Upgrading Of Wasteplasticsderived Heavy Oil Over Catalysts

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In the series described thus far, it was found that the degradation of waste plastics proceeds efficiently by both thermal pyrolysis and hydrolysis in a steam atmosphere. A wax and carbonaceous residue produced by the hydrolysis of PET are decomposed by reaction with steam over an FeOOH catalyst, the activity of which remains stable in a steam atmosphere. However, the liquid product from generated from the process mentioned above contains a large amount of heavy oil, as shown in Figure 6.10. Both catalysts and chemical processes are required for efficiently upgrading the quality of the heavy oil.

3.1 CATALYTIC CRACKING OF HEAVY OIL OVER SOLID-ACID CATALYSTS

The most widely used conventional chemical methods are pyrolysis [21-25] and catalytic cracking [13, 26-30]. The latter yields products with a smaller range of carbon numbers and of a higher quality than products generated by the former method. Several types of solid acid catalysts, which are known to be effective for catalytic cracking (e.g. HZSM-5, HY and rare earth metal-exchanged Y-type (REY) zeolite and silica-alumina (SA)) were evaluated by catalyst screening tests and are listed in Table 6.1. The acidic

1 1

1 1 C20+

Feedstock: PE/PET = 15/2

-

- Catalyst: FeOOH

W/F = 1 h

T= 500

. 1 1 1 1 1 . . 1 1

51 0 15 20

Carbon number / -

51 0 15 20

Carbon number / -

Table 6.1 Properties of the catalysts. (Reproduced with permission from Elsevier)

Properties

Catalyst

REY

HY

Silica-alumina

HZSM-5

HZSM-5

(SA)

(65)

(1000)

Si/Al

4.8

4.8

13%

65

1000

alumina

Pore size (A)

7.4

7.4

60-100

5.3x5.6

5.3x5.6

Amount of total

acid sitesb

1.048

1.207

0.560

0.235

0.067

[mol ■ kg-cat-1]

Amount of strong

acid sitesc

0.375

0.441

0.187

0.122

0.031

[mol ■ kg-cat-1]

Supercage

Yes (11.8A)

Yes (11.8A)

No

No

No

a Measured by conventional TPD experiment b Based on the total amount of ammonia desorbed in the TPD experiment c Based on the amount of ammonia desorbed above 300°C in the TPD experiment a Measured by conventional TPD experiment b Based on the total amount of ammonia desorbed in the TPD experiment c Based on the amount of ammonia desorbed above 300°C in the TPD experiment properties of the catalysts were measured from the temperature-programmed desorption spectra of ammonia (NH3-TPD) method. The feed oil was obtained by the pyrolysis of solid polyethylene plastics at 450°C. To ensure homogeneity and to remove the lighter hydrocarbons, the oil was distilled at 473 K. Table 6.2 shows the results of the elementary analysis of the oil, which was used as a feed oil in the catalytic reforming reaction. A continuous-flow, fixed-bed reactor was utilized for the catalytic reforming of the oil. The reaction was carried out at 400°C under a nitrogen stream. The oil was fed at a constant weight hourly space velocity (WHSV) of 1.0 kg-oilkg-cat-1h-1 for all catalysts.

Figure 6.11 shows the product yields for each catalyst. The products are classified into four lumps, i.e. gas (carbon number 1-4), gasoline (5-11), heavy oil (above 12), and a carbonaceous residue referred to as coke. In the figure, PE oil represents the feed oil and contains a 34% gasoline fraction. The feed oil was effectively cracked by solid acid catalysts. The gasoline yield was highest with REY zeolite. HZSM-5(65) yielded the

Table 6.2 Analysis of the feed oil. (Reproduced by permission of the American Chemical Society)

wt%

mol%

Heavy oil (>CJ2)

95

Gasoline (C5-Cn)

5

Elemental analysis

H

13.7

66.0

C

82.0

32.9

N

0.0

0.0

O

4.3

1.1

H/C

2.00

SILICA ALUMINA

HZSM-5(1000)

