Aromatic Hydrocarbon Production from Bio-Oil by a Dual-Stage

Subscriber access provided by HKU Libraries

Article

Aromatic hydrocarbon production from bio-oil by a dual-stage hydrogenation-cocracking process: furfural as a model compound Qinjie Cai, Jia Xu, Suping Zhang, and Shurong Wang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b02713 • Publication Date (Web): 28 Sep 2016 Downloaded from http://pubs.acs.org on October 2, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 37

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

Industrial & Engineering Chemistry Research

Aromatic hydrocarbon production from bio-oil by a dual-stage hydrogenation-cocracking process: furfural as a model compound Qinjie Caia,b, Jia Xub, Suping Zhanga,b, Shurong Wang*,b,c a

Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, East China University of Science and Technology, Shanghai 200237, China b

School of Resources and Environmental Engineering, East China University of Science and Technology, Shanghai 200237, China

c

State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China

Abstract: Bio-oil upgrading by catalytic cracking faces problems of low aromatic hydrocarbon yield and

coking

due

to

its

hydrogen-lacking

property.

In

this

work,

an

improved

hydrogenation-cocracking process was developed to achieve the appropriate hydrogen supply in two stages. Furfural was selected as the model compound of bio-oil and methanol was the coreactant. Hydrogen supply in the hydrogenation stage was successfully regulated by hydrogenation catalysts, and 5Ni-5Cu/SiO2 catalyst showed the best performance because of suitable hydrogenation degree of furfural over it, which favored the formation of aromatic hydrocarbons during cracking. With the optimum 5Ni-5Cu/SiO2 catalyst, hydrogenation-cocracking was compared with single-stage cocracking, hydrogenation-cracking and direct cracking processes. The results confirmed that hydrogen supplements by hydrogenation pretreatment and methanol-cocracking were both significant for generation of aromatic hydrocarbons and suppression of coke. Based on a proposed reaction mechanism, the corresponding hydrogen supply behaviors were revealed.

1

ACS Paragon Plus Environment


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 Introduction In view of depletion of traditional fossil fuels and pollution caused by their combustion, the development of renewable biobased liquid fuel has drawn the global attention. Bio-oil produced from biomass pyrolysis is considered to be a potential alternative of traditional fossil fuels. However, crude bio-oil has inferior properties such as high oxygen content, low heating value and strong acidity 1. Therefore, its upgrading is necessary 2. Bio-oil can be transformed into aromatic hydrocarbons by catalytic cracking over zeolite catalyst 2, while low deoxygenation efficiency, low aromatic hydrocarbon yield and high coke yield are the main problems 3. The serious hydrogen-lacking property of oxygenated bio-oil is the key reason for these problems, because it results in the cracking products with low H/C ratios, which enhances the formation of coke 4, and it also weakened the intensity of dehydration reaction, which happens more easily than decarbonylation and decarboxylation during cracking 5, leading to the decrease of deoxygenation efficiency. In terms of this hydrogen-lacking property, an appropriate hydrogen supply, which can regulate the H/C ratios of final products and enhance oxygen removal in the form of H2O, is important for the improvement of cracking process. Recently, researchers have developed two ways to supply hydrogen for bio-oil cracking, namely mild hydrogenation pretreatment and cocracking with hydrogen-rich chemicals. Mild hydrogenation pretreatment can realize hydrogen supplement to bio-oil components before cracking. It involves several reactions including saturation of double bonds and even further hydrocracking and hydrodeoxygenation. Under different hydrogenation conditions, the intensities of these reactions will show great difference, which correspond to different hydrogen supply behaviors, and this may affect the subsequent cracking process. For example, saturation of double bonds is 2


Page 2 of 37

Page 3 of 37

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


beneficial for cracking because oxygenated compounds with higher saturation degree have better cracking performance 4, while excess hydrocracking and hydrodeoxygenation which generate saturated gaseous hydrocarbons will decrease the available feedstock for cracking 3. Vispute et al. carried out hydrogenation pretreatment of bio-oil to implement saturation of some unsaturated components and successfully lowered coke selectivity in the subsequent cracking process from 32.3% to 12.6% 3. However, due to the complexity of bio-oil 6, it is difficult to saturate all unsaturated chemical bonds through a single-stage mild hydrogenation, and so that a certain yield of coke is still generated in the following cracking process, indicating the necessity of a secondary hydrogen supplement in the cracking stage. In addition, this hydrogen supply behavior is also strongly related to the hydrogenation catalyst. Sitthisa et al. found that in furfural hydrogenation Cu facilitated the saturation of aldehyde group while Ni could catalyze the saturation of furan ring and further hydrodeoxyegantion 7. Therefore, regulation of hydrogen supply by hydrogenation catalysts will help obtain the most suitable hydrogenated bio-oil for the subsequent cracking. Introduction of hydrogen-rich chemicals as coreactants is another way to supply hydrogen, and alcohols like methanol and ethanol and fluid catalytic cracking (FCC) feedstock like gasoil are often chosen as the cocracking reactants 8, 9. During cocracking the conversion of hydrogen-rich chemicals will generate some surplus hydrogen, which can be supplied to bio-oil components through hydrogen transfer reactions and then participated in their cracking

10

. Graça et al. performed

cocracking of a bio-oil model compound mixture with gasoil, and they found that the presence of gasoil could promote the conversion of bio-oil model compounds to gasoline-range products

11

.

Cocracking study of bio-oil and alcohols by Wang et al. also showed that the existence of alcohols could significantly increase the integral deoxygenation efficiency and the liquid hydrocarbon yield 8, 3



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

12

. However, because of the high unsaturation degree of bio-oil, sufficient hydrogen supply requires

a large amount of coreactant if there is no other hydrogen supplement, which will decrease the economy of this technology. The above discussion indicates the limitations of hydrogenation pretreatment and cocracking with hydrogen-rich chemicals when they are individually used. Therefore, in this work these two improving ways were combined as a dual-stage hydrogenation-cocracking process (methanol as the coreactant) to achieve a better hydrogen supplement. Furfural was selected as the model compound of bio-oil, because it is a typical bio-oil component and also its functional groups (aldehyde group and furan ring) contains C=O, C=C and C-O-C bonds which are representative for the unsaturated oxygen-containing characteristic of bio-oil 13. In view of this highly unsaturated oxygen-containing property, for furfural conversion through the dual-stage hydrogenation-cocracking process, it is supposed that hydrogen supply in the hydrogenation stage can saturate the double bonds in furfural to obtain compounds with higher saturation degrees and thus better cracking performances, and considering that complete saturation may not be achieved, secondary hydrogen supply from methanol in cocracking stage is supposed to promote the conversion of residual unsaturated compounds and thus ensure a high integral conversion efficiency. However, besides saturation of double bonds, hydrocracking and hydrodeoxygenation may also happen in the hydrogenation stage, and therefore controlling the intensities of different hydrogenation reactions to obtain a better feedstock for subsequent cracking is significant. Moreover, the supposed functions of hydrogen supply by hydrogenation pretreatment and methanol-cocracking should be verified and their necessities should be identified. To address these issues, regulation of hydrogen supply by hydrogenation catalysts was first studied to achieve an appropriate hydrogen supply in the 4


