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The influence of carbon dioxide and steam as activating agents on the porosity development of activated carbons produced from walnut shells was investigated. The study was made covering a wide range of burnoff (12−76%) and employing different temperatures and times: in carbon dioxide activation, 850 °C varying the activation time in the range 60−480 min, and in steam activation, 700, 850, and 900 °C (for 30−120 min). It was found that the gasifying agent has a profound influence on the activated carbon porosity development. First, steam is more reactive and produces, in general, activated carbons with greater N2 adsorption capacity. Second, the increase in the fraction of mesopores with activation time is more pronounced for steam. While steam generates micro-, meso-, and macropores from the early stages of the process, carbon dioxide produces highly microporous carbons, with broadening of the microporosity only for long activation times.

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The pyrolysis of almond shells residues were studied in nitrogen atmosphere in a laboratory fixed bed reactor. The influence of the temperature (300−800 °C) and the heating rate (5−20 K min-1) on the composition and properties of the different fractions were analyzed. As the temperature was increased a decrease in the char yield and an increase in the gas yield was observed. The oil fraction yield passed through a maximum at temperatures between 400 and 500 °C. The decline at higher temperatures was likely due to the strong cracking, which increased the gas yield. The increase of the heating rate leads to a slight decrease of the char and oil yields and an increase of the gas yield. The production varied in the ranges between 21.5 and 47.3% for char, 31−51.5% for oil, and 11.4−47.5% for gas, with a maximum higher heating value of 29.0 MJ kg-1, 14.1 MJ kg-1, and 15.5 MJ N-1 m-3, respectively. The char had a high fixed-carbon content (>76%) as well as a high heating value, and therefore it could be used as solid fuel, precursor in the activated carbons manufacture (specific surface area BET until 121 m2 g-1), or to obtain category-A briquettes. Aliphatic and aromatic hydrocarbons and hydroxyl and carbonyl compounds were the majority components of the oil fraction, which suggests their use as a source of chemicals of industrial interest. Also, it can be used as liquid fuel. The gas composition was identified as hydrogen, carbon monoxide, methane, and carbon dioxide and can be used to heat the pyrolysis reactor or to generate heat/electricity in a gas-turbine/vapor-turbine combined cycle.