HZSM-5(65)

PR OIL

0 20 40 60 80 100

Figure 6.11 Distribution of product yields under nitrogen. WHSV = 1, T = 400°C and t= 3 h. (Reproduced with permission from Elsevier)

largest quantity of gaseous compounds and the lowest amount of gasoline, which was even lower than the gasoline fraction in the feed oil. While coke loading was highest with HY zeolite, both HZSM-5 zeolites generated a negligibly small amount of coke deposition. As the amount of coke deposition increased, the catalytic activity decreased.

Table 6.3 summarizes the yield of gaseous products according to the carbon number. In this table, C2 = to C5 = indicate olefins corresponding to their respective carbon numbers.

Table 6.3 Yield of each gaseous product according to carbon number. The values in brackets refer to the corresponding olefins. (Reproduced with permission from Elsevier)

Catalyst

Table 6.3 Yield of each gaseous product according to carbon number. The values in brackets refer to the corresponding olefins. (Reproduced with permission from Elsevier)

Catalyst

Carbon

REY

HY

Silica-alumina

HZSM-5

HZSM-5

Number

(SA)

(65)

(1000)

C1

0.09

0.20

0.07

0.12

0.01

C2

0.76

1.39

0.23

6.32

0.43

(C2=)

(0.69)

(1.39)

(0.17)

(6.01)

(0.40)

C3

7.71

9.85

7.99

30.92

11.00

(C3=)

(5.85)

(3.25)

(6.91)

(29.90)

(11.00)

C4

16.28

20.50

17.35

23.80

14.21

(C4=)

(12.22)

(15.51)

(11.24)

(13.78)

(8.27)

C5

6.60

9.23

3.51

3.84

5.62

(C5=)

(0.0)

(0.0)

(2.30)

(1.80)

(1.52)

C6

2.81

1.55

0.06

1.48

1.09

C7

1.23

1.02

0.0

0.62

0.41

C8

0.40

0.46

0.0

0.14

0.75

Total yield, (wt%)

35.88

44.20

29.20

69.04

HZSM-5(1000)

HZSM-5(65)

PR OIL

0 20 40 60 80 100

Figure 6.11 Distribution of product yields under nitrogen. WHSV = 1, T = 400°C and t= 3 h. (Reproduced with permission from Elsevier)

A significant amount of C3-C5 gaseous compounds were produced. With the exception of ZSM-5(65) zeolite which favored the production of the C3 fraction, the other catalysts yielded C4 as the main component.

HZSM-5 zeolite has channels within its crystals. The size of the channel is nearly equal to that of benzene and is too small for easy penetration by oil molecules. Hence, the ends of only certain molecules can penetrate the channels and undergo cracking. This leads to a higher yield of gaseous products and a lower gasoline yield, indicating that HZSM-5 zeolite is not suitable for the cracking reaction of heavy oil. In contrast, the HY and REY zeolites have larger pores. Therefore, the oil molecules can penetrate into the pores and undergo cracking. Moreover, the existence of rare earth metals in REY zeolite results in a decrease in the amount of stronger acid sites (see Table 6.1). This in turn leads to a reduction in the deactivation rate and the amount of coke loading in comparison with that obtained with HY zeolite. Accordingly, REY zeolite has the proper acidic properties and pore size, and is suitable for the reaction with heavy oil.

3.2 PRODUCTION OF HIGH-QUALITY GASOLINE OVER REYZEOLITES

The effects of the reaction conditions and the catalytic properties of REY zeolites on reaction product yields and on the quality of the gasoline can now be examined.

