FIELD OF THE INVENTION

The present invention relates to the field of catalysts for the production of light olefins, and in particular to an ethanol dehydration system and process using co-catalysts in a catalytic reaction.

BACKGROUND OF THE INVENTION

Ethene is the most important platform molecule for the petrochemical industry. Its main application consists of the fabrication of polyethylene, which is widely used in packaging by the food industry. This polymer is also used to make storage drums, household goods, water, gas and irrigation pipes, garbage bags, industrial coatings and many other applications. It is also worth mentioning its application for generating a wide variety of important petrochemical products and/or intermediate goods such as ethylene oxide, ethylene glycol, styrene vinyl chloride, acrylate and others.

The production of this olefin is handled through routes that are widely known and used at the industrial level. Noteworthy among them is steam cracking, which may use a vast range of raw materials such as petrochemical naphtha, light refinery gases and shale gas.

Rising concerns over sustainability and particularly the reduction of greenhouse gases have prompted the chemical industry to seek out renewable raw materials. In this context, the use of ethanol made from biomass became a particularly interesting option, due to the widespread production of this alcohol in Brazil and its growth potential through second-generation ethanol made from lignocellulosic wastes.

Ethene production is handled through the ethanol dehydration reaction in the presence of a heterogeneous acid catalyst. One of the main technical problems in this process is the generation of some by-products, whose presence in the system affects olefin production costs. Acetaldehyde is rated as an unfavorable contaminant, as it decomposes under reaction conditions, generating residues on the catalyst surface, which leads to its deactivation, thus shortening its useful lifespan. As a result, catalyst regeneration is regularly required, causing halts in the process and additional costs. The formation of ethane as a by-product is also unwanted as, although inert, its presence increases separation costs. There is no doubt that lessening acetaldehyde and ethane concentrations in the reaction system will result in lower operating costs.

The present invention is focused on the removal of unwanted by-products. Specifically, the invention allows avoidance or reduction of the secondary formation of acetaldehyde and ethane.

U.S. Pat. No. 4,232,179 was the first to describe an adiabatic process for converting ethanol to ethene using silica-alumina and alumina catalysts. In the examples given in this patent, the reaction was initiated at temperatures between 390° C. and 470° C. and an inert/ethanol ratio between 2.85 and 7.15 by mass. Example 13 in this patent shows a higher conversion using alumina, fed with a mixture of water and ethanol with a mass ratio of 3:1, inflow temperature of 470° C. and a final temperature of 360° C. when leaving the reactor.

Some references—such as CN 104557394 and CN 102372558 for example—describe methods that optimize the mode of operation and the configuration of industrial plants, using power co-generation to lower energy costs. These references describe the steps in the ethene production route without modifying the catalyst.

U.S. Pat. No. 4,302,357 mentions the operating conditions and the short useful life of the catalyst resulting from carbon deposits on its surface, as disadvantages of the ethanol dehydration process. In order to prevent this deactivation that would result from the presence of olefins formed in parallel reactions, according to the authors, the invention suggests the use of alumina catalysts containing some specific oxides. Similarly, the most recent document—CN 102190543—also reports deactivation problems, although caused by CO2and H2as by-products CO, upgrading the reaction through the preparation of a new catalyst containing a metal oxide selected from Groups IA or IIA and alumina. Those proposals suggest new catalysts for ethanol dehydration and indicate different by-products as agents causing catalyst deactivation, making no reference to acetaldehyde.

Following this same direction, document CN 101121625 refers to an ethene preparation method through ethanol dehydration, proposing a reduction in the energy consumption of the reaction through using SiO2/Al2O3. Document CN 102671689 describes an ethene dehydration method for different ethanol concentrations and a catalyst preparation model using a catalyst with a USY base enriched with a transition metal. Document CN 101244971 describes a method synthesizing bioethanol dehydration in ethene, in order to make the process cheaper and more efficient through a catalyst with a modified zeolite base.

