In present days, H2 is mainly produced via natural gas from thermochemical methods. The importance of renewable H2 production has increased due to energy issues, global environmental, fossil fuel depletion, and pure hydrogen demand. Biogas is produced from anaerobic digestion or carbon-based waste fermentation methods. It might be a substitute resource to the creation of hydrogen. Methane (CH4) and carbon dioxide (CO2) are two significant constituents of biogas, and these are multipurpose feedstock materials for the generation of valuable chemicals and fuels. This paper presents major hydrogen generation techniques from biogas reforming in detail and a short discussion of biogas reforming's economic analysis. The effective operating parameters such as reaction temperature, gas hourly space velocity and O2/CH4 ratio are also discussed. Biogas has more potential; however, it needs more research on some issues such as deactivation of the catalyst, purification of biogas and removable of H2S. Various reforming methods can be nominated for H2 production depend on biogas composition, the need for hydrogen purity, investment availability and quantity of the desired hydrogen.
Research Article
Hydrogen Production from Biogas: Methods and Economic Analysis
https://doi.org/10.21203/rs.3.rs-457836/v1
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Growing concern about worldwide climate issues and diminution of fossil fuels, the utilization of renewable energy resources has been more focussed (Avraam et al. 2010). A large scale of H2 production developed via reforming techniques, mainly natural gas (CH4) and light hydrocarbons (HCs), used in the chemical industry field (Alves et al. 2013). Hydrogen is abundant and is the most available in renewable energy. Furthermore, only water vapor is produced from the combustion of hydrogen. At present, biogas is an important group from renewable energy sources.
Biogas can be an important path of hydrogen production. It is a combination of dissimilar gases developed via the anaerobic breakdown or fermentation of carbon-based waste material in the existence of microbes (Verma and Samanta 2016). The product of biogas, mainly carbon dioxide (CO2) and methane (CH4), associated with touches of additional gases like hydrogen (H2), ammonia (NH3), hydrogen sulfide (H2S), vapor water (H2O), nitrogen (N2), and oxygen (O2) (Alves et al. 2013). The unwanted component of biogas is hydrogen sulfide (H2S). It is corrosive gas and sustains to damage accessories and equipment during the process of producing energy. Another impurity, like CO2 and humidity, also decreases biogas' calorific value through explosion for thermal plants (Horikawa et al. 2004). Biogas generally carries different gases as a basis of volume percentage by CH4 (55–65), CO2 (35–45) and N2 (1) in sewage digesters while CH4 (60–70), CO2 (30–40) and N2 (1) in biological waste digesters and CH4 (45–55), CO2 (30–40) and N2 (5–15) in landfills (Lau et al. 2011). It is usually generated in biowaste digesters, sewage sludge and landfills that contain agricultural wastes, crop residue, animal wastes and animal dung etc. (Chattanathan et al. 2014). Some important chemical composites involve in biogas as basis of volume percentage listed in Table 1.
| Composite | Percentage |
|---|---|
| CH4 | 55–70 (volume %) |
| CO2 | 30–45 (volume %) |
| H2S | 500–4000 (ppm) |
| NH3 | 100–800 (ppm) |
| H2 | Below 1 (volume %) |
| N2 | Below 1 (volume %) |
| H2O | Below 1 (volume %) |
| O2 | Below 1 (volume %) |
H2 is the simplest element, an atom containing only one proton and one electron. It is a colorless and odorless gas. It is also the most plentiful component in the universe. It is combined with additional chemical substances and detected as part of a different element such as alcohol, hydrocarbon, and water. It is also available in inherent biomass, which contains animals and plants (Kalamaras and Efstathiou et al. 2013). The main benefits of hydrogen are net zero emission of greenhouse gases and high energy content compared to other known substances (LHV;120 MJ/kg and HHV;142 MJ/kg) (Ouyang et al. 2013).
