glocalized solutions for sustainability in manufacturing || consideration of the precautionary...

4
Consideration of the Precautionary Principle – the Responsible Development of Nano Technologies Marcel Weil 1 1 Institute for Technology Assessment and Systems Analysis (ITAS), Karlsruhe Institut of Technologie (KIT), Karlsruhe, Germany Abstract Carbon nanotube papers, referred to as bucky papers, are attracting a growing attention in different disciplines and application fields. The production of bucky papers is still considered to be too elaborate and costly for a broader application. Additional there are nano particle emission during production with unknown effects on environment and human health. For a planed upscale a carbon nanotube paper production is analysed, not only to identify optimisation potentials regarding technical and economic but also environmental and health aspects. For known environmental impacts, a streamlined Life Cycle Assessment (LCA) is conducted. Whereas for the unknown impact of nanotube emissions on environment and human health a qualitative method is used within a optimisation process, to foster the prevention of nano particle emissions, in respect of the precautionary principle. Keywords: Carbon Nanotube Paper; Streamlined LCA; Economic Assessment; Precautionary Principle 1 INTRODUCTION New materials on a nano scale have the potential to overwhelm existing technical barriers and are one of the most promising key technologies to enable the decoupling of economic growth and resource consumption. Developing these materials for industrial application means facing a complex qualification profile, which includes among others technical, economic, and ecological aspects. The two latter aspects are not sufficiently included in material development, especially from a life cycle point of view [1]. If and when economic/ecological assessment is carried out in material development, it is performed after technical investigations are finished. Quite often, these assessments are postponed until the subsequent phase of product development. In the presented prospective approach, system analysis is used to optimise the manufacturing process of carbon nanotube (CNT) paper by the consideration of technical, but also economic and ecological aspects, including nano specifics. 2 APPROACH Figure 1: Different levels of uncertainties regarding new technologies require the selection and combination of different methods and tools. The integration of system analysis in the early phase of technology development has one the one hand to struggle with the high degree of uncertainty and unknown effects, but on the other hand has the chance to use the high degree of freedom (for development options) to guide the development itself in a more sustainable direction. Life Cycle Assessment (LCA) is an appropriate tool to analyse the environmental impact of a technology or product (cf. Figure 1). Due to uncertainties, inconsistent scientific results and the lack of knowledge about the eco- and human toxicity of nano particle, the potential environmental and health impact of nano particle is not covered by traditional LCA. Therefore the chosen approach includes a qualitative method (ABC-method) to ensure that also potential environmental and health risks will be minimized during an optimisation process by reducing or even preventing the emissions of nano particles to the environment (Figure 1). The minimization of nano particle emission with unknown risks is a requirement of the precautionary principle. In parallel to LCA (cradle to gate) also an economic assessment is carried out to identify overall more sustainable options. The described approach is focused exemplarily on the production of CNT-paper production. 3 PRODUCTION OF CNT AND BUCKY PAPERS 3.1 Production of CNT Carbon Nano Tubes (CNT) belong to a interesting material group with very promising technological properties, like very low optical reflection, high tensile strength (by low weight), good electric and heat conductivity. They can be produced basically by three different methods: arc discharge laser ablation chemical vapour deposition (CVD) The CVD process shows the greatest promise for a large-scale manufacturing of CNT, in particular fluidized bed CVD techniques [2]. Due to the fact that to date the quality of CNT from fluidized bed CVD has not met all the requirements for bucky paper production, a CVD in the batch mode is considered and used for the production of multi-walled carbon nano tubes (MWNT) for the presented work. 185 J. Hesselbach and C. Herrmann (eds.), Glocalized Solutions for Sustainability in Manufacturing: Proceedings of the 18th CIRP International Conference on Life Cycle Engineering, Technische Universität Braunschweig, Braunschweig, Germany, May 2nd - 4th, 2011, DOI 10.1007/978-3-642-19692-8_32, © Springer-Verlag Berlin Heidelberg 2011

Upload: christoph

Post on 25-Dec-2016

212 views

Category:

Documents


0 download

TRANSCRIPT

Consideration of the Precautionary Principle – the Responsible Development of Nano Technologies

Marcel Weil1 1Institute for Technology Assessment and Systems Analysis (ITAS), Karlsruhe Institut of Technologie (KIT),

