SE543399C2 - A method for producing a low ash content biofuel mixture comprising tall oil pitch and lignin and use of the biofuel mixture in a petroleum refinery - Google Patents

Abstract

The present invention concern a low ash content biofuel mixture comprising tall oil pitch and lignin and optional additives characterized by, providing a stream TOP and providing a stream of lignin purified having an ash content below about 0.1 % preferably below about 0,01 % followed by mixing low ash lignin and TOP in a reactor and discharging a pumpable and substantially homogeneous low ash biofuel mixture comprising TOP and lignin from the reactor and using the biofuel mixture as a renewable feedstock in petroleum refineries, as a biofuel for power and/or heat generation, as a fuel for limekilns or kilns for iron ore processing or as a feedstock for fine chemicals or carbon fiber manufacturing.

Description

A METHOD FOR PRODUCING A LOW ASH CONTENT BIOFUEL MIXTURE COMPRISING TALLOIL PITCH AND LIGNIN AND USE OF THE BIOFUEL MIXTURE IN A PETROLEUM REFINERY Field of the inventionThe present invention relates to method for producing a low ash content biofuelmixture comprising tall oil pitch (TOP) and lignin for use as a renewable feedstock in a petroleum refinery Technical Background Lignin is a class of complex organic polymers that form key structural materials inthe support tissues of vascular plants and some algae. Lignin's are particularly important inthe formation of cell walls, especially in wood and bark, because they lend rigidity and donot rot easily. Chemically, lignin's are cross-linked phenolic polymers. Lignin is liberated inthe traditional kraft process and discharged from the kraft digester in the form of an alkalineliquor called black liquor. The black liquor is an aqueous solution of lignin residues,hemicellulose, and spent inorganic chemicals used in the pulping process. Lignin may also beliberated from wood or nonwood lignocellulosic plants by other processes than the kraftprocess such as the sulfite process, organosolv or hydrolytic processes. The lignin obtainedis therefore often referred to as kraft lignin, sulfite lignin (or lignosulfonates), organosolvlignin or hydrolytic lignin. Kraft lignin is dominant source for lignin for a foreseeable future,the sulfite processes are declining, organosolv and hydrolytic lignin is available in minutequantities only as these processes are still only operating in pilot scale. Kraft lignin extractedfrom black liquor is potentially available in tens of millions of tons per year. Most kraft ligninis burned in the kraft pulp mill recovery boiler for raising steam. Recently technologies forextracting kraft lignin from black liquor have been commercialized. These processes arebased on acidulation of the black liquor with acids and subsequent recovery of lignin byfiltration as exemplified by disclosure EP2247785. Another route for recovery of lignin isbased on membrane filtration and subsequent washing of the lignin by acids and/orsolvents. Such method is disclosed in SE 540451 included here as a reference in its entirety.

Tall oil pitch (herein after TOP) is an oily by-product obtained when processing of crude tall oil. Crude tall oil is obtained from the black liquor of alkaline digestion of 2 coniferous wood, most notably the kraft process. The black liquor from the kraft process istypically concentrated and settled to yield soap skimmings that contain sodium sa|ts of fattyacids, sodium sa|ts of resin acids and unsaponifiables (sometimes referred to as neutrals).The |atter group of su bstances include fatty alcohols, free sterols, steryl esters, and fattyacid esters. ln kraft pulp mills, the co||ected soap is routinely acidulated with a mineral acidsuch as su|phuric acid to yield an oil phase and an aqueous phase. The oil phase containsfree fatty acids, resin acids and unsaponifiables; it is commonly known as crude tall oil.Typically, the amount of unsaponifiables can range from 10 to 35% by weight of the crudetall oil, depending on the species and quality of coniferous wood used. The water phasecontaining sodium sulphate and any lignin entrained in the original soap is normally recycledback to the pulp mill chemical recovery system. ln the subsequent recovery of desired fattyacids and resin acids, crude tall oil is typically evaporated under low pressure conditions toyield a light phase, known as depitched tall oil, containing mainly fatty acids and resin acids,and a heavy phase, known as tall oil pitch (TOP), containing a substantial amount of theoriginal unsaponifiables. The TOP also contains varying amounts of fatty acids (straighthydrocarbon chain ranging from C12-C26 of varying unsaturation degree i.e. zero, one, two,three, etc. double bonds and containing primary/terminal carboxylic acid group) and rosinacids (typical examples being Pimaric, iso-Pimaric, Sandaracopimaric, Levopimaric, Palustric,Abietic, Dehydroabietic and Neoabietic acids occasionally referred to as resin acids) as wellas their derivatives .TOP is typically characterized by having a high viscosity. TOP normallyalso contain a considerable amount of ash, in particular calcium compounds and sodium ashcompounds such as sodium sulfate. The ash of an untreated TOP varies depending on thesource of crude tall oil and efficiency of upstream desalting steps, but is normally in therange from 0,1 % up to 2-3 % by weight of TOP.

