PROCESS AND APPARATUS FOR REMOVING BOTTOMS FROM A MIXTURE

Abstract: Process for removing bottoms or isolating useful products from a liquid mixture which in addition to, e.g., water contains solid matter, in which process the mixture is passed through a packed filter bed in a vessel, characterized in that the filter bed is composed of bottoms and useful products-absorbing filter particles and situated in such a space that, when the greater part of any present solid matter or the like is passed through it, expansion or fluidisation of the filter bed may occur as the pressure in it increases during operation.

Description: PROCESS AND APPARATUS FOR REMOVING BOTTOMS FROM A MIXTURE The invention relates to a process for removing bottoms or isolating useful products from a liquid mixture which in addition to, e.g., water contains solid matter, in which process the mixture is passed through a packed filter bed in a vessel. The invention further comprises an apparatus for working said process. In the recovery of petroleum and gas large quantities of waste matter are obtained in addition to the main product of oil or gas. A major portion of this waste matter takes the form of so-called production water, which is a mixture composed for the most part of a carrier liquid in the form of water containing said bottoms, such as a few thousand pp of oil and a few hundred pp of solids, such as sand, heavy metals, radioactive material or the like. Needless to say, with the present strict environmental requirements said waste matter increasingly comes to be problem. A problem is constituted- in particular by the aforementioned production water, since in that case usually a mixture of water, oil, and solids is involved. A process of the type mentioned in the opening paragraph is known from GB Patent Specification 1445692, where a mixture in the form of a water, oil, and solids-containing dispersion is passed through a densely packed filter bed, the solid matter being retained in the filter bed while the oil and the water flow through the filter and separate to collect at different levels as determined by their relative densities. Next, the separated oil and water layers are discharged individually. In this process the filter becomes saturated with solids after some time, whereupon the feeding of the aforementioned mixture is stopped and the filter is washed out with washing water, the washing out being simplified by the rinsing water fluidising the filter elements. The filter is composed of lengths of tubular knitted mesh structures composed of stainless steel wires and polypropylene filaments. Although, all things considered, reasonable results may be attained using this known process, it has the drawback that the mixture to be treated can be supplied only at a comparatively low rate. A too high feeding rate would cause the fiuidisation of the filter bed sections, which would prevent proper separation of the oil and the water into individual layers and would render the separate discharge of oil and water impossible, in other words, at higher feeding rates the known process ceases to function in a satisfactory manner. At comparatively low feeding rates the known system functions well enough initially, but because.of the densely packed filter bed employed in the process clogging will occur comparatively quickly due to caking of the filter bed, whereupon the process must be stopped. The invention has for its object to provide a process of the type mentioned in the opening paragraph in which said drawbacks have-been obviated, which will enable large quantities of mixture in the form of said production water supplied at a comparatively high rate to be treated, and in which bottoms, such as especially oil or other hydrocarbons, may be removed from the mixture virtually completely. The process according to the invention is first of all characterised in that the filter bed is composed of bottoms- or useful products- absorbing filter particles and situated in such a space that, when the greater part of any present solid matter is passed through it, expansion or fiuidisation of the filter bed may occur as the pressure in it increases during operation. Notably when the process according to the invention is used for removing bottoms such as hydrocarbons, advantageous use may be made of a process in which the filter particles are bottoms-absorbing filter particles, such as as polymer particles, of which the specific weight is lower than that of the supplied mixture, and the supplied mixture is passed through the filter bed essentially from the top downwards, such that during operation a buffer volume essentially composed of the carrier liquid, e.g., water, is present between the bottom of the filter bed and the bottom end of the vessel provided with an outlet for the mixture treated in the filter bed. When the process according to the invention is employed for isolating useful products, such as proteins, use is advantageously made of protein-absorbing filter particles, such as activated carbon 10 particles, of which the specific weight is higher than that of the supplied mixture, and the supplied mixture is passed