This glossary provides an overview of the most essential terms related to the concept of renewable carbon. The Renewable Carbon Initiative has done its best to provide our understanding and helpful definitions of common terms in the field of renewable carbon, with the goal to harmonize terminology and improve understanding.
“The atmosphere is a layer of gases which surrounds planets” (NASA*) like the Earth and is retained by the planet’s gravity. The Earth’s atmosphere is roughly made up of 78 % nitrogen, 21 % oxygen, 0.9 % argon, water vapor, 0.04 % carbon dioxide (before the industrial revolution about 0.026 %) and other gases. The atmospheres of other planets have a different composition. These gases keep the global temperatures within liveable limits, shield the surface of Earth from harmful cosmic particles and ultraviolet radiation from the sun, and provide oxygen for breathing and carbon dioxide for photosynthesis. The atmosphere is essential for the biosphere, as it protects life on the planet and acts as a source of carbon.
*NASA 2021, https://www.nasa.gov/audience/forstudents/k-4/dictionary/Atmosphere.html
Bio-based, according to the official European standard, means “Derived from biomass”*. An additional definition is “Composed or derived in whole or in part of biological products issued from the biomass (including plant, animal, and marine or forestry materials)”**.
The term bio-based is mainly used to describe products whose carbon atoms originate from biogenic instead of fossil sources. These products can be made entirely or partially from biomass such as plants, trees, marine organisms or animals and can be subject to physical, chemical or biological processes. Plants rich in starch and cellulose such as sugar beet and cane, corn or wood, but also oilseeds, provide the raw material for ‘bio-based’ products in the chemical industry.
The bio-based carbon content of chemicals, plastics, materials and fuels can be quantified accurately with radiocarbon analysis (see carbon).
* CEN/TC 411 2014
** Vert et al. 2012, http://publications.iupac.org/pac/pdf/2012/pdf/8402×0377.pdf
“Capability of being degraded by biological activity.”*
Biodegradation is a non-reversible process during which microorganisms in the environment, via biological activity, convert materials into basic substances such as carbon dioxide (aerobic conditions), methane (anaerobic conditions), water, and biomass via enzymatic action. The process of biodegradation is influenced by the surrounding environmental conditions: temperature, water content, nutrient availability, concentration and activity of microorganisms etc. affect the rate of biodegradation. Under similar environmental conditions, the rate of biodegradation strongly differs for different materials.
* Vert et al. 2012, http://publications.iupac.org/pac/pdf/2012/pdf/8402×0377.pdf
The bioeconomy […] encompasses the production of renewable biological resources and the conversion of these resources and waste streams into value-added products, such as food, feed, bio-based products and bioenergy.*
The bioeconomy is the production and conversion of biomass as a raw material or sustainable use of biotechnology for the production of a range of food, health, fibre and industrial products and energy carrier.
* EC 2012, Communication on Innovating a Sustainable Growth: A Bioeconomy for Europe
“Material of biological origin excluding material embedded in geological formations and/or fossilized.”*
Biomass describes organic matter that is available on a renewable basis, including agricultural crops and trees, wood and wood wastes and residues, plants (including aquatic plants), micro-organisms, fungi, grasses, residues, fibres, animal wastes, organic municipal wastes, and other waste materials**. Biomass encompasses any biological material to be used as raw material.
* CEN/TR 16208:2011; CEN/TC 411 2014
** Based on Biomass Research and Development Act of 2000 7 USC 7624 Note; USITC 2008
The biosphere is the part of the Earth, including air, land, surface rocks, and water, within which life occurs and the total sum of living organisms. These life processes require energy, mostly in the form of solar radiation which is converted to biomass by photosynthesis. The biosphere has a throughput or cycling of mass, mostly in the form of carbon and essential nutrients.
Biotechnology or Bioprocessing refers to any process that uses living cells or their components (e.g., bacteria, enzymes, or chloroplasts) to obtain desired products. It draws upon multiple areas of knowledge, but especially molecular biology, chemical engineering, and manufacturing.
