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  • B01D53/04—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with stationary adsorbents
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Definitions

• the invention relates to a method for purifying gas mixtures containing mainly hydrogen and carbon monoxide, commonly called mixtures.
• H 2 / CO and optionally containing methane (ChU), which are optionally polluted by various impurities to be removed, in particular oxygen and / or unsaturated hydrocarbons ei / or NOx.
• ChU methane
• H2 / CO gas mixtures can be obtained in several ways, including:
• ATR process Auto Thermal Reforming
• gases such as methane or ethane
• metals can be used to catalyze the formation of hydrocarbons from CO and H 2 .
• the following metals may be mentioned, for example: Ru, Ir, Rh, Ni, Co, Os, Pt, Fe 1 Mo, Pd or Ag, as explained by F. Fisher, H. Tropsch and P. Dilthey, Brennst.-Chem , vol. 6, 1925, p. 265.
• the methanol formation reaction is also carried out on many metals, including copper:
• impurities to be removed are O 2 , NOx and unsaturated hydrocarbons, particularly ethylene.
• H 2 / CO mixtures catalyst poisons such as mercury (Hg), arsenic (ASH3), sulfur (H 2 S, thiols, thio-ethers), halogen compounds (HBr, HCl , organic halides), carbonyl iron Fe (CO) s and nickel carbonyl Ni (CO) 4 , which it is also desirable to eliminate.
• catalyst poisons can also be encountered, such as antimony, tin, bismuth, selenium, tellurium and germanium, the presence of which depends on the carbonaceous raw material used.
• the removal of impurities from a gas can be carried out by adsorption, by catalysis or by any suitable chemical treatment.
• H2O and CO2 impurities can be removed from a gas stream on adsorbents, such as activated alumina or zeolite, while O2 type impurities can be reduced in the form of water and ethylenics can be hydrogenated. in alkanes.
• adsorbents such as activated alumina or zeolite
• the halogen compounds, the mercury or the sulfur present in a gas can be eliminated by adsorption on specific adsorbents, for example activated carbon chemically treated.
• specific adsorbents for example activated carbon chemically treated.
• certain compounds, such as for example organic halides can be decomposed into organic compounds and into halogenated mineral compounds, this in order to facilitate their subsequent elimination by adsorption, catalysis or the like.
• Adso ⁇ tion and catalysis can also operate alternately or simultaneously.
• ethylene can be catalytically converted to ethane or be adsorbed on a zeolitic adsorbent, or both.
• a recurring problem which arises, on the industrial level, is to put the gas to be purified in contact with a series of adsorbent or catalytic products, in a precise order and such that the poisons of a product will be eliminated upstream of the latter, knowing that the reactions taking place upstream can themselves generate other poisons not contained in the gas to be treated.
• the catalytic reactions used to remove the impurities must not lead to reacting the H2 / CO gas mixture to be purified. The same applies to the adsorbents used, in particular during their regeneration at high temperature.
• ethylene hydrogenation catalysts which are commonly based on platinum deposited on alumina lead to a Fisher-Tropsch reaction (reaction (I) above), with the formation of hydrocarbons, in particular ethylene which may be more concentrated at the reaction outlet than at the inlet, that is to say in the gas before reaction.
• the regeneration gas can also contain compounds capable of reacting chemically under the influence of the temperature and the catalytic power of the adsorbent (Fisher reaction (I) -Tropsch and reaction (III) of Boudouard described above).
• the problem which arises at the industrial level concerns both the number and the nature of the adsorption and catalysis operations to operate, but also and above all the choice of the particular order of course of the flow H2 / CO to be purified, so as to be able to produce and recover a flow of H2 / CO free of most of the impurities which it contains, while avoiding unwanted reactions of the compounds H2 and CO, in particular during the step or steps catalyst used to remove the impurities contained in the H2 / CO mixture or of the step or steps of regeneration of the adsorbents operating according to the principle of TSA, while avoiding or minimizing the formation of additional chemical species not present in the starting feed gas.
