WO2018124873A1

WO2018124873A1 - Process of producing palm-based polyol esters

Info

Publication number: WO2018124873A1
Application number: PCT/MY2017/050084
Authority: WO
Inventors: Zulina ABD MAURAD; Shoot Kian Yeong; Zainab Idris
Original assignee: Malaysian Palm Oil Board
Priority date: 2016-12-27
Filing date: 2017-12-26
Publication date: 2018-07-05
Also published as: MY194038A

Abstract

The present invention relates to a process of producing palm-based polyol esters (POE) through a solventless and autocatalytic reaction. The process comprising steps of esterifying (104) palm-based fatty acid and pentaerythritol under controlled condition followed by purifying (108) esterification reaction mixture using short path distillation method to remove unreacted acid. In particular, esterification reaction is conducted under vacuum pressure of at least 40 000 Pa (400 mbar), at a temperature in the range of at least 140 to 200 °C for a period between 2 to 6 hours. The purification of esterification mixture by using short path distillation is conducted attemperature ranging from at least 200 to 225 °C and reduced pressure of at least 5 Pa (0.05 mbar) to remove unreacted acid.

Description

PROCESS OF PRODUCING PALM-BASED POLYOL ESTERS FIELD OF INVENTION

The present invention relates to a process of producing palm-based polyol esters with low acid value and low hydroxyl value. In particular, the process of the present invention produces palm-based polyol esters with high purity tetra esters through solventless and autocatalytic reaction.

BACKGROUND OF INVENTION

Industrial lubricants based on mineral oils are highly toxic to the environment and they are not readily biodegradable by microorganisms. The awareness and concern over the use of petroleum-based fuels and lubricants and its impact on the environment has open the door for utilization of environment friendly lubricants from renewable resources like vegetable oils. Vegetable oils along with polyol esters are now used as lubricating base fluids and as an additive in lubricants. The potential suitability of synthetic esters as lubricants derives from a favorable viscosity temperature behavior as compared to conventional mineral oil based lubricants with lower pour points upon adjusting the comparable viscosities.

Polyol esters are produced from the reaction of polyols such as pentaerythritol and trimethylolpropane with various fatty acids such as fatty acids obtained by saponification of animal oils or fatty acids from vegetable oils. By combining the selected fatty acids and alcohols, it is possible to produce synthetic esters with required properties for any intended applications. It is preferred to use neopolyol due to the absence of any hydrogen in the β position for example trimethylol propane (TMP), neopentyl glycol (NPG), pentaerythritol (PE), di(trimethylol propane) (diTMP), and di(pentaerythritol) (diPE) which can lead to superior thermal stability. The resultant polyol esters would have the advantages of added polarity, reduced volatility and enhanced lubricity characteristics.

Properties of polyol ester depends on the structure of the constituent fatty acids and alcohols. One of the common disadvantage of polyol esters produced from saturated fatty acids is high pour point due to the linear structure of the acids which are highly resistant to oxidation and high temperature. In contrast, polyol esters produced from unsaturated fatty acids exhibit lower pour point and is highly susceptible to oxidation and thermal degradation. Palm oil contains primarily palmitic acid which is saturated fatty acid having 16 carbons in a chain configuration, about 44% and oleic acid which is monounsaturated fatty acid having 18 carbons in a chain configuration, about 39%. Palm oil possesses good inherent properties which are desirable for lubricant but limited to its poor low temperature fluidity due to the presence of high content of saturated fatty acids. Palm oil can be transformed into better adapted molecules of palm esters through esterification process. These palm ester molecules are similar to natural oils with a much better thermal, oxidative and hydrolytic stability as well as cold temperature fluidity without sacrificing its good properties as lubricant.

United States Patent No. US 9260372 B2 (US 372 B2 Patent) entitled "Method for the Production of Polyols and Uses Thereof" having a filing date of 28 February 2013 (Applicant: Petroliam Nasional Berhad) relates to polyol or derived lubricant base stock which comprises of esters polyols produced from the reaction product of ozone esters and excess primary polyol. In US 372 Patent, the intermediate fatty acid alkyl esters or ozone esters have a reduces saturated fatty acid content due to pre- treatment steps that partially removes saturated fatty acids or saturates by the process of fractional distillation.

