Co-processing in refineries

Definition

Co-processing refers to the simultaneous conversion of biogenic residues and intermediate petroleum distillates in existing petroleum refineries for the production of renewable hydrocarbon fuels. In contrast to the now common blending of biofuels into the finished petroleum product, co-processing makes use of biomass within the processing of petroleum.

Co-processing technologies

The requirements for the biogenic feedstocks for co-processing are high. They must have reliable material properties in order to be able to process them together with fossil fuels in a petroleum refinery. Suitable for co-processing are semi-processed biogenic feedstocks, such as  pyrolysis oil or triglycerides such as vegetable oils, used cooking oils etc. Lignin and sugars can also be co-processed in existing petroleum refineries.

Co-processing involves cracking, hydrogenation, or other reformation of semi-processed biogenic oils and fats in combination with petroleum intermediates to obtain finished fuels, like diesel or gasoline.

The following refining processes may be suitable for co-processing:

• Thermal cracking – In this process, the long-chain hydrocarbons are heated under pressure to 450-800°C. Due to the heating, the hydrocarbon molecules started to vibrate and the hydrocarbon chains are subsequently broken. This process produces products with a high oxygen content, which actually is not desirable in the production of fuels.
• Catalytic cracking – In this case the cracking process occurs in the presence of a catalyst. This process removes the oxygen in the feedstocks via simultaneous dehydration, decarboxylation and decarbonylation. No additional hydrogen or energy is required. This saves costs and reduce GHG emissions. The usual temperatures for this process are 350-500°C. (pyrolysis oil, lignin, glycerol)
• Hydrocracking – This is also a catalytic process at high temperature and high pressure. Hydrocracking is relatively expensive, but the advantages, among others the good product quality, often prevail.  (triglyceride) 
• Hydrotreating – The conversion occurs trough decarboxylation, decarbonylation and hydro-deoxygenation. The required temperatures for this process are 300-350°C. (triglyceride)

Motivation

As an infrastructure (transport, storage, refinery) already exists, the low-carbon and renewable fuels can be produced and sold at economically competitive prices. It is expected, that the proportion of renewable raw materials can be up to 20%. However, research is still ongoing.

Certainly, co-processing can help to achieve the climate goals in respect to the transportation sector.

• The petroleum industry must save 6% of GHG emissions. With co-processing this goal can be achieved.
• If it is acknowledged that the biogenic amount of such fuels can contribute to the energy targets, co-processing helps to achieve the targeted amount of renewable energy in the transport sector.

In addition, co-processing can be comparably cost-effective.

Challenges

Since co-processing in refineries is still in the stage of research, related technologies still face some challenges. Among other things, the following problems occur: differences in the stability during storage and handling, water and oxygenated organic compounds in biogenic feedstocks can cause corrosion etc.