• the primary aim of the invention is to improve the purification methods of H2 / CO mixtures of the prior art by proposing an effective method intended to purify an H2 / CO mixture of the oxygen impurities and unsaturated hydrocarbons which it contains, avoiding or minimizing Fisher-Tropsch, Boudouard type reactions, methanol formation, ... so as to avoid or minimize the transformation or conversion of H2 and CO into undesirable, harmful or difficult to eliminate compounds, such as methanol, for example, that is to say compounds capable of degrading the adsorbents or catalysts located downstream or liable to pose subsequent problems when using the H2 / CO mixture.
• the solution of the invention is then a process for purifying a gas stream containing at least hydrogen (Hfe), carbon monoxide (CO), at least one carbonyl metal and at least one impurity chosen from l oxygen (O2) and unsaturated hydrocarbons, in which: (a) the gas stream is brought into contact with a first catalyst bed (12) comprising at least one catalyst containing copper to convert, at a temperature between 10O 0 C and 200 0 C and at a pressure of at least 10 bars, at least part of the oxygen and / or at least one unsaturated hydrocarbon present in the gas flow in one or more catalysis products, and (e) said gas flow is brought into contact with a second adsorption bed (9) to adsorb at least one carbonyl metal.
• a first catalyst bed comprising at least one catalyst containing copper to convert, at a temperature between 10O 0 C and 200 0 C and at a pressure of at least 10 bars, at least part of the oxygen and / or at least one unsaturated hydrocarbon present
• the operating temperature range of the reactor is very important in the solution of the invention because it is the result of a compromise between the good conversion of the oxygen and of the unsaturated hydrocarbon or hydrocarbons present, and the limited formation of secondary products. , such as methanol and / or hydrocarbons.
• the catalysis products are, on the one hand, saturated hydrocarbons, in particular alkanes and, on the other hand, water and / or CO2.
• the process of the invention may include one or more of the following technical characteristics: - the gas stream contains at least hydrogen (H2), carbon monoxide (CO) and methane (CH4 ). - the temperature is between 120 ° C. and 180 ° C.
• the hourly space velocity (ie Gas Hourly Space Velocity) is between 1000 and 10000 Nm3 / h / m3, preferably between 2000 and 6000 Nm 3 / h / m 3 .
• the gas stream contains, in addition, one or more organo-sulfur, organo-nitrogen and / or organo-chlorinated compounds, and (b) the gas stream is brought into contact with a second catalyst bed to convert at least part organo-sulfur, organo-nitrogen and / or organo-chlorinated compounds into organic compounds and polar mineral compounds, and (c) the gas stream is brought into contact with a third adsorption bed to adsorb at least part of the compounds minerals produced in step (b).
• the organo-sulfur, organo-nitrogen and / or organo-chlorinated compounds are, for example, compounds of the CH 3 CI, CH 2 CI 2 , CCI 4 , CHCI 3 , CH 3 NH 2 , CH 3 NHCH 3 , CH 3 SH type. , CH 3 SCH 3 ...
• the saturated organic compounds produced in step (b) are, for example, alkanes, while the polar mineral compounds produced are compounds of the HCI 1 HBr, H 2 S, NH type. 3 ...
• the gas stream contains, in addition, HCN impurities and / or at least one compound of an element chosen from the group formed by mercury, sulfur, chlorine, arsenic, selenium, bromine and germanium , and (d) bringing said gas stream into contact with a first adsorption bed to adsorb at least part of the HCN impurities and / or said compound of an element chosen from the group formed by mercury, sulfur, chlorine, arsenic, selenium, bromine and germanium.
• This bed can be the succession of several different products.
• this bed is placed upstream of the catalysis bed (s) 12 and / or the beds 10 and 11 in order to protect it or them (see FIG. 1).
• the gas stream also contains at least one carbonyl metal, and (e) said gas stream is brought into contact with a second adsorption bed to adsorb at least one carbonyl metal, such as carbonyls of iron, nickel, chromium and cobalt, in particular carbonyls of iron or even nickel.
• a carbonyl metal such as carbonyls of iron, nickel, chromium and cobalt, in particular carbonyls of iron or even nickel.