Karlsruhe, Germany

Abstract Carbon nanotube papers, referred to as bucky papers, are attracting a growing attention in different disciplines and application fields. The production of bucky papers is still considered to be too elaborate and costly for a broader application. Additional there are nano particle emission during production with unknown effects on environment and human health. For a planed upscale a carbon nanotube paper production is analysed, not only to identify optimisation potentials regarding technical and economic but also environmental and health aspects. For known environmental impacts, a streamlined Life Cycle Assessment (LCA) is conducted. Whereas for the unknown impact of nanotube emissions on environment and human health a qualitative method is used within a optimisation process, to foster the prevention of nano particle emissions, in respect of the precautionary principle. Keywords: Carbon Nanotube Paper; Streamlined LCA; Economic Assessment; Precautionary Principle

1 INTRODUCTION

New materials on a nano scale have the potential to overwhelm existing technical barriers and are one of the most promising key technologies to enable the decoupling of economic growth and resource consumption. Developing these materials for industrial application means facing a complex qualification profile, which includes among others technical, economic, and ecological aspects. The two latter aspects are not sufficiently included in material development, especially from a life cycle point of view [1].

If and when economic/ecological assessment is carried out in material development, it is performed after technical investigations are finished. Quite often, these assessments are postponed until the subsequent phase of product development.

In the presented prospective approach, system analysis is used to optimise the manufacturing process of carbon nanotube (CNT) paper by the consideration of technical, but also economic and ecological aspects, including nano specifics.

2 APPROACH

Figure 1: Different levels of uncertainties regarding new technologies require the selection and combination of different

methods and tools.

The integration of system analysis in the early phase of technology development has one the one hand to struggle with the high degree

of uncertainty and unknown effects, but on the other hand has the chance to use the high degree of freedom (for development options) to guide the development itself in a more sustainable direction. Life Cycle Assessment (LCA) is an appropriate tool to analyse the environmental impact of a technology or product (cf. Figure 1). Due to uncertainties, inconsistent scientific results and the lack of knowledge about the eco- and human toxicity of nano particle, the potential environmental and health impact of nano particle is not covered by traditional LCA. Therefore the chosen approach includes a qualitative method (ABC-method) to ensure that also potential environmental and health risks will be minimized during an optimisation process by reducing or even preventing the emissions of nano particles to the environment (Figure 1). The minimization of nano particle emission with unknown risks is a requirement of the precautionary principle. In parallel to LCA (cradle to gate) also an economic assessment is carried out to identify overall more sustainable options. The described approach is focused exemplarily on the production of CNT-paper production.

3 PRODUCTION OF CNT AND BUCKY PAPERS

3.1 Production of CNT

Carbon Nano Tubes (CNT) belong to a interesting material group with very promising technological properties, like very low optical reflection, high tensile strength (by low weight), good electric and heat conductivity. They can be produced basically by three different methods:

arc discharge

laser ablation

chemical vapour deposition (CVD)

The CVD process shows the greatest promise for a large-scale manufacturing of CNT, in particular fluidized bed CVD techniques [2]. Due to the fact that to date the quality of CNT from fluidized bed CVD has not met all the requirements for bucky paper production, a CVD in the batch mode is considered and used for the production of multi-walled carbon nano tubes (MWNT) for the presented work.

185J. Hesselbach and C. Herrmann (eds.), Glocalized Solutions for Sustainability in Manufacturing: Proceedings of the 18th CIRP International Conference on Life Cycle Engineering, Technische Universität Braunschweig, Braunschweig, Germany, May 2nd - 4th, 2011, DOI 10.1007/978-3-642-19692-8_32, © Springer-Verlag Berlin Heidelberg 2011

3.2 Production Process of Bucky Papers

The synthesized MWCNT are purified in a liquid medium. After the separation of the liquide medium and the MWCNT by the help of vacuum filtering technique, the MWCNT are dispersed in a solvent, supported by the use of an ultrasonic treatment. Only well dispersed MWCNT are useful for CNT paper production.

Figure 2: Manufacturing process of CNT paper.

By using again filtration techniques, MWCNT build up a layer on the top of a filter medium. After drying under room temperature and separation of the filter medium and the MWCNT layer, a free standing paper is produced. The manufacturing process is shown in Figure 2. This paper consists of 100% MWNT, meaning that no supporting fibres are contained.

