Working towards a fossil-free future
The Delft e-Refinery research institute is developing sustainable technologies for energy and chemicals.
We are thinking about what the world will need in twenty to thirty years’ time and starting to work on that now,” says professor Paulien Herder about the e-Refinery research institute that she leads together with professor Bernard Dam. “If we all want a future free of fossil fuel – which we do – then it's important that we carry out all kinds of research to make that possible. It will take between 10 and 30 years to convert the entire industry and it's important to make a start now because research takes time.”
Away with all the energy-slurping separation processes in creating a greener industry
Last spring TU Delft, Shell and funds for knowledge and innovation jointly invested five million euros in the e-Refinery, with the aim of developing electrochemical technology and a sustainable petrochemicals industry. E-Refinery brings this together in a single project with fundamental materials science research into electrodes and membranes and chemicals research into electrochemical processes and separation techniques. Some researchers are working on scalable reactors, while others are working out how to fit the new technology into the existing industry. Yet others are exploring legislation, regulations and the markets needed to implement the new technologies in society. This whole range of disciplines is vital if new technology is to have any chance of success. Thanks to the collaboration between five faculties (Electrical Engineering, Mathematics and Computer Science (EEMCS), Mechanical, Maritime and Materials Engineering (3mE), Aerospace Engineering (AE),Technology, Policy and Management (TPM), and Applied Sciences (AS) all this knowledge is available within the e-Refinery research institute in the form of over 30 staff researchers and dozens of doctoral candidates and post-docs.
Carbon dioxide and Sabatier
Accumulation of CO2 in the atmosphere is the driving force behind climate change. This is why we need to drastically reduce the level of greenhouse gas emissions, including CO2, in the coming decades. Unfortunately there are some energy intensive processes, such as steel and concrete manufacturing in which CO2 emissions are almost unavoidable. Alternative processes are being developed for these, using alternative non-fossil energy sources. Various groups are also investigating how to recycle CO2 from the atmosphere to use as a replacement for fossil-based raw materials in industry. This does away with new CO2 emissions into the atmosphere. One way of using CO2 as a raw material is to combine it with hydrogen to create natural gas (methane) using the Sabatier process (CO2 + 4H2 -> CH4 + 2H20 + heat). French chemist Paul Sabatier discovered this process in 1879, together with Jean Baptiste Sederens, and in 1912 he was awarded the Nobel Prize in Chemistry for the discovery. Originally, at the end of the 19th century, the process was used to convert wood or coal into a natural gas substitute. Nowadays interest is being shown in the Sabatier process as it is seen as a way of storing surplus electricity from solar panels and wind. In this scenario, green electricity can be used to create hydrogen through electrolysis, which when combined with CO2 forms methane. Methane can be easily stored as an energy reserve, in empty gas fields for example. These can then be used alternatively as energy storage and energy supply.
Electrochemistry
Researchers are also working on a way of using electrochemistry to simplify the two steps of the Sabatier process (first creating and then converting hydrogen) into a single process step. Electrochemistry is a collective name for chemical conversions driven by electrical energy. In the electrochemical conversion of CO2, ethylene (C2H4) or methane (CH4), for example, are created in a special cell. Hydrogen, carbon monoxide (CO), formaldehyde (HCHO) or methanol (CH3OH) may also be produced. The substances produced depend on such things as the material used for the electrodes (such as copper, tin, nickel and graphene), the acidity (pH) and the voltage across the cell. Electrochemical processes may be used in the future to convert surplus electricity from solar cells and wind parks directly into chemical resources or fuel. Researchers are working on suitable materials for electrodes and membranes, and at scaling up the reactors.
Nowadays there is a lot of renewed interest in the Sabatier process
Separation processes
The scaling up should result in a 100 kW test plant in five years’ time. Herder explains: “This equipment would just about fit into our own labs. To build the equipment, we are thinking about what this means for the electrodes, for the type of cells we will be using, and how do we get the electricity inside with high power quality? And how can we keep it safe? We are presently working on all kinds of designs to be able to achieve this on a large scale.” “We will soon be making a mix of products, and in every chemical process you have to apply retrospective product separation. This will also be the case here, but how should we go about it? Today's chemicals industry uses a lot of energy for its separation processes, for example in distillation. Would it not be better to work with membranes, for example? Or might it be possible to organise the reaction process so that less separation is needed? Maybe the reactor could be designed with this in mind, killing two birds with one stone: doing away with all the energy-slurping separation processes while creating a greener industry.”And the long-term vision? “Just like all the climate-related research, our research is aimed at 2030 and 2050. I just mentioned the 100 kW plant that we want to build; we have set ourselves a five-year deadline for this. That's pretty ambitious. You can also see in our research programmes that we consistently look five to ten years ahead, even in consortia with the government, research institutes and industry. Together with them we want to work towards a fossil-free future.”
