Article pubs.acs.org/EF
Hydrocarbons from Spirulina Pyrolysis Bio-oil Using One-Step Hydrotreating and Aqueous Extraction of Heteroatom Compounds Yaseen Elkasabi,*,† Bruna M. E. Chagas,‡ Charles A. Mullen,† and Akwasi A. Boateng† †
Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, United States ‡ Department of Chemical Engineering, Federal University of Rio Grande do Norte, Natal, RN 59078-970, Brazil ABSTRACT: Biomass feedstocks such as algae and cyanobacteria are highly sought after because of their high reproduction rates and growth densities, but their high concentrations of O and N heteroatoms are problematic for biofuel applications. Mild upgrading processes are necessary for producing fungible fuels from these renewable sources. We developed a process to upgrade spirulina-based bio-oil from tail-gas reactive pyrolysis (TGRP), using a combination of catalytic hydrotreatment and purification of the upgraded product. The TGRP bio-oil was distillated at high organic yields, and the distillates served as the feedstock for catalytic upgrading. Simultaneous hydrodeoxygenation and hydrodenitrogenation (HDO/HDN) was carried out in one step using a commercial ruthenium catalyst on carbon support. Using bio-oil distillates as feedstocks for hydrotreatment produced hydrocarbons at high space velocities. Reactor temperature was the critical variable, wherein the optimal temperature compromised between excessive yields loss and catalyst inactivity. While the HDO/HDN product contained relatively significant amounts of residual O and N (∼1 wt % each), the remaining O and N-containing compounds were removed via single aqueousphase extraction with hydrochloric acid. The extraction step serves as a milder alternative to deep HDO/HDN processes that diminish final product yields.
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INTRODUCTION Sustainable biofuels technologies are sought after for both economic and environmental motivations.1,2 Whether they pertain to cellulosic or thermochemical conversion methods, biomass feedstocks need to satisfy some unique requirements. Namely, the biomass should provide little impact to the food supply, yet also grow quickly and efficiently enough to meet fuel demand. For these reasons, algal and cyanobacteria species are highly sought after as biomass feedstocks, especially owing to the combination of their very high growth densities3,4 and relatively quick growth−harvest cycle.5 The land area required to grow microalgae that can produce an equivalent amount of biofuel from plants is 0.5−4% of the plant cropping area, depending on the crop.3 The elevated content of protein and lipids found in algae made their conversion into biodiesel relatively straightforward from hydrothermal liquefactionderived oil6,7 and/or pressed oil extractions.8,9 To meet the much higher demand for gasoline and jet fuel, as well as to reduce the hefty processing costs, fast pyrolysis has been investigated as a way to thermally crack larger macromolecules into smaller molecular weight fuel compounds. Catalytic fast pyrolysis studies10−13 demonstrate the feasibility for increased aromatics content in algae-based bio-oil, depending on the process conditions used. Several aspects of algae biomass make pyrolysis bio-oil production and/or upgrading difficult, such as the high heteroatom (oxygen and nitrogen) content and abnormally high viscosity. For these reasons, algae bio-oil has not been produced on large scales like other feedstocks. The tail-gas reactive pyrolysis (TGRP) technology recently developed by USDA-ARS14−16 has enabled the production of low-viscosity, highly deoxygenated bio-oils from various biomass types, even © XXXX American Chemical Society
from feedstocks whose traditional pyrolysis is highly problematic from a process engineering standpoint. As an example, guayule bagasse17,18 possesses characteristics similar to algae, namely, the high content of high molecular weight paraffins. TGRP of guayule bagasse15 dramatically transformed the nearsolid bio-oil into a very low-viscosity fluid via increased production of BTEX aromatics (benzene, toluene, ethylbenzene, xylenes). Hence, the analogous product from algae holds potential for direct production of various fuel types besides diesel. While hydrodeoxygenation (HDO) of guayule bagasse bio-oil proceeded in significant yields, the elevated nitrogen