In the present scenario, hydrogen is produced from fossil fuels around 96% and 1% from biomass (Sinha and Pandey 2011). Currently, application H2 as raw material is widely used in a combustion engine, fuel cell, fertilizer industries, chemical industry, pharmaceutical industry, hydrogenation process, Fischere-Tropsch synthesis, production of ammonia and ammonia, among others (Armor 1999).
Overall, biogas reforming is a favorable and attractive method to generate clean hydrogen gas. The main biogas benefits for reforming purpose in H2 production are decreased greenhouse gas emissions, local availability, reliability and better environment, and economic (Nalbant and Colpan 2020). The key motive of this paper is to express the numerous biogas reforming technique for H2 production and its economic analysis.
There are several approaches for the invention of H2. It could be divided into two classes as traditional and non-traditional ways. In traditional methods, hydrogen is obtained from hydrocarbon reforming as natural gas (CH4) and hydrocarbon pyrolysis. In non-traditional methods or alternative methods that can use renewable sources (Nikolaiis and Poullikkas 2017).
Interestingly, methane is part of the biogas component, and biogas is generated from waste materials as adopted the renewable source. Therefore, biogas reforming seems to renewable energy from conventional techniques for the production of hydrogen (Nikolaiis and Poullikkas 2017).
To produce pure hydrogen, additional steps are included in any reforming process. A conversion reactor is utilized for converting the CO into CO2 by using shift reaction (Alves et al. 2013). The final process for hydrogen purification is done in a separate unit by pressure swing adsorption (PSA) (Nikolaiis and Poullikkas 2017). H2 could be obtained through the methane or reforming of biogas in various temperature limits (873–1273K) over reversible reactions and exothermic or endothermic. The reforming reactions are done by low pressure and high temperature. In several kinds of reforming methods, biogas responds along with representatives like oxygen or air and steam to generate syngas with H2 and other gases (Galvagno et al. 2013).
There are some purification techniques available for removing toxic and undesirable substances present in biogas: physiochemical and biological treatment (Alves et al. 2013). Figure 1 presents the important steps for the production of H2 from biogas.
Consequently, the biogas reforming reactions are parallel to natural gas (CH4) reforming. Table 2 illustrates the chemical reactions formed in reforming methods and its enthalpy of reaction at 298K and 1 atm. There are major reforming techniques for H2 production from biogas or methane as follows.
Table 2 Chemically reaction involved in reforming methods (Alves et al. 2013; Verma and Samanta 2016)
2.1 Steam Reforming (SR)
This process is done by methane and water (H2O) vapor with the catalyst that generates syngas (mixture of CO and H2, Eq. 1, Table 2). Methane is required a high temperature for reacting. The reaction of this process is extremely endothermic and needs a high temperature of nearly 650–850°C to attain a high yield of H2 in between 60 to 70% (Verma and Samanta 2016). The ratio H2/CO is three that means the higher yield of H2 nearly 75%. High temperature can also be reduced by using a suitable catalyst (Shanmugam et al. 2018).
This technique consists of a steam reformer, water gas shift reactor, and direct steam reforming reactions inside the reactor. Initially, methane responds with water in the steam reformer, and the syngas and CO and H2 are formed in the existence of a suitable catalyst. Then, the syngas is fed in the WGS reactor after cooling in a range of 300–500°C. CO reacts through the water to decrease the CO content of syngas and developed the H2 and CO2 (Eq. 2). High conversion of CO content and low kinetic reactions were done by high-temperature WGS reactor. While low CO conversion and high kinetic reactions are done by minimum temperature water-gas shift reactors (Minh et al. 2018). Fe, Cu, Fe-Pd and Mo alloys are mostly used catalysts in water gas shift (Verma and Samanta 2016).
In addition, combined reaction (Eq. (3)), also known as direct steam reforming reaction, is the addition of Eqs. 1 and 2. To yield pure hydrogen, need a separate unit for example, membrane or PSA (pressure swing adsorption), remove all gases as CO2, CO, and other gases except H2. Figure 2 shows the reactant and products for the steam reforming process.
