WO2022186709A1

WO2022186709A1 - Process for obtaining porous biochar structures, improved by microwave-assisted catalytic treatment of biochar and installation for the application of this process

Info

Publication number: WO2022186709A1
Application number: PCT/RO2021/050006
Authority: WO
Inventors: Mariana PĂTRAȘCU; Cosmin MĂRCULESCU; Dorin Boldor
Original assignee: UNIVERSITATEA POLITEHNICA DIN BUCURESTI
Current assignee: UNIVERSITATEA POLITEHNICA DIN BUCURESTI
Priority date: 2021-03-01
Filing date: 2021-04-29
Publication date: 2022-09-09
Anticipated expiration: 2023-09-01
Also published as: RO135107A0; RO135107A3

Abstract

The invention relates to a process for obtaining improved porous biochar structures, by processing biochar via a microwave-assisted heat treatment, at different frequencies, in the presence of zeolitic catalysts, of the type HZSM - 5 Mn+, where Mn+ represents a metal component selected from Co, Ni, Fe, Ag, Au, Pt, Ti, at a weight ratio of biochar: catalyst from 10: 1 to 15: 1 in a reactor placed in a single-mode or a multimode microwave cavity, at normal pressure, under a controlled gas atmosphere chosen from N2, Ar, CO, CO2, in which the biochar come from the pyrolysis of different types of biomass of vegetal nature. The invention also relates to an installation for applying this process. The invention is particularly useful for obtaining specific biochar microstructures with controlled properties obtained from biochar, with a large porosity and specific surface area and a uniform pore volume distribution.

Description

Process for obtaining porous biochar structures, improved by microwave- assisted catalytic treatment of biochar and installation for the application of this process The invention relates to a process for obtaining improved porous biochar structures, by processing biochar using a microwave-assisted heat treatment, at different frequencies, in the presence of zeolitic catalysts, of the type HZSM - 5 Mⁿ⁺, where Mⁿ⁺ represents a metal component. The invention also relates to an installation for the application and utilization of this process to modify the porosity of the biochar obtained through the pyrolysis of different types of biomass of vegetal nature, obtained by different methods of pyrolysis.

The invention is particularly useful for obtaining specific, biochar microstructures of controlled properties, with large porosity and specific surface area and a uniform pore volume distribution, to be used as catalysts in the process of removing pollutant particles PM2.5 - 10, to capture products used in seed treatment and other applications such as wastewater treatment, soil remediation and other applications that require rigorous control of finished products.

Biochar is a porous material rich in carbon obtained by heat and / or thermochemical treatment of biomass. Specific surface area and porosity are important physical properties of biochar, playing a crucial role in many applications, such as wastewater treatment, soil remediation and more. On the other hand, the transformation and use of biomass is of fundamental interest in the fields of energy and ecology. The composition of the biomass feedstock and the pyrolysis temperature are the main factors influencing the properties of the final product. It is suggested that lignocellulosic biomass is a remarkable candidate for this type of application. Moreover, in classical processes, moderate temperatures between 400- 700 ⁰ C are suitable for the development of pore structure. Further improvements can be achieved through additional treatments. Chemical activation is the most widely used and effective way to change the surface and porosity of biochar. The improvement can also be achieved by using other treatment methods, such as: carbon coating, ball milling and functionalization (L. Leng, Q. Xiong, L. Yang, Science of the total environment, Vol. 763, 144204, 2021 ). Biochars can be used as a support for nanoparticle-based catalysts, such as those of transition metals: Fe, Ag, Ni, Pd, etc., of bimetallic compositions such as Ru/Re, Fe/Ni, etc. and metal oxides such as Fe3C>4, C03O4, CuO, T1O2, etc., increasing the reactivity of the system, minimizing the rapid consumption of catalysts and allowing their reuse. These materials can be used in processes of degradation of contaminants in aqueous systems, soil and sediments, tar reforming reactions and synthesis of fine chemicals (R.P. Lopes, D. Astruc, Coordination Chemistry Review, Vol. 426, 213585, 2021).

