Hexane Removal Research Articles

Two phase partitioning membrane bioreactor: A novel biotechnique for the removal of dimethyl sulphide, n-hexane and toluene from waste air

Abstract This study is a comparative study between a flat sheet composite membrane bioreactor (MBR) and a new type of MBR, the two phase partitioning membrane bioreactor (TPPMB) to examine the merits of using silicone oil to improve the mass transfer in a membrane type bioreactor. Dimethyl sulphide (DMS), n-hexane and toluene removal from a waste air was carried out by a MBR under continuous feeding conditions. The performance of this reactor was compared with the performance of a TPPMB. In the TPPMB a 60/40 V% water/silicone oil emulsion inoculated with activated sludge was used as recirculation liquid in order to reach an acceptable removal for both hydrophobic and hydrophilic compounds. Removal efficiencies (RE) of respectively 76.8 ± 7.7, 77.6 ± 13.0 and 12.1 ± 12.3% were reached for toluene, DMS and hexane inlet concentrations ranging up to 2.6 g m−3 for each compound (Inlet load (IL) ⩽312 g m−3 h−1) in a MBR. This indicates that a MBR is suitable to treat DMS and toluene, but unreliable to treat hexane. In a TPPMB RE of 85 ± 5, 62 ± 5 and 53 ± 6% were reached for toluene, DMS and hexane inlet concentrations ranging up to 2.8 g m−3 for each compound (IL ⩽ 336 g m−3 h−1) respectively. The RE for hexane is significantly higher in a TPPMB, while the variability of the hexane removal decreased, so the TPPMB is suitable and more reliable for degrading hexane than a MBR. The increase in RE of hexane and toluene can be related to the increase in transfer when applying 40 V% silicone oil.

Hexane abatement and spore emission control in a fungal biofilter-photoreactor hybrid unit

The performance of a fungal perlite-based biofilter coupled to a post-treatment photoreactor was evaluated over 234 days in terms of n-hexane removal, emission and deactivation of fungal spores. The biofilter and photoreactor were operated at gas residence times of 1.20 and 0.14min, respectively, and a hexane loading rate of 115±5gm−3h−1. Steady n-hexane elimination capacities of 30–40gm−3h−1 were achieved, concomitantly with pollutant mineralization efficiencies of 60–90%. No significant influence of biofilter irrigation frequency or irrigation nitrogen concentration on hexane abatement was recorded. Photolysis did not support an efficient hexane post-treatment likely due to the short EBRT applied in the photoreactor, while overall hexane removal and mineralization enhancements of 25% were recorded when the irradiated photoreactor was packed with ZnO-impregnated perlite. However, a rapid catalyst deactivation was observed, which required a periodic reactivation every 48h. Biofilter irrigation every 3 days supported fungal spore emissions at concentrations ranging from 2.4×103 to 9.0×104CFUm−3. Finally, spore deactivation efficiencies of ≈98% were recorded for the photolytic and photocatalytic post-treatment processes. This study confirmed the potential of photo-assisted post-treatment processes to mitigate the emission of hazardous fungal spores and boost the abatement performance of biotechnologies.

Photocatalytic oxidation process used as a pretreatment to improve hexane vapors biofiltration

AbstractBACKGROUNDPhotolytic and photocatalytic oxidation processes were used as pretreatments for the purpose of producing more soluble and easily degradable byproducts that were subsequently treated in a biofiltration system for VOC treatment. n‐Hexane was chosen as a model hydrophobic VOC, and ZnO was used as a photocatalyst.RESULTSThe potential of this technology was evaluated at an inlet load of 200 g m−3 h−1 and a residence time of 94.2 s for the coupled system. The results showed that the photocatalytic pretreatment had a greater impact on the removal of hexane than the photolytic pretreatment with elimination capacities (EC) of 43 g m−3 h−1 and 24 g m−3 h−1, respectively. The EC of hexane and the CO2 production reached in the coupled system increased by at least 20%. This behavior was directly related to the high biodegradability of byproducts produced in the photocatalytic system, such as alcohols and ketones.CONCLUSIONPhotocatalytic oxidation used as a pretreatment system for hexane vapors using ZnO as photocatalyst enabled the generation of byproducts with high solubility that could be easily degraded in subsequent biological treatment. © 2014 Society of Chemical Industry

