NZ241950A - Heating lignocellulosic material to provide plant growth material and water treatment material - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £41 950 50 I ^ r>'h\R J Of; .» f -----...

I " PATENTS FORM 5 PATENTS ACT 1953 COMPLETE SPECIFICATION Number 241950 Dated MARCH 12, 1992 A BARK EXTRACTANT AND METHOD FOR PREPARING SAME We HER MAJESTY THE QUEEN in right of New Zealand, acting by and through the Secretary of Forestry, of Hunter House, Hobson Street, Wellington, New Zealand do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement 2 The invention comprises a method for providing material, suitable as an extraction agent or improved plant growth medium from lignocellulosic waste material such as bark, and a method for extraction.

Many industrial processes such as the treatment of effluent streams or extractive processes rely upon the use of a reactive system attached to a support medium to enable concentration and eventual removal of chemical or biological species from the fluid medium. These resins are however expensive to produce, with the result that many desirable processes, such as effluent cleanup, are uneconomic to perform.

Bark and related materials are known to complex heavy metals and also proteins. It is also known that catechol and its derivatives chelate with boron compounds to form esters of boric acid. These esters are labile, but establish an equilibrium with facility in water solutions of catechol and boric acid. It has also been suggested that bark can be used as an oil absorption medium, but a disadvantage is the tendency of entrained tannins and phenolics in bark to dissolve in water to give coloured effluents creating difficulties in the use of bark. These solubilised tannins show biological toxicity and can be released into a biological system such as a waterway for example, into which the bark is introduced as an extractant for oil or effluent or the like. This disadvantage also limits the use of the bark as a plant growth medium.

Previous treatments to control colour bleedout from bark in water have relied upon the reaction of formaldehyde with the entrained polyphenols under the influence of acid and heat. It has been proposed to react ground bark at 500C with aqueous formaldehyde and sulphuric acid, and also to react 100 mesh ground bark with nitric acid and formaldehyde at approximately IOOOC for 10-15 minutes both to acheive some reduction of colour leaching.

In broad terms the invention in a first aspect may be said to comprise a process for providing an extractant or plant growth medium, comprising heating and mechanically dividing lignocellulosic material containing phenolic compounds to a temperature and for a time sufficient to substantially immobilise a major proportion of the phenolic compounds in the lignocellulosic material against release during use of the lignocellulosic material as an extractant or plant growth medium.

By "lignocellulosic material" in this specification is meant most particularly bark, but also crop residues, wood, and the like.

Preferably heat treatment is carried out by steam treatment of the lignocellulosic material, but alternatively heat treatment may be carried out by, for example, oven roasting, radio frequency heating, or the like.

Preferably heat treatment is carried out to a temperature in the range 100-300'C, most preferably above 200'c or at least 180'c, and very preferably in the range 200-260'c. Typically heat treatment will be carried out for a matter of minutes, for example one to five minutes.

The lignocellulosic material may be mechanically divided into fibers or particles for example either before or after heat treatment.

Most preferably the lignocellulosic material is both heat treated and mechanically divided by steam treatment at the desired temperature followed by rapid decompression to explode the lignocellulosic material.

The steam treatment may be carried out in a suitably designed vessel. For example, a batch process may be carried out in a stainless steel vessel fitted with wide bore ball valves at each end. steam at various pressures, typically from 1.3 to 3.2 MPa, is supplied to the top of the vessel after the lignocellulosic material has been loaded. At the end of the desired treatment the bottom ballvalve is opened and the contents of the vessel discharged by the force of the expanding steam. other steam treatment procedures are possible, continuous processing for example, utilising design variables known to those skilled in the art.

Heat treatment in accordance with the invention, of bark and other lignocellulosic materials substantially immobilises the phenolic compounds, such as tannin naturally present in bark for example, into the bark structure, thus reducing extraction of these compounds into water. The result of fixing the tannins and related phenolics into the bark by heat treatment is to render the material an industrially useful product, at a cost which is acceptable, and without the addition of undesirable chemicals such as formaldehyde.

"Steam explosion" can be used both to immobilise the tannins into the bark structure and also to finely divide the bark at the same time, for use as an extractant or plant growth medium.

