The catalytic conversion of light alkane feedstock is one of the promising industrial routes to prepare valuable chemical products: owing to its use in car and gas turbine engines, heaters, incinerators, and hydrocracking furnaces. Although the combustion of hydrocarbon fuels appears to be conceptually simple; the details of how alkane conversion to carbon dioxide and water occurs with concomitant release of energy, are enormously complex. Without timely and effective measures to mitigate the adverse impacts of greenhouse gases emission, the living environment of the world will continue to deteriorate and become increasingly unbearable. On that ground, the development of technological methods for methanol production via alkane conversion in a manner that is energy-conserving, inexpensive, environmentally-sustainable, and least-damaging to human health & welfare are of crucial importance. The applied method in this work contributes to these objectives.
It is well known that in the petroleum refining process, a substantial amount of C3–C4 fraction (existing as a mixture rather than individual component), is primarily recovered from crude oil distillation and by cracking of heavy molecules: bulk of which is flared as hydrocarbon fuel into the atmosphere through refinery furnace. On that ground, owing to the higher chemical reactivities of propane and butane, in comparison to methane, the use of C3–C4 hydrocarbon mixtures has been investigated as an alternative feedstock for methanol production, which apparently, to a large extent, is an important aspect of chemical technology and economics.
The present work evaluates the theoretical concepts, quantum chemical calculations, and experimental investigations to explore novel pathways for the direct oxidation of propane and butane fraction to methanol using a photochemical reactor.
To test the validity of the mechanism, the photochemical oxidation of C3–C4 gas fraction was investigated under three experimental phases under mild reaction conditions at a temperature (T = 100°C), at a pressure (P = 1 atm.), and at reaction times (tr) within 5 – 120mins (a) without exposure to irradiation, (b) with exposure to visible light irradiation at a wavelength region (λ = 420 nm), (c) with exposure to visible light irradiation at a wavelength region (λ = 420 nm) under the auto-catalytic influence of nitric acid vapor. The oxidation products obtained are methanol, as well as ethylene and propylene (very important star
Contents
1. INTRODUCTION
1.1 Technical background
1.1.1 Methanol synthesis: A brief history
1.2 Production of methanol: From syn-gas, bio-sources, methyl formate, & CO2 recycling
1.2.1 Methanol from biomass and cellulosic sources
1.2.2 Methanol from chemical recycling of CO2
1.2.3 Methanol from methyl formate
1.2.4 Methanol from syn-gas
1.2.4.1 Syn-gas preparation techniques
1.2.4.1.1 Syn-gas via steam reforming
1.2.4.1.1.1 Steam reforming of methane (SMR)
1.2.4.1.1.2 Catalytic partial oxidation of methane (CPO)
1.2.4.1.1.3 Auto-thermal reforming (ATR)
1.2.4.1.1.4 CO2 reforming of methane
1.2.4.1.2 Syn-gas from petroleum oil & higher hydrocarbons
1.2.4.1.3 Syn-gas from coal
1.2.4.1.4 Syn-gas via combined-reforming
1.2.4.1.5 Syn-gas via heat-exchange reforming
1.3 Methanol: Application & Economy
1.3.1 Methanol as a chemical feedstock
1.3.2 Methanol as transportation fuel
1.3.2.1 Methanol as fuel in internal combustion engines (ICE)
1.3.2.2 Methanol as fuel in compression ignition engines (DIESEL)
1.3.3 Methanol as gasoline additive
1.3.4 Methanol for static power & heat generation
1.3.5 Methanol for waste-water denitrification
1.3.6 Methanol for bio-diesel trans-esterification
1.4 Market dynamics for methanol
2. LITERATURE REVIEW
2.1 Present-day investigations
2.2 Main products of the DMTM process
2.2.1 The ΔCH4/ΔO2 ratio
2.2.2 The CH3OH/CH2O ratio
2.2.3 The CO/CO2 ratio
2.2.4 By-products of the DMTM process
2.2.5 Yield of methanol & oxygenates
2.3 Main parameters of the DMTM Process
2.3.1 Effect of oxidant on the selectivity & yield of products
2.3.1.1 Influence of oxygen concentration on the temperature and rate of reaction
2.3.2 Effect of temperature on the yield of products
2.3.3 Effect of pressure
2.3.3.1 Effect of pressure on the temperature and rate of reaction
2.3.3.2 Effect of pressure on the rate of branched-chain quasi-stationary reaction
2.3.4 Effect of gas composition (3rd body effect)
2.3.4.1 Heavier homologues of methane
2.3.4.2 Inerts (N2, He)
2.3.4.3 Carbon oxides (CO, CO2)
2.3.5 Effect of homogeneous promoters
2.3.6 Effect of heterogeneous catalysts
2.3.6.1 Effect of catalyst’s surface area
2.3.7 Effect of feed-flow rate (residence time)
2.3.8 Surface-effect of reactor material
2.3.8.1 Role of diffusion of reactants to the reactor surface
2.3.8.2 Decomposition of products on the reactor surface
2.4 Key features of the mechanism
2.4.1 Mechanism for the gas-phase oxidation of methane in medium temperature range
2.4.2 Main kinetic features of the DMTM process
2.5 Role of heterogeneous process in the DMTM process
2.5.1 The interplay between the homogeneous and the heterogeneous catalytic processes of methane oxidation
2.6 Thermo-kinetic phenomena in partial oxidation of methane
2.6.1 Experimentally-observed thermo-kinetic phenomena in the partial oxidation of methane
2.7 Effect of physical promotion of the process
2.8 Effect of the process under supercritical conditions
2.9 Overview of experimental achievements on DMTM process
2.10 Conclusions
3. AIM & JUSTIFICATION FOR THE RESEARCH DIRECTION
3.1 Research justification
3.2 Aim of research
3.3 Theoretical concepts & mechanism for the autocatalytic photo-oxidation process of propane-butane fraction to methanol
4. EXPERIMENTALS
4.1 Experimental set-up
4.2 Experimental procedures
5. RESULTS AND DISCUSSION
6. CONCLUSIONS
Research Objectives and Thematic Focus
This work aims to investigate efficient and environmentally sustainable pathways for the direct conversion of C3–C4 hydrocarbon fractions into methanol. The central research question addresses how mild reaction conditions, specifically low temperatures (100°C), atmospheric pressure, and photochemical reactor technology under the auto-catalytic influence of nitric acid vapor, can optimize methanol production while minimizing energy waste and environmental impact.
