Rethinking quantified methods for arsenic speciation and risk in a biowaste hydrothermal liquefaction system.

Controversy exists to quantify the fate and speciation of Arsenic (As). We investigated its characteristics by As-containing algae in various pH hydrothermal liquefaction (HTL) system, specifically via two classical methods, i.e. the European Community Bureau of Reference (BCR) and Wenzel's method. Solid residue immobilized 11.23-16.55% of As, and 88.07-82.44% was in aqueous by the pH regulators (e.g., CH3COOH, HCl, and KOH). ICP-MS and XRD analysis revealed that As (V) was converted into As (III) and As (0) in the solid residue, while the As (V) was mainly converted into As (III) in the aqueous phase during HTL. When the classified forms of As in solid residue are compared, Wenzel's method was more appropriate for dividing the bio-availability forms of As, whereas BCR was better for estimating the toxic-potential forms of As. Subsequently, pH regulators raised the risk of As in solid residue associated with the increasing of unstable forms. The amide was hydrolyzed to carboxylic acid with acidic additives, which weakened the reducing environment in the HTL process. In contrast, the amide was hydrolyzed to ammonia with the alkaline additives, which enhanced the reducing environment and increased the risk of As in products. This work provided a new insight in systematically evaluating the risk and speciation of As in HTL.

Hydrothermal liquefaction accelerates the toxicity and solubility of arsenic in biowaste.

Arsenic (As) is one of notorious metalloids due to its high toxicity to human beings and ecological system. Understanding its fate and speciation transformation mechanism during hydrothermal liquefaction (HTL) of microalgae is of crucial importance for the application of its HTL products. 80.0-96.7% of As in raw microalgae was migrated into the liquid phase (aqueous phase and biocrude oil) with the increase of reaction severity from 0.108 to 0.517. HPLC-ICPMS reveals that 67% of the As in microalgae accounted for As(V) with a concentration of 68.4 mg/kg. The other fractions in microalgae were primarily As(III) with a concentration of 36.3 mg/kg. Model compounds experiments illustrate that over 30% of the As(V) in feedstocks was unexpectedly converted into more soluble and toxic As (III). Hydrochar containing O-containing groups (e.g., aliphatic C-OH) was probably contribute to the reduction transformation of As(V) to higher toxic As(III). Meantime, the aqueous phase facilitated the reduction reaction via providing a reducing environment and serving as hydrogen donator. This study firstly revealed the speciation transformation of As(V) to As(III) during HTL of wastewater cultivated microalgae.

In Situ hydrochar regulates Cu fate and speciation: Insights into transformation mechanism.

Cu is one of the dominant heavy metals toxic to human health and environmental ecosystems. Understanding its fate and chemical speciation is of great importance for hydrothermal liquefaction (HTL) of Cu-rich hazardous streams. Herein, we investigated its evolution during the HTL of wastewater algae through ICP-MS, XRD, XANES, and EXAFS. Cu-cysteine complexes (51.5%) and Cu2S (40.4%) were the main components of Cu in algae, whereas the predominant form was CuS (70.9%) in 220 °C-hydrochar. Model compound experiments indicated that Cu-cysteine could be converted into CuS, while Cu2S was stable during HTL. However, Cu2S was partially converted into CuS in the hydrochar. Subsequently, the positive Gibbs free energy (36.8 KJ/mol) indicates that the oxidation from Cu+ to Cu2+ can't occur spontaneously. Furthermore, cyclic voltammograms demonstrated that hydrochar facilitated the oxidation of Cu2S due to its higher capability of electron acceptance. All these results prove that hydrochar serves as a catalyst for the conversion of Cu2S to CuS during HTL. This study firstly elucidated that Cu2S was oxidized into CuS in the presence of hydrochar, and Cu-cysteine was converted into CuS under HTL. This study provides a critical insight into the transformation mechanism of Cu during the HTL of hazardous streams.

Effect of Crystallization on the Catalytic Cracking Performance of Zeolite Socony Mobil-5.

In the research, zeolite socony mobil-5 (ZSM-5) catalyst was prepared by hydrothermal method and characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), NH3-temperature programmed desorption (NH3-TPD) and Brunauer- Emmett-Teller (BET). The catalytic products from Jatropha carcass L. oil were analyzed by gas chromatography-mass spectrometer (GC-MS). The effects of crystallization time and crystallization temperature on catalytic cracking performance of ZSM-5 were investigated. According to the results, the catalytic cracking performance of ZSM-5 was closely associated with its pore structure. When the crystallization time was 60 h and the crystallization temperature was 170 °C, ZSM-5 with optimal catalytic cracking performance was synthesized. Catalyzed by the optimal ZSM-5, Jatropha carcass L. oil showed the liquid conversion rate of 26.60% and the acid value of 1.24 mg KOH·g-1. The main catalytic products from Jatropha carcass L. oil included benzene (10.02%), methylbenzene (20.52%), o-xylene (14.45%) and p-xylene (6.59%).