4 ANALYSIS OF CNT-PAPER PRODUCTION

4.1 System boundary of economic and life cycle assessment

Figure 3: System boundary for economic and ecological assessment.

The system boundaries for economic and ecological investigations are shown in Figure 3. The results of the assessment are used both to identify the economic and ecological hot spots and to select the most favourable optimisation strategy. The manufacturing process can be divided into three main steps: synthesis of catalyst, synthesis of MWNT, and production of bucky paper, conf. Figure 3.

For the investigation all prechains of inputs (e.g. electric energy) or services (e.g. transport) which are necessary for the whole manufacturing process are considered.

4.2 LCA

For the understanding of the ecological implications of bucky paper production a streamlined Life Cycle Assessment (LCA) is conducted. The CML method [3, 4] is used for the ecological impact assessment. Human and eco toxicity of nano-materials are not included in this investigation. In the presented contribution, we display only one impact indicator: Global Warming Potential (GWP).

Global warming or greenhouse effect is quantified by using GWP for substances having the same effect as CO2 in reflection of heat radiation. GWP for greenhouse gases are expressed as CO2-equivalents. Hence the impact indicator GWP describes the potential greenhouse effect of a product/process by calculating all emitted greenhouse gases (e.g. CO2) per functional unit, in this specific case, the production of bucky paper.

In Figure 4 the shares of all process steps and pre-chains (e.g. electric energy) in the GWP are presented. It reveals that the dispersion process of MWNT contributes most to the GWP result. Responsible for the GWP contribution is mostly the use of a solvent. In addition, the transport of the dispersion medium (solvent) has a significant contribution. Other impact categories [3, 4] demonstrate results similar to GWP, beside “photo-oxidant formation”.

Global Warming Potential

dispersion

transport ofsolvent

others

purification

transport acid(purification)

electric energy

Figure 4: Shares of all process steps and pre-chains in GWP.

4.3 Economic assessment

Figure 5 display the shares in production costs of bucky papers (including supplies). The costs for labour, leasing and depreciation are not included.

It indicates that the dispersion process of MWNT contributes most to the production costs. Again the use of solvents is the most important cost driver. The filtration process has a noteworthy contribution. All the other processes have only a small share to the production costs.

Material Costs

dispersion

synthesis MWNT

purification

catalyst

filtration

others

Figure 5: Shares in production costs.

CNT Synthese CNT Purification CNT Dispersion CNT Paper cut to order

CNT Paper

Filtering 2 Filtering 1

emissions (air, water, earth)

mixing processing

CNT synthesis purification filtration I

dispersing filtration II drying bucky paper

system boundary

resources

catalyst

MWNT

Life Cycle Design - Selected Applications186

5 DEVELOPMENT OF OPTIMISATION STRATEGIES

5.1 Lessons learned

Both the economic and ecological assessment identified the dispersion process, especially the use of solvent, as a major driver.

Hence an optimisation strategy has to be developed, which allows the minimization of solvent use, or alternatively which substitutes the use of the solvent.

But to focus during the optimization process only on economic and ecological goals can be described as insufficient, because the technical performance could be reduced or nano particle emissions increased. Thus the optimisation considers the following aspects:

Stabilisation of the production process and stabilisation of the product quality (only minimal reduced technical performance is acceptable)

Reduction of the production costs

Reduction of the environmental impact

Reduction (or prevention) of nano particle emission to the environment

It hast to be stated, that the latter focused on the nano particle emissions to water. Without any doubts, the CNT paper production process also causes nano particles emissions to air, but due to very efficient air cleaning machines, the nano particle concentration in the laboratory is lower than outside (background concentration of nano particle). This is shown by nano particle air measurements (10-1000 nm) of a German labour protection organisation.

5.2 Comparison of alternative optimization strategies

Together with the industry partners six different optimization strategies were developed (Table 1):

Use of an alternative solvent

Replacement of solvent by water (up to 30 %)

Use of a water tensideX1 mixture

Use of a water tensideX2 mixture

Use of a water tensideX3 mixture

Recycling of solvent

All six alternatives are analyzed and qualitative evaluated regarding the mention aspects mentioned above (Table 1).

