Thesis (MScEng)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Pure primary alcohols are very valuable as raw materials and solvents.
Close-boiling alcohol mixtures are produced as byproducts from the Fischer
Tropsch synthesis. These byproducts include the mixtures 1-butanol+2-
penta noI and 1-pentanol+2-hexanol. Due to the small difference in boiling
points these alcohols cannot be separated from one another by using
conventional distillation.
This study has been undertaken to determine whether primary and secondary
alcohols may be separated by exploitation of their chemical properties.
Esterification of the alcohols followed by distillation of the esters into cuts and
hydrolyses of the esters, has been attempted to separate the alcohols. This
however, was unsuccessful.
In this study the difference in dehydration rate of secondary and primary
alcohols in acidic media has also been investigated. Several acidic resins
and liquid catalysts have been used. The acidic resins gave no dehydration
or extremely low dehydration rates in the liquid phase. The liquid catalysts
H2S04, Oxalic Acid, NaHS04 and H3P04 were investigated. H3P04 gave
excellent results. Laboratory experiments were conducted at the boiling point
of the reaction mixture at atmospheric pressure. The reaction mixture was
sampled at varying time intervals and analysed. The secondary alcohol
dehydrated rapidly to the corresponding alkene. The primary alcohol formed
symmetrical ethers at a very low rate. The primary and secondary alcohol
also combined to form small amounts of unsymmetrical ethers. After the
dehydration reaction the organic products can be separated from the acid
with a'short path distillation unit. The primary alcohol can further be purified
by conventional distillation. Conceptual process designs were done for the
separation and purification of the reactor product streams of the alcohol
mixtures 1-butanol+2-pentanol and 1-pentanol+2-hexanol. n laboratory scale it was found that for the separation of 85% 1-butanol and
15% 2-pentanol (mass %), 90 % H3P04 (mass %) at an acid:alcohol ratio of
1,5: 1 results in suffcient dehydration of 2-pentanol. A reaction time of 70
minutes is required. A conceptual design on the purification of the 1-butanol
predicted a product quality of 99,5 % 1-butanol (mass %) and a 1-butanol
recovery of 75 %. The 1-butanol recovery is low, because a major part of the
1-butanol is lost in the purification as part of the ternary azeotrope with water
and n-butylether.
On laboratory scale it was also found that for the separation of 85 % 1-
pentanol+15 % 2-hexanol (mass %),90 % H3P04 (mass %) at an acid:alcohol
ratio of 1,5:1 gives sufficient dehydration of 2-hexanol. A reaction time of only
35 minutes is required. A conceptual design on the purification of the 1-
pentanol predicted a product quality of 99,9 % 1-pentanol and a 1-pentanol
recovery of > 98 %. The 1-pentanol recovery is excellent, only the 1-
pentanol that is converted to ethers is lost.
In this study it has been proven that a dehydration separation process can be
applied successfully to remove secondary alcohols from a primary+secondary
alcohol mixture. Especially the removal of 2-hexanol from a 1-pentanol+2-
hexanol mixture gave promising results. In order to assess the economic
viability of this dehydration process an economic evaluation should be done.
This could be part of subsequent studies.
The dehydration separation process should be investigated further. It is
believed that this dehydration separation process can be expanded to higher
alcohols, e.g. 1-hexanol+2-heptanol. It would be extremely advantageous if
a solid catalyst could be found for the separation. In this case the recovery of
the organics from the reaction mixture would be very much easier. If a solid
catatyst is not found, a continuous process using H3P04 as liquid catalyst
should be developed. / AFRIKAANSE OPSOMMING: Suiwer primêre alkohole is baie waardevolle rou materiale en oplosmiddels.
Alkohol mengsels, wat uit naby-kokende alkohole bestaan, word as neweprodukte
in die Fischer Tropsch Sintese gevorm. Hierdie newe-produkte sluit
alkohol mengsels soos 1-butanol+2-pentanol en 1-pentanol+2-hexanol in.
Weens die klein verskil in kookpunte van hierdie alkohole kan die alkohole nie
met konvensionele distillasie van mekaar geskei word nie.
Hierdie studie is onderneem om te bepaal of die chemiese eienskappe van
alkohole benut kan word om primêre en sekondêre alkohole van mekaar te
skei. 'n Poging is aangewend om die alkohole met behulp van esterifikasie te
skei. Die alkohole is eers ge-esterifiseer, daarna met behulp van distillasie in
verskeie snitte verdeel en die alkohol is vrygestel deur hidrolise van die
esters. Dit was egter onsuksesvol.
