FR3015477A1 - PROPYLENE PRODUCTION USING SELECTIVE DEHYDROGENATION STEP AND ISOMERIZATION AND METATHESIS STEP - Google Patents

Abstract

A process for producing propylene from a feedstock comprising linear paraffins having a carbon number of from 8 to 30, said process comprising: a) a step of selective dehydrogenation of the linear paraffins of the feed, b) a step of isomerization and metathesis, in the presence of ethylene, linear monoolefins contained in the effluent from step a), c) a step of separating the effluent from step b) .

Description

Field of the Invention The invention relates to a process for the production of propylene. It relates more particularly to a process for producing propylene from linear paraffins and ethylene.

PRIOR ART Propylene is one of the main petrochemical intermediates, with consumption in 2012 estimated at 84 megatonnes (Mt). Propylene demand in 2035 was estimated at 217 Mt / yr, which corresponds to an average annual growth over the period of 2011 to 2035 of 4.2%. This significant growth in propylene demand can be explained by the fact that polypropylene is booming and is gaining market share on polystyrene or high density polyethylene (HDPE).

The production of propylene can be divided into three major classes of process: steam crackers, which account for about 50% of production; refinery propylene, which accounts for just over one-third of production; and the so-called "on-purpose" methods, which provide the complement.

Steam cracker capacities are mainly dictated by the demand for ethylene. Since the ethylene demand is lower than that of propylene (the average annual growth rate is 3.4% for ethylene compared to 4.2% for propylene over the period 2011 to 2035), the proportion of steam crackers in the processes Propylene production is made to be less and less important.

Moreover, this phenomenon is accentuated by the development of shale gas, which, mainly in the United States, leads to a reduction in steam cracker load. Thus, between 2007 and 2011, the proportion of steam crackers fueled by ethane in the United States increased from 30% to 49% and the share of steam crackers fueled by naphtha rose from 43% to 21%. The propylene yield of a steam cracker fed with ethane is less than 3% against a yield greater than 25% for a steam cracker supplied with naphtha. This makes it possible to anticipate an additional deficit of propylene production capacity in the coming years.

Refinery propylene is correlated with the demand for fuel. It is therefore likely that refinery propylene will not be able to compensate for the production deficit of propylene from steam crackers. This deficit in propylene production should therefore be offset by new production processes.

Various processes for producing propylene from an olefinic feed have been proposed. Thus, Zhang et al., Chem. Eng. Tech., 2013, 36, 795-800 discloses a process of isomerization and ethenolysis of internal linear decenes in the presence of a heterogeneous W03 / SiO2 catalyst for the selective formation of propylene. The decene charge comes from by-products of the trimerization of ethylene to hexene-1 and contains 3% hexenes and octenes. The patent application US 2004/0242944 describes a process for the production of propylene by carrying out a metathesis reaction of C4-C9 olefins from steam crackers in the presence of an isomerization catalyst. Patent Application FR 2,880,018 describes a process for producing propylene from ethylene comprising a step of dimerizing ethylene to butene-1, a step of hydroisomerization of butene-1 to butene-2 and a metathesis step of butene-2 in propylene, in the presence of ethylene. The present invention proposes to produce propylene from a paraffinic feed less easily recoverable than the olefinic feeds. The invention relates to a novel process for the production of propylene from a feed comprising linear paraffins having a carbon number of from 8 to 30, combining a) a step of selectively dehydrogenating linear paraffins from the feedstock. in linear monoolefins, b) a step of isomerization and metathesis, in the presence of ethylene, linear monoolefins from step a). DETAILED DESCRIPTION OF THE INVENTION The invention relates to a process for producing propylene from a feedstock comprising linear paraffins having a number of carbon atoms of between 8 and 30, said process comprising: a) a dehydrogenation step selective linear paraffins of the feed so as to produce an effluent containing linear monoolefins produced, unconverted linear paraffins and hydrogen, b) a step of isomerization and metathesis, in the presence of ethylene, linear monoolefins contained in the effluent from step a) so as to produce an effluent containing ethylene, propylene, linear monoolefins having a number of carbon atoms of between 4 and 30 and unconverted linear paraffins, c) a step of separating the effluent from step b) into a hydrogen fraction, an ethylene fraction, a propylene fraction, a fr composition containing monoolefins having a carbon number of from 4 to 7, a fraction containing linear monoolefins having a number of carbon atoms of 8 to 30 and unconverted linear paraffins. The filler according to the invention comprises linear paraffins having a number of carbon atoms of between 8 and 30, preferably between 10 and 26, more preferably between 10 and 18.

The filler according to the invention is advantageously composed of at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight of linear paraffins.