Hexane biodegradation in two-liquid phase biofilters operated with hydrophobic biomass: Effect of the organic phase-packing media ratio and the irrigation rate

The hexane removal performance of three compost-based biofilters containing silicone oil at 0% (control), 10% and 20% v/v, and inoculated with a hydrophobic hexane degrading consortium was comparatively assessed under different irrigation strategies. The addition of 10% of silicone oil to the biofilter significantly improved its abatement performance by 72% compared to the control biofilter. However, when 20% of silicone oil was added to the compost no removal enhancement was observed, likely due to a severe reduction of the water holding capacity of the packing media (which decreased by 71%) together with a silicone-oil mediated gas flow channeling. An optimum mineral salt medium irrigation rate of 100mLLpacking-1d-1 resulted in a superior and more stable hexane abatement performance. No significant losses of silicone oil were observed at the end of the experimental period (⩽2.5%).

A membrane bioreactor for the simultaneous treatment of acetone, toluene, limonene and hexane at trace level concentrations

The performance of a flat-membrane biofilm reactor (MBR) for the removal of acetone, toluene, limonene and hexane at concentrations ranging from 1.3 to 3.2 mg m−3 was investigated at different gas residence times (GRT): 60, 30, 15 and 7 s. A preliminary abiotic test was conducted to assess the mass transport of the selected volatile organic compounds (VOCs) through the membrane. A reduced transport of limonene and hexane was observed with water present over the dense side of the membrane. The presence of a biofilm attached on the dense side of the membrane following bioreactor inoculation significantly increased VOC transport. High acetone and toluene removals (>93%) were recorded in the MBR regardless of the GRT. To remediate the low hexane removal performance (RE < 24%) recorded at the initial stages of the process, a re-inoculation of the membrane with a hexane-degrading consortium embedded in silicon oil was performed. Although hexane removal did not exceed 27%, this re-inoculation increased limonene removals up to 90% at a GRT of 7 s. The absence of inhibition of hexane biodegradation by substrate competition confirmed that hexane removal in the MBR was indeed limited by the mass transfer through the membrane. Despite the low carbon source spectrum and load, the microbiological analysis of the communities present in the MBR showed high species richness (Shannon–Wiener indices of 3.2–3.5) and a high pair-wise similarity (84–97%) between the suspended and the attached biomass.

Two liquid-phase bubble column bioreactors for the removal of volatile organic compounds from air streams

Two equal-sized bubble column bioreactors were used to investigate the effect of silicone oil on the removal efficiency (RE) of a bubble column bioreactor for hydrophobic volatile organic compounds (VOCs). In the first stage, the performance of the two liquid-phase bubble column bioreactors (in terms of hexane removal) containing 4 L mineral medium and 400 mL of silicone oil was compared to a control bioreactor (without silicone oil). With the airflow rate of 1.5 L min−1 and n-hexane concentration of 1.6 g m−3, the hexane RE of oil-added bioreactor was 27% compared to 16.3% for the control bioreactor. To obtain better removal efficiencies, in the second stage of the experiments, the airflow rate and the inlet n-hexane concentration were reduced to 0.9 L min−1 and 1 g m−3, respectively. In this stage, 150 mL of fermentation medium was replaced with fresh medium daily to avoid possible nutrient limitation and build up of toxicants. As a result of this replacement, the hexane RE of the oil-added bioreactor was 76% compared to 37% for the control bioreactor. In the third stage, the effect of silicone oil percentage on the bioreactor's hexane RE was investigated. The results showed that increasing silicone oil percentage from 5 to 15% had a significant positive effect on the hexane RE (for the hexane inlet concentration of 1.6 g m−3, the RE approximately doubled). However, the effect of oil percentage on the VOC RE was seen insignificant when silicone oil was above 15%. In the final stage of this work, the effect of adding expanded perlite particles to the liquid medium of two liquid-phase bubble column bioreactors was investigated. The results showed that perlite had a significant positive effect on the hexane RE of the bioreactor. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

