Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
  • C10L1/00—Liquid carbonaceous fuels
  • C10L1/02—Liquid carbonaceous fuels essentially based on components consisting of carbon, hydrogen, and oxygen only
  • C10L1/026—Liquid carbonaceous fuels essentially based on components consisting of carbon, hydrogen, and oxygen only for compression ignition
• • C—CHEMISTRY; METALLURGY
  • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
  • C11C—FATTY ACIDS FROM FATS, OILS OR WAXES; CANDLES; FATS, OILS OR FATTY ACIDS BY CHEMICAL MODIFICATION OF FATS, OILS, OR FATTY ACIDS OBTAINED THEREFROM
  • C11C3/00—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom
  • C11C3/003—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom by esterification of fatty acids with alcohols
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E50/00—Technologies for the production of fuel of non-fossil origin
  • Y02E50/10—Biofuels, e.g. bio-diesel
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P30/00—Technologies relating to oil refining and petrochemical industry
  • Y02P30/20—Technologies relating to oil refining and petrochemical industry using bio-feedstock

Definitions

• the present invention relates to a method of producing biodiesel from triglycerides combining thermal cracking and esterification.
• Biodiesels are fuels produced from the esterification of biomass-derived oils with alcohol.
• Biodiesel can be produced from triglyceride sources such as canola, corn, soybean, palm etc.
• Another potential source for biodiesels are the waste triglycerides from animal rendering facilities and waste cooking oils, such as those found as restaurant trap greases.
• waste triglycerides often have high contaminants content, including bacteria, which must effectively be removed before processing.
• waste triglycerides tend to have a high content of free fatty acid (FFA), anywhere in the range of from 50% to 100%. Mixtures of free fatty acids and triglycerides have been found to be very difficult to convert to useful fuels by any traditional methods.
• FFA free fatty acid
• Waste triglycerides are also often heavily contaminated by, for example, bacteria, detergents, silts and pesticides. These contaminants must be removed before esterification can take place, without adding significant additional cost to the overall processes.
• One known method of processing high FFA feedstocks involves adding glycerol to the feedstock to convert FFA's to mono- and diglycerides, followed by conventional alkali-catalyzed esterification. This method addresses the issue of high FFA content but does not treat or remove contaminants.
• a second method involves pre-treating an FFA-rich triglyceride feedstock with an acid catalyst to convert FFA to alkyl-esters and reduce FFA concentrations to less than about 0.5%, followed by traditional base-catalyzed esterification. This method again, only deals with the issue of high FFA content and not high contaminant levels.
• An alternate method involves performing both esterification and transesterification of triglycerides using a strong acid such as H 2 SO 4 or sulphamic acid; however the product clean up is cumbersome and usually involves neutralization of the acidic catalyst and the removal of resulting salts.
• Acid ion-exchange resins are another option, but due to possible resin degradation esterification must be carried out below the resin degradation temperature, which significantly slows down the process. As well, water formation by FFA esterification prevents this process from going to completion.
• Reaction time required for typical bio-diesel production by acid esterification ranges from 10 hours to 20 hours, which makes acid esterification of fatty acids an industrially unattractive route for fuel production.
• esterification temperature is raised above 100°C, satisfactory conversion can be achieved within 8 to 12 hours.
• carrying out acid esterification at above water's boiling point diminishes alcohol solubility in the methyl-esters. This is undesirable since, in order to bring esterification to near completion a high alcohol concentration must be maintained in the reactant mixture and this becomes difficult due to limited alcohol solubility.
• the present invention thus provides a method of producing biodiesel from a triglyceride feedstock, comprising pretreating the triglyceride feedstock by thermal cracking or rapid pyrolysis to remove contaminants and convert triglycerides, to form a middle distillate fraction rich in free fatty acids.
• the middle distillate fraction can then be treated by vapour phase esterification under vacuum and in the presence of an alcohol and a solid acid catalyst to produce a mixed biodiesel/diesel stream.
• the mixed biodiesel/diesel stream can then be treated with a basic solution to convert residual free fatty acids to non-foaming metallic soaps, which non-foaming metallic soaps can be separated by vacuum distillation, centrifugation, filtering or combinations thereof.