Microwave heating has been considered an excellent candidate for energy-efficient graphitization of coal. Several studies have described the heating of carbon-based materials using microwaves, for example, for the regeneration of activated carbon (C. O. Ania, J. A. Menendez, J. B. Parra and J. J. Pis, Carbon, 2004, 42, 1383- 1387), welding of carbon nanotubes / polymer composites (R. Xie, J. Wang, Y. Yang, K. Jiang, Q. Li and S. Fan, Compos. Sci. Technol., 2011 , 72, 85-90) and graphite exfoliates (Y. Geng, QB Zheng and JK Kim, J. Nanosci. Nanotechnol., 2011 , 11, 1084-1091 ). However complete graphitization through simple microwave heating has not yet been achieved. In addition, the microwave heating mechanism of coal and biochar has not been fully elucidated. The microwave heating mechanism may vary, depending on the properties of the energy absorbing material. Although dielectric relaxation is responsible for heating polar molecules, such as water, a very different heating mechanism works in electron-rich solids, such as metals, due to free electrons, or solid carbon materials, due to p electrons. It has been proposed that interfacial polarization, i.e., Maxwell - Wagner - Sillars polarization (MWS), be considered the main mechanism during microwave heating of carbon solids (T. Kim, J. Lee and KH Lee, Carbon letters, 2014, 15, 15-24).

Although microwave heating has previously been reported in terms of transformation of amorphous carbon powders, the complete method of graphitization / modification of their amorphous and crystalline structure is achieved by the addition of catalysts. The porous structure, pore morphology and pore properties of biochar can be influenced by heat and / or chemical treatments to obtain final characteristics that affect their nature depending on the desired end-application. For example, special attention has been paid to controlling the properties of porous carbonaceous materials, such as biochars, in conjunction with the control and regulation of plant and vegetation growth in agriculture. Lehmann (Lehmann, Chapter 12, p.207, 2006), a pioneer of biochar research, notes that the variability and inconsistency of biochar properties generate unpredictable properties of these materials, and the anticipated benefits can be difficult to control (US 10,023,503 B2).

For the conversion of biochar produced from the biomass pyrolysis processes into biogenic reagents with high carbon content, processes, systems and devices have been developed to obtain these materials in order to reduce CO2 emissions. The use of biogenic carbon to improve fuels can also contribute to the reduction of SO2 and Hg vapors, compared to conventional fuels used for energy production. The processes for obtaining these materials are undertaken in the absence of oxidizing agents (air and O2), and they can take place in the presence of additives. Depending on the operating conditions, for example low process temperature and high vapor residence time, the carbon production yield increases. The gas to create a controlled atmosphere can be N2, Ar, CO, CO2, H2, CF The process can take place in a continuous, semi-continuous or stationary regime. The additives selected may be from the category of acids, bases, metals or metal oxides, metal hydroxides or salts, for example NaOH, KOH, MgO, HBr, HCI, sodium silicate, potassium permanganate, Mg, Al, Ni, Cr, Si, Ce, Mo, P, W, V, iron chloride, iron bromide and / or combinations thereof (US 10,889,775 B2).

To develop the installation for microwave-assisted catalytic treatments of biochar resulting from biomass pyrolysis, we investigated the mechanism of microwave heating of biochar powders based on the phenomena of MWS polarization and ohmic (Joule) heating. According to literature data, during microwave heating, biochars change their dielectric loss factor (e ") due to polarization phenomena governed by the MWS theory. This phenomenon is experimentally monitored by the average power absorbed by the material exposed in the electromagnetic field, which is directly proportional to the effective dielectric loss factor of the material - it consists of various polarization phenomena and conduction components specific to microwave heating. Therefore, if the MWS polarization is responsible for microwave heating of biochar powders, the dielectric loss factor calculated based on the MWS polarization should have a value similar to or greater than the dielectric loss factor of microwave-susceptible materials because carbon undergoes extreme heating phenomena upon exposure to this type of radiation. The mathematical and numerical model for designing the microwave cavity and reactor were made using the COMSOL Multiphysics simulation software platform.

Known processes for obtaining graphite structures in the microwave field consist of mixing amorphous coal with metal salts - catalyst, in a quartz reactor, in an inert atmosphere and with temperature control and exposure to a microwave power between 1000 W and 1400 W, under normal pressure conditions. The process temperature is 1000 C, and the irradiation time is between 30 and 60 minutes.

