biorefineries. Based on the feature of the platform that links feedstocks and final products, we can find several different biorefinery configurations: syngas, pyrolysis oil, sugars, oil, biogas, organic solutions, lignin, hydrogen, and power and heat. 12 In this refinery configuration, pretreatment of the feeds to protect catalysts is crucial, and in this sense the role of adsorbents is very important. Feeds that can be processed are vegetable oils and UCO (used cooking oil, animal fats, tall oil, and so on). In oils, we find phosphorus, metals, chlorine and other contaminants. Different adsorbents are used in different units in biorefineries, depending on the stream and the contaminant to be removed: resins, activated carbon, clays, silica gel and zeolites. 13 These refineries must also process pyrolysis oil feeds from plastic recycling. This oil contains various elements that were added to manufacture the plastic and must be now removed to protect the catalyst downstream. The challenge is to design catalysts that are resistant to all these contaminants.
CO
Zeolites
CH OH
H
Metal oxide
HCOO *
Hydrocarbon
CO + H
*
COOH
CH
CO
Noble and non-noble metals
Iron based catalysts
Figure 2 Conversion of CO 2 to hydrocarbons, different catalytic routes
O
H
+
H O
O + H
+
H
H
Platinum
Seawater
Figure 3 Floating prototype equipped with the single-atom platinum catalysts for solar light-triggered hydrogen production directly from seawater
Production of green hydrogen
Production of biofuels and circular economy Another critical role for catalysts and adsorbents is producing biofuels, as many refineries are converting to biorefineries to adapt to new regulations and process not only biomass but also prepare to process recycled materials. IEA Bioenergy Task 42 has developed a classification scheme to describe different
Green hydrogen is produced by the electrolysis of water, meaning the breakdown of water molecules into the two individual elements, hydrogen and oxygen, and only electricity from renewable energies is used. Since electrocatalysts are needed, research in this field is enormous, especially as analysts estimate that clean hydrogen could meet 24% of the world energy demand by 2050. 14
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