Review of co-processing of biocrudes in oil refineries

Liquid intermediates from pyrolysis and hydrothermal liquefaction (HTL) can be co-processed in petroleum refineries along with conventional crude oil.In open access articles in journals energy and fuel, A team from the VTT Technical Research Center in Finland, together with colleagues from the Pacific Northwest National Laboratory (PNNL) and the University of Ghent, outlines such co-processing options for bioliquids.

Both fast pyrolysis and hydrothermal liquefaction (HTL) are processes for producing liquid fuels from dry/solid or wet biomass.

• In fast pyrolysis, biomass is rapidly heated to about 500 °C in the absence of oxygen. After pyrolysis, the vapor is condensed into a dark brown Fast Pyrolysis Bio-Oil (FPBO). The main compound groups of FPBOs are water (20–25 wt %), carboxylic acids (~5 wt %), aldehydes, ketones, and furfurals (25 wt %), sugar-like substances (30–35 wt %), and A lignin-derived compound (20 wt %). The presence of these oxygen-containing unsaturated compounds limits the stability of FPBO during storage and reduces its miscibility with conventional fuels.

• In HTL, wet feedstock is liquefied in a high temperature (250-374 °C) and pressurized (4-22 MPa) water environment into a bio-crude. Alkaline conditions are typically used to modify the ionic medium and promote certain base-catalyzed condensation reactions. This can lead to the formation of aromatic oils. Compared to FPBO, the biocrude from HTL is more deoxygenated, has less dissolved water and is more hydrophobic. Biocrude is more viscous than FPBO, but less dense. The major compound groups identified in Biocrude include acids, alcohols, cyclic ketones, phenols, methoxyphenols, and more condensed structures such as naphthols and benzofurans.

Oxygen must be removed from FPBO and HTL biocrude to obtain a product with properties similar to those of fossil fuels. Oxygen removal is typically accomplished by three types of reactions:₂); decarbonylation (oxygen removal as CO); and hydrodeoxygenation (HDO, oxygen removal as H₂O). However, upgrading liquid intermediates can be problematic.

One attractive option for upgrading liquid intermediates from pyrolysis and HTL is to co-process them in oil refineries. The concept was first proposed by VEBA OEL (now part of BP) in 1995, but at the time it was not considered competitive compared to other biomass alternatives and crude oil. was not The advantage of this approach is the use of distributed pyrolysis and HTL plants that can be located close to the biomass production site. Only bio-crude is transported to centralized refineries, which reduces transportation costs due to the increased volumetric energy of the oil compared to the original biomass.

Many oil refineries have different configurations and product profiles such as fuels, chemicals and asphalt. Therefore, there are many possible locations for inserting the bio-crude into the refinery, depending on the nature of the bio-crude and the target product. Proposed supply locations for bio-crude in refineries are (1) prior to the pre-distillation stage where the bio-crude is not processed, and (2) part of the processing unit after a mild upgrade of the bio-crude. , or (3) is a finished product. Or near-finished fuel after a serious upgrade of bio-crude.

Inserting upgraded biocrude with petroleum fuel as the final fuel is the least risky for the refinery, and inserting it in the pre-distillation stage is the most risky. The greatest benefits for refineries are achieved when some processing units are introduced with biocrude after a mild upgrade. These processing units require both cracking and the ability to remove oxygen from the biocrude, and therefore the potential for co-processing in fluid catalytic crackers, hydrotreaters, or hydrocrackers. I have.

— Lindforth and others.

A potential refinery insertion point for bio-intermediates.lind force and others.

Co-processing can occur in a fluid catalytic cracker (FCC), hydrotreater, or hydrocracker. The authors point out that FCC units are more tolerant of oxygenates in biocrude because the catalyst is burned continuously in the regenerator.

Co-processing has so far been tested primarily on FPBOs. The first short-term trials to commercialize this technology were conducted at his Preem refinery in Sweden. Introducing less than 10 wt% bio-oil or HTL bio-crude in an FCC does not significantly increase coke yield or decrease gasoline yield.

The measured renewable carbon efficiency with 10 wt % bio-oil feed was close to 30 wt %.

Research on cohydrotreating and hydrocracking is very limited. During the co-hydroprocessing of stabilized bio-crude and fossil fuels, competition between HDS and HDO reactions was observed, resulting in higher sulfur content in the final product. Therefore, co-hydroprocessing of vegetable oil and bio-crude may be a better option to extend this fuel to also include lignocellulosic feedstocks. Cohydrocracking can be used as a second step in biofuel upgrades when molecular weight reduction is still required.

— Lindforth and others.

means

• Christian Lindfors, Douglas C. Elliott, Wolter Prins, Anja Oasmaa, and Juha Lehtonen (2022) “Collaborative processing of bio-crude in oil refineries.” energy and fuel Doi: 10.1021/acs.energyfuels.2c04238