Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Reexamination Certificate
2000-07-18
2002-08-27
Brunsman, David (Department: 1755)
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
C127S043000, C127S046200, C127S048000, C127S052000, C127S054000, C127S056000
Reexamination Certificate
active
06440222
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for obtaining sucrose from sugar beets.
The conventional beet sugar manufacturing process involves cleaning the beets, slicing them into cossettes, extracting juice from the cossettes by diffusion, purifying the juice by liming and carbonation, concentrating the juice by multiple effect evaporation, multi-stage boiling of concentrated juice in pans, separation, washing, and drying the sugar.
Juice extraction in the conventional process is done by allowing the sugar to diffuse through the natural cell walls of beets. The cell walls allow sugars and other low molecular weight compounds to pass through but prevent the passage of high molecular weight compounds. This selective diffusion process has two advantages. Retaining the high molecular weight compounds helps produce a high purity juice. It also reduces filtration difficulties that are caused by polysaccharides and proteins that comprise the high molecular weight compounds.
Purification of beet juice in the conventional process is based on lime treatment. Lime serves many purposes in the juice purification process. It neutralizes the acidity of the juice and precipitates calcium salts of several organic and inorganic acids. The precipitate absorbs other impurities. The lime precipitate produces a porous mass, which facilitates subsequent filtration of juice.
The conventional diffusion process for juice extraction from beets has some disadvantages. It has a long retention time, which encourages microbial growth, resulting in sugar loss and formation of undesirable compounds. It is difficult to increase the temperature of sliced cossettes quickly enough to prevent growth of micro-organisms. Typically the pulp remaining after diffusion is pressed and the press juice is introduced back into the diffuser. A significant portion of the high molecular weight compounds retained by the cell walls in the diffusion process is released in pressing to be mixed with the diffusion juice. This partially negates the advantages of the selective diffusion process.
The conventional liming process uses large quantities of lime, amounting to about 2.5% of the total weight of beets processed. Beet sugar plants operate lime kilns and transport limestone over long distances for this purpose. The effluent from the liming-carbonation process, consisting of used lime and separated impurities, is disposed as waste. Production of lime and disposal of liming effluent are costly operations. Disposal of liming effluent is becoming increasingly difficult and expensive in many communities.
Conventional dead-end filtration is incapable of separating sucrose from macromolecular impurities in beet juice. Several methods of using microfiltration and ultrafiltration for purification of juice with reduced lime use have been reported, but these methods generally involve inserting microfiltration or ultrafiltration membranes into the conventional beet process at one or more points.
There is a long-standing need for improved processes for obtaining sugar from beets that avoid or at least minimize one or more of the problems existing in the previously used processes.
SUMMARY OF THE INVENTION
The present invention relates to a process for producing sugar from beets. A sucrose-containing feed juice that has been obtained from sugar beets is filtered through a first ultrafiltration membrane that has a first molecular weight cutoff. This ultrafiltration step produces a first ultrafiltration permeate and a first ultrafiltration retentate. The first ultrafiltration permeate is filtered through a second ultrafiltration membrane that has a second molecular weight cutoff that is lower than the first molecular weight cutoff. This second ultrafiltration step produces a second ultrafiltration permeate and a second ultrafiltration retentate. The second ultrafiltration permeate is nanofiltered through a nanofiltration membrane, thereby producing a nanofiltration permeate and a nanofiltration retentate. The nanofiltration retentate has a higher concentration of sucrose on a dry solids basis than the feed juice introduced into the first ultrafiltration step, and can be used in evaporation and crystallization operations to produce crystals of white sugar.
In one embodiment of the invention, the sucrose-containing feed juice is manufactured by macerating sugar beets or pieces thereof, thereby producing a macerated material that comprises pulp and liquid, and then separating the liquid in the macerated material from the pulp, for example by one or more of centrifugation, conventional filtration, or screening. In one particular embodiment, the beets are macerated by first passing them through a hammer mill, and optionally they can subsequently be passed through a grinder, whereby the beets are converted into a mixture of pulp and sucrose-containing liquid. Preferably, no more than about 5% by weight of the sucrose present in the beets remains in the pulp after the liquid is separated therefrom, more preferably no more than about 3%.
After separation of the fibrous pulp from the liquid, and before the first ultrafiltration, the process can optionally include an additional step or steps to remove residual beet fibers and silt from the separated liquid (juice). This can be done by screening and/or filtration. Preferably the screening or filtration removes at least 90% by weight of all fibers and silt having a largest dimension of about 150 &mgr;m or greater, more preferably at least 90% by weight of all fibers and silt having a largest dimension of about 50 &mgr;m or greater.
It is also possible to introduce air into the feed juice prior to the first ultrafiltration, in order to oxidize color-forming materials. This oxidation, while increasing the color of the juice, causes the color-forming materials to polymerise, which facilitates their removal in the subsequent ultrafiltration. (When this patent refers to polymerisation of color-forming materials, this is intended to include physical agglomeration as well as chemical polymerisation.) Another option is to introduce hydrogen peroxide, ozone, or both, into the feed juice prior to the first ultrafiltration. These materials also facilitate oxidation.
It is preferred to adjust the pH of the feed juice to about 6-8, for example by the addition of a base, prior to ultrafiltration. This can help minimize formation of invert.
The first ultrafiltration membrane preferably has a molecular weight cutoff of at least about 2,000 daltons and a pore size no greater than about 0.1 microns. More preferably, it has a molecular weight cutoff of about 4,000-200,000 daltons. The first ultrafiltration permeate preferably has a color of about 3,000-10,000 icu. (All color values given herein are determined on an ICUMSA scale.)
The process of the present invention can be operated at a number of different process conditions. As representative examples of such conditions, the feed juice can be at a temperature of about 140-200° F. during the first ultrafiltration, more preferably about 160-185 ° F.
The second ultrafiltration membrane preferably has a molecular weight cutoff of about 500-5,000 daltons, more preferably about 1,000-4,000 daltons. In one particular embodiment of the process, the second ultrafiltration is performed in two stages, the first stage using an ultrafiltration membrane having a molecular weight cutoff of about 3,500-4,000 daltons, and the second stage using an ultrafiltration membrane having a molecular weight cutoff of less than about 3,500 daltons. The second ultrafiltration permeate preferably has a color no greater than about 4,000 icu, more preferably no greater than about 2,500 icu.
In order to minimize loss of sucrose in the retentate from the first and second ultrafiltration steps, it is preferable to include diafiltration steps in the process. “Diafiltration” is used herein to mean ultrafiltration that employs added water in the feed to help flush sucrose through the membrane.
In one such embodiment of the process, the first ultrafiltration retentate is diafiltered
Donovan Michael
Hlavacek Marc
Jansen Robert P.
Reisig Richard C.
Walker Gordon
Brunsman David
Tate & Lyle Industries, Limited
Williams Morgan & Amerson P.C.
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