The disadvantages of the known processes are that high temperatures and a long duration of treatment are required.

The technical problem solved by the present invention consists in obtaining porous biochar structures with uniform distributions of pore volume and specific surface area, in a short reaction time and at lower reaction temperatures, as well as the design and building of an installation for the processing of biochar into these porous structures.

It has been found that zeolitic catalysts containing metals selected from transition metals such as Co, Ni, Fe, Ag, Au, Pt, Ti, have special properties compared to other catalysts, having a specific selectivity for pyrolysis products. Surprisingly, it has been found that the use of a HZSM5-Mⁿ⁺ -type zeolitic catalyst in the process of the present invention leads to unexpected results in obtaining porous biocarbon/biochar structures with specific morphological properties and controlled pore distribution. The present invention relates to a new process and to the installation for obtaining porous biochar structures, by means of a heat treatment in a microwave field, in the presence of a zeolitic catalyst of the type HZSM 5 - Mⁿ⁺, with high performance and properties with respect to structure, distribution, morphology, and pore properties of the biochar thus treated, by substantially reducing the temperature and the duration of the process, at the two permissible industrial frequencies of 2.45 GHz and 915 MHz.

The process for obtaining the porous biochar structures improved by microwave- assisted catalytic treatment of the biofuel according to the invention comprises the following steps:

- microwave exposure of a reaction mixture comprised of biochar and a zeolitic catalyst of the type HZSM-5Mⁿ⁺, where M is a transition metal selected from Co, Ni, Fe, Ag, Au, Pt, Ti, at a weight ratio biochar: catalyst from 10: 1 to 15: 1 , in a reactor placed in a single-mode or multi-mode microwave cavity, at normal pressure, under an gas atmosphere selected from N2, Ar, CO, CO2, until it reaches a temperature in the range of 200... 500 ⁰ C, with the energy transfer from the microwave source to the reaction mixture being optimized so that the reflected power reaches a minimum value of 1 W, followed by

- cooling the reaction mixture and separating the resulting treated biochar from the catalyst.

The process can be carried out in a continuous, semicontinuous or discontinuous regime and can be calibrated for each of the industrially allowed microwave frequencies, respectively 2.45 GHz and 915 MHz.

The reaction time is a maximum of 30 minutes. The biochar used according to the invention may come from, but not limited to, the pyrolysis of plant biomass such as beech, birch, poplar, willow, non-food plants and biomass, spontaneous flora, cellulose/lignocellulose waste, whereas said pyrolysis is carried out at temperatures in the range 500 ... 950⁰ C.

An installation for applying the process for obtaining improved porous biochar structures by microwave-assisted catalytic treatment of the biochar, according to the invention, comprises a microwave cavity, provided with a regulation and tuning system, manual or automatic, as well as a fine tuning system, connected to a 2.45 GHZ or 915 MHZ solid state or magnetron microwave generator equipped with an isolating system, assisted by multiphysics numerical software to establish optimal boundary conditions. The process and installation for applying the microwave-assisted catalytic treatment process to biochar resulting from the pyrolysis of biomass according to the invention have a number of advantages because it is a selective, energy efficient, environmentally friendly and extremely fast process and the installation is modular and versatile.

Also, the process and installation for the application of the process has the advantage that it can be dimensioned and applied industrially using the two types of industrial microwave frequencies of 2.45 GHz and 915 MHz, and can be adapted for continuous, semi-continuous or discontinuous/batch processes. At the same time, separating the catalyst from biochar is a simple operation, and the catalyst can be reused for successive treatments.

The present invention is further illustrated with reference to the following figures:

FIG. 1 Schematic representation of the installation for microwave-assisted catalytic treatment of biochar from biomass pyrolysis Fig.2 Mass loss of beech biochar samples during microwave heat treatments for the three samples obtained at different pyrolysis temperatures: 500° C, 600° C, 700° C

Fig.3 Thermal behavior of beech biochar samples in the microwave field depending on the pyrolysis temperature at which they were obtained

Fig.4 FT - IR analysis of beech biochar samples obtained by pyrolysis at 500°C, (a) - microwave exposed sample, (b) - untreated microwave sample

Fig.5 FT - IR analysis of beech biochar samples obtained by pyrolysis at 600°C, (a)