Die verskil in dehidrasie tempo van sekondêre en primêre alkohole in suur
mediums is ook ondersoek. Verskeie suur harse en vloeibare kataliste is
ondersoek. Die suur .harse het of geen dehidrasie of baie lae dehidrasie
tempo's in die vloeistoffase gegee. Die vloeistof kataliste H2S04, Oksaalsuur,
NaHS04 en H3P04 is ondersoek. H3P04 het uitstekende resultate gelewer.
Eksperimente is op laboratoriumskaal en onder atmosferiese druk uitgevoer.
Monsters is van die reaksiemengsels by verskillende tydsintervalle geneem
en geanaliseer. Die sekondêre alkohol het vinnig na die ooreenstemmende
alkeen gedehidreer. Die primêre alkohole het simmetriese eters teen 'n lae
tempo gevorm. Die primêre en sekondêre alkohole het ook gekombineer om
gemengde eters te vorm. Kort-pad-distillasie kan gebruik word om na die
dehidrase reaksie die organiese produkte van die suur te verwyder. Die
primêre alkohole kan verder met konvensionele distillasie gesuiwer word.
Konseptueie prosesontwerpe is uitgevoer vir die skeiding en suiwering van
die alkohol mengsels 1-butanol+2-pentanol en 1-pentanol+2-hexanol nadat
dehidrasie van die mengsels uitgevoer is. Op laboratoriumskaal is dit gevind dat vir die skeiding van 85% 1-butanol en
15% 2-pentanol (massa %), 90 % H3P04 (massa %) met 'n suur:alkohol
verhouding van 1,5:1 effektiewe dehidrase van 2-pentanol lewer. fn
Reaksietyd van 70 minute word benodig. fn Konseptueie ontwerp vir die
suiwering van die 1-butanol het fn produkkwaliteit van 99,5 % 1-butanol
(massa %) en fn 1-butanol opbrengs van 75 % voorspel. Die 1-butanol
opbrengs is laag aangesien fn groot deel van die 1-butanol verlore gaan as
deel van die ternêre azeotroop wat 1-butanol met n-butieleter en water vorm.
Dit is ook op laboratoriumskaal vasgestel dat vir die skeiding van 85 % 1-
pentanol+15 % 2-hexanol (massa %), 90 % H3P04 (massa %) met fn
suur:alkohol verhouding van 1,5:1 effektiewe dehidrase van 2-hexanollewer.
fn Reaksietyd van slegs 35 minute word benodig. fn Konseptueie ontwerp vir
die suiwering van die 1-pentanol het fn produkkwaliteit van 99,9 % 1-pentanol
en fn 1-pentanol opbrengs van > 98 % voorspel. Die 1-pentanol opbrengs is
uitstekend, en slegs die 1-pentanol wat omgeskakel word na eters gaan
verlore.
In hierdie studie is dit bewys dat fn dehidrasie skeidingsproses suksevol
aangewend kan word om sekondêre alkohole uit fn primêre+sekondêre
alkohol mengsel te verwyder. Veral die verwydering van 2-hexanol uit fn 1-
pentanol+2-hexanol mengsel het belowende resultate gelewer. Om die
ekonomiese lewensvatbaarheid van so fn skeidingsproses te bepaal moet fn
ekonomiese evaluasie van die proses gedoen word. Dit behoort deel van
verdere studies te vorm.
Die dehidrasie skeidingsproses behoort verder ondersoek te word. Dit word
verwag dat die proses na hoër alkohol mengsels, bv. 1-hexanol+2-heptanol
uitgebrei kan word. Dit sou baie voordelig wees indien fn geskikte soliede
katalis vir die skeiding gevind word. In so fn geval sou die herwinning van
die organiese produkte van die reaksiemengsel baie makliker wees. Indien fn
soliede katalis nie gevind word nie, behoort fn kontinu proses waarin H3P04
as vloeistof katalis gebruik word, ontwikkel te word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53172 |
| Date | 03 1900 |
| Creators | Nieuwoudt, Traute |
| Contributors | Nieuwoudt, Izak, Lorenzen, Leon, Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 186 p. : ill. |
| Rights | Stellenbosch University |
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