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Evaluation of co-processing of biocrudes in oil refineries


Liquid intermediates from pyrolysis and hydrothermal liquefaction (HTL) will be co-processed in an oil refinery together with typical crude oil. In an open-access paper within the journal Power & Fuels, a workforce from VTT Technical Analysis Heart of Finland, with colleagues from Pacific Northwest Nationwide Laboratory (PNNL) and Ghent College, gives an outline of co-processing choices for such bio-liquids.

Quick pyrolysis and hydrothermal liquefaction (HTL) are each processes for producing liquid fuels from dry/strong or moist biomass.

  • In quick pyrolysis, biomass is shortly heated to round 500 °C within the absence of oxygen. After pyrolysis, the vapors are condensed to offer a darkish brown quick pyrolysis bio-oil (FPBO). The main compound teams in FPBO are water (20–25 wt %), carboxylic acids (∼ 5 wt %), aldehydes, ketones, and furfurals (25 wt %), sugar-like materials (30–35 wt %), and lignin-derived compounds (20 wt %). The presence of those oxygen-containing unsaturated compounds offers FPBO restricted stability throughout storage and poor miscibility into typical fuels.

  • In HTL, moist feedstock is liquefied in a sizzling (250–374 °C) and pressurized (4–22 MPa) water atmosphere into biocrude oil. Usually, alkaline circumstances are used to switch the ionic medium to favor sure base-catalyzed condensation reactions, which might result in fragrant oil formation. Compared to FPBO, the biocrude from HTL is extra deoxygenated after which extra hydrophobic with much less dissolved water. The biocrude is extra viscous however much less dense than FPBO. The main compound teams recognized in biocrude embody acids, alcohols, cyclic ketones, phenols, methoxyphenols, and extra condensed constructions, like naphthols and benzofurans.

Oxygen have to be removing from FPBO and HTL biocrude to acquire a product with comparable properties in comparison with fossil fuels. Usually, the removing of oxygen takes place by way of three kinds of reactions: decarboxylation (oxygen removing as CO2); decarbonylation (oxygen removing as CO); and hydrodeoxygenation (HDO, oxygen removing as H2O). Upgrading the liquid intermediates will be problematic, nonetheless.

One engaging choice for upgrading the liquid intermediates from pyrolysis and HTL is to co-process them in an oil refinery. This idea was first advised by VEBA OEL (now a part of BP) in 1995, however at the moment, it was not seen as aggressive in comparison with different biomass alternate options in addition to compared to crude oil. The benefit of this strategy is using decentralized pyrolysis and HTL vegetation, which will be positioned close to the biomass manufacturing web site. Solely the biocrude is transported to a centralized refinery, which reduces transportation prices on account of the rise of the volumetric vitality of the oil in comparison with the unique biomass.

Many oil refineries have completely different configurations and product profiles, together with fuels, chemical compounds, and asphalt. There are due to this fact many potential places for inserting the biocrude in a refinery, relying upon the character of the biocrude and goal product. The proposed feeding places for the biocrude within the refinery are (1) earlier than the pre-distillation section with none remedy for the biocrude, (2) in a few of the processing models after delicate upgrading of the biocrude, or (3) with the completed or practically completed gas after high-severity upgrading of the biocrude.

Inserting of the upgraded biocrude with the petroleum fuels as completed fuels represents the bottom threat for the refinery, whereas inserting it on the pre-distillation section poses the best threat. The best profit for the refinery is achieved if the biocrude is launched in a few of the processing models after delicate upgrading. Each cracking and the aptitude to take away oxygen from the biocrude is required from these processing models, and due to this fact, co-processing may doubtlessly happen within the fluid catalytic cracker, hydrotreater, or hydrocracker.

—Lindfors et al.

Potential refinery insertion factors for bio-intermediates. Lindfors et al.


Co-processing may doubtlessly happen within the fluid catalytic cracker (FCC), hydrotreater, or hydrocracker. Within the FCC unit, the catalyst is constantly burned in a regenerator, and due to this fact, FCC models are extra tolerant to the oxygenates within the biocrudes, the authors word.

Co-processing has thus far been examined principally with FPBO; the primary short-term take a look at to commercialize the expertise has been carried out in Preem’s refinery in Sweden. Introducing lower than 10 wt % bio-oil or HTL biocrude within the FCC continues to be potential with out having a big enhance within the coke yield and discount within the gasoline yield.

The renewable carbon effectivity measured for the ten wt % bio-oil feeding has been near 30 wt %.

The analysis on co-hydrotreatment and hydrocracking is sort of restricted. Throughout co-hydrotreating of stabilized biocrude with fossil gas, a contest between HDS and HDO reactions was noticed, which resulted in the next sulfur content material within the ultimate product. Co-hydrotreatment of vegetable oils with biocrudes may due to this fact be a greater choice to increase this gas to include additionally lignocellulosic feedstocks. Co-hydrocracking could also be used as a second step in upgrading of biofuels if molecular weight discount continues to be wanted.

—Lindfors et al.

Assets

  • Christian Lindfors, Douglas C. Elliott, Wolter Prins, Anja Oasmaa, and Juha Lehtonen (2022) “Co-processing of Biocrudes in Oil Refineries” Power & Fuels doi: 10.1021/acs.energyfuels.2c04238

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