content of algae bio-oil will require robust methods of removal which compromise between purity and product yield (e.g., hydrodenitrogenation, HDN). TGRP oils have paved the way for efficient separation via distillation and/or extraction, each producing deoxygenated hydrocarbons purely by virtue of separation. Although some studies have investigated the effect of HDO/ HDN processing conditions on product yield distribution, NiMo sulfided catalysts are well-established as the norm for efficient HDN of petroleum-derived fuels.19 However, a combination of HDO/HDN with TGRP oil separation methods20,21 can provide an alternative to “deep HDO/ HDN” at longer times, the latter of which can destroy product yields through carbon loss. Furthermore, environmental NOx emissions from fuel combustion must be eliminated by removal of nitrogen from the liquid product down to trace levels. Recovery of nitrogenated compounds from TGRP bio-oils can Received: February 29, 2016 Revised: April 21, 2016
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DOI: 10.1021/acs.energyfuels.6b00473 Energy Fuels XXXX, XXX, XXX−XXX
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Figure 1. Integrated approach toward upgrading of spirulina-based TGRP bio-oil. Weight percent yields of each step are indicated in parentheses. two 3 in. layers of glass beads (5 mm diameter). The reactor was maintained at 1600−1700 psi with a backpressure regulator and at 350−400 °C (internal) isothermally using a tube furnace. After the catalyst was briefly reduced under hydrogen, a bio-oil sample was pumped into the reactor at varying flow rates (0.4−1.2 mL·min−1) using a high-performance liquid chromatography pump, with 3000 sccm (standard cm3 H2·min−1) entering the reactor concurrently. After exiting the reactor, the reactor product was air-cooled and entered a stainless steel vessel for separation of noncondensable gas and collection of liquid products. Collection of products proceeded every 15 min. Liquid products were filtered using a 0.45 μm PTFE filtration unit, and the filtrate was analyzed according to methods described in the Characterization and Analysis. Densities were measured by weighing the mass of 1 mL of product. Duplicate samples at steady state were each analyzed in duplicate, with all measurements averaged. Bio-oil Extractions. HDO/HDN products were used for extraction experiments performed in individual glass vials. Approximately 5−8 g of upgraded product were added into a vial, into which concentrated hydrochloric acid was added in a 15:1 oil:acid mass ratio. The mixture was shaken vigorously and then allowed to settle and separate. The resulting aqueous layer was removed, and white solid precipitates were isolated; the procedure was repeated until no more precipitates were observed. The top organic layer was washed with an excess amount of sodium hydroxide (∼0.9 g of 10 M NaOH), and these separated aqueous layers were removed. The white solid precipitates (amine salts from the HDO/HDN product) were further treated with sodium hydroxide to reconstitute the amine salts into free amines. Characterization and Analysis. Elemental analysis (CHNS) was conducted via a Thermo EA1112 CHNS analyzer, and results were verified by analysis from an outside party (Robertson Microlit Laboratories, Ledgewood, NJ). Oxygen content was calculated by difference, and moisture content was used to subtract H and O due to water and recalculate results on a dry basis. Moisture content was measured with Karl Fischer titration using methanol with Hydranal Karl Fischer Composite 5 (Fluka) as the titrant. Total acid number (TAN) was measured using a Mettler T70 autotitrator using 0.1 M KOH in isopropanol as the titrant and wet ethanol as the titration solvent. Density was measured by weighing the mass of 1 mL of the fluid in a 1 mL graduated cylinder. Solution-state 1H and 13C NMR spectra were collected using a 400 MHz 9 T Varian Inova NMR spectrometer (Palo Alto, CA) using a 5 mm dual broad-band probe equipped with z-axis pulsed field gradients in CDCl3 (reaction products) or methanol-d4 (bio-oil distillates). Gas chromatography
serve as a source of value-added specialty chemicals. Herein we detail a method for producing hydrocarbons from algae pyrolysis bio-oil through single-catalyst hydrotreating with selective aqueous-phase extraction of heteroatom-containing compounds.