Chinese Patent Publication No. CN 104341297 (CN 297 Publication) entitled "Method for Preparing Polyol by Using Bio-oil and Application" having a filing date of 16 September 2014 (Applicant: Zhejiang Hengfeng New Material Co., Ltd) relates to a method for preparing polyol by using bio-oil. In CN 297 Publication, polyol is prepared through methyl esterification and transesterification of biolipid and methanol under the catalysis of potassium fluoride loaded magnesium oxide solid alkali. Further, in CN 297 Publication, resultant product is converted into fatty acid methyl ester with small molecular weight and byproduct glycerol, followed by filtration to recycle the catalyst and separating lower-layer glycerol. Subsequently, in CN 297 Publication, epoxidation is performed on upper-layer fatty acid methyl ester in 30% of hydrogen peroxide under the catalysis of ionic liquid to form epoxidized fatty acid methyl ester. Glycerol is added into the methyl esterification process and continuously performing alkoxide ring- opening under the catalysis of ionic liquid, introducing hydroxyl, and finally separating liquid to recycle the ionic liquid catalyst, reducing pressure and distilling the upper-layer to remove water to obtain low-viscosity bio-oil-based polyol.

China Patent Publication No. CN 103833549 (CN 549 Publication) entitled "Fatty Acid Polyol Ester Preparation Method" having a filing date of 23 November 2012 (Applicant: Petrochina Company Limited) relates to a method of preparing fatty acid polyol ester which comprises steps of adopting metatitanic acid as a raw material, drying and crushing of the metatitanic acid, immersing the treated metatitanic acid in sulphuric acid solution, filtering, drying, crushing and calcining to prepare a titanium source solid acid catalyst; and adopting a polyol and a fatty acid as raw material, adding the titanium source solid acid catalyst, carrying out esterification reaction at certain temperature under the protection of nitrogen gas with water, and carrying out separation refinement treatment on the resultant fatty acid polyol ester crude product to obtain a purified fatty acid polyol ester. In CN 549 Publication, industrial metatitanic acid is adopted as the titanium source to prepare solid acid catalyst to avoid corrosion on equipment, complex product post-treatment, difficult catalyst separation, pollution generation and the like with the use of sulfuric acid and other liquid acid catalysts. Further, CN 549 Publication provides that, utilization of industrial metatitanic acid as the titanium source to prepare solid acid catalyst reduces the production cost, simple preparation process, high catalyst catalysis efficiency, and efficient fatty acid and polyol esterification reaction performed within a short time as compared to solid super acid.

The present invention is an improvement to existing process for producing palm- based polyol esters (POE) through esterification of palm-based fatty acids mixture with pentaerythritol via solventless and autocatalytic reaction. The resultant polyol ester is of low hydroxyl value and low acid value.

SUMMARY OF INVENTION

One aspect of the present invention provides a process (1 00) for producing palm- based polyol esters. The process (100) comprises steps of esterifying (104) palm- based fatty acids mixture with crystalline pentaerythritol through solventless and autocatalytic reaction to produce polyol ester; and purifying (1 08) resultant ester by removing residual acid from said esterification reaction mixture through short path distillation.

A further aspect of the present invention provides that the esterifying step is conducted through controlled reaction which further comprises steps of selecting a combination of reaction temperature, reaction time, pentaerythritol grade, molar ratio of fatty acid to pentaerythritol, efficiency of removing water and rate of heating to achieve a desired hydroxyl value and acid value; and raising the boiling point of the reaction mixture preferably from about 140 Ό to ab out 200 Ό.

Another aspect of the present invention provides that step of removing residual acid from resultant polyol ester further comprises steps of removing water at condenser temperature of at least 13 Ό and vacuum pressure o f at least 50 000 Pa (500 mbar).

Yet another aspect of the present invention provides for short path distillation which is conducted at varying evaporator temperature, residue temperature and condenser temperature of at least in the range of 200 to 225°C, at least 70 Ό and at least 25 Ό, respectively.

Still another aspect of the present invention provides that short path distillation which is conducted at reduced pressure of at least 5 Pa (0.05 mbar), feed rate of at least 100 rpm and wiper in the range of at least 300 to 31 0 rpm.

A further aspect of the present invention provides that palm-based fatty acids mixture comprising of at least 60.8% C₈, at least 38.9% Ci₀ and at most 2% Ci₂ preferably at

Another aspect of the present invention provides that purity of pentaerythritol is at least 98% monopentaerythritol, preferably at least 88% monopentaerythritol.

