Flash Distillation of Bio-Oils for Simultaneous Production of

Article Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

pubs.acs.org/IECR

Flash Distillation of Bio-Oils for Simultaneous Production of Hydrocarbons and Green Coke Yaseen Elkasabi,*,† Charles A. Mullen,† Akwasi A. Boateng,† Avery Brown,‡ and Michael T. Timko‡ †

Downloaded via IOWA STATE UNIV on January 30, 2019 at 00:48:45 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, Pennsylvania 19038, United States ‡ Chemical Engineering Department, Worcester Polytechnic Institute, 100 Institute Road, Worcester, Massachusetts 01609, United States ABSTRACT: Fast pyrolysis bio-oils from biomass can potentially integrate with petroleum refinery infrastructure for production of renewable fuels and chemicals. Besides hydrodeoxygenation, few feasible options exist for entry points. When considering advanced pyrolysis techniques such as catalytic and/or tail-gas reactive pyrolysis (TGRP), distillation for using both light and heavy ends becomes possible. Our goal was to demonstrate and optimize continuous production of liquid organic distillates and residual solids coke, both in appreciable yields for downstream conversion into renewable products. We fabricated a flash drum for continuous one-step distillations of four oils of varying oxygen content (ranging from 5 to 32 wt %). While a mesh demisting screen enhanced separation, removal of the screen ultimately improved overall yields. The flash drum proceeded to distill lower-oxygen oils (∼10 wt %) with 80 wt % time-on-stream yields over several hours; steady state was reached within 30−40 min. Bio-oils with moderate oxygen levels (20 wt %) took a noticeably longer time to attain steady state and gave 60 wt % yield. Under distillation conditions, oils from conventional pyrolysis (32 wt %) underwent condensation repolymerization due to reactive instabilities and produced only 6 wt % organic liquid yield. Solid coke residues were collected and converted into calcined coke, with Raman analysis indicating that catalytic and/or TGRP oil residues had higher molecular weight polyaromatics than those from traditional oil.

1. INTRODUCTION Methods for producing standard fuels and chemicals from renewable sources have become essential to mitigate negative environmental effects of climate change.1 Among the various processes available, fast pyrolysis2,3 uses biomass to produce liquid oils analogous to petroleum but also reduce greenhouse gas emissions. If optimized properly, biorenewable chemicals and advanced biofuels like pyrolysis can result in the net reduction of greenhouse gases by more than 50%4 (“carbon negative”). Another unique strength of pyrolysis lies in its similarity to specific processes found in petrochemical refineries.5 Pyrolysis uses a fluidized bed held at cracking temperatures (500−600 °C), similar to fluid catalytic cracking (FCC)5 processes. Furthermore, the process of upgrading pyrolysis oils (“bio-oils”) typically uses the same type of hydrotreatment catalysts and processes found in refineries. The aforementioned characteristics make pyrolysis a strong candidate for long-term cost savings, since existing refineries would mostly eliminate needs for new capital expenditures to refine bio-oil. Due to the bulky voluminous nature of biomass, bio-oil producers could more optimally make bio-oil off-site from a refinery, closer to the point of origin.6−8 Regardless of location, the biorefinery must adapt its configurations and © XXXX American Chemical Society

process variables to the nature of bio-oil. Distillation allows the separation of petroleum into light and heavy components, since a large molecular weight distribution often induces significant problems and issues downstream. Bio-oil traditionally cannot be easily distilled because it contains highly reactive oxygenates9,2 leading to condensation and polymerization reactions, which form adhesive and trapped solids. The traditional solution for refinery integration of bio-oils has been to perform hydrodeoxygenation (HDO) catalysis10,11 on bio-oils, which produces fuel-grade hydrocarbons by eliminating oxygen levels to less than 0.5 wt % and by hydrogenation. While HDO of whole bio-oil eliminates issues with distillation, several major issues remain with this particular refinery integration point: (1) Bio-oil plagues HDO catalysts with shortened catalyst lifetimes, via continued coking and/or metals poisoning. With the current state-of-the-art multistage HDO process,10,12 the longest demonstrated catalyst lifetime for time-on-stream performance amounts to less than a Received: September 17, 2018 Revised: December 10, 2018 Accepted: December 17, 2018