Carbon (from Latin: carbo = coal) is the chemical element with the symbol C. Carbon is highly prevalent in the biosphere, with almost any living being on Earth is made up of carbon, including humans and animals. It is essential for growth and reproduction and the major building block of life, for organic chemistry and derived materials such as plastics.
The major natural isotopes are 12C (6 neutrons, 98.9 % of the carbon on earth) and 13C (7 neutrons, 1.10 % of the carbon on earth). On earth, the stable isotopes are enriched differently, with 12C more in biological material and 13C more in inorganic material (carbonate) and in the atmosphere. The largest carbon sinks on earth are oceans, soils and plants. In the atmosphere, cosmic rays lead also to the formation of radioactive 14C from 14N (nitrogen). The half-life of 14C (the time it takes for half of a given amount of 14C to decay) is about 5,730 years. This carbon is taken up from plants, which enables the identification of bio-based carbon in materials via so-called radiocarbon dating.
Due to its electron configuration, C-atoms can form various molecules. They have the ability to form bonds with each other, which results in cyclic (e.g. benzene ring), long, straight or branched (e.g. paraffin, polyethylene) molecules. Furthermore, multiple bonds to other atoms can be formed. Altogether this allows the formation of an enormously large number of possible molecules (approx. 6,000,000-10,000,000).
Carbon dioxide represents a gaseous chemical compound containing carbon and oxygen with the molecular formula CO2. Carbon dioxide is a colourless and odourless gas that naturally occurs in the atmosphere and is a major greenhouse gas, besides methane (CH4) and nitrous oxide (N2O). In general, the emission of CO2, natural or technical, occurs when energy is produced via a combustion process or via decomposition/biodegradation of organic substances. Examples of the latter are the cellular respiration of living organisms, the decomposition of an organism as well as the production of volcanic gases or the combustion of coal, oil, gas and biomass.CO2 represents an essential molecule for the carbon cycle in which carbon is exchanged between the atmosphere, geosphere, hydrosphere, biosphere and technosphere.
Carbon monoxide represents a gaseous chemical compound containing carbon and oxygen with the molecular formula CO. The compound is mainly formed by incomplete combustion of carbonaceous material as well as through oxidation of hydrocarbons (e.g. methane). In the atmosphere, CO has an indirect effect on greenhouse gases since its presence affects the abundance of greenhouse gases such as methane and carbon dioxide.
A circular economy is “the economic space where the value of products, materials and resources is maintained in the economy for as long as possible, and the generation of waste minimised”.*
The circular economy is a model of production and consumption, which involves sharing, leasing, reusing, repairing, refurbishing and recycling existing materials and products as long as possible over multiple loops. In this way, the life cycle of products is extended. In practice, it implies reducing waste to a minimum. When a product reaches the end of its life, its materials are kept within the economy wherever possible. These can be productively used again and again, creating further value.
A circular economy is a departure from the traditional, linear economic model, which is based on a take-make-consume-throw away pattern. This linear model relies on large quantities of cheap, easily accessible materials and energy.**
* EC 2015, Closing the loop–An EU action plan for the Circular Economy
** EP 2021, Living in the EU: Circular Economy
Climate change refers to a change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings such as modulations of the solar cycles, volcanic eruptions and persistent anthropogenic changes in the composition of the atmosphere or in land use. The UNFCCC* makes a distinction between climate change attributable to human activities altering the atmospheric composition and climate variability attributable to natural causes.
* United Nations Framework Convention on Climate Change
CO2 equivalent (CO2-eq) emissions: The amount of carbon dioxide (CO2) emissions that would cause the same integrated radiative forcing or temperature change, over a given time horizon, as an emitted amount of a greenhouse gas (GHG) or a mixture of GHGs. The point of CO2-eq is to put all gases contributing to climate change into a single, commensurate unit, which can then be used for comparisons.
There are a number of ways to compute such equivalent emissions and choose appropriate time horizons. Most typically, the CO2-equivalent emission is obtained by multiplying the emission of a GHG by its global warming potential (GWP) for a 100-year time horizon. For a mix of GHGs, it is obtained by summing the CO2-equivalent emissions of each gas, with different factors for the different greenhouse gases. These factors have been established and are continuously updated by science and the IPCC*. To provide an example, 1 kg CO2 has a CO2-equivalent of 1 kg, while 1 kg methane (CH4) has a CO2-equivalent of 28 kg CO2e.
