Effect of MetalâAcid Balance on Hydroprocessed Renewable Jet Fuel

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Effect of Metal-Acid Balance on Hydroprocessed Renewable Jet Fuel Synthesis from Hydrocracking and Hydroisomerization of Bio-hydrogenated Diesel over Pt-supported Catalysts Tepin Hengsawad, Chayasari Srimingkwanchai, Suchada Butnark, Daniel E. Resasco, and Siriporn Jongpatiwut Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b04711 • Publication Date (Web): 16 Jan 2018 Downloaded from http://pubs.acs.org on January 25, 2018

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Industrial & Engineering Chemistry Research

Effect of Metal-Acid Balance on Hydroprocessed Renewable Jet Fuel Synthesis from Hydrocracking and Hydroisomerization of Biohydrogenated Diesel over Pt-supported Catalysts

Tepin Hengsawada, Chayasari Srimingkwanchaia, Suchada Butnarkb, Daniel E. Resascoc and Siriporn Jongpatiwuta, d*

a

The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok 10330, Thailand

b

PTT Research and Technology Institute, PTT Public Company Limited, Ayutthaya 13170, Thailand

c

School of Chemical, Biological and Materials Engineering, University of Oklahoma, Norman, Oklahoma 73019, USA d

Center of Excellence on Petrochemical and Materials Technology, Chulalongkorn University, Bangkok 10330, Thailand

Submitted to Industrial & Engineering Chemistry Research (I&EC)

*Address author correspondence: Tel.: +66-2-218-4139; Fax: +66-2-218-4459; E-mail addresses: [email protected]

ACS Paragon Plus Environment


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Table of content / Graphical abstract


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Abstract

2

The development of Pt-supported catalysts for a selective hydrocracking and

3

hydroisomerization of bio-hydrogenated diesel (BHD, n-C15–C18) to hydroprocessed

4

renewable jet (HRJ) fuel (C9 ̶ C14) was investigated. The different acidic supports (i.e. HY

5

zeolite with SiO2/Al2O3 ratios of 5.5 and 100, and ASA supports) loaded with 0.5 wt.% Pt

6

content were prepared and tested for the catalytic conversion of BHD to HRJ fuel. The Pt

7

supported on HY zeolite with SiO2/Al2O3 ratio of 100 denoted as Pt/HY(100) catalyst

8

exhibited the highest jet fuel yield with high branched isomers due to its well balance

9

between metal and acid function. The effect of the reaction temperature, reaction pressure,

10

and liquid hourly space velocity (LHSV) on the hydrocracking and hydroisomerization

11

performance was studied over Pt/HY(100) catalyst. The jet fuel yield was obtained at

12

maximum value of 33 wt.% at 310 ºC, 450 psig, LHSV of 1.0 h-1, and H2/BHD molar ratio of

13

30. A stability test was also conducted over Pt/HY(100) catalyst for 160 h. No significant

14

change in the catalytic activity and selectivity during the test was observed, indicating high

15

stability of the Pt/HY(100) catalyst.

16

Hydrocracking, Hydroisomerization, Bio-hydrogenated diesel, Pt-supported

17

Keywords:

18

catalyst, Hydroprocessed renewable jet fuel

19



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1. Introduction

2

The world consumption of conventional jet fuel is approximately 1.5 – 1.7 billion

3

barrels per year, accounting for 10% of global transportation energy [1, 2]. According to

4

aviation industry expansion in recent years, resulting from the growth in the tourism sector,

5

the demand of jet fuel has been increasing and gradually increasing for the next thirty years,

6

leading to more greenhouse gas (GHG) emission [3]. International Air Transport Association

7

(IATA) aims to reduce carbon emissions on a voluntary basis by 50% by year 2050 through

8

the use of alternative fuels [4]. These have attracted increased attention for developing

9

technologies to reduce GHG emissions such as improvement of air traffic management, use

10

of new technologies, use of new aircraft, but these will only slow down the emission process

11

[5]. In order to actually cut down the amount of GHG emission and provide a long-term

12

sustainable alternative to petroleum jet fuel, the development of green aviation biofuels has

13

been an important part of the aviation industry’s future [5 ̶ 8]. Jet fuels must meet very

14

stringent international specifications (i.e. freezing point, viscosity, etc.), which makes it much

15

more difficult to develop an alternative fuel for aviation than for automobile applications [9].

16

Currently, several bioenergy conversion technologies from biomass to hydrocarbons have

17

been explored and developed such as catalytic hydroprocessing of vegetable and animal oils

18

[7, 9 ̶ 16], Fischer-Tropsch synthesis using biomass-derived syngas [6, 17 ̶ 20], and catalytic

19

transformation of sugars to jet fuel [21 ̶ 23]. Among these technologies, the hydroprocessing

20

comprising hydrogenation, deoxygenation, hydroisomerization and hydrocracking is

21

particularly promising. This process is at a relative high maturity level, is commercially

22

available, and was recently used to produce jet fuel for military flights [1, 21].

23

Hydroprocessed renewable jet (HRJ) fuel can be used as the commercial and military

24

aviation fuels up to a 50/50 blend of HRJ with petroleum derived jet fuels (Jet A-1, Jet A and

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JP-8) [6, 7, 17] because of its advantages such as higher cetane number, lower aromatic

26

content, lower sulfur content, and potentially lower GHG emissions [1, 21]. Triglycerides in ACS Paragon Plus Environment

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biomass are hydrogenated and broken down into free fatty acids (FFAs). The fatty acid

2

products are sent to deoxygenation steps, either through decarboxylation/decarbonylation

3

route or hydrodeoxygenation route to remove oxygen content in form of CO, CO2 or H2O.

4

Subsequently, the n-alkanes in the diesel range from C15 to C18, called bio-hydrogenated

5

diesel (BHD), are produced, in which had poorer cold flow properties and lubricity compared

6

to biodiesel [24]. In order to improve cold flow properties, the BHD should have high

7

branching isomers obtained from hydroisomerization reaction. To meet the jet fuel

8

specification with good cold flow properties, the hydrocracking and hydroisomerization of

9

BHD over bifunctional catalysts under elevated temperature and pressure is required to

10

produce HRJ fuel product with carbon chains ranging from C9 to C14 [1].

11

The hydrocracking and hydroisomerization of long chain paraffins have received

12

increasing attention in the last two decades. Many studies have been conducted to investigate

13

reaction mechanisms, kinetics, and the nature of bifunctional catalysts by using model

14

compound (e.g. n-heptane, n-octane, n-decane, n-hexadecane, n-heptadecane, n-octadecane)

15

[4, 10, 25 ̶ 33]. However, there is less research for investigating the hydrocracking and

16

hydroisomererization of real feedstocks from industry. Hence, in this work, the BHD,

17

comprised of the hydrocarbon in the range of C15 to C18, obtained from the local

18

hydroprocessing plant utilizing jatropha oils as feedstocks, was used to investigate the

19

reaction mechanism and develop a bifunctional catalyst giving a high jet fuel yield under

20

mild conditions. Bifunctional catalysts for this process are composed of metal sites for

21

hydrogenation/dehydrogenation function and acid sites for isomerization/cracking function.

22

Various metals (e.g. Pt, Pd, Ni, Mo) and different acidic supports, such as zeolites, SAPO,

23

sulphated zirconia and amorphous silica–alumina, have been employed [19, 29, 34, 35].

