How the petrochemicals industry can reduce its carbon footprint

Not all syngas CO2 emissions are the same

Syngas production uses steam methane reformer (SMR) technology to convert natural gas into a mixture of predominantly hydrogen and carbon monoxide – referred to as syngas. Syngas gets its name from its use as a building block for the synthesis of other chemicals including ammonia fertilisers, cleaner burning fuels for transport, ethylene, propylene and butadiene for plastic production, and commodity chemicals such as methanol.

Methanol is used to make thousands of products used in practically every aspect of our lives, including acrylic plastic, synthetic fabrics and fibres used to make clothing, adhesives, paint, and plywood used in construction, and as a chemical agent in pharmaceuticals and agrochemicals. Hydrogen can also be used to power fuel-cell cars and trucks, and will work alongside battery technology to drive the decarbonization of the transport sector.

Steam reforming is an endothermic process, which means that high levels of heat need to be supplied to drive the reaction; in the traditional SMR process this heat is generated by burning methane in a separate process stream, which produces CO2 resulting in a high carbon intensity for this process. Carbon capture and storage (CCS), in which the CO2 is captured and subsequently stored (for example in depleted oil and gas fields), can reduce the carbon intensity of the SMR process.

Unfortunately, this “post combustion” (Fired CCS) CO2 is generated as a dilute, relatively low pressure stream, making it tricky and relatively expensive to capture. The other significant source of CO2 comes from the process side reactions during syngas production, and the capture of this process CO2 (Process CCS) is less complex and costly as it has a more consistent composition, fewer impurities, and leaves the reactor at a favourable (high) pressure for capture using established solvent and absorbent-based technologies.

The good news is that there is a proven way to generate syngas at scale in which all the CO2 (Process CCS) comes out in a single stream at high pressure, making it easy and economical to capture with very high efficiency – 95% and above. Advanced reforming, utilizing Gas Heated Reforming (GHR), and Autothermal Reforming (ATR), has been used at industrial scale for decades, and removes the need for a separate stream of methane to be used to generate the temperature to drive the reactions. This in turn eliminates the dilute, low pressure outlet stream containing CO2 (Fired CCS). Using advanced reforming with CCS enables the production of hydrogen with a very low carbon intensity, which will keep this process relevant through to 2050 and beyond.

A further advantage of advanced reforming is that it uses the natural gas within syngas production more efficiently, leading to lower operating costs.

As part of this drive, the industry is looking at ways to make chemicals using renewable carbon sources, such as biomass, municipal solid waste and captured CO2. Combining this carbon with hydrogen generated by electrolysis powered by renewable electricity enables further carbon footprint reductions.

For example, captured CO2 and renewable hydrogen can be directly transformed into methanol, or can be converted within the reverse water-gas shift reaction to a syngas containing CO, CO2 and hydrogen, which can be further processed through well-established Fischer-Tropsch synthesis processes to make chemicals and fuels. This is one route to make drop-in fuels for planes – such as Sustainable Aviation Fuel (SAF) which is regarded as critical to assist the decarbonization of aviation. In addition, syngas-based technologies can be used to store and transport renewable energy in the form of methanol and ammonia and are being proposed as fuels for sustainable shipping.