A graphene production method from biogas produced from domestic organic solid waste with graphene-assisted anaerobic reactor

Abstract

In order to apply the method of the invention, first of all, an increase in efficiency was achieved by using reduced graphene oxide (rGO) in the production of biogas from the organic fraction of domestic waste through anaerobic processes. Following the purification processes of the biogas produced in semi-continuous reactors, biomethane was obtained by pressurized with a compressor and stored in tubes. Activated carbon and silica gel filters were used in biogas purification processes. With the compressor, 95% pure biomethane was pressurized and stored in steel tubes. A monolayer graphene production method has been developed from biomethane in tubes using the chemical vapor deposition (CVD) method.

Description

[0001] A GRAPHENE PRODUCTION METHOD FROM BIOGAS PRODUCED FROM DOMESTIC ORGANIC SOLID WASTE WITH GRAPHENE-ASSISTED ANAEROBIC REACTOR

[0002] TECHNICAL FIELD

[0003] In order to apply the method of the invention, first of all, an increase in efficiency was achieved by using reduced graphene oxide (rGO) in the production of biogas from the organic fraction of domestic waste through anaerobic processes. Following the purification processes of the biogas produced in semi-continuous reactors, biomethane was obtained by pressurized with a compressor and stored in tubes. Activated carbon and silica gel filters were used in biogas purification processes. With the compressor, 95% pure biomethane was pressurized and stored in steel tubes. A monolayer graphene production method has been developed from biomethane in tubes using the chemical vapor deposition (CVD) method.

[0004] BACKGROUND

[0005] Currently, graphene is produced mostly from fossil sources raw materials (methane, benzene, etc.) from the petrochemical industry. This is an important problem for the sustainability of natural resources. In addition, there is a need to develop green transformation technologies to reduce the consumption of fossil resources within the scope of combating the global climate crisis. Sustainable solutions that will reduce fossil resource consumption are required in graphene production, and in the state of the art, methane from the petrochemical industry is used in graphene production. The production method of biogas to be used in graphene production is described in the article titled “Biomethane enhancement using reduced graphene oxide in anaerobic digestion of municipal solid waste” (H Muratgobanoglu, OB Gbkgek, F Muratgobanoglu, RA Mert, S Demirel, Bioresource Technology 354, 127163).

[0006] AIM OF THE INVENTION

[0007] The aim of the invention is the production of graphene from biogas. For this purpose, biomethane produced by anaerobic degradation process from domestic organic waste was passed through silica gel and activated carbon filters to remove impurities such as CO2 and H2S. The obtained 95% pure biomethane was stored in steel tubes with a pressure of approximately 20 bar (using a compressor) for graphene synthesis. A monolayer graphene film was synthesized by chemical vapor deposition method using stored biomethane.

[0008] Another aim of the invention is to produce "graphene film", which has a higher added value than the electricity produced from biogas, by applying it to biogas facilities.

[0009] Another aim of the invention is to create a method for storing the biomethane produced in biogas facilities in tubes and bringing it to a central graphene film production facility, also.

[0010] FIGURE LIST

[0011] Figure 1 . Time-temperature graph representing the synthesis process

[0012] Figure 2. Raman spectra of graphene films synthesized using different CH4 ratios Figure 3. C1s-XPS spectrum of doped graphene films synthesized with 40 seem CH4 Figure 4. Raman spectroscopy showing the quality of graphene with the change of growth times

[0013] Figure 5. C1s-XPS spectrum of doped graphene films synthesized with 40 minutes growth time

[0014] Figure 6. Optical transmittance measurement of graphene film with optimized synthesis parameters

[0015] Figure 7a. TEM bright field images obtained at different magnifications of the synthesized monolayer graphene film

[0016] Figure 7b. TEM bright field images obtained at different magnifications of the synthesized monolayer graphene film

[0017] Figure 7c. Diffraction pattern image obtained from the same area

[0018] Figure 7d. TEM bright field images obtained at different magnifications of the synthesized monolayer graphene film

[0019] DETAILED DESCRIPTION OF THE INVENTION

[0020] In order to apply the method of the invention, first of all, an increase in efficiency was achieved by using reduced graphene oxide (rGO) in the production of biogas from the organic fraction of domestic waste through anaerobic processes. Following the purification processes of this biogas produced in semi-continuous reactors, biomethane was obtained by pressured with a compressor and stored in tubes. Activated carbon and silica gel filters were used in biogas purification processes. With the compressor, 95% pure biomethane was pressurized and stored in steel tubes. A monolayer graphene production method has been developed from biomethane in tubes using the chemical vapor deposition (CVD) method.

