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- Arkell, Anders, et al.
(författare)
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Back-pulsing as an energy-saving method in the microfiltration of milk
- 2014
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Ingår i: International Dairy Journal. - : Elsevier BV. - 0958-6946. ; 35:1, s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- Extended shelf-life milk can be produced by a combination of microfiltration and pasteurisation. However, due to the need for high cross-flow velocity during microfiltration, the energy consumption is high. One way of decreasing the energy demand during microfiltration is to use back-pulsing for fouling control. Microfiltration was performed in constant flux mode on skim milk to measure the fouling rate. Different frequencies and durations of back-pulsing were investigated to determine the optimal conditions. The most promising conditions were used to evaluate the degree to which the cross-flow velocity could be decreased without significantly affecting the performance of the membrane. It was found that short pulses (0.2 s) at a frequency of 1 min-1 were most efficient, and the membrane performance was only slightly affected by reducing the cross-flow velocity from 5.8 m s-1 to 4.5 m s-1 with back-pulsing. This corresponds to a reduction in the energy requirement of 50%.
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| 4. |
- Arkell, Anders, et al.
(författare)
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Evaluation of membrane performance and cost estimates during recovery of sodium hydroxide in a hemicellulose extraction process by nanofiltration
- 2013
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Ingår i: Separation and Purification Technology. - : Elsevier BV. - 1873-3794 .- 1383-5866. ; 118, s. 387-393
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Tidskriftsartikel (refereegranskat)abstract
- The recovery the alkaline solvent from of a residual stream after the extraction of hemicelluloses in wheat bran was investigated. The solution was withdrawn from an ultrafiltration (UF) process in which hemicelluloses were recovered. The UF permeate, containing mainly NaOH, lignin and mono- and oligosaccharides, was treated by nanofiltration (NF). Seven NF membranes were tested in a parametric study, and the two membranes showing the best performance were further evaluated in a concentration study. The mean flux of a Koch SelRO MPF 36 and a Microdyn-Nadir NP010 membrane was about 200 l/m2 h during concentration to a volume reduction of 0.75. The retention of NaOH was <20%, while the retention of lignin and sugars was about 70% and >95%, respectively. Cost estimates for a NaOH recovery process indicated that an NF plant would have a pay-back time of less than 2 months if the plant was run continuously, and 7 months if it was used 25% of the time.
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| 6. |
- Arkell, Anders, et al.
(författare)
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Influence of heat pretreatment on ultrafiltration of a solution containing hemicelluloses extracted from wheat bran
- 2013
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Ingår i: Separation and Purification Technology. - : Elsevier BV. - 1873-3794 .- 1383-5866. ; 119, s. 46-50
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Tidskriftsartikel (refereegranskat)abstract
- Hemicelluloses extracted from wheat bran can be concentrated and purified by ultrafiltration. However, the viscosity of the process solution is rather high (about 5 mPa s at 80 C and a shear rate of 100 s1), which results in a relatively low flux. The solution was subjected to heat pretreatment in an attempt to decrease the viscosity and increase the flux. Pretreatment of the solution at 80 C for 72 h was found to reduce the viscosity by 25%. The flux during ultrafiltration with a 10 kDa ceramic membrane increased from 48 l/m2 h, for the untreated solution, to 62 l/m2 h. The increase in flux was lower than expected, and this was attributed to the formation of a fouling layer of acid-insoluble compounds on the membrane. Both hemicelluloses and lignin were partly degraded. The retention of lignin was reduced from about 30% to 18%, whereas the retention of hemicelluloses was above 95%, and was not affected by heat pretreatment. The decrease in lignin retention after heat pretreatment results in improved separation of hemicelluloses and lignin, facilitating the purification of hemicelluloses.
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| 10. |
- Krawczyk, Holger, et al.
(författare)
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Combined membrane filtration and enzymatic treatment for recovery of high molecular mass hemicelluloses from chemithermomechanical pulp process water
- 2013
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Ingår i: Chemical Engineering Journal. - : Elsevier. - 1385-8947 .- 1873-3212. ; 225, s. 292-299
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Tidskriftsartikel (refereegranskat)abstract
- Hemicelluloses with high molecular mass are needed for the manufacture of value added products such as food packaging barrier films. In this work such molecules were recovered from chemithermomechanical pulp (CTMP) process water using an innovative three-stage process comprising membrane separation and enzymatic treatment with laccase. Microfiltration followed by ultrafiltration was found to be a suitable combination in the first stage, providing a concentrated and purified hemicellulose fraction suitable for enzymatic treatment. In both membrane processes a high average flux (260 and 115 l/m(2) h) and a low fouling tendency were observed. A marked increase in the average molecular mass of hemicelluloses with bound lignin moieties was achieved by laccase treatment in the second stage. The enzymatically crosslinked hemicelluloses were finally recovered in the third stage using ultrafiltration. In the final high molecular mass solution the hemicellulose concentration was 54 g/l, the contribution of hemicelluloses to the total solids content 43%, and the viscosity of the solution 27 mPa s. The results demonstrate that a hemicellulose fraction of high quality can be produced from CTMP process water, and that this could constitute a suitable feedstock for the production of, for example, barrier films for renewable packaging.
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