CHEMSUSCHEM FULL PAPERS DOI: 10.1002/cssc.201301115

Synthesis and Application of Carbonated Fatty Acid Esters from Carbon Dioxide Including a Life Cycle Analysis Benjamin Schffner,*[a] Matthias Blug,[a] Daniela Kruse,[a] Mykola Polyakov,[b] Angela Kçckritz,[b] Andreas Martin,[b] Prasanna Rajagopalan,[b] Ursula Bentrup,[b] Angelika Brckner,[b] Sebastian Jung,[c] David Agar,[c] Bettina Rngeler,[d] Andreas Pfennig,[d, e] Karsten Mller,[f] Wolfgang Arlt,[f] Benjamin Woldt,[a] Michael Graß,[a] and Stefan Buchholz[a] Carbon dioxide can be used in various ways as a cheap C1 source. However, the utilization of CO2 requires energy or energy-rich reagents, which leads to further emissions, and therefore, diminishes the CO2-saving potential. Therefore, life cycle assessment (LCA) is required for each process that uses CO2 to provide valid data for CO2 savings. Carbon dioxide can be incorporated into epoxidized fatty acid esters to provide the corresponding carbonates. A robust catalytic process was developed based on simple halide salts in combination with a phase-transfer catalyst. The CO2-saving potential was determined by comparing the carbonates as a plasticizer with an es-

tablished phthalate-based plasticizer. Although CO2 savings of up to 80 % were achieved, most of the savings arose from indirect effects and not from CO2 utilization. Furthermore, other categories have been analyzed in the LCA. The use of biobased material has a variety of impacts on categories such as eutrophication and marine toxicity. Therefore, the benefits of biobased materials have to be evaluated carefully for each case. Finally, interesting properties as plasticizers were obtained with the carbonates. The volatility and water extraction could be improved relative to the epoxidized system.

Introduction The rise in global CO2 emissions is one of the current major global challenges.[1] A major share of these emissions are due to the burning of fossil fuels. Therefore, targets for climate protection were defined by the European Commission and an emission trading system was initiated for Europe.[3] In addition, a threefold strategy was developed in Germany: 1) reduction [a] Dr. B. Schffner, Dr. M. Blug, Dr. D. Kruse, Dr. B. Woldt, Dr. M. Graß, Prof. Dr. S. Buchholz Evonik Industries AG, Paul-Baumann-Str. 1 45772 Marl (Germany) E-mail: [email protected] Homepage: http://www.evonik.com http://ww.creavis.de [b] Dr. M. Polyakov, Dr. A. Kçckritz, Dr. A. Martin, Dr. P. Rajagopalan, Dr. U. Bentrup, Prof. Dr. A. Brckner Leibniz-Institut fr Katalyse e.V. Albert-Einstein-Str. 29a, 18059 Rostock (Germany) [c] Dr. S. Jung, Dr. D. Agar Institut fr Technische Chemie B, TU Dortmund Emil-Figge-Str. 66, 44227 Dortmund (Germany) [d] B. Rngeler, Prof. Dr. A. Pfennig AVT-Thermische Verfahrenstechnik - RWTH Aachen 52056 Aachen (Germany) [e] Prof. Dr. A. Pfennig Institute of Chemical Engineering and Environmental Technology TU Graz, Inffeldgasse 25, 8010 Graz (Austria) [f] Dr. K. Mller, Prof. Dr. W. Arlt Friedrich-Alexander Universitt Erlangen-Nrnberg Lehrstuhl fr thermische Verfahrenstechnik Egerlandstr. 3, 91058 Erlangen (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201301115.