[0021] A three-zone CVD system with six gas inlets was used for graphene synthesis. The quartz tube in the CVD furnace for graphene synthesis is 10 cm in diameter and 85 cm long, and the furnace area where the graphene synthesis process takes place is approximately 25 cm long. In the graphene synthesis processes carried out using the CVD system, GO was used as the carbon source, 95% pure biogas (methane (CH4)) obtained as a result of the purification process, and 99.9999% purity Hydrogen (H2) gas was used as the hydrogen source.

[0022] Polycrystalline copper foil was preferred as the substrate. The most important reasons for choosing copper are that it has low carbon solubility and is more economical. In addition, the fact that it is easier to obtain a homogeneous graphene structure over a large area on a copper substrate compared to some other substrates is another important factor in choosing copper substrate.

[0023] After preliminary cleaning of the copper foil to obtain monolayer graphene, the synthesis process was optimized by changing the CH4 flow rate and graphene growth time. Acetone, ionized water and I PA bath were used in the cleaning process of copper foil.

[0024] For graphene synthesis, the optimum flow rate was first determined by keeping the H2 flow rate constant and providing different rates of CH4 flow (20, 40, 60, 80 seem) to the CVD system. After determining the appropriate CH4 flow rate for graphene synthesis, growth parameters for graphene film synthesis were optimized by applying growth times of 20, 30, 40, 50 and 60 minutes. Additionally, the temperature was kept constant at 1000°C in all graphene synthesis processes. Graphene synthesis process was carried out under 10'1Torr vacuum. The time-temperature graph representing the synthesis process is shown in Figure 1.

[0025] The basic steps performed during graphene synthesis by CVD can be listed as follows:

[0026] • The copper substrate, which is pre-cleaned, is placed in the quartz pipe,

[0027] • The system is put under vacuum,

[0028] • Then, the system is heated, first annealing is carried out at appropriate temperatures and times, and then synthesis is carried out at the appropriate time and gas ratios determined, • After the process is completed, the synthesis process is completed by applying rapid cooling.

[0029] A polymer-assisted transfer technique called 'wet transfer' was used to transfer graphene from the copper foil surface to the application surface. In the mentioned technique, the graphene film is separated from the substrate and then the transfer process is carried out. However, in order to achieve this, it was first coated with a polymer called polymethylmethacrylate (PMMA) using a spin coating device in order to protect the surface and integrity of the graphene obtained on copper. After coating, the graphene film was separated from the metal substrate surface where it was synthesized with Ammonium Persulfate ((NH4)2S2O8) solution. After the copper foil was dissolved in (NH4)2S20s solution, the graphene+polymer structure on the solution surface was passed through a pure water bath several times to remove solvent residues. Graphene was then transferred onto the required substrates. For this purpose, transfer processes were carried out on Si / SiO2 for electrical measurements, on glass for optical measurements, and on the grid for TEM measurements. After the graphene was transferred to the substrate surface, the substrate was heated on the heating plate for 3 minutes at approximately 50-60 °C to remove excess water from the structure, and then the temperature was raised to 80 °C and dried for 5 minutes. After transfer and drying, the polymer layer used was removed from the graphene with acetone. Acetone application was carried out several times to remove polymer residues from the structure.

[0030] Effect of Purified Biogas (Methane) Flow Rate on Graphene Synthesis

[0031] The amount of carbon source, as well as the type of carbon source used, is one of the important parameters in graphene synthesis. In this context, synthesis optimization was carried out by changing CH4 gas flow rates. This optimization was made based on Raman spectroscopy analyses.