Biological treatment of mixtures of toluene and n‐hexane vapours in a hollow fibre membrane bioreactor

Membrane bioreactors are gaining interest for the control of contaminated air streams. In this study, the removal of toluene and n‐hexane vapours in a hollow fibre membrane bioreactor (HFMB) was investigated. The focus was on quantifying the possible interactions occurring during the simultaneous biotreatment of the two volatile pollutants. Two lab‐scale units fitted with microporous polypropylene hollow fibre membranes were connected in series and inoculated with activated sludge. Contaminated air was passed through the lumen at gas residence times ranging from 2.3 to 9.4 s while a pollutant‐degrading biofilm developed on the shell side of the fibres. When toluene was treated alone, very high elimination capacities (up to 750 g m−3 h−1 based on lumen volume, or 1.25 g m−2 h−1 when normalized by the hollow fibre membrane area) were reached. When toluene and hexane were treated simultaneously, toluene biodegradation was partially inhibited by n‐hexane, resulting in lower toluene removal rates. On the other hand, hexane removal was only marginally affected by the presence of toluene and was degraded at very high rates (upwards of 440 g m−3 h−1 or 0.73 g m−2 h−1 without breakthrough). Overall, this study demonstrates that mixtures of toluene and n‐hexane vapours can be effectively removed in hollow fibre membrane bioreactors and that complex biological interactions may affect one or more of the pollutants undergoing treatment in gas‐phase membrane bioreactors.

Purification of hexane with effective extraction using ionic liquid as solvent

The separation of hexane and ethanol is valuable but difficult due to the formation of an azeotropic mixture. This work demonstrates the ability of the ionic liquid (IL) 1-butyl-3-methylimidazolium methyl sulfate [BMIM][MeSO4] to act as an extraction solvent in petrochemical processes for the removal of hexane from its mixture with ethanol. Knowledge of the phase behavior of the system is key in order to optimize the separation process. For this reason, the experimental liquid–liquid equilibrium (LLE) for the ternary system hexane + ethanol + [BMIM][MeSO4] is investigated at 298.15 K. The separation sequence of the extraction process is checked by using conventional software for simulation. Experimental data are obtained in a laboratory-scale packed column extraction system for the separation of this azeotropic mixture by using [BMIM][MeSO4]. It is concluded that this IL has the highest extraction efficiency.

Effect of gas empty bed contact time on performances of various types of rotating drum biofilters for removal of VOCs

The effects of gas empty bed contact time (EBCT), biofilter configuration, and types of volatile organic compounds (VOCs) were evaluated to assess the performance of rotating drum biofilters (RDBs), especially at low EBCT values. Three types of pilot-scale RDBs, a single-layer RDB, a multi-layer RDB, and a hybrid RDB, were examined at various gas EBCTs but at a constant VOC loading rate. Diethyl ether, toluene, and hexane were used separately as model VOC. When EBCT increased from 5.0 to 60 s at a constant VOC loading rate of 2.0 kg COD/(m 3 day), ether removal efficiency increased from 73.1% to 97.6%, from 81.6% to 99.9%, and from 84.0% to 99.9% for the single-layer RDB, the multi-layer RDB, and the hybrid RDB, respectively, and toluene removal efficiency increased from 76.4% to 99.9% and from 84.8% to 99.9% for the multi-layer RDB and the hybrid RDB, respectively. When hexane was used as the model VOC at a constant loading rate of 0.25 kg COD/(m 3 day), hexane removal efficiency increased from 31.1% to 57.0% and from 29.5% to 50.0% for the multi-layer RDB and hybrid RDB, respectively. The single-layer, multi-layer, and hybrid RDBs exhibited, respectively, the lowest, middle, and highest removal efficiencies, when operated under similar operational loading conditions. Hexane exhibited the lowest removal efficiency, while diethyl ether displayed the highest removal efficiency. The data collected at the various EBCT values correlated reasonably well with a saturation model. The sensitivity of removal efficiency to EBCT varied significantly with EBCT values, VOC properties, and biofilter configurations. Process selection and design for RDB processes should consider these factors.