• the gas stream contains, in addition, at least one nitrogen oxide (NOx), and (f) said gas stream is brought into contact with a third catalyst bed to convert at least one nitrogen oxide present in the stream gas, especially NH 3 which will be stopped downstream.
• NOx can be broken down according to several reactions, for example for N 2 O: N 2 O ⁇ N 2 + Vz O 2
• steps (a) and (f) can be distinct, that is to say implemented in a dissociated manner by means of different catalysts, or combined, that is to say implemented simultaneously with the same catalyst.
• the first adsorption bed contains at least one material chosen from active carbon impregnated or not, activated aluminas, impregnated or not, and their combinations or mixtures, preferably an activated carbon charged with potassium iodide and / or sodium sulfide and / or elemental sulfur.
• the second catalysis bed contains a copper oxide deposited on a support, preferably the support is a zinc oxide.
• step (b) can be confused with steps (a) and / or (f).
• the third adsorption bed contains at least one activated alumina or activated carbon.
• the first catalysis bed comprises particles of copper catalyst deposited on a support, preferably a support of the alumina, silica or zinc oxide type.
• the catalysis bed comprises at least one catalyst chosen from catalysts based on copper or a transition metal of the third series, preferably platinum or palladium, deposited on a support .
• a catalyst bed is used to convert at least part of the oxygen present in the gas flow and an additional catalysis bed to convert at least one unsaturated hydrocarbon present in the gas flow, said catalysis beds being distinct from each other and placed in any order and can operate at different temperatures.
• step (d) includes a step during which a gas stream is recovered which essentially contains hydrogen (H 2 ) and carbon monoxide (CO), the proportion of hydrogen added to the proportion of carbon monoxide in said gaseous mixture produced being greater at 70% preferably at least 80% by volume.
• the first adsorption bed of step (d) is formed of two adsorption layers each containing at least one adsorbent distinct from that of the other layer.
• the gas flow is subjected to at least one compression step during which the heat of compression is used to heat the flow to be purified, which leads to reducing the dimensions of the heater located at the catalysis inlet.
• the gas stream from one or other of steps (a) or (f) is brought into contact with a fourth adsorption bed to remove H2O and / or CCk, and / or undergoes a washing step for eliminate the CO2 therein, in particular an amino wash.
• a washing step for eliminate the CO2 therein, in particular an amino wash.
• the purpose of this additional step is to eliminate H2O and / or CO2 or the other compounds which may have formed by catalysis or which were present in the initial feed gas, for example methanol, NH3, hydrocarbons with three or more carbon atoms in their hydrocarbon chain (hereinafter called "C3 +").
• the adsorption bed preferably contains at least one activated alumina or a zeolite.
• the adsorption steps are carried out according to a TSA process cycle with regeneration temperature less than or equal to 250 ° C.
• the catalysts used in the context of the invention may have identical or different sizes or compositions, for example sizes ranging from 0.25 to 1 cm.
• step (a) The gas flow is subjected to at least one compression step upstream of step (a) and in which the or part of the heat generated by the compression of the flow is used to reach the desired temperature in the reactor (s) located downstream. Supplementary heat obtained by means of a heat exchanger for heat recovery and / or an electric heater may be necessary in certain cases.
• FIGS. 1 and 2 represent operating diagrams of examples of industrial implementation of the method of the invention.
• a source 1 of gas supplies a first adsorption reactor 2 with a gaseous mixture H2 / CO to be purified, said supply gas being at a pressure of 20 bars and at a temperature of 35 ° C.
• the gas to be purified passes successively through a first reactor 2 and then through a second reactor 8 where it is freed from all or part of the impurities which it contains, in particular oxygen impurities and / or unsaturated hydrocarbons.
• the first adsorption reactor 2 comprises a first adsorption bed formed by two successive adsorption layers 3, 4, namely:
• a first adsorption layer 3 containing an adsorbent making it possible to remove the HCI and HBr impurities contained in the feed gas
• a second adsorption layer 4 containing an adsorbent making it possible to remove the impurities AsH3, H2S and Hg contained in the feed gas.