* Intergovernmental Panel on Climate Change
Strictly speaking, decarbonisation refers to the energy sector, and this is where the term comes from. It means the process of replacing carbon-containing fuels such as gasoline and diesel with carbon-free energy sources such as electricity and hydrogen, obtained from renewable energies. In the IPPC Special Report on Global Warming of 1.5 °C (2018), the term is defined slightly differently in relation to biofuels, which equals the terms decarbonisation and defossilisation (removal of fossil carbon): “The process by which countries, individuals or other entities aim to achieve zero fossil carbon existence. Typically refers to a reduction of the carbon emissions associated with electricity, industry and transport”.*
In the field of chemistry and materials, the strict definition is not applicable, since here carbon is an essential and indispensable component. And the IPCC’s broader definition repeatedly leads to misunderstandings. Therefore, we recommend not to use the term decarbonisation for embedded carbon in chemicals and materials. Instead, we recommend the utilisation of the term “renewable carbon”, coupled with renewable energy to reduce greenhouse gas emissions of the sector to zero.
* IPCC, https://www.ipcc.ch/sr15/chapter/glossary
Direct CO2 utilisation includes the capture and utilisation of carbon dioxide and carbon-containing gases, also known as Carbon Capture and Utilisation (CCU). CO2 and carbon-containing gases can be captured from industrial point sources (technosphere), such as coal-fired power plants, steel plants, cement plants, biogas plants, refineries etc. or from the atmosphere, directly from the ambient air (Direct Air Capture).
The utilisation of CO2 and carbon-containing gases includes two conversion routes: chemical conversion and biotechnological conversion.
Chemical conversion includes the use of conventional chemical reaction systems, catalysts and energy input to convert CO2 and other carbon-containing gases into various products as e.g. chemicals, gases, polymers or synthetic fuels.
Electrochemical and photochemical conversion are special forms of chemical conversion that use electrical energy to reduce CO2 or sunlight to convert CO2 into various products.
Biotechnological conversion includes the use of so-called biocatalysts (enzymes (non-living) or microorganisms (living)) to convert CO2 and other carbon-containing gases into various products as e.g. polymers, proteins, chemicals or gases.
Because CO2 is a stable molecule it requires a large amount of energy for conversion. The energy needed for utilising CO2 and other carbon-containing gases must stem from renewable resources to provide an environmental benefit compared to other sources of carbon.
A feedstock is the unprocessed raw material of a manufacturing process. In general, any natural material can be viewed as a feedstock. These include minerals or materials from vegetation or water, including crops, wood or algae, but also fossil resources like petroleum, coal and natural gas. Therefore, the term “feedstock” is often used as a synonym for raw material.
Fossil carbon is the carbon present in fossil feedstocks like crude oil, coal or natural gas. It has been formed millions of years ago, in the geological past, from dead plants and animal matter that was deposited in the ground and subject to increased temperature and pressure. As fossil carbon takes millions of years to generate, it is a finite and non-renewable source of carbon.
The geosphere, often also referred to as the lithosphere, is the solid outer layer of the earth with an average thickness of about 75 km. It comprises the earth’s crust and the solid or outer part of the mantle of the earth. The geosphere contains deep storage of carbon in the form of fossil fuels like oil, coal and natural gas. Together with the atmosphere, hydrosphere and biosphere, it describes the systems of the earth.
The European Green Deal is the EU’s plan to make its economy sustainable and to become climate neutral by 2050. To achieve this ambitious goal, an action plan was developed as well as plans to implement a European Climate Law to make this goal a legal obligation. To ensure that the EU stays on track, Commission and Parliament have agreed upon an intermediate goal of 55% emissions reduction by 2030 (for the whole of the EU, compared to the baseline of 1990). Policy areas to implement and carry out these actions have been identified in a wide range of fields. For the EU Green Deal, the key factors towards climate neutrality are biodiversity, more sustainable agriculture and food systems, clean energy, sustainable industry, building and renovating, sustainable mobility and overall eliminating pollution rapidly. That said, the Green Deal is heavily focused on the transformation of the European energy system towards renewable energy and does not yet properly consider the substitution of fossil carbon in chemicals and materials.
