Biochar substitute obtained by pyrolysis of a construction material comprising a plant-based aggregate

Abstract

Biochar substitute comprising from 1% to 25% total organic carbon (TOC), from 1% to 30% total inorganic carbon (TIC), and from 0.5% to 40% C2S total ; process for preparing said biochar substitute by pyrolysis of a construction material comprising a plant-based aggregate or of a mixture comprising a construction material and a plant-based aggregate; and use thereof as a clinker or aggregate substitute.

Description

[0001] BIOCHAR SUBSTITUTE OBTAINED BY PYROLYSIS OF A BUILDING MATERIAL COMPRISING A VEGETABLE GRANULATE

[0002] The present invention relates to the valorization of a construction material containing a plant aggregate at the end of its life, and more particularly a biochar substitute prepared by pyrolysis of such a construction material and its use as a substitute clinker.

[0003] The manufacture of binders, particularly hydraulic binders, and especially cements, essentially consists of calcining a mixture of carefully selected and measured raw materials, also known as "raw material." Firing this raw material produces an intermediate product, clinker, which, when ground with calcium sulfate and possibly added minerals, yields cement. The type of cement produced depends on the nature and proportions of the raw materials as well as the firing process. Several types of cement are distinguished: Portland cements (which represent the vast majority of cements produced worldwide), aluminous cements (or calcium aluminate cements), natural quick-setting cements, sulfoaluminate cements, sulfobelic cements, and other intermediate varieties.

[0004] The most common cements are Portland cements. Portland cements are made from Portland clinker, which is produced by clinkerizing a raw material rich in calcium carbonate in a kiln at a temperature of around 1450°C. The production of one tonne of Portland clinker results in the emission of significant quantities of CO2 (approximately 0.8 to 0.9 tonnes of CO2 per tonne of cement in the case of clinker).

[0005] However, in 2014, the quantity of cement sold worldwide was approximately 4.2 billion tons (source: French Cement Industry Association - SFIC). This figure, which is constantly increasing, has more than doubled in 15 years. The cement industry is therefore currently searching for a viable alternative to Portland cement, that is to say, cements with at least the same strength and quality characteristics as Portland cement, but which, during their production, emit less CO2.

[0006] During the production of clinker, the main component of Portland cement, CO2 emissions are linked to:

[0007] - up to 40% for heating the cement kiln, grinding and transport; - up to 60% for so-called chemical CO2, or decarbonation.

[0008] Decarbonation is a chemical reaction that occurs when limestone, the main raw material for the manufacture of Portland cement, is heated to a high temperature. The limestone is then transformed into quicklime and CO2 according to the following chemical reaction:

[0009] The natural carbonation of cement-based materials, particularly concrete, is a potential way to reduce the carbon footprint associated with cement manufacturing and use. However, although concrete made from these cements naturally recarbonates during its service life, accounting for 15% to 20% of the CO2 emitted during manufacturing, the overall carbon balance associated with Portland cement production remains positive. Therefore, it remains necessary to reduce CO2 emissions during Portland cement production and / or improve the processes for recycling concrete at the end of its life.

[0010] To reduce CO2 emissions related to Portland cement production, several approaches have been considered so far:

[0011] - the adaptation or modernization of cement processes in order to maximize the efficiency of heat exchange;

[0012] - the development of new "low carbon" binders such as sulfo-aluminous cements prepared from raw materials less rich in limestone and at a lower firing temperature, which allows a reduction in CO2 emissions of approximately 35%;

[0013] - the recycling of end-of-life construction materials which can have a significant impact on the carbon footprint associated with their production;

[0014] - or even the (partial) substitution of clinker in cements by materials that limit CO2 emissions.

[0015] Among the approaches mentioned above, the (partial) substitution of clinker in cements has been the subject of much development.

[0016] Among the substitute materials used are blast furnace slag and fly ash from coal-fired power plants. However, the closure of coal-fired power plants is causing a shortage of good-quality fly ash. Furthermore, substituting clinker with limestone filler (i.e., an inactive material) essentially dilutes the material and results in a significant decrease in strength, which is problematic.

[0017] As alternative substitute materials, the use of biochar, carbonated or not, is also being considered.

[0018] In the publication "The use of Biochar to reduce the carbon footprint of cement-based materials," Procedia Structural Integrity, 26 (2020), 199-210, the authors Suarez-Riera et al. describe the use of biochar as a cementitious additive (or filler) to reduce the carbon footprint of both cement production and the building material made from it. International patent application WO-A-2023 / 281220 describes the use of carbonated biochar as a clinker substitute.