Four types of REY zeolite (Si/Al = 4.8) with different crystal sizes and acidic properties were used. The physical and chemical properties of the fresh zeolites are given in Table 6.4. Polyethylene plastics-derived heavy oil, shown in Table 6.2, was used as the feed oil. The cracking reaction was conducted in a tubular reactor filled with catalyst particles under the following conditions: time factor W/F = 0.2-3.0 kg-cat kg oil-1 h-1 and reaction temperature = 300-450°C. The lumping of reaction products were gas (carbon number 1-4), gasoline (5-11), heavy oil (above 12), and a carbonaceous residue referred to as coke. The index of the gasoline quality used was the research octane number (RON), which was calculated from Equation 6.1 [31].

RON = —1.0729Ynp2 + 0.7875YIP1 + 0.09787^2 + 0.3395YCP + 0.4049YAR + 69.0306

Table 6.4 Physical and chemical properties of the fresh REY zeolites. (Reproduced by permission of the American Chemical Society)

Catalyst

Table 6.4 Physical and chemical properties of the fresh REY zeolites. (Reproduced by permission of the American Chemical Society)

Catalyst

Property

REY-1

REY-2

REY-3

REY-4

Si/Al

4.8

4.8

4.8

4.8

Crystal size (^m)

0.1

1.0

0.1

0.1

Amount of total acid sitesa

2.91

2.44

2.99

2.78

(mol kg cat-1)

Amount of strong acid sitesb

0.79

0.57

0.66

a Based on the total amount of ammonia desorbed in the TPD experiment b Based on the amount of ammonia desorbed above 300°C in the TPD experiment

a Based on the total amount of ammonia desorbed in the TPD experiment b Based on the amount of ammonia desorbed above 300°C in the TPD experiment

Figure 6.12 Dependence associated with the reaction temperature and the time factor, W/F, on the conversion of heavy oil: zeolite crystal size = 0.1 |xm. (Reproduced by permission of the American Chemical Society)

Figure 6.12 Dependence associated with the reaction temperature and the time factor, W/F, on the conversion of heavy oil: zeolite crystal size = 0.1 |xm. (Reproduced by permission of the American Chemical Society)

where Yi is the weight fraction of the ith component in the gasoline fraction. The subscript NP2 denotes the n-paraffins without C5, IP1 the total isoparaffins from C5 to C7, IP2 the total isoparaffins without C5-C7, CP the total cycloparaffins, and AR the total aromatics.

The relationship between the conversion of heavy oil and the time factor, W/F, at different reaction temperatures is shown in Figure 6.12. Conversion was defined as the mass fraction of heavy oil (components above C12) converted to gasoline, gas, and coke. This value was calculated from the following equation:

mass of heavy oil at the outlet conversion =1--(6.2)

mass of heavy oil at the inlet

As the reaction temperature increased, the reaction proceeded. Although conversion was greater as the temperature increased, there was no significant difference between the conversions at 400 and 450° C. The effects of temperature on the respective yields of the reaction products are shown in Table 6.5. As the temperature increased, the amount of unreacted heavy oil decreased, and the yields of both gas and coke increased. The gasoline yield reached a maximum value at 400° C, and then decreased with further increases in temperature.

Table 6.5 Effect of temperature on product yield at W/F = 0.75 kg-cat kg oil :h. (Reproduced by permission of the American Chemical Society)

Temperature

Heavy oil

Gasoline

Gas

Coke

C'C)

(wt%)

(wt%)

(wt%)

(wt%)

300

55.45

37.22

6.96

0.37

350

30.77

48.04

20.76

0.43

400

15.84

51.93

31.71

0.52

450

11.43

39.61

48.42

0.54

Figure 6.13(a) shows the effect of the reaction temperature on the relationship between gasoline yield and the conversion of heavy oil. The gasoline yield increased with increasing conversion to the maximum value, and then decreased significantly. This suggests that the gasoline formed by the cracking of heavy oil subsequently undergoes further cracking, which in turn yields gaseous products and coke. Thus, gasoline is an intermediate product. The maximum gasoline yield, which is related to the rates of gasoline formation and cracking, was observed at about 400°C. The same optimum temperature has been found for the catalytic cracking of gas oil [32]. Figure 6.13(b) shows the relationship between the gas yield and the conversion of heavy oil at various reaction temperatures. Because almost all of the data lie on a single curve, the reaction temperature had no significant effect on the gas yield at a constant conversion level. The yield of gas products increased

