21 |
Studies on the pectin network of the tomato fruit cell wallTibbits, C. William January 2000 (has links)
No description available.
|
22 |
Reaction Of Bio-Oil With Alcohols: Effect On Long Term Stability And Properties Of Bio-Oil For Use As FuelBhattacharya, Priyanka 10 December 2010 (has links)
Bio-oil is produced by the rapid pyrolysis of biomass and is a source of renewable fuel. The increase in viscosity during storage is a major problem that can be controlled by the addition of methanol or other alcohols. The objective of this research was to determine how alcohols stabilize bio-oil by investigating the reactions of alcohols with low molecular weight aldehydes and acids. The reaction of methanol with hydroxyacetaldehyde (HA) and acetic acid to form the respective acetal or ester was catalyzed by the 7 x 10-4 M strong acids such as sulfuric, hydrochloric, p-toluene sulfonic acid, and methylsulfonic acid. HA formed 2,2-dimethoxyethanol (DME) and AT 60°C, equilibrium was reached in less than one hour. Smaller amounts of DME were formed in the absence of strong acid. HA, acetaldehyde, and propanal formed their corresponding acetals when reacted with methanol, ethanol, 1-propanol or 1-butanol. Esters of acetic acid and hydroxyacetic acid were observed from reactions with these same four alcohols. Other acetals and esters were observed by GC/MS analysis of the reaction products. The results from accelerated aging experiments at 90°C suggest that the presence of methanol slows polymerization by formation of acetals and esters from low molecular weight aldehydes and organic acids. The other objective of this study was to improve the bio-oil quality as fuel in a single step by adding methanol to the pyrolysis gases. Therefore, a methanol/sulphuric acid mixture was injected into the pyrolysis vapor zone prior to the water cooled condensers of the auger reactor. The chemical and physical properties of bio-oils were determined and the results of these tests were compared with the results of tests with raw bio-oils. The amount of methanol injection varied from 1 to 20 wt % with and without catalysts. The results showed that the addition of 10% methanol was required for stability with the accelerated aging test. The bio-oil viscosity was reduced to 11.7 cSt from 15.45 cSt with the 10% methanol addition and after 5 days of ageing at 90°C the viscosity only increased by 17% whereas raw bio-oil turned into a highly viscous phase separated material. GC/MS analysis indicated the formation of the esters and quantified the amount of methanol present in the bio-oil after the reaction. The acid value was 87 compared to 99.8 for raw bio-oil. The lower acid value of the esterified bio-oil supports the hypothesis that the formation of esters lowered the amount of free acids present. The flash point of the bio-oil was improved to 37°C and it burned intensely in the waste oil burner. A Principal component analysis supported these findings by indicating that the esterified bio-oil properties differed significantly from the raw bio-oil.
|
23 |
Characterization and Stability of Bio-Oils Upgraded by Esterification and OlefinationTao, Jingming 11 May 2013 (has links)
Raw bio-oil is produced by fast pyrolysis of biomass. The high level of oxygen content in bio-oil causes negative properties of polymerization over time, high acidity, pungent odor and low heating value relative to petroleum fuels. The objective of this study was to develop and identify upgrading processes to produce a boiler fuel with reduced acid value, reduced polymerization over time and increased higher heating value. By one upgrading method, raw bio-oil was upgraded by esterification over acid catalyst by batch reaction; a second approach was an in-reactor reaction, produced by injecting methanol or 1-butanol with acid catalyst into the pyrolysis vapor stream. An olefination reaction method combined with an alcoholation reaction was also studied. The resulting fuel produced from in-reactor esterification fuel was compared in terms of physical and chemical properties with esterifed bio-oil produced by the batch method. The olefination reaction was examined in terms of higher heating value, acid value, viscosity, and water content. The influence of reaction conditions such as reaction time, reaction temperature, and catalyst content relative to upgraded bio-oil properties were examined, and optimal conditions were identified. Analysis of variance (ANOVA) and empirical analysis was utilized to analyze the difference in physical and chemical properties between treatment groups.
|
24 |
Catalyst studies of vapor phase esterification of n-octyl alcohol and acetic acid /Venkatesham, Yerram January 1953 (has links)
No description available.
|
25 |
Lipase selectivity in reactions involving natural and synthetic fatty acids and fatty alcohols富洵, Fu, Xun. January 2000 (has links)
published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy
|
26 |
Titania derived nanotubes and nanoparticles : catalyst supports in hydrogenation, oxidation and esterification reactionsSikhwivhilu, Lucky Mashudu 20 January 2009 (has links)
Nanotubular titanates were synthesized by a simple methodology using a commercial
TiO2 (Degussa P25 containing anatase and rutile phases) and a base (KOH) solution.
Prior to the removal of KOH, the samples of TiO2 were aged for three different time
intervals (0, 2 days, 61 days). The freshly prepared synthetic samples were
characterized for their structural and morphological properties by BET, XRD,
Raman, TEM, HRTEM, EDX and SEM. Both TEM and SEM analysis revealed that
ageing time influenced the tubular structure and morphology of the new materials.
Raman and surface analysis data also showed that ageing time affected both the
structural and surface properties of TiO2. The XRD results showed that the
crystallinity of the TiO2 decreased with increasing ageing time. Energy dispersive Xray
spectroscopy (EDX) showed that the tubes derived from TiO2 are comprised of
potassium, titanium and oxygen. Catalysts A, B and C were prepared by the addition
of 1 wt% Pd (wet impregnation) to the titanate formed after ageing of the TiO2 in
KOH for 0, 2 and 61 days, respectively. The catalysts were tested for the vapour
phase hydrogenation of phenol in a fixed-bed micro reactor within the temperature
range of 165 to 300oC under atmospheric pressure. Of the three catalysts, catalyst B
showed the best activity (conversion 97%) and total selectivity to cyclohexanone
(99%). In contrast, catalyst C, which showed a moderate activity favoured selectivity
to cyclohexanol. These results are attributed to differences in surface morphologies
between the two catalysts B and C, associated with the surface area and a change in
the surface acid-base properties. Catalyst B also showed a higher resistance towards
deactivation and maintained a higher total selectivity to cyclohexanone than did
catalyst C.
