We use a high-pressure semicontinuous batch electrochemical reactor with a tin-based cathode to demonstrate that it is possible to efficiently convert CO 2 to formic acid (FA) in low-pH (i.e., pH < pK a ) electrolyte solutions. The effects of CO 2 pressure (up to 50 bar), bipolar membranes, and electrolyte (K 2 SO 4 ) concentration on the current density (CD) and the Faraday efficiency (FE) of formic acid were investigated. The highest FE (∼80%) of FA was achieved at a pressure of around 50 bar at a cell potential of 3.5 V and a CD of ∼30 mA/cm 2 . To suppress the hydrogen evolution reaction (HER), the electrochemical reduction of CO 2 in aqueous media is typically performed at alkaline conditions. The consequence of this is that products like formic acid, which has a pK a of 3.75, will almost completely dissociate into the formate form. The pH of the electrolyte solution has a strong influence not only on the electrochemical reduction process of CO 2 but also on the downstream separation of (dilute) acid products like formic acid. The selection of separation processes depends on the dissociation state of the acids. A review of separation technologies for formic acid/formate removal from aqueous dilute streams is provided. By applying common separation heuristics, we have selected liquid−liquid extraction and electrodialysis for formic acid and formate separation, respectively. An economic evaluation of both separation processes shows that the formic acid route is more attractive than the formate one. These results urge for a better design of (1) CO 2 electrocatalysts that can operate at low pH without affecting the selectivity of the desired products and (2) technologies for efficient separation of dilute products from (photo)electrochemical reactors.

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In this research, the separation of Li, Ni, and Co by solvent extraction was studied from synthetic Li-ion battery waste leachate. The purpose was to propose a process for producing all the metals with over 99.5% purities, as the purity demands for battery grade metals are high. Emphasis was also placed on obtaining pure Li raffinate in the early stage of the process, as societal interest in Li is growing rapidly. Thus, the purpose was to first extract Co and Ni selectively yielding pure Li raffinate, and consequently separating Co and Ni as pure products in the stripping stage. The equilibrium behavior of the separation system was studied by constructing the pH isotherms as well as loading and stripping isotherms. Bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) and (2ethylhexyl)phosphonic acid mono-2-ethylhexyl ester (PC-88A) were used as extractants, both as unmodified and modified with 5% v/v TOA or TBP. Based on the equilibrium results, bench-scale continuous counter-current separation experiments were designed and conducted using 1.0 M Cyanex 272 modified with 5% v/v TOA. Co and Ni were loaded in two stages from the sulfate feed solution containing 2.8 g/L of Li, 14.4 g/L of Co, and 0.5 g/L of Ni. In this step, over 99.6% yields for Co and Ni were achieved, giving 99.9% pure Li raffinate. However, 17-26% of Li was co-extracted, but efficient scrubbing with NiSO4 was designed with equilibrium experiments and demonstrated in continuous operation. In the stripping step, 99.5% pure aqueous Ni solution and 99.2% pure organic Co solution were obtained using two counter-current stages. Adding one more stage increased the Ni and Co purities to 99.7 and 99.6%, respectively. In addition to the high purities of the metals, the suggested process has fewer process steps compared to previously suggested flowsheets for similar fractionation.

The activity of a commercial NiMo hydrotreating catalyst was investigated to convert distilled tall oil (DTO), a byproduct of the pulp and paper industry, into feedstocks for the production of base chemicals with reduced oxygen content. The experiments were conducted in a fixed bed continuous flow reactor covering a wide temperature range (325−450 °C). Hydrotreating of DTO resulted in the formation of a hydrocarbon fraction consisting of up to ∼50 wt % nC 17 +C 18 paraffins. Comprehensive 2D GC and GC−MS analysis shows that the resin acids in DTO are converted at temperatures above 400 °C to cycloalkanes and aromatics. However, at these temperatures the yield of nC 17 +C 18 hydrocarbons irrespective of space time is drastically reduced because of cracking reactions that produce aromatics. The commercial NiMo catalyst was not deactivated during extended on-stream tests of more than 30 h. Modeling the steam cracking of the highly paraffinic liquid obtained during hydrotreatment of DTO at different process conditions indicates high ethylene yields (>32 wt %).