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of CO2 emissions by higher efficiency and alternative energy sources, 2) utilization of CO2, and 3) storage of CO2.[3, 4] The utilization of CO2 as a carbon source has been discussed intensively throughout the last two decades.[5, 6] However, the lack of chemical activity of CO2 is a major challenge for its utilization. Usually, hydrogen, epoxides, or electrical energy are required to transform this stable molecule into other compounds. However, additional energy sources and reagents have to be considered with regard to their sustainability impact to the overall process. Despite countless research activities to investigate the utilization of CO2, only a few approaches have provided a complete life cycle analysis (LCA) to prove their environmental benefit. Therefore, the incorporation of CO2 estimations should be an essential part of the discussion about CO2 utilization. For example, methanol can be synthesized from CO2 by hydrogenation.[7] A prerequisite for sustainable production is supplying hydrogen from sustainable sources, for example, water splitting through photocatalysis[8] or electrolysis by using renewable energy to reduce the carbon footprint of H2 (currently 10–14 kg CO2 per kg H2).[9] Alternatively, CO2 can be used without the need for hydrogen to form acrylates or other carboxylates.[10–13] Already today, CO2 is used in the synthesis of urea, salicylic acid, and for mono-[14] and polymeric carbonates.[15, 16] Furthermore, special carbonates are available from epoxidized fatty acids. These materials offer a variety of interesting properties, for example, in the synthesis of non-isocyanate polyurethanes (NIPUs), for lubricants and plasticizers.[17]

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CHEMSUSCHEM FULL PAPERS Increased attention is being directed towards plasticizers from biobased materials within the European market. In previous years the European market for plasticizers reached a volume of over 1.1 million tonnes, of which approximately 80–90 % are used in the phthalate-dominated soft polyvinyl chloride (PVC) market.[18] Due to toxicological issues, so-called low-molecular-weight phthalates, such as di-2-ethylhexyl phthalate (DEHP), will be restricted to only a few applications.[19] Although the share of DEHP is limited on the European market, globally it is the dominating plasticizer (45 %).[18] Therefore, a large substitution potential exists that currently is primarily covered by nontoxic high-molecular-weight phthalates, such as diisononyl phthalate (DINP), and phthalate-free solutions, such as 1,2-diisononyl cyclohexyl dicarboxylate. Alternatively, demand can also be covered by plasticizers from biorenewables (succinates, citrates, or fatty acid esters).[20] The synthesis of carbonated fatty acid methyl esters (CFAME) is described in Scheme 1. The triglyceride is converted

www.chemsuschem.org pylene, butylene, or cyclohexylyl carbonates[29] were not suitable for disubstituted, unstrained epoxides, such as EFAME. Recently, a few examples of the carbonation of disubstituted systems have been developed. Soluble polyoxometalates (POMs) as catalysts for the carbonation of fatty acids were introduced by Leitner and co-workers.[30] Furthermore, some new salen and amino triphenolate type ligands were described for 1,2substituted epoxides by the groups of North and Kleij.[31] An efficient carbonation with an affordable catalyst was a key aspect of this work.

Results and Discussion A selection of screening results for the carbonation of EFAME is shown in Table 1. Further results are available in the Supporting Information. A conversion of 69 % was observed with TBABr as a traditional catalyst for this reaction (Table 1, entry 1). If the catalyst was adsorbed on silica, the yield dropped significantly. Reduced reactivity was observed for various adsorbed catalysts (see the Supporting Information) and could be due to mass-transfer limitations. Unfortunately, all tested heterogeneous catalysts were inactive (see the Supporting Information). Furthermore, no conversion was observed with the bimetallic Al–salen complex of North et al.[31b] in the absence of an organic halide source (e.g., NH4Br). However, in combination with soluble TBABr, a conversion of 80 % was achieved with a selectivity of 94 % (Table 1, entry 3). With SnCl4 the selectivity

Table 1. Catalyst screening for the carbonation of EFAME.[a]

Scheme 1. Conversion of fatty acid methyl ester into carbonated fatty acid esters.

in the presence of methanol and NaOMe to form a fatty acid methyl ester (FAME or so-called biodiesel).[21] In the subsequent step, FAME is converted by the use of H2O2 into EFAME. Industrially, this process is applied by using peracetic or performic acid.[22] Due to safety issues (explosion protection), direct conversion of FAME with aqueous H2O2 would be preferred. Various catalytic systems (tungstates,[23] molybdates,[24] methyl trioxorhenium,[25] alumina,[26] or aldehyde/oxygen[27]) have been studied in the literature to obtain EFAME from FAME. In contrast to the other reactions, the carbonation procedure towards CFAME has received only limited attention. Some early work was performed by Doll and Kenar with a focus on using the obtained CFAME as an intermediate for new materials.[28]Additionally, the catalysts used for the formation of pro 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Catalyst

PTC

Conversion[b] [%]

Selectivity[c] [%]

TBABr[d] TBABr[d] on SiO2 Al–salen[e] TBAI[f] SnCl4·(H2O)5 ZnBr2 POM[g] BuMeImCl[h] BuMePyI[i] KI KBr KI NaI LiI CsI