through the filter bed essentially from the bottom upwards, such that during operation a buffer volume essentially composed of the carrier liquid, e.g., water, is present between the top of the filter bed and the top end of the vessel provided with an outlet for the mixture treated in 15 the filter bed. Favourable results are generally obtained when, during operation, the buffer volume makes up 5 to 50% of the overall volume of filter bed 2 Q and buffer volume. Preferably, the filter bed used according to the invention essentially contains filter particles, such as polymer particles, of a size in the range of 50 μm to 5000 μm, preference being given to the use of 25 polymer particles made of polyolefin, in particular polypropylene. According to the invention, the polymer particles used preferably are porous particles having pores with an average diameter in the range of 0,1 μm to 50 μ , which pores are interconnected and make up 10 to 90 , π vol.%, preferably 60 to 90 vol .%, of the particles. The pores are filled wholly or in part with an extracting agent composed of a hydrophobic substance exhibiting great affinity for the constituents to be extracted from the water. According to the invention, advantageous use may be made in the filter bed of polymer particles of the type manufactured by cooling a solution composed of a polymer and a substance inert to said polymer down to the temperature range in which decomposition occurs and to below the temperature at which the polymer solidifies, optionally with the porous polymer being reduced to the desired particle size and followed by washing out of the inert substance if so desired. According to the invention, it is also possible to easily attain favourable results when the process is characterised in that use is made of a filter bed essentially composed of polymer particles, such as polystyrene particles, which respond to contact with hydrocarbons, such as benzene, by swelling. Using the process according to the invention it proved possib.le to purify waste water composed of 80 wt.% of water and for the rest containing a quantity of 0 to 100000 ppm of bottoms such as hydrocarbons, more particularly 10 to 10000 ppm of bottoms, and, optionally, a quantity of 0 to 100000 ppm of solids, more particularly 10 to 10000 ppm. The results to be attained are such that the treated water and solid matter discharged from the vessel will contain not more than 40 ppm of bottoms such as hydrocarbons, preferably 0 to 15 ppm ' of bottoms, more particularly oil. A process in which the supplied mixture also contains solid particles enclosed in hydrocarbons, such as oil, is characterised according to the invention in that such a treatment is carried out in the filter bed that solid particles present in the treated liquid downstream of the filter bed are virtually free of hydrocarbons. This is of major importance in actual practice because, as a result, the solid matter from which oil or the like has been removed can easily be separated from the water at a later stage, e.g., by means of centrifuging or precipitation. It should be noted that the porous polymer particles described herein, their manufacturing process, and their use as oil absorbents are known as such, in principle, from DE 2 737 745, DE 2833623, US 4454 198, US 4379860, and US 4391 920 in the name of Akzo. The invention further comprises an apparatus for carrying out the process described hereinbefore, said apparatus having a treatment vessel with an inlet and an outlet, with the vessel containing a filter bed, and being characterised in that the treatment vessel is positioned essentially vertically, with the inlet at the one end, preferably the upper end, of the vessel and the outlet at the other end, preferably the lower end, of the vessel, the vessel preferably has an expanding cross-section from the top downwards, and the filter bed is composed of a plurality of filter particles, such as polymer particles, having a density smaller than that of the supplied mixture, preferably smaller than 1. According to the invention, the filter bed in that case also may essentially be composed of filter particles containing a plurality of void spaces, said void spaces being wholly or partially filled or not with an extracting agent for the extraction of hydrocarbons dissolved in the water. According to the invention, in an alternative embodiment the filter bed may essentially be composed of polymer particles, such as polystyrene particles, which respond to contact with hydrocarbons, such as benzene, by swelling. In employing the process according to the invention preference is given to a vessel through which the mixture to be treated flows in essentially vertical direction. Use is preferably made in this case of a cylindrical vessel of virtually even cross-section in the mixture's direction of flow, or of a vessel of widening cross-section in the direction of flow of the mixture, preferably a conical vessel. Because of the permitted high feeding rate, the process according to the invention makes it possible for bottoms, such as oil, to be removed from a large quantity of said mixture per unit of time, while any