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Sustainability & Environment

Introduction

This latest SCI Energy Group blog introduces the possible avenues of carbon dioxide utilisation, which entails using carbon dioxide to produce economically valuable products through industrial processes. Broadly, utilisation can be categorised into three applications: chemical use, biological use and direct use. For which, examples of each will be highlighted throughout.

Before proceeding to introduce these, we can first consider utilisation in relation to limiting climate change. As has been discussed in previous blogs, the reduction of carbon dioxide emissions is crucial. Therefore, for carbon dioxide utilisation technologies to have a beneficial impact on climate change, several important factors must be considered and addressed.

1) Energy Source: Often these processes are energy intensive. Therefore, this energy must come from renewable resources or technologies.

2) Scale: Utilisation technologies must exhibit large scaling potential to match the limited timeframe for climate action.

3) Permanence: Technologies which provide permanent removal or displacement of CO2 emissions will be most impactful¹.

 CO2 sign

Figure 1: CO2 sign 

Chemical Uses

Carbon dioxide, alongside other reactants, can be chemically converted into useful products. Examples of which include urea, methanol, and plastics and polymers. One of the primary uses of urea includes agricultural fertilisers which are pivotal to crop nutrition. Most commonly, methanol is utilised as a chemical feedstock in industrial processes.

 Fertilizing soil

Figure 2: Fertilizing soil

One of the key challenges faced with this application of utilisation is the low reactivity of CO2 in its standard conditions. Therefore, to successfully convert it into products of economic value, catalysts are required to significantly lower the molecules activation energy and overall energy consumption of the process. With that being said, it is anticipated that, in future, the chemical conversion of CO2 will have an important role in maintaining a secure supply of fuel and chemical feedstocks such as methanol and methane².

Biological Uses

Carbon dioxide is fundamental to plant growth as it provides a source of required organic compounds. For this reason, it can be utilised in greenhouses to promote carbonic fertilisation. By injecting increased levels of COinto the air supplied to greenhouses, the yield of plant growth has been seen to increase. Furthermore, COfrom the flue gas streams of chemical processes has been recognised, in some studies, to be of a quality suitable for direct injection³.

 Glass greenhouse

Figure 3: Glass greenhouse planting vegetable greenhouses

These principles are applicable to encouraging the growth of microorganisms too. One example being microalgae which boasts several advantageous properties. Microalgae has been recognised for its ability to grow in diverse environments as well as its ability to be cultured in numerous types of bioreactors. Furthermore, its production rate is considerably high meaning a greater demand for CO2 is exhibited than that from normal plants. Micro-algal biomass can be utilised across a range of industries to form a multitude of products. These include bio-oils, fuels, fertilisers, food products, plant feeds and high value chemicals. However, at present, the efficiency of CO2 fixation, in this application, can be as low as 20-50%.

 Illustration of microalgae

Figure 4: Illustration of microalgae under the microscope

Direct Uses

It is important to note that, at present, there are many mature processes which utilise CO2 directly. Examples of which are shown in the table below.

 CO2 processes

Summary

Many carbon dioxide utilisation technologies exist, across a broad range of industrial applications. For which, some are well-established, and others are more novel. For such technologies to have a positive impact on climate action, several factors need to be addressed such as their energy source, scaling potential and permanence of removal/ displacement of CO2.

The chemistry of carbon dioxide and its role in decarbonisation is a key topic of interest for SCI Energy Group. In the near future, we will be running a webinar concerned with this. Further details of this will be posted on the SCI website in due course.

Links:

1. http://co2chem.co.uk/wp-content/uploads/2012/06/CCU%20in%20the%20green%20economy%20report.pdf

2. https://www.carbonbrief.org/guest-post-10-ways-to-use-co2-and-how-they-compare

3. https://www.intechopen.com/books/greenhouse-gases