– – TBABr[d] – TBABr[d] C5H5N – – – – [18]crown-6 [18]crown-6 [15]crown-5 [12]crown-4 [18]crown-6

69 15 80 75 64 88 73 26 65 2 55 90 94 18 10

> 99 > 99 94 98 82 56 97 > 99 > 99 > 99 97 97 89 98 99

[a] Further reaction conditions: EFAME (2.5 g). The reaction scheme uses epoxidized methyl linoleate as a model structure for the EFAME mixture. PTC = phase-transfer catalyst. [b] Conversion was determined by 1H NMR spectroscopy and GC. [c] Selectivity was determined by 1H NMR spectroscopy and GC. [d] TBABr = tetrabutyl ammonium bromide. [e] Aluminum– salen complex.[31b] [f] TBAI = tetrabutyl ammonium iodide. [g] ((C7H13)4N)5[a-SiW11O39Fe]·(C7H8)2, (2 mol %) with epoxidized methyl oleate as a substrate. [h] BuMeImCl = 1-butyl-3-methyl imidazolium chloride. [i] BuMePyI = 1-butyl-4-methyl pyridinium iodide.

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CHEMSUSCHEM FULL PAPERS was reduced due to the higher Lewis acid character of this catalyst. This promotes hydrolysis of the epoxide to the corresponding diol (Table 1, entry 5). The strong trend of SnCl4 to form diols from epoxides was further proven by a reaction of SnCl4·(H2O)5 in the absence of TBABr. Within 17 h full conversion to the diols was observed. Soluble POMs have been tested by Leitner and co-workers as hydrates with high conversions and very good cis/trans selectivity.[30] In the case of the toluene–adduct complexes, the reactivity was reduced from 98 to 73 % (Table 1, entry 7). Unfortunately, the use of POMs is limited to epoxidized methyl oleate because various side products were observed with linoleates and linolenates. This effect was described earlier by the Leitner group.[30] Halide-containing ionic liquids (ILs), such as imidazolium or pyridinium salts, were also employed in the reaction and resulted in low or moderate conversion rates (Table 1, entries 8 and 9). In mixtures with EFAME and CFAME, two phases were formed with the ILs. This offers an interesting approach for separating the catalyst from the product mixture. Unfortunately, detailed studies have shown that an unacceptable large quantity of the IL leached into the fatty acid phase and could not be recovered efficiently. The efficient use of simple halides for the carbonation step has been shown for the low-molecular-weight carbonates.[6] However, to achieve sufficient solubility for these salts, a PTC is required. The characteristics of this system have been described by the groups of Rokicki and Wang.[32] KBr, KI, and NaI were tested with suitable crown ethers in the reaction with EFAME (Table 1, entries 11–13). The best conversion of 94 % was observed with NaI and [15]crown-5, but the selectivity dropped to 89 %. Better selectivity with slightly lower reactivity was obtained with KI and [18]crown-6. In comparison to these findings, only low conversions rates were observed with the use of CsI and LiI with suitable crown ethers (Table 1, entries 14 and 15). KBr could also be used as a catalyst, but the conversion was reduced from 90 to 55 %. If harder nucleophiles such as KCl were used, no conversion was observed (see the Supporting Information). These findings are in line with previous observations for carbonation in which Cl was the least efficient halide. The formation of ketones as major side products by Meinwald rearrangement[33] was confirmed by NMR spectroscopy. Because economically attractive, simple halides showed superior results with crown ethers, a second screening was completed to search for other, potentially cheaper PTCs. The results are shown in Table 2. Glycols are particularly of interest because their properties can be tuned by their polymer size and they are commercially available on a large scale for acceptable prices. Although only 17 % conversion was observed with monoethylene glycol, the conversion was increased to 84 % by using PEG 400 (Table 2, entries 1–5). A reaction mechanism for this PTC was described very recently in a publication by Kumar and Jain.[34] The conversion decreased again with larger PEGs (Table 2, entries 6–8). One possible reason could be the limited solubility of these PEGs with the substrate. Furthermore, due to their viscous nature, the mobility of the reaction mixture is greatly reduced with large PEGs. Other PTCs, such as podands  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemsuschem.org Table 2. Variation of the PTC in carbonation with KI.[a]

1 2 3 4 5 6 7 8 9 10 11 12 13

Cat.