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EXPERIMENTAL SECTION
Fast-Pyrolysis of Biomass. Dried and milled USDA certified organic spirulina (Arthrospira platensis and Arthrospira maxima) was obtained from herbstoreusa.com (Walnut, CA) ready for use. The characterization of this material was previously reported.22 Fastpyrolysis of feedstock was carried out in the Eastern Regional Research Center (ERRC) fluidized bed fast pyrolysis system, as described previously.23,14 For TGRP experiments, a fraction of the noncondensable gas stream was mixed with N2 and recycled into the fluidized bed, using a preheater and gas blower. The pyrolysis system recycled the tail gas in the range of 50−70 vol %, with the balance consisting of nitrogen. Phase-separated organic fractions from the pyrolysis condensers were combined with the electrostatic precipitator (ESP) oil fraction, and this mixture served as the basis for all experiments. Bio-oil Distillation. The bio-oil mixture was distilled in a batch short-path distillation apparatus. A 1000 mL round-bottom flask containing 100−200 g of bio-oil was clamped to a distillation adapter with water-cooled condenser. A heating mantle continuously heated the flask throughout the experiment, and quartz wool was used to insulate the flask. The flask was heated quickly at ∼10−20 °C·min−1. Both the overhead and bottoms temperatures were recorded at the overhead vapor and bottoms flask, respectively. Five distillate fractions were collected at five different temperatures. When the overhead temperature exceeded 150 °C, the condenser water was shut off, and the condenser was heated as needed. When the bottoms temperature reached 350 °C and distillate collection ceased, the heating mantle was shut off. When the bottoms temperature subsequently cooled to 320 °C, a vacuum was applied to collect the final fraction. After room temperature and pressure were reached, the bottoms product remaining in the flask was collected and pulverized with a mortar and pestle. All analyses of distillates were performed after removing any phase-separated aqueous layers. HDO/HDN. Bio-oil distillates were pumped through a continuous downdraft fixed-bed reactor. For a 100 mL stainless steel reactor (1.86 cm internal diameter), approximately 30 g of catalyst pellets (1 wt % Ru on carbon extrudate, Johnson Matthey Inc.) were loaded between B
DOI: 10.1021/acs.energyfuels.6b00473 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels with mass spectroscopy (GC-MS) analysis of liquid products was performed on a Shimadzu GCMS QC-2010 instrument. The column used was a DB-1701, 60 m × 0.25 mm, 0.25 μm film thickness. The oven temperature was programmed to hold at 45 °C for 4 min, ramp at 3 °C·min−1 to 280 °C and hold at 280 °C for 20 min. The injector temperature was 250 °C, and the injector split ratio set to 30:1. Helium carrier gas flowed at 1 mL·min−1. Higher heating values of combustion were calculated using the IGT empirical method.
organic layers appeared in the condenser fractions. Because this behavior indicates quality and composition that are comparable with that of the ESP oil, all condenser organic fractions were combined with the ESP oil. While we studied different sequences for merging HDO with distillation,15 we conducted distillation first before catalytic upgrading of the distillates and subsequent extraction (Figure 1) in order to (1) reduce coking of the catalyst and (2) isolate residual bottoms product for eventual downstream cracking processes and/or conversion into high-quality coke.25,26 While short-path distillation is the more economical method for volatiles separation compared with fractional distillation, some fractionation of the lighter cuts was performed in order to facilitate water removal. The combined organic distillate fractions were used in the HDO/ HDN study. As Table 1 indicates, distillation produced a 60 wt % yield of organics. The distillates possess a relatively low oxygen concentration of 18 wt % as compared with most biooils; however, the 10 wt % nitrogen concentration is considered excessive, to the extent of requiring HDN. The remaining oxygenates are mainly in the form of nonmethoxylated phenolic compounds (brought on by the TGRP process), while the remaining nitrogen-containing compounds include heteroaromatics (e.g., pyrroles, pyridines, and indoles), alkyl nitriles, and longer-chain alkyl amides. While it is possible to separate hydrocarbons from phenolics,21 the presence of nitrogenated compounds would complicate the normal one-step extraction procedure.21 As seen in the GC-MS data, higher molecular weight straight-chain compounds (C16−C18) were detected in abundance, both as-is and functionalized with amides and nitriles. HDO/HDN. To eliminate the necessity and cost burdens associated with multiple catalytic hydrotreating steps, we subjected the combined bio-oil distillates (sans bottoms) to a single catalytic upgrading step which can simultaneously remove nitrogen and oxygen. Because most of the nitrogen occurs as part of heteroatom ring structures, it is hypothesized that temperatures higher than what are normally used for HDO are required to eliminate both oxygen and nitrogen.19 Ruthenium was chosen because of its selective nature in oxygen removal in comparison with other precious metal catalysts.27,28 Carbon supports were used in order to avoid
