NAMS 2002 Workshop - ICOM 2008

Ultra- and Microfiltration II - Processes – 1 – Keynote
Thursday July 17, 8:15 AM-9:00 AM, Moloka’i
Membrane Applications in the Pulp and Paper Industry: New Developments
and Case Studies
F. Lipnizki (Presenting), Alfa Laval Product Centre Membranes, Soborg, Denmark -
frank.lipnizki@alfalaval.com
T. Persson, Lund University, Lund, Sweden
A.-S. Jönsson, Lund University, Lund, Sweden
Every year, 100,000 tons of dissolved hemicelluloses are discharge unused with
wastewater from thermomechanical pulp mills around the world. Isolation of
these hemicelluloses from the wastewater would not only reduce the treatment
costs for the pulp mills but would also provide an excellent raw material for high
value applications such as oxygen barriers in food packaging. The isolation of the
hemicelluloses can be combined with polishing of the wastewater by using
different filtration processes. The initial step in this combination is either a drum
filter or a microfiltration treatment to remove solid residues from the wastewater
followed by ultrafiltration to concentrate the hemicelluloses. The permeate from
the ultrafiltration can then be further polished by reverse osmosis before
recycling. The focus of this paper is on the optimisation of the ultrafiltration step
concentrating on the membrane selection and its impact on the process
economics. The membrane selection includes the newly developed commercial
UFX5 pHt membrane (Alfa Laval, Denmark) based on hydrophilised
polyethersulfone. The feed studied in this paper is process water from the
thermomechanical pulp mill Stora Enso Kvarnsveden (Sweden). The temperature
of this process stream is 75°C. To reduce the need for cooling and preserve the
energy, temperature tolerance is an important membrane selection parameter.
Further, since the process water contains resin and lignin, which tend to foul
membranes, the hydrophilicity of the membrane is another important selection
parameter. Based on this, five membranes with molecular weight cut- offs
(MWCOs) between 1 - 10 kD were pre-selected: (1) a hydrophilised fluoro
polymer membrane ETNA10PP, MWCO: 10 kD, (2) a hydrophilised fluoro
polymer membrane ETNA01PP, MWCO: 1 kD, (3) a hydrophilised
polyethersulfone membrane UFX5 pHt, MWCO: 5 kD (all Alfa Laval, Denmark),
(4) a regenerated cellulose membrane UC005, MWCO: 5 kD, and (5) a
polyethersulfone membrane UP005, MWCO: 5 kD (all Microdyn-Nadir,
Germany). The ETNA10PP, ETNA01PP, and UC005 are limited to a temperature
of 60/55°C and to a pH range of 1 to 11, whereas the UP005 and UFX5pHt can
be operated up to 75°C and in a pH range from 1 to 14/13. In the initial study, a
small flat test module was used to study the pure water fluxes and the fouling
behaviour of the membranes related to octanoic acid, a fouling substance which
represents a significant number of small hydrophobic substances. Based on this,