Hydrocracking of a HDPE/VGO Blend: Influence of Catalyst-to-Feed Ratio on Fuel Yield and Composition

Ci a ion: Vela, F.J.; Palos, R.; Bilbao, J.;
A andes, J.M.; Gu ié ez, A.
Hyd oc acking o a HDPE/VGO
Blend: In luence o Ca alys - o-Feed
Ra io on Fuel Yield and Composi ion.
Ca alys s 2024,14, 203. h ps://
doi.o g/10.3390/ca al14030203
Academic Edi o s: Ines G aca,
Augus e Fe nandes and Alan
J. McCue
Recei ed: 20 Feb ua y 2024
Re ised: 7 Ma ch 2024
Accep ed: 14 Ma ch 2024
Published: 19 Ma ch 2024
Copy igh : © 2024 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
ca alys s
A icle
Hyd oc acking o a HDPE/VGO Blend: In luence o
Ca alys - o-Feed Ra io on Fuel Yield and Composi ion
F ancisco J. Vela , Robe o Palos , Ja ie Bilbao , JoséM. A andes and Alazne Gu ié ez *
Depa men o Chemical Enginee ing, Uni e si y o he Basque Coun y UPV/EHU, P.O. Box 644,
48080 Bilbao, Spain; anciscoja ie [email p o ec ed] (F.J.V.); [email p o ec ed] (R.P.);
ja ie [email p o ec ed] (J.B.); [email p o ec ed] (J.M.A.)
*Co espondence: alazne.gu ie [email p o ec ed]
Abs ac : The e ec s ha he ca alys - o- eed a io ha e on he yields o p oduc s and composi ion o
he naph ha and ligh cycle oil (LCO) ac ions in he hyd oc acking o a blend composed o high-
densi y polye hylene (HDPE) and acuum gasoil (VGO) using a P Pd/HY ca alys we e assessed.
The hyd oc acking uns we e ca ied ou in a ba ch eac o ixing he ollowing ope a ion condi ions:
420
◦
C, 80 ba , 120 min and an HDPE- o-VGO a io o 0.2 g
HDPE
g
VGO−1
, a ying he ca alys - o- eed
mass a io wi hin he 0.05–0.1 g
ca alys
g
eed−1
ange. The ob ained esul s exposed ha a ca alys - o-
eed mass a io o 0.075 g
ca alys
g
eed−1
p o ided he bes esul s, since he con e sion o he hea y
cycle oil (HCO) ac ion and o he HDPE o e ed qui e high alues (73.1 and 63.9%, espec i ely)
wi hou causing an excessi e o e c acking in he o m o gas p oduc s ( he yield o gases was o 25%).
Mo eo e , an in e es ing yield o naph ha (37.0 w %) wi h an RON wi hin he comme cial s anda ds
(92.5) was ob ained. Wi h ega d o coke o ma ion, no -so-de eloped s uc u es we e o med
o a ca alys - o- eed mass a io o 0.075 g
ca alys
g
eed−1
, easing hei combus ion and p esumably
ex ending he li espan o he ca alys .
Keywo ds: hyd oc acking; plas ic; acuum gasoil; coke; chemical ecycling; was e e ine y
1. In oduc ion
The consciousness- aising o ci izens abou he en i onmen al damage ha he exces-
si e use o plas ics and especially he mismanagemen o was e plas ic cause has p opelled
in es men s and e o s o ecycle plas ics in an e ec i e way; ha is o say, was e plas ic
ecycling is gaining momen um [
1
]. Fu he mo e, he low was e plas ic ecycling a es
(<9% in he USA [
2
] and abou 30% in he EU [
3
]) and he dissa is ac ion ha i c ea es ha e
de ini ely pushed go e nmen s o adop ins i u ional amendmen s in o de o amelio a e
he si ua ion. Among hese amendmen s, he es ablishmen o axes o he use o i gin
plas ic, he phase-ou o single-use plas ic and he e o s in educa ing he public o min-
imize he use o plas ic, especially he single-use ones, can be highligh ed [
4
]. Howe e ,
hese measu es a e no enough o a ain he sus ainable managemen o was e plas ics, and
e o s mus be ocused on imp o ing he cu en was e plas ics ecycling echnologies and
de eloping new ones.
In his con ex , chemical ecycling echnologies could po en ially handle was e plas ic
s eams ha a e cu en ly mismanaged, land illed o incine a ed and p oduce high-added-
alue p oduc s [
5
]. Among he main ou es o he chemical alo iza ion o was e plas-
ics [
6
], py olysis and gasi ica ion s and ou gi en he simplici y o hese echnologies and
hei cu en deploymen scale. The o me could be used o he di ec p oduc ion o ligh
ole ins [
7
], monome s [
8
], a oma ics [
9
] and waxes [
10
], making i highly e sa ile. In con-
as , gasi ica ion aims a he p oduc ion o syngas [
11
] o di ec ly hyd ogen [
12
] om was e
plas ics. None heless, he possible indus ial implemen a ion o hese echnologies will
equi e impo an in es men s wi h he high deg ee o unce ain y ha i en ails. Hence,
Ca alys s 2024,14, 203. h ps://doi.o g/10.3390/ca al14030203 h ps://www.mdpi.com/jou nal/ca alys s
Ca alys s 2024,14, 203 2 o 13
he possibili y o commi ing o a ully de eloped and widesp ead echnology wi h al eady
dep ecia ed uni s becomes c ucial. In his ega d, he concep o was e e ine ies comes up,
which consis s o using he indus ial uni s a ailable wi hin he acili ies o oil e ine ies
o ecycling was e plas ics [
13
]. Among he uni s a ailable in e ine ies, luid ca aly ic
c acking (FCC) and hyd oc acking uni s a e he mos sui able ones o handling hese al e -
na i e eeds. Howe e , he ac o handling a solid always implies ope a ional di icul ies.
Acco dingly, blending he was e plas ics wi h a benchma k e ine y eeds ock, such as
acuum gasoil (VGO) o ligh cycle oil (LCO), is a s a egy ha eases he p ocess [
14
]. E en
hough he FCC uni is app op ia e o handling blended plas ics, he hyd oc acking uni
is by a mo e e sa ile, and i s p oduc ion can be easily o ien ed owa ds he p oduc ion
o gasoline o diesel by jus modi ying ope a ion condi ions.
The e o e, a p ope assessmen o he e ec s ha he ope a ion condi ions ha e on
he yields and composi ion o he p oduc s is c ucial o uning he hyd oc acking p ocess.
Thence, he e ec s o empe a u e [
15
], hyd ogen p essu e [
16
] and con ac ime [
17
] in
he hyd oc acking o a blend o HDPE and VGO ha e been al eady s udied, whe eas
he in luence o he ca alys - o- eed a io emains ye un aced. Consequen ly, his wo k
speci ically ocuses on he e ec s ha his ope a ional pa ame e has on he yields o
p oduc s and on he composi ion o he naph ha and LCO ac ions. Mo eo e , ca alys
deac i a ion has been also assessed, dis inguishing be ween di e en ypes o coke, which
we e a ibu ed o cokes o di e en na u e loca ed on di e en poin s o he ca alys .