The filler according to the invention can be obtained from a petroleum cut and / or from a renewable resource such as biomass.

The filler according to the invention can be obtained from a petroleum fraction by selective adsorption on an adsorbent in order to separate linear paraffins from cycloparaffins and isoparaffins or by extractive crystallization, for example with urea.

The filler according to the invention can also be obtained by FischerTropsch synthesis from synthesis gas (CO / H2 mixture). The synthesis gas can be obtained from natural gas by a reforming reaction with steam or from coal by a gasification reaction.

The filler according to the invention can also be obtained from a renewable resource. Advantageously, the filler according to the invention is obtained by a Fischer-Tropsch synthesis from a synthesis gas obtained by gasification of the biomass. Biomass refers to any type of biomass, in particular lignocellulosic biomass. Examples of non-limiting types of biomass include, for example, farm residues (including straw, corn cobs), logging residues, logging products, sawmill residues, crops dedicated to short rotation coppice, poplar, miscanthus, rice straw or wheat, spruce ... The filler according to the invention can also be obtained by hydrotreating vegetable oils or animal fats advantageously containing triglycerides and fatty acids or esters with carbon chains of 8 to 30, preferably 10 to 26, more preferably 10 to 18 carbon atoms. These oils may be palm oil, copra, castor oil, cotton, peanuts, flax, crambe, jatropha; all oils derived from sunflower or obtained by genetic modification or hybridization, as well as algae oils. Household waste oils, various animal oils such as fish oil, tallow or lard can also be used. The filler according to the invention may be a mixture of a filler obtained from a petroleum fraction and / or a filler obtained by Fischer-Tropsch synthesis from a synthesis gas obtained by gasification of biomass. and / or a filler obtained by hydrotreating vegetable oils or animal fats as described above.

Step a) Selective dehydrogenation The selective dehydrogenation step a) is carried out by contacting the feedstock with a dehydrogenation catalyst. The dehydrogenation catalyst may be a homogeneous or heterogeneous catalyst.

Step a) can be carried out with a homogenous dehydrogenation catalyst well known to those skilled in the art as described by M. Brookhart et al. Chem. Rev. 2011, 111, 1761-1779.

Step a) can be carried out in the presence of hydrogen. Dehydrogenation catalysts are well known to those skilled in the art and examples are described in FR 2,945,224 B1, GB2,353,734 B2, US6,600,082 BB. The selective dehydrogenation step a) can be carried out in the presence of a platinum catalyst deposited on a support, preferably alumina. Preferably, said platinum catalyst is promoted by another metal, such as tin. Preferably, the selective dehydrogenation step a) is carried out in gaseous phase, and advantageously in the presence of hydrogen. Optionally, the selective dehydrogenation step a) is carried out in the presence of a flow of water vapor, advantageously added to the feedstock. This flow of water vapor can come from a dehydration reaction of a biosourced molecule, for example the dehydration of ethanol to ethylene and water.

The selective dehydrogenation step a) is advantageously carried out with a molar ratio H 2 / charge of between 0.5 and 10, preferably between 4 and 8, when stage a) is carried out in the presence of hydrogen.

The selective dehydrogenation step a) is advantageously carried out with a temperature of between 300 and 800.degree. C., preferably between 400 and 550.degree. C. and more preferably between 450 and 520.degree. C., a total pressure of between 0.014.degree. and 2 MPa, preferably between 0.1 and 1 MPa and more preferably between 0.1 and 0.5 MPa, a space velocity hour (expressed as the hourly flow rate of charge in m3 / h at 25 ° C and 1 atm divided by the catalyst volume in m3) between 0.5 and 300 h -1, preferably between 1 and 100 h -1 and more preferably between 10 and 50 h -1. The selective dehydrogenation step a) of the process according to the invention is preferably carried out in a fixed-bed unit. The catalyst may be reduced ex situ or in situ under hydrogen at a temperature between 400 and 500 ° C. The effluent from the selective dehydrogenation step a) is an effluent containing the linear monoolefins produced and the unconverted linear paraffins which have similar sizes, i.e. linear monoolefins produced and linear paraffins having 8 to 30, preferably 10 to 26, more preferably 10 to 18 carbon atoms. These compounds have close boiling points and are therefore difficult to separate. The effluent from step a) of selective dehydrogenation also comprises hydrogen from the dehydrogenation reaction, optionally methane and ethane. According to the invention, the effluent from step a) and containing linear monoolefins produced and unconverted linear paraffins is sent to step b) of isomerization and metathesis. Advantageously, said effluent resulting from step a) is previously subjected to a separation step making it possible to separate from said effluent a hydrogen fraction and optionally a fraction comprising methane and ethane, before being sent to step b ) isomerization and metathesis. Preferably, said hydrogen fraction is recycled to the selective dehydrogenation step a), preferably when the selective dehydrogenation step a) is carried out in the presence of hydrogen. The effluent from step a) of selective dehydrogenation is likely to contain traces of diolefins. Optionally, the effluent from the selective dehydrogenation step a) can be subjected to a selective hydrogenation step to convert the diolefins that can be formed at the end of the dehydrogenation step a) to monoolefins. The catalysts for carrying out this selective hydrogenation are well known to those skilled in the art. This hydrogenation can for example be carried out with a catalyst based on palladium on carbon. Step b) Isomerization and Metathesis The isomerization and metathesis step b) is carried out by contacting the linear monoolefins contained in the effluent resulting from the selective dehydrogenation step a) with ethylene. presence of an olefin isomerization catalyst and an olefin metathesis catalyst to produce an effluent containing hydrogen, ethylene, propylene, linear monoolefins having a number of carbon atoms between 4 and 30 and unconverted linear paraffins.