solids present are mostly passed through, thus greatly simplifying the subsequent processing of the saturated filter bed material. According to the invention, due to their great affinity for oil the filter particles used in the filter bed are capable of rapid and complete absorption of the oil from the mixture. Since, according to the invention, highly porous filter particles may be employed in the filter bed, it is capable of absorbing a large volume of oil. When, at last, the filter bed particles are saturated with oil, a change-over can be made to a next vessel containing a fresh filter bed. The filter particles saturated with oil may be processed in a manner known in itself. Particularly when, according to the invention, the flow through the vessel is vertically from the top downwards and when use is made of a filter bed composed of filter particles of a density smaller than that of the supplied mixture, preferably smaller than 1, an especially favourable effect is achieved. In such a case, due to the upward force, the filter bed will be situated as much as possible in the upper section of the treatment vessel, while beneath the filter bed there will be a buffer volume essentially composed of water which contains virtually no filter particles at all. Clogging of the filter bed is all but excluded in this process, since the filter expands as the pressure rises. Alternatively, it is easy in this process to feed the mixture at such a rate as will cause the filter bed to be permanently expanded or fluidised, which is attended with good and high permeability of the filter bed, notably for solids. It is particularly favourable to employ a conical vessel which gradually expands in the downward direction of flow. The rate of flow in the vessel will gradually decrease from the top downwards in such a case. This means that the larger and lighter polymer particles from the filter bed can be fluidised in the upper section of the vessel, while the smaller and heavier polymer particles from the filter bed can be fluidised in a lower vessel section. This permits even a filter bed composed of filter particles of greatly differing sizes and/or densities to function properly. Alternatively, there may be transport of filter particles in the upper supply section of the conical vessel, resulting in a good mixing of the mixture as desired, and fiuidisation at about the centre of the filter bed, while the lower section of the filter bed forms an almost dense bed. Since the mixture's speed gradually decreases in said conical vessel, the process in addition is less susceptible to the generally unavoidable fluctuations in the feeding rate of the mixture. Furthermore, the lower speed in the bottom section of the filter bed acts as a safeguard against the smallest filter particles being washed out. The moment of saturation of the filter bed can easily be determined by measuring the oil content or the hydrocarbons content of the mixture discharged from the vessel. When such a measurement shows that the hydrocarbons content or the oil content of the discharged mixture exceeds a predetermined value of, say, 0-40 ppm, then the supply of mixture to the treatment vessel in question can be stopped and a_ change-over made to a next vessel containing a fresh filter bed. The invention will be further illustrated with reference to the highly schematic drawing. Fig. 1 is a view of the treatment vessel with an expanded filter bed Fig. 2 is a view of the treatment vessel with a fluidised filter bed Fig. 3 is a view of a conical treatment vessel with a fluidised filter bed. In Fig. 1 the aforementioned treatment vessel is indicated in general with 1. The vessel 1 is in the vertical position during operation and is cylindrical, i.e., it is of even cross-section along its entire height. Inside the vessel 1 is arranged a filter bed 2, which is situated in the upper section of the vessel since the porous polypropylene particles which make up the filter bed are lighter than the supplied mixture. At the top end of the vessel 1 said mixture of, e.g., water, oil, and solids which is to be treated is supplied along the direction of the arrow 3. Because of the selected feeding rate of the mixture, the filter bed 2 is expanded such that it extends across the area of the vessel 1 indicated with 4. For elucidation it is noted that an unexpended, dense filter bed would extend across an area 5 of the vessel 1. Beneath the expanded filter 2 in the area 4 is situated the aforementioned buffer volume 6, which essentially contains water and hardly any filter particles. At the bottom end of the vessel 1 the 10 treated, virtually oil-free mixture of water and solids is continuously discharged along the direction of the arrow 7. Fig. 2 depicts the process according to the invention with a rate of feeding of the mixture to be treated being employed which is so much higher that the polymer particles in the filter bed form a bed 15 completely fluidised by the liquid. Corresponding parts in Fig. 2 are indicated with the same reference numerals. Due to the fiuidisation of the filter bed 2, the area 4 across which the filter bed extends is of greater length, and the buffer volume 6 is smaller. 