• the pre-purified gas in the first reactor 2 is then conveyed to a compression unit 5 where it is compressed to a pressure of 47 bars; the temperature of the gas also increasing due to compression up to approximately 85 ° C.
• the gas thus compressed (at 5) is subjected to a first reheating step by means of one (or more) heat exchanger 6 in which a countercurrent heat exchange takes place with the purified gas, as explained above. after.
• the gas leaving the heat exchanger 6 is conveyed to an electrical reheating unit 7 where it undergoes a second reheating step, its temperature being brought or adjusted between 120 and 180 ° C.
• the pre-purified gas leaving the electric heater 7 then feeds a second treatment reactor 8 comprising successively, considering the direction of progression of the gas flow, the second adsorption bed 9, the second catalysis bed 10, the third bed d adsorption 11 and the first catalysis bed 12 used to convert at least part of the oxygen and the unsaturated hydrocarbons present in the gas.
• the bed 9 is placed upstream of the catalysis bed 12 and / or the beds 10 and 11 in order to protect it or them.
• any NOx that may be present can be eliminated on a third catalyst bed.
• the gas thus purified is then recovered, subjected to a heat exchange (in 6) with the pre-purified gas compressed in 5, then sent to a site 13 for use, storage or the like.
• the first adsorption bed 3,4 is used to retain the easily condensable compounds including in particular the compounds of mercury, sulfur, chlorine, arsenic, selenium or germanium.
• the second adsorption bed 9 is intended to adsorb carbonyl metals, such as Fe (CO) 5 and Ni (CO) 4 .
• the second catalysis bed 10 is intended to convert the organo-chlorinated, organo-nitrogenous and organosulphurized compounds into organic compounds and into polar mineral compounds.
• the third adsorption bed 11 is intended to adsorb at least the polar mineral compounds originating from the reaction of the second catalytic bed 10.
• the first catalysis bed 12 eliminates traces of oxygen and unsaturated hydrocarbons, such as ethylene.
• the beds 10 and 11 are placed upstream of the catalysis bed 12 in order to protect it.
• the adsorption bed (11) can be a catalysis bed - possibly the same as bed 10 - which will therefore be deliberately poisoned in certain cases to preserve bed 12.
• NOx present are removed on a 3rd catalyst bed. It is also possible to provide, downstream of the catalyst bed 12, a fourth adsorption bed making it possible to adsorb at least the products coming from the second catalytic bed, or even a fifth adsorption bed or another treatment, such as a washing with amines or the like, used to remove the remaining impurities, which were formed during the catalysis reactions or which were present from the start in the input stream but which have not been stopped until then, for example methanol, NH3 and C3 + hydrocarbons.
• a fourth adsorption bed making it possible to adsorb at least the products coming from the second catalytic bed, or even a fifth adsorption bed or another treatment, such as a washing with amines or the like, used to remove the remaining impurities, which were formed during the catalysis reactions or which were present from the start in the input stream but which have not been stopped until then, for example methanol, NH3 and C3 + hydrocarbons.
• the adsorption beds can be composed of several different adsorbents specific for a particular impurity, which can be mixed with each other, or else be arranged in layers.
• the first catalysis bed can be composed of several different catalysts, for example a hydrogenation catalyst and an oxidation catalyst, or else comprise only one multifunctional catalyst.
• the catalysts used in each of the catalytic beds have an operating temperature of between 10 0 ° C. and 200 ° C. approximately, an operating pressure of between 10 and 80 bars approximately, and chosen so as to generate a minimum of parasitic reactions involving H2 and CO, such as the Fisher-Tropsch reactions and the formation of methanol.
• the adsorbents downstream of the catalyst bed 12 are used according to cycles
• a regeneration temperature less than or equal to 250 0 C and are also chosen so as to generate minimum parasitic reactions such as Fisher-Tropsch reactions, polymerization of unsaturated and Boudouard's reaction.
• adsorbents used in the context of the invention for the adsorption of various gaseous compounds are for example chosen from:
• - active carbon having a mass area of between 700 and 1300 m 2 / g
• - silica gels having a mass area of between 350 and 600 m 2 / g
• the so-called compensation cations can be alkaline or alkaline-earth.
