Catalytic system and process for the production of light olefins from ethanol

Abstract

The present invention relates to a catalytic system for the preparation of light olefins through the dehydration of alcohols, including 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.

Claims

1. A catalytic system for the preparation of light olefins from ethanol, which comprises at least one ethanol-dehydration catalyst and at least one acetaldehyde-to-acetone catalyst, wherein the ethanol-dehydration catalyst:acetaldehyde-to-acetone catalyst mass ratio is within a range of 1:0.5 to 1:5, wherein the catalytic system exhibits an ethene selectivity of at least 97.2%, wherein the ethanol-dehydration catalyst comprises gamma alumina, wherein the acetaldehyde-to-acetone catalyst comprises at least one of Y.sub.2O.sub.3, ZrO.sub.2, and La-ZrO.sub.2, and wherein the catalytic system, when present during a continuous operation of a preparation of light olefins, exhibits a reaction conversion of 99%, without deactivation, for a period more than five times longer than a useful life of the ethanol dehydration catalyst when used alone.

2. The catalytic system as recited in claim 1, wherein the catalytic system is a physical mixture of the ethanol-dehydration catalyst and acetaldehyde-to-acetone catalyst.

3. The catalytic system as recited in claim 1, wherein the catalytic system is a physical mixture of the ethanol-dehydration catalyst with the acetaldehyde-to-acetone catalyst presented as pellets of each one of the components in isolation, or a pellet made from a mixture of the two components laid out in sequential layers or beds, mixed or not, or in the form of powder, wherein the particles contain both the ethanol-dehydration catalyst and the acetaldehyde-to-acetone catalyst or individual particles of each one of the components.

4. The catalytic system as recited in claim 1, wherein the ethanol-dehydration catalyst:acetaldehyde-to-acetone catalyst mass ratio is within a range of 1:0.5 to 1:3.

5. A process for the production of light olefins from ethanol, the process comprising contacting the catalytic system as recited in claim 1 with a flow of alcohol, hydrated or not, in a reactor, at a temperature between 200° C. and 800° C. and a pressure between 1 bar and 60 bar.

6. The process as recited in claim 5, wherein temperature variations occur between 360° C. and 470° C.

7. The process as recited in claim 5, wherein pressure variations occur between 1 bar and 20 bar.

8. The process as recited in claim 5, wherein the alcohol is a hydrated alcohol having a water:alcohol mass ratio of between 0.25:1 and 5:1.

9. The process as recited in claim 5, wherein the reaction occurs in a Plug Flow Reactor (PFR), fixed or fluid bed, batch or a Continuous-Stirred Tank Reactor (CSTR), being adiabatic or not.

10. The process as recited in claim 5, wherein the catalytic system operates continuously, maintaining the reaction conversion at 99%, without deactivation, for a period more than five times longer than the useful life of the dehydration catalyst when used alone.

11. The process as recited in claim 5, wherein the hydrated alcohol has a water:alcohol mass ratio of between 1:1 and 3:1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to illustrate more clearly and objectively the technical solutions shown in the examples of the invention, a brief presentation of the appended drawing is given, for one embodiment of the invention.

(2) FIG. 1 shows an ethanol conversion progress over time for a conventional ethanol dehydration catalyst (y-alumina) and a catalyst:co-catalyst mixture with ZrO.sub.2 in a proportion of 1:1, as an example.

DETAILED DESCRIPTION OF THE INVENTION

(3) The present invention is based on the use of a mixture of a catalyst dehydrating ethanol into ethene and one co-catalyst causing oxy-ketonization, in other words, transforming the acetaldehyde formed during the process into acetone, thus giving rise to a catalytic system and process for the production of light olefins from ethanol.

(4) The present invention relates to a catalytic system for the preparation of light olefins from the dehydration of alcohols comprising at least one catalyst and at least one co-catalyst. Light olefins are taken to mean olefins containing 2 to 6 carbon atoms, preferably ethene. The catalyst:co-catalyst mass ratio is between 0.5:0.125 to 2:10, preferably within a range of 1:0.25 to 1:5.

