N.
Schwaiger
*ac,
D. C.
Elliott
b,
J.
Ritzberger
c,
H.
Wang
b,
P.
Pucher
c and
M.
Siebenhofer
a
aInstitute of Chemical Engineering and Environmental Technology, NAWI Graz, Central Lab Biobased Products, Graz University of Technology, Inffeldgasse 25/C, 8010 Graz, Austria. E-mail: nikolaus.schwaiger@tugraz.at
bPacific Northwest National Laboratory, PO Box 999, Richland, WA 99352, USA
cBDI-BioEnergy International AG, Parkring 18, 8074 Grambach/Graz, Austria
First published on 13th February 2015
Continuous hydroprocessing of liquid phase pyrolysis Bio-oil, provided by BDI-BioEnergy International bioCRACK pilot plant at OMV Refinery in Schwechat/Vienna Austria was investigated. These hydroprocessing tests showed promising results using catalytic hydroprocessing strategies developed for unfractionated Bio-oil. A sulfided base metal catalyst (CoMo on Al2O3) was evaluated. The bed of catalyst was operated at 400 °C in a continuous-flow reactor at a pressure of 12.1 MPa with flowing hydrogen. The condensed liquid products were analyzed and found that the hydrocarbon liquid was significantly hydrotreated so that nitrogen and sulfur were below the level of detection (<0.05), while the residual oxygen ranged from 0.7 to 1.2%. The density of the products varied from 0.71 g mL−1 up to 0.79 g mL−1 with a correlated change of the hydrogen to carbon atomic ratio from 2.1 down to 1.9. The product quality remained high throughout the extended tests suggesting minimal loss of catalyst activity through the test. These tests provided the data needed to assess the quality of liquid fuel products obtained from the bioCRACK process as well as the activity of the catalyst for comparison with products obtained from hydrotreated fast pyrolysis Bio-oils from fluidized-bed operation.
The Bio-oil product from fast pyrolysis and liquid phase pyrolysis, however, is not of sufficient quality for direct use as petroleum refinery feedstock. Catalytic hydroprocessing has been developed to convert the highly oxygenated Bio-oil components into hydrocarbons.5 Conventional hydrotreating processes cannot be directly applied for upgrading of fast pyrolysis Bio-oil. Specifically, the necessity of a two-temperature strategy was identified.6
The objective of this research project was to develop a catalytic hydrotreating process for the production of crude petroleum refinery feedstock from biomass, specifically from condensate of the bioCRACK process. From bioCRACK pyrolysis two different fractions of condensate, high aqueous Bio-oil and Dehydrated Bio-oil, are collected. These feedstocks need hydroprocessing to produce a refinery compatible hydrocarbon-like feedstock. Previous hydrodeoxygenation studies have been performed in a batch reactor with the bioCRACK Bio-oil and Dehydrated Bio-oil using precious and base metal catalysts at lower temperature. The process resulted in a partially deoxygenated Bio-oil with some improvements in reduced heavy product compared to conventional fast pyrolysis Bio-oil hydroprocessing.7
Investigations focused on hydrotreating of condensate from liquid phase pyrolysis of spruce wood pellets. The Bio-oils were produced in a bioCRACK reactor located at the OMV refinery complex in Schwechat, Austria. The Bio-oil products were hydrotreated in a bench-scale, continuous-flow, packed-bed catalytic reactor at Pacific Northwest National Laboratory (PNNL).
The flow sheet of the bioCRACK pilot plant is shown in Fig. 2. Biomass and liquid heat carrier oil are fed simultaneously into the impregnator. From there a biomass heat carrier slurry is transferred into the reactor 1 and 2 were the biomass is immediately heated to 375 °C. The biogenic and the fossil vapors are cooled in the condenser. The settling vessel separates the condensed vapors into an aqueous Bio-oil fraction and the non-polar bioCRACK oil fraction. In the following distillation step high boiling heat carrier residues are separated from the nonpolar bioCRACK oil fraction. After pyrolysis the heat carrier is separated from biochar.
