Development prospects of synthetic oil production from natural gas

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This post was last edited by lsl343952854 on 2014-10-10 18:15. The development prospects of synthetic oil produced from natural gas. GTL (Gas to Liquid) technology for producing synthetic oil from natural gas has been a topic of significant interest in the industry over the past few years. The authoritative American magazine Oil & Gas Journal has, for decades, reported on topics in five categories: petroleum refining, petrochemicals, natural gas processing, desulfurization, and pipelines. Recently, in order to keep track of the developments in hydrocarbon conversion technologies that are industrially viable in the field of GTL, a sixth category was added – synthetic natural gas. All this demonstrates clearly the great potential for market development and application of synthetic natural gas. Currently, GTL technology has progressed from the experimental stage to commercial application, and its unique advantages are earning it increasing favor among industrialists. Experts estimate that a large number of GTL products will soon flood the market, to the point that authorities in the oil industry are declaring that the era of GTL is upon us. Synthetic oil produced from natural gas is a type of clean fuel; its advantage lies in the fact that it contains no sulfur, nitrogen, nickel impurities, or other undesirable components such as aromatics. It meets the strict requirements of modern engines as well as the increasingly stringent environmental regulations, thus opening up a new pathway for the production of clean energy. Over the next 15 years, the production capacity of GTL plants is expected to increase to 45–67.5 million tons per year. According to statistics, there are already 10 GTL plants under construction or planned worldwide, with capacities ranging from 220,000 to 4.5 million tons per year. Currently, as oil prices remain high, it is expected that more GTL plants will be built worldwide. Therefore, both from the perspective of production technology and economic benefits, there are ample reasons to believe that the 21st century will see a peak in the development of synthetic oil produced from natural gas. 1 GTL production process The GTL production technology can be divided into two main categories: direct conversion and indirect conversion. Direct conversion processes do not require syngas production facilities, but the high stability of methane molecules during this process poses significant technical challenges. Several direct conversion processes that have been developed to date are not economically viable, and thus have not been commercialized yet. Indirect conversion mainly involves the production of syngas, which is then used to synthesize synthetic oil via the Fischer-Tropsch process. Compared to the direct method, the indirect process has lower operational costs, and it has thus become the widely accepted synthetic route. Its main process flow consists of four parts: syngas production, F-T synthesis, synthetic oil treatment, and reaction water treatment. A brief introduction to each of these main process units is as follows: 1.1 Syngas Production In the GTL process, the capital investment for the syngas production stage accounts for approximately 60% of the total investment, and its production costs make up around 60% of the total production costs. Therefore, reducing the capital investment and production costs associated with syngas production plays a decisive role in improving the economic efficiency of GTL. The main methods for syngas production currently include steam methane reforming (SMR), partial oxidation (POX), and autothermal reforming (ATR). The production of syngas via natural gas steam reforming is an endothermic reaction that requires a large amount of heat during the process, resulting in high energy consumption. This reaction is slow, and the production facilities need to be large-scale with high investment costs. The H/CO ratio of the syngas produced by this method is too high, generally exceeding 3/1 (when no CO2 is recovered), making it unsuitable as a feed gas for synthetic oil production. The catalytic partial oxidation of natural gas with pure oxygen is a mild exothermic reaction ； The reaction can be carried out at very high space velocities; the H2/CO ratio of the resulting syngas is generally lower than 2/1, with the reaction temperature ranging from 1,200 to 1,500°C. The autothermal conversion method is a new syngas production process that combines steam conversion and partial oxidation in a single step; it offers advantages such as low reaction temperature, low oxygen consumption, an H/CO ratio of 2/1, and a composition suitable for the production of synthetic oils. Among them, in the POX and ATR methods, the production of pure oxygen requires expensive investment in air separation equipment as well as high costs for