- microwave exposed sample, (b) - untreated microwave sample

Fig.6 FT - IR analysis of beech biochar samples obtained by pyrolysis at 700°C, (a)

- microwave exposed sample, (b) - untreated microwave sample Fig.7 Linear isotherm of the beech biochar sample obtained by pyrolysis at 500°C, subsequently treated in the microwave field (" + " adsorption, " o " desorption) FIG. 8 Pore size and pore volume analysis by the Barrett-Joyner-Halenda (BJH) method of the 500°C pyrolysis beech sample treated in the microwave field

FIG. 9 Differential diagram between pore size and volume of beech biochar obtained by pyrolysis at 500°C and subsequently treated in the microwave field Fig.10 Linear isotherm of the beech biochar sample obtained by pyrolysis at 600°C, subsequently treated in the microwave field (" + " adsorption, " o " desorption)

FIG. 11 Pore size and pore volume analysis by the Barrett-Joyner-Flalenda (BJH) method of the 600°C pyrolysis beech biochar sample treated in the microwave field

FIG. 12 Differential diagram between pore size and volume of beech biochar obtained by pyrolysis at 600 ° C and subsequently treated in the microwave field

Fig.13 Linear isotherm of the beech biochar sample obtained by pyrolysis at 700°C, subsequently treated in the microwave field (" + " adsorption, " o " desorption)

Fig.14 Pore size and analysis of pore volume by the Barrett-Joyner-Halenda (BJH) method of the 700°C pyrolysis beech biochar sample treated in the microwave field Fig.15 Differential diagram between the pore size and volume of the beech biochar obtained by pyrolysis at 700°C and subsequently treated in the microwave field

Fig.16 TEM - EDX analysis for the biochar sample treated with microwave at the frequency of 915 MHz

Fig.17 FT - IR analysis for the microwave treated biochar sample at 915 MHz Fig.18 Simulations of the microwave field heating process with COMSOL Multiphysics software, for TE 10 cavity, in a 500 mm long WR 975 waveguide

Fig.18 a Temperature profile of a 5 g beech biochar sample, obtained by pyrolysis at 500°C, at a distance of 250 cm from the microwave source

Fig.18 b Temperature profile of a 5 g beech biochar sample, obtained by pyrolysis at 500°C, at a distance of 365 cm from the microwave source Fig.18 c Temperature profile of a 5 g beech biochar sample, obtained by pyrolysis at 500°C, at a distance of 155 cm from the microwave source

Fig.18 d Temperature profile of a 5 g beech biochar sample, obtained by pyrolysis at 500°C, at a distance of 15 cm from the microwave source Fig.18e Temperature profile of a 5 g beech biochar sample, obtained by pyrolysis at 500°C, at a distance of 490 cm from the microwave source

The process for obtaining the improved porous biochar structures by microwave- assisted catalytic treatment of biochar resulting from the pyrolysis of biomass according to the invention comprises the following steps: - Introduce the biochar resulting from the biomass pyrolysis inside the reactor from the single-mode microwave cavity type TEio or a multimode cavity, together with a zeolitic catalyst type FIZSM-5 Mⁿ⁺

- the catalyst being in pill form, at a weight ratio biochar: catalyst from 10: 1 to 15: 1. where M is a transition metal selected from Co, Ni, Fe, Ag, Au, Pt, Ti; - Mount the connecting system for introducing gas to the reactor;

- Close the microwave enclosure with the security system so that accidental radiation leaks do not occur;

- Turn on the water source to cool the microwave generator;

- Switch on the microwave source and check for microwave leakage from the installation using a mobile device calibrated to a maximum value of 5 mW / cm², calibrated for both microwave frequencies of 2.45 GFIz and 915 MFIz;

- The microwave cavity is tuned using a manual or automatic system to optimize the energy transfer from the microwave source to the sample;

- The sample temperature is measured using an infrared sensor, mounted directly in the microwave cavity;

- After completion of the treatment, the sample is left to cool to a temperature of 60°C, remove it from the reactor, separate the catalyst from the mass of treated biochar;

- The treated biochars are stored in an airtight container, away from moisture. - The biochar thus treated can be used for various applications, which include impregnation of HEPA filters, impregnation with pectins for seed treatment and many other applications.