For further lab scale processing the residual heat carrier is separated from biochar by solid liquid extraction. Biochar can then undergo liquefaction.8–10
Dehydration was performed by short path distillation. The apparatus had a heat exchanger surface of 0.1 m2. The heat carrier operating temperature was 130 °C and operating pressure was 130 mbar. It has been reported,13 that upgrade of Bio-oil distillate with ethanol may increase economic revenue.
Campaigns were performed for each feed over the course of a five-day test, and the products and feed were collected to assess performance for each Bio-oil for comparison with the results obtained from processing of fast pyrolysis Bio-oil.
The hydroprocessing tests performed well with CoMo catalyst, sulfided in situ. The reactor tube containing the catalyst was heated to 150 °C in H2 flow, followed by a temperature ramp from 150 °C to 350 °C over 3 h and H2 flow and sulfiding agent (35% di-tertiarybutyl-disulfide (DTBDS) in decane). Then temperature was raised to 400 °C and held constant for 5 h with H2 and sulfiding agent flow.
For the hydroprocessing tests the flow ratio of H2/liquid was 2508 L H2 (L Bio-oil)−1. The operating pressure was 12.1 MPa (1750 psi). The Bio-oil feedstock was spiked with DTBDS equaling 150 ppm of sulfur. Fig. 4 shows a schematic of the catalyst bed with a super-imposed temperature profile for the single stage testing mode. The temperatures were monitored at the center line of the catalyst bed by a thermocouple which was adjustable within a full length thermowell. The isothermal part of the catalyst bed is clearly shown and the length of the isothermal part of the catalyst was used to calculate the space velocity.
The Bio-oils and hydrotreated products were characterized at PNNL for elemental analysis, including C, H, N, O, & S, Total Acid Number (TAN), water content, metals content, and by GC-MS. Using a DB-5 column over a temperature program, separation of the Bio-oils was performed and mass spectrometric analysis undertaken with a Mass Selective Detector.
Proximate analysis (wt%) | Ash | Ultimate analysis (wt%) | |||||
---|---|---|---|---|---|---|---|
Volatiles | Fixed carbon | C | H | N | O by diff. | ||
Spruce pellets | 84.94 | 14.68 | 0.38 | 50.67 | 6.30 | 0.04 | 42.99 |
![]() | ||
Fig. 5 Biogenous carbon mass balance of liquid phase pyrolysis as performed in the bioCRACK pilot plant at OMV Refinery Vienna.14 |
During liquid phase pyrolysis in the bioCRACK process biochar (BCH) and gas/vapor is formed from biomass constituents. Table 2 shows the elemental composition of the product streams. Differently to flash pyrolysis three liquid product streams are formed in the bioCRACK process. The first fraction is a high boiling fraction of decomposed biomass, which is dissolved during liquefaction into the heat carrier. 15 (wt%) of the biogenous carbon feed is solved into this fraction and the concentration of biogenous carbon in this fraction is 2.0 (wt%). The second liquid fraction is the so called bioCRACK oil (BCO). This is a non-polar phase of biomass decomposition products and the degraded heat carrier. During pyrolysis 21% of the biogenic carbon from biomass is directly dissolved into this hydrocarbon fraction and the concentration of biogenous carbon is 6.7 (wt%). The bioCRACK oil can be fractionated into a gasoline, kerosene, diesel and high boiling fraction by distillation or further processed to a Diesel like Fuel by catalytic co-hydrodeoxygenation with Bio-oil.15
Product stream | C (wt%) | H (wt%) | N (wt%) | Residual (wt%) |
---|---|---|---|---|
Biochar (BCH) | 80.9% | 5.4% | <1 | 13.5% |
BioCRACK oil (BCO) | 84.8% | 12.4% | <1 | 2.4% |
Liquid heat carrier (LHC) | 86.5% | 12.1% | <1 | 0.9% |
This bioCRACK oil is evaporated together with the Bio-oil fraction, which is the third liquid fraction of the bioCRACK process. The dissolution of biogenic compounds into the heat carrier and the bioCRACK oil phase is the major reason for the low carbon content, the high acid content and the high water- and oxygen content of the polar aqueous bioCRACK Bio-oil.