The Earth’s atmosphere contains gases that largely allow short-wave solar radiation to pass through, but absorb (long-wave) thermal radiation and thus heat the system. In analogy to a greenhouse – which lets solar radiation pass through and “holds” heat radiation – the greenhouse effect refers to this process. The gases that cause this effect are called greenhouse gases. Water vapour and carbon dioxide, in particular, absorb part of the thermal radiation emitted from the Earth’s surface and therefore reduce the proportion of thermal radiation emitted into space.
Greenhouse gases constitute a group of atmospheric gases that add to the greenhouse effect, contributing to global warming and climate change. The Kyoto Protocol, an environmental agreement adopted by many of the parties to the United Nations Framework Convention on Climate Change (UNFCCC) in 1997 to curb global warming, covers six greenhouse gases:
• the non-fluorinated gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O)
• the fluorinated gases: hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6)
Converting them to carbon dioxide (or CO2) equivalents makes it possible to compare them and to determine their individual and total contributions to global warming (Eurostat Glossary).
Greenhouse gas emissions describe the release of greenhouse gases (GHG) into the earth’s atmosphere. As these emissions are the major driver of climate change, global GHG emissions are increasingly monitored. Scenarios for climate change are derived from current and projected GHG emissions and most targets toward mitigating climate change are based on quantifying the reduction of these emissions.
Green hydrogen is a form of hydrogen (H2) produced with the use of renewable energy such as solar, wind and bioenergy without using fossil carbon feedstocks. The hydrogen in this case is produced via electrolysis of water with electricity produced from solar, wind or hydro energy. In carbon capture and utilisation (CCU) the green hydrogen is then used to react with the carbon monoxide (CO) or carbon dioxide (CO2) as an energy carrier to form syngas, hydrocarbons such as methane or ethylene, alcohols such as methanol and ethanol or other chemicals such as formic acid.
The hydrosphere includes the waters of the Earth, as distinguished from the rocks (geosphere), living things (biosphere), and the air (atmosphere). It includes the waters of the ocean, rivers, lakes, and other bodies of surface water in liquid form as well as snow, ice, and glaciers on the continents. In addition, liquid water, ice, and water vapour in both the unsaturated and saturated zones below the land surface are included.
Life Cycle Assessment is defined as a systematic analysis of environmental impacts of a product or service throughout its entire life cycle. For this analysis, the material and energy inputs and outputs along all steps of the life cycle (this includes raw material extraction, production, distribution, use and disposal at end-of-life) are collected and then assessed in terms of potential environmental impacts of a product system. LCA is accepted as one of the main methods to identify environmental impacts and is standardised on the widely accepted standards ISO 14040 and ISO 14044.
Becoming carbon-negative describes the idea that more CO2 equivalents are removed from the atmosphere than are emitted by a given actor or entity. Because carbon is removed from the atmosphere, negative carbon emissions are implied. Removal of greenhouse gases (GHGs) from the atmosphere occurs through deliberate human activities in addition to the removal that would occur via natural carbon cycle processes. Achieving negative carbon emissions in a process requires that it removes more CO2 from the atmosphere than it emits.
In our current economic system, the term should be used with caution, as there are principally no products that actually provide negative carbon emissions when considering emissions from all processes involved and end-of-life emissions. Often, negative emissions are rather based on calculations that include storage or offsetting activities in order to achieve negative or net neutral results.
The IPCC defines net zero as the point when “anthropogenic emissions of greenhouse gases (GHG) to the atmosphere are balanced by anthropogenic removals over a specified period”.*
Net zero, also net carbon neutral or carbon neutrality, means that the CO2 equivalents released into the atmosphere from human activity are equalized by removing the same amount via technological processes or offsets. The terms are sometimes distinguished between their applications, with net zero being used for companies and countries and net carbon neutral being used for products and brands.
