Kinetic modelling of methyl formate hydrolysis in the presence of formic acid as a homogenous catalyst
1 1
O. Jogunola, 1T. Salmi, 1,2J.-P. Mikkola bo Akademi Universit , !e". #$emi%al &ngineering, 'isko"sgatan (, 2)*)), bo+Turku ,inalnd- ,a.. /0*(221*1123, &-mail4 5olatund6abo.7i- 2Ume8 Universit , !e". #$emistr , 3)1(2, Ume8, S9eden. Met$ l 7ormate :Me,o; $ drol sis, a "rominent industrial "ro%ess 7or "rodu%ing 7ormi% a%id :,A;, a versatile, environmentall benign %$emi%al, a%%ounts 7or more t$an 2)< o7 t$e 9orld "rodu%tion %a"a%it . =o9ada s, ne9 uses are being soug$t 7or t$e a%id b resear%$ers and t$e %$emi%al industr due to its relativel strong a%idit , redu%ing "o9er, and e%o7riendliness. T$e met$ l 7ormate $ drol sis "ro%ess is a slo9, endot$ermi% and e>uilibriumlimited rea%tion, 9$i%$ "rodu%es met$anol :MeO?; and ,A in almost e>uimolar amount. ?o9ever, ,A "rodu%ed in t$e rea%tion %atal sed t$at same rea%tion. ?#l and ? 2SO1 $ave been re"orted to s"eed u" t$e rea%tion, but t$ese a%ids $ave to be se"arated 7rom t$e rea%tion mi.ture and t$is adds to t$e %ost o7 energ . T$e endeavour is to use 7ormi% a%id as an initial %$arge to s"eed u" its o9n rea%tion. T$e $ drol sis e."eriments :9it$ or 9it$ ,A %atal st; 9ere done in a stirred laborator s%ale, almost isot$ermal bat%$ rea%tor at () @ 11) O# and 2) bar nitrogen "ressure using a %onstant initial 9ater-to ester molar ratio :?2O+Me,o A 1.(;. T$e $ drol sis o7 met$ l 7ormate %an be sim"l re"resented as4 ?#OO#?0 :A; / ?2O :'; ?#OO? :#; / #?0O? :!; Bn t$e absen%e o7 t$e %atal st, t$e rea%tion is auto%atal sed and t$e rea%tion rate %an be e."ressed as4
r = :k + k C C ;:C A C B 1 CC C D ; KC
Using ,A %atal st in t$e 7orm o7 an initial %$arge, t$e rate o7 t$e rea%tion be%omes4 C C r = k :C A C B C D ;: K d C C ; ).* KC 9$ere Cd is t$e disso%iation %onstant o7 7ormi% a%id. T$e model e>uations 9ere solved b di77eren%e met$od. T$e so7t9are, Mod&st solved t$e model e>uations and minimiDed t$e ob5e%tive 7un%tion :SSE A F: model- e.";2 b ad5usting t$e t$ree "arameters, k ) , K )C , and E a 9it$ t$e Gevenberg-Mar>uardt-sim"le. met$od, 9$ile H ro 9as 7i.ed at /*.11 kJ+mol. T$e kineti% and e>uilibrium "arameters in%luded in t$e rate e>uations 9ere estimated 7rom t$e e."erimental data b non-linear regression anal sis. T$e "redi%tive "o9er H 2 :%oe77i%ient o7 determining bet9een "redi%ted and e."erimental values; is given as4
R
2
:c =1 :c
i ,e.", k
ci , k ; 2 c ,i , k ; 2
i ,e.", k
9$ere c i , k is t$e model "redi%tion %on%entration, c i , k is t$e observation mean %on%entration. Results Bn t$e absen%e o7 t$e %atal st, t$e rea%tion 9as slo9 as indi%ated b t$e indu%tion "eriod. ,urt$ermore, auto%atal sis :S-s$a"ed; 9as "ronoun%ed as s$o9n in ,ig. 1. U"on addition o7 t$e %atal st, t$e indu%tion "eriod %eased to e.ist and t$e rea%tion rate 9as s"ed u". ?o9ever,
t$e "rodu%t ield 9as su""ressed. Bt %an be dedu%ed 7rom ,ig. 1 t$at t$e o"timal initial a%idto-ester molar ratio, 9$i%$ 9ill in%rease t$e rea%tion rate 9it$out $aving a drasti% e77e%t on t$e ield is ).1. T$e model "redi%tion o7 t$e rea%tion rate o7 bot$ t$e auto%atal sed "ro%ess and t$e ,A-%atal sed s stem :,A+Me,o A ).1; is de"i%ted in ,ig. 2.