Page 4 of 37

Page 5 of 37

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


hydrogenation stage. Afterwards, functions of hydrogenation pretreatment and methanol-cocracking in the integral process were studied by comparison of different cracking processes. 2 Experimental section 2.1 Catalyst preparation The studied hydrogenation catalysts were 5%Ni-5%Cu/SiO2, 10%Ni/SiO2 and 10%Cu/SiO2, prepared by incipient impregnation. The preparation method is as follows: a requisite amount of metal nitrate precursor was added into deionized water to obtain metal nitrate solution; then SiO2 particles were impregnated in the solution; after stabilization for 12 h, the mixture was dried in an oven at 110 °C overnight; finally the mixture was calcined in static air at 550 °C for 2 h. The catalyst used in cracking stage was HZSM-5 (Si/Al=25) purchased from The Catalyst Plant of Nankai University, and it was pretreated in static air at 550 °C for 2 h before reaction. 2.2 Catalyst characterization Metal contents in hydrogenation catalysts were determined by inductively coupled plasma optical emission spectrometer (ICP-OES) using an Agilent 725ES instrument. Powder X-ray diffraction (XRD) patterns of reduced catalysts were recorded on a RINT2000 vertical goniometer with Cu Kα radiation, operating at 40 kV and 100 mA. The average crystallite sizes of metals were calculated based on Scherrer equation, and corresponding dispersions were estimated according to Eq. (1)

14

and Eq. (2)

15, 16

, in which “D” represents dispersion and “d”

represents metal average crystallite size. DNi (or Ni-Cu) = 1/d

(1)

DCu = 1.1/d

(2)

5



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

2.3 Catalytic reaction Catalytic experiments were performed in a fixed-bed reaction system as shown in Fig. 1. This reaction system included two tubular reactors. For the hydrogenation experiments, only one reactor (Reactor-1) was used, and gaseous and liquid products were directly collected after this reactor. When conducting dual-stage hydrogenation-cocracking experiments, two reactors were connected to realize direct cracking of gaseous hydrogenation product without condensation. Feedstocks, including furfural (FF, 99.0% purity) and methanol (MeOH, 99.5% purity), were introduced into the reactor by a plunger pump. Hydrogen was the carrier gas with a flow rate of 50 ml/min, and it also participated in the hydrogenation reaction. Researches in literatures showed that furfural could be efficiently hydrogenated at 250 °C 7, 17, and our previous cocracking study of bio-oil components and alcohols confirmed that 400 °C was a suitable cracking temperature for the formation of aromatic hydrocarbons 8. Therefore, in this study, the reaction temperatures for hydrogenation and cracking were set as 250 °C and 400 °C, respectively. The pressure of reaction system was maintained at 4 MPa, and a consistent feedstock weight hourly space velocity (WHSV) of 2 h-1 was used. Each catalytic run lasted for 5 h. For those catalytic runs involving hydrogenation, the hydrogenation catalyst was reduced at 500 °C for 2 h before reaction, and the hydrogen flow rate was 50 ml/min. 2.4 Product analysis All the experimental data were obtained after 5-hour catalytic run except for time-on-stream tests. Noncondenable gaseous products were analyzed by a gas chromatography (GC). Light olefins and alkanes were separated on a HP-Plot Q capillary column and detected by a flame ionization detector (FID). CO and CO2 were separated on Porapak N, Porapak Q and Carbon Sieve-11 columns and measured by a thermal conductivity detector (TCD). The GC oven temperature was maintained 6


Page 6 of 37

Page 7 of 37

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


at 50 °C for 1 min and then increased to 180 °C at a rate of 10 °C/min. The homogeneous liquid products from hydrogenation and the oil phase products from cracking were analyzed by a gas chromatography-mass spectrometry (GC-MS) equipped with a 30 m × 0.25 mm × 0.25 µm HP-5MS capillary column. The GC oven temperature was maintained at 60 °C for 2 min and then increased to 250 °C at a rate of 10 °C/min. The identified chemicals were quantified by the area normalization method. All the residual reactants in liquid products were quantified to calculate their conversions. In addition, spent catalysts were analyzed by thermogravimetric analysis to determine the amount of carbonaceous deposits. Conversions of reactants (X) and yields of products (Y) were defined by the following equations, in which the symbol “m” represents the weight of the corresponding substance. Xi = Yi =

(mi )in − (mi )out ×100% (i = FF, MeOH) (mi )in mi (m Liquid Reactants )in

(3)

×100% (i = Liquid, Gas, Carbonaceous Deposits)

(4)

3 Results and discussion 3.1 Characterization of hydrogenation catalysts Some physicochemical properties of reduced 5Ni-5Cu/SiO2, 10Ni/SiO2 and 10Cu/SiO2 catalysts were summarized in Table 1. The loadings of Ni and Cu in these three catalysts determined by ICP-OES were close to the nominal loadings. Fig. 2 presents the XRD patterns of reduced catalysts under the diffraction angle from 40° to 54°. Two diffraction peaks at 43.5° and 50.7° for metallic Cu were seen in 10Cu/SiO2, and two diffraction peaks at 44.6° and 51.9° for metallic Ni were observed in 10Ni/SiO2. It was found that the reduced 5Ni-5Cu/SiO2 showed two relatively strong diffraction peaks at 44.2° and 51.5°, located in the middle of the peaks of Ni and Cu, indicating the formation of Ni-Cu alloy as reported by other 7



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

researchers

18, 19

Page 8 of 37

. The average crystallite sizes of Cu, Ni and Ni-Cu calculated using the peaks at

43.5°, 44.6° and 44.2° showed that 10Cu/SiO2 had the largest crystallite size (29.5 nm), followed by 10Ni/SiO2 (18.6 nm), and 5Ni-5Cu/SiO2 showed the smallest crystallite size (14.9 nm). Correspondingly, the Ni-Cu alloy in 5Ni-5Cu/SiO2 had higher dispersion than metallic Ni in 10Ni/SiO2 and metallic Cu in 10Cu/SiO2, as listed in Table 1, which was beneficial for hydrogenation reactions. 3.2 Regulation of hydrogen supply by hydrogenation catalysts Hydrogenation catalysts were considered to affect the hydrogenation route of furfural and thus the hydrogen supplement on it 17. Therefore, to regulate hydrogen supply in the hydrogenation stage, influences

of

5Ni-5Cu/SiO2,

10Ni/SiO2

and

10Cu/SiO2

on

the

hydrogenation

and

hydrogenation-cocracking of 25%FF75%MeOH were first studied. 3.2.1 Hydrogenation behavior Conversions of reactants are shown in Fig. 3 (a). Over 5Ni-5Cu/SiO2 and 10Cu/SiO2, the conversions of FF were up to 98.9% and 99.6% respectively, while that over 10Ni/SiO2 decreased to 92.1%. Meanwhile, a small amount of MeOH was converted. The yields of liquid and gaseous products are presented in Fig. 3 (b). The liquid product yield over 10Cu/SiO2 reached 96.2%, while that over 10Ni/SiO2 was only 92.7%. The main gaseous product were light saturated hydrocarbons, including CH4, C2H6, C3H8 and C4H10, which were produced from hydrodeoxygenation of MeOH and FF 7. The gaseous product yield over 10Ni/SiO2 was higher than that over 10Cu/SiO2, indicating a higher intensity of hydrodeoxygenation reaction, In view of the low reactivity of saturated gaseous hydrocarbons during cracking over HZSM-5