oxygen production. To this end, Syntroleum improved the ATR process by using air in place of oxygen, thereby avoiding the need for pure oxygen production. Additionally, since the system is self-thermally balanced, a heat transfer system is not required, which makes the ATR reactor simpler and more compact. The water-to-carbon ratio is also lower than that of the traditional ATR process, resulting in a significant improvement in its economic efficiency. By selecting the appropriate water-to-carbon ratio, oxygen-to-carbon ratio, and reaction temperature, an ideal raw gas for synthetic oil can be obtained; however, this method has a low effective utilization rate of natural gas due to the inability to recycle the exhaust gases. Air Products has developed a new ion exchange membrane for syngas production (referred to as ITMSyn-gas); using this technology at temperatures above 700°C eliminates the need for oxygen production plants and other processes involved in syngas production. It is characterized by a high oxygen flow rate, and slurry reactors can be used to synthesize liquid hydrocarbons; it is reported that this technology can reduce costs by 25%. 1.2 FT Synthesis Process: A method for converting syngas into liquid hydrocarbons under the action of catalysts. It was invented in 1923 by German scientists Frans Fischer and Hans Tosch; it is commonly referred to as FT synthesis. Petroleum companies around the world have invested substantial resources in developing catalysts and processes for this synthesis, and significant progress has been made. Below, we will focus on the relevant processes employed by Exxon, Shell, Sasol, Syn-troleum, Rentech, and Intevep. 1.2.1 Exxon’s AGC-21 process: Exxon’s Advanced Gas Conversion for 21st Century technology, abbreviated as AGC-21 technology. Over the past 20-plus years, Exxon has invested $300 million in developing AGC-21 technology, holding 400 U.S. patents and 500 international patents related to this technology. A 3-year pilot plant test with a capacity of 200 barrels per day was carried out at the Baton Rouge refinery from 1990 to 1993; currently, Exxon claims to be able to design GTL plants with a daily production capacity of up to 50,000 barrels. The process involves the reaction of natural gas, oxygen, and water vapor in a nickel-based catalyst reactor to produce syngas with an H/CO ratio of approximately 2:1. Subsequently, under the action of a highly active cobalt-based catalytic system, an FT synthesis reaction takes place in a slurry bed reactor to yield an alkane mixture with a wide range of molecular weights. Finally, this mixture is subjected to fixed-bed hydroisomerization to be converted into liquid hydrocarbon products. 1.2.2 Shell’s SMDS process: Shell’s Middle Distillate Synthesis technology, abbreviated as the SMDS process, is considered to be the most successful example of GTL plants in the world today. The industrial plant for this process was successfully put into use in Malaysia in May 1993, with a total investment of 850 million dollars. Its production capacity is 12,500 barrels per day, and the capital cost per barrel per day is 68,000 yuan. The process involves using a shell-and-tube gasification technique to react natural gas, oxygen, and water vapor in a gasifier; the resulting syngas undergoes an F-T reaction in a tubular fixed-bed reactor equipped with cobalt-based catalysts to produce heavy paraffin. This paraffin is then subjected to hydrocracking and distillation to yield various liquid hydrocarbon products for sale. The facility has now been modified to enable the production of diesel, naphtha, high-quality paraffin, and other products. 1.2.3 Sasol’s SSPD process: The South African company Sasol uses coal as a raw material and the PT synthesis process to produce various types of oils. Since 1955, the company has operated three production facilities – Sasol I, Sasol II, and Sasol III – with a total construction cost of around $6 billion. These facilities are used for the large-scale production of synthetic oils and related products; currently, the company produces 7.1 million tons of oils and related chemicals each year. In 2001, sales amounted to $5.399 billion, with operating profits reaching $1.4 billion. The SasolSlurry Phase Distillate technology is abbreviated as SSPD process. It consists of three stages: the first stage is the conversion of natural gas into syngas, the second stage is the synthesis of paraffinic hydrocarbons in a suspended-bed reactor, and the third stage is the distillation of the intermediate fractions. Currently, Sasol has transferred its technology to South Africa’s Mossgas company, which has built a plant with a capacity of 1.24 million da to convert offshore natural gas into synthetic oil; it is the largest GTL plant in the world to utilize FT technology. 