Achieving this neutrality is based on balancing anthropogenic greenhouse gas emissions with anthropogenic greenhouse gas (GHG) removals over a specified period – which means the less anthropogenic GHG emissions remain, the fewer removals are necessary. Achieving net carbon neutrality has been demonstrated to be necessary in order to bring our climate system back into balance, stabilise global temperatures and stop climate change.
Similar to negative carbon emissions, net zero / net carbon neutral should be used with caution, as the same principles for calculations that include storage or offsetting apply.
* IPCC 2018, Summary for Policymakers. In: Global Warming of 1.5°C
Offsets are discrete greenhouse gas (GHG) reductions used to compensate for (i.e., offset) GHG emissions elsewhere, for example, to meet a voluntary or mandatory GHG target or cap. The term “offset” is frequently used with reference to third-party greenhouse gas mitigation activities, e.g. regulated schemes in the framework of the Kyoto Protocol (CDM – Clean Development Mechanism, JI – Joint Implementation, ETS – Emissions Trading Schemes). Offsets are calculated relative to a baseline that represents a hypothetical scenario for how high emissions would have been in the absence of the mitigation project that generates the offsets.
Offsets are often considered critical for several reasons. For one, there is the possibility of abuse, meaning that offsetting measures are purchased without them actually reducing the quantified amount of global GHG emissions. Furthermore, they are expensive options that often replace a bad activity (e.g. burning wood) with another activity that emits less GHG emissions, but still does emit overall (e.g. clay ovens). In that regard, offsets purchase more time in regards to the overall available emissions budget but do not support true innovations towards reducing GHG emissions.
Organic chemistry is the chemistry of the (multiple) compounds of carbon. The term “organic“ was created at a time when it was believed that only biomass (animals and plants) could produce these substances. For this reason, some carbon compounds traditionally classified as inorganic, such as carbon monoxide, carbon dioxide or hydrogen cyanide, are still classified as inorganic together with mineral substances like calcium carbonate. In our understanding, organic chemistry may be better understood as the chemistry of hydrocarbons and their derivatives. This includes all fossil fuels.
Point source means any “discernible, confined and discrete conveyance […], from which pollutants are or may be discharged.”*
In general, a point source refers to a localised and stationary point of pollution. From the perspective of the RCI, a carbon dioxide (CO2) point source refers to a single identifiable and localised direct emitter of CO2 such as fossil power plants, industrial processes or food fermentation. Automobiles with internal combustion engines are also a point source, albeit not industrial. These point sources are generally suitable to be coupled with direct CO2 utilisation if the emissions are captured at their point of origin.
* Clean Water Act, section 502(14).
Power-to-X (PtX) is a broader term for technologies that use electrical energy to produce other and more required forms of energy (e.g. heat), compounds that serve the purpose of energy storage (e.g. in the form of hydrogen or methane (Power-to-Gas, PtG), fuels (Power-to-Liquids, PtL), and chemicals and materials (Power-to-Chemicals, PtC). The technologies are mainly used to store high capacities of surplus renewable energy over long periods of time, which would hardly be possible with batteries, but can also provide renewable raw materials and renewable carbon to the chemical and material industry.
The term mechanical recycling refers to operations which neither change the formulation of a plastic (or material) nor substantially change the molecular structure of the polymer. The involved steps of mechanical plastic or textile recycling deviate from each other and may cover collection/segregation, cleaning and drying, mechanical disintegration (e.g. chipping/sizing), colouring/agglomeration, extrusion and granulation, re-spinning into yarns, and manufacturing of the end product.
Chemical recycling represents a set of various recycling technologies for a range of different plastics and polymers. The main technologies can be separated into solvent-based (alcoholysis, hydrolysis, ammonolysis and aminolysis, combined methods), thermochemical (pyrolysis, gasification) and enzymolysis. In general, two characteristic traits are mainly associated with the term chemical recycling which are the change of the polymers molecular structure and the change of the plastics formulation. The underlying definitions may therefore vary depending on the design which can either be based more on natural sciences or on politics. Chemical recycling is often associated with more generic terms such as “advanced recycling”.