The treated bark or lignocellulosic material may be used as an extractant for effluent for cleanup purposes, for absorbing hydrocarbons and solvents, to remove metal ions from solutions, to entrain protein-containing materials, and for other extractions. The treated bark is also rendered more suitable for use as a plant growth medium.

The invention will be further described with reference to the accompanying examples.

EXAMPLES (1) Preparation of steam explosed bark samples.

Whole P. radiata bark was freshly removed from the lower 6 metres of logs from trees 22-29 years old grown in the central North Island of New Zealand and milled in early summer after a long wet period of weather. This material was stored in plastic bags, hammermilled the next day to size - reduce it, and stored at 4°C until steam exploded one week after collection according to the regimes in Table 1. Where SOt was added, this was at a rate of 3 wt% on wet bark (5.2% on oven dry basis) added 15 minutes prior to the steam explosion process and sealed in polythene bags until required.

TABLE I.

Temperature/Time regimes for Steam Explosion Sample A 13 C D E 1: G H Steam 'Iemp. (°C) (untreated) (control) 150 170 170 210 210 245 245 Sample Temp.* (°C) (untreated) (control) 109 -131 155 -165 155 -164 197 -203 204 -208 231 -236 231 -236 Time (minutes) (untreated) (control) 3 3 3 3 3 3 3 SO-> addition No No No Yes No Yes No Yes measured as reactor wall temperature 1 minute after steam injections.

Each of the samples A-H (Table 1) was processed in two nominal batches of 5 x 500 gram lots each and the product from each batch weighed, bagged, and stored overnight at 4°C store. The first batch of each sample A-H was initially frozen whilst the second was immediately air dried (over four days) and weighed. A portion of this air dried material was ground in a Wiley mill and oven dried to determine the moisture content. For convenience, the other frozen bags of product were air dried two weeks later and the same procedure followed.

Material to be used in microbial experiments was stored frozen to inhibit growth of contaminating organisms. Thin bark (hogged pole peelings) treated as above at 195°C for 20 minutes, was chosen for this study on the basis of water flow through a packed column of bark. To lOOg of thawed material was added 40ml deionised water, the mixture stirred for ten minutes, centrifuged, and the supernatant poured off. This washing was repeated four times. (2) Extractives.

The coarsely ground (<20 mesh) air dried steam exploded barks (20 g) were soxhlet extracted with solvent until no further colour could be observed in the returning solvent. The samples were extracted for five hours with hexane, fourteen hours with toluene (overnight), eight hours with ethyl acetate, twenty hours with acetone, forty one hours with methanol, and thirty two hours with water. Solvents were removed by rotary evaporator, except for water which was removed by freeze drying.

Analysis of extractibility of colour was carried out by vacuum impregnation (tap vacuum) of 200 gram aliquots of bark with 2 litres of distilled water. The pH of the solution obtained was adjusted to 7.5 using 1% NaOH solution and optical density measured at 465 nm and compared to a known chloroplatinate standard (based upon APHA-AWWA-WPCF standard method 204A 16th Ed).

A further sample of 25 yr old P. radiata bark, was steam treated at 225°C for 3 minutes, explosively decompressed, and analysed for extractable tannins in comparison with the untreated material. The steam exploded and unmodified P. radiata bark samples were extracted separately with aqueous acetone (3 x 60% aq. acetone). The extracts were concentrated and the residual aqueous suspensions filtered. The filtrate was extracted with ethyl acetate (5x) and the aqueous layer treated with equal volume of methanol. The aqueous methanol solutions were 6 applied to a Sephadex LH20 column, washed exhaustively with 30% aqueous methanol and the purified tannins eluted with 60% aqueous acetone. (3) Metal Ion adsorption 100 ml aliquots of various salt solutions were stirred with bark samples at ambient (20°C) temperature, filtered and the filtrate analysed by atomic adsorption spectroscopy. Hg was analysed as the hydride. (4) Protein Interaction with Bark. 4.1 Bark, treated with S02, steam exploded at 245°C (Sample H) was air dried, washed twice with hexane and the residual hexane allowed to evaporate. 100ml aliquots of the protein solution were added to duplicate 10 gram samples of the bark and stirred for two minutes, left to stand at ambient temperature (25-2S°C), stirred at the end of the time period and filtered using suction. To 0.1ml of Bovine Serum Albumin (BSA) protein solution from the treatment was added 4 ml of Bradfords reagent (diluted 1:4 with distilled water and filtered) the absorbance read at 595nm, and protein concentration determined. 4.2 Two bacterial and one viral species were used as a model for immobilisation. They were Escherichia coli (Gram negative), Enterococcus faecalis (Gram positive) and the bacteriophage MS2 which is an icosahedral untailed virus. A combined inoculum of the microorganisms containing approximately 1 x 10^ cfu/ml of each bacteria and 1 x 10^ pfu/ml of MS2 was prepared in sterile tap water and used to inoculate bark association experiments. Inoculum mixtures were prepared freshly for each experiment and microbial levels confirmed by culture at the time of addition to individual experiments.