PTC

Conversion [%]

Selectivity [%]

KI KI KI KI KBr KI KI KI KI KI KI LiI CsI

monoethylene glycol diethylene glycol diethylene glycol[b] PEG 200 PEG 200[b] PEG 400 PEG 600 PEG 1000 PEG 100 000 [2.2.2]cryptand[c] podand[d] PEG 200[b] PEG 200[b]

17 64 73 79 71 84 83 62 17 83 23 43 89

> 99 97 98 99 97 99 99 98 99 99 99 95 97

[a] For reaction conditions and analytical details, see Table 1. PEG = polyethylene glycol. [b] 60 wt %. [c] [2.2.2]Cryptand = 4,7,13,16,21,24-hexaoxa1,10-diazabicyclo[8.8.8]hexacosan. [d] Podand = tris[2-(2-methoxyethoxy)ethyl]amine.

or cryptands, were less active in this reaction (Table 2, entries 10 and 11) and are less attractive due to limited availability and high prices. In addition to KI, other halides could also be successfully used with PEGs. However, in many cases, only good conversions were obtained with high loadings of PEG 200. For example, excellent results were only obtained for CsI with 60 wt % PEG 200 (Table 2, entry 13). The conversion rate was greatly reduced if the loading of PEG 200 was lowered to 3.5 wt % (see the Supporting Information). As described above, LCA calculations were used to evaluate the environmental effect of the replacement of DINP with CFAME. All calculations were performed based on common ISO standards (ISO 14040 and ISO 14044; see the Supporting Information). DINP was chosen as the plasticizer benchmark for this study. This plasticizer combines low toxicity, high performance, and an acceptable price. The LCA was based on two ASPEN simulations. The flow sheets of the ASPEN simulation are shown in the Supporting Information. The ASPEN simulation for DINP was based on known patents. The new process was defined by laboratory results for the carbonation step. The epoxidation step was based on literature results.[23–27] Although all data for the CFAME process have been defined carefully based on existing data, some details, for example, downstream separation of a catalyst, are not incorporated into the simulation at this stage of process development. Similar assumptions were taken into account for both simulations to obtain comparable results. Therefore, the CO2 emissions shown for the new process indicate the maximum saving potential for the potential use of biocarbonates as plasticizers. A variety of raw materials were considered in both processes along with their individual carbon footprint (upstream emissions). The shares of these raw materials are shown in Table 3. In the case of the DINP process, the major upstream emissions are identified by the use of Crack C4. It must be noted that the C4 mixture used is butadiene poor. Furthermore, a buteneand butadiene-poor C4 stream is obtained after the dimerizaChemSusChem 2014, 7, 1133 – 1139

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Table 3. Global warming potentials (GWPs) of various starting materials for the benchmark and the new processes (carbon dioxide equivalents, CO2e [kg kg 1 product]).[a]

Table 4. GWPs of the overall process, including raw materials, energies, and side stream benefits/burdens (CO2e [kg kg 1 product]).[a] Category

1 2 3 4 5 6 7 8

Chemical compound

Soybean USA

Soybean Brasil

Canola Europe

Crack C4 C4 allocation[b] H2 phthalic anhydride syngas FAME[c] LUC[d] H2O2

– – – – – 0.7 – 0.2

– – – – – 1.1 1.7 0.2

– – – – – 2.1 – 0.2

DINP Germany 2.4 1.3 0.1 0.6 0.2 – – –

[a] 1 kg product is defined as 1 kg CFAME or DINP. [b] Reduction of the original GWP of the Crack C4 cut by the removal of butadiene and the obtained Raffinate II stream as a side product. [c] FAME = Fatty acid methyl ester. [d] LUC = land use change.

