CA1199890A

CA1199890A - Method for beneficiation of hydrophobic materials or hydrophilic materials

Info

Publication number: CA1199890A
Application number: CA000417595A
Authority: CA
Inventors: Andrew Rainis; Clifford M. Detz
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1981-12-14
Filing date: 1982-12-13
Publication date: 1986-01-28
Also published as: FR2517989A1; AU555453B2; AU9095982A; NL8204749A; DE3246240A1; GB2112808B; GB2112808A

Abstract

ABSTRACT OF THE DISCLOSURE

A process is disclosed which removes hydrophilic substances from hydrophobic solids by forming an aqueous slurry of the hydrophobic solid and its substances, then using a low-boiling nonpolar, water insoluble bridging hydrocarbon to selectively agglomerate the hydrophobic solid.

Description

A METHOD FOR BENEFICIATION OF HYDROPHOBIC MATERIALS
OR HYDROPHILIC MATERIALS

BACKGROUND OF THE INVENTION
The present invention relates to a method of separating substances from a solid wherein the substances have a different affinity ~or water than the pure solid, such as removing impurities from coal, or removing gangue minerals from phosphates.
There are a variety of known techniyues for removing impurities from solids, based on differences in characteristics between the pure solid and its impurities.
For instance, materials can be separated based on their size, their density, their ability to hold an electrical charge, or their magnetic characteristics. These methods are useful for most solid separation applications, but there are some solids that cannot be economically sepa-rated by these methods because the pure solid and its impurities are too similar in these characteristics.
A solution to this problem is to use a differentcharacteristic, such as afEinity for water, to separate the solid from its impurities. In one known method, ash 2S (a hydrophilic impurity) is separated from coal (a hydro-phobic solid) by forming a coal slurry, mixing oil into the slurry to produce agglomerates, and racovering the agglomerates as product~ Most of the ash remains in the aqueous phase of the slurry.
A major disadvantage of this method is that the oil used to agglomerate the coal becomes part of the prod-uct. This means that one is selling oil at the price of coal. This also means that this process could not be used to separate other hydrophobic materials from their hydro-philic impurities whenever oil would not be a desirablepart of the final product~ It is possible to try to recover the oil from the agglomerates, but this would require extremely high temperatures (in excess of 260C) and, even at these high temperature~, -the oil recovery would not be complete.

~' Pyritic sulfur is not normally removed by this 05 process. The fuel oil has components in it which activate the surfaces of both the coal and the pyritic sulfur to make both more hydrophobic, thus the pyritic sulfur is agglomerated with the coal.
r~i~Vtl;e~ sthoJ C_ s_p ;ating two solids is by froth flotation. Froth flotation is a process fcr sepa-rating finely ground valuable minerals from their asso-ciated gangue. The process is based on the affinity of properly prepared surfaces for air bubbles, A froth is formed hy introducing air into a pulp of finely divided ore in water containing a frothing or foaming agent.
Surface modifying reagents (collectors) may be also added to increase the affinity of the mineral surface ~or air bubbles, Minerals with a specific affinity for air bubbles rise to the surface in the froth and are thus