The working conditions of steam reforming lead to corresponding reactions that reason carbon formation occur over the surface of catalytic as methane cracking reaction (Eq. (4)), Boudouard reaction (Eq. (5)), and reduction of CO reactions (Eq. (6)). When carbon development seems like the form of nanotubes, it offers a lower distribution of carbon at the surface of the catalyst. Consequently, the catalyst activity is conserved for a long duration (Gregorie et al. 2020).
The possibility of carbon formations is a serious issue since coke deposits and leading deactivation on catalyst surfaces such as Ni-catalyst surface and solid material of carbon; denoted by C. The basic arrangements can control the deposition of coke as if they promoted carbon gasification in water improving and its properties of adsorption (Nawfal 2015). The most popular catalyst is Ni-based on ceramic supports for this process due to its affordable, easily available, and high-quality catalytic properties. There are several catalysts established as Ni-based to improve system performance in the term of selectivity and reactivity (Nawfal 2015).
The Combine components to develop catalysts with oxides that are basic properties such as potassium, calcium and magnesium have been studied. Different catalysts such as pd and Pt-based catalyst have mere stability about coke formation (Alves et al. 2013). Ruthenium-based catalyst is also mostly used in the methane steam reforming method due to its more activity, the high selectivity of H2 and outstanding stability (Nawfal 2015). Another way to decrease the deposition of coke as a result of a reaction (Eq. 6) is to perform under the condition of high partial pressure of water to shift the equilibrium in the right direction and control the carbon formation (Noh et al. 2019). Some other studies explain significant development in separation unit process through the selective membrane reactors or filters (Mahecha-Botero et al. 2009).
All chemical reactions are done in a single vessel from a membrane reactor. To membrane system, both the reactions such as steam methane reforming reaction and shift reaction (Eqs. 1 and 2) co-occur inside the reactor, which comprises a catalyst bed. Additionally, membrane offers the good ability to shift the reaction towards a chemical equilibrium that improves hydrogen production and performs the temperature nearly below 500°C for reforming reaction in the direction of chemical equilibrium (Lin et al. 2003; Sato et al.2010).
2.2 Partial Oxidation Reforming (POR)
Partial oxidation reforming technique (Eq. 7, Table 2) is another alternative path to produce H2 from methane reforming. This technique reduces energy consumption/cost due to the exothermic nature and is contrary to the steam reforming process that endothermic nature (Verma and Samanta 2016).
A methane (CH4) molecule is incompletely oxidised to produce H2 and CO (known as syngas). The ratio of H2/CO is two that means yields of hydrogen around 67%. The process needs a temperature range (700-900oC) (Patinvoh et al. 2017). The molar ratio of O2/CH4 is a key parameter to control this process since the ratio of O2/CH4 more than 0.50 leads to perfect combustion of CH4 (Eq. 8, Table 2) (Lin et al. 2003).
Since CO selectivity slightly decreases, CH4 reacts with O2 and obtains CO2 that permits complete combustion and sudden temperature rise. That reason initiated a hot spot in the reactor bed that deposits coke formation over the surface of the catalyst (Patinvoh et al. 2017). Researchers have been studied the activity and stability of numerous catalysts with the purpose of POR of biogas. Temperature range more than 800°C, catalyst as a solid solution of (Ca–Sr–Ti–Ni), (Ni–Mg–Cr–La–O), (NiO–MgO), and mixed metal oxides and they are used as higher resistance of coke development (Verma and Samanta 2016; Nalbant and Colpan 2020; Gregorie et al. 2020).
2.3 Auto-Thermal Reforming (ATR)
This process is the union approach of SMR and POR and endothermic in nature. This process reduces steam reforming challenges due to its endothermic process and difficulty producing low yield of hydrogen of partial oxidation reforming (Gregorie et al. 2020).