This isomerization and metathesis step may be carried out in the liquid phase or in the gas phase. The olefin isomerization catalyst may be a homogeneous catalyst or a heterogeneous catalyst. The olefin metathesis catalyst may be a homogeneous catalyst or a heterogeneous catalyst. In a preferred variant, is used for the implementation of step b) a homogeneous catalyst of isomerization combined with a homogeneous metathesis catalyst. In another preferred embodiment, is used for the implementation of step b) a heterogeneous catalyst of isomerization combined with a heterogeneous metathesis catalyst.

By homogeneous catalyst is meant a catalyst soluble in the reaction medium. By heterogeneous catalyst is meant a catalyst insoluble in the reaction medium.

When the isomerization and metathesis step b) is advantageously carried out in the liquid phase, it may preferably be carried out in an organic solvent. Advantageously, the solvent is toluene. Step b) of isomerization and metathesis is advantageously carried out with an ethylene / effluent molar ratio resulting from step a) of between 0.5 and 500, preferably between 1 and 100, a total pressure of between 0 and 100.degree. , 01 and 20 MPa, preferably between 0.1 and 10 MPa and more preferably between 0.1 and 5 MPa, a temperature between 10 and 500 ° C. When the reaction is catalyzed by homogeneous catalysts, the temperature is preferably between 10 and 200 ° C, and more preferably between 20 and 120 ° C. When the reaction is catalyzed by heterogeneous catalysts, the temperature is preferably between 10 and 500 ° C, more preferably between 300 and 500 ° C. The olefin isomerization and olefin metathesis catalysts are known to those skilled in the art. The homogeneous olefin isomerization catalyst may be an organometallic complex of a metal selected from columns 3 to 16 of the Periodic Table. Preferably, the metal of the homogeneous isomerization catalyst is selected from Ti, Zr, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, preferably from Ti, Zr, Fe, Ni, Pd, Ir. Examples of homogeneous isomerization catalysts can be found in the following scientific publications: J. Am. Chem. Soc. 1999, 8755-8759; Chem. Cat. Chem. 2011 p 1567-1571; Appl. Organomet. Chem. 2011 p 601-607; J. Catal. 1973 p 403-8; Australian J. Chem. 1991 p 171-80. Optionally, the organometallic complex may be combined with an activator to form the homogeneous olefin isomerization catalyst.

The homogeneous olefin metathesis catalyst may be an organometallic complex of a metal selected from rhenium, iron, osmium, molybdenum, ruthenium and tungsten. A description of complexes of rhenium, iron, osmium, molybdenum, ruthenium or tungsten catalyzing the metathesis reaction of olefins can be found in Handbook of Metathesis, Wiley (Editor: R. H. Grubbs). Preferably, the olefin metathesis catalyst is a ruthenium complex. The heterogeneous olefin isomerization catalyst is chosen from: - ion exchange resins, amorphous or crystallized carbonaceous compounds which have or have not undergone sulphonation and / or carboxylation, the oxides of the elements chosen from aluminum and magnesium , titanium, silicon, zirconium, cerium and niobium, and the mixed oxides chosen from zinc, copper and cobalt aluminates, said oxides being dopable or non-dopable by at least one metal compound selected from the group consisting of tungsten, tin, molybdenum and antimony, crystallized or non-crystalline aluminosilicates and aluminophosphates, - among the solids comprising a metal chosen from the metals of groups 6 to 11 of the periodic table and a support chosen from the oxides of elements selected from aluminum, magnesium, titanium, silicon, zirconium, cerium and niobium, and mixed oxides selected from zinc aluminates, copper e and cobalt, said oxides may be doped or not by at least one metal compound selected from tungsten, tin, molybdenum and antimony, alone or in a mixture, crystallized aluminosilicates or not, aluminophosphates and amorphous or crystalline carbon compounds. The oxides and mixed oxides may comprise from 0.1% to 20% by weight of a sulphate salt or sulfuric acid on the surface.

