Process for extracting volatile constituents contained in a mass of regolith

Abstract

A process for extracting volatile constituents from a mass of regolith, particularly of lunar or Martian origin, comprising the following steps: progressive heating of the regolith leading to selective degassing of the various volatile constituents over time, according to the temperature reached by said regolith, with those having the highest vapor pressures degassing before those having lower vapor pressures; selection of at least a first temperature range (T1, T2) during which a gaseous mixture enriched in at least one valuable constituent and depleted in at least one undesirable constituent is collected, notably by degassing the regolith, relative to the initial concentrations of these constituents in the regolith. (Simplified figure: Fig. 2)

Description

Title of the invention: process for extracting volatile constituents contained in a mass of regolith

[0001] The present invention relates to an improvement in the degassing step of the regolith present on the surface of the Moon or Mars, prior to the production of the water contained therein. More particularly, it allows for the direct extraction from the regolith of a stream enriched in water and depleted in other volatile constituents. The proposed process can also be integrated as a first step upstream of the production of oxygen obtained by deoxygenating the regolith thus degassed.

[0002] The possibility of maximizing the use of local resources to produce oxygen, water, and other compounds necessary to maintain or extend future space missions is a primary objective of all private companies and government agencies working on these projects. Given their relative proximity to Earth, the Moon and Mars will be the first extraterrestrial bodies where long-duration missions will be conducted in the relatively near future, and consequently, the problem of ensuring reliable and efficient on-site production of these vital resources must be addressed in advance. The main material constituting the lunar or Martian soil is regolith, composed, among other things, of oxygen, silicon, iron, calcium, and aluminum in the form of oxides, but which also contains, among these oxides, small quantities of other constituents trapped by adsorption or solidification.

[0003] According to the most recent knowledge, the water content of regolith, as found at least locally in the coldest locations on the surface of the Moon, Mars, and even on the surface of asteroids, could reach several percent by weight, making this regolith the basic raw material for water production. This water, once purified, could then also meet oxygen requirements by simple electrolysis. To address the possibility that the potential water production might nevertheless be insufficient to supply the oxygen needed for the mission, several processes are being studied to extract oxygen from the regolith by reducing oxides and directly generating oxygen in the initial form of a gas mixture. In order to be used as a potential resource, the oxygen will need to be separated, purified, and packaged.The regolith will then advantageously be degassed beforehand to remove volatile compounds that could be undesirable during the deoxygenation reaction or oxygen purification. Integrating a water extraction process during this degassing can then be a good solution, combining the production of water and oxygen and benefiting from interesting synergies (thermal integration, shared equipment).

[0004] Whether for the production of oxygen by electro-deoxidation of the various oxides constituting the regolith or for the production of pure water, the presence of numerous diverse molecules in said regolith greatly complicates the operations required to obtain products sufficiently pure for use. Several documents in the literature describe methods for removing or, more generally, recovering the constituents trapped in the regolith and then possibly separating them.

[0005] US8357884 B1 describes a first method of recovering volatile constituents by directing microwave-type radiation into holes drilled in the regolith and recovering the released gas, in particular water, in transportable and interchangeable containers.

[0006] Document US2019271228 A1 proposes placing an enclosure on the surface of the regolith, this enclosure being equipped with a device for heating the ground surface using solar energy. The released gas is captured in a cold trap whose temperature can be, for example, between 200 and 270 K.

[0007] US documents 11168013 B2 and US 11608285 B2 propose to degas the regolith of its volatile compounds and also to capture these in a cold trap whose temperature is chosen in order to trap the water while not retaining the most volatile compounds.

[0008] This trapping at a controlled temperature allows for the recovery, after vaporization of the contents of the cold trap, of a gaseous mixture partially deballasted of the lightest compounds, but it only partially solves the problem of the final water purification. Indeed, the lightest compounds are generally the least adsorbable and the most volatile, and are relatively easy to remove by adsorption, condensation, distillation, etc. Conversely, the heavier compounds, trapped simultaneously with the water, compete with it in these same types of processes, and purifying the water of these constituents will require more complex separation methods.

[0009] There is therefore a need to simplify the proposed water purification processes, especially since these are subject to particular constraints related to the environment (local gravity and atmospheric pressure, absence of many materials which will have to be imported).

[0010] The present invention aims to effectively overcome these drawbacks by proposing a process for extracting volatile constituents contained in a mass of regolith, particularly of lunar or Martian origin, comprising the following steps: - gradual heating of the regolith leading to selective degassing over time, depending on the temperature reached by said regolith, of the different volatile constituents, those with the highest vapor pressures degas before those with lower vapor pressures; - selection of at least one first temperature range T1, T2 during which a gaseous mixture is collected, notably by degassing the regolith, enriched in at least one valuable constituent and depleted in at least one undesirable constituent compared to the initial levels of these constituents in the regolith.

[0011] According to one embodiment, the regolith contains water and other volatile compounds, the progressive and controlled evolution of the temperature of the regolith allowing the selection during heating of the first temperature range T1, T2 during which a gaseous mixture enriched in water and depleted in other volatile compounds is recovered, in particular with a higher or lower vapor pressure.

[0012] According to one embodiment, the initial temperature of the regolith before its progressive heating is less than -15 °C, preferably less than -30 °C, for example less than -75 °C.

[0013] According to one embodiment, the first temperature range Tl, T2 is between a first temperature Tl and a second temperature T2.

[0014] According to one embodiment, the fraction of constituents degassed before a first temperature T1 and the fraction degassed after a second temperature T2 are non-recovered impurities and are released into the local atmosphere, for example by directly taking advantage of the low atmospheric pressure, in particular of the Moon, or possibly via a pumping device.

[0015] According to one embodiment, at least part of the fraction of constituents degassed before the first temperature T1 and / or of the fraction degassed after the second temperature T2 is also recovered and reclaimed by aspiration, and / or by entrainment using a sweeping gas.

