Technoeconomic Evaluation of the Industrial Implementation of Catalytic Direct Nonoxidative Methane Coupling

Abstract

This paper presents a process design for catalytic nonoxidative natural gas conversion to olefins and aromatics, highlighting the opportunities and challenges concerning industrial implementation. The optimal reactor conditions are 5 bar and 1000 °C. Heat exchange over the reactor is challenging due to the high temperature and low gas pressure. Recovery of ethylene is economically unattractive due to the low ethylene concentration in the product stream, leading to a methane-to-aromatics process, recycling ethylene. Benzene is the most valuable product at an efficiency of 0.31 kgbenzene/kgmethane with hydrogen as a major valuable byproduct. Naphthalene, with a low value, is unfortunately the dominant product, at 0.52 kgnaphthalene/kgmethane. It is suggested to hydrocrack the naphthalene to more valuable BTX products in an additional downstream process. The process is calculated to result in a 107 $ profit per ton CH4.

Oxidative Addition of Methane and Reductive Elimination of Ethane and Hydrogen on Surfaces: From Pure Metals to Single Atom Alloys

“…5,6 It would be of economic interest to evaluate the possibility of using natural gas as a feedstock for chemical synthesis. 7 Direct conversion of methane to light hydrocarbons by oxidative or nonoxidative coupling of methane (OCM or NOCM) has a potential for more efficient one-step methane upgrading, avoiding the energy-intensive syngas generation stage. 8,9 The primary products of OCM and NOCM, C 2 species (i.e., ethane or ethylene), are precursors to a variety of higher value chemical products, such as plastics and resins.…”

“…To achieve industrially important methane conversion rates (>10% conversion), reactions are typically performed at temperatures above 900 °C. 7,25,26 This results in high operating costs. But that is not the only problem.…”

“…Coke formation is inevitable in reactions at such high temperatures and can lead to practical limitations, such as catalyst deactivation, process impairments, and loss of carbon yield. 7,27,28 To improve the NOCM reaction, great efforts have been made to find catalyst systems that work efficiently to activate the C−H bond of methane and promote C−C coupling, as well as to inhibit coking. 26,29−34 According to the 1991 report by Belgued et al, 21 continuous feeding of CH 4 to a 6 wt % Pt/SiO 2 catalyst at 250 °C yielded C 2 H 6 and hydrogen.…”

“…In recent years, it has been reported that reserves of methane-rich natural gas, such as tight gas, shale gas, and coalbed methane, are rapidly increasing . Much research has been conducted to convert methane into useful chemicals, such as light alkanes, olefins, alcohols, and aromatic compounds. − Currently, indirect methods are most widely used for producing value-added products from methane: methane is partially oxidized or reformed to syngas (a mixture of CO and H 2 ), from which long-chain hydrocarbons and alcohols are produced by Fischer–Tropsch synthesis. , It would be of economic interest to evaluate the possibility of using natural gas as a feedstock for chemical synthesis . Direct conversion of methane to light hydrocarbons by oxidative or nonoxidative coupling of methane (OCM or NOCM) has a potential for more efficient one-step methane upgrading, avoiding the energy-intensive syngas generation stage. , The primary products of OCM and NOCM, C 2 species (i.e., ethane or ethylene), are precursors to a variety of higher value chemical products, such as plastics and resins .…”

“…OCM was first reported in 1982, and since then its study has been active worldwide. − The presence of an oxidant in OCM not only lowers the activation barrier for methane conversion but also contributes to making the reaction thermodynamically favorable. ,, However, the formation of overoxidized species (CO or CO 2 ) is inevitable; improving the selectivity of C 2 formation in OCM has been a longstanding issue since the 1980s . Although hundreds of catalyst candidates have been prepared and tested for OCM, the selectivity toward CO/CO 2 is typically about 50%, and the carbon utilization efficiency remains low. , …”