Catalytic co-pyrolysis of lignocellulose and polyethylene blends over

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Kinetics, Catalysis, and Reaction Engineering

Catalytic co-pyrolysis of lignocellulose and polyethylene blends over HBeta zeolite Ellen K. L. Morais, Sergio Jiménez Sánchez, Héctor Hernando, Cristina OchoaHernández, Patricia Pizarro, Antonio S Araujo, and David Pedro Serrano Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b06158 • Publication Date (Web): 29 Mar 2019 Downloaded from http://pubs.acs.org on March 29, 2019

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Industrial & Engineering Chemistry Research

Catalytic co-pyrolysis of lignocellulose and polyethylene blends over HBeta zeolite

Ellen K. L. Morais,† Sergio Jiménez-Sánchez,‡ Héctor Hernando,‡,§ Cristina OchoaHernández,⊥ Patricia Pizarro,‡,§ Antonio S. Araujo,† David P. Serrano*‡,§

†Federal

University of Rio Grande do Norte, Institute of Chemistry, Natal RN, 59078-

970, Brazil. ‡Thermochemical §Chemical

Processes Unit, IMDEA Energy, 28935, Móstoles, Madrid, Spain.

and Environmental Engineering Group, ESCET, Universidad Rey Juan

Carlos, c/ Tulipán s/n, 28933 Móstoles, Madrid, Spain. ⊥Max-Planck-Institut

für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an

der Ruhr, Germany

*Corresponding author: David P. Serrano [email protected]

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Abstract

Co-processing of Eucalyptus woodchips (EU) and low-density polyethylene (LDPE) has been investigated using two HBeta zeolites as catalyst. The reactions were carried out in a two-step (thermal/catalytic) system, varying the catalyst to feed (C/F) ratio. A maximum in the yield of the liquid organic fraction (oil*) was observed for both HBeta samples at intermediate C/F ratios due to the occurrence of sequential cracking reactions, which were accompanied by a significant reduction of the oil* oxygen content. This finding, together with the results obtained when feeding pure EU and LDPE, denote that remarkable synergetic effects occur during the co-processsing of lignocelllulosic biomass and polyolefinic plastics over HBeta zeolite, mainly by DielsAlder condensation between furans and light olefins. The presence of acid sites with moderate strength in the HBeta samples is an essential factor to obtain high oil* yields since it limits the extension of severe cracking reactions. ________ Keywords: catalytic pyrolysis, HBeta zeolite, lignocellulose, biomass, plastics

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1. Introduction Lignocelllusic biomass is a renewable resource with a great potential due to its availability and versatility. In addition to its direct combustion to produce energy, lignocellulose can be converted into different biofuels and bio-based chemicals throughout a variety of biological and thermochemical processes. Moreover, lignocellulose is a very abundant feedstock that can be found in diverse forms, such as agriculture and forestry residues and dedicated energy crops, as well as in municipal and industrial wastes.1 Likewise, the use of lignocelluosic biomass as raw material may have relevant environmental beneﬁts in terms of reduction of CO2 emissions and valorization of residues.2,3 Among the various routes investigated for the conversion of lignocellulose into biofuels, pyrolysis is considered a promising alternative that provokes its thermal decomposition under inert atmosphere to yield gases, liquids (bio-oil) and a solid residue (char).4,5 This process has received increased attention because it can produce a high liquid yield (up to 75 wt%) under moderate temperatures (500 - 600 °C) and short residence times.6,7 Although the liquid bio-oil has been proposed to be used directly as fuel in a variety of applications, including diesel engines, boilers, turbines for the generation of electricity and furnaces,8 its properties are not really suitable due to its high oxygen content, corrosiveness, high viscosity and chemical unstability.9,10 These undesired properties are a consequence of the existence of a large diversity of oxygenated compounds in bio-oil, as well as of high amounts of water. A number of catalytic treatments, such as catalytic pyrolysis and hydrodeoxygenation, have been explored for bio-oil upgrading, which usually are aimed to remove most of its oxygen content. Different types of catalysts have been investigated in the literature for lignocellulose catalytic pyrolysis,11 including zeolites,12,13 metal oxides14 and metal salts.15,16 The catalyst promotes a number of reactions, such as cracking, deoxygenation and aromatization, which are coupled with those already occurring just by thermal degradation of the biomass. In particular, deoxygenation may proceed by three main pathways: decarboxylation, decarbonylation and dehydration, leading to the formation of CO2, CO and H2O, respectively.17 Acidic zeolites usually show the best performance 3



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in lignocellulose catalytic pyrolysis exhibiting a high selectivity towards the formation of aromatic hydrocarbons. However, the strong zeolite acidity causes also a sharp decrease of the bio-oil yield as it promotes excessive cracking, whereas the catalyst suffers from extensive coking, which results in its fast deactivation.18–20 On the other hand, the management of plastic wastes is increasingly viewed as an issue of strong environmental concern due to their relatively low recycling rates and the progressive accumulations of huge amounts of plastics in the oceans, where they can remain for decades affecting quite negatively the ecosystems.21 Plastic residues consist of a number of polymers, such as PE, PP, PS, PET and PVC. Several thermochemical processes, like gasification, pyrolysis and catalytic cracking, have been explored in the past for the conversion and valorization of plastic wastes into fuels and/or chemicals,22 although their large scale application has been limited by a number of technical, economical and policy issues. In recent years, the co-processing of biomass and plastics has been explored as an interesting way for the joint valorization of these two types of materials.17 Several works have reported a significant improvement in the quality and quantity of the pyrolysis oil, in particular when polyolefinic plastics are co-pyrolyzed with biomass, claiming the existence of synergistic effects during the co-pyrolysis process. Thus, it has been proposed that the plastic components play the role of hydrogen donor agents decreasing the char formation and favouring the biomass deoxygenation.23 In addition, it has been suggested that radicals generated from biomass thermal decomposition promote the polymer degradation.24 These synergistic effects may be very beneficial for the large scale application of these processes as it may reduce the production costs and overcome some of the limitations present in plastic waste management.25 Nevertheless, the synergistic effects are tricky to predict and strongly depend on several factors such as the type of feedstocks blended, their extent of contact (determined by the type of reactor) and the operation conditions.17 Despite the improvement that can be achieved by thermally co-processing biomass and plastics via non-catalytic pyrolysis, the liquid fraction so obtained still lacks appropriate properties to be used as fuel in the transport sector. The main technical limitations are excessive oxygen concentration and high amounts of heavy hydrocarbons.26,27 Introducing a catalytic upgrading step, in the form of catalytic co4


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pyrolysis, has been shown as an effective way to enhance the synergistic effects of cofeeding biomass and plastics. In this way, zeolites have exhibited remarkable properties because their dual Brønsted-Lewis acidity promote the formation of aromatic hydrocarbons by Diels-Alder cycloaddition of dienes and dienophiles, followed by dehydration or dehydrogenation reactions.28,29 As reviewed recently,26,30 most works so far published on the co-processing of biomass and plastics by catalytic pyrolysis with zeolites are based on the use of HZSM-5 catalysts, whereas just a few examples can be found using other zeolite framewoks.31 HBeta zeolite can be viewed as a promising catalyst for the co-pyrolysis of biomass and plastics due to its high thermal stability, unique three-dimensional microporous system with 12-ring openings and controlled acidity, which can be adjusted varying the Si/Al ratio in a wide range. The good performance of HBeta zeolite has been demonstrated in a variety of chemical and petrochemical processes, such as isomerization, alkylation, cracking and acylation.32–34 Zeolite HBeta has been investigated in the catalytic pyrolysis of plastics and biomass in an independent way,35– 39

but almost no works can be found dealing with the joint co-processing of these two

types of materials. Just in a recent work zeolite HBeta has been tested in the catalytic co-pyrolysis of torrified cellulose and polypropylene.40 However, as far as we know, this material has not been explored yet in the catalytic co-pyrolysis of lignocellulose and plastics. Accordingly, the present work is aimed to study the behavior of zeolite HBeta for the catalytic co-pyrolysis of a mixture of lignocellulic biomass and polyolefinic plastic in order to produce upgraded oils that could be employed in the formulation of advanced fuels for the transport sector or as a source of raw chemicals. Thereby, the effects of both the zeolite acidity and the catalyst to feed ratio have been investigated, showing that both parameters play essential roles determining the yield and composition of the so produced oils.