20

, for the integral hydrogenation-cocracking process,

the formation of saturated gaseous hydrocarbons in the hydrogenation stage would lower the final 8


Page 9 of 37

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


aromatic hydrocarbon yield. Upon 5Ni-5Cu/SiO2, the liquid product yield reached 95.6%, while the yield of gaseous product was low indicating the low intensity of hydrodeoxygenation of MeOH and FF, and therefore the influence of hydrodeoxygenation over 5Ni-5Cu/SiO2 on the integral hydrogenation-cocracking was very limited. Liquid products over these three catalysts were analyzed by GC-MS. Relative contents of main components excluding unconverted FF and MeOH are listed in Table 2, and they are classified into four groups namely single-furan-ring compound (SFRC), tetrahydro-single-furan-ring compound (THSFRC), alcohols and furanic dimers (FD). SFRC included Furfuryl alcohol (FFA), 2-(methoxymethyl)-furan, .beta.-methoxy-(s)-2-furanethanol and 2-methyl-furan. More SFRC were found in the liquid product from hydrogenation over 10Cu/SiO2 than those over 5Ni-5Cu/SiO2 and 10Ni/SiO2. Meanwhile, few THSFRC like tetrahydrofurfuryl alcohol (THFFA) and chain alcohols like 1,2-pentanediol were generated over 10Cu/SiO2, while certain amounts of THSFRC and alcohols were generated over 5Ni-5Cu/SiO2 and 10Ni/SiO2. In addition, the formation of 2-(methoxymethyl)-furan, which was produced from etherification of FFA and MeOH, indicated the possible etherification reaction of two MeOH molecules to generate dimethyl ether (DME). Because DME has a low boiling point, it might be released in the form of gas phase. Although it was not measured, the total yields of liquid and detectable gaseous products were close to 100%, suggesting the limited production of DME. Moreover, because chain ethers had good cracking performances 21, 22

, the formation of 2-(methoxymethyl)-furan and DME would not affect the production of aromatic

hydrocarbons in the integral hydrogenation-cocracking process. The distribution of hydrogenation products corresponded to the different hydrogen supply behaviors over these hydrogenation catalysts, in which how the supplied hydrogen participated in the 9



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

hydrogenation reactions was very important. The main hydrogenation products of FF over 10Cu/SiO2 were SFRC and FD, indicating that the supplied hydrogen participated in hydrogenation of aldehyde group but barely further hydrogenation of furan ring. Compared to that over 10Cu/SiO2, some THSFRC and alcohols were formed over 5Ni-5Cu/SiO2 and 10Ni/SiO2, showing that hydrogenation of partial furan rings and even some further hydro-ring-opening were achieved. In addition, some supplied hydrogen also took part in hydrodeoxygenation reactions to produce saturated gaseous hydrocarbons, which was obvious in the case of hydrogenation over 10Ni/SiO2. And over 10Ni/SiO2, it was also found that a few FF were not converted, suggesting the less amount of hydrogen supplied for the saturation of aldehyde group. 3.2.2 Hydrogenation-cocracking behavior Based on the research of hydrogen supply for hydrogenation of 25FF75MeOH over different catalysts, the corresponding hydrogenation-cocracking behaviors of the same feedstock were studied. In the conducted hydrogenation-cocracking experiments, reactants including FF and MeOH were completely converted. However, there were some differences in the distributions of products as shown in Fig. 4 (a). All the liquid products generated from hydrogenation-cocracking had two phases: the upper layer was the oil phase and the bottom layer was the aqueous phase. Using 5Ni-5Cu/SiO2 as the hydrogenation catalyst for hydrogenation-cocracking achieved the highest oil phase yield of 26.4%, whereas those using 10Cu/SiO2 and 10Ni/SiO2 decreased to 22.6% and 21.5%, respectively. Because hydrogenation over 10Cu/SiO2 only supplied hydrogen for the saturation of aldehyde group but not the furan ring, compared with that over 5Ni-5Cu/SiO2, the higher unsaturation degree led to the increased carbon selectivities of gaseous COx and carbonaceous deposit during cracking and thus 10


Page 10 of 37

Page 11 of 37

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


the decreased oil phase yield. For hydrogenation-cocracking using 10Ni/SiO2, because the supplied hydrogen participated in the hydrodeoxygenation reaction in the hydrogenation stage to produce more saturated gaseous hydrocarbons with low cracking reactivity, the yield of gaseous hydrocarbons was higher than that using 5Ni-5Cu/SiO2, which also lowered the yield of oil phase. Composition of oil phases was measured by GC-MS, and the identified components were classified into five groups, namely mono-aromatic hydrocarbons (including benzene, toluene, xylenes, trimethylbenzenes, methyl ethyl benzenes etc.), naphthalenes (including methylnaphthalene, dimethylnaphthalene etc.), indenes, aliphatic hydrocarbons and furan derivatives as shown in Fig. 4 (b). Oil phases from hydrogenation-cocracking with 5Ni-5Cu/SiO2 and 10Cu/SiO2 were both completely composed of hydrocarbons, in which the majorities were aromatic hydrocarbons. However, more naphthalenes were observed in the latter oil phase, attributed to the higher unsaturation degree of hydrogenation products over 10Cu/SiO2. In consideration of the higher difficulty in combustion of naphthalenes compared to monoaromatics, the former oil phase was a better gasoline component. Although the aromatic hydrocarbon content in the oil phase from hydrogenation-cocracking with 10Ni/SiO2 was high, some furan derivatives were also found, which might be owing to the lower FF conversion in the hydrogenation stage. The above facts showed that hydrogen supply behaviors on FF in the hydrogenation stage, including the insufficient hydrogenation of furan ring over 10Cu/SiO2 and the relatively low conversion of aldehyde group as well as some excessive hydrodeoxygenation over 10Ni/SiO2, consequently affected the yield and quality of oil phases in the subsequent cracking stage. Therefore, as a regulation way of hydrogen supply behavior to benefit the generation of liquid aromatic hydrocarbons, 5Ni-5Cu/SiO2 was the optimum hydrogenation catalyst. 11



