Letter pubs.acs.org/journal/ascecg
Cite This: ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Single-Step Catalytic Upgrading of Microalgae Biomass Dennis Pingen, Nele Klinkenberg, and Stefan Mecking* Chair of Chemical Materials Science, University of Konstanz, Universitätsstrasse 10, Konstanz 78464, Germany
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S Supporting Information *
ABSTRACT: A direct catalytic upgrading on as-cultivated microalgae biomass is demonstrated. Via CO-free alkoxycarbonylation of the contained lipids with the use of formates, diesters were produced in high conversion and selectivity from monounsaturated fatty acids from Phaeodactylum tricornutum microalgae. Via this procedure, extraction and functionalization occur in one step, circumventing the need for separate workup procedures of the biomass. The products are valuable building blocks for renewable polyester materials. KEYWORDS: Carbonylation, Fatty acids, Lipids, Sustainable process, Phaeodactylum tricornutum, Diatoms, Catalysis, Palladium
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and is well-suited for genetic engineering.23 Algae lipids differ from traditional plant oils in that they contain unusual fatty acid chain lengths and multiple unsaturated fatty acids. The P. tricornutum employed here contain significant amounts of palmitoleic acid (16:1), oleic acid (18:1), eicosapentenoic acid (20:5), and the saturated 16:0 and 14:0. This composition is compatible with Pd catalysts for isomerizing alkoxycarbonylation, as demonstrated by carbonylation of a chloroform extract of P. tricornutum. Gaseous CO is a coreagent here. In view of a technically simple approach that could, for example, be practiced at remote locations on-site of an algae cultivation, reagents that are easy to transport and handle are desirable. Rather than gaseous carbon monoxide, liquid carbonylation reagents appear beneficial in this regard. We therefore employed formates, which have been demonstrated to be suitable CO surrogates by Beller et al.24−26 For the elaboration of suitable reaction conditions, methyl oleate was studied as a model substrate (Table 1). Methanol is commonly used as a solvent and reagent for alkoxycarbonylation as it is most reactive in the rate-determining step compared to higher alcohols. At the same time it is also a lowcost solvent that is accessible from virtually any carboncontaining feedstock, with natural gas predominating today. Pd(II) catalysts with the established diphosphine ligand α,α′bis(di-tert.-butylphospino)xylene (dtbpx) and different metal sources were employed. High conversions and selectivities for the desired linear diester were observed with Pd(acac)2 or Pd(OAc)2, with the defined diphosphine-coordinated precursor [Pd(dtbpx)(OTf)2] only slightly superior (Table 1, entries 1−3). Excess diphosphine was found beneficial; with only 1 equiv of
INTRODUCTION Biomass in its many varieties offers attractive traits as a feedstock for the production of chemicals. Beyond its renewable nature, possibly advantageous carbon dioxide balance, and local production independent of oil producers, most particularly it possesses unique molecular motifs that can be complementary to petrochemistry.1−3 However, biomass represents multicomponent mixtures of different classes of compounds. Its workup and extraction generally is a bottleneck and limitation in its utilization, and frequently requires multistep procedures. Moreover, advanced catalytic processes for the introduction of functional groups are usually developed for high-purity uniform petrochemical feedstocks, oftentimes neat hydrocarbons.4−8 They are not necessarily facile to adopt to renewable feedstock streams, even if these are already subject to extraction procedures. A recent successful example to this end is