Fungal removal of gaseous hexane in biofilters packed with poly(ethylene carbonate) pine sawdust or peat composites

The removal of volatile organic compounds (VOC) in biofilters packed with organic filter beds, such as peat moss (PM) and pine sawdust (PS), frequently presents drawbacks associated to the collapse of internal structures affecting the long-term operation. Poly(ethylene ether carbonate) (PEEC) groups grafted to these organic carriers cross linked with 4,4'-methylenebis(phenylisocyanate) (MDI) permitted fiber aggregation into specific shapes and with excellent hexane sorption performance. Modified peat moss (IPM) showed very favorable characteristics for rapid microbial development. Water-holding capacity in addition to hexane adsorption almost equal to the dry samples was obtained. Pilot scale hexane biofiltration experiments were performed with the composites after inoculation with the filamentous fungus Fusarium solani. During the operation of the biofilter under non-aseptic conditions, the addition of bacterial antibiotics did not have a relevant effect on hexane removal, confirming the role of fungi in the uptake of hexane and that bacterial growth was intrinsically limited by an adequate performance of the composites. IPM biofilter had a start-up period of 8-13 days with concurrent CO(2) production of approximately 90 g m(-3) h(-1) at day 11. The final pressure drop after 70 days of operation was 5.3 mmH(2)O m(-1) reactor. For modified pine sawdust (IPS) packed biofilter, 5 days were required to develop an EC of about 100 g m(-3) h(-1) with an inlet hexane load of approximately 190 g m(-3) h(-1). Under similar conditions, 12-17 days were required to observe a significant start-up in the reference perlite biofilter to reach gradually an EC of approximately 100 g m(-3) h(-1) at day 32. Under typical biofiltration conditions, the physical-chemical properties of the modified supports maintained a minimum water activity (a(w)) of 0.925 and a pH between 4 and 5.5, which allowed the preferential fungal development and limited bacterial growth.

Characterization of cyclohexane and hexane degradation by Rhodococcus sp. EC1

Cyclohexane is a recalcitrant compound that is more difficult to degrade than even n-alkanes or monoaromatic hydrocarbons. In this study, a cyclohexane-degrading consortium was obtained from oil-contaminated soil by an enrichment culture method. Based on a 16S rDNA polymerase chain reaction-denaturing gradient gel electrophoresis method, this consortium was identified as comprising Alpha-proteobacteria, Actinobacteria, and Gamma-proteobacteria. One of these organisms, Rhodococcus sp. EC1, was isolated and shown to have excellent cyclohexane-degrading ability. The maximum specific cyclohexane degradation rate ( V max) for EC1 was 246 μmol g-DCW −1 (dry cell weight) h −1. The optimum conditions of cyclohexane degradation were 25–35 °C and pH 6–8. In addition to its cyclohexane degradation abilities, EC1 was also able to strongly degrade hexane, with a maximum specific hexane degradation rate of 361 μmol g-DCW −1 h −1. Experiments using 14 C-hexane revealed that EC1 mineralized 40% of hexane into CO 2 and converted 53% into biomass. Moreover, EC1 could use other hydrocarbons, including methanol, ethanol, acetone, methyl tert-butyl ether, pyrene, diesel, lubricant oil, benzene, toluene, ethylbenzene, m-xylene, p-xylene and o-xylene. These findings collectively suggest that EC1 may be a useful biological resource for removal of cyclohexane, hexane, and other recalcitrant hydrocarbons.