Growing pains
Mechanical engineer Tom Burdyny (32) is working on the scaling up of electrolysis plants. The basis of the electrochemical reduction of CO2 is developed with a small reactor which converts half of a CO2 gas stream into other gases such as carbon monoxide (CO), methane (CH4) and ethylene (C2H4) using electrical energy. When you scale up this kind of reactor, you encounter all sorts of problems of a chemical, electrical and mechanical nature, explains Burdyny. How can you supply electricity to a multi-cell system? How do you separate the gas flows? And how do you make such a reactor part of a far larger process? A small electrolyser uses 5 watts of electricity and a larger one 200 watts, but Burdyny's goal is to build a 1 kilowatt electrolyser the size of a shoebox within 30 months. In laboratory terms that is a colossal device, but Burdyny is well aware that industry operates in megawatts and tens of thousands of process hours. “The e-Refinery programme was set up to bridge this gap,” he says.
Formic acid
The plant for the electrochemical conversion of CO2 to formic acid (HCOOH) is sturdily built, to cope with an internal pressure of 50 bars. This is needed in order to convert the gas in sufficient concentration on the tin-based cathode. The voltage is low (3.5 volt) with 1.5 amp current. In a recent publication researchers Prof. Wiebren de Jong, Prof. Thijs Vlugt (Process & Energy at 3mE), and Mariette de Groen (Coval Energy) reported achieving a current efficiency of 80 percent conversion. “That means a good selectivity of the desired product,” says De Jong. That liquid product, formic acid, can be used in the agricultural sector. It can also be used as a base material for synthesis gas (CO and H2), from which methanol (solvent, chemical building block, and candidate marine fuel) can be made. This is an interesting conversion for industry as a way of reducing carbon emissions. Waste processor Twence, for example, is keen to use electrochemical conversion to largely meet the compulsory reduction of carbon emission from flue gases. Points for attention in the scaling up needed for this are heat dissipation (tens of percent of the electrical input) and even current distribution.
Think the other way round
In the Sabatier process, CO2 and hydrogen are heated to 650 °C in the cylindrical reactor in the oven, producing methane (CH4) plus water vapour. The reverse process, making hydrogen from methane, is the most important industrial source of hydrogen. “We already have most of the processes at our fingertips,” says Applied Sciences researcher Dr Wim Haije. “We just have to learn to think the other way round.” Moreover, the conversion is an equilibrium reaction with 4H2 and CO2 on one side and 2H2O with CH4 on the other. So you have a mixture of gases, unless you push the reaction one way by capturing water, for example. Then the water cannot react back, leaving you with almost pure methane. Haije captures the water vapour using zeolites, molecular sponges, that can absorb up to 25 percent of their own weight in water. The zeolites are also impregnated with a nickel catalyst. Once the zeolite is saturated it can be heated for re-use.
Barrel of surprises
In Dr Ruud Kortlever’s research group, electricity is used in electromagnetic cells to convert CO2 into other substances that can be used as fuel or chemical material. This process is called electrocatalysis, the electrochemical reduction of CO2 as it bubbles through the cell. What substances are formed depends greatly on the material used for the cathode, as well as the electrical voltage. A gold or silver cathode produces carbon monoxide (CO) in the solution. A copper cathode produces a mixture of hydrocarbons such as methane (CH4) and ethylene (C2H4), an important base material for the chemicals industry. Formic acid (HCO2H) and methanol (CH3OH) may also be formed. The modest electrochemical cell turns out to be a barrel of surprises. The research is aimed at gaining better control of the chemical processes through the choice of electrode materials and other variables. What Kortlever would most like to see is longer chain hydrocarbons grow on the cathode like in the Fischer-Tropsch process in refineries.
Electric bacteria
When the French Dr Ludovic Jourdin joined the e-Refinery-programme, he brought his own bacteria culture with him. He had extracted the bacteria from mud in Queensland, Australia for his PhD research, and fed them purely on electricity. These electric bacteria live in a reactor as a biofilm on the cathode where they reduce CO2 to organic molecules such as acetate (CH3COO-) or caproic acid, both of which are platform chemicals for the chemicals industry. This conversion process is known as microbial electrosynthesis and is the third conversion route in the e-Refinery programme (alongside electrocatalysis, and the indirect route using hydrogen). Two PhD candidates have joined Jourdin's research group in the Faculty of Applied Sciences: Merijn Winkelhorst is studying the bacterial genomes to unravel the molecular processes of their CO2 conversion, while Oriol Cabau Peinado is working on the reactor design. He is systematically eliminating the obstacles to creating a scalable design.