the development and implementation of transition-metal-catalyzed schemes for generating value-added difunctional monomers from plant oil feedstocks.9−13 These yield long-chain dicarboxylic acids via olefin metathesis14−16 or isomerizing carbonylation of unsaturated fatty acids.17−20 For the advancement of the valorization of biomass, straightforward and robust schemes are desirable. We now report on a selective catalytic functionalization of algae biomass as obtained from cultivation in a single step (Scheme 1). Long-chain diesters are produced as products, which can serve as valuable building blocks toward renewable polycondensates. Algae biomass was chosen as a prospective lipid source as its cultivation does not require arable land, and growth is very rapid.21,22
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RESULTS AND DISCUSSION
Received: June 22, 2018 Revised: July 25, 2018 Published: July 27, 2018
The diatom Phaeodactylum tricornutum was studied as a biomass source, as it grows rapidly, has a high lipid content, © XXXX American Chemical Society
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DOI: 10.1021/acssuschemeng.8b02939 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Letter
ACS Sustainable Chemistry & Engineering Scheme 1. Concept of Single-Step Catalytic Upgrading of Microalgae Biomass
Table 1. : Optimization and Catalyst Precursor Screening of the Alkoxycarbonylationa of Methyl Oleate with Methyl Formate entry
catalyst precursor (mol %)
dtbpx ligand (loading mol %)
substrate loading (mmol)
conversionb (%)
linear diester selectivityc (%)
1 2d 3 4 5 6e 7f
Pd(acac)2 (0.400) Pd(OAc)2 (0.400) Pd(dtbpx)(OTf)2 (0.400) Pd(dtbpx)(OTf)2 (0.400) Pd(dtbpx)(OTf)2 (0.038) Pd(dbpx)(OTf)2 (0.038) Pd(dtbpx)(OTf)2 (0.400)
1.600 1.600 1.600
10 10 10 10 27 27 3.33
94 87 92 38 41 55 96
93 90 89 24 54 58 92
0.144 0.144 1.600
Conditions: Pd precursor, dtbpx (if applicable), methyl oleate, methyl formate (5 mL), methanol (5 mL), methanesulfonic acid (10 μL), 100 °C, 20 h. bDetermined by gas chromatography analysis. cThe selectivity is determined as the linear diesters compared to all other products, including isomerization products. dEthyl formate in methanol was used; the methyl esters were the resulting ester. eReaction time was 65 h. fHigh-oleic sunflower oil, triglyceride, was used in this reaction. a
Table 2. Combined Extraction and Alkoxycarbonylationa with Formate and Alcohol of Algae Biomass of the Type P. tricornutum
diphosphine (introduced with the precursor) the conversion was much lower (Table 1, entry 4). At a low catalyst loading of 0.038 mol % (substrate to metal 2500:1), only partial conversion was achieved (Table 1, entry 5). A prolonged reaction time did not result in much higher yields (Table 1, entry 6). As the fatty acids are mainly present as triglycerides, instead of free fatty acids, the alkoxycarbonylation of triglycerides was tested. As a model compound high-oleic sunflower oil (HOSO) was used. In microalgae, the oil is also present as diglycerides bearing an additional polar (ionic) group though these are also soluble in methanol. Esterification of the triglycerides occurs under the reaction conditions for alkoxycarbonylation. The reaction of HOSO using methyl formate and methanol provided 96% conversion, and the 1,19diester was produced in a selectivity of 92% (entry 7, Table 1). Algae biomass was obtained from the cultivation broth by centrifugation to separate off water. This wet biomass (ca. 75 wt % water) contains the entire cell constituents, namely, carbohydrates, proteins, chlorophylls, and lipids. For comparison, this biomass was also freeze-dried to remove water for the largest part. The direct functionalization of algae biomass without an intermediate extraction or workup step was pursued with reaction conditions identified