A

DOI: 10.1021/acs.iecr.8b04556 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research month.13 (2) Complete HDO of the bio-oil into fuel hydrocarbons, as the initial point of entry, eliminates available and cost-effective opportunities for producing chemical coproducts, especially since the oxygenated coproducts from petroleum are some of the more expensive chemicals due to specialty processes and/or catalysts required. While nonfuel coproducts make up less than 20% of the total volume of petroleum, they contribute to half of a refinery’s revenue.14 (3) HDO of whole bio-oil blocks the availability of heavier coproducts from distillation residues15,16 such as green coke, which is used to produce calcined coke. Feasible bio-oil fractionation methods become necessary, and distillation remains as the only realistic method for oil fractionation based on relative volatility. Previous studies illustrated that bio-oil distillation proceeds well when the starting bio-oils contain relatively less oxygen as-produced from advanced pyrolysis methods. Tail-gas reactive pyrolysis17 (TGRP) and/or catalytic fast pyrolysis (CFP)18,19 oils distill to yields of 55−60 wt % organics under typical batch distillation conditions. The lack of oxygen greatly decreases the concentration of highly reactive groups, which provides a level of thermal stability that makes the oil suitable for distillation. It should therefore be possible to distill TGRP or CFP bio-oils continuously; however, some nontrivial aspects of continuous processing still remain unanswered, mainly pertaining to the collection of distillates and oil residues. Bio-oil batch distillation inevitably separates the water content into an aqueous phase, which could emulsify with distilled phenolics if not fractionated carefully. If bio-oil was distilled through a fractionation column, the fouling of stage plates would likely occur, leading to excessive operation downtimes. One could possibly feed the oil into the bottom stage, as that could avoid fouling from heavy polycyclic aromatic hydrocarbons (PAHs)/phenolics. However, doing so would not make for optimal fractionation, based on process design heuristics.20 Bio-oil distillation residues are solid at room temperature and would require continuous heating for it to flow, assuming it would be possible. Aside from direct combustion for energy, bio-oil distillate residues do not have particularly useful applications as-is, mainly due to the volatiles and/or fixed carbon content and a lack of meaningful structure. Performing a one-stage flash distillation would serve a few purposes: (1) It would serve as a predistillation step before fractionation, in order to sequester residues. (2) It would enable processing of the residues continuously with appropriate heat treatments, so that production of coke can introduce some structural order. (3) Since flash distillation is the simplest form of continuous distillation, it would serve as the most straightforward test for continuously distilling bio-oil, with the shortest times to reach steady state. (4) The coke residues that would form in the drum could either accumulate and be collected semicontinuously or flow directly into another vessel, thereby not affecting distillates processing. This paper presents our initial experiments and findings into the continuous distillation of pyrolysis bio-oil, a topic of which little investigation exists in previous literature. Our goals were to (1) maximize product value in continuous processing of bio-oil, (2) elucidate optimal working conditions for bio-oil distillation, and (3) demonstrate continuous production of bio-oil distillate residues (as green coke) for conversion into calcined coke.