1 2 3 4 5 6 7

raw materials process emissions[b] biogenic CO2 uptake benefit steam CO2 use incineration (end of life) total

Soybean USA 0.9 0.3 2.1 – 0.2 2.4 1.3

Soybean Brasil 3.0 0.3 2.1 – 0.2 2.4 3.4

Canola Europe

DINP Germany

2.3 0.3 2.1 – 0.2 2.4 2.7

2.0 2.5 – 1.3 – 2.5 5.7

[a] 1 kg of product is defined as 1 kg of CFAME or DINP. [b] Utilities and other emissions (e.g., waste stream incineration).

stream emissions (raw materials; Table 4, entry 1). In all cases, biogenic CO2 uptake is given as a credit because large amounts of CO2 are bound during the growth phase of each plant. Interestingly, CO2 utilization did not have a significant impact on the CO2 savings of the material, although about 230 g of CO2 were bound per kg of EFAME, based on soybean oil, which is about 20 % of the molecular weight. The amount of CO2 bound in the carbonates is overcompensated by emissions during the process and upstream (compare Table 4 entries 1 and 2 with entry 5). This result underlines the importance of the LCA in CO2-utilizing processes. In many instances, chemically bound CO2 cannot compete with the upstream emissions. Although CO2 utilization has little impact on the GWP of CFAME, it still enables new pathways for the synthesis of these molecules to be used. Due to the new reaction pathways, the emissions for CFAME are lowered by almost 80 % when US soybean-based CFAME is compared to DINP. If Brazilian soybean or European canola are used, CO2 savings of 40– 60 % can still be obtained. Beside the GWP, other criteria have to be taken into account for a full LCA. A mixed picture was obtained for other categories, as shown in Table 5. Eutrophication, ozone creation and depletion potential, abiotic depletion potential, and aquatic toxicity are all negatively influenced by the use of biobased raw materials. For CFAME, comparable numbers are calculated in the acidification potential (Table 5, entry 2). However, the eutrophication potential increased by a factor of 20 (Table 5, entry 3This is mainly due to the use of phosphate fertilizer. The