[0019] The term "biochar" is an abbreviation of "bio-charcoal," in which the prefix "bio" denotes biological origin and "charcoal" refers to the English term for charcoal. Thus, "biochar" designates any product obtained by the pyrolysis of organic biomass from various sources, such as plants, including wood, straw, and agricultural or green space residues, or organic compounds such as sewage sludge, poultry manure, or cattle manure.

[0020] Biochar differs from charcoal in that it is used as a fertilizer rather than a fuel and in its environmental impact, since it acts as a carbon sink rather than releasing CO2 into the atmosphere when burned.

[0021] Biochar is therefore interesting for two reasons: it concentrates a large amount of biogenic carbon (between 40 and more than 80%); and its structure develops a large specific surface area capable of adsorbing large quantities of CO2.

[0022] Biochar is thus traditionally used in agriculture to improve soil quality, and therefore its productivity. However, although carbon sequestration in the soil through biochar incorporation has been practiced for many years to combat soil acidification and increase fertility, losses and emissions of carbon in the form of CO2 have been identified when the soil's chemical balance (pH, leaching, incorporation depth, etc.) varies.

[0023] The main difficulty associated with the use of biochar as a substitute clinker lies in the fact that biochar production devices use plant resources from by-products of the wood or agricultural sector, which are also used in many other applications (soil amendment, heating pellets, particle boards etc...) which leads to competition for use.

[0024] Other approaches, such as carbon capture and storage, have also been developed to limit CO2 emissions from cement plants or coal-fired power plants. For example, international patent application WO-A-2019 / 115722 describes a process for both cleaning CO2-containing exhaust gases and manufacturing additional cementitious material. The described process involves using recycled concrete fines in stockpiles or a silo as a starting material, rinsing the starting material to provide a carbonaceous material, removing the carbonaceous material and the cleaned exhaust gas, and deagglomerating the carbonaceous material to form the additional cementitious material. It also describes the use of stockpiles or a silo containing recycled concrete fines as a starting material for cleaning CO2-containing exhaust gases and simultaneously manufacturing additional cementitious material.However, this process requires drying the carbonated product before it can be used.

[0025] As of the date of the present invention, it therefore remains necessary to identify alternative substitute materials that can significantly reduce CO2 emissions during the production of Portland cement, but also to improve the recycling processes of used concrete, which can have a significant impact on the carbon footprint associated with the production of construction materials.

[0026] However, it has now been found, quite surprisingly, that the pyrolysis of construction material containing a plant aggregate (or a mixture including a construction material and a plant aggregate) makes it possible to obtain a biochar substitute with particular characteristics allowing its use as a clinker substitute or as an aggregate substitute, and thus to significantly lower the carbon footprint of both the construction material finally prepared while maintaining mechanical properties, and in particular medium and long-term compressive strengths compatible with the intended uses, and of the construction material from which it is obtained.

[0027] Thus, the present invention relates to a biochar substitute comprising: 1% to 25% total organic carbon (TOC); 1% to 30% total inorganic carbon (ITC); and 0.5% to 40% C2Stotai.

[0028] The biochar substitute according to the present invention offers a twofold benefit in terms of carbon footprint. First, it can be used as a substitute clinker or aggregate, which significantly reduces the carbon footprint of the final construction material while maintaining mechanical properties, particularly compressive strength in the medium and long term, compatible with the intended uses. Furthermore, since the biochar substitute according to the present invention is obtained from an end-of-life construction material, such as concrete, it also significantly reduces the carbon footprint associated with the production of said construction material.

[0029] Within the scope of the present invention:

[0030] - The term "biochar substitute" refers to any material obtained by a pyrolysis process of a construction material comprising a plant aggregate or of a mixture comprising a construction material and a plant aggregate. The term "C2Stotai" refers to all the polymorphs constituting the belite phase, in particular the C2Sp polymorph and the C2S polymorph. a and the C2S polymorph Y ;

[0031] - "Building material" means concrete or mortar, preferably concrete;

[0032] - the term "binder" refers to any hydraulic or aerial binder;