The installation for the application of the process for obtaining the improved porous biochar structures, via catalytic assisted treatment of the biochar obtained from pyrolysis of biomass, according to the invention, is represented in Fig. 1 and consists of the following components:

- 2.45 GHz or 915 MHz solid state or magnetron microwave generator with isolator;

- System for adjusting and tuning, manually or automatically, the microwave cavity; - Microwave cavity;

- System for fine tuning of the microwave cavity.

Taking into account the characteristics assigned to the two frequency bands, namely for the frequency of 2.45 GHz, the associated wavelength being 12.25 cm, and for the frequency 915 MHz, the wavelength of 33.3 cm and based on a complex calculation performed using multiphysics numerical software for coupling and integration of electromagnetic field equations in sinusoidal regime in complex form with thermal transport equations, the optimal boundary conditions are defined, inside the microwave applicator and therefore the establishment and realization of the biochar heat treatment installation, as represented in Fig. . 18 a ÷ e. The following are some examples of embodiments of the invention.

Example 1

A 5 g sample (weighted using a calibrated balance) of beech biochar obtained by classical pyrolysis at 500°C, was placed in a 25 ml conical borosilicate glass reactor in the TE10 microwave cavity. WR 340. The moisture content dry basis of the biochar sample was between 30 - 40% RH. 0.5 g of HZSM-5 Co catalyst was introduced into the reactor in the form of a pellet, which was positioned in the center of the biochar mass. A system of connectors was attached to create the controlled atmosphere and N2 was introduced into the reactor chamber, at a flow rate of 0.2 I / min. The microwave cavity sealing system was attached, the water recirculation bath for cooling the microwave generator, set to a temperature of 18°C, was started, after which the microwave generator was started and set to a power of 50 W and a frequency of 2.45 GHz. The reflected power was adjusted with the help of the manual tuning system of the cavity, until it reached a minimum value of 1 W. The biofuel sample was thus exposed in the microwave field until the temperature of 250°C was reached.

After completion of the treatment, the sample was kept in the microwave cavity for 10 minutes, until the sample temperature dropped to below 55°C. After the sample was cooled, the microwave cavity security system was disassembled, the glass reactor was removed, and the treated biochar sample was mechanically separated from the catalyst. The treated charcoal was sieved and stored in an airtight container, away from moisture.

Example 1 was repeated under the same conditions, with the mention that the beech biochar that underwent the treatment was obtained by classical pyrolysis at 600°C.

Example 1 is repeated under the same conditions, with the statement that the beech biochar that underwent the treatment was obtained by classical pyrolysis at 700°C.

The biochar samples obtained according to examples 1 - 3 were analyzed from a structural and absorption capacity point of view by FT - IR analysis and by Brunauer- Emmett-Teller (BET) analysis of the specific surface cumulated with the analysis of Barrett-Joyner pore size and volume -Halenda (BJH). The results obtained for the three biochar samples are presented in Figs. 4 ÷ 15 and in table 1 .

The higher the biomass pyrolysis temperature, the higher the mass loss during microwave-assisted catalytic treatment of the biochar obtained from the biomass pyrolysis (Fig.2).

Depending on the pyrolysis temperature at which the biochars were obtained, the biochar absorbed microwave energy differently, such that the samples obtained at lower temperatures absorbed the microwave energy more difficultly. This is explained by a higher content of volatile compounds that remained in the system, and therefore visibly affected the dielectric properties of the biochar undergoing treatment (Fig. 3). From the BET and BJH analysis of the beech biochar samples obtained at different pyrolysis temperatures and subsequently treated in the microwave field at a maximum incident power of 50 W at the frequency of 2.45 GFIz, it can be seen that: a) a uniform distribution of pore volume in the range 10 - 500 nm is obtained, as shown in the graphs in Figures 9, 12 and 15. Also, the distribution of pore volume in the range 10-500 nm is even more uniform as pyrolysis temperature of beech biomass subjected to microwave heat treatment is higher b) the samples thus treated are microporous. Also, the duration of the process is even shorter for the biochar samples obtained from pyrolysis of biomass at a higher temperature. This aspect is highlighted by the hysteresis curves in Figures 7, 10 and 13, which indicate that the lower the pyrolysis temperature, the longer it takes for the microporous degassing process. In the biochar sample obtained by pyrolysis at 700°C, the degassing process is reduced to half the time compared to the samples obtained below this temperature; c) uniform distributions of pore volume and specific surface area in a much narrower size range are obtained. d) the microwave heating process is efficient given the presence of the N2 atmosphere and of the catalysts