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2. Experimental 2.1. Materials Low-density polyethylene (LDPE, MW = 416,000), supplied by REPSOL (Alcudia grade), was used as representative of polyolefinic plastics, whereas Eucalyptus woodchips (EU), provided by ENCE, were employed as lignocellulosic biomass. The HBeta zeolites with different Si/Al ratios were purchased from CLARIANT, being designated as HBeta (24) and HBeta (72), respectively (the number in brackets corresponds with the Si/Al ratio of the samples).

2.2. Catalysts characterization The zeolite HBeta samples were characterized by a number of techniques in order to determine their physicochemical and structural properties. X-Ray Diffraction (XRD) measurements were performed in a Philips PW 3040/00 X’PERT MPD/MRD powder diffractometer using Cu-Kα radiation (λ =1,542 Å), operated at 45 kV potentials and 40 mA intensity. The measurements were carried out using the following conditions: scan intervals 2θ = 5-90º, step size = 0.013º, time per step = 57.82 s, analysis duration = 1584 s. Metal contents were determined by means of Optical Emission Spectroscopy with Induced Coupled Plasma (ICP-OES) collected in a Perkin Elmer Optima 7300 DV instrument. The acidity of the zeolite samples was measured by Temperature Programmed Desorption (TPD) of NH3 using an AUTOCHEM 2920 Micromeritics instrument with thermal conductivity detector (TCD). The standard procedure for the NH3-TPD measurements involved the degassing of the sample by flowing He at 550 °C for 1 h, cooling to 120 °C, adsorbing NH3 from a mixture of 10% NH3 in He, removing the weakly adsorbed NH3 by flowing He at 120 °C for 30 min, and finally carrying out the TPD experiment by raising the temperature of the catalyst sample up to 550 ºC with a ramp of 10 °C min-1. In order to determine the concentration and strength of Brønsted acid sites (BAS) and Lewis acid sites (LAS), in situ FTIR spectroscopy of pyridine adsorption 6


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was performed. Samples were pressed into ca. 10 mg cm-2 self-supporting wafers, mounted into a quartz IR cell with CaF2 windows, degassed at 450 °C for 4 h under high vacuum and cooled down to room temperature prior to record their corresponding spectra before adsorption. Pyridine adsorption (3 mbar) was carried out at 150 °C during 20 min. Desorption of the probe molecule was controlled stepwise by evacuating the cell for 20 min at different temperatures (150 °C, 250 °C, 350 °C and 450 °C) under high vacuum. A Nicolet iS50 spectrometer equipped with a MCT detector was used to collect spectra accumulating 150 scans with 4 cm-1 resolution. Concentration of BAS and LAS were calculated considering their characteristic absorption bands at 1545 cm-1 (PyH+) and 1455 cm-1 (PyL) and applying the following integrated molar extinction coefficients: εB = 1.67 cm μmol-1 and εL = 2.22 cm μmol-1, respectively. Argon physisorption isotherms were recorded at 87 K on an AUTOSORB iQ system (Quantachrome Instruments) equipped with a vacuum turbo-molecular pump for the determination of the textural properties. Thereby, the samples were degassed at 300 °C under vacuum for 3 h. The total surface area was obtained by application of the BET (Brunauer–Emmet–Teller) equation in the range of relative pressures (P/P0) between 0.05 and 0.2. Pore size distribution, as well as textural properties corresponding to microporosity and mesoporosity/external surface, were calculated using the NL-DFT model assuming cylindrical pore geometry. Solid-state 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) of the zeolite samples were performed on a Varian Infinity 400 MHz spectrometer fitted with a 9.4 T magnetic field and using 4 mm ZrO2 rotors. All the measurements were carried out at room temperature, spinning the sample at 12 kHz for

27Al

with a pulse

width of 1 s.

2.3. Catalytic co-pyrolysis tests The catalytic co-pyrolysis experiments were carried out in a downflow fixed-bed reactor comprising two independently heated zones (thermal and catalytic ones). Both zones were separated by an internal cylinder having a distance between them of 6.5 cm, which ensured that the corresponding temperarures could be fixed and controlled independently. The internal diameter of the reactor was 1.6 cm with a total length of 38 7



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cm. The average residence time in both thermal and catalytic zones of the vapours coming from the cracking of the feedstock is in the range of 2-4 s. A detailed scheme of the experimental set up employed in the catalytic pyrolysis tests can be found elsewhere.11 The reactor was loaded with different catalyst amounts (0.8, 1.6, 2.0 or 3.0 g) to operate with catalyst to feed ratios (C/F) in the range 0.2 - 0.75. Thereby, the zeolite powder was previously pelletized, crushed and sieved to a particle size between180 and 250 μm. The feedstock consisted in a mixture of 60 wt% dried EU and 40 wt% LDPE with a particle size about 0.5 - 1 mm. The co-pyrolysis tests were run at atmospheric pressure using temperatures of 550 and 500 °C for the pyrolysis and catalytic zones, respectively. In addition, two reference tests were performed with a catalyst load of 2 g by feeding pure EU and LDPE, respectively, using amounts of these raw materials equal to those present in the test performed with C/F = 0.5. Prior to each co-pyrolysis experiment, and during the heating up of the reactor, all the reaction system was purged with a N2 flow until the O2 concentration levels dropped to < 0.1 vol% to ensure that pyrolysis takes place in inert atmosphere. Once inertization was achieved, the feed was loaded into the reactor at once by opening a valve located in the top part of the reaction system. The volatiles so generated in the pyrolysis zone were swept by a N2 stream (100 cm3 min-1), passed through the catalyst bed and left rapidly the reactor. The pyrolysis vapors were then condensed by means of four 125 cm3 flasks connected in series refrigerated by an ice-water bath (0 - 4 °C).

2.4. Analysis of the co-pyrolysis products Permanent gases and light hydrocarbons (C1 – C4) were collected in a sampling bag for their further analysis in a dual channel Agilent® CP-4900 Micro Gas Chromatograph (Micro-GC). The micro-GC was equipped with molecular sieve (Molsieve 5 Å) and HayeSep A columns and a thermal conductivity detector (TCD), using Helium as carrier gas. The TCD was periodically calibrated with a standard gas mixture containing N2 (internal standard), O2, H2, CO, CO2, CH4, C2H4, C2H6, C3H6, C3H8, C4H8 and C4H10.

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After each experiment, both the char and used catalysts were recovered and weighed. Coke deposited on the catalyst was determined as the weight loss undergone by the used catalyst when it was burned in a TGA analyzer NETZSCH STA 449 using a heating program of 20 °C min-1 up to 550 °C in air atmosphere. In most of the catalytic co-pyrolysis tests, the liquid fraction was formed by two phases (aqueous phase and organic phases), being separated by centrifugation. KarlFischer titration (ASTM E203-08) was used to determine their water content using a Mettler-Toledo V20S compact volumetric KF titrator. The elemental analysis of pyrolysis products (char, coke, wax and oil) was carried out in a micro-elemental analyser (Thermo Scientific FLASH 2000 CHNS/O). C, H, N, S elements were directly measured, whereas O was calculated by difference. The ash content in solid samples were determined by muffle calcination, calculating the weight loss undergone by a certain amount of sample (previously dried) after being treated in air at 550 °C for 3 h. The high heating value (HHV) of both feedstocks and product fractions, except the gas phase, was calculated from the ultimate analysis according to the correlation reported by Channiwala and Parikh.41 The HHV of the gas phase was calculated from the HHV of their individual components. The energy yield of the different fractions and components, defined as the proportion of the chemical energy contained in the initial biomass that remains in each product, was calculated following the procedure earlier described 42. Finally, the components present in the liquid fractions were analyzed by a Gas Chromatograph Mass Spectrometer (GC-MS) Bruker® SCION 436-GC, using the following conditions: electron energy = 70 eV, emission = 300 V, He flow rate = 1 cm3 min-1, column = WCOT fused silica 30 m x 0.25 mm ID x 0.25 µm. NIST EI-MS spectral library (v2.0) was used for the compounds identification with a minimum match score of 700. These components were further grouped into families according to their main functional groups.