tion reaction towards octene (Raffinate 2). Therefore, the original GWP of Crack C4 is reduced by 1.3 kg CO2e (Table 3, entry 2). Other feedstocks, such as hydrogen, syngas, and phthalic anhydride, have only small shares in the upstream emissions. In the case of CFAME production, the major share of CO2e comes from FAME. Although only small variations between feedstock soy from the USA and that from Brazil are observed (Table 3, entry 6), a major impact is calculated due to LUC (Table 3, entry 7). Allocation of LUC has to be considered for all areas that have been reshaped from forest, meadows, or swamps into agricultural areas within the last 20 years. Therefore, the GWP of FAME from Brazilian soy is adjusted by 1.7 kg CO2e. Alternatively, European canola oil could be used for the production of CFAME (Table 3, entry 6). Additional nitrogen fertilizers are required for growing canola and these fertilizers are usually provided by a mixture of mineral nitrogen salts and organic nitrogen fertilizers (liquid manure). Due to the manure, a significant amount of N2O, which is a very potent greenhouse gas, is released. Table 4 gives an overview of the emissions of both processes. The GWP of DINP is increased by 2.5 kg CO2e due to the intensive use of heat and electricity in the process. Additional energy is required for hydroformylation and for the final treatment of DINP (Table 4, entry 2). Lower pressure steam (4 bar) is produced and is considered to be a benefit (Table 4, entry 4). Because the use phase is similar Table 5. Other LCA criteria for comparison between kg of CFAME (US soybean) and kg of DINP as a plasticizer for soft PVC.[a] for both the benchmark and new process (no improvement Category CFAME DINP or deterioration of the plasticiz1 abiotic depletion potential [mg Sb equiv] 1.3 0.7 ing properties is expected), no 5.4 5.7 2 acidification potential [g SO2 equiv] adjustment was considered for 3 eutrophication potential [g phosphate equiv] 9.1 0.5 the LCA calculations. Finally, 4 freshwater aquatic ecotoxicity potential [g DCB equiv] 9.3 0.4 5 ozone layer depletion potential [mg R11 equiv] 60 8 2.5 kg CO2e are released during 6 photochemical ozone creation potential [g ethylene equiv] 1.8 0.8 incineration at the end of life for 7 terrestrial ecotoxicity potential [g DCB equiv] 2.6 3.4 DINP (Table 4, entry 6). 8 primary energy demand [MJ] 46 98 The major CO2 burdens for [a] Source CML2001 database, year 2010. CFAME are obtained from up 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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CHEMSUSCHEM FULL PAPERS water toxicity also increased because most herbicides, insecticides, fungicides, and fertilizers tend to migrate from the soil into the water system; this leads to a higher toxicity potential for this product (Table 5, entry 4). This trend is also visible for other categories related to the agricultural sector.[35] Whether these points outweigh the CO2 savings of renewable resources is debatable. As already indicated by the CO2 savings, the primary energy demand improved by almost 50 % compared with DINP (Table 5, entry 8). All calculations with regard to sustainability were based on the assumption that the obtained CFAME has similar properties to that obtained by the benchmark process. Otherwise the functional unit for the LCA has to be adjusted. To prove this assumption, plasticizing tests were performed with CFAME based on Nexo E1 (EFAME, soybean mixture) in transparent liquid paste compositions (plastisol) of PVC. The use of fatty acid derivatives as plasticizers has been known for a long time.[36] Epoxides are of special interest because they can scavenge formed hydrochloric acid in PVC and increase the thermal stability of the polymer. Therefore, epoxidized soybean oil (ESBO) is used in various applications as a coplasticizer, but is not suitable for plastisols due to its high viscosity. Alternatively, EFAME can also be used as a plasticizer. However, its observed high volatility inhibits its use in specific applications. By incorporating CO2 into EFAME, the volatility and water extraction rate should be improved, whereas the other properties of EFAME should be preserved. Because several experiments were also performed with epoxidized methyl oleate, the corresponding carbonated methyl oleate (CMO) was also tested. However, the use of HO-sunflower oil in plasticizers is not likely because the material is more expensive than that of soybean oil. For the application tests, 100 parts of PVC were mixed with 50 parts of soybean-based CFAME or HO-sunflower-based CMO and 5 parts of stabilizers. The obtained plastic material was tested for plasticizing efficiency, water solubility, gelation, and compatibility. Furthermore, the volatility of the pure plasticizers was determined. The results are shown in Figure 1. In all cases, acceptable compatibility has been observed without sweating to the PVC surface. For comparison, the properties of soybeanbased EFAME and DINP were added to Figure 1 (for detailed procedures, see the Supporting Information). Gelation is one key aspect for plasticizing properties in which the PVC plastisols undergo physical cross-linking.[37] The conversion process can be tracked with various techniques, such as complex viscosity, during heating of the plastisol.[38] As for epoxides, the gelation temperature was reduced for CMO and CFAME. Interestingly, the isolated carbonate group in CMO leads to better gelation than that in the CFAME mixture with a larger share of linoleic acid. Thus, the gelation properties of CFAME are still better than the results for DINP. Volatility and extraction to water are often described as major drawbacks for EFAME use as a multipurpose plasticizer. The incorporation of carbonate functional groups should reduce the volatility through further interactions between the molecules. To test the water extraction properties, the plasticized PVC sheets were placed in a water bath for seven days. After this time, the swelling of the samples was measured. Ad 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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Figure 1. Plasticizing properties of soybean-based CFAME and EFAME and HO-sunflower-based CMO in PVC in comparison with DINP.

ditionally, the material was measured after drying to indicate the loss of plasticizer. Relative to EFAME, the weight loss could be reduced from > 5 to 1 %. The water extraction rate was further reduced by CMO, for which only 0.5 % of material was lost over the 7 days. However, the weight loss for DINP as the benchmark was almost 0 % at similar conditions. To determine the volatility of the material, the weight losses of CFAME, EFAME, and CMO samples were measured over the course of 10 min at 200 8C. Although more than 20 % of EFAME was lost during this time, the volatility of CFAME from soybean was already reduced to 10 %. By using CMO the volatility was further reduced to 9 %. The best volatility values were observed with DINP, with only 5 % weight loss after 10 min. The efficiency of the plasticizer describes the intensity of its softening effect. During a Shore A hardness test, the resistance of the plastic material towards penetration of a needle is measured. Efficient plasticizers lead to lower values of Shore A hardness, and therefore, a better softening effect. The best results were obtained for EFAME as the plasticizer. Unfortunately, the high plasticizing efficiency of EFAME could not be preserved with the introduction of carbonate groups. Although similar efficiency was exhibited by CMO, the efficiency of CFAME was reduced to that of the level of DINP. Overall, CMO and CFAME exhibit interesting properties as plasticizers. It is possible to reduce some drawbacks of the known EFAME system. However, further investigation is required to optimize the systems to reach the level of DINP.

