PROCESS FOR GASIFYING A CARBON-CONTAINING SUBSTANCE BY MOLTEN SALT CATALYSIS, AND ASSOCIATED PLANT

Abstract

The present invention relates to a gasification process of a solid carbonaceous material by catalysis in molten salts. A carbonaceous material is contacted, for a defined period in the presence of air with a first molten salt bath. The first molten salt bath includes at least one chloride type salt chosen from NaCl, MgCl.sub.2, CaCl.sub.2), KCl, FeCl.sub.2 and which has a melting point greater than or equal to 300? C., a density greater than 1 measured in the liquid state and at atmospheric pressure. The gases formed are recovered, and are contacted with a second molten salt bath optionally different from said first bath and, at the outlet of said second bath, the recovered gases are either stored optionally under pressure, or reinjected into said first bath or said second bath.

Claims

1. A gasification process of a solid carbonaceous material by catalysis in molten salts comprising: contacting the carbonaceous material with a first molten salt bath for a defined period, said first molten salt bath comprising at least one chloride type salt selected from the group consisting of NaCl, MgCl.sub.2, CaCl.sub.2), KCl and FeCl.sub.2 and having a melting point greater than or equal to 300? C., a density greater than 1 measured in the liquid state and at atmospheric pressure and a specific heat capacity measured in the liquid state and at atmospheric pressure lower than the specific heat capacity of water measured at a temperature of 25? C. and at atmospheric pressure, said contacting is carried out in the presence of air, recovering formed gases; and contacting the recovered formed gases are contacted with a second molten salt bath optionally different from said first bath and in that, at an outlet of said second bath, the received formed gases are either stored optionally under pressure, or reinjected into said first bath or said second bath.

2. The process according to claim 1, wherein said recovered formed gases are contacted with said second bath by bubbling the gases in said second bath.

3. The process according to claim 2, wherein said recovered formed gases are injected from a bottom of a tank containing the second bath.

4. The process according to claim 1, wherein said first bath furthermore contains at least one hydroxide selected from the group consisting of LiOH, NaOH, KOH, Ca(OH).sub.2 and Fe(OH).sub.2 and/or at least one oxide selected from a group consisting of K.sub.2O, Na.sub.2O, CaO and P.sub.2O.sub.5 and/or at least one carbonate selected from a group consisting of Li.sub.2CO.sub.3, Na.sub.2CO.sub.3, K.sub.2CO.sub.3 and CaCO.sub.3 and/or at least one nitrous compound selected from a group consisting of NaNO.sub.2 and NaNO.sub.3.

5. The process according to claim 1, wherein said first bath contains at least one carbonate and in that a mass content of carbonate(s) is less than 10%.

6. The process according to claim 1, wherein said first bath contains at least one salt wherein the melting point is lower than a melting point of said chloride or than a lowest melting point of said chlorides.

7. The process according to claim 1, wherein said second bath has a melting point greater than 300? C. and/or in that it furthermore comprises at least one chloride different from sodium chloride.

8. The process according to claim 1, wherein said second bath contains at least one iodide and/or one fluoride.

9. The process according to claim 1, wherein said second bath comprises more than 10% by mass of at least one carbonate.

10. The process according to claim 1 wherein the contacting between said first bath and said carbonaceous material is implemented in an enclosure containing air and rendered hermetic after introducing said carbonaceous material into said enclosure.

11. The process according to claim 10, wherein said hermetic enclosure contains a gaseous mixture containing less than 20% by volume of gaseous oxygen.

