Chemical Enginee ing Jou nal 493 (2024) 152191
A ailable online 16 May 2024
1385-8947/© 2024 The Au ho (s). Published by Else ie B.V. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-
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P oduc ion o a syngas and CaO by deso p ion-enhanced e e se wa e –gas
shi o CaCO
3
wi h H
2
J.C. Abanades
a
, G. G asa
b
,
*
a
CO
2
cap u e g oup, Ins i u o de Ciencia y Tecnología del Ca bono (Spanish Resea ch Council, INCAR-CSIC) F ancisco Pin ado Fe, 26, 33011 O iedo, Spain
b
En i onmen al Resea ch g oup, Ins i u o de Ca boquímica (Spanish Na ional Resea ch Council, ICB-CSIC), Miguel Luesma Cas ´
an 4, 50018 Za agoza, Spain
ARTICLE INFO
Keywo ds:
Syngas p oduc ion
Re e se wa e –gas shi
Calcina ion
CO
2
cap u e
Packed bed eac o
ABSTRACT
A syngas p oduc ion me hod is in es iga ed ha combines in a single eac o he enhanced decomposi ion o
CaCO
3
wi h H
2
and he e e se wa e –gas shi (RWGS) o pa o he CO
2
e ol ed du ing calcina ion. The
me hod exploi s Le Cha elie ’s p inciple, o o e come RWGS equilib ium limi a ions by conduc ing such e-
ac ions wi h an excess o CaCO
3
and a su icien ly high empe a u es o main ain he pa ial p essu e o CO
2
close o he calcina ion equilib ium. The decomposi ion and RWGS eac ions esul in a ‘deso p ion-enhanced
e e se wa e –gas shi ’ (DERWGS) equilib ium o CaCO
3
on H
2
, obse ed in expe imen s pe o med in a packed-
bed eac o ope a ed be ween 1023 and 1123 K and 1 and 5 a m when eeding H
2
o a mix u e o CaCO
3
, wi h o
wi hou a RWGS ca alys . P oduc gases con aining o e 25 ol% CO, wi h an H
2
/CO mola a io o 2 and below,
we e ob ained. In expe imen s wi hou he use o an RWGS ca alys , he DERWGS equilib ium was also
app oached hanks o he ca aly ic ac i i y o CaO o RWGS. The syngas analogue ob ained om hese eac ions
opens he doo o new p ocesses o syn he ic uel p oduc ion om CaCO
3
and enewable H
2
.
1. In oduc ion
Sus ainable ca bon-con aining uels om enewable ene gy and
enewable ca bon ha e a key ole o play in deca bonising he a ia ion
and eigh anspo sec o s, among o he s, al hough imp o emen s o
p oduc ion p ocesses and cos educ ions a e equi ed [1]. Mos exis ing
p ocess ou es o he manu ac u e o syn he ic gas and liquid hyd o-
ca bons s a om a syngas con aining a ious p opo ions o CO +CO
2
+H
2
, accompanied by a di e se ange o con aminan s (i.e. H
2
S, HCl,
hyd oca bons and alkalis), which equi es deep pu i ica ion be o e
en e ing he ca aly ic syn hesis p ocess [2–6]. An al e na i e ou e o
syngas p oduc ion ha has been ecei ing inc easing a en ion in
esea ch is he hyd ogena ion o me al ca bona es, also known as “di ec
educ ion” o “ educ i e calcina ion”, as e iewed in [7] and explo ed in
o he ecen wo ks [8,9]. Among he di e en ca bona e candida es his
wo k is ocused on CaCO
3
:
CaCO3+H2→CaO +CO +H2OΔH 298K=220.3kJ/mol (1)
The use o he exp ession “di ec educ ion” o “ educ i e calcina ion” in
[8,9] e e s o he possibili y o ob aining in a single eac o he p oduc s
o wo sepa a e eac ions: as o example he CaCO
3
decomposi ion and
he Re e se Wa e Gas Shi [8]. The use o hese exp essions does no
necessa ily imply a eac ion mechanism wi h a single eac ion s ep o
di ec educ ion o CaCO
3
. Indeed, a he high empe a u es o in e es in
his wo k (T >750 ◦C) he kine ics o calcina ion a e known o be su -
icien ly as [10] o eac ion (1) o be he se ies o wo eac ions:
CaCO3←→CaO +CO2ΔH 298K=178.8kJ/mol (2)
CO2+H2←→CO +H2OΔH 298K=41.5kJ/mol (3)
In such case, when eac ions (2) and (3) occu in su icien p oximi y as
o allow hem o p og ess acco ding o he o e all eac ion (1), and he
CaCO
3
ac s as a di ec sou ce o pu e CO
2
in he gas eac ion medium,
he educ i e calcina ion o CaCO
3
p o ides oppo uni ies o p ocess
in ensi ica ion and e iciency gains [7,8].
The use o CaCO
3
as a sou ce o CO
2
and CaO can con ibu e o GHG
mi iga ion when he CaO is used as a egene able CO
2
so ben in a a-
ie y o CO
2
cap u e sys ems [11–14]. Also, in la ge scale eme ging
p ocesses o di ec CO
2
cap u e om ai [15–18], ha in ol e CO
2
ex ac ion om a CaCO
3
calcina ion s ep a some poin in hei p o-
cesses. Finally, CaO mus be p oduced o mee he global demand o
* Co esponding au ho a : En i onmen al Resea ch g oup, Ins i u o de Ca boquímica (Spanish Na ional Resea ch Council, ICB-CSIC), Miguel Luesma Cas ´
an 4,
50018 Za agoza, Spain. Tel.: +34 976 733 977.
E-mail add ess: [email p o ec ed] (G. G asa).
Con en s lis s a ailable a ScienceDi ec
Chemical Enginee ing Jou nal
jou nal homepage: www.else ie .com/loca e/cej
h ps://doi.o g/10.1016/j.cej.2024.152191
Recei ed 5 Sep embe 2023; Recei ed in e ised o m 5 Ap il 2024; Accep ed 11 May 2024
Chemical Enginee ing Jou nal 493 (2024) 152191
2
cemen and lime. Fig. 1 shows a simpli ied scheme o a CaCO
3
egen-
e a ion s age wi h H
2
in eg a ed in he ame o a gene al CaL CO
2
cap u e p ocess ( om poin sou ces o he a mosphe e).
Reac ion (1) is highly endo he mic, mainly due o he en halpy
needed o he CaCO
3
calcina ion eac ion (178.8 kJ/mol a 298 K). This
means ha hyd oca bon syn hesis ou es s a ing om CaCO
3
a e
ene ge ically un a ou ed wi h espec o he equi alen ou es s a ing
om CO
2
(g). Howe e , i could be a gued ha such a o m o o e all
hyd ogena ion o CaCO
3
can s ill compe e in ene gy e ms wi h he
equi alen ou e s a ing om CO
2
when he ene gy sa ings in he
downs eam uses o he CaO esul ing om Eq. (1) a e aken in o
conside a ion.