A preferred aspect of the present invention provides that resultant polyol esters containing mixture of mono-, di-, tri- , and tetra ester with at least 96% w/w tetra ester. Another preferred aspect of the present invention provides that resultant polyol esters having kinematic viscosity ranging from at least 3e-05 to 3.5e-05 m²/s (30 to 35 cST) at 40 ^<C.

A preferred aspect of the present invention provides that resultant polyol esters having flash point ranging from at least 160 Ό to 300 Ό.

Yet another preferred aspect of the present invention provides that resultant polyol esters having pour point ranging from at least -3 °C to -9 Ό.

Another preferred aspect of the present invention provides that resultant polyol esters having wear scar diameter ranging from at least 0.6 to 0.8 mm at 400 N. A further preferred aspect of the present invention provides that resultant polyol esters having oxidative stability ranging from at least 34 to 50 min at temperature of ±150 ^<C and under pressure of ± 1 103000 Pa (160 psi ).

The present invention consists of features and a combination of parts hereinafter fully described and illustrated in the accompanying drawings, it being understood that various changes in the details may be made without departing from the scope of the invention or sacrificing any of the advantages of the present invention.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING

To further clarify various aspects of some embodiments of the present invention, a more particular description of the invention will be rendered by references to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the accompanying drawings.

FIG 1 .0 is a flowchart illustrating the process of producing palm-based polyol ester.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to an improved process of producing palm-based polyol esters (POE) with high purity tetra ester through a solventless and autocatalytic reaction. In the present invention, palm-based fatty acid of a mixture of 60.8% C₈ and 38.9% C₁₀ and pentaertyhritol undergo autocatalytic reaction in an esterification process under vacuum pressure. The resultant ester is purified by distilling out unreacted acid using short path distillation. Hereinafter, this specification will describe the present invention according to the preferred embodiments. It is to be understood that limiting the description to the preferred embodiments of the invention is merely to facilitate discussion of the present invention and it is envisioned without departing from the scope of the appended claims.

POE of the present invention is prepared from C₈.C₁₀ palm-based fatty acid. The specification of the said palm-based fatty acid is shown in Table 1 . The preferable palm-based fatty acid mixture comprising at least 60.8% C₈, at least 38.9% C₁₀ and at most 2% C₁₂ preferably at most 0.1 % C₁₂.

Test parameter Specifications

Iodine value 0.22 gl₂/100 g

Acid value 361 .5 mgKOH/g

Fatty acid composition

c₈ 50 - 62%

Table 1 : Specification of C₈-Ci₀ palm-based fatty acid

Reference is made to FIG. 1 .0 which is a flowchart illustrating a process of producing palm-based polyol ester. As illustrated in FIG. 1 .0, the process for producing POE first undergo esterification whereby C₈-Ci₀ of palm-based fatty acid mixture (102) is esterified (104) with white crystalline pentaerythritol via solventless and autocatalytic reaction under a controlled condition. Subsequently, water is removed (106) from resultant polyol ester at condenser temperature of at least 13 Ό and vacuum pressure of at least 50 000 Pa (500 mbar) and followed by purification (108) of resultant polyol ester via short path distillation to remove unreacted acid. The controlled esterification step includes selecting a combination of reaction temperature, reaction time, pressure, pentaerythritol grade, molar ratio of fatty acid to pentaerythritol, efficiency of removing water and rate of heating to achieve the desired hydroxyl value and acid value. The esterification reaction temperature is in the range of at least 140 Ό to 200 Ό. The control led esterification reaction is conducted under vacuum pressure of at least 40 000 kPa (400 mbar). The purity of pentaerythritol used in the present invention is at least 98% monopentaerythritol with di- and tripentaerythritol as impurities, and most preferably at least 88% monopentaerythritol. The molar ratio of fatty acid to pentaerythritol is in the range of at least 4.1 to 4.8. The efficiency of removing water and rate of heating are controlled to ensure complete esterification reaction is achieved. The boiling point of the reaction temperature is raised from about 140 Ό to about 200 Ό. The reaction time of the esterification step is controlled for only 2 to 6 hours with a staggered increase in reaction temperature to achieve the desired hydroxyl value.