This wo k closes wi h a deep s udy o he ope a ion condi ions in he hyd oc acking o a
HDPE/VGO blend, exposing ha he p ocess could be scaled up.
2. Resul s and Discussion
2.1. Hyd oc acking Yields and Con e sion
Figu e 1a collec s he dis ibu ion o he yields o p oduc s ob ained in he hyd oc-
acking o he HDPE/VGO blend o he h ee di e en C/F mass a ios, oge he wi h
he HCO and HDPE con e sions a ained. A ending o he esul s ob ained o a C/F o
0.05 gca alys g eed−1
, i can be seen ha an HCO con e sion o 70.7% was ob ained, which
en ails a educ ion in he con en o HCO om 95.4 w % in he eed o 28.0 w %. Conse-
quen ly, he naph ha ac ion became he majo p oduc (yield o 25.9 w %), ollowed by
gas and LCO ac ions (yields o 15.0 and 14.4 w %, espec i ely). Howe e , he HDPE
con e sion a ained emained low a a alue o 20.9%.
Ca alys s2024,14,xFORPEERREVIEW3o 14
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

Figu e1.P oduc syieldsdis ibu ionandcon e sione olu ion(a)ob ained o  hedi e en C/F
mass a ios.E olu iono  heselec i i y o uelindex(b) o  he es edC/Fmass a ios.
Thee olu iono  heselec i i y o uelindex(SF)depic edinFigu e1bsumma izes
hep oduc dis ibu ionob ained.Thus, o aC/Fmass a ioo 0.05gca alys g eed−1, helowes 
selec i i y o uelwasob ained(0.67).This esul maybeadi ec consequenceo (i) he
lowHDPEcon e sion(20.9%)and hemode a eHCOcon e siona ained(70.7%);and
(ii) heimpo an gas o ma ion(15.0w %).Aninc easein heC/Fmass a io o0.075
gca alys g eed−1inc eased heselec i i y o uel o0.84,exposing ha  heinc easein heyield
o naph hacon ibu ed oinc easing hisindex.Howe e ,a u he inc easeup o0.1gca ‐
alys g eed−1didno en ailahighe selec i i y o uel;i  emainedalmos cons an a a alue
o 0.83.The e o e, hehighe yieldo naph hap oducedwascoun e balancedby hegas
o ma ionanddidno ha eaposi i ee ec in he o ma iono  he ac ionso in e es .
Ino de  oassess hee ec so  headdi iono  heHDPE o hehyd oc ackinguni s,
he esul sha ebeencompa edwi h hosep e iously epo edabou  hehyd oc acking
o nea VGO o aC/Fmass a ioo 0.1gca alys g eed−1[15].In his ega d, heHCOcon e ‐
sionwas91.7%,sligh lyhighe  han heoneob ained o  heHDPE/VGOblend(85.6%).
Thedis ibu iono yieldswasmo ein luencedby headdi iono  heHDPE,since hegas
o ma ioninc eased om22.5 o34.6w %,and heyieldo  henaph ha ac ionwas e‐
duced om59.6 o39.4w %.The e o e, headdi iono  heHDPEmodi ied hedis ibu‐
iono p oduc ssince hemac omoleculeso HDPE eac  as e  han hebulkypolya o‐
ma icscompoundswi hin heVGO,leading oasupe io  o ma iono gasp oduc s.Fu ‐
he mo e, heexis enceo possiblesyne gis ice ec sde i ed om he oleo dissol ed
HDPEmac omoleculesac ingashyd ogendono smus bealsoconside ed.This ac was
a i iedwi h heselec i i y o uelindexob ained o  heVGO(2.12) ha isconside ably
highe  han ha o  heHDPE/VGOblend(0.83).Oneshouldno e ha  his alueisim‐
po an lya ec edby hecon e sionle ela ained.
2.2.Cha ac e iza iono  heGasF ac ion
Figu e2displayshow hecomposi iono  hegas ac ione ol edwi h heC/Fmass
a io.Asi canbeseen, his ac ionwascomposedo ligh pa a inscomposedo hyd o‐
ca bonsbe weenoneand ou ca bona oms:me hane,e hane,p opane,n‐bu aneandiso‐
bu ane.Oneshouldno e ha noligh ole inswe ede ec edin his ac ionbecause hey
a eeasilysa u a edunde  he es edope a ioncondi ions.Byspli ing hegas ac ion
0.05 0.075 0.1 0.65
0.70
0.75
0.80
0.85
0.90
15.0
25.0
34.6
25.9
37.0
39.4
14.4
8.7
6.2
28.0
20.5
13.8
15.8
7.2 3.7
15.0
25.0
34.6
25.9
37.0
39.4
14.4
8.7
6.2
28.0
20.5
13.8
15.8
7.2 3.7
0.05 0.075 0.1
0
20
40
60
80
100
(b)
(a)
Yield (w %)
C/F mass a io (g
ca alys
g
-1
eed
)
Gas LCO
Coke
X
VGO
Naph ha
HCO
Wax
X
HDPE
0
20
40
60
80
100
Con e sion (%)
Selec i i y o uel

C/F mass a io (g
ca alys
g
-1
eed
)
Figu e 1. P oduc s yields dis ibu ion and con e sion e olu ion (a) ob ained o he di e en C/F
mass a ios. E olu ion o he selec i i y o uel index (b) o he es ed C/F mass a ios.
Ca alys s 2024,14, 203 3 o 13
An inc ease in he C/F mass a io up o 0.075 g
ca alys
g
eed−1
b ough a posi i e e ec
on he ob ained esul s due o he g ea e a ailabili y o ca aly ically ac i e si es. Conse-
quen ly, bo h he HCO and HDPE con e sions achie ed inc eased no ably, especially ha o
HDPE (63.9%). A he same ime, he yield o HCO was educed o 20.5 w %, which en ails
an HCO con e sion o 78.5%. Naph ha was he main p oduc wi h a yield o 37.0 w %,
whe eas he yield o he LCO ac ion was sha ply educed (8.7 w %). Ne e heless, he
highe ca aly ic ac i i y also p o oked a highe o ma ion o gases (25.0 w %).
A he highes C/F mass a io es ed (0.1 g
ca alys
g
eed−1
), he yield o HCO was
educed, eaching a alue o 13.8 w %. This ac pushed he HCO con e sion up o 85.6%.
Naph ha emained as he main p oduc (yield o 39.4 w %) bu was closely ollowed by
he yield o gases p oduced (yield o 34.6 w %). The inc ease in he C/F mass a io also
imp o ed he HDPE con e sion, eaching a e y a ac i e alue o 81.3%, which is almos
equal o ha ob ained o he HCO con e sion. These esul s a e in good ag eemen wi h
hose p e iously epo ed by Uça e al. [
18
] in he hyd oc acking o a blend composed o
low-densi y polye hylene and hea y VGO.
Wi h ega d o he o ma ion o coke, i can be seen ha he highe he C/F mass a io
used, he highe he amoun o coke deposi ed on he ca alys . Thus, he yield o coke was
o 0.9 w % o he lowes C/F mass a io used (0.05 g
ca alys
g
eed−1
), bu i inc eased up o
2.5 w % o a C/F mass a io o 0.1 gca alys g eed−1.