The hyd ogena ion o CaCO
3
was i s epo ed in 1968 [20], when
he o ma ion o CO and o he hyd oca bons was iden i ied wi hin a
ange o empe a u e and p essu es du ing expe imen s wi h an o e -
whelming p esence o H
2
(>99 ol%). Subsequen ly, in a seminal pape
in he ield o ca bona e educ ion, Relle e al. [21] obse ed he
comple e calcina ion o small samples o CaCO
3
in an H
2
a mosphe e,
de ec ed he p esence CO as a gaseous eac ion p oduc , and epo ed
ca aly ic e ec s and subs an ial educ ions (>150 K) in CaCO
3
calcina-
ion empe a u es, wi h hese e ec s enhanced by he admix u e a close
o a omic le el o ansi ion me als wi h he CaCO
3
. In a ecen e iew o
hese phenomena by R. Han e al. [13], a wide ange o dual unc ional
ma e ials combining CaO as CO
2
so ben and a ansi ion me al as hy-
d ogena ion ca alys ha e been desc ibed. Examples include he in ense
wo k ca ied ou on he design o dual unc ional ma e ials (DFM) by
Sun e al. [19,22], who e alua ed he pe o mance o a numbe o me als
ac ing as ca alys s o he e e se wa e –gas shi (RWGS) eac ion, and
who mo e ecen ly [23] con i med in independen expe imen s he
ca aly ic ac i i y o CaO o he RWGS ha had been epo ed by
Giamma ia and Le e s [24]. Such DFM ma e ials ha e shown o ha e
p omising p ope ies ha enable hem o ope a e in a wide ange o
p ocess concep s, as e iewed by Lux e al. [7]. These p ocesses usually
in ol e means o ci cula ing solids be ween a ca bona o (whe e CO
2
con ained in a gas eac s wi h CaO o o m CaCO
3
) and a hyd ogena o
(whe e he CaCO
3
will decompose in p esence o H
2
o o m CaO and a
hyd oca bon-con aining gas). Al e na i ely, i has been p oposed ha
hese p ocesses ope a e acco ding o p inciples o p essu e and/o
empe a u e swing adso p ion, by swi ching be ween ca bona ion and
hyd ogena ion condi ions in he same essel [8,19,22,23]. We ha e
ecen ly p oposed a a ian o his app oach in o de o accommoda e
he hea supply s eps needed by including a edox loop, ha p o ides he
ene gy o d i e he endo he mic eac ions (2) and (3) ha unde goes he
CaCO
3
con ained in a packed bed o solids [25]. The aim o his wo k is
o epo on a phenomenon ha has been ound o occu in hese sys ems
when ope a ing a condi ions ha allow bo h he calcina ion and RWGS
equilib ia o be ul illed. To ou knowledge, his is he i s ime ha his
phenomenon has been epo ed wi h expe imen al e idence, and i
scaled, i could lead o new p ocess ou es o hyd oca bon p oduc ion
om CaCO
3
( o med in calcium looping sys ems shown in Fig. 1) and
enewable H
2
.
2. Deso p ion-enhanced e e se wa e –gas shi o CaCO
3
The i s epo ed expe imen s in ol ing CaCO
3
decomposi ion in
p esence o H
2
[20] p oduced a a ie y o hyd oca bons and ca bon
deposi s, depending on p essu e and empe a u e condi ions. Mo e
ecen ly, Sun e al. [23] epo ed expe imen s o CaCO
3
calcina ion wi h
H
2
a a mosphe ic p essu e and empe a u es o 873–973 K, obse ing
ha while CO
2
concen a ions in he p oduc gas whe e simila o hose
ob ained in expe imen s using N
2
eed, he CO concen a ions whe e
o e 3 imes highe han hose o CO
2
. They con i med by dedica ed
expe imen s ha CaO ca alyses he RWGS eac ion o he CO
2
e ol ed
om CaCO
3
. Howe e , despi e he high selec i i y a ibu ed o CO, he
ac ual concen a ions o CO in he p oduc gas we e e y low (<3% ol
CO), equi ing challenging gas sepa a ion s eps downs eam o he hy-
d ogena ion s ep be o e such a gas can be p ocessed as a syngas. Shi e al.
[26] analysed he e ec o p essu e on p oduc gas dis ibu ion a a
simila ange o empe a u es and H
2
p essu es up o 60 a m. They
concluded ha p essu es o e 40 a m and empe a u es below 975 K
a ou ed he p oduc ion o CH
4
wi h espec o CO when CaCO
3
was
calcined wi h H
2
.
Ou in e es in his wo k is na owed down o a high empe a u e
window o 1023–1223 K ( o a p essu e ange 1–10 a m), whe e he
in insic CaCO
3
calcina ion eac ion is su icien ly as [10,27] as o
apidly app oach he equilib ium o CO
2
in CaO, wi h a pa ial p essu e
o CO
2
gi en by [28]:
PCO2eq =e(16.3−19130
T(K))=Kcalc (4)
Fig. 2 illus a es wo di e en calcina ion equilib ia in an o iginal ba ch
o CaCO
3
( ed do s) in a con ol olume whe e he o al numbe o
ca bon a oms in he sys em (as CaCO
3
, CO o CO
2
) is main ained con-
s an . The discussion ha ollows is only alid i he e is an excess o
CaCO
3
(i.e. wi h bo h CaO and CaCO
3
p esen in he solid phase, as
shown) wi hin he con ol olume. In Fig. 2 a), he pa ial p essu e,
P
CO2_eq
, and he mola con e sion o CaCO
3
o CaO, X
cal
, a e eached a
equilib ium. I an ine gas is added o he con ol olume, hen he o al
p essu e, P
T
=P
CO2_eq
+P
ine
, will inc ease wi hou al e ing ei he
P
CO2_eq
o X
cal
. A a cons an o al p essu e, he in oduc ion o H
2
o he
con ol olume ins ead o he ine gas i s equi es an inc ease in
olume, as shown in Fig. 2 b), because he e is a edis ibu ion o he
ca bon a oms in he gas and solid phase caused by he RWGS (Eq. (3). Le
Cha elie ’s p inciple, ep esen ed in Fig. 2 b), dic a es ha a ce ain
Nomencla u e
a, b Appa en eac ion o de s in Equa ion (12)
DERWGS Deso p ion-enhanced e e se wa e –gas shi
E
a
Appa en ac i a ion ene gy in Equa ion (12), kJ/mol
k
o
Appa en p e-exponen ial ac o in kine ic exp ession o
Equa ion (12), s
-1
ba
–(a+b)
K
calc
Calcina ion equilib ium cons an , a m
K
H2O
Abso p ion equilib ium cons an in Equa ion (12)
K
WGS
Wa e -gas shi equilib ium cons an
P
CO
,
CO2
,
H2O
,
H2
Gas pa ial p essu es (subsc ip
_eq
a
equilib ium), a m
P
T
To al p essu e (a m)
R
CO
CO o ma ion a e in Equa ion (12), s
-1
T
DERWGS
A e age empe a u e a he DERWGS eac ion on o
egion, K
X
cal
CaCO
3
mola con e sion o CaO
X
N
CaCO
3
con en in a CaO/CaCO
3
ma e ial
X
RWGS
CO
2
con e sion ia RWGS acco ding o Equa ion (11)
Δz Elemen olume heigh (m) in Figu es 4 and 9
Fig. 1. Simpli ied CaL scheme, including so ben egene a ion h ough CaCO
3
calcina ion in H
2
, inspi ed by e e ences in li e a u e [7,8,19].
