Background of the Invention A historical method of removing colored impurities from oils entails intimately contacting the oil with a bleaching clay, such as Fuller's earth (bentonite) or an acid-activated clay [A. D. Rich,"Bleaching Clay,"Industrial Minerals & Rocks, 3rd Ed., AIMMPE, N. Y., pgs 93-101 (1960)]. Though it is naturally-occurring, Fuller's earth is not very effective in bleaching oil as compared to a commercially acid-activated clay product. Therefore, acid- activated clays are more widely used for bleaching purposes.

In effect, conventional acid treatment replaces exchangeable cations, such as K+, Na+, and Ca2+, by H+ in the intralamellar space of the clay's crystalline lattice and also leaches out some of the A13+, Fe3+, and Mg2+ metal cations. Thus acid treatment renders the clay physically more porous and electrochemically more active.

A commercial process for the production of acid-activated bleaching clay entails mixing an aqueous clay slurry with a high dose of concentrated acid at elevated temperatures (100°C to 121°C), followed by washing and drying of the acidulated product. However, this prior art method results in high levels of residual acid effluent and salts thereof whose removal and disposal costs are expensive (U. S. Pat. No. 3,617,215 to Massaire et. al.).

Another commercial manufacturing process for the production of bleaching clay avoids the use of large amounts of concentrated acid but requires an extremely high temperature (about 1000°F) to calcine the raw clay (U. S. Pat. No.

3,029,783 to Sawyer et. al.). Recently, a method of making bleaching clay has been described whereby an aqueous clay slurry is mixed with a relatively lower

dose of acid with the elimination of the subsequent washing, filtering, and calcination steps (U. S. Patent No. 5,008,226 to Taylor et. al.). The use of less acid in the process is made possible by the selection of a specific ratio of raw clay sources. The present invention is an improvement over prior art methods of making bleaching clay because a wider variety of raw clay sources can be utilized in an environmentally-friendly, non-slurry process. Thus, production expenses are diminished and recycling costs are eliminated. Also, the lower moisture content bleaching clay is very stable during storage unlike higher moisture content bleaching clay.

Summary of the Invention A bleaching clay product and an environmentally-friendly, non- slurry method for the manufacture of the bleaching clay product is described. A clay with a moisture content in the range of no more than about 45 % by weight is combined with a relatively small amount of an aqueous acid solution, ground to a mean particle size in the range of about 25 to about 45 microns in a grinder, and dried to a moisture content of no more than about 13% by weight. The foregoing operations can occur sequentially or concurrently as long as the acidified product has a moisture content of no more than about 13% by weight. The acid content in the dried clay product is in the range of about 1 to about 5 % by weight, based on the dry weight (zero moisture) of the clay product. The obtained clay product may be utilized for bleaching purposes in numerous applications.

Detailed Description of Preferred Embodiments A bleaching clay useful in the removal of colored impurities in oils is produced by a non-slurry process whereby a relatively small amount of acid is misted onto ground clay. The clay starting material (raw clay) preferably is of the palygorskite-smectite variety having a slurry pH value of about 7.2 to about 8.4 units. The moisture content of this clay starting material is no more than about 45% by weight. If necessary for the type of grinder used, the raw clay may be pre-dried to reduce its moisture content prior to comminution. The clay is acidified and ground to a mean particle size of about 25 to about 45 microns in

a grinder, such as an impact mill, e. g. a Williams mill, or a roller mill, such as a Raymond mill. Preferably, the ground clay is dried to a moisture content of no more than about 13% by weight prior to the addition of acid; however, the acid can be added first to the raw clay which is then dried and ground, either sequentially or concurrently. Depending upon the grinder used, the desired relatively low moisture content can be attained concurrently with grinding.

Alternatively, the ground clay can be dried, e. g., in a cyclone-type drier, after grinding but prior to acidification. A clay product moisture content in excess of about 13% by weight adversely affects the stability of the acidified clay during storage.

