METHOD FOR PREPARING WATER GAS SHIFT CATALYSTS, CATALYSTS AND PROCESS FOR REDUCING CARBON MONOXIDE CONTENT

Abstract

The present invention relates to HTS catalysts applied in hydrogen or synthesis gas production units, whether in steam reforming, autothermal reforming, dry or gasification reforming, chromium-free, consisting of iron oxide, containing platinum contents between 0.1 to 0.4% w/w, promoted by sodium contents between 0.1 to 0.3% w/w, and optionally aluminum contents between 5.0 to 6.0% w/w inserted into the crystal lattice of an iron oxide with a hematite (Fe.sub.2O.sub.3) crystal structure, thus, allowing high activity to be reconciled with excellent resistance to deactivation by exposure to high temperatures. In a second aspect, the present invention provides a carbon monoxide conversion process by bringing said catalyst into contact with a synthesis gas stream, where the maximum bed temperature can be limited by the injection of water or steam next to the feed of CO-containing gas at the reactor inlet.

Claims

1. A method for preparing water gas shift catalysts, the method comprising the following steps: 1) coprecipitating a solution containing a soluble iron salt, a soluble platinum compound and optionally a soluble aluminum salt, in a polar solvent, with a soluble sodium salt, 2) maintaining the pH of the suspension between 7.5 and 8.0, under stirring, and at temperatures between 20 and 80 degrees Centigrade (? C.), followed by aging of the precipitate in this condition for 0.5 to 2.0-hours (h); 3) filtering and washing the precipitate formed with a polar solvent until the residual sodium content of the final product is between 0.1 and 0.3% weight in weight (w/w); 4) drying the precipitate obtained at temperatures between 60? C. and 150? C. for 1 to 6 h, followed by calcination between 300? C. and 400? C., for 1 to 5 h; 5) formatting the material and, then, calcinating at temperatures between 300? C. and 450? C. to obtain hematite promoted with platinum and sodium and, optionally, with aluminum.

2. A method according to claim 1, wherein the soluble iron salt comprises iron nitrate.

3. A method according to claim 1, wherein the soluble platinum compound comprises hexachloroplatinic acid (H.sub.2PtCl.sub.6.Math.6H.sub.2O).

4. A method according to claim 1, wherein polar solvent comprises water or ethanol.

5. A method according to claim 1, wherein the soluble sodium salt comprises sodium carbonate or sodium hydroxide.

6. A method according to claim 1, wherein coprecipitation occurs at temperatures between 50 and 70? C.

7. A method according to claim 1, wherein aluminum is inserted into a hematite crystal lattice which has a unit cell parameter between 0.05005 and 0.5010 nanometers (nm) and has a specific surface area greater than 100 meters squared per gram (m.sup.2/g).

8. The catalysts, as obtained by the method as defined in claim 1, wherein the catalysts have a platinum content between 0.1 and 0.4% w/w, a sodium content between 0.1 and 0.3% w/w and an aluminum content between 5.0 and 6.0% w/w in iron oxide balance with hematite structure and a specific surface area greater than 50 m.sup.2/g.

9. A process for reducing the carbon monoxide content by the water gas shift reaction, the process comprising: placing in contact with one or more of the catalysts, as prepared by the method described in claim 1, with a synthesis gas containing between 5 and 30% CO, a steam/dry gas ratio between 0.2 and 1.0 mol/mol, and a reactor entry temperature between 250? C. and 350? C.

10. A process, according to claim 9, wherein the synthesis gas contains between 8 and 20% CO, a steam/dry gas ratio between 0.3 and 0.8 moles per mol (mol/mol) and a reactor inlet temperature between 280? C. and 300? C.

11. A process, according to claim 9, wherein the reactor outlet temperature is a maximum of 370? C. controlled by the joint supply of the synthesis gas with a stream of steam or condensate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be described in more detail below, with reference to the attached figures which, in a schematic way and not limiting the inventive scope, represent examples of its implementation. In the drawings, there are:

[0028] FIG. 1 illustrating a graph of the CO conversion activity in the water gas shift reaction in the catalysts prepared in accordance with EXAMPLE 1, with different residual sodium contents;

[0029] FIG. 2 illustrating a graph of the CO conversion activity in the water gas shift reaction in the catalysts prepared in accordance with EXAMPLE 2, with different residual sodium contents. The results obtained for a commercial catalyst based on iron, chromium and copper oxides and a catalyst prepared according to EXAMPLE 1 are also shown in the graph;

[0030] FIG. 3 illustrating a graph of the correlation between the conductivity of the washing water and the sodium content in the catalyst prepared in accordance with the present invention (EXAMPLE 2).