• the present invention also provides a method of producing a biodiesel/naphtha mixture from a triglyceride feedstock.
• the method involves first pretreating the triglyceride feedstock by thermal cracking or rapid pyrolysis to remove contaminants and convert triglycerides, to produce a middle distillate fraction rich in free fatty acids, a naphtha stream and a gas stream.
• the naphtha stream and middle distillate fraction are treated by vapour phase esterification under vacuum and in the presence of an alcohol and a solid acid catalyst to produce a mixed biodiesel/naphtha stream.
• the mixed biodiesel/naphtha stream can then be treated with a basic solution to convert residual free fatty acids to non-foaming metallic soaps, which non-foaming metallic soaps are separated by vacuum distillation, centrifugation, filtering or combinations thereof.
• Fig. 1 is a flow sheet of a first preferred process for carrying out the present invention.
• Fig. 2 is a flow sheet of a second preferred process for carrying out the present invention.
• the present process employs a novel combination of thermal cracking followed by solid acid esterification under vacuum and elevated temperatures to convert triglycerides, and particularly low quality and waste triglycerides, into usable biodiesel.
• thermal cracking is used as a pre-treatment step to break down the triglycerides into a broad range of free fatty acids and lower molecular weight components.
• Thermal cracking also serves to remove contaminants found in waste triglycerides, which can cause problems downstream.
• the resulting product from the cracking step can then be treated by solid acid esterification under vacuum and elevated temperatures to convert fatty acids into alkyl esters (biodiesel). The esterification is carried out in the vapour phase.
• thermal cracking is considered to loosely cover the process of breaking down large molecules into smaller molecules at a predetermined temperature and pressure.
• Rapid pyrolysis of triglycerides can also be used in the present process and is considered to be encompassed by the term thermal cracking. Details of rapid pyrolysis are given below.
• a flow diagram of the process steps and streams of one embodiment of the present invention is shown in Fig. 1.
• a feedstock 12 of triglycerides, and particularly low quality or waste triglycerides is fed to a thermal cracking unit 10.
• the feedstock 12 can be any variety of triglyceride including oils such as canola, soy, corn, palm, cottonseed, mustard seed, fish or algae oils and waste or low quality triglycerides such as restaurant trap greases, waste greases from animal rendering facilities and other forms of waste oils and greases and low-quality vegetable oils.
• the feedstock stream 12 can be heterogeneous in nature and can contain water and other contaminants.
• the triglyceride feedstock stream 12 can also have free fatty acid (FFA) content as high as 50 to 100 wt.%.
• FFA free fatty acid
• the triglyceride feedstock 12 may be filtered to remove any macroscopic contaminant particles prior to thermal cracking.
• thermal cracking unit 10 triglycerides in the feedstock stream 12 are destroyed since they are converted into free fatty acids, thus forming a mixture of free fatty acids and conventional hydrocarbons, such as paraffins, olefins and aromatics.
• Thermal cracking is preferably carried out at mild cracking conditions which, for the purposes of the present invention, are described as an operating temperature preferably in the range of from 390 to 46O 0 C, more preferably from 410 to 43O 0 C, and preferably at an operating pressure of from 0 to 60 psig (6.9 to 515 kPa), more preferably from 30 to 40 psig (308 to 377 kPa).
• Thermal cracking produces various fractions including gases 14, naphtha 16, middle distillate 22, and residue 18.
• Gases mainly comprise of CO, CO 2 , hydrogen, methane, ethane, ethylene, propane, and propylene. Contaminants from the feedstock 12 end up in the residue stream 18. It was noted that the mild thermal cracking conditions used in the present invention to crack the feedstock 12 produces a mainly diesel-like fraction, having a boiling range of between 165 0 C and 345 0 C, rather than naphtha (IBP to 165 0 C), as was produced from thermal cracking of triglycerides at higher temperatures and pressures.
• the middle distillate fraction 22 makes up more than half of the thermally cracked product and has been found to have suitable characteristics for further treatment by esterification.