24

Fig. 1 illustrates the generalized reaction pathways of hydroisomerization and

25

hydrocracking of BHD (n-C15-C18) over bifunctional catalysts [31, 36-40]. The reactant as

26

n-alkanes, n-CiH2i+2 is dehydrogenated on metal sites to the mixture of n-alkenes, n-CiH2i,

27

and followed by desorption from metal sites and diffusion to Brønsted acid sites. The ACS Paragon Plus Environment


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formation of alkylcarbenium ions, n-Ci H+2i+1 as key intermediates are generated through

2

protonation of n-alkenes on Brønsted acid sites. On the other ways, the carbenium ions can be

3

produced via addition of protons to alkanes on Brønsted acid sites, and then dehydrogenation

4

of carbonium ions on metal sites. The formation rate of carbenium ions via Path A is much

5

faster than that via Path B. On Brønsted acid sites, alkenes and alkylcarbenium can undergo

6

competitive adsorption–desorption. Alkylcarbenium ions can either go through skeletal

7

rearrangements, or undergo cracking through β-scission. It is well known that if the rate

8

controlling elementary step is the rearrangements of carbenium ions on acid sites, the

9

formation of isomerized alkenes, iso-CiH2i, can be released and diffuse to metal sites where

10

they are hydrogenated to isomerized alkanes, n-CiH2i+2 [29, 36, 41, 42]. Therefore, the

11

formation of isomerized products can be considered as an indirect measurement of the acid

12

function activity. In the case of cracking by β-scission reactions, the fragments are a smaller

13

alkylcarbenium ion, Cj H+2j+1 and an alkene, C(i-j) H2(i-j) , which is immediately hydrogenated.

14

At Brønsted acid sites, monobranched isomers could convert to dibranched isomers in

15

consecutive reactions, and then dibranched isomers could convert to tribranched isomers.

16

Therefore, bifunctional catalysts for hydrocracking and hydroisomerization of BHD require

17

an appropriate combination of metallic sites for hydrogenation/dehydrogenation and acidic

18

sites of the support for isomerization/cracking for high jet fuel yield with good cold flow

19

properties.

20

In this work, the performances on the hydrocracking and hydroisomerization activity

21

and the selectivity to jet fuel with branched isomer content (C9 ̶ C14) and selectivity to

22

isomerized diesel (i-C15 ̶ C18) were investigated over Pt supported on different acidic

23

supports, such as HY zeolite and amorphous silica-alumina. The performance of the

24

hydrocracking and hydroisomerization of BHD to produce HRJ fuel depends on many factors

25

that affect their activity, selectivity, and stability. Thus, the influence of metal-acid balance,


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cidity of supports, reaction temperature, reaction pressure, contact time, and long-term

2

experiments were also studied.

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2. Experimental

5

2.1 Material

6

HY zeolites with SiO2/Al2O3 ratios of 5.5 and 100 were provided by Tosoh and the

7

amorphous silica-alumina with support grade of 135 (93.5 wt.% of SiO2 and 6.5 wt.% of

8

Al2O3) was supplied by Sigma–Aldrich. Tetraammineplatinum (II) chloride hydrate

9

(Pt(NH3)4Cl2.H2O, 99.99 % purity) was purchased from Sigma–Aldrich. The bio-

10

hydrogenated diesel (BHD) using jatropha oils as feedstock was obtained from PTT Public

11

Company Limited, Thailand. The compositions of BHD contained 56.28 wt.% of n-

12

octadecane (n-C18), 23.69 wt.% of n-heptadecane (n-C17), 14.25 wt.% of n-hexadecane (n-

13

C16), 4.38 wt.% of n-pentadecane (n-C15), and 1.4 wt.% of iso-paraffins (i-C15-18). The BHD

14

produced from jatropha oils had higher cetane number, higher heat of combustion (MJ/kg),

15

higher flash point, lower density, and poorer cold flow properties than the petroleum-based

16

diesel as shown in Table 1.

17

2.2 Catalyst preparation

18

The HY zeolites with SiO2/Al2O3 ratios of 5.5 and 100 denoted as HY(5.5) and

19

HY(100), respectively and the amorphous silica-alumina denotes as ASA were used as the

20

catalyst supports. Incipient wetness impregnation technique was used to prepare the Pt-

21

supported catalysts. Prior to Pt loadings, the support was dried in an oven at 120 ºC for 12 h and

22

calcined at 500 ºC with a heating rate of 10 °C/min for 3 h. Platinum was deposited using

23

volume of aqueous solutions corresponding to the total pore volume of the support, containing

24

the appropriate amounts of tetraammineplatinum (II) chloride hydrate (Pt(NH3)4Cl2.H2O) to

25

achieve the desired 0.5 wt.% Pt loadings. After impregnation, the prepared catalyst was dried ACS Paragon Plus Environment


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overnight at 120 °C and then calcined at 500 °C for 4 h with heating rate of 10 °C/min. All Pt-

2

supported catalysts were pelletized and subsequently crushed and sieved to particle size ranging

3

from 20 to 40 meshes.

4

2.2. Catalyst characterization

5

The textural properties and pore size distribution of the prepared catalysts were

6

determined by the nitrogen adsorption–desorption isotherm measured by Quantachrome/

7

Autosorb-1 MP instrument. The acid properties of the catalysts were characterized by

8

temperature programmed desorption of isopropylamine (IPA-TPD) and temperature

9

programmed desorption of ammonia (NH3-TPD). The IPA-TPD and NH3-TPD was

10

performed in a homemade apparatus using a quarter inch quartz tube reactor connected to an

11

online MS detector (MKS Cirrus series 903). The catalysts were heated under the process gas

12

(He or H2) at 500 °C for 1 h and cooled to room temperature. The IPA-TPD experiments

13

were carried out in the range of 30–800 °C at a ramp rate of 10 °C/min, whereas NH3-TPD

14

experiment was monitored at the range of 50–800 °C at a heating rate of 10 °C/min. The Pt

15

dispersion of the Pt-supported catalyst was observed by H2 chemisorption using an in-house

16

system connected to a thermal conductivity detector (TCD). The catalyst was reduced in H2

17

at 500 ºC for 1 h, purged with N2 for 1 h and cooled down to room temperature. The H2

18

chemisorption was performed at room temperature. It was supposed that the adsorption

19

stoichiometry was one H atom for one surface Pt atom. The Pt dispersion was given by the

20

total number of Pt atoms presented on the surface (Ns) divided by the total number of Pt

21

atoms (surface and bulk). The reducibility of Pt-supported catalysts was characterized by

22

temperature-programmed reduction (TPR) under a reducing gas containing 10% H2 in Ar

23

with a thermal conductivity detector (TCD). The temperature was raised from 30 to 800 °C

24

with a heating rate of 10 °C/min. The temperature-programmed oxidation (TPO) was

25

exploited to determine the amounts and characteristics of coke formed on the spent catalysts.

26

TPO was carried out in a continuous flow of 2% oxygen in helium. The oxidation ACS Paragon Plus Environment

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temperature was raised from 30 to 800 °C at a heating rate of 10 °C/min. The CO2 produced

2

by the oxidation of the coke species was converted to methane using a methanizer filled with

3

15% Ni/Al2O3 and operated at 400 ºC in the presence of H2. The evolution of methane was

4

analyzed using a flame ionization detector (FID).

