Classifications

• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11B—PRODUCING, e.g. BY PRESSING RAW MATERIALS OR BY EXTRACTION FROM WASTE MATERIALS, REFINING OR PRESERVING FATS, FATTY SUBSTANCES, e.g. LANOLIN, FATTY OILS OR WAXES; ESSENTIAL OILS; PERFUMES
  • C11B3/00—Refining fats or fatty oils
  • C11B3/02—Refining fats or fatty oils by chemical reaction
  • C11B3/06—Refining fats or fatty oils by chemical reaction with bases

Definitions

• the invention relates to the alkali refining of glyceride oils containing free fatty acids and other impurities.
• the glyceride oils concerned include animal and vegetable glyceride oils which are normally solid, as well as those which are normally liquid.
• Glyceride oils obtained by solvent extraction, pressing or other methods, from animal or vegetable raw material always contain a greater or smaller amount of free fatty acids.
• the impurities must be removed. It has become standard practice to reduce or remove these impurities by a treatment wherein the oil is contacted with aqueous alkali at temperatures below the boiling point of water and generally at atmospheric pressure and the soap so formed, together with the other reaction products of impurities initially present, is removed in solution and subsequently split to recover fatty material therefrom.
• the present invention therefore, provides a process for alkali refining a glyceride oil with an aqueous liquid by contacting said oil with aqueous alkali and removing in aqueous solution the soap formed, characterised in that the oil and aqueous liquid are contacted at a temperature not less than 105 C. and not high enough to lead to significant saponification of the oil, under a superatmospheric pressure which is sufficiently high to prevent boiling in a space which is free from obstructions such as would prevent straight line movement of either oil or aqueous liquid.
• the optimum temperature depends primarily on the nature of the crude oil treated, especially the chain length and proportion of the predominating free fatty acids and the strength of the alkaline solution used.
• oils in which the predominating free fatty acids contain-at least 16 carbon atoms, and oils in which the free fatty acid content is high, e.g. 810% or more relatively high temperatures, e.g. or to or C., are most advantageous, although even at temperatures between 105 and 130 C., e.g. 1l0120 C., some advantage is achieved with such oils.
• oils in which acids of lower chain length predominate in the free fatty acid e.g.
• temperatures of 105 to 110 or 120 have given excellent results even when the initial free fatty acid content has been as high as 8%.
• the temperature should not be higher than is necessary to obtain the desired reduction in refining losses and in general it has not been found desirable to Work at temperatures higher than about 160 or 170 C.
• the pressure should be so chosen with regard to the temperature that the formation of Vapour bubbles is avoided completely. Pressures higher than are required toachieve this end are in general to be avoided especially when an inert gas is used in obtaining the desired total pressure. At unduly high pressures the consumption of such gas tends to be prohibitively costly.
• the process of the invention may be carried out in a variety of ways.
• the oil may be neutralised in a stirred pressurised cylindrical kettle having a coneshaped bottom, the alkali being sprayed onto the oil.
• the oil in the form of droplets may be caused to rise through a static body of aqueous alkali, in a vessel which, in accordance with the present invention, is suitably pressurised and heated.
• Another advantageous method of carrying out the invention is by applying at suitable elevated temperatures and pressures the method of neutralisation described in British application No. 19008/ 63, corresponding to US. application Ser. No. 366,240, filed may 11, 1964, now US. Pat. No. 3,454,608; where the oil and the aqueous solution are caused to flow in the same or opposite directions through a succession of treating regions in each of which the oil flows smoothly, horizontally or upwards at a small angle, on the surface of the aqueous solution, and transfer between each such region and the next is effected in such a way that any layer of aqueous soap solution that has formed immediately below the oil layer is displaced to bring the oil into direct contact with aqueous alkaline solution containing less soap and more unreacted alkali than is present in such layer, substantial intermixture of the aqueous and oil phases being avoided throughout.
• the process of the present invention is also applicable to the continuous alkali refining of glyceride oils with the aid of centrifuges.
• the process of the invention is also applicable to refining processes other than neutralisation which involve treatment with aqueous alkaline liquids and hence tend to lead to refining losses due to emulsification.
• Such processes include the desliming of these oils, which still contain some mucilage by treating them with suitable aqueous alkaline liquids, such as sodium silicate.
• the process according to the invention is of particular importance for the application to types of oils that during neutralisation have a tendency to form emulsions, especially spontaneous emulsions.
• the difference in behaviour during neutralisation of the oils is especially determined by the type of free fatty acid that is predominantly present in the oil.
• oils of the second as well as the third kinds give rise to many difiiculties during refining, as indicated above, owing to spontaneous emulsification. It is understood that many oils take an intermediate position, especially between the last-mentioned two kinds of oils.