The e olu ion o he selec i i y o uel index (S
F
) depic ed in Figu e 1b summa izes
he p oduc dis ibu ion ob ained. Thus, o a C/F mass a io o 0.05 g
ca alys
g
eed−1
, he
lowes selec i i y o uel was ob ained (0.67). This esul may be a di ec consequence o
(i) he low HDPE con e sion (20.9%) and he mode a e HCO con e sion a ained (70.7%);
and (ii) he impo an gas o ma ion (15.0 w %). An inc ease in he C/F mass a io o
0.075 gca alys g eed−1
inc eased he selec i i y o uel o 0.84, exposing ha he inc ease in
he yield o naph ha con ibu ed o inc easing his index. Howe e , a u he inc ease up o
0.1 g
ca alys
g
eed−1
did no en ail a highe selec i i y o uel; i emained almos cons an
a a alue o 0.83. The e o e, he highe yield o naph ha p oduced was coun e balanced
by he gas o ma ion and did no ha e a posi i e e ec in he o ma ion o he ac ions
o in e es .
In o de o assess he e ec s o he addi ion o he HDPE o he hyd oc acking uni s,
he esul s ha e been compa ed wi h hose p e iously epo ed abou he hyd oc acking
o nea VGO o a C/F mass a io o 0.1 g
ca alys
g
eed−1
[
15
]. In his ega d, he HCO
con e sion was 91.7%, sligh ly highe han he one ob ained o he HDPE/VGO blend
(85.6%). The dis ibu ion o yields was mo e in luenced by he addi ion o he HDPE, since
he gas o ma ion inc eased om 22.5 o 34.6 w %, and he yield o he naph ha ac ion
was educed om 59.6 o 39.4 w %. The e o e, he addi ion o he HDPE modi ied he
dis ibu ion o p oduc s since he mac omolecules o HDPE eac as e han he bulky
polya oma ics compounds wi hin he VGO, leading o a supe io o ma ion o gas p oduc s.
Fu he mo e, he exis ence o possible syne gis ic e ec s de i ed om he ole o dissol ed
HDPE mac omolecules ac ing as hyd ogen dono s mus be also conside ed. This ac was
a i ied wi h he selec i i y o uel index ob ained o he VGO (2.12) ha is conside ably
highe han ha o he HDPE/VGO blend (0.83). One should no e ha his alue is
impo an ly a ec ed by he con e sion le el a ained.
2.2. Cha ac e iza ion o he Gas F ac ion
Figu e 2displays how he composi ion o he gas ac ion e ol ed wi h he C/F
mass a io. As i can be seen, his ac ion was composed o ligh pa a ins composed o
hyd oca bons be ween one and ou ca bon a oms: me hane, e hane, p opane, n-bu ane
and iso-bu ane. One should no e ha no ligh ole ins we e de ec ed in his ac ion because
hey a e easily sa u a ed unde he es ed ope a ion condi ions. By spli ing he gas ac ion
in o d y gas (C
1
and C
2
compounds) and lique ied pe oleum gases (LPG, C
3
and C
4
compounds), he concen a ion o he la e was by a p edominan as i eached alues
abo e 70 w % o all he C/F mass a ios s udied.
Ca alys s 2024,14, 203 4 o 13
Ca alys s2024,14,xFORPEERREVIEW4o 14
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in od ygas(C1andC2compounds)andlique iedpe oleumgases(LPG,C3andC4com‐
pounds), heconcen a iono  hela e wasby a p edominan asi  eached aluesabo e
70w % o all heC/Fmass a ioss udied.
Fo aC/Fmass a ioo 0.05gca alys g eed−1, heconcen a iono d ygasaccoun ed o 
30.2w %,wi h heconcen a iono e hanehighe  han ha o me hane(17.1 s.13.1w %,
espec i ely).On heo he hand,LPGswe ecomposedo 26.7w %p opane,26.2w %
iso‐bu aneand16.9w %n‐bu ane.Asimila composi iono  hegas ac ionwas epo ed
byMe ecane al.[19]in hehyd oc ackingo ablendo polyole inplas ics(HDPE,LDPE
andPP).When heC/Fmass a iowasinc eased,ama kedo e all endwasobse ed.
In his ega d, heconcen a iono d ygasdec easedincon as  o ha o LPG, eaching
alueso 26.6w %and73.4w %, espec i ely.Wi h ega d o heindi idualcomponen s,
i canbeseen ha  heconcen a iono me hanewas educed,while ha o e hane e‐
mainedalmos cons an .A ending o hecomponen so  heLPG ac ion, heconcen a‐
iono p opanewasno ablyinc easedsincei wen  oma alueo 26.7w % o aC/F
mass a ioo 0.05gca alys g eed−1 oa alueo 52.2w % o aC/Fmass a ioo 0.1gca alys g eed−1.
This endcanbeaconsequenceo  hep omo iono  heo e ‐c acking eac ions ha lead
oaninc easein heconcen a iono  heC1–C3p oduc s,wi h ha o p opanebeinges‐
pecially ema kable.Fu he mo e, heconcen a iono iso‐bu anewen  om26.2w % o 
aC/Fmass a ioo 0.05gca alys g eed−1 o13.1w % o aC/Fmass a ioo 0.1gca alys g eed−1.
Thus,i canbededuced ha  hemechanism ha go e nsgas o ma ionis hep o oly ic
c ackingins eado β‐scission eac ions.

Figu e2.Composi iono  hegas ac ionob ained o  hedi e en C/Fmass a io es ed.
Thecomposi iono  hegas ac ionwasqui esimila  o ha ob ainedin hehy‐
d oc ackingo nea VGO o aC/Fmass a ioo 0.1gca alys g eed−1[15].In ha case, heyield
o d ygaswassligh lylowe (24.3w % s.26.6w %), husbeinghighe  ha o LPG(75.7
w % s.73.4w %)bu wi hou  hedi e encebe ween hembeingso ema kable.Wi h
ega d oindi idualcomponen s,p opanewasalso hecompoundwi h hehighes yield
(50.4w %),whichwassligh lylowe  han heoneob ainedwi h heHDPE/VGOblend
(52.2w %).
2.3.Cha ac e iza iono  heNaph haandLCOF ac ions
Since he ac ionso in e es inhyd oc ackingp ocessesa ebo hnaph haandLCO
ac ions,whichcanbe espec i elyassimilablebygasolineanddiesel ac ionso  e in‐
e ies, heyha ebeenanalyzedinde ail.Thus, hePIANOcomposi iono  hese ac ions
o  he es edC/Fmass a iosisdepic edinFigu e3.Focusingon hePIANOcomposi ion
8.1
14.2
16.9
13.1
24.4
26.2
52.2
32.6
26.7
16.5
16.5
17.1
10.2
12.4
13.1
8.1
14.2
16.9
13.1
24.4
26.2
52.2
32.6
26.7
16.5
16.5
17.1
10.2
12.4
13.1
0.05 0.075 0.1
0
20
40
60
80
100
C/F mass a io (g
ca alys
g
-1
eed
)
C
1
C
2
C
3
iC
4
nC
4
Concen a ion (w %)
Figu e 2. Composi ion o he gas ac ion ob ained o he di e en C/F mass a io es ed.