• the catalysts commonly used for chemical reactions in the gas phase can be formed: - from an "active metal deposited on a support, such as, for example, ⁇ alumina, silica, cordierite, perovskite, hydrotalcite, zinc oxide, oxide titanium, cerium oxide, manganese oxide or their mixture or defined compounds, or
• an active metal precipitated alone or with another compound to form a mixture or else a defined compound.
• defined compound is meant a substance consisting of a single phase and which can therefore be considered as a pure body in the physico-chemical sense
• the active metal can be a transition metal (Pt, Pd, Ru, Rh, Mo, Ni, Fe, Cu, Cr, Co ...) or a lanthanide (Ce, Y, La ).
• the catalysts can be additive with elements or compounds having an indirect role in the catalytic process and which facilitate its unfolding or increase its stability, selectivity or productivity.
• a number of catalysts must be activated on site before use, for example, copper-containing catalysts are delivered in oxidized form to CuO, and must be reduced in situ by controlled heating in an atmosphere of hydrogen diluted in a neutral gas, such as nitrogen.
• Other catalysts can be used as such, such as platinum catalysts.
• adsorbents can be used as such, for example carbon impregnated with sulfur, while others must be regenerated before first use, such as aluminas or zeolites.
• the macroscopic shape of the catalyst plays an important role. Indeed, the catalytic reaction comprises three stages:
• the overall speed of the chemical reaction will depend on the arrangement of these three mechanisms which will depend on the size and shape of the catalyst particles, their porosity, the state of dispersion catalytic sites (surface or core).
• the first adsorption bed can be composed upstream of an activated carbon loaded with potassium iodide to remove the mercury, arsenic and sulfur compounds, followed by a second bed composed of an activated alumina or an activated carbon impregnated with soda or sodium carbonate to remove acids, such as H2S, HCI, HBr, HNCk, HNO3, HCN ...
• This type of adsorbent can be obtained from CECA companies (AC 6% Na ⁇ CCb, ACF2,
• activated carbon containing 6% by weight N32CO3 referenced Acticarbone AC40 at CECA activated carbon containing KOH referenced Picatox KOH at PICA, or doped alumina referenced SAS 857 at Procatalyse.
• chromium-copper activated carbon available from Norit under the reference RCM 3, or lead oxide alumina available from Procatalyse under the reference MEP 191, or activated carbon to iron. marketed by CECA.
• a Grade A alumina from the company Procatalyse or an equivalent product from the companies La Roche, ALCOA or ALCAN can be used.
• the second catalyst bed used to remove the organic chlorides there can be found a copper and molybdenum oxide deposited on zinc oxide, for example the catalyst G1 from the company S ⁇ d-Chemie or the catalyst Cu 0860T from Engelhard.
• an impregnated alumina can be used, such as the product G-92 C from the company S ⁇ d-Chemie, or the product Acticarbone AC40 6% Na2C ⁇ 3 from the company CECA, or Picatox KOH from the company PICA. .
• a copper-based catalyst is used, deposited on a support, such as the product H5451.
• a support such as the product H5451.
• the NOx possibly present can be removed on a third catalyst bed, for example the catalysts mentioned above or the catalyst Pd 4586 from the company Engelhard.
• adsorption beds As fourth and fifth adsorption beds, one can use an activated alumina type grade A from the company Procatalyse or an equivalent alumina from the companies La Roche, ALCOA or ALCAN, then a zeolite of type 13X from the company UOP, or 4A, or 5A from the company UOP.
• the various adsorption beds can be contiguous, that is to say juxtaposed beds, in the process or be separated by stages of compression or decompression, reheating and / or cooling. Additional steps can also be introduced, such as absorption washing.
• the volumes of adsorbents and catalysts are given for information only because they depend on the concentration of the impurities to be removed as well as on the properties of the specific products. As a general rule, it can be considered that for a given case, the quantity of adsorbent to be used is approximately proportional to the quantity of pollutant to be removed, while the quantity of catalyst is approximately proportional to the contact time or to the inverse of the hourly volumetric speed (VVH) which is the volume of gas to be treated per hour, relative to the volume of catalyst.