DETAILED DESCRIPTION OF THE INVENTION

[0031] Broadly speaking, the present invention relates to catalysts applicable to the conversion of CO to CO.sub.2 and H.sub.2 by the water gas shift reaction. Such catalysts are made up of an iron oxide support with a crystalline structure identifiable by the X-ray diffraction technique as hematite, promoted by platinum (Pt) contents between 0.1 and 0.4% m/m and with a content of sodium (Na) between 0.1 and 0.3% m/m, based on the oxidized material. Optionally, the catalyst contains aluminum with a content of 5.0 to 6.0% m/m.

[0032] The catalysts thus constituted are prepared using the method described in the following steps: [0033] 1) coprecipitating an aqueous solution containing a soluble iron salt, preferably iron nitrate Fe(NO.sub.3).sub.3.Math.9H.sub.2O, a soluble platinum compound, preferably hexachloroplatinic acid (H.sub.2PtCl.sub.6.Math.6H.sub.2O), and optionally a soluble aluminum salt, preferably nitrate aluminum Al(NO.sub.3).sub.3.Math.9H.sub.2O, with an aqueous solution of sodium carbonate, optionally, sodium hydroxide, maintaining the pH of the suspension between 7.5 and 8.0, under stirring, and at temperatures between 20? C. and 80? C., preferably, between 50? C. and 70? C., followed by aging the precipitate in this condition for 0.5 to 2.0 h; [0034] 2) filtrating the precipitate, followed by washing with water or ethanol, until the residual sodium content of the product is 0.1 to 0.3% m/m; [0035] 3) drying the precipitate obtained, at temperatures between 60? C. and 150? C., for 1 to 6 h, followed by calcinating between 300? C. and 400? C., for 1 to 5 h; [0036] 4) formatting the material obtaining catalyst tablets with typical dimensions between 0.3 and 0.7 cm in diameter and 0.5 to 1.0 cm in length and then calcinating at temperatures between 300? C. and 450? C. to obtain a hematite promoted with platinum and sodium and, optionally, with aluminum inserted into the crystalline structure of the iron oxide, so that the platinum content is between 0.1 and 0.4% m/m, the sodium content between 0.1 and 0.3% m/m and, optionally, aluminum content between 5.0 and 6.0% m/m in iron oxide balance with hematite structure and a specific surface area greater than 50 m.sup.2/g.

[0037] The material can be shaped into cylindrical shapes with a hole in the middle or cylinders with a wavy outer surface.

[0038] The catalysts thus prepared avoid additional sodium incorporation steps. The presence of sodium in controlled levels, surprisingly, allows to obtain a high CO conversion activity while maintaining a high resistance to deactivation by exposure to high temperatures, as widely demonstrated in the examples. Very low sodium contents in the final product produce a catalyst with lower activity and very high sodium contents produce a catalyst with low resistance to deactivation by prolonged exposure to high temperatures.

[0039] The catalyst containing aluminum (Al) inserted into the hematite crystalline structure shows a change in the unit cell parameter to values between 0.5005 and 0.5010 nm, as measured by the X-ray diffraction technique. Aluminium provides greater catalyst activity allowing the reduction of Pt levels required in the final product.

[0040] The catalysts thus prepared are in the form of hematite promoted by platinum and sodium and optionally aluminum, being activated by a reduction procedure to transform the hematite phase (Fe.sub.2O.sub.3) into the magnetite phase (Fe.sub.3O.sub.4). The procedure is well established in the industry and consists of passing a gas containing H.sub.2 or CO and water vapor, with a vapor/gas ratio typically between 2 and 6 mol/mol, at temperatures between 250? C. and 400? C., during a period of 1 to 3 h.