5

2.3. Catalytic activity testing

6

The hydrocracking and hydroisomerization of BHD was tested by using a continuous

7

flow fixed-bed reactor (a 3/4 inch O.D, stainless steel). The catalyst was firstly reduced under

8

H2 flow at 500 °C for 3 h. The BHD was fed together with a H2 carrier at a flowrate giving a

9

molar ratio of H2/BHD of 30:1.The reaction was carried out at temperature of 290 ̶ 320 °C,

10

pressure of 400 ̶ 600 psig, and LHSV (liquid hourly space velocity) of 0.5 ̶ 2.0 h-1. The liquid

11

products were collected in a cold trap and analyzed by an Agilent 7890A gas chromatograph

12

equipped with a capillary DB-5HT column, while the gas products were analyzed online by a

13

Shimadzu GC-17A gas chromatograph equipped with a capillary HP-PLOT/Al2O3 "S"

14

deactivated column. Hydroprocessed renewable jet (HRJ) fuel (C9 ̶ C14) was separated from

15

liquid products using automatic distillation glass apparatus (B/R instrument) with ASTM

16

D86-12 test method. The freezing point of HRJ fuel was measured using ASTM D2386 test

17

method.



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3. Results and Discussion

2

3.1. Catalyst characterization

3

Fig. 2 shows the N2 adsorption–desorption isotherms of the unloaded ASA, HY (5.5)

4

and HY (100) supports and the corresponding Pt-supported catalysts and the pore size

5

distributions of these catalysts, determined from the desorption branch of isotherms using the

6

Barrett-Joyner-Halenda (BJH) method, are displayed in the insets of Fig. 2. The isotherm of

7

the HY (5.5) was assigned to type I in IUPAC classification, indicating the microporosity of

8

the materials containing cylindrical-narrow pores [43, 44]. As seen in the inset of Fig. 2a, the

9

pore size distribution of HY (5.5) was relatively narrow with centered at pore diameter less

10

than 2 nm, confirming the microporous structure. The isotherm of the HY (100) was assigned

11

to a combination of type I and type IV due to the formation of mesopores during

12

dealumination [45, 46]. As confirmed in the pore size distribution (inset of Fig. 2b), the high

13

amounts of micropores with centered at pore diameter less than 2 nm and low amounts of

14

mesopores with centered at pore diameter of 3.6 nm. The isotherm of the ASA was attributed

15

to type IV with the H2 hysteresis loop, indicating the characteristic of mesoporous material

16

consisting of conical and cylindrical pores that are closed at the tapered end [47, 48]. As

17

displayed in the inset of Fig. 2c, the ASA possessed pores in the range of 1 to 15 nm with

18

strong peaks at pore diameters of 1, 3.6 and 4.6 nm, confirming the formation of mesopores

19

and micropores. It was also found that the pore size distribution of the ASA was broader than

20

those of HY(100) and HY(5.5), respectively. After impregnation of the Pt on the acidic

21

supports, the N2 adsorption–desorption isotherms of Pt-supported catalysts were similar to

22

those of the corresponding supports, but their textural properties were slightly changed as

23

revealed in Table 2. Table 2 shows the textural properties of the unloaded acid supports and

24

the corresponding Pt-supported catalysts obtained from the N2 adsorption–desorption

25

isotherms such as total surface area, mesopore volume, micropore volume and total pore

26

volume. The HY (5.5) showed the higher surface area (SBET) and lower total pore volume ACS Paragon Plus Environment

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(Vtotal) than the HY (100) and ASA, respectively. After the Pt loadings, it can be obviously

2

seen that both surface area and total pore volume slightly decreased, indicating that the metal

3

species were supported in the pore channel and on the external surface of supports [49]. For

4

all Pt supported catalysts, the micropore and mesopore volumes decreased, probably caused

5

by some pore blockages of the incorporation of metal particles or a slight modification in the

6

porous structure in the second calcination [25].

7

The types and amounts of acid sites of the unloaded HY(5.5), HY(100) and ASA

8

supports and the corresponding Pt-supported catalysts determined by NH3-TPD and IPA-TPD

9

are summarized in Table 3. As shown in the NH3-TPD profiles in Fig. 3, both HY zeolite and

10

amorphous silica-alumina (ASA) exhibited two desorption peaks at low and high temperature

11

regions, corresponding to the weak and strong acid sites, respectively. These acid sites were

12

consisted of both types of Brønsted and Lewis acids [50–52]. It was found that the HY(5.5)

13

possessed higher numbers of weak and strong acidity than ASA and HY(100), respectively.

14

With increasing the SiO2/Al2O3 ratio of HY zeolite from 5.5 to 100, the desorption peaks of

15

both weak and strong acid sites were shifted to higher temperatures, indicating an increase in

16

the acid strength [53]. Meanwhile, the desorption peaks of ASA was located at lower

17

temperature than those of HY zeolite, suggesting that the ASA had the lower acidic strength

18

than HY zeolite. According to types of acidity, Brønsted acid site played an important role in

19

the hydrocracking and hydroisomerization reactions [33, 38, 41, 54, 55]. Generally, the

20

decomposition of isopropylamine (IPA) to ammonia (NH3) and propylene (C3H6) over

21

Brønsted acid sites via Hofmann elimination reaction can be used to estimate the quantity of

22

Brønsted acid sites [56]. The results revealed that the number of Brønsted acid sites increased

23

remarkably in the sequence: ASA < HY(100) < HY(5.5). After the Pt impregnation on the

24

supports, the Pt-supported catalysts had an acid feature similar to the corresponding supports,

25

but the acid strength slightly decreased. However, the number of Brønsted acid sites

26

significantly decreased, while the number of Lewis acid sites increased, leading to an ACS Paragon Plus Environment


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increase in the total acidity of the Pt-supported catalysts. This was because the Pt species

2

([Pt(NH3)4)]2+ ions) had high affinity for strong acid sites and thus covering the Brønsted acid

3

sites more than Lewis acid sites [19, 43, 51]. In addition, the coordinately unsaturated

4

platinum atoms could provide new Lewis acid centers, compensating for the original Lewis

5

acid sites covered by metal [51, 57].

6

The Pt dispersion of the catalysts determined from H2 chemisorption are listed in

7

Table 3. For the Pt-supported catalysts with the same Pt content (0.5 wt.%), the Pt dispersion

8

values were relatively dependent on the type of supports with different Brønsted acidity [19].

9

The results showed that the Pt dispersion increased remarkably in the order of Pt/ASA
Pt/HY(100) > Pt/HY(5.5),

15

indicating that the Pt/ASA had higher active metal site densities (higher capability for

16

hydrogenation and dehydrogenation) than the Pt/HY(100) and Pt/HY(5.5) catalysts,

17

respectively.

18

Fig. 4 shows the H2-TPR profiles for the calcined catalysts with different acidic

19

supports. It can be observed that Pt-supported catalysts exhibited two H2 consumption peaks,

20

corresponding to the reduction of Pt oxides (Pt2+) to the metallic state (Pt0). The first

21

reduction peaks at 100 ̶ 300 ºC were attributed to the reduction of large particle size of PtO

22

species located on the external surface which interacted relatively weakly with the support

23

[51, 60]. The second reduction peaks at 400 ̶ 580 ºC indicated the corresponding PtO species

24

were more difficult to reduce because the highly dispersed PtO (small particle size) interacted

25

strongly with the acidic supports and most possibly located in the internal pore [51, 61]. The

26

H2 consumption of second reduction peaks decreased in the following order: Pt/HY(5.5) > ACS Paragon Plus Environment

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Pt/HY(100) > Pt/ASA, suggesting that the Pt/HY(5.5) had higher well-dispersed Pt (smaller

2

Pt particles) and stronger metal-support interaction than Pt/HY(100) and Pt/ASA,

3

respectively.