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3. Results and Discussion 3.1. Properties of the HBeta catalysts The zeolite HBeta materials employed as catalysts in this work were two samples having different Al content (Si/Al ratios of 24 and 72, respectively). From their resultant X-ray diffraction patterns, illustrated in Figure 1.a, it is verified that both zeolite samples exhibit the typical BEA diffractions with their characteristic Miller indexes.33 The narrow dffractions peaks present in the patterns, as well as the absence of any amorphous background in the 2θ range 20 - 25º, indicate the high crystallinity of these materials. Figure 1.b shows the Ar adsorption-desorption isotherms of the HBeta samples. Both zeolites under study possess isotherms characteristic of microporous materials but with a relevant contribution of mesoporosity. Thus, three adsorption regions can be identified: low relative pressure zone (P/P0 < 0.1), arising from the zeolitic micropores, intermediate relative pressure zone (0.1 < P/P0 < 0.9), associated with the adsorption in the mesopore range, and high relative pressure zone (P/P0 > 0.9), related to the existence of interparticular voids. The textural properties of the samples derived from the adsorption-desorption isotherms have been also included in the inset of Figure 1.b. Both materials show relatively high BET areas (≥ 600 m2 g-1), which agree well with the values typical of zeolites with the BEA framework. Moreover, both samples exhibit a significant contribution of the mesopore/external surface area, with values of 150 and 190 m2 g-1 for HBeta (24) and HBeta (72), respectively. This is a relevant finding since the mesopore/external surface is expected not to be hindered by difussional or steric limitations in contrast with the micropores. Accordingly, both HBeta samples present high potential for being used as catalysts in the conversion of bulky molecules, as it is the case of those derived from the pyrolysis of lignocellulose and polyolefins.

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Intensity (a.u.)

(a)

HBeta (24)

HBeta (72) 5

10

15

20

25

35

40

45

50

55

60

(b)

SBET (m 2 g-1)

SMICRO (m 2 g-1)

SMESO/EXT (m 2 g-1)

VMICRO (cm 3 g-1)

VTOTAL (cm 3 g-1)

HBeta (24)

598

448

150

0.27

0.45

HBeta (72)

648

458

190

0.28

0.52

500 400

30

2 

600

Volume adsorbed (cm3/g, STP)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


HBeta (72) 300 HBeta (24) 200 100 0 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

P/P0 Figure 1. XRD patterns (a) and Ar adsorption-desorption isotherms (b) of the HBeta samples.

TEM images of the HBeta samples are illustrated in Figure S1, showing they are formed by particles in the range 0.5 - 1 m. A closer inspection of these particles indicates that they really consist of aggregates of nanocrystals with sizes about 30-50 nm. The voids existing among these nanocrystals confirm the occurrence of mesoporosity in both samples, explaining the significant adsorption earlier denoted in the Ar isotherms at intermediate relative pressures. No significant differences can be observed in the TEM images between both samples in terms of particles and nanocrystals sizes.

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The NH3-TPD curves of the zeolite samples are shown in Figure S2. Three overlapping peaks are distinguished, which can be assigned to different phenomena occuring during the sample heating: a) peak with maximum at about 170-180 ºC, corresponding to NH3 weakly adsorbed on the acid sites; b) peak with maximum at about 300-310 ºC, associated with NH3 more strongly chemisorbed, and c) peak at about 510-520 ºC, which at least in part is generated by the water release due to the occurrence of dehydroxylation reactions.43 The overall acidities so obtained for the HBeta (24) and HBeta (72) materials were 0.497 and 0.179 mmol g-1, respectively. These values are proportional to the Al content of the samples, although somewhat lower than the theoretical ones according to their respective Si/Al ratios (0.67 and 0.23 mmol g-1, respectively), indicating that not all the Al species are linked to acid sites, probably because of the presence of extraframework Al species, or exhibit a very weak acidity releasing the ammonia during the physisorption treatment applied in the TPD tests. On the other hand, although some differences can be observed between the two HBeta samples regarding the temperature of the peak maxima, they are not large enough to gain solid conclusions about the strength of the corresponding acid sites. In order assess the distribution of Brønsted and Lewis acid sites in the samples, as well as their specific strength, pyridine/FTIR was performed. After adsorption of the probe molecule at 150 °C, evacuation at different temperatures was carried out. The FTIR spectra so obtained are illustrated in Figure S3. Bands arising at 1546 cm-1, 1455 cm-1 and 1490 cm-1 are ascribed to the presence of pyridinium ions (PyH+), coordinatively bound pyridine on Lewis acid sites (PyL) and to the common band for pyridine interacting with both types of acid sites, respectively. In addition, the sample HBeta (72) presents a small band (1445 cm-1) at 150 °C associated to pyridine interacting with silanol groups. After pyridine desorption at 350 °C, a shoulder appears at 1462 cm-1 in both zeolites becoming more evident at higher temperatures. This band could be attributed to the formation of new coordinated pyridine species as it has been already reported.44,45 Concentrations of BAS and LAS in both samples have been calculated from the pyridine/FTIR spectra, being depicted in Figure 2. As expected, the HBeta (24) sample presents a higher concentration of both types of acid sites than HBeta (72). Moreover, BAS are predominnat in both samples, although having also a significant concentration 12


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of LAS. The LAS/BAS ratio is quite higher for the HBeta (24) sample than for HBeta (72) with values, at the lowest outgassing temperature, of 0.61 and 0.27, respectively. On the other hand, a decrease in the concentration of both BAS and LAS when the temperature rises from 150 °C up to 450 °C is observed for the two samples, being more pronounced in the case of HBeta (24). These findings denote the great differences between the acidity of both samples, not only in terms of acid site concentration, but also regarding the nature and strength of the acid sites. Thus, the HBeta (24) sample exhibits in overall a weaker acidity, as well as a higher proportion of LAS, than HBeta (72). HBeta (24)

HBeta (72)

0.30

Concentration (mmol/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.25

0.20

0.15

0.10

0.05

0.00 150°C

250°C

350°C

450°C

150°C

250°C

BAS

350°C

450°C

LAS

Figure 2. Evolution of Brønsted and Lewis acid sites concentrations with the pyridine evacuation temperature. Figure S4 illustrates the

27Al

MAS NMR spectra of the HBeta samples, two

peaks being observed at about 50 and 0 ppm originated by Al atoms in tetrahedral and octahedral coordinations, respectively. The occurrence of the latter denotes that both materials contain extra-framework Al species, with a proportion of 5.7% and 13.3% for HBeta (72) and HBeta (24), respectively. Likewise, the FWHM (Full Width Half Maximum) corresponding to the tetrahedral Al peak is higher for the HBeta (24) sample than in the case of HBeta (72), with values of this parameter of 7.99 and 7.51 ppm, respectively. These results evidence that the sample with the highest Al content present, in addition to a larger share of Al extra-framework species, a higher diversity of 13



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environments for the Al species in framework positions, which is in agreement with the weaker acidity and LAS concentration in this material as concluded from the pyridine/FTIR measurements.