Recycling processes may not fit into the mechanical or chemical recycling category or may refer to other materials such as paper via mechanical or chemical pulping. Such recycling concepts for cellulose are somewhere between these two concepts. Breaking down to monomers and re-polymerisation does not work for cellulose recycling. The molecular structure may be kept intact or be modified throughout the process, a separation of the cellulose molecules takes place to some extent as well as the formulation may change. Another recycling process that cannot be clearly categorised into mechanical or chemical recycling is the solvent-based purification of plastics in which the molecular structure of the polymer is kept intact but the formulation of the plastic is changed throughout the process which is often referred to as physical recycling.
Renewable carbon entails all carbon sources that avoid or substitute the use of any additional fossil carbon from the geosphere. Renewable carbon can come from the biosphere, atmosphere or technosphere – but not from the geosphere. Renewable carbon circulates between the biosphere, atmosphere and technosphere, creating a carbon circular economy.
The Renewable Carbon Initiative (RCI) launched in September 2020 with the aim to support and speed up the transition from fossil carbon to renewable carbon for all organic chemicals and materials.
The Renewable Carbon Initiative addresses the core problem of climate change, which is extracting and using additional fossil carbon from the ground that will eventually end up in the atmosphere. Companies are encouraged to focus on phasing out fossil resources and to use renewable carbon instead.
The initiative wants to drive his message, initiate further actions by bringing stakeholders together, providing information and shaping policy to strive for a climate-neutral circular economy.
A renewable carbon refinery refers to an industrial process that uses all kinds of renewable carbon as the primary input for the manufacture of fuel and chemical products.
A refinery is a technical plant for the purification and refinement of raw materials (e.g. fractionation of crude oils via distillation which is based on the different boiling points of the respective fractions). Often, it refers to a petroleum oil refinery, which consists of a group of chemical engineering processing and refining units to convert crude oil into basic chemicals for further utilisation. This is usually done via cracking (steam cracking or catalytic cracking), a process in which large hydrocarbon molecules are broken down into smaller and more useful ones. A key product of a refinery is fossil-based petroleum naphtha, an intermediate liquid hydrocarbon stream, which serves as a raw material for the production of many other chemicals. Petroleum naphtha can be replaced with naphtha derived from renewable carbon alternatives (either bio-based, CO2-based or chemical recycling). Different refineries also exist for other raw materials, e.g. sugar, salt, natural gas, edible oils, metals etc.
Sustainable fuels are fuels made from renewable and alternative raw material in replacement of petroleum-based fuels and complying with sustainability criteria and reduced emission or even emission neutrality. While the electrification of transport is an increasingly strong opportunity, some transport sectors (e.g. aviation, long-distance hauling) will likely continue to require liquid fuels. In that regard, a range of potentially sustainable fuel options includes biofuels, recycled carbon fuels, green hydrogen and synthetic fuels that can for example be derived from captured carbon dioxide (CO2) and renewable energy.
In its most well-known definition, sustainability or sustainable development means meeting our own needs without compromising the ability of future generations to meet their own needs*. In a simpler form, sustainability refers to the avoidance of natural resource depletion and greenhouse gas emissions in order to maintain an ecological balance and stability of earth systems. Modern sustainability definitions refer to it as a holistic approach that considers ecological, social and economic dimensions with the goal to consider all three of these so-called pillars of sustainability to find lasting prosperity for everyone.
* Brundtland Report 1987, https://sustainabledevelopment.un.org/content/documents/5987our-common-future.pdf
The technosphere or anthroposphere is the part of the environment that is made or modified by humans for use in human activities and its interaction with the Earth’s and extra-terrestrial systems. It includes any technologically derived product manufactured by humanity and represents a centrepiece for the renewable carbon strategy.
It is maintained by a flow of material and energy from the geosphere, biosphere, and sun. The technosphere is the youngest of all the Earth’s spheres, yet has made an enormous impact on the Earth and its systems by converting more than three-quarters of wild Earth in a very short time by using technology. In contrast to the biosphere, the technosphere is currently highly inefficient at sustaining itself.