from the model studies of methyl oleate as a starting point (Table 2, entries 1 and 2). Within the diester product formed, a high selectivity for the desired linear product is retained. Within experimental error, the linear selectivity is the same as in the above model studies on methyl oleate (ca. 90%). A small difference in using MSA vs TFA was observed now; however, in both cases, the conversion was not complete (Table 2, entry 3). Longer reaction times of 96 h further increased the conversion (Table 2, entries 4 and 5). The selectivity toward the diesters did not suffer at the same time. Performing the reactions at higher temperatures only led to a strong decrease in both the conversion and selectivity, most likely due to catalyst decomposition (Table 2, entries 6− 9). In addition to methyl formate, ethyl formate in combination with ethanol was employed. A slower reaction resulted in lower conversion. The selectivity remained high
entry
time (h)
1 2 3e 4 5 6 7 8 9 10f 11f 12 13 14 15
20 20 20 96 96 20 20 96 96 96 96 96 96 96 96
temp (°C) 100 100 100 100 100 120 140 120 140 100 100 100 100 100 100
°C °C °C °C °C °C °C °C °C °C °C °C °C °C °C
typeb
amount (g)
conversionc (%)
selectivity for diesterd (%)
W FD W FD W W W W W FD W FD W FD W
4.0 1.0 4.0 1.0 4.0 4.0 4.0 4.0 4.0 0.5 2.0 0.5 2.0 2.0 8.0
64 61 78 >99 95 45 54 56 52 58 55 >99 87 >99 57
94 90 >99 94 95 91 98 >99 >99 >99 92 96 97 95 95
a Conditions: Pd(acac)2 (0.0472 mmol, 14.4 mg), dtbpx (0.1888 mmol, 74.5 mg), algae, 5 mL of methanol, 5 mL of methyl formate, methanesulfonic acid (15 μL). bWet algae containing 75% water (W) or freeze-dried algae (FD). cThe conversion is determined as the consumption of all unsaturated fatty acids. dThe selectivity is determined as the diesters formed of all converted unsaturated fatty glyceride esters. eTfOH was used as acid. fReaction performed with 5 mL of ethyl formate and 5 mL of ethanol.
though (Table 2, entries 10 and 11). Varying the amount of algae biomass employed in the reaction while keeping the solvent volume constant showed that high diester selectivity and satisfactory conversion could be achieved at high biomass concentration (Table 2, entries 12−15).
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CONCLUSIONS In conclusion, a catalytic upgrading of biomass without laborious additional workup and extraction steps can greatly simplify the utilization of biomass feedstocks. This is B
DOI: 10.1021/acssuschemeng.8b02939 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
Letter
ACS Sustainable Chemistry & Engineering
(7) Zhao, C.; Bruck, T.; Lercher, J. A. Catalytic deoxygenation of microalgae oil to green hydrocarbons. Green Chem. 2013, 15 (7), 1720−1739. (8) Santillan-Jimenez, E.; Crocker, M. Catalytic deoxygenation of fatty acids and their derivatives to hydrocarbon fuels via decarboxylation/decarbonylation. J. Chem. Technol. Biotechnol. 2012, 87 (8), 1041−1050. (9) Biermann, U.; Bornscheuer, U.; Meier, M. A. R.; Metzger, J. O.; Schäfer, H. J. Oils and Fats as Renewable Raw Materials in Chemistry. Angew. Chem., Int. Ed. 2011, 50 (17), 3854−3871. (10) Furst, M. R. L.; Goff, R. L.; Quinzler, D.; Mecking, S.; Botting, C. H.; Cole-Hamilton, D. J. Polymer precursors from catalytic reactions of natural oils. Green Chem. 2012, 14 (2), 472−477. (11) Deuss, P. J.; Barta, K.; de Vries, J. G. Homogeneous catalysis for the conversion of biomass and biomass-derived platform chemicals. Catal. Sci. Technol. 2014, 4 (5), 1174−1196. (12) Goldbach, V.; Roesle, P.; Mecking, S. Catalytic Isomerizing ωFunctionalization of Fatty Acids. ACS Catal. 