(5) For the dehydration catalyst addressed by this invention, a catalyst is used for the catalytic dehydration of ethanol, namely, oxides, molecular sieves, zeolites, metal salts, ion-exchange resins, activated carbon, α-boron, WS.sub.2, alumina modified by different chemical elements or aluminosilicates.

(6) As a co-catalyst, the use of an oxy-ketonization reaction catalyst is proposed, which may be simple oxides or mixed oxides, in addition to also considering the different polymorphic ruptures of a single oxide. For the co-catalyst, it is important that it has a high specific area and is heat-stable up to at least 500° C., with basic surface sites.

(7) In a preferred embodiment, the co-catalyst comprises at least one oxide of a metal selected from among the transition metals in Groups 1B, 2B, 3B, 4B, 5B, 6B and 7B of the Periodic Table, lanthanides and metals in Groups 3A and 4A. In a second preferred embodiment of the invention, the co-catalyst is selected from the group that comprises zirconium oxide, yttrium oxide, mixed lanthanum and zirconium oxide and mixtures thereof. The co-catalyst used in this invention causes the oxy-ketonization reaction, which refers to the acetaldehyde transformation forming acetone, CO.sub.2 and H.sub.2.

(8) The catalytic system addressed by this invention may be prepared through a physical mixture of at least one catalyst and at least one co-catalyst, which may be in the form of pellets, either as pellets with each one of the components in isolation, meaning catalyst pellet+co-catalyst pellet, or a single pellet blending both of them. It may also be in the form of sequential layers or beds, not necessarily mixed. They may also be used in the form of powder, wherein the particles may contain both the catalysts or individual particles of each one of the components.

(9) Furthermore, this invention refers to a process for the production of light olefins through dehydrating alcohols using an alcohol flow in contact with the catalytic system.

(10) The dehydration reaction may occur in a reactor 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.

(11) The alcohol used in the process addressed by this invention may be comprised of 2 to 6 carbon atoms, and may be hydrated or not. When hydrated alcohol is used, the water:alcohol mass ratio is between 0.25:1 and up to 5:1, preferably between 1:1 and 4:1. The reaction occurs in a reactor as described above, which may be a Plug Flow Reactor (PFR), fixed or fluid bed, batch or Continuous-Stirred Tank Reactor (CSTR), being adiabatic or not.

(12) Through using the catalytic system addressed by this invention, it is possible to convert alcohols to olefins at 97% at least and preferably 99%, and with olefin selectivity of at least 97%, preferably 99%.

EXAMPLES

(13) The following examples are merely illustrative and are not intended to curtail the scope of the protection sought for this invention.

(14) Performance tests of the catalytic system (catalyst+co-catalyst) were run under conditions representing the industrial process as set forth in U.S. Pat. No. 4,232,179 (example 13). An inflow was used containing a water/ethanol mass ratio of 3 and a reaction temperature of 470° C. The laboratory tests were conducted under isothermal conditions, thus keeping the reactor at 470° C. for the entire duration of the experiment. It is appropriate to mention that there is a temperature variation along the reactor for the adiabatic process, due to the endothermal reaction. In order to evaluate the performance of the catalytic systems proposed in the invention, tests were also conducted under isothermal conditions at a lower temperature (360° C.). Finally, it is noted that the performance of the catalytic systems proposed in the invention was compared on the same laboratory scale with a typical catalyst used for producing ethene from ethanol, namely alumina.

(15) The performance of ten different co-catalysts were evaluated, and may be organized into three groups: simple oxides (ZrO.sub.2, TiO.sub.2, Y.sub.2O.sub.3 and CeO.sub.2), simple oxide polymorphs (ZrO.sub.2 with a monocline crystal structure, m-ZrO.sub.2, and with a tetragonal crystal structure, t-ZrO.sub.2) and mixed/doped oxides (Y.sub.2O.sub.3—ZrO.sub.2, La.sub.2O.sub.3—ZrO.sub.2, TiO.sub.2—ZrO.sub.2, SiO.sub.2—ZrO.sub.2 and Ag—CeO.sub.2). Many of these materials are available commercially, with only Y.sub.2O.sub.3, CeO.sub.2 and Ag—CeO.sub.2 synthesized in the laboratory.