2. EXPERIMENTAL SECTION 2.1. Fast Pyrolysis. Bio-oils were produced using a continuous dual-bed fast pyrolysis system, described elsewhere.21,22 Briefly, switchgrass and/or hardwood biomasses were fed into a dual-bed, continuous, fast-pyrolysis reactor; one bed performs pyrolysis on fed biomass (T = 550 °C, N2 atmosphere, 40 kg/h biomass) with fresh sand, while the other performs combustion on spent sand. The vapors pass through a cyclone to collect solid char, followed by three cold-water condensers to collect aqueous liquid streams. After the condensers, oil is collected from an electrostatic precipitator (ESP). Tail gases are recycled at a rate of 70 vol %. Distillation experiments utilized the oils produced from the ESP and/or oil phases from the condenser. Catalytic fast pyrolysis of switchgrass was performed over pelletized HZSM-5 with SiO2/Al2O3 = 80. The catalyst was continually regenerated from coke deposits using the dual-bed system described above, and a detailed description has been reported elsewhere. 2.2. Flash Distillation. A 6 in. diameter vertical flash drum (24 in. height) was welded together from compression tubing with sanitary fittings and caps (see Figure 1). For both the top and bottom flanges, a Teflon and/or graphite gasket and sanitary clamp were used to seal the flanges. Compression fittings (1 in.) were welded on the top and bottom flanges, as well as halfway along the height (12 in. from the top). A wire mesh (0.5 in. square) was cut into a 6 in. circle and placed internally 4 in. from the top, held in place by the tube material.

Figure 1. (a) Diagram and (b) image of a fabricated vertical flash drum for simultaneous distillation and coke collection. (1) Support frame; (2) heating mantle; (3) ring clamps. The demisting mesh screen was located 6 in. from the top. (c) Inside cross section of flash drum post-run with nozzle, with residue. (d) Inside cross section of flash drum post-run without nozzle. B


Article

Industrial & Engineering Chemistry Research

0.05°. The areas of the XRD patterns were measured using Jade6 software.

The wire mesh acted as a demister to enhance separation of vapors from entrained liquids. A ceramic band heating mantle, consisting of two 9 in. sections (Nordic Sensors Inc., Montreal, Canada), was clamped directly onto the drum and controlled with a single proportional temperature controller. Vapors flowed out the top through a 1/8 in. tube, leading into a coldwater condenser connected to a 0 °C recirculation bath. Residual bottoms accumulated on the bottom of the drum internally and were collected altogether postdistillation. For any experiments utilizing a spray nozzle, a 416 SS 254 mm orifice diameter was used. For each experiment, the heating mantle preheated the drum to the experimental temperature. An HPLC pump, fitted to the drum entry with 1/8 in. tubing, began flowing the oil at rates between 2 and 5 g/min. After the initial entry of bio-oil, samples were collected every 15 min. The actual flow rate and consumption of bio-oil were monitored by weighing the reserve flask at timed intervals. Upon ending the flow of biooil, water was reintroduced into the flash drum, with more organics collected and the fed water collected as well. 2.3. Coke Devolatilization/Calcination. Bio-oil distillation residues were devolatilized and calcined according to previous methods.15 Briefly, residues were gradually heated in a muffle furnace under an inert N2 atmosphere. Residues were heated to 400 °C and held for 20 min, then raised to 450 °C in 25 °C increments, and then gradually heated to 1100 °C over a period of 2 h. Samples remained in the furnace and were allowed to cool gradually to room temperature. Percent fixed carbon was calculated based on the amount of mass remaining after calcination. 2.4. Characterization. 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, USA). Oxygen content was calculated by difference, and water content was used to subtract H and O and recalculate results on a dry basis. Moisture content was measured with Karl Fischer (KF) titration in 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. Gas chromatography with mass spectroscopy (GC− MS) analysis of liquid products was performed on a Shimadzu GCMS QC-2010. 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. Raman spectra of the coke samples were obtained using a Horiba XploRa Raman microscope operating with a 532 nm laser line at a power of 13 mW. A 20 s scan time was used with an accumulation of 20 scans. An 1800-line grating was used with an aperture of 100 and slit width of 300. The laser focused on the coke samples with a 100 magnification lens from Olympus. All samples were pressed into pellets comprised of approximately 10 mg of sample and 300 mg of potassium bromide. The Raman spectra were fit using the procedure of Smith et al.23 Powder X-ray diffraction (XRD) spectra were measured with an X-ray powder diffractometer (Rigaku Geigerfl ex) using Cu Kα radiation (1.5406 Å). The spectrum was measured in the 2θ range from 10 to 50° and a step of