4

3.2. Catalytic performance in hydrocracking and hydroisomerization of BHD over Pt-

5

supported catalysts

6

Table 4 shows the hydrocracking and hydroisomerization behavior of BHD (n-C15–

7

C18) over the unloaded HY(5.5), HY(100) and ASA and the corresponding Pt-supported

8

catalysts carried out at 310 ºC, 500 psig, and H2/BHD ratio of 30. The main products of

9

hydrocracking and hydroisomerization of BHD (n-C15–C18) over Pt-supported catalysts

10

were (1) isomerized diesel fuel (i-C15–C18) as a consequence of the isomerization reaction

11

controlled by the acid function and (2) cracked products consisted of normal and branched

12

hydrocarbons in the range of light gases (C1–C4), gasoline (C5–C8) and jet fuel (C9–C14),

13

resulting from cracking reaction partly controlled by the metal and acid functions. It was

14

found that all bare acid support catalysts exhibited relatively low conversion of BHD. This

15

could be explained that the carbenium ions were slowly formed in the absence of platinum

16

that had no hydrogenation/dehydrogenation function to facilitate the formation of carbenium

17

ions (as followed Path B in Fig. 1). In contrast, the Pt-supported catalysts exhibited

18

significantly high conversion of BHD which could be because the presence of Pt catalyzed

19

the dehydrogenation of the alkanes to alkenes, thus rapidly transform into carbenium ions.

20

The carbenium ions were ready to form isomers via skeletal rearrangements before cracking

21

on acid sites [62–64]. Moreover, a possible explanation of platinum’s superior performance

22

was its efficiency in hydrogen spillover phenomena, resulting in the generation of protonic

23

acid sites [65–69]. For the Pt-supported catalysts, the BHD conversion and selectivity to

24

cracked products tended to decrease in the following order; Pt/HY(5.5) > Pt/HY(100) >

25

Pt/ASA, consistent with the sequence of Brønsted acidity and Pt dispersion. This indicated

26

that the activities of the catalysts mainly depended on the Brønsted acid sites and Pt ACS Paragon Plus Environment


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1

dispersion. The larger number of Brønsted acid sites and higher Pt dispersion might cause

2

closer interaction between acid and metal sites, and then more carbenium ions were rapidly

3

generated. With the higher acid density, each carbenium ion came into contact with more acid

4

sites between two Pt sites (as seen in Fig. 5, Path II), leading to more cracked products

5

formation. As a result, the Pt/HY(5.5) catalyst with larger number of Brønsted acid sites and

6

higher Pt dispersion showed higher activity and selectivity to cracked products than the other

7

Pt-catalysts. On the other hand, the selectivity to isomerized products tended to increase in

8

the order of Pt/HY(5.5) < Pt/HY(100) < Pt/ASA and the balance between metal and acid

9

functions (nPt/nA) showed the same sequence over these catalysts. According to the reaction

10

pathways, the balance between metal and acid functions (nPt/nA) had an important influence

11

on the isomerization selectivity [33, 41, 51, 59, 70]. At the higher nPt/nA value of the Pt/ASA

12

catalyst with the higher hydrogenation/ dehydrogenation ability (Pt sites) or lower

13

isomerization/cracking ability (Brønsted acid sites), each carbenium ion formed at Pt

14

dehydrogenating site came into contact with very few Brønsted acid sites between two Pt

15

sites (as seen in Fig. 5, Path I). Thus, the hydrogenation and desorption of isomerized diesel

16

fuel (i-C15–C18) were favored and the consecutive cracking reaction of the carbenium ions

17

on the acid sites was suppressed, resulting in higher isomerized products [25, 29, 31, 36].

18

Another difference between these Pt-supported catalysts was the degree of branching in the

19

cracked products influenced by the balance between metal and acid functions (nPt/nA). As

20

seen in Table 4, the ratio between branched and linear hydrocarbons in cracked products

21

reached values of 2.34 and 2.03 for the Pt/HY(100) and Pt/HY(5.5) catalysts, respectively

22

and was three time lower for the Pt/ASA catalyst. According to the bifunctional mechanism,

23

as the weaker hydrogenation/ dehydrogenation function, carbenium ions went through the

24

successive skeletal rearrangements and spent longer time on the acid sites before being

25

hydrogenated, leading to an increase in the degree of branching. However, if the Brønsted

26

acid sites were excessive, the secondary cracking would increase, resulting in an increase in

27

light gases (C1–C4) and gasoline (C5–C8). This indicated that the Pt/HY(100) catalyst ACS Paragon Plus Environment

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1

possessed the well-balanced metal and acid function, resulting in high branching in cracked

2

products, high selectivity to jet fuel (C9–C14) and low selectivity to gasoline (C5–C8) and

3

light gases (C1–C4) as compared to other Pt-supported catalysts.

4

The catalytic behavior could also be described by considering at the carbon number

5

distribution of the cracked products. If the catalysts followed the bifunctional mechanism of

6

ideal hydrocracking catalyst (i.e. Pt/CaY), the carbon number distribution would be

7

symmetrical centered at C8 (hydrocracking of C16); no C1, C2, C14 or C15 should be

8

presented [38]; and only primary cracking products (C4–C12) as branched and linear

9

fragments were obtained, with a content of branched isomers amounting to ca. 50 % [71].

10

Fig. 6 displays the cracked product distribution per carbon atom for Pt-supported catalysts.

11

For all Pt-supported catalysts, no C1 and C2 were formed; C3 was only formed as a linear

12

fragment; and each higher cracked product between C4 and C14 was formed as two types,

13

which were linear and branched fragments in line with the cracking reaction through β-

14

scission (Fig. 7). Type A β-scission required a tribranched carbenium ion and produced two

15

branched fragments, whereas type B β-scission gave one branched and one linear fragment

16

obtained from dibranched carbenium ion. Type C β-scission occurred on monobranched

17

which gave two linear fragments. And type D β-scission, which would start from dibranched

18

carbenium ion to monobranched carbenium ion, probably did not play a role for

19

hydrocracking due to the high energy content of the monobranched carbenium ions involved

20

[38]. Thus, it was worth noting that the hydrocracking reaction via type D β-scission did not

21

take place for all Pt-supported catalysts, leading to no C1 and C2 formation [28, 38]. For the

22

Pt/HY(5.5) catalyst, the cracked products distribution per carbon atom was similar to bell-

23

shaped with a maximum at C8 and skewed toward the lower carbon number products. The

24

cracked products in the range of C5 – C12 were remarkably formed as a consequence of the

25

secondary cracking [30, 72]. The amount of branched fragments was higher than the amount

26

of linear fragments, suggesting that cracking reaction was favored via type A and type B β-

27

scission. However, with increasing SiO2/Al2O3 ratio (decreasing Brønsted acidity), the ACS Paragon Plus Environment


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1

cracked products distribution per carbon atom of Pt/HY(100) catalyst was a flatter bell-

2

shaped and skewed toward the higher carbon number products, which closed to an ideal

3

hydrocracking catalyst, implying well-balanced between metal and acid function [38, 73, 74].