J.C. Abanades and G. G asa
Chemical Enginee ing Jou nal 493 (2024) 152191
3
ac ion o CaCO
3
will decompose o CaO o compensa e o he CO
2
ha
is emo ed om he gas phase owing o he RWGS eac ion. In conse-
quence, CaCO
3
con e sion o CaO will inc ease, and he ca bon con en
in he p oduc gas (P
CO_eq
+P
CO2_eq
) will be highe when compa ed wi h
he e e ence case o Fig. 2 a) (i.e. P
CO2_eq
alone). A cons an p essu e,
he con ol olume will inc ease as a esul (Fig. 2 b)). In o he wo ds,
he CaCO
3
calcina ion equilib ium and he RWGS equilib ium can be
simul aneously ul illed (as long as he e is an excess o uncon e ed
CaCO
3
in he con ol olume (Fig. 2 b)). Owing o i s simila i y o well-
known so p ion-enhanced eac ions [29–33] aking place in he e e se
di ec ion o hese eac ions, we ha e named his equilib ium ‘deso p-
ion-enhanced e e se wa e –gas shi ’ (DERWGS).
To allow a quan i a i e analysis o he DERWGS equilib ium, some
u he assump ions a e adop ed. When in oducing H
2
in o he con ol
olume, se e al CO
2
educ ion eac ions can ake place ha lead o he
o ma ion o a omic ca bon, CO and hyd oca bons [7]. Howe e , we
assume ha a he empe a u es o in e es in his wo k (>1023 K), only
CO and H
2
O
(g)
a e p oduced, in ag eemen wi h he wa e –gas shi
equilib ium:
KWGS =PCO2eq*PH2eq
PCO eq*PH2O eq
(5)
To acili a e he equilib ium calcula ions below, an app oxima e equa-
ion is used o es ima e K
WGS
[34]:
ln(KWGS) = 5693.5
T+1.077ln(T) + 5.44*10−4T−1.125*10−7T2
−49170
T2−13.148
(6)
Pa icula solu ions o he DERWGS equilib ium can be ob ained when
he con ol olume is occupied by he app op ia e ini ial quan i y o
pu e H
2
and CaCO
3
o yield a inal gas p oduc a a ce ain a ge o al
p essu e. Again, his means ha he e should be su icien CaCO
3
in he
ini ial con ol olume o supply all he necessa y ca bon (P
CO_eq
and
P
CO2_eq
) in o de o ul il bo h he calcina ion and RWGS equilib ia in he
gas phase. In hese condi ions:
PT =PH2eq +PH2O eq +PCO eq +PCO2eq (7)
PH2O eq =PCO eq (8)
PH2eq =PT −2PCO eq −PCO2eq (9)
Which allows he calcula ion o equilib ium pa ial p essu es by sol ing
he quad a ic equa ion esul ing in he mass balance abo e, he e sol ed
o P
CO_eq
:
PCO eq =⎛
⎜
⎜
⎝
−2+
4+4KWGS
Kcalc (PT −Kcalc)
√2KWGS
Kcalc
⎞
⎟
⎟
⎠
(10)
As can be seen in Fig. 3 a), a a mosphe ic p essu e, he DERWGS
equilib ium (solid lines) allows he pa ial p essu e o CO o be highe
han he pa ial p essu e o CO
2
( o empe a u es below T =1080 K in
Fig. 3 a)), eaching a maximum o abou 0.25 in he pa ial p essu e o
CO a 1088 K. To illus a e such enhancemen in RWGS due o CO
2
deso p ion Fig. 3 a) also plo s in do ed lines he RWGS equilib ium
composi ion ha would be ob ained in a non-enhanced sys em whe e
pCO
2
a eac o inle is equal o ha ma ked by he CaCO
3
calcina ion
equilib ium wi h empe a u e. As i can be seen, CO yields a e highe
due o he DERWGS equilib ium un il a empe a u e o 1103 K is
eached, a e which a maximum o 0.26 in CO pa ial p essu e is p e-
dic ed by he RWGS equilib ium. F om such maxima, he CO yields
decline owa ds ze o as he s eep equilib ium cu e o CO
2
on CaO
displaces all o he gases in he con ol olume and app oaches he o al
p essu e (1 a m in Fig. 3 a). Fig. 3 b) illus a es he P
CO
_eq cu es when
he inal o al p essu e a equilib ium eaches di e en alues (no e ha
he cu e o P
CO_eq
a PT =1 a m is iden ical o ha p esen ed in Fig. 3 a),
bu he T scale has changed). No e ha he a io o expe imen al yields
o CO and CO
2
epo ed by Sun e al. [23] a 973 K in hei hyd oge-
na ion expe imen s o CaCO
3
was abou 3.1, consis en wi h he alue o
3.6 es ima ed om equa ions 4–10.
As i will be expe imen ally demons a ed in he ollowing pa a-
g aphs, he DERWGS equilib ium can be exploi ed in p ac ice a highe
empe a u es, a emp ing he hyd ogena ion o a packed bed o CaCO
3
-
con aining pa icles (o mo ing beds mo ing ela i ely slowly wi h e-
ga d o gas eloci ies) when mixed wi h a sui able RWGS ca alys . These
pa icles can be limes one (i.e. he hyd ogena ion eac o will esemble a
kiln o he p oduc ion o CaO om he hyd ogena ion o he CaCO
3
con ained in limes one, wi h means o mechanically sepa a e he ca a-
lys and CaO pa icles a he ou le ) o ca bona ed CaO pa icles (e.g.
ca bona ed pa icles exi ing a p e ious ca bona ion s age [19,23] in
calcium looping p ocesses, in pa icula when using adiaba ic packed
beds [32,33,35–39], which gene a e ca bona ed beds a empe a u es
o e 1023 K). On he o he hand, po en ial ca alys s o use o enhance
close- o-equilib ium condi ions in he RWGS eac ions could include
con en ional suppo ed me al ca alys s wi h Cu as he ac i e phase [40],
al hough o he p ecious me als (such as P and Rh) and bime allic sys-
ems ha e been p oposed. As s a ed in he same e e ence [40], i he aim
o he RWGS eac ion is o play a majo ole in e- uels p oduc ion, a
ca alys wi h ea h-abundan ma e ials, such as Fe, would be p e e able.