3. RESULTS AND DISCUSSION 3.1. Bio-Oil Properties. We hypothesized that the yields and product quality produced from continuous bio-oil distillation, similar to their batch experiments, vary proportionally to the oxygen contents. Bio-oil with elevated levels of oxygen contains wider populations of reactive oxygenated functional groups, including those most directly responsible for yield losses during bio-oil distillation (e.g., ketone, aldehydes, carboxylic acids, and carbohydrates).24 Hence, we tested biooils with varying oxygen contents produced by traditional pyrolysis, TGRP, and CFP. The latter two processes produce oils of reduced oxygen content based upon the process conditions. Table 1 displays the characterization of the four bio-oils used in this study. Oils 1 and 2 were produced by CFP, oil 3 was Table 1. Characterization of Pyrolysis Oils Produced from the Pilot-Scale Mobile Reactor process biomass KF (wt %) wt % (db) N C H O BTEX phenolsa naphthalenes olefins acetic acid acetol furfural levoglucosan syringol

1

2

3

4

catalytic switchgrass 0.847

catalytic switchgrass 1.01

TGRP hardwood 9.1

traditional switchgrass 20.9

0.47 86.25 7.98 5.29 32.70 2.73 4.41 1.17 0.02 0.23 0.04 0 0

0.245 81.49 7.63 10.635 26.35 2.08 5.33 1.24 0.05 0.00 0.02 0.01 0.19

0.45 72.45 7.18 19.93 0.8 4.07 0.43 0.51 5.22 2.24 0.96 0.5 0.45

0.37 61.15 6.44 32.04 0.01 0.26 0 0 2.98 1.91 0.3 2.00 0.28

a

Includes phenol; o-, m-, and p-cresols; 2,4-dimethylphenol; and 4ethylphenol.

produced by TGRP, and oil 4 was produced by traditional pyrolysis. Elementally, these processes produced the desired variations in oxygen content, with a similar variation in moisture content. With both catalytic experiments (oils 1 and 2), the oils contained significantly elevated levels of benzene− toluene−ethylbenzene−xylenes (BTEX) (>25 wt %). The TGRP oils (oil 3) have higher levels of phenols, characteristically marked by their relatively higher viscosity (data not shown). While oil 3 also contains some acetic acid and acetol, the amount of levoglucosan still remains relatively low (∼0.5 wt %). Compared with the traditional pyrolysis bio-oil (oil 4) levoglucosan content of 2.0 wt %, the levoglucosan in oil 3 is similar to measured in previous TGRP distillation studies and is expected to have negligible effects. 3.2. Flash Distillation Hardware Development. From our previous work,24,25 batch distillation of TGRP-based oils proceeded to yields in the range 50−60 wt %. A variety of biooils distilled and produced both distillates and residual coke (“bottoms”), regardless of the biomass source. Continuous processing of these oils would be feasible if (1) no plugging or C


