Pyrolysis oil

Petroleum substitute
synthetic liquid fuel derived by pyrolysis from biomass

Pyrolysis oil, sometimes also known as bio crude or bio oil, is a synthetic fuel with limited industrial application and under investigation as substitute for petroleum. It is obtained by heating dried biomass without oxygen in a reactor at a temperature of about with subsequent cooling, separation from the aqueous phase and other processes. Pyrolysis oil is a kind of tar and normally contains levels of oxygen too high to be considered a pure hydrocarbon. This high oxygen content results in non volatility, corrosiveness, partial miscibility with fossil fuels, thermal instability, and a tendency to polymerize when exposed to air. As such, it is distinctly different from petroleum products. Removing oxygen from bio oil or nitrogen from algal bio oil is known as upgrading.

There are few standards for pyrolysis oil because of limited efforts to produce it. One of the few standards is from ASTM.

Pyrolysis is a well established technique for decomposition of organic material at elevated temperatures in the absence of oxygen into oil and other constituents. In second generation biofuel applications—forest and agricultural residues, waste wood, yard waste, and energy crops can be used as feedstock.

Algae may be subjected to high temperatures (~500 °C) and normal atmospheric pressures. The resultant products include oil and nutrients such as nitrogen, phosphorus, and potassium. There are numerous papers on the pyrolysis of lignocellulosic biomass. However, very few reports are available for algal bio oil production via pyrolysis. Miao et al. (2004b) performed fast pyrolysis of Chllorella protothecoides and Microcystis areuginosa at 500 °C, and bio oil yields of 18% and 24% were obtained, respectively. The bio oil exhibited a higher carbon and nitrogen content, lower oxygen content than wood bio oil. When Chllorella protothecoides was cultivated heterotrophically, bio oil yield increased to 57.9% with a heating value of 41 MJ/kg (Miao et al., 2004a). Recently when microalgae become a hot research topic as the third generation of biofuel, pyrolysis has drawn more attention as a potential conversion method for algal biofuel production. Pan et al. (2010) investigated slow pyrolysis of Nannochloropsis sp. residue with and without the presence of HZSM 5 catalyst and obtained bio oil rich in aromatic hydrocarbons from catalytic pyrolysis. Algal pyrolytic liquids separate into two phases with the top phase called bio oil (Campanella et al., 2012; Jena et al., 2011a). The higher heating values (HHV) of algal bio oil are in the range of 31−36 MJ/kg, generally higher than those of lignocellulosic feedstocks. Pyrolytic bio oil consists of compounds with lower mean molecular weights and contains more low boiling compounds than bio oil produced by hydrothermal liquefaction. These properties are similar to those of Illinois shale oil (Jena et al., 2011a; Vardon et al., 2012), which may indicate that pyrolytic bio oil is suited for replacing petroleum. In addition, the high protein content in microalgae led to a high N content in the bio oil, resulting in undesirable NOx emissions during combustion and deactivation of acidic catalysts when co processed in existing 10 crude oil refineries. Algal bio oil had better qualities in many aspects than those produced from lignocellulosic biomass. For example, algal bio oil has a higher heating value, a lower oxygen content and a greater than 7 pH value. However, upgrading towards the removal of nitrogen and oxygen in the bio oil is still necessary before it can be used as drop in fuels.

Hydrothermal liquefaction (HTL) is a thermal depolymerization process used to convert wet biomass into an oil—sometimes referred to as bio oil or bio crude—under a moderate temperature and high pressure of 350 °C (662 °F) and 3,000 pounds per square inch (21,000 kPa). The crude like oil (or bio oil) has high energy density with a lower heating value of 33.8 36.9 MJ/kg and 5 20 wt% oxygen and renewable chemicals. The HTL process differs from pyrolysis as it can process wet biomass and produce a bio oil that contains approximately twice the energy density of pyrolysis oil. Pyrolysis is a related process to HTL, but biomass must be processed and dried in order to increase the yield. The presence of water in pyrolysis drastically increases the heat of vaporization of the organic material, increasing the energy required to decompose the biomass. Typical pyrolysis processes require a water content of less than 40% to suitably convert the biomass to bio oil. This requires considerable pretreatment of wet biomass such as tropical grasses, which contain a water content as high as 80 85%, and even further treatment for aquatic species, which can contain higher than 90% water content. Per Algal HTL, the properties of the resulting bio oil are affected by temperature, reaction time, algae species, algae concentration, reaction atmosphere, and catalysts, in subcritical water reaction conditions.

Bio oil typically requires significant additional treatment to render it suitable as a refinery feedstock to replace crude oil derived from petroleum, coal oil, or coal tar. Tar is a black mixture of hydrocarbons and free carbon obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. or plants. Black liquor and Tall oil is a viscous liquid by product of wood pulp manufacturing. Rubber oil is the product of the pyrolysis method for recycling used tires.

Biofuels are synthesized from intermediary products such as syngas using methods that are identical in processes involving conventional feedstocks, first generation and second generation biofuels. The distinguishing feature is the technology involved in producing the intermediary product, rather than the ultimate off take. A Biorefinery is a facility that integrates biomass conversion processes and equipment to produce fuels, power, heat, and value added chemicals from biomass. The biorefinery concept is analogous to today's petroleum refinery, which produce multiple fuels and products from petroleum. Biodiesel is a diesel fuel derived from animal or plant lipids (oils and fats). A variety of oils can be used as biodiesel feedstock. Wood diesel. A new biofuel was developed by the University of Georgia from woodchips. The oil is extracted and then added to unmodified diesel engines. Either new plants are used or planted to replace the old plants. The charcoal byproduct is put back into the soil as a fertilizer. This biofuel can actually be carbon negative not just carbon neutral. Carbon negative processes decrease carbon dioxide in the air reversing the greenhouse effect not just reducing it. Algae fuels, can be produced from various types of algae, and are dependent on the technique and the part of the cells used, some species of algae can produce 50% or more of their dry weight in the form of oil. The lipid, or oily part of the algae biomass can be extracted and converted into biodiesel through a process similar to that used for any other vegetable oil, or converted in a refinery into "drop in" replacements for petroleum based fuels. Algaculture can use waste materials such as sewage and without displacing land currently used for food production.

Bio oil is a recent contender technique for carbon sequestration. Corn stalks are converted by pyrolysis into bio oil, which is then pumped underground.

Currently, bio oil has limited industrial uses. A reported application is in the production of zinc oxide as thermal source. In this use, the fuel has substituted heavy fuel oils as a biogenic source of heat. The bio oil is used in the kiln burners as a direct substitute with little to no change in the operational results. The fuel has higher water and oxygen content which makes a higher volumetric flow for the same heat capacity.