Chemical apparatus and process disinfecting – deodorizing – preser – Physical type apparatus – Means separating or dissolving a material constituent
Reexamination Certificate
2000-09-05
2003-12-23
Thornton, Krisanne (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Physical type apparatus
Means separating or dissolving a material constituent
C422S261000, C422S278000, C554S012000
Reexamination Certificate
active
06667015
ABSTRACT:
This invention concerns apparatuses and a method for “extraction” of biomass, i.e. the extraction of flavours, fragrances or pharmaceutically active ingredients from materials of natural origin (these materials being referred to as “biomass” herein).
Examples of biomass materials include but are not limited to flavoursome or aromatic substances such as coriander, cloves, star anise, coffee, orange juice, fennel seeds, cumin, ginger and other kinds of bark, leaves, flowers, fruit, roots, rhizomes and seeds. Biomass may also be extracted in the form of biologically active substances such as pesticides and pharmaceutically active substances or precursors thereto, obtainable e.g. from plant material, a cell culture or a fermentation broth.
There is growing technical and commercial interest in using near-critical solvents in such extraction processes. Examples of such solvents include liquefied carbon dioxide or, of particular interest, a family of chlorine-free solvents based on organic hydrofluorocarbon (HFC) species.
By the term “hydrofluorocarbon” we are referring to materials which contain carbon, hydrogen and fluorine atoms only and which are thus chlorine-free.
Preferred hydrofluorocarbons are the hydrofluoroalkanes and particularly the C
1-4
bhydrofluoroalkanes. Suitable examples of C
1-4
hydrofluoroalkanes which may be used as solvents include, inter alia, trifluoromethane (R-23), fluoromethane (R-41), difluoromethane (R-32), pentafluoroethane (R-125), 1,1,1-trifluoroetane (R-143a), 1,1,2,2-tetrafluoroethane (R-134), 1,1,1,2-tetrafluoroethane (R-134a), 1,1-difluoroethane (R-152a), heptafluoropropanes and particularly 1,1,1,2,3,3,3-heptafluoropropane (R-227ea), 1,1,1,2,3,3-hexafluoropropane (R-236ea), 1,1,1,2,2,3-hexafluoropropane (R-236cb), 1,1,1,3,3,3-hexafluoropropane (R-236fa), 1,1,1,3,3-pentafluoropropane (R-245fa), 1,1,2,2,3-pentafluoropropane (R-245ca), 1,1,1,2,3-pentafluoropropane (R-245eb), 1,1,2,3,3-pentafluoropropane (R-245ea) and 1,1,1,3,3-pentafluorobutane (R-365mfc). Mixtures of two or more hydrofluorocarbons may be used if desired.
R-134a, R-227ca, R-32, R-125, R-245ca and R-245fa are preferred.
An especially preferred hydrofluorocarbon for use in the present invention is 1,1,1,2-tetrafluoroethane (R-134a).
It is possible to carry out biomass extraction using other solvents such as chlorofluorocarbons (“CFC's”) or hydrochlorofluorocarbons (“HCFC's”), and/or mixtures of solvents.
Known extraction processes using these solvents are normally carried out in closed-loop extraction equipment. A typical example
10
of such a system is shown schematically in FIG.
1
.
In this typical system
10
, liquefied solvent is allowed to percolate by gravity in downflow through a bed of biomass held in vessel
11
. Thence it flows to evaporator
12
where the volatile solvent vapour is vaporised by heat exchange with a hot fluid. The vapour from evaporator
12
is then compressed by compressor
13
: the compressed vapour is next fed to a condenser
14
where it is liquefied by heat exchange with a cold fluid. The liquefied solvent is then optionally collected in intermediate storage vessel
15
or returned directly to the extraction vessel
1
to complete the circuit.
A feature of this process is that the principal driving force for circulation of solvent through the biomass and around the system is the difference in pressure between the condenser/storage vessel and the evaporator. This difference in pressure is generated by the compressor. Thus to increase the solvent circulation rate through the biomass it is necessary to increase this pressure difference, requiring a larger and more powerful compressor.
The large difference in solvent liquid and vapour densities means that a modest increase in liquid circulation rate can require significant additional capital and operating cost. This is because any vapour volumetric flow increase requires an increase in compressor size. This means that the system designer has to compromise between the rate at which liquid can be made to flow through the biomass and the rate at which vapour can be compressed.
The purchase cost and, perhaps more significantly, the operating cost of a compressor increase with increasing size. Also many biomass extraction apparatuses are constituted as approximately room-sized plant or smaller, in which there is limited scope for simply increasing the size of the compressor.
A potential problem for efficient design of equipment arises because it is known that, for most extractions, the rate at which the majority of the extract material is removed from the biomass is influenced by the rate at which solvent flows through the bed. A faster solvent rate gives better mass transfer from the biomass to the solvent, enabling more material to be removed for a given period of time. Consequently the size of compressor
13
selected for the apparatus
10
ultimately determines the rate at which the material may be extracted and therefore affects the time taken to effect an extraction.
Equipment designed for this type of extraction process is typically used for multiple extractions of different biomasses, yielding a range of products which may need to be extracted to meet a variety of customers' production schedules. The biomasses of interest to industry can range from relatively large, pellet-like seeds or beans, to much finer powdered or shredded vegetation.
The smaller the particle size of a bed of biomass the greater its resistance to liquid flow. Consequently with a fixed size of solvent vapour compressor the speed at which an extraction plant of this design can process a range of materials will vary widely (hence affecting batch extraction time) and may therefore compromise the overall economic performance of the plant or its liability to meet external scheduling demands.
Another potential problem with the
FIG. 1
arrangement is the existence of a vapour/liquid interface at the top of the biomass bed in the extractor vessel
11
. This means that the solvent flowing through the bed is essentially saturated liquid. In other words, it is close to boiling. This means that, if its pressure is reduced, a portion of the liquid flowing through the bed will vaporize even in the absence of external heat input. A packed bed of biomass can offer a significant resistance to flow. Thus it is possible to conceive of a critical rate of flow at which the pressure loss caused by flow through the bed offsets the hydrostatic head gained as the liquid flows down through the bed. As flow increases beyond this value, vapour bubbles will form in the liquid flowing through the system toward the evaporator. This is a form of flash vaporization of the solvent/extract mixture.
Therefore any reduction in compressor suction pressure (i.e. at the intake side of the compressor), effected with the intention of increasing the circulation rate, can have only limited success because the solvent flowing out of the bed will eventually form a mixture of liquid and vapour, with an effective density significantly lower than that of the liquid solvent.
The frictional resistance to flow in any fluid system increases as effective density of the fluid decreases. The presence of vapour arising from a pressure drop as described above will eventually cause sufficient increase in frictional resistance to flow to offset an increased pressure difference over the compressor and will therefore negate any further benefit to reducing the compressor suction pressure. The maximum liquid throughput of the system is therefore additionally constrained by this design of equipment.
For these reasons, simply increasing the compressor size is of limited benefit in improving efficiency of the biomass extraction
Heat recovery is often employed in such processes to reduce the cost of operating the process. This can be achieved by either of two methods: direct or indirect heat integration. In the former, the solvent condenser
14
is combined with the solvent evaporator
12
. The hot, compressed solvent vapour is condensed in this unit and acts as the hot fluid for
Corr Stuart
Low Robert E.
Morrison James David
Murphy Frederick Thomas
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Ineos Fluor Holdings Limited
Thornton Krisanne
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