The summation of reactions is expressed by Eqs. 3,7 and 8 (Table 2). It also happens in CO2, as denoted by Eq. 9 (Table 2) (Araki et al. 2009). When the steam and oxygen are provided into the reformer, reason reforming and oxidation reactions occur parallelly, become self-sustainable the whole process, and require less energy. (Nikolaiis and Poullikkas 2017; Verma and Samanta 2016). This process produces the maximum hydrogen yield of approximate 74% (about ratio of H2/CO is 2.8) (Nikolaiis and Poullikkas 2017).
‘Autothermal’ means that no need to supply from an external source for the process. ATR process stabled the heat requirement of the endothermic process through the heat released by the exothermic process and adopted it as an effective system (Nahar et al. 2017). ATR has more advantages, such as fast reactor processing, higher ratio of H2/O2 compared with POR, temperature control of processing, and minimize the hot spots that prevent the deactivation of catalysts (Verma and Samanta 2016; Patinvoh et al. 2017).
To obtain the H2 through the biogas, the various the ratios range for H2O/CH4, O2/CH4, and H2/CO are taken as 1.0–2.5, 0.25–0.55, and 2.0–3.5, respectively (Verma and Samanta 2016; Patinvoh et al. 2017; Mosayebi et al. 2012; Cai et al.2006).
The maximum efficiencies of plant to biogas reforming with ATR method are about 75%, range of temperature 500 -700oC and the ratio of O/C close to 0.8–0.9 (Rau et al. 2019).
2.4 Dry Reforming (DR)
In this approach, CH4 reacts with CO2 and obtains the mixture of CO and H2 (Syngas) (Verma and Samanta 2016), refer Eq. 10 Table 2. This process requirements temperature more than 640oC and work on the endothermic process so need the heat of external source. Biogas is very useful for this process because it has two basic compounds available as CH4 and CO2 (Gregorie et al. 2020). This reaction of this process can be attractive an environmental point of view because they are strong greenhouse gases (CH4 and CO2), but this process can consume it. Contrarily, the rise in CO2 emissions due to the proven external heat (other burned fuels) to endothermic reaction (Nalbant and Colpan 2020). Dry reforming uses the ratio of H2/CO nearly 1 and attaining the yield of H2 about 50%. The H2/CO ratio built this reaction attractive about requirements to further use synthesis gas as Fischer–Tropsch synthesis (Gregorie et al. 2020).
Based on the previous finding, the main reaction (Eq. 10 in Table 2) could modify by competing along with some parallel reactions, which shifts the CO2 conversion in (CH4) methane. These important reactions are mainly such as the reaction of reverse gas water shift (Eq. 2 reverse), Boudouard reaction (breakdown of CO2, Eq. 5 in Table 2), and decomposition of methane (Eq. 4, Table 2). DR method attains the ratio of CH4/CO2 close to 1-1.5 (Verma and Samanta 2016; Serrano-Lotina et al. 2012). The essential issue of DR method is the coke establishment that causes the deactivation of catalyst and blockage of the pipes and reactors (Alves et al. 2013). Pt-, Ru- and Rh-based catalysts improve the H2 generation rate, but they are more expensive, very limited availability, and not established at an industrial scale. Generally, common catalysts such as Co- and Ni- based catalysts are more used (Cai et al. 2006).
2.5 Dry Oxidation Reforming (DOR)
This method has been established for governing the congestion of carbon formation over catalyst surface. It is a joined approach of DR and POR process. This process decreases the energy demand of reaction because the exothermic for partial oxidation releases high temperature that is beneficial to the endothermal and dry oxidation reforming process. The ratio of H2/CO also increases and achieving yield of H2 approximately 60% (Gregorie et al. 2020).
