Understanding Environmental Impact is Critical in Developing New Materials and Products
Scientists and innovators are eager to develop new materials and products, such as graphene, that allow consumers to reap the benefits of technological improvements and advancements. However, given the rapidly increasing risk of global climate change and its effects on mankind, manufacturers have a great responsibility to understand the environmental impact of their processes and products.
One way manufactures evaluate the potential environmental impacts of a product or service is a life cycle analysis (LCA). However, this can be a complicated and nuanced process for many products like graphene-related materials. While the International Organization for Standardization provides guidelines and requirements for conducting a Life Cycle Assessment according to ISO 14040 and 14044, there remains the need to make this process even more accessible.
At HydroGraph, we are dedicated to environmental responsibility and using eco-friendly and green processes in the production of graphene.
Graphene: A Nanomaterial with Limitless Potential
Because graphene’s markets and applications are almost limitless it appears to be on a fast tract, but must overcome some difficulties involving price, purity, consistency, energy demands, and eco-unfriendly processes. Graphene, a “super-material” poised to explode in the commercial market, is stronger than steel, harder than diamond, more conductive than copper, with better electron mobility than silicon. The product is added to other materials to enhance strength, water resistance, flexibility, electrical conductivity; and it supports clean energy by improving battery, solar panel and supercapacitor technology.
Graphene comes in a variety of forms and there are two major pathways to produce graphene: one is called bottom-up, and the other top-down. For example, Chemical Vapor Deposition or CVD, produces thin film, single-layer graphene. This is a bottom-up method since it begins with a molecular carbon source and builds graphene structure at the atomic level. The other approach is to use well-formed graphite as a starting point to obtain single layer graphene by exfoliating the parent graphite particles. This method is called top-down. There are also a variety of forms of graphene such as bi-layer, few layer and multi-layer graphene. And, to complicate it more, there are different geometrical forms as well, nano-sheets, nano-ribbons, nano-spheroids, nano-polyhedrons, and fractal graphene, etc.
Measuring Environmental Impact
No matter what the origin or production route is, there are some obvious and some non-obvious concerns of these processes and their effect on the environment.
One approach is the standard Life Cycle Assessment or LCA methodology, with multiple measures or parameters to quantify the environmental impact of the process, including Cumulative Energy Demand CED, Global Warming Potential GWG, Cumulative Water Use CWU, Ozone Depletion Potential ODP, and more.
First a boundary must be defined in which the analysis is takes place, whether it be cradle-to-gate or cradle-to-grave etc.
Then, a functional unit of the product is selected, i.e., 1 kg of graphene powder, is then estimated the key impact parameters per that functional unit.
One common parameter is the energy use in the process which has a direct association with environmental impact. The cumulative energy demand for producing a material has two parts: one is the energy used in raw materials, and the other is the energy used in actual production process.
For example, acetylene and oxygen gas can be used as raw materials in fractal graphene production. The two elements are put in a closed container and the mixture is ignited with a tiny electric spark to immediately result in bulk graphene powder. Since the process is a gas phase reaction without any catalysts, the resulting graphene is elementally pure; the carbon content is 99.8%, and very consistent from batch to batch.
This type of process has an environmental advantage in terms of energy demand when compared to industrial graphene production methods with large energy demand. In fact, the explosion reaction of acetylene and oxygen is an exothermic one which results in a miniscule CED per kg of graphene for the LCA process for 2.7 MJ/kg of graphene produced. To put that number into perspective and to appreciate the magnitude of energy, if you look at a very common material like aluminum, not a nanomaterial, just a conventional material, it takes 200 MJ per kg of aluminum using a very mature production process which has been refined for over more than a century now.
To get the total CED, the values of the contribution from acetylene and oxygen must be added which will depend on the source of raw materials. If no water is used the CWU is zero and the by-product, commodity gases, can be captured and used in other application.
However, it takes more to describe the impact of a product or a process. In the case of graphene, the toxicity to humans, animals, etc. must be measured. One approach gaining in popularity in academic publications is to look at cradle-to-gate impacts rather than cradle-to-grave journey.
The environmental impact of the applications of graphene, which can be numerous, should also be considered. Since these application pathways happen after graphene is shipped out from the production site, or the gate, that is called gate-to-grave assessment. So in a comparison of different graphene production methods, a cradle-to-gate analysis should be preferred. Then once applications are defined, consider all the aspects of the lifecycle such as transportation, application process, end-of-life, and, finally, disposal.
This is a long-involved process, but graphene producers have a shared interest in developing the most stable and environmentally advantageous methodology. The world depends on it.