Two ongoing projects for clients involve building plants that will generate fuels – from solid waste and from natural gas. The environmental engineering work we do for these clients is – we believe – exceptionally important both to the growth prospects of our company and to our overarching company goal of helping foster a sustainable future for the world. We also believe that as part of our role as environmental stewards, it’s important to promote education in the areas of science, technology, and environmental engineering. For that reason, This 4-part series of short articles will explain the history and process of conversion of natural gas into usable fuels. First, let’s dive into the chemistry:
The Chemistry of Natural Gas into Usable Fuels
In theory, it is possible to convert any run-of-the-mill hydrocarbon, such as methane, which makes up about 85% of natural gas, into almost any other hydrocarbon. In fact, nature does this sort of thing all the time. Plants, comprised of many complex hydrocarbons, are converted through time, heat and pressure into crude oil, coal and natural gas. Plants themselves are chemical factories in miniature. Through photosynthesis, plants convert sunlight and carbon dioxide into complex sugars, cellulose and myriad other complex hydrocarbons with myriad physical and chemical properties. By adding in some nitrogen, oxygen and few other ingredients from the soil, plants can make proteins, oils, sugars, and in some cases, such as the nightshade plant, alkaloid poisons. Plants create chemicals that mankind refines into medicines and drugs. For example, morphine, nicotine, aspirin and caffeine are four plant supplied chemicals that directly impact man’s wellbeing, for better or worse. The conversion of natural gas into liquid fuels in our client projects is not nearly as complex as what is going on in that oak tree growing in your back yard.
In brief, the process goes something like this: methane from natural gas is partially oxidized, that is partially burned in a low oxygen environment to form carbon monoxide (CO) and hydrogen (H2). Water vapor is added as a source of additional hydrogen. Some of the CO reacts with the water vapor (the “water gas shift reaction”) to form hydrogen (H2) and carbon dioxide (CO2). The CO2 formed in the reaction is then stripped from the gas mixture. In some designs, direct steam reforming is used where water vapor is directly reacted at high temperature, with methane to form CO and H2. The CO and H2 are then pushed through a catalyst, which converts the two simple chemicals into larger molecules, typically alkanes, which are saturated hydrocarbons like methane or propane. The catalyst selected controls whether synthetic gasoline, diesel, jet fuel or paraffin waxes is produced.
Jump to part 2 of this series, Natural Gas Conversion: A Brief History