• the superatmospheric pressure may be due simply to the vapour pressure of the aqueous liquid or may be imparted by an inert gas like nitrogen so that the total pressure is well above the saturated vapour pressure of the water at the treating temperature.
• the total pressure being the sum of the vapour pressure and the pressure of the inert gas is generally in the range of 1-10 atmospheres especially 3-5 atmospheres, depending on the processing temperature.
• aqueous sodium carbonate may be used.
• This kind of alkali reagent generally gives rise to a strong spontaneous emulsification.
• This stronger emulsification of carbonate in proportion to sodium hydroxide can be overcome by increasing the temperature during refining as compared with the temperature applied when sodium hydroxide is used.
• solutions of sodium carbonate of 0.05 to 2.0 molar are suitable.
• reaction is carried out using a temperature that is about 25 C. higher than that convevntional for the use of sodium hydroxide, the detrimental effect of the sodium carbonate can be completely oercome and the same low refining losses are obtained as when using so dium hydroxide.
• aqueous solutions of cauetic soda of normality 0.05-2.0 are suitable.
• the kind of free fatty acid present in the crude oil strongly depends upon the glyceride structure of the oil because these fatty acids are to a great extent degradation products of the triglycerides present in the oil.
• the fatty acids in the oil can in general be distinguished in acids containing a long carbon chain and acids containing a relatively short carbon chain.
• the relatively high refining losses in refining glyceride 'oils containing long chain free fatty acids can be effectively reduced to the level of say coconut oil by choosing a temperature in the refining process which is about 40 C. higher as compared with that normally used.
• the long chain free fatty acids give rise to higher refining losses when using higher concentrations of alkali than the short chain free fatty acids so that the use of stronger alkaline solutions involves a further increase in temperature to counteract the detrimental effects. In these cases it will be necessary to choose the maximum temperature allowable in the range of 160 to 170 C., at which last temperature the rate of the hydrolysis reaction becomes rather strong and competes with the reduced loss due to avoid ance of the spontaneous emulsification.
• neutralisation neutral sodium salts especially sodium chloride may be applied for instance in an amount of 0.3 to 3% and especially 0.5 to 2%, dissolved in the alkaline solution, to promote the separation of oil phase and soap solution.
• salt also promoted spontaneous emulsification and the thus emulsified oil could no more be separated by the salt, for the influence of the salt does not extend to spontaneously emulsified oil, which is lost.
• the detrimental effect of salt in this respect can be reduced by choosing a higher neutralisation temperature to reduce the spontaneous emulsification. In this way the advantage of salt in the separation of oil and aqueous phase is still maintained without having the disturbing effect of increased spontaneous emulsification.
• the refining factor is 1.15. If under the same conditions safflower oil is treated with 0.1 N lye containing 2% salt at a temperature of above 100 C., the refining loss is at the same level.
• the process of the invention is specially applicable to oils such as soybean oil, rapeseed oil, cottonseed oil, linseed oil and groundnut oil, which usually contain a relatively high proportion of mucilage.
• This mucilage is normally removed by a desliming operation, e.g. by treating the crude oil with hot water to hydrate the phosphatides and precipitate them.
• this treatment does not remove all phosphatides, and for instance in the case of soybean oil about 0.3% by weight of phosphatide is commonly still present.
• neutralisation the greater part of the remaining mucilage is removed, but in general so much mucilage remains in the oil that a post-desliming is necessary if very pure oils are desired.
• a postdesliming step can be avoided if the mucilage-containing oil is mixed with an aqueous acid, preferably 1 to 5 N hydrochloric acid in amount ranging from 1 to 5% of the weight of the oil, and this mixture, without removal of the acid, is subjected to neutralisation by contacting the mixture with an alkaline agent under the conditions characterising the process of the present invention.
• an acid pretreatment it is particularly desirable to effect the subsequent neutralisation according to the present invention in a totally unobstructed space.
• crude tallow (free fatty acid content 4.9%) was deacidified in a stirred cylindrical kettle having a cone-shaped bottom, with an alkaline solution of 0.8 N in an excess of 10% over the theoretical amount required. Then the oil was post-treated with 15 volume percent of dilute lye solution of 0.2 N followed by 3 washing treatments with water in an amount of 10% based on the amount of oil.
• EXAMPLE 2 A batch of 16 kg. of crude safflower oil was neutralised in the same apparatus as used in Example 1 at a temperature of 90 C. with an 0.8 N alkaline solution. Thereupon a post-treatment with a 0.2 N lye solution followed by water 3 washings were required to remove the soap which was formed by neutralisation.
• the neutralising factor was 1.6, so that 0.6 kg. neutral oil was lost for each kg of fatty acid removed.
