We live in a world full of colourful plastics. From tooth brushes to shopping bags and computers, we rely on plastic for countless everyday items. It’s even used to sole our shoes. In less than a hundred years, the use of synthetic polymers has exploded, making it the most commonly used material of our time. Polyethylene (PE) is a real all-rounder here. It is used in countless applications from flexible foils and food packaging through interior and exterior car fittings to children's toys, pipes and cables. Polyethylene is made up of countless interconnected ethylene molecules. This compound with two carbon atoms bound to four hydrogen atoms is one of the most important building blocks in the chemical industry: Around 180 million tonnes of ethylene are consumed each year – and demand is steadily rising at a rate of three to four percent annually.
Highest value creation: Oxidative Coupling of Methane (OCM) pilot plant in La Porte, USA.
Successful results with a new catalyst and process - “Gemini”
For the downstream petrochemical industry, ethylene is one of the most important building blocks, with an annual demand growth of 3 to 4 percent. For example, plastics such as polyethylene are produced by polymerization of ethylene. The predominant process route for ethylene production is steam cracking of C2+ hydrocarbons. However, methane (C1) as a cheap, alternative feedstock from abundant conventional or unconventional gas resources cannot be converted to ethylene through steam cracking.
Production of ethylene from methane using an integrated, multi-stage process comprising of synthesis gas generation, methanol production and MTO (= Methanol-To-Olefins, i.e. ethylene and propylene) has not materialized so far due to hefty capital investment requirements and related poor project economics. US start-up Siluria has now changed that by finding a suitable catalyst and, together with Linde Engineering, developing an economically viable process called “Gemini”. The Gemini process is based on the Oxidative Coupling of Methane (OCM), a catalyst mediated reaction that converts methane, in the presence of oxygen, to ethylene.
Effectively harnessing reaction heat
In the first reaction step, methane and oxygen must be fed uniformly to the OCM catalyst. The catalyst converts these to ethylene and also produces small amounts of ethane, which can then be converted to ethylene in a second reaction section. In this second section, additional ethane and propane can also be injected and converted to ethylene. This process is powered by the heat released during the first reaction step. OCM technology is a particularly attractive option for regions that have access to low cost natural and natural gas liquids such as ethane and/or propane.
From pilot plant to commercial viability
Building on its wealth of experience in ethylene generation, Linde Engineering joined forces with Siluria Technologies to advance the new process to industrial-scale commercial maturity. The two companies complement each other perfectly with their expertise: The start-up developed the innovative OCM catalyst and accompanying reaction unit, while Linde focused on integrating this reaction unit into commercially viable plant concepts, including the requisite product separation and purification processes. “The need to mix hydrocarbons with oxygen and reach reaction temperatures of up to 900°C are challenging process conditions for the OCM catalyst and the reactor unit,” explains Florian Penner, Head of Product Management at Linde. “But Siluria’s demonstration plant in La Porte, Texas, with a capacity of approx. 400 tonnes of ethylene per year, has confirmed excellent and stable process performance since its initial start-up in 2014.” Commercial readiness of the technology was demonstrated at the end of 2016. The experts at Linde Engineering now want to explore project opportunities with prospective customers.
Flexible design with great potential
The development collaboration between Linde and Siluria has resulted in novel process applications that enable ethylene to be efficiently produced from natural gas. The plant design is flexible, supporting capacities ranging from 30 to 1,000 kilotonnes of ethylene per year. The entire OCM process is designed to deliver maximum added value to customers.
Linde has already successfully integrated OCM reaction technology into commercial-scale applications, including product separation and purification. “In addition, the process consumes considerable quantities of oxygen. So it also creates interesting follow-on opportunities for Linde’s air separation business and for Linde Gas,” adds Ernst Haidegger, Head of Technology & Operations at Linde Petrochemical Plants, highlighting the potential for future projects.