(68f) Feasibility of Demand Response for Electrohydrodimerization Reactions in the Chemical Industrie

In the field of power generation, the aim is to increase the part of renewable energy. This also brings an increase in fluctuations in power supply, which leads to a higher need for adaptability, meaning more flexibility in production and consumption of electricity. Load changes in energy-intensive industries like the chemical industry would be a way to provide this. In the joint project ChemEFlex the feasibility of demand response in various electrochemical processes of the chemical industry is analyzed. In this work, two processes with different levels of development were studied. Suitable operating parameters and their tolerable limits were evaluated.

The commercialized process for the electrohydrodimerization of Acrylonitrile (ACN) to Adiponitrile (ADN) was the first case considered suitable for further studies:

Fig. 1: Electrohydrodimerization of Acrylonitrile to Adiponitrile.

Adiponitrile is an intermediate in the production of Nylon. Worldwide the production rate of ADN is around 1.31 Mio. t/a, of which 300.000 t are made through cathodic hydrodimerization. This makes the so-called Monsanto-Process the most important electroorganical synthesis.

On an experimental scale different load changes were applied in various time periods to see, if there are changes in activity and stability. The results were then used to model the process in order to evaluate the economical and technical feasibility of the applied flexibility profiles.

The second case is the piloted process of the electrohydrodimerization of Formaldehyde to Ethylene glycol.

Fig. 2 : Electrohydrodimerization of Formaldehyde to Ethylene glycol.

Ethylene glycol nowadays is almost exclusively made from direct oxidation of Ethylene, followed by hydrolysis of Ethylene oxide. Even though this process has a poor selectivity and is high in energy consumption, the use of mineral oil results in a very low price. Still, with increasing prices for crude oil and the additional profit from the control energy market, the electrochemical process could be a good alternative.

For the electrochemical synthesis of Ethylene glycol, suitable operating conditions for the laboratory setup had to be defined at first. Afterwards, different flexibility profiles were applied and the reaction parameters as well as the aging of different parts of the electrochemical cell were studied.

Experimental section

Two experimental setupswere built on a laboratory scale ^{[1], [2]} to test the application of demand-side management. The changes in selected parameters like aging of electrodes, product quality, etc. are documented and evaluated while various flexibility profiles (load changes in seconds or minutes, adapted to the requirements of the control energy market) were applied. The Selectivity towards the desired product and the yield was determined using gaschromatographie for the adiponitrile synthesis (Fig. 3).

SEM Imaging was used to see if any differences in electrode aging occur due to the applied flexibility operations. Additionaly the cathode surface was measured in a Profilometer to quantify the loss of electrode material.

For the synthesis of Ethylene glycol the selectivity and yield were monitored by samples of the catholyte, which were analysed by high performance liquid chromatographie. These parameters were monitored for applied loag changes and are then compared to the results obtained for constant load operations.

Figure 3: a) Example of an operation profile with load changes of 25% for 15 minute periods. b) Selectivity towards adiponitrile (ADN), the trimerization product (TRI), and propionitrile (PN) and yield of ADN with a change of current density by 0.5 kAm−2 over varying time periods.

Experiments were carried out in Microflowcells by ElectroCell AB (Sweden). For the Monsanto-Process the effects on an undivided cell were studied, whereas for the synthesis of Ethylene glycol, a Nafion 324 membrane was used for separation.

References

[1] N. L. Weinberg, D. J. Mazur, J. Appl. Electrochem., 21 (1991) 895 – 901.

[2] K. Scott, B. Hayati, Chem. Eng. Sci. 45, 8 (1990) 2341–2347.