[0016] According to one embodiment, the recovered fraction of the degassed constituents before the first temperature Tl is selected in a second temperature range T3, T4 with T3 < T4 < Tl.

[0017] According to one embodiment, the second temperature range is between a third temperature T3 and a fourth temperature T4.

[0018] According to one embodiment, the recovered fraction of the degassed constituents after the second temperature T2 is selected in a third temperature range T5, T6 with T2 < T5 < T6.

[0019] According to one embodiment, the third temperature range is between a fifth temperature T5 and a sixth temperature T6.

[0020] According to one embodiment, the sweeping gas used to carry away water vapor and possibly other valuable constituent fractions includes at least one of the constituents of the group comprising CO2, O2, H2, Ar, Ne, N2, Kr.

[0021] According to one embodiment, the sweeping gas circulates in a semi-closed circuit, the recoverable constituent(s) being at least partially removed from the circulation loop before reuse of the sweeping gas, in particular during degassing.

[0022] According to one embodiment, the variation of the regolith heating temperature as a function of time follows a function T(t) which may include plateaus during which the heating power allows the targeted constituent to be vaporized, sublimed or desorbed at that temperature, whether it is water or another constituent.

[0023] According to one embodiment, the evolution of the temperature of the regolith as a function of time is controlled from the analysis of the contents of the constituents present in the degassing and / or the flow rate of this degassing.

[0024] According to one embodiment, the degassing process is discontinuous, with the regolith being introduced in batches into a heating furnace.

[0025] Such a batch introduction is also called batch introduction.

[0026] According to one embodiment, the technology used as a means of heating the regolith allows the homogenization of the temperature of the regolith to less than + or - 10 °C, preferably less than + or - 5°C, at least when the average temperature of the regolith being heated is within previously selected temperature ranges.

[0027] According to one embodiment, the temperature of the regolith is at least made homogeneous before the first temperature Tl and before the second temperature T2, the first temperature range Tl, T2 being that during which the gaseous mixture is collected enriched in at least one valuable target constituent and depleted in at least one undesirable constituent compared to the initial contents of the regolith.

[0028] According to one embodiment, the temperature of the regolith is maintained at the first temperature Tl + or - 10 °C, preferably at the first temperature Tl + or - 5 °C until the undesirable constituents lighter than the valuable constituent collected in the first temperature range Tl, T2 have a content and / or a flow rate below a previously determined threshold, this threshold being able to be a function of the content and / or the flow rate of the valuable constituent degassed simultaneously.

[0029] According to one embodiment, the temperature of the regolith is maintained at the second temperature T2 + or - 10°C, preferably at the second temperature T2 + or - 5°C until the valuable constituent collected in the first temperature range T1, T2 has a content and / or a flow rate below a previously determined threshold, this threshold being a function of the content and / or flow rate of the heavier undesirable constituents degassed simultaneously.

[0030] According to one embodiment, the degassing process is continuous or semi-continuous, with the regolith being introduced into the inlet of a furnace and circulating until it exits the latter, from where it is evacuated.

[0031] According to one embodiment, the regolith is in circulation in a furnace, said continuous or semi-continuous circulation being carried out by means of an appropriate drive system, the heating power being controlled throughout the path of the regolith so that the latter follows a programmed temperature rise T(t) and the furnace being designed so that the zone corresponding to the first temperature range T1, T2 selected for the recovery of the fraction of the degassing enriched in the valuable constituent is sufficiently sealed with respect to the upstream and downstream zones to prevent an undesirable introduction into it of the gas flows generated in the upstream and downstream zones.

[0032] According to one embodiment, the first temperature T1 and second temperature T2, possibly the third temperature T3 and fourth temperature T4 and / or the fifth temperature T5 and sixth temperature T6 are adapted to the variation in composition of the regolith in volatile compounds over time.

[0033] According to one embodiment, the fraction of water recovered between the first temperature T1 and the second temperature T2 contains more than 50%, preferably more than 70%, even more preferably at least 85% of the total quantity of water extracted during the degassing of the regolith.

[0034] According to one embodiment, the valuable constituent being water, the gaseous fraction recovered between the first temperature T1 and the second temperature T2 contains less than 50%, preferably less than 20%, and even more preferably significantly less than 10% of the total quantity extracted during the preheating of at least one constituent more volatile than water.

[0035] According to one embodiment, the valuable constituent being water, the fraction recovered between T1 and T2 contains less than 50%, preferably less than 20%, and even more preferably significantly less than 10% of the total quantity extracted during the preheating of a constituent less volatile than water.

[0036] According to one embodiment, one of the constituents more volatile than water at least partially eliminated from the water-enriched fraction produced between the first temperature T1 and the second temperature T2 is ammonia (NH3), methylchloride (CH3Cl), hydrogen sulfide (H2S), sulfur dioxide (SO2), ethylene (C2H4), carbon dioxide (CO2).

[0037] According to one embodiment, one of the less volatile constituents than water partially removed from the water-enriched fraction produced between the first temperature T1 and the second temperature T2 belongs to the group of carbon compounds with more than six carbon atoms, such as linear and branched alkanes, heavy alcohols, or benzene derivatives obtained by substituting one or more hydrogen atoms with other atoms or functional groups such as phenols, mercury.

[0038] According to one embodiment, the gas mixture, in particular collected on the first temperature range, is extracted from the regolith volume by connecting this volume to a device allowing its aspiration, and / or by entrainment by means of a sweeping gas.

[0039] According to one embodiment, the evolution of the temperature of the regolith is controlled from the analysis of the composition and / or flow rate of the gas mixture and by action on the heating power.

[0040] According to one embodiment, the water-enriched gas mixture recovered during degassing feeds a water production unit, in particular pure water, the water being preferably produced in liquid form.

