Downloaded from orbit.dtu.dk on: Oct 05, 2021 Electrically Enhanced Ultrafiltration of Industrial Enzyme Solutions Enevoldsen, Ann Dorrit Publication date: 2007 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Enevoldsen, A. D. (2007). Electrically Enhanced Ultrafiltration of Industrial Enzyme Solutions. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Electrically enhanced ultrafiltration of industrial enzyme solutions Ann Dorrit Enevoldsen PhD Thesis November 2007 T U D D C E Supervisors: Gunnar Jonsson and Ernst Hansen Copyright © Ann Dorrit Enevoldsen, 2007 ISBN 978-91435-64-1 Printed by Frydenberg a/s, Copenhagen, Denmark Preface 1 This industrial PhD thesis is the outcome of 3 2 years’study. The project was done in collaboration with the Department of Chemical engineering at the Technical University of Denmark and the Recovery Pilot Plant at Novozymes A/S under the supervision of Associated Professor Gunnar Jonsson and Ernst Hansen. I would like to take the opportunity to thank the people who have contributed to this thesis. First of all I like to thank my main supervisor Gunnar Jonsson, for his kind- ness, helpfulness and great patience. I’m grateful for the opportunity to carry out my project under his competent supervision. I would also like to thank Ernst Hansen for his comprehensive and competent guidance and for being a continu- ous source for relevant discussion. I also owe thanks to the people at the Recovery Pilot Plant at Novozymes A/S who has been a great help throughout my project. A special thanks to Sune Jakobsen for always being helpful and for taking the time to answer my questions. I would also like to thank Jesper Haugaard for his help and motivation, especially with the economical aspects of my project. I’m also grateful to my mother, who has always supported me. Finally, I would also like to thank Peter for his help and patience. English Abstract Fouling and concentration polarization are well known problems in cross‡ow ultra…ltration of proteins. Application of an external dc (direct current) electric force …eld across the membrane is a promising method to reduce fouling and concentration polarization. The electric …eld imposes an electrophoretic force on the charged proteins, which drags them away from the membrane surface. The concentration polarization layer is thereby reduced and the ‡ux increases. The solvent ‡ow through the membrane might also be enhanced by the electroosmotic e¤ect; but this e¤ect is considered secondary. In this Industrial PhD project, cross‡ow electro-ultra…ltration (EUF) is car- ried out with enzyme solutions from Novozymes A/S, Denmark. The aim is to investigate the use of EUF in industrial application. Five di¤erent enzymes have been tested including two amylase solutions where the application of an electric …eld across the membrane resulted in a sig- ni…cant ‡ux enhancement. The other three solutions, which consisted of a lipase and two proteases, did not show any ‡ux improvements during EUF, mainly due to a low surface charge of the enzymes and impurities in the solutions. The relative ‡ux improvement increases as the enzyme concentration in- creases. The ‡ux increases around 6-7 times at a concentration of around 100 g/L. EUF is therefore applicable as a …nal concentration step during enzyme production. The e¤ect of a pulsed electric …eld has also been tested, but showed no improvement compared to a constant electric …eld due to the quick formation of the concentration polarization layer. The e¤ect of the trans membrane pressure (TMP) and cross‡ow velocity has also been studied. An increased TMP and cross‡ow velocity did not improve the ‡ux considerably -since the process is controlled by the strength of the electric …eld. A study of the conductivity of the enzyme solutions showed that the ‡ux in EUF is not a¤ected by conductivities up to around 3 mS/cm. Energy calculations show that EUF is economically pro…table when …ltering solutions of high enzyme concentration if the conductivity of the solution is low. In case the enzyme concentration is low UF is more cost-e¢ cient. The conductivity is however a key factor for the economical feasibility of the EUF process; since the energy requirements increases proportional to the conductivity of the enzyme solution. If the conductivity becomes too high, the advantage of using EUF disappears. Dansk resume Fouling og koncentrationspolarisation er velkendte problemer i cross‡ow ul- tra…ltrering af proteiner. Påtrykning af et eksternt elektrisk felt hen over mem- branen er en lovende metode til reduktion af fouling og koncentrationspolar- isation. Det elektriske felt introducerer en elektroforetisk kraft på de ladede proteiner, som