[0041] The catalysts thus prepared and activated can be used in the conversion reaction of CO with water vapor to produce hydrogen, at reactor inlet temperatures between 250? C. and 350? C., preferably at temperatures between 280? C. and 300? C. Optionally, it may be advantageous, to reduce the CO content and increase the useful life of the catalyst in accordance with the present invention, to maintain the maximum temperature throughout the reactor at 370? C. by injecting steam or condensate at the reactor inlet or at multiple points along the bed. The operating pressure in the reactor can be in the range of 10 to 40 kgf/cm.sup.2, preferably between 20 and 30 kgf/cm.sup.2. The steam/dry gas molar ratio at the reactor inlet is 0.2 to 1.0 mol/mol, preferably between 0.3 and 0.8 mol/mol. The dry gas at the reactor inlet typically contains CO contents between 5 and 30% v/v, preferably between 8 and 20% v/v.

EXAMPLES

[0042] The examples shown below aim to illustrate some ways of implementing the invention, as well as proving the practical feasibility of its application, without constituting any form of limitation of the invention.

Example 1

[0043] This comparative example illustrates that the presence of sodium is harmful to a catalyst made up of iron oxides. A 1.0 M aqueous solution of iron nitrate (Fe(NO.sub.3).sub.3.Math.9H.sub.2O) and a second 1.5 M aqueous solution of sodium carbonate (Na.sub.2CO.sub.3) were added simultaneously for 1 h under stirring, maintaining the temperature between 45? C. and 50? C. and pH between 7.5 and 8.0. After the end of precipitation, the suspension was maintained at the previous conditions of temperature, pH and agitation for another 1 h to age the precipitate. The precipitate was then filtered and separated into several parts to be washed with different amounts of water in order to obtain different levels of residual sodium in the product.

[0044] The monitoring parameter of the washing step was the conductivity of the washing water. The washed material was then dried at 100? C. for 5 h and calcined at 400? C. for 2 h to obtain a catalyst identified as FeO.sub.x.sub.yNa, where .sub.yNa is the sodium (Na) content in the product in oxidized form.

[0045] The crystalline phases in the samples were characterized through X-ray diffraction (XRD), using the Rigaku Miniflex II diffractometer, with a Cu tube and monochromator, with a speed of 2?/min and angle variation from 5? to 90?. The catalyst has an X-ray diffraction profile corresponding to the presence of hematite. Textural analysis (BET) was conducted by nitrogen adsorption to determine specific area on Micromeritics ASAP 2400 equipment. For determinations, samples were previously treated at 300? C. in vacuum. The composition analysis was carried out by X-ray Fluorescence (XRF) on the PANAlytical MagiX PRO equipment equipped with a 4 kW Rh tube.

[0046] The activity of the catalysts in the water gas shift reaction was measured in a fixed bed reactor and at atmospheric pressure, in commercial equipment (AutoChem Micromeritcs). The sample was initially heated in an argon flow to 100? C. and then to 350? C., at a rate of 5? C./min, in a flow of 5% H.sub.2 in argon saturated with water vapor at 73? C. After this pre-treatment, the gas mixture was replaced by a mixture containing 10% v/v CO, 10% v/v CO.sub.2, 2% v/v methane in H.sub.2 balance, maintaining the saturator temperature with water at 73? C., corresponding to a steam/gas ratio of 0.55 mol/mol. The reaction was conducted at different temperatures with the reactor effluent being analyzed by gas chromatography. The activity of the catalysts was expressed as CO conversion (% v/v).

[0047] The results shown in Table 1 and FIG. 1 allow to conclude that, to obtain a high activity of the catalyst consisting of iron oxide, it is necessary to reduce the residual sodium content to values below 0.02% m/m. Thus, the effect of sodium on the performance of the catalyst depends on its concentration, and its complete elimination is desirable when the catalyst consists only of iron oxides.

TABLE-US-00001 TABLE 1 Comparative CO conversion activity in the water gas shift reaction as a function of sodium content (EXAMPLE 1). Reaction temperature (? C.) Na Fe 350? 370? 390? 420? 450? Sample % m/m % m/m C. C. C. C. C. FeO.sub.x1.8Na 1.78 69 0 2.8 3.7 5.7 10.4 FeO.sub.x0.41Na 0.41 68 4.8 5.5 6.8 10.2 16.0 FeO.sub.x0.01Na <0.02 69 29.7 36.4 41.0 47.1 46.9 Note: The balance for finalizing the composition of the samples is in oxygen (O).