The comparison of the six different optimization options reveals that the last option, recycling of solvent, shows the best overall performance and is in addition the only option, which reaches a comparable technical quality of the gained CNT paper, which is an important requirement.

Subsequently it was investigated if a continuously recycling of the solvent causes an accumulation of substances, which might have a negative impact on the bucky paper quality.

But also a continuous recycling of the solvent over more than 30 cycles doesn’t have any quantifiable negative effects on the produced quality of the buck papers.

6 QUANTITATIVE RESULT OF CHOSEN OPTIMIZATION OPTION

At comparable bucky paper quality, the recycling of solvent represents the best of six investigated optimisation option. Within the dispersion process, up to 70% of the solvent can be recycled with low efforts for reprocessing. The quantitative effects of the optimisation option “recycling solvent” are shown in Figure 6. The Global Warming Potential (GWP) is reduced by 65%, the production costs are decreased by 59% (total costs by 16%) in comparison to the reference case (status quo of CNT paper production) [5]. In addition by a continuously recycling of the solvent the nano particle emission to the water path could be prevented.

100% Solvent (Reference)

Solvent replacement by

100% alternative

solvent

Solvent replacement up to 30% by water

Solvent replacement by

100% water/tensideX1

mixture

Solvent replacement by

100% water/tensideX2

mixture

Solvent replacement by

100% water/tensideX3

mixture

Recycling of reference

solvent

Quality bucky paper

A A/B B/C B C C A

Economic profile

C A/B B A/B A/B C A/B

Ecological profile C C B A/B A/B A/B A/B

CNT emissions (to water)

C C C C C C A/B

0

10

20

30

40

50

60

70

80

90

100

reference recyclingsolvent

reference recyclingsolvent

reference recyclingsolvent

Global WarmingPotential

Material Costs CNT Emissions to Water(Dispersion)

Figure 6: Quantitative effect of the optimisation process

Table 1: Qualitative comparison of optimisation strategies.

Life Cycle Design - Selected Applications 187

7 SUMMARY

The use of multi-walled carbon nanotubes for the production of bucky papers has opened up new application fields. But the production of bucky papers still is considered to be too elaborated and costly for a broader application. Furthermore the ecological implications of the bucky paper production are unknown. The economic and ecological assessment of the carbon nanotube paper production on a laboratory scale reveals that the dispersion of the MWNT has a great impact on the ecological profile and the costs. Mainly responsible is the use of solvents for dispersing nanotubes. The economic and ecological results concerning the status quo of bucky paper production is essential for the development of optimisation strategies. Different optimisation strategies are investigated and qualitative evaluated. The selection of the most promising optimisation option is based on technical, economic, and ecological aspects, including nano particle emissions.

A substantial decrease of costs and ecological impact with good product quality (of bucky paper) is reached by the optimisation option “recycling of solvent”. The gained information is essential for an upscale of bucky paper production in a continuous mode. Further investigations are needed to compare bucky papers with traditional materials in different application fields over the entire life cycle. The presented work showed one possible approach enabling a more responsible development of a new technology, which might bear some unknown risks. 8 REFERENCES

[1] Weil, M., Buchwald, A., Dombrowski, K., Jeske, U., Buchgeister, J. - Eds. - (2007): Materials Design and Systems Analysis, Shaker-Verlag, p. 321.

[2] See, C. H., Harri, A.T. (2007): A Review of Carbon Nanotube Synthesis via Fluidized-Bed Chemical Vapor Deposition. Ind. Eng. Chem. Res., 46 (4), pp 997–1012.

[3] Guinée, J.B. - Eds - (2002): Life cycle assessment. An operational guide to the ISO standards, CML Leiden, p. 708.

[4] Heijungs, R., Guinée, J.B., Huppes, G., Lankreijer, R.M., Udo de Haes, H.A., Wegener Sleeswijk, A., Ansems, A.M.M., Eggels, P.G., Duin, R. van, Goede, H.P. de (1992): Environmental Life Cycle Assessment of Products; Guide & Backgrounds, CML Leiden.

[5] Weil, M., Schebek, L., Forero, S., Crizeli, S. (2009): Bucky papers - a prospective economic and ecological investigation for the upscale of the production process. SETAC Europe 19th Annual Meeting. Göteborg, Sweden.

Life Cycle Design - Selected Applications188