3.2. EU/LDPE catalytic co-pyrolysis The feedstock employed in the catalytic co-pyrolysis tests consisted in a mixture of 60 wt% dried lignocellulosic biomass (EU) and 40 wt% of polyolefinic plastic (LDPE). Catalytic co-pyrolysis runs were conducted using a two-step reaction system by fixing 550 °C in the thermal pyrolysis zone and 500 °C in the catalytic one. Accordingly, the primary products generated in the thermal zone were, subsequently, passed through the catalyst bed for further upgrading. This configuration avoids the direct contact between the feed and the catalyst, attenuating its deactivation and making easier its recovery, and allows operating with independent temperatures for the thermal and catalytic zones. Different catalyst to feed (C/F) ratios were employed covering the range of 0.2 - 0.75 g g-1. The co-pyrolysis of the biomass/plastic feed produces the following fractions: char (carbonaceous residue accumulated in the thermal zone), coke (carbonaceous residue deposited over the catalyst), wax (waxy solid recovered at the exit of the reactor), condensed liquids and non-condensable gases. In most of the catalytic tests, the condensed liquid consists really of two fractions: organic-rich and water-rich phases. Accordingly, the so-called “oil*” fraction has been calculated in a water-free basis by considering together the organic components present in both liquid phases. Regarding the char fraction, its mass yield was very similar in all experiments (around 20 wt%), which is an expected result since this carbonaceous solid is produced in the non-catalytic reaction zone and, therefore, being independent of the presence of the catalyst.

i) Effect of the Al content in zeolite HBeta Previous characterization of the two HBeta samples has shown that, although they exhibit some differences in the textural properties, the major contrast is observed in 14


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terms of the Al content, which has also a direct effect on the proportion of Al extrafamework species and on the acidic features (concentration, type and strength of the acid sites). Accordingly, significant variations should be expected in the catalytic behavour of both samples for the copyrolyis of the EU-LDPE mixture. Figure 3 represents the results obtained in terms of mass yields of the different fractions, excluding the char, in the catalytic tests carried out with both HBeta samples varying the catalyst to feed ratio. In addition, the results corresponding to a pure thermal test, performed without any catalyst in the reactor, are included in the graph as reference. In this last test, the highest yield (43.5 wt%) corresponds to the wax fraction, which consists of long-chain hydrocarbons (> C18) formed mainly from the polyolefin contained in the feed according to a random craking mechanism that takes place at any point in the polymer chain.46 The next fraction in terms of mass yield is the organic liquid (oil*), followed by water and gases. The product distribution is sharply modified in the presence of the zeolite HBeta catalysts, as they cause a strong reduction of the wax yield, whereas the production of gases and coke is enhanced. Interestingly, increasing the C/F ratio causes the complete transformation of the wax fraction, whereas the oil* yield exhibits a maximum. Thus, compared to the thermal test, the oil* yield is significantly improved in the presence of the HBeta catalysts at low C/F ratios and tends to decrease when operating at high C/F values. These results denote the effectiveness of zeolite HBeta for catalyzing the conversion of the wax into liquid components, although the latter may undergo subsequently cracking reactions at high C/F ratios. Regarding the water production, no clear trend is observed at low and intermediate C/F ratios, showing that the zeolite HBeta catalysts are not particularly selective for promoting dehydration reactions of the biomass-derived components. Nevertheless, increased water production can be appreciated at high C/F ratios over the HBeta (72) sample.

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50 45 40

Mass Yield (wt%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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35 30 25 20 15 10 5 0 COKE

Non-catalytic

H2O H2O

WAX

OIL*

GAS

HBeta (24):

C/F=0.2

C/F=0.4

C/F=0.5

C/F=0.75

HBeta (72):

C/F=0.2

C/F=0.4

C/F=0.5

C/F=0.75

Figure 3. Mass yields of the fractions obtained in the EU/LDPE catalytic co-pyrolysis at different catalyst/feed (C/F) ratios.

Figure 4 illustrates the yields corresponding to the different compounds present in the gases. In the pure thermal test, the gaseous fraction is formed mainly by CO2 and CO, produced by decarboxylation and decarbonylation, respectively, of biomassderived fragments, whereas light paraffins and olefins are detected just in small concentrations. The incorporation of the HBeta zeolites as catalysts leads to great changes in the production of gases, increasing significantly the yields of CO, CO2, and in particular of light paraffins and olefins. Interestingly, the production of gaseous hydrocarbons at low C/F ratios is relatively small, being sharply increased for C/F = 0.5 and 0.75, i.e. it takes places once the wax fraction has been almost completely converted. Therefore, this finding denotes that gaseous hydrocarbons do not come directly from the wax fraction, but they are formed from the aliphatic hydrocarbons present in the oil* according to an end-chain scission mechanism.46,47 On the other hand, although being obtained with low yields, the production of hydrogen is significantly enhanced by HBeta zeolites, specially when working at high C/F ratios with the HBeta (24) catalyst. This result is an indication of the occurrence of dehydrogenation reactions under those conditions. 16


Mass yield (wt%)

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

(a)

0.10 0.09 0.08 0.07 0.06 0.05 0.04

H2 (wt%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Mass yield (wt%)

Page 17 of 34

0.03 0.02 0.01

(C1- C4)p

(C2- C4)o

CO

CO2

0.00

H2

(b)

CH4

C2 H4

C2 H6

C3 H6

C3 H8

C4H8 C4H10

Non-catalytic HBeta(24):

C/F=0.2

C/F=0.4

C/F=0.5

C/F=0.75

HBeta(72):

C/F=0.2

C/F=0.4

C/F=0.5

C/F=0.75

Figure 4. Mass yield of the gaseous components obtained in the EU/LDPE catalytic copyrolysis at different catalyst/feed (C/F) ratios: a) (C1-C4)p (paraffins), (C2-C4)o (olefins), CO, CO2 and H2; b) yield of individual gaseous hydrocarbons.

As shown in Figure S5, the CO2/CO ratio, which is directly linked to the relative extension of decarboxylation and decarbonylation reactions, tends to decrease with the C/F ratio in a similar way for both HBeta samples. This finding shows that increasing catalyst loadings favour the removal of oxygen through decarbonylation rather than by 17



Page 18 of 34

decarboxylation, probably because of the consumption at low C/F ratios of the functional groups leading to CO2. In qualitative terms, both HBeta samples behave similarly when varying the C/F ratio. Nevertheless, some relevant differences are observed between them when assessing the results in detail. Thus, wax conversion is faster over HBeta (24) in respect to HBeta (72). Moreover, for the HBeta (24) sample a higher value of the maximum oil* yield is obtained and it occurrs at a lower C/F ratio in comparison with HBeta (72). These results can be assigned to the higher concentration of acid sites, as well as to their milder strength, present in HBeta (24), which result in a larger cracking activity, but with limited severity, leading mainly to liquid hydrocarbons when working at low and intermediate C/F ratios. The overall gas yields are very similar for both zeolite samples (see Figure 3), with the exception of the tests performed with the highest C/F ratio, for which the HBeta (24) sample shows enhanced gas production, in particular of gaseous paraffins and H2, denoting that hydrogen transfer reactions take place extensively under those conditions over the catalyst having the highest Al content. Likewise, noticeable differences are observed between both HBeta samples regarding the evolution of specific gaseous hydrocarbons (Figure 4.b). While for HBeta (72) the yield of all gaseous hydrocarbons increase continuously with the catalyst loading, a maximum is observed in the case of ethylene and propylene at C/F = 0.5 when using HBeta (24). This finding evidences that these light olefins are nost just products of the cracking reactions but they are consumed and participate as reactants in several of the chemical transformations occurring in the system. Figure 5 summarizes the main reactions that take place during the EU-LDPE coprocesssing, starting from biomass pyrolysis and LDPE cracking. According to this scheme, both liquid aliphatic hydrocarbons and light olefins are intermediate compounds, which explains the maxima observed in their yields when varying the C/F ratio. In particular, due to their high reactivity, light olefins may participate in the following reactions: i) saturation by H-transfer; ii) conversion according to the sequence oligomerization / cyclization / aromatization (OCA pathway);46 and iii) formation of aromatic hydrocarbons through Diels-Alder condensation with furans (DAC pathway).28,29 Pathways i) and ii) have been proposed to occur in the conversion of polyolefinic plastics over zeolite catalysts,46 being not completely independent since the 18


Page 19 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


final aromatization step in ii) is expected to provide most of the hydrogen necessary for H-transfer reactions in i). Likewise, pathway iii) is of high interest in the system here investigated as it involves the reaction between compounds coming from the transformation of the two types of materials contained in the feed: light olefins from the polyolefin and furans from the lignocellulose. The presence of a high concentration of relatively mild acid sites in HBeta (24) explains its enhanced activity for the conversion of the light olefins at high C/F ratios, thus resulting in the observed maximum for ethylene and propylene over the former.