- Direct partial oxidation of propane and butane to methanol.
- Application of photochemical reactor technology to optimize reaction pathways.
- Role of nitric acid vapor as an auto-catalytic promoter in methane and alkane oxidation.
- Evaluation of theoretical concepts and quantum chemical calculations regarding reaction intermediates.
- Assessment of economic feasibility and energy efficiency in comparison to conventional industrial syngas methods.
Excerpt from the Book
2.3.1 EFFECT OF OXIDANT ON THE SELECTIVITY AND YIELD OF PRODUCTS
The seemingly-straightforward oxidative transformation of methane with oxygen is in principle an attractive approach. Notwithstanding, the yields to desired products are typically limited by severe over-oxidation pathways. Desired targets such as methanol, formaldehyde and ethylene are far more reactive with oxygen than methane, and are rapidly converted into more thermo-dynamically stable products, principally CO2. Furthermore, the reactions with O2 are highly exothermic, and can increase local temperatures within reactors by 150 – 300oC, thereby presenting significant heat management and reactor design issues. New catalytic strategies to enhance the selective conversion of methane to value-added intermediates with lower heat emission are therefore pivotal to developing viable methane conversion processes. The maximum methanol selectivity of 42% was achieved at [O2]o = 1.5%, and at the lowest oxygen concentration in the work.[195] That the selectivity of formation of liquid organic products decreases with increasing oxygen concentration naturally results in an extreme behaviour of their yield. Nevertheless, the yield of liquid DMTM products (Fig. 2.6) passing through a maximum with increasing oxygen concentration was observed in the work.[125]
Summary of Chapters
1. INTRODUCTION: Provides a comprehensive overview of existing methanol production technologies, emphasizing the need for more energy-efficient and direct methods of converting light alkanes.
2. LITERATURE REVIEW: Analyzes the history and current state of research regarding the partial oxidation of methane and other light alkanes, identifying key parameters, mechanisms, and catalytic influences.
3. AIM & JUSTIFICATION FOR THE RESEARCH DIRECTION: Discusses the rationale for utilizing C3–C4 hydrocarbon fractions as a feedstock and outlines the objectives for using photochemical reactors with nitric acid.
4. EXPERIMENTALS: Describes the materials, photochemical reactor configuration, and procedures used in the three experimental phases to test the oxidative conversion process.
5. RESULTS AND DISCUSSION: Presents experimental findings and quantum chemical calculations, evaluating the impact of nitric acid and photochemical conditions on product yields and reaction pathways.
6. CONCLUSIONS: Synthesizes the experimental success in achieving high methanol selectivity and offers a conceptual framework for future industrial implementation.
Keywords
Methanol synthesis, Direct partial oxidation, C3–C4 hydrocarbons, Photochemical reactor, Nitric acid, Auto-catalytic process, Chemical kinetics, Quantum chemical calculation, Selectivity, Energy efficiency, Green chemistry, Alkane conversion, Petrochemical industry, Heterogeneous catalysis, Reaction mechanism.
Frequently Asked Questions
What is the primary objective of this research?
The primary objective is to develop a more energetically efficient and sustainable method for the direct conversion of C3–C4 hydrocarbon fractions into methanol, using mild reaction conditions and photochemical activation.
Which specific feedstock is investigated in this work?
The research focuses on the C3–C4 hydrocarbon fraction, typically recovered from crude oil distillation, which is often underutilized or flared in refinery processes.
What is the role of nitric acid in the described process?
Nitric acid vapor acts as an auto-catalytic agent that, under photochemical conditions, facilitates the formation of reactive species necessary to initiate the oxidation chain of light alkanes at lower temperatures.
What main experimental method is proposed?
The study proposes a photochemical oxidation process operating at 100°C and atmospheric pressure, utilizing visible light radiation and nitrogen oxides to promote the conversion.
How is the methanol yield measured in this study?
Methanol yield is analyzed by collecting liquid reaction products through a condensate collector after cooling, followed by identification using gas and high-pressure liquid chromatography.
What are the main scientific challenges regarding the oxidation of methane?
The main challenges involve controlling the highly exothermic nature of the oxidation reaction and preventing the "over-oxidation" of methanol into undesirable carbon oxides like CO2.
What is the significance of the B3LYP/6-311++G(3df,3pd) calculations in this research?
These quantum chemical calculations provide a theoretical basis for understanding the electronic states and reaction barriers of the intermediates, helping to explain why certain pathways are more favorable for methanol formation.
How does the pressure affect the reaction kinetics according to the study?
The study indicates that higher pressures are crucial for shifting the reaction into a steady-state branched-chain mode, which enhances the selectivity of methanol formation by minimizing heterogeneous decay.
- Citar trabajo
- Ayodeji Ijagbuji (Autor), 2015, The Eco-Friendly and Promoting Influence of Nitric Acid–Steam Vapors on the Oxidation of C3–C4 Parrafins into Methanol, Múnich, GRIN Verlag, https://www.grin.com/document/288794
