Waste solvent recovery apparatus

A waste solvent recovery apparatus to recover tetrahydratfuran (THF) from waste sludge. THF sludge enters the apparatus container through a sludge jet generally pointing in a downward direction. Steam is directed downwardly and at the THF waste sludge jet tending to vaporize the THF while solid contaminants fall to the bottom of the container. The flow rate of steam with respect to waste sludge is adjusted so that the temperature at the bottom of the container exceeds the boiling point of THF and the temperature at the top of the container is less than the boiling point of water.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to reclamation of relatively low boiling point 
solvents when such solvents are contaminated from prior use and/or 
manufacturing processing. In particular, the invention relates to the 
solvent recovery of tetrahydrafuran (THF) when formed with other 
particulate and chemical contaminants into a sludge-like waste product. 
2. Description of the Prior Art 
Many solvents of relatively low boiling point are utilized in manufacturing 
processes, and by their use they become contaminated commonly with 
particulates and other chemicals. Often such solvents are flammable, 
toxic, and dissolve many organic materials with which they come in 
contact. Thus, their disposition as a waste product presents serious 
problems from both an environmental and a waste-hauling standpoint. 
Moreover, many solvents are derived from hydrocarbon materials which are 
becoming increasingly expensive to procure, if available at all. Thus, a 
need exists to extract spent solvents which have become contaminated from 
waste materials and recycle such solvents back to relatively pure status. 
In particular, THF is a solvent used in many industrial processes. In one 
instance, THF is utilized as a solvent carrier in the manufacture of 
magnetic recording media. In producing such magnetic recording media 
including flexible disks, cassettes, data recording cartridges, and other 
media devices, THF is mixed with other materials including iron oxide 
particles and resins to form a liquid within which such particles are 
evenly dispersed. This liquid is used for coating suitable substrates. In 
the coating process, relatively large filter housings hold the liquid or 
"ink" prior to being pumped into the coating station. Such filter housings 
retain a residue on the order of several gallons of ink per filling which 
is left as a sludge at the bottom of the container. In addition, THF is 
used as a solvent to clean parts on the magnetic media coating line. Thus, 
a significant amount of contaminated THF is generated often in the form of 
a thick slurry or so-called "slop". 
In the prior art THF has been extracted from such "slop" by use of a 
container having hot water therein maintained at a temperature less than 
100.degree. C. (the boiling point of water) but greater than 66.degree. C. 
(the boiling point of THF). Theoretically, the "slop" is supposed to 
contact the hot water and have the THF driven off in the form of vapors 
which can be collected and condensed to form a mixture of THF plus water. 
This liquid can thereafter be further purified by known techniques. In 
practice, this process is extremely inefficient. By its nature, the "slop" 
contains a significant quantity of binder material and cross linking 
material which is used in the formation of the magnetic media. When the 
binder and cross linking material hits the hot water, the temperature is 
high enough so that the binder cures and tends to encapsulate significant 
amounts of THF within small nodules. Efficiencies for this prior art 
process are in the range of 40% to 50% yield as a percentage of the total 
THF contained within the raw "slop". 
SUMMARY OF THE INVENTION 
It is thus an object of the present invention to provide an apparatus which 
can effectively remove solvent from waste sludge materials. 
It is another object of the present invention to provide a solvent recovery 
apparatus which recovers virtually all of the solvent contained within the 
waste sludge. 
It is yet another object of the present invention to provide a waste 
solvent recovery apparatus which is effective in the recovery of THF. 
It is yet another object of the present invention to provide a waste 
solvent recovery apparatus which is inexpensive in capital outlay and 
simple to operate. 
In a preferred embodiment according to the present invention, a cylindrical 
container is adapted to receive a jet of solvent laden sludge or "slop" 
and direct such jet in a generally downward direction. Into the stream of 
"slop" are directed a pair of steam jets. On top of the cylindrical 
container is a condenser and an exit orifice. In addition, in the lower 
portion of the container is a door for removal of waste particulates. In 
operation, waste "slop" is forced out of the "slop" orifice. The steam 
directed at the "slop" jet causes a fine particulate dustlike material to 
be generated which ends up as a residue at the bottom of the container. 
The THF is vaporized by the water vapor and rises into the condenser 
column on top of the container. The rate of "slop" entry into the 
container and the rate of steam flow is adjusted so that the temperature 
at the bottom of the container is greater than the boiling point of THF, 
and the temperature at the top of the container just below the condenser 
is less than the boiling point of water. The liquid effluent from the 
waste solvent recovery apparatus of the present invention is a mixture of 
water and THF. 