2~ separated from those wetted by water. As a first step, the ore must first be ground to liberate the intergrown valuable mineral constituent from its worthless gangue matrix. The size reduction, usually to about 208 microns (65 mesh), reduces the minerals to such a particle size that they may be easily levitated by the bubbles.
Froth flotation can be used to produce a metal-lurgical grade coal. In froth flotation o~ bituminous coal, the fraction most easily and rapidly floated is rich in vitrinite, a constituent of coal, with a low ash con-tent and good coking properties. Vitrinite is the mate-rial needed to make a good metallurgical grade coal. The remaining fraction has a high content of ash and pyriti~
sulfur. It would be advantageous if this ash and pyritic sulfur could be removed from the remaining fraction~
It would also be advantageous if a separation method could achieve a better separation of two differing solids than has been achieved by the prior art processes.
It would also be advantageous if a separation method was more energy efficient than the prior art processes. It 4~ would also be advantageous if a separation method could $~D
separate two solids without agglomerant being in the final pro-duct.
S~r~MARY OF THE IMVENTION
The present invention overcomes the deficiencies of the prior art by selective agglomeration of the hydrophobic mat-erial. In the present invention, an aqueous slurry is formed of the hydrophobic material and hydrophilic substances; a nonpolar water insoluble bridging hydrocarbon is used to selectively form agglomerates of the hydrophobic material; and the agglomerates are separated from the slurry containing the hydrophilic sub-stances. Preferably, the bridging hydrocarbon is recovered and recycled. An essential element of this invention is the bridging hydrocarbon used. It is essential that the bridging hydrocarbon have a low boilirg point (70C or lessl, such as butane, pentane, hexane and mixtures thereof.
In one embodiment of the present invention, the hydro-phobic material and hydrophilic substances are ground in a slurry so that the particle size dis-tribution of the hydrophobic mater-:
ial and~hydrophilic substances has at least 90% of the particles less than 10 microns in size and the agglomerates are formed by subjecting the hydrophobic material, the hydrophilic ~ substances, and the bridging hydrocarbon to high shear agglomera-: tion and low shear agglomeration.
Preferably the initial slurry of hydrophobic material should contain 10 to 20~ by weight solids and the separation step should be carried out using screening means or a centrifuge ~ hus in detail this invention provides a method of separating ash and pyritic sulfur from coal comprising: (a) forming an aqueous slurry of the coal, ash and pyritic sulfur;

(b) using a nonpolar, water insoluble bridging hydrocarbon ,~

- 3 --8~

having a boiling point of less than 70C to selectively form agglomerates of the coal; (c) separating the agglomerates from the slurry containing the ash and pyritic sulfur; and (d) sub-jecting said agglomerates of coal to solution in a hydrogen donor solvent to produce a liquid product.
BRI~F DESCRIPTION OF THE DRAWINGS
. . .
In order to facilitate the understanding of this in-vention, reference will now he made to the appended drawings of preferred embodiments of the present invention. The drawings should not be construed as limiting the invention but are exem-plary only~ In the drawings:

- 3a -_aS -FIG. 1 is a graph showing the effect of agglo-merant and particle size on product ash from a Pittsburgh ~eam coal.
FIG. 2 is a graph showing the effect of agglo-merant on product sulfur from a Pittsburgh Seam coal.
DESCRIPTION OF THE PREFERRED EMBODIME~l~
In its broadest application the present inven-tion involves separating hydrophilic substances from a hydrophobic material by forming an aqueous slurry of the hydrophobic material and hydrophilic substances, then selectively agglomerating the hydrophobic material in such a way as to agglomerate the hydrophobic material but not the hydrophilic substances. This selective agglomeration is carried out by the use of a nonpolar, water insoluble bridging hydrocarbon. After the selective agglomerati~n takes place, the agglomerates can be separated by a 2~ screening device or a centrifuge, and the bridging hydro-carbon can be recovered and recycled.
This process can be used to remove hydrophilic substances from hydrophobic materials, or it can be used ~o remove hydrophobic impurities from hydrophilic substan-ces. When the impurities are hydrvphilic, tbe final prod-ucts are agglomerates of hydrophobic material, and the slurry containing the hydrophilic impurities is a waste s~ream. When the impurities are hydrophobic, the ~inal product is a slurry of hydrophilic substances which may be 3~ dried, and the agglomerates of hydrophobic material is waste.
In one particularly advantageous embodiment, oxidized or low rank coal is mixed with water to form an aqueous slurry wherein coal and the hydrophilic substances (ash and pyritic sulfur) associated with the coal are dis-persed in w~ter and the resulting slurry has from 30 to 40% by weight solids, the coal is ground in the slurry so that the particle size distribution of the coal has at l~ast 90% of the particles less than 10 microns in size.
Water is then added to the slurry to give a 10 to 20% by weight solids slurry and pentane and fuel oil are mixed into the slurry so that the pentane is 30 to 40~ by weight on a pentane and dry coal ~asis, and the fuel oil is less than ~% by weight on a dry coal and oil basis; then the slurry is subjected to both high shear agglomeration and low shear agglomeration to form agglomerates of the coal ~th_ ash and pyritic sulfur remain dispersed in the slurry); then the coal agglomerates are separated from the slurry by passing the slurry through a screen and the coal agglomerates are heated in the absence of air to remove pentane; then the pentane is recovered and is recycled.
In another particularly advantageous embodiment, phosphate rock is mixed with water to form an aqueous slurry wherein the phosphate rock and gangue mi~erals are dispersed in water and the resulting slurry has from lO~
to 20% by weight solids; the p~ of the slurry is adjusted to between lO and ll; pentane and oleic acid are added to the slurry; then agglomerates of phosphates are formed;
the phosphate agglomerates are separated from the slurry by passing the slurry ~hrough a screen and the phosphate agglomerates ~re heated in an inert atmosphere to remove the pentane; then the pentane is recovered from the inert atmosphere and this pentane is recycled.
The present invention can be used to separate ~any hydrophilic~substances from a hydrophobic material.
This invention is especially useful in separating gangue minerals rom ~phosphates, and in separating ash and pyri-` tic sulur from coal The first step in this invention is forming an aqueous slurry of the hydrophobic material and hydrophilic substances. Preferably this slurry has a solids content of from 30 to 40% by weight prior to grinding. When there is no grinding stepr the slurry should have a solids con-tent of from lO to 20% by weight.
As a preferred additional step, the hydrophobic material can be ground in the slurry so that the particle size distribution of the hydrophobic material and the hydrophilic substances has at leas~ ~0% oE the particles less than 75 microns in size, more preferably, less than lO microns, Such a grinding step would be used whenever the hydrophilic substances are fine grained. The grinding step helps to liberate the hydrophilic substances from the hydrophobic material. The grinding step occurs prior to the addition of the bridging hydrocarbon, otherwise agglo-2er?.' eS W^':l d ~-rm dur~.rlg grinding and reduce the grinding efficiency.
An agglomerant is added to the slurry in order to selectively agglomerate the hydrophobic material.
This agglomerant is a low-boiling nonpolar, water insol-uble hydrocarbon having a boiling point of 70C or less.
This agglomerant may be butane, pentane, hexane or a mix-ture thereof. The slurry should contain from lO to 40% of the agglomerant on an agglomerant and dry hydrophobic material weight basisO
The agglomerant shou]d be low boiling so that it can be readily recovered at low temperatures and can be recycled to reduce the agglomerant requirement. High-boiling hydrocarbo~s9 such as fuel oil, are hard to recover, even at temperatures of 260C and higherO If ~fuel oil is used as an agglomerant, extremely high tem-~ peratures are required to recover the agglomerant and these high temperatures represent a severe penalty in en~ergy~requirements. Even at these high temperatures, ~fuel oil recovery is incomplete. For these reasons, low-~boiling agglomerants are preferred over fuel oil. As a ~30 ~ general rule, increases in agglomerant boiling point cause recovery of the agglomerant to be more difficult since the agglomerant i5~ more strongly adsorbed on the hydrophobic material surface.
The agglomerant should be nonpolar for a better distribution of the organic between the aqueous phase and the hydrophobic solid. As polarity increases, more agglo-merant is lost in the aqueous phase.
The agglomerants should be a hydrocarbon, instead of other nonpolar insoluble agglomerants such as freon, because these hydrocarbons are cheaper than other nonpolar agglomerants and because halogens in the product could cause problems downstream, such as corrosion.
One advantage of using as agglomerant either butane, pentane, hexane or mixture thereof, is that these agglomerants result in a greater degree of removal of impurities than when fuel oils are used.
Another advantage of these low-boiling agglo-merants is that they have lower densities than other agglomerants. In agglomeration, that is an optimum vol-ume of agglomerant that is needed to give good, easily separable agglomerates. The energy required to remove the agglomerant depends upon the weight present. Thus, if two liquids of equal heat of vaportization are used, the energy required to remove equal volumes will be less for the liquid of lower density.
When the hydrophobic material is coal, the agglomerant needs to have a low viscosity to achieve low ash in the final product. High viscosity increases the time needed to from agglomerates and with fuel oils, increases the ash and sulfur content of the product.
If an agglomerant-free product is desired, then the agglomerant must be volatile, it must be recoverable at a reasonable temperature (30° - 70° C) and it should not be strongly absorbed into the hydrophobic material. The agglomerants of the present invention satisfy these criteria.
Preferably the agglomerant is added to the slurry in a premixer to give a homogeneous feed. In the premixer, a surface conditioner can be added to make the hydrophobic material more hydrophobic (5% or less by weight on a hydrophobic material and surface conditioner basis). Fuel oil is a preferred surface conditioner for oxidized or low rank coal. A high molecular weight orga-nic acid is a preferred surface conditioner for phos-phates.
If the slurry had been ground, the slurry is diluted to a solids content of from 10 to 20% by weight prior to agglomeration.