Figure 5. Main reaction pathways involving light olefins during the EU/LDPE catalytic copyrolysis over HBeta zeolite.

Some differences are also observed between both HBeta samples regarding coke deposition, mainly when working at low C/F ratios (Figure 3). Under those conditions, HBeta (24) undergoes the formation of larger amounts of coke, which can be assigned to its larger concentration of acid sites compared to HBeta (72), although this difference is progressively attenuated when increasing the C/F ratio. As shown in Table 1, in addition to carbon and hydrogen, the coke deposited over the two zeolitic catalysts possesses some oxygen and a small amount of nitrogen. Some modifications in the coke composition take place when varying the C/F ratio, with an increase in the carbon content and reduction of the oxygen proportion, whereas the hydrogen and nitrogen contents are less affected. These results can be directly related with the lower concentration of oxygenated organic compounds present in the reaction system as the 19



Page 20 of 34

catalyst loading is increased, which in turn is reflected in the composition of the coke deposited over the HBeta samples. Table 1. Amount and elemental composition of the coke deposited over the HBeta samples as a function of the catalyst/feed (C/F) ratio in the EU/LDPE catalytic co-pyrolysis. Coke C (g/g cat.) (wt%)

H (wt%)

N (wt%)

O (wt%)

79.7

10.1

0.5

9.1

0.19

80.6

10.4

0.4

8.6

0.40

0.24

82.2

9.6

1.2

7.0

HBeta (72)

0.40

0.18

84.5

9.5

1.0

5.0

HBeta (24)

0.50

0.20

84.4

9.6

1.0

5.0

HBeta (72)

0.50

0.17

87.1

9.4

1.1

2.3

HBeta (24)

0.75

0.14

86.9

9.5

1.4

2.3

HBeta (72)

0.75

0.14

87.7

9..1

1.2

2.0

Sample

C/F

HBeta (24)

0.20

0.35

HBeta (72)

0.20

HBeta (24)

ii) Assesment of the presence of synergistic effects during EU/LDPE catalytic copyrolysis In order to assess the occurrence of interactions between both components in the feed (EU and LDPE), the results obtained in the experiment with C/F=0.5 over the HBeta (24) catalyst were compared with those of two reference tests performed using pure EU and LDPE as raw materials, respectively. In these reference tests tha amounts of catalyst, biomass and plastic were adjusted to be equal to those employed in the experiment with the EU/LDPE mixture for C/F = 0.5. Figure 6 compares the results so obtained in the co-processing experiment with those feeding the pure raw materials. Regarding the char fraction, no solid was formed in the thermal zone when using pure LDPE, whereas the relative amount produced with pure EU was very similar to that produced in the co-processing tests. This finding confirms that the solid fraction deposited in the thermal zone of the reaction system proceeds from the biomass and indicates that no clear synergistic effect in terms of char formation occurs during the thermal degradation of the feed. However, this is not the case when comparing the results obtained once the thermal cracking vapours pass through the catalyst bed, as illustrated in Figure 6. 20


(a)

45

Mass Yield (wt%)

40 35 30 25 20 15 10 5 0 COKE

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

WAX

H2O

OIL*

GAS

20 18

(b)

16 14 12 10 8 6 4 2 0

0.20

(c)

0.18 0.16 0.14 0.12 0.10 0.08

H2 (wt%)

50

Mass yield (wt%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Bio-oil* oxygen concentration (wt%)

Page 21 of 34

0.06 0.04 0.02 0.00

(C1- C4)p

(C2- C4)o HBeta (24) - C/F=0.5

CO

CO2 LDPE

H2 EU

Figure 6. Comparison of the results obtained in the co-processing of EU/LDPE and the pyrolysis of pure EU and LDPE over HBeta (24): a) mass yield of the fractions, b) mass yield of the gaseous components.

In terms of fractions distribution (Figure 6.a), the most relevant differences are associated to the production of oil* and gases. The co-processing of the EU-LDPE mixture leads to a great enhancement of the oil* yield, from 18.8 to 30.8 wt%, at the expense mainly of a strong reduction of the gaseous fraction (from 36.8 to 24.6 wt%). Interestingly, this improvement of the organic liquid fraction yield is accompanied by a remarkable reduction of its oxygen content compared to the conversion of the pure raw materials, from 17.1 to 10.0 wt% in terms of oxygen concentration, showing that coprocessing of the EU/LDPE mixture is also very positive for upgrading the oil* fraction (Figure 6.b). As shown in Figure 6.c, the reduction of the gas yield in the co-pyrolysis test is mainly due to a quite lower production of both gaseous hydrocarbons, specially of gaseous paraffins. In particular (see Figure S6), the yields of propane, butenes and 21



Page 22 of 34

butanes are quite lower when using the EU/LDPE feed regarding to the tests carried out with the pure raw materials. Note that those gaseous hydrocarbons are formed mainly from the plastic, being able to react and form heavier components when the biomass is also present in the feed. On the other hand, the hydrogen content in the gases decreases significantly for the co-pyrolysis test, hindering the saturation of olefins into paraffins, so the former are really more available for producing aromatic hydrocarbons either directly by the OCA pathway or through Diels-Alder condensation (DCA pathway) with furans coming from EU pyrolysis. On the other hand, whereas no wax is detected in any of the products of these experiments, a slight decrease takes place in the case of the coke deposited over the catalyst in the pyrolysis of the EU/LDPE mixture, which can be considered other positive effect derived from the co-processing of lignocelllose and polyethylene. Some interesting variations can be also observed in the final products of the deoxygenation reactions. Thus, the CO yield decreases whereas the water and CO2 productions are enhanced in the copyrolysis test. This fact denotes that EU/LDPE coprocessing favours the most efficient deoxygenation pathways (decarboxylation and dehydration) at the expense of decarbonylation and explain the lower oxygen content present in the oil* obtained from the EU/LDPE mixture compared to the overall composition of the organic fractions coming from the pyrolysis of the pure raw materials. In summary, these results prove clearly the existence of a strong synergistic effect in the catalytic co-pyrolysis of EU and LDPE over zeolite HBeta, which occurs mainly through the reaction between gaseous olefins from LDPE and EU-derived furans according to Diels-Alder reactions. This effect results in the production of an oil* fraction with higher yield and lower oxygen content in respect to the pyrolysis of pure EU and LDPE. iii) Effect of the catalyst to feed ratio on the oil* yield and composition Important changes occur in the elemental composition of the oil* fraction when increasing the C/F ratio, as illustrated in Figure 7. This graph represents the evolution of the oil* composition in terms of the so called “effective H/C ratio”,48 defined as (H2O)/C, versus the O/C ratio. When increasing the catalyst loading, the oil* fraction 22


Page 23 of 34

contains progressively less oxygen and more hydrogen, with a decrease of the O/C ratio and an enhancement of the effective H/C ratio, approaching the values typical of fossilderived fuels. Most of the points are aligned on the same trend, showing that both HBeta catalysts provoke very similar variations in the oil* elemental composition. Just when working at the highest catalyst loading, the oil* produced over HBeta (72) possesses a value of the Heff/C ratio clearly below the overall trend, which can be assigned to its high concentration of aromatic hydrocarbons, as explained later when commenting the GC-MS analyses. 1.75 HBeta (24) 1.50

Heff / C (mol/mol)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1.25

HBeta (72)

1.00

0.75 Non-catalytic 0.50 0.0

0.1

0.2

0.3

0.4

0.5

O / C (mol/mol) Figure 7. Van-Krevelen diagram obtained in the EU/LDPE catalytic copyrolysis at different catalyst/feed (C/F) ratios over the HBeta samples.