[0041] According to one embodiment, the process includes a regolith deoxidation step by introducing the regolith into an electro-deoxidation unit for the metal oxides it contains, in order to extract the oxygen, the deoxidation step being implemented after the step of selecting at least a first temperature range (T1, T2) during which a gaseous mixture enriched in at least one valuable constituent and depleted in at least one undesirable constituent is collected, in particular by degassing the regolith, compared to the initial levels of these constituents in the regolith.

[0042] According to one embodiment, the electro-deoxidation unit is configured to allow an electrochemical reduction of metal oxides.

[0043] According to one embodiment, the electro-deoxidation unit comprises a reactor, such as a high-temperature reactor, for example of the MRE type for "Molten Regolith Electrolysis" or of the FFC type, for "FRAY, FARTHING, CHEN".

[0044] The invention further relates to a regolith degassing unit, comprising a control unit for implementing the process as described above.

[0045] The invention may also relate to any alternative device or method comprising any combination of the above or below features.

[0046] The invention will be better understood upon reading the following description and examining the accompanying figures. These figures are given only to illustrate, but in no way limit, the invention.

[0047] [Fig. 1] The [Fig. 1] is a graph representing the evolution of the vapor pressure of several constituents as a function of temperature;

[0048] [Fig.2] [Fig.2] is a graph representing a typical heating of the regolith over time;

[0049] [Fig.3] [Fig.3] is a schematic representation of a degassing unit of a regolith;

[0050] [Fig.4] [Fig.4] is a schematic representation of a detail of [Fig.3].

[0051] The main material constituting the lunar, Martian, and certain celestial soils is regolith. This is the surface layer, which can range in thickness from several centimeters to a few meters. Regolith can include, in particular, blocks, millimeter-sized particles, and dust a few tens of microns in size. The basic material is chemically composed of, among other things, oxygen, sodium, magnesium, silicon, iron, calcium, aluminum, titanium, and potassium, in the form of metallic oxides. It originates from the disintegration of rocks such as basalt, feldspar, olivine, and magnetite, caused by the continuous bombardment of meteorites and particles from space. It also contains, in small quantities, generally in trace amounts, various volatile constituents trapped by adsorption, solidification, electrostatic effects, etc.in the regolith, particularly when it is continuously kept at low temperatures and protected from solar radiation. In such regions, it is thought that material containing between 1 and 7% H2O by weight can be collected. The list of other potentially present volatile constituents is growing with each analysis and currently includes at least H2S, NH3, SO2, C2H4, CO2, CH3OH, CH4, H2, CO, HG, and He. These secondary constituents could represent approximately 10% of the water content. Regolith is therefore considered the primary material for providing the elements necessary for exploration or long-term settlement on the Moon or Mars, particularly water and oxygen, but also potentially other compounds derived from volatile constituents (fertilizers from NH3, etc.).

[0052] In this document, regolith means both the surface layer as it is arranged on the surface of the Moon or Mars and the same material after extraction and possible mechanical treatments such as grinding, sieving.

[0053] Water and volatile constituents are extracted by heating the regolith, which causes their degassing through sublimation and desorption. The resulting gaseous mixture is then treated to extract the water and possibly other constituents of interest. In addition to providing the necessary water for various human needs, this constituent can also be used to produce oxygen via an electrolysis unit.

[0054] The term "degassing" now refers both to the process by which, through heating and possibly pumping or elution with a purging gas, the volatile constituents of the regolith are extracted, and to the resulting gaseous flux. The latter is sometimes referred to as a "gaseous mixture" from the regolith.

[0055] Other processes are being studied for directly extracting oxygen from regolith by reducing oxides, directly generating this oxygen in the form of a gas mixture. These processes all operate within high temperature ranges. In order to be used as a potential resource, this oxygen will then have to The gas must be separated from the other components released during the process, purified, and conditioned. It is therefore important to eliminate volatile components so that they do not interfere with the deoxidation process or contaminate the oxygen produced. This degassing can be carried out upstream of the reactor or during the deoxidation process. If it is beneficial, water can be extracted from the resulting gas mixture.

[0056] Heating regolith can be carried out in various ways. Some documents recommend proceeding in situ, that is, not extracting the regolith for subsequent processing, but, for example, covering a limited area of ​​the ground with an airtight seal, then heating the top layer and collecting the resulting gas release, or drilling holes in the regolith and introducing energy in various forms into them in order to sublimate or desorb the constituents closest to the wall. The advantage is that large quantities of material are not required to be handled in order to extract only a few percent.

[0057] Conversely, regolith can be extracted for subsequent processing. This can involve fixed extraction such as mines with galleries or open-pit mines, or mobile extraction using rovers that primarily collect surface material.

[0058] Regardless of the solution chosen, the regolith can be ground, sieved, and possibly separated into several fractions by various means such as electrostatic processes, centrifugation, etc., depending on the composition of the regolith and how the volatile constituents are sequestered within it. For example, these constituents may be strongly agglomerated with the metal oxides or, conversely, form independent micronodules. In all these cases, we speak of pretreatment before degassing, and we continue, as previously stated, to call the material thus obtained regolith, which will generally consist of centimeter-sized grains, millimeter-sized particles, and dust, the water content of which may range, for example, from 0.5 to 10 wt% depending on the initial content of the regolith and the potential enrichment obtained during the pretreatment.

[0059] Regolith temperatures, whether on the Moon or Mars, are extremely variable depending on location (equator, poles, exposure to sunlight, etc.) and time of day (day or night, season, etc.). Data vary from one document to another, but for the Moon, variations from +130°C to -130°C are generally accepted, with some locations where the temperature remains below -200°C. For Mars, a range of +30°C to -150°C is cited. It should also be noted that the Moon's atmospheric pressure can be considered negligible and its gravity on the order of 0.16 g. As for Mars, its atmospheric pressure is variable, but an average value of 610 Pa is generally accepted, that is, approximately 6 mbar composed of 96% CO2, with a gravity of 0.38 g.