• the ultimate free fatty acid content in this case was then 0.05%, the soap content 0.05% and the neutralising factor 1.2 corresponding to an oil loss of 0.2 kg. per kg fatty acid removed, that is to say that the neutral oil loss was diminished from 0.6 kg. per kg. of fatty acids removed, to 0.2 kg.
• the apparatus consisted of 36 zig-zag mounted guide plates, having a length of 18 cm. and a width of 5 cm. placed in a slope of 5 in a housing having a length of 18 cm., a Width of 5 cm. and a height of 100* cm.
• a pipe was mounted in a hole of 0.9 cm. diameter in the middle of the plate at a distance of 1 cm. from the end of the plate.
• the pipe has to carry the alkaline solution upwards through the oil layer onto the plate below.
• a batch of tallow having a free fatty acid content of 4.5% was neutralised at 110 C. with a 0.1 N alkaline solution, in an excess of 25% of the theoretical amount required, and washing treatments were not required at all.
• EXAMPLE 4 The detrimental influence of a high caustic soda concentration on the neutralisation can be compensated for by increasing the temperature during neutralisation. This can be demonstrated by neutralisation of tallow at 95 C., having a free fatty acid content 4.3% with a 0.1 N caustic soda solution (25% excess of the theoretical amount required) in the same apparatus as described in Example 3, and by comparison of this result with a similar treatment but using a stronger caustic soda solution.
• the neutralising factor was 1.10 and when neutralised under the same conditions with a 0.4 N caustic soda solution, a neutralising factor of 1.45 was obtained.
• a temperature of 140 C. was required in the neutralisation of tallow with 0.4 N caustic soda solution to obtain a neutralisation factor equal to that when using a 0.1 N caustic soda solution.
• EXAMPLE 5 Three batches of tallow were neutralised using a 0.1 N caustic soda solution containing 1% sodium chloride in the apparatus according to Example 3, the first having a free fatty acid content of 1%, the last two having a free fatty acid content of 5.0%. Trials with the tallow with a low and a high free fatty acid content showed that the neutralisation factor in the latter case was considerably higher. When neutralising the tallow with a high free fatty acid content under the same conditions, except that the temperature during neutralisation was chosen 20 C. higher, a neutralising factor was obtained equal to that when neutralising a tallow with low free fatty acid content.
• Tempera- Free fatty Neutralture, acid content ising Oil C. in g. equiv/kg. Alkali factor Coconut 95 0. 17 0.1 N with 1% salt. 1. 1 Tallow-.- 95 0.17 do 1.6 Safllower-.- 95 1. 25 Tallow- 1. 1 Safiiower- 120 1. 1
• EXAMPLE 8 This example illustrates effecting neutralisation according to the invention in a totally unobstructed space.
• a column of stainless steel with a height of cm. and a diameter of 10 cm., and having a conical bottom, a tallow was neutralised.
• the column was closed to the atmosphere and the neutralisation effected under a pressure of about 5 atm., the atmosphere being composed of nitrogen saturated with water vapour.
• the oil and alkaline solution flowed counter-currently, the oil being introduced at the bottom and flowing upwards from numerous small apertures to form the dispersed phase and the alkaline solution flowing downwards.
• the soap solution formed was continuously withdrawn from the bottom below the oil inlet.
• the alkaline solution had a concentration of 0.3 N and was present in an excess of 25%.
• the temperature during the neutralisation was kept at 140 C.
• the oil throughput amounted to 4 ton/m. /h.
• the initial free fatty acid content was 5.62%.
• the neutralised oil had a free fatty acid content of 0.15%, and a soap content of 0.08%.
• the neutralising factor was estimated at 1.16.
• part of the refined oil is continuously fed back into the crude oil stream entering the space in which the refining is effected, the proportion fed back being such as to reduce the free fatty acid content of the oil coming into contact with the aqueous solution to such an extent that the soap content of the refined oil is not more than 0.1% by weight.
• a process for neutralizing the free fatty acids contained as impurities in glyceride oil comprising contacting said oil with aqueous alkali and removing in aqueous solution the soap formed, characterised in that the oil and aqueous liquid are contacted at a temperature not less than 105 C. and not high enough to lead to significant saponification of the oil, under a superatmospheric pressure which is sufficiently high to prevent boiling, in a space which is free from obstructions such as would prevent straight line movement of either oil or aqueous liquid.
• aqueous liquid is an aqueous solution of caustic soda of normality 0.052.0.
• aqueous liquid is a 0.05-2 molar sodium carbonate solution.

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Citations (10)

• 1965
  • 1965-03-18 LU LU48219A patent/LU48219A1/xx unknown
• 1966
  • 1966-03-14 US US541437A patent/US3510501A/en not_active Expired - Lifetime
  • 1966-03-16 GB GB11430/66A patent/GB1143366A/en not_active Expired
  • 1966-03-16 CH CH375766A patent/CH482014A/de not_active IP Right Cessation
  • 1966-03-16 CS CS178166A patent/CS155137B2/cs unknown
  • 1966-03-17 NL NL666603470A patent/NL152928B/xx unknown
  • 1966-03-18 SE SE03653/66A patent/SE338121B/xx unknown
  • 1966-03-18 DE DE1617019A patent/DE1617019C3/de not_active Expired
  • 1966-03-18 ES ES0324415A patent/ES324415A1/es not_active Expired
  • 1966-03-18 AT AT259766A patent/AT279778B/de active
  • 1966-03-18 NO NO162182A patent/NO122326B/no unknown

Patent Citations (10)

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