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RESULTS AND DISCUSSION Distillation of Spirulina Bio-oil. The TGRP process has worked well in converting specific proteinaceous biomass Table 1. Spirulina TGRP Bio-oil Characterization, before and after Short-Path Distillation wt % (db) N C H O KF wt % TAN wt % yield (dry) wt % yield (aq) wt % pyrrole pyridine indole indene styrene phenols naphthalenes BTEX PAHs paraffins hexadecanamide
bio-oil
combined distillates
11.56 67.75 7.47 13.22 7.85 25
9.97 64.35 7.67 18.02 3.2 18 60 8.4 0.94 0.29 1.45 0.27 0.53 4.63 0.41 2.68 0.03 1.48 0.67
feedstocks, including horse manure, into stable bio-oils.20 We used spirulina because of the especially high biomass protein content (∼70 wt %). For TGRP of spirulina,24 phase-separated
Table 2. Characterization of Spirulina TGRP Bio-oil Distillates post-HDO/HDN over 1% Ru/C run condition −1
Voil (mL·min ) H2 flow (sccm) P (psi) T (°C) LHSV (hr−1) WHSV (hr−1) wt % (db) N C H O density (g·mL−1) wt % yield from distillates (org) wt % moisture TAN (mg KOH·g−1) theoretical HHV (MJ·kg−1) a
1
2-aa
2
3
4
0.65 3000 1610 385−390 0.624 1.22
0.45 3000 1730b 400 0.488 0.9
0.65 3000 1610 400 0.704 1.3
0.65 3000 1660 350 0.704 1.3
0.9 3000 1660 350 0.975 1.8
6 wt %) remained. At those conditions, the long-chain amides are eliminated as evidenced by the lack of signals in the 13C NMR around 180 ppm as compared with the starting distillates. These are likely the source of the high E
DOI: 10.1021/acs.energyfuels.6b00473 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels Table 4. Detailed Compositions of Measured Paraffinic Compounds Found in HDO/HDN Products of Spirulina TGRP Bio-oila
a
Table 5. Detailed Compositions of Measured BTEX Compounds Found in HDO/HDN Products of Spirulina TGRP Bio-oila
run condition
1
2
3
4
run condition
1
2
3
4
2-methylbutane n-pentane 2-methylpentane n-hexane 2,4-dimethylpentane n-heptane n-octane n-nonane n-decane n-dodecane n-tridecane n-tetradecane n-pentadecane n-hexadecane n-heptadecane n-octadecane n-nonadecane n-eicosane n-heneicosane
1.28 1.58 2.45 1.73 0.16 1.25 0.94 0.69 0.64 0.56 0.49 0.62 1.96 3.61 2.13 0.36 0.04 0.01 0
1.55 2.94 3.79 0 0.08 5.71 4.16 2.73 1.25 0.1 0 0 0 0 0 0 0 0 0
0.08 0.19 0.17 0.17 0 0.12 0.13 0.15 0.26 0.34 0.37 0.59 0.02 2.54 2.28 1 0.09 0.05 0.04
0.06 0.16 0.11 0.15 0.01 0.08 0.11 0.15 0.3 0.4 0.44 0.71 1.53 2.91 2.54 1.14 0.13 0.11 0.12
benzene toluene ethylbenzene p-xylene o-xylene
0.68 2.95 2.04 0.65 0.44
8.6 9.32 3.58 2.03 0.42
0.29 2.23 1.83 0.48 0.37
0.42 3.19 2.53 0.7 0.49
a
All values are in units of mass %.
The most surprising HDO/HDN trend is with regards to BTEX production. The overall concentration of BTEX compounds largely remains identical except for a dramatic 3fold increase in BTEX concentration for condition 2, the highest reaction temperature. Aromatics concentrations usually decrease as they hydrogenate into naphtha. However, at sufficiently high temperatures, paraffinic compounds can crack and undergo aromatization reactions by carbenium ion transition states, especially over acidic zeolite catalysts.30 Also given the depletion of heavy paraffins (hexadecane, heptadecane, etc.) from this product, this produced fuel is almost entirely in the gasoline range, which upholds the possibility of producing diverse fuel products from a lipid and protein-rich biomass. However, as can be seen from the specific distribution of paraffins measured (Table 4), the paraffins from condition 2 are gasoline/jet range compounds. Hence, in addition to the aromatization reactions occurring, cracking of the larger wax compounds into smaller-chain compounds occurs (hexane, heptane, etc.) (Figure 5). BTEX compounds serve as valuable commodity chemicals for separation and sale as coproducts, but the specific compound compositions will determine their proportion of product use. Table 5 further breaks down the BTEX category into their individual compound concentrations. Toluene and ethylbenzene are the most abundant compounds in this category, but for condition 2 where the overall BTEX concentration was abnormally high, the benzene concentration was extremely high (>8 wt %). From a fuels standpoint, alternative methods must be employed to alter the product distribution because environmental regulations set strict limits on the minimization of fuel benzene content.31 Hence, it may be more economical in this instance to separate the benzene and/or aromatics compounds into marketable commodity chemicals by distillation. Extraction of Heteroatom-Containing Compounds. Although reactor temperature optimization mitigates the balance between excessive yield loss and excessive impurities, the requirements for deep HDO/HDN still exists. Generally,
All values are in units of mass %.