It is thus an advantage of the present invention that THF may be recovered 
from waste "slop" in an efficient and inexpensive manner. 
It is another advantage of the present invention that the apparatus 
disclosed herein has wide latitudes in its operating parameters making 
operation of the apparatus relatively uncritical. 
It is yet another advantage of the present invention that the disclosed 
waste solvent recovery apparatus may recover a wide variety of solvents of 
different chemistry and contaminated in different ways. 
It is yet another advantage of the present invention that the particulate 
solid biproduct of operation of the waste solvent recovery apparatus is 
simple to remove from the apparatus and can be easily disposed of, because 
it contains such a low percentage of toxic solvent therewithin. 
These and other objects and advantages of the present invention will no 
doubt become apparent to those skilled in the art by referring to the 
following detailed description of a preferred embodiment and by reference 
to the several drawing figures.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a perspective view of a waste solvent recovery 
apparatus of the present invention is shown and referred to by the general 
reference character 10. Waste solvent recovery apparatus 10 is constructed 
from a container 12 generally of circular cross-section. Attached to the 
top of container 12 and approximately positioned concentric therewith is a 
condenser 14. Container 12 is supported upon level ground by a plurality 
of legs 16. As will be described in greater detail hereafter, a bottom 
surface 18 of container 12 is generally planar and inclined from the 
horizontal in order to assist in removal of solid residue particles which 
are produced as a result of operation of waste solvent recovery apparatus 
10. 
Container 12 has an outer cylindrical surface 20. Generally, in the area 
where bottom surface 18 interests cylindrical surface 20 is located an 
access port 22. Access port 22 permits solid wastes to be removed 
therethrough that are produced within container 12 during operation of 
waste solvent recovery apparatus 10. During operation of waste solvent 
recovery apparatus 10, access port 22 is closed by a door 24 which is 
secured in a closed position by conventional means. In addition to access 
port 22, a pair of thermometers 26 and 28 are located on cylindrical 
surface 20. Thermometer 26 is located generally near the bottom of 
container 12 with its temperature sensing end extending into container 12 
so as to measure the internal temperature at the bottom of said container 
12 when the waste solvent recovery apparatus 10 is in operation. 
Thermometer 28 is located generally near the top of container 12 with its 
temperature sensing end extending through cylindrical surface 20 to read 
the interior temperature at the top of container 12 when the waste solvent 
recovery apparatus 10 is in operation. The use of thermometers 26 and 28 
will be described in greater detail hereafter. 
Connected to the cylindrical surface 20 of container 12 generally opposite 
from access port 22 and door 24 are a plurality of supply tubes. A waste 
sludge supply tube 30 is so connected to cylindrical surface 20 in order 
to supply the waste sludge material containing the contaminated solvent to 
be recovered. In addition to waste sludge supply tube 30 are connected a 
pair of steam supply tubes 32a and 32b as shown in FIG. 1. As it is 
desirable to control the flow rate of steam with respect to waste sludge 
material, a valve 34 is positioned between waste sludge supply tube 30 and 
container 12 in order to regulate the flow of waste sludge material 
therethrough. 
Referring to FIG. 2, an interior view of container 12 is shown in order to 
illustrate the disposition of the steam jets with respect to the waste 
sludge jet. Generally, waste sludge material is conducted through waste 
sludge supply tube 30 to a portion 36 of waste sludge supply tube 30 which 
is oriented in a vertical disposition as shown in FIG. 2. Portion 36 is 
terminated in a nozzle element 38 having an orifice 40 through which waste 
sludge material exists under pressure during operation of waste solvent 
recovery apparatus 10. Steam supply tubes 32a and 32b enter container 12 
and extend into the vicinity of waste sludge supply tube 30 being 
terminated in the vicinity of nozzle 38. Steam supply tube 32a and 32b are 
disposed at approximately 45.degree. angles with respect to the horizontal 
and steam emanates in a jet therefrom focused by a pair of nozzles 42a and 
42b as shown in FIG. 2. Nozzles 42a and 42b have openings 44a and 44b, 
respectively, which form the shape of the steam jets. 