Howe e , since he issue o ca alys de elopmen o RWGS is ou side
he scope o his wo k, o he sake o simplici y, all expe imen s we e
Fig. 2. a) calcina ion equilib ium; b) deso p ion-enhanced e e se wa e –gas shi equilib ium.
J.C. Abanades and G. G asa
Chemical Enginee ing Jou nal 493 (2024) 152191
4
pe o med wi h he use o a comme cial Cu-ca alys .
In addi ion, also o simplici y pu poses, we assume he e ha he e is
an op ion, when needed, o p ehea he packed bed o solids o he a ge
empe a u e egion in o de o achie e maximum yields o P
CO
+P
CO2
,
as gi en by he DERWGS equilib ium a T
DERWGS
, and ha H
2
can be
p ehea ed o T
DERWGS
. A his s age, we can also igno e he adiaba ic
cooling ha endo he mic DERWGS eac ions will cause in he eac ion
zone (which can be compensa ed by pe iodically i ing a uel in he bed
o hea up he solids again o a empe a u e sligh ly abo e T
DERWGS
, as
claimed in [25]).
Unde such condi ions, ha implici ly assumes as kine ics o bo h
calcina ion and RWGS eac ions Fig. 4 ep esen s a pa icula poin in
ime in a DERWGS expe imen when he bo om pa o he bed o solids
has been al eady calcined (zone 1) and he calcina ion on is p o-
g essing upwa ds owa ds he uncon e ed solid egion in he bed (zone
4). A di e en ial olume o H
2
ed in o he eac o will i s pass
un eac ed h ough a egion o CaO (ma ked as egion 1). When H
2
eaches he CaO/CaCO
3
in e phase in he packed bed, calcina ion will
ake place as a esul o he pa ial p essu e swing imposed by he in lux
o pu e H
2
in o he bed o CaCO
3
, and CO
2
concen a ion will inc ease
sha ply om his poin (indica ed by he blue line in he Figu e on he
igh ), also causing an expansion o he con ol olume. Assuming ha
he e is su icien ca aly ic ac i i y in he elemen o olume wi h Δz as
heigh , ma ked in Fig. 4, he RWGS eac ion will also p og ess om he
poin a which he CO
2
om calcina ion becomes a ailable in he gas
phase. The RWGS eac ion a e will accele a e downs eam in he z di-
ec ion ( egion 2 in Fig. 4, and ed line in he Figu e on he igh ) as he
CO
2
concen a ion inc eases owing o calcina ion. I RWGS eac ion
kine ics do no ake place wi h su icien speed o allow equilib ium o
be achie ed wi hin he bed con ol olume (ma ked in he Figu e by i s
heigh , Δ
Z
), he gas s eam con aining H
2
, CO
2
, CO and H
2
O will
con inue eac ing o app oach K
WGS
equilib ium downs eam o he
ini ial calcina ion on , aided by he p esence o he RWGS ca alys
( egion 3 in he Figu e) in he bed o solids. As CO
2
is being con e ed o
CO along he bed leng h in egion 3, some addi ional calcina ion o he
solids may ake place, and bo h CO
2
and CO concen a ions will e ol e
u he owa ds he DERWGS equilib ium, whe e he eac ions will be
negligibly slow ( om poin 4 onwa ds). In p inciple, he DERWGS e-
ac ion on , ma ked by egions 2–3, will ad ance owa ds he end o he
eac o , as shown in Fig. 4. Depending on he kine ics o all eac ions
in ol ed, he low a es o H
2
o he eac o can be adjus ed o each
sui able space imes in o de o achie e a p oduc gas composi ion close
o he DERWGS equilib ium a he eac o exi un il a b eak h ough
occu s when he ini ial ba ch o CaCO
3
has been calcined and he e-
ac ion on ma ked by egions 2–3 eaches he end o he bed.
The ollowing sec ion p o ides he i s expe imen al p oo o
concep o he p ac ical iabili y o he DERWGS equilib ium and a
discussion o he condi ions o empe a u e and p essu e (as well as
kine ic cha ac e is ics o he RWGS ca alys ) needed o ensu e ha bo h
he kine ics o calcina ion and RWGS eac ions a e su icien ly as in
o de o exploi he bene i s o he DERWGS equilib ium as shown in
Figs. 3 and 4.
3. Expe imen al se up and ma e ials
The main se up used o in es iga e DERWGS eac ions was ha
desc ibed in o he s udies o high empe a u e solid looping cycles [37]
and is schema ically ep esen ed in Fig. 5. I consis ed o a packed bed o
solids con ined in a Kan hal ube wi h an in e nal diame e o 18 mm,
and a maximum solid bed heigh o 325 mm. The bed was ex e nally
hea ed by an elec ic hea ing wi e (powe 1.25 kW and 5 m in leng h). As
shown in he pho og aph in Fig. 5, an ex e nal insula ion laye wi h a
hickness o abou 200 mm co e ed bo h he eac o and hea ing wi e.
The sys em was equipped wi h gas mass low con olle s ha ed he
eac ing gases (H
2
, CO
2
and N
2
o close he mass balance) downwa ds
om he op o he eac o . A he eac o exi , downs eam o he wa e
condense , he e was a back-p essu e egula o al e ha allowed he
ope a ion o be pe o med a p essu es up o 5 a m. Gas analysis was
Fig. 3. a) solid lines: solu ion o he de wgs equilib ium equa ions (4–10) when PT =1 a m. Do ed lines: RWGS equilib ium when pCO
2
a eac o inle is equal o
CaCO
3
calcina ion equilib ium CO
2
pa ial p essu e. b) dependency o P
CO_eq
wi h empe a u e o di e en o al p essu es acco ding o DERWGS equilib ium.
Fig. 4. Rep esen a ion o he p og ess o he DERWGS on h ough a packed-
bed eac o ini ially con aining CaCO
3
and an RWGS ca alys . G aph on he
igh ep esen s he e olu ion o CO
2
and CO wi h bed leng h e e ed o
equilib ium.