Conversion (mol-%)
30
ri (mol/g min)
0.02 0.016 0.012 0.008 0.004 0 0 50 100 Time (min) Autocatalysis Formic acid catalysed 150
20 10
FA/Me Fo FA/Me Fo FA/Me Fo FA/Me Fo FA/Me Fo = = = = = 0.0 0.1 0.2 0.05 0.15
0 0 50 100 150 200 250
Time (min)
,igure 1. T$e e77e%t o7 t$e a%id %atal st on t$e rea%tion rate and e>uilibrium %onversion at () #- ?2O+Me,o A 1.(
o
,igure 2. #om"arison o7 t$e rea%tion rate o7 t$e ,A-%atal sed s stem 9it$ t$at o7 t$e auto%atal sed "ro%ess at 3)o#- ?2O+Me,o A 1.(
The results of the kinetic modelling for the two systems is depicted in Table 1. Table 1. #om"arison o7 t$e "arameters bet9een auto%atal Ded and ,A-%atal Ded rea%tions Hea%tion t "es Auto%atal sed ,A-%atal Ded
k
:kg+mol min;
k k 2 2 :kg +mol min;
Ea
Ea
I Ea
C#
:kJ+mol; :kJ+mol; :kJ+mol;
).)0 @
0.12 @
@ 0.39
((.2 @
@ 67.8
66.4 @
).2 ).2
,A-%atal sed rea%tion is more t$an t$ree times 7aster t$an t$e auto%atal sed rea%tion and t$eir a%tivation energies are in t$e %orre%t range. T$e e>uilibrium %onstant remains t$e same. Some o7 t$e 7its o7 t$e t9o models to t$e e."erimental results are de"i%ted in ,ig. 0.
C i (mol/kg)
20
20
C i (mol/kg)
15 10 5 0 0
A (expt) A (mo de l)
15 10 5 0 0
A (m ode l) D (m ode l) C (e !")
50
B (e xpt)
100
150
C (e xpt) C (mo de l)
100
Time (min)
B (m ode l) A (e !") D (e !")
200
C (m odel) B (e !")
Time (min)
B (mo de l)
,igure 0a. T$e model 7it to e."erimental data at 3)o#,A+Me,o A ).1 and ?2O+Me,o A 1.(
,igure 0. T$e model 7it to e."erimental data at 3)o#,A+Me,o A ).) and ?2O+Me,o A 1.(
Conclusion T$e $ drol sis o7 met$ l 7ormate 9it$ or 9it$out t$e 7ormi% a%id %atal st 9as a%%om"anied in a bat%$ rea%tor. T$e models develo"ed 7or t$e t9o "ro%esses 9ere able to "redi%t t$e e."erimental results su%%ess7ull . T$is a""roa%$ %an also be used 7or ot$er alk l 7ormates. Reference [1] O. Jogunola, T. Salmi, J. Wrn, J.-P. Mikkola, Kinetic studies of alkyl formate hydrolysis using formic acid as a catalyst, J. Chem. Technol. Biotechnol. (2011) DOI 10.1002/jctb.2714 [2] O. Jogunola, T. Salmi, K. Ernen, J. Wrn, M. Kangas, J.-P. Mikkola, Reversible autocatalytic hydrolysis of alkyl formate: kinetic and reactor modelling, Ind. Eng. Chem. Res. 49 (2010) 4099-4106.
