Direct Conversion Of Natural Gas Research Articles

Exergy analysis of direct method for conversion of natural gas to methanol

The exergy analysis of a direct method for the conversion of natural gas to methanol is reported in this work. The study is part of a process development effort to identify areas of improvement to the technology of direct conversion of natural gas to methanol. Prior to the exergy analysis, different configurations of the direct conversion process were developed and simulated. Two heat-integrated configurations designated as Case I and Case II were considered plausible. The exergy efficiency, excluding exergy of the rejected heat, of Case I and Case II were determined as 33% and 36%, respectively. The 9% increase in efficiency of Case II relative to Case I did not justify the installation of an expander and was therefore screened out. Exergy balance in Case I showed that a total of 56% of the exergy input was lost to internal consumption. The majority of exergy destruction was found to be due to the methanol synthesis reactor (36.0%), heat exchangers (30.1%) and combustion (25.0%). Further analyses of the losses across all heat exchangers indicated a nonlinear relationship between exergy destruction contribution and minimum approach temperature (ΔTmin), with a minimal at ΔTmin of 10 °C. The methanol product was determined to represent 18% of exergy input, excluding the air separation unit. The overall process efficiencies were found to be 18% (LHV) and 24% (LHV) for recycle split fractions of 90% and 98%, respectively. The results of this work would provide further insight into the exergy viability of the technology of direct conversion of natural gas to methanol.

Direct conversion of natural gases in solid oxide cells: A mini-review

The direct one-step electrochemical conversion of natural gas is an attractive and economic approach to the synthesis of the higher value-added alkenes with co-product hydrogen or hydrocarbons, which is enabled by the combination of solid oxide cells (SOCs) and catalysts. Compared to traditional chemical alkene synthesis, the integration of SOC as a membrane reactor can overcome the thermodynamic equilibrium limit by applying electrochemical current to effectively mitigate coke formation. In this scheme, the dehydrogenation reaction supplies protons from natural gas hydrocarbons for use in CO2 reduction, electricity generation, and hydrogen production. The main approaches for natural gas direct conversion have been reviewed to understand the current technology development status including catalysts and SOC system integration.

An integrated methane dehydroaromatization and chemical looping process

Most of the natural gas co-produced in oil wells is flared due to the high transportation costs of bringing it to market. Onsite upgrading of natural gas to liquid products could address this issue but there are few processes for effective direct conversion of natural gas to liquid products. Methane dehydroaromatization (DHA) over Mo/H-ZSM-5 offers a potential route to a value-added liquid product, however, DHA conversion is severely limited by thermodynamics at most industrially relevant temperatures. Here we propose an integrated process coupling methane DHA, chemical looping for selective hydrogen oxidation, and subsequent water removal to achieve higher yields of aromatic products limited by the thermodynamics in one-pass systems. We validate this process via the construction and operation of a one-of-a-kind multibed recirculating reactor, and achieve a combined aromatics yield of 42%. Detailed technoeconomic analysis of the process for mobile applications show that such a process could be economically viable under certain circumstances.

Non-oxidative Conversion of Natural Gas to Aromatics (GTA), Ethylene (GTE), and Hydrogen Using Mo Loaded on HZSM-5 and Hydro-fluorinated HZSM-5 Catalysts

The direct conversion of natural gas to aromatics (benzene and naphthalene), ethylene, and hydrogen were investigated using 6%Mo/HZSM-5 catalysts and hydrofluorinated 6%Mo/HZSM-5 catalysts. The catalysts were characterized via pore volume distribution, temperature programmed desorption, X-ray diffraction patterns, and thermogravimetric analysis. Treatment of HZSM-5 with 2% hydrofluoric acid was found to significantly enhance ethylene production and selectivity associated with improving the coke resistance, even though aromatics formation was diminished. These effects could be attributed to decreasing the acid sites strength and increasing the catalytic pore diffusion restriction via partial blockage by deposited non-framework aluminum species.

A review of cleaner production methods for the manufacture of methanol

Growing population and expanding economies are important causes of increasing global energy demand. In wake of the continuous hike in the petroleum prices, depleting world resources and increased constant threat to planet's environment, the need for environment friendly alternative fuels has augmented many times. Methanol has been in the limelight over the past few years. High production cost, catalyst deactivation, economy of scale, huge energy requirements are the leading bottlenecks, which should be resolved to move towards the cleaner production. To address the issues, various reactors and their configurations have been modelled over years and the need to summarise all these efforts seems obligatory. One-dimensional to three-dimensional models for traditional packed bed reactors to processes for direct conversion of natural gas to methanol is available in literature. The presented study is an attempt to compile most of these efforts in order to guide future work in this area for cleaner and healthier environment.