[0033] - The term "hydraulic binder" means any aggregate-free hydraulic binder conventionally used to prepare mortar or concrete. Examples of hydraulic binders include hydraulic lime (conforming to standard NF EN 459-1 in force at the date of the present invention) or cement such as aluminous cement, sulfo-aluminous cement, Portland cement or natural rapid cement;

[0034] - The term "air binder" refers to any air binder free of aggregates that is conventionally used to prepare mortar or concrete. An example of an air binder is air lime (conforming to standard NF EN 459-1 in force at the date of the present invention). Among the air limes preferably used in the context of the present invention are: a calcium air lime (CL) containing calcium oxide (CaO) and / or calcium hydroxide (Ca(OH)2) in which the sum of CaO + MgO is at least 70% and the MgO content is < 5%; or a dolomitic lime (DL) containing calcium magnesium oxide (CaO MgO) and / or calcium magnesium hydroxide (Ca(OH)2 Mg(OH)2) of which the sum CaO + MgO is at least 80%, and the MgO content varies from 5% to more than 30%;

[0035] - "Aluminous cement" means any cement, amorphous or not, obtained by firing a mixture of limestone and bauxite and containing at least 5% monocalcium aluminate CA;

[0036] - The term "natural rapid-setting cement" means any hydraulic binder with rapid setting and hardening conforming to standard NF P 15-314: 1993 in force at the date of the present invention. Preferably, "natural rapid-setting cement" means a cement prepared from a clinker comprising: 0% to 20% C3S; 40% to 60% C2S; 7% to 12% C4AF; 2% to 10% C3A; 10% to 15% CaCO3 (calcite); 10% to 15% Cas(SiO4)2CO3 (spurrite); 3% to 10% of sulfate phases: yeelimite C4A3$, langbeinite (K2Mg2(SO4)3, anhydrite (CaSO4); and 10% to 20% of lime, periclase, quartz and / or one or more amorphous phases;

[0037] - "Portland cement" means any Portland clinker-based cement classified as CEM (I, II, III, IV, V or VI) according to standard NF EN 197-1, NF EN 197-5 or NF EN 197-6 in force at the date of the present invention;

[0038] - "sulfo-aluminous cement" means any cement prepared from a sulfo-aluminous clinker containing 5% to 90% of 'yeelimite' C4A3$ phase, a sulfate source, and, optionally, a limestone addition;

[0039] - "Sand" means any sand that can be used by a person skilled in the art for the preparation of construction material; - "Clinker substitute" means any composition that can partially replace clinker in the preparation of a cementitious composition while allowing for an increase in the performance of the cementitious binder resulting from this combination;

[0040] - The term "aggregate substitute" refers to any composition capable of partially replacing aggregates in the preparation of a construction material; and

[0041] - The term "specific surface area" refers to the specific surface area measured by the BET (Brunauer, Emett and Teller) method, which represents the ratio of the actual surface area of ​​a material to the mass of matter of that material.

[0042] In the context of the present invention, the following notations are adopted to designate the mineralogical components of cement:

[0043] - C represents CaO;

[0044] - A represents AI2O3;

[0045] - F represents Fe2C>3;

[0046] - S represents SiC>2; and

[0047] - $ represents SO3.

[0048] Within the framework of the present invention, the "organic carbon content" or "Total Organic Carbon" or "TOC" corresponds to the quantity (% w / w) of organic carbon contained in an entity (e.g., biochar substitute) relative to the total weight of said entity (e.g., said biochar substitute), and the "inorganic carbon content" or "Total Inorganic Carbon" or "ITC" corresponds to the quantity (% w / w) of inorganic carbon contained in an entity (e.g., biochar substitute) relative to the total weight of said entity.

[0049] To determine these levels, approximately 180 mg of the sample to be analyzed is placed in a nickel capsule. This capsule is then introduced into a quartz tubular furnace, allowing for a gradual temperature increase and temperature plateaus to separate the different carbon species in a sample. This allows us to determine: the "TOC," which is the quantity (% w / w) of total organic carbon in the identified entity, determined by analyzing the signal obtained between 100°C and 500°C with a plateau at 450°C for 180 seconds; and the "ITC," which is the quantity (% w / w) of total inorganic carbon in the identified entity, determined by analyzing the signal obtained between 600°C and 1000°C with a plateau at 800°C for 180 seconds. The quantity (% w / w) of total carbon in the entity, or "TC," is determined according to the following formula:

[0050] CT=COT+CIT

[0051] Within the framework of the present invention, the median diameter or d vso corresponds to the diameter below which 50% of the total volume of particles in the sample under consideration is found. This can be determined by any method known to those skilled in the art, in particular by dry laser granulometry.