J.C. Abanades and G. G asa
Chemical Enginee ing Jou nal 493 (2024) 152191
5
pe o med on an aliquo o he p oduc gas using a mic o-GC (Va ian CP-
4900) appa a us. The axial empe a u e p o ile du ing ope a ion was
measu ed and logged a 15 di e en poin s placed along he leng h o
he eac o . An impo an de ail o discussions below is ha he con ol
o he powe inpu o he hea ing wi e was based on he bed empe a u e
as measu ed by he he mocouple imme sed a he bo om pa o he
bed (i.e. he las po ion o bed in con ac wi h he gas).
In addi ion o he se up in Fig. 5, a qua z mic o packed-bed eac o
(4 mm i.d.) placed inside a empe a u e-con olled u nace (capable o
ope a ing up o 1123 K), and ed by gas mass low con olle s o N
2
, H
2
and CO
2
, was used o wo pu poses: o ule ou signi ican ca aly ic
e ec s om he Kan hal wall in he expe imen s o Fig. 5 [41]; and o
sepa a ely assess he ca aly ic ac i i y o he RWGS o he Ca-ma e ials
used in he expe imen s, as he e has been ecen e idence epo ing
ca aly ic ac i i y o CaO o RWGS [24] and [23]. In such expe imen s,
he p oduc gas composi ion was analysed wi h a Va ian CP-3800,
equipped wi h a HayesepQ and a Molsie e 13x, wi h a TCD de ec o .
A mo e de ailed s udy on he ca aly ic ac i i y o RWGS o he solids
used in his wo k is conside ed beyond i s scope.
Wi h ega ds o ma e ials, a s anda d high pu i y na u al limes one
(98.96 w % CaCO
3
wi h MgO as main impu i y) wi h a 1–2 mm size cu
was used in he packed bed eac o expe imen s, while a ine size cu o
100–200
μ
m was used o assess ca aly ic e ec s in he mic o packed-bed
eac o . Expe imen s wi h cycled CaO/CaCO
3
ma e ials (i.e. wi h
dec easing CaCO
3
con en due o he ca bona ion/calcina ion cycling
[42]) we e ca ied ou a di e en gas eloci ies be ween 0.04 m/s and
0.2 m/s in o de o gi e a gas–solid con ac ime o be ween 7.5 and 0.74
s. To ensu e as RWGS eac ion a es, as equi ed o app oach he
DERWGS equilib ium, he ini ial es s we e ca ied ou by mixing solids
con aining CaCO
3
wi h a comme cial Cu-based WGS ca alys known o
ha e RWGS ac i i y. As CaO has ecen ly been epo ed o beha e as a
RWGS ca alys [23,24], expe imen s using only CaO/CaCO
3
wi h
di e en ca bona ion con en s we e also ca ied ou . The sys em ope -
a ed cyclically du ing hese expe imen s, and once he CaCO
3
was
comple ely calcined in a DERWGS s age, a CaO ca bona ion s age was
pe o med by in oducing a CO
2
/N
2
gas s eam wi h known composi ion
in o he eac o . By sol ing he CO
2
mass balance du ing he ca bona ion
s ages, i was possible o calcula e he CaO ca bona ion con e sion o
CaCO
3
mola con en
,
X
N
, a he beginning o he ollowing DERWGS
cycle. The e olu ion o X
N
wi h inc easing numbe o cycles was
consis en wi h he s anda d CO
2
ca ying capaci y decay cu e p e-
sen ed by limes one when subjec ed o epe i i e calcina ion-
ca bona ion cycles [39,42]. Fu he mo e, he a e age calcina ion a e
and a e age CO p oduc ion a e we e de e mined in all he expe imen s
om he mass balance applied o he sys em. The CO
2
and CO lows a
he eac o exi we e calcula ed based on p oduc gas composi ion and
N
2
low a he inle . In his way he a e age CaCO
3
calcina ion a e was
calcula ed as he sum o CO
2
and CO lows di ided by he eac o c oss
sec ion, while he CO p oduc ion a e was es ima ed om he CO low a
he eac o exi di ided by eac o c oss sec ion.
4. Resul s and discussion
Fig. 6 shows a i s example o expe imen al esul s exhibi ing
DERWGS phenomena. The expe imen was ca ied ou by loading he
packed-bed eac o wi h a ba ch comp ising 0.04 kg o he 1–2 mm
ca bona ed ma e ial (wi h CaCO
3
ca bona e con en , X
N
=0.74) and
pelle s o a Cu-based RWGS ca alys wi hin he same pa icle size in-
e al, o each a Cu concen a ion in he bed o 8 w %. The solids we e
i s p ehea ed o an a e age empe a u e o 1053 K in an a mosphe e o
pu e CO
2
o p e en CaCO
3
decomposi ion. A as swi ching o al es
allowed he sudden eed o H
2
in o he p ehea ed solids ( o con e-
nience, in o de o ace exis ing gas concen a ions inside he analyse ,
7.5 ol% N
2
was used o dilu e he H
2
eed), a an inle gas eloci y o
0.19 m/s, esul ing in a esidence ime o he gas o 1.7 s. The dashed
lines, ma ked as T
DERWGS
, we e es ima ed as he empe a u e a which
P
CO2_eq
equals he expe imen al P
CO2
measu ed in he p oduc gas, which
is consis en wi h he expe imen al empe a u e p o iles in he bed, as i
will be discussed below. As i can be seen in Fig. 6 a), du ing he i s
1000 s o he expe imen , he p oduc gas composi ion is ully consis en
wi h he DERWGS equilib ium a T
DERGWS
o 1043 K, calcula ed wi h
Equa ions (4)–(10) and ep esen ed wi h do ed lines. Expe imen al
P
H2O
is assumed o be equal o P
CO
as he e a e no o he eac ions apa
om hose in Fig. 2 b) ha could consume H
2
O (i.e. no Ca(OH)
2
o -
ma ion [43]). As o ha poin , a b eak h ough appea s in all gas com-
posi ions ha coincides wi h he ime a which he bed is app oaching
ull calcina ion and he concen a ion o H
2
a he ou le is he same as a
he inle .
No e ha T
DERWGS
in his case is abou 10 K lowe han he ini ial
empe a u e o he bed o solids. This can be explained by he endo-
he mic na u e o he DERWGS eac ion, which gene a es empe a u e
p o iles in he bed ha a e una oidable in he expe imen al se up used
o hese expe imen s, as i will be discussed below. Acco ding o mass
balance applied o he p oduc gas, 0.29 mol CaCO
3
was calcined in his
es a an a e age calcina ion a e du ing he DERWGS pe iod o 1.07
mol CaCO
3
/(m
2
•s) and a CO p oduc ion a e o 0.62 mol CO/(m
2
•s).