12. The process according to claim 1 wherein said solid carbonaceous material is one selected from solid waste containing or consisting of plastic(s) selected from a group consisting of ABS, cellulose acetates (CA), polyamides, polybutylene terephthalate (PBT), polycarbonates, polyethylenes, PET, HDPE, PP, PVC, PTFE, LDPE, PMMA, poly formaldehydes (POM), PVACs, styrene-acrylonitrile copolymers, optionally expanded polystyrene, PEEK, thermoset resins, in particular silicones and mixtures of at least two of these plastics; waste containing or consisting of animal and/or plant-based organic material, optionally processed, in particular paper, cardboard, wood, plant waste; andmixtures of these two types of waste; and wherein the solid waste and waste cited above, optionally in a mixture or contained in bags made of plastic selected from a group consisting of ABS, cellulose acetates (CA), polyamides, polybutylene terephthalate (PBT), polycarbonates, polyethylenes, PET, HDPE, PP, PVC, PTFE, LDPE, PMMA, poly formaldehydes (POM), PVACs, styrene-acrylonitrile copolymers, optionally expanded polystyrene, PEEK, thermoset resins, in particular silicones and mixtures of at least two of these plastics.

13. The process according to claim 1, wherein said contacting with said second bath is implemented in a closed enclosure containing a gaseous mixture containing 20% or less of oxygen, said gaseous mixture optionally being at a pressure lower than atmospheric pressure.

14. The process according to claim 1, wherein said recovered formed gases from the first bath contain water vapor, said water vapor is condensed prior to introduction into the second bath.

15. A facility allowing the implementation of the process according to claim 1 wherein it comprises: an enclosure containing a first salt mixture optionally in the molten state, said first salt mixture comprising at least one chloride type salt selected from a group consisting of NaCl, MgCl.sub.2, CaCl.sub.2), KCl; and FeCl.sub.2, having a melting point greater than or equal to 300? C., a density greater than 1 measured in the liquid state and at atmospheric pressure and a specific heat capacity in the liquid state and at atmospheric pressure lower than the specific heat capacity of water measured at a temperature of 25? C. and at atmospheric pressure; means for heating said first mixture of salts enabling the melting thereof; at least one conveyor of carbonaceous material, which comprises an inlet whereby said carbonaceous material is introduced and an outlet disposed such that said material drops into said first bath; means for recovering gases which are connected to said enclosure and which open above said first bath; and a second reactor which comprises an inlet connected to said means for recovering gases and capable of containing a second molten salt mixture; heating means capable of melting said second salt mixture, said second reactor optionally including at least one screen for forming gas bubbles of given size and including a first pipe which connects an outlet of said second reactor to a storage tank and optionally a second pipe which connects the outlet of said second reactor with a zone of said enclosure located under a surface of said first molten salt bath or to the inlet of said second reactor.

16. The facility according to claim 15, wherein said second reactor includes a tank containing said second molten salt mixture and in that said inlet of said second reactor is disposed below a level of a free surface of said second molten salt mixture.

17. The facility according to claim 15, wherein said second reactor comprises means for rendering it gas-tight and in that said facility comprises means acting as a pump for reducing the pressure of the gaseous mixture contained in said second reactor prior to the contacting of said second molten salt mixture with the recovered gases.

18. The facility according to claim 15, further comprising means for condensing water vapor and in that said condensation means are disposed upstream from said storage tank and/or on said second pipe and upstream from said first enclosure and/or said second reactor.

19. The facility according to claim 15 further comprising means for isolating/closing said enclosure and/or said second reactor with respect to the external environment.

Description

FIGURES

[0082] The present invention, the technical features thereof and the various advantages provided thereby will become more apparent on reading the following description, of a specific embodiment of the invention, presented by way of non-limiting example and which refers to the appended drawings wherein:

[0083] FIG. 1 represents a schematic view of a specific embodiment of the invention;

[0084] FIG. 2 represents a specific embodiment of the tank and the conveyors; and

[0085] FIG. 3 represents three alternative embodiments of the second molten salt bath.