[0060] Over time, the regolith in regions least exposed to sunlight has acted as a cold trap for various free molecules. These molecules are mostly present in trace amounts, representing a small volume, and these volatile constituents can be considered, a priori, as grains of solidified or adsorbed matter, independent of one another, without having to take into account mixing, co-adsorption, or even reaction effects between these constituents. Thus, the vapor pressure of each constituent can be estimated at a given temperature T. By implementing a sufficiently slow and homogeneous heating of the regolith mass, the kinetics of heat and mass transfer become secondary.By understanding the nature of the volatile constituents of the regolith and their respective concentrations, we can estimate, based on temperature changes over time, the quantities that will be released and when a constituent will be depleted. This model can be likened to evaluating the respective evaporation times of, for example, separate droplets of different sizes containing NH3, water, and a heavy alcohol, or the sublimation times, at lower temperatures, of these same constituents.

[0061] It appears that a majority of the volatile constituents present with water have vapor pressures much higher than those of water, for example at temperatures of the order of -20 to -30°C by a factor of the order of 10 for methanol, and much higher by two orders of magnitude for SO2, NH3, H2S... Thus, instead of degassing the regolith in its entirety, collecting the complex gaseous mixture obtained and then separating the water and possibly other constituents from this mixture, it is possible by progressive degassing to collect a fraction enriched in water and especially depleted in the other constituents considered as impurities at the level of the production of pure liquid water.

[0062] In the description, the term "impurities" will be used to designate constituents likely to pollute the water production, even if some of these impurities have a use elsewhere and are also recovered separately from the water in the degassing process.

[0063] It should be noted that by setting a temperature limit for said degassing just above that used for the recovery of the water-rich fraction, it is possible to eliminate from the regolith the heaviest constituents that may be present, such as mercury or carbon chains with 6 or more carbon atoms.

[0064] This depletion of the water-rich fraction of other impurities in the regolith can be achieved while recovering the majority of the water due to differences in vapor pressure and the respective quantities of water and impurities. Furthermore, the goal is not necessarily to produce degassing containing only water, but rather to significantly reduce the number and quantity of said impurities. It is understandable that under such conditions, the extraction of pure water will be considerably simplified, which is of considerable interest under extraterrestrial conditions. The potential processes for extracting, purifying, and liquefying water from the mixture thus enriched in H2O and depleted in other constituents are not described in this document, but all known and accepted methods for this application could benefit from this preferential degassing.

[0065] The invention described in this document therefore relates essentially to a selective degassing process by means of progressive heating of regolith containing water and other volatile compounds, this progressive heating during which the evolution of the temperature T of the regolith is controlled makes it possible to select during said heating a first temperature range T1, T2 during which a gaseous mixture enriched in water and depleted in the other volatile compounds is recovered.

[0066] The first temperature range T1, T2 is between a first temperature T1 and a second temperature T2. In this description, T1 will be called the first temperature T1 and T2 the second temperature T2.

[0067] Nevertheless, the degassing principle proposed here can be applied to the recovery of constituents other than water. Thus, more generally, it concerns a process for extracting volatile constituents contained in a mass of regolith of lunar or Martian origin, employing a progressive heating of the regolith leading to selective degassing over time, according to the temperature reached by said regolith, of the different volatile constituents, those having the highest vapor pressures degassing before those having lower vapor pressures, the process being characterized by the selection of at least a first temperature range T1, T2 during which the degassing stream is collected enriched in at least one valuable constituent and depleted in at least one undesirable constituent compared to the initial concentrations of these constituents in the regolith.

[0068] The term target constituent is also used to designate the valuable constituent that one wishes to recover. It is possible that, locally, the regolith may be rich in a volatile constituent, other than water, which would be of definite use for a longer-term human settlement. Ethylene has been cited as a raw material, and ammonia as a source of nutrients for future crops...

[0069] It should be noted that the term "regolith" here refers both to the surface layer of regolith as it is found on the surface of the Moon or Mars, and to the same material after extraction and any mechanical processing such as grinding, transport, sieving, etc. The heating process(es) used will depend on these characteristics (heating in situ or after extraction and any mechanical processing), but also on the volume of regolith to be treated and the type of energy involved. This last point will be addressed later.

[0070] The gaseous mixture generated between temperatures T1 and T2 is extracted from the volume of regolith located within this first temperature range by connecting this volume to a device that allows its aspiration, and / or by entrainment using a scavenging gas. In the latter case, this will be a low flow rate, allowing the material to be eluded and assisting in the degassing of water. Preferably, the degassing is carried out at low pressure to promote the sublimation or desorption of volatile constituents.

[0071] In particular, the fraction of constituents degassed before temperature T1, as well as the fraction degassed after temperature T2, assuming they are non-recoverable impurities, are discharged to the outside, for example by taking advantage of the low lunar atmospheric pressure or possibly via a low-pressure pumping device. On Mars, it will be necessary to compare extraction at a pressure of 6 mbar in the presence of atmospheric CO2 with, for example, extraction by vacuum pumping, or even with vacuum pumping including a CO2 elution step followed possibly by removal of residual CO2. Those skilled in the art will be best placed to define the most suitable solution based on actual data concerning said degassing.

[0072] However, as already indicated, at least a portion of the fraction of constituents degassed before temperature T1 and / or of the fraction degassed after temperature T2 may be recoverable and will then be collected by suction and / or by sweeping with a gas. The procedure will be the same as for water in order to obtain gas streams enriched in these constituents. For example, the recovered fraction of constituents degassed before temperature T1 is selected from a second temperature range T3, T4 with T3 < T4 < T1 and / or the recovered fraction of constituents degassed after temperature T2 is selected from a third temperature range T5, T6 with T2 < T5 < T6.

[0073] The second temperature range is between a third temperature T3 also called T3 and a fourth temperature T4 also called T4.

[0074] According to one embodiment, the third temperature range is between a fifth temperature T5 also called T5 and a sixth temperature T6 also called T6.