Article


improved, but by only 5−10 wt % difference. Overall, while a demister screen can inhibit total organic yields long term, we found the demister screen to still allow distillation toward a comparable steady-state yield. Ultimately, the optimal configuration consisted of using neither a nozzle nor a demisting screen. 3.3. Flash Distillation Yields. Apart from time-on-stream yields, the overall total yields (including the start-up phase) of collected samples were calculated to evaluate the time to reach steady state for this reactor. Based on the recorded total yields (Table 2), total mass balance closures ranged from 84 to 90%, with the exception of oil 4. Any losses in yields can be attributed to production of noncondensable gases due to cracking, adhesion of oil tar/coke to the walls, and/or losses of coke during post-run collection. Generally, most runs produced a relatively small yield of aqueous phase, as the original starting oils had little water, with the exception of oils 3 and 4. As the bio-oil oxygen content increases, the yield of aqueous phase tended to increase, which indicates the proportionality of bio-oil reactivity. Simultaneously, a decrease in recovered organic distillates occurred, likely because the organic components in high-oxygen bio-oil underwent condensation polymerization to produce the excess water. When comparing total organic yields with steady-state organics yields, the biggest differences occurred for oil 3, as this oil did not reach an entirely distinct steady state. Nonetheless, the steady-state yield recorded is 20% greater than the total overall yield, which starkly contrasts with the 4−10% difference of other bio-oils. 3.4. Distillation Process Variables. To assess suitability for long-term experiments, various oils were first distilled over relatively shorter time scales, until steady-state conditions were reached. While both oils 1 and 2 involved catalytic pyrolysis, oil 2 contained slightly more oxygen and formed the basis of experiments to investigate the effects of specific process variations. When optimal configurations are established, loweroxygen-content oil 1 can undergo distillation for longer periods. As seen in Figure 3, distilling oil 2 at 330 °C produced a steady-state yield of approximately 50−60 wt %, which compares similarly with batch distillations up to this temperature.24 Lowering the flow rate from 3.0 to 2.0 g/min initially increased yields but decreased again, which resulted in no net change in steady-state yields. However, the component yields reveal varying trends that reveal certain phenomena that occur. The two lighter groups (BTEX and olefins), in response to the flow rate decrease, revert back to yields similar to that of the higher flow rate. However, the two heavier groups (phenols and naphthalenes) maintain the increase in steady-state yield well past the transient period of flow change. Hence, bio-oil flow rate affects individual component yields. Since yield increases in one component compensate for yield decreases in another component, total yield does not change with varying flow rate. For this distillation temperature (330 °C), the lighter components would still undergo rapid vaporization due to their much lower boiling points. The bio-oil residues can easily entrain the heavier component groups, so a lower flow rate allows for more thorough heating and volatilization, leading to greater yields. One observation from Figure 2 (demister variation) that differs from Figure 3 (temperature variation) concerns the differences in group component yields. Group component yields in Figure 2 for oil 2 tended to converge toward nearly the exact same values for each time point, with the exception of

accumulation of residues occurs in the process. (2) The process can sequester coke without introducing excessive porosity; low porosity is important for maintaining adequate density and crystallinity of calcined coke. (3) The process attained expected yields based on previous batch work. (4) The process sufficiently removed volatiles from the coke. Before performing most of the experiments discussed, some preliminary tests employed equipment modifications, in order to examine which variables produced any desired effects. Flash distillations often employ injection nozzles, in order to enhance the volatilization of liquids. We injected oil 3 into the flash drum with a nozzle (see Figure 1c), as this oil represents an intermediate amount of oxygen in bio-oil. While the experiments employing the nozzle successfully produced distillates with reasonable yields at 230 °C, performing the experiments at 280 °C caused the nozzle to plug prematurely, approximately 30 min after appearance of the first product sample. The latter temperature alone cannot sufficiently remove enough distillates. Furthermore, a solid porous char accumulated on the wall directly in front of the nozzle, due to the direct spraying onto the heated wall surface. For these reasons, the nozzle was removed for higher temperature runs (see Figure 1d). While a nozzle produced more problems than it solved, the question of whether a demister would improve distillation needed to be addressed separately. Figure 2 displays results

Figure 2. (a) Overall time-on-stream yields for oil 2 (with and without demister), and component yields based on the (b) presence or (c) absence of the mesh demister at 380 °C.

from the distillation of oil 2, from experiments with and without the demisting screen. Both configurations allowed for steady state operation, requiring approximately the same amount of time to reach steady state (∼40−45 min). Not using the demister resulted in a 15−20 wt % overall organic yield improvement. Total group component yields overall were D