Example 2

[0048] This example in accordance with the present invention illustrates the method of preparing the hematite-based catalyst promoted by platinum and sodium at low levels. A 1.0 M aqueous solution of iron nitrate (Fe(NO.sub.3).sub.3.Math.9H.sub.2O) containing a platinum compound soluble in water or polar solvents such as, but not restricted to, Pt(NH.sub.3).sub.4(NO.sub.3).sub.2 (CAS 20634-12-2), H.sub.2PtCl.sub.5.Math.xH.sub.2O (CAS 26023-84-7), PtCl.sub.4 (CAS 13454-96-1), (NH.sub.4).sub.2PtCl.sub.4 (CAS 13820-41-2) and (NH.sub.4).sub.2PtCl.sub.6 (CAS 16919-58-7) and a second 1.5 M aqueous solution of sodium carbonate (Na.sub.2CO.sub.3), were added simultaneously for 1 h, under stirring, maintaining the temperature between 45? C. and 50? C. and the pH between 7.5 and 8.0. After the end of precipitation, the suspension was maintained at the previous conditions of temperature, pH and agitation for another 1 h to age the precipitate. The precipitate was then filtered and separated into several parts to be washed with different amounts of water in order to obtain different levels of residual sodium in the product.

[0049] Monitoring the conductivity of the washing water allowed, in a simple way, to obtain different sodium (Na) contents in the final product (FIG. 3). The washed material was then dried at 100? C. for 5 h and calcined at 400? C. for 2 h to obtain samples identified as PtFeO.sub.x-yNa, where yNa is the sodium (Na) content in the product in oxidized form. The catalyst was characterized and its CO conversion activity was measured by the water gas shift reaction carried out as described in EXAMPLE 1.

[0050] Additionally, the characterization of the platinum metallic area was carried out by the cyclohexane dehydrogenation reaction, conducted at atmospheric pressure, in a fixed bed reactor, using a saturator with cyclohexane maintained at 10? C. and hydrogen as carrier gas. The reduction of the catalyst was carried out at 300? C. for 2 hours in a hydrogen flow (40 ml/min) and then the reaction was carried out at the same temperature.

[0051] The results shown in Table 2 and FIG. 2 allow to conclude that to obtain high activity in the conversion of CO, the catalyst consisting of iron oxide and platinum, differently from that observed for the catalyst consisting of iron oxide (Table 2), the presence of the sodium promoter is necessary, with levels above 0.04% m/m, with levels above 2.0% m/m being desirable, in principle.

[0052] The catalysts containing platinum and promoted by sodium showed a much higher CO conversion activity than a commercial catalyst based on iron, chromium and copper oxides (FIG. 2). Although the results do not allow to say conclusively, it is believed that sodium interacts with Pt atoms forming species that have high CO conversion activity. Catalysts containing Pt have dehydrogenating activity, so the null activity for dehydrogenation is an unusual result, raising doubts regarding the effect of the interaction between Na and Pt. Such interaction is capable of reducing the dehydrogenation activity of cyclohexane, characteristic of platinum with a predominantly metallic function (Table 2). To evaluate this hypothesis, a series of catalysts with different sodium contents was evaluated, finding dehydrogenating activity for samples with low Na contents, as can be seen in Table 2.

TABLE-US-00002 TABLE 2 Comparative CO conversion activity in the water gas shift reaction at different temperatures as a function of sodium content (EXAMPLE 2). R.sub.D Reaction temperature (gmol/ Sample 350? C. 330? C. 300? C. 280? C. gcat*s) PtFeOx > 2.0Na 80.8 73.5 50.2 26.5 0 PtFeOx1.58Na 0 PtFeOx0.66Na 72.2 63.8 40.2 23.1 0 PtFeOx0.28Na 0 PtFeOx0.09Na 72.2 49.4 33.1 18.1 2.6 PtFeOx0.04Na 51.7 35.5 18.4 9.8 4.4 Note: The Pt content in the samples determined by the XRF technique was 0.20 ? 0.0.1 and the Fe content was 69 ? 1 m/m, with oxygen balance. RD refers to the rate of the dehydrogenation reaction of cyclohexane.