[0075] When degassing is facilitated by sweeping with a gas stream external to the regolith, the constituents of this stream will be chosen so as not to solidify, adsorb, or react chemically, to be easily separable from water, and to be available locally, at least in small quantities, to compensate for inevitable losses during the process. This stream can be recycled. Examples include nitrogen, oxygen, hydrogen, argon, krypton, neon, and, above a certain regolith temperature, carbon dioxide.

[0076] It is understood that since the composition of the regolith in volatile constituents varies from one location to another, the temperatures T1 and T2, possibly T3 and T4 and / or T5 and T6, must be adapted to this variation in regolith composition over time. The same applies to the flow rate of the purging gas, which must be optimized so as not to dilute the degassing too much while promoting the sublimation and desorption of the constituents.

[0077] The operating conditions are such that the fraction of water recovered between T1 and T2 contains, depending on the volatile gas composition of the regolith and the target water content, more than 50%, preferably more than 70%, and even more preferably at least 85% of the total quantity of water extracted during the degassing of the regolith. This represents the extraction efficiency of the quantity of water recovered relative to the quantity initially contained in the treated regolith. Generally speaking, the more water molecules are willing to be lost during the simultaneous extraction of impurities that are more or less volatile than water, the more water-enriched the degassing fraction will be and the more impurity-poor it will be.

[0078] Since the valuable constituent is always water, the gaseous fraction recovered between T1 and T2 and depleted of impurities contains less than 50%, preferably less than 20%, and even more preferably significantly less than 10% of the total quantity extracted during the preheating of at least one constituent more volatile than water.

[0079] One of the constituents more volatile than water partially removed from the water-enriched fraction produced between T1 and T2 is ethylene (C2H4), ammonia (NH3), methyl chloride (CH3Cl), hydrogen sulfide (H2S) or sulfur dioxide (SO2) or carbon dioxide (CO2)

[0080] Similarly, the fraction recovered between T1 and T2 contains less than 50%, preferably less than 20%, and even more preferably significantly less than 10% of the total quantity extracted during the preheating of a constituent less volatile than water.

[0081] One of the constituents less volatile than water partially eliminated from the water-enriched fraction produced between T1 and T2 then belongs to the group of carbon compounds with more than 6 carbon atoms, such as linear and branched alkanes, heavy alcohols, or benzene derivatives obtained by substituting one or more hydrogen atoms with other atoms or functional groups such as phenols, mercury.

[0082] The initial temperature of the regolith before its selective degassing depends on its initial geographical location and any pretreatments it may have undergone. For example, it could be between -200°C and -70°C. The first temperature range T1, T2 in which the water-enriched and impurity-depleted fraction is recovered will depend essentially on the nature of the impurities. contained in the regolith and the importance of avoiding their presence in this fraction. This latter point depends on the ease of their removal in the downstream pure water production process. It is understandable that constituents highly soluble in water or corrosive to equipment are more problematic than constituents easily adsorbed onto highly hydrophobic adsorbents. The vapor pressure of water in its solid (ice) and liquid states varies enormously over a few tens of degrees. For the record, we go from, for example, 0.09 mbar at 230K, to 0.7 mbar at 250K, 6 mbar at 273K, 32 mbar at 298K, 123 mbar at 323K... For example, if at -30°C, we have already eliminated almost all traces of troublesome impurities more volatile than water and it is only at more than 50°C that we desorb heavy constituents, we can indeed adopt the temperature range of -30°C, +50°C for the preferential degassing of water.In other cases, it may be necessary to use narrower temperature ranges, such as -20°C to +20°C. It should be noted that within these temperature ranges, depending on the capabilities of the heating method used, there may be, starting from temperature T1, an initial rapid temperature rise followed by a second stage corresponding to a temperature plateau close to the upper end of the range, T2. This allows for a faster recovery of the water contained in the regolith.

[0083] More generally, the temperature variation of the regolith over time follows a function T(t) which may include plateaus or pseudo-plateaus during which the heating power compensates for the vaporization, sublimement, or desorption of the targeted constituent at that temperature, whether it be water or another constituent. These plateaus may occur after more or less rapid temperature increases.

[0084] By pseudo-steps, we mean that the temperature of the regolith is not necessarily controlled to within / 2 degrees Celsius over a given period of time but that it can vary, for example increase, but at a much slower rate, for example ten times slower, than during other so-called rapid temperature rise stages.

[0085] If, at a given instant, the temperature level used determines the vapor pressure of the various constituents present in the regolith, then at least periodic analysis of the degassing composition is necessary to determine the function T(t) defined previously. In practice, the evolution of the regolith temperature T over time will be monitored based on at least periodic analysis of the constituent content of the degassing. The frequency of these analyses will depend on the potential variation in the composition of the regolith thus treated.

[0086] The heating system itself can be very varied, both in terms of the technology used and the energy source. However, it must allow for a certain homogenization of the regolith temperature during degassing, in order, for example, to avoid excessively hot areas that would simultaneously lose their contained water. with excessively cold zones that would retain impurities which must then be removed before the actual degassing of the water begins at temperature T1. In the case of a continuous supply of regolith circulating in a furnace (furnace being taken in the broadest sense), the temperature of the regolith is obviously not the same between the inlet and outlet of said furnace, but it will at least be homogeneous in a given zone of the furnace to avoid the problem mentioned above. By homogeneous, we mean that within a degassing range of interest T1, T2, the entire regolith will, for example, initially have a temperature between T1 ± 5°C and at the end of this degassing a temperature between T2 ± 5°C.It is understood that, depending on the volatile composition of the regolith, particularly the presence of constituents with vapor pressures closer to or further from that of water and their quantity relative to the quantity of water, the ranges of initial and final temperatures can be more or less wide and different, for example T1 ± 5°C and T2 ± 10°C. It should be noted that between T1 and T2, there can be larger temperature differences between zones of the regolith without altering the overall degassing process. This can allow for faster heating of the regolith between two well-controlled temperature plateaus around T1 and then T2.