• the middle distillate fraction 22 is rich in Cl 6 and Cl 8 fatty acids, comprising free fatty acids formed from thermal cracking of triglycerides, the original free fatty acids present in the feedstock and conventional hydrocarbons.
• Middle distillates typically encompass a range of petroleum equivalent fractions from kerosene to lubricating oil and include light fuel oils and diesel fuel.
• the middle distillate fraction 22 was found to have a boiling point range of from 150 to 36O 0 C, and more preferably from 165 to 345 0 C.
• the middle distillate fraction 22 still has some fuel quality issues such as high viscosity, high acid number, high cloud point and high concentrations of nitrogen and/or sulphur.
• the present invention incorporates a vapour phase esterification process that overcomes the alcohol solubility issue and thus substantially accelerates acid esterification rates.
• acid esterification is operated under vacuum and high temperature, higher than normally used in liquid esterification, to achieve free fatty acids conversion higher than 97% in less than 10 minutes.
• High temperature accelerates the reaction rate and high vacuum and temperature ensure all components are in vapour phase.
• the middle distillate fraction 22 is fed to an esterification unit 20, where vapour phase esterification is carried out in the presence of an alcohol stream 24 and a solid acid catalyst to produce alkyl esters (biodiesel).
• the esterification process is carried out at a temperature preferably ranging from 150 to 350 0 C, more preferably from 200 to 25O 0 C.
• the esterification process operates under a vacuum, preferably in the range of 0.1 to 1.16 psia (6 to 60 mmHg), and is more preferably 0.1 to 0.58 psia (6 to 30 mmHg).
• the alcohol stream 24 can be any suitable alcohol known in the art, or mixtures thereof.
• the alcohol stream 24 is preferably methanol.
• the ratio of middle distillate stream 22 to alcohol 24 is preferably in the range of from 3 : 1 to 0.1 : 1 and is more preferably in the range of from 2:1 to 1:1.
• Residence time in the esterification unit 20 can range from 6 to 425 minutes and preferably ranges from 6 to 43 minutes.
• residence time is defined by dividing the catalyst volume by the total liquid feed rate.
• the ability to conduct the esterification at higher temperatures is further advantageous since this circumvents the catalysis quenching by water. Since water is a co-product of acid esterification, it can detrimentally quench the esterification reaction if not removed continuously. In the present invention, as water forms by esterification, it immediately evaporates from the catalyst surface, thereby avoiding deactivation of the esterification catalyst.
• the solid acid catalyst is preferably chosen from super acids such as, for example TiO 2 solid support doped with Zr(SO 4 ) 2 , SnO 2 doped with sulphuric acid, and sulphated zirconium oxide (ZrO 2 /SO 4 2" ).
• Other solid acids suitable for the current application are superacids including sulphated iron oxide or halogenated alumina, sulphated tin oxide, trifluoromethyl-imines (R 1 CF 3 CNR 2 , where R 1 and R 2 are hydrocarbon chains), tungstated zirconia-alumina (W/SiZr-Al), silica-supported aluminum chloride.
• Free fatty acids can be acid esterified by the following reaction, here shown with the alcohol optionally being methanol:
• the water byproduct can inhibit the reaction, and may prevent esterification from proceeding to completion.
• esterification at high temperatures and under vacuum conditions has been surprisingly found to alleviate this problem in the present invention.
• the present inventors have conducted acid esterification of middle distillate derived from thermal cracking of triglycerides using the methods of the present invention. Results are given in Table 1 below. Table 1 : Acid esterificatio ⁇ of middle distillates derived from thermal cracking of triglycerides
• Residence time (min) is based on the volumetric liquid feed rate and reactor volume.
• Esterification produces a raw diesel stream 26 of approximately 50% alkyl esters (biodiesel) and 50% hydrocarbons.
• hydrocarbons can include tetradecane, pentadecane, 1 -hexadecene, hexadecane, heptadecane, 1 -octadecene, octadecane, nonadecane, 1-eicosene, eicosane, heneicosane, 1-docosene, docosane, tricosane, tetracosane, pentacosane, hexacosane, heptacosane, octacosane, nonacosane, triacontane, untriacontane, dotriacontane, tritriacontane, tetratriacontane, pentatriacontane, hex
• the raw diesel stream 26 may exceed acidity limits allowed by ASTM specifications for biodiesel, namely 0.5 mg KOH/g.
