Methanol Stream Reforming For Hydrogen Production Essay Example

into various applications. Although the technology has shown promising results in laboratory models, it has not been widely implemented on a commercial scale. The main challenge lies in controlling not only the reactants and products but also the reaction itself. Only a few successful models have been proposed and commercially implemented. Methanol has demonstrated positive results in both direct use as a fuel cell and as a precursor for hydrogen fuel cells.

Methanol can be obtained from natural perishable hydrocarbon sources as well as from petroleum oil and natural gas. For commercial purposes, methanol is primarily produced from natural gas through a syngas route. Syngas is then converted to methanol using a copper catalyst at around 200°C. In 1960, a highly effective copper-based catalyst was developed, bringing about a revolutionary change in the catalytic process (Jiang, 1993). Since then, there has been significant progress in the field of heterogeneous catalysis for hydrogen formation from methanol.

Currently, the procedure uses a Cu/ZnO with Al2O3 composition. The steam reforming of methane results in a combination of CO2, CO, and H2, according to their combining weights (1) and (2). Methanol can be transformed into hydrogen at lower temperatures (150-350 °C) compared to other fuels (> 500 °C), as it does not have carbon-carbon bonding. Methanol can be easily activated at lower temperatures than methane.

The low-temperature transition results in low levels of CO formation, even if the accelerator does not have a specific mechanism for selecting CO2 over CO. However, at low temperatures, there will be a longer residence time and a higher degree of methane formation without an accelerator. This poses a significant problem for hydrogen production. On the other

hand, with the presence of an accelerator, the reforming of methyl alcohol into hydrogen will occur at a higher rate and with good selectivity. The effectiveness of Cu-based accelerators in the production of methyl alcohol has naturally led to their investigation in the steam reforming of methyl alcohol, which can be seen as the reverse reaction equation. By using an excess of steam in the same reaction with various Cu-based accelerators, the equation can be adjusted to ensure that the reaction proceeds forward.

Various accelerators were utilized to convert methyl alcohol to H. There are numerous accelerators suggested for the process, each with different selectivity and rate of transition. It is generally observed that higher temperatures result in increased CO formation, which may cause accelerator toxicity. CO, unlike CO2, has a high surface absorption rate to the accelerator, which can affect the overall transition rate and degrade the accelerator. Several combinations of accelerators have been proposed to tackle this issue, but only at small or micro-scale levels. Additionally, deriving the rate equation for these combinations is more complicated than for individual accelerators. Micro-reactors are devices with micro-channels arranged on an inert or active substrate that may or may not participate in the reaction mechanism. These devices aim to achieve high efficiency outputs by working at a molecular level.

Micro-reactors enhance mass and heat transportation by reducing the effective transport distance and increasing the interfacial area per unit reactor. They also mitigate heat accumulation areas, resulting in safer operations. These reactors can operate under conditions that are difficult to achieve in conventional systems due to their fixed and well-defined characteristics, as well as their high rates of heat

and mass transfer. They also offer spatial and temporal control over temperature, mixing, and residence time. This project aims to create a model that optimizes the rate of transition and selectivity of a micro-reactor used in the methanol steam reforming process for hydrogen production. Additionally, the project strives to develop a high-capacity model with simplified rate equations within a range of safer process parameters.

Challenges faced:

Developing a methanol-based system for hydrogen production is not easy. There are various technologies involved, such as Partial Oxidation, Auto-thermal Reforming, and Pyrolysis. It goes beyond steam reforming and other associated procedures. Specific system challenges impact the selection, operation, deployment, and performance of the system. This study focuses on the technical challenges of the entire system, with a particular emphasis on portable power applications, where most of the research on methanol steam reforming is directed.

Literature study:

Various methods can be used to produce hydrogen, including:

Plasma Reforming

Using electricity to create a plasma that generates energy and produces the necessary free radicals for reforming.

(Biniwale, 2004; Bromberg, 1999; O'Brien, 1996; Paulmier, 2005; Czernichowski, 2003; Sekiguchi, 2003). Usually, steam is used to organize free groups like H+, OH-, and O- when injected with fuel to facilitate redox reactions (Sekiguchi, 2003). Plasma reforming has many advantages such as deficiency of accelerator, smaller systems and lower operating temperature, high response time and elimination of poisoning factor (Biniwale, 2004; Bromberg, 1999; O'Brien, 1996; Czernichowski, 2003). However, the main disadvantage of Plasma reforming is the need for electricity. Additionally, the electrodes used in the process tend to corrode during operation which adds to maintenance costs.

Pyrolysis

Decomposition of hydrocarbons into H and C in a water and air less/free environment is known as pyrolysis and can be done with organic material.

(Muradov, 2003) If there is no H2O or air, then no C oxides will form, resulting in important emissions reduction. This procedure eliminates the need for additional secondary reactors in down watercourse reactors because there is no CO or CO2 present. Pyrolysis can address the increasing concerns over CO2 emissions and play a significant role in environmental protection by recovering a substantial amount of the C as a solid (Muradov, 2003; Guo, 2005).

Pyrolysis procedure involves the use of vaporisers, a pyrolysis reactor, and restorative heat exchangers in a typical apparatus. However, one of the main disadvantages is the deposition of carbon (C) as a fouling agent for efficient heat transfer, which is produced as a by-product (Guo, 2005). This limits the applicability of the process to relatively large installations where carbon removal can be easily achieved.

