrations of solids in the fluidised bed. Therefore, the density of the bed is preferably between 150 kg/m ³ and 1800 kg/m ³ . More preferably, the density of the bed is between 500 kg/m ³ and 1800 kg/m ³ .

In an embodiment, the density of the bed is between 500 kg/m ³ and 600 kg/m ³ , more preferably between 520 kg/m ³ and 580 kg/m ³ , more preferably between 530 kg/m ³ and 560 kg/m ³ , and more preferably between 540 kg/m ³ and 550 kg/m ³ .

In an alternative embodiment, the density of the bed is between 1600 kg/m ³ and 1800 kg/m ³ , more preferably between 1680 kg/m ³ and 1740 kg/m ³ , more preferably between 1710 kg/m ³ and 1740 kg/m ³ , and more preferably between 1720 kg/m ³ and 1730 kg/m ³ .

These reactions result in carbonaceous material, in particular coke, depositing on the surface of the particles of catalyst. The hydrocarbon and steam vapours fluidise the powdered catalyst. The mixture of hydrocarbon vapours and catalyst flows upward to enter the reactor.

Preferably, following the steam cracking reactions, the cracked product vapours are separated from the used catalyst. This may be done by flowing the mixture of vapours and catalyst through a set of cyclones. The products produced in the reaction depend on the composition of the feed, the hydrocarbon to steam ratio and on the cracking temperature.

Preferably, the catalyst then flows downward through a steam stripping section to remove any hydrocarbon vapours from the catalyst before the catalyst enters the regenerator.

Preferably, catalyst transfer in the apparatus for steam cracking is carried out through standpipes. A standpipe is a simple catalyst transfer conduit with very few critical design requirements. The standpipes isolate the regeneration section from the reaction section since they act as catalyst seals. In other words, the standpipes minimize the mixing between the molecules produced by the reforming reactions (i.e. the steam cracking) and the molecules produced from the combustion of material deposited onto the catalyst surface.

With the use of such standpipes, catalyst circulation between the reactor and the regenerator is driven by unit pressure balance. Although the pressure balance of the unit (i.e. the apparatus for steam cracking) consists of numerous parameters, most of these parameters are set by overall unit layout and process conditions and, therefore, seldom vary. Accordingly, the flow of catalyst to the regenerator may be regulated by a slide valve in the standpipe from the reactor to the regenerator.

As mentioned above, the steam cracking reactions produce some carbonaceous material that deposits on the surface of the catalyst. Such coking reduces the catalyst reactivity. According to the present invention, the catalyst is regenerated by burning off the deposited coke in the regenerator. Air is blown into the regenerator vessel to promote the combustion of the coke.

The combustion of the coke is exothermic. Hence, it produces a large amount of heat that is partially absorbed by the regenerated catalyst. In this way the heat required for the vaporisation of the charge and the endothermic steam cracking reactions that take place in the reactor is provided through the transfer of the heated catalyst from the regenerator to the reactor. Preferably, substantially all of the heat required for the steam cracking reactions is provided by the heat produced from the regenerator. The hot catalyst leaving the regenerator flows into a catalyst withdrawal well where any entrained combustion flue gases are allowed to escape and flow back into the upper part to the regenerator. The flow of regenerated catalyst to the charge/steam injection point below the catalyst riser is regulated by a slide valve in the regenerated catalyst line. The hot flue gas exits the regenerator after passing through multiple sets of two-stage cyclones that remove entrained catalyst from the flue gas.

An embodiment of the present invention provides a method for the production of ethene and synthesis gas in a reactor with two independent sections and a circulating fluidized bed, which method includes the following stages:

1 ) The provision of a charge of hydrocarbons or of a raw material with a high oxygen content;

2) The promotion of contact between the said charge and a catalyst, such that steam-based cracking reactions take place in the second section of the reactor;

3) The separation of the resulting products;

4) The continuous regeneration of the said catalyst in the first section of the reactor, through the burning of the deposited coke with air;

5) The reconveyance of the said regenerated catalyst to the second section of the reactor, to restart the process.