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

3.3 Study on the function of hydrogen supply by comparison of different cracking processes On the basis of the optimum hydrogenation catalyst 5Ni-5Cu/SiO2, a further comparison of different cracking processes was carried out to study the functions of hydrogen supply from hydrogenation pretreatment and methanol-cocracking for the promotion of FF conversion. The cracking processes included dual-stage hydrogenation-cocracking of FF and MeOH with 5Ni-5Cu/SiO2, single-stage cocracking of FF and MeOH, hydrogenation-cracking of pure FF with 5Ni-5Cu/SiO2 and direct cracking of FF. Reactant conversions are presented in Fig. 5 (a). Compared with the complete conversion of reactants in hydrogenation-cocracking, conversions of FF in single-stage cocracking and hydrogenation-cracking of pure FF decreased to 98.9% and 96.6%, respectively. Moreover, FF conversion in the direct cracking of pure FF was only 21.2%. This result showed that single-stage hydrogen supply, no matter hydrogenation pretreatment or methanol-cocracking, could promote the conversion of FF, and the combination of these two methods as dual-stage hydrogen supplement could achieve the best promoting effect. Distributions of products are shown in Fig. 5 (b). Except for direct cracking of FF which produced a mixed liquid product, the other cases all obtained separable oil phases and aqueous phases. The oil phase yield in hydrogenation-cocracking was obviously higher than that in single-stage cocracking, while single-stage cocracking had higher yields of gaseous products and carbonaceous deposits. Hydrogenation-cracking of pure FF produced a high oil phase yield of 54.8%, but the aqueous phase yield was much lower than that in hydrogenation-cocracking. Considering that the yield of COx did not increase remarkably, the much lower aqueous phase yield indicated the significant decrease of integral deoxygenation efficiency. Therefore, the oil phase quality required 12


Page 12 of 37

Page 13 of 37

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


further analysis. The mixed liquid product from direct cracking of FF appeared homogeneous, and the yields of liquid product and carbonaceous deposit were 86.7% and 8.8%, respectively, with only a few gaseous hydrocarbons. In addition, because only partial FF was converted in the processes of single-stage cocracking of FF and MeOH, hydrogenation-cracking of pure FF and direct cracking of FF, the coking tendency could be better reflected by the selectivity of carbonaceous deposits. Therefore, the product selectivity is presented in Fig. 5 (c). Selectivities of carbonaceous deposits in the processes of hydrogenation-cocracking, single-stage cocracking, hydrogenation-cracking of FF and direct cracking of FF were 3.1%, 6.2%, 9.2 and 41.5%, respectively, indicating that hydrogen supply supplements in two stages both suppressed carbonaceous deposit formation. Based on the analysis of oil phases and mixed liquid product, the identified components were classified into mono-aromatics, aliphatics, naphthlenes and indenes, unconverted FF, SFRC (excluding FF), FD, THSFRC, ketones, alcohols and others as shown in Fig. 6. The oil phase from hydrogenation-cocracking was completely composed of hydrocarbons. For single-stage cocracking of FF and MeOH, besides aromatic hydrocarbons, some unconverted FF and SFRC were also observed. Meanwhile, compared with hydrogenation-cocracking, more double-ring naphthlenes and indenes were found in the oil phase from single-stage cocracking, showing that hydrogen supply in hydrogenation stage not only facilitated the formation of oil phase, but also favored monoaromatic hydrocarbon formation. When pure FF was converted by hydrogenation-cracking, the production of hydrocarbons was limited. Besides a small amount of unconverted FF and some incomplete deoxygenation products like alcohols and ketones, SFRC and FD accounted for a large proportion. Therefore, although the oil phase yield reached 54.8%, the actual yield of aromatic hydrocarbon was low. By the comparison with the hydrogenation-cocracking process, it could be deduced that the 13



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

hydrogen supply by MeOH in cocracking stage could help activate and transform furan rings to liquid hydrocarbons, which increased the integral deoxyegnation efficiency and the desired aromatic hydrocarbon yield. Because the conversion of FF was low in direct cracking of FF, although the liquid product yield was very high, the majority in it was the unconverted FF, accompanied by a few SFRC, FD and alcohols. The above discussion of carbonaceous deposit yield and selectivity as well as the oil phase composition suggests the possible deactivation of cracking catalysts. Therefore, time-on-stream tests of different cracking processes were carried out to investigate catalyst stability, as shown in Fig. 7. The yield and composition of oil phase in dual-stage hydrogenation-cocracking were relatively stable in the 5-hour run, while an obvious decrease of oil phase yield from 21.8% to 9.6% was observed in single-stage cocracking, accompanied with the increase of gaseous product yield. Combining with the higher yield of carbonaceous deposits on the cracking catalyst surface, it was deduced that the decrease of catalyst activity was quicker in single-stage cocracking than that in dual-stage hydrogenation-cocracking, and this reflected in the weakening of catalytic ability for aromatization first, which suppressed the formation of liquid oil phase product and promoted the release of gaseous hydrocarbons. Our previous cracking study also observed the massive release of gaseous hydrocarbons when the catalyst activity obviously decreased

23

. The difference in product

yield showed that hydrogen supply in the hydrogenation stage, which successfully saturated aldehyde group and partial furan rings, led to less carbonaceous deposits in the following cracking stage and thus the catalyst activity was better maintained. Hydrogenation-cracking of FF produced oil phases with stable yields in the 5-hour run, but the aromatic hydrocarbon contents in them were limited and kept decreasing and a lot of furanic compounds were found. This could be attributed to 14


Page 14 of 37

Page 15 of 37

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


the low cracking reactivity of furanic compounds which were not completely saturated during hydrogenation 24, and the quicker formation of carbonaceous deposit as indicated by its yield in Fig. 5 further led to the decrease of aromatic hydrocarbon yield. Therefore, the hydrogen supply by MeOH not only promoted the conversion of furanic compounds but also improved the catalyst stability by reducing carbonaceous deposit yield. Direct cracking of FF had low but stable reaction intensity, showing its very inferior cracking performance without any hydrogen supply. Through the comparison of different cracking processes, it could be concluded that the hydrogen supplements from hydrogenation pretreatment and methanol-cocracking were both significant. Hydrogen supply by hydrogenation pretreatment increased saturation degree of feedstock for cracking and so that production of carbonaceous deposits was suppressed, while hydrogen supply by methanol-cocracking enhanced transformation of furan ring structure and also weakened carbonaceous deposit formation. Therefore, the dual-stage hydrogenation-cocracking process which could supply hydrogen in two stages was the most superior in the conversion of FF to liquid aromatic hydrocarbons. 3.4

Discussion

of

hydrogen

supply

behaviors

based

on

a

proposed

dual-stage

hydrogenation-cocracking mechanism The above experimental results revealed the functions of hydrogen supply by hydrogenation pretreatment and methanol-cocracking, as well as the regulation of hydrogen supply by different hydrogenation catalysts. To further understand how the hydrogen was supplied and regulated, hydrogen

supply

behaviors

were

discussed

based

on

a

proposed

dual-stage

hydrogenation-cocracking mechanism as shown in Fig. 8. The comparison of single-stage cocracking and hydrogenation-cocracking showed that 15