• the raw diesel stream 26 can optionally be fed to a base treatment unit 30, together with a basic solution 28.
• the basic solution 28 reacts with any unreacted fatty acids in the raw diesel stream 26 to produce non-foaming metallic soaps with low solubility in biodiesel.
• These non-foaming metallic soaps can then be separated by conventional known methods such as vacuum distillation, centrifugation, filtering or combinations thereof.
• the inventors note that the non-foaming metallic soaps, which include salts such as calcium, magnesium, potassium and lithium salts, have a high viscosity and can be sold as a valuable bio-lubricant by-product.
• Base treatment is preferably carried out at temperatures of from 30 to 60 0 C, and more preferably at temperatures of from 40 to 50 0 C and preferably at atmospheric pressure.
• the basic solution is preferably chosen from lithium hydroxide (LiOH), potassium hydroxide (KOH), magnesium hydroxide (Mg(OH) 2 ), and calcium hydroxide (Ca(OH) 2 ). Most preferred are LiOH and Ca(OH) 2 .
• the base treatment step results in a mixed biodiesel/diesel product 32 that has been found to have excellent fuel properties.
• the boiling point distribution of the resultant biodiesel/diesel product 32 is found to be broader than that of biodiesel produced by conventional transesterification alone.
• the mixed biodiesel/diesel product 32 can be used both neat or can optionally be further blended with regular diesel.
• the naphtha stream 16 from the thermal cracking unit 10 contains oxygenates and can optionally be sold as a valuable by-product such as octane improver.
• the residue stream 18 can be discarded by well known means in the art.
• the step of thermal cracking can optionally be replaced by a step of rapid pyrolysis.
• This process is shown in Fig. 2.
• Rapid pyrolysis is a process of decomposing a chemical at very high temperatures and in the absence of an oxidizing agent. Rapid pyrolysis has very short residence times when compared to thermal cracking.
• rapid pyrolysis of triglycerides can be conducted at temperatures ranging from 480 0 C to 600 0 C for approximately 2 seconds.
• the triglycerides 12 are fed to a fluidized bed reactor 34 which is preferably fluidized with steam 36, although other suitable fluidizing media known in the art can also be used and are encompassed by the present invention.
• Steam 36 may be fed to the reactor at a ratio ranging from 0.5 to 1.5, relative to the triglyceride feed stream.
• the preferred steam to triglyceride feed ratio is 0.9.
• any known inert gas 38 can optionally be added to the reactor to purge the reactor of free oxygen during pyrolysis.
• the inert gas 38 is preferably nitrogen.
• a catalyst may also be added, and suitable catalysts include, but are not limited to acid washed activated carbon, calcined sewage sludge solids and silica sand, such as silica alumina. The catalyst acts to enhance the selective cracking of triglyceride molecules to largely free fatty acid molecules.
• Sample data of rapid pyrolysis conducted by the inventors on a trap grease feedstock is listed in Table 2 below. The resultant pyrolysis products are shown in Table 3.
• the liquid fraction identified in Table 3 above contains middle distillates 22 as well as naphtha 16 and some residue 18.
• the boiling point distribution of the liquid fraction was determined by thermogravimetric analysis (TGA) and is given in Table 4 below.
• TGA thermogravimetric analysis
• the middle distillates yield is given in Table 5.
• the middle distillate fraction 22 produced by rapid pyrolysis was found to have varying free fatty acids (FFA) content, depending on the pyrolysis conditions. These details are shown in Table 6 below:
• a preferred temperature range for rapid pyrolysis of the present process is therefore from 550 0 C to 600 0 C and a most preferred range is from 565 0 C to 585 0 C.
• middle distillates yield between the run at 575 0 C and the run at 580 0 C is thought to be due to the difference in catalysts rather than the small difference in temperature.