DETAILED DESCRIPTION

[0086] With reference to FIG. 1, a specific embodiment of the facility and mode of implementation of the process according to the invention will be described. The facility includes an enclosure 1 which contains the first molten salt bath. The surface of the first liquid bath is represented by the line L. Heating means (not shown) make it possible to melt the initially solid salts and form a liquid phase, which forms the molten salt bath. The enclosure is provided with a draining pipe 3 which opens into the bottom of the enclosure, under the bath and makes it possible to drain the enclosure 1. The enclosure also includes a removable screen 11 which makes it possible to retain the solid materials which are not degraded by the bath. Two conveyors 5 lead to above the surface of the bath and make it possible to transport the waste deposited at the inlet 51 thereof into the bath. The enclosure 1 can be hermetically sealed at the outlet of the conveyors 5 by means for example of hatches or other. The facility includes a column 2 containing a second molten salt bath. A valve V1 makes it possible to regulate the gas flow from the enclosure 1 and entering the column 2. The outlet of the column 2 is connected to a storage tank 6 for pressurizing the gases. A valve V2 is used to regulate the gas flow entering the storage tank 6. Upstream from the valve V2, a bypass pipe 23 is located, which makes it possible to connect the outlet of the column 2 with the enclosure 1. The bypass pipe 23 opens into the enclosure 1, at a level located below the surface L of the first molten salt bath. A valve V3 equips the bypass 23 and is used to regulate the flow of recycled gases to the first bath. The dotted line SS represents the surface of the floor. In FIG. 1, the enclosure 1 is buried and the inlet 51 of the conveyors is flush with ground level. It is also possible to also bury the column 2.

[0087] A mode of implementation of the process according to the invention will now be described with reference to FIG. 1. The carbonaceous materials to be processed are carried, for example, by truck to the facility. They may consist of solid waste. Waste in the form of suspended solid particles in a liquid (sludge) cannot be processed with the process according to the invention. The waste is introduced into the conveyors 5 at the inlet 51 thereof. The conveyors 5 carry the waste into the enclosure and drop it into the first molten salt bath. The bath has been previously formed by melting the salts thanks to the heating means (not shown). According to the density thereof, the waste sinks into the bath or floats on the surface thereof. Inert waste (rubble, bricks, concrete, stones and others) which has a greater density than carbonaceous waste, in particular plastics, falls to the bottom of the bath and accumulates on the screen 11. It will subsequently be removed at the end of the process. After introducing the waste, the inlets 51 are hermetically sealed by means for example of hatches or other means and the salts are molten (batch operation). The enclosure 1 contains air located above the surface of the first bath. The cracking reaction of the carbonaceous material into hydrocarbons is catalyzed by the ions of the first bath. This reaction consumes the oxygen of the air contained in the enclosure 1, above the surface L of the first bath. The enclosure 1 being hermetic, the reaction starts in an air atmosphere. It then continues in an atmosphere that is oxygen-depleted, or even containing no more oxygen. The absence of oxygen increases the yield of hydrocarbons, particularly of volatile hydrocarbons, regardless of the type of carbonaceous material processed. The pressure above the first bath increases on account of the formation of hydrocarbons. When it reaches a given value which indicates that the enclosure contains mostly hydrocarbons (volatile or not), the value V1 is opened. The gases enter the column 2 containing the second molten salt bath. They then undergo a second catalytic degradation in this second bath. The second bath makes it possible to increase the volatile hydrocarbon yield. The second bath can be used in a column 2 wherein the gases to be processed are bubbled. The column 2 and the various alternative embodiments thereof will be described in more detail with reference to FIG. 3. In the column 2, the gases undergo a second degradation. At the outlet of the column 2, according to the composition of the outflowing gas flow, this flow is either directed (partially or completely) toward the storage tank 6. All or part of the flow can be redirected toward the first bath located in the enclosure 1 for a new processing. The gases are injected into the bath in order to pass through it in the form of bubbles and be once again degraded therein.