Preferably, the ground clay is dried to a moisture content of about 8 to about 10% by weight and combined with a relatively small amount of an aqueous acid solution to provide an acid content of the clay in the range of about 1 to about 5 % by weight, based on the dry weight (zero moisture) of the product.

Preferably the acid content of the clay is in the range of about 2.5 to about 5% by weight, based on the dry weight of the product. The aqueous acid solution preferably contains an acid selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, and citric acid. Acid mixtures can be used as well. Preferably a concentrated aqueous sulfuric acid solution is utilized. The sulfuric acid solution preferably contains sulfuric acid at a level in the range of about 93 to about 98% by weight in water. Concentrated hydrochloric acid usually contains about 36% by weight hydrochloric acid, concentrated phosphoric acid usually contains about 85 % by weight phosphoric acid, and concentrated citric acid solution usually contains about 50% by weight citric acid.

The technique used to combine the dried clay and the acid can be any technique that is convenient, although misting or spraying the acid onto the dried clay is preferred. The acidulated clay may be used for bleaching purposes without further work-up.

The present invention is illustrated further by the following examples.

EXAMPLE 1: Manufacture and Evaluation of Bleaching Clay Raw palygorskite-smectite clay with a moisture content of about 45 % by weight was acidified with sulfuric acid (95 % by weight) by misting with an atomizer, then ground and concurrently substantially dried in an impact mill (Williams Mill) to a mean particle size of about 30 to about 34 microns and to a relatively low moisture content. The moisture content of the ground, dried clay was about 10% by weight. Enough acid was misted onto the ground clay to provide an acid content of either about 1% by weight (Sample A) or about 3.5% by weight (Sample B), based on the dry weight of the clay (zero moisture), as determined by measurement with a LECO sulfur analyzer, corrected for moisture.

The pH of an aqueous solution of the clay (5 % by weight) was measured using a pH meter. Control samples, Sample A'and Sample B', were also made using the Williams Mill according to the same acid specifications but with a relatively higher moisture content than Samples A and B.

To determine the activity of the bleaching clay, about 100 g of canola oil was heated to about 60°C (140°F) and contacted with an acidified clay sample in a distillation flask which was heated to a temperature of about 110°C (230°F) with agitation and held at that temperature for 30 minutes under 660 mm Hg (26 inches Hg) vacuum.

ForSampleA(0.9% acidbyweight),about1.5% byweightofthe bleaching clay based on the weight of the oil was added. For Sample B (3.7% acid by weight), about 1 % by weight of the bleaching clay was added based on the weight of the oil. The amount of chlorophyll in the canola oil before treatment was about 17,000 ppb as determined on a Beckman DU40 Spectrometer (AOCS Official Method Cc 13d-5s). The color level of the untreated oil was greater than 20/70 on AOCS Red/Yellow scale as measured by PFX 990 Lovibond Tintometer with 5'/4"spath length. The performance of bleaching clays, Samples A and A', was compared to the performance of a processed, commercially available palygorskite-smectite clay containing no acid, and this comparison is expressed as the chlorophyll ratio. The performance of bleaching

clays, Samples B and B', was compared to the performance of the standard, commercially available bleaching clay, Optimum FF, expressed as a chlorophyll ratio.

The following data presented in Tables 1 and 2, below, demonstrate the performance stability of the present product over an extended time period at an elevated temperature. In the accelerated stability study (Table 2), about 20 g of each clay was placed into five glass bottles and the lids sealed with tape. The samples were placed into an oven at a temperature of about 110°F and one of each clay sample was removed at a given time interval for testing. The samples were compared to the standards defined above, stored at ambient temperature.