1.2.4 Syntroleum Process: Syntroleum Corporation was established in 1984 and has built two GTL demonstration plants. Syntroleum’s syngas production utilizes its own ATR process, in which air is used in place of oxygen for autothermal conversion to produce nitrogen-containing syngas, thereby achieving an H2/CO ratio that is nearly ideal for the desired reactions. The syngas is then passed once through a fluidized-bed reactor at a high space velocity without a recirculation loop, to directly synthesize liquid hydrocarbons with a certain chain length under conditions of 2.1–3.5 MPa and 190–232°C. This approach prevents the aggregation of N, reduces the need for a hydrocracking step, and also results in lower operating pressures. The Syntroleum process features a simple reactor structure, easy start-up and shutdown, and low investment, which helps to reduce costs. This technology is suitable for small-scale operations processing 5,000 barrels per day, or even as low as 2,500 barrels per day; the investment cost ranges from $12,000 to $27,000 per barrel per day. 1.2.5 Rentech: Since 1981, Rentech has been engaged in this processing technology; it uses suspended-reactor systems and iron catalysts to convert natural gas into liquid hydrocarbons. In 1992, the company built a pilot plant with a capacity of 250 barrels per day. Currently, Rentech is planning to convert a methanol plant with a capacity of 75,000 tons per year in Commerce, Colorado, USA, into a GTL plant with a production capacity of 1,000 barrels per day, producing diesel, kerosene, and paraffin. 1.2.6 Intevep: The company Intevep began developing the FT process in 1991. It uses a unique fluidized bed reactor that combines the advantages of both slurry reactors and tubular fixed-bed reactors, ensuring uniform mixing of the reactants without any backmixing. The catalyst particles used have a larger size than those in slurry reactors, allowing them to be easily separated from the product paraffin through the free space above the fluidized bed layer; this facilitates online catalyst loading and unloading. Since the catalyst particles are kept within the fluidized bed, a catalyst recovery system can be eliminated. At the same time, the syngas passes through the reactor once, with no gas recovery system in place. Intevep expects to commercialize its technology within the next two years. 1.3 Product separation and hydrogenation: The processing of synthetic oils involves subjecting paraffins and other synthetic oil products to hydrogenation, followed by product distillation, in order to obtain the products required by the market. The processing of synthetic oils follows basically the same procedures as those used for conventional oils; it is a highly mature process. Currently, Chevron has a strong competitive advantage in providing hydrogenation technologies specifically tailored for the GTL sector. 1.4 Treatment of reaction water: Water is a by-product of FT synthesis reactions, and it also contains various oxygen-containing hydrocarbons such as acids, alcohols, ketones, and aldehydes. These oxygen-containing hydrocarbons must be removed from the reaction water before it can be reused or discharged, in order to meet the requirements for use or disposal. The typical treatment method is to use a simple distillation system to remove most of the oxygen-containing compounds from the top of the tower (with the exception of acids), while the acids remain in the liquid at the bottom of the tower. Due to their small quantity, the oxygenated compounds at the top of the tower have no value for recovery and are generally sent to a heating furnace for burning. The bottom liquid from the tower, along with other wastewater from the facility, is sent to a biochemical wastewater treatment plant for treatment. 2 Factors promoting the development of natural gas synthetic oil 2.1 Resource advantages The world’s natural gas sector is facing opportunities to acquire more reserves. Currently, the proven global reserves of natural gas amount to 1.38×1014 m3, with potential reserves estimated at 2.52×1014 m3. Based on an annual natural gas consumption of 2×1012 m3, the currently proven reserves will last for 70 years, while the potential reserves will last for 126 years; together, they will suffice for 196 years. In addition, there is a large amount of coalbed methane available for use worldwide. Based on the current level of technology for converting natural gas into synthetic oil, approximately 1,900 m3 of natural gas can be used to produce 1 ton of oil. Based on the currently known proven reserves and potential reserves, it is possible to produce hundreds of millions of tons of synthetic oil. Energy experts around the world generally believe that the 21st century will be the century of natural gas. Around 2040, the world’s natural gas supply will exceed that of oil and coal, with natural gas’s share of primary energy rising from 24.5% today to 51% by 2040. The natural gas to synthetic oil (GTL) approach is becoming one of the optimal ways to make efficient use of natural gas. 