There are additional advantages for this process where parallel feeding of CH4 with CO2 and O2 such as the improved conversion of methane, decreased total energy of the process, higher catalyst activity, improved H2 yield at lower temperatures, and enhanced resistance of deactivation (Chen et al. 2010). Eq. 11 represents the DOR process where β is stoichiometric ratio of CO2 fed with the traditional DR (Table 2). If β value is 1, the reaction would be non-oxidative type DR reaction; now, if β value is 0, the reaction would be partial oxidation hence, as the β value must be in between 0–1(Alves et al. 2013; Verma and Samanta 2016; Nalbant and Colpan 2020).
In the DOR process, the process of changing parameters like reaction temperature and O2 concentration feed supports the control of the ratio of H2/CO and the appearance of reaction such as exothermic or endothermic. At a specific temperature, the nature of exothermic is increased by the increasing concentration of O2. As known, the reaction of POR (Eq. 7) is exothermic and reaction of DR (Eq. 10) is endothermic by nature. Therefore, DOR method can be used as a preferable substitute over the convention DR method using various molar ratios of oxygen. Thus, the production of syngas from biogas through this method has improved energy performance and requires less exterior energy (Avraam et al.2010; Alves et al. 2013).
H2 generation from biogas through steam reforming processes has reported almost the same efficiency as natural gas or methane. An economic investigation by 2013 presented that US$0.27/kWh is attained with payback 8 years (time periods) and some others factors such as maintenance cost, operation and investment (Braga et al. 2013). Since the lower heating value (LHV) of H2 (120 MJ/kg), the parallelly outcome conclusion of US$8.98/kgH2 (approx. 8 €/ kgH2) (Braga et al. 2013).
More current results in order to stream reforming connecting membrane reactors confirm that more than 20% increases the system efficiency by considering the membrane reactor. Indeed, the system efficiencies are informed closely to 25–28% along with a fraction of S/C = 3 for a traditional ATR method and between 46–52% and the fraction of S/C = 4 to traditional SR. At the same time, the membrane reactor expresses efficiencies approx.70% along with the fraction of S/C = 3 (Di Marcoberardino et al. 2018).
H2 production using membrane reactor gets less cost than traditional reforming WGS-PSA methods from economic analysis. In the year 2018, it described that H2 obtaining 100 kg per day at H2 cost rate 4 €/kg by using fluidized membrane reactor approach, whereas H2 cost rates are 4.2 €/kg and 6.4 €/kg respectively described by using the SR and ATR traditional approaches at the same parameters (Di Marcoberardino et al. 2018). The cost of H2 production from biogas must depend on methane content in biogas—technology scale and carbon price, both factors that are relevant from an economic point of view. Tradition reforming techniques have been fully established at large scale for reforming natural gas since the globally natural gas generation, which is reached by about 3750 billion m3 in 2017 and is situated at specific locations (leading to centralized H2 generation) (Enerdata 2018). Decentralized H2 generation could be minimum the requirement of distribution infrastructure and reforming methods like dry reforming (DR). Membrane reactors are much more feasible or competitive at a low generation scale. Since biogas has a decentralized feature related to natural gas (CH4) and a small scale global production of approximately 36 billion m3 of methane (CH4) in the year 2015 (Scarlat et al. 2018), it looks more appropriate to decentralized production of H2. In addition, decentralized H2 generation makes impractical Carbon Capture and Storage (CCS), which is the method to decrease carbon emissions from the sources of natural gas. Hence, biogas and decentralized generation seem fascinating renewable sources and carbon-free hydrogen production, either if few additions are expensive about impurities removal for biogas reforming like sulphur and siloxanes. Additionally, the dry reforming technique seems to be interesting for biogas reforming and mainly depends on biogas compounds as a reactant.
The advancement conversion of biogas needs to address thermodynamic problems such as the need for temperature and high pressure to raise the cost of energy intake. Biogas conversion to syngas requires high temperature (500–800°C) due to endothermic reaction (Chen et al. 2017).