Fo a C/F mass a io o 0.05 g
ca alys
g
eed−1
, he concen a ion o d y gas accoun ed o
30.2 w %, wi h he concen a ion o e hane highe han ha o me hane (17.1 s. 13.1 w %,
espec i ely). On he o he hand, LPGs we e composed o 26.7 w % p opane, 26.2 w %
iso-bu ane and 16.9 w % n-bu ane. A simila composi ion o he gas ac ion was epo ed
by Me ecan e al. [
19
] in he hyd oc acking o a blend o polyole in plas ics (HDPE, LDPE
and PP). When he C/F mass a io was inc eased, a ma ked o e all end was obse ed.
In his ega d, he concen a ion o d y gas dec eased in con as o ha o LPG, eaching
alues o 26.6 w % and 73.4 w %, espec i ely. Wi h ega d o he indi idual componen s, i
can be seen ha he concen a ion o me hane was educed, while ha o e hane emained
almos cons an . A ending o he componen s o he LPG ac ion, he concen a ion o
p opane was no ably inc eased since i wen om a alue o 26.7 w % o a C/F mass a io
o 0.05 g
ca alys
g
eed−1
o a alue o 52.2 w % o a C/F mass a io o 0.1 g
ca alys
g
eed−1
. This
end can be a consequence o he p omo ion o he o e -c acking eac ions ha lead o an
inc ease in he concen a ion o he C
1
–C
3
p oduc s, wi h ha o p opane being especially
ema kable. Fu he mo e, he concen a ion o iso-bu ane wen om 26.2 w % o a C/F
mass a io o 0.05 g
ca alys
g
eed−1
o 13.1 w % o a C/F mass a io o 0.1 g
ca alys
g
eed−1
.
Thus, i can be deduced ha he mechanism ha go e ns gas o ma ion is he p o oly ic
c acking ins ead o β-scission eac ions.
The composi ion o he gas ac ion was qui e simila o ha ob ained in he hyd o-
c acking o nea VGO o a C/F mass a io o 0.1 g
ca alys
g
eed−1
[
15
]. In ha case, he
yield o d y gas was sligh ly lowe (24.3 w % s. 26.6 w %), hus being highe ha o LPG
(75.7 w % s. 73.4 w %) bu wi hou he di e ence be ween hem being so ema kable.
Wi h ega d o indi idual componen s, p opane was also he compound wi h he highes
yield (50.4 w %), which was sligh ly lowe han he one ob ained wi h he HDPE/VGO
blend (52.2 w %).
2.3. Cha ac e iza ion o he Naph ha and LCO F ac ions
Since he ac ions o in e es in hyd oc acking p ocesses a e bo h naph ha and LCO
ac ions, which can be espec i ely assimilable by gasoline and diesel ac ions o e ine ies,
hey ha e been analyzed in de ail. Thus, he PIANO composi ion o hese ac ions o he
es ed C/F mass a ios is depic ed in Figu e 3. Focusing on he PIANO composi ion o
he naph ha ac ion (Figu e 3a) in he i s place, i can be seen ha i is mainly alipha ic
independen ly o he alue o he C/F mass a io. Indeed, he less alipha ic one is ha
ob ained o a C/F mass a io o 0.1 g
ca alys
g
eed−1
(49.6 w % o alipha ics). A ending o
he dis ibu ion o n- and iso-pa a ins, he e is a clea p edominance o he ami ied ones,
e en hough hei concen a ion dec eased wi h he C/F mass a io and wen om 30.2 o
Ca alys s 2024,14, 203 5 o 13
21.3 w % o an inc ease in he C/F mass a io om 0.05 o 0.1 g
ca alys
g
eed−1
. Mo eo e ,
he concen a ion o linea pa a ins also dec eased, leading o an inc ease in he naph henes
ha eached hei maximum concen a ion (20.3 w %) a 0.1 g
ca alys
g
eed−1
. On he o he
hand, he concen a ion o a oma ics inc eased wi h he C/F mass a io, and he maximum
alue o 50.4 w % was ob ained a 0.1 g
ca
g
eed−1
. Howe e , he a oma ic ac ion was
mainly composed o monoa oma ics, he concen a ion o dia oma ics being in e io o
4 w % independen ly o he C/F mass a io used. Fu he mo e, he concen a ion o
monoa oma ics inc eased wi h he C/F mass a io, while ha o he dia oma ics dec eased.
This esul is di ec ly ela ed o he hyd odea oma iza ion (HDA) o he hea y and bulky
a oma ics om he LCO and HCO ac ions o he VGO [
20
]. Thus, he HDA o hose
high-molecula -weigh molecules led o he o ma ion o pa ially hyd ogena ed molecules
wi hin he naph ha ac ion, such as e alin-like compounds. Mo eo e , i should be
aken in o accoun ha he o ma ion o a oma ics om he HDPE mac omolecules is e y
unlikely o occu .
Ca alys s2024,14,xFORPEERREVIEW5o 14


o  henaph ha ac ion(Figu e3a)in he i s place,i canbeseen ha i ismainlyalipha ic
independen lyo  he alueo  heC/Fmass a io.Indeed, helessalipha iconeis ha 
ob ained o aC/Fmass a ioo 0.1gca alys g eed−1(49.6w %o alipha ics).A ending o he
dis ibu iono n‐andiso‐pa a ins, he eisaclea p edominanceo  he ami iedones,
e en hough hei concen a iondec easedwi h heC/Fmass a ioandwen  om30.2 o
21.3w % o aninc easein heC/Fmass a io om0.05 o0.1gca alys g eed−1.Mo eo e , he
concen a iono linea pa a insalsodec eased,leading oaninc easein henaph henes
ha  eached hei maximumconcen a ion(20.3w %)a 0.1gca alys g eed−1.On heo he 
hand, heconcen a iono a oma icsinc easedwi h heC/Fmass a io,and hemaximum
alueo 50.4w %wasob aineda 0.1gca g eed−1.Howe e , hea oma ic ac ionwas
mainlycomposedo monoa oma ics, heconcen a iono dia oma icsbeingin e io  o4
w %independen lyo  heC/Fmass a ioused.Fu he mo e, heconcen a iono mono‐
a oma icsinc easedwi h heC/Fmass a io,while ha o  hedia oma icsdec eased.This
esul isdi ec ly ela ed o hehyd odea oma iza ion(HDA)o  hehea yandbulkya o‐
ma ics om heLCOandHCO ac ionso  heVGO[20].Thus, heHDAo  hosehigh‐
molecula ‐weigh moleculesled o he o ma iono pa iallyhyd ogena edmolecules
wi hin henaph ha ac ion,suchas e alin‐likecompounds.Mo eo e ,i shouldbe aken
in oaccoun  ha  he o ma iono a oma ics om heHDPEmac omoleculesis e yun‐
likely ooccu .