• Catalyst derived from sewage sludge is less acidic than silica sand.
• the run with silica sand produced a slightly larger liquids fraction by deoxygenation, this was accompanied by higher coke and residue formation, resulting in an overall lower level of middle distillates.
• the sewage sludge appears to provide a preferred balance between higher middle distillate yield and lower coke formation.
• the middle distillate stream produced by rapid pyrolysis comprises practically no nitrogen.
• Nitrogen content in the middle distillate obtained by mild thermal cracking was in the order of 5200 ppm whereas that in the middle distillate obtained by rapid pyrolysis was 0.3 ppm. This is particularly advantageous since the presence of nitrogen diminishes the quality of the final biodiesel product.
• total sulphur in the middle distillate obtained by mild thermal cracking was in the order of 500 ppm whereas that in the middle distillate obtained by rapid pyrolysis was 150 ppm. Both pre-treatment steps produce free fatty acids and other components containing sulphur and nitrogen.
• a metal screen was placed in the bottom of a stainless steel micro-reactor (reactor volume 10 mL) and covered with a thick layer of glass wool.
• the reactor was loaded with a measured amount of catalyst and was tightly shut. When the predetermined temperature was reached, vacuum was applied and two syringe pumps containing feedstock and methanol respectively were started and the feeds entered the microreactor. Vapour leaving the reactor was condensed and analyzed for FFA conversion.
• Example 1 Example 1 :
• the esterification system consists of 1) a feed syringe pump, 2) a micro-reactor (10 mL), 3) a water-cooled condenser, 4) a room temperature trap, 5) an ice-water trap and 6) a mechanical vacuum pump.
• the vacuum pump attached to the exit side of the system maintained constant vacuum during the esterification.
• Thermally cracked palm oil and methanol were premixed at a weight ratio of 1 :1 and loaded in an 8 mL syringe pump.
• Calcined TiO 2 /Zr(SO 4 )2 in an amount of 4.1 g was charged in the micro-reactor between the layers of compacted glass wool and used as the acid catalyst. The catalyst occupied about 8 mL of the reactor volume.
• the reactor was heated to near 200°C, the vacuum pump was turned on and feed was started at a feed rate of 20 ⁇ L/min.
• the system pressure was maintained at 57 mmHg (1.1 psia) by bleeding a small stream of air into the vacuum pump inlet.
• TAN total acid number
• the total amount of cracked palm oil was 10.84 g and the total amount of reacted oil (free of methanol) was 8.7 g.
• the TAN number of the feed mixture was 120.0mg KOH/g and that of the product was 20.632mg KOH/g.
• the free fatty acids conversion based on the TAN number was 82.8 %.
• the esterification system consists of 1) a feed syringe pump, 2) a micro-reactor (10 mL), 3) a water-cooled condenser, 4) a room temperature trap, 5) a liquid-nitrogen trap, and 6) mechanical vacuum pump.
• the vacuum pump attached to the exit side of the system was intended to maintain the system pressure during esterification.
• Thermally cracked palm oil and methanol were premixed at a weight ratio of 1 : 1 and loaded in a 50 ml syringe pump.
• Calcined ZrO 2 /SO 4 2" in an amount of 5.7g was loaded into the micro-reactor as the solid acid catalyst, between the layers of compacted glass wool. The catalyst occupied 8.7 mL of the reactor volume.
• the reactor was heated to near 250 0 C, the vacuum pump was turned on and feed was started at a feed rate of 1000 ⁇ L/min.
• the system pressure was maintained at 5 mmHg (0.1 psia) by bleeding a small stream of air into the vacuum pump inlet.
• TAN total acid number
• the total amount of input (feed) was 40.0 g, the total amount of output was 36.0 g including 0.8 g collected on the catalyst bed.
• the mass balance for this experiment was 90.0%.
• the TAN number of the feed was 113 mg KOH/g and that of the product was 2.219 mg KOH/g.
• the free fatty acids conversion based on the TAN number was 98.0%.

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• 2007
  • 2007-11-30 WO PCT/CA2007/002161 patent/WO2009067779A1/en active Application Filing
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