concentrations of the C16−C17 hydrocarbons found at these conditions (Table 3). Also at this condition, nitriles are still present predominantly as paraffin nitriles, especially at condition 4. These along with some cracking of larger paraffins are likely the source of some of the smaller-chain paraffins noted in Table 3. Pathways for the HDN of the major functional groups present are shown in Figure 3. The first step in elimination of the nitrogen-containing aromatics, which was only fully accomplished under conditions 1 and 2, is likely the saturation of the aromatic ring. This is supported by the observation of small amounts of the intermediate hydrogenated products (e.g., piperidine) in the GC of the products from the milder conditions (conditions 3 and 4). The small NMR signals present at 50 ppm in the 13C (Figure 2) and ∼3.5 ppm in the 1 H NMR (Figure 4) that are absent in the starting material and products of conditions 1 and 2 could be indicative of intermediate saturated amines. Because indene and styrene are among the most abundant compounds in TGRP oil, their total concentrations are representative of the olefins that must be eliminated from the final fuel product because olefins can repolymerize and cause gum formation in fuel systems.29 However, in the case of commodity chemicals, styrene and indene are valuable to separate as-is from TGRP bio-oil20 before upgrading.
Figure 5. Secondary reactions leading to smaller paraffins and aromatics observed at condition 2. F
DOI: 10.1021/acs.energyfuels.6b00473 Energy Fuels XXXX, XXX, XXX−XXX
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Figure 6. GC-MS chromatograms of two fractions extracted from the HDO/HDN product 1.
gradually reduced the pH, which removed the residual phenolics as a phase-separated layer at pH 3−5 prior to precipitation of any amine salts at pH 2 or less. This suggests that many of the phenolics, although existing in their native phenol form, have a tendency to form acid/base adducts with amines in solution, which then break apart and precipitate upon acidification. When acidification is complete (pH < 2), all organic ammonium chloride salts precipitate into a white solid that is immiscible in the acidic aqueous phase formed, separate from the phenolic phase. After isolation, the white solid dissolved readily in neutral pH water and was treated with NaOH. The GC-MS chromatograms of both phenolics and resulting free amines are shown in Figure 6. While the phenolics consist of mainly 5 compounds (phenol, o/m/pcresols, and 4-ethylphenol), the populations of amine compounds were widely distributed. Furthermore, the majority of these amine compounds were aromatic, indicative of the HDN recalcitrance of the isolated amines. When compared with the structures of typical amino acids, these heteronuclear aromatic amines most likely originated as products from the cyclization of amino acids; the only natural amino acids with heteronuclear aromatics contain five-membered rings, whereas the amine rings isolated are six-membered. The two largest peaks were aniline and methylaniline. While the amines removed may have particular petrochemical uses (e.g., pyridine, aniline), their removal would eliminate or reduce the formation of NOx from fuels when subjected to combustion. Elementally, the benefits of extraction posthydrotreatment can be visualized in Figure 7. The van Krevelen diagrams shown are configured for oxygen only (3a) and for both oxygen and nitrogen heteroatoms together (3b). Condition 2 already eliminated both heteroatoms in totality, so no further extraction was necessary. However, condition 2 yielded only 27% by mass overall based on bio-oil. Although condition 3 yielded 65% from the hydrotreating, due to the large presence of heteroatoms remaining, the extraction step left behind very little of the isolated product (∼22% mass yield). Again, the moderate conditions of condition 1 used both the highest hydrotreating yield attained (48%) with the highest
Figure 7. (a) Traditional and (b) modified van Krevelen diagrams illustrating the extent of upgrading spirulina bio-oil into fuel-quality hydrocarbons: before HDO (black diamonds), after HDO (orange diamonds), and after HDO and extraction (open triangles). Inset: finished product 1 after HDO and extraction.