Enhanced hexane biodegradation in a two phase partitioning bioreactor: Overcoming pollutant transport limitations

The use of an organic solvent can allow to increase the mass transfer, and thereby biodegradation, of hydrophobic gaseous pollutants. The biodegradation of hexane by a Pseudomonas aeruginosa strain was thus optimized in a two phase partitioning bioreactor (TPPB). Silicone oil was first selected among various organic solvents based on its biocompatibility and resistance to P. aeruginosa and its high affinity for hexane (air-organic partitioning of 0.0034). A silicone oil based TPPB was then compared with a conventional biofilter packed with foamed glass beads for the removal of hexane. The use of silicone oil significantly improved the process performance, allowing removal efficiencies (RE) and elimination capacities (EC) of 70 ± 5% and 135 ± 17 g m reactor − 3 h − 1 , respectively, which were approximately five times higher than those in a similar system deprived from organic phase. When a conventional packed-bed biofilter was used, the average RE and EC achieved were 7 ± 4% and 12 ± 7 g m reactor − 3 h − 1 , respectively. This study therefore confirms the potential of TPPBs for enhancing the transport and subsequent biodegradation of poorly soluble gaseous contaminants.

Gaseous Hexane Biodegradation by Fusarium solani in Two Liquid Phase Packed-Bed and Stirred-Tank Bioreactors

Biofiltration of hydrophobic volatile pollutants is intrinsically limited by poor transfer of the pollutants from the gaseous to the liquid biotic phase, where biodegradation occurs. This study was conducted to evaluate the potential of silicone oil for enhancing the transport and subsequent biodegradation of hexane by the fungus Fusarium solani in various bioreactor configurations. Silicone oil was first selected among various solvents for its biocompatibility, nonbiodegradability, and good partitioning properties toward hexane. In batch tests, the use of silicone oil improved hexane specific biodegradation by approximately 60%. Subsequent biodegradation experiments were conducted in stirred-tank (1.5 L) and packed-bed (2.5 L) bioreactors fed with a constant gaseous hexane load of 180 g x m(-3)(reactor) x h(-1) and operated for 12 and 40 days, respectively. In the stirred reactors, the maximum hexane elimination capacity (EC) increased from 50 g x m(-3)(reactor) x h(-1) (removal efficiency, RE of 28%) in the control not supplied with silicone oil to 120 g x m(-3)(reactor) x h(-1) in the biphasic system (67% RE). In the packed-bed bioreactors, the maximum EC ranged from 110 (50% RE) to 180 g x m(-3)(reactor) x h(-1) (> 90% RE) in the control and two-liquid-phase systems, respectively. These results represent, to the best of our knowledge, the first reported case of fungi use in a two-liquid-phase bioreactor and the highest hexane removal capacities so far reported in biofilters.

Supercritical fluid chromatographic analysis for on-line monitoring of hexane removal from soybean oil miscella using liquid carbon dioxide

Liquid carbon dioxide (L-CO 2) can be used to separate hexane from hexane/soybean oil (SBO) mixtures (i.e., miscella). An on-line supercritical fluid chromatographic (SFC) method was developed to monitor this separation. L-CO 2 (25 °C and 9.31 MPa) was passed through 50 mL of a 25% (w/w) hexane miscella and then directed on-line through a SFC injector. After passing 300-L expanded CO 2, the hexane concentrations in the L-CO 2 were 0.05% and 0.04% for n-hexane and isohexane, respectively and the residual hexane concentrations in the SBO were 3.8 and 3.3 ppm, respectively. This technique provided real time on-line monitoring of the hexane separation process.