[0052] Finally, within the framework of the present invention, the proportions expressed in % correspond to mass percentages relative to the total weight of the entity (e.g. biochar substitute, construction material...) considered.

[0053] The present invention therefore relates to a biochar substitute comprising from 1% to 25% total organic carbon (TOC), from 1% to 30% total inorganic carbon (TIC), and from 0.5% to 40% C2Stotai. Preferably, the present invention relates to a biochar substitute as defined above having the following characteristics, chosen alone or in combination: the biochar substitute comprises from 2% to 25% TOC, preferably from 3% to 25% TOC, preferably from 4% to 23% TOC, most preferably from 5% to 15% TOC; the biochar substitute comprises from 1% to 15% TIC, preferably from 1% to 6% TIC, preferably from 1.5% to 5% TIC, most preferably from 2% to 4.5% TIC; The biochar substitute comprises 1% to 35% C2St otai, preferably still from 1.5% to 30% of C2Stotai, most preferably from 2% to 30% of C2Stotai; and / or the biochar substitute has a specific surface area varying from 3 m 2 / g at 500 m 2 / g, preferably still 5 m 2 / g at 350 m 2 / g, in a completely preferred manner of 5 m 2 / g at 100 m 2 / g.

[0054] The biochar substitute according to the present invention can therefore be obtained by pyrolysis of a construction material comprising a plant-based aggregate or of a mixture comprising a construction material and a plant-based aggregate. Thus, the present invention also relates to a process for preparing a biochar substitute as defined above, comprising the following steps: a) grinding of a construction material comprising a plant-based aggregate or of a mixture comprising a construction material and a plant-based aggregate; and b) pyrolysis under an inert atmosphere at a temperature ranging from 300°C to 1000°C.Preferably, the process according to the present invention is carried out under the following conditions, taken alone or in combination: the building material comprising a plant aggregate or the mixture comprising a building material and a plant aggregate comprises from 1% to 60% binder, from 5% to 50% plant aggregate and from 0% to 50% earth, preferably from 10% to 45% binder and from 15% to 40% plant aggregate and from 0% to 40% earth; the binder contained in the building material is chosen as hydraulic lime, aluminous cement, a sulfo-aluminous cement, Portland cement or a natural rapid cement and / or air lime; the building material comprising a plant aggregate or the mixture comprising a building material and a plant aggregate is ground to obtain a particle size d. vso varying from 0.5 cm to 15 cm, preferably from 1 cm to 10 cm, most preferably from 4 cm to 7 cm; pyrolysis is carried out under hydrogen, CO2, nitrogen or pyrolysis gas; most preferably pyrolysis is carried out under nitrogen; pyrolysis is carried out at a temperature varying from 350°C to 900°C, most preferably at a temperature varying from 400°C to 800°C; pyrolysis is carried out for 5 minutes to 120 minutes, preferably from 10 minutes to 60 minutes, most preferably from 15 minutes to 45 minutes; the process includes an additional cooling step, preferably under an inert atmosphere, to ambient temperature; the process includes an additional grinding step to obtain a particle size compatible with its use as a clinker substitute or as an aggregate substitute; and / or the process includes an activation step at approximately 800°C under a CO2 and / or water vapor atmosphere.

[0055] The biochar substitute described above can therefore be used as a clinker substitute. Thus, the present invention also relates to the use of a biochar substitute as defined above as a clinker substitute. Finally, the biochar substitute described above can also be used as an aggregate substitute. Thus, the present invention also relates to the use of a biochar substitute as defined above as an aggregate substitute.

[0056] The present invention can be illustrated in a non-limiting way by the following examples.

[0057] Example 1 - Biochar substitute according to the invention 1.1 - Construction material subjected to pyrolysis

[0058] Construction materials comprising a plant aggregate whose composition is reported in the following Table 1 are used to prepare biochars according to the invention.

[0059] Table 1 - Construction material 1.2 - Preparation process

[0060] The previous construction material 1 is ground until a particle size of v so of about 20 mm then placed in an oven to be pyrolyzed under nitrogen at a temperature of 600°C or 800°C for 30 minutes.

[0061] After returning to room temperature in the oven, the resulting biochars are ground until a particle size of v so around 10 pm.