4

The vast majority of hydrocarbon products were in the range from C6 to C13, indicating that

5

the secondary cracking of the primary fragments could be slightly occurred. In addition, the

6

high degree of branching of cracked products was obtained, suggesting that the

7

hydrocracking reaction tended to favor the type A and type B β-scission. The cracked product

8

distribution per carbon atom of Pt/ASA catalyst exhibited a lack of symmetry with a

9

maximum at C5 and was skewed to the lower carbon number products, which the formation

10

of cracked products in the range of C4 – C8 was much more pronounced, due to the presence

11

of secondary cracking. The amount of linear fragments was higher than the amount of

12

branched fragments, implying that type C β-scission could occur to some extent [41].

13

Fig. 8 shows the products yield consisting of cracked products, i.e. light gases (C1–

14

C4), gasoline (C5–C8), and jet fuel (C9–C14) with both linear and branched hydrocarbons,

15

and isomerized diesel (i-C15–C18). As a result, the yields of jet fuel and gasoline tended to

16

decrease in the following order: Pt/HY(5.5) > Pt/HY(100) > Pt/ASA and the yields of light

17

gases slightly decreased in the sequence of Pt/ASA > Pt/HY(5.5) > Pt/HY(100). On the other

18

hand, the yields of isomerized diesel significantly decreased in the order of Pt/HY(100) >

19

Pt/HY(5.5) > Pt/ASA. Thus, it was worth noting that the Pt/HY(100) catalyst was the most

20

suitable for hydrocracking and hydroisomerization of BHD, as it exhibited of high jet fuel

21

yield (ca. 33 wt.%) with large amount of branched isomers, leading to good cold flow

22

properties (freezing point = -47 ºC), while the yields of gasoline and light gases was

23

relatively low. The high yield of isomerized diesel was also obtained (ca. 34 wt.%).

24

To determine the formation and the amount of carbonaceous deposits, the spent

25

catalysts obtained after reaction (TOS of 8 h) were characterized by temperature programmed

26

oxidation (TPO). The TPO profiles and amount of coke deposits over the Pt-supported

27

catalysts are illustrated in Fig. 9 and listed in Table 3, respectively. The TPO profiles of the ACS Paragon Plus Environment

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1

unloaded acid catalysts gave the higher oxidation temperature than the bifunctional Pt-

2

supported catalysts, indicating the larger amount of hard-to-remove carbon (polyaromatic

3

compounds) in the absence of Pt. For the Pt supported on HY(5.5) and HY(100) catalysts,

4

both TPO profiles showed the same trend as pronounced a larger peak at 320 ºC with a

5

shoulder at 250 ºC, indicating that the soluble coke was formed by rearrangement and

6

condensation products and located on the metal, or metal and zeolite interface [75, 76], and

7

subsequently oxidized at low temperature (320 ºC). On the contrary, the TPO profile of the

8

Pt/ASA catalyst exhibited a small peak at 260 ºC, implying that a small amount of soluble

9

coke formed in mesopores of ASA support could be completely removed at 260 ºC [77]. As

10

shown in Table 3, the amount of coke tended to decrease in the following order: Pt/HY(5.5) >

11

Pt/HY(100) > Pt/ASA, corresponding to the activity and selectivity to cracked products in

12

hydrocracking and hydroisomerization of BHD.

13

3.3. Influence of reaction condition parameters

14

To investigate the effect of reaction conditions (i.e. temperature, pressure and liquid

15

hourly space velocity) on the hydrocracking and hydroisomerization performance and to

16

determine the optimal reaction condition for achieving high jet fuel yield, the Pt/HY(100)

17

catalyst was selected to use in a series of experiments under different operating conditions.

18

Fig.

10

shows

the

effect

of

temperature

on

the

hydrocracking

and

19

hydroisomerization behavior of BHD over Pt/HY(100) catalyst under the same reaction

20

conditions (H2 pressure = 500 psig, LHSV = 0.5 h-1, and H2/BHD molar ratio = 30 mL/mL).

21

With increasing the reaction temperature, the BHD conversion apparently increased up to

22

97% at 320 ºC and the selectivity to total cracked products also increased from 10 to 86 wt.%,

23

but the selectivity to isomerized diesel drastically decreased from 90 to 14 wt.%. In terms of

24

cracked products distribution, by increasing the temperature from 290 to 320 ºC, the

25

selectivity to light gases slightly increased from 0.1 to 3 wt.%, while the selectivity to

26

gasoline and jet fuel remarkably increased from 4 to 39 wt.% and from 5 to 44 wt.%, ACS Paragon Plus Environment


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1

respectively. This behavior could be explained by the thermodynamic equilibrium of

2

hydroisomerization reaction. At lower temperature, the equilibrium reaction might shift to the

3

side of isomerized diesel formation, on the other hand at higher temperature, the isomerized

4

alkylcarbenium ions might shift towards the consecutive cracking reaction [27, 63].

5

Additionally, the degree of branching in the cracked products (iso/normal ratio) increased

6

from 1 to 2.3 by increasing temperature from 290 to 310 ºC, and then decreased to 1.9 at 320

7

ºC. In line with the proposed transformation of alkylcarbenium ions through β-scission

8

reaction by Weitkamp et al. [32, 38], the increase in iso/normal ratio at the higher

9

temperature could be the consequence of more enhancements in the cracking rate through

10

type A- and type B β-scission reactions (Fig. 7). However, as the temperature increased up to

11

320 ºC the secondary and primary carbenium ions were increasingly cracked through type C-

12

and type D β-scission reactions (Fig. 7), leading to the decrease in iso/normal ratio. Yet,

13

despite the highest selectivity to jet fuel (C9–C14) obtained at 320 ºC, the highest selectivity

14

to light gases (C1–C4) and gasoline (C5–C8) were also obtained. In order to suppress the

15

excess of light hydrocarbon products and achieve the desired products; jet fuel and

16

isomerized diesel, the reaction temperature at 310 ºC was determined to be the optimum

17

temperature for further investigation.

18

Since the optimum reaction temperature for the high BHD conversion and selectivity

19

to jet fuel was found at 310 ºC, the effect of pressure was studied from 400 to 600 psig at this

20

temperature. As depicted in Fig. 11, with increasing hydrogen pressure, the BHD conversion

21

was slightly decreased from 95 to 84 % and the selectivity to jet fuel, gasoline and light gases

22

was also decreased. In contrast, the increase of hydrogen pressure led to reduce the selectivity

23

to isomerized diesel due to a decrease in the hydroisomerization reaction rate [78]. This

24

behavior could be plausibly explained by considering the bifunctional mechanism as shown

25

in Fig. 1. At high hydrogen pressure, the iso-alkenes (i-Ci H+2i+1) could be rapidly

26

hydrogenated to iso-alkanes (i-Ci H2i+2) on the Pt sites, which could be due to a shorter

27

residence time for rearrangement and cracking of alkylcarbenium ion on the acid sites, and ACS Paragon Plus Environment

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1

thus suppressing the cracking activity [4, 19, 79]. Although the highest selectivity to jet fuel

2

was obtained at 400 psig, the lowest degree of branching in cracked products (iso/normal

3

ratio) was attained, leading to poor cold flow properties of the liquid hydrocarbon products.

4

However, the choice of a high operating pressure offers disadvantages for industrial operation

5

in terms of higher cost of equipment and pumping, compared with low pressure processes.

6

Therefore, the optimum reaction pressure at 450 psig was selected for further investigation.