The heterogeneous metathesis catalyst for olefins may be a catalyst based on chlorides, oxides or carbonyls of metals selected from rhenium, tungsten or molybdenum supported on an acidic support of silica, alumina, silica / alumina, zeolite and other supports of that type. Preferably, the heterogeneous olefin metathesis catalyst is selected from Re 207 / Al 2 O 3 and WO 3 / SiO 2. According to a variant of the present invention, step b) of isomerization and metathesis can be carried out in the presence of hydrogen. The ethylene used in step b) of isomerization and metathesis can be produced by a steam cracker or be derived from a process of fluid catalytic cracking (FCC or "Fluid Catalytic Cracking" in the English terminology) .

The ethylene used in step b) of isomerization and metathesis is preferably produced by dehydration of bio-sourced ethanol. Stage c) of separation of the effluent resulting from stage b) of isomerization and metathesis According to the invention, the effluent resulting from stage b) of isomerization and metathesis is subjected to a separation step for separating a hydrogen fraction, an ethylene fraction, a propylene fraction, a fraction containing the monoolefins having a carbon number of between 4 and 7, a fraction containing the linear monoolefins having a number of carbon atoms between 8 and 30 and unconverted linear paraffins. The step c) of separation can be implemented by any method known to those skilled in the art. This method can be selected from distillation, extraction, absorption, membrane separation, precipitation or crystallization. Preferably, this separation is carried out by one or more fractionation columns. To increase the production yield of propylene, at least a portion, preferably all of the fraction resulting from the separation step c) and containing the linear monoolefins having a number of carbon atoms of between 8 and 30 and the Unconverted linear paraffins is advantageously returned to the selective dehydrogenation step a). Advantageously, at least a part, preferably all of the fraction resulting from the separation step c) and containing the monoolefins having a number of carbon atoms of between 4 and 7 is returned to step b) d isomerization and metathesis. Advantageously, at least a portion, preferably all of the ethylene fraction from step b) is recycled in said step b). The dehydrogenation step a) has a partial conversion of linear paraffins of the feedstock and therefore produces a mixture of monoolefins and linear paraffins which are difficult to separate. One of the advantages of the invention is that this mixture is directly fed to the isomerization and metathesis step b) in which the monoolefins from step a) are converted and converted to propylene and linear monoolefins. having a number of carbon atoms of between 4 and 30 while the paraffins remain inert with respect to the isomerization and metathesis catalysts.

Another advantage of the invention is that at the end of step b) of isomerization and metathesis, the propylene fraction and the fraction containing the monoolefins having a number of carbon atoms of between 4 and 7 are easily separable unconverted linear paraffins.

Examples. 1) Selective dehydrogenation A feed from a coconut oil hydrotreating reaction is used, comprising 98% linear paraffins having 10 to 14 carbon atoms. The reaction is carried out in a fixed bed over a Pt / Al 2 O 3 catalyst. The ratio H2 / load is 6. A water supplement is provided at 2000 ppm weight relative to the load. The hourly space velocity is 20. Over the duration of the test (21 days) and to compensate for deactivation of the catalyst, the temperature is increased from 454 to 515 ° C. The relative pressure goes from 0 to 1.4 bar. The table below indicates the composition of the feedstock and the effluent of step a) of selective dehydrogenation. Composition (% by weight) Fresh feed Effluent from step a) dehydrogenation Paraffins C10-C14 98.0 87.0 C10-C14 olefins 0.0 11.0 Aromatics 0.5 0.5 Isoparaffins 1.0 1.0 Cycloparaffins 0.5 0.5 Flow (T / h) 15 15 2) Isomerisation / Metathesis The selective dehydrogenation effluent of paraffins is modeled by a dodecane / dodecene mixture in a 90/10 mass ratio. 376 mg of dodecene and 3.1 g of dodecane in solution in 30 ml of toluene are introduced into a reactor made of 316L stainless steel of 100 ml. 4.3 mg of di-p-bromobis (tri-t-butylphosphino) dipalladium isomerization catalyst (I) in 4 mL of toluene and 4.2 mg of Umicore M2 metathesis catalyst ([1,3-Bis (2 , 4,6-trimethylphenyl) -2-imidazolidinylidene] dichloro (3-phenyl-1H-inden-1-ylidene) (tricyclohexylphosphine) ruthenium (II)) in 1.5 mL of toluene are added. The reactor is then placed under dynamic pressure of ethylene for 5 hours. At the end of this reaction time, the reactor is degassed in a gas flow meter and the gas phase is analyzed by GC. 10 mg of butylvinyl ether are added to the liquid phase to neutralize the metathesis catalyst. This liquid phase is then analyzed by GC. The analyzes of the gas and liquid phases indicate that the mass distribution of the products contained in the reactor, excluding toluene, is as follows: ethylene = 31%; propylene = 15%; - butenes = 6% - dodecane = 49%. It thus appears that all the dodecene present in the feed has been converted into propylene and butenes. Given the difference in boiling points of these compounds, it is easy to separate: - ethylene which can be recycled to the isomerization and metathesis reactor; propylene, the product of the process; butenes which can be recycled at the isomerization and metathesis stage; - Dodecane which can be recycled to the paraffin dehydrogenation stage.