EXAMPLES

Tables 1 , 2, and 3, respectively, present some of the characteristics of the catalysts . and charges employed in the tests that illustrate the present invention.

EXAMPLE 1

Comparative example. This example shows the effect of the deactivation of the catalyst over a period of 4 hours of uninterrupted kerosene processing, using a single pilot unit and a commercial reforming catalyst. A reaction temperature of 728 ⁰ C was employed, with a 4:1 mass-base steam/kerosene ratio.

The unit was operated under pressure of 101 kPa. Table 4 shows the hydrogen yield loss (% by mass) in terms of the dry base over time.

TABLE 4

HYDROGEN YIELD LOSS OVER TIME

Time (minutes) 0 47 69 109 130 162 202 231 262 280

% H ₂ 0 3.32 3.27 3.43 3.24 2.90 2.70 2.73 2.68 2.63 EXAMPLE 2

Comparative example. In this example a single DCR (Davison Circulating Riser) unit with an adiabatic reactor was used in an ascending-flow dragged bed (riser). The pilot unit operated with nitrogen, during the dispersion of the catalyst and also during the rectification stage (that is, no steam was injected). In this case, all of the water in the reaction medium came solely from the reaction in which the ethanol in the process charge was dehydrated. The catalyst-to-hydrocarbon (CtH) ratio was adjusted in accordance with the change in the temperature of the charge. Simulated distillation in compliance with the ASTM D 2887 method was performed so that the resulting hydrocarbons could be analyzed, and the gasoline and heavy hydrocarbon flows, as defined by the 220 ⁰ C cut-off point, were determined. Ethanol was introduced into the riser reactor, which used a catalyst-density fluidization regime on the order of 45 kg/m ³ , so as to come into contact with catalyst "A". Table 5 shows the process conditions and the product-yield results. The results show the ethene yield resulting from the dehydration of the ethanol, along with the absence of CO and CO ₂ , as well as with the extremely low hydrogen values obtained under these conditions.

EXAMPLE 3

Table 6 shows the results obtained through the use of the method taught in the present invention. A single pilot unit was used that had two circulating fluidized beds that were interconnected so that the tests could be performed. The first bed was dedicated to the reforming reactions and the second bed was dedicated to the reactions consisting of the combustion of the coke with air. A stream of hydrated ethanol, whose properties are listed in Table 2, was injected into the first fluidized bed, along with a water stream using the catalysts listed in Table 1. The density in the reaction bed was between 500 and 1800 kg/m ³ , and the ethanol/water ratio was between 4.0 and 6.1. The reaction temperature varied between 618 ⁰ C and 831 °C. The results indicate the generation of hydrogen, CO, and CO ₂ , as well as the generation of ethene, which is extremely useful in the petrochemical industry. In Test 3, which used catalyst "C", no ethene was generated. Instead, only hydrogen, CO, and CO ₂ were generated.

EXAMPLE 4

Likewise, Table 7 shows the results achieved through the use of the method taught in the present invention.

The tests were performed with the use of a single pilot unit with two circulating fluidized beds. The first bed was dedicated to the reforming reactions and the second bed was dedicated to the coke-combustion reactions. A stream of kerosene and a stream of water were injected respectively into the first fluidized bed, along with the catalysts listed in Table 1 , so as to produce a density between 500 and 1800 kg/m ³ in the reaction bed and a kerosene-to-water mass ratio between 6.2 and 6.8. The reaction temperature varied between 727°C and 823°C. The results indicate the generation of hydrogen, CO, and CO ₂ , as well as the generation of ethene.

This application is based upon, claims the benefit of, priority of, and incorporates by reference, the contents of Brazilian Patent Application No. Pl 0804120-2 filed September 9, 2008.