Still regarding the use of a single catalysis system, CN 101439294 and WO 2014171688 were retrieved. The invention described in document CN 101439294 refers to an ethylene preparation technology through ethanol dehydration. The main component of the catalyst is ZSM-5 with the addition of one or two elements selected from among aluminium, magnesium, phosphorus and lanthanum, in order to promote catalytic activity. Document WO 2014171688 describes an ethanol dehydration catalyst for converting a raw material that comprises anhydrous or hydrated ethanol in ethylene, wherein the ZSM-5 contains 0.1-0.5% by weight of lanthanum (La) or 0.05 to 1% by weight of gallium (Ga). It is apparent from the state of the art that these alterations (in both documents) are intended to control the acidity of zeolite, as they are generally very acidic. This characteristic triggers reactions leading to heavy compounds that deactivate the catalyst, not fostering the formation of ethene and leading to a dehydration reaction that extends well beyond the output of the desired product.

Documents CN 101121625, CN 102671689, CN 101244971, CN 101439294 and WO 2014171688 present catalysts or catalytic systems that may be used in the system proposed in this invention; however, they would not prevent the formation of acetaldehyde, which is an unwanted by-product of the ethanol dehydration reaction.

Document WO 2011002699 describes a process for preparing olefins from aliphatic alcohols, using catalysts that may contain alumina, silica-alumina and zirconia, among others. Nevertheless, although mentioning the use of oxides, this reference addresses the ethanol dehydration reaction in two steps, using separate reactors forming ethyl ether in the presence of a dehydration catalyst in the first reactor at a temperature of 200° C. to 450° C., and placing it to react in a second reactor operating at a higher temperature level than the first reactor, in the presence of a second dehydration catalyst. The document also reports that this temperature system helps reduce the formation of by-products, which in turn lessens the formation of coke, encrustations, and the need to use large amounts of water, thus lowering energy and capital costs. However, it may be noted from the state of the art that using two reactors requires heavier investments and higher production costs than using just one reactor, which might in turn not be offset through reduced water use.

Current research in this field describes new catalysts that require meticulous preparation. Already costly, the process requires commercial catalysts such as alumina and silica-alumina that are already efficient, although subject to deactivation through the formation of by-products. From this standpoint, documents CN 104084182 and CN 103121900 describe the development of catalysts with larger pore volumes, greater surface areas and enhanced hardness than the usual alumina catalyst used for ethanol dehydration, through modifications to the preparation process. These catalysts present greater activity under certain conditions, with better ethene selectivity and longer useful lifespans, in other words, they are more stable than conventional alumina. Furthermore, enhanced hardness is very convenient for use in a fluid bed reactor. However, these documents do not provide clear data on the extension of the useful lives of the catalysts.

The use of zeolites for ethanol transformation is widely described in the scientific literature. In general, the formation of ethene, propene and heavy compounds is observed. The latter are precursors of coke, which causes the deactivation process, greatly shortening the useful lives of these zeolite-based catalysts. By adjusting the operating conditions and acid strength of these materials, it is possible to reduce this effect. However, due to the nature of these catalysts, this issue must always be present.

From a technological standpoint, current industrial dehydration processes for short-chain alcohols operate reliably and with good results. Ethene production processes using fossil-based raw materials are generally fine-tuned, leading to lower production costs. Without doubt, they establish a production costs threshold that drives improvements in processes for obtaining ethene through ethanol.

Although current catalysts are efficient, they are subject to limitations, due to the inevitable formation of by-products to even in small quantities. In addition to representing a loss of part of the green carbon supplied by the alcohol, these by-products affect catalyst performance, leading to higher operating costs.

Formed as a by-product during ethanol dehydration using ethene, acetaldehyde is an important dehydration catalyst deactivation agent. Hydrogen, ethane and other by-products may also be formed, usually generated from degraded acetaldehyde.