Claims (17)

1) A process for producing propylene from a feed comprising linear paraffins having a carbon number of between 8 and 30, said process comprising: a) a step of selective dehydrogenation of the linear paraffins of the feed so as to to produce an effluent containing linear monoolefins produced, unconverted linear paraffins and hydrogen, b) a step of isomerization and metathesis, in the presence of ethylene, linear monoolefins contained in the effluent from the step a) to produce an effluent containing ethylene, propylene, linear monoolefins having a carbon number of between 4 and 30 and unconverted linear paraffins, c) a step of separating the effluent from step b) into a hydrogen fraction, an ethylene fraction, a propylene fraction, a fraction containing the monoolefins having a number of of carbon atoms of between 4 and 7, a fraction containing linear monoolefins having a number of carbon atoms of between 8 and 30 and unconverted linear paraffins. 2) Process according to claim 1 wherein the effluent from step a) is previously subjected to a separation step for separating said effluent a hydrogen fraction and optionally a fraction comprising methane and ethane, before to be sent to step b) of isomerization and metathesis. 3) Method according to one of the preceding claims wherein the hydrogen fraction is recycled to the step a) of selective dehydrogenation. 4) Process according to one of the preceding claims wherein at least a portion of the fraction resulting from the separation step c) and containing linear monoolefins having a number of carbon atoms of between 8 and 30 and linear paraffins unconverted is returned to the selective dehydrogenation step a). 5) Process according to one of the preceding claims wherein at least a portion of the fraction resulting from the separation step c) and containing the monoolefins having a number of carbon atoms of between 4 and 7 is returned in the step b) isomerization and metathesis. 6) Method according to one of the preceding claims wherein the ethylene used in step b) of isomerization and metathesis is produced by dehydration of bio-sourced ethanol. 7) Method according to one of the preceding claims wherein at least a portion of the ethylene fraction from step b) is recycled in said step b). 8) Method according to one of the preceding claims wherein the step a) of selective dehydrogenation is carried out in the gas phase. 9) The method of claim 8 wherein the step a) of selective dehydrogenation is carried out in the presence of a steam flow rate. 10) Method according to one of the preceding claims wherein the step a) of selective dehydrogenation is carried out in the presence of hydrogen. 11) The method of claim 10 wherein the step a) of selective dehydrogenation is carried out with a molar ratio H2 / load between 0.5 and 10. 12) Method according to one of the preceding claims wherein the step a) of selective dehydrogenation is carried out with a temperature between 300 and 800 ° C, a total pressure of between 0.014 and 2 MPa, a space velocity including time between 0.5 and 300 h-1. 13) Method according to one of the preceding claims wherein the step a) of selective dehydrogenation is carried out in the presence of a platinum catalyst deposited on a support, preferably alumina. 14) Method according to one of the preceding claims wherein the step b) of isomerization and metathesis is carried out with a molar ratio ethylene / effluent from step a) between 0.5 and 500, a total pressure between 0.01 and 20 MPa, a temperature between 10 and 500 ° C. 15) Method according to one of claims 1 to 14 wherein the filler is obtained by Fischer-Tropsch synthesis from a synthesis gas obtained by gasification of the biomass. 16) Method according to one of claims 1 to 14 wherein the filler according to the invention is obtained by hydrotreating vegetable oils or animal fats advantageously containing triglycerides and fatty acids or esters with carbon chains composed of 8 to 30. 17) Method according to one of claims 1 to 14 wherein the filler according to the invention is obtained from a petroleum fraction by selective adsorption on an adsorbent or by extractive crystallization.