Figure 6.13 Effect of the reaction temperature on the relationship between product yield and the conversion of heavy oil (zeolite crystal size = 0.1 |xm): (a) gasoline yield; (b) gas yield; (c) coke yield. (Reproduced by permission of the American Chemical Society)

Conversion of heavy oil [%]

Figure 6.13 (continued)

Conversion of heavy oil [%]

Figure 6.13 (continued)

as the reaction progressed. Figure 6.13(c) shows the effect of different reaction temperatures and conversion levels of heavy oil on the coke yield. At the same conversion level, high temperatures reduced coke formation. The difference between the coke yields at 400 and 450°C was small. Similar findings have been reported for the catalytic cracking reaction of gas oil, in which coke formation proceeded well at reaction temperatures below 400°C [32].

The effect of reaction temperature on gasoline quality and its main components are shown in Figure 6.14. Below 400°C, the RON value increased with temperature due to an acceleration of the formation rate of the IP1 fraction and the cracking rate of the NP2 fraction. Above 400°C, however, the cracking of IP1 proceeded (i.e. a reduction in the yield of IP1), leading to a decrease in the RON value. On the basis of the gasoline, coke,

O 90 cc

250 300 350 400 450 500

Temperature [°C]

Figure 6.14 Effect of the reaction temperature on the RON value of the gasoline and main components (zeolite crystal size = 0.1 |xm, W/F = 0.75 kg-cat kg-oil-1 h): NP2 = n-paraffins without C5, IP1 = C5-C7 isoparaffins, AR = aromatics. (Reproduced by permission of the American Chemical Society)

O 90 cc

250 300 350 400 450 500

Temperature [°C]

Figure 6.14 Effect of the reaction temperature on the RON value of the gasoline and main components (zeolite crystal size = 0.1 |xm, W/F = 0.75 kg-cat kg-oil-1 h): NP2 = n-paraffins without C5, IP1 = C5-C7 isoparaffins, AR = aromatics. (Reproduced by permission of the American Chemical Society)

Figure 6.15 Effect of the time factor, W/F, on the RON value of the gasoline and the main components (zeolite crystal size = 0.1 |xm, reaction temperature = 400°C): NP2 = n-paraffins without C5, IP1 = C5-C7 isoparaffins, AR = aromatics. (Reproduced by permission of the American Chemical Society)

Table 6.6 Comparison of commercial gasoline and the gasoline obtained from heavy oil derived from waste plastics. (Reproduced by permission of the American Chemical Society)

Component

Gasoline obtained (optimized)

Regular gasoline

High-octane gasoline

IP1 (wt%) AR (wt%) NP2 (wt%) RON (-)

  1. 44 29.03 12.36 100.92
  2. 47 33.23 15.41 90.44
  3. 78 50.53 9.96 108.01

and gas yields, as well as the RON value, the most favorable reaction temperature was determined to be approximately 400°C.

The effect of the time factor, W/F, on gasoline quality and its main components obtained at 673 K is shown in Figure 6.15. Below a W/F value of 0.75 kg-cat kg-oil-1 h, the increase in the RON value was due to the significant increase in the IP1 fraction and the large reduction in the NP2 fraction. Above a W/F value of 1 kg-cat kg-oil-1 h, only the reaction of IP1 to AR took place, producing a slight decrease in the RON value. These results suggest that the optimum W/F value for the production of gasoline of the highest quality is in the range 0.75-1 kg-cat kg-oil-1 h.