MS2 bacteriophage was assayed by plaquing on the host strain Salmonella typhimurium WG49. Luria medium containing CaCl2-2H20 (300mg/L), MgS04-7H20(300 mg/L), glucose (lg/L), naladixic acid (Sigma,100 mg/L) and kanomycin (Sigma, 20 mg/L) was used for bacteriophage host culture. Plaque assays were carried out in solid medium prepared as above but with the addition of Davis agar (9 g/L). to produce a solid medium. Samples were spread plated onto prepared plates of mE agar (Difco) and EMB agar (Difco) for selective enumeration of Enterococcus faecalis and Escherichia coli respectively.

Steam exploded thin bark (20 ml) was packed into a 30mm diameter column (syringe barrel) with a disc of 3mm filter paper (Whatman) at the base and on the surface of the bark. The flowrate through the column with a 40 ml head volume was established using sterile water. Microbial immobilisation on the column was established by adding 40 ml of bacteria/virus inoculum to the column and sampling the effluent after passage of 20ml, 30ml, 40ml, and 50ml. Sterile water was used to prevent the column drying out and maintain the head volume. Samples were diluted in sterile tap water immediately prior to assay. (5) Boron Salts Interaction with Bark.

Bark, treated with S02, steam exploded at 245°C (Sample H) was air dried, washed twice with hexane and the residual hexane allowed to evaporate. Duplicate lOg samples of bark were treated for 24 hours at ambient temperature with 0.1M boric acid (adjusted to pH 2.6,7.0 and 8.7 with NaOH soln.). The bark samples were filtered and washed twice with 100ml portions of distilled water. The initial filtrates and both washings were analysed for boron content by titration (mannitol/NaOH) to the bromothymol blue end point. (6) Sorption of oil.

Bark, steam exploded at 245°C, was air dried, and (a) sprinked over a layer of "Arab Light" crude oil spread on water. (b) contained within a stainless steel wire baskets, and immersed through a layer of "Arab Light" crude oil covering into the water below in such a matter that the oil was allowed to contact the entrained bark. (c) Measurement of the maximum absorption of oil over 5 minutes of the steam Exploded Bark was determined by total immersion of weighed bark samples into an Arab Light grade of crude oil for 5 minutes, followed by removal and drainage and drainage for 10 seconds, followed by drainage on paper towels for a further 15 minutes. Ten replicates were measured.

^ A / . ? i A. The Effect of Steam Explosion on the Appearance and Yield of the Bark Increasing temperature of steam treatment (see Table I) darkens the bark colour and more finely divides the structure. SO2 Treatment appears to have little effect on particle size, and only a small darkening effect on colour. The wet weight of material is considerably increased by steam explosion, with up to 67% additional moisture gained by the bark, as seen in the data in Table II. The effect of SO2 pretreatment is to reduce this uptake of moisture, as seen in a comparison of samples D, F and H (with SO2) versus C, E and G (without SO2). Only a small effect is seen upon yield of dry matter with increasing temperature except for the highest temperature used in conjunction with SO2 pretreatment (treatment H).

TABLE II.