Conclusions Carbonated fatty acid methyl esters were synthesized from the corresponding epoxides by the use of simple halide salts in combination with PTCs in a carbonation reaction. During the optimization process, the conversion increased from 69 % with TBABr to 90–94 % within 17 h with reduced amounts of byChemSusChem 2014, 7, 1133 – 1139

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products were achieved through the use of alkali halides with PTCs. Furthermore, the carbon footprint estimation indicated great CO2-saving potential for CFAME as a plasticizer candidate compared with that of the DINP benchmark. However, calculations showed that the utilization of CO2 had only a minor impact on the final CO2 savings. This underlines the necessity to perform carbon footprint estimations at a very early phase of a research project with regard to CO2 utilization. CO2 utilization cannot automatically be considered to be a sustainable process. The use of energy-intensive reagents, such as epoxides, boranes, silanes, or hydrogen, will have a major impact on the carbon footprint of alcohols, alkanes, or formic acid. Furthermore, it has to be estimated whether a product that uses CO2 has a sufficient value on the market to justify the use of (mostly) expensive reductants. CO2 should be used as an enabler to open up new reaction pathways that will lead to existing molecules, for example, carboxylic acids, or to new molecules for existing applications, for example, CFAME as a plasticizer. By doing so, new processes could improve the carbon footprint for the customer. Further work in this field is currently ongoing to improve the properties of the plasticizer as well as searching for alternative applications for CFAME and CMO.

uct was analyzed by NMR spectroscopy in CDCl3 (spectra are shown in the Supporting Information). 1H NMR (300 MHz, CDCl3, 25 8C): d = 4.21–4.92 (m, 1 H; CH O C(O) O ), 3.65 (s, 3 H; OCH3), 2.29 (t, J = 7.3 Hz, 2 H; CH2 C(O)OCH3), 1.87–1.20 (multiple signals), 0.88 ppm (t, J = 6.8 Hz, 3 H; CH3-CH2-); 13C NMR (75 MHz, CDCl3, 25 8C): d = 174.2, 153.9, 157.4, 75.4–80.1, 51.5, 22.4–34.2 (multiple signals), 14.1 ppm.

Experimental Section

[1] ICC Reports available from: http://www.unesco.org/new/en/natural-sciences/environment/ecological-sciences/man-and-biosphere-programme/about-mab/icc/icc-reports/. [2] A. Biedermann, Klimaschutzziele in den deutschen Bundeslndern 2011, available from: http://www.uba.de/uba-info-medien/4146.html. [3] CO2-emission trading system in Europe and Germany: www.dehst.de. [4] Positioning paper Dechema and VCI, Utilization and Storage of CO2 2009, available from: http//www.dechema.de/dechema_media/Downloads/Positionspapiere/Positionspapier_co2_englisch.pdf. [5] Carbon Dioxide as Chemical Feedstock (Ed.: M. Aresta), Wiley-VCH, Weinheim, 2010. [6] T. T. Sakakura, J. C. Choi, H. H. Yasuda, Chem. Rev. 2007, 107, 2365. [7] a) G. A. Olah, A. Goeppert, G. K. S. Prakash, Beyond Oil and Gas: The Methanol Economy, Wiley-VCH, Weinheim, 2006; b) S. Wesselbaum, T. Stein, J. Klankemayer, W. Leitner, Angew. Chem. Int. Ed. 2012, 51, 7499; Angew. Chem. 2012, 124, 7617. [8] a) A. Kudo, Y. Miseki, Chem. Soc. Rev. 2009, 38, 253; b) K. Maeda, K. Domen, J. Phys. Chem. Lett. 2010, 1, 2655; c) S.-P. Luo, E. Meija, A. Friedrich, A. Pazidis, H. Junge, A.-E. Surkus, R. Jackstell, S. Denurra, S. Gladiali, S. Lochbrunner, M. Beller, Angew. Chem. Int. Ed. 2013, 52, 419; Angew. Chem. 2013, 125, 437. [9] E. Cetinkaya, I. Dincer, G. F. Naterer, Int. J. Hydrogen Energy 2012, 37, 2071. [10] a) H. Hoberg, Y. Peres, C. Krger, Y. H. Tsay, Angew. Chem. Int. Ed. Engl. 1987, 26, 771; Angew. Chem. 1987, 99, 799; b) R. Fischer, J. Langer, A. Malassa, D. Walther, H. GÅrls, G. Vaughan, Chem. Commun. 2006, 2510; c) S. Y. T. Lee, M. Cokoja, M. Drees, Y. Li, J. Mink, W. A. Herrmann, F. E. Khn, ChemSusChem 2011, 4, 1275. [11] M. L. Lejkowski, R. Lindner, T. Kageyama, G. E. Bdizs, P. N. Plessow, I. B. Mller, A. Schfer, F. Rominger, P. Hofmann, C. Futter, S. A. Schunk, M. Limbach, Chem. Eur. J. 2012, 18, 14017. [12] With Ni-catalysts : a) D. Jin, T. J. Schmeier, P. G. Williard, N. Hazari, W. H. Bernskoetter, Organometallics 2013, 32, 2152; with Mo-catalysts: b) Y. Zhang, B. S. Hanna, A. Dineen, P. G. Williar, W. H. Bernskoetter, Organometallics 2013, 32, 3969. [13] P. N. Plessow, L. Weigel, R. Lidner, A. Schfer, F. Rominger, M. Limbach, P. Hofmann, Organometallics 2013, 32, 3327. [14] B. Schffner, F. Schffner, S. P. Verevkin, A. Bçrner, Chem. Rev. 2010, 110, 4554. [15] D. J. Darensbourg, Chem. Rev. 2007, 107, 2388.

