Life cycle assessment for the direct synthesis of adipic acid in microreactors and benchmarking to the commercial process

A check on environmental sustainability of microreaction technology is given based on a new process idea as a study case, which is the direct synthesis of adipic acid (ADA) in a continuous flow process using a milli-packed bed reactor with micro-sized fluid interstices. Main aim is to determine impactful process parameters and to have a holistic idea of the environmental profile for this new process by means of life cycle assessment. Second main aim is to benchmark the flow process against conventional technology to produce ADA which takes place in two steps.Whereas the conventional process for ADA synthesis occurs in two steps from oxidation of cyclohexane by air followed by nitration oxidation, the direct route is from cyclohexene and uses hydrogen peroxide as oxidant. This results in higher ADA yield and simplified process with one step less. Drawbacks of the direct synthesis are long reaction time and increased safety issues, which can be overcome by using microreactors. The reaction rate is increased by the largely improved mass transfer and the use of higher temperature.Life cycle assessment (LCA) shows that for a number of impact categories the direct process is greener; yet there are also categories for which the conventional route is more environmentally sustainable. The results, analyzed from cradle to factory gate, shed some light on the truth and comprehensiveness of the statement frequently found in the literature, that H2O2 is a green oxidant because of atom economy and non-toxicity of water produced (Noyori et al., 2003; Grigoropoulo et al., 2003; Usui and Sato, 2003; Podgorsek et al., 2009; Edwards et al., 2005; Tse et al., 2005) [1-6]. Further, cooling energy plays also an important role for the environmental profile. In this way, fast decisions and recommendations for process variants in the newly designed route can be given and lead to a more focused research plan which is exemplified at the end of the paper

Kinetic study of hydrogen peroxide decomposition at high temperatures and concentrations in two capillary microreactors

On the background of the direct adipic acid synthesis from cyclohexene and H2O2, a kinetic model was derived for the H2O2 decomposition catalyzed by sodium tungstate at high H2O2 concentrations and high temperatures. A perfluoroalkoxy (PFA) and a stainless steel micro-flow capillary match commonly used microreactor materials. In the PFA capillary, the decomposition of hydrogen peroxide increased with residence time, reaction temperature and catalyst loading. The reaction order with respect to hydrogen peroxide and sodium tungstate was zero and one, respectively. Simulated data fit well with experimental data in the PFA capillary. While showing a similar trend as that in the PFA capillary, the stainless steel capillary exhibited much higher reaction rates. The steel surface participated in the decomposition process as a heterogeneous catalyst. Key influencing factors of the H2O2 decomposition provided some clues on the reaction mechanism of the adipic acid synthesis and its process optimization

High pressure direct synthesis of adipic acid from cyclohexene and hydrogen peroxide via capillary microreactors

The direct synthesis of adipic acid from hydrogen peroxide and cyclohexene was investigated in capillary microreactors at high temperature (up to 115°C ) and pressure (up to 70 bar). High temperature was already applied in micro-flow packed-bed reactors for the direct adipic acid synthesis. In our previous work we showed that the process suffered from unavoidable gas generation due to hydrogen peroxide decomposition when working at low pressure. Herein, we used a high pressure strategy to minimize hydrogen peroxide decomposition. Huge hotspots were observed inside a micro-flow packed-bed reactor under high pressure conditions. Capillary microreactors display a better heat transfer efficiency and thus may provide a better alternative for scaling-up. Consequently, capillary microreactors were selected for the reaction process with high pressure. One assisting element is the addition of phosphoric acid which is generally known to reduce the decomposition of H2O2. The use of phosphoric acid had a positive influence on the isolated yield. We could improve the yield further by increased interfacial mass transfer between the organic and aqueous slugs, when increasing the flow rate whilst keeping the same residence time. A further gain was given by using the of 2-stage temperature ramping strategy which we recently introduced for the micro-flow packed bed reactor. Applying all these aspects led to a maximum yield of 59% at 70-115 ˚C and 70 bar. The stabilizing effect of phosphoric acid on H2O2 is more obvious in a the 2-stage temperature ramping scenario as in a single-temperature operation. In addition, channel clogging by adipic acid precipitation in microreactor was observed. Therefore, several useful strategies were proposed to prevent the channel clogging at high temperature and high pressure