[0087] The T1 step aims to remove from the regolith almost all, or at least a significant fraction, of a constituent that is more volatile than water and likely to pollute and complicate the subsequent production of pure water, while limiting the loss of water molecules. The T2 step aims to extract as much water as possible from the regolith without carrying over constituents heavier than water, particularly if these are likely to complicate its final purification.

[0088] Figures 1 and 2 illustrate very schematically the principles described above.

[0089] Figure 1 represents, on a logarithmic ordinate, the orders of magnitude of the vapor pressure in Pascals (Pa, kPa = 1000 Pa, MPa = 10⁶ Pa) above the solid and possibly liquid phase of water 21, of a lighter constituent 22, for example H₂S, and of a heavier constituent 23, for example Hg, as a function, on the abscissa, of the temperature in Kelvin. Its sole purpose is to show that differences of more than three orders of magnitude can be observed at both T₁ and T₂ in the vapor pressures between water 21 and the impurities 22 and 23, thus making it possible to create selective degassing, that is, to recover a majority of the water molecules while carrying away only a few impurities.

[0090] It should be noted that, given the amount of water in the regolith, the way this water accumulates over time, and the impurities, it is highly unlikely that the presence of ice would block the degassing of the lighter constituents (H2S, NH3, etc.) during the initial heating phase. If such a configuration were to exist Locally, pretreatment such as grinding would allow degassing as described in this document.

[0091] Figure 2 represents a typical heating of the regolith over time t, i.e., the function T(t) with T being the temperature of the regolith. The heating curve shows five zones labeled 30 to 34, successively showing the heating of the degassed regolith from its initial temperature to temperature T1 (label 30), which is maintained (label 31) until almost all of the lighter-than-water constituent 22 has been extracted.

[0092] Analysis of the degassing composition makes it possible to monitor the content of constituent 22, which drops at the end of the plateau, and to control the water loss. The regolith is then heated to temperature T2 (reference point 32), which is also maintained until the water is exhausted (reference point 33).

[0093] Depending on the final destination of the regolith, from which valuable constituents have been extracted, it can be released onto the surface of the celestial body from which it was extracted, after possible thermal integration to recover at least a fraction of the energy expended, or it can serve as a raw material in a downstream unit for oxygen production or as a construction material, for example. Depending on the case, it may continue to be heated to a high temperature, and the gradual degassing will then be only one step in a larger process. It is understood that if it is desired to recover another valuable constituent, the same procedure will be followed at temperature levels below or above T1, T2.

[0094] The energy required for heating and degassing the regolith can come from various sources: solar radiation, a nuclear power plant, or thermal integration with other processes, for example, with a reactor for deoxygenating the metal oxides that constitute the bulk of the regolith. For each source, the energy transfer method will be chosen according to the technology selected for the furnace in the broadest sense of the term. For example, with solar energy, incident radiation can be used directly to heat regolith collected at -150°C to -70°C. This regolith has been placed in a thin layer on a suitably positioned platform and then cooled to -45°C by concentrating the radiation using mirrors before being introduced into a furnace heated by electricity supplied by solar panels to undergo the major part of the degassing process, including water extraction.This final part of the degassing process can then be carried out continuously, semi-continuously, or in batches.

[0095] More generally, the degassing process can be continuous, semi-continuous, batch or consist of a hybrid process implementing successively two -or more- different heating methods as in the example above.

[0096] According to a variant intended a priori for the production of a large quantity of water, for example one m3 / day by treating about fifty tons of regolith, the latter will preferably be introduced continuously (or semi-continuously) into the inlet of a furnace and will progress to the outlet of the latter from where it will be evacuated, said circulation being carried out by means of an appropriate drive system, the heating power being controlled throughout the journey so that the regolith follows a programmed temperature rise T(t) and the furnace being designed in such a way that the zone corresponding to the first temperature range T1, T2 selected for the recovery of the water-enriched degassing fraction is sufficiently sealed with respect to the upstream and downstream zones to prevent an undesirable introduction into it of the gas flows generated in the upstream and downstream zones.Regarding this last point, various sealing systems can be considered as long as they are compatible with the movement of regolith into the kiln, such as brush-type systems or double brush systems with intermediate drainage.

[0097] A slight overpressure in the central zone corresponding to temperatures T1 to T2 linked to the pressure regulation of a sweep gas can help to avoid any undesirable pollution of the selected gaseous fraction.

[0098] The drive means can be of the type industrial conveyor, conveyor belt, conveyor belt, gravity system adapted to local conditions, provided that this system is compatible with the temperature variations between the inlet and outlet of the furnace, for example from -100°C to +100°C and allows the homogenization of the temperature of the regolith during heating.

[0099] This homogenization of the temperature can be obtained by integrating means of stirring the regolith along its path (blades, vibrations, obstacles arranged appropriately) or more simply by dimensioning the drive system leading to obtaining a thin layer of regolith, a few centimeters thick, heated for example from above and below.

[0100] This description is given only by way of example and is not limiting. Any means of circulating and heating the regolith can be suitable as long as it allows control of its temperature T(t) during the process, homogenization of this temperature in particular at least before the start of preferential degassing of water at T1 and at the end of this degassing at T2, preferential extraction of the fraction enriched in water and depleted in impurities and possibly the introduction of a scavenging gas.

[0101] According to another embodiment, the degassing process is discontinuous, with the regolith being introduced in batches into the heating furnace. The temperature rise is controlled by the heat input, and the degassed fraction between the selected temperatures T1 and T2 is extracted for processing to produce pure water. Such a process can be used, for example, to produce a few liters of water per batch from the recovery of the water-enriched fraction.