The TOP residue fraction represents typically between 20-30 % by weight of CTOprocessed. The TOP typically has an acid value in the range of 30 - 60 (mg KOH/g) andalready comprises a significant amount of valua ble carboxylic acids in their free acid form.However, even larger amounts of these valua ble components are present within the TOP ascarboxylic acid derivatives i.e. as in their bound form, such examples but not limited to are fatty acid steryl esters, fatty acid esters with fatty alcohols, etc. 3 The present invention is directed to a su bstantially homogeneous low ash contentmixture of TOP and lignin that can be used as a renewable feedstock in petroleum refineries.

Summary of the invention A method for producing a low ash content biofuel mixture comprising tall oil pitch(TOP) and lignin for use as a renewable feedstock in a petroleum refinery, wherein saidmethod comprises the following steps: - providing a stream of purified TOP with an ash content below 0.1 %; - providing a stream of organosolv lignin, hydrolytic lignin or purified kraft ligninsaid lignin having an ash content below 0.1 %, wherein the lignin has been purified by one ofacid refining with an acid, solvent extraction, or solvent dissolution to remove ash from thelignin to a level below 0.1 %; - dissolving the purified lignin in an organic solvent; - mixing the purified lignin dissolved in an organic solvent, a surfactant, and thepurified TOP in a reactor followed by evaporation of the organic solvent upon heating; and - discharging a pumpable and homogeneous low ash biofuel mixture comprising TOP and lignin from the reactor.

Further details of the |nvention According to one specific embodiment of the present invention, the original TOPand components therein has an average molecular weight substantially above 350 g/mol,e.g. in the range of 350 - 800 g/mol, and any fatty acids and/or rosin acids, and/orderivatives thereof, and/or unsaponifiables and their derivatives present in the TOP have anaverage molecular weight below 350 g/mol, such as molecular weight in the range of 200 -330 g/mol. The latter compounds may be separated by fractionation prior to use of theresidue TOP as blending stock for lignin. Optionally, the thermal treatment of TOP isperformed in the presence of water or steam. lt is important to keep the TOP hot at alltimes as viscosity is a direct function of temperature. The TOP is kept at a temperatureabove 100 ”C and preferably at a temperature over 150 ”C at all times during processing inaccordance with the invention. Optionally, the thermal treatment of TOP is performed in the presence of water or steam. One focus of the method according to the present invention is 4 to decrease the viscosity of the TOP fraction produced and to further simplify purificationfrom salts and other impurities and to facilitate blending with lignin.

The TOP may be recovered from any position in a crude tall oil fractionation plant orfrom a plant treating crude tall for the manufacturing of crude tall diesel. Prior to the use asblending stock for lignin the TOP is purified in one or more steps. Purification of TOP isspecifically targeting ash removal and is suitably performed by acid refining with an acidsuch as sulfuric acid, filtration, solvent refining and/or distillation. The ash of the TOPcontent is lowered to a level below about 0.1 % more preferably to an ash content belowabout 0.01 %.