[0088] An embodiment of the process of the invention will now be described with reference to FIG. 1, in the case of waste containing plastics, optionally wet or partially covered with organic material (such as food packaging). The waste is introduced, for example, by a garbage truck into the conveyors 5. After introducing the waste, the inlets 51 are hermetically sealed by means for example of hatches or other means and the salts are molten. The waste is contained in plastic bags. The bags drop into the first molten salt bath. The bags sink immediately in the bath on account of the density thereof. The enclosure 1 communicates with the outside at the conveyors 5. The catalytic reaction is immediate and various gases are produced above the bath. The enclosure does not communicate with the outside. The enclosure optionally has a flange cover which is connected to the column 2 or to the tank 6. On account of the presence of oxygen in the air, ethanal type compounds are also produced at the same time as volatile hydrocarbons. The temperature above the bath is at least 100? C. when the temperature of the bath is 500? C. and the pressure is 1 bar. Once the pressure reaches a given value above the first molten salt bath, the gases produced are passed in the second molten salt bath. This second bath makes it possible to convert the compounds containing oxygen into volatile hydrocarbons. Analysis means mounted at the outlet of the column 2 make it possible to indicate the volatile hydrocarbon concentration of the gaseous mixture at the outlet of the column 2. If the composition is considered to be satisfactory, i.e., containing more than 90% by volume of volatile hydrocarbons, the gaseous flow is oriented toward the storage tank. Otherwise, the gaseous flow is oriented toward the first molten salt bath or toward the second molten salt bath according to the composition thereof and the compounds desirable to be degraded to volatile hydrocarbons (see Table 2).

[0089] With reference to FIG. 2, a specific embodiment of the enclosure 1 and the conveyors 5 will now be described. The elements in common with those of FIG. 1 are referenced the same. In FIG. 2, the enclosure 1 includes in the lower part thereof a cylindrical container 11 which contains the first bath (the liquid is not shown). The upper part of the enclosure is parallelepipedal and open to the outside via the conveyors 5. Three faces of this part are connected to a conveyor 5. The hatches are not shown. The catalytic reaction is always performed after introducing the waste, the hermetic closure of the inlets 51 and the melting of the salts. The outlet 61 is connected to the storage tank 6. The outlet 231 enables the recirculation of the gases formed toward the first bath. The entire facility does not necessarily include a second bath.

[0090] With reference to FIG. 3, three alternative embodiments of the second bath will now be described. It should be noted that the second bath is optional.

[0091] With reference to FIG. 3, the column 2 comprises two screens 220 disposed on top of one another along the height of the column. These screens make it possible to divide the gas flow to be processed into a bubble of given size. The black arrows indicate the gas circulation, from the bottom upward. The molten and therefore liquid salts circulate from the top downward from the inlet 210 to the outlet 211. The gases and the salts circulate at countercurrent. The bubbles promote and accelerate the catalytic reaction by increasing the contact surface area between the gases and the salts.

[0092] In FIG. 3, the second reactor contains the second bath. The reactor not being full, air can remain above the second bath short of filling the space unoccupied by the molten salt by an inert atmosphere. The gases are sent to the center of the reactor by the inlet pipe 25 so as to bubble in the second molten salt bath. The inlet pipe 25 is immersed in the bath and opens at the center of the reactor. After the reaction inside the second bath, the processed gases come out at the top of the reactor at the outlet 27.

[0093] With reference to FIG. 3, a third alternative embodiment will now be described. The second reactor 2 is horizontal and contains the second bath. Preferably, the second bath fills the second reactor 2 by half. The inlet and outlet pipes includes screens 220 which enable the formation of bubbles at the inlet and at the outlet of the reactor. The second salt bath is static as in the second alternative embodiment.

Example 1

[0094] The different types of waste indicated hereinafter in Table 1 were processed according to the process of the invention.

TABLE-US-00001 TABLE 1 Type of waste Name of gas Gas sample Sample analysis processed sample receptacle method HDPE Alpha 1 2 L multilayer bag ?GC/MS HDPE and PP Alpha 2 2 L multilayer bag ?GC/MS HDPE, PP and Alpha 3 2 L Tedlar? bag ?GC/MS PET

[0095] Tedlar? is a semi-crystalline thermoplastic polyvinyl fluoride.

[0096] Table 2 lists the non-methane VOCs produced by the process according to the invention during the processing of the plastics of Table 1 in the presence of air and in a closed reactor containing only the first molten salt bath at 500? C. (+/?20? C.).