Direct conversion of natural gas into COx-free hydrogen and MWCNTs over commercial Ni–Mo/Al2O3 catalyst: Effect of reaction parameters

A commercial hydrotreating nickel molybdate/alumina catalyst was used for the direct conversion of natural gas (NG) into COx-free hydrogen and a co-valuable product of multi-walled carbon nanotubes (MWCNTs). The catalytic runs were carried out atmospherically in a fixed-bed flow reactor. The effect of reaction temperature between 600 and 800°C, and dilution of the NG feed with nitrogen as well as pretreatment of the catalyst with hydrogen were investigated. At a reaction temperature of 700°C and dilution ratio of NG/N2=20/30, the optimum yield of H2 (∼80%) was obtained with higher longevity. However, using the feed ratio of NG/N2=30/20, the optimum yield of MWCNTs was obtained (669%). X-ray diffraction pattern for the catalyst after the reaction showed that the MWCNTs were grown on the catalyst at all reaction temperatures under study. TEM pictures revealed that the as-grown MWCNTs at 600, 650 and 800°C are short and long with a low graphitization degree. At 700°C a forest of condensed CNTs is formed, whereas both carbon nanofibers and CNTs were formed at 750°C.

Novel Natural Gas to Liquids Processes: Process Synthesis and Global Optimization Strategies

An optimization‐based process synthesis framework is proposed for the conversion of natural gas to liquid transportation fuels. Natural gas conversion technologies including steam reforming, autothermal reforming, partial oxidation to methanol, and oxidative coupling to olefins are compared to determine the most economic processing pathway. Hydrocarbons are produced from Fischer–Tropsch (FT) conversion of syngas, ZSM‐5 catalytic conversion of methanol, or direct natural gas conversion. Multiple FT units with different temperatures, catalyst types, and hydrocarbon effluent compositions are investigated. Gasoline, diesel, and kerosene are generated through upgrading units involving carbon‐number fractionation or ZSM‐5 catalytic conversion. A powerful deterministic global optimization method is introduced to solve the mixed‐integer nonlinear optimization model that includes simultaneous heat, power, and water integration. Twenty‐four case studies are analyzed to determine the effect of refinery capacity, liquid fuel composition, and natural gas conversion technology on the overall system cost, the process material/energy balances, and the life cycle greenhouse gas emissions. © 2013 American Institute of Chemical Engineers AIChE J, 59: 505–531, 2013

Direct Conversion of Natural Gas to Petrochemicals Using Monofunctional Mo/SiO2 and H-ZSM-5 Zeolite Catalysts and Bifunctional Mo/H-ZSM-5 Zeolite Catalyst

The components of the standard catalyst globally used for natural gas direct conversion (6% Mo/H-ZSM-5) have been separately prepared and examined to represent: (a) monofunctional metallic component (6% Mo/SiO2) and (b) acidic component (H-ZSM-5 zeolite) to numerically investigate the extent of activity of each catalytic component in comparison to the activity of the standard catalyst in a fixed-bed flow-type reactor. The temperature and gas hourly space velocity are 700°C and 1500 mLg−1 h −1, respectively, which are very close to those used in the industrial gas conversion reactions. Time on stream up to 240 min was examined. The gaseous products were ethylene, propylene, and hydrogen, whereas the liquid products were benzene, toluene, and naphthalene. Carbon was also produced as deposited particles on the catalyst.

Molybdenum substitution by copper or zinc in H-ZSM-5 zeolite for catalyzing the direct conversion of natural gas to petrochemicals under non-oxidative conditions

This work aims to investigate the influence of substituting half the Mo content in a standard 6%Mo/H-ZSM-5 catalyst with either Cu or Zn in H-ZSM-5 support, on the direct conversion of methane in a flow-type fixed-bed reactor atmospherically at 700 °C at a gas hourly space velocity 1500 cm 3 h −1 g −1 and times-on stream (TOS) up to 240 min. The most active was 6%Mo/H-ZSM-5 catalyst while Mo–Zn/H-ZSM-5 was more active than Mo–Cu/H-ZSM-5. The XRD data showed that the crystallite (particle) sizes were found compatible with the catalytic activities. At the initial TOS (5 min), methane splitting selectivity to C and H 2 approached 100%. Higher carbon deposition on Mo–Cu catalyst caused more inhibition of ethylene further conversion to larger hydrocarbons thus leading to ethylene accumulation. TPR showed an almost complete reduction of Cu oxides at relatively lower temperatures such that the Mo–Cu catalyst acquired the highest dehydrogenation activity that enhanced markedly ethylene formation. An outstanding accomplishment is obtaining the highest benzene yield and selectivity using Mo–Zn/H-ZSM-5 catalyst, which is a prosperous challenge against the standard monometallic one. The large size of naphthalene molecule caused significant diffusion restriction on its formation in catalytic pores. The exceptional enhancement of naphthalene yield and selectivity at longer TOS using the Mo–Cu/H-ZSM-5 catalyst can be indicative that naphthalene was mostly formed on external zeolitic surface.