The major gas components are given in Table 3.
Sample | CO (v/v%) | CO2 (v/v%) | CO2![]() ![]() |
---|---|---|---|
43.8 | 44.5 | 1.01 |
Sample | C (wt%) | H (wt%) | N (wt%) | O (wt%) | Ash (wt%) | H2O (wt%) | Density (g mL−1) | pH |
---|---|---|---|---|---|---|---|---|
Dehydrated Bio-oil | 50.5 | 7.1 | 0.4 | 41.5 | 0.5 | 9.9 | 1.22 | 2.7 |
Bio-oil | 23.2 | 9.4 | 0.3 | 67.1 | NA | 56.3 | 1.07 | 2.6 |
Bio-oil condensate | 14.4 | 9.97 | 0.3 | 75.3 | NA | 68.9 | 1.04 | 3.0 |
The Bio-oils were analyzed at PNNL. The results are shown in Table 5. The C, H, O composition is calculated from wet oil composition by subtracting the amount of oxygen and hydrogen of the measured moisture content. Detailed trace element analysis of the wet Bio-oils was performed by ICP. The results are shown in Table 6. The Bio-oils are essentially mineral free, but with a significant amount of sulfur. The TAN (total acid number) was also determined by PNNL. Viscosity and density were determined with a Stabinger viscosimeter according to ASTM D7042.
Sample name | C (wt% dry) | H (wt% dry) | H/C ratio dry basis | O (wt% dry) | Moisture (wt%) | N (wt% wet) | S (wt% wet) | Density (g ml−1 @40 °C) | TAN (mg KOH g−1) | Viscosity (mm2 s−1 @40 °C) |
---|---|---|---|---|---|---|---|---|---|---|
Dehydrated Bio-oil | 59.1 | 6.7 | 1.36 | 33.4 | 10.24 | 0.14 | 0.50 | 1.226 | 135 | 105 |
Bio-oil | 51.1 | 6.2 | 1.45 | 42.6 | 57.43 | <0.05 | 0.03 | 1.097 | 101 | 2.3 |
S (ppm) | Al (ppm) | Si (ppm) | K (ppm) | Fe (ppm) | Ca (ppm) | Mg (ppm) | P (ppm) | |
---|---|---|---|---|---|---|---|---|
Dehydrated bio-oil | 3372 | <15 | <15 | 24 | 39 | 17 | <15 | <15 |
Bio-oil | 557 | <15 | <15 | <15 | <15 | <15 | <15 | <15 |
Semi-quantitative analysis of the two bioCRACK feedstocks was performed with gas chromatography-mass spectrometry (GC-MS). With the Agilent peak matching program tentative identifications were applied to the components and their relative quantities were determined based on total ion current. The results are presented in Table 7, showing the relative quantities of the identified components. The two bio-oil fractions show some distinct differences in composition. Overwhelmingly they contain typical fast pyrolysis Bio-oil components, a mixture of guaiacols and light oxygenates. The guaiacol (2-methoxyphenol) compounds have the typical alkyl and carbonyl substituents on the 4 position. There is a significant amount of levoglucosan in both Bio-oil fractions, but significantly lower concentration in the whole Bio-oil. The Bio-oil product has a large number of light oxygenates, which were not found in the Dehydrated Bio-oil. These compounds, e.g. acetic acid and acetol (hydroxyacetone), were separated during distillation. On the other hand the Dehydrated Bio-oil has a larger concentration of all the phenolic compounds, with the exception of guaiacol and methyl guaiacol.
