Background

“We cannot solve our problems with the same thinking we used when we created them” – Albert Einstein

Rigg

The world’s vast reserves of natural gas offer perhaps the best opportunity to reduce our dependency on crude oil. However, the physical and chemical properties of natural gas prevent it from being directly interchangeable with oil, thus new technology will be required to allow natural gas to reach its potential.

Methane, the primary constituent of natural gas, is the simplest hydrocarbon molecule, consisting of a single carbon atom bound to 4 atoms of hydrogen. In contrast, liquid transportation fuels, such as gasoline and diesel, consist of mixtures of hydrocarbon molecules, typically containing 5 to 12 (gasoline) and 8 to 14 (diesel) carbon atoms, respectively. The larger hydrocarbons found in transportation fuels impart the desirable properties (energy dense, stable liquid, etc.) that give existing fuels their value.

Natural gas, being far less dense than crude oil, is inherently more expensive to move from source to market. The transportation of natural gas is currently limited to 1) compression and delivery in dedicated pipeline systems, or 2) liquefaction and shipment as Liquefied Natural Gas (LNG).The cost-effective chemical transformation of natural gas into a liquid or other higher value product has been a longstanding goal of the petroleum and petrochemical industries. The few technologies that do exist (often categorized as “Gas to Liquids” or GTL Processes, even if the high value product is remains as gas) are very capital intensive, requiring massive facilities operating on a scale economy basis and relegating the technology only to the largest gas fields. Consequently, the natural gas found in smaller gas fields is often flared or vented because there is no economic means to bring it to market.

F-T Process

Any process using natural gas as feedstock must overcome the intrinsic stability of methane. Indeed, it is the non-reactive nature of the methane molecule that has proven to be the largest impediment to producing high value products from natural gas.

The most prominent GTL process is known as Fischer-Tropsch (FT), initially developed in Germany between the two World Wars. Originally used to produce synthetic crude oil from coal, the process has been modified to use natural gas as a feedstock. The FT Process consists of multiple steps, the first of which is referred to as reforming and entails the partial oxidation of natural gas with oxygen to form synthesis gas or “syngas”, a mixture of carbon monoxide (CO) and hydrogen (H2). In a subsequent step, the syngas is reacted over a catalyst to produce synthetic crude oil, which in turn can be refined into different hydrocarbon products. The actual process is quite complex, requiring extremes of temperature and pressure, especially in the reforming step, and is energy intensive. In spite of the cost, complexity and unfavorable energy requirements, the process appears economically feasible at large scale. Companies such as Shell and Sasol have recently constructed large FT facilities, all in the massive gas fields of the Middle East.