Product
distributions in bio-crude, aqueous phase, and solid residue
were rigorously analyzed during the hydrothermal liquefaction (HTL)
of Chlorella sp. KR1 in order to optimize utilization
of energy and chemicals. A non-asphaltene (paraffinic) fraction in
the bio-crude, which can be readily upgraded to high-quality fuels
via a subsequent catalytic process, was mainly produced due to lipid
extraction. Above 170 °C, lipid extraction was almost complete,
and hence, the non-asphaltene content did not increase further with
increasing temperature. Carbohydrates could be extracted, mainly as
polysaccharides, in the aqueous phase at mild temperatures (<200
°C). At high temperatures (>200 °C), they decompose and
react with proteins via the Maillard reaction to form asphaltene (polycyclic
aromatics), which contains large amounts of heteroatoms such as N
and S. Although high-temperature carbohydrate conversion could yield
more bio-crude with high energy values, it dominantly contributed
to formation of the asphaltene fraction, which is difficult to upgrade
catalytically. As high-temperature HTL requires a large energy input,
the recovery and utilization of intact carbohydrates and proteins
at mild temperatures (<200 °C) appears to be more promising.
Energy Return on Investment (EROI) analysis also showed that 170 °C
is the optimum HTL temperature for maximizing the energy production.
Isobutane/butene alkylation is an important refinery process for producing high-octane gasoline components (e.g., trimethylpentane), in which highly caustic liquid acids (H 2 SO 4 and HF) are still predominantly used as catalysts. Zeolites are promising solid acid alternatives to such liquid acids but suffer from fast deactivation owing to the formation of bulky carbonaceous deposits within the micropores. In this study, a series of BEA zeolites with different secondary pore structures were synthesized to investigate the effects of facilitated molecular transport on trimethylpentane selectivity and catalyst deactivation. The results showed that the hierarchical BEA zeolite containing trimodal micro-/meso-/macroporosity synthesized by the pseudo-solid-state crystallization of diatomaceous earth exhibited significantly enhanced selectivity to trimethylpentane and catalytic lifetime. The highly promising catalytic properties of this zeolite could be attributed to enhanced diffusion of the hydride donor (isobutane) and bulky alkylate products to or from the zeolite micropores owing to the hierarchical pore structure. Upon supporting Pt, all zeolite catalysts could be efficiently regenerated by a hydrogenative treatment as long as they were regenerated before heavy coke formation. The hierarchical BEA zeolite with trimodal porosity required four times less frequent regeneration than an ordinary BEA zeolite containing only micropores. The remarkable catalytic performance of the hierarchical BEA zeolite will greatly contribute to the reduction of the operating costs of solid-acid-based alkylation processes.
A versatile process for coproducing green diesel and value-added lube base oil from natural triglycerides (e.g., vegetable oil, waste cooking oil, and microalgal oil) was developed. The twostep reaction process comprises (i) thermal oligomerization of triglycerides via Diels−Alder and/or radical-mediated addition of the CC bonds within the fatty acid units and (ii) catalytic deoxygenation of the oligomerized triglycerides via hydroupgrading. Different triglyceride sources, that is, palm oil, soybean oil, and linseed oil, were investigated as the starting feedstock. Thermal oligomerization of the triglycerides at 300 °C proceeded at the expense of the CC bonds within the unsaturated fatty acid units. Thus, the degree of triglyceride oligomerization was enhanced when the reactant triglycerides contained more unsaturated fatty acid units (palm oil < soybean oil < soybean + linseed oil < linseed oil). The oligomerized triglycerides were subsequently deoxygenated over a Pt-MoO x /TiO 2 catalyst, which converted the oligomerized and monomeric fatty acid units into lube base oil (C 30 −C 54 ) and green diesel (C 15 −C 18 ) fractions, respectively. The produced lube base oils were completely saturated with very high viscosity indexes (>120) and a nondetectable sulfur content, which could meet the specifications of high-quality group III lube base oil.
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