Article


Table 2. Overall Mass Distribution and Mass Balance Closure of Bio-Oil Flash Distillation Products, Based on Averages of Values at Steady State and/or Total Collected Post-Runa distillates (org) distillates (aq) bottoms % closure steady-state yield (org)

oil 1b

oil 2 (330 °C)

oil 2 (380 °Cb)

oil 2 (380 °C)

oil 3

oil 3b

oil 4b

76.3 1.6 12.5 90.4 80

62.8 2.6 23.4 88.8 50

68.3 1.1 15.9 85.3 62

75.1 2.4 6.7 84.2 80

30.4 8.5 47.9 86.8 50

38.1 4.2 29.6 72 45

4.1 45.6 13 62 5.5

Default drum temperature was 380 °C. bNo demister used.

a

convergence of yield values, caused by less entrainment of heavier components. While distillation at 330 °C would theoretically remove the heavier componentsas was confirmed from batch experimentsthe actual temperature required exceeds the theoretical temperature required. Due to the larger volume that requires a continuous heat duty by the heating mantle, and also due to greater surface areas where heat could escape, the actual temperature required for flash distillation exceeds that of batch experiments. Since distillation of traditional pyrolysis bio-oil gives poor yields due to excessive reactions, it would benefit to elucidate what bio-oil oxygen levels introduce instabilities in continuous distillation. While past studies examined TGRP vs regular biooil distillation, this study allows for a closer examination of the direct role(s) of bio-oil oxygen content and/or the concentration of specific types of oxygenated species. Oil 3 contains approximately 20 wt % oxygen, midway between the average TGRP or CFP oxygen values (10−12 wt %) and regular bio-oil (33 wt %). In Figure 4, there is a longer period before the steady state is reached for distillation of oil 3, when a demister is used. Even though the total organic yield did not converge to a clear value during the times tested, the convergence of group component yields appears to converge near a similar value of 50−60 wt %. The pattern of group component yields also uniquely differs from previous results, in that the yield values for each group widely vary to start, and then change patterns with an eventual convergence. Longer transient periods can be attributed to several applicable factors:

Figure 3. Time-on-stream yields of flash distillation of oil 2 at 330 °C, using varying flow rates.

the transient period. The higher temperature used for these experiments (380 °C) likely plays the biggest factor in the

Figure 4. Time-on-stream yields of oil 3 flash distillation at 380 °C, based on total organic phase (top) and component yields (bottom). (a) With demister; (b) without demister. E


Article

Industrial & Engineering Chemistry Research (1) heavier molecular weight and/or higher viscosity oils require longer times and more energy to conduct the same amount of heat; (2) higher molecular weight compounds can cause more interactions with lighter components (especially when they are more polar due to oxygenated groups), which delays the eventual volatilization. However, the eventual convergence of component yields shows that this oil can attain steady state, albeit slowly. Possible solutions to remedy slow start-up include greater surface area of heating/contact, and either faster flow rates or a smaller total drum volume. When the demister is removed for oil 3 (Figure 4b), the system reaches steady state more rapidly, though the steady-state yields remain nearly identical to that of the demister. This indicates that the demister plays a more active role in hindering volatilization for oils that are heavier and more viscous, such as oil 3. As primarily a control sample, bio-oil with 33 wt % oxygen was also subjected to flash distillation (Figure 5). While data

Figure 6. Oil 1 flash distillation at 420 °C, over longer time-onstream, based on total organic phase (top) and component yields (bottom).