[0032] Raman spectroscopy is one of the characterization methods for graphene that is very important, does not damage the structure, and can be applied quickly and easily. Graphene has 3 different Raman peaks: D, G, 2D. The positions, intensities and full widths at half maximum (FWHM) of these peaks are important parameters in determining the quality of graphene. D peak shows sp3 hybridization of carbon atoms formed in the structure and also represents defects in the structure. D peak is generally not observed in the monolayer and pure graphene structure. The G peak is associated with sp2 hybridization of carbon atoms and is one of the most important peaks revealing the graphene structure. The G peak having a certain intensity indicates the high crystallinity value of graphene. The 2D peak can be called the trace peak of graphene layers. From the Raman measurement results, the I2D / G ratios of graphene films produced using 20 seem, 40 seem, 60 seem and 80 seem CH4 flow were 1.02, respectively; It was found to be 1.72, 1.01 and 0.38. In addition to the main peaks, D' appeared in the graphene structure synthesized with biogas. The D' peak occurs only in the presence of impurity atoms in the graphene structure, and therefore D' is considered the characteristic peak of the impurity (Hao et al., 2010; Xue et al., 2012). The main reason for the D' peak to appear in the synthesized graphene structure was evaluated as biogas-derived impurities. In graphene synthesis studies carried out using different CH4 gas flow rates while keeping the H2 flow rate constant, a decrease in graphene quality was observed after 40 seem with the increase of CH4 flow. It was determined that with the increase in the amount of CH4 after 40 seem, the two-layer graphene structure was moved away and towards the multilayer graphene structure. This situation is directly related to the amount of carbon and the purity of the gas. Increasing the flow rate of the carbon source may cause more carbon accumulation on the surface, and thus a transition from a single-layer graphene structure to a multilayer graphene structure occurs. A similar situation exists in similar studies conducted in the literature, and it has been observed that the number of graphene layers increases with the increase in carbon source flow rate. In addition, the relatively low purity of CH4 used (methane with 99.999% purity is used under normal conditions) was interpreted as the possibility that more contamination / impurity from the gas used may have entered the structure by increasing the flow rate.

[0033] Based on the obtained Raman spectroscopy results, the optimum CH4 flow rate was determined as 40 seem under the specified parameters. Bilayer graphene synthesis could only be achieved by changing the CH4 flow rate. In order to synthesize monolayer graphene, in the next step, the appropriate value for monolayer graphene synthesis was investigated by changing the growth times.

[0034] Table 1. Raman spectroscopy peak positions of graphene films synthesized using different CH4 ratios

[0035] The C1s spectrum obtained as a result of the XPS analysis performed for graphene synthesized using 40 seem CH4 ratios is given in Figure 3. In the XPS-C1s spectrum, the central band where carbon is located was determined to be around 284.2 eV, which indicates the C-C sp2 structure. At the same time, the peak occurring at 286.1 represents the sp2 C structure. The value measured in the 288.3 eV band shows the sp3 C structure. Although no foreign atoms (dopers) were used during graphene synthesis, sp2 C and sp3 C hybridization occurred, which is directly related to the purity of the gas used. In this context, CH4, whose purity is relatively low, brought about sp2 C and sp3 C hybridization due to the foreign atoms it contains. The obtained XPS results are in agreement with the literature values (Matsoso et al., 2016; Wei et al., 2009; Zafar et al., 2013).

[0036] Effect of Growth Time on Graphene Synthesis

[0037] After graphene synthesis was carried out by changing the CH4 ratios, 40 seem CH4 was kept constant in the subsequent synthesis optimization experiments, as the graphene films synthesized using 40 seem CH4 were considered to be the most suitable in terms of the number of layers. In this context, the effect of growth time on the graphene synthesis process was examined. For this purpose, graphene synthesis was carried out by keeping the other synthesis parameters constant as in the first experimental group and by applying growth times of 20, 40 and 60 minutes. When the Raman spectra of the synthesized graphene films given in Figure 4 were examined, it was determined that the 40-minute growth time was optimum and the quality of the synthesized graphene decreased in other periods. From the Raman spectra, it was observed that the graphene quality increased with the increase in the growth time, but after 40 minutes, the graphene quality decreased and graphitic structures began to be seen more frequently.

[0038] In Table 2, Raman peak positions of the films synthesized using the investigated growth times are given. The I2D / G ratio was determined as 0.46, 2.01 and 0.26 for graphene films with growth times of 20, 40 and 60 min, respectively. This indicates that the graphene synthesized using a growth time of 40 minutes is a monolayer. In addition, D' peak was observed in the synthesized graphene structure, similar to the previous experimental group. This situation has been similarly associated with impurities from a low-purity CH4 source. After the appropriate growth time, increasing the growth time allows more carbon atoms to accumulate on the surface, therefore, after 40 minutes of growth time, the monolayer graphene structure transitioned to a multilayer structure again.