Partial Oxidation and Auto-thermal Reforming

Hydrocarbon is widely used for large-scale hydrogen production, such as for automotive fuel (Trimm et al.).

, 2001; Hohn et al., 2001; Krummenacher et al., 2003 & A; Pino et al., 2002). It utilizes non-catalytic partial oxidation of hydrocarbons in the presence of O and steam at temperatures ranging from 1300-1500 & A; deg; C in order to achieve high conversion and minimize the formation of carbon black (Rostrup-Nielsen et.al., 2003).

An accelerator is a clip that is used to decrease the operating temperature. However, it is difficult to control due to issues such as coking and heat accumulatione (Trimm et.al., 2001; Song, 2002; Pietrogrande et al., 1993; Hohn,

2001; Krummenacher et al., 2003; Pino et al., 2002).

(Krummenacher et al.) has shown good results in non-portable forms, but it is not suitable for light and portable devices.

Aqueous Phase Reforming

When H is produced from oxygenated hydrocarbons and saccharides, it is known as Aqueous Phase Reforming. (Cortright, 2006; Cortright, 2002; Davda, 2003) These reactions occur at high pressures (25-30 MPa) and temperatures (220-750°C) even with a catalyst. This method is not suitable due to high heat and pressure requirements. Catalysts are being researched to overcome this problem.

Ammonia Cracking is a process that involves breaking down ammonia into its constituent elements. Ammonia is a strong competitor to methyl alcohol steam reforming and has been suggested as a fuel for portable power applications in fuel cells. The energy density of ammonia is 8.9 kilowatt H kg-1, which is higher than that of methyl alcohol (5.5 kilowatt h kg-1) but lower than that of diesel (13.2 kilowatt h kg-1). Ammonia cracking occurs under endothermal conditions and is considered the reverse reaction of synthesis. However, the synthesis of ammonia occurs at high temperatures and pressures, which has led to relatively less research on ammonia until now.

The production of H can be done through various techniques, such as reforming and fuel cells. However, it is generally safer to produce H rather than store it in molecular form. The choice of technology depends on the user's needs, but usually safer technologies are preferred. One feasible option for steam reforming of methyl alcohol is to use micro-reactors.

Various catalysts used in micro-reactors are:

1. Cu/ZnO
2. Cu/ZnO/Alumina ( Al2O3

)

Both forms of catalysts (separately and in combination) face many challenges in micro-reactors, such as deriving rate equations and poisoning.

Methodology:

Three broad steps are involved in the creation of a new micro-reactor. These steps include:

1. Writing the mirror images of the micro-reactors.
2. Joining the two mirror imaged micro-reactors as MicroR+.
3. Stacking the individual units of MicroR+ to form Mega-M1.

Writing the mirror images of the micro-reactors:

The creation of the Primary unit involves two basic steps.The first step in the Mega-M1 process involves creating the basic micro-reactor using lithographic writing on a PMMA +ve template, which results in the production of the parent -ve template. The second step utilizes the Electron beam vapor deposition technique to apply the catalyst onto the channel surfaces. This first step serves as the foundation for the new reactor, where an even number of identical micro-reactors will be fabricated on ceramic substrates using a PMMA template created from the parent ceramic template itself.

The only change in the design will be to leave a small hole in all reactors, except for two which will have a hole only on one side of the substrate plate, so that they are arranged alternately. In the second step, layers of copper and Pd catalyst, along with ZnO and Alumina, will be coated.

However, these will be in separate zones within the micro-reactors. The zones were separated with the belief that the micro-reactor would be resistant to high temperature and toxicity, as well as have a high conversion rate.

Stacking the individual unit of MicroR+ to form Mega-M1:

The individual unit of microR+ is carefully stacked on top of each other to create a sandwiched superimposed structure of the micro-reactor.

The stacking should hold the recess on one face and the mercantile establishment on the other face of the reactor but at the bottom. This construction will allow for the equal distribution of reactants over the catalytic surface inside the channels. Traditionally, micro-reactors were used as a single unit and homogenously coated with the accelerator or mixture of accelerators.

Mega M compared to conventionally used micro-reactors has the following advantages:

Mega M is a multiple bed micro-reactor that can produce more volume through them. It can also facilitate the scaling up design of the micro-reactor.

The rate of the micro-reactors can be calculated using a simple method based on the surface area of the country and the Langmuir-Hinshelwood dynamics. The temperature and CO poisoning have minimal effects on this reactor, as the initial transition is catalyzed by Pd, which produces very little CO.

Freshness:

The process can be considered novel in several ways:

1. Layered surfacing for micro-reactor channels provides a better way of reforming.
2. MicroR+ is a safer way to increase output volume without affecting the rate transition. Stacking MicroR+ into Mega M1 can also be considered a fresh approach to producing high volume output, but the percentage transition needs to be studied through experimentation.

Conclusion

The new reactors, Micro-R+ and MegaM1, show promising advancements in the field of micro-reactors by providing a new and fresh method of keeping the rate equation simple and increasing reactor output volume.

There is a possibility of heat buildup in the MegaM1 due to a low heat transfer rate between the ceramic substrate. However, this issue can be resolved by introducing thermocouples between the two MicroR+ units.

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