4.1 Reaction Temperature
Reaction temperature has found more influencing parameters on catalyst activity in biogas conversion to syngas. Ni-based catalysts are broadly utilized for biogas conversion to syngas due to their low prices and more potential of catalytic activity than other metals (Zain and Mohamed 2018). An increase in conversion of methane and carbon dioxide rises in temperature attributable to the reaction of endothermicity (Serrano-Lotina and Daza 2014). According to Xu et al. (2010) methane and caron dioxide conversions are higher than the estimation of thermodynamic equilibrium. This could be related to further secondary reactions as a breakdown of methane, steam reforming or RWGS. Shen et al. (2011) informed that renovation of CO2 is always more than methane conversion due to RWGS reaction. However, Chen et al. (2005) detected higher methane (CH4) transformation than carbon dioxide (CO2) transformation, representing that methane decomposition an outsized role on the catalytic performance, as Yasyerli et al. (2011) also conveyed the same process.
Over the catalyst, low variance between the renovation of CH4 and CO2 at a temperature less than 450°C or higher than 750°C, RWGS was unfavorable due to endothermic reaction. Conversion of CO2 was appeared low due to the favorable condition of Boudourad equation. At a temperature of more than 750°C, methane decomposition, methane steam reforming could occur; thus, methane conversion may improve, approaching the transformation of CO2. A rise in ratio of H2/CO was detected as the temperature is increased. However, there was below unity in all cases what recommended that reaction of RWGS was always occur but in low range when temperature is raised (Chen et al.2005; Yasyerli et al.2011). A detail of the effective terms in catalytic conversion of methane to syngas using Ni-based catalysts is offered in Table 3.
|
Catalyst |
Temperature(oC) |
GHSV(h− 1) |
CH4 Conversion (%) |
CO2 Conversion (%) |
Ref. |
|---|---|---|---|---|---|
|
3 wt% Gd-promoted Ni/Y2O3 |
700.0 |
8000 |
84.0 |
85.0 |
(Pechimuthu et al. 2007) |
|
ZrOx/Ni-MnOx/SiO2 |
500.0 |
- |
23.0 |
18.0 |
(Yao et al. 2017) |
|
15 wt% Ni–ZrO2 |
750.0 |
24000 |
95.0 |
98.0 |
(Zhang et al. 2015) |
|
Yb-promoted Ni (20 wt%)/γ-Al2O3 |
700.0 |
52000 |
82.0 |
89.0 |
(Amin et al. 2012) |
|
5 wt%Ni − 10 wt%Co/Al2O3 |
700.0 |
36000 |
67.0 |
71.0 |
(Siang et al. 2018) |
|
15 wt% Ni-MgO-Al2O3 |
750.0 |
43000 |
75.0 |
80.0 |
(Akbari et al. 2017) |
|
Ni-CeO2/ZrO2 |
600.0 |
- |
55.0 |
70.0 |
(Wolfbeisser et al. 2016) |
|
Mg-promoted Co-Ni/SBA-15 |
700.0 |
8000 |
80.0 |
75.0 |
(Al-Fatesh et al.2017) |
|
Ni/CeO2-Al2O3 |
800.0 |
90000 |
75.0 |
85.0 |
(Fouskas et al. 2014) |
|
10% Ni/γ- Al2O3 |
700.0 |
1150 |
90.0 |
86.0 |
(Rathod and Bhale 2014) |
4.2 Gas Hourly Space Velocity (GHSV)
It is volumetric feed gas flow rate to the volume of the reactor (Gregorie et al. 2020). It is an important parameter to design and optimize purpose in steam reformers and has more effect on conversion on methane distribution of temperature inside the reactor (Sadooghi et al. 2015).
Hamedi et al. (2014) investigated the GHSV ranges from 16,500 per hour to 34,500 per hour and it related to the rate of gas feed flow on reforming performance and temperature profile. An increase in the GHSV changes the location of the maximum temperature drift of the catalyst. However, the extreme temperature remains the same. The normal catalyst temperature is rather higher when raising the flow rate due to the uniform distribution of temperature. It found a low yield of hydrogen to entirely simulated ratios of O2/CH4 when increasing feed gas space velocity. It must be well known that the residence time reduces from 0.22 second to 0.11second.