[0102] Figures 3 and 4 schematically represent a batch-type device 1 comprising several cylindrical tanks 3.i that can operate independently or in parallel depending on the quantity of water to be produced or the amount of regolith available. This could be, for example, a mobile system, i.e., mounted on a rover and supplemented by a small filtration, condensation, and final purification unit designed to supply the liquid water and possibly oxygen, via an electrolyzer, required by an exploration team. In this case, the purity of the degassed water will be prioritized over its extraction yield so that only safety filtration may be required, and the water can be directly condensed using the ambient temperature as a cooling source.

[0103] Figure 3 shows the operating principle. Figure 4 illustrates a detail of a achievable.

[0104] The regolith 2, collected directly at low temperature in the form of small fragments or ground to obtain particles of millimeter or centimeter size, is placed in cylindrical tanks 3i approximately ten centimeters in diameter, each capable of holding about thirty kilograms. These cylinders, whose outer shell is porous to the gas but retains the regolith particles, are equipped with a heating element 4, symbolically represented here by a heating cord wound around the cylinders, to maintain a uniform wall temperature throughout their height. The material of the cylinders is a good thermal conductor, as are the fragments and particles of metallic oxides that constitute almost all of the regolith. The small diameter allows for a low temperature gradient to be maintained throughout the mass of the regolith.If necessary, a regolith movement system (not shown, for example, a screw conveyor) can be provided to achieve a nearly uniform temperature. The wall temperature will be increased gradually to maintain the desired temperature gradient. A small-diameter perforated tube 5 is shown in the center of the heating tubes. This tube can be used, depending on the application, to collect outgassing in the central section or to inject a small flushing flow 12 to facilitate the sublimation, desorption, or vaporization of water. Associated valves 5.1 and 5.2 allow selection of the preferred operating mode. It would be beneficial to provide a means of heating the wall of this tube 5 to supply additional energy to the central section of the tank, which can help homogenize temperatures. In [Fig. 3], the outgassing gas is shown to be extracted from the outside of the heating tube 3.1 and through the central perforated tube 5.Valve 5.2 will be closed and valve 5.1 open. This system can also allow the injection of a low flow rate of scavenging gas 12 during. Degassing, in particular to aid vaporization and water removal. In this case, the cover 13 shown in dotted lines should be fixed to the top of the tank and the valve 5.1 closed to force radial circulation of the purge gas and degassed constituents.

[0105] In [Fig. 4], seven of these heating cylinders 3.1 to 3.7 are housed in a single thermally insulated enclosure 6. These seven cylinders lead to a device 1 capable of processing approximately 200 kg of regolith. The quantity of water contained can range, depending on the case, from about 1 liter up to ten or fifteen liters for water-rich regoliths located in particularly cold areas. As previously indicated, there is every reason to believe that the various impurities trapped over time are independent and exist as almost pure crystals, rather than as intimately bound agglomerates of these constituents. As already explained, the process proposes to remove these impurities from the regolith separately from the water simply by taking advantage of the differences in partial tension, which can be very high at given temperatures.

[0106] Thus, by making rises with heating stages at determined temperatures, for example below -25°C, it is possible to vaporize constituents such as NH3, H2S, SO2 while sublimating only a very small quantity of water, the respective vapor pressures being in ratios of 100 or even 1000.

[0107] We will therefore use the available heating power to heat the regolith quite rapidly from its initial temperature to, for example, -30°C while venting to the atmosphere, i.e. at very low pressure, the products that can sublimate or desorb at this temperature, then we will heat the regolith more slowly, let's say up to -25°C in order to homogenize the temperatures as much as possible thanks to the thermal conduction of the materials and maintain this temperature as long as we detect, as shown in [Fig.3], a flow in the degassing vent line 8 to the atmosphere 9 then we will raise the temperature again so as to go above 0°C, for example by staying between 25 and 35°C to vaporize all the water in the regolith while degassing only a little of the heavy constituents such as carbon compounds for example.During this period, the gas extracted from the regolith is pumped via the vacuum pump 10 and stored under pressure in the tank 11 or sent directly to the pure liquid water extraction unit.

[0108] Once most of the water has been recovered, the heating of the regolith will either be stopped at temperature T2, or the heating and extraction of residual impurities will continue if, for example, this regolith is intended to be deoxidized in an FFC-type reactor. If the sole purpose of the degassing is water recovery, thermal integration should be planned, for example with another degassing device ready to A heating cycle can be initiated to recover most of the energy supplied to the regolith. For example, the principle of thermal regenerators can be used, which involves transferring energy directly from one component to another, or via an intermediate storage tank with adequate heat capacity. This is not shown in [Fig. 3], as the idea here is to supply a reactor producing oxygen in series. The method of extracting the hot regolith to the reactor is not directly related to the present invention. It is understood that the operating mode of the degassing system will need to be adapted depending on the atmospheric pressure and the composition of the local atmosphere. The description given above is more suited to lunar regolith with a local atmospheric pressure that is practically zero.The scavenging gas used only during water extraction could, for example, be argon, oxygen, or hydrogen, constituents that are very easy to separate from water vapor.

[0109] On Mars, it will probably be possible to use CO2 by pulling the tanks under vacuum (vacuum relative to local atmospheric pressure) to extract the volatiles of no interest and return them to the atmosphere or even to possibly elute the water vapor, which is quite easily separable from this gas, to promote its degassing.

[0110] Here again, this example is introduced in the description only to demonstrate that there are several ways of implementing the particular features of this invention, namely a progressive and controlled heating of the regolith allowing to extract at a given time a fraction of the degassing enriched in water and depleted in volatile impurities compared to the composition of a complete degassing of the regolith, the aim being to obtain a gaseous mixture from which it will be significantly easier to extract pure water.