7

The effect of varying the LHSV from 0.5 to 2.0 h-1 on product distribution and

8

conversion was investigated. The hydrocracking and hydroisomerization of BHD (n-C15-18)

9

were carried out at 310 ºC, 450 psig, and H2/BHD molar ratio of 30. As observed in Fig. 12,

10

with increasing LHSV the BHD conversion and selectivity to cracked products decreased

11

while the selectivity to isomerized products increased. Similar results were also reported by

12

Chica and Corma [80], when the hydroisomerization of n-C5, n-C6 and n-C7 over platinum-

13

loaded different zeolite supports was investigated. In terms of product distribution, it was

14

found that the selectivity to jet fuel, gasoline and light gases significantly increased as LHSV

15

decreased. The highest degree of branching in cracked products (iso/normal ratio) was

16

obtained at LHSV of 1 h-1. Therefore, LHSV of 1.0 h-1 was chosen for stability testing.

17

3.4. Stability testing of Pt/HY(100) catalyst

18

The catalytic stability testing over the Pt/HY(100) catalyst were conducted in a long-

19

term operation of 160 h. The reaction was conducted under the optimal operation conditions

20

of 310 ºC, 450 psig, H2/BHD molar ratio of 30, and LHSV of 1.0 and 4.0 h-1. Fig. 13

21

illustrates the BHD conversion and the products distribution as a function of the time on

22

stream (TOS). These results in both high and low conversions show that the BHD conversion

23

and selectivity to jet fuel did not significantly change over the 160 h of the experiments,

24

indicating high stability of the Pt/HY(100) catalyst. In terms of coke formation, the amounts

25

of coke deposit as a function of time on stream (TOS) were investigated. The amounts of

26

coke after 1, 3, 8, and 160 h were 8.8, 9.1, 9.3, and 12.8%, respectively. It can be noticed that ACS Paragon Plus Environment


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1

the coke deposit rapidly formed at the first 1 h due to the high activity of the fresh catalyst.

2

However, after 1 h, the amounts of coke slightly increased which correlated well with the

3

catalytic activity.

4 5

4. Conclusions

6

To produce the hydroprocessed renewable jet (HRJ) fuel with good cold flow

7

properties, the hydrocracking and hydroisomerization of the bio-hydrogenated diesel (BHD)

8

derived from jatropha oils was performed over Pt supported different acid supports (i.e. HY

9

zeolite and amorphous silica-alumina). The Pt/HY(100) catalyst exhibited the well-dispersed

10

Pt particles, the large amount of Brønsted acid sites and the well balance between metal and

11

acid functions, leading to the high activity in hydrocracking and hydroisomerization of BHD

12

and high yield of jet fuel consisting of high branched isomers, resulting in good cold flow

13

properties (freezing point = -47 ºC). In addition, the effects of temperature, pressure, and

14

liquid hourly space velocity (LHSV) on the hydrocracking and hydroisomerization behavior

15

over the Pt/HY(100) catalyst were investigated. The maximum yield of jet fuel was 33 wt.%

16

achieved at 310 °C, 450 psig, and LHSV of 1.0 h-1. The Pt/HY(100) catalyst was found to be

17

stable for hydrocracking and hydroisomerization of BHD during the reaction time of 160 h,

18

which was suitable for in the commercial scale.

19 20

Acknowledgements

21

The authors acknowledge the contributions and financial support of the following

22

organizations: the Thailand Research Fund through the Royal Golden Jubilee Ph.D. Program

23

(Grant No. PHD/0262/2553), the Center of Excellence on Petrochemical and Materials

24

Technology, and the Petroleum and Petrochemical College, Chulalongkorn University.

25

Moreover, the authors would like to thank PTT Public Company Limited, Thailand for partial

26

research funding. ACS Paragon Plus Environment

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Wang, W. -C. Techno-economic analysis of a bio-refinery process for producing Hydro-processed Renewable Jet fuel from Jatropha. Renew. Energ. 2016, 95, 63–73.

[2]

Diederichs, G. W.; Ali Mandegari, M.; Farzad, S.; Görgens, J. F. Techno-economic comparison of biojet fuel production from lignocellulose, vegetable oil and sugar cane juice. Bioresour. Technol. 2016, 216, 331–339.

[3]

Hwang, K.-R.; Choi, I.-H.; Choi, H.-Y.; Han, J.-S.; Lee, K.-H.; Lee, J.-S; Bio fuel production from crude Jatropha oil; addition effect of formic acid as an in-situ hydrogen source. Fuel. 2016, 174, 107–113.

[4]

Rossetti, I.; Gambaro, C.; Calemma, V. Hydrocracking of long chain linear paraffins. Chem. Eng. J. 2009, 154, 295–301.

[5]

Liu, G.; Yan, B.; Chen, G. Technical review on jet fuel production. Renew. Sust. Energ. Rev. 2013, 25, 59–70.

[6]

Wang, J.; Bi, P.; Zhang, Y.; Xue, H.; Jiang, P.; Wu, X.; Liu, J.; Wang, T.; Li, Q. Preparation of jet fuel range hydrocarbons by catalytic transformation of bio-oil derived from fast pyrolysis of straw stalk. Energy. 2015, 86, 488–499.

[7]

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[10] Bezergianni, S.; Voutetakis, S.; Kalogianni, A. Catalytic hydrocracking of fresh and used cooking oil. Ind. Eng. Chem. Res. 2009, 48, 8402–8406. [11] Gong, S.; Shinozaki, A.; Shi, M.; Qian, E. W. Hydrotreating of Jatropha Oil over Alumina Based Catalysts. Energy & Fuels. 2012, 26, 2394–2399. [12] Bezergianni, S.; Kalogianni, A.; Vasalos, I. A. Hydrocracking of vacuum gas oilvegetable oil mixtures for biofuels production. Bioresour. Technol. 2009, 100, 3036– 3042. [13] Wang, H.; Yan, S.; Salley, S. O.; Ng, K. Y. S. Hydrocarbon fuels production from hydrocracking of soybean oil using transition metal carbides and nitrides supported on ZSM-5. Ind. Eng. Chem. Res. 2012, 51, 10066–10073. ACS Paragon Plus Environment


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[27] Calemma, V.; Peratello, S.; Perego, C. Hydroisomerization and hydrocracking of long chain n-alkanes on Pt/amorphous SiO2–Al2O3 catalyst. Appl. Catal. A: Gen. 2000, 190, 207–218. [28] Regali, F.; Liotta, L. F.; Venezia, A. M.; Montes, V.; Boutonnet, M.; Järås, S. Effect of metal loading on activity, selectivity and deactivation behavior of Pd/silica–alumina catalysts in the hydroconversion of n-hexadecane. Catal. Today. 2014, 223, 87–96. [29] Lanzafame, P.; Perathoner, S.; Centi, G.; Heracleous, E.; Iliopoulou, E. F.; Triantafyllidis, K. S.; Lappas, A. A. Effect of the structure and mesoporosity in Ni/Zeolite catalysts for n-hexadecane hydroisomerisation and hydrocracking. ChemCatChem. 2017, 9, 1632–1640. [30] Kang, J.; Ma, W.; Keogh, R. A.; Shafer, W. D.; Jacobs, G.; Davis, B. H. Hydrocracking and hydroisomerization of n-hexadecane, n-octacosane and Fischer–Tropsch wax over a Pt/SiO2–Al2O3 catalyst. Catal. Lett. 2012, 142, 1295–1305. [31] Park, K.-C.; Ihm, S.-K. Comparison of Pt/zeolite catalysts for n-hexadecane hydroisomerization. Appl. Catal. A: Gen. 2000, 203, 201–209. [32] Weitkamp, J., Jacobs, P. A., Martens, J. A. Isomerization and hydrocracking of C9 through C16 n-alkanes on Pt/HZSM-5 zeolite. Applied Catalysis. 1983, 8, 123–141. [33] Alvarez, F., Ribeiro, F. R., Perot, G., Thomazeau, C., Guisnet, M. Hydroisomerization and hydrocracking of Alkanes: 7. Influence of the balance between acid and hydrogenating functions on the transformation of n-decane on PtHY catalysts. J. Catal. 1996, 162, 179–189.