Improving hexane removal by enhancing fungal development in a microbial consortium biofilter

The removal of hydrophobic pollutants in biofilters is often limited by gas liquid mass transfer to the biotic aqueous phase where biodegradation occurs. It has been proposed that the use of fungi may improve their removal efficiency. To confirm this, the uptake of hexane vapors was investigated in 2.6-L perlite-packed biofilters, inoculated with a mixed culture containing bacteria and fungi, which were operated under neutral or acid conditions. For a hexane inlet load of around 140 g.m-3.h-1, elimination capacities (EC) of 60 and 100 g.m-3.h-1 were respectively reached with the neutral and acid systems. Increasing the inlet hexane load showed that the maximum EC obtained in the acid biofilter (150 g.m-3.h-1) was twice greater than in the neutral filter. The addition of bacterial inhibitors had no significant effect on EC in the acid system. The biomass in the acid biofilter was 187 mg.g-1 (dry perlite) without an important pressure drop (26.5 mm of water.m-1reactor). The greater efficiency obtained with the acid biofilter can be related to the hydrophobic aerial hyphae which are in direct contact with the gas and can absorb the hydrophobic compounds faster than the flat bacterial biofilms. Two fungi were isolated from the acid biofilter and were identified as Cladosporium and Fusarium spp. Hexane EC of 40 g.m-3.h-1 for Cladosporium sp. and 50 g.m-3.h-1 for Fusarium sp. were obtained in short time experiments in small biofilters (0.230 L). A biomass content around 30 mg.g-1 (dry perlite) showed the potential for hexane biofiltration of the strains.

Performance of an Internal-Loop Airlift Bioreactor for Treatment of Hexane-Contaminated Air

Hexane is a toxic volatile organic compound that is quite abundant in gas emissions from chemical industries and printing press and painting centers, and it is necessary to treat these airstreams before they discharge into the atmosphere. This article presents a treatment for hexane-contaminated air in steady-state conditions using an internal-loop airlift bioreactor inoculated with a Pseudomonas aeruginosa strain. Bioprocesses were conducted at 20-mL/min, a load of 1.26 gm3 of C6H14, and a temperature of 28 degrees C. The results of hexane removal efficiencies were presented as a function of the inoculum size (approx 0.07 and 0.2 g/L) and cell reuse. Bioprocess monitoring comprises quantification of the biomass, the surface tension of the medium, and the hexane concentration in the fermentation medium as well as in the inlet and outlet airstreams. The steady-state results suggest that the variation in inoculum size from 0.07 to 0.2 g/L promotes hexane abatement from the influent from 65 to 85%, respectively. Total hydrocarbon removal from the waste gas was achieved during experiments conducted using reused cells at an initial microbial concentration of 0.2 g/L.

Removal of Hexane in Biofilters Packed with Perlite and a Peat–Perlite Mixture

Removal of hexane from air–hexane mixtures in biofilters packed with different solid media under nitrogen supplementation was performed for 70 days. Two columns containing Perlite or a mixture of peat and Perlite, were used. The solid media were supplemented with nitrogen source up to 1 kg/m3 per week for high nutrient supplementation and 0.2 kg/m3 per month for low nutrient supplementation. A high rate of hexane removal: 95 g/m3 h was achieved under high nutrient supplementation, high air flow rate and high hexane concentration. However, the percentage of hexane removal decreased with increasing air flow rate and hexane inlet concentration. For high nutrient supplementation the type of solid medium did not significantly affect the biodegradation capacity. With low nutrient supplementation, the highest removal rate was achieved in the column containing the peat–perlite mixture. The column containing perlite had a significantly lower pressure drop (20 Pa/m) than the 2400–2930 Pa/m observed for the column containing the mixture. Perlite offers an opportunity of running a biofiltration process at a lower and stable pressure drop if the nutrient supplementation is managed properly.

