Biogas upgrading in palm oil mill effluent (POME)

Renewables play a key role in clean energy transitions and the deployment of renewable power is one of the main enablers of keeping the rise in average global temperatures below 1.5°C. According to the International Energy Agency, the share of renewables in global electricity generation reached 28.7% in 2021. Still, renewable electricity needs to expand faster to reach the milestones in the Net Zero Emissions by 2050 Scenario. 

Beside wind, water and sun, biogas is becoming increasingly important in today's renewable energy mix - quite rightly, because it is a highly efficient energy source and an important component of decentralized supply structures.

Palm oil is a very productive crop. Grown only in the tropics, the oil palm tree produces high-quality oil used primarily for cooking in developing countries. It is also used in food products, detergents, cosmetics and also as biofuel. Furthermore, palm oil offers a far greater yield at a lower cost of production than other vegetable oils.

The global production of and demand for palm oil is increasing rapidly. Although the expansion of palm oil industry has boosted the economies, it also concurrently generated abundant of by-products such as palm oil mill effluent (POME), empty fruit bunch, palm kernel shell and mesocarp fiber in palm oil mills during the processing of palm oil from fresh fruit bunch. Out of these by-products, POME still remained relatively untapped and will be a threat to the environment if directly discharged to the watercourse. Because POME containes high organic value it has a great potential for biogas production which is becoming increasingly important as part of the plant's efforts to manage its wastewater.

POME is the liquid waste generated from the oil extraction process from fresh fruit bunch in palm oil mills. For each tonne of crude palm oil (CPO) produced, it is estimated that 5–7.5 tonnes of water is used and more than 50% of water ends up as POME. This implies that about 2.5–3.75 tonnes of POME will be generated per tonne of CPO production.

In the past, POME has been usually treated via pond systems. Modern facilities today are equipped with technologies for capturing biogas. Most mills will either use the captured biogas for internal energy demand such as boilers or generate electricity. Excess biogas are usually flared. By upgrading these excess biogas into biomethane, it presents more economic value to mill operators.

Evonik's gas separation membrane SEPURAN® Green makes it possible to purify the biogas that accumulates during palm oil extraction process into high-purity biomethane and return it to the circular economy. The CO₂-neutral gas can be fed directly into natural gas grid or used as a green fuel Bio-CNG (Compressed Natural Gas) or Bio-LNG (Liquefied Natural Gas) to power vehicles.

Evonik's SEPURAN® Green membrane has been especially developed for efficient upgrading of biogas into high purity biomethane. The market entry of Evonik into the Biogas upgrading industry in 2011 revolutionized the market and set new technology standards. The introduction of a highly selective SEPURAN® Green membrane in combination with a patent protected 3-membrane-stage process allowed for high methane yields and high product purities with an optimized energy consumption.

Various technologies are available for separating CO₂ from the raw biogas and upgrading it to biomethane. In addition to wellknown technologies such as pressurized water scrubbing, amine scrubbing or pressure swing absorption, membrane technology has become increasingly established in recent years. Thanks to highly efficient and highly selective membranes, it is possible to separate CO₂ almost completely from methane in a compact 3-stage process.

Polyimide-based membranes are the most widely used membrane treatment systems. The advantage of membrane upgrading plants over conventional technologies lies, among other things, in the simplicity of the process and the low maintenance requirements. Of course, the spread of biogas upgrading plants is also influenced by local conditions and regulations as well as national incentives.