Table 6.6 compares the contents of the main components of regular and high-octane gasoline with those of gasoline obtained under the optimal conditions, namely, temperature = 673 K, time factor = 0.75 — 1 kg cat kg oil-1 h, crystal size of the REY zeolite catalyst = 0.1 |m, and the number of strong acid sites on the used catalyst = 0.28 mol kg-1. The gasoline obtained under the optimum contained a larger amount of IP1 and a smaller amount of AR than the corresponding amounts in commercial gasoline. The amount of NP2 in the gasoline obtained in this study was between that of regular and high-octane gasoline.

3.3 KINETICS OF THE CATALYTIC CRACKING OF HEAVY OIL OVER REY ZEOLITES

A rare earth metal-exchanged Y-type (REY) zeolite catalyst was found to be an effective catalyst for the catalytic cracking of heavy oil. The influence of the reaction conditions and the catalytic properties of REY zeolite on the product yield and on gasoline quality have been described above. In this section, a reaction pathway is proposed for the catalytic cracking reaction of heavy oil, and a kinetic model for the cracking reaction is developed [14,33].

Figure 6.16 shows the typical relationship between product distribution and the time factor, W/F, at different temperatures [13]. The experimental conditions are described in Section 3.2. As the W/F value increased, heavy oil was cracked to produce gasoline and gaseous products. Moreover, the gasoline product subsequently underwent further cracking to yield gaseous products. Hence, the gasoline yield was shown to have a maximum value

Figure 6.16 Kinetic runs performed using a catalyst with a crystal size of 0.1 |xm: (a) 300°C; (b) 350°C; (c) 400°C; (d) 450°C. (Reproduced by permission of the American Chemical Society)

Figure 6.16 Kinetic runs performed using a catalyst with a crystal size of 0.1 |xm: (a) 300°C; (b) 350°C; (c) 400°C; (d) 450°C. (Reproduced by permission of the American Chemical Society)

Figure 6.16 (continued)

Figure 6.16 (continued)

that appeared at a low W/F value and a high reaction temperature. The yield of coke gradually increased and was considered to be the product of gasoline and heavy oil.

Figure 6.17 illustrates a possible reaction pathway that could account for the product distributions shown in Figure 6.16. The proposed reaction pathway separately takes into account the heavy oil, gasoline, gas, and coke lumps and is considered to represent the product distribution.

The experimental conditions were set up to ensure that both the heat and mass transport limitations across the film would be negligible. Moreover, limitations due to intraparti-cle diffusion were assumed to be insignificant. The mass balance equation of the ¿th component can be written as follows:

where Fi is the mass flow rate of the ¿th lump (kg h-1); W is the mass of catalyst (kg); ri is the production rate of the ¿th lump per unit mass of catalyst (kg (kg cat)-1 h-1); and suffixes A, B, C and D refer to heavy oil, gasoline, gas, and coke lumps, respectively.

Plastic Oil Catalyst Zsm
Figure 6.17 Reaction pathway proposed in this study. (Reproduced by permission of the American Chemical Society)

Figure 6.18 shows the Arrhenius plots using the evaluated kinetic parameters. The data were found to lie on a straight line for each parameter. The slopes of these straight lines gave the activation energies, which are listed in Table 6.7. The activation energy for the reaction of gas formation from heavy oil k2 is 75.5 kJ mol-1 and is comparable with other data for gasification reactions: 58.6 kJ mol-1 in the case of a CaX catalyst (Ca ion-exchanged X-type zeolite catalyst) [34], and 61.5 kJ mol-1 in the case of the silica alumina [35] for the gasification of a polymer waste, and 75 kJ mol-1 for the reaction of gas oil [36]. The difference in the activation energies between gaseous formation k2

If 101

it 3

f 100

If 101

it 3

f 100

Figure 6.18 Arrhenius plots of the kinetic parameters. (Reproduced by permission of the American Chemical Society)

Figure 6.18 Arrhenius plots of the kinetic parameters. (Reproduced by permission of the American Chemical Society)

Table 6.7 Activation energies using a catalyst with a crystal size of 0.1 |m. (Reproduced by permission of the American Chemical Society)

Rate constants

Ea (kJ mol)

Rate constants

Ea (kJ mol)

ki

50.7

k4

35.1

k2

75.5

ks

42.1

k3

18.5

and gasoline formation k1 accounts for the fact that the selectivity of gaseous products increases, while that of gasoline decreases with increases in temperature, especially at temperatures above 400° C.