Since he ini ial CaCO
3
mass p esen in he bed was 0.3 mol, he e was
good closu e o he ca bon mass balance in his expe imen . Fig. 6 b)
con i ms he easibili y o p oducing a syngas wi h he maximum CO
con en p edic ed by he DERWGS equilib ium when ope a ing he
sys em a di e en empe a u es and p essu es. In he example o Fig. 6
b), he packed-bed eac o had been ope a ed a 5 a m o al p essu e and
p ehea ed a an a e age empe a u e o 1123 K, wi h an inle gas low
con aining 95 ol% H
2
and 5 ol% N
2
, esul ing in a linea gas eloci y o
Fig. 5. Schema ic diag am a) and pic u e o he expe imen al packed bed ins alla ion b).
J.C. Abanades and G. G asa

Chemical Enginee ing Jou nal 493 (2024) 152191
6
0.043 m/s (gas/solid con ac ime 7.5 s). A b eak h ough is again
obse ed in he gas composi ion cu es ha co esponds o he comple e
consump ion o he CaCO
3
in bed; howe e , he cu es a e less sha p
han in Fig. 6 a) as he mola low a e o H
2
in o he eac o inc eased by
1.43 imes. Acco ding o ca bon mass balances, 0.32 mol CaCO
3
we e
calcined in he bed a an a e age a e o 1.07 mol CaCO
3
/(m
2
•s) du ing
he DERWGS pe iod, wi h an a e age CO o ma ion a e o 0.65 mol CO/
(m
2
•s). The a e age expe imen al H
2
/CO a io was 2.1, which was e y
close o he one p edic ed by he DERWGS equilib ium a 5 a m and
1113 K (H
2
/CO =2.2).
As no ed p e iously, Giamma ia and Le e s, [24], and la e Sun
e al. [23] ecen ly epo ed he RWGS ca aly ic ac i i y o he CaO
su ace esul ing om CaCO
3
calcina ion. The e o e, addi ional se o
expe imen s we e pe o med in a bed wi hou Cu- ca alys . Fo his
pu pose, 70 g limes one (app oxima ely 0.7 mol CaCO
3
) was in oduced
in he eac o , esul ing in a bed leng h o 150 mm. Nine consecu i e
DERWGS s ages, each ollowed by a CaO ca bona ion s age in 90 ol%
CO
2
, we e pe o med in he eac o . The H
2
inle gas low a es we e
a ied om 10 lN/h o 50 lN/h, esul ing in linea gas eloci ies be ween
0.062 and 0.2 m/s.
Fig. 7 a) shows expe imen al esul s om a es s a ing wi h lime-
s one only in he bed. The eac o was p ehea ed o an a e age bed
empe a u e o 1035 K in pu e CO
2
o p e en any CaCO
3
decomposi-
ion, a e which 10 lN/h H
2
and 3 lN/h N
2
we e in oduced in o he
eac o , esul ing in a linea gas eloci y o 0.062 m/s and a gas–solid
con ac ime o 2.47 s. A s able p oduc gas wi h 56 ol% H
2
, 17 ol%
CO
2
and 27 ol% CO was ob ained a he eac o ou le , which was ully
consis en wi h he DERWGS equilib ium a 1028 K. Fig. 7 b) shows he
empe a u e e olu ion as measu ed by he six he mocouples imme sed
in he bed o solids. Because he gas en e ed om he op, he he mo-
couple a 25 mm was he i s o ace he eac ion on . As p e iously
men ioned, he he mocouple a 150 mm con olled he powe inpu o
he sys em. As can be obse ed in he Fig. 7 b) once he es s a ed, he
empe a u e a 25 mm dec eased as CaCO
3
calcina ion and RWGS e-
ac ions we e aking place. The empe a u e in his i s bed slice
dec eased o app oxima ely one hou . A his poin , he CaCO
3
in he
slice mus ha e been calcined, and he eac ion p og essed o he
ollowing bed slice (no e he T dec ease a 50 mm om he gas inle ).
The ac ha no a ia ions in empe a u e occu ed downs eam o he
slice being calcined indica es ha bo h CaCO
3
calcina ion and RWGS
eac ion ook place in p oximi y. O he wise, he gas composi ion would
ha e a ied along he bed leng h, and he bed empe a u e would ha e
been a ec ed by he eac ions. Acco ding o mass balances, he calci-
na ion a e in he eac o was de e mined as 0.351 mol CO
2
/(m
2
•s) and
he CO p oduc ion was es ima ed as 0.213 mol CO/(m
2
•s). Fu he mo e,
he ob ained a io H
2
/CO was 2.1, consis en wi h equilib ium p e-
dic ions as a a io H
2
/CO equal o 2.15 was calcula ed o a T
DRWGS
o
1028 K.
The esul s o Fig. 7 con i m ca aly ic ac i i y in he CaO bed o
RWGS, since he kine ics o he homogeneous RWGS eac ion a hese
Fig. 6. P oduc gas composi ion o e ime o DERWGS s ages pe o med in a eac o con aining CaCO
3
/CaO and RWGS ca alys a : a) 1 a m o al p essu e, wi h inle
gas eloci y o 0.19 m/s a T
DERWGS
1043 K. b) 5 a m o al p essu e, wi h inle gas eloci y o 0.043 m/s a T
DERWGS
1113 K. Do ed-dashed lines in he igu es
co espond o DERWGS equilib ium composi ions acco ding o Equa ions (4–10) calcula ed a T
DERWGS
. Inle gas composi ion ma ked by H
2
in he eed gas (being he
es N
2
).
Fig. 7. A) p oduc gas composi ion o e ime o a de wgs s age pe o med in a eac o con aining caco
3
/CaO a 1 a m o al p essu e, wi h inle gas eloci y o 0.062
m/s a T
DERWGS
1028 K. Do ed lines in he igu e co espond o DERWGS equilib ium composi ions acco ding o Equa ions (4–10) calcula ed a T
DERWGS
. Inle gas
composi ion ma ked by H
2
in he eed gas (being he es N
2
). b) Bed empe a u e p o ile e olu ion o e ime o he same es .