TABLE-US-00002 TABLE 2 Alpha 1 Alpha 2 Alpha 3 List of hydrocarbons mg/(n)m.sup.3 % by mass mg/(n)m.sup.3 % by mass mg/(n)m.sup.3 % by mass Pentane 206 1.57 31020 24.43 96981 35.18 Propene 1798 13.69 52886 41.65 96001 34.82 Ethane 318 2.42 9227 7.27 15991 5.80 Ethylene 1427 10.87 10450 8.23 12418 4.50 Acetaldehyde 1283 9.77 429 0.34 7454 2.70 2-Methylpentene 591 4.50 2526 1.99 5375 1.95 Hexene 587 4.47 2526 1.99 5375 1.95 2-Butenal 66 0.50 544 0.43 4242 1.54 2-Butene 887 6.75 1847 1.45 3326 1.21 Acrolein 715 5.44 214 0.17 1633 0.59 Methylcyclopentane 75 0.57 348 0.27 1491 0.54 Benzene 694 5.28 583 0.46 1404 0.51 Formaldehyde 92 0.70 530 0.42 1360 0.49 Isobutane 212 1.61 147 0.12 1337 0.48 2-Hexanone 47 0.36 627 0.49 1209 0.44 Iso hexane 254 1.93 372 0.29 1204 0.44 3-Pentanone 252 1.92 836 0.66 918 0.33 2,4-Dimethylpentene 4 0.03 139 0.11 833 0.30 Ethylcyclopropane 394 3.00 662 0.52 791 0.29 n-Hexane 217 1.65 717 0.56 787 0.29 1,3-Pentadiene 66 0.50 343 0.27 634 0.23 Toluene 14 0.11 88 0.07 315 0.11 Methyl Vinyl Ketone 187 1.42 55 0.04 242 0.09 Cyclopentene 76 0.58 153 0.12 240 0.09 1,4-Cyclohexadiene 23 0.18 59 0.05 236 0.09 Acetone 331 2.52 190 0.15 188 0.07 Isobutene 51 0.39 141 0.11 171 0.06 Butanal 295 2.25 112 0.09 144 0.05 2,4-Hexadiene 30 0.23 126 0.10 133 0.05 1,3-Cyclohexadiene 12 0.09 66 0.05 116 0.04 Pentanal 660 5.03 182 0.14 92 0.03 2-Pentanone 121 0.92 122 0.10 75 0.03 Cyclohexane 5 0.04 41 0.03 44 0.02 Methacrolein 51 0.39 48 0.04 43 0.02 Hexanal 109 0.83 117 0.09 39 0.01 THF 40 0.30 20 0.02 19 0.01 C7 alkane/acene isomers 676 5.15 4141 3.26 3185 1.16 C8 alkane/acene isomers 223 1.70 2511 1.98 3086 1.12 Alkane/alkene isomers ? C9 43 0.33 1824 1.44 6569 2.38 TOTAL 13132 100 126969 100 275701 100

[0097] The results of Table 2 shows that the majority volatile hydrocarbons produced are pentane, propene, ethane and ethylene using a catalyst containing only one chloride salt (sodium chloride in this case), a salt having a melting point lower than that of chloride and less than 5% of oxide(s) and carbonate(s).

[0098] Table 3 groups together the sum of certain hydrocarbons obtained.

TABLE-US-00003 TABLE 3 Alpha 1 Alpha 2 Alpha 3 List of hydrocarbons mg/(n)m.sup.3 % by mass mg/(n)m.sup.3 % by mass mg/(n)m.sup.3 % by mass Alkane/alkene isomers ? C7 942 7.17 8476 6.68 12840 4.66 Ethylene, propylene and butenes 4112 31.31 65183 51.34 111745 40.53

[0099] In the light of Table 3, it is observed that hydrocarbons comprising 7 and more carbon atoms respectively represent only 7.17%, 6.68% and 4.66% by mass of the hydrocarbons present in the samples Alpha 1, Alpha 2 and Alpha 3.

[0100] Linear unsaturated hydrocarbons with 2, 3 and 4 carbon atoms respectively represent 31.31%, 51.34% and 40.53% by mass of the hydrocarbons present.

[0101] The presence of oxygen enabled the production of aldehyde and ketones. These oxygen compounds can be broken down predominantly into hydrocarbons and carbon monoxide during the pass in the second bath, particularly by bubbling and therefore in the absence of oxygen.