Component | Dehydrated Bio-oil | Bio-oil | ||
---|---|---|---|---|
Retention time | Quantity | Retention time | Quantity | |
a ND = not detected. | ||||
Methyl acetate | 1.756 | 1.3 | 1.737 | 3 |
Formic acid | NDa | 1.96 | 0.5 | |
Acetic acid | 2.37–2.49 | 6.8 | 2.7 | 25.9 |
Acetol (hydroxyacetone) | 2.79–3.01 | 3.8 | 2.82 | 21.1 |
Propionic acid | ND | 4.20–4.34 | 1.5 | |
1-Hydroxy-2-butanone | ND | 5.10–5.16 | 0.3 | |
Butanedial | ND | 5.74–5.90 | 0.4 | |
Methylene cyclopropane | ND | 7.92–7.95 | 0.2 | |
Cyclopentenones | ND | 8.00–8.10 | 0.2 | |
Methyl cyclopentenone | ND | 10.86–10.90 | 0.4 | |
γ-Butyrolactone | 11.64–11.77 | 0.4 | 11.34–11.44 | 1.3 |
Methyl furfural | ND | 12.51 | 0.5 | |
3-Methyl-2,5-dihydrofuran | ND | 13.04 | 0.4 | |
Corylone (hydroxymethylcyclopentenone) | 13.79–13.91 | 6.1 | 13.71–14.02 | 7.5 |
Methyl-2,3-dihydrofuran | 13.92–13.96 | 5 | ND | |
Trans-cyclopentanediol | ND | 14.05 | 1 | |
Guaiacol | 14.63–14.65 | 1.2 | 14.56 | 2.4 |
Methyl guaiacol | 16.02–16.08 | 3.8 | 15.99 | 3.8 |
Catechol | 16.94 | 1.4 | 16.94 | 0.8 |
Ethyl guaiacol | 17.06 | 3.4 | 17.06 | 2.2 |
Hydroxy dimethyl cyclopentenone | 17.21 | 0.3 | 17.26 | 1.1 |
Hydroquinone | 17.76 | 4.1 | 17.81–17.92 | 2.8 |
Propyl guaiacol | 18.05 | 2.9 | 18.05 | 1.6 |
Guaiacol formaldehyde (vanillin) | 18.68 | 6.6 | 18.73 | 2.4 |
Methyl benzaldehyde | 19.03 | 3.6 | ND | |
Guaiacol ethanone | 19.55 | 4.3 | 19.57 | 1.6 |
Guaiacol propanone | 19.92 | 8.2 | 19.93 | 3.3 |
Levoglucosan | 20.15–20.38 | 35.3 | 20.20–20.69 | 13.7 |
Ethyl homovanillate | 26.54 | 1.4 | 26.58 | 0.3 |
The Dehydrated Bio-oil feedstock was pumped directly into the mini-hydrotreater without pre-processing. The feedstock was assumed to have <0.1% filterable solids content, based on BDI data provided. A fixed bed of pre-sulfided CoMo on alumina catalyst (3.5% CoO and 14% MoO3) from AlfaAesar (#40435) ground to a 30–60 mesh particle size was used at standard conditions of nominally 400 °C, 12.1 mPa, and a liquid hourly space velocity of 0.2. Three oil samples selected to represent the product over the 54 h test were analyzed as reported in Table 8. Elemental contents are normalized to 100%; S and N were <0.02 and <0.05, respectively.
C content dry basis | H content dry basis | O content dry basis | H/C ratio dry basis | Density, g ml−1 | Moisture content | Total acid number | Mass balance | Carbon balance |
---|---|---|---|---|---|---|---|---|
85.04 | 13.86 | 1.10 | 1.94 | 0.755 | 0.24 | <0.01 | 93.6 | 90.6 |
85.55 | 13.24 | 1.21 | 1.84 | 0.784 | 0.26 | <0.01 | 99.2 | 98.5 |
85.41 | 13.51 | 1.08 | 1.88 | 0.789 | 0.30 | <0.01 | 92.4 | 88.3 |
Trace element analysis of the feedstock showed only small amounts of a few expected biomass components, 17 ppm Ca and 24 ppm K with 38 ppm Fe and 3320 ppm S. The iron is likely a corrosion product. The high sulfur level is unexpected. The S number for the feedstock was found by inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurement, but it is similar to that by the thermal method (0.50 wt%). Since a sulfided catalyst was used for the processing there was no conflict. In fact, we added di-tertiarybutyl-disulfide to the feedstock to maintain at least 150 ppm of sulfur.