2015, 5 (10), 5951− 5972. (13) Llevot, A.; Dannecker, P. K.; Czapiewski, M. v.; Over, L. C.; Söyler, Z.; Meier, M. A. R. Renewability is not Enough: Recent Advances in the Sustainable Synthesis of Biomass-Derived Monomers and Polymers. Chem. - Eur. J. 2016, 22 (33), 11510−11521. (14) Chikkali, S.; Mecking, S. Refining of Plant Oils to Chemicals by Olefin Metathesis. Angew. Chem., Int. Ed. 2012, 51 (24), 5802−5808. (15) Zimmerer, J.; Williams, L.; Pingen, D.; Mecking, S. Mid-chain carboxylic acids by catalytic refining of microalgae oil. Green Chem. 2017, 19 (20), 4865−4870. (16) Pingen, D.; Zimmerer, J.; Klinkenberg, N.; Mecking, S. Microalgae lipids as a feedstock for the production of benzene. Green Chem. 2018, 20 (8), 1874−1878. (17) Jiménez-Rodriguez, C.; Eastham, G. R.; Cole-Hamilton, D. J. Dicarboxylic acid esters from the carbonylation of unsaturated esters under mild conditions. Inorg. Chem. Commun. 2005, 8 (10), 878−881. (18) Quinzler, D.; Mecking, S. Linear Semicrystalline Polyesters from Fatty Acids by Complete Feedstock Molecule Utilization. Angew. Chem., Int. Ed. 2010, 49 (25), 4306−4308. (19) Roesle, P.; Stempfle, F.; Hess, S. K.; Zimmerer, J.; Río Bártulos, C.; Lepetit, B.; Eckert, A.; Kroth, P. G.; Mecking, S. Synthetic Polyester from Algae Oil. Angew. Chem., Int. Ed. 2014, 53 (26), 6800− 6804. (20) Pingen, D.; Schwaderer, J. B.; Walter, J.; Wen, J.; Murray, G.; Vogt, D.; Mecking, S. Diamines for Polymer Materials via Direct Amination of Lipid- and Lignocellulose-based Alcohols with NH3. ChemCatChem 2018, 10, 3027. (21) Shuba, E. S.; Kifle, D. Microalgae to biofuels: ‘Promising’ alternative and renewable energy, review. Renewable Sustainable Energy Rev. 2018, 81, 743−755. (22) Yongmanitchai, W.; Ward, O. P. Growth of and omega-3 fatty acid production by Phaeodactylum tricornutum under different culture conditions. Appl. Environ. Microbiol. 1991, 57 (2), 419−425. (23) Hess, S. K.; Lepetit, B.; Kroth, P. G.; Mecking, S. Production of chemicals from microalgae lipids − status and perspectives. Eur. J. Lipid Sci. Technol. 2018, 120 (1), 1700152. (24) Fleischer, I.; Jennerjahn, R.; Cozzula, D.; Jackstell, R.; Franke, R.; Beller, M. A Unique Palladium Catalyst for Efficient and Selective Alkoxycarbonylation of Olefins with Formates. ChemSusChem 2013, 6 (3), 417−420. (25) Wu, L.; Liu, Q.; Jackstell, R.; Beller, M. Carbonylations of Alkenes with CO Surrogates. Angew. Chem., Int. Ed. 2014, 53 (25), 6310−6320. (26) Sang, R.; Kucmierczyk, P.; Dong, K.; Franke, R.; Neumann, H.; Jackstell, R.; Beller, M. Palladium-Catalyzed Selective Generation of CO from Formic Acid for Carbonylation of Alkenes. J. Am. Chem. Soc. 2018, 140 (15), 5217−5223.
demonstrated here for microalgae as a feedstock with significant potential, and for a sophisticated but robust remote functionalization to yield valuable linear long-chain diesters which can serve as building blocks for polyesters. The utilization of easily handleable liquid rather than gaseous coreagents would simplify implementation also at isolated production sites, integrated with algae cultivation. While higher catalyst activity in isomerizing carbonylation would be desirable in general, the selectivities and conversions observed compare reasonably with isolated fatty acid ester feedstocks. The findings reported outline an approach to debottleneck utilizations of renewable feedstock as a source of chemicals.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.8b02939.
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Detailed information on the analysis, experimental procedures, origin of chemicals, algae cultivation, and additional experiments (PDF)
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Dennis Pingen: 0000-0001-5440-7752 Stefan Mecking: 0000-0002-6618-6659 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS D.P. gratefully acknowledges a Marie Curie Zukunftskolleg Incoming Fellowship.
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DOI: 10.1021/acssuschemeng.8b02939 ACS Sustainable Chem. Eng. XXXX, XXX, XXX−XXX
