CO conversion covers a wide range of possible application areas from fuels to bulk and commodity chemicals and even to specialty products with biological activity such as pharmaceuticals. In the present review, we discuss selected examples in these areas in a combined analysis of the state-of-the-art of synthetic methodologies and processes with their life cycle assessment. Thereby, we attempted to assess the potential to reduce the environmental footprint in these application fields relative to the current petrochemical value chain. This analysis and discussion differs significantly from a viewpoint on CO utilization as a measure for global CO mitigation. Whereas the latter focuses on reducing the end-of-pipe problem "CO emissions" from todays' industries, the approach taken here tries to identify opportunities by exploiting a novel feedstock that avoids the utilization of fossil resource in transition toward more sustainable future production. Thus, the motivation to develop CO-based chemistry does not depend primarily on the absolute amount of CO emissions that can be remediated by a single technology. Rather, CO-based chemistry is stimulated by the significance of the relative improvement in carbon balance and other critical factors defining the environmental impact of chemical production in all relevant sectors in accord with the principles of green chemistry.

A large variety of energy storage systems are currently investigated for using surplus power from intermittent renewable energy sources. Typically, these energy storage systems are compared based on their Power-to-Power reconversion efficiency. Such a comparison, however, is inappropriate for energy storage systems not providing electric power as output. We therefore present a systematic environmental comparison of energy storage systems providing different products. As potential products, we consider the reconversion to power but also mobility, heat, fuels and chemical feedstock.Using life cycle assessment, we determine the environmental impacts avoided by using 1 MW h of surplus electricity in the energy storage systems instead of producing the same product in a conventional process. Based on data for several countries including the United States, Brazil, Japan, Germany and the United Kingdom, our analysis determines the highest reduction of global warming and fossil depletion impact for using surplus power in heat pumps with hot water storage and battery electric vehicles. Third highest environmental benefits are achieved by electrical energy storage systems (pumped hydro storage, compressed air energy storage and redox flow batteries). Environmental benefits are also obtained if surplus power is used to produce hydrogen but the benefits are lower. Our environmental assessment of energy storage systems is complemented by determination of CO 2 mitigation costs. The lowest CO 2 mitigation costs are achieved by electrical energy storage systems. Broader contextEnvironmental impact reduction is the major motivation for increasing the use of renewable energies. Since renewable energy sources like wind and solar are intermittent in nature, their increased installation leads to unused surplus power. Therefore, storage for surplus power is required. Since the potential of pumped hydro storage as the only installed large scale storage system is nearly exhausted, a large variety of concepts are currently investigated to use the surplus power. The proposed concepts span from electrical storage over storage in battery electric vehicles to production of hydrogen. Hydrogen can then be used in several ways including reconversion to power in fuels cells or conversion of hydrogen with CO 2 to hydrocarbons. However, surplus power is limited and therefore only storage systems with the highest contribution to the reduction of environmental impacts should be implemented. This article therefore provides a method to compare energy storage systems based on their environmental impact reductions using life cycle assessment.

The intended audience for this document are practitioners that want to learn how to create comprehensible and consistent techno-economic assessments and life cycle assessments in the CCU field. These practitioners may come from academia, industry or government and may work in technology assessment and technology research and development, or funding, they may be part of the CCU community, the TEA community or the LCA community. Readers of TEA and LCA, such as investors, policy Part A: General Assessment Principles Part B: TEA guidelines Part C: LCA guidelines PART A: GENERAL ASSESSMENT PRINCIPLES TEA & LCA Guidelines for CO2 Utilization 8makers or funding decision makers are not the intended audience for these TEA and LCA guidelines, but may use this document to understand the challenges and pitfalls for TEA and LCA. A.2.4 Limitations of this documentThese guidelines have been developed to enable consistent and comparable LCA and TEA studies for CCU. They are not intended to serve as an assessment standard or rulebook. Instead they are meant to help practitioners to conduct sound assessments efficiently, avoid common mistakes and to derive meaningful results that can be compared to other studies. This document serves as an addition to conventional existing standards (in particular for LCA) and literature and does not replace any chemical engineering, economics or project planning principles. However, since the guidelines aim to enhance the comparability and transparency of studies, the LCA guidelines are more restrictive than the general ISO-framework. In some cases, there may be need to add further tasks to the ones discussed in this guideline since they are important to a specific study. Such additions are not excluded by the present guideline. However, the guidelines provide a consistent methodological core for conducting all LCA and TEA CCU studies.This document is intended as the first step of a longer framework development process. TEA and LCA remain two separate approaches in this document as is common in current assessment practice in academic literature and industry. However, a combined approach is in strong demand to include trade-offs in decision making. The integration of TEA and LCA into one singular study is a next major development step that is subject to future work. This document provides some initial guidance to those who wish to carry out an integrated TEA & LCA study, however many facets of the integration process are still to be determined. A.2.5 The guidelinesThe guidelines for TEA are presented in part B of this document and LCA in part C. At the end of each guideline chapter there is a box listing rules that these guidelines recommend. The box contains three categories, shall, should and may:TEA & LCA Guidelines for CO2 Utilization 9TEA & LCA Guidelines for CO2 Utilization 14 A.4.2.4 GuidelinesGuideline A.1 -Technology maturity Shall 1) Technology maturity shall be defined in each assessment -first for each system element and second for the overall product system 2) The maturity of the over...

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We present a comparative life cycle assessment (LCA) for the CO2-based production of formic acid, carbon monoxide, methanol, and methane.