[34] Akhmedov, V. M., Al‐Khowaiter, S. H. Recent advances and future aspects in the selective isomerization of high n-alkanes. Catal. Rev. 2007, 49, 33–139. [35] Ling, H., Wang, Q., Shen, B.-x. Hydroisomerization and hydrocracking of hydrocracker bottom for producing lube base oil. Fuel Process. Technol. 2009, 90, 531–535. [36] Corma, A., Martinez, A., Pergher, S., Peratello, S., Perego, C., Bellusi, G. Hydrocracking-hydroisomerization of n-decane on amorphous silica-alumina with uniform pore diameter. Appl. Catal. A: Gen. 1997, 152, 107–125. [37] Guisnet, M. Ideal bifunctional catalysis over Pt-acid zeolites. Catal. Today. 2013, 218, 123–134. [38] Weitkamp, J. Catalytic hydrocracking—mechanisms and versatility of the process. ChemCatChem. 2012, 4, 292–306. [39] Girgis, M. J.; Tsao, Y. P. Impact of catalyst metal−acid balance in n-hexadecane hydroisomerization and hydrocracking. Ind. Eng. Chem. Res. 1996, 35, 386–396. ACS Paragon Plus Environment


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[62] Chu, H. Y.; Rosynek, M. P.; Lunsford, J. H. Skeletal isomerization of hexane over Pt/H-beta zeolites: Is the classical mechanism correct? J. Catal. 1998, 178, 352–362. [63] Wang, Z. B.; Kamo, A.; Yoneda, T.; Komatsu, T.; Yashima, T. Isomerization of nheptane over Pt-loaded zeolite β catalysts. Appl. Catal. A: Gen. 1997, 159, 119–132. [64] Chao, K.-J.; Lin, C.-C.; Lin, C.-H.; Wu, H.-C.; Tseng, C.-W.; Chen, S.-H. n-Heptane hydroconversion on platinum-loaded mordenite and beta zeolites: the effect of reaction pressure. Appl. Catal. A: Gen. 2000, 203, 211–220. [65] Pajonk, G. M. Contribution of spillover effects to heterogeneous catalysis. Appl. Catal. A: Gen. 2000, 202, 157–169. [66] Pope, T. D.; Kriz, J. F.; Stanciulescu, M.; Monnier, J. A study of catalyst formulations for isomerization of C7 hydrocarbons. Appl. Catal. A: Gen. 2002, 233, 45–62. [67] Li, W.; Chi, K.; Liu, H.; Ma, H.; Qu, W.; Wang, C.; Lv, G.; Tian, Z. Skeletal isomerization of n-pentane: A comparative study on catalytic properties of Pt/WOx– ZrO2 and Pt/ZSM-22. Appl. Catal. A: Gen. 2017, 537, 59–65. [68] Karthikeyan,

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Hydroisomerization of n-octane over bifunctional Ni−Pd/HY zeolite catalysts. Ind. Eng. Chem. Res. 2008, 47, 6538–6546. [69] Mendes, P. S. F.; Lapisardi, G.; Bouchy, C.; Rivallan, M.; Silva, J. M.; Ribeiro, M. F. Hydrogenating activity of Pt/zeolite catalysts focusing acid support and metal dispersion influence. Appl. Catal. A: Gen. 2015, 504, 17–28. [70] Iliopoulou, E. F.; Heracleous, E.; Delimitis, A.; Lappas, A. A. Producing high quality biofuels: Pt-based

hydroisomerization catalysts

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surrogates. Appl. Catal. B: Env. 2014, 145, 177–186. [71] Weitkamp, J. The influence of chain length in hydrocracking and hydroisomerization of n-alkanes, Hydrocracking and Hydrotreating. 1975, 1–27. [72] Corma, A.; Orchillés, A. V. Current views on the mechanism of catalytic cracking. Microporous Mesoporous Mater. 2000, 35, 21–30. [73] Rezgui, Y.; Guemini, M. Effect of acidity and metal content on the activity and product selectivity for n-decane hydroisomerization and hydrocracking over nickel–tungsten supported on silica–alumina catalysts. Appl. Catal. A: Gen. 2005, 282, 45–53. [74] Galperin, L. B.; Bradley, S. A.; Mezza, T. M. Hydroisomerization of n-decane in the presence of sulfur. Appl. Catal. A: Gen. 2001, 219, 79–88. [75] Kim, S.; Sasmaz, E.; Lauterbach, J. Effect of Pt and Gd on coke formation and regeneration during JP-8 cracking over ZSM-5 catalysts. Appl. Catal. B: Env. 2015, 168–169, 212–219. ACS Paragon Plus Environment

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38 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 captions

Table 1

Properties of bio-hydrogenated diesel (BHD) derived from jatropha oils (Jatropha-BHD) compared to specification of conventional diesel limits.

Table 2

Textural properties of the unloaded HY(5.5), HY(100) and ASA and the corresponding Pt-supported catalysts.

Table 3

Quantities of acid, metal coke over the unloaded HY(5.5), HY(100) and ASA and the corresponding Pt-supported catalysts.

Table 4

Catalytic performance in hydrocracking and hydroisomerization of BHD over the monofunctional acid catalysts and bifunctional Pt-supported catalysts. Reaction conditions: T = 310 ºC, P = 500 psig, LHSV= 1.0 h-1, H2/BHD = 30, and TOS = 8.

Figure captions

Figure 1

Classical bifunctional pathways of hydroisomerization and hydrocracking of an n-alkane on Pt supported catalysts..

Figure 2

N2 adsorption–desorption isotherms of the unloaded supports and the corresponding Pt-supported catalysts: (a) HY(5.5) and Pt/HY(5.5), (b) HY(100) and Pt/HY(100), and (c) ASA and Pt/ASA (Insets are pore size distribution).Figure 3 TPR profiles of (a) HY-based catalysts and (b) ASAbased catalysts.

Figure 3

NH3-TPD profiles of the unloaded HY(5.5), HY(100) and ASA supports and the corresponding Pt-supported catalysts:

Figure 4

TPR profiles of Pt-supported catalysts.

Figure 5

Scheme of hydrocracking and hydroisomerization of BHD over Pt-supported catalysts. ACS Paragon Plus Environment

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39 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 6

Cracked products distribution per carbon number of Pt-supported catalysts: (a) Pt/HY(5.5) (b) Pt/HY(100) and (c) Pt/ASA. Reaction conditions: 310 ºC, 500 psig, LHSV of 1.0 h-1, H2/BHD molar ratio of 30, and TOS of 8 h.

Figure 7

Classification of β-scission reaction of alkylcarbenium ions

Figure 8

Products distribution in fuel range hydrocarbons, comprising light gases (C1 ̶ C4), gasoline (C5 ̶ C8), and jet fuel (C9 ̶ C14) over Pt-supported catalysts Reaction conditions: 310 ˚C, 500 psig, LHSV of 1.0 h-1, H2/BHD molar ratio of 30, and TOS of 8 h.