On the other hand, it must be taken into account that the upgrading process of the oil* fraction is accompanied by significant changes in its yield. In this way, the relationship between the oxygen content of this fraction and its mass and chemical energy yield (referered to the EU/LDPE feed) is shown in Figure 8. For both catalysts a maximum in the oil* yield is also observed in this figure. This means that increasing the C/F ratio has initially a remarkable positive effect on the oil* fraction since it provokes a decrease of its oxygen content and an enhancement of its mass and energy yield. However, once this maximum is passed, the increase of the C/F ratio leads to a sharp reduction in the oil* yield, whereas the deoxygenation process is attenuated. Accordingly, both the HBeta catalyst and the C/F ratio must be selected carefully in order not to overpass this maximum in the oil* yield. As above commented, the highest oil* yield for the optimum C/F ratio corresponds with HBeta (24), which can be 23



assigned to its higher concentration of mild acid sites that promote wax cracking reactions into liquid hydrocarbons. Anyway, it must be pointed out that both HBeta samples are able to produce oil* fractions with high deoygenation levels, reaching values of the oxygen content even below 10 wt%, while keeping relatively high mass and energy yields. 45

(a)

OIL* Mass Yield (wt%)

40 35

HBeta (24)

30

HBeta (72)

25 20 Non-catalytic

15 10 5

6

8 10 12 14 16 18 20 22 24 26 28 30 32 34 36

OIL* Oxygen concetration (wt%)

55

(b)

50

OIL* Energy Yield (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 34

45

HBeta (24)

40

HBeta (72)

35 30 25 20 15 10

Non-catalytic 6

8 10 12 14 16 18 20 22 24 26 28 30 32 34 36

OIL* Oxygen concetration (wt%) Figure 8. Oxygen concentation versus oil* mass (a) and energy (b) yields obtained at different catalyst/feed (C/F) ratios in the EU/LDPE catalytic co-pyrolysis over both HBeta samples.

Figure 9 illustrates how the chemical energy initially contained in the raw feed is distributed among the different fractions, comparing the results obtained with the two HBeta samples for C/F = 0.4 with those of the thermal test. For the three experiments, 24


Page 25 of 34

the energy yield of the char was very similar, being about 20%, as this fraction is formed in the thermal zone of the reactor. In the thermal test, the wax accounts for the highest energy yield, followed by far by the oil* fraction and with an almost negligible contribution of the gases. This picture changes drastically in the catalytic tests, the oil* fraction becoming the most important in terms of chemical energy yield due to the conversion of the wax into liquid hydrocarbons. Nevertheless, it must be taken into account that in the catalytic tests a small, but noticeable, part of the chemical energy is contained in both the gaseous stream and the coke deposited over the catalyst. Comparing both HBeta samples, the best performance of HBeta (24) is evidenced from this graph, showing a chemical energy yield of the oil* fraction that represents about 48% of that in the raw biomass/plastic feed. COKE

GAS

OIL*

WAX

CHAR

100 90

Energy Yield (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


80 70 60 50 40 30 20 10 0

Non-catalytic

HBeta (24)

HBeta (72)

Figure 9. Distribution of the chemical energy yield among the different fractions obtained in the EU/LDPE catalytic co-pyrolysis over both HBeta samples (C/F = 0.4).

The main types of components present in the oil* fraction have been determined by GC-MS, the results being illustrated in Figure 10 grouped by families: carboxylic acids (AC), light oxygenates (LO), furans (FUR), sugars (SUG), oxygenated aromatics (O-AR), and aromatic (AR) and aliphatic hydrocarbons (ALIPH). It must be noted that these results should be interpreted in semi-quantative terms because the graph is expressed as GC-MS area%, whereas it is known that a part of the components in the oil*, mainly oligomers from the lignocellulose conversion, cannot be detected by this technique. 25



Page 26 of 34

A wide product distribution was obtained in the case of the thermal experiment, with significant amounts of the different families of oxygenated compounds being present, whereas almost no hydrocarbons were detected in the thermal oil*. A sharp change in the composition of the organic liquid fraction occurs when incorporating the HBeta samples at the reaction system. In this case, aromatic and aliphatic hydrocarbons were the main components, whereas several of the other families are absent, showing the high catalytic activity of the HBeta zeolite for the conversion of oxygenated compounds. In particular, AC, FUR and SUG were almost completely transformed by the HBeta catalysts. Increase of the C/F ratio led to a higher concentration of aromatic hydrocarbons, at expense of the aliphatic ones, which is an expected result since the former are final products of the oligomerization/cyclization/aromatization and DielsAlder condensation pathways. Interestingly, some differences can be appreciated in the product distribution of both catalyst samples, mainly in respect to the relative proportion of aromatic and aliphatic hydrocarbons. Thus, HBeta (72) is more selective for the production of aromatics, whereas the oil* obtained over HBeta (24) contains more aliphatic hydrocarbons. These results can be assigned to the differences existing between the acid site concentration and the acid strength of both samples. Thus, the stronger acidity of HBeta (72) is responsible of its higher activity through the Diels-Alder condensation pathway, leading to oil* fractions with lower oxygen content and higher concentration of aromatic hydrocarbons.

26


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


COMPOUNDS FAMILIES (% Relative Area)

Page 27 of 34

80 70 60 50 40 30 20 10 0 AC

LO

F UR

SUG

Non-catalytic Beta (24): Beta (72):

O -AR

AR

C/F = 0.4 C/F = 0.4

ALIP

H

UNK

C/F = 0.5 C/F = 0.5

Figure 10. Components, grouped by families, present in the oil* fraction (from GC-MS analysis) obtained in the EU/LDPE catalytic co-pyrolysis over both HBeta samples (C/F = 0.4 and 0.5). As reference, the composition of the thermal oil* is also included.

5. Conclusions Zeolite HBeta materials, possessing different Si/Al ratios and nanocrystalline features (HBeta (24) and HBeta (72)), have been found to be efficient catalysts for the catalytic co-pyrolysis of lignocellulose (eucalyptus, EU) and polyolefin (low-density polyethylene, LDPE) mixtures into a hydrocarbon-rich liquid fraction (oil*). Variation of the HBeta acid site concentration, as well as of the catalyst/feed (C/F) ratio, has allowed the yield of the oil* fraction to be maximized, while decreasing its oxygen content and, hence, approaching the elemental compostion of fossil-derived fuels. Characterization of the HBeta samples has shown that they possess convenient properties (mild acidity and high mesopore/external surface area) for the processing of bulky compounds, as it is the case of those derived from the thermal conversion of lignocellulose and polyolefins. The following fractions have been obtained by the co-pyroysis of the EU/LDPE mixture: char (formed in the thermal section of the reactor), coke (deposited over the catalyst), wax, oil*, water and gases. While the char yield was similar in all experiments 27



Page 28 of 34

(including a pure thermal test), the coke yield increased with the catalyst loading. In the thermal test, the wax fraction represented the major product, but it was rapidly converted into liquid hydrocarbons within the oil* fraction in the presence of the HBeta catalysts. The oil* yield exhibited a maximum regarding the C/F ratio, while its oxygen concentration was progressively decreased. Accordingly, by adjusting the value of the catalyst loading, it was possible to increase both the amount and the quality of the produced oil* in comparison with the reference thermal test. Comparing both zeolite samples, the material with lower Si/Al ratio (HBeta (24)) led to a higher value of the oil* maximum yield. This finding has been assigned to its higher concentration of acid sites with moderate strength, that promote the formation of liquid hydrocarbons while attenuating the severity of the cracking process. Interestingly, important differences can be appreciated in the oil* composition as a function of the Al content and, therefore, of the zeolite sample acidity, mainly in respect to the relative proportion of aromatic and aliphatic hydrocarbons. Thus, the stronger acidity of HBeta (72) is responsible of its higher activity through the Diels-Alder condensation pathway, leading to oil* fractions with lower oxygen content and higher concentration of aromatic hydrocarbons. In order to assess the occurrence of interactions between both components in the feed (EU and LDPE), two reference tests were performed using pure EU and LDPE as raw materials, respectively. Based on these results, it was proved clearly the existence of a strong synergistic effect in the catalytic co-pyrolysis of EU and LDPE over zeolite HBeta, which results in the production of an oil* fraction with higher yield and lower oxygen content in respect to the pyrolysis of pure EU and LDPE.