20 Fig. 3 depicts the process according to the invention in which use is made of a vertically positioned conical treatment vessel 1, with corresponding parts once again being indicated with the same reference numerals. For easy to use systems it is recommended for the cone to ? have a fictitious apex angle of less than 30°. The aforementioned mixture is supplied from the top along the arrow 3 at such a high rate that the filter bed 2 composed of porous polypropylene particles extending across the area 4 is fluidised in its entirety. Due to the increase in the cross-section of the vessel 1 in the direction of flow __ of the mixture, the speed of the mixture is gradually reduced. Example An experiment using the process according to the invention employed an apparatus of the type shown in Fig. 3 with a conical treatment vessel in the form of a truncated cone with a vertical axis, with a fictitious apex angle of 15° for the conical shape, an upper surface of 0,05 in diameter, a lower surface of 0,60 m in diameter, and a height of 2,12 . The mixture to be treated was fed to the top of the vessel, while the treated mixture was discharged from the bottom of the vessel. The supplied mixture was composed of water containing: 150 ppm of oil (°56 API) 100 ppm of solids (silicon dioxide having an average particle diameter of 50 μm) 100 ppm of surface-active material (triethylene glycol) 20 ppm of anti-corrosion agent (based on an aminoamide compound) 10000 ppm of NaCl . The rate of flow of the supplied mixture was 0,9 π h. The filter bed was made up of 2 kg of polymer particles of macroporous polypropylene of the following specifications: particle diameter 350-1000 μm porosity 3 ml/g average pore diameter 10 μm The temperature of the liquid in the treatment vessel was 20°C. Said mixture was fed to the vessel for a period of 20 hours without interruption. During this time the composition of the discharged treated mixture was measured at 2-hour intervals, the measurements showing that the treated mixture was composed of water containing 0-15 ppm of oil and 80-100 ppm of solids. It was found that these passed through solid particles contained only 0,002 g of oil per g of solids. The use of a treatment vessel of a transparent plastics material also enabled visual observations to be made. Here it was found that the polymer particles in the upper half of the filter bed permanently formed a fluidised bed, while the polymer particles in the lower half of the filter bed formed a densely packed bed. In principle, it is also possible to use the process according to the invention for isolating biological products from fermentation mixtures. Conventional isolation of biological products, such as proteins, from fermentation mixtures is by adsorption, with the component to be isolated being selectively adsorbed by solid particles in a packed bed. A major drawback to this known separating technique is that the column becomes clogged comparatively quickly owing to the accumulation of solid impurities (cell residues) in the column. Use of the process according to the invention permits continuous adsorption without clogging, with the desired biological products being absorbed by the filter particles. In this process, therefore, the desired biological products constitute the bottoms to be removed from the mixture. Use of the process according to the invention will give a substantial reduction of the cost of isolating and purifying biological products, which is of major importance given that these costs may amount to half or more than half of the overall production costs when the conventional process is used. Within the framework of the invention various changes may be made. It will be clear that the bottoms removed from the mixture may be a useful and serviceable product as well as waste matter. The invention is directed primarily to removing liquid or gaseous bottoms, especially hydrocarbons, such as oil, from a liquid mixture. In some applications, however, e.g., the aforementioned treatment of a fermentation mixture, the bottoms to be removed also may be solid. An alternative favourable embodiment of the process is characterised according to the invention in that a vessel is employed through which the mixture essentially flows in vertical direction, filter particles, such as polymer particles, which have a greater density than the supplied mixture are used for the filter bed, and the supplied mixture is passed through the filter bed essentially from the bottom upwards, such that during operation a buffer volume essentially composed of the treated, bottoms-poor mixture is present between the top of the filter bed and the top end of the vessel provided with an outlet for the mixture treated in the filter bed. It should be noted that ppm is an abbreviation of parts per million. In the description and the claims, 1 ppm of hydrocarbon or oil or solid matter in the aforementioned mixture means, 1.10 -6 parts by weight of this substance for 1 part by weight of the mixture. The term oil in the description first and foremost refers to substances based on refined or unrefined mineral oil.