entire duration of the run, indicative of the stability and feasibility for long-term distillations. At the same time, however, the group component yields had wider differences in values and gradually converged toward an average value of 75 wt % based on averages. While this longer convergence of yields was unexpected, some process differences explain this result. During the first portion of time-on-stream, the bottoms residue began accumulating on a surface without any residue, in direct contact with the heating mantle. This can provide higher localized temperatures, which can propel heavier groups into vapors. As the run progresses, bottoms residue accumulates, which creates two effects: (1) reduction in contact temperature of new oil entering the drum, and (2) opportunity for heavier compounds to dissolve in the bottoms, which more accurately represents flash distillation. Besides oxygen content, several differences among the oils exist, including the process differences. Although oils 1 and 2 utilized catalytic pyrolysis, in the end, distillation feasibility relates to oil composition differences more than any other variables. Even within catalytic pyrolysis, significant variations in oil quality exist,18 in terms of oxygenated species concentrations. While our previous work examined the presence of acetic acid and/or acetol, this variable alone cannot sufficiently explain the differences in yields and reactions. Some TGRP oils still contain some acid groups but can distill to similar yields as other TGRP oils. Also, some regular bio-oils contain relatively less acetic acid/acetol but still exhibit significant yield losses (such as oil 4). While TGRP and catalytic oils contain less problematic oxygenated species, levoglucosan content represents a critical difference that remains consistent. The indicated concentration of levoglucosan can also be indicative of the presence of other anhydrosugars and oligosaccharides present in the bio-oil that will have similar behaviors. Levoglucosan has a reported boiling point of 385 °C, so it is not easily volatized at the conditions used.26 Therefore, it is likely to undergo chemical reactions when heated. There are several possibilities including condensation-type reactions to form intractable humins, either

Figure 5. Dry organics yields from flash distillation of oil 4 (traditional pyrolysis bio-oil) at 380 °C.

indicate a relatively unstable steady-state value, total organic yields significantly drop, down to ∼6 wt %. Surprisingly, distillation of this oil produced significantly less than the analogous results from batch experiments (∼16−20 wt %). However, the past batch distillation experiments on similar oils fractionated more organics, possibly because the batch heating process for fractionation distillation occurs gradually and slowly, which affects the polymerization kinetics of condensation reactions. Since bio-oil directly entered the drum at 380 °C, the conditions increase reaction rates, likely leading to more rapid condensation polymerization, low organic distillate yields, and higher water yields. Figure 5 does not show group component yields, as the total organic yield suffices as evidence of lack of feasibility. 3.5. Optimal Time-on-Stream Results. In considering the aforementioned results, the optimal process conditions utilize a distillation temperature of at least 380 °C with no demisting screen, with an oil pumping rate of at least 3 g/min. For longer time-on-stream (TOS) studies, we distilled oil 1 as this represents the highest quality oil, with the potential for producing the best quality coke residue. We distilled oil 1 at 420 °C, in an attempt to learn if yields would improve by driving off more volatiles. We also anticipated that the coke content of oil 1, based on the low oxygen content and high volatiles, would be much less than that of the other oils. Based on the results in Figure 6, distillation attained steady state with a response time of ∼40 min, indicating that the greater severity of distillation had little to no effect on the transient time length. Total organic yields maintained at 80 wt % for the F


Article

Industrial & Engineering Chemistry Research with other sugar-type molecules or with aldehyde or ketones present. It can also dehydrate to HMF which may volatize or itself can further react into humins-type bottoms.27 3.6. Coke Bottoms Collection and Properties. The mechanism of coke formation depends highly on the temperature profile that the coke experiences, as well as the coke composition. Hence, accumulation of the coke can facilitate proper crystallite formation at the right temperature(s).28 While the flash drum system allowed residues to accumulate rather than flow continuously, this setup creates an opportunity for refinery integration by means of that accumulation. The coke was collected postdistillation by opening the drum and manually removing the coke. If the experiments had a second identical drum on standby, the setup would allow for semicontinuous operation analogous to a delayed coker. In both processes, one drum operates with coke accumulating in the drum, until the coke fill limit is reached. Then, the oil switches into the standby drum, allowing for continuous volatiles collection from the second drum and coke collection from the first drum. In all experiments, the coke accumulated without incident; the coke occupied very little volume of the drum (

Flash Distillation of Bio-Oils for Simultaneous Production of

Recommend Documents