Supporting Information Figure S1. TEM images of the HBeta samples. Figure S2. NH3-TPD analyses of the zeolite samples. Figure S3. FTIR spectra of pyridine desorption from the zeolite samples at different evacuation temperatures. Figure S4. 27Al-MAS NMR spectra of the HBeta samples. 28


Page 29 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure S5. Evolution of the CO2/CO molar ratio as a function of the catalyst/feed ratio. Figure S6. Comparison of the gaseous hydrocarbons yield obtained in the coprocessing of EU/LDPE and the pyrolysis of pure EU and LDPE.

Acknowledgements The authors gratefully acknowledge the financial support from the Spanish Ministry of Economy and Competitiveness through CATPLASBIO project (Ref: CTQ2014‐602209‐R) and from CAPES (PDSE – Programa de Doutorado Sanduíche no Exterior, Brazil, Process number 88881.132233/2016-01).

References (1)

Easterly, J. L.; Burnham, M. Overview of Biomass and Waste Fuel for Power Production. Biomass and Bioenergy 1996, 10 (2–3), 79–92.

(2)

Bildirici, M. E. Economic Growth and Biomass Energy. Biomass and Bioenergy 2013, 50, 19–24.

(3)

Ahtikoski, A.; Heikkilä, J.; Alenius, V.; Siren, M. Economic Viability of Utilizing Biomass Energy from Young Stands-The Case of Finland. Biomass and Bioenergy 2008, 32 (11), 988–996.

(4)

Bulushev, D. A.; Ross, J. R. H. Catalysis for Conversion of Biomass to Fuels via Pyrolysis and Gasification: A Review. Catal. Today 2011, 171 (1), 1–13.

(5)

Bridgwater, A. V. Review of Fast Pyrolysis of Biomass and Product Upgrading. Biomass and Bioenergy 2012, 38, 68–94.

(6)

Bridgwater, A. V. Biomass for Energy. Sci. Food Agric. 2006, 86 (12), 1755– 1768.

(7)

Guillain, M.; Fairouz, K.; Mar, S. R.; Monique, F.; Jacques, L. Attrition-Free Pyrolysis to Produce Bio-Oil and Char. Bioresour. Technol. 2009, 100 (23), 6069–6075. 29



(8)

Page 30 of 34

Vitolo, S.; Seggiani, M.; Frediani, P.; Ambrosini, G.; Politi, L. Catalytic Upgrading of Pyrolytic Oils to Fuel over Different Zeolites. Fuel 1999, 78 (10), 1147–1159.

(9)

Bridgwater, A. V.; Meier, D.; Radlein, D. An Overview of Fast Pyrolysis of Biomass. Org. Geochem. 1999, 30 (12), 1479–1493.

(10)

Diebold, J. P. A Review of the Chemical and Physical Mechanisms of the Storage Stability of Fast Pyrolysis Bio-Oils; NREL (National Renewable Energy Laboratory): Golden, Colorado, 1999.

(11)

Hernando, H.; Jiménez-Sánchez, S.; Fermoso, J.; Pizarro, P.; Coronado, J. M.; Serrano, D. P. Assessing Biomass Catalytic Pyrolysis in Terms of Deoxygenation Pathways and Energy Yields for the Efficient Production of Advanced Biofuels. Catal. Sci. Technol. 2016, 6, 2829–2843.

(12)

Taarning, E.; Osmundsen, C. M.; Yang, X.; Voss, B.; Andersen, S. I.; Christensen, C. H. Zeolite-Catalyzed Biomass Conversion to Fuels and Chemicals. Energy Environ. Sci. 2011, 4 (3), 793–804.

(13)

Zhang, B.; Zhong, Z.; Chen, P.; Ruan, R. Microwave-Assisted Catalytic Fast Pyrolysis of Biomass for Bio-Oil Production Using Chemical Vapor Deposition Modified HZSM-5 Catalyst. Bioresour. Technol. 2015, 197, 79–84.

(14)

Zhang, X.; Sun, L.; Chen, L.; Xie, X.; Zhao, B.; Si, H.; Meng, G. Comparison of Catalytic Upgrading of Biomass Fast Pyrolysis Vapors over CaO and Fe(III)/CaO Catalysts. J. Anal. Appl. Pyrolysis 2014, 108, 35–40.

(15)

Wang, K.; Zhang, J.; Shanks, B. H.; Brown, R. C. The Deleterious Effect of Inorganic Salts

on Hydrocarbon Yields from Catalytic Pyrolysis of

Lignocellulosic Biomass and Its Mitigation. Appl. Energy 2015, 148, 115–120. (16)

Yildiz, G.; Ronsse, F.; Venderbosch, R.; Duren, R. Van; Kersten, S. R. A.; Prins, W. Effect of Biomass Ash in Catalytic Fast Pyrolysis of Pine Wood. Appl. Catal. B Environ. 2015, 168, 203–211.

(17)

Abnisa, F.; Wan Daud, W. M. A. A Review on Co-Pyrolysis of Biomass: An Optional Technique to Obtain a High-Grade Pyrolysis Oil. Energy Convers. Manag. 2014, 87, 71–85.

(18)

Mukarakate, C.; Zhang, X.; Stanton, A. R.; Robichaud, D. J.; Ciesielski, P. N.; Malhotra, K.; Donohoe, B. S.; Gjersing, E.; Evans, R. J.; Heroux, D. S.; et al. Real-Time Monitoring of the Deactivation of HZSM-5 during Upgrading of Pine 30


Page 31 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Pyrolysis Vapors. Green Chem. 2014, 16 (3), 1444–1461. (19)

Fermoso, J.; Hernando, H.; Jana, P.; Moreno, I.; Přech, J.; Ochoa-Hernández, C.; Pizarro, P.; Coronado, J. M.; Čejka, J.; Serrano, D. P. Lamellar and Pillared ZSM-5 Zeolites Modified with MgO and ZnO for Catalytic Fast-Pyrolysis of Eucalyptus Woodchips. Catal. Today 2016, 277, 171–181.

(20)

Mihalcik, D. J.; Mullen, C. A.; Boateng, A. A. Screening Acidic Zeolites for Catalytic Fast Pyrolysis of Biomass and Its Components. J. Anal. Appl. Pyrolysis 2011, 92 (1), 224–232.

(21)

Rochman, C. M.; Browne, M. A.; Halpern, B. S.; Hentschel, B. T.; Hoh, E.; Karapanagioti, H. K.; Rios-Mendoza, L. M.; Takada, H.; Teh, S.; Thompson, R. C. Classify Plastic Waste as Hazardous. Nature 2013, 494, 169–171.

(22)

Aguado, J.; Serrano, D. P. Feedstock Recycling of Plastic Wastes; Clark, J. H., Ed.; RSC Clean Technology Monographs (The Royal Society of Chemistry), 1999.

(23)

Lu, P.; Huang, Q.; (Thanos) Bourtsalas, A. C.; Chi, Y.; Yan, J. Synergistic Effects on Char and Oil Produced by the Co-Pyrolysis of Pine Wood, Polyethylene and Polyvinyl Chloride. Fuel 2018, 230 (January), 359–367.