The hydrophobic material is selectively agglo-05 merated and the hydrophilic substances ~emain dispersed in the slurry. The hydrophobic material can be subjected to either low shear agglomeration alone or in combination with high shear agglomeration~ Low shear agglomeration is sufficient to selectively agglomerate phosp'la'es bu~ b~th 1~ high shear agglomeration and low shear agglomeration are preferred when agglomerating coal.
Whenever high shear agglomeratlon is used, it must be followed by a period of relatively low turbulence so that the agglomerates formed in the high shear zone can lS form a more compact, more easily separable product. The agglomerates coming out of the high shear zone are quite small and would cause separation problems if the subse-quent period of relatively low turbulence is missingO
After the agglomerates of hydrophobic material 2() are formed they can be separated from the slurry by any known separat~on technique. Preferably the agglomerates are removed from the slurry by using either a screen or a centrifuge~ A~ieve bend is a particularly advantageous screening means because of its low cost.
~ ~ After ~he agglomerates are separated from the 25~
~slurry they are heated or flashed to remove the agglo-merant. To maximize~recovery of the agglomerant, the product leaving the heated zone should be discharged at a temperature in excess of the boiling point of the agglo-meran~. An inert atmosphere or vacuum should be used in the heating step to reduce the chance of either the hydro-phobic material or the agglomerant from thermally decom-posing.
An advantage of the present invention is that the low-boiling agglomerants of the present invention do not require high temperatures in order to be removed, thus saving energy.
The agglomerant can be recovered from the inert atmosphere and can be recycled. In one agglomerant recovery process the agglomerant and the inert gas are passed through a bag filter for dust removal, then the nl agglomerant and inert gas are passed through a compressor 0 and an agglomerant recovery condenser, which recovers the agglomerant from the gas. The gas leaving the condenser is passed through a carbon adsorption system which further removes agglomerant~ The agglomerant is then recycled as a sou~ce of make-up agglomerant for the premixer and the 0 inert gas is recycled to the heating zone.
EXAMPLES
The invention will be further illustrated by the following examples which set forth particularly advanta-geous method embodiments. While the examples are provided to illustrate the present invention, they are not intended to limit it.
Example I
A series of runs were made using a Sunnyside (Utah) coal. In each run a Sunnyside (Utah) coal having 5.58 weight percent ash and grc)und to a median particle size of 5.4 microns was mixed with water to form an aqueous sIurry of l0 weight percent solids; an agglomeran~
~was~added ;to the slurry so that it constituted 36 weight percent on a coal and agglomerant basis; the agglomerant was;used to~selectively fonm agglomerates of coal; and the ~agglomerates~were separated from the slurry and heated in an inert atmosphere to remove the agglomerant. When the agglomerant was an oil, the product coal was extracted with pentane to remove the oils so that product ash is on an oil-~free basis. The moisture-free weight percent ash for each product is shown in the following table.
TABLE I
Effect of Agglomerant on the Product Ash in Coal 3S Agglomerant Weight ~ Ash in Product Pentane 1.01 Kerosene 1.14 White Oil (Heavy) 1.35 No. 2 Fuel Oil 1.42 40 No. 4 Fuel Oil 2.24 Thus, in operation, a low-boiling nonpolar, water insoluble bridging hydrocarbon, such as pentane, gives excellent ash removal.
Example II
A series of runs were made using a Pittsburgh S~ r~l Tr e?~ run, a Pittsburgh Seam coal was mixed with water to form an aqueous slurry; the slurry was ground to a specified median particle size; an agglomerant was used to selectively form agglomerates of coal; the agglomerates were separated from the slurry; and the agglomerates were heated in an inert atmosphere to remove the agglomerant. The moisture free weight percent ash for each run i5 shown in Figure l. The moisture-free weight percent sulfur for each run i5 shown in Figure 2.
These figures show that the use of a low-boiling nonpolar, water insolublbe bridging hydrocarbon, such as pentane, give superior ash removal and sulfur removal than No. 4 Fuel Oil. These figures also show that optimum removal o~ ash and sulfur is achieved when the slurry has been ground prior to agglomeration such that the particle size distribution has a median of less than 5 microns.
Example III
An aqueous slurry was formed containing an Illino1s No.~6 coal having an ash content of 32.92 weight ~ on a dry coal basis. A No. 4 fuel oil was added ; to the s1urry as a surface conditioner (weight ratio oll~coal=0.033) pentane was then adde~ to the slurry such that the slurry contained 40 weight % pentane on a pentane and dry coal basis. The pentane was used to selectively form ayglomerates of coal and the agglomerates of coal were separated from the slurry. These agglomerates had a product ash of only 4.10 weight ~, which was a 88~ ash red uc t ion O
Example IV
A series of runs were made to show the effect of fuel oil concentration on product ash. In each run, an Illinois No. 6 coal was mixed with water to form an aqueous slurry~ No. 6 fuel oil was used at various levels to selectively form agglomerates of coal and the agglomerates were separated from the slurry. The results of these runs are shown in the following table.