A single step methane conversion into synthetic fuels using microplasma reactor

Direct conversion of natural gas into synthetic fuels such as methanol attracts keen attention because direct process can reduce capital and operating costs of high temperature, energy intensive, multi-step processes. We report a direct and selective synthesis of organic oxygenates such as methanol, formaldehyde, and formic acid via methane partial oxidation at room temperature using non-thermal discharge microreactor. Heat generated by methane partial oxidation is removed efficiently in the microreactor configuration: liquid components are condensed on the reactor wall and separated from O 2-rich reactive plasma, enabling selective synthesis of oxygenates while high methane conversion is achieved in a single reactor. As a result, organic oxygenates were synthesized with one-pass yield of 5–20% with 70–30% selectivity. In addition to oxygenates, syngas was produced with selectivity of 40% and H 2/CO = 1. Assuming one step catalytic DME synthesis as a post-discharge process, one-pass liquid yield of 30% with 80% selectivity is feasible.

Trajetórias Tecnológicas em Combustíveis Sintéticos: análise dos mecanismos de seleção e indução

O artigo identifica e delimita a existência de duas trajetórias tecnológicas em combustíveis líquidos sintéticos. O conceito de trajetória tecnológica é delimitado em função do ambiente de seleção e dos programas de pesquisa tecnológica, sendo aplicável ao nível das tecnologias. A primeira trajetória tecnológica tem por ambiente de seleção as limitações econômicas e militares observadas pelos países não-produtores de petróleo, o que culminou com os embargos da Segunda Guerra Mundial. Os programas de pesquisa buscavam desenvolver as tecnologias Fischer-Tropsch, hidrogenação em alta pressão e LTC (low temperature carbonization). O ambiente de seleção da segunda trajetória é delimitado pelo aumento das reservas de gás natural, pelas restrições ambientais e pela demanda por flexibilidade na cadeia de gás e energia. Os programas de pesquisa têm por objeto de estudo o processo de produção do gás de síntese necessário ao processo Fischer-Tropsch. A conversão direta do gás natural para combustíveis líquidos sintéticos apresenta-se como a promessa de uma inovação radical. Por fim, o artigo compara as duas trajetórias, identificando aspectos comuns e diferenças entre elas.

METAL LOADED ZEOLITE CATALYSTS FOR THE DIRECT CONVERSION OF NATURAL GAS TO PETROCHEMICALS

ABSTRACTThe direct conversion of natural gas (methane) under non-oxidative condition to liquid fuels and chemicals of commercial importance is a process of prime importance. This process applies natural gas conversion to ethylene, benzene and little naphthalene via using fixed-bed flow reactor at 700oC, gaseous hourly space velocity (GHSV) of 1500 ml g-1 h-1 and at time-on-stream up to 240 min. This paper describes the data obtained using a catalysts prepared via impregnating the catalytic support (H-ZSM-5) with a molybdenum promoter (ammonium heptamolybdate) was compared with another catalyst prepared via mechanical mixing of Mo oxide powder with H-ZSM-5 zeolite. The data obtained reveal that the later catalyst is more active for benzene production throughout the whole time-on-stream range investigated. A Mo/SiO2 (monfunctional) catalyst was tested and found of very low activity, substantiating the necessity of combining with a zeolitic support with the Mo component. Moreover, the unloaded H-ZSM-5 was tested and found also less active. Comparing replacing H-ZSM-5 with H-BEA zeolite in the bifunctional catalyst shows the superiority of the former zeolite.

Transportation fuels and chemicals directly from natural gas: how expensive?

Natural gas provides intermediates for both the chemical and the transportation fuel industries. Although these industries face very different market constraints, a common research objective is the design of efficient processes for direct conversion of methane. New routes have emerged, such as oxidative coupling, which could be used to liquefy and transport economically remote gas. Oxidative coupling is also seen as an alternative to steam cracking for ethylene production in industrialized countries. Recalling several recently published process evaluations, we review the merits of oxidative coupling for direct conversion of natural gas in comparison to proven indirect technologies via synthesis gas. Also, attention is given to new routes based on natural gas for the production of chemicals currently derived from ethylene, such as vinyl chloride.

天然ガス有効利用技術

天然ガス有効利用技術

Thermal plasma reactor for the processing of gaseous hydrocarbons

An experimental thermal plasma reactor is developed to study the direct conversion of natural gas to liquid hydrocarbons. A preliminary theoretical study of the equilibrium composition and of the reaction kinetics underlined the need to maintain the reaction mixture at temperature in the range of 1300 to 1500 K for at least one second residence time in the reactor. While the relatively long residence time required is incompatible with standard plasma reactor technology, it was achieved by the combined use of a d.c. plasma torch for the rapid heating of the reaction mixture to the required temperature, and of resistive heating elements to extend the high temperature zone throughout the one-meter long tubular reactor.