[0053] The stability of the catalysts in the water gas shift reaction was measured in a fixed bed reactor and at atmospheric pressure, in commercial equipment (AutoChem Micromeritcs). The sample was initially heated in an argon flow to 100? C. and then to 350? C., at a rate of 5? C./min, in a flow of 5% H.sub.2 in argon saturated with water vapor at 73? C. After this pre-treatment, the gas mixture was replaced by a mixture containing 10% v/v CO, 10% v/v CO.sub.2, 2% v/v methane in H.sub.2 balance, maintaining the saturator temperature with water at 73? C., corresponding to a steam/gas ratio of 0.55 mol/mol to measure the initial activity at a temperature of 350? C. Next, the gaseous mixture was replaced by hydrogen and the temperature was raised to 500? C., being maintained under these conditions for 18 h. The temperature was then reduced to 350? C., the hydrogen was replaced by the reaction gas and a new measurement of the catalyst activity was carried out. The reactor effluent was analyzed by gas chromatography. The activity of the catalysts was expressed as CO conversion (% v/v).

[0054] Table 3 shows the initial activity and stability results. Surprisingly, however, the present invention teaches that high sodium contents, despite allowing greater activity, reduce the stability of the catalyst upon exposure to high temperatures, with the sodium content being between 0.1 and 0.3% m/m allows to get the best combined activity and stability performance.

TABLE-US-00003 TABLE 3 Comparative activity of initial conversion and after a period of accelerated deactivation of CO in the water gas shift reaction as a function of sodium content (EXAMPLE 2). X% CO X% CO after Sample initial deactivation PtFeOx > 2.0Na 70.0 25.0 PtFeOx1.58Na 62.3 27.8 PtFeOx0.66Na 64.6 31.0 PtFeOx0.28Na 68.4 40.0 PtFeOx0.09Na 59.8 35.2 PtFeOx0.04Na 47.0 33.0

Example 3

[0055] This comparative example illustrates that the preparation method, by incorporating platinum through impregnation of the hematite phase, produces a catalyst with lower activity than that obtained by the catalyst preparation method described in the present invention, that is, by coprecipitation. A catalyst prepared according to EXAMPLE 2, containing a sodium content of less than 0.05% m/m was impregnated by the wet point method with an aqueous solution of a water-soluble platinum compound or polar solvents, such as, but not restricted to the compounds Pt (NH.sub.3).sub.4(NO.sub.3).sub.2 (CAS 20634-12-2), H.sub.2PtCl.sub.5.Math.xH.sub.2O (CAS 26023-84-7), PtCl.sub.4 (CAS 13454-96-1), (NH.sub.4).sub.2PtCl.sub.4 (CAS 13820-41-2) and (NH.sub.4).sub.2PtCl.sub.6 (CAS 16919-58-7). The catalyst was then dried at 100? C. for 2 h and calcined at 400? C. for 2 h to obtain a hematite-based catalyst promoted by 0.2% platinum (Pt) based on the oxidized product. The catalyst was characterized and its CO conversion activity was measured by the water gas shift reaction carried out as described in EXAMPLE 1 and by the cyclohexane dehydrogenation activity described in EXAMPLE 2.

[0056] Table 4 shows that the catalyst prepared by the coprecipitation method, in accordance with the present invention, (EXAMPLE 2) allows obtaining a higher CO conversion activity than the catalyst prepared by the impregnation method (EXAMPLE 3), in which despite the smaller metallic area estimated by the cyclohexane dehydrogenation activity. Although the results do not allow to say conclusively, it is believed that in the coprecipitation method, sodium interacts more efficiently with Pt atoms, forming species with high CO conversion activity. The greater interaction between sodium and platinum would reduce the dehydrogenation activity of cyclohexane, characteristic of platinum with a predominantly metallic function (Table 4), but would increase the activity for the CO conversion reaction through the water gas shift reaction.

TABLE-US-00004 TABLE 4 CO conversion activity in the water gas shift reaction of catalysts prepared by impregnation (EXAMPLE 3) and in accordance with the present invention (EXAMPLE 2). Na Pt Reaction temperature (? C.) R.sub.D % % 350? 330? 300? 280? (gmol/ Sample m/m m/m C. C. C. C. gcat*s) EXAMPLE 2 0.04 0.20 51.7 35.5 18.4 9.8 4.4 EXAMPLE 3 <0.05 0.20 25.0 14.5 6.2 3.4 13.2 Note: The Fe content was 69 ? 1 m/m, with oxygen balance. RD refers to the rate of the cyclohexane dehydrogenation reaction [gmol/g .Math. s].