3.4 USAGE OF STEAM AS A CARRIER GAS

As it is both inexpensive and easy to handle, steam is a potential candidate carrier gas for waste plastic recycling in chemical plants. Furthermore, as mentioned in Section 2.1, the degradation temperatures for polyester resins are remarkably shifted to low-temperature regions, and the amount of carbonaceous residue produced in the degradation process is reduced in a steam atmosphere, as compared with that in a nitrogen atmosphere. Accordingly, the preparation of a catalyst that could demonstrate both stable activity for the catalytic cracking of PE-derived heavy oil, but that would also remain stable in a steam atmosphere, was examined [16].

Nickel is a well-known catalyst component and is thought to play an important role in the transformation of the hydrogen of steam to hydrocarbons. Hence, a part of the rare earth metal in REY is exchanged with Ni to become prepared Ni and the rare earth metal-exchanged Y-type zeolite catalyst (Ni-REY) [14, 15]. The physical and chemical properties of the catalysts are listed in Table 6.8. The polyethylene plastics-derived heavy oil shown in Table 6.2 was used as the feed oil.

A continuous-flow, fixed-bed reactor was utilized for the catalytic cracking of the heavy oil. Reactions were conducted under temperature conditions ranging from 300 to 600°C, at a catalyst weight W of about 1.0 x 10-3 kg and a feed oil mass flow rate F of about 1.0 x 10-3 kg h-1. In order to examine the catalysis of Ni in Ni-REY for hydrogenation, experiments using hydrogen as the carrier gas were also conducted.

Table 6.8 Physical and chemical properties of the catalyst samples. (Reproduced with permission from Elsevier)

REY

Ni content 0.5 wt%

Ni-REY 1.0 wt%

3.0 wt%

HY

MFI

SiO2/Al2O3

4.8

4.8

4.8

4.8

4.8

65

Crystal size (mm)

0.1

0.1

0.1

0.1

0.1

1.1

Number of strong acid sites (mol kg-1)

0.375

0.441

0.122

The selectivity of the products of the reaction in nitrogen and hydrogen stream at 400°C was compared among the catalysts used at a feed oil conversion of about 80%. Hydrocarbons with carbon numbers ranging from 1 to 4 were regarded as gaseous compounds, and those with carbon numbers from 5 to 11 were regarded as gasoline fractions. MFI-type zeolite (ZSM-5) yielded the largest quantity of gaseous compounds (selectivity: 64%) and the lowest amount of gasoline (35%) because its pores are too small for the penetration of heavy oil, and reactions such as dewaxing are likely to proceed inside. As HY-type zeolite had a large umber of strong acid sites, and excessive cracking occurred, a low yield of gasoline was obtained (46%). The usage of REY, on which the number of strong acid sites is lower than that on the HY-type zeolite, gave a higher yield of gasoline (57%) as compared with that of HY. On the other hand, when the reaction was conducted using the Ni-REY catalyst in hydrogen stream, the selectivity towards gasoline was found to be the highest at 64%, at the same temperature and conversion of the feed oil.

The reactions over HY, MFI, and REY zeolite catalysts in nitrogen proceed over their acid sites. During the reactions, paraffins are first decomposed to yield lighter olefins and paraffins. The produced olefins are preferentially adsorbed on acid sites and undergo further reaction, yielding gaseous compounds and aromatics. When a Ni-REY catalyst is employed in a hydrogen atmosphere, the decomposition of hydrogen to hydrogen atoms also proceeds over Ni in the catalyst. These hydrogen atoms diffuse on the pore surface (e.g. the spillover phenomenon) and when they make contact with the olefins adsorbed on the acid sites, the hydrogenation of the olefins occurs. The paraffins formed in this manner easily desorb from the acid sites without undergoing any further reactions. Therefore, the reactions using Ni-REY in this series showed the highest selectivity towards gasoline.