Figu e3.PIANOcomposi ionob ained o  henaph ha(a)andLCO(b) ac ions o  hedi e en 
C/Fmass a ios.Key:n‐P,n‐pa a ins;i‐P,iso‐pa a ins;N,naph henes;A1,monoa oma ics;A2,di‐
a oma icsandA3+,polya oma ics.
I mus bealso akenin oaccoun  ha  woaddi ional ou escouldha eled o he
o ma iono ligh a oma iccompounds:(i) hecycliza iono  heole ins ha a e o med
asaconsequenceo  hec acking eac ions;and(ii) hehyd ogen ans e  eac ions ha 
mayoccu wi hin henaph henes.E en hough hea o emen ioned ou escouldoccu 
wi hin hena owe po eso  hezeoli e, hei con ibu ion o he eac ionisno expec ed
obec ucial.None heless,conside ing hehighconcen a iono monoa oma icsin he
naph ha ac ion(Figu e3a), heymus bealsocon empla ed.The e o e, hese eac ions
oge he wi h heHDA ou ea elikely op omo e hep oduc iono benzene, oluene,
xylenes(BTX)andalkylbenzenes.Thisassump ionwasco ela edbyanalyzing hea o‐
ma icsp esen in henaph ha ac ion.In his ega d, heconcen a iono BTXinc eased
wi h heC/Fmass a io oma alueo 20.6w % o aC/Fmass a ioo 0.05gca alys g eed−1
oa alueo 29.2w % o aC/Fmass a ioo 0.1gca alys g eed−1.
Ino de  o ullycha ac e ize henaph ha ac ion, he esea choc anenumbe (RON)
wascompu ed o  hedi e en C/Fmass a ios.Tocalcula ei , heme hodde elopedby
Ande sone al.[21],whichisbasedonch oma og aphic esul s,wasused.A  helowes 
8.0
9.8
11.6
21.3
27.8
30.2
20.3
14.0
14.1
48.3
46.6
40.3
8.0
9.8
11.6
21.3
27.8
30.2
20.3
14.0
14.1
48.3
46.6
40.3
18.1
11.0
10.7
52.4
45.6
38.7
4.8
5.9
7.5
22.9
33.9
38.3
18.1
11.0
10.7
52.4
45.6
38.7
4.8
5.9
7.5
22.9
33.9
38.3
0.05 0.075 0.1
0
20
40
60
80
100
(b)
Composi ion (w %)
C/F mass a io (g
ca alys
g
-1
eed
)
(a)
0.05 0.075 0.1
0
20
40
60
80
100
Composi ion (w %)
C/F mass a io (g
ca alys
g
-1
eed
)
n-P i-P N A
1
A
2
A
3+
Figu e 3. PIANO composi ion ob ained o he naph ha (a) and LCO (b) ac ions o he di e -
en C/F mass a ios. Key: n-P, n-pa a ins; i-P, iso-pa a ins; N, naph henes; A
1
, monoa oma ics;
A2, dia oma ics and A3+, polya oma ics.
I mus be also aken in o accoun ha wo addi ional ou es could ha e led o he
o ma ion o ligh a oma ic compounds: (i) he cycliza ion o he ole ins ha a e o med as
a consequence o he c acking eac ions; and (ii) he hyd ogen ans e eac ions ha may
occu wi hin he naph henes. E en hough he a o emen ioned ou es could occu wi hin
he na owe po es o he zeoli e, hei con ibu ion o he eac ion is no expec ed o be
c ucial. None heless, conside ing he high concen a ion o monoa oma ics in he naph ha
ac ion (Figu e 3a), hey mus be also con empla ed. The e o e, hese eac ions oge he
wi h he HDA ou e a e likely o p omo e he p oduc ion o benzene, oluene, xylenes (BTX)
and alkylbenzenes. This assump ion was co ela ed by analyzing he a oma ics p esen
in he naph ha ac ion. In his ega d, he concen a ion o BTX inc eased wi h he C/F
mass a io om a alue o 20.6 w % o a C/F mass a io o 0.05 g
ca alys
g
eed−1
o a alue
o 29.2 w % o a C/F mass a io o 0.1 gca alys g eed−1.
In o de o ully cha ac e ize he naph ha ac ion, he esea ch oc ane numbe (RON)
was compu ed o he di e en C/F mass a ios. To calcula e i , he me hod de eloped by
Ande son e al. [
21
], which is based on ch oma og aphic esul s, was used. A he lowes
C/F mass a io (0.05 g
ca alys
g
eed−1
), an RON o 94 was ob ained, which is a alue e y sim-
ila o he one equi ed by comme cial gasoline (95). This esul is mainly based on he high
concen a ion o ami ied pa a ins ha undoub edly boos ed i . Howe e , an inc ease in
he C/F mass a io up o 0.075 g
ca alys
g
eed−1
b ough a de imen in he RON (92.5), which
con inued dec easing (92.3) o he highes C/F mass a io (
0.1 gca alys g eed−1
). The e o e,

Ca alys s 2024,14, 203 6 o 13
hese naph ha ac ions may equi e o be submi ed o a ca aly ic e o ming s age o adap
hei composi ion and be sui able o being used in he blending o comme cial gasoline.
In he hyd oc acking o nea VGO wi h a C/F mass a io o 0.1 g
ca alys
g
eed−1
[
15
],
he naph ha ac ion ob ained was less a oma ic (32.3 w %) han he one ob ained wi h he
blend (50.4 w %). These esul s exposed ha he HDPE mac omolecules in e e ed in he
access o he molecules wi hin he VGO o he ac i e si es o he ca alys , hus a ec ing i s
pe o mance. The e o e, i can be concluded ha a ce ain deg ee o ouling may be caused
by he deg aded HDPE mac omolecules ha occlude he channels o he zeoli e.
Focusing on he PIANO composi ion o he LCO ac ion (Figu e 3b), i can be
seen ha i is highly in luenced by he C/F mass a io used. The lowes C/F mass a-
io (
0.05 gca alys g eed−1
) p oduced an almos balanced composi ion be ween alipha ics
and a oma ics (49.5 and 50.5 w %, espec i ely). A ending o pa a ins dis ibu ion, he
concen a ion o iso-pa a ins exceeded o la ge ex en in con as o ha o n-pa a ins
(
38.7 w % s. 10.7 w %
, espec i ely). Likewise, dia oma ics a e he main compounds in
he a oma ics ac ion (38.3 w %), wi h ha o mono- and polya oma ics subs an ially
being smalle (7.5 and 4.7 w %, espec i ely). An inc ease in he C/F mass a io b ough
an inc ease in he pa a ins and a subsequen dec ease in he a oma ics. Pa icula ly, o
a C/F mass a io o 0.1 g
ca alys
g
eed−1
, pa a ins accoun ed o mo e han 70 w % o
he compounds in he LCO ac ion, whe e iso-pa a ins p edomina ed o e n-pa a ins
(52.4 s. 18.1 w %, espec i ely). Consequen ly, he concen a ion o a oma ics dec eased
no ably, especially ha o dia oma ics (22.9 w %). One should no e also ha he am-
ily o naph henes has no been included in he esul s depic ed in Figu e 3b, since i s
concen a ion was negligible (<1 w %) and independen o he C/F mass a io es ed.