Figure 9

TPO profiles of the spent catalysts after TOS of 8 h:

Figure 10

Effect of temperature on BHD conversion and products distribution in fuel range hydrocarbons over Pt/HY(100) catalyst. Reaction condition: 500 psig, LHSV of 1.0 h-1, H2/BHD molar ratio of 30, and TOS of 8 h.

Figure 11

Effect of pressure on BHD conversion and products distribution in fuel range hydrocarbons over Pt/HY(100) catalyst. Reaction condition: 310 ºC, LHSV of 1.0 h-1, H2/BHD molar ratio of 30, and TOS of 8 h.

Figure 12

Effect of LHSV on BHD conversion and products distribution in fuel range hydrocarbons over Pt/HY(100) catalyst. Reaction condition: 310 ºC, 450 psig, H2/BHD molar ratio of 30, and TOS of 8 h.

Figure 13

BHD conversion and the distribution of fuel range hydrocarbon products as a function of the time on stream (TOS) over Pt/HY(100) catalyst: (a) High conversion at LHSV of 1.0 h-1 and (b) Low conversion at LHSV of 4.0 h-1 Reaction condition: 310 ºC, 450 psig, and H2/BHD molar ratio of 30.



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40 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 1

Properties of bio-hydrogenated diesel (BHD) derived from jatropha oils (Jatropha-BHD) compared to specification of conventional diesel limits.

Properties

Unit

Paraffinic

EU’s Conventional

Thailand’s

Diesel Limit

Diesel Limit

Limit

(EN 15940)

(EN 590)

(EN 14214)

Jatropha-BHD

Density at 15 °C

kg/m3

765 –800

800 –845

810-870

786

Viscosity at 40 °C

mm2/s

2.0 - 4.5

2.0 - 4.5

1.8 - 4.1

3.3

Color

-

-

-

Red

no color

Cetane index

-

-

> 46

> 50 (2012)

111.6

Flash point

°C

> 55

> 55

> 52

124

Pour point

°C

-

-

< 10

26

MJ/kg

-

-

45,968

47,354

Lower heating value


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41 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

Textural properties of the unloaded HY(5.5), HY(100) and ASA and the corresponding Ptsupported catalysts. SBET

Vtotal

Amicro

Vmicro

Ameso

Vmeso

(m2/gcat)

(cm3/gcat)

(m2/gcat)

(cm3/gcat)

(m2/gcat)

(cm3/gcat)

HY(5.5)

572

0.36

471

0.34

101

0.02

Pt/HY(5.5)

553

0.34

454

0.33

99

0.01

HY(100)

656

0.48

468

0.35

188

0.13

Pt/HY(100)

612

0.44

441

0.32

171

0.12

ASA

495

0.70

140

0.19

355

0.51

Pt/ASA

488

0.64

135

0.18

352

0.46

Catalyst



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42 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 3

Quantities of acid, metal dispersion and coke formation over the unloaded HY(5.5), HY(100) and ASA and the corresponding Pt-supported catalysts. Total acidity

Acidity (µmol/g)

Pt dispersion

nPt/nA

% Coke

(µmol/g)

Brønsteda Lewisb

(%)c

(mol/mol)

(wt.%)d

Catalyst

HY(5.5)

703

227

476

-

-

7.5

Pt/HY(5.5)

746

134

612

65.3

0.12

15.1

HY(100)

189

85

104

-

-

3.5

Pt/HY(100)

243

58

185

56.3

0.25

9.3

ASA

574

49

525

-

-

0.8

Pt/ASA

716

28

688

31.2

0.29

1.0

a

Brønsted acidity was determined from IPA-TPD (propylene, m/e = 41).

b

Lewis acidity was calculated from the difference of total acidity (from NH3-TPD) and Brønsted acidity.

c

Metal disperstion was measured by H2 chemisorption.

d

Coke content was obtained from TPO after catalytic activity test at 8 h.


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Table 4

Catalytic performance in hydrocracking and hydroisomerization of BHD over the monofunctional acid catalysts and bifunctional Pt-supported catalysts. Reaction conditions: T = 310 ºC, P = 500 psig, LHSV= 1.0 h-1, H2/BHD = 30, and TOS = 8 h. Conversion

Selectivity (wt.%)

Iso/normal ratio

Catalyst (%)

HY(5.5)

Cracked products Isomerized products in cracked products

9.6

72.2

27.8

1.14

93.2

75.6

24.4

2.03

5.1

75.7

24.3

0.54

Pt/HY(100)

90.6

62.8

37.2

2.34

ASA

13.3

87.7

12.3

0.52

Pt/ASA

69.9

52.0

48.0

0.90

Pt/HY(5.5) HY(100)



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44 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

Fig. 1. Classical bifunctional pathways of hydroisomerization and hydrocracking of an nalkane on Pt supported catalysts.


Page 35 of 46 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


(a)

(b)

(c)

Fig. 2. N2 adsorption-desorption isotherms of the unloaded supports and the corresponding Pt-supported catalysts: (a) HY(5.5) and Pt/HY(5.5), (b) HY(100) and Pt/HY(100), and (c) ASA and Pt/ASA (Insets are pore size distribution).



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Fig. 3. NH3-TPD profiles of the unloaded HY(5.5), HY(100) and ASA supports and the corresponding Pt-supported catalysts.


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Fig. 4. TPR profiles of Pt-supported catalysts.



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Fig. 5. Scheme of hydrocracking and hydroisomerization of BHD over Pt-supported catalysts.


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Fig. 6. Cracked products distribution per carbon number of Pt-supported catalysts: (a) Pt/HY(5.5), (b) Pt/HY(100) and (c) Pt/ASA. Reaction conditions: 310 ºC, 500 psig, LHSV of 1.0 h-1, H2/BHD molar ratio of 30, and TOS of 8 h. ACS Paragon Plus Environment


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50 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

Fig. 7. Classification of β-scission reaction of alkylcarbenium ions.


Page 41 of 46


51 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

Fig. 8. Products distribution in fuel range hydrocarbons, comprising light gases (C1 ̶ C4), gasoline (C5 ̶ C8), and jet fuel (C9 ̶ C14) over Pt-supported catalysts Reaction conditions: 310 ºC, 500 psig, LHSV of 1.0 h-1, H2/BHD molar ratio of 30, and TOS of 8 h.



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52 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

Fig. 9. TPO profiles of the spent catalysts after TOS of 8 h.


Page 43 of 46


53 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

Fig. 10. Effect of temperature on BHD conversion and products distribution in fuel range hydrocarbons over Pt/HY(100) catalyst. Reaction condition: 500 psig, LHSV of 1.0 h-1, H2/BHD molar ratio of 30, and TOS of 8 h.



Page 44 of 46

54 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

Fig. 11. Effect of pressure on BHD conversion and products distribution in fuel range hydrocarbons over Pt/HY(100) catalyst. Reaction condition: 310 ºC, LHSV of 1.0 h-1, H2/BHD molar ratio of 30, and TOS of 8 h.


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55 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

Fig. 12.

Effect of LHSV on BHD conversion and products distribution in fuel range

hydrocarbons over Pt/HY(100) catalyst. Reaction condition: 310 ºC, 450 psig, H2/BHD molar ratio of 30, and TOS of 8 h.



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(a)

(b)

Fig. 13. BHD conversion and the distribution of fuel range hydrocarbon products as a function of the time on stream (TOS) over Pt/HY(100) catalyst: (a) High conversion at LHSV of 1.0 h-1 and (b) Low conversion at LHSV of 4.0 h-1 Reaction condition: 310 ºC, 450 psig, and H2/BHD molar ratio of 30.


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