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 16 of 37

hydrogen supply in the hydrogenation stage was important. Meanwhile, the results of hydrogenation over 10Cu/SiO2, 5Ni-5Cu/SiO2 and 10Ni/SiO2 indicated that this hydrogen supply behavior was regulated by hydrogenation catalysts. According to the distribution of hydrogenation products, it could be deduced that the primary conversion of FF was the hydrogenation of aldehyde group to form FFA. Conversions of FF over 10Cu/SiO2 and 5Ni-5Cu/SiO2 were higher than that over 10Ni/SiO2, suggesting that the presence of Cu facilitated the primary conversion of FF. Further conversion of FFA mainly followed two routes: hydrogenation of furan ring to generate THSFRC like THFFA and even hydro-ring-opening reaction to generate alcohols like 1, 2-pentanediol; side-chain reactions to form other furanic compounds, such as condensation to form FD, terminal hydroxyl group elimination to form 2-mthyl-furan and etherification with MeOH to form 2-(methoxymethyl)-furan. On the aspect of furan ring hydrogenation, 5Ni-5Cu/SiO2 and 10Ni/SiO2 showed much higher catalytic activity than 10Cu/SiO2, while over 10Cu/SiO2 side-chain reactions predominated to produce furanic compounds. Moreover, some THSFRC and alcohols further underwent cracking and hydrodeoxygenation reactions to produce saturated C3-C4 gaseous hydrocarbons over 5Ni-5Cu/SiO2 and 10Ni/SiO2, which was also observed by Li et al.

25

. These

reactions were more intensive over 10Ni/SiO2. The difference in hydrogenation pathways of FF was related to the interactions between furan ring and aldehyde groups with the active metals

26, 27

. In the study of FF hydrogenation over

Cu-based catalyst through density functional theory (DFT) calculation, Sitthisa et al. proposed that hydrogenation started with the adsorption of oxygen atom in aldehyde group on Cu surface, while the interaction between furan ring and Cu was much weaker 28. For Ni-based catalysts, experimental and theoretical studies showed that both the aldehyde group and the furan ring could interact with 16


Page 17 of 37

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


metallic Ni and be adsorbed

29, 30

. Therefore, over 10Cu/SiO2, because the interaction between

aldehyde group and Cu predominated, the primary conversion of FF to FFA was favored, and due to the difficulty in the adsorption of furan ring on Cu, the further conversion of FFA mainly followed side-chain reactions. When FF hydrogenation was conducted over 10Ni/SiO2, because both aldehyde group and furan ring could be adsorbed on Ni surface, the hydrogenation efficiency of aldehyde group was lower than that over 10Cu/SiO2, but further furan ring hydrogenation and hydro-ring-opening could be realized to produce saturated compounds such as THFFA and 1,2-pentanediol. The bimetallic 5Ni-5Cu/SiO2 catalyst comprised the both advantages of Cu- and Ni-based catalysts: the existence of Cu promoted the primary conversion of FF to FFA and the existence of Ni achieved the further hydrogenation of furan ring. Therefore, the conversion of FF over 5Ni-5Cu/SiO2 was higher than that over 10Ni/SiO2 and it was competitive with that over 10Cu/SiO2, and meanwhile higher hydrogenation degree was achieved over 5Ni-5Cu/SiO2 than that over 10Cu/SiO2. In addition, because Ni was more active in cracking and hydrodeoxygenation reactions than Cu 31, more saturated gaseous hydrocarbons were generated over 10Ni/SiO2. Besides the different catalytic functions of Ni and Cu, as indicated by the characterization of catalysts, higher dispersion of metals in 5Ni-5Cu/SiO2 which could provide more accessible active sites would also promoted the desired saturation of aldehyde group and furan ring reactions. Different hydrogen supply behaviors over these three catalysts led to different hydrogenation degree of FF, which ultimately affected the cracking performance. The insufficient hydrogenation of furan ring over 10Cu/SiO2 and some excessive hydrodeoxygenation over 10Ni/SiO2 decreased the yield of oil phase in the cracking stage as discussed in section 3.1.2. However, hydrogenation-cracking with any hydrogenation catalyst produced obvious higher oil phase yield 17



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

and lower carbonaceous deposit yield than that in direct cocracking, suggesting the significance of hydrogen supply for the saturation of the aldehyde group and furan ring. The comparison of hydrogenation-cracking of pure FF and hydrogenation-cocracking of FF and MeOH showed that hydrogen supply by MeOH in the cocracking stage could promote the conversion of FF hydrogenation products to liquid hydrocarbons. To discuss this hydrogen supply behavior, first it is important to understand how the supplied hydrogen was produced from MeOH. It is generally believed that for the conversion of oxygen-containing compounds (including alcohols, acids, aldehydes, ketones etc.) over HZSM-5 catalyst, deoxygenation reactions first occurred to form intermediates like light olefins, which further undergo aromatization to form aromatic hydrocarbons 32

. In the cracking of individual MeOH, light mono-olefin intermediates like C2H4 and C3H6 were

first generated by deoxygenation

33, 34

. Then these light mono-olefins underwent oligomerization to

form C6-C10 mono-olefins, which could be dehydrogenated to form C6-C10 dienes, and afterwards the C6-C10 dienes further underwent cyclization and dehydrogenation to form the primary mono-aromatic hydrocarbons

35, 36

. By alkylation and isomerization reactions, these primary

mono-aromatic hydrocarbons could be transformed into other mono-aromatic hydrocarbons. In addition, the mono-aromatics could also undergo condensation to generate naphthalenes and other polyaromatic hydrocarbons. It was notable that in the conversions of mono-olefins to dienes, dienes to primary aromatic hydrocarbons and further condensation of aromatics, dehydrogenation reactions happened, which could produce surplus hydrogen for supplement. The supply behavior of surplus hydrogen produced by MeOH was determined by the coreactants (namely different FF hydrogenation products) in the cracking stage. As stated in section 3.1.1, hydrogenation of FF mainly generated two kinds of products that were available for the 18


Page 18 of 37

Page 19 of 37

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


subsequent cracking: furanic compounds such as FFA, 2-mthyl-furan, 2-(methoxymethyl)-furan and some FD; saturated oxygenated compounds such as THSFRC and alcohols. For the cracking of THSFRC and alcohols, because of the high saturation degrees, their deoxygenation to produce olefins and the following aromatization could happen without or with only a little hydrogen supply. However, for furanic compounds with high unsaturation degrees, hydrogen supply was required. As discussed in section 3.2, hydrogenation-cracking and direct cracking of FF, in which furanic compounds were the main reactants for cracking, produced more carbonaceous deposits, resulting in quick deactivation of cracking catalysts and thus inferior cracking performances. Therefore, understanding furan ring conversion route especially how carbonaceous deposits were formed from this structure is significant. The study of furan conversion over HZSM-5 by Cheng and Huber showed that the primary condensation product benzofuran was an important coke precursor

