Conversion of refinery natural purge gases to liquid hydrocarbons in GTL loop with hydrogen-permselective membranes: An alternative to gas flaring M.R. Rahimpour * , A. Ghorbani, A. Asiaee, A. Shariati Chemical Engineering Department, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz 71345, Iran article info Article history: Received 29 January 2011 Received in revised form 24 April 2011 Accepted 25 April 2011 Available online 12 June 2011 Keywords: Natural gas Purged gas CO 2 emissions Gas flaring GTL loop Hydrogen-permselective membrane abstract One of the main issues facing mankind in this century is the global warming which is induced by the increasing concentration of carbon dioxide and other greenhouse gases in the atmosphere. A promising process for controlling the atmospheric CO 2 level is prevention of combustion in flares. In the present work, a novel GTL loop is proposed to convert the natural gas wasted by a gas refinery to higher molecular weight hydrocarbons. The process proposes an alternative method instead of conventional gas-burning flares, aims to minimize CO 2 emissions and produce liquid fuel such as gasoline. For this purpose, purged natural gas is converted to synthesis gas in a novel hydrogen-permselective membrane reactor with recycle stream and then it is converted to liquid fuel in Fischer-Tropsch membrane reactor. In this configuration, a loop is constructed by returning and mixing a portion of the product with the original feed through a recycle stream. This approach produces large amounts of higher molecular weight hydrocarbons, hydrogen production and decreases environmental impacts owing to purge gases emission. The simulation results of the aforesaid loop, show decrease in CO 2 emission rate with a value of 1/10 to that of flaring with production of 0.018 kgmol/s of hydrogen and more than 90 barrels per day of heavy fraction hydrocarbons containing gasoline and butane fraction for a specified value of (about 4 MMscfd) purge gases. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The increase in concentration of carbon dioxide and other greenhouse gases in the atmosphere since the industrial revolution have led to the serious irreversible changes in the global climate. Due to the global population growth and increase in living stand- ardsdespecially in developing countriesdthe greenhouse gas emissions will undoubtedly increase during the next years (Rahimpour and Alizadehhesari, 2009). Therefore, the petroleum industry has struggled with how to curb the age-old practice of burning the natural gas that often comes out of the earth along with crude oil. The controversial practice called flaring is a conventional method of disposing of purge gas in refineries. This method has been the source of much controversial debate as not only does it waste a considerable amount of valuable energy but also results in severe environmental problems in the petroleum and related industries (Tolulope, 2004). The ever -increasing shortage in non- renewable fossil resources on one hand and growing environ- mental concerns and toughening regulations on the other make radical changes in energy policies inevitable. Despite this, little progress has been made globally in reducing the total amount of natural gas burned off in flares. According to research by the World Bank’s Global Gas Flaring Reduction Partnership (GGFR), each year the equivalent of almost one third of Europe’s natural gas consumption is burned in flares, sending about 400 million tons of carbon dioxide (CO 2 ) into the aireroughly 1.5% of the global CO 2 emissions (Broere, 2008). Replacement by alternative methods of disposal appears to be the most plausible solution. Recent experience at Shell illustrates the various issues that companies have to deal with as they try to put out flares. Their issue in Nigeria is to gather gas from more than 1000 wells by building gas collection facilities at the oilfields and constructing an extensive pipeline network to carry the gas to an industrial facility where it is turned into liquid for transportation (Tolulope, 2004). Among the various alternatives of combustion, there has been an increased interest in the development of gas to liquid technologies recently. Such technologies play an important role in bringing gas to markets as both fuel and/or petrochemicals (Iandoli and Kjelstrup, 2007). The process, known as GTL, was based on three steps: first, reforming of natural gas into synthesis gas (catalytic partial oxidation, steam reforming and auto-thermal reforming); Second, catalytic conversion of synthesis gas into hydrocarbons; and third, * Corresponding author. Tel.: þ98 711 2303071; fax: þ98 711 6287294. E-mail address: rahimpor@shirazu.ac.ir (M.R. Rahimpour). Contents lists available at ScienceDirect Journal of Natural Gas Science and Engineering journal homepage: www.elsevier.com/locate/jngse 1875-5100/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jngse.2011.04.004 Journal of Natural Gas Science and Engineering 3 (2011) 461e475