2.2 Continuous progress in production technology: Since the early 1990s, research and development efforts in the GTL field have seen significant improvement. According to statistics, by the end of 2002, there were 2,639 patents worldwide related to the 1T process, of which 1,008 were granted between 1996 and 2002. The improved Fischer-Tropsch synthesis technology, which utilizes new catalysts and advanced reactors, helps to reduce the investment and operating costs of GTL plants; as a result, production costs are significantly lowered while production efficiency is greatly increased. The production cost of GTL is now competitive with the price of crude oil, injecting new economic momentum into the construction of natural gas refineries. 2.3 Rising oil prices As oil prices have recently risen to record highs of over $100 per barrel, analysts believe that the era of low oil prices may be over. This situation undoubtedly helps to enhance the economic viability of the GTL project. 2.4 Product upgrading: Natural gas-to-liquid (GTL) is the cleanest and highest-quality fuel. Currently, the global refining industry is facing the challenge of producing low-sulfur and ultra-low-sulfur gasoline and diesel to meet increasingly stringent environmental regulations. For example, the sulfur content in diesel in the EU will be reduced from 350 g/g to 50 g/g by 2005 and to 30 g/g by 2008, while the sulfur content in diesel in the United States will also be reduced from 500 g/g to 15 g/g by 2006. Diesel fuel produced by the Fischer-Tropsch process from natural gas has a sulfur content of less than 1 g/g, an aromatic content of less than 1%, and a cetane number of over 70. As fuel standards move toward zero sulfur content, GTL technology becomes more cost-competitive compared to the hydroprocessing methods currently in use. For lubricant products, the properties of natural gas synthesis oil base oils are similar to those of poly. It is similar to olefins (category IV base oils), but its production cost is 87% lower than that of polyα-olefins, showing a trend toward replacing polyα-olefins. 2.5 Requirements for flexibility in energy trade: Due to their high investment costs, natural gas transmission pipelines and LNG projects are generally built for specific users. Currently, many **natural gas markets are moving toward liberalization, and the aforementioned projects may struggle to secure stable long-term revenues due to an inability to obtain a sufficient number of long-term purchase contracts. For CTL projects, since the final product is essentially the same as conventional refined oil products, they have a significant advantage in terms of product sales flexibility. 3. The development prospects of natural gas-based synthetic oil in China: China once had a synthetic oil production facility with a capacity of 30 tons per year, which was brought online in the 1950s thanks to the efforts of domestic technicians. Subsequently, the Dalian Institute of Chemical Physics developed the 362-2 nitrided solder catalyst. On the basis of experimental successes in 50mm and 150mm sulfurization bed reactors, experiments were also conducted in three more sulfurization bed reactors with capacities of 600mm, 800mm, and 1,500mm; however, these operations were halted due to the development of the Daqing oil field. The Shanxi Coal Chemistry Institute of the Chinese Academy of Sciences has been engaged in research on coal-to-oil technology (using a process similar to CTL), and it is reported that significant breakthroughs have been achieved in the key technologies involved. China has become the world’s second-largest oil importer, with its oil imports exceeding 100 million tons last year. However, due to its limited oil resources and scarce natural gas reserves, the industrialization of gas-to-liquid technology (GTL) in China seems unfeasible. On the other hand, China has abundant coal reserves, and coal gasification technology makes it possible to apply GTL in this country by converting coal into gas, thereby providing the raw material needed for GTL processes. In fact, implementing coal conversion has been identified as one of the strategic priorities for China in addressing its energy challenges during development. At present, China’s largest coal company, Shenhua Group, will use Shell’s technology to build a coal-to-oil plant in Yijinhuoluo Banner, Ordos City, Inner Mongolia; this plant is set to begin operations in 2007 and will produce 1 million tons of oil products per year from coal. It will be China’s first plant to produce oil directly from coal. The 2008 Beijing Olympics explicitly adopted the slogan of a \"Green Olympics,\" and the widespread use of cars has made sustainable development in Chinese cities rely urgently on cleaner energy sources. Combining the technologies of gasification and natural gas to produce synthetic oil will open up new avenues for the development of a clean fuel market in our country.