37

.A

theoretical calculation of furan cracking mechanism upon HZSM-5 by Vaitheeswaran et al. indicated that the formation of benzofuran involved ring-opening reaction 38: The protonated furan molecule underwent double-bond rearrangement, allyl shift, oxonium formation and ring-opening reactions to form a protonated butenoic aldehyde intermediate. This highly unsaturated intermediate was quite unstable and tended to react with another furan molecule to form benzofuran when there was no external hydrogen supply. However, if adsorbed surplus hydrogen was created after aromatization 35, the adsorbed protonated butenoic aldehyde intermediate could be stabilized by interaction with the adsorbed hydrogen to form compounds with higher saturation degrees 39. As a result, the formation of benzofuran as well as coke induced by this precursor was suppressed, and complete deoxygenation reactions were promoted 4. Therefore, the surplus hydrogen generated from MeOH could facilitate the complete deoxygenation of furanic compounds to form light mono-olefins and 19



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 20 of 37

dienes, which further underwent aromatization to produce aromatic hydrocarbons as described before. Based on the above mechansim, for hydrogenation-cracking of pure FF, furanic compounds produced in the hydrogenation stage were not efficiently converted without hydrogen supply by MeOH in the cracking stage, resulting in many furanic compounds in the final oil phase and also higher carbonaceous deposit yield. This tendency was even more severe in the direct cracking of FF without

any

hydrogen

supply.

Through

hydrogen

supply

by

MeOH

using

a

hydrogenation-cocracking process, the low cracking reactivity and high coking tendency problems of furanic compounds was overcome, indicating the necessity of combining two hydrogen supply ways. Similarly, for the conversion of bio-oil, the hydrogenation-cocracking process will also ensure sufficient hydrogen supply for the transformation of unsaturated and oxygenated functional groups. 4 Conclusions Hydrogen supply behaviors in hydrogenation-cocracking of FF and MeOH were investigated. It was found that hydrogenation catalysts could regulate hydrogen supply in the hydrogenation stage and consequently affect the integral hydrogenation-cocracking performance. The insufficient hydrogenation of furan ring over 10Cu/SiO2 resulted in higher unsaturation degree of feedstock for cracking, which promoted the formations of carbonaceous deposits and COx to certain extents and thus lowered the oil phase yield. Hydrodeoxygenation was relatively intensive over 10Ni/SiO2, which facilitated the production of saturated gaseous hydrocarbons with low cracking activities and therefore also decreased the ultimate oil phase yield. Hydrogenation-cocracking with 5Ni-5Cu/SiO2 generated the highest oil phase yield of 26.4%, mainly composed of monoaromatics. Comparison of different cracking processes showed that hydrogen supply in the hydrogenation stage increased the 20


Page 21 of 37

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


saturation degree and hydrogen generated from MeOH promoted the conversion of furan-ring structure, which both facilitated aromatic hydrocarbon production and suppressed carbonaceous deposit formation. Therefore, the hydrogenation-cocracking process was the most superior for FF conversion, and it is promising for upgrading of actual hydrogen-lacking bio-oil. AUTHOR INFORMATION Corresponding Author *Shurong Wang. *Tel: +86 571 87952801; Fax: +86 571 87951616. Email address: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China [grant number 51606069] and the China Postdoctoral Science Foundation [grant number 2016M591616]. References (1) Mohan, D.; Pittman, C. U.; Steele, P. H., Pyrolysis of wood/biomass for bio-oil: A critical review. Energy Fuels 2006, 20, 848-889. (2) Mortensen, P. M.; Grunwaldt, J. D.; Jensen, P. A.; Knudsen, K. G.; Jensen, A. D., A review of catalytic upgrading of bio-oil to engine fuels. Appl. Catal., A 2011, 407, 1-19. (3) Vispute, T. P.; Zhang, H. Y.; Sanna, A.; Xiao, R.; Huber, G. W., Renewable Chemical Commodity Feedstocks from Integrated Catalytic Processing of Pyrolysis Oils. Science 2010, 330, 1222-1227. (4) Mentzel, U. V.; Holm, M. S., Utilization of biomass: Conversion of model compounds to 21



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

hydrocarbons over zeolite H-ZSM-5. Appl. Catal., A 2011, 396, 59-67. (5) Gayubo, A. G.; Aguayo, A. T.; Atutxa, A.; Aguado, R.; Olazar, M.; Bilbao, J., Transformation of oxygenate components of biomass pyrolysis oil on a HZSM-5 zeolite. II. Aldehydes, ketones, and acids. Ind. Eng. Chem. Res. 2004, 43, 2619-2626. (6) Guo, X.; Wang, S.; Wang, Q.; Guo, Z.; Luo, Z., Properties of bio-oil from fast pyrolysis of rice husk. Chin. J. Chem. Eng. 2011, 19, 116-121. (7) Sitthisa, S.; Resasco, D. E., Hydrodeoxygenation of furfural over supported metal catalysts: a comparative study of Cu, Pd and Ni. Catal. Lett. 2011, 141, 784-791. (8) Wang, S.; Cai, Q.; Wang, X.; Zhang, L.; Wang, Y.; Luo, Z., Biogasoline production from the co-cracking of the distilled fraction of bio-oil and ethanol. Energy Fuels 2013, 28, 115-122. (9) Ibarra, Á.; Rodríguez, E.; Sedran, U.; Arandes, J. M.; Bilbao, J., Synergy in the Cracking of a Blend of Bio-oil and Vacuum Gasoil under Fluid Catalytic Cracking Conditions. Ind. Eng. Chem. Res. 2016, 55, 1872-1880. (10) Wang, S.; Cai, Q.; Chen, J.; Zhang, L.; Wang, X.; Yu, C., Green aromatic hydrocarbon production from cocracking of a bio-oil model compound mixture and ethanol over Ga2O3/HZSM-5. Ind. Eng. Chem. Res. 2014, 53, 13935-13944. (11) Graça, I.; Ribeiro, F. R.; Cerqueira, H.; Lam, Y.; De Almeida, M., Catalytic cracking of mixtures of model bio-oil compounds and gasoil. Appl. Catal., B 2009, 90, 556-563. (12) Wang, S.; Cai, Q.; Wang, X.; Zhang, L.; Wang, Y.; Luo, Z., Biogasoline production by co-cracking of model compound mixture of bio-oil and ethanol over HSZM-5. Chin. J. Catal. 2014, 35, 709-722. (13) Wang, C.; Guo, Z.; Yang, Y.; Chang, J.; Borgna, A., Hydrogenation of furfural as model 22