J.C. Abanades and G. G asa
Chemical Enginee ing Jou nal 493 (2024) 152191
7
condi ions would no ha e been able o jus i y CO
2
con e sion o highe
han 1 % in he absence o ca alys [41]. Al hough he de ailed analysis
o such ca aly ic e ec s o RWGS is ou side he scope o his wo k,
expe imen s we e ca ied ou in he p e iously desc ibed qua z mic o
packed-bed eac o o elucida e on he main sou ce o such ca aly ic
ac i i y. Fo his pu pose, 280 mg limes one was in oduced in he mic o
packed-bed eac o . The expe imen al ou ine o de e mine CaCO
3
ca -
aly ic ac i i y was o hea up he ma e ial in CO
2
o 1073 K o p e en
calcina ion; hen a mix u e o 52 ol% H
2
and 41 ol% CO
2
balanced in
N
2
(50 Nml/min o al gas low) was in oduced in o he eac o and he
p oduc gas analysed. A simila es wi h no solids was ca ied ou o
de e mine RWGS con e sion in he emp y eac o . A e 30 min o
eco ding s able p oduc gas composi ion, he ex en o RWGS eac ion
was de e mined acco ding o Eq. (11) as he a io be ween he equilib-
ium cons an a hese ini ial eac ing condi ions acco ding o Eq. (6)
[34] and he obse ed K
WGS, obs
calcula ed h ough Eq. (5):
XRWGS =KWGS
KWGS,obs
(11)
The alue o X
RWGS
was lowe han 10 % in expe imen s wi h CaCO
3
,
and e y simila o ha ob ained in he emp y eac o . In con as , and in
ag eemen wi h he ecen indings by Giamma ia and Le e s [24], he
equi alen es conduc ed wi h CaO in he bed esul ing om he
calcina ion in N
2
o he ca bona ed ma e ial a 1073 K yielded a X
RWGS
alue o 87 % (in his case, when eeding a mix u e o 30 ol% H
2
and 19
ol% CO
2
balanced in N
2
o p e en any CaO ca bona ion). The e o e,
CaO p esen ed a ca aly ic ac i i y o 0.11 mol CO p oduced/g CaO/h a
1073 K and 0.048 s esidence ime in he eac o . Such le el o ac i i y is
consis en wi h he RWGS kine ic model in he p esence o CaO as
desc ibed by Giamma ia e al. [24], om which he equa ion o CO
o ma ion eac ion a es can be ew i en using he uni s and no a ion o
his wo k as:
RCO =
koe(−Ea
RT )PCO2aPH2b(1−KWGS
KWGS,obs)
1+PH2OKH2O
(12)
wi h kine ic pa ame e s wi hin he ange o hose p oposed in he
e e enced wo k (ln ko (s-1 ba -(a +b) =21; E
a
(kJ/mol) =135; a =0.6;
b =0.8 and ln K
H2O
=6.7).
F om addi ional es s (some o which a e shown in Figs. 8 and 9) wi h
di e en alues o he ac ion o ac i e CaO in he bed ( a ying om X
N
=1 o 0.24), i was obse ed ha he ca aly ic ac i i y o RWGS
dec eased wi h dec easing alues o X
N
. Fu he mo e, o a gi en alue
o X
N
, inc easing he H
2
low esul ed in a p opo ional educ ion in
b eak h ough ime and he sha pness o he DERWGS eac ion on . As
an example, Fig. 8 shows he e olu ion o he p oduc gas composi ion
and bed empe a u e p o ile o e ime o wo expe imen s: a) a an inle
gas eloci y o 0.14 m/s and a e age bed empe a u e o 1003 K in a bed
con aining 36.6 % moles CaCO
3
, being he es CaO; b) o an inle gas
eloci y o 0.2 m/s, a an a e age bed T o 1038 K in a bed con aining
31.6 % moles CaCO
3
. F om he empe a u e p o iles in hese wo ex-
pe imen s, i can be obse ed ha inc easing he inle H
2
low inc eased
he eloci y o he DERWGS on , which eached he las po ion o bed
a abou 2200–2400 s o he es pe o med a he lowe gas eloci y,
compa ed o 900–1000 s o he expe imen pe o med a 0.2 m/s gas
eloci y. These ends a e consis en wi h he desc ip ion o he
DERWGS eac ion on gi en in Fig. 4. A calcina ion a e o 0.346 mol
CO
2
/(m
2
•s) wi h a CO p oduc ion a e o 0.24 mol CO/(m
2
•s) was
de e mined om he es in Fig. 8 a), while a calcina ion a e o 0.79 mol
CO
2
/(m
2
•s) and he p oduc ion o 0.454 mol CO/(m
2
•s) we e de e -
mined o he es a he highes inle gas low. As can be obse ed, a gas
wi h s able composi ion was ob ained in bo h cases while he e was s ill
CaCO
3
in he bed; howe e highe H
2
/CO a ios han p edic ed by
Fig. 8. P oduc gas composi ion, and bed empe a u e p o ile o e ime o a DERWGS s age pe o med in a eac o con aining CaCO
3
/CaO a 1 a m o al p essu e: a)
inle gas eloci y o 0.14 m/s a T
DERWGS
1001 K; b) inle gas eloci y 0.2 m/s a T
DERWGS
1030 K. Do ed lines in he igu e co espond o DERWGS equilib ium
composi ions acco ding o Equa ions (4–10) calcula ed a T
DERWGS
. Inle gas composi ion ma ked by H
2
in he eed gas (being he es N
2
).
J.C. Abanades and G. G asa
Chemical Enginee ing Jou nal 493 (2024) 152191
8
equilib ium we e ob ained (i.e. Fig. 8 a) H
2
/CO a io =4.49 s 3.67
p edic ed by equilib ium; Fig. 8 b) H
2
/CO a io =4.05 s 2.35 p edic ed
by equilib ium).
Fig. 9 shows an example wi h expe imen al condi ions as in Fig. 7,
bu wi h a lowe CaCO
3
con en in he bed (25.6 w %), being he es
inac i e CaO esul ing om he consecu i e calcina ion-ca bona ion
cycles expe ienced by his ba ch o ma e ial. As can be obse ed in
Fig. 9 a), bo h he gas concen a ion p o iles and empe a u es show ha
he eac ion on is occu ing in a wide bed leng h and ha he gas a
he eac o ou le does no each he DERWGS equilib ium (only CO
2
gas
is a equilib ium). This indica es ha he modes ac ion o CaO
gene a ed by calcina ion does no p o ide su icien ca aly ic ac i i y o
he RWGS eac ion, as i seems easonable o assume ha he ac ion o
inac i e CaO (i.e. he (1-X
N
) ac ion o CaO unable o eac wi h CO
2
in
ca bona ion expe imen s because i is co e ed by a CaCO
3
p oduc laye
[44,45]) canno con ibu e o any ca aly ic ac i i y. The e o e, in he
absence o an e ec i e RWGS ca alys downs eam o he calcina ion
on (see Fig. 9 b), he p oduc gas composi ion a he eac o ou le
(zone 4) should be close o ha p oduced a he exi o he calcina ion
on (zone 3).