TABLE 1 PHYSICAL PROPERTIES OF BLEACHING CLAY Sample A A'B B' pH (5% slurry) 5.0 5.1 2.9 2.9 moisture (wt. %) 10.2 15.8 9.0 14.0 acid (wt. %) 0.9 1.0 3.7 3.5 mean particle size 33.48 35.19 35.43 38.32 (Um) median particle 29.00 31.30 30.92 33.78 size (ym) filtration time 125 136 62 68 (s/50 ml) TABLE 2 ACCELERATED AGING STUDY OF ACTIVITY OF BLEACHING CLAY (CHLOROPHYLL RATIO) Sample A A'B B' 0 hrs/25°C 0.56 0.49 0.77 1.16 14 hrs/110°F 0.51 0.57 0.86 1.42 24 hrs/110°F 0.58 0.54 0.89 1.48 49 hrs/110°F 0.62 0.50 0.80 1.38 73 hrs/110°F 0.60 0.60 0.94 1.72 145 hrs/110°F 0.59 0.61 0.93 1.70 (RED COLOR) 0 hrs/25°C 5.15 4.75 6.00 6.25 14 hrs/110°F 5.30 4.90 5.80 6.60 24 hrs/110°F 5.05 4.90 5.95 6.60 49 hrs/110°F 4.90 4.65 6.25 6.90 73 hrs/110°F 4.20 4.40 5.20 5.50 145 hrs/110°F 4.50 4.50 5.50 5.70 Samples C-G shown in Table 3, below, were prepared by drying the raw clay (moisture content about 45 % by weight) and grinding the dried clay to a free moisture content (FM) as indicated. The mean particle size of the dried ground clay was in the range of about 28 to about 35 microns. The type of oil used for testing purposes was canola oil.

TABLE 3 ROOM TEMPERATURE AGING STUDY OF ACTIVITY OF BLEACHING CLAY (CHLOROPHYLL RATIO) Sample C D E Opt. FF F G P-smec.

Days 9.6% FM 9.8tFM 16.7tFM--9. 6WFM 13.4-. FM 10.0tFM 3sacid 5oacid 4oacid 9.4Wacid lWacid lWacid 0tacid 0 0.70 0.74--1 0.47 0.46 1 6 0.85 0.84 0.81 1 0.49 0.43 1 13 0.92 0.85 0.97 1 0.45 0.54 1 15------1--0.53 1 17 0.73 0.81 0.89 1 0.46 0.43 1 27 0.85 0.86 0.84 1 0.50--1 37 0.68 0.72 0.77 1 0.51 0.56 1 51 0.82 0.83 1.29 1 0.42 0.64 1 69 0.75 0.86 1.07 1 0.46 0.41 1 95* 0.79 0.85 0.93 1 0.47 0.55 1 120* 0.83 0.81 1.25 1 0.40 0.51 1 (RED COLOR) 0 5.40 5.50----4.65 4.20-- 6 5.60 5.60 5.60 7.73 4.70 4.75 5.85 13 5.70 5.90 6.30 7.70 4.70 4.95 6.00 15----------5.10 5.70 17 5.30 5.80 6.00 7.60 5.15 5.35 6.35 27 5.70 5.80 6.40 7.90 5.40 7.10 6.20 37 5.65 5.30 6.30 6.95 5.30 5.70 6.70 51 5.70 5.90 5.70 7.25 4.85 5.10 5.50 69 5.85 5.70 6.10 7.20 5.15 5.90 6.25 95* 5.85 5.50 5.90 7.50 5.50 5.65 6.90 120* 5.55 5.90 5.40 7.40 3.95 4.20 5.20 *New drum of oil, same lot number P-smec. =palygorskite-smectite

EXAMPLE 2: Bleaching Clay Products Raw palygorskite-smectite clay (pH 7.37) having a moisture content of about 45 % by weight was fed to an impact mill (Williams Mill) and was ground to a mean particle size of about 38.8 microns while being dried to a free moisture content of about 9 to about 10% by weight. Thereafter, the obtained clay product was sprayed with aqueous concentrated sulfuric acid to provide a sulfuric acid content in the bleaching clay product of either about 2.8 to about 3.5% by weight, based on the dry weight of the product. Samples of each such products were then tested for bleaching activity and stability using canola oil containing about 16,000 ppb chlorophyll, as determined on a Beckman DU40 Spectrometer (AOCS Official Method Cc 13d-5s). The color level of the untreated canola oil was in excess of 20/70 on AOCS Red/Yellow scale as measured by PFX 990 Lovibond Tintometer with 5 lh"path length.