Effect of Steam Explosion on Solids Content of P. radiata Bark Initial % Solids dry weight Increase in wet wt on steam explosion Solids yield (% of initial o.d. solid) Yield of solids on S.E. cf. Sample A Sample A 81% 58.5% Control Sample B 78% 44% 60.6% 103.6% Sample C 67% 60% 55.3% 94.5% Sample D* 77% 50% 57.5% 9S.270 Sample E 84% 61% 53.8% 92.0% Sample P 76% 44% 54.3% 92.S% Sample G 71% 67% 53.5% 91.3"/o Sample H* 78% 38% 47.9% 81.9% SO2 treated samples.

B. The Effect of Steam Explosion on the Extractives of Bark The resulting weights of extracted material are given in Table III. Increasing the temperature from ambient to 240°C for three minutes has the effect of reducing the level of extractives to half the original level (from 36.6 wt% to 18.7 wt%). Higher temperatures decrease all the extractives obtained using polar organic solvents. The level of water extractives decreases with increasing temperature for all temperature treatments.

TABLE III.

Results of Sequential Solvent Extraction Studies on Steam Treated Barks (wt % of O.D. bark sample) Sample No. Hexane Toluene Eth.Ac. Acetn. Meth. Water Total Extractives A 2.72 0.99 2.90 14.01 9.75 6.26 36.6 B 2.83 1.01 2.85 6.96 11.47 6.66 31.8 C 3.30 0.93 3.95 7.90 12.00 6.5S 34.7 D 3.16 1.52 3.78 9.78 14.OS 3.16 .5 E 3.26 0.98 4.40 .66 9.12 3.41 26.8 F 3.30 0.66 .27 3.24 .88 1.93 .3 G 3.44 1.23 2.92 4.18 .06 1.90 18.7 H 3.23 0.88 3.46 6.82 4.22 1.72 .3 Markham and Porter 1.7 1.6 4.0 13.3 5.0 (1973) A dramatic drop in extractive levels in the acetone fraction upon heat treatment is accompanied by an initial rise followed by a fall, in the level of methanol extractives. Brown coloured bands, not present in thin layer chromatogram of extracts from the untreated bark (A), are observed in the thin-layer chromatogram of the methanol extractives from sample H. We therefore conclude that condensation of lower molecular weight material to higher molecular weight material occurs - In For example the nature and amount of extractives in P. radiata bark steam treated at 225°C for three minutes and explosively decompressed are compared with those of untreated bark as shown in Table IV.

TABLE IV.

Level of Extracted Tannins from Untreated and Steam Exploded P. radiata Bark Unmodified Sample Steam Exploded yields yields (% based on dry weight) (i)* precipitates 6.7 3 (li) ethyl acetate extractives 0.7 2 (iii) Residues from 30% 4 6 methanol eluants (iv) purified tannins 6 0.2 Total extracts 17.4 11.2 material filtered from suspension after concentration of aqueous acetone extractives Marked loss of tannin from 6% purified tannins, isolated from an untreated bark, to 0.2% isolated from the steam exploded bark, was noted. From this result it is concluded that even with treatment at 225°C almost complete loss immobilisation of tannins is effected. The process of steam explosion condenses the tannins to form non-extractable species, whilst generating extractable carbohydrate material. Thus the level of extractives presented in Table III result from steam treatment on both the carbohydrate and phenolic materials, and thus at higher temperature treatment regimes the extractives observed are mostly carbohydrates. Analysis of leachable colour (Table V) also shows a decrease in colour with the more severe treatment conditions.

TABLE V.

Colour analysis of effluent from treated barks after a vacuum impregnation of 200 gram aliquots of bark with 2 litres of distilled water.

B C Sample D E F G H Colour (Std. units) 3240 3128 6040 5493 3240 753 2021 C. Metal Ion Binding to Steam Exploded Bark The results of study of metal ion binding to the bark substrate formed in treatment 'H' (Table I), are shown in Table VI. Mercury is strongly bound to the treated bark. It was found that a mercuric ion solution (21740 ng/ml, 100 ml) treated with 5 grams of bark material gave only 52 ng/ml of mercury in the filtrate. Lower mercury levels were recorded when greater amounts of the bark was used. This represents more than 99.8% of metal ion removed from solution by adsorption, and occurs despite calcium ion present initially in the bark.

TABLE VI.

The Adsorption of Metal Ions to Steam Exploded Bark, measured by AA spectroscopy, as observed from remaining levels in filtered leachates.