Page 22 of 37

Page 23 of 37

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


reaction of bio-oil stabilization under mild conditions using Multiwalled Carbon Nanotube (MWNT)-supported Pt catalysts. Ind. Eng. Chem. Res. 2014, 53, 11284-11291. (14) Manfro, R. L.; Pires, T. P. M. D.; Ribeiro, N. F. P.; Souza, M. M. V. M., Aqueous-phase reforming of glycerol using Ni–Cu catalysts prepared from hydrotalcite-like precursors. Catal.Sci.Technol. 2013, 3, 1278-1287. (15) Dandekar, A.; Vannice, M. A., Determination of the Dispersion and Surface Oxidation States of Supported Cu Catalysts. J. Catal. 1998, 178, 621-639. (16) Rao, R. S.; Walters, A. B.; Vannice, M. A., Influence of crystallite size on acetone hydrogenation over copper catalysts. J. Phys. Chem. B 2005, 109, 2086-2092. (17) Zheng, H.-Y.; Zhu, Y.-L.; Teng, B.-T.; Bai, Z.-Q.; Zhang, C.-H.; Xiang, H.-W.; Li, Y.-W., Towards understanding the reaction pathway in vapour phase hydrogenation of furfural to 2-methylfuran. J. Mol. Catal. A 2006, 246, 18-23. (18) Lin, J. H.; Biswas, P.; Guliants, V. V.; Misture, S., Hydrogen production by water–gas shift reaction over bimetallic Cu–Ni catalysts supported on La-doped mesoporous ceria. Appl. Catal., A 2010, 387, 87-94. (19) Saw, E. T.; Oemar, U.; Tan, X. R.; Du, Y.; Borgna, A.; Hidajat, K.; Kawi, S., Bimetallic Ni–Cu catalyst supported on CeO 2 for high-temperature water–gas shift reaction: Methane suppression via enhanced CO adsorption. J. Catal. 2014, 314, 32-46. (20) Bhan, A.; Nicholas Delgass, W., Propane Aromatization over HZSM-5 and Ga/HZSM-5 Catalysts. Catal. Rev. 2008, 50, 19-151. (21) Wang, W.; Buchholz, A.; Seiler, M.; Hunger, M., Evidence for an initiation of the methanol-to-olefin process by reactive surface methoxy groups on acidic zeolite catalysts. J. Am. 23



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

Chem. Soc. 2003, 125, 15260-15267. (22) Ni, Y.; Peng, W.; Sun, A.; Mo, W.; Hu, J.; Li, T.; Li, G., High selective and stable performance of catalytic aromatization of alcohols and ethers over La/Zn/HZSM-5 catalysts. J. Ind. Eng. Chem. 2010, 16, 503-505. (23) Wang, S.; Cai, Q.; Chen, J.; Zhang, L.; Zhu, L.; Luo, Z., Co-cracking of bio-oil model compound mixtures and ethanol over different metal oxide-modified HZSM-5 catalysts. Fuel 2015, 160, 534-543. (24) Cheng, Y. T.; Jae, J.; Shi, J.; Fan, W.; Huber, G. W., Production of Renewable Aromatic Compounds by Catalytic Fast Pyrolysis of Lignocellulosic Biomass with Bifunctional Ga/ZSM-5 Catalysts. Angew. Chem., Int. Ed. 2012, 124, 1416-1419. (25) Li, N.; Huber, G. W., Aqueous-phase hydrodeoxygenation of sorbitol with Pt/SiO2–Al2O3: Identification of reaction intermediates. J. Catal. 2010, 270, 48-59. (26) Zhang, B.; Zhu, Y.; Ding, G.; Zheng, H.; Li, Y., Selective conversion of furfuryl alcohol to 1, 2-pentanediol over a Ru/MnOx catalyst in aqueous phase. Green Chem. 2012, 14, 3402-3409. (27) Mizugaki, T.; Yamakawa, T.; Nagatsu, Y.; Maeno, Z.; Mitsudome, T.; Jitsukawa, K.; Kaneda, K., Direct transformation of furfural to 1, 2-pentanediol using a hydrotalcite-supported platinum nanoparticle catalyst. ACS Sustain. Chem. Eng. 2014, 2, 2243-2247. (28) Sitthisa, S.; Sooknoi, T.; Ma, Y.; Balbuena, P. B.; Resasco, D. E., Kinetics and mechanism of hydrogenation of furfural on Cu/SiO 2 catalysts. J. Catal. 2011, 277, 1-13. (29) Roy, J.-R.; Laliberté, M.-A.; Lavoie, S.; Castonguay, M.; McBreen, P. H., Adsorption states of acetaldehyde and butane-2, 3-dione on Ni (111). Surf. Sci. 2005, 578, 43-56. (30) Wang, S.; Li, X.; Zhang, F.; Cai, Q.; Wang, Y.; Luo, Z., Bio-oil catalytic reforming without 24


Page 24 of 37

Page 25 of 37

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


steam addition: application to hydrogen production and studies on its mechanism. Int. J. Hydrogen Energy 2013, 38, 16038-16047. (31) Ardiyanti, A.; Khromova, S.; Venderbosch, R.; Yakovlev, V.; Heeres, H., Catalytic hydrotreatment of fast-pyrolysis oil using non-sulfided bimetallic Ni-Cu catalysts on a δ-Al2O3 support. Appl. Catal., B 2012, 117, 105-117. (32) Adjaye, J. D.; Bakhshi, N. N., Catalytic conversion of a biomass-derived oil to fuels and chemicals I: Model compound studies and reaction pathways. Biomass Bioenergy 1995, 8, 131-149. (33) Haw, J. F.; Song, W.; Marcus, D. M.; Nicholas, J. B., The mechanism of methanol to hydrocarbon catalysis. Acc. Chem. Res. 2003, 36, 317-326. (34) Olsbye, U.; Bjørgen, M.; Svelle, S.; Lillerud, K.-P.; Kolboe, S., Mechanistic insight into the methanol-to-hydrocarbons reaction. Catal. Today 2005, 106, 108-111. (35) Choudhary, V. R.; Devadas, P.; Banerjee, S.; Kinage, A. K., Aromatization of dilute ethylene over Ga-modified ZSM-5 type zeolite catalysts. Microporous Mesoporous Mater. 2001, 47, 253-267. (36) Lukyanov, D. B.; Gnep, N. S.; Guisnet, M. R., Kinetic modeling of ethene and propene aromatization over HZSM-5 and GaHZSM-5. Ind. Eng. Chem. Res. 1994, 33, 223-234. (37) Cheng, Y. T.; Huber, G. W., Chemistry of Furan Conversion into Aromatics and Olefins over HZSM-5: A Model Biomass Conversion Reaction. ACS Catal. 2011, 1, 611-628. (38) Vaitheeswaran, S.; Green, S. K.; Dauenhauer, P.; Auerbach, S. M., On the Way to Biofuels from Furan: Discriminating Die is Alder and Ring-Opening Mechanisms. ACS Catal. 2013, 3, 2012-2019. (39) Xue, Y.; Zhou, S.; Bai, X. L., Role of Hydrogen Transfer during Catalytic Copyrolysis of Lignin and Tetralin over HZSM-5 and HY Zeolite Catalysts. ACS Sustain. Chem. Eng. 2016, 4, 4237-4250. 25



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 26 of 37

Table 1 Physicochemical properties of reduced catalysts

Metal loadinga (%)

Metal average

Catalyst

Dispersion (%)