In purification of the esterified mixture, residual acid is removed from said esterification reaction mixture through short path distillation. Short path distillation is conducted at varying evaporator temperature of at least in the range of 200 to 225Ό, residue temperature of at least 70 Ό and condenser temperature of at least 25 Ό. Further, the short path distillation is conducted at reduced pressure of at least 5 Pa (0.05 mbar), feed rate of at least 100 rpm and wiper in the range of at least 300 to 310 rpm.

The resultant POE contains mixture of mono-, di-, tri-, and tetra ester with at least 96% w/w tetra ester with low acid value in the range of at least 0.30 - 0.99 mg KOH/g that can reduce the corrosion effect and low hydroxyl value of at least 4 mg KOH/g indicating reactivity of the acylating component in eliminating the entire hydroxyl group on pentaerythritol. Further, the yield of higher tetra-ester is determined by rate of heating and distillation treatment.

The resultant POE is characterized for hydroxyl value, acid value, iodine value, kinematic viscosity, flash point, pour point, wears scar diameter, oxidative stability and biodegradability and is found to be potential to be employed as lubricants especially as a hydraulic fluids or refrigeration lubricants. The hydroxyl value is preferably determined by AOCS (Cd 13-60) (Firestone, 2009) and the acid value is preferably determined by AOCS (Te 2a-64) (Firestone, 2009). POE for lubricants

The present invention provides a base stock lubricant composition comprising POE, prepared as described. The present base stock lubricant is a readily biodegradable lubricant and much faster as compared to vegetable oils and commercial polyol ester from coconut based (ZELEC 874 from Stepan) (Siti Afida et al., 2015). Lubrication properties using ASTM method (Nadkarni, 2007) of the produced POE compared to commercial ZELEC 874 are shown in Table 2.

Lubrication properties POE Zelec 874

Kinematic viscosity at 40^<C (ASTM D445) 3e-05 to 3. 5e-05 3e-05 m2/s m²/s (30 to 35 cSt) (30 cSt)

Flash point (ASTM D92) 160-300^<C 210^<C

Pour point (ASTM D97) -3 to -9^<C -6^<C

Wear scar diameter at 400N (ASTM 0.6-0.8 mm 0.7 mm

D4172)

Oxidative stability (ASTM D2272), 34-50 min 67 min

±150 °C, ±160 psi

Biodegradability OECD 301 F

60% passed level 5-9 days 8 days

100% passed level 9-15 days 15 days Table 2: Comparison of lubrication properties of POE and commercial ZELEC 874 Example 1

Charge 961 1 .81 g of palm-based fatty acid, PALMAC 56-08 (available from Chung Chemicals Sdn. Bhd., Malaysia) and 1769.95 g pentaerythritol (> 98% purity, obtained from Merck Sdn. Bhd., Malaysia) without catalyst and solventless to a 20 L glass reactor equipped with a mechanical stirrer (1800 rpm) having stainless steel turbine blades with immersed electrical heating coil. The molar ratio of fatty acid to pentaerythritol ranging from 4.1 to 4.8. The esterification reaction temperature set to the boiling point of the reaction mixture using controller at immersed electrical heating coil from 140 to the highest 200 . The efficiency of removing water need to be controlled by applying vacuum to the process system where, the condenser is attached with a chiller set at 13 and vacuum pump < 50 000 Pa (500 mbar). In order to achieve the desired OHV at < 4 mg KOH/g, reaction time can be control for only 2 to 6 hours with staggered increase of reaction temperatures. The resulted ester mixture still having residual fatty acid with AV range from 40 to 50 mg KOH/g will be removed using a short path distiller.

Example 2

Charge 3008 g of the resulted ester mixture at a feed rate of 100 rpm to a 1 L short path distiller (Hickman, 1944) which consists of a cylindrical body with a heating jacket by varying the evaporator temperature 200 to 225 , a rotor and condenser set temperature at 25 . The wiper blade s fix at 300-310 rpm creates a mechanically agitated, thin ester mixture film on the heating surface inside of the body. The distilled ester (non-volatile portion) reaches the lower part of the evaporator and leaves it through the bottom product outlet at residue temperature 70 . The residual vapours flow through the vacuum nozzle to the vacuum system at pressure 5 Pa (0.05 mbar). The distilled ester having POE containing at least 96% w/w tetra-ester with low acid value in the range of from 0.30 - 0.99 mg KOH/g and low hydroxyl value < 4 mg KOH/g.