The second component of the bio oil mixture of the present invention is pure lignin.While it is of great importance to use a pure lignin, the method of purification and processesupstream lignin purification may vary to a great extent. US 2016/0137680 A1 discloses amethod to obtain, fractionate, and purify lignin. The method was subsequently alsodisclosed in Chem. Commun., 2015, 51, 12855. The method comprises one or severalseparation steps where biomass containing lignin is extracted and fractionated with anaqueous solvent with may comprise an organic acid. The mixture separates and one obtainsone liquid phase where high molecular weight lignin is abundant and one phase where thesolvent is more abundant, but which phase also comprises low molecular weight lignin. Thelignin phase can then be further treated with solvents to obtain a purified lignin. Thoughmetal content of the lignin is lowered, the method does not allow for nearly completeremoval of sodium. Further, some lignin is lost, lowering the overall yield in the process.ln a process of repeated washing of solid, dispersed lignin, with an acidic aqueous phase (cf.WO 2018/004447) a threshold is reached, as concluded in the 30 experimental part hereinbelow. lt seems that entrapped sodium will not be released even if the washing steps arerepeated a number of times.

One particularly advantageous method for purification of lignin upstream the TOPlignin mixing step of the present invention is by a solvent refining process specificallytargeting ash removal and in particular lowering the sodium content of lignin. The lignin maybe lignin obtained from biomass, e.g. wood, in a kraft pulping 5 process. As an example, thefeedstock may be black liquor comprising lignin. Given the high pH of black liquor due to theuse of sodium hydroxide in the kraft process, at least some of the phenolic hydroxyl groups of the lignin dissolved in black liquor are typically deprotonated with sodium acting as counter ion. At high pH, lignin is water soluble, whereas lignin will precipitate if the pH 10 islowered as the phenolic hydroxyl groups will become protonated, lowering the watersolubility of lignin.

A specifically advantageous solvent refining process for purifying lignin, said lignincomprising metal cations such as sodium and calcium ions, comprises the consecutive stepsof: (a) providing lignin to be purified; (b) dissolving the lignin in an acidic, aqueous solvent, at a temperature of at least 50°C, such as at least 70 °C, 80 ”C or 90 °C, to provide a liquid one-phase system comprisingdissolved lignin; (c) triggering phase separation by diluting the one-phase system by adding water,and/or by lowering the temperature, to provide a two-phase system, in which two-phasesystem the first phase is a lignin rich phase, and the second phase is a liquid, aqueous phasepoor in lignin and comprising metal cations extracted from the lignin; and (d) separating the lignin rich phase from the two-phase system to recover purifiedlignin. lt was found that by employing a step in which lignin is dissolved in a liquid one-phase system to su bsequently be separated there form, a number of advantages areprovided.

By employing a method in which lignin is dissolved in an acidic, aqueous solvent,efficiently extracts sodium and other metal ions, whereby metal cations efficiently areremoved from the lignin, as they remain dissolved once the lignin is separated.

Secondly, if employing many, repeated washing steps, the overall yield of lignin maybe lowered. ln a process in which a step of dissolving lignin in a liquid one phase system isincluded, the overall number of steps may be reduced, whereby improving the yield.

Thirdly the washing efficiency is improved by completely dissolving lignin in liquidone-phase system and subsequently triggering phase separation to form a two-phasesystem, compared to processes in the art (cf. e.g. US 2016/0137680) relying on liquid/liquidtwo-phase system.