Avraam et al. (2010) reported catalytic behavior at temperature 715°C of 5%Ru/Al2O3 catalyst by the effect of space velocity. Gas feed molar composition was CH4(25%), CO2 (25%), H2O (50%) and 1 bar inlet pressure. The results were found methane conversion raises from 46–93% as GHSV reduces from 76,000–10,000 per hour.
4.3 O2/CH4 Ratio
Leading the ratio of O2/CH4 increases the peak temperature in the reactor. The concentration of O2 is increased in feeding gas that promotes the rates of oxidation reaction as additional fuel energy is delivered as a form of heat (Hamedi et al. 2014). Lau et al. (2012) stated that there is no activity of reforming observed at lower exhaust gas temperatures. The main point is that the enthalpy of the reactant is inadequate to control the activation energy barrier of reforming reactions. An increase in the reactor's temperature could be seen by providing the oxygen in reactor feed as a result of incomplete oxidation catalytic incineration of the CH4 nearby entrance of catalyst (when the temperature of the reactor is high than the catalyst temperature light-off) (Lee et al. 2005).
Reforming biogas is a promising method to generate green H2 and minimize the overload on natural gas (CH4). The main difficulties of biogas reforming methods are raised associated with coke establishment over the catalyst surface done by most researchers and specialists. It also reviewed related to toxic conditions on account of sulfur content which causes catalyst inactivation and diminishes the production of H2. Ni-based catalysts are mostly used in miscellaneous reforming techniques such as natural gas reforming and biogas reforming. A huge quantity of examining works is also attentive to the effectiveness of catalyst support and some additional promoter elements to reduce the issues of coke formation.
The utilization of catalyst in the reaction of H2 generation must be advanced to a longer usage life cycle to avoid coke formation over the active catalyst surface. The ideal catalysts are Ni-based in reforming processes because of their lower cost. DR and DOR methods are appeared more attractive techniques for H2 generation from biogas. However, these methods are not favorable as carbon development on the surface of catalysts and extra oxidant is needed.
ATR process could be attractive because of higher conversion efficiency and H2 yields; however, this technique is a highly complex control system. At present, mostly H2 generation form biogas is attained in steam reforming method though conventional reformer. However, it is possible to obtain H2 from biogas with advanced membrane reactors (only in one step) and at low temperatures (i.e., reforming process and separation happens at the same location).
GHSV is an essential parameter to design and optimization purpose in steam reformers and has more effect on conversion on methane distribution of temperature inside the reactor. Important operating parameters such as temperature mostly utilized the range from 700-800oC for maximum conversion of CH4 and CO2 and different catalysts as reviewed by this present paper.
The economic analysis point of view that more current results to stream reforming connecting membrane reactors confirm that more than 20% increases the system efficiency by considering the membrane reactor. The cost of H2 production from biogas must depend on methane content in biogas. Hydrogen generation cost from biogas (0.07 €/ kWh) is higher than natural gas (0.03 €/kWh).
Various reforming methods can be nominated for H2 production depend on biogas composition, the need for hydrogen purity, investment availability, and quantity of the desired hydrogen.
Ethics approval and consent to participate: Not applicable.
Consent for publication: Not applicable.
Availability of data and materials: The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Funding: There is no funding.
Competing interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Author contribution: Conceptualization: Anil Kumar, and Ravindra Kumar; Formal analysis and investigation: Anil Kumar; Writing - original draft: Ravindra Kumar; Writing - review and editing: Anil Kumar; Supervision: Anil Kumar and Amit Pal.
Acknowledgments: Authors are highly grateful to Department of Mechanical Engineering and Centre for Energy and Environment, Delhi Technological University Delhi (India), for providing basic facilities to compile this work.
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