Polyoxymethylene dimethyl ethers (CH3–O–(CH2O)n–CH3, PODEn) are potential environmentally benign coal-based diesel fuel blending compounds. They are synthesized from dimethoxymethane (DMM) and paraformaldehyde (PF). Among the PODEn homologues, PODE3–4 have a good match with diesel as a fuel, while the undersized PODE1–2 and oversized PODEn>4 have unsuitable properties. This work studied the molecular size reforming of undersized PODE1–2 and oversized PODEn>4 by two different methods, namely, self-reforming and reacting with DMM over an acidic ion exchange resin. The molecular size reforming of PODE1–2 and PODEn>4 by self-reforming gave a high concentration of formaldehyde, which shifted the distribution to longer chain PODEn and formed solid PF. In contrast, PODE1–2 and PODEn>4 were mainly converted to PODE3–4 by the reaction with DMM and the high concentration of formaldehyde was also diminished. The equilibrium reorganized molecular size distribution of PODE1–2 and PODEn>4 followed the Schulz–Flory distribution. A proposed kinetic model described well the molecular size reforming pathways of PODE1–2 and PODEn>4. A methanol-to-PODEn close-loop process was proposed to enhance atom-economy by recycling the PODE1–2 and PODEn>4 streams.

Plant oil asphalt (POA) is an underutilized lipid-based biomass residue mainly generated in the biodiesel industry. This work presents application of the lumping strategy in kinetic modeling of vacuum pyrolysis of POA in a pilot-scale semi-batch reactor. Pyrolysis experiments were conducted under different reaction temperatures (410, 430, and 450 °C) and reaction times (10, 15, 20, 25, 40, 50, and 60 min). The reaction scheme was divided into five lumps, namely, feedstock lump (POA) and four pyrolytic product lumps (including biogas, biochar, hydrocarbon components in pyrolytic oil, and oxygenated components in pyrolytic oil). In the kinetic model, reactions from the feedstock lump to the four pyrolytic product lumps were assumed to be independent parallel, while the secondary reactions between four pyrolytic product lumps were neglected because of the short residence time of the pyrolytic vapor in the pyrolysis zone. Results showed that four independent parallel reactions all followed first-order kinetics. The kinetic model estimated the Arrhenius parameters and showed high capability to predict the concentration of pyrolytic product lumps, especially the relative distribution of hydrocarbon components and oxygenated components in pyrolytic oil.

Plant oil asphalt (POA) is a new concerned lipid-based residue biomass generated from the oleochemical industry. In this work, the pyrolysis kinetics of POA was studied by thermogravimetric analysis at heating rates of 7, 10, 20, and 30 K min–1 under a nitrogen atmosphere using the distributed activation energy model (DAEM). The kinetic parameters, including the activation energy E, distribution function of activation energy f(E), and pre-exponential factor k0, were obtained. The activation energy E ranged from 75 to 300 kJ mol–1, and the f(E) curve showed a broad peak around 155–200 kJ mol–1. The linear relationship between ln k0 and activation energy E indicated that there existed a kinetic compensation effect in pyrolysis of POA. A double-Gaussian DAEM was employed for simulation of POA pyrolysis by assuming POA as a mixture of two pseudo-components. In comparison to the single-Gaussian DAEM, the double-Gaussian DAEM was better to predict the pyrolysis behavior of POA. This work validated the applicability of the double-Gaussian DAEM to the lipid-based material POA.

The promoter effects of Zn and Sn in the direct synthesis of methylchlorosilanes were studied using a stirred bed. Zn and Sn were introduced not only before but also during the reaction. The activity and selectivity were characterized by online GC analysis and correlated with the Cu3Si content that was measured by the leaching method. It was found that Zn enhanced the formation of Cu3Si when it was added before the reaction. Zn improved the selectivity for dimethyldichlorosilane, but the excess Zn deactivated the reaction. Sn accelerated the consumption of Cu3Si. Added during the reaction, Sn led to a drastic reduction of Cu3Si coupled with a temporary rise in the formation of dimethyldichlorosilane. These results provided a new explanation for the role of promoters and suggested that the regulation on the direct synthesis process is probably due to the trade-off between the production and consumption of Cu3Si.

A bi-component catalyst comprising CuCl and metallic copper was used in the direct synthesis of methylchlorosilane to study the catalytic synergy between the different copper sources. The catalyst exhibited high activity and high selectivity of dimethyldichlorosilane (M2) in the stirred bed reactor. The effect of the proportion of CuCl used was studied and 10%-30% CuCl gave the best yield of M2. The use of CuCl decreased the induction period of reaction, improved the selectivity in the induction stage, and gave a longer stable stage. These results suggest that bi-component catalyst has advantages in the direct synthesis reaction.

To enhance the process of phenyltrichlorosilane synthesis using gas phase condensation, a series of chloralkanes were introduced. The influence of temperature and chloralkane amount on the synthesis was studied based on the product distribution from a tubular reactor. The promoting effect of chloralkane addition was mainly caused by the chloralkane radicals generated by the dissociation of C–Cl bond. The promoting effect of the chloromethane with more chlorine atoms was better than those with less chlorine atoms. Intermediates detected from the reactions with isoprene and bromobenzene demonstrated that both trichlorosilyl radical and dichlorosilylene existed in the reaction system in the presence of chloralkanes. A detailed reaction scheme was proposed.To enhance the process of phenyltrichlorosilane synthesis using gas phase condensation, a series of chloralkanes were introduced. The influence of temperature and amount of chloralkane on the synthesis was studied based on the product distribution from a tubular reactor. The promoting effect by addition of chloralkanes was mainly caused by the chloralkane radicals generated by dissociation of the C–Cl bond. The promoting effect of the chloromethane with more chlorine atoms was better than those with less chlorine atoms. Intermediates detected from the reactions with isoprene and bromobenzene demonstrated that both trichlorosilyl radical and dichlorosilylene existed in the reaction system in the presence of chloralkanes. A detailed reaction scheme was proposed.Download full-size image