The inventors of the present invention have surprisingly found that a purified TOPwith low ash content can be mixed with a pure lignin to form a substantially homogenous bio oil mixture that can be used in various applications as a renewable fuel or feedstock for 6 fine chemicals. The lignin can be mixed with TOP in pure powder form or dissolved in anorganic solvent. The mixing efficiency, stability of and rheological properties of the bio oilmixture can be improved by the addition of one or more additives to the lignin/TOPblending step or directly thereafter. Such additives are standard surfactants with a selectedhydrophilic lipophilic balance, preferably ethylene oxide adducts, an anionic surfactant, cationic surfactants, zwitter ionic surfactants modified polyesters or polyelectrolytes. Also,water can be added to the mixture in low amounts where 10 % of lignin weight has beenshown to give improved mixing properties of lignin in organic solution. The amount of wateris preferably kept as low as possible in a range from 1 % to 15 % of the lignin content. Otheradditives such as carboxymethylcellulose and/or guar gums may also be used to improvemixing or rheological properties of the TOP lignin bio fuel mixture. Also, solvents may beadded to the biofuel mixture prior or during mixing, such solvents including green solventssuch as methanol, ethanol, turpentine, desalted low acid value crude tall oil (for example talloils with acid value below about 140 mg KOH/g) acetone or fossil blend stocks such as lightcycle oil or vacuum gas oil (VGO). Additives are added in an amount from about 0.1 % to 10% and solvents may be added in any rage from 1 to about 60 %. The proportion betweenlignin and TOP may also be varied within a broad range from 10 % lignin up to 90 % lignin(relative to TOP in the biofuel mixture). The mixing of the components can be performedboth in batch mixing reactors semi batch reactors or continuous reactors such as CSTRs ortubular reactors with static mixers or combinations of reactors designs. The temperatureduring mixing should be kept high in order to facilitate for the proper mixing of lignin,additive and TOP into a homogeneous mixture. The temperature in the mixing reactor(s) should be higher than 100 ”C and preferably higher than 130 °C.

Claims (7)

1950531-2 Claims

1. A method for producing a low ash content biofuel mixture comprising tall oilpitch (TOP) and lignin for use as a renewable feedstock in a petroleum refinery, said methodbeing characterized by the following steps: - providing a stream of purified TOP with an ash content below 0.1 %; - providing a stream of organosolv lignin, hydrolytic lignin or purified kraft ligninsaid lignin having an ash content below 0.1 %, wherein the lignin has been purified by one ofacid refining with an acid, solvent extraction, or solvent dissolution to remove ash from thelignin to a level below 0.1 %; - dissolving the purified lignin in an organic solvent; - mixing the purified lignin dissolved in an organic solvent, a surfactant, and thepurified TOP in a reactor followed by evaporation of the organic solvent upon heating; and - discharging a pumpable and homogeneous low ash biofuel mixture comprising TOP and lignin from the reactor.

2. The method in accordance with claim 1, wherein the TOP has been purified byone of acid refining with an acid and subsequent removal of the acid phase from TOP, finemesh filtration, centrifugation, solvent refining and distillation in order to remove ash fromthe TOP to a level below about 0.1 % by weight preferably to a level below about 0.01 % byweight; and/or wherein the TOP has been thermally treated, optionally in the presence of Water Of' Steam.

3. The method in accordance with claim 1 and 2, wherein the lignin has beenpurified by one of acid refining with an acid, solvent extraction or solvent dissolution to remove ash from the lignin to a level below 0.01 % by weight.

4. The method in accordance with claim 3, wherein the lignin has been purified by: (a) providing lignin to be purified; (b) dissolving the lignin in an acidic, aqueous solvent, at a temperature of at least50 °C, such as at least 70 °C, 80 ”C or 90 °C, to provide a liquid one-phase system comprising dissolved lignin; 2 (c) triggering phase separation by diluting the one-phase system by adding water,and/or by lowering the temperature, to provide a two-phase system, in which two-phasesystem the first phase is a lignin rich phase, and the second phase is a liquid, aqueous phasepoor in lignin and comprising metal cations extracted from the lignin; and (d) separating the lignin rich phase from the two-phase system to recover purified lignin.

5. The method in accordance with any of the prior claims, wherein the organic so|vent is ethanol, methanol, vacuum gas oil, acetone or low acid value tall oil.

6. The method in accordance with any of the prior claims, wherein step ofdischarging a pumpable and homogeneous low ash biofuel mixture comprising TOP andlignin from the reactor comprises discharging the pumpable and homogeneous low ashbiofuel mixture in the form of a slurry with lignin dispersed on a molecular level stabilized by the su rfacta nt.

7. Use of the biofuel mixture produced according to any of claims 1-6 as a renewable feedstock in petroleum refineries.