[0111] It is understood that one of the key points in the application of the process is the control of the regolith temperature throughout the heating process. Assuming that the goal is to recover volatile compounds likely to be degassed between T1 and T2, for example -30°C and +30°C, and that these compounds are water, it is essential that the regolith entering the zone of interest, and therefore at a temperature of -30°C, has not previously experienced hot spots during its initial heating, for example at +5°C, which would have locally led to premature degassing of water molecules, molecules lost because they were eliminated along with volatile impurities. Similarly, it is essential that this regolith does not contain cold pockets which would still contain undesirable impurities not yet degassed and which would pollute the water-enriched stream.One method to achieve this result is to heat the regolith in a thin layer via one or more heating walls whose temperature is maintained just above the temperature of the regolith, a temperature which is therefore measured during heating and which plays a role in regulation. A consistent temperature. A homogeneous temperature of +30°C is necessary to avoid losing water that would not have been degassed in colder areas and to prevent contamination of the recovered fraction by excessively hot areas that have released heavy compounds. It is possible to design several furnaces to provide homogeneous heating of thin regolith layers and to recover the degassed gas mixture; for example, alternating series of heated and permeable plates create compartments to contain the regolith and spaces to collect the degassing. However, such arrangements appear rather limited to the production of small quantities of water.

[0112] As already mentioned, a probably more efficient method is to homogenize the temperature of the regolith by means of suitable mechanical stirring adapted to the geometry of the furnace (vibrations, rotations, mixers of any type). This should make it possible to process larger quantities of regolith and to heat it more quickly.

[0113] The duration of the successive heating stages can be estimated using software that takes as input the composition of the regolith, its particle size distribution, the mass or flow rate to be treated, its inlet temperature, the operating pressure, and stores the physical properties of the constituents (heat capacities, thermal conductivities, enthalpies of sublimation, desorption, vaporization, vapor pressures) as well as the characteristics of the furnace. However, it seems useful, even essential if a high level of performance in terms of extraction yield and purity is sought, to monitor the analysis of the degassed flow over time, either continuously or periodically according to the heating kinetics. Such an analysis makes it possible to detect when the regolith has been freed of most of an undesirable impurity (around temperature T1) or when the regolith is depleted of water (at temperature T2).

[0114] The operating pressure will depend on the integration of degassing into a larger process chain, extending, for example, to the treatment of at least partially degassed regolith in a deoxidation reactor for oxygen production, or to the production of pure or even ultrapure water for feeding an electrolyzer. A priori, it will be a low pressure, ranging from a few millibars to a few tens or hundreds of millibars, to promote degassing. The presence of a sweep flow, particularly during preferential water extraction, provides an additional degree of freedom. In most cases, this sweep flow will then be recycled to avoid the loss of recovered gas molecules. In particular, the sweep flow may include one or more components from the group comprising CO2, O2, H2, Ar, Ne, N2, and Kr.

[0115] Optionally, the sweep gas circulates in a semi-closed circuit, the recoverable component(s) being removed from said circulation loop as well as the residual impurities by appropriate processes before reuse of said sweeping gas in the degassing process.

[0116] It should be noted that by simply compressing the water-enriched gas mixture followed by condensation on a cold surface, for example at +1°C, it will generally not be possible to obtain liquid water directly usable for either human consumption or for supplying an electrolyzer. One possible use might be the irrigation of greenhouse crops. The water-enriched gas mixture recovered during selective degassing will more likely supply a pure water production unit, the water being preferentially produced in liquid form. The description of such a final water purification unit is not the subject of this document, which is limited to the extraction of regolith from a water-enriched stream.It should be noted again that by adjusting the temperature levels T1 and T2, the purity of the degassing water and its extraction yield can be modified, these two parameters being inversely related: very pure water with a low yield or a large amount of water of lower purity. Thus, two potential uses for the degassing of the same regolith can be anticipated.

[0117] Such selective degassing can be advantageously integrated into a preheating step of the regolith before its introduction into an electro-deoxidation unit for the metal oxides it contains, in order to extract the oxygen. The degassing can then, if necessary, be carried out to temperatures considerably higher than those required for the recovery of water molecules in order to eliminate very heavy constituents that are undesirable for subsequent operations.

[0118] The invention also relates to a regolith degassing unit implementing the process described above.

Claims

Demands

1. A process for extracting volatile constituents contained in a mass of regolith, in particular of lunar or Martian origin, comprising the steps: - progressive heating of the regolith leading to selective degassing over time, according to the temperature reached by said regolith, of the different volatile constituents, those having the highest vapor pressures degassing before those having lower vapor pressures; - selection of at least a first temperature range (T1, T2) during which a gaseous mixture enriched in at least one valuable constituent and depleted in at least one undesirable constituent is collected, in particular by degassing the regolith, compared to the initial contents of these constituents in the regolith.

2. A method according to the preceding claim, the regolith containing water and other volatile compounds, the progressive and controlled evolution of the temperature of the regolith allowing selection during heating of the first temperature range (T1, T2) during which a gaseous mixture enriched in water and depleted in the other volatile compounds with higher or lower vapor pressure is recovered.

3. A method according to any one of the preceding claims, characterized in that the gaseous mixture, in particular collected on the first temperature range (T1, T2) is extracted from the regolith volume by connecting this volume to a device allowing its aspiration, and / or by entrainment by means of a sweeping gas.

4. A method according to any one of the preceding claims, characterized in that the evolution of the temperature of the regolith is controlled from the analysis of the composition and / or flow rate of the gas mixture and by action on the heating power.

5. A method according to any one of the preceding claims, comprising a regolith deoxidation step by introducing the regolith into an electro-deoxidation unit for the metal oxides it contains, in order to extract the oxygen, the deoxidation step being carried out after the step of selecting at least a first temperature range (T1, T2) during which the following are collected, in particular by degassing the regolith, a gaseous mixture enriched in at least one valuable constituent and depleted in at least one undesirable constituent compared to the initial levels of these constituents in the regolith.

6. A process according to any one of claims 2 to 5, characterized in that the water-enriched gas mixture recovered during degassing feeds a water production unit, in particular pure water, the water being preferably produced in liquid form.

7. Regolith degassing unit, comprising a control unit for implementing the process according to any one of the preceding claims.

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