Salt Initial Time Bark Weight Filtrate Bound Concentration conc. ng/gram ng/ml minutes grams ng/ml bark Cn2 + 4120 2 30000 * (sulphate) (Same result for all samples from 2 mins to 2 hours) Cu2+ 6S70 2 3990 28.S (sulphate) 4 3790 .8 3990 2S.8 3650 32.2 80 3260 36.1 1069 3020 38.5 1320 4 3350 88 1320 2530 21.7 Cu2+ 6930 1320 3120 76.2 (acetate) 1320 2920 40.1 rewash HC1 2250 17.6 1320 2490 29.6 Fe2+ 6500 1320 3490 60.2 (sulphate) 6500 1320 4740 17.6 rewash HC1 4740 0 6500 1320 5620 .9 Pb2+ 101800 1320 37700 1282 (acetate) 1320 34800 670 rewash HC1 22700 443 1320 27400 496 Hg2+ 21740 1320 52 3308 (acetate) 1320 34 1834 1320 rewash HC1 102 1154 1320 21 1309 P radiata bark contains calcium at about 0.5 wt% and iron at about 0.2 wt% as contaminants initially present.

The comparison of bound metal ions to bark between the 4 g, 10 g and 20 g bark experiments indicate an equilibrium process is occurring, and also that the counter ion has little effect. These results were obtained on batch samples. Greater bound metal ion loadings can be expected with use of a column of bark.

D. Binding of Protein to Steam Exploded Bark D.l The binding of protein to bark is slow and dependant upon the protein concentration. At an initial level of 500 ppm protein added to 10 g of bark the half life for the binding of protein is about 100 minutes. Small amounts appear to be quickly bound (Table VII), but as the concentration rises it takes longer to bind all the protein present until a limit is reached at around 2 to 3% of the weight of the bark (Table VIII). Protein binding to the treated bark therefore seems to be both feasible and of high capacity.

Protein levels in filtrate from 100ml of 500ppm BSA solution after treatment for vary ing time by 10 grams of hexane washed Sample H steam exploded bark. Results reported are for replicates carried out on separate bark samples TABLE VII.

Time Protein Level Analysed 500ppni initially added lOOppm initially added 2 mins 3 mins 4 mins 60 mins mins 20 mins 40 mins 475ppm 395ppm 392ppm, 405ppm 410ppm 365ppm( 365ppm, 352ppm 348ppm 353ppm, 315ppni 315ppm, 305ppm 298ppm 240 mins 23ppm 30ppm 270 mins 1020 mins 1350 mins 1770 mins 187ppm, 188ppm 72ppm, 78ppm 75ppm, 75ppm 30ppm, 20ppm 15ppm Oppm Oppm: all Oppm : essentially Oppm : zero TABLE VIII.

Protein levels in filtrate from 100ml alicjuotes of varying protein concentration treated with 10 grams of hexane washed Sample H steam exploded bark, and in the filtrate from washing of the residual bark material with succesive 100ml aliquotes of distilled water.

Initial Time Initial 1st wash 2nd wash comments Protein filtrate level 11,650ppm 4632ppm lt)S9ppm 52 hours 52 hours 52 hours 7400ppm 2230ppm 70ppm, 115ppm 1200ppm 260ppm Oppm 205ppm 20ppm Oppm retained 0.2S5grams retained 0.212gran\s retained 0.190grams (virtually all) 500ppm 29.5 hours Oppm retained 0.05 grams (all) Plow rate under gravity in the bark columns packed to a depth of 20 ml was very slow and somewhat variable between columns (Table IX). Removal of E. faecalis and bacteriophage MS2 by the bark columns was quite high (Table IX) and tended to be more efficient at higher flow rates for the bacteria. 14 TABLE IX.

Removal of Enterococcus faecalis and Bacteriophage MS2 from Solution by Passage through a Column Packed with Steam Exploded Pinus radiata Thin Bark.