The p e ious obse a ions highligh he need o an adequa e cha -
ac e isa ion o he ca aly ic ac i i y o RWGS o all he solids loca ed
downs eam o he calcina ion on gene a ed when H
2
eaches he
sec ion o he bed con aining CaCO
3
( egion 2 in Fig. 9 b). Howe e , he
expe imen al da a ob ained in Figs. 7–9 show ha ca aly ic ac i i y o
CaO in he sho gas esidence ime expec ed wi hin he calcina ion on
(which can be es ima ed om empe a u e p o ile e olu ion) is cohe en
wi h he ca aly ic ac i i y measu ed in he qua z eac o , which is in
u n consis en wi h he esul s ob ained by Giamma ia and Le e s [24]
despi e hei di e en ield o applica ion.
Fu u e wo k should expand on hese indings o o he ma e ials, such
as combined CaO and RWGS ca alys ma e ials (as he ma e ials de el-
oped in o he DFM applica ions e iewed in [13]). F om he p ocess
design pe spec i e, i will be impo an o explo e he implica ions o
scaling up he DERWGS p ocess o he 10–20 m heigh eac o se up ha
is cha ac e is ic o simila high- empe a u e solid looping cycles using
packed beds [46]. Two majo p ocess al e na i es can be en isaged. The
i s is he p oduc ion o CaO and syngas om he calcina ion o p e-
hea ed limes one (o a solid wi h a high CaCO
3
con en i.e. om a DAC
sys em) wi h an H
2
s eam, whe e he CaO RWGS ca aly ic ac i i y may
be su icien , and no addi ional ca alys migh be needed. The second
majo p ocess ou e in ol es he in eg a ion o hese eac ions as pa o
a la ge CaL CO
2
cap u e sys em (i.e. by ca bona ing CaO wi h CO
2
and
elying on he modes Ca-con e sion o CaCO
3
cha ac e is ic o hese
CaL sys ems) as has been concep ually desc ibed when using dual
unc ional ma e ial ope a ing a lowe empe a u es [13,19,22]. In his
case, he low ca aly ic ac i i y o he sin e ed CaO, cha ac e is ic o
highly cycled Ca-ma e ials, equi es an RWGS ca alys in he bed o
solids. Howe e , since ca bona ion and DERWGS eac ions would
ope a e cyclically, no solid sepa a ion is equi ed. In his case, in addi-
ion o he ca bona ion s age, an in-si u chemical looping combus ion
s age is needed o es o e ini ial bed empe a u e in he ca bona ed bed
equi ed o launch a new DERWGS eac ion s age [25]. The indings
p esen ed in his wo k open up a p omising ou e o he calcina ion o
CaCO
3
wi h H
2
ollowed by RWGS, acco ding o eac ions (2) and (3), o
manu ac u e hyd oca bons and CaO. A DERWGS p ocess can be seen as
he e e se eac ion o wha has been in es iga ed o e many decades as
so p ion-enhanced eac ions o H
2
p oduc ion om uels and CaO o
o m CaCO
3
. This pa adigm shi is a sign o he enewable ene gy
e olu ion in which he wo ld is engaged oday.
5. Conclusions
The calcina ion o CaCO
3
wi h enewable H
2
( ollowing eac ions (2)
and (3), while gene a ing CaO as an indus ial commodi y o as a CO
2
cap u e so ben , may become a iable ou e o he p oduc ion o a
syngas wi h sui able (CO
2
+CO)/H
2
mola a ios o hyd oca bon
manu ac u e.
Fig. 9. a) p oduc gas composi ion, and bed empe a u e p o ile o e ime o a de wgs s age pe o med in a eac o con aining caco
3
/CaO a 1 a m o al p essu e,
same condi ions as in Fig. 6. CaCO
3
con en 25.6 w %. Inle gas composi ion ma ked by H
2
in he eed gas (being he es N
2
). b) P og ess o he DERWGS on along
a packed-bed eac o con aining CaO/CaCO
3
, wi h calcina ion and RWGS occu ing in a wide eac ion on . G aph on he igh ep esen s he e olu ion o CO
2
and
CO wi h bed leng h e e ed o equilib ium.
J.C. Abanades and G. G asa
Chemical Enginee ing Jou nal 493 (2024) 152191
9
The equilib ium limi a ions imposed by he RWGS eac ion, can be
o e come a empe a u es be ween 1023 and 1173 K by conduc ing such
a eac ion wi h an excess o CaCO
3
in o de o keep he pa ial p essu e
o CO
2
close o he equilib ium o CO
2
in CaO, esul ing in a deso p ion-
enhanced e e se wa e –gas shi equilib ium o CaCO
3
on H
2
, DERWGS,
which has been obse ed in a wide ange o empe a u es (be ween
1003 K o 1113 K) p essu es (be ween 1 o 5 a m), ca bona e con en (X
N
om 1 o 0.24) and sui able gas–solid con ac imes o la ge scale
applica ions.
The i s necessa y condi ion o enable DERWGS o be expe imen-
ally obse ed in packed-bed eac o s con aining CaCO
3
solids is he
de elopmen o a su icien ly as calcina ion eac ion on when H
2
eaches he bed o CaCO
3
solids (i.e. empe a u es exceeding 1000 K a 1
a m in he eac ion on a e equi ed). The second condi ion o
DERWGS is ha he e is su icien ca aly ic RWGS ac i i y in he bed o
solids loca ed downs eam o he calcina ion eac ion on . This can be
achie ed by mechanically mixing an RWGS ca alys wi h he bed o
solids con aining CaCO
3
, o by using CaO ma e ials wi h su icien ac-
i i y in ela ion o CO
2
cap u e, which ha e been shown o display
ca aly ic ac i i y o RWGS consis en wi h he model by Giamma ia and
Le e s [24]. P oduc gases con aining CO, CO
2
and H
2
, and H
2
O
( )
wi h
an H
2
/CO mola a io o 2 o lowe a e ob ained in a wide ange o
ope a ing condi ions ha can o m he basis o scaling up his p ocess o
di ec ou es o syngas and hyd oca bon p oduc ion by he educ i e
calcina ion o CaCO
3
wi h enewable H
2
( h ough equa ions (2) and (3).
CRediT au ho ship con ibu ion s a emen
J.C. Abanades: W i ing – e iew & edi ing, Me hodology, Concep-
ualiza ion. G. G asa: W i ing – o iginal d a , In es iga ion,
Concep ualiza ion.
Decla a ion o compe ing in e es
The au ho s decla e ha hey ha e no known compe ing inancial
in e es s o pe sonal ela ionships ha could ha e appea ed o in luence
he wo k epo ed in his pape .
Da a a ailabili y
Da a will be made a ailable on eques .
Acknowledgemen s
This esea ch is pa o he CSIC p og amme o he Spanish Reco -
e y, T ans o ma ion and Resilience Plan (PTI +TRANSENER) unded by
he Reco e y and Resilience Facili y o he Eu opean Union, es ablished
by he Regula ion (EU) 2020/2094.
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