To a 200 gram aliquot of the canola oil which had a temperature of about 60°C (140°F) was added about 1.25% by weight of the acidified clay product. The resulting admixture was then heated to a temperature of about 110°C (230°F) and held at that temperature, with agitation, for about 30 minutes and under 686 mm Hg (27 inches Hg) vacuum. The observed results are presented in Table 4, below.

TABLE 4 BLEACHING AND AGING PERFORMANCE Temp. Time Product Acid Content (wt. %) oc (°F) (2.8%) (3.5%) Red Yellow Chll Red Yellow Chl 43 (110) 0 4.8 70 74 4.0 70 48 28h 4.3 70 116 4.0 70 126 119h 5.6 70 144 5.5 70 147 168h 4.8 70 155 4.6 70 147 RT2 0 4.8 70 74 4.0 70 48 6d 4.8 70 104 4.8 70 55 45d 4.3 70 150 4.7 70 80 lChl=chlorophyll, ppb 2RT=room temperature

For comparison purposes in Table 4, Optimum FF clay sample under the same conditions was observed to give the following results: Red = 6.1, Yellow=70, and chlorophyll=159 ppb. The foregoing data demonstrate good stability and performance for products embodying the present invention.

EXAMPLE 3: Use of Mixed Acids for Clay Activation Raw palygorskite-smectite clay (pH 7.37) having a moisture content of about 45 % by weight was fed to an impact mill (Williams Mill) and was ground to a mean particle size of about 38.8 microns while being dried to a free moisture content of about 9 to about 10% by weight. Thereafter the obtained clay product was sprayed with concentrated sulfuric acid (95 % by weight), aqueous phosphoric acid (85 % by weight), and mixtures thereof at levels indicated in Table 5, below. The obtained products were then tested for bleaching activity using canola oil in the same manner as described in Example 2, above. The observed results are compiled in Table 5, below.

TABLE 5 BLEACHING PERFORMANCE WITH MIXED ACIDS Acid (wt. %) Performance H2SO4 H3PO4 Total Chl3 Red4 0 0 0 825 0.519 2 0 2 103 0.279 4 0 4 45.3 0.260 2 2 4 83.7 0.302 2 1 3 125 0.283 4 2 6 43.8 0.248 3 1 4 45.3 0.248 4 1 5 53.1 0.331 0 2 2 511 0.441 0 4 4 341 0.353 3.5 0.25 3.75 48.7 0.273 3Chl=chlorophyll, ppb 4Red=red absorbance at 550X, 10 cm cell

The foregoing data indicate good bleaching performance obtainable with sulfuric acid/phosphoric acid mixtures on clay having a relatively low free moisture content.

Example 4: Bleaching Clay Activated with Hydrochloric Acid (HCl) Raw palygorskite-smectite clay (pH 7.3) having a moisture content of about 45 % by weight was ground and dried in an impact mill (Williams Mill) to a mean particle size of about 31.6 microns and a free moisture content of about 3 to about 5 % by weight. Thereafter, the obtained dried clay product was sprayed with an aqueous hydrochloric acid solution (36% by weight). The obtained acidified products were then tested for bleaching activity using canola oil in the same manner as described in Example 2, above, except that 660 mm Hg was the applied vacuum. The observed results are compiled in Table 6, below.

TABLE 6 HYDROCHLORIC ACID ACTIVATED BLEACHING CLAY Acid (wt. %) Performance Red Yellow Chls 0 4.5 70 1161 0.5 4.8 70 856 1.0 4.8 70 694 3.0 5.1 70 408 sChl=Chlorophyll, ppb The preceding data shows effective bleaching activity with HCl activated clay at a relatively low free moisture content.

The foregoing is intended to be illustrative of the present invention, but not limiting. Numerous variations and modifications of the present invention may be effected without departing from the true spirit and scope of the invention.