Example 4

[0057] This example in accordance with the present invention illustrates the method of preparing the hematite-based catalyst promoted by aluminum, platinum and sodium in low levels. A 1.0 M aqueous solution of iron nitrate (Fe(NO.sub.3).sub.3.Math.9H.sub.2O) containing a platinum compound soluble in water or polar solvents such as, but not restricted to, the compounds Pt(NH.sub.3).sub.4(NO.sub.3).sub.2 (CAS 20634-12-2), H.sub.2PtCl.sub.5.Math.xH.sub.2O (CAS 26023-84-7), PtCl.sub.4 (CAS 13454-96-1), (NH.sub.4).sub.2PtCl.sub.4 (CAS 13820-41-2) and (NH.sub.4).sub.2PtCl.sub.6 (CAS 16919-58-7) and the aluminum salt Al(NO.sub.3).sub.3.Math.9H.sub.2O and a second 1.5 M aqueous solution of sodium carbonate (Na.sub.2CO.sub.3), were added simultaneously for 1 h under stirring, maintaining the temperature between 55? C. and 65? C. and the pH between 7.5 and 8.0. After the end of precipitation, the suspension was maintained at the previous conditions of temperature, pH and agitation for another 1 h to age the precipitate. The precipitate was then filtered and separated into several parts to be washed with different amounts of water in order to obtain different levels of residual sodium in the final product.

[0058] Monitoring the conductivity of the washing water made it possible to easily and simply obtain different sodium (Na) contents in the final product. The washed material was then dried at 100? C. for 5 h and calcined at 400? C. for 2 h. The catalyst had its CO conversion activity measured as described in EXAMPLE 1.

[0059] In accordance with the present invention, aluminum is inserted into the crystalline structure of hematite, reducing the size of the parameter a of the hematite unit cell to a value between 0.05005 and 0.5010 nm (Table 5).

TABLE-US-00005 TABLE 5 Type of crystalline phase with the dimensions of its unit cell measured using the X-ray diffraction technique. tC crystalline A B C EXAMPLE (nm) phase (nm) (nm) (nm) EXAMPLE 1 43 Hematite 0.50303 0.50303 1.37219 EXAMPLE 2 44 Hematite 0.50354 0.50354 1.37440 EXAMPLE 4 34 Hematite 0.50049 0.50049 1.36339 Note: tC = average size of the hematite crystallite. A, B and C unit cell parameters

[0060] Table 6 illustrates that, with the introduction of aluminum into the formulation, the hematite phase is obtained at higher calcination temperatures. On the other hand, higher values for specific surface area are observed (Table 7), which contribute to greater catalyst activity.

TABLE-US-00006 TABLE 6 Crystalline structure and crystallite size of samples prepared in accordance with EXAMPLES 1, 2 and 4 identified with the X-ray diffraction (XRD) technique. Calcination EXAMPLE 1 EXAMPLE 2 EXAMPLE 4 T = 60? C. Goetite Goetite Hydroxide 14 nm (8 nm) mixture T = 300? C. Hematite Hematite Hydroxide (24 nm) (24 nm) mixture T = 400? C. Hematite Hematite Hematite (43 nm) (44 nm) (34 nm) Note: Sodium content in samples <0.1% m/m, Pt content of 0.2% m/m in EXAMPLES 2 and 4. Aluminum content in EXAMPLE 4 of 5.2% m/m.

TABLE-US-00007 TABLE 7 Composition properties, specific area and CO conversion activity as a function of temperature in the water gas shift reaction. S Pt Al Reaction temperature (? C.) Sample Type (m.sup.2/g) (% m/m) (% m/m) 350? C. 330? C. 300? C. 280? C. EXAMPLE 1 FeOx 47.9 0 0 8.1 3.3 0.4 0 EXAMPLE 2 PtFeOx 51.1 0.2 0 48.9 36.6 21.2 12.1 EXAMPLE 4 PtAlFeO.sub.x 125.0 0.2 5.4 63.6 39.4 21.4 14.9 Note: S = specific surface area determined by the N.sub.2 adsorption technique after calcination at 400? C.

[0061] It should be noted that, although the present invention has been described in relation to the attached drawings, it may undergo modifications and adaptations by persons skilled in the subject, depending on the specific situation, but as long as they are within the inventive scope defined here.