Hence, acco ding o hese las esul s, i can be concluded ha an inc ease in he C/F
mass a io esul ed in (i) a p omo ion o he HDA capabili y o sa u a e (a leas pa ially)
he a oma ics wi hin he LCO ac ion, esul ing in an impo an educ ion in he a oma ics
wi hin his ac ion; and (ii) a bigge amoun o acidic si es becoming a ailable, especially
on he ou side o zeoli e c ys als, o he c acking o he HDPE molecules o hyd oca bons
wi hin he LCO ac ion [22].
Finally, he ce ane index o he LCO ac ion has been also calcula ed in o de o ob ain
a ull pic u e o he quali y o his ac ion. Ce ane indexes we e de e mined acco ding
o he p ocedu e explained on he ASTM D4737 S anda d. The e is a ma ked and clea
e ec o he C/F mass a io on he alues o he ce ane index ob ained, which a e a
consequence o he a o emen ioned changes in he composi ion o he LCO ac ion. The
lowe he concen a ion o a oma ics, especially polya oma ics, in he LCO ac ion, he
highe he ce ane index will be [
23
]. Thus, he ce ane index inc eased wi h he C/F mass
a io, and alues o 40.5, 44.7 and 54.9 we e ob ained o 0.05, 0.075 and 0.1 g
ca alys
g
eed−1
,
espec i ely. These alues a e high enough o LCO o be sui able o being used in he
blending o comme cial diesel in e ine ies.
In con as o he esul s ob ained o he naph ha ac ion, hese ones imp o ed hose
ob ained in he hyd oc acking o nea VGO wi h a C/F mass a io o 0.1 g
ca alys
g
eed−1
[
15
].
In his ega d, he LCO ac ion ob ained om he nea VGO was mo e a oma ic (36.2 w %)
ha he LCO ac ion o he blend (29.4 w %). This esul d i es o conclude ha he HDPE
mac omolecules a e decomposed in o long alipha ic compounds wi h a boiling poin wi hin
he ange o he LCO ac ion.
2.4. Cha ac e iza ion o he Coke
The spen ca alys s we e analyzed ia TPO analysis in o de o ob ain in o ma ion
abou he na u e and loca ion o he coke deposi ed on each case. The ob ained esul s a e
collec ed in Figu e 4, whe e he e ec s ha he C/F mass a io has on he o ma ion o his
ca bonaceous deposi can be seen. A ending o he shape o he TPO p o iles, i can be
seen ha hey a e qui e wide and ha hei decon olu ion was encou aged o eally assess
he con ibu ion o he di e en ypes o coke [
24
]. Thus, h ee di e en ypes o coke we e
dis inguished. Coke ype I, which bu ns a he lowes empe a u e ange (375–435
◦
C) was
Ca alys s 2024,14, 203 7 o 13
a ibu ed o amo phous coke wi h high H/C a ios [
25
] ha p esumably was deposi ed on
he ou side o ca alys pa icles and was mainly composed o pa ially deg aded HDPE
molecules [
26
]. Coke ype II was composed o mo e de eloped s uc u es (lowe H/C a io)
and was mainly loca ed in he mesopo es o he zeoli e, bu i could be also o med in he
mic opo es. This ype o coke bu n a in e media e empe a u es (435–490
◦
C). Finally,
coke ype III is asc ibed o highly condensed a oma ic s uc u es ( e y low H/C a io).
These s uc u es a e o med wi hin he c ys alline channels o he zeoli e by means o
condensa ion and hyd ogen ans e eac ions ha ake place on he inne acidic si es o he
zeoli e [
27
]. Due o i s in e nal loca ion and he possible pa ial blocking o he mic opo es
ha i could c ea e, he combus ion o his las ype o coke can be a ec ed by di usional
es ic ions. Hence, highe empe a u es we e equi ed o combus ing his ype III o coke
(490–540 ◦C).
Ca alys s2024,14,xFORPEERREVIEW7o 14
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
collec edinFigu e4,whe e hee ec s ha  heC/Fmass a iohason he o ma iono  his
ca bonaceousdeposi canbeseen.A ending o heshapeo  heTPOp o iles,i canbe
seen ha  heya equi ewideand ha  hei decon olu ionwasencou aged o eallyassess
hecon ibu iono  hedi e en  ypeso coke[24].Thus, h eedi e en  ypeso cokewe e
dis inguished.Coke ypeI,whichbu nsa  helowes  empe a u e ange(375–435°C)was
a ibu ed oamo phouscokewi hhighH/C a ios[25] ha p esumablywasdeposi ed
on heou sideo ca alys pa iclesandwasmainlycomposedo pa iallydeg adedHDPE
molecules[26].Coke ypeIIwascomposedo mo ede elopeds uc u es(lowe H/C a‐
io)andwasmainlyloca edin hemesopo eso  hezeoli e,bu i couldbealso o medin
hemic opo es.This ypeo cokebu n a in e media e empe a u es(435–490°C).Fi‐
nally,coke ypeIIIisasc ibed ohighlycondenseda oma ics uc u es( e ylowH/C
a io).Theses uc u esa e o medwi hin hec ys allinechannelso  hezeoli ebymeans
o condensa ionandhyd ogen ans e  eac ions ha  akeplaceon heinne acidicsi es
o  hezeoli e[27].Due oi sin e nalloca ionand hepossiblepa ialblockingo  hemi‐
c opo es ha i couldc ea e, hecombus iono  hislas  ypeo cokecanbea ec edby
di usional es ic ions.Hence,highe  empe a u eswe e equi ed o combus ing his
ypeIIIo coke(490–540°C).
Fo  heC/Fmass a ioso 0.05and0.075gca alys g eed−1, heTPOp o ileswe edecon‐
olu edin o wodi e en peaks,meaning ha jus coke ypeIand ypeIIwe e oundon
hesesamples.Howe e ,compa ing hepeakso bo hsamples,i canbeseen ha  hose
ob ained o aC/Fmass a ioo 0.075gca alys g eed−1shi ed owa dshighe  empe a u es.In
his ega d, hecombus iono  hecokeo  hissamplewascomposedo s uc u eswi ha
highe condensa iondeg ee,andhighe  empe a u eswe e equi ed o bu ning hem.A 
hehighes C/Fmass a io(0.1gca alys g eed−1), h eepeakswe e equi ed o decon olu ing
heTPOp o ile.So,in his hi dsample, hea o emen ioned h ee ypeso cokewe e
de ec ed.Mo eo e , his hi dp o ilewasshi ed owa dse enhighe  empe a u es han
hose equi ed o bu ning hesampleob aineda 0.075gca alys g eed−1.The e o e,anin‐
c easein heC/Fmass a ioaugmen ed heacidicsi esa ailable o c ackingmolecules
bu also hei a ailabili y o condensing hecokep ecu so s,ob ainingmo econdensed
s uc u es.