In order to optimize the Ni content of Ni-REY, the compositions of the obtained gasoline fraction were measured and were divided into lumps as shown in Figure 6.19. Figure 6.20 shows the RON value calculated from the data in Fig. 6.19 using Equation (6.1). The results obtained with commercial regular-grade and high-RON-grade gasoline are also shown in these figures for comparison. Commercial gasoline with a high RON value contains large amounts of isoparaffins (IP1), aromatics (AR), and cycloparaffins (CP), as well as a small amount of n-paraffins (NP2). For the complete combustion of gasoline, the AR content must be low. Therefore, high-quality gasoline must contain large amounts of IP1 and CP and small amounts of NP2 and AR. Using Ni-REY with a 0.5 wt% Ni content, gasoline with larger amounts of CP and IP1 and smaller amounts of AR and NP2 was obtained, as compared with a commercial high-RON-grade gasoline. Furthermore, the RON value of the gasoline produced over Ni-REY (0.5 wt%) was larger than that of commercial gasoline. As the content of Ni increased, the number of strong acid sites decreased, resulting in a reduction in cracking. This explains why the amount of IP1 decreased and that of NP2 increased with the increase in the Ni content (from 0.5 to 3.0 wt%), leading to the reduction of the RON value of the gasoline produced in this manner. Based on the above information, it was concluded that Ni-REY with a Ni content of 0.5 wt% could be used for the following experiments.

The effects of reaction temperature on the conversion of the heavy oil and the gasoline yield are shown in Figure 6.21 for reactions using Ni-REY in steam and hydrogen streams. At temperatures below 400°C, both the conversion and the gasoline yield increased as temperature increased. However, at temperatures above 400°C, excessive

Cycloparaffin| |Aromatics (AR)

^m iso-paraffin (IP2)

n-paraffin (NP)

iso-paraffin (IP1)

Cycloparaffin| |Aromatics (AR)

n-paraffin (NP)

iso-paraffin (IP1)

Isoparaffin

HY MFI

Regular High RON grade grade in N2

Ni-REY in H

Commercial gasoline

Figure 6.19 Comparison of gasoline fractions produced by catalytic cracking over the various catalysts used (T = 400°C, W/F = 1 h). (Reproduced by permission from Elsevier)

Figure 6.19 Comparison of gasoline fractions produced by catalytic cracking over the various catalysts used (T = 400°C, W/F = 1 h). (Reproduced by permission from Elsevier)

HY MFI REY

in N2

Ni-REY in H2

HY MFI REY

in N2

Ni-REY in H2

Figure 6.20 Research octane umber (RON value) of the gasoline fraction produced with the catalysts used. (Reproduced by permission from Elsevier)

cracking proceeded, followed by coke formation, leading to a decrease in both conversion and gasoline yield. This tendency was clearly observed in the case of hydrogen stream. Strong acid sites, on which coke formation proceeds and is accelerated at higher temperatures, are partially covered by water molecules in a steam atmosphere. Therefore, the catalyst is able to maintain activity above 400°C in a steam atmosphere.

"S 60

"S 60

300 400 500 600 Reaction temperature/°C

Figure 6.21 Dependence of both conversion and gasoline yield on reaction temperature (W/F = 1 h)

T. MASUDA AND T. TAGO 100

to "o

300 400 500 600 Reaction temperature/°C

Figure 6.21 Dependence of both conversion and gasoline yield on reaction temperature (W/F = 1 h)

Figure 6.22 shows the typical carbon number distribution of products obtained using Ni-REY in steam at 400°C and with a time factor W/F of 1 h. The results obtained with MFI-type (ZSM-5) and REY zeolites in N2 are also shown for comparison. Although steam was used as a carrier gas, Ni-REY gave the largest amount of fuel, e.g. gasoline, kerosene, and gas oil, thus suggesting the potential use of steam as a carrier gas.