Effect of Oil Concentration on Product Ash in the Agglomeration of Illinois No~ 6 Coal Weight % Ash in Product l0 Weight Ratio of Oil to CoalMoisture-free 0.167 3.17 2.64 ~017 2.47 0.007 2.01 Thus, in operation, the presence of increasing amounts of fuel oil in a slurry has an adverse effect on weight % ash in the final product, Example V
O A series o~ runs were made using an unweathered western phosphate rock. In eac:h run, an unweathered western phosphate rock having a particle size distribution such that at lea~t 50% of the E)articles are less than 400 mesh, and containing 20.73 weight percent P2O5, was mixed with water~to form an aqueous slurry; the pH of the slurry was adjusted to a particular level; oleic acid and hexane were used to selectively form agglomerates of phosphate;
the phosphate agglomerates were separated from the slurry;
; and the agglomerates were heated in an inert atmosphere to remove the hexane. The results o these runs are shown in the following table.

~3L9913~6~

TABLE II
0~ Effect of pH on P O5 Recovery From Unweathered Weste~n Phosphate Rock Product GradeP2O Recovery (Wt. % P2O5)_~Wt. %) pH
30.26 21.2 /.
28.32 43.0 7.5 29.5~ 42.2 7.9 30.04 46.2 9.1 31.04 76.~ ll.0 30.09 70.7 ll.9 Thus~ in operation, selective agglomeration of phosphate using hexane as an agglomerant is an effective means of beneficiation of phosphate rock, but such benefi-ciation must occur at a pH of at least lO.
Example VI
Another series of ruils were made to determine the effect of recycle solvent on ash content. In each run an Illinois No. 6 coal having 10~87 wt. % ash and ground ~to a median particle ~ize of 3.9 microns was mixed with ~25 water to form an aqueous slurry o~ lO wt. % solids; the ~agglomerations were carried out with different weight ratios of recycle solvent to coal; in each case the wt.
recycle solvent~ plus pentane was 40% on a coal, recycle solvent and pentane basis.
; 30 ~ Wt.~atio Recycle Solvent to Coal Wt. ~ Ash in Product 3.82 0.1667 3 43 0.0333 2~08 0.0233 1.80 Thus in operation, decreasing the ratio of recycle solvent to coal decreases the wt. % ash in the product.
In one embodiment of the present invention, ~o small quantities of fuel oil are added to low grade coal to make the coal more hydrophobic. Some coals are ~g~