higher levels of heteroatom purity require more severe hydrothermal processing conditions, which significantly increase equipment capital and operating costs. To circumvent this issue, we subjected the upgraded hydrocarbon products to a subsequent extraction procedure, wherein concentrated hydrochloric acid effectively precipitated amines as amine hydrochloride salts. Acid titration of the neutral hydrocarbon G
DOI: 10.1021/acs.energyfuels.6b00473 Energy Fuels XXXX, XXX, XXX−XXX
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(11) Liu, C.; Wang, H.; Karim, A. M.; Sun, J.; Wang, Y. Chem. Soc. Rev. 2014, 43, 7594−7623. (12) Lorenzetti, C.; Conti, R.; Fabbri, D.; Yanik, J. Fuel 2016, 166, 446−452. (13) Thangalazhy-Gopakumar, S.; Adhikari, S.; Chattanathan, S. A.; Gupta, R. B. Bioresour. Technol. 2012, 118, 150−157. (14) Mullen, C. A.; Boateng, A. A.; Goldberg, N. M. Energy Fuels 2013, 27, 3867−3874. (15) Boateng, A. A.; Mullen, C. A.; Elkasabi, Y.; McMahan, C. M. Fuel 2015, 158, 948−956. (16) Boateng, A. A.; Elkasabi, Y.; Mullen, C. A. Fuel 2016, 163, 240− 247. (17) Cornish, K.; Williams, J. L.; Kirk, M.; Teetor, V. H.; Ray, D. T. Ind. Biotechnol. 2009, 5, 245−252. (18) Van Beilen, J. B.; Poirier, Y. Crit. Rev. Biotechnol. 2007, 27, 217− 231. (19) Furimsky, E.; Massoth, F. E. Catal. Rev.: Sci. Eng. 2005, 47, 297− 489. (20) Elkasabi, Y.; Mullen, C. A.; Boateng, A. A. ACS Sustainable Chem. Eng. 2014, 2, 2042−2052. (21) Elkasabi, Y.; Mullen, C. A.; Boateng, A. A. ACS Sustainable Chem. Eng. 2015, 3, 2809−2816. (22) Chagas, B. M. E.; Dorado, C.; Serapiglia, M. J.; Mullen, C. A.; Boateng, A. A.; Melo, M. A. F.; Ataide, C. H. Fuel 2016, 179, 124−134. (23) Boateng, A. A.; Daugaard, D. E.; Goldberg, N. M.; Hicks, K. B. Ind. Eng. Chem. Res. 2007, 46, 1891−1897. (24) Chagas, B. M. E.; Mullen, C. A.; Dorado, C.; Elkasabi, Y.; Boateng, A.; Melo, M. A. F.; Ataide, C. H. Ind. Eng. Chem. Res., accepted for publication, 2016. (25) Elkasabi, Y.; Mullen, C. A.; Jackson, M. A.; Boateng, A. A. J. Anal. Appl. Pyrolysis 2015, 114, 179−186. (26) Elkasabi, Y.; Boateng, A. A.; Jackson, M. A. Biomass Bioenergy 2015, 81, 415−423. (27) Wildschut, J.; Mahfud, F. H.; Venderbosch, R. H.; Heeres, H. J. Ind. Eng. Chem. Res. 2009, 48, 10324−10334. (28) Wildschut, J.; Iqbal, M.; Mahfud, F. H.; Cabrera, I. M.; Venderbosch, R. H.; Heeres, H. J. Energy Environ. Sci. 2010, 3, 962− 970. (29) Nagpal, J. M.; Joshi, G. C.; Singh, J.; Rastogi, S. N. Fuel Sci. Technol. Int. 1994, 12, 873−894. (30) Caeiro, G.; Carvalho, R. H.; Wang, X.; Lemos, M. A. N. D. A.; Lemos, F.; Guisnet, M.; Ramoa Ribeiro, F. J. Mol. Catal. A: Chem. 2006, 255, 131−158. (31) Summary and analysis of the 2011 gasoline benzene pre-compliance reports; EPA-420-R-12-007; U.S. Environmental Protection Agency, 2012.
extraction yield (>86%). Taking into account all steps, the overall biomass-to-hydrocarbon yield is approximately 8−10 wt %, and the final hydrocarbon HHV represents 65% of the starting bio-oil energy value (and approximately 20% of the biomass HHV). The extraction process could be fine-tuned to add just the right amount of acid, such that minimal amounts of HCl and NaOH are used.
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CONCLUSIONS We detailed a methodology for producing clean fuel-grade hydrocarbons from spirulina biomass TGRP bio-oil. The high heteroatom-containing bio-oil distillate was successfully upgraded with one catalyst into fuel-grade hydrocarbons, with the reactor temperature being the most important variable that affects final product quality. Acid−base extraction post-HDO/ HDN enhanced the hydrocarbon quality by reducing the heteroatom concentration down to below EA detector limits (