Catalyst screening: EFAME or EMO (2.5 g) was poured into a 25 mL autoclave (Parr Inst.). The catalyst (0.125 g, 5 wt %) and a cocatalyst (0.1 g, 3.5 wt %) were added to the reactor. The autoclave was sealed and purged three times with CO2. Subsequently, the system was pressurized with CO2 to 35 bar and thereafter heated with stirring to 100 8C. At 100 8C, the CO2 pressure was increased to 100 bar. The reaction was stirred (500 rpm) for 17 h. Afterwards, the reactor was slowly depressurized and the crude samples were analyzed by 1H NMR spectroscopy (AV 300 (Bruker) spectrometer in CDCl3) and GC to determine the conversion. The carbonation of epoxy rings was calculated by using 1H NMR spectroscopy in CDCl3. The conversion of epoxy to cyclic carbonate groups was calculated by comparison of signal integrals between d = 2.8 and 3.1 ppm (proton atoms in the epoxy ring) with the integral between d = 4.2 und 5.1 ppm (cyclic carbonate protons). To determine the conversion of epoxidized methyl oleate and epoxidized methyl linoleate to their carbonates, GC analyses (GC-2012, Shimadzu with HP-5 (15 m  1.5 mm  0.53 mm) column, FID) were performed. The conversion was calculated by using methyl palmitate as an internal standard. Sample synthesis on larger scale: EFAME (160 g) was poured into a 250 mL autoclave (Parr Inst.). KI (8 g, 5 wt %) and [18]crown-6 (3.7 g, 2.3 wt %) were added to the reactor. The autoclave was closed and purged three times with CO2 then the autoclave was pressurized with CO2 to 35 bar, and thereafter, heated under stirring to 100 8C. After achieving the desired temperature, the CO2 pressure was increased to 100 bar. The reaction mixture was stirred for six days under these conditions. To maintain the pressure, CO2 was reinjected if necessary. After the reaction time, the autoclave was slowly depressurized and the crude product was analyzed by 1 H NMR spectroscopy and GC to determine the conversion. The catalysts were extracted by dissolving the product in ethyl acetate and washing five times with water. The solvent was evaporated by using a rotary evaporator under reduced pressure. The final prod 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Acknowledgements We greatly acknowledge Prof. M. North for providing samples of Al–salen complexes for the carbonation reaction. We also acknowledge Dr. H. Becker for the fruitful discussion about plasticizer. We thank M. Bruckner for work on the life cycle analysis and the DAAD for providing a stipend for M. Bruckner as part of the RISE program. This work has been supported by the State of North Rhine-Westphalia within the scope of a Target 2 project, and cofinanced by the European Union Investing in our Future, European Regional Development Fund as well as by Evonik Industries AG. Keywords: carbon dioxide fixation · fatty homogeneous catalysis · sustainable chemistry

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Synthesis and application of carbonated fatty acid esters from carbon dioxide including a life cycle analysis.

Carbon dioxide can be used in various ways as a cheap C1 source. However, the utilization of CO2 requires energy or energy-rich reagents, which leads ...
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