The operating results as shown in Fig. 6 were fairly consistent throughout the test period. The liquid oil yield from the bioCRACK Dehydrated Bio-oil was 0.5 to 0.6 g g−1, with lower but still significant gas and water production. The hydrogen consumption was a bit higher than typically seen with fast pyrolysis Bio-oil.
Gas products were analyzed through the test using gas chromatography. The gas product was composed of carbon oxides (21–26% CO2 and 4–5% CO) and alkane hydrocarbon gases (22–25% CH4, 22–19% C2, 14–12% C3, 6–11% C4, 5% C5) diluted with the excess hydrogen (93–94 vol% of off gas).
The 316 SS tubular reactor is depicted in Fig. 7 and the area of fouled catalyst after the test is shaded in red.
ICP analysis of the spent catalyst bed showed some evidence of deposits in the bed. As might be expected the feed contaminants, iron, calcium, and potassium, were found at levels higher than in the fresh catalyst with exceptionally high levels at the point in the catalyst bed where the reactants exceeded 300 °C. Zinc and manganese (below detection limit in the feed) also followed this trend, as did chromium and nickel, which are likely reactor wall corrosion products.
A similar test was performed with the bioCRACK Bio-oil product. The Bio-oil feedstock was pumped directly into the mini-hydrotreater without pre-processing. Four oil samples selected to represent the product over the 62 h test were analyzed as reported in Table 9. Elemental contents are normalized to 100%; S and N were <0.05 and <0.05, respectively.
C content dry basis | H content dry basis | O content dry basis | H/C ratio dry basis | Density, g ml−1 | Moisture content | Total acid number | Mass balance | Carbon balance |
---|---|---|---|---|---|---|---|---|
84.30 | 14.96 | 0.74 | 2.11 | 0.712 | 0.36 | <0.01 | 85.6 | 84.9 |
83.94 | 15.22 | 0.84 | 2.15 | 0.722 | 0.34 | <0.01 | 85.4 | 81.7 |
84.27 | 14.77 | 0.96 | 2.08 | 0.730 | 0.30 | <0.01 | 84.2 | 77.8 |
84.41 | 14.91 | 0.68 | 2.10 | 0.726 | 0.44 | <0.01 | 86.5 | 85.2 |
The operating results as shown in Fig. 8 were fairly consistent throughout the four test periods. The liquid oil yield from the bioCRACK Bio-oil was only 0.3 g per g of dry feed with significant gas and water production as well. The yield of dry oil product on a carbon basis is similar to the Dehydrated Bio-oil, at about 50%. The hydrogen consumption was also high at about 7 wt% on a dry feed basis.
Gas products were analyzed through the test using gas chromatography. The gas product was composed of carbon oxides (6–9% CO2 and 0% CO) and alkane hydrocarbon gases (21–17% CH4, 30–35% C2, 25–21% C3, 18–11% C4, 0–5% C5) diluted with the excess hydrogen (95–97 vol% of off gas).
No trace elements were detected in the Bio-oil by ICP (<15 ppm) except sulfur. There were elements found deposited onto the catalyst after the test including Si, Ca, Mg, and Na, which were likely derived from the feedstock. In addition, there were elevated levels of Fe and Cr, which could be attributed to corrosion.
The consistency of the operating results and the products over the time of these experiments suggests little loss of catalyst activity through the test. The apparent drop in oil and gas production in the last data window, when feeding the dehydrated Bio-oil, may be better explained as experimental variability in correction of the higher production in the previous data window. The consistency contrasts with most reports in the literature for hydrotreating Bio-oil.16 Similar consistency of operation has only been achieved by a pretreatment of low severity hydroprocessing prior to the actual hydrotreating.17 In addition, a two-temperature stage hydrotreating was used to avoid fouling of the hydrotreating catalyst bed18 or the use of precious metal catalysts.19
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