Figure 6.22 shows the typical carbon number distribution of products obtained using Ni-REY in steam at 400°C and with a time factor W/F of 1 h. The results obtained with MFI-type (ZSM-5) and REY zeolites in N2 are also shown for comparison. Although steam was used as a carrier gas, Ni-REY gave the largest amount of fuel, e.g. gasoline, kerosene, and gas oil, thus suggesting the potential use of steam as a carrier gas.

Carbon number/-

Figure 6.22 Carbon number distribution of products of the catalytic cracking of oil obtained by the pyrolysis of PE. (Reproduced with permission from Elsevier)

From the results discussed above, the combination of Ni-REY as the catalyst and steam as the carrier gas was considered preferable for achieving a realistic recycling process. In order to confirm the long-term stability of Ni-REY, repeated sequences of reaction and regeneration were conducted. Reaction and regeneration were conducted at 400°C for 3 h in a steam atmosphere, and at 500°C for 3 h in an air stream, respectively. This experiment was also conducted using an MFI-type zeolite catalyst for comparison by exchanging the carrier gas in the reaction from steam to nitrogen. Figure 6.23 shows changes in the conversion of the feed oil and the selectivity towards gasoline for REY and Ni-REY catalysts during the sequences of reaction and regeneration. The carrier gas in the reaction was steam for the REY and Ni-REY catalysts. Both the activity and the selectivity remained almost constant for REY and Ni-REY, indicating that both catalysts are stable in a steam atmosphere. The stable activity observed with REY and Ni-REY could be ascribed to the stability of the acid sites on the REY and Ni-REY catalysts [37]. Furthermore, Ni-REY showed higher selectivity towards gasoline (78%). A small amount of hydrogen was detected in the exit gas of the reactor. This finding suggested that Ni plays an important role in the hydrogen transportation from steam to hydrocarbons, resulting in a high selectivity towards gasoline. The above findings thus confirmed that PE-derived heavy oil can be efficiently upgraded to useful fuels when it is reacted over Ni-REY in a steam atmosphere.

In order to verify the high efficiency of Ni-REY in an actual system, the catalytic cracking of the oil derived from a mixture of PE and PET was conducted in a bench-scale reactor (see Figure 6.8). The Ni-REY catalyst was placed in reactor 3, shown in Figure 6.7. Figure 6.24 represents the carbon number distribution of the feed oil and the product of the reaction over Ni-REY in a steam atmosphere. The fraction of aliphatic heavy oil was completely converted to gasoline and kerosene, indicating that the Ni-REY catalyst can be used for the upgrading of oil derived from a mixture of PE and PET. The

1 1 1

  • MFI ■*-9—■ d
  • o- . -tfl _q .

- A . D

Ni-REY

_ Ni-REY.

i i i

----k----r, i

12 3 4 Number of sequences of reaction and regeneration/-

12 3 4 Number of sequences of reaction and regeneration/-

Figure 6.23 Changes in the catalytic activity of the MFI-type zeolite, Ni-REY, and REY catalysts during the repetition of a sequence of reaction and regeneration (T = 400°C, W/F = 1 h), carrier gas in the reaction: nitrogen for MFI, steam for REY and Ni-REY. (Reproduced with permission from Elsevier)

Figure 6.24 Carbon number distribution of products obtained by the catalytic cracking of oil derived from a mixture of PE and PET (reaction conditions: T = 400°C, W/F = 1 h). (Reproduced with permission from Elsevier)

products with carbon numbers from C5 to C11 (i.e. the gasoline fraction) contained about 30% aromatics, almost the same result observed in the case of the products obtained from the reaction over Ni-REY in H2 (see Figure 6.19). This finding suggests that cracking, followed by hydrogenation, proceeds in a steam atmosphere due to the existence of Ni in the catalyst.

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