Liquid phase oxidation chemistry in continuous-flow microreactors

Continuous-flow liquid phase oxidation chemistry in microreactors receives a lot of attention as the reactor provides enhanced heat and mass transfer characteristics, safe use of hazardous oxidants, high interfacial areas, and scale-up potential. In this review, an up-to-date overview of both technological and chemical aspects of liquid phase oxidation chemistry in continuous-flow microreactors is given. A description of mass and heat transfer phenomena is provided and fundamental principles are deduced which can be used to make a judicious choice for a suitable reactor. In addition, the safety aspects of continuous-flow technology are discussed. Next, oxidation chemistry in flow is discussed, including the use of oxygen, hydrogen peroxide, ozone and other oxidants in flow. Finally, the scale-up potential for continuous-flow reactors is describe

Life cycle assessment for the direct synthesis of adipic acid in microreactors and benchmarking to the commercial process

A check on environmental sustainability of microreaction technology is given based on a new process idea as a study case, which is the direct synthesis of adipic acid (ADA) in a continuous flow process using a milli-packed bed reactor with micro-sized fluid interstices. Main aim is to determine impactful process parameters and to have a holistic idea of the environmental profile for this new process by means of life cycle assessment. Second main aim is to benchmark the flow process against conventional technology to produce ADA which takes place in two steps.Whereas the conventional process for ADA synthesis occurs in two steps from oxidation of cyclohexane by air followed by nitration oxidation, the direct route is from cyclohexene and uses hydrogen peroxide as oxidant. This results in higher ADA yield and simplified process with one step less. Drawbacks of the direct synthesis are long reaction time and increased safety issues, which can be overcome by using microreactors. The reaction rate is increased by the largely improved mass transfer and the use of higher temperature.Life cycle assessment (LCA) shows that for a number of impact categories the direct process is greener; yet there are also categories for which the conventional route is more environmentally sustainable. The results, analyzed from cradle to factory gate, shed some light on the truth and comprehensiveness of the statement frequently found in the literature, that H2O2 is a green oxidant because of atom economy and non-toxicity of water produced (Noyori et al., 2003; Grigoropoulo et al., 2003; Usui and Sato, 2003; Podgorsek et al., 2009; Edwards et al., 2005; Tse et al., 2005) [1-6]. Further, cooling energy plays also an important role for the environmental profile. In this way, fast decisions and recommendations for process variants in the newly designed route can be given and lead to a more focused research plan which is exemplified at the end of the paper

CEPC Technical Design Report -- Accelerator

International audienceThe Circular Electron Positron Collider (CEPC) is a large scientific project initiated and hosted by China, fostered through extensive collaboration with international partners. The complex comprises four accelerators: a 30 GeV Linac, a 1.1 GeV Damping Ring, a Booster capable of achieving energies up to 180 GeV, and a Collider operating at varying energy modes (Z, W, H, and ttbar). The Linac and Damping Ring are situated on the surface, while the Booster and Collider are housed in a 100 km circumference underground tunnel, strategically accommodating future expansion with provisions for a Super Proton Proton Collider (SPPC). The CEPC primarily serves as a Higgs factory. In its baseline design with synchrotron radiation (SR) power of 30 MW per beam, it can achieve a luminosity of 5e34 /cm^2/s^1, resulting in an integrated luminosity of 13 /ab for two interaction points over a decade, producing 2.6 million Higgs bosons. Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons, facilitating precise measurements of Higgs coupling at sub-percent levels, exceeding the precision expected from the HL-LHC by an order of magnitude. This Technical Design Report (TDR) follows the Preliminary Conceptual Design Report (Pre-CDR, 2015) and the Conceptual Design Report (CDR, 2018), comprehensively detailing the machine's layout and performance, physical design and analysis, technical systems design, R&D and prototyping efforts, and associated civil engineering aspects. Additionally, it includes a cost estimate and a preliminary construction timeline, establishing a framework for forthcoming engineering design phase and site selection procedures. Construction is anticipated to begin around 2027-2028, pending government approval, with an estimated duration of 8 years. The commencement of experiments could potentially initiate in the mid-2030s