Ni

Cu

crystallite sizeb (nm)

5Ni-5Cu/SiO2

5.2

5.3

14.9c

6.8c

10Ni/SiO2

10.3

\

18.6

5.4

10Cu/SiO2

\

10.2

29.5

3.7

a

Determined by ICP-OES analysis.

b

Calculated by Scherrer equation

c

Ni-Cu alloy

26


Page 27 of 37

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


Table 2 Contents of main components in the hydrogenation liquid products Relative content (%) Categories

SFRC

SFRC

Compounds

Molecular structure 5Ni-5Cu/SiO2

10Ni/SiO2

10Cu/SiO2

13.5±0.3

25.2±0.5

34.1±0.5

28.9±0.6

26.9±0.2

24.8±0.3

1.9±0.2

2.1±0.2

5.1±0.2

7.7±0.2

4.6±0.4

23.4±0.7

52.0±1.3

58.8±1.3

87.4±1.7

25.4±0.5

25.6±0.6

1.7±0.2

0.8±0.1

0.7±0.2

0.7±0.1

26.2±0.6

26.3±0.8

2.4±0.3

13.1±0.5

6.7±0.4

1.5±0.1

1.1±0.1

2.2±0.1

0.7±0.1

14.2±0.6

8.9±0.5

2.2±0.2

1.2±0.2

0.6±0.0

1.9±0.1

0.9±0.2

0.7±0.1

3.1±0.2

0.6±0.1

0.5±0.0

1.3±0.1

2.7±0.5

1.8±0.1

6.3±0.4

2-(methoxymethyl)-furan

furfuryl alcohol

SFRC .beta.-methoxy-(s)-2-furanethanol

SFRC

2-methyl-furan

Total SFRC THSFRC

THSFRC

tetrahydrofurfuryl alcohol

tetrahydro-2-methyl-furan

Total THSFRC

Alcohol

Alcohol

1,2-pentanediol

1-butanol

Total Alcohol

FD

FD

FD

2,2'-[oxybis(methylene)]bis- furan

2-(2-furanylmethyl)-5-methyl-furan

2,2'-methylenebis-furan

Total FD

27



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 captions Figure 1 Fixed-bed reaction system. Figure 2 XRD patterns of reduced catalysts. Figure 3 Hydrogenation of 25FF75MeOH over different catalysts: (a) reactant conversion (b) product yield. Figure 4 Hydrogenation-cocracking of 25FF75MeOH with different hydrogenation catalysts: (a) product yield (b) oil phase composition. Figure 5 Comparison of different cracking processes: (a) reactant conversion (b) product yield (c) product selectivity. Figure 6 Composition of oil phases from different cracking processes. Figure 7 Time-on-stream tests of different cracking processes: (a) oil phase (mixed liquid) yield (b) gaseous product yield (c) hydrocarbon content in oil phase (mixed liquid) (d) furanic compound content in oil phase (mixed liquid) Figure 8 Dual-stage hydrogenation-cocracking mechanism of FF and MeOH.

28


Page 28 of 37

Page 29 of 37

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 1 Fixed-bed reaction system.

29



○

○

◇

Cu Ni Ni-Cu alloy

●

○ Intensity (a.u.)

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

10Cu

◇ ◇

10Ni

● ○

40

42

○ 44

46

48

50

● 5Ni-5Cu

52

54

2 theta

Figure 2 XRD patterns of reduced catalysts.

30


Page 30 of 37

Page 31 of 37

100

100

5Ni-5Cu 10Ni 10Cu

80

60

5Ni-5Cu 10Ni 10Cu

90

Yield %

Conversion %

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

40

4

20

2

0

0

FF

Liquid

MeOH

(a)

COx

Gaseous Hydrocarbons

(b)

Figure 3 Hydrogenation of 25FF75MeOH over different catalysts: (a) reactant conversion (b) product yield.

31



50

90

5Ni-5Cu & HZSM-5 10Ni & HZSM-5 10Cu & HZSM-5

30

5Ni-5Cu & HZSM-5 10Ni & HZSM-5 10Cu & HZSM-5

80

Content %

40

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 32 of 37

20

70

60 20

10

10

0

0

Oil Phase Aqueous Phase

COx

Gaseous Carbonaceous Hydrocarbons Deposits

Mono Naphthalenes -aromatics

(a)

Indenes

Aliphatics

Furan derivatives

(b)

Figure 4 Hydrogenation-cocracking of 25FF75MeOH with different hydrogenation catalysts: (a) product yield (b) oil phase composition.

32


Page 33 of 37

25FF75MeOH~5Ni-5Cu & HZSM-5 25FF75MeOH~HZSM-5 100FF~5Ni-5Cu & HZSM-5 100FF~HZSM-5


100

100

80

Yield %

80

Conversion %

60

60

40

40 20

20 0

Oil Aqueous Phase Phase

0

FF

MeOH

Mixed liquid

(a)

COx


(b) 25FF75MeOH~5Ni-5Cu & HZSM-5 25FF75MeOH~HZSM-5 100FF~5Ni-5Cu & HZSM-5 100FF~HZSM-5

60

50

Selectivity %

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


40

30

20

10

0

Oil Phase

Aqueous Phase

Mixed liquid

COx


(c) Figure 5 Comparison of different cracking processes: (a) reactant conversion (b) product yield (c) product selectivity.

33



100


80

Content %

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 34 of 37

60

40

20

0 Mono-aromatics Aliphatics Naphthalenes & Indenes

FF

SFRC

FD

THSFRC

Alcohols

Ketones

Figure 6 Composition of oil phases from different cracking processes.

34


Others

Page 35 of 37

100

60

(b)

(a) 25FF75MeOH~5Ni-5Cu & HZSM-5 25FF75MeOH~HZSM-5 100FF~5Ni-5Cu & HZSM-5 100FF~HZSM-5

60

40

Yield %

Yield %


50

80

30

40 20 20

10

0

0 1

2

3

4

5

1

2

Time h

3

4

5

Time h 100

100

(d)

(c) 25FF75MeOH~5Ni-5Cu & HZSM-5 25FF75MeOH~HZSM-5 100FF~5Ni-5Cu & HZSM-5 100FF~HZSM-5

60

Content %

80

80

Content %

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


40


60

40

20 20

0 0 1

2

3

4

5

1

2

Time h

3

4

5

Time h

Figure 7 Time-on-stream tests of different cracking processes: (a) oil phase (mixed liquid) yield (b) gaseous product yield (c) hydrocarbon content in oil phase (mixed liquid) (d) furanic compound content in oil phase (mixed liquid)

35



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

O O O O O O O

O

O O

O

O

O

OH

OH

O OH

OH

Figure 8 Dual-stage hydrogenation-cocracking mechanism of FF and MeOH.

36


Page 36 of 37

Page 37 of 37

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


Table of Contents

O O O O O O O

O

O O

O

O

O

OH

OH

O OH

OH

37


Aromatic Hydrocarbon Production from Bio-Oil by a Dual-Stage

Recommend Documents