In a working model constructed in accordance with the present invention, 
container 12 has an external diameter for cylindrical surface 20 of 
approximately 42 inches. The height of container 12 is generally 60 inches 
which creates an internal volume for container 12 of approximately 400 
gallons. In addition, waste sludge orifice 40 has been constructed to have 
a circular opening approximately 1/8 of an inch in diameter, and steam 
orifices 44a and 44b have slotted openings approximately 1/8 of an inch 
wide by 3/4 of an inch long. It has been found convenient moreover to 
incline surface 18 at an angle approximating 30.degree. from the 
horizontal in order to easily remove solid biproducts from container 12 
through access port 22 after operation of waste solvent recovery apparatus 
10. 
In operation of waste solvent recovery apparatus 10 when the solvent to be 
recovered is THF, it is required that the bottom of container 12 be 
maintained at a temperature in excess of 66.degree., that is, the boiling 
point of THF. In addition, it is required that the top portion of 
container 12 be maintained at a temperature less than 100.degree. C., that 
is, the boiling point of water. Thus, at all times of operation for waste 
solvent recovery apparatus 10, thermometer 26 must read an excess of 
66.degree. C. and thermometer 28 must read less than 100.degree. C. In 
practice, thermometer 26 is generally operated in the range of 75.degree. 
C. and thermometer 28 is generally operated in the range of 90.degree. C. 
While the general dimensions and physical positioning of components for 
waste solvent recovery apparatus 10 is uncritical, in order to efficiently 
operate waste solvent recovery apparatus 10 the temperatures should be 
maintained as discussed hereinabove. Thus, the flow rate of waste sludge 
with respect to steam is simply adjusted so that generally steam jets 42a 
and 42b have approximately equal flows, and the flow of waste sludge with 
respect to steam in general is adjusted to achieve the desired operational 
temperatures. 
When the waste sludge exists from orifice 40 and contacts steam jets 
emanating from orifices 44a and 44b, a fine particulate material is formed 
which settles at the bottom of container 12 upon inclined surface 18. 
Water vapor and gaseous THF tend to rise within container 12 and enter 
condenser 14. The interior of condenser 14 in a working model in 
accordance with the present invention has been constructed from stainless 
steel packing materials in order to provide condensation sites for water. 
The exterior of condenser 14 has been constructed in the form of a right 
circular cylinder approximately 12 inches in diameter and 36 inches long 
concentric with container 12. The purpose of condenser 14 is to collect 
and remove as much water as possible from the gases flowing therethrough 
so that the exit gases from condenser 14 leaving through a port 46 shown 
in FIG. 1 will be primarily THF. In fact, it has been found that the 
actual gaseous output from condenser 14 through output port 46 is 
approximately 60% to 80% THF and 20% to 40% water. While that ratio of THF 
to water in the end product gaseous material through use of the present 
invention is approximately the same for prior art waste solvent recovery 
systems, the present invention has an efficiency of approximately 98% to 
99% as opposed to an efficiency of some 40% to 50% for prior art waste 
solvent recovery systems. That is, the waste solvent recovery apparatus 10 
permits reclamation of approximately 98 to 99% of the THF contained within 
the input waste sludge. The resulting solid waste ash is consequently so 
low in THF content that it may be disposed of without significant 
environmental problems. 
While for the sake of clarity and in order to disclose the present 
invention so that the same can be readily understood, a specific 
embodiment has been described and illustrated, it is to be understood that 
the present invention is not limited to the specific means disclosed. It 
may be embodied in other ways that may suggest themselves to persons 
skilled in the art. For example, the shape of container 12 is not limited 
to a cylindrical cross-section, and it is not necessarily required that 
the attitude of the sludge and steam jets be in a generally vertical 
position. Moreover, a plurality of sludge jets and steam jets may be 
assembled in order to enhance certain applications of the waste solvent 
recovery apparatus 10. It is also conceivable that operation of waste 
solvent recovery apparatus 10 could be automated to the extent that the 
flow rates of the individual waste materials and steam could be controlled 
by electromagnetically actuated valves under guidance from a 
microprocessor wherein thermometers 26 and 28 provide the necessary input 
information for control of the process by the microprocessor according to 
certain algorithmic models. Moreover, the apparatus of the present 
invention as disclosed is not limited to the reclamation of THF as other 
solvents could easily be reclaimed in an apparatus employing a similar 
structure. It is believed that this invention is new and that all such 
changes that come within the scope of the following claims are to be 
considered as part of this invention.