Claims: CLAIMS 1. A process for removing bottoms or isolating useful products from a liquid mixture which in addition to, e.g., water contains solid matter, in which process the mixture is passed through a packed filter bed in a vessel, characterised in that the filter bed is composed of bottoms- or useful products- absorbing filter particles and situated in such a space that, when the greater part of any present solid matter is passed through the it, expansion or fiuidisation of the filter bed may occur as the pressure in it increases during operation. 2. A process according to claim 1 for removing bottoms, such as hydrocarbons, characterised in that the filter particles are bottoms-absorbing particles, such as polymer particles, of which the specific weight is lower than that of the supplied mixture, and the supplied mixture is passed through the f lter bed essentially from the top downwards, such that during operation a buffer volume essentially composed of the carrier liquid, e.g., water, is present between the bottom of the filter bed and the bottom end of the vessel provided with an outlet for the mixture treated in the filter bed. 3. A process according to claim 1 for isolating useful products, such as proteins, characterised in that the filter particles are protein-absorbing particles, such as activated carbon particles, of which the specific weight is higher than that of the supplied mixture, and the supplied mixture is passed through the filter bed essentially from the bottom upwards, such that during operation a buffer volume essentially composed of the carrier liquid, e.g., water, is present between the top of the filter bed and the top end of the vessel provided with an outlet for the mixture treated in the filter bed. A process according to claim 1 in which the supplied mixture contains solid particles enclosed in hydrocarbons, such as oil, characterised in that such a treatment is carried out in the filter bed that solid particles present in the treated liquid downstream of the filter bed are virtually free of hydrocarbons. A process according to claim 2 or 3, characterised in that during operation the buffer volume makes up 5 to 50% of the overall volume of filter bed and buffer volume. 6. A process according to claim 2 or 3, characterised in that use is made of a filter bed essentially of filter particles, such as polymer particles, of a size in the range of 50 μ to 5000 μ . 7. A process according to claim 2, characterised in that use is made of a filter bed of which the filter particles are essentially composed of polyolefin, preferably polypropylene. 8. A process according to claim 2, characterised in that use is made of filter particles having pores with an average diameter in the range of 0,1 to 50 μ , which pores are interconnected and make up 10 to 90 vol .%, preferably 60 to 90 vol .%, of the particles. 9. A process according to claim 8, characterised in the pores are filled wholly or in part with an extracting agent composed of a hydrophobic substance exhibiting great affinity for the constituents to be extracted from the water. 10. A process according to claim 8, characterised in that the porous particles are obtained by cooling a solution composed of a polymer and a substance inert to said polymer down to the temperature range in which decomposition occurs and to below the temperature at which the polymer solidifies, optionally with the porous polymer being reduced to the desired particle size and followed by washing out of the inert substance if so desired. 11. A process according to claim 1, characterised in that use is made of a vessel through which the mixture flows essentially in 10 vertical direction. 12. A process according to claim 11, characterised in that a preferably cylindrical vessel of virtually even cross-section in the mixture's direction of flow is employed. 15 13. A process according to claim 11, characterised in that a preferably conical vessel of increasing cross-section in- the mixture's direction of flow is employed. 2 Q 14. A process according to claim 2, characterised in that a filter bed is used which is essentially composed of filter particles, such as polystyrene particles, which respond to contact with hydrocarbons, such as benzene, by swelling. ?ς 15. An apparatus for carrying out the process according to claim 1, said apparatus having a treatment vessel with an inlet and an outlet, with the vessel containing a filter bed, characterised in that the treatment vessel is essentially in the vertical position, with the inlet at the one end, preferably the upper end, and the outlet at the other end, preferably the lower end, of the vessel, the vessel preferably has an expanding cross- section from the top downwards, and the filter bed is composed of a plurality of filter particles, such as polymer particles, having a density smaller than that of the supplied mixture, preferably smaller than 1. 16. An apparatus according to claim 15, characterised in that the 5 filter bed is essentially composed of a plurality of porous filter particles of which the pores are wholly or partially filled or not with an extracting agent for the extraction of bottoms present in the water. ιn 17. An apparatus according to claim 15, characterised in that the filter bed is essentially composed of filter particles, such as polystyrene particles, which respond to contact with hydrocarbons by swelling. 15 20 25 30

Inventors: VAN DER MEER ABELE BROER, VAN DER MEER, ABELE, BROER
Applicants: AKZO NV, MEER ABELE BROER V D, AKZO N.V.
Application year: 1993
Main classification: B01D15
IPC codes: B01D15, B01D24, C02F1