Example 4 A 20 g (weighted on a calibrated balance) sample of biochar obtained from willow biomass pyrolyzed at 700°C, was placed in a 250 ml borosilicate glass reactor. The glass reactor was then introduced into a single-mode microwave cavity TE 10 - WR 975 waveguide operating at a frequency of 915 MHz. 2 g of zeolitic catalyst HZSM - 5 Ni, in the form of a pellet was introduced into the reactor, being positioned in the center of the biochar mass. The dry basis moisture content of the biochar sample was between 30 - 40%. The system of connectors was attached to create the controlled atmosphere and N2 was introduced into the reactor chamber at a flow rate of 0.5 I / min. The sealing system of the microwave cavity was attached, and the recirculation bath for cooling, set at a temperature of 18°C, was started, after which the microwave generator was started and set to a power of 80 W and a frequency of 915 MHz. The reflected power was adjusted using the manual cavity tuning system, until it reached a minimum value of 1 W. The biochar sample was thus exposed in the microwave field until the temperature reached 350°C. After completion of the treatment, the sample was kept in the microwave cavity for 10 minutes, until its temperature dropped to below 55°C. After the sample was cooled, the security system of the microwave cavity was disassembled, the glass reactor was removed, the treated biochar sample was mechanically separated from the catalyst. The treated biochar was sieved and stored in an airtight container in a place away from moisture.

The biochar sample thus obtained was analyzed from a structural and absorption capacity point of view by FT - IR and TEM analysis, the results of which are shown in Figures 16 and 17.

For the biochar sample processed at a frequency of 915 MHz, in addition to the peaks specific to C = C, C - H, C - O, which were also observed for biochars processed at 2.45 GHz, two additional peaks from vibrations specific to the aliphatic O - H, C - H groups were observed. From the TEM analysis it is observed a controlled distribution of pores on the surface.

Claims

1. A process for obtaining enhanced porous biochar structures by microwave- assisted catalytic treatment of biochar characterized in that it comprises the following steps: - microwave exposure of a reaction mixture comprising biochar and a zeolitic catalyst of the type HZSM-5 Mⁿ⁺, where M is a transition metal selected from Co, Ni, Fe, Ag, Au, Pt, Ti, at a weight ratio of biochar: catalyst from 10: 1 to 15: 1 in a reactor placed in a single-mode or multi-mode microwave cavity, at normal pressure, under a controlled gas atmosphere selected from N2, Ar, CO, CO2, until it reaches a temperature in the range of 200... 500⁰ C, the energy transfer from the microwave source to the reaction mixture being optimized so that the reflected power is minimal, followed by

- cooling of the reaction mixture and separating the resulting treated biochar from the catalyst.

2. Process according to claim 1 , characterized in that the biochars are derived from the pyrolysis of plant biomass such as beech, birch, oak, poplar, pine, willow, technical plants, spontaneous flora, cellulosic/lignocellulosic products, agricultural waste, food waste and more.

3. Process according to claim 1 characterized in that the biochar is derived from pyrolysis of biomass carried out at temperatures in the range of 500 to 950⁰ C.

4. Process according to claim 2, characterized in that the biochar is derived from pyrolysis of biomass carried out at temperatures in the range of 500 to 950⁰ C.

5. Process according to any of claims 1 to 4, characterized in that the resulting biochars have a uniform pore volume distribution in the range of 10... 500 nm.

6. Installation for applying a process for obtaining improved porous biochar structures by microwave-assisted catalytic treatment of biochars according to claim 1, comprising of a microwave cavity, provided with a regulation or tuning system, either manually or automatically, and a fine tuning system, connected to a 2.45 GHZ or 915 MHZ solid state or magnetron microwave generator equipped with an isolating system, assisted by multiphysics numerical software to establish the optimal boundary conditions and dimensions.