(24)

Alvarez, J.; Kumagai, S.; Wu, C.; Yoshioka, T.; Bilbao, J.; Olazar, M.; Williams, P. T. Hydrogen Production from Biomass and Plastic Mixtures by PyrolysisGasification. Int. J. Hydrogen Energy 2014, 39 (21), 10883–10891.

(25)

Panda, A. K.; Singh, R. K.; Mishra, D. K. Thermolysis of Waste Plastics to Liquid Fuel. A Suitable Method for Plastic Waste Management and Manufacture of Value Added Products-A World Prospective. Renew. Sustain. Energy Rev. 2010, 14 (1), 233–248.

(26)

Hassan, H.; Lim, J. K.; Hameed, B. H. Recent Progress on Biomass Co-Pyrolysis Conversion into High-Quality Bio-Oil. Bioresour. Technol. 2016, 221, 645–655.

(27)

Lin, X.; Zhang, Z.; Sun, J.; Guo, W.; Wang, Q. Effects of Phosphorus-Modified HZSM-5 on Distribution of Hydrocarbon Compounds from Wood-Plastic Composite Pyrolysis Using Py-GC/MS. J. Anal. Appl. Pyrolysis 2015, 116, 223– 230.

(28)

Zhang, X.; Lei, H.; Zhu, L.; Zhu, X.; Qian, M.; Yadavalli, G.; Yan, D.; Wu, J.; Chen, S. Optimizing Carbon Efficiency of Jet Fuel Range Alkanes from Cellulose Co-Fed with Polyethylene via Catalytically Combined Processes. 31



Page 32 of 34

Bioresour. Technol. 2016, 214 (April), 45–54. (29)

Settle, A. E.; Berstis, L.; Rorrer, N. A.; Roman-Leshkóv, Y.; Beckham, G. T.; Richards, R. M.; Vardon, D. R. Heterogeneous Diels-Alder Catalysis for Biomass-Derived Aromatic Compounds. Green Chem. 2017, 19 (15), 3468– 3492.

(30)

Zhang, X.; Lei, H.; Chen, S.; Wu, J. Catalytic Co-Pyrolysis of Lignocellulosic Biomass with Polymers: A Critical Review. Green Chem. 2016, 18 (15), 4145– 4169.

(31)

Kim, B. S.; Kim, Y. M.; Lee, H. W.; Jae, J.; Kim, D. H.; Jung, S. C.; Watanabe, C.; Park, Y. K. Catalytic Copyrolysis of Cellulose and Thermoplastics over HZSM-5 and HY. ACS Sustain. Chem. Eng. 2016, 4 (3), 1354–1363.

(32)

García-Muñoz, R. A.; Serrano, D. P.; Vicente, G.; Linares, M.; Vitvarova, D.; Čejka, J. Remarkable Catalytic Properties of Hierarchical Zeolite-Beta in Epoxide Rearrangement Reactions. Catal. Today 2015, 243 (C), 141–152.

(33)

Higgins, B.; LaPierre, R. B.; Schlenker, J. L.; Rohrman, A. C.; Wood, J. D.; Kerr, G. T.; Rohrbaughv, W. J. The Framework of Zeolite Beta. Zeolites 1988, 8, 446– 452.

(34)

Bellussi, G.; Perego, C. New Catalysts and New Processes in the Industrial Alkylation of Aromatics. Catal. Today 2002, 73, 3–22.

(35)

Hernando, H.; Moreno, I.; Fermoso, J.; Ochoa-Hernández, C.; Pizarro, P.; Coronado, J. M.; Serrano, D. P. Biomass Catalytic Fast Pyrolysis over Hierarchical ZSM-5 and Beta Zeolites Modified with Mg and Zn Oxides. Bioresour. Technol. 2017, 7 (3), 289–304.

(36)

Caldeira, V. P. S.; Peral, A.; Linares, M.; Araujo, A. S.; Garcia-Muñoz, R. A.; Serrano, D. P. Properties of Hierarchical Beta Zeolites Prepared from Protozeolitic Nanounits for the Catalytic Cracking of High Density Polyethylene. Appl. Catal. A Gen. 2017, 531, 187–196.

(37)

Bi, Y.; Lei, X.; Xu, G.; Chen, H.; Hu, J. Catalytic Fast Pyrolysis of Kraft Lignin over Hierarchical HZSM-5 and Hβ Zeolites. Catalysts 2018, 8 (2), 82.

(38)

Kim, Y.-M.; Park, R.; Lee, E.-H.; Jeon, J.-K.; Kim, S. C.; Jung, S.-C.; Kim, S.; Park, Y.-K. In-Situ Catalytic Pyrolysis of Dealkaline Lignin Over MMZ-Hβ. J. Nanosci. Nanotechnol. 2017, 17 (4), 2760–2763.

(39)

Mukarakate, C.; Watson, M. J.; Ten Dam, J.; Baucherel, X.; Budhi, S.; Yung, M. 32


Page 33 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


M.; Ben, H.; Iisa, K.; Baldwin, R. M.; Nimlos, M. R. Upgrading Biomass Pyrolysis Vapors over β-Zeolites: Role of Silica-to-Alumina Ratio. Green Chem. 2014, 16 (12), 4891–4905. (40)

Lee, H. W.; Kim, Y. M.; Jae, J.; Jeon, J. K.; Jung, S. C.; Kim, S. C.; Park, Y. K. Production of Aromatic Hydrocarbons via Catalytic Co-Pyrolysis of Torrefied Cellulose and Polypropylene. Energy Convers. Manag. 2016, 129, 81–88.

(41)

Channiwala, S. A.; Parikh, P. P. A Unified Correlation for Estimating HHV of Solid , Liquid and Gaseous Fuels. Fuel 2002, 81, 1051–1063.

(42)

Hernando, H.; Fermoso, J.; Ochoa-Hernández, C.; Opanasenko, M.; Pizarro, P.; Coronado, J. M.; Čejka, J.; Serrano, D. P. Performance of MCM-22 Zeolite for the Catalytic Fast-Pyrolysis of Acid-Washed Wheat Straw. Catal. Today 2018, 304, 30–38.

(43)

Wang, H.; Xin, W. Surface Acidity of H-Beta and Its Catalytic Activity for Alkylation of Benzene with Propylene. Catal. Letters 2001, 76 (3–4), 225–229.

(44)

Maache, M.; Janin, A.; Lavalley, J. C.; Joly, J. F.; Benazzi, E. Acidity of Zeolites Beta Dealuminated by Acid Leaching: An FT.i.r. Study Using Different Probe Molecules (Piridine, Carbon Monoxide). Zeolites 1993, 13, 419–426.

(45)

Linares, M.; Vargas, C.; García, A.; Ochoa-Hernández, C.; Čejka, J.; GarcíaMuñoz, R. A.; Serrano, D. P. Effect of Hierarchical Porosity in Beta Zeolites on the Beckmann Rearrangement of Oximes. Catal. Sci. Technol. 2017, 7 (1), 181– 190.

(46)

Serrano, D. P.; Aguado, J.; Escola, J. M. Developing Advanced Catalysts for the Conversion of Polyole Fi Nic Waste Plastics into Fuels and Chemicals. ACS Catal. 2012, 2, 1924–1941.

(47)

Aguado, J.; Serrano, D. P.; Escola, J. M.; Peral, A. Catalytic Cracking of Polyethylene over Zeolite Mordenite with Enhanced Textural Properties. J. Anal. Appl. Pyrolysis 2009, 85 (1–2), 352–358.

(48)

Chen, N. Y.; Degnan Jr., T. F.; Koenig, L. R. LIQUID FUEL FROM CARBOHYDRATES. Chem. Tech. 1986, 16 (8), 506–511.

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Graphical Abstract

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Catalytic co-pyrolysis of lignocellulose and polyethylene blends over

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