Gas 2023 Issue

sector. Brazilian state-owned oil company Petrobras oper- ates a petroleum refinery in Rio Grande do Sul, Brazil, that produces about 1,500 tons per day of ammonia using the KAT process. As the demand for ammonia-based prod - ucts continues to increase, more refineries may explore the opportunities and benefits of producing ammonia. Hydrogen Despite the interest in blue hydrogen production from auto - thermal reforming and partial oxidation (ATR/PO) to produce blue hydrogen, steam methane reforming (SMR) is still the primary method of producing hydrogen (i.e., grey hydrogen) for refinery operations. However, the reaction is not always efficient, and several factors can affect the yield of hydrogen. However, increasing the yield of hydrogen from SMR units may be achievable with the following strategies: • Increasing the steam-to-carbon ratio (S/C) : The S/C ratio is the amount of steam required to react with one unit of car - bon in the methane. Increasing the S/C ratio can increase the yield of hydrogen by shifting the equilibrium towards hydro - gen production. However, the S/C ratio cannot be increased beyond a certain point, as it can lead to carbon deposition on the catalyst, reducing its effectiveness • Catalyst selection : The choice of catalyst used in SMR reactors can significantly affect hydrogen yields. Nickel- based catalysts are commonly used in SMRs. However, other catalysts, such as ruthenium and iridium, have shown higher hydrogen yields. The catalyst’s activity and selectivity depend on its structure, composition, and preparation method. One of the main advantages of using ruthenium and iridium catalysts in SMR is that they are highly selective, meaning they promote the desired reaction while minimising unwanted byproducts. Additionally, these catalysts have a long lifespan and can be used repeatedly, making them cost- effective and efficient catalysts for SMR processes. SMR challenges However, some challenges are associated with using ruthe - nium and iridium catalysts in SMR. These metals are expen - sive, about $6,250 per kg for iridium and about $16,500 for ruthenium. They are mainly found in the Norilsk region of Russia and, to a lesser extent, in South Africa, Zimbabwe, and Canada, which can increase the overall cost of the SMR process. Iridium may be somewhat more accessible. The largest iridium reserves are located in the Bushveld Igneous Complex in South Africa. Other countries with sig - nificant reserves include Russia, Canada, and the US state of Montana’s Stillwater Complex. Additionally, they can be sensitive to impurities and con - taminants in the reactant gas stream, which can degrade their performance and reduce their lifespan. Despite these chal - lenges, the use of ruthenium and iridium catalysts in SMR is a promising approach to increasing hydrogen yields in refinery processes. Ongoing research is focused on improving cata - lytic efficiency and reducing the cost of these catalysts to make them more widely accessible for industrial uses. Temperature and pressure are critical parameters that affect the SMR reaction’s equilibrium position. Increasing the reaction temperature and pressure can increase the yield

of hydrogen. However, these conditions can also promote undesirable side reactions, such as carbon deposition and methanation. Therefore, optimal temperature and pressure conditions must be carefully selected to maximise hydrogen production while minimising the formation of byproducts. Along with hydrogen and CO, the SMR reaction produces CO2, which is why there is so much interest in producing blue and green hydrogen, albeit still at insignificant levels (for green hydrogen), to benefit commercial refinery opera - tions. Removing CO2 from the reaction mixture can shift the equilibrium towards hydrogen production. Several methods, such as absorption, adsorption, and membrane separation, can be used to remove CO2 from the reaction mixture. The choice of method depends on the operating conditions and the desired purity of the hydrogen product. Long-term hydrogen alternatives Autothermal reforming (ATR) has emerged as a viable alter - native to SMR. ATR combines partial oxidation and steam reforming of hydrocarbons. The partial oxidation of hydro - carbons provides the energy required for the endothermic steam reforming reaction, resulting in higher energy effi - ciency. This leads to lower overall energy consumption and a higher yield of hydrogen per unit of feedstock. The ATR process has lower operating costs compared to SMR. ATR requires less steam than SMR, reducing the cost of steam production. Furthermore, ATR can use a wider range of hydrocarbon feedstocks, including natural gas, liq - uid petroleum gas, and naphtha, which can be cheaper than methane. This flexibility in feedstock choice can lead to cost savings for the process. The crucial advantage of ATR is that it produces fewer CO2 emissions than SMR. The partial oxidation of hydrocar - bons in ATR produces less CO2 than the complete oxidation of hydrocarbons in SMR. Carbon capture and storage (CCS) technology can also further reduce CO2 emissions in ATR. Hydrogen produced through ATR has a higher purity than that produced through SMR. This is because ATR produces less CO than SMR. CO is a common impurity in hydrogen pro - duced through SMR, and its removal requires additional pro - cesses. The high purity of hydrogen produced through ATR reduces the need for additional purification steps, reducing costs and improving process efficiency. By most standards, ATR is a highly scalable process that can be easily adjusted to meet the changing demands of hydrogen production. The process can be easily modified to increase or decrease hydrogen production, depending on the market demand. Conclusion Natural gas will continue to play a dominant role in supply - ing the world’s municipal heating requirements and power grids. In parallel, increasing volumes of natural gas produc - tion will be monetised through LNG, hydrogen, and ammonia production. All three products serve the fuels markets, but their potential commercialisation seems to be accelerating in areas benefiting the agricultural industry (fertiliser), pet - rochemical feedstocks (ethane to ethylene), and increasing needs for hydrogen in refinery operations for the production of near-zero sulphur products.

Gas 2023