Figu e4.TPOp o ileso  hecombus iono  hecokedeposi ed o  hes udiedC/Fmass a ios,
g een,0.05gca alys g eed−1;pu ple,0.075gca alys g eed−1;o ange0.1gca alys g eed−1
140 150 160 170 180 190 200
De i a i e Weigh (mg min
-1
)
Time (min)
0.1
404
444
502
469
436
423
460
0.05 g
ca alys
g
-1
eed
0.075 g
ca alys
g
-1
eed
0.1 g
ca alys
g
-1
eed
300 350 400 450 500 550 600
Tempe a u e (ºC)
Figu e 4. TPO p o iles o he combus ion o he coke deposi ed o he s udied C/F mass a ios, g een,
0.05 gca alys g eed−1; pu ple, 0.075 gca alys g eed−1; o ange 0.1 gca alys g eed−1.
Fo he C/F mass a ios o 0.05 and 0.075 g
ca alys
g
eed−1
, he TPO p o iles we e
decon olu ed in o wo di e en peaks, meaning ha jus coke ype I and ype II we e ound
on hese samples. Howe e , compa ing he peaks o bo h samples, i can be seen ha hose
ob ained o a C/F mass a io o 0.075 g
ca alys
g
eed−1
shi ed owa ds highe empe a u es.
In his ega d, he combus ion o he coke o his sample was composed o s uc u es
wi h a highe condensa ion deg ee, and highe empe a u es we e equi ed o bu ning
hem. A he highes C/F mass a io (0.1 g
ca alys
g
eed−1
), h ee peaks we e equi ed
o decon olu ing he TPO p o ile. So, in his hi d sample, he a o emen ioned h ee
ypes o coke we e de ec ed. Mo eo e , his hi d p o ile was shi ed owa ds e en highe
empe a u es han hose equi ed o bu ning he sample ob ained a
0.075 gca alys g eed−1
.
The e o e, an inc ease in he C/F mass a io augmen ed he acidic si es a ailable o
c acking molecules bu also hei a ailabili y o condensing he coke p ecu so s, ob aining
mo e condensed s uc u es.
The esul s ob ained om he decon olu ion o he TPO p o iles a e summa ized in
Figu e 5. In his igu e, he ollowing can be ound: (i) he o al amoun s o coke o med
o each C/F mass a io oge he wi h he con ibu ion o each ype o coke (Figu e 5a);
and (ii) he maximum empe a u e a which each ype o coke bu n (Figu e 5b). Wi h
ega d o he amoun o coke, he C/F mass a io had an impo an e ec on coke o ma ion.
Hence, he highe he C/F mass a io, he highe he amoun o coke p oduced. I inc eased
Ca alys s 2024,14, 203 8 o 13
om 18.6 o 26.7 w % when inc easing he C/F mass a io om 0.05 o 0.1 gca alys g eed−1.
Rega ding coke dis ibu ion, an inc ease in he C/F mass a io caused an inc ease in bo h
ypes o coke, he inc easing a e o coke ype I being highe . In his ega d, a 0.05 g
ca alys
g
eed−1
, he con en o coke ype I and II was 4.6 and 13.9 w %, espec i ely, whe eas he
alues ob ained a 0.075 g
ca alys
g
eed−1
we e 6.7 and 14.5 w %, espec i ely. Howe e , as
explained be o e, he maximum combus ion empe a u e o each peak inc eased, esul ing
in mo e complex coke s uc u es. A he highes C/F mass a io (0.1 g
ca alys
g
eed−1
), he
ends ollowed by he ypes o coke we e simila , wi h he excep ion ha coke ype III
was also de ec ed. This ac mean ha coke ype II was capable o de eloping o a g ea e
ex en , leading o mo e condensed s uc u es and causing i s spli ing in o wo di e en
ypes o coke (coke ype II and ype III). In his ega d, coke ype I inc eased o a alue o
7.6 w %, while coke ype II sligh ly dec eased down o 14.3 w %. Finally, he amoun o
coke III o med was 4.8 w %.
Ca alys s2024,14,xFORPEERREVIEW8o 14
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
The esul sob ained om hedecon olu iono  heTPOp o ilesa esumma izedin
Figu e5.In his igu e, he ollowingcanbe ound:(i) he o alamoun so coke o med
o eachC/Fmass a io oge he wi h hecon ibu iono each ypeo coke(Figu e5a);
and(ii) hemaximum empe a u ea whicheach ypeo cokebu n (Figu e5b).Wi h
ega d o heamoun o coke, heC/Fmass a iohadanimpo an e ec oncoke o ‐
ma ion.Hence, hehighe  heC/Fmass a io, hehighe  heamoun o cokep oduced.I 
inc eased om18.6 o26.7w %wheninc easing heC/Fmass a io om0.05 o0.1gca alys 
g eed−1.Rega dingcokedis ibu ion,aninc easein heC/Fmass a iocausedaninc easein
bo h ypeso coke, heinc easing a eo coke ypeIbeinghighe .In his ega d,a 0.05
gca alys g eed−1, hecon en o coke ypeIandIIwas4.6and13.9w %, espec i ely,whe eas
he aluesob aineda 0.075gca alys g eed−1we e6.7and14.5w %, espec i ely.Howe e ,as
explainedbe o e, hemaximumcombus ion empe a u eo eachpeakinc eased, esul ‐
inginmo ecomplexcokes uc u es.A  hehighes C/Fmass a io(0.1gca alys g eed−1), he
ends ollowedby he ypeso cokewe esimila ,wi h heexcep ion ha coke ypeIII
wasalsode ec ed.This ac mean  ha coke ypeIIwascapableo de eloping oag ea e 
ex en ,leading omo econdenseds uc u esandcausingi sspli ingin o wodi e en 
ypeso coke(coke ypeIIand ypeIII).In his ega d,coke ypeIinc eased oa alueo 
7.6w %,whilecoke ypeIIsligh lydec easeddown o14.3w %.Finally, heamoun o 
cokeIII o medwas4.8w %.
A ending o he esul scollec edinFigu es4and5, hecon en o cokeand hede‐
elopmen deg eeinc easedwi h heC/Fmass a io.Ag ea e amoun o ca alys sim‐
pliedanenhancemen o  heca aly ic eac ions,lea ing he oleo  he mal eac ionsin
secondplace.Fu he mo e, he o ma iono cokep ecu so sand hei subsequen con‐
densa ion ha lead o he o ma iono cokewe ealsoboos edwi h heC/Fmass a io.
Simila  esul swe ep e iously epo edbyWange al.[28]in hehyd op ocessingo 
acuum esidue.Theyobse ed ha  he mal eac ionsp oducedsmalle amoun so coke
and ha  hecoke o med h ough hismechanismwaslessde eloped(highe H/C a io)
han hecokep oducedbyca aly icmeans.This ac isaconsequenceo  helacko  eac‐
iono  hepolya oma icswi hin heVGO ha  ended op oducebulkybu poo lyde el‐
opedagglome a eson heex e nalsu aceo  heca alys .Howe e ,when hosepolya o‐
ma icswe ehyd oc acked,leading o hep oduc iono smalle andligh e compounds,
bo halipha icsanda oma icscoulden e in o heinne channelso  hezeoli e.The e, hey
we econdensedin ocomplexpolya oma icsmolecules hanendedup o mingcoke,
which equi eshigh empe a u es obebu n becauseo i scondensa iondeg eeandi s
loca ionin heinne channelso  hezeoli e.