[0039] Table 2. Raman peak positions of nitrogen-doped graphene films synthesized with different growth times

[0040] Figure 5 shows the C1 s spectrum using XPS analysis for graphene synthesized with a growth time of 40 minutes. As a result of the C1s-XPS analysis, it was determined that the central band where carbon was located was around 284.6 eV. This situation similarly indicates the C-C sp2 structure. At the same time, the peak occurring at 285.6 represents the sp2 C structure and the value measured in the 288.7 eV band represents the sp3 C structure. Other peaks next to the central band are due to impurities, and this is directly related to the purity of the carbon source, similar to the previous experimental groups.

[0041] Synthesis parameters have been optimized; In the electrical measurements (4 point probe) made for the graphene film obtained as a result of 40 minutes of growth at 1000 °C using 40 seem CF and 20 seem H2, the layer resistance was found to be in the range of 500-600 ohm / sq.

[0042] Additionally, when the optical properties given in Figure 6 for the synthesized graphene were examined, it was determined that the optical transmittance value was around 97% for the visible region. The electrical and optical values of graphene films synthesized using biogas, the efficiency of which is increased by using rGO in powder form during the production process and the purity of which is subsequently increased, have been very promising for the use of these films in opto-electronic applications, and the cost of graphene film production has been significantly reduced with the CVD approach.

[0043] Figures 7a-7d show the bright field (7a, 7b, 7d) TEM micrographs of the monolayer graphene film with optimized synthesis parameters and the diffraction pattern (7c) obtained from the same region. Figure 7a shows a low magnification micrograph representing the general view of the graphene film transferred onto the carbon-supported microscope grid. This figure was obtained from an area of approximately 12 pm and is meaningful and valuable to demonstrate film homogeneity in this area. Figure 7b is taken by zooming towards the center of Figure 8a, and some small fluctuations observed in the film structure in the resulting image are due to contamination on the surface during transfer and measurements. These contaminations on the surface, known as hydrocarbons in the literature, are encountered in almost every electron microscope image obtained at low magnification and cannot be prevented. This is due to the high sensitivity and interaction of the monolayer graphene structure to moisture, oxygen and other carbon groups. It can also be seen in the image given in Figure 7d, especially obtained at high magnification and high resolution. However, in this image obtained from the 20nmx20nm area, the honeycomb structure of graphene is clearly observed. Additionally, the selected area diffraction pattern obtained on the surface imaged in Figure 7b is given in Figure 7c. The diffraction pattern obtained in the form of bright spots on the rings is an expected situation for monolayer graphene and is compatible with the bright field image. The bright spots that appear six in each ring (especially the first and second ring) on the diffraction pattern are close to each other in brightness, representing the single-layer state of the structure and the single crystal structure. The diffraction pattern contributed to both the verification of the layer number information obtained with other measurements and the correct interpretation of the obtained bright-field TEM image. The results obtained with TEM imaging are compatible with both the literature and other measurements. TEM images were generally obtained with the FEI-Tecnai device with 300kV acceleration voltage, and the high-resolution image was obtained with Jeol ARM 200 under 80kV acceleration voltage.

Claims

CLAIMS1 . A method of obtaining graphene on copper substrate by chemical vapor deposition from the biomethane gas obtained from the organic fraction of domestic waste, by anaerobic processes, by using reduced graphene oxide (rGO) in semi-continuous reactors, and after purification processes, by pressurizing it with the help of a compressor and storing it in tubes characterized by comprising the steps below;- Pre-cleaning the copper substrate,- Placing the copper substrate, which has been pre-cleaned, into the quartz pipe in the CVD furnace,- Putting the CVD furnace system under vacuum,- Then, by heating the CVD furnace system, annealing takes place first, and then GO, CH4 and H2 are given to the CVD furnace system at a certain flow rate, and the synthesis takes place during a certain growth period,- Completing the synthesis process by applying rapid cooling after the completion of the process,- Coating graphene with polymethylmethacrylate so that it can be removed from the substrate,- Removing the coating from the graphene with acetone after removal.

2. The method according to claim 1 characterized by the CH4 flow rate being between 20-80 seem.

3. The method according to claim 2 characterized by the CH4 flow rate preferably of 40 seem.

4. The method according to claim 1 characterized by the growth time being between 20-60 minutes.

5. The method according to claim 4 characterized by the growth time preferably being between 40 minutes.

6. The method according to claim 1 characterized by the application temperature being 1000°C throughout the process.

7. The method according to claim 1 characterized by the vacuum value being 10'1Torr throughout the process.

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