The resultant POE having low hydroxyl value of at least 4 mg KOH/g and low acid value in the range of 0.30 - 0.99 mg KOH/g and exhibit desirable physical properties of a viscosity at 40 ^<C of at least 3e-05 to 3.5e-0 5 m²/s (30 to 35 cST), a flash point in the range of at least 160 to 300 Ό, and a pour poi nt in the range of at least -3 to -9 ^<C.

The POE as produced through esterification of palm-based fatty acids mixture with pentaerythritol via solventless and autocatalytic reaction followed by purification of the resultant ester using short path distillation resulting in POE with low acid value and hydroxyl value. The corrosiveness of fatty acid based esters are reduced through the resultant ester with low acid and hydroxyl value. The resultant palm-based polyol ester exhibits desired lubricant properties indicating potential application of the POE to be employed as lubricants to replace the used of conventional lubricants based on mineral oils which are highly toxic to the environment. Unless the context requires otherwise or specifically stated to the contrary, integers, steps or elements of the invention recited herein as singular integers, steps or elements clearly encompass both singular and plural forms of the recited integers, steps or elements. Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated step or element or integer or group of steps or elements or integers, but not the exclusion of any other step or element or integer or group of steps, elements or integers. Thus, in the context of this specification, the term "comprising" is used in an inclusive sense and thus should be understood as meaning "including principally, but not necessarily solely".

Claims

1 . A process (100) for producing palm-based polyol esters comprises steps of:

esterifying (104) palm-based fatty acid mixture with crystalline pentaerythritol through a solventless and autocatalytic reaction to produce polyol ester; and

purifying (108) resultant polyol ester by removing residual acid from said esterification reaction mixture through short path distillation.

2. The process (100) according to claim 1 , wherein the esterifying step (104) is conducted through controlled reaction which further comprises steps of:

selecting a combination of reaction temperature, reaction time, pentaerythritol grade, molar ratio of fatty acid to pentaerythritol, efficiency of removing water and rate of heating to achieve the desired hydroxyl value and acid value; and

raising the boiling point of the reaction mixture preferably from about 140 <C to the highest of about 200 ^<C.

3. The process (100) according to claim 1 , wherein removing residual acid from esterification mixture further comprises steps of removing water at condenser temperature of at least 13 Ό and vacuum pressure o f at least 50 000 Pa (500 mbar).

4. The process (100) according to claim 1 , wherein the short path distillation is conducted at varying evaporator temperature, residue temperature and condenser temperature of at least in the range of 200 to 225Ό, at least 70 Ό and at least 25 Ό, respectively.

5. The process (100) according to claim 1 , wherein the short path distillation is conducted at reduced pressure of at least 5 Pa (0.05 mbar), feed rate of at least 100 rpm and wiper in the range of at least 300 to 310 rpm.

6. The process (100) according to claim 1 wherein the said palm-based fatty acids mixture comprising at least 60.8% C₈, at least 38.9% Ci₀ and 2% Ci₂ preferably 0.1 % Ci₂.

7. The process (100) according to claim 1 wherein purity of pentaerythritol is at least 98% monopentaerythritol, preferably at least 88% monopentaerythritol.

8. The process (100) according to claim 1 , wherein the resultant polyol ester containing mixture of mono-, di- , tri- , and tetra ester with at least 96% w/w tetra ester.

9. The process (100) according to claim 1 , wherein the resultant polyol esters having kinematic viscosity ranging from at least 3e-05 to 3.5e-05 m²/s (30 to 35 cST) at 40 ^<C.

10. The process (100) according to claim 1 , wherein the resultant polyol esters having flash point ranging from at least 160 to 300 Ό.

1 1 . The process (100) according to claim 1 , wherein the resultant polyol esters having pour point ranging from at least -3 to -9 Ό .

12. The process (100) according to claim 1 , wherein the resultant polyol esters having wear scar diameter ranging from at least 0.6 to 0.8 mm at 400 N.

13. The process (100) according to claim 1 , wherein the resultant polyol ester having oxidative stability in the range of at least 34 to 50 min at temperature of ±150^<C and under pressure of ± 1 103000 Pa (160 p si).