(16) In all tests conducted at the higher temperature (470° C.), ethanol conversion exceeded 97%, with ethene selectivity between 97% and 99%. When using only the dehydration catalyst (alumina), the formation of acetaldehyde and ethane occurred, with selectivities between 1% and 2% and 0.1% to 0.2%, respectively. In contrast, when using the catalyst and co-catalyst system, acetaldehyde selectivity fell below 0.3%, with the formation of this aldehyde not even detected in some examples. Ethane production also dropped, with selectivities between 0.05% and 0.2%.

(17) With the alumina and m-ZrO.sub.2 system, tests were conducted with different catalyst:co-catalyst proportions, namely: 1:0.5, 1:1, 1:2, 1:3 and 1:5. No modifications in ethanol conversion into ethene were observed for any of these proportions, with olefin selectivity always exceeding 97%. Acetaldehyde production was consistently low, always below 0.1%, and not forming at all in one example. At any of the studied proportions, ethene selectivity remained between 0.05% and 0.2%.

(18) Long-duration tests lasting 168 hours were conducted only with the 1:1 catalyst:co-catalyst mixture, with its performance compared to pure alumina (catalyst) over the same duration. These tests demonstrated the superiority of using the mixture, as deactivation of the pure catalyst was observed from approximately 35 hours onwards, while the catalyst and co-catalyst system remained stable throughout the 168 hours monitored. It is worth pointing out that when deactivation occurs, a gradual drop in alcohol conversion is noted. In the mentioned example, conversion fell from 99% at the start of the reaction to 90% at the end of 168 hours, when using only the catalyst. Using the mixture maintained conversion at 99% for the entire duration. This result indicates that the catalytic system described in this document can operate continuously without deactivation for a period more than five times longer than the useful life of the dehydration catalyst when used alone.

(19) Catalyst deactivation is also clear for acetaldehyde production, which begins at about 1.5% selectivity, varying by values of up to 0.8% during the 168 hours using only the dehydration catalyst. When using the catalyst:co-catalyst mixture at a 1:1 ratio, the formation of acetaldehyde as a by-product was not observed throughout this entire period.

(20) In addition to the products already mentioned, the formation of light products occurs, specifically CO, CO.sub.2, H.sub.2 and CH.sub.4, in all cases, whether using only the catalyst or the catalytic system (catalyst and co-catalyst). However, there is a striking difference in acetone production as well when using the catalyst and co-catalyst mixture. This is the outcome of the oxy-ketonization reaction, transforming the acetaldehyde on the co-catalyst. Non-existent in known industrial ethanol dehydration processes using acid catalysts, acetone is formed with a selectivity of between 0.2% and 1%, depending on the type and proportion of co-catalyst used.

(21) The advantage of removing the acetaldehyde and its transformation in situ—this conversion occurring in the dehydration reactor—by the acetone during the process consists of the chemical advantages of this molecule, as acetone is stable and less reactive under the reaction conditions. Furthermore, in terms of economic advantages, it is simple to separate the acetone from the final olefin stream, with its production also favoring production lines for other products, as it may be repurposed for other industrial uses (as an important solvent in the polymers and drugs segments) or for generating chemicals such as isopropanol and propene. Similarly, the concomitant reduction in ethane formation also endows the process with economic advantages through lowering associated separation costs.

(22) For the purposes of analysis, a mass catalyst value interval of 11.4 to 11.8 mg was used, with a water:ethanol mass ratio of 3 for feeding into the process, operating condition at 470° C. for the reaction and a mass ratio of catalyst:inert matter (silicon carbide) of 0.0765. Short and long duration tests were conducted, lasting 14 hours and 168 hours respectively, the purposes of comparing catalyst deactivation and ethanol conversion.