difficult to agglomerate by use of hydrocarbons alone (kerosene, light fuel oils, e.g. No. 2, hexane, pentane, etc.) because they have more hydrophilic surfaces. Exam-ples are low rank coals (subbituminous), coals which have been oxidized, or coals such as Illinois No. 6. In such cases, No. 4, 5, 6 fuel oils or heavy crude oils such as Kern River can be mixed in with the hydrocarbon agglomerant to make the surface of the coal more hydro-phobic. The fuel oil stays on the product and is not recovered, but the economic penalty is not severe because of the small amount of fuel oil used (less than 5% by weight on a dry coal and oil basi~). The agglomerant constitutes from 30 to 40% by weight.
In another embodiment: of the present invention, phosphates having a particle size of less than 500 microns are surface conditioned prior to agglomeration with high molecular weight organic acids at a pH of greater than lO
to make the phosphates more hyclrophobic so they could be separated from gangue minerals such as clays, calcite, dolomite, silica, etc. The phosphates are conditioned with oleic acid or other fatty acids or high molecular weight organic acid having surfactant properties.
The present invention could also be used to recover coal from coal preparation plant tailings ponds ~and to~recover coal from coal preparation plant fine coal circuits. Because these fines are dif~icult to remove ~30 from the process water, these coal fines usually are stored in tailing ponds as waste. Since these fines have significant BTU content in the form of coal and, since it is costly to maintain these tailing ponds, it would be advan~ageous to recover these fines as a useful product.
This can be accomplished by the process of the present invention.
Also the present invention could be used in conjunction with short residence time froth flotation to separate metallurgical grade coal from lower grade coals, and produce a byproduct suitable as a fuel for power plants. A metallurgical grade coal and a low ash steam coal are produced by forming an aqueous slurry of coal con-taining vitrinite, ash and pyritic sulfur; adding a froth flotation reagent to the slurry; subjecting the slurry to froth flotation to produce an underflow and an overflow; filtering and drying the overflow to produce a metallurgical grade coal;
then selectively agglomerating the underflow in such a way as to agglomerate the coal, but not the ash and pyritic sulfur.
This selective agglomeration is carried out by the use of a nonpolar, water insoluble, bridging hydrocarbon. After the selective agglomeration takes place, the agglomerates can be separated by a screening device or a centrifuge, then the bridging hydrocarbon can be recovered and recycled.
Also the present inven-tion could be used to recover carbonaceous components from coal liquefaction residue.
The low ash coal agglomerates of the present invention can be used as a feed for a coal liquefaction process. In this embodiment, the coal agglomerates are subjected to solution in a hydrogen donor solvent to produce a liquid product. When a low ash feed is desired, the agglomerant should be a low boiling, nonpolar, water insolublel hydrocarbon fraction derived from the coal liquefaction process. When a feed having a higher ash content can be tolerated, then recycle solvent is a very econo-mical source of agglomerant. United States Paten-t 3,594,304 shows an advantageous method o~ subjecting coal to solution in a hydrogen donor solvent.
While the present inven-tion has been described with reference to specific embodiments, this application is intended to cover those changes and substi-tutions which may be made by those skilled in the art without departing from the spirit and scope of the appended claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of separating ash and pyritic sulfur from coal comprising:
(a) forming an aqueous slurry of the coal, ash and pyritic sulfur;
(b) using a nonpolar, water insoluble bridging hydro-carbon having a boiling point of less than 70°C to selectively form agglomerates of the coal;
(c) separating the aggolmerates from the slurry containing the ash and pyritic sulfur; and (d) subjecting said aggolmerates of coal to solution in a hydrogen donor solvent to produce a liquid product.