derved bliver trukket væk fra membranover‡aden. Koncentra- tionspolarisationslaget bliver derved reduceret og ‡uxen stiger. Solvent ‡owet igennem membranen kan også stige pga. den elektroosmotiske e¤ekt, men denne e¤ekt bliver betragtet som sekundær. I dette ErhvervsPhD-projekt er der udført cross‡ow elektro-ultra…ltrering (EUF) med enzymopløsninger fra Novozymes A/S, Danmark. Formålet er at undersøge industriel anvendelse af elektro-ultra…ltrering. Fem forskellige enzymer er blevet testet herunder to amylaseopløsninger, hvor påtrykning af et elektrisk felt hen over membranen resulterede i en signi…kant ‡ux forbedring. De andre tre opløsninger, som bestod af en lipase og to proteaser, viste ikke nogen ‡ux stigning ved EUF, hovedsageligt fordi enzymerne har en lille over‡adeladning og pga. urenheder i opløsningerne. Den relative ‡ux forbedring stiger med stigende enzymkoncentration. Fluxen stiger ca. 6-7 gange ved en koncentration på omkring 100 g/L. EUF er derfor anvendelig som et sidste koncentrationstrin i en enzymproduktion. E¤ekten af et pulserende elektrisk felt er også blevet testet, men viste ingen forbedring sammenlignet med et konstant elektrisk felt, da koncentrationspolarisationslaget hurtigt bliver gendannet. E¤ekten af det transmembrane tryk (TMP) og cross‡ow hastigheden er også blevet undersøgt. Øgning af TMP og cross‡ow hastigheden forbedrede ikke ‡uxen betragteligt -da processen er kontrolleret af det elektriske felts styrke. Et studie af enzymopløsningernes ledningsevnen viste at ‡uxen i EUF ikke er påvirket af en ledningsevne op til omkring 3 mS/cm. Energiberegninger viser at EUF er en økonomisk fordel når opløsninger med en høj enzymkoncentration og lav ledningsevne bliver …ltreret. Hvis enzymkon- centrationen er lav er omkostningerne ved UF lavere. Ledningsevnen er en væsentlig parameter for den økonomiske gennemførlighed af EUF processen, da energibehovet stiger proportionalt med ledningsevnen af enzymopløsningen. Hvis ledningsevnen bliver for høj forsvinder fordelene ved at bruge EUF. Contents 1 Introduction 1 2 Theory 3 2.1 Ultra…ltration . 3 2.1.1 Gellayermodel ........................ 5 2.1.2 The osmotic pressure model . 7 2.2 Electro-ultra…ltration . 9 2.3 Models................................. 12 2.4 Summary ............................... 15 3 Description of protein fouling 17 3.1 Protein fouling of MF and UF membranes . 19 3.1.1 E¤ect of feed properties . 20 3.1.2 Membrane properties . 24 3.1.3 Operating conditions . 26 3.2 Methods to prevent fouling . 28 3.2.1 Flow manipulation . 29 3.2.2 Turbulence promoters . 31 3.2.3 Cleaning............................ 33 3.3 Summary ............................... 34 4 Literature review: Cross‡ow electro…ltration 37 4.1 Processdesign............................. 38 4.2 Electric…eld.............................. 39 4.2.1 Pulsed electric …eld . 41 4.3 E¤ect of feed properties . 42 4.3.1 Feed concentration . 42 4.3.2 -potential and conductivity . 43 4.4 E¤ect of cross‡ow velocity and TMP . 45 4.5 Retention ............................... 47 4.6 Selectivity ............................... 48 4.7 Processeconomy ........................... 48 4.8 Electrical cleaning of membranes . 49 vii viii CONTENTS 4.9 Dead-end electro…ltration . 50 4.10 Acoustic and Electroacoustic . 51 4.10.1 Ultrasonic cleaning of membranes . 53 4.11Summary ............................... 53 5 Experimental 55 5.1 Enzymes................................ 55 5.2 Determination of the enzyme concentration . 57 5.3 EUFmodule.............................. 58 5.3.1 Calculation of E over the feed chamber . 60 5.3.2 EUF-rig ............................ 62 5.3.3 Experimental procedure . 63 5.3.4 Cleaning............................ 64 5.4 Ultra…ltration experiments . 65 5.5 Summary ............................... 66 6 Results and discussion 69 6.1 Electro-ultra…ltration . 69 6.1.1 Enzymes............................ 70 6.1.2 E¤ect of concentration . 72 6.1.3 Batch variations . 76 6.1.4 E¤ect of TMP and cross‡ow velocity . 78 6.1.5 E¤ect of a pulsed electric …eld . 79 6.1.6 Model development of the data . 80 6.2 Ultra…ltration . 84 6.2.1 ModelofUFdata....................... 86 6.3 Summary ............................... 88 7 Process design & economy 89 7.1 Energy consumption and membrane area . 90 7.1.1 Membrane area . 91 7.2 Energy calculations . 91 7.2.1 Pumpenergy ......................... 91 7.2.2 Energy used by the electric …eld . 94 7.3 Energy considerations . 95 7.3.1 Energy used in UF . 97 7.3.2 Energy used in EUF . 98 7.4 Summary ............................... 104 8 Conclusion 105 9 Future of the project in Novozymes 107 CONTENTS ix A Other EUF modules 109 A.1 Description of the modules .