Formation of dibenzenevanadium by the reaction of dysprosium diiodide with vanadocene in benzene

Recently, we have found1 that diiodides DyI2 (1) and NdI2 possessing strong reducing properties can success fully be used as an alternative to alkali metals in the syn thesis of vanadocene (2) and cobaltocene. As part of our continuing investigations of the properties of these salts, in the present study we demonstrated that diiodide 1 can also be used for the preparation of dibenzenevanadium (3). Heating of a mixture of 1 and 2 in benzene at 85 °C was accompanied by a gradual change in the color of the solution from violet to red brown. After separation of the precipitate and removal of benzene in vacuo, we obtained a solid dark brown substance. The major portion of this substance is soluble in hexane. Study by ESR spectro scopy demonstrated that only traces of 2 were present in the hexane solution. However, heating of a brown crystal line substance, which was obtained after removal of hex ane, in vacuo to 60 °C led to sublimation of compound 2 in an amount of >35% of that introduced into the reac tion. Upon further heating of the residue to 110 °C, com pound 3 was sublimed in a yield of 15% with respect to the amount of compound 2 used in the reaction. In benzene, diiodide 1 readily reacts with VCl4, but this reaction re sults only in reduction of the latter to VCl3. An attempt to synthesize compound 3 in the Dy—DyI3—VCl4—C6H6 system analogous to the Fischer system (Al—AlCl3—VCl4—C6H6) 2 failed. An attempt to use com pound 2 instead of VCl3 under these conditions was also unsuccessful. The above described reaction is unsuitable for preparative purposes because of a low yield of the product. However, the results of the present study are of basic importance, because they demonstrated that the reactions of "new" diiodides of divalent lan thanides (Nd, Dy, and Tm) with substrates can be carried out not only in solvating ethereal solutions3 but also in benzene.

A novel approach to process crude oil membrane concentrate using a centrifuge

AbstractThe present work discusses an alternative process to handle crude oil membrane concentrate during a degumming process. In this process, the membrane concentrate, which typically consists of 15–30% phospholipids (PL) by weight of oil, is first stripped of hexane and then centrifuged to produce two phases—supernatant (PL&lt;0.6%) and lecithin concentrate (PL&gt;62%). The main advantages of this method are limited oil loss, potential lecithin by‐product, and a supposedly simpler process. In this work, we first show that the phase behavior of an oil‐PL‐hexane system can be exploited to identify the various steps of the process. The steps include membrane degumming, hexane evaporation, and centrifugation. Although much knowledge already exists on these unit operations for miscella degumming, it is the combination and sequence of these steps that is proposed here. Since the novelty of this process lies in using a centrifuge after the membrane separations, we focus on this step. Here, we evaluate the dependence of hexane removal, moisture, temperature, hexane amount, residence time, centrifuge g‐force, and nonhydratable PL on the phase separations.

HPLC determination of ethoxyquin and its major oxidation products in fresh and stored fish meals and fish feeds

A new method was developed to determine 1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline (EQ, ethoxyquin), 2,6-dihydro-2,2,4-trimethyl-6-quinolone (QI) and 1,8′-di(1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline) (DM) in fish meals or fish feeds, QI and DM being the oxidation products of EQ. The sample was first extracted with hexane. After the removal of hexane the three analytes were extracted from the resulting oil with acetonitrile and determined by C18 reverse phase high-performance liquid chromatography with a UV detector set at λ = 280 nm. The mobile phase was acetonitrile–0.01 M ammonium acetate (80:20 v/v). The recoveries for EQ, QI and DM from the samples spiked at different levels varied in the ranges 90–100 per cent, 75–85 per cent and 90–100 per cent respectively. At room temperature, QI and DM were the major oxidation products of EQ in stored fish meals and fish feeds. Loss of EQ from fish meals is faster than that from feeds, resulting in relatively higher accumulations of QI and DM in the fish meals. Both QI and DM, especially the former, were not stable during storage of either and could be further oxidised to unidentified compounds. The residue levels of these two compounds were thus unpredictable during storage intervals. When the storage temperature was increased to 50 °C, EQ disappeared more rapidly, but neither QI nor DM accumulated. © 2000 Society of Chemical Industry