A hydrothermal treatment of NaOH and TiO2 was employed to prepare two
materials, TiO2-B and TiO2-C with relatively small crystallite size and large specific
surface area. The hydrogenation of phenol was used to evaluate the activity of the
catalysts Pd/TiO2-B and Pd/TiO2-C. The reaction proceeds in a single step and
involves the formation of a partially hydrogenated product, namely cyclohexanone.
The larger surface area catalyst (Pd/TiO2-C, 89 m2/g) showed better activity and
selectivity to cyclohexanone than its counterpart (Pd/TiO2-B, 45 m2/g). The catalyst
activity showed significant dependency on the surface area whereas the selectivity
was greatly influenced by surface basicity.
Titania derived nanotubes synthesized by treating P25 Degussa TiO2 with a
concentrated KOH solution and aged for 2 days was used as a catalyst support for the
hydrogenation of o-chloronitrobenzene (O-CNB) with Pd as the active phase. The
vapour-phase hydrogenation of O-CNB was carried out in ethanol at 250 oC and
atmospheric pressure over a Pd/TiO2 derived nanotube catalyst (Pd/TiO2-M).
Pd/TiO2-M gave complete conversion (100%) of O-CNB with a selectivity to orthochloroaniline
(O-CAN) of 86 %. The stability of the Pd/TiO2 catalyst was tested over
5 hours during which time the conversion slowly dropped to 80 % (selectivity 93 %)
due to poisoning. TPR analysis revealed the existence of a strong palladium-support
interaction and this was found to be crucial to the overall activity of the catalyst.
It has been found that gold supported on potassium titanate, KTiO2(OH) can, under
some circumstances, exhibit a superior performance for the oxidation of carbon
monoxide, relative to that obtained with titania as a support. It appears that the
dispersions of gold on the two types of support are sufficiently similar that other
factors are responsible for the improved activity noted. It may be that the higher
basic character and detailed structural features of the titanate surface play a role.
The effect of the addition of alkali metal ions on the anatase to rutile transformation
of titanium dioxide (P25 Degussa) was investigated using X-ray diffraction, Raman
spectroscopy, and surface area measurements. Both Li and Cs ions accelerated the
anatase to rutile transformation whereas Na and K ions did not show any effect.
Furthermore, the effect was more pronounced after addition of the Li ions so that the
transformation temperature dramatically decreased from ~800 oC for commercial
TiO2 to ~600 oC. The surface area of the TiO2 material decreased with sintering due
to the increase in crystalline size. Moreover, the acceleration of the transformation
occurred at lower temperatures and at higher Li content.
Mesoporous nanocrystalline TiO2 (HSA TiO2) was prepared by hydrothermal
treatment of TiO2 with NaOH. The material was very amorphous and underwent the
phase transformation from amorphous to anatase phase and subsequently from
anatase to rutile phase with sintering. The anatase to rutile transformation was
delayed after doping and grain growth was inhibited. After sintering at 800 oC the
material (HSA TiO2) still contained a significant amount of the anatase phase. The
complete transformation only occurred at ~1000 oC.
The esterification of benzoic acid and butyric acid with propanol over alkali metal
ions supported on TiO2 was investigated. K/TiO2-D showed the highest conversion
for both benzoic acid and butyric acid. The selectivity to propylbenzoate and
propylbutyrate was influenced by the basic nature of the catalysts. Butyric acid was
found to be more reactive than benzoic acid. The difference in reactivity was
explained in terms of steric and inductive effects. The differences in boiling points
and pH values were also considered.
|
27 |
Lipase selectivity in reactions involving natural and synthetic fatty acids and fatty alcohols /Fu, Xun. January 2000 (has links)
Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 182-189).
|
28 |
Extractive polyesterificationKeister, William Pierce, January 1969 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.
|
29 |
Photochemical preparations of salicylate/resorcylate esters/amides asymmetric synthesis of SCH 351448 /Soltani, Omid. January 2006 (has links)
Thesis (Ph.D.) -- University of Texas Southwestern Medical Center at Dallas, 2006. / Embargoed. Vita. Bibliography: 257-258.
|
30 |
Physical and chemical properties and antioxidant activity of modified and unmodified pectins extracted from orange bagasseVenzon, Simoni Spohr January 2013 (has links)
Modified pectin is a polysaccharide rich in galacturonic acid altered by pH adjustment and thermal treatment used especially as an anti-cancer agent. The aim of this work was to study the physical and chemical properties of modified and unmodified pectins extracted from orange bagasse by using citric and nitric acids. The galacturonic acid content, degree of esterification, Fourier Transform Infrared 30 Spectroscopy profile, molar mass, intrinsic viscosity, rheological properties and antioxidant activity of the pectins were evaluated. The modification process caused the de-esterification of pectins, responsible for improving the intestinal absorption of modified pectin and a decrease of molecular weight due to removal of neutral sugars, maintaining the linear chain of galacturonic acid. Such changes also caused a significant increase in the in vitro antioxidant activity and influenced the rheological properties of pectin, reducing its viscosity. This work showed that the modification of pectin from orange bagasse with citric and nitric acids altered its structural and physical characteristics as well as its biological activity toward a free-radical, suggesting that some functional properties related to antioxidant activity activity and absorption of nutrients may be increased.
|
Page generated in 0.1353 seconds