Influence of Impurities in a Methanol Solvent on the Epoxidation of Propylene with Hydrogen Peroxide over Titanium Silicalite-1

Abstract

The recycled methanol solvent of the HPPO (liquid-phase epoxidation of propylene and hydrogen peroxide to propylene oxide) process usually contains many kinds of trace impurities, such as fusel alcohol, aldehyde, ketone, ester, acetal, and amine. In this study, the influence of these impurities on the catalytic performance of titanium silicalite-1 (TS-1) in the liquid-phase epoxidation of propylene with H 2 O 2 was investigated with a batch reactor and simulated methanol solvents. The results show that amine and acetone are the most hazardous impurities, as they could remarkably suppress the conversion of H 2 O 2 . Furthermore, competitive adsorption experiments and IR and UV-Raman spectroscopic studies indicate that the suppression effect of impurities on the catalytic activity of TS-1 can be attributed to the competitive adsorption of the impurities on the tetra-coordination framework Ti sites. With this funding, the suppression mechanism of different impurities in a methanol solvent on the catalytic activity of TS-1 in the liquid-phase epoxidation of propylene was discussed.Catalysts 2020, 10, 15 2 of 14 or co-product issues. In fact, due to the highest active oxygen content and the formation of water only being a by-product, the use of H 2 O 2 as an oxidant is among the key aspects of modern Green Chemistry nowadays. For example, H 2 O 2 has become the primary oxidant in the selective oxidations of numerous organic substances, such as imines [20], olefins [21][22][23], and alcohols [24].In recent years, the HPPO process based on a TS-1 catalyst, as well as the H 2 O 2 oxidant and methanol solvent, has been industrialized by BASF and Dow, Evonik and Uhde, and Sinopec Changling Refining and Chemical. Nevertheless, the HPPO process still suffers from the use of a methanol solvent. One of the problems related to the methanol solvent is that, upon recycling, it accumulates dozens of trace impurities, such as fusel alcohol, aldehyde [25,26], ketone [27], ester [26,28], acetal [27], and amine [29,30], despite successive purification measures, including distillation, hydrogenation, and adsorption being employed [27,28,31,32]. It was believed that the trace impurities carried by the recycling of the methanol solvent were responsible for the accelerated catalyst deactivation and lowered PO selectivity. So far, however, little is known about the exact influence of each kind of impurity on the catalytic performance of the TS-1 zeolite catalyst in the liquid-phase epoxidation of propylene with H 2 O 2 .Therefore, in this study, a systematic investigation was carried out to understand the influences of different impurities in a methanol solvent on the catalytic performance of TS-1. This was accomplished by using simulated methanol solvents that contained a single impurity each time they were selected from the fusel alcohol, aldehyde, ketone, ester, acetal, and amine. Competitive adsorption experiments, as well as an FT-IR (Fourier-transform infrared) and UV-Raman spectroscopic study, were also carried out to understand the...

Liquid-Phase Epoxidation of Propylene with H2O2 over TS-1 Zeolite: Impurity Formation and Inhibition Study

“…In the foregoing investigations, trace impurities like acetals and esters, which have been observed in the commercial HPPO process where recycled methanol solvent was used, were not detected. However, in our previous epoxidation study, acetals were once detected in the products when the methanol that contained acetaldehyde, propionaldehyde, or acetone impurities was used as a solvent. This means that the trace impurities carried by the recycled methanol solvent in the commercial HPPO process might promote the formation of some vital impurities.…”

“…According to the investigation in Sections 3.1 and 3.2, the reaction network of the liquid-phase epoxidation of propylene and H 2 O 2 over the TS-1 zeolite is summarized, as shown in Scheme 1. According to our previous study, 57 the recycled methanol solvent of the HPPO process would contain a small amount of formaldehyde, acetaldehyde, propionaldehyde, acetone, formic acid, and acetic acid. Therefore, the side reactions triggered by the added aldehydes, ketones, and carboxylic acids are included.…”

“…As a result, they increase not only the technological complexity and energy consumption of the HPPO process, 50−56 but also the deactivation rate of the TS-1 catalyst. 57 Obviously, efforts to know more about the formation of these trace impurities and to access effective methods to inhibit their formation are definitely necessary for a better HPPO process. Unfortunately, to the best of our knowledge, there have been a few studies related to this topic until now.…”

“…In addition to the ring-opening byproducts, dipropylene glycol (DPG) and dipropylene glycol monomethyl ether (DPGME) were supposed to form via the condensation of PO with PG and 2M1P during epoxidation. , Besides, many patents provided methods for the removal of trace impurities such as aldehydes, − ketones, ,− ,, esters, ,,, and acetals. , Unlike the ring-opening byproducts that are generally easy to be cut out as tower bottom fractions, it is very difficult to get rid of these trace impurities from both the recycled methanol solvent and the crude PO stream. As a result, they increase not only the technological complexity and energy consumption of the HPPO process, − but also the deactivation rate of the TS-1 catalyst . Obviously, efforts to know more about the formation of these trace impurities and to access effective methods to inhibit their formation are definitely necessary for a better HPPO process.…”

Greening Oxidation Catalysis: Water as a Solvent for Efficient Alkene Epoxidation over a Titanosilicate/H2O2 System

“…Titanosilicate-catalyzed epoxidation of alkenes involving hydrogen peroxide (H 2 O 2 ) as the oxidant is a vital route for the production of epoxides, following the principles of green carbon science. , It is an environmentally benign chemical process that avoids equipment corrosion, environmental pollution, and low atom economy in the conventional chlorohydrin process. However, a limitation of this epoxidation reaction in terms of sustainability is the use of volatile and toxic solvents, such as methanol (MeOH) or acetonitrile (MeCN). − One of the problems related to organic solvents (e.g., MeOH) is that it generates a series of trace impurities from the side reactions (Scheme S1), resulting in the deactivation of the catalyst and the reduced selectivity of epoxides. , …”