Example 1

(23) A gamma alumina type catalyst was combined with an yttrium oxide (Y.sub.2O.sub.3) in an alumina and oxide proportion of 1:1 and added into a stainless steel isothermal fixed bed Plug Flow Reactor (PFR) with an internal diameter of 0.9 cm. At atmospheric pressure and a temperature of 470° C., a feeder inflow of water and ethanol with a mass ratio of 3:1 to 44 mL/min was admitted into the reactor and left to react for a total period of 14 hours. When analyzing the effluent, it was noted that the ethanol conversion in this example was 99% and the selectivity levels for ethene, acetaldehyde and ethane varied between 97.6 to 98.9%, 0.09 to 0.17% and 0.15 to 0.20%, respectively.

Example 2

(24) A gamma alumina type catalyst was combined with a zirconium oxide (ZrO.sub.2) in an alumina and oxide proportion of 1:3 and added into a stainless steel isothermal fixed bed Plug Flow Reactor (PFR) with an internal diameter of 0.9 cm. At atmospheric pressure and a temperature of 470° C., a feeder inflow of water and ethanol with a mass ratio of 3:1 to 44 mL/min was admitted into the reactor and left to react for a total period of 14 hours. When analyzing the effluent, it was noted that the ethanol conversion in this example was 99.5% and the selectivity levels for ethene, acetaldehyde and ethane varied between 97.2% to 98.8%, 0.03% to 0.07% and 0.09% to 0.19%, respectively.

Example 3

(25) A gamma alumina type catalyst was combined with a mixed lanthanum and zirconium oxide (La—ZrO.sub.2) in an alumina and oxide proportion of 1:1 and added into a stainless steel isothermal fixed bed Plug Flow Reactor (PFR) with an internal diameter of 0.9 cm. At atmospheric pressure and a temperature of 470° C., a feeder inflow of water and ethanol with a mass ratio of 3:1 to 44 mL/min was admitted into the reactor and left to react for a total period of 14 hours. When analyzing the effluent, it was noted that the ethanol conversion in this example was 100% and the selectivity levels for ethene and ethane varied between 98% to 98.9% and 0.17% to 0.22%, respectively. The formation of acetaldehyde was not observed.

Example 4

(26) A gamma alumina type catalyst was combined with a zirconium oxide with a monocline-type crystal structure (m-ZrO.sub.2) in an alumina and oxide proportion of 1:1 and added into a stainless steel isothermal fixed bed Plug Flow Reactor (PFR) with an internal diameter of 0.9 cm. At atmospheric pressure and a temperature of 470° C., a feeder inflow of water and ethanol with a mass ratio of 3:1 to 44 mL/min was admitted into the reactor and left to react for a total period of 168 hours. When analyzing the effluent, it was noted that the ethanol conversion in this example was 99.8% throughout the entire reaction time (168 h) and the selectivity levels for ethene and ethane varied between 98.3% to 99.6% and 0.08% to 0.22%, respectively. There was no acetaldehyde formation throughout the entire reaction time.

(27) The above-mentioned examples were summarized and compared as set forth in Table 1 below.

(28) TABLE-US-00001 TABLE 1 Example 1 2 3 4 Catalyst γ-alu- γ-alu- γ-alu- γ-alu- mina mina mina mina Co-catalyst Y.sub.2O.sub.3 ZrO.sub.2 Lα-ZrO.sub.2 ZrO.sub.2 Proportion cat:co-cat (mass) 1:1 1:3 1:1 1:1 Reaction time (h) 14 14    14 168 Ethanol conversion (%) 99 99.5 100   99.8 Selectivity for ethene (%) 97.6 to 97.2 to 98 to 98.3 to 98.9 98.8 98.9 99.6 Selectivity for 0.09 to 0.03 to  0  0 acetaldehyde (%) 0.17 0.07 Selectivity for Ethane (%) 0.15 to 0.09 to 0.17 to 0.08 to 0.20 0.19 0.22 0.22 Selectivity for acetone (%) 0.18 to 0.32 to 0.35 to 0.13 to 0.55 0.88 0.75 0.70