• VVH hourly volumetric speed
• the volume of the gas can be related to the inlet pressure of the reactor (the VVH then depends on the pressure), or else expressed under defined conditions, at 1 bar and O 0 C for example (the VVH then does not depend on pressure) ; there is latitude in the choice of reference conditions which it is up to each to choose.
• the contact time and the VVH 1 are only approximately proportional since the contact time depends, in addition to the pressure, the temperature along the column, the variation in the number of moles during the reaction and the pressure losses. However, for given reaction conditions, the two parameters can be used as desired.
• Another parameter to take into account is the content of the impurities to be removed at the outlet of the gaseous effluents. Overall, the lower the desired content, the greater the amount of adsorbent or catalyst. Certain steps can be performed at specific pressures or temperatures. Thus, the adsorption is preferably carried out below 80 ° C., while the catalytic reactions take place above 100 ° C. but below 200 ° C. to avoid or minimize parasitic reactions of the Fisher-Tropsch type or similar.
• the different beds can be placed in several receptacles or treatment reactors, so that the gas passing from one to the other is heated or cooled, compressed or expanded, according to the optimal conditions of operation of the adsorption operations. or catalysis.
• the adsorbent functions in a cyclic manner, according to the principle of TSA, for example for the elimination of water on alumina or of CO2 on zeolite) and in other cases , the adsorbent is at lost charge 1 , that is to say it is replaced by a fresh adsorbent when it reaches saturation.
• Some beds can be made of the same compound, either to carry out two catalytic operations, such as for example hydrogenating both oxygen and ethylene on a palladium catalyst, or to carry out two adsorption operations such as for example adsorbing CO2 and H2O on an alumina / zeolite composite of the 13X type, either for carrying out an adsorption and catalysis operation, for example the decomposition of the organochlorines and the adsorption of the resulting HCl, for example on the Engelhard product referenced 0860T.
• FIG. 2 represents a simplified diagram of the method of FIG.
• the examples below aim to illustrate the present invention by proposing several possible arrangements of catalyst beds and adsorbents which can be used industrially to treat a mixture of gases of H2 / CO type to be purified containing impurities to be eliminated.
• the starting gas contains approximately 80% by volume of H2 and CO 1, the remainder consisting of methane and the impurities to be removed.
• the configurations given below are considered in the direction of gas flow in the tank or tanks containing the different beds or produced, that is to say that the first adsorbent or catalyst is the one located most upstream (supply side of the gas to be purified) and the n th adsorbent or catalyst is the one located most downstream (production side of purified gas).
• Example 1 H2 / CO gas mixture with various impurities
• the gas to be purified contains, in addition to the compounds H2 and CO to be recovered, the following impurities to be eliminated, namely arsenic, mercury compounds, carbonyl metals, organic hetero atoms, oxygen, unsaturated hydrocarbons, water, methanol and CO2.
• This gas can be purified by TSA process using the succession of adsorption and catalysis beds given in Table 1 below.
• Example 2 H2 / CO gas mixture of Example 1 additionally containing a sulfur compound (COS)
• composition of the gas to be purified is broadly identical to that of the gas of example 1 but additionally comprises a sulfur product (COS).
• COS sulfur product
• This gas can be purified by implementing the succession of adsorption and catalysis beds given in the following Table 2.
• Table 2
• Example 3 H2 / CO gas mixture of Example 1 additionally containing nitrogen oxides
• composition of the gas to be purified is broadly identical to that of the gas of example 1 but also comprises nitrogen oxides (NOx).
• NOx nitrogen oxides
• Example 4 H2 / CO gas mixture of Example 1 additionally containing a sulfur compound (COS) and nitrogen oxides
• the composition of the gas to be purified is broadly identical to that of the gas of example 1 but additionally comprises a sulfur compound (COS) as in example 2 and nitrogen oxides (NOx) as in Example 3.
• This gas can be purified by implementing the succession of adsorption and catalysis beds given in Tables 4 or 5 below.

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