Column 1* ~ ~~ Column 2 Column Plow rate Reduction- (%) Flow rate Reduction- (%) effluent ml/min compared with ml/min compared with volume innoculum innoculum Ent. faecalis MS2 Ent. MS2 faecalis 5m 1 0.85 nil 17b .... .... 0.9S — — ml 1.84 .... — 1.10 — — ml 1.86 >99.9 >99.9 1.16 S7.3 >99.9 ml .... .... .... 1.19 — — ml 2.00 >99.9 >99.9 — 9S.2 >99.9 ml 2.12 .... — 1.35 — — 40 ml ^ T) >99.7 >99.9 1.45 97.S >99.9 50 ml >99.6 >90 Q — 99.9 >90.9 Mean 1.97 >99.8 >99.9 1.15 95.8 >99.9 1. Column bed volumn = 20 ml 2 Initial microbial inoculum volume was 40 ml.

Suspending fluid was sterile tap water.

Enterococcus faecalis concentration 3.95 x 104 colonv forming units per ml.

Bacteriophage MS2 concentration 1.09 x 105 plaque forming units per ml.

Study of BSA and viral protein indicates that adsorption of these species is not fast, but near complete removal of protein can be acheived at low protein/bark ratios. Brief investigation of other proteins indicates that the adsorption is a general phenomenon, but dependant upon factors such as specific type of protein and environmental factors such as pH.

E. Sorption of Oil (a) Oil is rapidly absorbed by the steam exploded bark, so that no free oil on the water surface is able to be observed within 5 minutes treatment. (b) Oil is absorbed by the entrained bark, and rapid movement of the oil layer on water towards the bark is observed, indicating that there is a active absorption phenomon occurring. The amount of oil absorption is dependent upon the quantity of bark present. (c) The absorption capacity of the bark for oil was determined to be 1S0% by weight (Table X).

Claims (8)

TABLE X. The Absorption of Crude Oil onto Steam Exploded Bark Weight of Bark Oil Uptake Ratio of Oil/Bark (g) (g) 3.190 6.132 1.92 3.510 6.510 1.85 3.320 6.084 1.83 3.499 6.469 1.85 3.504 6.503 1.86 3.389 6.160 1.82 3.227 5.874 1.82 3.857 6.793 1.76 3.262 5.822 1.78 3.210 6.024 1.8S Average 1.84 F. As a plant growth medium The entrained tannins and phenolic materials in bark render the bark somewhat phytotoxic. Tomato seeds, (which would not normally germinate in a bed of bark) were placed in a bed of steam exploded bark and observed to readily germinate, thus indicating that heat treatment of bark renders it less phytotoxic than normal bark. The foregoing describes the invention and examples thereof Alterations and modifications as will be obvious to those skilled in the art are intended to be incorporated in the scope hereof. 241 ijt l\ i-. l/i LHiMriS 16

1. A process for providing an extractant or plant growth medium, comprising heating and mechanically dividing lignocellulosic material containing phenolic compounds, to a temperature and for a time sufficient to substantially immobilise a major proportion of the phenolic compounds in the lignocellulosic material against release during use of the lignocellulosic material as an extractant or plant growth medium.

2. A process as claimed in claim 1, wherein the lignocellulosic material is bark.

3. A process as claimed in either one of claims 1 and 2, wherein the lignocellulosic material is heated to at least 180'C.

4. A process as claimed in either one of claims 1 and 2, wherein the lignocellulosic material is heated to at least 200'C.

5. A process as claimed in either one of claims 1 and 2, wherein the lignocellulosic material is heated to a temperature in the range 2 00* to 260 'C.

6. A process as claimed in any one of the preceding claims wherein the lignocellulosic material is both heated and mechanically divided by steam treating the lignocellulosic material followed by rapid decompression to explode the bark.

7. A method of removing oil, heavy metals, or proteinaceous materials including soluble proteins, meat and dairy industry wastes, and viral material from water comprising contacting the water containing oil, heavy metals, or proteinaceous material with bark which has been mechanically divided and heated to a temperature and for a time sufficient to substantially immobilise a major proportion of the phenolic compounds in the bark from release into the water.

8. A process for providing an extractant or plant growth medium as claimed in claim 1 and substantially as herein described with reference to the accompanying examples. WEST-WALKER McCABE Per: iV. ^ ATTORNEYS FOR THE APPLICANT •.V' ■s' t 20 DlC W s>