0.05 0.075 0.1
0
5
10
15
20
25
30
0.05 0.075 0.1
375
400
425
450
475
500
525
Coke con en w %
C/F mass a io (g
ca alys
g
-1
eed
)
To al coke
Type II
Type I
Type III
(a)
T
3
max
T
2
max
T
1
max
T
max
(ºC)
C/F mass a io (g
ca alys
g
-1
eed
)
(b)
Figu e 5. E olu ion o he (a) o al coke, con en s o he di e en ypes o coke, and he (b) maximum
coke combus ion empe a u e o he in es iga ed C/F mass a ios.
A ending o he esul s collec ed in Figu es 4and 5, he con en o coke and he
de elopmen deg ee inc eased wi h he C/F mass a io. A g ea e amoun o ca alys s
implied an enhancemen o he ca aly ic eac ions, lea ing he ole o he mal eac ions
in second place. Fu he mo e, he o ma ion o coke p ecu so s and hei subsequen
condensa ion ha lead o he o ma ion o coke we e also boos ed wi h he C/F mass a io.
Simila esul s we e p e iously epo ed by Wang e al. [
28
] in he hyd op ocessing o
acuum esidue. They obse ed ha he mal eac ions p oduced smalle amoun s o coke
and ha he coke o med h ough his mechanism was less de eloped (highe H/C a io)
han he coke p oduced by ca aly ic means. This ac is a consequence o he lack o eac ion
o he polya oma ics wi hin he VGO ha ended o p oduce bulky bu poo ly de eloped
agglome a es on he ex e nal su ace o he ca alys . Howe e , when hose polya oma ics
we e hyd oc acked, leading o he p oduc ion o smalle and ligh e compounds, bo h
alipha ics and a oma ics could en e in o he inne channels o he zeoli e. The e, hey we e
condensed in o complex polya oma ics molecules han ended up o ming coke, which
equi es high empe a u es o be bu n because o i s condensa ion deg ee and i s loca ion
in he inne channels o he zeoli e.
3. Ma e ials and Me hods
3.1. Feeds
The acuum gasoil (VGO), kindly p o ided by Pe ono Re ine y (Muskiz, Spain),
consis ed o a mix u e o di e en seconda y e ine y s eams. E en hough i was mainly
composed o he gasoil p oduced in he acuum dis illa ion column, ce ain amoun s o
Ca alys s 2024,14, 203 9 o 13
gasoils p oduced in he isb eaking and coking uni s we e also used in i s o mula ion.
In addi ion, i was p ehyd o ea ed wi hin e ine y acili ies, impo an ly a ec ing hei
physicochemical p ope ies and composi ion, as i can be seen in Table S1. In sho , i
consis ed on a low-sul u -con aining (510 ppm) and highly a oma ic (50.7 w %) s eam
wi h a boiling ange o 156–519 ◦C.
The high-densi y polye hylene (HDPE) was pu chased om Dow Chemical (Ta ag-
ona, Spain). I s main physicochemical p ope ies a e also collec ed in Table S1. Some o
hem, i.e., a e age molecula weigh , densi y and dispe si y, we e di ec ly p o ided by he
supplie , whe eas highe hea ing alues we e de e mined acco ding o Dulong o mula
om he esul s ob ained in he elemen al analysis.
3.2. Ca alys
A P -Pd ca alys suppo ed on a HY zeoli e was used o he s udy since i o e s p ope
ca aly ic beha io in hyd oc acking p ocesses [
15
]. I was in-house p epa ed ollowing a
well-es ablished p ocedu e [
16
]. In sho , me als we e inco po a ed o he suppo ia ion
exchanges ollowed by we imp egna ion. A e wa ds, i was d ied and ai calcined, be o e
being sie ed and able ed o he desi ed pa icle size (150–300 µm).
The ca alys con ained a 1.19 w % P and a 0.53 w % Pd, acco ding o ICP-AES analy-
sis. The ex u al p ope ies o he ca alys s we e measu ed ia N
2
adso p ion–deso p ion
iso he ms, esul ing in a speci ic su ace a ea o 620 m
2
g
−1
and an a e age po e diame e o
84 Å. The acidic p ope ies o he ca alys we e measu ed ia e -bu ylamine-TPD and py i-
dine FTIR. F om hese analyses, a o al acidi y o 1.69 mmol
-ba
g
−1
and a B øns ed/Lewis
acidic si es a io o 1.53 we e ob ained, espec i ely. A mo e de ailed explana ion o he
me hods and p ocedu es used o measu ing hese p ope ies oge he wi h a mo e de ailed
cha ac e iza ion o he ca alys can be ound elsewhe e [17].
3.3. Hyd oc acking Uni and Reac ion Condi ions
The eac ions we e pe o med in a 100 mL s ainless s eel semi-ba ch eac o (Pa ke
Au ocla e Enginee s, E ie, PA, USA). A schema ic ep esen a ion o he se up is p o ided in
Figu e S1. The expe imen s we e ca ied ou in a semi-con inuous egime, while he VGO
and he HDPE we e loaded a he beginning o he eac ion; hyd ogen was con inuously
ed o he eac o in o de o ensu e ha he o al p essu e emained cons an he whole
ime. A de ailed explana ion abou he expe imen al p ocedu e was al eady p o ided in a
p e ious wo k [15].
Since he aim o he wo k was o s udy he e ec s o he ca alys - o- eed (C/F) mass
a io, he ollowing alues we e es ed: 0.05, 0.075 and 0.1 g
ca alys
g
eed−1
. The es o he
ope a ing condi ions we e kep cons an a 420
◦
C, 80 ba and 120 min since hese alues
we e es ablished, by means o a kine ic model [
29
], as he op imal ones o maximize he
p oduc ion o he naph ha ac ion. The eac o essel was loaded wi h a o al mass o eed
o 40 g, wi h a HDPE- o-VGO a io o 0.2 g
HDPE
g
VGO−1
. Fu he mo e, a igo ous s i ing
a e was used (1300 pm) o ensu e a good mix u e o he phases.
A he end o he eac ion, he eac o was cooled down ollowing a hea ing a e
o 20
◦
C min
−1
using an open wa e sys em. The gases we e collec ed in a sampling
bag and analyzed ia gas ch oma og aphy. The liquids we e sepa a ed ollowing he
sol en ac iona ion me hod summa ized in Figu e S2. The i s ex ac ion was ca ied
using THF as he sol en , ob aining a ac ion soluble in THF ha was composed o
hyd oca bons and ano he insoluble ac ion whe e bo h he wax and he ca alys emained.
A e wa ds, xylene was used as he sol en agen o he second ex ac ion o sepa a e he
wax (uncon e ed and deg aded HDPE) and he ca alys .
3.4. Analysis o he P oduc s
The hyd oc acking o he HDPE/VGO blend led o he o ma ion o bo h gas and liquid
p oduc s. The gases we e collec ed om he eac o in a sampling bag once he eac ion
ime elapsed. They we e analyzed in an Agilen Technologies 6890 GC sys em equipped