Membrane module for the separation of fluid mixtures

Details Membrane module for the separation of fluid mixtures Membrane module for the separation of fluid mixtures

2002-12-02

2004-09-14

Prince, Fred G. (Department: 1724)

Liquid purification or separation

With heater or heat exchanger

For filter

C210S321790, C210S321880

Reexamination Certificate

active

06790350

ABSTRACT:

The present invention relates to an apparatus for the separation of fluid mixtures according to the preamble of claim
1
.
It is known to those skilled in the art that fluid mixtures can be separated by passing at least one component of a mixture selectively through a membrane while the other components are partially or fully retained. Such a process may be a filtration process in which particles or macromolecules of a fluid mixture are retained according to their size, e.g. in Microfiltration or Ultrafiltration. In other membrane processes molecules can be separated according to their chemical nature. e.g. in Reverse Osmosis, Pervaporation, Vapor Permeation, or Gas Separation
Membranes suitable for such separations may be produced in a plane form, often referred to as flat sheet form, or in a tubular form, referred to as hollow fibers, capillaries or tubes. The direction of the transmembrane flux in such tubular membranes may be from the inside outwards or from the outside inwards.
For practical applications such membranes have to be incorporated into an apparatus known to those skilled in the art as a membrane module, in which a feed side of the membrane which is in contact with the mixture to be separated is separated and tightly sealed against a permeate side of the membrane, and both are separated from the outside environment. It is well known to those skilled in the art that especially in the membrane processes of molecular separation the tightness of the sealing between the feed and the permeate side of the membrane is essential. Whereas for flat membranes plate modules or spiral wound modules are widely used, tubular membranes are often incorporated as a bundle in a module similar to a tube-and-shell heat exchanger.
A tubular membrane may have the feed side as the outside or the inside surface and the permeate side respectively. If the direction of the transmembrane flux is from the inside to the outside of a tubular membrane the feed has to flow through the inner lumen of the tubular membrane and both ends of the tubular membrane have to be fixed into means sealing the inside of the lumen from the outside and allowing for a free flow of a fluid through the inside lumen of the tubular membrane. If the direction of the transmembrane flux is from the outside to the inside of the tubular membrane at least one end of the tubular membrane has to be fixed and sealed to the outside, the second side may just be closed or fixed and sealed.
It is known in the art that the transmembrane flux of matter and, in the case of pervaporation, of energy, can be split into several consecutive steps, the most important being at least:
i. the transport of matter and energy from the bulk of the feed fluid to the feed side of the membrane,
ii. the respective transport through the membrane, and
iii. the transport from the permeate side of the membrane into the bulk of the permeate.
The slowest of these consecutive steps will determine the overall flux through the membrane. For membranes with a low transmembrane flux the upstream and downstream mass (and energy) transport is usually sufficiently fast to be of negligible influence on the overall flux. If, however, the transmembrane flux is high the mass transport out of the bulk of the feed fluid to the membrane surface may be limiting the overall flux.
In a pervaporation process the lost energy needed for evaporation of the permeate will lead in all cases to a drop in the operation temperature and thus in a decrease of the overall membrane flux.
To those skilled in the art the effect of limiting mass transport to the feed surface of the membrane is known as concentration polarization and the limiting energy transport is known as temperature polarization, respectively. It is furthermore known that the polarization effects depend on the flow regime of the feed fluid which can best be described by the Reynolds number, which depends on the linear velocity of the feed flow tangential to the membrane surface and the geometry of the space adjacent to the feed surface.
For tubular membranes with the feed fluid in the inner lumen of the tube the flow regime can be determined and high Reynolds numbers can be achieved although, depending on the diameter of the inner lumen high volume flows may result. At high Reynolds number the polarization effects thus can be reduced, at the costs of a high volume flow rate and a high pressure loss.
The energy lost in a pervaporation process cannot be influenced by the Reynolds number.
For tubular membranes with the feed fluid flowing over the outside of the membrane the direction of the flow is mainly perpendicular to the outside surface of the tubular membrane. The Reynolds number cannot easily be determined and influenced: It is common in the art to use baffle plates in order to reverse the direction of the feed flow in a zigzag manner, in order to create a local turbulence and local high Reynolds numbers, however, the success of such means is limited and creates high pressure losses and volume flows. Therefore it is very difficult to realize, the full potential flux of such membranes in an industrial module.
EP 0652098A discloses a filtering device wherein the feed, preferably a molten polymer is introduced in parallel to the annular spaces between a filter cartridge and a surrounding further tube. The feed is substantially transferred through the filter cartridge and the remaining amount of the feed rejected by the filter cartridge is collected at the end of the annular space. The annular space is there converted into a small gap through which the rejected part of the feed is combined with the filtrate which has passed through the filter cartridge.
In this filter device the filtrate and the retentate are again combined in a collection chamber and discharged as one stream. The filter device thus has only one inlet for the feed and one outlet for the combined filtrate and retentate. It therefore cannot be used to split a feed stream into a retentate and a permeate stream which have to be discharged separately.
From U.S. Pat. No. 4,976,866 an apparatus is known according to the preamble of claim
1
. A single tubular membrane is surrounded on the one hand by a larger diameter feed tube and inside the membrane a further membrane is provided. The annular gap between the two membranes is filled with an ion exchanging or absorbent material. At this device the Reynolds number can not easily be determined or influenced.
It is an object of the present invention to provide a membrane module for tubular membranes with the transmembrane flux from the outside to the inside of the tubular membrane, allowing to operate at high Reynolds numbers with a well defined tangential flow of the feed fluid over the membrane surface, allowing to realize the full potential flux through such membranes but avoiding unnecessary high volume flows and pressure losses.
It is a further object of the present invention to provide a membrane module which allows to optimize the feed fluid flow regime.
It is a further object of the present invention to provide a membrane module which allows for a continuous exchange of thermal energy with the feed fluid, e.g. the energy lost in a membrane separation (e.g. pervaporation) process through the membrane or the energy produced or consumed in a reaction in the feed fluid and thus to operate at constant temperatures of the feed fluid.
It is a further object of the present invention to provide a membrane module having an inlet for the feed, and outlet for the retentate and an outlet for the permeate, thus separating the feed stream into two distinct product streams.
This aim is realized in a separation device having the characterizing features of claims
1
.
In a membrane module of the present invention one end of at least one tubular membrane is fixed and sealed into a membrane tube sheet and the second end is closed. The tubular membrane is installed coaxial into a second tube, the feed tube, a first end of said feed tube is fixed and sealed into a first feed tube sheet and a second end is fixed and sealed int

Affiliated with

Also associated with

Rating

Membrane module for the separation of fluid mixtures does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Membrane module for the separation of fluid mixtures, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Membrane module for the separation of fluid mixtures will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3222807