[0062] Biochar substitutes 1A (pyrolysis at 600°C) and 1B (pyrolysis at 800°C) are thus obtained.

[0063] Similarly, biochar substitutes 2A / 2B, 3A / 3B, 4A / 4B, 5A / 5B, 6A / 6B, 7A / 7B, 8A / 8B and 9A / 9B are obtained from (respectively) construction materials 2 to 9 pyrolyzed at 600°C or 800°C.

[0064] 1.3 - Composition of biochar substitutes according to the invention

[0065] The composition of the biochar substitutes thus obtained is reported in Tables 2 and 3 below.

[0066] Table 2 - Biochar substitutes 1A to 9A (pyrolysis at 600°C)

[0067] Table 3 - Biochar substitutes 1B to 9B (pyrolysis at 800°C)

[0068] 1.4 - SEM Analysis

[0069] Biochar substitutes 1A and 1B as well as the reference SOLER biochar were metallized (LEICA EM ACE200) and then observed by scanning electron microscopy (FEI QUANTA 200F) using a "high vacuum" mode and an ETD detector - Magnification used: x3469 (biochar 1A), x2837 (biochar 1B) and x1289 (SOLER biochar).

[0070] The images obtained are shown in Figure 1.

[0071] On biochar substitutes 1A and 1B, a mineral deposit is observed on the pyrolyzed plant particles which is not present on the reference biochar.

[0072] Example 2 - Use of biochar as a clinker substitute

[0073] Each biochar substitute used as a clinker substitute is ground to a particle size of D v5 o = 10 pm.

[0074] The ground biochar substitutes 1A and 1B are used to prepare the mortar compositions M1 and M2 respectively, as shown in Table 4 below. The reference mortar (M r (ef.) is prepared without the addition of biochar.

[0075] Table 4 - Composition of M1, M2 and M mortars r ef

[0076] In M1 and M2 mortars, the mass substitution rate of clinker is 18%.

[0077] Example 3 - Mechanical properties of mortars 3.1 - Spreading

[0078] The spreading properties of the previously obtained mortars were measured according to the protocol of standard NF EN 1015-3. The results of the spreading measurements are reported in Table 5 below.

[0079] Table 5 - Spreading of mortars M1 & M2 The results show spreading values ​​for mortars M1 and M2 lower than that of the reference mortar M r e.g., these values ​​nevertheless remaining compatible with conventional implementation. 3.2 - Compressive strength

[0080] The compressive and flexural strengths of the previously obtained mortars were measured at 1, 2, 7, and 28 days according to the protocol of standard NF EN 196-1. The results of the strength measurements are reported in Table 6 below.

[0081] The results show that the mechanical strengths are comparable between M1, M2, and the Mref at 1 and 2 days. Substituting clinker with the biochar substitute according to the invention does not affect the early-age strengths. Furthermore, the results show very good strengths, particularly in compression, for the M1 and M2 mortars, which exhibit 28-day strengths compatible with their use as construction materials.

Claims

DEMANDS 1. Biochar substitute comprising: 1% to 25% total organic carbon (TOC); 1% to 30% total inorganic carbon (ITC); and 0.5% to 40% C2Stotai.

2. Biochar substitute according to claim 1, characterized in that it comprises from 3% to 25% of TOC.

3. Biochar substitute according to claim 1 or 2, characterized in that it comprises from 1% to 6% of CIT.

4. Biochar substitute according to any one of claims 1 to 3, characterized in that it comprises from 1% to 35% of C2St o tai.

5. Biochar substitute according to any one of claims 1 to 4, characterized in that it has a specific surface area ranging from 3 m² 2 / g at 500 m 2 / g.

6. A process for preparing a biochar substitute according to any one of claims 1 to 5 comprising the following steps: a) grinding a construction material comprising a plant aggregate or a mixture comprising a construction material and a plant aggregate; and b) pyrolysis under an inert atmosphere at a temperature ranging from 300°C to 1000°C.

7. A process according to claim 6, characterized in that the pyrolysis of step b) is carried out at a temperature ranging from 350°C to 900°C.

8. A process according to claim 6 or 7, characterized in that the building material or mixture comprising a building material and a plant aggregate comprises 10% to 60% binder and 16% to 50% plant aggregate.

9. Use of a biochar substitute according to any one of claims 1 to 5 as a clinker substitute.

10. Use of a biochar substitute according to any one of claims 1 to 5 as a granule substitute.

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