C. P. Rodrigues, P. C. Zonetti, C. G. Silva, A. B. Gaspar, L. G.Appel, Applied Catalysis A: General, Vol. 458, 2013, 111 to 118 doi:10.1016/j.apcata.2013.03.028) and A. F. F. de Lima, P. C. Zonetti, C. P. Rodrigues, L. G. Appel, available online on May 26, 2016, Catalysis Today, doi:10.1016/j.cattod.2016.04.038, recently showed that certain catalysts can transform ethanol into acetone in the presence of water. These authors also ascertained that acetaldehyde is one of the intermediate products in this reaction.

The purpose of the present invention is to thus provide a new catalytic process and systems for the production of olefins through dehydrating alcohols with higher performance, avoiding and/or reducing the formation of by-products during the reaction, with a high conversion rate and high selectivity for olefins.

This purpose is achieved through this invention by means of a catalytic system comprising at least one catalyst and at least one co-catalyst, wherein the catalyst causes the dehydration of the alcohol into olefin and the co-catalyst prompts the oxy-ketonization reaction, in other words, through adsorption and transformation of generated by-products into substances that are less harmful, particularly the uptake and transformation of acetaldehyde into acetone.

Surprisingly, the addition of a new component (the co-catalyst) to the catalytic system resulted in longer usage time for the catalyst and an increase in its deactivation resistance, although without lowering the ethene selectivity and ethanol conversion values; in other words, the addition of a co-catalyst enhancing the efficiency of the ethanol dehydration reaction. Moreover, an improvement is noted in the dehydration reaction selectivity through the partial removal of an unwanted by-product that causes undesired reactions when present in the reaction environment; its removal thus leads to more favorable operating costs.

As there is no need for modification to the composition of the commercial catalysts nor any rearrangement of the plant operating mode configuration, the process of the present invention also differs from the documents constituting the state of the art.

SUMMARY OF THE INVENTION

The present invention relates to a catalytic system for the preparation of light olefins through the dehydration of alcohols, comprising at least one catalyst and at least one co-catalyst, wherein the catalyst is selected from among catalysts for the catalytic dehydration of ethanol and with the co-catalyst selected from among oxy-ketonization reaction catalysts, wherein the catalyst:co-catalyst mass ratio is within a range of 0.5:0.125 to 2:10, and preferably within a range of 1:0.25 to 1:5.

With the catalyst selected from the catalysts for the catalytic ethanol dehydration, namely, oxides, molecular sieves, zeolites, metal salts, ion-exchange resins, activated carbon, α-boron and WS2, and the selected co-catalyst being an oxy-ketonization reaction catalyst selected from among simple or mixed oxides, including the different polymorphic structures of a simple oxide, comprising at least one metal selected from among transition metals in Groups 1B, 2B, 3B, 4B, 5B, 6B and 7B of the Periodic Table, lanthanides and metals in Groups 3A and 4A, it may be selected from the group that comprises zirconium oxide, yttrium oxide, mixed lanthanum and zirconium oxide and mixtures thereof.

Another purpose of this invention is the catalytic system, characterized in that it is a physical mixture of the catalyst and the co-catalyst consisting of pellets of each one of the components in isolation, or a pellet made from a mixture of the two components in the form of sequential layers or beds, mixed or not, or in the form of powder, wherein the particles may contain both the catalysts or individual particles of each one of the components.

Another purpose of this invention is the process for the production of light olefins from ethanol, using an alcohol flow, hydrated or not, in the presence of the catalytic system, at a temperature varying between 200° C. and 800° C., preferably between 360° C. and 470° C., and at a pressure varying between 1 bar and 60 bar, preferably 1 bar and 20 bar, wherein the hydrated alcohol presents a water:alcohol mass ratio of between 0.25:1 and up to 5:1, preferably between 1:1 and 3:1, occurring in a Plug Flow Reactor (PFR), fixed or fluid bed, batch or Continuous-Stirred Tank Reactor (CSTR), being adiabatic or not, wherein use of the catalytic system presents alcohol conversions of at least 97%, preferably 99%, and olefins selectivity of at least 97%, preferably 99%, and the catalytic system operates continuously without deactivation for a period more than five times longer than the useful life of the dehydration catalyst when used alone, in other words, without the co-catalyst.

